As Many Exceptions As Rules

The titan beetle (Titanus giganteus), is not necessarily

a gentle giant. Its jaws can snap pencils and easily cut

into human flesh…. and they fly. Calm down, the adults

don’t feed, they just look for mates, so you won’t wake

to one nibbling your toes away.

Today, the biggest insects are goliath beetles, atlas moths, and giant stick insects. But during the carboniferous period (360 -300 million years ago), there were millipedes that were 2 m (6 ft) long and dragonflies (order Protodonata) the size of eagles!

Today’s question is:

How did insects get so big, and if they were big once, why are they so much smaller now?

It wasn’t just the insects that grew large way back then, the first large plants flourished in this same time period. Some ferns grew to be 20 m (65 ft) or more in height, and the diameters of trunks were increased. While not as big as today’s largest plants, the change was significant, as plants before this period did not exceed 3 to 5 ft in height.There was plentiful carbon dioxide in the atmosphere and the environment was warm all year round. This allowed lots of photosynthesis and lots of growth.

Nice picture to give scale, but humans and the

Arthropleura never co-existed. Even though the

species alive today aren’t as big, you still have

to beware. Many centipedes are venomous and

some millipedes can emit hydrogen cyanide gas.

Plants were evolving lignan in this carboniferous period (carbonis = coal, and ferrous = producing). Lignan is the stiffest of the plant molecules and is what allows them to grow tall. This is also what gives the carboniferous period its name, as the lignan of plants is the major component of the coal that formed from their remains.

Horsetails, another type of plant of the carboniferous age and which are still around today, also grew much bigger. Horsetails today do not get any taller than about 1 m (3 ft), but in the carboniferous period, they were often 10-15 m (33-48 ft) tall.

Butit was the arthropods that get all the publicity. Scorpions almost a meter in length deserve to have a lot of attention paid to them! And consider the yuck factor of a 7 inch cockroach scurrying around at your feet.

The plants got big during the Carboniferous period.

Some lycophyte trees were 30 m (98 ft) tall and had

trunks of 2 m (6.5 ft) diameter. Their closest

relatives today are the club mosses, which are about

20 cm or less in height. Talk about deflating your ego.

What allowed these animals to grow so large? Scientists think it was related to the lignan. With lignan, the plants could grow larger and support more photosynthetic material. The carboniferous period is when the first forests appeared.

With more and bigger plants, more carbon dioxide was converted to carbohydrate, and more oxygen was produced as a result. The oxygen content of the air in the carboniferous period reached levels of 35% or more (today it is about 21%).

More oxygen in the air meant that more oxygen could be transferred into the blood of animals. They could carry out more oxidative phosphorylation and produce more cellular energy (ATP), especially since there was all this plant material around to eat to gain carbohydrates (or plant-eaters to hunt down and eat). This growth spurt especially applied to animals without traditional circulatory systems. Insects, for instance.

Insectsuse spiracles on the sides of their bodies to take in air. The oxygen and other gases are moved through a system of smaller and smaller tubes (called trachea) to bring the oxygen to all the cells of the body. The carbon dioxide produced during cellular respiration is removed in the same way.

The spiracles of a flea are on the side of its abdomen

and the air travels through the tracheae to bring

oxygen to every cell. It seems like he would drown if

he took a dip in the hot tub.

This is not a particularly efficient way to move gases in and out of cells. A slightly bigger bug must have a much more voluminous system of trachea, and at some point, the respiratory system would have to be bigger than the entire volume of the insect! There would be no room for all the other organs. But with a high concentration of oxygen, the spiracle/tracheae system is efficient enough, and the insects can grow very large.

Highoxygen in the air also meant high oxygen in the water. Carboniferous era fish and amphibians grew large as well. Some toothed fishes of this time were impressive predators, and were more than 7 meters (23 ft) in length. Isopods in the oceans were also huge. Even today some of these crustaceans can be pretty impressive. Bathynomus giganteus can grow to more than over 16 inches in length.

So big plants brought big oxygen levels, which brought big animals. But why are the arthropods so much smaller today as compared to then? Well, the oxygen levels are lower now, so according to a 2006 study the inefficient spiracles system could not support the large body. Insects had to get smaller.

Here is an isopod that grabbed a ride when a deep sea remotely operated

vehicle was recovered. They look even creepier from the front with

silver eyes. Isopods are related to shrimp and crabs; I think we’re going

to need much more butter and lemon.

But there is an additional hypothesis that may also contribute to the small size of many insects, especially flying insects. According to a 2012 study, the size of flying insects is related to another aspect of oxygen. When the explosion of plants in the carboniferous period raised the oxygen levels, the air became more dense (oxygen is a heavier gas). The insects were able to become better fliers, since their wings could move more air.

The data says that one reason flying insect

got smaller was to avoid being easy catches for the birds

that were becoming better fliers and hunters. Really?

Name me a couple birds that would go after this guy if

he was flying today.

Millionsof years later, birds evolved. As they became better fliers (their ability was also based on their ability to move air over their wings), they became better hunters. Better hunting birds could catch flying insects (and terrestrial insects for that matter) better. So it became a disadvantage to be big. The smaller insects now had a reproductive advantage; they were the only ones surviving to have offspring. Over a period of time, the insects grew smaller on the whole.

So today we have fairly small arthropods and insects, although my wife has personally never seen a small insect. According to her they are all large enough to carry off small children and have evil looks in their eyes.

Matthew E. Clapham1 and Jered A. Karr (2012). Environmental and biotic controls on the evolutionary history of insect body size Proc. Natl. Acad. Sci. USA DOI: 10.1073/pnas.1204026109

Next week – ideas for long studies on the nature of science.

I have judged many a science fair project in my

day. It is a learning experience, so adherence to

the steps of the scientific method taught in most

classes is O.K. But the students should realize

that there isn’t just one scientific method. This

young lady’s strategy was to take all the available

time and be the only project that got judged;

therefore, she's the winner.

A summaryof the usual (but hopefully disappearing) lecture on the scientific method –

1. Define a problem

2. Research what is known

3. Hypothesize a cause

4. Test your hypothesis

5. Analyze your results

6. Support or refute your hypothesis

In the next few class periods, a few examples are identified and the class works through them. And there is always the "design an experiment to prove your hypothesis."

The question of the day:

Is this the only method to conduct science?

I don’t have room to go into all the things that are wrong with the process as it is enumerated above, but let’s hit a couple.

One big problem is the idea of supporting or refuting your hypothesis (hypo = under, and thesis = proposition; a supporting basis for an argument). True, your experiment may do one or the other, but it doesn’t have to. Many experiments end up with ambiguous results, especially if the scientist is doing his or her job.

I am using this picture because I couldn’t find a

way to work the quote into the post. But in truth,

science is like life, better results often come from

many trials. So... science is like life which is like
science.

The design of the experiment should minimize any confounding effects that would render the results less than explicit. But, as the old saying goes, “You don’t know what you don’t know.” The middle of an experiment is often a learning moment. It is when you get into a study that you find the things that are going to make the study useless. Then you go back and design a better experiment.

Let’s say you have designed an experiment that will have a definitive result. What result are you going for? Most will say that you are trying to see if your hypothesis is supported. But anyone can design an experiment to give a desired result. Your hypothesis says “A” should occur if you do “B,” so you design an experiment to make sure “A” occurs. It doesn’t even have to be a conscious effort, your design will just tend toward that result.

The truly scientific experiment is designed to REFUTE your hypothesis. You design an experiment to prove your hypothesis is not true. If, under those, conditions, your hypothesis is still supported, then you really have something. If a scientist tries his/her best to refute their own hypothesis and can’t, the chances that the hypothesis is correct go way up. Then you report your results and let other scientists try to design an experiment to show your hypothesis is wrong. If they can’t do it either, then you are really onto something. Real scientists try to prove themselves wrong, not right. The big idea - you can never PROVE a hypothesis, you just have data to support it. But the next experiment may refute it. You can always design another experiment to test the hypothesis, so no hypothesis is ever proven absolutely. True science proceeds when you refute a hypothesis; only then can you make a concrete change to move closer to the truth.

Negative results and refuted hypotheses are the basis of science;

too bad they get a bad rap. Can you think of another profession

where being wrong is your goal?

This leadsto the next problem implied by the process outlined above. It is usually taught that negative data is a bad thing. Even people in the profession often downplay the importance of negative data; ie. data that does not give a result that is publishable.

Editors don't get excited over studies saying we tried this and it didn't work. But, an experiment that doesn’t work isn’t necessarily bad – you can learn a lot from it and so can other scientists. Unfortunately, journals don’t like to publish this data, so those who might learn from it don’t get to hear it.

This is one reason why it is important for scientists to have meetings and talk to one another personally, not to just write journal manuscripts and funding applications. Case in point, it turns out that studies that show new drugs aren't cure-alls, that they don't do what they say or don't do it as well as they say don't published. Ben Goldacre gave a recent TED talk on the subject, and has numbers to back up his assertions that negative data studies on drug efficacies hardly ever see the light of day.

In fact, negative data is the most common data and often the most useful. Refuting your hypothesis is a type of negative data. When faced with this result, you modify or discard your hypothesis and try again. You can design a thousand experiments that support your hypothesis and still not prove that your idea is the true mechanism - you may just not have thought of the experiment to disprove it yet. Like we discussed above, just one experiment that DISPROVES your hypothesis results in a step forward. Like Thomas Edison said, "If I find 1000 ways something won't work, I haven't failed. I am not discouraged, because every wrong attempt discarded is another step forward."

Negative data truly moves us forward, in fact failing is the only way we move forward. But this still leaves a problem with the way science is taught. Is there good data that is neither positive or negative? We tend to think of data only as that information that supports or refutes a hypothesis, but do you have to have a hypothesis?

This is the black walnut tree (Juglans nigrans).

The one in our front yard is about 70 feet tall and

produces over 200-300 kg (500-650 lb) of fruit.
Black walnut dye comes from the husk, not the
nut, and is yellow when immature and black
when mature.

Consider an experiment I have been conducting for the last 10 years. We have a black walnut tree in our front yard, and I have been counting the number of black walnuts it drops every year since we moved in. I had no mechanism I was trying to define, I just wanted to know how many walnuts the tree produced.

Here is my data:

Year # of walnuts

2003 3662

2004 604

2005 3508

2006 368

2007 4917

2008 0

2009 6265

2010 0

2011 6395

Now we can ask a question and hypothesize a mechanism. What is responsible for the pattern in nut production, and why do the results keep diverging? Does that mean that my original observations aren’t science? True – you could say that I was answering a question about how many nuts the tree produces, but I did not have a hypothesis that I was trying to dispute. This is true science, but not the kind we teach in school.

Black walnut meats are expensive because
they are hard to get out of the shell. But the

shell is also economically important, used in

paints, oil wells, explosives, cosmetics, cleaning

and polishing agents, and jet blasting of metallic

and plastic surfaces.

Try thisexperiment at your school. Find a tree and start to count the nuts, or find a sapling and count the leaves each year. You can keep this experiment going over a number of years, with each class adding their data.

But the real learning is in defining the limits and possible confounding effects that could lead to errors. Did the tree lose a limb and therefore produce fewer nuts the next year? Was there an explosion in the squirrel population, and they stole all the nuts before you could count them? What was the weather over the time period you observed, could a change in weather account for a change in number? Is there another walnut tree too close, and the nuts are getting mixed up? Am I just getting better at finding and counting the nuts each year?

Squirrels are kind cute, if you forgive them for

carrying rabies. Here, he represents one source

of possible error in my black walnut counts. Can

you assume that every year they steal about the

same percentage of nuts before I can count them?

I have asked these questions and am observing multiple parameters to see if they account for the pattern in nut production. But there may also be a biologic reason, something to do with energy output versus opportunity to produce offspring. All these items can be investigated and used to better explain the observations.

Each might be considered a hypothesis – the weather affects nut production, so you try to show that different weather years had the same nut production – hypothesis refuted. The squirrel population exploded – talk to the local nature experts, if the number has been fairly constant- hypothesis refuted. There is an almost infinite number of possible confounding effects, and your class can come up and test as many as their brains can think up. Now that is a true scientific method!

Next week – a question about animals and speech.

Ben Goldacre (2012). What doctors don't know about the drugs they prescribe. TED MED 2012

Humans have the ability to make language, although too

many choose not to use it well. Our speech involves

anatomy, genes, and our higher brain functions that

allow us to attach meaning to words and abstract

concepts. Donkeys only speak in ogre movies.

Question of the day – Why do humans speak and use a vocal language when other animals don’t?

To begin to answer this question, you first must decide what a language is. Linguists have four criteria for sounds to be a language. One, each vocalization has a certain order – the short "i" sound always precedes the "en" sound in the word “in.” Second, the must be order between vocalizations – this is syntax. Three, the vocalizations can not be tied to or defined by a specific emotional state – you can yell the word “Hey,” either to let someone know to stop doing something, or to call out to a friend you haven’t seen. And four, novel localizations are understood – you can say something that has never been said before, but those people listening to you will understand its meaning.

If sounds follow those four rules, then they are an oral language. So humans have spoken language and other animals don't - although the majority of people don’t use it very well. A discussion could be had as to whether whale song is language, whether American Sign Language is true language, and whether parrots can really talk.

But the question remains, why are humans so much better at making sounds and language. We share 98% of our genes with chimpanzees, but they can make only three dozen or so vocalizations. Humans can make hundreds of different sounds – every noise required for every language on Earth. Where did we separate from apes in terms of speaking?

Current hypotheses focus on two areas; brain molecular biology and body anatomy. First the anatomy – we can make more vocalizations because of how our throats and chests have evolved.

The hyoid is the only human bone that is attached

to only muscles, not to another bone. Our hyoid is attached to

tongue muscles, throat muscles, and jaw muscles. They all

work together to help us produce thousands of vocalizations.
Next week we will look at a bone in cheetahs that attaches to
only muscles.

To make sounds, you must be able to expel air in a controlled manner, this requires rib muscles and innervation to allow controlled exhalation – we got it, apes don’t. The air that is expelled passes over the vocal folds and vibrates them – this produces sound waves. The wave that is produced is based on the way your muscles change the shape of the vocal fold cartilage, and one way to alter the laryngeal muscle tone and shape is by moving your tongue.

The tongue is a muscle, and ours goes further back in our throat as compared to that of apes. Theirs is housed completely within their mouth, but ours is attached much deeper, and we can change the shape of our voice box by using our tongue. You can stick out your tongue and move it side to side and feel your Adam’s apple move.Your adam's apple is NOT the same thing as your hyoid bone; the adam's apple is the laryngeal prominence associated with your voice box, but you can see that moving your tongue can modulate the vocal folds.

The other characteristic of the tongue that makes a difference is that it is our most sensitive touch appendage. We can make small and discrete moves with the tongue, and sense where it is in relation to our teeth and cheeks. This is another reason we can make so many different sounds, and is also why babies put everything in their mouths.

The intercostal muscles between the ribs are arranged

in several diagonal layers. The external muscles help with

inspiration, while the internal intercostals help with forced

exhalation. Humans have much more innervation of these

muscles (see the nerve traveling with the artery and vein in

Fig. B), so we can control exhalation for vocalization. It is

said that the human thoracic nerves allow for as much

control as the innervation of the hand and fingers.

Anotheranatomical difference is that humans have a free-floating hyoid bone; it is the only bone in the human body that is not anchored to another bone. By attaching to the pharyngeal and tongue muscles, our hyoid helps us to make more sounds than just hoots and grunts. While apes do have a hypoid bone, it is not located as deep in their throat as is ours. In fact, humans infant larynx and hyoid bone anatomy looks a lot like ape anatomy, but as we grow, our voice box and hyoid bone descend in our throat, while those of the apes do not. This is one reason it takes babies a while to learn to speak, muscle tone being another.

Your ribs muscles, your tongue attachment and your hyoid bone are all good reasons why humans can make more vocalizations as compared to no human animals, but our brains matter too. The shear size of our brain means that we can devote more neurons to abstract thought, assigning meanings to vocalizations – this is the basis of a large dynamic language. But there is a molecular issue as well.

The brain has several areas that work in language.

Broca’s area is involved in making sounds, while

Wernicke’s area is important for understanding

speech. The understanding comes from integrating

the sounds with memories and feelings in other parts

of the brain.

The Fox2p protein is involved in vocalization and in understanding language. In songbirds with a mutated fox2p, their song is incomplete and inaccurate. In humans, defects in fox2p activity lead to severe language impairments in both speaking and in understanding. The fox2p protein acts in just about every cell, so it has functions beyond language, but two small changes in the human fox2p amino acid sequence as compared to other animals make it so important in developing true language.

On the down side, our ability to speak and make language also makes us vulnerable to choking to death. The lowering of the voice box in humans puts the vocal folds and larynx very close to the esophagus. This means that your hotdog is much more likely to get lodged somewhere that will block your air flow and suffocate you. Doubly bad, the act of having a hotdog stuck in yout throat prevents you from using your spoken language abilities to tell your tablemates that you are choking - one of nature's cruel jokes.

Next week we will take a quick look at the speeds at which organisms can move - is distance per unit time the best way to measure this?

The cheetah is one quick cat, but it often confused

with the leopard. Here is a guide. The cheetah has

single black spots, while the leopard has rosettes -

dark spots or circles with light fur in the middle. The
cheetah is taller and skinnier, with a barrel chest.

Finally, the cheetah has “tear stains” dark lines that

run from its eyes to its mouth.

Take a lookat these short videosand then we will ask today’s question. Those little guys are awfully fast, especially the Chromatium. Some seem to dart all the way through the field while others move around in circles or stay mostly still. Bacteria must be the fastest things around.

The question of the day:

Just how fast are microscopic organisms? And for that matter, what is the best way to measure speed in organisms of vastly different sizes?

The fastest terrestrial animal is the cheetah; it is scary fast, to the tune of 70 mph over short distances, like in this video. From a dead stop, the cheetah can hit 60 miles per hour in just three seconds. Cheetah races are popular attractions in many zoos right now. You run and the zoo keepers time you. Then they have the cheetah run and you get to compare times – you won’t win. Biologically, they're built for this speed.

We talked a couple weeks ago about how the hyoid is the only bone in humans that is not attached to any other bone, but in cheetahs, the clavicle bones of their shoulders are built this way. They attach only to muscle, so that it offers the cat extra length in its stretch as is reaches forward for its next step.

The cheetah uses it tail as a rudder and counterbalance as it

runs. In these pictures, you can see that its tail flattens out to

act as a sail. It can catch wind or cut through the wind to help

in turns and balance. This is the only cat that can flatten its

tail without the aid of a slamming door or a rocking chair.

Anyprey animal worth his or her salt will try to turn and have the cheetah run past them, but this cat can go from a top speed to near zero in a mere second. It has claws on the backs its front paws so it can slam its front legs into the ground and have them catch like extra brakes.

Turning is also engineered into this fast cat. Its tail, unlike other cats, is flat, so it can use it as a rudder in turns. Also unique to cats, cheetah claws do not retract. They are always sticking out, so that they can grip the ground and push off for more speed and control in the turns. (click here for the newest mechanism identified in cheetah speed)

If we look up in the sky, there are some pretty fast animals there too. The peregrine falcon is considered to be the fastest bird, hitting over 220 mph when in its hunting dive. The falcon uses this speed to catch other birds right out of the air, as they almost always take their prey on the wing.

The difference is that this speed is achieved with the aid of gravity, it is only in diving that they can go this fast. In horizontal flight, the peregrine can manage only a measly 55-60 mph, not quite as good as the cheetah. If you tossed a cheetah out of a plane, it could achieve a terminal velocity of 200 mph, nearly the same as the falcon, the difference being that a cheetah is not accustomed to assuming an aerodynamic position going straight down. It would probably look rather scared and flail a lot – I don’t recommend trying this.

The white-throated needletail is a sleekly designed

bird, with swept back wings and a large chest. The

chest is large to accommodate huge breast muscles

and a larger than normal heart a lungs. Its tail can be

splayed out for turns, or turned into a needle shape

to reduce drag.

If youwant top speed in flapping flight from a bird, bet on the white-throated needletail. It used to be considered a member of the swift family (appropriately named), but is now in its own genus. With a tail wind and the proper motivation, these small birds can reach speeds of 100 mph. Living on the northern coasts of Australia, it is bigger than you might expect for a fast bird, especially one that used to be considered a swift. It has long, swept back wings that help it pick up speed and still be able to maneuver.

Most airplanes have this swept wing design to improve flight characteristics; and as with many of humans so called ideas, we stole it from nature. However, we are getting better at stealing. New aircraft wing designs are based on the swifts’ ability to wing morph, changing the shape of its wings to take better advantage of the flying conditions at the time.

If we drop down into the seas, we can look at speed in the fishes. The sailfish is considered to be fastest. It is of course built in a streamlined fashion, meant to build the speed needed to catch the fish and octopuses it eats. It has been clocked at 68 mph, which in my book makes it faster than the cheetah, since it is moving through water, a much more dense medium as compared to air.

The long upper jaw of the sailfish isn’t just for cutting

through the water. It can skewer large fish with it while

hunting, although this isn’t its normal hunting behavior.

Sailfish have been seen to cut mackerel in half with a

flick of the bill. Its cousin the marlin has a bill that can

cut through the hull of small boats.

Sohow do bacteria stack up against these speeds? Not too well, despite what we saw in the first video. The fastest bacteria, members of the Vibrio family, move about 200 µm/sec – this is about 0.00045 mph (0.00072 kph). Even my teenage son on his way to clean his room moves faster than that! However, when you sneeze, you send bacteria (and mucus) out of your nose and mouth at over 100 mph – you can almost hear the little bugs screaming.

Because we are looking at a very small area under the microscope, it appears that the bacteria are covering a good distance. But at 1000x magnification, the least magnification you would need to observe bacteria, the field is usually just 500-800 µm across (0.02-0.03 inches). This makes the bacteria appear to be moving quickly.

Vibro cholerae is a gram negative bacteria with a single

polar (meaning at one end) flagellum. This long

appendage rotates and provides the locomotive force for

this fastest species of bacteria. The flagellar motor can

spin in either direction and is driven by a sodium ion

gradient. Too much salt and it slows down; not enough

salt, it slows down. It’s like a microbial Goldilocks.

Like the fish, bacteria are moving through an aqueous (water) medium, so the density is much greater. But it is even worse for them because of their small size. The effects of density are much larger on small organisms, sort of like us trying to walk through a pool filled with caramel (not a bad idea).

Butwhat if we measured speed in a different manner, say….. bodies lengths per second. Vibrio are approximately 2 µm (0.00008 inches) in length and they move about 200 µm/sec. This is about 100 body lengths per second. Now that seems pretty fast, especially for swimming through something thick.

How does that compare to our other candidates:

Avg. Length Top speed (kph) Body lengths/sec

Cheetah 125 cm 112.7 25.0

White throated needle tail 25 cm 160.9 178.7

Sailfish 340 cm 109.4 8.9

Vibro choleraebacteria 0.0002 cm 0.00072 100

S. Giant Darner dragonfly 12.7 cm 57.9 126

Australian tiger beetle 0.10 cm 9.01 2502.8

So the bacteria are pretty fast, it just depends on how you measure it. But the needletail still holds its own, even though it is only traveling through air. Comparatively, Usain Bolt moves at a top speed of about 6.2 body lengths/sec. Since humans walk upright, we could measure him at body depths/sec, which makes him sound faster, about 30 body depths/sec (assume 15 in body depth). But we don’t all run like Usain Bolt.

Black horseflies can measure up to 1 inch in length. They

pester people and domestic animals, but worse, can carry

anthrax and tularemia (rabbit fever) organisms. Like

mosquitoes, only the females feed on blood, the gentler

males prefer nectar and help pollinate many flower species.

I could make an analogy between horseflies and humans,

but I won’

In the table above I gave you a couple more examples so that we can find an overall winner. As always, nothing seems to top the insect world, the Australian tiger beetle can move at over 2500 body lengths/sec, while the darner dragonfly shown above is merely the scientifically confirmed fastest flying insect. However, if you want to go with the most recent estimate for the male horsefly (Hybomitra hinei wrighti), we are talking about speeds of 145 kph when he's in pursuit of a female- typical male behavior. That works out to roughly 4000 body lengths/second!

Next week we can look at plants lifting weights; they have to be in shape in order to photosynthesize!

Penny E. Hudson, Sandra A. Corr and Alan M. Wilson (2012). High speed galloping in the cheetah (Acinonyx jubatus) and the racing greyhound (Canis familiaris): spatio-temporal and kinetic characteristics J Exp Biol DOI: 10.1242/jeb.066720

We have talked about the reactions of photosynthesis

before. Basically, the plant uses the energy of the sun to

fix carbon (change it from gas to solid) by adding water

to it chemically. Then it splits them again to make energy.

