As Many Exceptions As Rules

Wednesday, June 15, 2016

Tricky Little Buggers

Biology concepts – immune defense, antibiotic resistance

Naim Süleymanoğlu is better known as Pocket

Hercules (4' 10"). He was born in Bulgaria, but is

of Turkish descent. He competed and retired

several times, and won gold medals from 1983

to 1998. He is one of the first competitors to

lift more than 2.5x his own body weight.

There was a small Turkish weightlifter a few years back whose nickname was “Pocket Hercules.” He won gold medals in three separate Olympics and was the one the best examples of big things in little packages. Last week we talked about the immune systems of vertebrates, invertebrates and plants, now let’s talk about the defenses of the smallest organisms – bacteria are the Pocket Hercules of biology.

Do bacteria have defense mechanisms? You bet – they get attacked all the time. For bacteria that stray into or purposefully target animal or plant hosts, the perils are many and varied. Antimicrobial peptides try to burst them, antibodies try to bind them up and point them out to killer cells. Macrophages and other phagocytic cells try to eat them or wall them off from the other host cells. Organisms will even sacrifice their own cells just to make sure they kill the bacteria. It’s a jungle out there.

We don’t have the time nor the room to go into the thousands of ways that bacteria protect themselves from plant, invertebrate, and vertebrate immune attack, but we can give a few examples, like deception. Mimicry is when a bacterial antigen looks much like one of our molecules, so that the body is either fooled into not attacking, or tempers its attack.

Other bacteria change their clothes to remain hidden. Just when an immune system sees it and starts the attack, Neisseria gonorrhoeae changes its surface molecules and becomes invisible again. On the other hand, Yersinia pestis remains invisible by living inside macrophages.

Some bacteria stunt our antibody response. The best way to keep from being attacked is to not allow the host to recognize and identify you. The bacteria that cause TB inhibit our immune system from producing specific antibodies.

Some bacteria vary the antigens they show on

their surface in order to evade the immune system.

In this bacterium, the dark areas are stained for

one particular surface antigen. You can see that

some of the cells have none of that protein, some

have only that surface protein, and some have

discrete areas where that protein is expressed.

The defense is a good offense, so some bacteria attack. Pseudomonas strains kill the phagocytic cells that would try to eat them by releasing chemicals called aggressins. Staphylococcus aureus just confuses the phagocytes, producing toxins that stop their movement or make them move erratically.

These are but a few of the many bacterial defenses against our immune system. But they have evolved defenses against other threats as well, like our attempts to kill them with antibiotics.

We talked earlier about multidrug efflux pumps in bacteria that pump out the antibiotics with which we try to kill them. This is related to the stories in the media about antibiotic resistance in bacterial pathogens, but classic antibiotic resistance genes are often plasmid based defenses, as we have discussed. Recently, an additional defense against antibiotics has been recognized.

It seems most bacteria produce hydrogen sulfide (H₂S, smells like rotten eggs), which was previously thought to be only a metabolic byproduct. A late 2011 study shows that H₂S is part of an integrated defense system used by almost all bacteria. The gas works to prevent oxidative damage. This is not unheard of since a few bacteria produce nitric oxide to do the same thing, but it is being recognized now that oxidative stress induction is a big part of how many antibiotics work. When the H₂S system was turned off in several pathogens, they became much more sensitive to antibiotics. Maybe this a lesson we can exploit in the future.

In addition to our attempts to kill them, the universe itself is a tough place to survive if you are a bacterium. They may end up in bright sunlight for long periods of time, or hurtling through space on a rocket or meteor. Bacteria have ways to protect themselves here as well. Ultraviolet radiation from the sun is a mutagen (causes mutations in DNA), but it also can break down cellular molecules to release oxygen radicals, like hydrogen peroxide or superoxide.

It has been known since the 1950’s that pyruvate and catalase, as well as the newly discovered H₂S discussed above, do some work in protecting the cell against oxidative damage, but a 2009 study described a whole new mechanism. It seems that E. coli has two proteins that seek out, identify, and repair oxygen radical-mediated damage to sulphur-containing cysteine amino acids within proteins.

