Your Body Has A Photographic Memory

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.

Think of 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 immunity vs. 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 immunity vs. 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 cells vs. 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.

During the 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.

The problem 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.

Mathews, J., McBryde, E., McVernon, J., Pallaghy, P., & McCaw, J. (2010). Prior immunity helps to explain wave-like behaviour of pandemic influenza in 1918-9 BMC Infectious Diseases, 10 (1) DOI: 10.1186/1471-2334-10-128

Kash, J., Qi, L., Dugan, V., Jagger, B., Hrabal, R., Memoli, M., Morens, D., & Taubenberger, J. (2010). Prior infection with classical swine H1N1 influenza viruses is associated with protective immunity to the 2009 pandemic H1N1 virus Influenza and Other Respiratory Viruses, 4 (3), 121-127 DOI: 10.1111/j.1750-2659.2010.00132.x

Cowling, B., Ng, S., Ma, E., Cheng, C., Wai, W., Fang, V., Chan, K., Ip, D., Chiu, S., Peiris, J., & Leung, G. (2010). Protective Efficacy of Seasonal Influenza Vaccination against Seasonal and Pandemic Influenza Virus Infection during 2009 in Hong Kong Clinical Infectious Diseases, 51 (12), 1370-1379 DOI: 10.1086/657311

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/

Lucky For Me, I’m Diseased

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!

You rarely 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.

Attenuated vaccines 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 antigenic part 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.

Many in 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.

This also brings up the idea of herd immunity. There are some people who have been vaccinated, but protection is not complete. The elderly may not be able to react completely even if vaccinated, as might the very young. Some vaccinations may not take - how many time have you had an antibody titer test to make sure your vaccine worked? It is very rare to get titers unless something is suspected and you are already sick. Therefore, many people must count on the vaccination of the herd - a critical percentage of population needs to be protected in order to keep the incidence of the disease below a crucial level. If the level rises - as with too many people choosing not to vaccinate - then the incidence will sky rocket because it will affect those people who don't happen to know they are not protected. Un vaccinated people affect everyone, not just themselves.

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

Grin and Water Bear It

Biology concepts – tardigrade, cryptobiosis, anhydrobiosis, eutely, hyperplasia, hypertrophy, dry vaccine, dormancy

The original toughman contests were supposed to show us the

toughest of the general population. I’m not so sure how tough

it is to have a nickname like “Butterbean,” but maybe that

proves his toughness. On the other hand, do you get a cereal

box cover and a mohawk because your tough, or do you get

tough because you have a mohawk.

In the early 1980’s, a forerunner to the mixed martial arts craze was temporarily popular in the United States. Called the “ToughMan” contests, non-boxers would enter the ring for fights against other nonprofessional fighters. The rules were supposedly the same as in boxing, although many contests were run without proper supervision, and the tournaments sometimes required a participant to fight several times in one evening. Think legalized bar fights.

Famous participants in the toughman contests included “Butterbean” Esch – a 350 lb. boxer with one punch and an iron jaw, and of course, who can forget Mr. T. The contests are still held in many states, but MMA now has the majority of the fan base, even more than traditional boxing between trained fighters.

These guys were tough, but were they the toughest? Humans as a rule are weak for their size, scared of more things than they should be, and less inclined to fight to the death for a morsel of food or potential mate – well most are. So…..

Questions of the Day: What is the world’s toughest animal?

Ask a hundred people and you may get a hundred different answers. The bull elephant can fight off an entire pride of lions and can lift five tons. But can you really give the prize to an animals that is scared of a mouse?! Maybe they aren’t afraid of mice, but they will avoid them if possible, according to one of the more scientifically consistent episodes of Mythbusters.

A good second choice might be the honey badger. It supposedly knows no fear, and proves it by depriving lions of the prey they just killed. In one case, three honey badgers stole a entire carcass from seven lions! The South Africa National defense calls their armored personnel vehicles ratels, the afrikaans word for honey badger.

This is the toughest animal on Earth, although it may not

look it. The water bear looks more like a teddy bear,

although the claws might do some damage if you are a

bacterium or a protist. The mouth has stylets to puncture

plant cells and suck out the liquid nutrition.

But I will try to convince you that a type of bear is the toughest animal on the face of the Earth, a water bear to be specific. This animal has long claws on each foot and a mouth that takes up a good portion of its head. On the other hand, it's less than 1 mm long!