In previous posts we have talked about photosynthesis – carbohydrates and made from carbon (carbo-) with water added (-hydrate, as in- when you are very thirsty, you are dehydrated). Therefore, the leaves must have a constant and reliable source of carbon (from carbon dioxide in the air) and water.

Question of the day:

How do trees move the water up into their leaves, against the force of gravity, in order to carry out photosynthesis?

Water is quite massive (1kg/L or 8.3 pounds/gallon), and a mature oak tree needs 40-60 gallons of water every day. So how does this huge amount of water get to the top of the tree? Does it travel there from someplace else? Could it be absorbed by the leaf from the air in the same way carbon dioxide is brought in? Or maybe plants don’t have to drink and they use the water they make during metabolism, like the kangaroo rat we talked about last year -they don’t drink at all and seem to get along just fine.

We might be able to eliminate one possible explanation right away – what happens when you don’t water your houseplants? Do they grow or do they die? So do you think most plants need a source of external water or could get along on the water they make during aerobic respiration? Right… I think we are down to absorption or movement from some other place on the plant, namely the roots.

Keep in mind that not every plant has to move water from its roots to its leaves, take the bromeliads for instance. Many of these plants don’t have roots, we have discussed how they have special structures that help them absorb water at the base of their leaves.

You could test other types of plants to see if water on just the leaves is enough to keep them alive. How might you do that? Cover the dirt with something that repels water and then just mist the leaves – that might do it. Try it for a while and see how the plants do.

I think that you will find that they do not thrive after the moisture in the dirt is used up. For most plants, 99% or more of the water they use must be absorbed by the roots and transported up the stem (trunk if it is a tree) to the leaves.

Celery stalks and carnations are good to show the flow

of water against gravity. Dark colors show up better.

Maybe you could have races between the two plants and

then cut them crosswise to look at the size of the vessels.

I bet the smaller ones move water faster.

To modelthe answer to our question of the day all you need is a straw. But that isn’t very illustrative or fancy – so how about cut carnation stems or celery stalks (with the leaves) in a glass of colored water. Lighter colored flowers and darker colored water works best (I use blue food coloring), but I have had students who have really gotten into this and tried to measure the time by adding one color, then switching to another and seeing how long it takes the color to change in the flower and if all the color is lost along with the water.

Over a couple of days, the color will indeed be drawn into the petals of the flower. How does the color get there? Is the water level the same? Water is moving up and taking dye with it. So you can see that it does happen – but this still doesn’t explain HOW it happens.

To answer this, you might ask what happens to the water that is being drawn up into the leaves (and flowers of the carnation model). Try putting a baggie over the end of a tree branch and tying it tight. You will see condensation develop over a day or so. Where did this water come from?

Here are the vessels in a tree. 1) pith– it gets crushed as the tree grows

2&3) annual growth ringsmade of water carrying xylem. Why

do you see different rings if they are all xylem? Because spring

xylem vessels are big, and summer xylem (less water available, so

less growth) vessels are smaller. The line is the change from

small to big. 6) phloem– this is what carries the carbohydrate to

the roots and other parts of the tree.

The answer is a process called transpiration (or evapotranspiration). The water evaporates from the leaves, out of pores called stomates, and this creates a negative pressure – like the negative pressure in your mouth when you suck on a straw. This negative pressure actually pulls water up from the roots through the xylem of the plant, to the leaves. In the case of the carnation flower or celery, it also pulled up the very small dye molecules in the water. This evaporative force is quite strong, but not strong enough on its own to lift that 350-500 lb.s (40-60 gallons) needed for an oak tree each day.

The water itself helps in the process. Water is a social molecule, it likes to stick to itself and to other things. It will climb up the sides of container, just look at the meniscusformed in a narrow graduated cylinder when water is added, or note how water travels up a thin capillary tube.

The capillary action comes from the water’s cohesive force, and helps the tree stay hydrated. Evapotranspiration’s negative pressure pulling water up is combined with water’s ability to climb up, and together this is enough to keep the tree’s leaves in the pink, no matter how tall it grows.

But like everything else, there are exceptions, like the plants that don’t have xylem. The non-vascular plants (like mosses and hornworts) only survive based on water absorption and capillary movement from cell to cell. Therefore, they cannot be very tall; you need vessels (xylem) to allow water movement and tall growth. The tallest of the non-vascular plants, the Polytrichummosses, may get to be two feet tall, but that’s it.

Evapotranspiration via vasculature and leaf stomates leads to another question – if water is being lost through the leaves all the time, doesn’t this hurt the plant in times of drought. Well… yes. But plants have evolved some pretty neat tricks to help out.

Some plants don’t use the most forward strategy of

photosynthesis because it would drain them of all their

water during the hottest weather. CAM plants can close

their stomates during the day and only fix carbon dioxide

at night when it is cooler. We should probably talk about

these plants in more detail later this year, they have some

mighty cool adaptations.

1) Stomatescan open and close to regulate water loss. Some plants can close their stomata completely during the hot day, and save their built up radiate energy to convert carbon dioxide and water into carbohydrates only at night, when they will lose less water. Cacti are a good example of this.

2) Leaves, especially the sun-exposed sides of leaves, are covered with a waxy substance called cuticle that greatly reduces the loss of water by diffusion through the cell wall. If water were allowed to travel through the cell membrane and wall, then it would evaporate and set up a negative osmotic and evaporative pressure that would quickly dehydrate every surface cell.

3) Here's a trick many people don’t really consider – many plants have two types of leaves! You might be able to find a tree or two with which to investigate this.

Big leaves have large surface area, so more water will be lost as compared to smaller leaves. Leaves in the direct sunlight should be structured in order to carry out the most photosynthesis, but if they are small, how can this be maximized?

Many trees have sun leaves and shade leaves. Sun leaves are smaller, thicker, have more stomata, and are located where the direct sunlight hits the tree during a good portion of the day. Shade leaves are bigger, thinner, and have fewer stomates to reduce water loss.

Sun leaves have more layers of pallisade cells, the cells that have the most chlorophyll and do most of the photosynthesis. They are located at the ends of branches, especially on the north side, and on the crown (top) of the tree.

Sun leaves are a smaller and thicker, and they often have

fewer in and outs in their shapes. The smaller shape

reduces water loss, the thicker body provides extra layers

of cells for photosynthesis, the reduced number of cuts

and points…. I have no idea. It is a continuum, leaves that

get a good amount of light land somewhere in the middle.

Shadeleaves have to rely on lower levels of sunlight (they are in the shade), so they have even higher concentrations of chlorophyll than sun leaves, although they are thinner. They can process light more efficiently than sun leaves, so they are actually very important to the plant despite their little time in the sun.

Look at the trees around you, do some have large leave on inner branches and lower on the canopy, while having smaller leaves on top or on the ends? These are probably shade tolerant trees. They have developed the ability to still do enough photosynthesis despite low levels of light.

On the other hand, do you see a tree that has just one size of leaf (not including newly formed leaves) and only has leaves on the ends of the branches? This is probably a shade intolerant tree.

The conifers are an interesting exception, some are shade tolerant, usually the firs, while others are shade intolerant, mostly the pines. However, neither type has sun leaves and shade leaves. Their shade tolerance has more to do with their branch geometry and ability to allow just about all their leaves (needles) see the same amount of sunlight.

Next week, we will ask if there is any limit to interspecies mating, can you cross a cat with a dog?

A full grown liger is a biiggg cat! A male lion and

a female tiger get to know each well, and their

love child is huge. It doesn’t happen in the wild

because the ranges of lions and tigers don’t

overlap, and they don’t have computer dating

services. The liger is bigger than either parent,

and this is a problem during birthing. They have

many birth defects and often die young.

Whenputting organisms into categories (taxonomy), we go from bigger, more general categories to smaller more specific ones. The more similar two organisms are, evolutionarily and genetically, the more levels of their taxonomic classification they will have in common.

Question of the day:

A tigon is the result of a cross between male tiger and a female lion, while a liger is the offspring of a male lion and a tigress. But are these new species? And just how far can you go when you cross-breed?

There are instances when different species mate, but the outcomes, while interesting, may or may not be new species. It helps to know the classification levels.

Kingdom (domain) - Insects, dogs and people are all very different, but they are all animals.

Phylum (Division for plants) – usually these group things by a common body plan or some other morphologic character, or a certain degree of genetic relatedness. Arthropods are all related by a chitin exoskeleton, so flies and lobsters are both arthropods, but flowering plants have fruits and conifers have cones, so they are in different divisions.

Class– these groups have more in common, either physiologically or genetically. Cows and dogs both have hair and give birth to live young, so they are both in the class Mammalia. However, flowering plants are divided into two classes, monocots and dicots, based on seed and vascular tissue differences.

Here is the classification scheme for several familiar

mammals. Cats are all in the same family, but there are

several genera, while all dogs fit in one genus and all

wolves in another. Black bears and Kodiak bears are a

different genus than polar bears, but hikers and bigfoot

monsters have reported sightings of polar and Kodiak

bear hybrids…. well hikers have been reporting them.

Order– Even more specific, this level of classification has been altered greatly by molecular biology. Armadilloes and anteaters are both in the Order Edentata– as toothless mammals. However, roses and magnolia trees are both dicots, but they belong to different orders (Magnoliidae and Rosidae).

Family– Now we are getting down to smaller differences, but still just as important. All the big-eared bats and all the thick thumbed bats are both included in vespertine family, because they come out to feed in the evenings. On the other hand, maples and mahogany trees are both in the order of Sapindalae, but they belong to different families based on their leaf and flower anatomies.

Genus–comes from the Greek for “kin,” so these organisms in the same genus are closely related. In animals, both moths and butterflies are in the same order, but they are broken into 124 different families, and the family Nyphalidae, which contains the Monarch butterfly, has over 600 genera (the plural of genus).

Species– These are the individual distinct group of organisms. Usually, the distinction is made based on whether their breeding can produce fertile offspring. So bulldogs and St. Bernards are both species of dog, since they can make mutts.

The africanized honeybee is more likely to swarm and

migrate when food supplies are low, so they can be seen

in masses like the one above. For hives, they usually

invade an existing hive, quit out the queen and install their

own. The danger in these bees is that they are more likely

to swarm when agitated, and they will chase the agitator

for a much longer distance (a mile or more) than regular

honeybees (100 yards or so).

Sub-Species - this is like the different breeds of cats we keep or that unfortunate incident where African bees were crossed with South American honeybees and created killer bees!

Now that we have that information – let’s rephrase our question of the day. Can you breed (hybridize) different species and create a new species?

Cross-breeds are common within species (intraspecies hybridization), like with cats or dogs – not cats with dogs, you’d never want to do that! And we know they are fertile, so you end up with some dogs that are ¼ this, 1/8 that, and ¼ the other. What about between species?

Interspecies hybridsusually don’t give you fertile offspring. Since the definition of a species is a group of animals that can mate to give fertile offspring, then you would be hard pressed to create a new species by breeding different species together.

For example, the liger and tigon males are always sterile, so even thought the females are sometimes fertile, they still can’t mate a tigon to a tigon. This would be necessary to make a stable species. So the chances are low on the interspecies level.

That would mean that new species coming from breeding of animals from different genera would be even less likely to produce new species. However, individuals can be hybridized. Intergeneric hybridization is easier to do in plants; orchid growers have made many different intergeneric crosses, like little Dr. Frankensteins with green thumbs.

Compare the two marine mammals that are jumping. One

is bigger, darker colored, and apparently can jump

higher. That one is the wolphin. Her name is Kekaimalu,

the offspring of a bottlenose dolphin and a false killer

whale. Her offspring, Kawili Kai, is bigger than a dolphin

as well, but is lighter colored than mama.

Butthey can occur in animals. A wolphinwas born at Hawaii Sea Park in 1985, the result of a mating between a bottlenose dolphin and a false killer whale. These species are in the same family (Delphinidae) but different genera. Named Kekaimalu, this female is fertile and has mated with male bottlenose dolphins. The first two offspring did not live very long, but her third calf is still alive and well, at ¾ dolphin and ¼ false killer whale. However, this wouldn’t be a new species unless wolphins mated with wolphins and produced fertile wolphins.

The rarest hybridization is the interfamilial hybrid. Most examples have occurred in birds, where game fowl are housed together. The Pea-guinea is a hybrid between a peacock and a guinea fowl hen. They look weird and don’t survive beyond a year or two, so there is no way that these could form a stable species.

It would take a bunch of posts to talk about why certain hybrids will work and others won’t, and why new species are not generally produced in this way. But for now - how about two exceptions?

What do you get when you cross a blueberry with a

snowberry (maggots, that is)? You get a Lornicera fly –

O.K. not a funny joke, but a pretty cool twist in

evolution. As fruitflies go, this is a pretty cool looking

one; you don’t have the ghoulish red eyes to deal with

and three stripes make it look a little like a lightbulb!

The Lonicera fly is a new species produced by natural interspecies hybridization! Just when you think you understand nature, there it goes again, kicking you in the seat of your pants.

The creation of this new fruit fly species did have a little help from humans. For about 250 years, honeysuckle plants have been imported to the North America from Europe. In the 1990’s scientists found the Lonicera fly and tried to see what other flies it was related to. Low and behold it was a hybrid of the snowberry maggot and the blueberry maggot. But why didn’t the hybrids breed with the parent species and dilute the hybrid genome back into the two stable species? How did the hybrid become a new, stable species?

These hybrid flies preferred to feed on the honeysuckle, so they lived on the imported plants, while the parent species lived on their favorites (snoberry or blueberry). This was a kind of geographic isolation; the Lonicera hybrids found only Lonicera hybrids when it came time to mate and they ended up mating hybrid to hybrid for many generations. This resulted in a stable species, the process is called hybrid speciation.

The Heliconius heurippa butterfly has an unusually

large black bar that crosses its body. This must be

fairly obvious to other butterflies of the same

hybridization and it must also be pretty attractive.

Both male and female hybrids search out the wide

black bands. I would love to know the molecular

biology of that specificity of attraction.

The second exception is the Heliconius heurippa butterfly in South America. An interesting 2006 study in which hybridization was repeated in the laboratory showed that H. heurippa in nature is the result of breeding of two other species of butterflies. The hybrid does produce fertile offspring, both male and female, but that isn’t the end of the story. In this case, there isn’t any geographic isolation forcing hybrid-hybrid mating - they chooseto mate together. Their choice is related to the fact that the hybrids have bold black stripes on its wings, while neither parent species does.

The hybrids preferentially mate with other butterflies with the bold stripes, so they are mating hybrid to hybrid and are stabilizing the new species. Darwin would blow his top – or maybe not. He never said this couldn’t happen, just that it was less likely.

Stay tuned, molecular techniques are beginning to show us that this may not be such an exception – a 2011 study identified another butterfly species created by hybrid speciation and it happens all the time in plants, like sunflowers. Three younger species, the desert, the puzzle, and the sand – seem to live where their parent species cannot, so they tend to pollinate with their similar hybrid brethren and make new species.

Next week we will ask why some birds migrate while others stay put year round.

Jesús Mavárez1, Camilo A. Salazar, Eldredge Bermingham1, Christian Salcedo, Chris D. Jiggins & Mauricio Linares (2006). Speciation by hybridization in Heliconius butterflies Nature, 41, 868-871 DOI: 10.1038/nature04738

The snowy owl is sedentary, meaning it does not

migrate. The males are almost perfectly white,

while the females and juveniles can have black

barring. They sit, look, and listen for their prey,

which includes small rodents and even other birds.

Their hearing is good enough to let them target a

mouse under the snow from hundreds of yards away.

The Arctic tern travels from north of the Arctic Circle to Antarctica and back again every year. On the other hand, the Snowy Owl lives in the arctic region year-round; it doesn't migrate at all.

The Question of the Day:

Why do some birds migrate while other birds stay in one place?

The possible explanations are many. Maybe the type of food they eat is present only part of the year, or maybe they can’t stand the cold temperature. They might need to have their babies in a place away from predators, or perhaps migration is an evolutionary holdover that had a reason in the past, but no longer isnecessary.

How could you start to determine the reason for migration in only some bird species? I would start by looking at how closely related the migratory and non-migratory species are. Maybe all the birds that migrate are more closely related to one another than to the birds that don’t move around during the year. This would suggest that there is a genetic basis for why only some species migrate.

One research group did just this in 2007. The looked at 379 species of flycatchers, a closely related group of birds. They found that almost equal numbers of species were migratory or resident, so it doesn’t appear that genetic relatedness is the answer.

The painted bunting is among the most colorful

birds in North America. This male has several colors,

while the female is a brilliant green. They breed in

south central US or on the southern east coast, but

winter in Central America; therefore, they are

seasonally migratory.

Maybethe need to migrate has to do with the geographic region. About 90% of birds in the arctic migrate, some are present there only in the mid-summer months. The arctic tern is a good example. Arctic terns move with the summer, breeding in the arctic in May-July, moving down along continental coasts to arrive in Antarctica for the months of December to February. The entire distance traveled could be as much as 32,000 km (20,000 miles) in a single year.

Similar to the arctic region, the east coast of North America has species that migrate and species that are sedentary. About 80% of the birds species of the east coast move south during the colder months, but on the Pacific coast, almost all the bird species are non-migratory.

So migration is not due to the type of geography around the birds. However, the east coast of North America does have larger temperature swings than the west coast, so maybe it is just that some birds can’t deal with the cold.

Some non-migratory birds can control the amount

of blood that travels to the legs in order to conserve

body heat. This works even better if they can reduce

the amount of contact with the cold surfaces, so some

of these birds perch on one leg at a time.

Manybirds that do not migrate have special adaptations to deal with the cold. Trying to keep a constant body temperature (endothermy) takes a lot of energy, and birds live right on the edge of having enough energy anyway. Flying requires a huge amount of energy and they must eat almost constantly just to keep enough carbohydrates in their system to be able to move around to find more food.

Burning more energy to keep warm might tip them over the edge into starvation. To alleviate this problem, many birds can allow parts of their bodies cool down to freezing or near freezing, while keeping their internal organs at a temperature that will preserve their function. Blood flow is a major way to keep parts of the body warm, a duck standing on the ice can reduce the blood flow to its feet and reduce the amount of heat lost to the cold ice. The duck’s chest may be 40˚C, but its feet could be just one degree above freezing.

But let us look again at the arctic tern. It migrates from the north polar region to the Antarctic region in such a way that it sees two summers each year. But these are summers in name only. The arctic summer has an average temperature from -10˚C to 10˚C, so much of the time the tern is there, the temperatures are near zero.

The arctic tern has a ghastly commute each year.

The trip is even more amazing when you consider

that during its yearly molting, the tern flies very

little. So, all that distance must be fit in to just a part

of the year, not the entire 365 days. I guess they

vacation by NOT traveling.

Thenwhen they reach the Antarctic, the summer there has an average temperature of -2˚C to 2˚C. This is hardly a balmy vacation destination for the tern. The temperatures in both its breeding grounds and wintering grounds would require it to have elaborate temperature control and energy-saving adaptations. Therefore, inability to tolerate cold temperatures is not the reason for migration, at least not for many birds.

The group who carried out the 2007 study concluded that the main reason that only some flycatcher species migrate is not due to what they eat, or when they breed, or what is trying to et them, but to how available their food source is. Whether they are fruit eaters, or insect eaters, or seed eaters, how easy it is to find their food is the most common reason that migration has evolved for a specific species in a specific location.

The food availability hypothesis is supported by certain types of migration that are common in North America. Irruptive migration is characterized by a population moving to another place, but there is no yearly, seasonal, or geographic pattern. The birds may migrate one year, then not again for a dozen years, or they might go for several years in a row. North American seed-eating birds are famous for these migrations. The distance and number of individuals that migrate are also not very predictable, and this all makes it sound like the movement is linked to food availability. However, it could also be to escape some population explosion in a predator species or for some other reason.

It isn’t only birds that might undergo partial migration.

Some crab species will migrate for breeding purposes,

like these Christmas Island Red Crabs. Individuals

that won't breed just don’t make the trip. They may be

too young, too old, too lazy. In other cases, when

populations migrate away from the breeding grounds,

some individuals may remain there the year round.

Anothertype of migration is partial migration, a pattern wherein not all birds of a species in a certain location will migrate, only some of them leave in non-breeding times, while others stick around year-round. Food may be available for some, but not all, or the environment may be unsuitable for some weaker individuals to have enough time to forage for a sufficient amount of food. These (and other reasons) might explain why partial migration exists, but one question remains, who stays and who goes? The choices could be based on age, altruism, suitability, dominance… laziness?

As an aside, it isn’t just birds that migrate. Mammals move from place to place, sometimes with a defined pattern during the year, but sometimes they just follow the food, a process called random migration. And some insects migrate as well.

For many years, the migration of the Monarch butterfly was believed to be the longest insect migration. But this is not the typical migration we think of, where an individual moves from one place to another and then back again. The migration of the monarch butterfly takes four generations to complete. Some generations are born and fly a long distance to lay their eggs, while others are born, live, and reproduce in a small area. But altogether, this butterfly moves from as far north as Canada to the high mountains of Mexico and back each year, about 7000 km (4400 miles).

Globe skimmer dragonflies breed in freshwater pools,

so they migrate from India’s monsoon season to the rainy

season in East Africa, all in search of a place to lay

eggs. They make stopovers on the Indian Ocean islands,

but only to rest, because there are very few

pools of freshwater on these coral cay islands.

A few years ago, a biologist in the Maldive Islands started to wonder about the movement of globe skimmer dragonflies where he lived. They seemed to be plentiful in some periods and absent in others. He started to track them, and found that they have an even larger migration pattern than the monarch butterfly. What is more, they fly long distances over the ocean with no place to stop and rest.

Over a series of generations, the dragonflies move from India to the Maldives, some 600-800 km across the open sea. Then they move to east Africa, from Uganda to Kenya and Mozambique. In January, they start back toward India, and complete their migration of more than 18,000 km (>11,000 miles).

So birds may get most of the publicity, but insects hold their own in the migration game. Of course, it does take four generations of dragonflies or butterflies to make their complete journey, where a single arctic tern may make its entire 20,000 mile trip thirty times in its lifetime. O.K., they are both pretty impressive when you consider most people need a car to go down the street to the grocery store and back.

Wrigley Field was originally called Weeghman Park,

after a local lunchroom owner. The first team to call

the park home was the Chicago Whales - strange name

for a city on a freshwater lake. The ivy on the outfield

wall is actually Boston Ivy and Japanese Bittersweet,

since English Ivy would have a tough time with Chicago

winters- just like everyone else.

Wrigley Field is the venerable 1914 baseball stadium on Chicago’s north side. One of its most characteristic features is the ivy covered outfield wall that occasionally swallows a hit ball, never to be seen again – a ground rule double.

The question of the day:

Does ivy stick to a wall or grab it, and will ivy have enough strength to destroy the wall over time?

English ivy (Hedera helix) is of the Araliacae family, but doesn’t have spines like some other species in the family, like the aptly named devil’s walking stick (Aralia spinosa). I can’t imagine a Chicago Cub outfielder diving into a wall covered with Devil’s walking stick to make a catch; although being a Cubs fan can feel like that.

English ivy is an evergreen climbing vine, but it will grow along the ground just fine if there is nothing available to climb. Not unlike Kudzu in the US south, ivy can become invasive and choke out other plants, creating “ivy deserts.”

As English ivy grows along the ground, it shows its juvenile form. It has light colored leaves with lobes and points, no flowers, and can form roots very easily. When the ivy finds something on which to grow vertically, it transitions to the adult stage, with leaves that are less lobed or pointy, less root growth and can produce flowers and berries.

The stem of ivy is not capable of supporting the weight of the vine – it can’t stand up on its own, but yet it easily grows 30 m (98 ft) against the force of gravity and can reach heights of more than 90 m (300 ft) in conifer trees with seemingly no problem whatsoever. The mechanism by which it accomplishes this was investigated by none other than Charles Darwin, but much more recent work is showing the ivy plant to be quite a surprise.

English ivy sends out thousands of adventitious roots

per foot. These roots are responsible for the ivy’s

adherence to the substrate. They are aerial roots, but

can also grow into the ground and act as regular roots

as well.

Darwinnoted that ivy sends out adventitious roots from its stem. This is where the devil’s club or walking stick and the ivy are similar, but in the case of ivy, they are induced by a vertical substrate and don’t cause pain.

Adventitious roots are those that arise from someplace other there where you would expect them, like directly from the sides of stems, or off leaves, or off old woody roots. In the case of ivy, they are aerial, adventitious roots, since they do not get buried in dirt. They can still collect water, but are protected from dehydration by having a thicker, waxier surface.

Darwin also noted that ivy was not wrapping the adventitious roots around some protruberance on the vertical surface to allow the vine to cling. Those that do wrap around and grab are called tendril climbers, andinclude clematis, grapes, and sweet peas. In some cases, the clinging apparatus will have only that function, in other plants they will grasp, but can leaf or fruit as well.