Cysteine is the most reactive of the 20 common amino acids, which means that it are often located in the functional site of enzymes (where the enzyme reacts with the substrate). However, this reactivity also makes cysteine vulnerable to reaction with radicals, especially oxygen radicals, after which it becomes modified and non-functional.

Disulphide bonds are formed between adjacent cysteines on the

same peptide, far apart cysteines on the same peptides,

or between cysteines on different peptides. When

you (not me) get a permanent wave for your hair, the

disulphide bonds are broken or rearranged by a reducing agent.

To prevent this radical-mediated damage, cysteines often occur in pairs, where links between the sulphurs of the two cysteines help to prevent oxidation (called disulfide bonds, they also serve to link peptides together and give proteins their proper form). A 2008 study showed that this mechanism provides unusual oxidative stability to a cysteine-containing enzyme of the bacterium, Desulfovibrio africanus.

But there are exceptions; lone cysteines do occur, and these are the cysteines most vulnerable to oxidative damage. The DsbG and DsbC proteins of E. coli patrol the cytoplasm looking for oxidized cysteines to fix.

Here is how ingenious the system is – oxidizing a cysteine may or may not unfold the protein, so DSbG is charged and can interact with the still-folded proteins to correct the cysteine problem, but DsbC is uncharged, so it works better with proteins that have been unfolded. Amazing - and bacteria developed it all on their own – well, with the help of the evolutionary pressure of things trying to kill them.

I mentioned that radiation is also a DNA mutagen. The mutagenic properties of radiation affect bacteria just like they affect us; it is just that some bacteria can protect themselves better once their DNA is damaged. Follow me closely here - by using protein repair and protection systems, bacteria like E. coli, with its DsbG and C enzymes, can keep protein functions going when other organisms would break down and die. Some of these protein functions include DNA repair after mutagenesis. So - some bacteria don’t survive radiation because they protect their DNA better, they survive because they repair the damage better.

This is an overlap of different types of images of a

radiodurans bacterium. The circles of blue green and

pink show high concentrations of manganese, while

red is iron. The manganese is clustered around the

DNA and works to repair it after radiation damage.

Other bacteria have a different mechanism to maintain protein function. According to a 2010 study, a shield of manganese metal atoms and phosphates was found in D. radiodurans. It had been long known that manganese was present in very high levels in bacteria that are most resistant to radiation, but its function was unknown.

The recent study shows that these manganese complexes work together to protect proteins from radiation damage, but not DNA. The key for this system is to keep proteins functioning, which can then repair any radiation damage to the DNA. This mechanism allows D. radiodurans to withstand prolonged radiation that is 1000x stronger than that which would kill a human.

So, bacteria have defenses against immune and environmental attacks. Does anything else attack bacteria? How about other bacteria - it’s dog eat dog out there, competition for resources is brutal. Many bacteria have poisons (bacteriocins) that inhibit or kill bacteria that are distantly related (because related types of bacteria are likely to be in the same places looking for the same food).

One type of bacteriocin are the lantibiotics. These protein toxins contain a nonstandard amino acid, called lanthionine. We mentioned above that cysteines are very reactive; lanthionine is a modified circular (polycylic) cysteine that gives the toxin its reactivity. And because it is cyclic, it is much less vulnerable to oxidative damage itself – funny how bacteria seem to cover their bases so well.

This is so cool. Bacteria that are engineered to produce

light were injected into rats. The rat in the middle was

also given a bacterium producing a bacteriocin to the

light producing bacteria. The whole rat bodies were

imaged while they were still alive to see if the bacteria

were alive and reproducing. Live animal imaging is a

great tool that is becoming more popular. Image by S.

C. Corr and P. G. Casey.

Lantibiotics come in two types, they either form pores in Gram⁺ bacterial cell walls or inhibit the cell wall formation. Because they attack only specific types of bacteria, lantibiotics are useful in cheese-making; they allow some bacteria to grow and ripen the cheese, while killing those that would cause the cheese to spoil. One type B lantibiotic just came through its phase I clinical trial in July 2012 with flying colors (phase I trials are meant only to test safety, not effectiveness).