The water bear is more scientifically known as a tardigrade (latin for slow walker), a phylum that falls somewhere near arthropods and nematode worms. There are two classes (eutardigradia and heterotardigradia) and more than 900 species, but there may be some overlap in those descriptions.

The adult tardigrade will have 40,000 cells, and will never have more. What is more, every species of tardigrade is matures with a specific number. This is called eutely (eu = good, and telos = end). Many lower organisms may be eutelic; their cells have a limited number of divisions, so they grow to that number and then stop.

It isn’t just whole organisms that might be eutelic, organs can be as well. For example, the nematode Ascaris ALWAYS has 162 neurons. The research model nematode C. elegans has exactly 959 somatic cells, although a 2011 study has shown that C. elegans can lose critical cell nuclei as they age – tell me about it. Other nematodes, rotifers, and gastrotrichs have also been shown to have cell constancy at the body and/or organ level.

Tardigrades do grow after they reach adulthood, just not by adding cells. Growth by additional cells is called hyperplasia (excess formation), while growth by existing cells becoming larger is called hypertrophy (excess nourishment). 

The gingiva around the teeth can overgrow in response

to some developmental disorders, but more often it is a

result of drugs given for epilepsy or other diseases. The

point here is that whether it is from hypertrophy

(increased cell size) or hyperplasia (increased cell

number), it looks the same. These are histologic

determinations and don’t really matter for clinical evaluation.

Prostate enlargement is often due to an increase in cells, hence the name benign prostatic hyperplasia, but hyperplastic growth doesn’t have to be pathologic. When you lose part of your liver, some can grow back by through hyperplasia. Likewise, hypertrophy is great when it is your muscles getting bigger, but not necessarily so good when your heart’s ventricles overgrow (ventricular hypertrophy).

Different tardigrade species are adapted to nearly every environment on Earth. They live in the Arctic and the Antarctic, in the mountains and the oceans, in the deserts and the jungles. All are found near water, some marine and some limnal (freshwater), some in the water and some just next to the water held in mosses or lichens.

But wherever you find them, you’ll find them in great numbers. The density of tardigrades can approach two million per square meter. Yellow crazy ants (Anoplolepis gracilipes) form supercolonies of incredible density, yet they can only muster about 2000 individuals per square meter. Haven’t heard of crazy ants? You will – look them up.

Tardigrade toughness doesn’t come from their pursuit of prey or their ability to fend off predators, but their willingness to live in conditions that would kill anything else, and I mean anything, else.

Cold, not a problem. Tardigrades can have liquid nitrogen (-346˚F/-210˚C) poured on them and they’re just fine. Heat – boil them for a couple of hours and then watch them lay eggs and go back to eating. Radiation isn’t a problem either; they can take 5700 grays of ionizing radiation without blinking.... well, they could if they had eyes. Humans curl up in a ball and die when exposed to 5 gray.

It is important to know how much radiation is absorbed

by the body, not just how much is in the air. The Gray,

named for Harold Louis Gray, is equal to 1 joule of energy

absorbed per kilogram of matter. Harold Gray is considered

the Father of Radiobiology. The old dose name was the

rad, and 1 Gray is equal to 100 rads. A chest X-ray is

typically about 0.0006 Grays.

Some tardigrades live in black smokers at the bottom of the ocean, yet most of them can take 6000x normal pressure in stride. To sum it all up, in 2007 the Russians fired tardigrades into space for 12 days (near absolute zero, total vacuum, cosmic radiation). They came back and starting having babies. Now that’s tough.

How do they manage these amazing feats? Basically – they die and then come back to life. Technically, it’s called cryptobiosis (hidden life), but death and self-resurrection is not a bad description. During cryptobiosis, metabolism is reduced by 1000x fold or even more, down to the level where there is NO detectable chemical activity.

There are five recognized types of cryptobiosis, based on the noxious environmental condition that triggers it – anhydrobiosis (without water), chemobiosis (chemicals), cryobiosis (cold), anoxybiosis (lack of oxygen), and osmobiosis (change in osmotic potential).