Other vines use their stems to wrap around a vertical substrate, the stem twiners and tendril climbers are both examples of thigmotropism (thigmo = to touch, and trope = turn). Interestingly, honeysuckle always coils clockwise while wisteria always turns counterclockwise.

Pea plants grab hold of vertical surfaces using tendrils

that coil upon contact with a surface. The tendrils are

modified leaves, stems, or shoots. Supposedly they taste

good and are a vogue ingredient in cooking nowadays.

English ivy doesn’t twine, it doesn’t tendril wrap, and it doesn’t burrow into a flat surface to gain an anchor, although it will exploit a crack and grow through or along it. Neither does it just grow up until it touches something and then use its growth to ramble through and around the substrate. Climbing rose is an example of a rambler, it will use its hook shaped thorns to help it stand up as it grows through and around another plant.

No, English ivy uses a chemical adhesive secreted by it adventitious rootlet ends in order to stick to a vertical surface – it can even cling to something as smooth as glass. The secretion is yellowish and forms circular dots on the vertical surface. It is very sticky, and becomes stickier as it dehydrates.

The compound contains polysaccharides that act as a carrying agent for discrete nanoparticles (70 nm diameter) that are responsible for the adhesion to the wall. Amazingly, the way ivy clings to a wall is very similar to how a gecko walks up a wall or hang upside down.

This is an electron micrograph of the nanoparticles of

ivy adhesive. The particles have an average diameter

of about 65 nm and can get so close to the substrate

that the electrons and nuclei of each will interact and

attract one another.

The nanoparticles are like the nanohairs on a gecko’s (or fly’s) foot. They increase the surface area of the material greatly and are so small that they can make very intimate contact with the surface. They get so close to one other that they can use van der Waal’s forces on the atomic level to attract one surface to the other. Studies from 2010 showed that the interactions of the nanoparticles in the yellowish ivy secretion were enough to create the bond, and mimics using polystyrene nanoparticles have become excellent adhesives.

But the amazing abilities of the ivy nanoparticles don’t stop there. They seem to disperse and absorb light energy much better than the metal nanoparticles that we currently use in our sunscreens. Titanium oxide and zinc oxide are the current state of the art in terms of reflecting, dispersing and absorbing ultraviolet rays, but it seems that ivy nanoparticles are 70X better at these jobs than are the metal oxide particles. Our next generation of sunblock may come from ivy – talk about green technologies!

Ivy can help with sun damage in another way as well. By covering the walls of a building, ivy keeps the heat in during the winter by acting as insulation and reflects the sunlight away in the summer, keeping the building warmer or cooler as the case may be. Ivy also deflects much of the rain from getting to the surface that is covered, so it can protect against acid rain damage or other weathering.

But ivy can do damage as well. Any surface that has gaps, like shutters against a wall or wood siding will allow ivy to grow in the cracks and pull them from the wall over time. It may not create holes in mortar or brick, but it will grow into them and then expand when the stem fills with water. This hydraulic action can break down stone over time and bring a building down if given enough time and opportunity.

The mass of an ivy vine can also cause damage. It can cover an entire plant and keep it from getting enough sunlight to live, but it can also make it top heavy and cause it to fall in a strong wind. I have wondered about this in terms of ivy growing on a building. How much weight does it add to the wall, and would it ever be enough to pull the wall down?

The quintessential ivy covered cottage. How much weight

must this add to the house? The roof could easily collapse,

and who knows what is living in there. But there is no

arguing that it looks great.

Look atan ivy-covered wall. How much must all that vine weigh? Forestry workers pulling ivy off of conifers say it is not unusual for there to be over 2000 lb.s (907 kg) of ivy on a single tree.

I have been wondering how to estimate the mass of ivy that is clinging to a wall. You might estimate the square footage covered, then cut out one square foot and find its mass, and then do the math to find the total. But if you cut from the bottom, then everything above it will die – not the best experimental design. If you cut from the top or edge, the vine will be immature and have less mass per sq/ft than the average along the entire wall.

Maybe you could advertize free ivy removal, find a client, measure the square footage and the find the mass of everything you take down. But remember, that is one great adhesive; you will probably leave a decent amount behind, leading to a low estimate. Or, you will bring parts of the wall with it, leading to an overestimation. Any ideas?

Next week we will begin a series of posts on getting sick - the exceptional thing is that sometimes it is good for you to get sick.

Lijin Xia, Scott C Lenaghan, Mingjun Zhang, Zhili Zhang and Quanshui Li (2010). Naturally occurring nanoparticles from English ivy: an alternative to metal-based nanoparticles for UV protection Journal of Nanbiotechnology DOI: 10.1186/1477-3155-8-12

Biology Concepts – disease, vaccination, single nucleotide polymorphisms

Jill Bolte Taylor is an Indiana University neuroscience

professor who suffered a massive stroke. She recognized

what was happening and has translated her thoughts

and feelings into a narrative to help us understand. She

is eloquent in describing how her stroke has affected her

in a positive way. --- Soon to be a major motion picture!

Yourarely hear someone say how glad they are to be sick – unless a business meeting, unit test, or visit to the in-laws is involved. Robust health is a sign of good genes, and animals (including humans) instinctually seek out good genes when selecting mates. We don’t like to be sick, and we don’t want others (potential mates) to see us being sick.

True, there is that one person in a thousand who argues quite eloquently that an illness showed them another side of life, expanding their world-view and making them a better person. I applaud this attitude, but did you ever notice that it’s only the survivors that can gain this insight?

Our entire health care system is based on the idea that it is preferable to not be sick. The best way to bring this about is to reduce the chances that we will encounter anything that might provoke a response from our body, including pathogens (disease causing organisms, from pathos = disease and genique = to produce) and allergens (living or non-living molecules that can induce an allergic response).

But what does it mean to be “sick?” If you are infected by a pathogen, are you necessarily sick? There are infections that are subclinical or asymptomatic (without signs of disease), and there are carrier states, when a person is infected and can transmit the disease, but does not have symptoms. Are these people still sick?

You can be in a social situation where you feel empathy or regret, “I feel just sick about how I treated her.” Is this true sickness? Your mental state of mind is important in your health; if you talk yourself into being sick, are you really sick?

Single nucleotide polymorphisms (SNPs) are one base

changes in a gene sequence. “Polymorphism” means

that the population will show different sequences at this

point. SNPs may produce no change in the protein, but in

some cases they may change the shape or function of the

protein just slightly. This may not cause disease, but may

affect the course of a disease, or how drugs will work in

that individual. SNPs may one day lead to personalized

medicines in a new science called pharmacogenomics.

Drugs will be designed to work best for your particular

DNA sequence.

What about genetic mutations? Can everyone with a genetic mutation be considered sick? If yes, then we are all sick, because everyone one of us has thousands, perhaps millions of single nucleotide polymorphisms (differences in a single base of DNA that might lead to change in function of a protein). I would suspect that most of us have larger mutations as well; the older we are, the more mutations we have. Some mutations render a person predisposed (more likely) to develop a disease – is this person sick even before he/she acquires the illness?

Osteoarthritis is a disease that can wear away joint surfaces and necessitate hip or knee replacement. My father has two artificial hips due to osteoarthritis, but does that make him sick or ill?

You see someone coughing, sneezing and blowing his/her nose. It could be due to respiratory allergies or a bacterial or viral infection. Are they sick in one instance, but not the other? I have seen TV ads that try to convince allergy sufferers that they are a menace to society, and should be embarrassed about their condition (unless they use their wonderful product). The entirety of the message in our society is that any illness or condition is a deficit.

To summarize our man-made rule: diseases are bad, and being exposed to diseases is bad, so keep your environment clean and antiseptic. Don’t get me wrong – I am not mocking the rule. I would rather not be sick - so much so that I am careful where I go and what I touch – in some places I simply choose not to breathe, just to be on the safe side. Disease prevention is an important part of life expectancy.

But are there exceptions? Is it sometimes good to get sick, either in general or with some specific disease? I think you know there must be exceptions, otherwise we would just be left with an interesting discussion of what it means to be sick. I bet you can even come up with at least example on your own. There are in fact boatloads of general and specific exceptions to this rule. Let’s take a few weeks and cover a few examples that are exceptions to "disease is bad" rule.

Our first exception is one that you may have already thought of – vaccines. With many vaccines, getting the disease is the key to not getting the disease – counterintuitive, isn’t it? I will use smallpox as an example of the idea that sickness prevents sickness, but there are many others.

Smallpox survivors had a very distinct look. It was

unfortunate that the lesions showed up most heavily on

the face and arms. Thankfully, the disease has been

eradicated, and the virus only exists now in two

laboratories, at the Centers for Disease Control in Atlanta

and the “vector” lab in Siberia. Whether these stocks

should be destroyed is a matter of some debate.

Smallpox, until recently, had been a scourge on mankind for thousands of years. The infection is caused by a virus (Variola major or minor) and may present in several different forms. It was a very dangerous disease, the hemorrhagic form was almost universally lethal. Those that survived smallpox were marked for life (see picture).

In the 1790’s, Edward Jenner of Gloucestershire, England noticed that milk hands and milkmaids seemed to be immune (from Latin, immunis = exempt) to smallpox and he wondered why that might be. The milking workers told him they felt protected because they worked with diseased cows, those that had a mild disease called cowpox. For some reason, having had cowpox kept the milkmaids from catching smallpox.

It turns out that cowpox and smallpox are enough alike that having one will prevent you from having the other. It was on this basis that Jenner developed the first vaccine (Latin from vaccinus = from cows, coined by Louis Pasteur as a tribute to Jenner). By pricking the skin of a young boy with a needle contaminated with the pus from a young milkmaid with cowpox, Jenner showed that this could prevent infection with smallpox (Jenner wasn’t the first to vaccinate with cowpox, just the first to prove it prevented smallpox).

Contracting cowpox, a mild disease that did not kill or scar, could prevent one from catching smallpox, a terrible disease that often killed and left survivors with permanent reminders of their ordeal. Maybe getting sick ain’t always so bad. We will talk more next week about just how vaccination works to produce a protective immune response.

Cowpox vaccination is an example of using one disease to prevent another, but even 100 years before Jenner it was recognized that you could prevent smallpox by giving people smallpox. Strange, isn’t it? Variolation was performed by blowing ground smallpox scabs up the nose of another person, or by pricking them to place the material under the skin.

The virus in the olds scabs was definitely variola, it was just weakened (attenuated) by its age and its time outside of healthy cells. The virus was recognized by the body and an immune response is mounted, but the virus was too weak to produce a fulminant infection was eliminated by the body. But not before it helped the vicitim become immune to subsequent smallpox infection.

Poliomyelitis infection led to a paralysis of the muscles.

This could include the respiratory muscles, so iron lungs

were used to force air in and out of the patients’ lungs.

Before a vaccine was developed, a treatment was

developed by an unaccredited nurse from Australia.

Sister Elizabeth Kenny overcame much professional and

gender prejudice to show that heat and passive exercise

to retrain muscles was better than the then used

immobilization therapy. Try to see the biopic “Sister

Kenny” on TCM some time.

Attenuatedvaccines do carry some risk. Paralytic poliomyelitis has almost been eradicated thanks to Jonas Salk’s inactivated (dead) vaccine injections and Sabin’s orallly taken, attenuated vaccine. The attenuated vaccine is better at preventing a natural infection, but in rare cases the vaccine virus can revert back to a wild form and result in iatrogenic (iatro = doctor and genique = to cause) polio, also called vaccine associated paralytic poliomyelitis (VAPP). Thankfully, widespread use of the Salk and Sabin vaccines in the 1950’s has made vaccination in the US (as of 2000) and UK (2004) unnecessary.

Many of the vaccines used today are engineered in a laboratory from just a portion of the organism. By using only the antigenic portion (that part that elicits an immune response) of the virus, there is no risk of iatrogenic disease. If the viral portion is produced in a laboratory using DNA technologies, it is called a recombinant vaccine. In some cases, the antigenicpart of the virus is weak on its own, so these subunit vaccines may be conjugated (joined to) some other molecule that will elicit a stronger immune response.

Unfortunately, there is a growing number of people ignoring history and putting are their children and the population at large at risk. Some parents’ reluctance to vaccinate is based on a single 1998 study in which vaccination was linked to autism, even though the author of the paper, Andrew Wakefield, has been convicted of scientific fraud and banned from the practice of medicine. Wakefield was an investor in a company that was going to offer medical testing for vaccine-associated autism and as well as assist in autism/vaccine lawsuits, so he falsified his data in an effort to make his company profitable.

As a result of the vaccine scare, the UK has seen a rise in the number of measles, mumps, and rubella cases in the last decade. These are diseases associated with childhood, but can cause severe disease or death in many victims, especially adults.

Pertussis, also called whooping cough, is transmitted only

from person to person. If no around you has it, you can’t

get it. However, symptoms may not show for 6 weeks after

infection, so everyone should be vaccinated. The coughing

can be so violent that it breaks blood vessels around the

eyes and nose – and it can kill young children.

Manyin the US are also selecting to apply for vaccination exemption due to medical, religious, or personal beliefs; therefore, disease incidence is rising in America as well. In July, 2012, the CDC reported that the US had 18,000 cases of pertussis (whooping cough) in the past year, including an epidemic of more than 2500 cases in Washington state from January to June. This points out the need for vigilance in monitoring, as some of these patients had been vaccinated. This suggests that that the protection may not be lifelong; a booster vaccination may be necessary, although it is also telling that Washington state has one of the highest vaccination exemption rates in the country.

Next week we will look at vaccine driven immune responses in a bit more depth, in an effort to understand why we have to get a flu vaccination every year.

Centers for Disease Control and Prevention (CDC) (2012). Pertussis epidemic - washington, 2012. MMWR. Morbidity and mortality weekly report, 61, 517-22 PMID: 22810264

For more information on these subjects, or classroom activities, see:

Sick/diseased/ill:

http://rheumablog.wordpress.com/2011/04/02/sick-vs-chronically-ill/

http://genetics.thetech.org/about-genetics/mutations-and-disease

http://www.nytimes.com/2012/05/18/science/many-rare-mutations-may-underpin-diseases.html

http://learn.genetics.utah.edu/content/disorders/whataregd/

Single nucleotide polymorphisms and pharmacogenomics:

http://ghr.nlm.nih.gov/handbook/genomicresearch/snp

http://www.ornl.gov/sci/techresources/Human_Genome/faq/snps.shtml

http://www.youtube.com/watch?v=9rPDa2ACtog

http://serc.carleton.edu/genomics/units/snp.html

www.biotech.iastate.edu/publications/mendel/ModuleIIP1.pdf

http://teach.genetics.utah.edu/content/health/pharma/snp_analysis.html

http://teach.genetics.utah.edu/content/health/pharma/exploring.html

http://teach.genetics.utah.edu/content/health/pharma/mapping.html

http://teach.genetics.utah.edu/content/health/pharma/module_guide.html

Vaccines:

http://www.pbs.org/wgbh/nova/teachers/activities/2909_meningit.html

http://www.historyofvaccines.org/content/educators

www.centreofthecell.org/lessonplans/New_Vaccines.pdf

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=8&ved=0CFwQFjAH&url=http%3A%2F%2Fwww.historyofvaccines.org%2Fsites%2Fdefault%2Ffiles%2Finline-pdfs%2FHistory_of_Vaccines_How_Vaccines_Work.pdf&ei=2I8pULWaI6OxyQHmz4GYBg&usg=AFQjCNHCWt12nRDNdLuYWk-lhPa0bhgiug

www.chop.edu/service/vaccine.../vaccine-information-for-educators/

http://www.niaid.nih.gov/topics/vaccines/understanding/pages/typesvaccines.aspx

http://www.historyofvaccines.org/content/articles/different-types-vaccines

http://health.howstuffworks.com/wellness/preventive-care/vaccine2.htm

Lack of vaccination:

www.pbs.org/wgbh/pages/frontline/health-science-technology/the-vaccine-war/why-arent-parents-vaccinating-their-children/

http://www.forbes.com/sites/gerganakoleva/2012/03/14/vaccine-debate-acknowledged-explained-at-global-conference/

http://www.parenting.com/article/the-end-of-the-autismvaccine-debate

http://www.nytimes.com/2011/04/24/magazine/mag-24Autism-t.html?pagewanted=all

http://www.guardian.co.uk/society/2012/jan/05/andrew-wakefield-sues-bmj-mmr

www.pbs.org/wgbh/pages/frontline/teach/vaccine/vaccine.pdf

Biology Concepts – innate immunity, acquired immunity, memory response, influenza

Your body is exposed to tens of thousands of foreign molecules every day. Some can do you harm, some can’t. Your immune system sorts them by matching receptors on immune cells to molecules on the foreign objects.

Legos and biology are a good fit. They can be used to analogize the

rearrangement T cell receptor genes or hypervariable regions

of antibody genes, or they can be used to model the entire

body. One scientist uses them to model building

complex systems from repetitive units. And they’re fun.

Thinkof the receptors as Legos; your DNA provides for several different types of Lego blocks to be made, and your immune cells can rearrange the different types and put them together as a receptor, so there can be millions of different receptors. Each immune cell has just one type of Lego receptor, although it may have many copies of that one form. Each different Lego receptor will fit, key in lock style, with a specific foreign molecule.

The receptors exist on many types of cells, and antibodies sometimes function as receptors when attached to the surface of specialized immune cells. Even circulating antibodies (Ab) in the blood take the form of key and lock systems, whether as single Ab, dimers (2) or pentamer (5) complexes.

The immune system of higher animals can be described as several sets of pairs. Each member of a pair attacks a problem in a certain way, and has independent pathways, but each pair also has overlap and must work together in an overall response. We could spend weeks just on this system, but lets look at the major parts by describing each pair, from largest to smallest.

Innate immunityvs. adaptive immunity– the innate immune responses are fast but short. They don’t depend on your immune system recognizing the specific foreign molecule (antigen) with a specific receptor, but respond with the same types of reactions no matter what it is. Almost all plants and animals have some form of innate immune system.

Vertebrates take the immune system further. They have developed an adaptive immune system that does depend on your immune system recognizing the specific foreign invader. It then generates a tailored response to that one foreign organism or molecule. The faster, but more general, innate response helps the slower, but longer lasting and more specific, adaptive response to kick in.

These are cartoons of an antibody. The model on the left is a much

more realistic image. The Fc portion is the same through most

antibodies (c= constant), while the gene rearrangement takes place

in the light chain and heavy chain variable regions. The

different variable regions are the Lego blocks that can be put

together differently to make the millions of different antigen

binding sites.

Humoral immunityvs. cellular immunity– when an antigen is recognized by an adaptive immune cell (often through antigen presentation by the innate system), an early response is for the cell to divide and make more of itself. You don’t get sick from one bacterium infecting you; many infect you at once and then divide to become many more. You need many copies of that specific immune cell in order to battle the invading horde of bacteria.

The immune cells can generate an antibody response (humoral immunity) and/or trigger specific killing and directing cells to be produced (cellular immunity). The antibody (produced by B lymphocytes) is a protein that recognizes the specific antigen. The cellular immune response is mediated primarily by T lymphocytes.

However, B cell-produced antibodies are important for T cells to do their work, and antibodies also help the innate immune response to keep working after specific recognition has been made. In addition, the cellular immune response can control and ramp-up the humoral response. You see what I mean about each pair being separate but connected.

Effector T cellsvs. regulatory T cells– There are pairs of T cells as well. I use the term “effector T” cells to lump CD8⁺and CD4⁺ lymphocytes together (CD = cluster of differentiation markers on the cell surfaces). Effector T lymphocytes are either directly cytotoxic (CD8⁺, cyto = cell and toxic = damaging) or command (CD4⁺) the many adaptive responses. Effector cells are contrasted with regulatory cells, which include regulatory and suppressor T lymphocytes. The purpose of these cells is to stem the effector response so it doesn’t get out of hand; parts of the immune response are inflammation and non-specific cell killing – too much of that and you die too.

Memory Immune System– This last part of the immune response is not a member of a pair. When your innate immune system is activated, it ramps up, does its job, and hopefully is turned back off. The adaptive immune system responds to the antigen by producing more cells, antibodies and chemical signals (cytokines), and after the invader is vanquished you want this response to diminish as well. The innate system always starts over from zero, but the adaptive system remembers the infection you had.

The dendritc cell on the left is an innate immune cell that works

to present the antigen to the adaptive immune cells (Th1,

Th2, and B cells). The adaptive cells reproduce and make

cytokines to stimulate other immune cells. They also generate

some memory cells that recognize the same antigen, but stay

around for a long time and can react strongly and quickly.

Duringthe adaptive response, some of the produced immune cells become “memory cells,” they still recognize the antigen from the initial infection, but hang around in larger numbers; in many cases they circulate in your body for the rest of your life. If your body sees that specific antigen again, the memory response can be re-initaited very quickly and very aggressively. You might be infected again, but your memory response is so fast and effective that you never know it.

In a world without vaccines, you are infected, get the disease, recover (hopefully), and then have a memory immune system for that antigen. Vaccines take the initial infection and disease out of the equation; you get to develop a memory without having had the experience!

As we discussed last week with smallpox, vaccines present your immune system with the antigen in the form of a dead or weakened pathogen, or just the antigen molecule itself. Your body doesn’t know the difference, it develops an adaptive and memory response just as if it were the real infection.

In the majority of cases, you develop memory B and T lymphocytes when infected or vaccinated. However, there are exceptions. Most antigens cannot fully activate B cells to make antibody, they have to be helped along by antigen-activated T cells. But there are T cell-independent antigens that can fully activate B cells on their own. In these infections, you can develop a B cell memory without a T cell memory.

On the other hand, there are other infections that develop a full memory response, but it is not useful. Influenza is an example of this. Influenza has been around for thousands of years; some years we have severe epidemics or even world-wide pandemics. The 1918-1919 Spanish flu pandemic killed over 50 million people, many more than the contemporaneous WWI (16 million deaths).

Flu is difficult to vaccinate against because it keeps changing. Influenza virus has two antigens, called H (hemagglutinin) and N (neuraminidase). These are the molecules on the virus particle that your body mounts an immune response against.

The H molecule on the viral coat binds to sialic acid receptors on respiratory cells and allows the virus to enter. When the newly produced viruses bud off of the cell, they place H on the cell surface, but there are still host sialic acid receptors there as well. These receptors would bind up the H and prevent the new viral particles from attaching to and infecting other cells, so the N molecule cleaves the sialic acid receptors from the new viral particles.

Influenza virus can mutate by antigenic drift or antigenic

shift. The top line shows that by passing from person to

person, the antigens (and virulence) shift slightly. The lower

line shows that by passing through other animals and

recombining, the antigens can have small or big changes. When

shifted virus moves into humans, it’s a recipe for a pandemic.

Theproblem arises when the H and N antigens mutate.... and they do. Scientists have identified 16 different classes of H’s and 9 different N’s, and they can be paired up in many combinations. Small changes (antigenic drift) usually mean that memory might have a slight protective effect, and major epidemics do not occur. But major changes in H and N (antigenic shift) mean that previously infected people have no memory protection.

Different strains of influenza virus can infect the same animal (often pigs and ducks – thus avian flus and swine flus) and can mix their H’s and N’s. What emerges and might be transmitted to humans can be a virus with H’s and N’s similar to years past, or with new H’s or N’s. That is why a new vaccine must be produced each year, after scientists see which H’s and N’s the new virus has and how much they have drifted. Avian flu is H5N1, while swine flu is H1N1. However, antigenic drift means that each H1N1 will not be exactly like the previous H1N1 to emerge. The 1918 pandemic was caused by an antigenically shifted H1N1 sub-strain.

Like flu, other infections may not provide life-long memory. If the memory response is weak or the initial response was not strong, then memory may fade over time. This is why some vaccinations require boosters in later years. A fading of the memory response to influenza is also implicated in the need for yearly vaccinations.

Here's a great book that discusses both the biology

and sociology of influenza. There are great personal

stories as well as medical detective work. This

pandemic was a jolt that brought infectious

disease research into a new century. I highly

recommend it.

Now for the exception to the exception. Influenza changes each year, so memory does not help much, but a 2010 report from scientists in Hong Kong suggests that prior exposure to any seasonal influenza (either by infection or vaccination) might have been a contributing factor as to why the 2009 pandemic of antigenically shifted swine flu (H1N1) was much milder than expected.

The 2009 seasonal flu vaccine did not have any cross-reactivity with pandemic H1N1, so the scientists suggest that previous years seasonal influenzas did generate some memory response that was partially effective against 2009’s H1N1 swine flu. Cross-reactivity means that the H and N antigens were not identical to previous version; the Legos don’t fit together exactly, but they were similar enough to fit together and initiate a partial response. Once again, we see that getting sick may save your life down the line.

Next week will look at examples wherein having one disease can protect you from catching another.

For more information or classroom activities, see:

innate immunity:

http://pathmicro.med.sc.edu/ghaffar/innate.htm

http://www.arthritis.org/innate-immunity.php

http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter22/animation__the_immune_response.html

http://www.virology.ws/2009/06/03/innate-immune-defenses/

www.garlandscience.com/res/pdf/9780815342434_ch02.pdf

www.youtube.com/watch?v=2CPbXaXKREg

http://missinglink.ucsf.edu/lm/immunology_module/prologue/objectives/obj02.html

http://www.nobelprize.org/educational/medicine/immunity//immune-detail.html

http://faculty.ccbcmd.edu/courses/bio141/lecguide/unit4/innate/phagoprocess.html

adaptive immunity:

http://pulse.pharmacy.arizona.edu/10th_grade/disease_epidemics/science/pathogen.html

http://sciencegeekgirl.wordpress.com/2008/10/24/the-drama-of-the-immune-system/

http://www.virology.ws/2009/07/03/adaptive-immune-defenses/

http://faculty.ccbcmd.edu/courses/bio141/lecguide/unit5/intro/overview/overview.html

http://textbookofbacteriology.net/adaptive.html

http://www.biology.arizona.edu/immunology/tutorials/immunology/page3.html

http://www.nature.com/nri/posters/dendriticcells/index.html

http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter32/

http://www.learnerstv.com/animation/animation.php?ani=319&cat=biology

http://www.youtube.com/watch?v=L32Na8fGjzA

memory immune response:

http://www.cs.unm.edu/~immsec/html-imm/memory.html

http://www.webmd.com/cold-and-flu/news/20071107/study-immune-system-has-long-memory

http://web.mit.edu/newsoffice/2010/vaccine-t-cell-1221.html

http://news.wustl.edu/news/Pages/23214.aspx

http://www.sciencedaily.com/releases/2010/01/100128165848.htm

http://sepa.duq.edu/regmed/immune/memory.html

influenza virus:

http://www.pbs.org/wgbh/nova/teachers/activities/3318_02_nsn.html

http://www.pbs.org/wgbh/nova/teachers/viewing/3302_04_nsn.html

http://www.brainpopjr.com/health/bewell/coldsandflu/grownups.weml

http://www.worldofviruses.unl.edu/curricula/curricula/category/21

http://www.teachervision.fen.com/illness/printable/67364.html

http://articles.cnn.com/2009-04-27/living/activity.swine.flu_1_h1n1-swine-flu-virus?_s=PM:LIVING

http://www.yourgenome.org/teachers/handshakehazard.shtml

http://www.cdc.gov/flu/about/viruses/index.htm

http://virus.emedtv.com/influenza-virus/influenza-virus.html

http://www.virology.ws/2009/04/29/influenza-virus-transmission/

www.clintoncountypa.com/.../Influenzavirustypes.pdf

http://www.sumanasinc.com/webcontent/animations/content/influenza.html

http://www.youtube.com/watch?v=YSgkoldBNkI

http://www.xvivo.net/zirus-antivirotics-condensed/

Biology concepts – fever, infectious disease, sexually transmitted disease, innate immune system

Would you be willing to be a human guinea pig, to

see if one disease might stop another? The term

“human guinea pig” refers to the fact that from the 1890’s

to the 1920’s guinea pigs were a major model for medical

research. Later replaced by rats and mice that could be

bred faster, guinea pigs were used to develop the first

diphtheria antitoxins, which subsequently saved

millions of lives.

Wouldyou be willing to let a doctor give you a disease? What if that might save you from another disease? You suppose this might be O.K., if the disease you were being given on purpose wasn’t too nasty.

What if the disease you're to be given as treatment is a form of the infection that kills a million people each year, the second most of any infection? Now you're thinking the disease you already have must be pretty horrible if this is the best idea for a cure. Let’s investigate and see if it might be worth it to save you from.... neurosyphilis.

Syphilis is a sexually transmitted disease that has distinct stages. The primary infection is marked by a lesion on those parts of your body that are most at play in the contracting of a sexually transmitted disease. It is amazing that some scientists believe that sexually transmitted diseases such as syphilis, in their primary stages, actually make sexual relations feel better. The organism (Treponema pallidum) benefits from this because the infected individuals might be more likely to have sex more often and this is an opportunity for the organism to be transmitted to additional hosts. Called “host manipulation” this is an evolutionary process that is just now gaining more attention, and will be something we will talk a lot more about in this blog in the near future.

The gumma lesions (left side) of secondary syphilis are not

meant for polite society. It's no wonder the Elizabethans

opted for the ruff collar (right side).

Thesecond stage of syphilis is marked by lesions, called gumma, on many parts of your body. You know those huge collars that the Elizabethans wore in 1500-1600 England? (see picture) As the story goes, the collars actually came into fashion as an attempt to keep syphilitic gummas out of sight. Syphilis ran roughshod through the English royal families at the time. Whatever the royals did everyone else wanted to do, so the collars became a fashion hit.

The tertiary (3^rd) stage of syphilis is much more likely to be fatal. Appearing anywhere from 3-15 years after the primary lesion, tertiary syphilis attacks the brain, heart, liver, or bone tissues of the victim. Neurosyphilis can bring dementia, hallucinations, psychosis, as well as unsteady gait and movements (ataxia or paresis). While only a quarter of the patients reach this stage, it is a nasty way to go.

Do you agree that being purposefully infected with one disease to avoid the ravages of neurosyphilis might be worth considering? Even if the doctors were going to give you....... malaria?

This is the spirochete bacterium Treponema pallidum,

the causative organism of syphilis. Recent evidence

suggests that the bacterium is flatter and less like a

corkscrew than previously thought. They don’t look like

they have a flagella to move around, but they do. It is

located INSIDE the cell, which makes the whole cell

whip back and forth, not just the tail.

In the modern day, the treatment for syphilis is antibiotics; penicillin G can easily kill T. pallidum in the primary and secondary stages. However, antibiotics do not cross the blood brain barrier very easily (this barrier is made by very tight junctions between the cells and reduced movement of molecules through the cells, in order to protect your brain from toxins and infectious agents). Very high doses of drugs must be used to treat neurosyphilis. They may not work at all and might bring side effects.

But in the days before antibiotics, other treatments had to be sought. In the state of Indiana, USA, just as in all states and countries at the turn of the 20^th century, syphilis was rampant in mental hospitals. This was both the cause and effect for some of the incarcerations, and was a source of constant battle in the institutions.

For better or worse, these patients were a stable population for the testing of different therapies for neurosyphilis, and Walter Bruetsch at the Central State Hospital in Indiana was a leading American researcher on the use of malaria to combat neurosyphilis.

Originally developed by Professor Julius Wagner-Jauregg of Vienna, Austria, the “malaria cure” was used to originally to treat paresis (very unsteady) and general paralysis patients; he suggested that fevers were helpful in paresis and tertiary syphilis.

Wagner-Jauregg had noted as early as 1887 that in the tropics, both malaria and syphilis were common, but those with syphilis rarely progressed to the tertiary stage, with the paresis that if often brought. In 1917, he treated nine paretic patients with good results, so other institutions expanded the study of this treatment. In Indiana, several decades of work were summarized in a series of papers in the 1940’s, making Indiana the prime American spot for “malaria cure work.”

The female Anopheles mosquito can take in quite a bit

of blood in just a short time. Take too long and they

could get squished.....but take hot blood in too fast

and they roast. That drop of fluid at the end of their

abdomen evaporates and helps cool their body as they

suck up the 37˚C blood, according to a 2011 study.

So how might malaria help in the treatment of syphilis? To discuss this, we have to know a few things about malaria. It is an infectious disease caused by an apicomplexan parasite called Plasmodium falciparum, although early hypotheses implicated bad air in the disease – hence the name; mal= bad, and airia = air. This organism has a complex life cycle, part of which occurs in the gut and salivary glands of the Anopheles mosquito and part of which occurs in human liver and then red blood cells (erythrocytes, RBCs).

There are five species of malaria parasites; P. falciparum is the one that causes the most severe disease. Other species include P. vivax and P. malariae, which are dangerous but do not cause as many deaths. They are also the prevalent species outside of Africa.

The merozoite (meros= portion, and zoo = animal, so like half an animal) stage of the organism invades the RBC’s and reproduces asexually. Periodically the merozoites burst out of the depleted erythrocytes and look for new blood cells to infect. These periodic bursts are timed differently in the different species, from every 48 hours for P. falciparum, or every 36 hours for P. vivax. When they break the RBCs and escape into the bloodstream, an immune reaction is stimulated by the broken cells, including a very high fever, from 103-110˚F!

The fever itself may be lethal, but there other factors, such as the fact that infected cells have parasite proteins on their surface that makes them sticky. The infected RBC's don't pass through the entire circulation and can block circulation in the brain or spleen and cause other problems. So which part of the infection was helpful in tertiary syphilis?

The consensus idea was that the malarial fever killed the T. pallidum of syphilis. Microorganisms like to live inside us because we provide them with something they need, and they have evolved to live best at our temperature. A fever is one way your body tries to make you a bad host for the organism. A high fever, induced by malaria, would make you a very inhospitable host for T. pallidum, and could be lethal to the organism.

Think about this the next time you want to take an Advil or Tylenol for that low grade fever. By medicating yourself, you are preventing your body from using one of its natural defenses against infectious agents. But high fevers cause damage on their own, so declining an anti-febrile (anti-fever) drug when your temperature is 100˚F is much different that counting on your body alone when the fever is 105˚F and you're having convulsions.

Here is a macrophage (false color image) ingesting

bacteria. The macrophage is part of the innate

immune system, it can phagocytose (eat) many

different foreign invaders. One macrophage can

take up and destroy hundreds of bacteria. They

stick to tissue culture plates not because they are

sticky, but because they're trying to eat the plate!

Work done by Dr. Walter Bruetsch at Central State Hospital during the 1940’s questioned whether it was the high temperature of the fever that stimulated T. pallidum destruction. Artificial fevers were not as effective as malarial fever in treating neurosyphilis; Bruetsch suggested that malarial fever and the RBC destruction it brought stimulated innate immune macrophage activity, while artificial fever stimulated only adaptive immune lymphocytes and resulted in lowered Ab concentrations (called titers) at the same time, making the adaptive response less effective. Bruetsch concluded that it was the activation of the innate system that produced results in treating general paralysis and neurosyphilitic paresis. The obvious answer isn't always the complete answer.

In later years, antibiotics took over as the major treatment for syphilis, and only rarely does the infection progress to the tertiary stage. However, proponents of fever therapy have, over the years, suggested that malaria as a treatment could be used for a variety of infections, from lyme disease to HIV.

The primary cheerleader for using malaria to treat HIV infection was none other that Henry Heimlich, inventor of the Heimlich maneuver. In the late 1990’s and early 2000’s Heimlich carried out a series of highly questionablestudies on malaria fever in HIV infection. It is not altogether clear whether proper informed consent was used, and the results of the studies have been universally discounted. But that is not where HIV and malaria part company.

A schematic cartoon shows how HIV replicates. It

first attaches and uncoats. The RNA is reverse transcribed

and then transcribed and translated into protein.

When the new virus assembles itself, the coat proteins

have to be chopped up into usable pieces. This is the

job of the HIV protease. Protease inhibitors stop this

and prevent virus maturation.

It turns out that protease inhibitors used to treat HIV infection may be potent inhibitors of P. falciparum as well. HIV takes over a cell and forces it to produce the proteins and RNA to form new HIV particles. Many of the proteins must have portions cut off to make them functional; this is the job of the protease (prote= protein, and ase = cut). Protease inhibitors prevent this cleavage and therefore stop the formation of new viral particles.

It turns out that malaria parasites use proteases very similar to those of HIV, and preliminary studies indicate that these drugs can prevent reproduction of the organisms. As hard as it has been to come up with useful malaria drugs, here’s hoping that human studies are successful.

Finally, there is some speculation that malaria and HIV are linked. The dangerous P. falciparum was not used to induce fevers in syphilis patients; doctors used less virulent Plasmodium species, such as P. malariae or P. vivax. Charles Gilks, in a 2001 paper in Philosophical Transactions of the Royal Society, suggests that some primate strains of malaria were also used, wherein infected monkey blood was injected directly into the syphilis patients. Gilks wonders if this is where a simian immunodeficiency virus made the jump to mankind. I think that is an extremely long leap.

Next week let’s work the other side of the street; do some diseases keep you from getting malaria? Yes, and there are more than you might have guessed.

C. Gilks (2001). Man, monkeys, and malaria Philos Trans R Soc Lond B Biol Sci DOI: 10.1098/rstb.2001.0880

For more information and classroom activities, see:

Syphilis –

http://www.metapathogen.com/syphilis/#biology

http://www.news-medical.net/health/Syphilis-History.aspx

http://microbewiki.kenyon.edu/index.php/Treponema_pallidum

http://www.microbiologybytes.com/video/Tpallidum.html

http://faculty.ccbcmd.edu/courses/bio141/lecguide/unit2/bacpath/contactcell_spiro.html

http://www.biomeds.eu/cms/show_article/30007.html

http://www.cdc.gov/osels/ph_surveillance/nndss/casedef/syphiliscurrent.htm

http://www.slideshare.net/shahparind/syphilis-and-neurosyphilis-101

Malariotherapy in syphilis and other infectious diseases –

http://www.cdc.gov/mmwr/preview/mmwrhtml/00001850.htm

http://books.google.com/books?id=d3wdy3b9VUkC&pg=PA72&lpg=PA72&dq=malariotherapy+syphilis&source=bl&ots=CvlucP551q&sig=6-whBW3Z4lsumtrhTq9aOdFKJt8&hl=en#v=onepage&q=malariotherapy%20syphilis&f=false

http://www.foxnews.com/health/2012/02/07/malaria-cure-claim-sparks-vienna-probe/

http://triviaextreme.com/technology/malaria_cures_syphilis.php

http://scientopia.org/blogs/whitecoatunderground/2010/09/14/syphilis-malaria-and-other-oddities/

http://www.nobelprize.org/nobel_prizes/medicine/laureates/1927/wagner-jauregg-lecture.html

Malariotherapy in HIV –

http://www.ncbi.nlm.nih.gov/pubmed/9089572

http://www.circare.org/malariotherapy.htm

http://www.lightparty.com/Health/MalarioTherapy.html

http://www.thelancet.com/journals/laninf/article/PIIS1473-3099%2803%2900642-X/fulltext

Protease inhibitors-

http://www.aidsmeds.com/archive/PIs_1068.shtml

http://biosingularity.com/2007/07/04/super-3d-animation-that-shows-the-mode-of-action-of-an-hiv-drug/

http://faculty.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/pianim.html

http://www.hhmi.org/biointeractive/disease/protease_inhibitor.html

http://www.cellsalive.com/hiv4.htm

www.hhmi.org/.../guides/.../HHMI_AP_%20Biology_%20Guide.pdf

www.biotechinstitute.org/sites/default/files/publications/yw92tg.pdf

http://inventors.about.com/library/inventors/bl_protease_inhibitors.htm

http://www.thebody.com/content/art12606.html

Biology concepts – evolution, reproductive advantage, natural selection, co-dominance, X-linked genes

Last week we learned how less aggressive strains of malaria were used to treat neurosyphilis and how they may be useful in treating HIV infection. This week, we will turn 180˚ and see if other diseases can help prevent or lessen the effects of malaria. In the process, much can be learned about natural selection and reproductive advantage.

Plasmodium-infected red blood cells develop knobs,

the surface protrusions seen on the left erythrocyte.

These knobs are covered in a certain protein that

inhibits the immune system’s ability to recognize this

cell as infected and respond to it. The cell on the right

is also infected with P. falciparum, but has a mutation

that prevents knob formation. Image credit: Ross

Waller and Alan Cowman.

As youundoubtedly remember from last week, malaria is a parasite-caused infectious disease that is transmitted from human to human by mosquitoes. The parasite, Plasmodium falciparum, takes up residence in the red blood cells (RBC) to reproduce. The red cells burst to release the organisms, and this brings fever and weakness.

As far back as the 15^th and 16^thcenturies, quinine, made from the bark of the cinchona tree, was being used in Peru to treat malaria. Chloroquine, mefloquine, and quinine all work against malaria in similar fashion. Because of their neutral pH, they move across membranes easily including the lysosomemembrane. Once inside the lysosome, they become charged and can’t get out. This includes the trophozoite-containing lysosomes. In the RBC, trophozoites consume hemoglobin to obtain amino acids, and the heme is digested in the lysosomes to form a black malaria pigment. The quinine drugs in the lysosome bind up the heme and produce a toxic product (cytotoxic heme) that kills the parasite.

There are other classes of drugs that are useful against P. falciparum. Primaquine and the artemisinin drug, artesunate, act by a completely different mechanism from that the quinine drugs. Artesunate is excellent for treating P. falciparum malaria, while primaquine is often used in conjunction with quinine to treat P. vivax or P. ovale forms of the disease.

These drugs work by breaking down – weird, but this is how many drugs work. It isn’t what you swallow that kills the organism, it's the metabolites (the products made by your biochemistry breaking down the drug) that are active. In the case of artesunate and primaquine, the heme molecule in the red blood cells releases peroxide from the parent compound (the drug you take). This is just like the peroxide you use to wipe out cut in order to prevent infection.

Artusenate comes from the sweet wormwood

plant. Chinese herbal medicine has used it for

thousands of years. A recipe for an Artemisia

based malaria medicine was found on a tablet

from the Han Dynasty (206 BCE to 20 CE). It is

now being investigated as a treatment for breast

cancer, also based on its ability to form radicals.

Oxygenis crucial for cellular function because it can gain electrons and can react with many other atoms. Unfortunately, this also makes it harmful to your cells as well. Without proper supervision, forms of oxygen that have picked up an extra electron or two (peroxide, superoxide, nitric oxide) can react with many important molecules in your cells and leave the cell impossibly damaged.

The cell has defenses against free radical damage, but higher than normal concentrations render the RBC fragile; on the tipping point of destruction. Treatment with primaquine or artesunate makes the cell inhospitable for the parasite, the red blood cells become flop houses instead of five star hotels. The parasite’s operating instructions are to survive and reproduce, but these drugs pull up the erythrocyte welcome mat and the parasite seeks moves on to seek friendlier accommodations.

Unfortunately, some strains of P. falciparum have become resistant to some quinine drugs, especially chloroquine. The free radical generating drugs are still useful, but scientists in Western Cambodia recently reported artesunate drug resistance there. The parasite has evolved – evolutionary pressure is everywhere. The actions of humans have put pressure on the organism to evolve; those parasites with mutations to resist the drugs have a reproductive advantage, and those mutations get passed on. We had better have something else on our plate to combat malaria – we're working on it, but nature has provided some help as well.

There are natural defenses against malaria. We have seen that a fragile red blood cell helps in preventing are lessening the disease course of malaria. What else might do that? This is where human genes come into play.

Sickle cell diseasecreates a very fragile RBC. The mutation is just a single DNA base change in the hemoglobin beta chain peptide, but the result is a hemoglobin molecule that becomes pointy and can tear the red blood cell apart, or can get stuck in small blood vessels and prevent good blood flow. Reduced blood flow starves the downstream tissues of oxygen.

You get one gene for hemoglobin beta chain from each parent. The disease comes when an individual receives mutated genes from both parents. But that doesn’t mean that sickle cell anemia is a recessive trait. If you have one copy of the mutated gene, then you will have sickling problems when oxygen concentrations are low, like during exercise or at high altitude.

Sickle cell disease or a sickle cell trait episode can result in red blood

cells clogging up vessels and organs. On the left is an absolutely

HUGE spleen from a sickle cell patient. On the right is a normal sized

spleen, about 20% the size of the injured spleen on the left. A normal
spleen is about the size of your hand, maybe a little skinnier.

If sickle cell anemia was a recessive disease, then a single wild type (normal) gene would be dominant, and you would show no disease. Instead, sickle cell anemia is co-dominant, one mutated allele (copy of the gene) is like having half the disease; it only shows up in certain circumstances.

This can still be a pebble in your shoe, just ask Ryan Clark, the Pro-Bowl safety for the Pittsburgh Steelers. In a 2007 game in Denver (altitude 5300 ft, 1616 m), Ryan almost died from a sickling attack during the game, and ended up having his spleen and gall bladder removed (remember that sickled RBCs can clog blood vessels, especially in blood rich organs like the spleen).

When Pittsburgh next played Denver, Clark didn’t even make the trip. This just happened to be the 2011 playoff game in which Tim Tebow threw a long touchdown pass in overtime to the receiver being covered by Clark’s replacement. Sometimes disease can change how sports evolve as well.

Thalassemia is another example. This is a group of inherited disorders wherein there is reduced production of one of the subunits of hemoglobin (hemoglobin is made from 2 alpha and 2 beta subunits). Alpha-thalassemias have mutations in the alpha subunit; likewise for beta-thalassemia.

Reduced subunit number means reduced hemoglobin number; the blood won’t carry enough oxygen, and the patient is constantly oxygen-poor in his/her tissues. Having two mutated alpha genes is lethal in the very young (called hydrops fetalis), but you can live with one mutated alpha gene, one mutated beta gene, or even two mutated beta genes.

This the broad bean, or fava bean in opened pod

and out of the pod in a bowl. The ancient Greeks

used to vote with fava beans, a young white bean

meant yes, and old black one meant no.

Sickle cell trait (one mutated allele), and thalassemias result in fragile erythrocytes. This makes them poor hosts for malaria, and confer a resistance to the disease - bad genes aren’t bad in every case. And just for good measure here is another example.

Favism, better called glucose-6 phosphate dehydrogenase deficiency (G6PDH), is an X-linked genetic disease; the gene is on the X chromosome. A female (XX) has two copies, so having one mutant copy is no problem, but a male (XY) has only one, so getting a mutated copy from your mother means that you ONLY have the mutated gene – this brings the disease.

The enzyme G6PDH works in several pathways; in your red blood cells, it is the only source of reduced glutathione, an important antioxidant. This means that things that trigger free radical formation in your red blood cells will trigger the disease – lots of weakness and lack of energy. If there is enough erythrocyte destruction, one could die.

Triggers include broad beans (fava beans), hence the name favism. Other triggers include many drugs, including primaquine and artesunate, the anti-malaria drugs that induce free radicals. Having G6PDH-deficiency is like having your own artesunate pharmacy right in your cells - you naturally have higher oxygen radical levels in your RBCs, so the malarial parasite can't live there.

Not by accident, sickle cell mutation is more prevalent in people of Sub-Saharan African descent, thalassemia mutation is more common in people from the warm, moist Mediterranean, and G6PDH-deficiency is found most commonly in the Mediterranean and Southeast Asia. These just happen to be the areas where malaria-carrying mosquitoes are most abundant. Evolutionary biologists make the argument that natural selection has maintained these genes in the populations because they provide a reproductive advantage to the species.

Left image: dark green is where there is thalassemia and yellow and red are where there is sickle cell. Right image, light green is where there is favism, and inside the blue outline is duffy antigen mutation. It is

interesting that these areas are also where malaria is endemic.

Youmight die from sickle cell disease, but probably not from sickle cell trait or beta-thalassemia. Learning not to eat fava beans makes the G6PDH mutation less lethal. One might very well live to an age where one could mate and pass on his/her genes. The diseases might still kill the patient, just not as soon as malaria would.

Malaria is a killer, and significantly, a killer of the young. In East Africa, children are bitten by the anopheles mosquito on average 50-80 times each month. They very well might not reach an age to reproduce. Therefore, having sickle cell trait, thalassemia, or favism provides a reproductive advantage in these environments and natural selection has resulted in these genes remaining in the populations in these areas.

The Duffy antigen (DARC) is important for P. vivax

entrance into the red blood cell. The Duffy binding

protein (DBP) interacts with DARC, the yellow parts

of the DBP are variable, and can be used to bind an

antibody. These variable areas overlap the binding

site, and can be used to make a vaccine for P. vivax.

Evolution maintains some diseases in order to combat others. It isn’t by design, it is by biology; no big plan is involved. This is exemplified by the Duffy antigen. All your cells have proteins on their surfaces. One, called DARC (Duffy Antigen Receptor for Chemokines, or Duffy antigen) helps your cells receive signals from your immune system. In those people with a single nucleotide polymorphism(SNP) for Duffy Ag, the antigen is not present on red blood cells (it is still on all other cells).

SinceP. vivax uses Duffy Ag as a way to enter the red blood cells, those with the Duffy SNP are resistant to P. vivax malaria – they don’t even have to suffer with some other disease, just a simple case of chance. And chance favors the prepared mind – the Duffy antigen binding protein is now a candidate for use as a P. vivax vaccine.

Next week, how the plague was defeated by a genetic disease.