The primary form for tardigrades is anhydrobiosis. They drop their claws, retract their legs and roll up into a ball called a tun. 99% loss of water, roll up into “tun” this is important because it regulates the rate of evaporative water loss. At this level, they don't hold enough water for damaging reactions to take place or even enough water to form ice crystals. The water is replaced by a sugar called trehalose.

Trehalose production is similar to the way many organisms can protect their structures and biochemistry from environmental damage, but apparently scientists have just touched the surface of how tardigrades react to uncomfortable environments. A 2013 study indicates that there are many unidentified organic molecules present in the tuns of tardigrades that are not present in the organisms under normal physiologic situations.

The tun of a tardigrade is a very regulated structure.

When the claws are dropped and the legs retracted, the

tardigrade coils into almost a ball. In this situation, the

loss of water can be carefully controlled. The plates on

the back also form a protective armor for non-

environmental assaults – the spikes look imposing.

Amazingly, tardigrades are the only animal that can undergo all five types of cryptobiosis.  It's really like dying and coming back to life. Reviving from cryptobiosis can take a little while, usually the longer they have been in anhydrosis, the longer it takes to recover. They can’t survive this way forever either.

Earlier reports had professed that 120 year old tardigrades were revived from dried lichen and moss samples in the British Museum, and that decades old samples were just fine. But Dr. James Garey of the University of South Florida tells me that many of these reports have been called into question and cannot be repeated.

Dr. Garey’s estimate is that tardigrades can survive 1-5 years as a tun, with decreasing viability upon hydration after that. Still, could any other animal you know of be dead for five years, with no air, no water, high radiation, liquid nitrogen, and taunts about their size and lineage – and then come right back to life when the opportunity is right?

Cryptobiosis is quite different than dormancy. Dormancy doesn’t bring a huge change in physiology – like 99% dessication. Also, dormancy is preemptive while cryptobiosis is reactive. However, a very good 2011 review of tardigrade reactions shows that they can undergo both dormancy and crytobiosis – sometime simultaneously!

The question is – how do they survive the bad conditions WHILE they are forming the tun? It takes about 20 minutes for tun formation to occur, so it appears that many of the conditions they can endure require them to already be in the cryptobiologic state. They can survive the radiation when they are dessicated, they can survive boiling when they are dessicated. I don’t think it makes them any less amazing.

In early 2013, researchers from King’s College in England

developed a silicon mold with dissolvable sugar micro-

needles that can deliver a dry vaccine powder.  The system

would induce immunity through activation of skin immune

cells, would require almost no training to deliver, and no

refrigeration. The anhydrobiotic live vaccine is based on

tardigrade cryptobiotic features.

Tardigrades aren’t even considered extremophiles, since they are not designed to live in extreme environments. But this is precisely why I think they are so tough, because few of them are adapted to extreme conditions, but they can survive deadly situations anyway.

Can the exploits of this microanimal help humanity? You betcha. Tardigrades' ability to undergo anhydrobiosis has begun to influence the design of medicines. In third world countries, a lack of reliable refrigeration requires vaccines and medicines don’t need refrigeration, and can be reactivated upon ingestion.

Dry vaccines are a current goal, so the National Institutes of Health recently put out a call for proposals for research into more thermostable and reactivateable preparations. A late 2012 paper has identified a tablet form for deliver of some protein drugs, with reactivation of the molecules with saliva. This would be much better than the current reliance on hypodermics and refrigeration. So tardigrades are tough for themselves, and may fight for us as well.

Next week, just how do you describe the climate of your hometown? Biomes are scientific entities, but it seems we can't agree on what each looks like or is called.



Borde, A., Ekman, A., Holmgren, J., & Larsson, A. (2012). Effect of protein release rates from tablet formulations on the immune response after sublingual immunization European Journal of Pharmaceutical Sciences, 47 (4), 695-700 DOI: 10.1016/j.ejps.2012.08.014
 
McGee, M., Weber, D., Day, N., Vitelli, C., Crippen, D., Herndon, L., Hall, D., & Melov, S. (2011). Loss of intestinal nuclei and intestinal integrity in aging C. elegans Aging Cell, 10 (4), 699-710 DOI: 10.1111/j.1474-9726.2011.00713.x  

Guidetti, R., Altiero, T., & Rebecchi, L. (2011). On dormancy strategies in tardigrades Journal of Insect Physiology, 57 (5), 567-576 DOI: 10.1016/j.jinsphys.2011.03.003