Chootong P, Panichakul T, Permmongkol C, Barnes SJ, Udomsangpetch R, et al. (2012). Characterization of Inhibitory Anti-Duffy Binding Protein II Immunity: Approach to Plasmodium vivax Vaccine Development in Thailand. PLoS ONE , 7 (4) DOI: 10.1371/journal.pone.0035769

For more information or classroom activities, see:

Malaria –

http://www.hhmi.org/biointeractive/disease/malaria-human.html

http://www.hhmi.org/biointeractive/disease/malaria-mosquito.html

http://www.microbeworld.org/index.php?option=com_jlibrary&view=article&id=5835

http://www.science.org.au/nova/011/011act.html

www.ncgovdocs.org/lessonplans/K1Science.lesson3.docx

www.planetseed.com/.../Malaria.../malaria_workshop_outline.pdf

www.yourgenome.org/teachers/malariachallenge.shtml

www.gigers.com/matthias/engmala/teachmal.htm

www.windows2universe.org/teacher.../infectious_disease.html

sickle cell mutation –

http://genetics-education-partnership.mbt.washington.edu/class/high.htm

www.hhmi.org/biointeractive/activities/sicklecell.html

www.nepscc.org/NewFiles/teacher_and_school_nurse_12_04.pdf

www.nsa.gov/academia/_files/collected.../sickle_cell_puzzle.pdf

http://sped.wikidot.com/sickle-cell-anemia-in-the-classroom

www.tea.state.tx.us/Sickle_Cell.pdf

www.kumc.edu/gec/lessons.html

http://donnaldaniels.spurgeonfinearts.com/WisTEB01/materials/sca_simulation/sca-simulation.html

thalassemia –

www.cooleysanemia.org/updates/pdf/Activity%20Book_5.pdf

http://www.marchofdimes.com/baby/birthdefects_thalassemia.html

http://www.nhlbi.nih.gov/health/health-topics/topics/thalassemia/

http://www.genome.gov/10001221

www.cdc.gov/ncbddd/hbd/thalassemia.htm

favism –

http://g6pddeficiency.org/index.php

http://kidshealth.org/parent/general/aches/g6pd.html

http://emedicine.medscape.com/article/200390-overview

duffy antigen –

https://www.23andme.com/health/Malaria-Resistance-Duffy-Antigen/

http://www.geneplanet.com/your_personal_dna_analysis/what_you_can_learn_from_dna_analysis/traits_and_talents/malaria_resistance_%28duffy_antigen%29

http://www.frontiersin.org/Chemoattractants/abstract/29465

Biology concepts – iron, genetic disease, infectious disease, immune evasion

It is strange to think of people as rusting, but there are

days when I get up and swear that my joints have

frozen – my age makes me assume it is rust.

In truth the molecules of rust are very much like

some molecules in your body; too many of these in

the wrong places, and maybe you are rusting.

Believeit or not, someone you know is rusting - and it probably saved his/her ancestor’s life.

Animals require iron to survive; normal adult humans carry about 3.5-4 grams of iron in their bodies. It’s vital for every cell. Red blood cells use iron as part of the hemoglobin molecule that carries oxygen, But all other cells use iron in part of electron transport chain that makes ATP, and in the synthesis of DNA.

In plants, iron is used in chlororphyll production, in nitrogen fixation, and in regulation of transpiration (moving water and nutrients up to the leaves). Plants are a decent source of dietary iron, but heme iron (from meat) is much more easily absorbed.

In both plants and animals, the amount of iron is highly regulated. Iron is most often bound to proteins; one type in cells, another in the blood, and they lock it up tight. When you need more, your gut cells (enterocytes) release some of their stored iron and then take in more from the food you eat.

People who absorb too little iron (from poor diet or absorption defects) have a hard time carrying oxygen to their tissues because they don’t have enough hemoglobin. They are fatigued, dizzy, lose their hair, and less able to fight off infections. Weirdly, they may demonstrate pagophagia; a compulsion to eat ice! The reason for this is open for discussion, but one hypothesis says there is an ancient crunching desire, related to chewing on bones to get at the iron-rich marrow.

Pagophagia (eating ice) is one type of pica. In pica, a

person craves to eat something that is not a food source.

Some people with pica will eat hair (trichophagia)

or dirt (geophagy). I guess if you have to have pica,

ice craving isn’t so bad. And yes, some people crave

plastic, like parts of your keyboard.

Too little iron keeps you sick - and apparently always refilling the ice tray. But too much iron is just as bad; both ends of the scale can kill you.

Hereditary hemochromatosis (HH) is an autosomal recessive (need two mutated copies) disease of iron storage and transport. Patients with this disease may have as much as 20-40 grams of iron in their bodies; they can even set off metal detectors at airports!

All this iron causes medical problems too. People with HH will accumulate iron in their liver, heart, skin and other tissues. Excess iron plus fats can produce free radicals and oxygen radicals. The radicals can react with many molecules, including those you need in order to keep your cells functioning properly.

Radicals can break down enzymes, destroy mitochondria, and even react with the iron itself to produce iron oxide – rust; biological rust being called hemosiderin. Could HH patients be like the frozen Tin Man that Dorothy finds in the Wizard of Oz? Of course not, tin doesn’t rust – it’s a good thing L. Frank Baum was a writer and not a metallurgist!

The brown color is hemosiderin pigment that has been

deposited in the tissues. Most times, your body will

resorb this colored material, like when a bruise goes

away over time. In hemochromatosis, there is too

much hemosiderin to be completely removed.

Over time, the damage from free radicals and from hemosiderin buildup causes systems to shut down. Without treatment HH is lethal - so it is important to know how all that iron gets there.

We said above that enterocytes are the storage area for iron absorbed from your diet. In HH, the export signal is broken and they keep dumping their stored iron into the bloodstream. Even worse, the enterocytes lose the ability to sense if the body needs more iron. As a result of HH, gut cells keep absorbing more iron and releasing it into the bloodstream.

It’s a bad thing to inherit hemochromatosis…..EXCEPT if Yersinia pestis is lurking in the environment. Y. pestis is the bacterium that causes the plague. The organism can be passed from person to person, but also from fleas to people, and from fleas to animals to people.

You can read about how Y. pestis ensures it is transmitted to a new host from the flea’s midgut, but for reasons of decorum, I won’t go into it here. And I suggest you don’t eat before you read about it.

Y. pestis plague comes in three flavors; septicemic(travels through the blood), bubonic(causing swellings), and pneumonic(some organisms go to the lungs). In the case of pneumonic plague, coughing promotes transmission from person to person and is more lethal. But bubonic plague is more painful.

The plague has been a killer throughout human history, but Y. pestis’ relationship to the flea is evolutionary rather new. About 20,000 years ago, Yersinia killed the flea as well. According to new research, it took relatively few genetic changes to allow plague bacteria to keep the flea alive and to survive in its midgut. It was at this point that humans' trouble really began. It is estimated that a third of the population of Europe was lost to plague in 14^th century. The infection still occurs today, but is highly treatable with antibiotics. Your immune system has problems getting rid of Y. pestis on its own.

Normally, your immune system recognizes foreign organisms and eliminates them, through either innate or adaptive mechanisms. However, Y. pestis has several tricks up itsleeve to avoid recognition and destruction by your immune system.

The lymphatic system is comprised of vessels, and

is considered part of your circulatory system. It

helps in eliminating wastes from the blood and

tissues, aids in absorbing fats and fat soluble

vitamins, and regulates fluid levels. A main function

is to move fluid and cells through the checkpoints,

the lymph nodes. Here, the fluid is checked for

foreign molecules and antigen presentation to the

immune cells in the nodes.

Immune cells can circulate in your blood, move in and out of your tissues, or may be located in your lymphatic system. In the lymph nodes, they gather to exchange information, like workers gossiping around the water cooler. If an antigen processing immune cell (APC) has encountered a foreign antigen, the APC will break it down and place pieces of the antigen on its surface, so the antigen can stimulate other immune cells.

The processed antigen is presented to the many types of immune cells in and moving through the lymph nodes, including B cells that make antibodies, and T cells that direct immune responses or directly kill organisms. This quickly increases an immune response; one cell encounters the invader, but by going to a central location (lymph node), thousands of cells can be stimulated.

Amazingly, Y. pestisactually lives and reproduces in your lymph nodes! The painful swellings in bubonic plague are the inflamed lymph nodes where the organism is reproducing. Each swollen node is called a buboe, hence the name of the plague. Buboes occur most commonly in the armpit (axilla), on the neck, or in the groin area – not a pleasant way to spend a weekend - maybe your last weekend.

The lymph nodes are the headquarters for stimulating immune responses, yet the Y. pestis lives here very happily. It manages this through several evasion mechanisms:

1) antiphagocytic proteins– Y. pestis can inject proteins into phagocytic cells that makes them poor at eating and killing. These proteins also makes immune cells unable to signal other immune cells that Y. pestis is there.

2) invasion proteins – plague bacteria can avoid immune detection by living insideseveral different host cell types; the macrophage is the major example.

3) survival proteins– Y. pestis can live inside the macrophages that are supposed to destroy them by turning off macrophage killing mechanisms.

4) heme stealing proteins– Y. pestis can steal iron from the host. And here is where HH comes in.

Here is a buboe on a plague patient’s neck. It is not unlike the parotid

salivary gland swelling that takes place during the mumps, just

bigger, more painful, and more lethal. I chose to show one from the

neck precisely because I didn’t want to show you one from the groin.

Hereis an organism that is perfectly happy living inside and in the company of the cells that are supposed to kill it - we’re doomed. Yet having a disease like hemochromatosis can save us. How can that be? Well, microorganisms need iron too. For much the same reasons as animals and plants, bacteria and other microorganisms must have a supply of iron. They may get it from their diet, or, as is the case with Y. pestis, they steal it from their host.

I can hear what you're saying - this doesn’t seem to make sense since HH results in lots of iron in cells. True, but there is an exception. HH leaves two cell types starved for iron - the enterocyte, which we already know about, and the macrophage. The reason for iron-poor macrophages during hemochromatosis is not completely understood, but one possibility is that the HH mutation affects macrophages the same way it affects enterocytes.

One important function of macrophages is to eat and destroy old host cells, including erythrocytes. The iron of the hemoglobin from all those degraded RBC’s is stored and recycled; this is an important mechanism that the body uses to reuse the iron it already has. But in HH, the macrophages may be pumping out the iron they take up from old RBCs, just as the enterocytes keep pumping out the iron they take up from the gut contents.

The iron-poor macrophage essentially starves the intracellular plague bacteria by not providing them with iron. This is a happy accident for us, but it isn’t as if the macrophage doesn’t already know this trick. Iron can be an important immune weapon. In mycobacterial infections (that cause pneumonia), macrophages actually raise the iron concentration in the ingested bacteria and kill them that way. In other infections, macrophages sequester their iron and starve the organisms.

Bloodletting is an old time treatment for nearly every

disease. They thought that disease was caused by too

much blood. Strange, but bleeding (phlebotomy) is now

the accepted treatment for hemochromatosis. Leeches

are now used as anti-clotting mechanisms, and fly

maggots are used to clean out dead tissue – all are

gross, and all are effective!

Macrophageiron manipulation is not a natural immune response to Y. pestis, but HH helps to bring about the same effect, and this makes HH valuable. It is believed that many survivors of the plague in the 12^ththrough 15^th centuries had hemochromatosis. What is more, the gene is present in as many as 1/3 of living people of European descent, meaning that HH is probably massively underdiagnosed. It is likely that you know someone with HH, whether they not it or not.

Natural selection kept this mutation in the gene pool because it presented a reproductive advantage in times of plague. With antibiotics, we probably do not need this mutation any longer, but it is here and will take quite a while to be bred out of the population, especially since HH treatments (like bleeding, see the picture at right) help people live with the disease long enough to pass on their genes.

There are more examples of bad genes saving us from disease, like chemokine receptor mutations preventing HIV infection and aldehyde dehydrogenase mutations discouraging alcoholism. But next week we will focus on immune systems run amok and how parasites can reel them in.

Chouikha I, Hinnebusch BJ. (2012). Yersinia-flea interactions and the evolution of the arthropod-borne transmission route of plague. Curr Opin Microbiol. DOI: 10.1016/j.mib.2012.02.003

For more information or classroom activities, see Survival of the Sickest, by Dr. Sharon Moalem, or the following sites:

Iron in biochemistry –

http://www.webelements.com/iron/biology.html

http://www.ncbi.nlm.nih.gov/pubmed/11160590

http://bloodjournal.hematologylibrary.org/content/112/2/219...

http://www.chemistry.wustl.edu/~edudev/LabTutorials/Ferritin/Ferritin.html

http://astrobiology.nasa.gov/articles/finding-iron-s-role-in-life-on-early-earth/

http://nautilus.fis.uc.pt/st2.5//scenes-e/elem/e02640.html

http://serc.carleton.edu/sp/mnstep/activities/36016.html

http://healthymeals.nal.usda.gov/hsmrs/Illinois.../Classroom_Activities.pdf

http://kidshealth.org/parent/medical/heart/ida.html

http://www.doctoroz.com/vp-videos/iron-absorption-animation

http://www.youtube.com/watch?v=g97zy_G_mYk

Hereditary hemochromatosis –

https://koshland-science-museum.org/sites/all/exhibits/exhibitdna/inh05text.jsp

http://www.youtube.com/watch?v=UeRr-S2aWrY&feature=related

http://www.authorstream.com/Presentation/MKDah-923675-hereditary-hemochromatosis/

http://kidshealth.org/parent/general/aches/hh.html

http://thisisnotaperfectworld.blogspot.com/

http://www.jbcc.harvard.edu/programs/manville/Sci_genetic%20sym.html

Y. pestis plague –

http://medievaleurope.mrdonn.org/lessonplans/plague.html

www.michrenfest.com/the_black_plague_classroom_simulation.pdf

http://www.mademan.com/mm/bubonic-plague-facts.html

http://theweek.com/article/index/233008/the-7-year-old-who-caught-the-bubonic-plague

http://www.themiddleages.net/plague.html

http://rarediseases.about.com/cs/bubonicplague/a/111602.htm

http://plague.emedtv.com/yersinia-pestis/yersinia-pestis.html

http://www.who.int/mediacentre/factsheets/fs267/en/

http://web.uconn.edu/mcbstaff/graf/Student%20presentations/Y.%20pestis/Yersinia%20pestis.html

http://www.atsu.edu/faculty/chamberlain/Website/lectures/lecture/plague.htm

http://www.youtube.com/watch?v=7l4gLPzE-B4

Immune evasion strategies –

http://crohn.ie/archive/primer/imunevad.htm

http://www.ncbi.nlm.nih.gov/books/NBK27176/

http://textbookofbacteriology.net/antiimmuno.html

http://www.nature.com/news/2011/110921/full/news.2011.550.html

http://www.science20.com/catarina_amorim/how_friendly_bacteria_avoid_immune_attack_to_live_happily_in_the_gut

http://www.wellcome.ac.uk/news/2009/news/wtx053411.htm

http://www.thepigsite.com/pigjournal/articles/1284/porcine-immunology-the-battle-between-the-immune-system-and-pathogens

http://f1000.com/reports/b/3/1/

http://www.sciencedaily.com/releases/2010/05/100523205818.htm

http://www.genengnews.com/gen-news-highlights/researchers-discover-how-some-pathogens-evade-the-immune-system/81243811/

Biology Concepts – immune hypersensitivity, allergy, autoimmune disease

Stone Mountain in Georgia is one big hunk of

granite. There is a bas-relief carving of Jefferson

Davis, Robert E. Lee, and Stonewall Jackson that

covers three full acres of space! Stonewall Jackson

is on the far right. Stonewall immortalized on a

stone wall, interesting…. but didn’t their side lose?

C.S. Lewis was a 20^th century British writer who penned the Chronicles of Narnia books. Thomas “Stonewall” Jackson was a brilliant general in the Army of the Confederacy during the American Civil War. Can you name something these men had in common, but wish they didn’t?

---– They were both shot by their own troops during battle. It wasn’t on purpose; Lewis was wounded by a British shell that didn’t have enough oomph to get over the British’s own lines during World War I. One piece of metal lodged deep in his chest and could not be safely removed. It remained near to his heart until 1944.

During the Battle of Chancellorsville in 1863, Stonewall Jackson led a night reconnaissance mission that was mistaken for Union scouts. A confederate patrol fired on Jackson as he looked over the Northern lines from horseback. His left arm was amputated in an effort to save his life, but he died of pneumonia eight days later.

These were incidents of “friendly fire,” in which people meant to help you fend off the enemy end up hurting you. Too often, incidents of friendly fire take place in your body as well. In biology, these are called immune injuries and they can be dangerous exceptions. The immune system is designed to help the body fight off foreign invaders and dangerous molecules, but there are those instances when its actions harm the host.

Allergies are a good example of immune reactions gone wrong. Originally (1906) meant to denote any immune injury, we now we look at allergic reactions as immune responses to non-pathogenic, and in many cases, non-harmful antigens. Who could be harmed by a peanut, except for those allergic to it.

Peanut allergy is nothing to take lightly. It is

estimated that 3 million people now react to

peanuts, even to foods prepared in kitchens

where there are peanuts. This is an immediate

anaphylaxis response, with inflammation and

often respiratory distress.

A person can have an allergic reaction to an aeroallergen– something carried in the air, like dust, pollen, or pet dander. Food allergies occur generally with milk, wheat, peanut, or egg; many of these dissipate as children mature. Drug allergies can develop when small molecule pharmaceuticals break down, combine with host proteins or cells, and are then recognized as foreign. Some people are allergic to some venoms, like bee venom; their reactions can go beyond the pain of the sting.

In allergic reactions (atopic reactions – atopy is from Greek for “out of place”), there is first a sensitizing dose, wherein your body develops a hypersensitivity to the allergen. This is when your body builds an immunologic memory for the antigen, like we talked about a few weeks ago. Any exposure to the allergen after this brings a stronger response.

The exception to this sensitizing dose idea is when a new allergen looks like another allergen, ie. cross reactivity. Many latex allergies do not seem to have a sensitizing dose, but the patients also happen to have an allergy to banana, kiwi, or avocado. This is called the latex-fruit syndrome…catchy name, isn’t it?

Allergic reactions can occur just where the allergen contacts the immune system, like itchy hives (urticaria) for contact dermatitis, or a runny nose for pollens grains that are breathed in. Sometimes the hypersensitivity goes further and there is a life threatening reaction. We should describe the different kinds of hypersensitivity so you can diagnose your friends at parties.

Type I hypersensitivity is an immediate reaction, with symptoms lasting for a short time. Sometimes there is a more chronic response, especially if the antigen sticks around. Type I reactions are the allergies we all know and hate. The term for the reaction is scary, “anaphylaxis” (ana = exceedingly, and phylaxis = guarding), but it isn’t always life threatening.

In type I hypersensitivity, the allergen is recognized by specific IgE antibodies. Antibodies come in several flavors, including IgG (circulating antibody), IgM (antibody as cell receptors for first encounters), and IgA (in saliva and tears, etc.). IgE immunoglobulins are present in the tissues or on the surface of certain immune cells from some previous, sensitizing dose. The antibody has a variable end that recognizes the antigen and a constant end (Fc) which is recognized by other immune cells. When two or more IgE antibodies bind to the antigen (called crosslinking) and the Fc portion attaches to a mast cell or basophil, these immune cells will release their contents.

On the left is an electron micrograph of a mast cell,

an innate immune cell that mediates allergic responses.

On the right, you can see the granules inside the mast

cell that contain histamine, bradykinin, and other mediators.

When IgE and an antigen crosslink on the surface of the

cell, the granules release their contents into the

extracellular space.

Mast cells contain histamine, which causes blood vessels to dilate, airway smooth muscle to contract, itching, and stomach acid secretion. Mast cells also have bradykinin that increases mucous production, as well as other chemicals. Mast cell degranulation (release of internal granules containing the histamine, etc.) makes your eyes water, your skin get hot and itch, makes it harder for you to breathe, and might produce hives on your skin.

The reaction might remain local, but if it triggers the same reaction throughout your circulatory system, it can cause anaphylactic shock, a true medical emergency characterized by low blood pressure and respiratory difficulty. It can and will kill you if not treated immediately. And all this because some innocuous small molecule and an IgE antibody caused your immune system to over react!

Type II hypersensitivity reactions are also mediated by antibodies (IgM or IgG type). The triggering antigen might be some foreign molecule bound to a host cell or even an antigen on your own cells that your body has mistaken for foreign. In the case of penicillin allergy, the drug becomes bound to your cells; this complex triggers the immune response. If the antibodies are directed toward your cells or mistake your cells as foreign, this is called an autoimmune reaction. Examples could be systemic lupus erythematosus (SLE), some type I diabetes, or Hashimoto’s thyroiditis.

In some type II reactions, the antibodies that bind to the antigens trigger the complement system in your tissues to activate. Complement is part of your innate immune system that ends up marking cells for destruction by phagocytosis, or destroys them itself by punching holes in the target cells. In some cases, the antibodies bound to the cell trigger innate immune cells called natural killer lymphocytes– you can guess what they do to the target cell. I guess everyone is a natural born killer on the inside.

Natural killer cells are lymphocytes, but are part

of the innate immune system. These two are

attacking a cancer cell (red). Natural killers

specialize in killing cancer cells and virus-infected

cells. Natural killers are unique in that they can

recognize stressed cells in the absence of binding

antibodies.

The last type of immediate hypersensitivity is type III. The danger of this type of reaction comes from masses of antigens surrounded by antibodies. When these immune complexes (also called Ag-Ab complexes) become large, they can get stuck in tight places and bring an inflammatory response. Examples of immune complex diseases are autoimmune rheumatoid arthritis, some types of glomerulonephritis (inflammation of the filtering units of the kidney), and SLE also triggers this response.

Type IV hypersensitivity is the exception; this response can take several hours to develop and is the only hypersensitivity reaction that does not involve antibodies. Lymphocytes of the adaptive immune system interact with the antigen (be it foreign or domestic) and release many chemical mediators, called cytokines, that mediate immune and inflammatory reactions. Allergic contact dermatitis from poison ivy is a common, but relatively benign, example of this type of hypersensitivity.

Most hypersensitivities are reactions to things that shouldn’t have been problems in the first place. Allergies are just the most common manifestation of immune hypersensitivity. I don’t have them to any degree, but I see the havoc they wreak on my wife and our son. He is so allergic to wool that he breaks out when he counts sheep in bed!

But even allergies might have a hidden benefit. A study in 2008 indicated that people with allergies actually have a 25% less chance of developing a certain type of immune cell cancer, called B-cell non-Hodgkin’s lymphoma (NHL). If that person has three different allergies, they are 40% less likely to develop NHL.

This seems amazing, but it is supported by a 2011 study showing that people with allergies are 25% less likely to develop a type of brain tumor called a glioma. Glial cells protect and support the neurons in the brain; abnormal growth of these cells can lead to pressure and death of brain cells. Still think allergies are annoying?

Sneezes leave your mouth at over 100 miles and

hour and can spread droplets over 30 feet. Sneezes

may help get ride of unwanted antigens, but other

people don’t want them either, so cover your mouth.

Sneezing into the crook of your elbow is best for

limiting spray and contamination – I saw it on

MythBusters.

Researchersdon’t know the reason for this benefit yet, but hypotheses include that allergic reactions (watery eyes, sneezing, runny nose) help to eliminate potentially carcinogenic pollutants from our bodies, or that allergies stimulate the immune system and make it better at detecting and destroying cancer cells.

Learning that allergies might prevent cancer may make you less likely to take that antihistamine capsule. In fact, the treatment for all immune hypersensitivity reactions involve avoiding the molecule, removing the offending antigen and antibodies, and/or suppressing the immune system. We take corticosteroids, antihistamines, and other drugs to prevent the actions that might be saving us from cancer. However, you can help protect yourself without drugs as well—just catch a parasitic infection.

Parasitic worm infections, whip worm (Trichuris trichiura) or schistosoma for example, have a tendency to dampen the immune response, and can prevent some relapses in autoimmune diseases such as multiple sclerosis. A 2005 study indicates that some success has been had after dosing Crohn’s disease patient’s with intestinal worms.

Meet Pediculus humanus capitis, the common head

louse magnified only 80x. It is an ectoparasite,

meaning it lives on the host, not in the host. They

have been around for a long time; they have been

found on Egyptian mummies. This is why most

Egyptians shaved their heads and wore wigs.

For those of us without life-threatening autoimmune disorders, a 2009 study suggests that Pediculus humanus capitis infestations (head lice) can dampen the immune system enough to prevent allergies and some asthma attacks. Your choice - but don’t let anyone borrow your comb!

Parasites seem to have evolved specific mechanisms that inhibit the reactions that would eliminate them from the host, so they dampen immune responses as a defense. The mechanisms have not been worked out and may be parasite specific. Even malarial and leishmaniasis parasites can suppress the immune response, but I don’t recommend that you contract a deadly infection just to alleviate your allergies.

These last studies suggest that we may be living too cleanly – let’s take a look at that next week.

Calboli FC, Cox DG, Buring JE, Gaziano JM, Ma J, Stampfer M, Willett WC, Tworoger SS, Hunter DJ, Camargo CA Jr, Michaud DS. (2011). Prediagnostic plasma IgE levels and risk of adult glioma in four prospective cohort studies. J Natl Cancer Inst. DOI: 10.1093/jnci/djr361

Joseph A Jackson, Ida M Friberg, Luke Bolch, Ann Lowe, Catriona Ralli, Philip D Harris, Jerzy M Behnke, Janette E Bradley (2009). Immunomodulatory parasites and toll-like receptor-mediated tumour necrosis factor alpha responsiveness in wild mammals BMC Biology DOI: 10.1186/1741-7007-7-16

For more information or classroom activities, see:

Allergy –

http://onwebmanager.net/asthma/view/view.php?read_id=158

http://www.instructables.com/id/How-to-Teach-an-AllergyTissue-Lesson-for-the-Seas/

http://cilie-yack.org/sousclubcurriculum/99-unit-2/163-food-allergy-craft.html

http://missbakersbiologyclass.com/blog/2010/10/18/have-no-fear-food-allergy-prevention-is-here/

http://www.coloradoent.com/is-pediatric-atopy-preventable/

http://www.youtube.com/watch?v=JgTLBe2BfXY&feature=relmfu

Immune hypersensitivity –

http://pathmicro.med.sc.edu/ghaffar/hyper00.htm

http://archive.ajpe.org/view.asp?art=aj7308144&pdf=yes

http://sciencecases.lib.buffalo.edu/cs/files/immunology_notes.pdf

http://kidshealth.org/parent/firstaid_safe/emergencies/anaphylaxis.html

http://www.authorstream.com/Presentation/doctorrao-1213853-hypersensitivity-reactions-basics/

http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter33/animation_quiz_5.html

http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter22/animation__immune_complex_type_3_hypersensitivity.html

http://www.kosvi.com/courses/vpat5200/inflammation/imi/imi04.html

http://www.cehs.siu.edu/fix/medmicro/hyper.htm

http://highered.mcgraw-hill.com/sites/0073525634/student_view0/chapter14/animation__delayed__type_iv__hypersensitivity.html

http://www.proprofs.com/flashcards/story.php?title=lesson-17immune-disorders

http://loudoun.nvcc.edu/vetonline/vet211/immune%20dx.htm

http://www.enotes.com/topic/Type_III_hypersensitivity

http://www.lessonplanet.com/search?keywords=delayed+hypersensitivity

http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=1014407503&topicorder=2&maxto=20&minto=1

http://www.youtube.com/watch?v=e1qpbOivO_Y

http://www.youtube.com/watch?v=JBLHPBRHHl8&feature=related

http://www.youtube.com/watch?v=hfODOGuKvEI&feature=relmfu

Autoimmune diseases –

http://www.nlm.nih.gov/medlineplus/ency/article/000816.htm

http://www.lessoncorner.com/Health/Disease_Prevention?page=13

http://ebookbrowse.com/lesson-7-autoimmunity-lesson-plan-eng-f1-doc-d74948975

http://www.scienceteacherprogram.org/biology/mjoseph201.html

http://www.lessonplanet.com/lesson-plans/autoimmune-disease

http://www.fas.org/immuneattack/teachersguide/lesson-plan

http://www.ck12.org/concept/Autoimmune-Diseases/

http://labtestsonline.org/understanding/conditions/autoimmune/

http://www.cidpusa.org/disease.html

Biology concepts - hygiene hypothesis, immune regulation, bacterial drug resistance

Christian Slater starred in a 2008 American TV

series called, “My Own Worst Enemy.” Slater was

a secret agent with a chip in his brain that allowed

his employers to turn him from a mild mannered

family man to a super spy without each knowing

of the other’s existence. The showed last only nine

episodes; apparently the drama was its own

worst enemy.

Is everyone their own worst enemy? Google it---- apparently scientists are their own worst enemy; Christians are too. Chad Johnson is, and so was Whitney Houston. Someone out there even thinks bassists are their own worst enemies! I think that if this is true, everyone must be leading pretty lucky lives; the only thing stopping us appears to be us.

So it comes as no surprise that some scientists believe that people are their own worst enemies when it comes to protecting their health. Good intentions can have bad results. How might this relate to our topic of the past few weeks, the benefits of disease and infection?

Some diseases have had a positive effect on survival in specific conditions (like hemochromatosis and plague) and even how malarial fever can kill bacteria. This goes against the popular idea that less disease is better, and that whatever we do to kill infectious organisms is good. We try to be as sterile as possible; just look at what surgeons do before entering the operating room. The health industry has given us antibacterial soaps, cleaning products, plastics, cosmetics, toothpastes, pencils, and even antibacterial computer keyboards!

The majority of these products use triclosan as the active ingredient. First introduced as a pesticide in 1972, triclosan (chemical name: 2,4,4’-trichloro-2’-hydroxydiphenyl ether) is an antibacterial and antifungal agent. Triclosan’s mechanism of action at low concentrations is to disrupt fatty acid synthesis as a bacteriostatic agent (slows bacterial growth and reproduction); at high levels it can disrupt membranes and act as a biocidal agent (kills organisms).

Just because something is an antibiotic, it doesn’t mean it kills

bacteria. Many of the common antibiotics we use are bacteriostatic,

meaning that they inhibit the growth. This allows our immune

system time to overcome the intruder on its own.

Bactericidal agents do actually kill the bug, but they still need

help from the immune system. If you took enough to

kill all the bacteria, you’d need a capsule the size of a bus!

Triclosancan control bacterial contamination on hands and skin; hospital staff are encouraged to bathe or shower in triclosan solutions to prevent the spread of MRSA (pronounced “mersa” – methicillin resistant Staphylococcus aureus) in hospital wards. However, this is for control of contamination, not necessarily infection.

Triclosan has been proven effective in reducing infections rates only in cases of gingivitis (inflammation of the gums). However, a 2009 study stated that 75% of Americans over the age of six years have detectable levels of triclosan in their urine. This is significant since there is emerging data that suggests that triclosan might be harmful to people’s health.

High triclosan levels in urine and the environment mean high levels around microorganisms as well. But this shouldn’t be bad – it is supposed to kill germs, isn’t it? Many scientists worry that high triclosan levels also promotes bacterial evolution, selecting for the mutants that are resistant to the chemical. We all have good reason to worry about this because it’s happened before. Many bacteria, from MRSA to Mycobacterium tuberculosis, to vancomycin-resistant enterococcus, are wreaking havoc because we have fewer drugs that are effective against them.

In the laboratory, triclosan exposure has resulted in resistant strains of E. coli, salmonella, and rhodospirillium, and other organisms. Industry scientists argue that there is no data that triclosan causes resistance to develop in the wild, but a 2011 EU report suggests that this very well may be taking place; the levels of triclosan seen in people and the environment are similar to the levels used to drive resistance in the laboratory.

The bacterial resistance mechanism at work might be more dangerous than the resistance to triclosan itself. Several studies have deduced that triclosan interacts with proteins in the bacterial multidrug efflux pump. Many prokaryotes have this system; it works to pump non-bacterial small molecules, including antibiotics and toxins, out of the cell.

This cartoon represents a model of the E. coli

multidrug efflux pump. Protons pumped out are

allowed back in, and this produces the force needed

to pump out the drugs. This is another reason that

you need your immune system to overcome a

bacterial infection – the little buggers are working

against you!

In a situation where an organism is exposed to low or medium levels of triclosan, the multidrug efflux pump actually becomes more active because the triclosan binds to, and suppresses, the pump’s off switch. Think about that - you’re taking an antibiotic for a respiratory infection. But your household products are contaminating your body with triclosan. As a result, the respiratory organism is very efficiently expelling the antibiotics you are taking! Now the bacteria are being exposed to lower levels of antibiotic and will have a better shot at developing resistance! Perhaps anti-bacterials aren’t such a great idea.

Want more evidence? An August 2012 study showed that triclosan has an immediate and dangerous affect on muscle activity. You remember your heart?- it’s a muscle. In mice, triclosan exposure caused a 25% reduction in cardiac muscle function, and an 18% reduction in mouse grip strength. An idea for your next arm wrestling contest – wear a glove and slather it with liquid hand soap. You now have an 18% better chance at winning….if you are competing against a mouse.

Triclosan also affects endocrine function. A new study indicates that triclosan exposure in pregnant rats lowers mother, fetal, and neonatal levels of thyroid hormone. Triclosan has a structure similar to a thyroid hormone; it may trick the body into believing it has enough hormone. The thyroid would then reduce the production of the hormone, leaving the system starved of thyroid hormone. Most of this work has been done in amphibians, fish and rats, but a similar affect on human thyroid function is predicted.

Your body is exposed to many antigens from many sources.

If you are an only child or have parents that microwave

your toys, you are exposed to many fewer antigens. Many

scientists hypothesize that your immune system needs

these exposures to balance your developing system

between the Th1 responses and Th2 responses. Too much

Th2 and you will start to overreact to innocuous antigens –

allergies, asthma, and autoimmunity can result.

Antibacterial agents might be harmful through their actions on us and on bacteria. But does being too clean have other effects? Consider the hygiene hypothesis; mounting evidence indicates that efforts to produce near-sterile living environment, or even the movement from a rural to an urban environment, can negatively affect our health.

Case in point - most everyone has an idea that food allergies and asthma seem to be on the rise. The CDC stated in 2008 that there had been a 20% increase in food allergies in the years between 1997 and 2007. In a large number of these cases, children with food allergies also had eczema or skin allergies (27%) or respiratory allergies (30%), compared to only 8-9% of kids without food allergies. Basically, allergies are significantly on the rise, and if you have one, you are much more likely to have more than one.

Importantly, the rise isn’t occurring everywhere. Rural Africa - no increase in allergies or asthma. The arctic inuit peoples – very little allergy or asthma despite high levels of childhood smoking. Farm kids in just about every country – far lower levels of respiratory allergies, food allergies, asthma, and autoimmune diseases.

The hygiene hypothesis states that a lack of immune stimulation when young leads to exuberant responses to antigens that would normally be innocuous. Isn’t it interesting that the increase in allergies and asthma also correlates with the onset of antimicrobial agents being added to everything?

Different ideas abound as to how being clean might lead to increased immune hypersensitivities. One hypothesis is that a lack of antigen exposure in urban kids leads to a loss of balance between different T lymphocyte responses (see picture above). Infections tend to stimulate Th1 responses. A too clean, urban environment results in less stimulation of Th1 and therefore a relative over stimulation of the Th2 response. Increased Th2 leads to the kinds of responses seen in asthma and allergies. Indeed, atopic (allergy) patients do show an increase in Th2-driven cytokines.

Are we too clean as a society? Maybe we can back off

on the antimicrobial agents and spend more time in

the woods and the park. A brisk hike is as good for

your health as a spotless bathtub – and its more fun.

Then again, increased immune hypersensitivity in at risk populations might be due to an imbalance between the innate and adaptive immune systems. Many of the microbiologic antigens to which neonates and children need exposure stimulate innate immune receptors. The innate immune system then stimulates the adaptive immune system and balances the Th1 and Th2 responses. An absence of innate immune stimulation leaves the adaptive system to its own devices, and Th2 will often win this battle.

Additionally, the exposure to bacteria, viruses and parasites stimulates the immune regulatory system as well. Antigen presentation can be stimulatory or suppressive; suppressive presentation leads to regulatory (suppressive) lymphocyte production. It is hypothesized that regulatory lymphocytes help to balance the Th1 and Th2 responses and reduce the incidence of allergy.

We see that several portions of the immune system could be involved in helping the natural environment fine tune our immune responses. But what is it that induces this wonderful balance and state of good health?

A 2010 study suggested that the important molecule is something called arabinogalactan. This is a ubiquitous polysaccharide made of arabinose and galactose monomers. It is a component of many cell walls – bacterial, parasite, worm, grasses and other plants, and is in farm (unprocessed) milk.

Arabinogalactan is present in cow’s milk, in the grasses

that cows are fed, and in the dung patties that they leave

behind. And they last as well – there is a cowshed in

Wales that dates to 1402, making it the oldest building

in Wales. Cowshed – uninterrupted immune stimulation

for six centuries!

The hygiene hypothesis can be expanded to test the idea that farm kids' exposure to farm milk and cowshed dust (big sources of arabinogalactan) stems allergy and asthma development. However, there are studies that do not support the hygiene hypothesis, such as influenza virus actually promoting the development of asthma and the fact that daycare children have more respiratory infections, but do not have lower incidence of allergy. More needs to be known before we start shipping our infants to the country for the summer.

Two final notes to bring this full circle. Triclosan use has now been linked to higher rates of allergy. In particular, urinary triclosan levels correlate with development of food allergy. Correlation does not equal cause and effect, but it does ask a question that needs to be answered.

Lastly, increases in autism parallel increases in asthma and allergy, and a recent study shows that kids with autism and behavioral fluctuations have less stimulation of regulatory immune response after infection. Like allergy and asthma, autism definitely has a genetic component, but could the hygiene hypothesis and autism be linked as well?

With Halloween approaching, let's take a three week break from our "disease benefits" stories to look at the biology of some of our Halloween traditions and myths.

Gennady Cherednichenkoa, Rui Zhanga, Roger A. Bannisterb,Valeriy Timofeyevc, Ning Lic, Erika B. Fritscha, Wei Fenga, Genaro C. Barrientosa, Nils H. Schebbd, Bruce D. Hammockd, Kurt G. Beame, Nipavan Chiamvimonvatc, and Isaac N. Pessaha (2012). Triclosan impairs excitation–contraction coupling and Ca2+ dynamics in striated muscle PNAS DOI: 10.1073/pnas.1211314109

For more information or classroom activities, see:

Anti-microbial products –

http://www.protectiveindustrialpolymers.com/Antimicrobial_Products.html

http://drbenkim.com/articles/triclosan-products.htm

http://greenandcleanmom.org/triclosan-and-a-non-toxic-classroom/

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CEEQFjAA&url=http%3A%2F%2Fwatoxics.org%2Ffiles%2Fantimicrobials.pdf&ei=IsNgUNysAqiBywGUkYDYCg&usg=AFQjCNEf06t0FZ-MaPjDxJXgGQPxlhlffA

http://npic.orst.edu/ingred/ptype/amicrob/select.html

http://www.epa.gov/oppad001/influenza-disinfectants.html

http://www.rtpcompany.com/products/color/antimicrobials.htm

http://www.fda.gov/AboutFDA/CentersOffices/OrganizationCharts/ucm185542.htm

https://asunews.asu.edu/20120816_antimicrobials_riverslakes

http://healthychild.org/blog/comments/antibacterials_and_disinfectants_are_they_necessary/

Triclosan and health –

http://www.prnewswire.com/news-releases/canadian-government-urges-removal-of-triclosan-from-personal-care-products-146140385.html

http://www.washingtonpost.com/wp-dyn/content/article/2010/04/07/AR2010040704621.html

http://toxsci.oxfordjournals.org/content/107/1/56.abstract

http://www.healthiertalk.com/antibacterial-products-aren-t-just-useless-they-can-be-killers-0595

http://www.mnn.com/health/healthy-spaces/blogs/more-bad-news-about-triclosan

http://www.grinningplanet.com/2005/10-04/triclosan-article.htm

www.vkm.no/dav/f97997ef0d.pdf

http://ourneedtoknow.com/2012/06/the-dangers-and-effects-of-triclosan/

Hygiene hypothesis –

http://coolimmunology.blogspot.com/2007/03/hygiene-hypothesis.html

http://www.pbs.org/wgbh/evolution/library/10/4/l_104_07.html

http://www.sciencedaily.com/releases/2007/09/070905174501.htm

http://www.scientificamerican.com/podcast/episode.cfm?id=can-it-be-bad-to-be-too-clean-the-h-11-04-06

http://www.naturalnews.com/035447_hygiene_hypothesis_dirt_health.html

http://www.medscape.org/viewarticle/452170

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=8&ved=0CF4QFjAH&url=http%3A%2F%2Fccis.stanford.edu%2Fnewsarticles%2Fumetsu2%2FNIReview.pdf&ei=9r9gULavDsWDywHH8YGQCw&usg=AFQjCNGMt5pyarrUN7EUMUqw8BjxbHmang

http://www.infection-research.de/perspectives/detail/pressrelease/parasites_and_the_hygiene_hypothesis/

http://www.mydr.com.au/asthma/asthma-and-the-hygiene-hypothesis

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=24&ved=0CC8QFjADOBQ&url=http%3A%2F%2Fimb.usal.es%2Fformacion%2Fdocencia%2Falergenos%2FAsma%2C%2520rinitis%2C%2520conjuntivitis%2Fasthma.pdf&ei=rcBgULjzEsX5ygGthoDQCg&usg=AFQjCNEYyUl8LMU5UIyk21_YnfO5tcYmkQ

“Nosferatu” was the first film (1922, directed by F.W. Murnau)

made about the blood sucking undead. It followed the Stoker

novel so closely that his estate sued and a court ordered all the

copies destroyed. Only five survived, and were used to restore

the film in 1994. One area where did deviate from the novel

was in the way the vampire dies. Murnau introduced the idea

of sun sensitivity, which caught on and was accepted as part

of the myth.

Itmay not be surprising, but there’s a lot of pathology in Halloween. Pathology is the study of disease, and being dead is the worst disease - O.K., maybe being undead is worse. Let’s look at the biology of vampirism.

One prerequisite for being a vampire is that you have a taste for blood, but if that was the only rule, then almost everyone would be a vampire. Hematophagy (hemo = blood, and phagy = eat) is as common as bad Dracula impressions. Almost every culture consumes blood.

Many people eat cooked blood. The Poles eat blood soup (czernina), and the Brits love their blood pudding as much as the Chinese love their fried blood tofu. The next time you go to a French restaurant for the coq au vin, remember that the sauce is made with rooster blood!

There are also those cultures that drink blood. The inuit peoples drink fresh seal blood, and the Maasi in Africa rely on a mixture of cow’s milk and cow’s blood as a staple of their diet. And why not, blood is a decent source of nutrition.

Blood has a lot of protein and is a good source of lipids. Of course it is iron rich, and is a source of fluid and salt if you happen to be caught in the desert. If a vampire happens to pick out an uncontrolled diabetic, a drink of blood could also be a good source of carbohydrates.

These are Finnish blood pancakes. You have to

wonder about a recipe whose first ingredient is

40 ml of blood. But the lingonberry jam on top is a

nice touch; you would hardly remember that you

are eating blood.

Manyanimals practice hematophagy. Female mosquitoes consume blood; both sexes of the Cimicidae family (bed bugs) survive solely on blood, as do arachnids of the Ixodida order (ticks). Some of the 700 species of leeches feed on blood only, but most eat small invertebrates as well. There is even a vampire finch on the Galapagos Islands that bites the rumps of other birds and licks off the blood. And then there are the vampire bats.

As members of the Chiroptera order (chira = hand, and ptera = wing), vampire bats are members of a grand biologic exception. Bats are the only mammals that truly fly. True flying requires lift, being able to sustain a rise in altitude by mechanical means. Closest to this is soaring, which is the use of upwelling air currents to gain altitude. The most common type of aerial motion in reptiles, amphibians, mammals, and even fish is gliding. Gliding is really controlled falling, moving at less than a 45˚ angle to the ground.

Bats are so finely evolved for flying that they have lost most of their ability to walk, but vampire bats are an exception in the world of bats. They often approach their victims by walking or running up to them from behind. Vampire bats were quite the biologic discovery.

The vampire bat wasn’t named as such until 1774, but vampire legends (4000 BCE) and the word vampire (circa 1734) had been around much longer. Therefore, the bat was named after the undead, blood-drinking person, not the other way around.

Three species of bat, ranging from Mexico to Chile, subsist exclusively on blood. Each has evolved tricks to help them secure the blood they need. Their noses house special thermoreceptors to help them find areas of flesh where blood vessels lay close to the surface. The way their brain perceives and interprets this information is very similar to the way pit viper snakes sense live prey.

Common vampire bats like to bite and lick blood

from around the hooves of cattle and such. They are

so sneaky, they run up to the animals from behind

instead of flying. Their wings are stronger than most

bats, so they can help support their body weight when

they run or hop.

Two species (Diphylla ecaudata, Diaemus youngi) feed on the blood of birds, while the other (Desmodus rotundus, aka common vampire bat) feeds on mammals, including humans, but they all feed exclusively at night. This may have helped to link the bats to the monsters, as vampires are supposedly harmed by sunlight.

The common vampire bat will shave away the hair away with its teeth and then plunges its incisors in about 7-8 mm to bring blood, as its incisors are conical and are designed for cutting. Vampire bats are an exception in that they are the only bat species that do not have enamel on their incisors.

Enamel is very strong in compression and wear, but is brittle and rounds off the points of the teeth. Vampire bats need very sharp incisors, so they have forgone the enamel. Broken enamel would blunt their teeth, a lethal problem for a bloodsucker (although they don't suck).

Importantly, vampire bat salvia contains anticoagulants to keep the blood flowing and vessel relaxants to keep the local blood vessels from constricting. A new study has shown that bat saliva may have potential in human medicine. The common vampire bat is the source of a new clot-dissolving compound called desmoteplase; it activates an enzyme called plasminogen, which breaks down early clot formation.

Desmoteplase is structurally similar to a currently used clot buster called tPA (tissue plasminogen activator), but has some differences that make it more selective for fibrin. Importantly, it doesn’t cause nearly as much neuronal apoptosis or breakdown of the blood-brain barrier as does tPA. Desmoteplase is in phase III clinical trials for use in ischemic stroke patients (a brain blood vessel is blocked by clot). I wonder if human vampires have such useful saliva.

Ischemic stroke occurs when a blood vessel in the brain

is occluded so oxygen rich blood can’t reach the brain

tissue beyond the occlusion. The middle cerebral artery is

a common site for these cerebrovascular accidents.

Desmoteplase appears to be effective against occlusions

caused by blood clots, but there can be other occlusions,

name scar tissue from infection or atherosclerotic plaques.

Vampire bats usually slice open a small vessel with their incisors, and then lick the 20-25 ml of blood that flows out. This is very different from the idea of vampires sucking out all the blood from a human; something not consistent with long life. But could losing blood ever be considered a good thing? You know there has to be an exception.

In certain diseases, removing excess blood is beneficial. We talked earlier about excess iron in hereditaryhemochromatosis, for which bloodletting is an appropriate treatment, but there are others. Polycythemia vera is a genetic disease in which too many red blood cells are produced, leading to high blood volume and pressure, excess bleeding and clotting. To bring the volume closer to normal, a pint of blood may be removed once a week.

Finally, in chronic hepatitis C infection there is damage to the liver, a major storehouse of iron. This releases iron into the blood, and causes a secondary hemochromatosis. Small amounts of blood can be removed to help lessen the iron overload. Maybe old-timey medicine didn’t have everything wrong.

These same old cultures had myths about the undead that would feed on human flesh, but our current vampire myths date from early 1700’s Southern Europe. There are diseases that could be mistaken for some or all of the aspects of vampirism, but are they the chicken or the egg? In many cases, myths and folklore have some basis in fact, but in these cases hindsight is hardly ever 20/20.

Tuberculosis and rabies have a few aspects that are similar to the common tales of vampires. TB leaves its victims emaciated; they end up pale with swollen eyes that make them sensitive to light. They might cough up blood, and the first victim often gave the disease to other members of the house, so it have might appeared that the first was draining the others.

Similarly, people with rabies may exhibit a bloody froth from the mouth because lesions on the throat make it very painful to swallow. They may also be driven to bite people due to the encephalitis (encephalo = brain, and itis = inflammation) that the rabies virus causes. Other behaviors associated with rabies are sleeplessness (night time activity) and fear of looking at one’s own reflection.

Rabies spreads through the nerves, and the brain is the main

organ affected by the infection. Without vaccination or

treatment rabies is 100% fatal. Animals with the infection lose

fear of man, and become very aggressive, and then so do people

who contract the virus. Two cases of human bit rabies have been

confirmed (both in Ethiopia in the 1990’s).

Vampirebats are carriers of rabies, and this may contribute to their use in vampire lore, but recent evidence says bat rabies may not be such a bad thing. A 2012 CDC study shows that many Peruvian natives have a natural immunity to rabies, a disease that kills 55,000 people each year. The vampire bat maybe helping drive this immunity. It’s bite can deliver a sub-pathogenic dose of virus, enough to convey immunity, but not enough to cause disease. A case of vaccination by bite!

Another disease that mimics some vampire characteristics is xeroderma pigmentosum (XP). XP leads to an extreme sensitivity of the skin to the radiation of the sun. XP was first described in the scientific literature in 1874, just a couple of years before the first tales of sun sensitivity in vampires. There are several different types of XP, but all are autosomal recessive genetic diseases. Most involve mutation and inactivation of nuclear excision repair enzymes.

Sunlight contains UV radiation that causes DNA mutation. Excision repair enzymes usually fix the DNA damage. Without them, afflicted individuals manifest hundreds of skin cancers, and acquire others that are lethal (malignant melanoma). The patients’ eyes are very sensitive to light; they sunburn almost instantly, and must be kept out of sunlight. The children from the 2001 film, “The Others” had XP (while they were alive).

Congenital Erythropoietic Porphyria (CEP) is by far the disease most often associated with vampirism. Exceedingly rare, this autosomal recessive genetic disease has only been diagnosed in about 200 people, but there are many variants of porphyria that carry some or most of the same symptomology as CEP.

Porphyria can lead to deposits of porhyrins in the enamel

of developing teeth. The word porphyrin comes from the

Greek word for purple, so the discoloration is often darker

than what is shown here. Interestingly, tetracycline use in

pregnant women and children can lead to a similar

deposition, but for very different reasons.

The mutation common to the porphyrias is in the gene for an enzyme called uroporphyrinogen cosynthetase. Involved in heme synthesis, the loss of this enzyme leads to the buildup of heme intermediates called porphyrins. The porphyrins accumulate in the skin and organs and act as a sun-activated toxin.

The symptoms of the porphyrias do make you think of vampires: sun sensitivity with extreme burning, white skin, bloodshot eyes, sensitive eyes, anemia (low number and therefore a need for red blood cells), reddish tears, reddish urine, red pigment in the enamel of the teeth (erythrodontia).

The redteeth really bring to mind feeding on flesh or blood, and porphyrias also bring increased body and facial hair (hirsutism), so they may contribute to the werewolf legend as well. This is interesting because Medieval Europeans would burn the corpses of people who were thought to be werewolves, so as to prevent them from returning as vampires - better safe than sorry!

Next week we will continue our look at Halloween by investigating death – how likely is that you could be buried alive?

For more information or classroom activities, see:

Hematophagy –

http://www.mnn.com/earth-matters/animals/photos/13-vampire-animals/bloodthirsty-monsters

http://www.sciencedaily.com/articles/h/hematophagy.htm

http://www.nytimes.com/2008/10/21/science/21blood.html?pagewanted=all&_r=0

http://mbe.oxfordjournals.org/content/19/10/1695.full

http://bayareabedbugs.com/2012/05/well-that-sucks-hematophagy/

http://www.bbc.co.uk/nature/adaptations/Hematophagy

http://www.ars.usda.gov/research/publications/publications.htm?seq_no_115=95885

http://www.framepool.com/en/bin/1885745,Flea,Hematophagy,Pediculosis,Computer-Animation/

http://www.youtube.com/watch?v=h6fqrDShlMM

http://www.youtube.com/watch?v=Y_fYQRbF1ks&feature=fvwrel

Vampire bats –

http://suite101.com/article/halloween-lesson-plan-on-bats-a153520

http://www.educationworld.com/a_lesson/lesson/lesson031.shtml

http://video.nationalgeographic.com/video/news/animals-news/vampire-bats-missions-wcvin/

http://video.nationalgeographic.com/video/animals/mammals-animals/bats/bat_vampire_feeding/

http://www.arkive.org/common-vampire-bat/desmodus-rotundus/

http://animals.nationalgeographic.com/animals/mammals/common-vampire-bat/

http://kids.nationalgeographic.com/kids/animals/creaturefeature/vampire-bat/

http://www.conservationcentre.org/scase7.html

http://www.pitt.edu/~slavic/courses/vampires/images/bats/vambat.html

http://www.ehow.com/how_5538683_make-bat-school-project.html

Xeroderma pigmentosum –

http://www.youtube.com/watch?v=WtLtByN1mQA

http://www.dnalc.org/view/16613-Animation-28-Some-types-of-mutations-are-automatically-repaired-.html

http://www.dnaftb.org/28/problem.html

http://www.xps.org/

http://ghr.nlm.nih.gov/condition/xeroderma-pigmentosum

http://www.rarediseases.org/rare-disease-information/rare-diseases/byID/339/viewAbstract

http://www.youtube.com/watch?v=6Tiv9q_ltRo

Congenital Erythropoietic Porphyria –

http://pathman.smpdb.ca/pathways/SMP00345/pathway?level=2

https://rarediseasesnetwork.epi.usf.edu/porphyrias/patients/CEP/

http://dermatology-s10.cdlib.org/113/case_reports/porphyria/cepENGLISH.html

http://www.webmd.com/a-to-z-guides/porphyria-congenital-erythropoietic

http://flipper.diff.org/app/items/info/548

http://sickdujour.blogspot.com/2009/04/gunthers-disease.html

http://emedicine.medscape.com/article/1389981-overview

Medcalf RL (2012). Desmoteplase: discovery, insights and opportunities for ischaemic stroke. Br J Pharmacol. DOI: 10.1111/j.1476-5381.2011.01514.x

Amy T. Gilbert, Brett W. Petersen, Sergio Recuenco, Michael Niezgoda, Jorge Gómez, V. Alberto Laguna-Torres and Charles Rupprecht (2012). Evidence of Rabies Virus Exposure among Humans in the Peruvian Amazon Am J Trop Med Hyg DOI: 10.4269/ajtmh.2012.11-0689

Miracle Max had his own methods for determining if

someone was all dead or just mostly dead. They involved

a bellows and Carol Kane’s voice. But the point is made,

for centuries, people were just guessing if others were

really dead. There were few experts, and they were

probably just comedians in make-up.

Halloweenhas morphed into a holiday where people see how much it takes to scare them. Horror movies, haunted houses, dangerous pranks; people like to be scared.

What scares you the most– spiders, public speaking, death? These three are high on every list of common fears, but it wasn’t so long ago that another fear was in first place – taphophobia. Never heard of it? I bet that its mere definition will be enough to send a chill up your spine.

Technically, taphophobia means “fear of graves” (taphos = tomb, and phobia = fear of), but its common use is “fear of being buried alive.” Premature burial is not an urban legend, incidents have been documented in nearly every society – and not all of them were just in the movies or books.

In the 1800’s and earlier, being dead was a lot like being a duck….. you know, if it looks like a duck, walks like a duck, and quacks like a duck….. The appearance of death was often enough to make a diagnosis and start going through their pockets.

As a good example of the wisdom of the age, George Washington had these last words, "Have me decently buried, but do not let my body be put into a vault in less than three days after I am dead…….., tis well." He wanted a sufficient amount of time to pass to ensure that he was in fact dead.

The Irish wake probably originated in the leaving of the

tomb unsealed for several days, just in case the dead

person might wake. Later, stories came about concerning

the lead in pewter tankards from which the Irish would

drink. Lead poisoning could induce a state that resembled

death. Sometimes, a wake is just another reason to raise

a glass of ale.

Manycultures built time delays into their death rites to make sure someone was truly dead. Greeks washed the dead….. and some would wake up. In more difficult cases, they would cut off fingers or dunk the bodies in warm baths. The custom of the Irish wake began with the Celts watching the body for signs of life. But mistakes were made, often in times of epidemic.

The hopes of preventing the spread of infection often lead to burying the dead before they were quite dead. I give you plague victim Eric Idle in Monty Python’s Search for the Holy Grail – “But I’m not dead yet…. I’m feeling much better.”

Even without epidemic, most people in the 18^th, 19^th, and early 20^th centuries died at home, having never seen a doctor. If someone couldn’t hear a heartbeat or feel a pulse, then the patient was dead. But these were lay people, did they know how to feel for a pulse? Maybe they relied on another indicator of death - rigor mortis (rigor = stiffness, and mort = death).

In humans, rigor mortis begins 2-6 hours after death. Rigor is caused by a loss of ATP production. Follow me here--- no breathing, no oxygen; no oxygen, no ATP production. With no ATP, the muscle can’t relax. This may seem strange, since it takes ATP to contract a muscle in the first place.

As described in the text, the thick filament (myosin) pulls

itself along the thin filament (actin) by grabbing and releasing

actin monomers. A single sarcomere (contractive subunit,

~100,000 in a muscle cell) has millions of myosin heads. They

grab actin fibers that run on all sides of the myosin fiber.

Thepicture at the side should help with this explanation, but I won’t give you all the gory details. Your muscle cells have systems that look like ratchets, using to proteins called myosin and actin which pull past one another to shorten (contract) the muscle fiber. The myosin is bound by ATP, which then hydrolyses to form ADP + P. When ADP + P is bound to myosin, it can reach out and bind to the actin.

The ADP + P is released from the myosin and it flexes the head of the protein, which pulls it along the actin. When a new ATP is bound, the myosin lets go from the actin, and the cycle is repeated. Each muscle fiber in each cell has millions of myosin heads resulting in a contracted muscle.

In rigor, there is no more ATP, so the myosin doesn’t let go of the actin, therefore, no relaxation can take place. The muscles remain the length they were at death. After about 72 hours, the muscle proteins start to break down, rigor will lessens and the body will become limp again. But as we will see below, some conditions can mimic the signs of rigor, increasing the chances of premature burial.

In an effort to see how bad the situation was, the English reformer, William Tebb, in 1905 made a study of accidental premature burial. Tebb was quite the joiner; the weirder the society, the more he wanted to join or lead it. He worked with the Vegetarian Society, the anti-vivisection movement, the national Canine Defense League, and formed National Anti-Vaccination League in 1896.

William Tebb’s book on premature burial was a best seller.

You’d think he had a product to sell given the way he

described some of the incidents. In one, Madame Blunden

was buried in a crypt under a boys school. The next day, the

students heard noises from below. They opened the tomb

and coffin just in time to see her die from lack of oxygen.

In his book, Premature burial, and how it may be prevented, with special reference to trance catalepsy, and other forms of suspended animation, Tebb professed that he had found 219 cases of near premature burial and 149 live burials. He had some stunning stories of scratches on the lids of coffins and noises from newly filled graves.

In her 1996 book, The Corpse: A History, Christine Quigley documents many instances of premature burial and near-premature burial (I LOVE the title). Skeletons were outside their coffins, sitting up in the corner of their vault after being opened years later. Others were found turned over in their caskets, with tufts of their own hair in their hands.

How might this happen? What conditions might make it look so much like you were dead that even your loved ones would let them plant you in the ground? The list is long and varied, but here are some of the more common things that can make you look dead:

Asphyxiation– anything that cuts off your supply of air can make you look dead once you fall unconscious – continuation of this condition leads to actual death. You look dead enough and won’t respond to external stimuli, so people assume you are dead. Close the coffin lid, and soon you really will be dead of asphyxia.

Catalepsy– Many things can bring on this catatonic state in which the muscles are rigid (like rigor mortis after death) and no pain is enough make you respond, one example is epilepsy. Hypnotists call their trances catalepsy (Greek for to grab and take down), but true catalepsy is much more severe and can last hours to days. Severe emotional trauma can also bring it on, so you can certainly be scared enough to look like you are dead.

Catalepsy is denoted by muscle rigidity, so it can look like

rigor mortis. But there is also waxy flexibility in some cases.

The dead-looking not dead people can be posed, and they

will hold the pose indefinitely. What little girl wouldn’t love

a cataleptic doll for Christmas!

Coma– In medicine, a coma is unconsciousness that lasts more than six hours and from which a person cannot be roused and will not respond to stimuli. Injury or inflammation of the cerebral cortex and/ or the reticular activating system in the brain stem can lead to coma. The things that can injure these structures are myriad, from traumatic injury, to drug overdose, to stroke or hyperthermia, etc.

To show how medicine has changed, there is now a battery of assessments called the Glasgow coma scale (GCS) that are carried out on coma victims to assess their state and prognosis. In centuries past, you might look at them, hold a mirror under their nose, maybe lift and drop an arm….. bury them.

The GCS has traditionally been used in the hospital environment, but new evidenceshows that a prehospital GCS (assessment at scene or in route) can be just as accurate and may benefit treatment choice in pediatric traumatic brain injury patients. The study compared prehospital and emergency department GCS scores and showed that they were similar. They also compared outcomes with prehospital scores and showed a positive correlation. If assessment and treatment can be begun earlier, outcomes should improve.

Apoplexy– this not a very accurate term any longer, and has meant different things at different times. It can refer to bleeding within an organ or bleeding during a stroke. A stroke is very likely to leave survivors that look like they are dead, and are unresponsive. Nevertheless, there are stroke victims who regain consciousness.

Due to the above conditions, many people in the 1700’s and 1800’s made a hunk of change by promoting safety coffins and vaults. These might be as simple as attaching a rope to the hand of the deceased, and running this rope to the surface where it was attached to a bell.

In other coffins the alterations were more elaborate. There might be glass plates to view the face of the dead or a periscope to keep an eye on the corpse. Some thirty designs were patented just in Germany in the second half of the 19^th century, including some that contained vibration sensors, and later… a telephone line.

Waiting mortuaries were built in the 1800’s, mostly in

Germany. Since the best sign of death was the beginning

of the rotting process, these mortuaries were basically

holding cells for bodies while nature took its course. If they

didn’t start to smell, they had to look for fangs or a way to

arouse them.

To be successful, those folks above ground must have been very alert. A coffin has only about 20-40 minutes of air, so a person could go from dead to live to dead without the change being noted. To counteract this small window of time, Germany also built waiting mortuaries, where dead bodies could be held for longer periods of time. It came to be accepted that the only reliable sign death was putrefaction --- waiting mortuaries did not smell like flowers or fresh baked bread.

Modern EEG and EKG have reduced the chance of premature burial or cremation, but mistakes do get made. In 2007, a Venezuelan man awoke during his own autopsy, and Quigley also writes of several modern instances of near-premature burial. Furthermore, the need for quick burial during epidemics has been replaced by the need for timely organ harvests – maybe they aren’t done with that kidney yet!

Next week we will take Halloween and death one-step further – could Halloween, or anything else for that matter, literally scare you to death?

Christopher Dibble (2010). The Dead Ringer: Medicine, Poe, and the fear of premature burial. Historia Medicinae

Nesiama JA, Pirallo RG, Lerner EB, Hennes H. (2012). Does a prehospital glasgow coma scale score predict pediatric outcomes? Pediatr Emerg Care. DOI: 10.1097/PEC.0b013e31826cac31

For more information or classroom activities, see:

Rigor mortis –

http://australianmuseum.net.au/Death-The-Last-Taboo

http://pa.slu.edu/pdf/forensicautopsycsd.pdf

http://health.howstuffworks.com/diseases-conditions/death-dying/rigor-mortis-cause1.htm

http://www.foxnews.com/story/0,2933,357463,00.html

muscle contraction –

http://www.education.txstate.edu/ci/faculty/dickinson/PBI/PBIFall05/Diet/Content/Muscles1.htm

http://www.melissagetz.com/biotech0910/muscle.html

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__action_potentials_and_muscle_contraction.html

http://www.brookscole.com/chemistry_d/templates/student_resources/shared_resources/animations/muscles/muscles.html

http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP2904

http://www.blackwellpublishing.com/matthews/myosin.html

http://www.wiley.com/college/pratt/0471393878/student/animations/actin_myosin/actin_myosin.swf

http://www.liquidjigsaw.com/science/animation/animations/bigpicture/muscle-contraction.html

www.colorado.edu/Outreach/BSI/pdfs/muscleContraction.pdf

http://www.accessexcellence.org/AE/AEC/AEF/1996/lazaroff_contraction.php

http://www.youtube.com/watch?v=4OruOk-P8yU

Halloween is a time when fear is invited. The rush of

adrenaline in a controlled environment is life-

affirming. Not much else to comment on here,

except that he seems to have excellent oral hygiene

for a chainsaw-wielding maniac.

The big man with the chainsaw and the gaping wound on his face jumps out from around the corner and growls. You leap backward, your heart pounding in your ears. You’re ready to either take that power tool and teach him a lesson or to run like the kid from Home Alone.

Haunted houses are great examples of stimuli that induce the fight or flight response. The name is suggests two mechanisms are fighting it out, but there is really only one biologic pathway. Whether an animal tries to escape or tries to defend itself, its muscles and mind need to be ready.

In response to a threat, the brain triggers the release of epinephrine and cortisol from your adrenal glands into the blood. As a result, your heart beats faster and stronger, your blood vessels dilate to move more blood, and your lung vessels dilate to exchange more oxygen for carbon dioxide. Equally as important, your liver breaks down glycogen (a sugar storage molecule) to glucose and dumps it into your bloodstream.

All these processes work together to increase your alertness and increase the power of your muscles for a short time - like mothers who lift cars off their small children. You are now ready to respond to the threat; however, there is an exception – you may do nothing at all.

One of the major control mechanisms of the fight or flight response is the autonomic nervous system. This is part of the peripheral nervous system (PNS, outside the brain and spinal cord) and transmits information from the central nervous system to the rest of the body. The autonomic system controls involuntary movements and some of the functions of organs and organ systems.

Parts of the autonomic system acts like a teeter-totter, doing different jobs. It is their relative balance that controls the outcomes. In the fight or flight response, the sympathetic system predominates and your heart rate increases and your blood vessels dilate.

The autonomic nervous system is divided into sympathetic

and parasympathetic. Much of the sympathetic innervation

comes from the thoracic and lumbar regions, while most

parasympathetic innervation is carried by the vagus nerve.

You can see that the two systems have largely opposite effects.

Butwhat if the parasympathetic systemgained an upper hand for a short time? The parasympathetic system controls what is sometimes called the rest and digest response – the opposite, get it? The heart slows, the blood vessels constrict in the muscles, blood moves from muscles to the gut, and glycogen is produced from glucose. Remember the old adage - don’t swim after your dine; eating puts you in a parasympathetic state of mind! (O.K., I just made it up)

Many people have had the experience of parasympathetic domination coincident to a threat, for some folks it proceeds long enough to have an observable result – they faint. The vagus nerve (a primarily parasympathetic cranial nerve) controls much of this response, so it may be called the vasovagal response. The parasympathetic-mediated reduction in blood oxygen and glucose do not spare the brain - and when your brain is starved of oxygen and glucose, you pass out. Fighting or fleeing is difficult when you are unconscious.

Lower animals will faint as well, but they have additional defenses along these lines. Mammals, amphibians, insects and even fish can be scared enough to fake death – ever hears of playin’ opossum?

There are overlapping mechanisms for feigned death, from tonic immobility (not moving) to thanatosis (thanat = death, and osis= condition of, playing dead). When opossums employ thanatosis, they fall down, stick their tongue out, and even emit a foul smelling odor from glands around their anus. One study in crickets showed that those who feigned death the longest were more likely to avoid being attacked, so this is definitely a survival adaptation – except for the opossums scared by cars and decide to play dead in the street.

Feigned death deters predation, so being scared ain’t all bad. Many predators won’t eat something that is already dead, so not moving could protect them from attack. Another theory is the clot formation hypothesis; it contends that slowing the heart and blood flow forces blood clots to form faster. This will reduce the amount of blood lost during an attack, improving chances for survival.

New evidence is suggesting that even humans undergo tonic immobility. Post-traumatic stress patients asked to relive their trauma show definite signs of tonic immobility, although first they show signs of "attentive immobility," which is more voluntary then the tonic form.

I highly recommend this new book for popular

biology and medicine readers. Zoobiquity explores

a powerful reality. No disease--whether physical or

psychiatric--is uniquely human. We have much to

learn from animal patients and from the doctors who

care for them. The impact on human medicine

will be significant.

We havediscovered one exception to the rule; instead of fight or flight, it is really fight, flight or faint – but can we take it further? Should it be fight, flight, faint, or fatality? The answer is yes, but it is very rare. Sometimes animals (including us) don’t just feign death when afraid – they actually die.

In their new book, Zoobiquity, What animals can teach us about health and the science of healing, Barabara Natterson-Horowitz and Kathyrn Bowers talk about capture myopathy in animals. Small traps that limit movement, cause pain, or are associated with loud noises can cause spontaneous death in live-trapped animals. Several decades ago it was not unusual for 10% of trapped animals to die. In birds, the death rate often rose to 50%! More humane methods of live trapping have reduced the death rate, but point is made – these animals were scared to death.

A human analogy of capture myopathy may have been identified. People that have had a sudden emotional shock, perhaps the death of a loved one, some other tragic occurrence, or crippling fear can undergo something that looks a lot like a heart attack, even if they have no history of heart disease.

This sudden loss of heart rhythm has been called broken-heart syndrome, but is more accurately termed stress cardiomyopathy (SCM). In these cases, the heart actually changes shape! The part of the heart that pumps blood out to the body (left ventricle) balloons out and loses the ability to pump efficiently. Dramatically less efficient pumping leads to symptoms just like a heart attack.

In the normal left ventricle of the heart (left image), the muscle is

thick around the space (in red) and contracts strongly. In SCM, the

space is ballooned at the based (middle image) and the muscular wall

is thin, giving a weak contraction. The change in shape can be seen in

the superimposed images on the right, as is the octopus trap (tako-tsubo)

that the original Japanese describers thought the lesion looked like,

hence the early name takotsubo cardiomyopathy.

In most cases, SCM and the change in heart shape resolve after a time and there is little left to show they were present, but if they go too far for too long, they can cause death – called sudden cardiac death. There are many causes for sudden cardiac death, but emotion and fear are definitely among them.

I was wondering if there was a link between SCM in humans and capture myopathy in animals, so I asked Dr. Natterson-Horowitz. She told me that those studies have not been done yet; we don’t know if there is a heart shape change in captured animals. I think it would be hard to get approval for studies that would intentionally scare animals to death.

One interesting connection amongst fight or flight, capture myopathy, and SCM is the catecholamine dump involved. Epinephrine and norepinephrine control all three responses, and in humans, they control even more. Recent evidence shows that catecholamines mediate the production of fear memories.

You remember fearful events more readily and more vividly as a survival adaptation. Strong memories help you to avoid dangerous situations in the future. In this way, your mind can affect how your body responds to a threat. We will see this again in just a bit.

All babies have an exaggerated startle reflex until

they are several months old, but in some cases it may

contribute to SIDS. An exaggerated startle can lead to

apnea (temporary breathing cessation) and this can be

compounded by a depressed heart rate if the baby is

sleeping on its stomach. Some clinicians also theorize

that swaddling may contribute by exaggerating the startle

due to confinement stress, but by far the greatest

association with SIDS is stomach sleeping.

However, dying or nearly dying from fright isn’t all in your head either; some conditions can predispose you to dying from a sudden shock. One unfortunate condition is called hyperekplexia, or startle disease of the newborn. Newborns with one or more of several mutations in the glycine receptor (an inhibitory receptor in the brain used in neuron signal transmission) can lead to these babies dying from loud noises or a sudden touch.

The startle reflex involves squinting to protect the eyes, raising the arms, hunching the body to protect the back of the neck, as well as inducing the fight or flight response. With the loss of inhibitory signaling, the signals that ramp up a startle response are unchecked and can lead to uncontrolled beating of the heart (ventricular fibrillation, VF) and sudden cardiac death.

Just as some cases of the fight or flight response going too far, the startle can sometimes lead to VF. A recent study has shown that the bigger the perceived threat, the bigger the startle reflex will be. Also, if there is a fearful environment prior to the threat, then the startle will be bigger. Once in a long while, it goes too far.

Similar to hyperekplexia, there is another condition that could lead to VF and death in the environment of fear. Long QT syndrome can either be inherited or acquired later in life, and affects the time between beats of the heart. In long QT, the interval is variable and longer, and can lead to inefficient beating and VF.

On echocardiogram tracings a heartbeat has a certain shape, and

each point has a corresponding name which is represented

by a letter. If the time between the Q point and the T point

is too long, the heart rhythm is subject to disintegrating

into chaos. In the 1990’s, the antihistamine Seldane was

taken off the market due to QT interaction when it was

given with the antibiotic erythromycin.

Highlightingour circle of fear and the body, evidence presented here and here suggest that SCM can cause acquired long QT syndrome. Dr. Natterson-Horowitz said today many patients with long QT may have implantable defibrillators. In earlier days, however, these patients were warned not to use alarm clocks or to jump into cold water – they could startle themselves to death.

Last weekwe talked about premature burial. It would be easy to envision a person waking up inside a coffin, and then dying from the fright of being buried alive! Does this mean that you are putting yourself in peril every time you visit a haunted house at Halloween? Probably not, remember that deaths from fright are exceedingly rare. Maybe you could just feign death, and the horrible monster will leave you alone.

Next week, something less macabre. Let’s look at the biology of two Halloween staples - jack o’ lanterns and candy corn.

Greek, R. (2012). Zoobiquity: What Animals Can Teach Us About Health and the Science of Healing. By Barbara Natterson-Horowitz and Kathryn Bowers. Knopf Doubleday Publishing: New York, NY, USA, 2012; Hardback, 320 pp; $16.23; ISBN-10: 0307593487 Animals, 2 (4), 559-563 DOI: 10.3390/ani2040559

Volchan, E., Souza, G., Franklin, C., Norte, C., Rocha-Rego, V., Oliveira, J., David, I., Mendlowicz, M., Coutinho, E., Fiszman, A., Berger, W., Marques-Portella, C., & Figueira, I. (2011). Is there tonic immobility in humans? Biological evidence from victims of traumatic stress Biological Psychology, 88 (1), 13-19 DOI: 10.1016/j.biopsycho.2011.06.002

For more information or classroom activities, see:

Fight or flight –

http://www.fearexhibit.org/brain

www.bam.gov/teachers/activities/stress_big_test.pdf

http://learn.genetics.utah.edu/content/begin/cells/cellcom/

http://science.howstuffworks.com/environmental/life/inside-the-mind/emotions/fear2.htm

http://ase.tufts.edu/biology/labs/romero/research/fightOrFlight.htm

http://www.onlinelearningexchange.com/texas_demo/assets/bio/eng2.html

http://www.atomicmeme.com/learninghub/stressbio/fight_flight.htm

Autonomic nervous system –

http://www.bioedonline.org/slides/slide01.cfm?tk=5&dpg=27

http://education-portal.com/academy/lesson/the-sympathetic-and-parasympathetic-nervous-systems.html

http://www.brighthubeducation.com/middle-school-science-lessons/65233-parts-of-nervous-system-overview/

http://teachers.net/lessons/posts/1874.html

http://store.heartmath.org/Inside-Story/inside-story-classroom

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CCsQFjAC&url=http%3A%2F%2Fscience.education.nih.gov%2Fsupplements%2Fnih4%2Fself%2Fguide%2Fnih_self_curr-supp.pdf&ei=4JJ9UKXWNerWyQGyp4H4BQ&usg=AFQjCNGau9FhwFYgDoAGBCBTd1RwY7NXSw

http://www.kidshealth.org/classroom/9to12/body/systems/nervous.pdf

http://classroom.sdmesa.edu/.../Anatomy%20ANS%20-%20chap%2017.ppt

http://www.wiziq.com/tutorial/7264-Introduction-to-the-Autonomic-Nervous-System

http://www.ndrf.org/ans.html

http://faculty.washington.edu/chudler/auto.html

http://www2.ivcc.edu/caley/107/lectures_unit_3/ans.html

http://www.youtube.com/watch?v=JvuugFKe1PE

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/PNS.html

Thantosis/tonic immobility –

http://www.mapoflife.org/topics/topic_368_Thanatosis-%28feigning-death%29-in-spiders-and-insects/

http://www.youtube.com/watch?v=RamV-AjID8E

http://intentblog.com/playing-dead-how-survive-hero-binghamton-massacre/

http://insects.about.com/od/Insect_Defenses/qt/Insects-That-Defend-Themselves-By-Playing-Dead.htm

http://wow.joystiq.com/2007/12/05/boy-attacked-by-moose-feigns-death-thanks-wow/

www.howfishbehave.ca/pdf/Feigning%20death.pdf

http://rspb.royalsocietypublishing.org/content/274/1609/555.full

http://www.youtube.com/watch?v=5usnMtNVyp8

http://www.sharkdefense.com/Repellents/Tonic_Immobility/tonic_immobility.html

http://www.telegraph.co.uk/earth/wildlife/6668575/Killer-whales-attack-and-eat-sharks.html

Stress cardiomyopathy –

http://www.hopkinsmedicine.org/asc/faqs.html

http://emedicine.medscape.com/article/1513631-overview

www.thedoctorschannel.com/view/takotsubo-cardiomyopathy-carries-excellent-long-term-prognosis-3/

http://www.mayoclinic.com/health/broken-heart-syndrome/DS01135

http://www.hopkinsmedicine.org/press_releases/2005/02_10_05.html

http://www.pbs.org/newshour/rundown/2012/02/broken-heart-syndrome-yes-its-real.html

http://www.webmd.com/heart/features/broken-heart-syndrome-stress-cardiomyopathy

Hyperekplexia –

http://www.foxnews.com/health/2012/08/09/new-cause-rare-tartle-disorder-found/

http://www.medterms.com/script/main/art.asp?articlekey=8304

http://ghr.nlm.nih.gov/condition/hereditary-hyperekplexia

http://www.hyperekplexia.org/page1.aspx

http://www.hockscqc.com/articles/startle-reflex/startle-reflex.htm

http://www.ehow.com/about_6687971_hyperstartle-response_.html

Long QT syndrome -

http://www.mayoclinic.com/health/long-qt-syndrome/DS00434

http://www.qtdrugs.org/

http://www.sads.org/About-SADS/Long-QT-Syndrome

http://my.clevelandclinic.org/heart/disorders/electric/longqtsyndrome.aspx

http://www.sciencedaily.com/releases/2012/07/120725150152.htm

The link between Halloween, corn, and pumpkins

has more to do with harvest time than vampires or

ghosts. But there is a lot of biology in Halloween,

and it’s not because biology is scary.

Dead (or undead) humans have often been associated with the "dying" of summer and the end of the growing season. The Celts believed that there was a link between the death of the growing period and the affects that the dead could have on the sun's life-giving power. Thus, Halloween and Fall have always been linked.

Because of the time of the harvest, several food crops have been pulled into the Halloween traditions. Let’s talk about two of them - from more of a biological point of view.

Jack O’ Lanterns

The pumpkin is native to North and parts of South America, but Halloween originated in Europe. So how did the pumpkin get so involved with the holiday?

Besides making great pies, Native Americans had been eating pumpkin for thousands of years. They are healthy as can be, with lots of fiber, vitamin A, and potassium; plus they are low in fat. But their health value goes beyond what even the natives might have considered.

The point is that pumpkin flesh is useful for

preventing or treating diaper rash. But the

picture is a blatant attempt to keep you on the
page longer.

Recentstudies have looked at the health benefits of various parts of the pumpkin. The rind has antimicrobial peptide activity, it has been a well-used herbal remedy for diaper rash for years. But it may be that pumpkin seeds are truly the bee’s knees when it comes to cure alls.

It turns out that the seeds (aka pepitas) have some amazing talents. In ostriches, they are being used to prevent and treat gastrointestinal worm infections. In fact, pumpkin seeds have been used for centuries to expel parasites. The question still remains as to how they do this.

Even without a worm infection, pumpkin seeds can do you much good. While they are often considered a waste product (or more politely termed, an “agro-industrial residue”) from production of canned pumpkin, the ground or pressed seeds have much potential as food additives. A study from the Journal of Food Science in June, 2012 has determined the amount of bioactive compounds (components of foods that have actions beyond their caloric value) in the seeds of various pumpkin species - it turns out they are a superfood.

Pumpkins have high levels of carotenoids and tocopherols, the building blocks of vitamins. The fats are mostly polyunsaturated, which is better for us, and they tend to have a relaxing effect on gastrointestinal and bladder sphincters, so they can been used to treat irritable bowel and bladder.

Stingy Jack carried his lantern and wandered the

countryside – a spirit with no place to go. For

spending a life of drinking and debauching, he looks

to be a fine physical specimen.

Maybe most amazing, the seeds of the pumpkin are reported to reduce or eliminate the intestinal damage caused by methotrexate, a potent anti-cancer drug. They are anti-inflammatory and antioxidant, and provide a potential adjunct to cancer therapy.

This is all very interesting, but it doesn’t explain Jack O’ Lanterns and Halloween. I like the story of Stingy Jack as a viable connection. In brief, Stingy Jack lived in Ireland. He was fond of drink and gambling. These led him into a series of bets with the Devil for the fate of his soul. In each case, Stingy Jack was able to trick the Devil into both giving him something he wanted, and putting Stingy Jack’s soul out of the Devil’s reach.

OnceStingy Jack died, heaven didn’t want him because of his transgressions, and Hell couldn’t take him because of his deal with the Devil. So he was forced to wander the Earthly night, using only a coal ember in a hollowed out vegetable to light his way. He became Jack of the Lantern = Jack O’ Lantern.

The Irish would hollow out potatoes or turnips and put hot coals in them to ward off Stingy Jack in the night. If big enough, they would carve out faces in their lanterns to ward off the spirit of Stingy Jack. So where does a pumpkin fit into this story?

C. maxima pumpkins can grow are favorites at fall

festivals. All giant pumpkins (>100 lb.s) are of this

variety, but other C. maxima varieties include banana

squash and buttercup squash; these only get to be a

couple of pounds each.

When the Irish began their emigration pattern to the United States, they brought their traditions to America as well, including Stingy Jack. In North America they found pumpkins. Bigger than turnips or potatoes, pumpkins were easy to hollow out. This made them perfect for Jack O’ Lanterns. The change stuck and that is how we came to use pumpkins at Halloween.

The largest pumpkins are of the variety C. maxima. The current record is over 1818 pounds (824.6 kg). However, they are tough to use as Jack O’ Lanterns, as their rinds can be 10 inches (25cm) thick, requiring electric saws to get into and hollow them out. I think Stingy Jack can be warded off without resorting to power tools.

Candy Corn

Candy corn was invented in the 1880’s by a candy manufacturer named the Wunderlee Candy Company. It was instantly popular with the largely agrarian society of that time; a much larger portion of the population were farmers, and they enjoyed the sweetness of bringing in their corn harvest.

Pouring three differently dyed mixtures into molds one after another resulted in the layered effect, a revolution for the time. Dried corn (like in the picture below) are indeed yellow, white, and orange, just like the candy. The order is different, but that may have had more to do with possible mixing of the layers than with a misremembered early life on the farm by the inventor, George Renninger.

Some companies now sell Indian candy corn as well, and the colors of even the traditional candy corn remind one of the colors in Indian corn. Indian corn is sometimes called flint corn because it has a thicker, harder shell, hard as flint. Indian corn isn’t as sugary as sweet corn for roasting or boiling, but it can be used for popcorn and is actually preferred for making hominy. In some future post we should talk about the use of corn in the discovery of genes that can jump around in the chromosomes.

Dried corn turns colors as the sugars change to starch and

the carotenes in different parts mature or resorb. The order

of the colors is different in candy corn, but it is amazing to us

city folk that the colors of candy corn have a basis in biology,

not in marketing.

So isthere more to know about corn in the candy corn story? You bet. It takes a lot of corn to make candy corn. Take the endosperm for instance. This is the area under the shell that has the sugars that provide energy for the embryonic plant as it germinates - before it has leaves and can produce its own carbohydrates.

The corn endosperm is full of starch as it matures, but sweet corn has a recessive mutation which slows the conversion of sugars to starch. This makes it sweeter, but once it is picked, the ears mature rapidly as a survival mechanism and the glucose is converted to starch. This is why it is it is best to eat sweet corn as soon as possible after it has been picked.

As a long chain of glucose molecules, starch is not sweet; the glucoses are not available to our taste buds. Break down the starch into smaller units, and then it becomes something tasty, like candy corn. You can achieve this breakdown with heat (boiling the corn will break up some of the starch), but it is more likely that this will be done with enzymes.

This enzyme activity is good for us; it gives us corn syrup, which is the main ingredient in candy corn! Even more amazing, we owe our corn syrup (and thus our candy corn) to bacteria and fungi, because they are the sources of the enzymes industry uses to break down the cornstarch.

To make corn syrup, mix some cornstarch (the dried and powdered endosperm) with some water and add a healthy portion of alpha-amylase. This enzyme is secreted by bacteria and can be isolated from their growth medium. The alpha-amylasebreaks starch chains into short oligosaccharides (oligo= few, sackaron = sugar). This is a little sweeter than starch, but is hard to work use.

To make it even sweeter and more liquid (starch doesn’t melt in water as well as glucose; it is less soluble), a second enzyme is added. Glucoamylaseis isolated from a fungus called Aspergillus. This enzyme chops up the oligosaccharides into individual glucose molecules. Now it is sweet and liquid enough with which to work.

Glucose and fructose are very similar chemically.

They both have six carbons; they both have twelve

hydrogens and six oxygens. But the devil is in the

details, and the different position of one oxygen

makes fructose sweeter and more soluble.

Of course that isn’t good enough for industry. They have given us a newer product, called high fructose corn syrup (HFCS). One additional enzyme is enough to make the change; glucose isomerase isolated from bacteria converts some of the glucose to fructose, making the concoction sweeter and more fluid.

Therehave been health concerns about HFCS, including that it promotes obesity. The latest research suggests that there is no relationship between HFCS specifically and increased obesity. However, other concerns are more grave. A recent review of studies about epigenetics (epi = beyond) and autism proposes links between HFCS and heavy metals. HFCS may be low in zinc, and zinc is crucial for heavy metal detoxification as well as controlling the expression of some learning genes. This may be exacerbated by mercury or high levels of copper in HFCS. But good old candy corn still uses regular corn syrup.

But this isn’t the end of corn in the process. The molds used to make candy corn are pressed out of cornstarch. The powdery substance is compressible enough to hold a shape, but can be disrupted with minimal force (give it a whack). The finished product is turned out, the cornstarch becomes powder, and can be reused to make new molds. This Halloween candy turns out to be very corny.

Next week we will return to our investigation of immune system functions, beneficial diseases, and immune system malfunctions - did you know plants have immune responses?

El-Boghdady NA (2011). Protective effect of ellagic acid and pumpkin seed oil against methotrexate-induced small intestine damage in rats. Indian journal of biochemistry & biophysics, 48 (6), 380-7 PMID: 22329239

Thais Ferreira Feitosa, Vinícius Longo Ribeiro Vilela, Ana Célia Rodrigues Athayde, Fábio Ribeiro Braga, Elaine Silva Dantas, Vanessa Diniz Vieira and Lídio Ricardo Bezerra de Melo (2012). Anthelmintic efficacy of pumpkin seed (Cucurbita pepo Linnaeus, 1753) on ostrich gastrointestinal nematodes in a semiarid region of Paraíba State, Brazil Tropical Animal Health and Production DOI: 10.1007/s11250-012-0182-5

Biology concepts – innate immunity, adaptive immunity, defense mechanisms, endotoxin

The Jardin des Tuileries is the setting for the

final scene of “The Happening.“ Located in

Paris between the Louvre and the Palace de

la Concorde, this garden was once a royal

promenade, but became public after the

revolution. The trees that line the walk are

chestnuts. Several species of Chestnut are

pollen sterile, meaning they don’t produce

pollen and must be cross pollinated from a

species that has pollen.

M. Night Shyamalan likes to make movies that have “hide in plain sight” twists: the psychologist is a ghost (The Sixth Sense); the villagers live in modern times (The Village); the mentor is the arch-villain (Unbreakable). In his movie, “The Happening,” mankind is under attack. Something is making us commit suicide in mass numbers. What is attacking us – or might something be defending itself from humans? If it is defensive, could be considered an immune response? If yes, then can we figure it out by deciding just who has immune responses?

Immune systems of defense can be very evolved, as in humans. Ours make use of two specific circulatory systems (blood and lymph), has organs designed to aid their generation and functions (lymph nodes, thymus, bone marrow, and spleen), and has mobile cells designed only to patrol and protect. These components function in both innate and adaptive immune cascades and webs.

Other organisms’ defense systems are not so intricately developed, but still deserve respect. Arthropods (insects, crustaceans and the like) have a highly developed innate immune system, with circulating immune cells of several types.

Mollusks (clams, octopods, and the like) also have an innate immune system with a few types of circulating immune cells. However, immune responses don’t have to be only from circulating cells. Sometimes they are proteins that kill bacteria, or merely surrounding the pathogen and keep it from the host cells. Many kinds of mollusks protect themselves by encapsulating invading parasites in a solid prison of shell-like material -we call them pearls! Any mollusk with a shell can make pearls – even snails.

Conch is a species of giant snail. It produces lovely

pearls, so pearls don’t just come from oysters. Any

shelled mollusk will react to a parasite that gets

through its shell by walling it off in layers of mother

of pearl (nacre). This is the very smooth material

that covers the inside of the shell.

Everyanimal has some sort of immune response built into its physiology, but supposedly only vertebrates have an adaptive immune system. Invertebrates have the older, innate system, but not the ability to adjust their recognition and response to particular pathogens like the adaptive system can. The specific, or adaptive immune system was believed to have arisen in the first of the jawed fishes (gnathostomes; gnath = jaw, and stoma = mouth), about 410 million years ago and been handed down and modified by mammals. But there are exceptions – there are always exceptions.

The Agnathans (jawless fishes, such as lampreys and hagfish) seem to have an adaptive system all their own. It has features similar to the adaptive system of jawed vertebrates, but the way that foreign antigens are recognized is completely different. The lampreys and similar organisms use a different kind of receptor molecule on immune cells. The receptors are variable, but not in the same manner as mammalian immunoglobulins. In jawed vertebrates, the antibody genes rearrange to form the basis of both circulating and receptor immunoglobulins.

This "similar but different" adaptive system would indicate that specific immune responses have sprung up at least twice in evolutionary history. I say at least twice because it is beginning to look like insects and worms may have a sort of adaptive system as well. Earthworms will reject grafts from other earthworms, and will reject a second graft faster than the first graft. So, we see that most organisms have elaborate ways to defend themselves.

This brings us back to “The Happening,” and the attack on the humans ---– it turns out that it was the trees trying to protect themselves from being overrun by mankind! Plants have defenses? Plants can sense attack and respond? Yep.

Plants don’t have immune cells, those that move around and whose job it is to protect and attack. But they do have immune defenses against pathogens, and pretty sophisticated ones at that.

This is a cartoon which shows plant immune response. First

a pathogen tries to gain entry and the plant recognizes its

surface molecules (PTI). Some pathogens survive the response

and emit effectors (ETS, effector-triggered susceptibility). The

effectors trigger ETI which increases the response proteins.

Some pathogens may survive and too much ETI and ETS

triggers the hypersensitive response. Image: Nature

444:323-329, 2006.

PlantPTI (Pattern Triggered Immunity) is similar to our innate immune system, just without the specific immune cells. In this system, plants recognize molecules that are common to microbes (MAMPS, microbe associated molecular patterns) using pattern recognizing receptors (PRRs).

This is similar to mammalian PRR systems for PAMPs (pathogen associated molecular patterns), the toll-like receptors for example. When triggered, resistance molecules and plant hormones are released to make the plant less appealing to the pathogen, or to interrupt the infection process. There are many of these resistance mechanisms, we can talk about a couple below and more in the future.

On the other hand, plant ETI (Effector Triggered Immunity) is signaled by the effector molecules released by the microbes that manage to set up shop inside plant cells or tissue. ETI is really just an increase in the amplitude of the same response molecules seen in PTI, plus another defense mechanism, called the hypersensitive response.

Some pathogens like the hypersensitive response.

Necrotrophic (necro = death, and troph= loving) fungi,

like Botrytis cinerea, or gray mold (the spots on the

leaves), must have dead tissue. They wait until some

thing else triggers the hypersensitive response, or they

trigger it themselves, and then feed of the dead plant tissue.

When a pathogen is successful at making entry into a plant at a specific site, the plant may respond by releasing oxygen and nitrogen radical compounds (those with free electrons that will attack dang near anything). This will kill the plant cell as well as the invader (hence the name “hypersensitive”), but it reduces the probability of infection by taking out everything in the area. It is a sacrifice of host cells that the plant is willing to make.

This response is much like the apoptosis (programmed cell death) that virally-infected animal cells may initiate. It is a small loss in order to protect the whole organism. Recent evidencesuggests a central role for S-nitrothiols (nitric oxide linking cysteines) in both turning on and limiting the hypersensitive response by controlling the amount of NADPH oxidase, an enzyme that produces reactive species. We will see next week that this suicide mechanism is very old.

Reactive species for cell suicide is cute, but plant responses get even cuter. When threatened by some herbivorous insects, 2012 research shows that plants can call in mercenaries to help. Members of the cabbage family are troubled by the larvae (caterpillars) of the large cabbage butterfly (Pieris brassicae). When this butterfly lays its eggs on a black mustard plant, the plant sends out a chemical signal that attracts two species of wasps (Trichogramma brassicae and Cotesia glomerata).

When the male cabbage butterfly fertilizes the female

and she lays her eggs on a brussel sprout plant, the

chemicals from the male semen will trigger the plant to

make a pheromone that attracts the Trichogramma

brassicae wasp. It lays its eggs INSIDE the butterfly

eggs (yellow cones) and they feed off the butterfly eggs

as larvae. Up to 50 wasps can come out of one butterfly

egg. Image:Nina E. Fatouros.

These wasps are natural enemies of the white cabbage butterfly and will attack its eggs and larvae. Voila, the plant stops the white cabbage caterpillar from eating its leaves even before the attack begins. Most amazing, the chemical signal isn’t triggered by other, less ravenous pests, so it is a specific response. That smells like an adaptive immune response to me. While many animals can’t specify a distinct response to a particular foreign organism, it looks like many plants can. Once again, plants show us how advanced they are.

Even more in support of the idea that plants have a form of adaptive response is the discovery that they have an immune memory of sorts. In 2009, researchers at the U. of Chicago found that when attacked by a certain bacterium, Arabidopsis plants (of the mustard family, a very common plant in research) make a chemical at the site of attack called azelaic acid.

The scientists found that this compound can stimulate a faster and stronger immune response when and if the plant was ever attacked again. Azelaic acid acts by stimulating salicylic acid (a compound very similar to aspirin) production in the plant directly, and by stimulating a newly discovered protein called AZ11. The increased salicylic acid then stimulates the defense mechanism.

More recent work (2012) in the same field has identified five additional compounds from Arabidopsis that also prime immune defenses. These new compounds work by inactivating enzymes that break down salicylic acid; the plant is therefore always ready to initiate a defense. These natural chemicals may be important for agriculture in that crops could be sprayed with a primer and be ready for a quick and strong response if they are ever attacked.

Priming is important for plant immunity. Priming can

induce production of more response proteins that may

be stored in vacuoles until needed. Priming can also lead

to modification of DNA regulators, so that more response

proteins can be made over time.

An important factor in this strategy is that the primers do not affect plant growth or seed/fruit production. Many plant defense mechanisms come with an energy or growth cost, the hypersensitive response for example. The time and ATP that a plant spends on defending itself ends up costing it in growth and flower/seed/fruit production. This is important when we are talking about cash crops that feed the world’s people. The newly discovered priming agents can stoke up a plant’s immune response with no loss of growth or productivity. It’s a win-win situation for plants and people.

So animals and plants have independently developed immune responses, including adaptive memory and host cell death mechanisms. Or have they been independent?

The S-nitrosylation regulatory step in the production of reactive species is conserved (the same function, in this case mediated by the same amino acids in similar proteins) in animals, so we and they have developed a similar control – is it conserved from an ancient time before plants and animals diverged? Has the same system developed independently two time – unlikely, many orthologous systems exist, but nature is hit and miss, it rarely twice stumbles upon exactly the same way to do something. The adaptive systems developed by the jawed and jawless fishes may be an example of this. They do much the same things, but through different mechanisms. Perhaps plants and animals shared information at some point in time – horizontal gene transfer, like we talked about a long time ago?

Plants and insects can protect themselves and can adapt to different pathogens, so we have learned not to assume humans are so special. How about if we take another step along this line next week? Can bacteria protect themselves? Do they need to?

Fatouros, N., Lucas-Barbosa, D., Weldegergis, B., Pashalidou, F., van Loon, J., Dicke, M., Harvey, J., Gols, R., & Huigens, M. (2012). Plant Volatiles Induced by Herbivore Egg Deposition Affect Insects of Different Trophic Levels PLoS ONE, 7 (8) DOI: 10.1371/journal.pone.0043607

Yun, B., Feechan, A., Yin, M., Saidi, N., Le Bihan, T., Yu, M., Moore, J., Kang, J., Kwon, E., Spoel, S., Pallas, J., & Loake, G. (2011). S-nitrosylation of NADPH oxidase regulates cell death in plant immunity Nature, 264-268 DOI: 10.1038/nature10427

For more information or classroom activities, see:

Invertebrate immune systems –

http://pulse.pharmacy.arizona.edu/10th_grade/disease_epidemics/science/pathogen.html

http://www.sciencedaily.com/releases/2007/06/070621102626.htm

http://www.ncbi.nlm.nih.gov/pubmed/15199951

http://www.reefs.org/library/aquarium_net/0498/0498_1.html

http://www.fu.uu.se/jamfys/jamimm3.html

http://www.sciencedaily.com/releases/2012/01/120105111946.htm

http://www.uwosh.edu/today/7365/scientists-study-insect-immune-systems/

pearl formation –

www.yvel.com/Assets/PearlGuide.pdf

http://marinelife.about.com/od/invertebrates/f/How-Do-Pearls-Form.htm