A recent discovery illustrates just how bacteriocins are delivered to the target organism. It seems that bacteria can build a spike and a spike launching system anywhere on their cell membrane. The spike is spring loaded in a tube just 80 atoms long, and is fired at the target cell. Then the bacteriocin is released at the end of the spike to do its damage.

The release of toxin was already known, called a type IV secretion system, but the CalTech study that identified the spring-loaded spike as the delivery system is very new. Once fired, the whole system is broken down, ready to be rebuilt somewhere else in the cell. Amazing. (click for video)

Of course, for every punch there is an evolutionary counterpunch, so there are bacteriocin resistance mechanisms as well. Nisin, a bacteriocin active against strains of listeria, is approved as a food preservative. But listeria can spontaneously develop resistance to nisin. It appears that some strains change their membrane chemistry in order to render nisin ineffective. Therefore resistance could be a problem if we pursue the use of bacteriocins as antibiotics; we might end up back in the same situation that we're in now.

Regardless of this possible downside, scientists have found a way to bring bacteriocins into the battle against antibiotic resistance. An E. coli has been engineered to contain the gene for pyocin, a bacteriocin that kills strains of Pseudomonas bacteria. E.coli and Pseudomonas are not closely related, so E. coli would not naturally possess this toxin, scientists added the gene to the E. coli.

This is schematic of the engineered bacteria to kill Pseudomonas.

P. aeruginosa make chemicals when their numbers reach a

certain density. These trigger pyocin production in the E. coli,

but also triggers the production of the protein that lyses the

E. coli. When lysed, the pyocin attacks the P. aeruginosa.

When the engineered bacteria encounters Pseudomonas, it does two things; it produces the pyocin toxin to kill the target cell, and the engineered E. coli commits suicide. No release system has been engineered into the E. coli, so the only way they get the pyocin to the target is to have the E. coli produce a lysin that destroys its own cell membrane.

This suicide accomplishes two things, it releases the pyocin to kill the target, and it prevents the engineered E. coli from hanging around forever, possibly trading genes with other bacteria or causing havoc in some unforeseen way.

So it looks like bacteria have it made. They can resist immune system attacks, some can resist environmental onslaughts, they even have ways to protect themselves against competition and threats from other bacteria. No wonder they have always been the predominate life form on Earth. But bacteria do have foes of considerable power – veritable “Micro-Hercules” – we will meet them after Thanksgiving.

Let’s take a couple weeks to talk about the biology of turkeys and the so-called “tryptophan nap.”

Basler, M., Pilhofer, M., Henderson, G., Jensen, G., & Mekalanos, J. (2012). Type VI secretion requires a dynamic contractile phage tail-like structure Nature, 483 (7388), 182-186 DOI: 10.1038/nature10846

Saeidi, N., Wong, C., Lo, T., Nguyen, H., Ling, H., Leong, S., Poh, C., & Chang, M. (2011). Engineering microbes to sense and eradicate Pseudomonas aeruginosa, a human pathogen Molecular Systems Biology, 7 DOI: 10.1038/msb.2011.55

For more information or classroom activities, see:

Bacterial defenses–

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CB8QFjAA&url=http%3A%2F%2Fwww.pct.edu%2Fdegreesthatwork%2Fdocs%2Fword%2F1_2-Science_Teacher_Series-Nanotechnology.doc&ei=kOFlUKW8OcjnyAHv8ICgAg&usg=AFQjCNFIooLBtpkA1vko0-lRwai7x7v1Zw

http://www.smallerquestions.org/blog/2012/5/21/from-soil-to-human-evolution-of-bacterial-immune-evasion-mec.html

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CC4QFjAC&url=http%3A%2F%2Fwww.educationscotland.gov.uk%2FImages%2FInfectiousDiseasesandImmunityTeachersNotes_tcm4-669755.doc&ei=o99lUJN5woXLAdeYgHg&usg=AFQjCNH-uSO824WJUdpVkxUg4xhP1C_fZA

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

http://textbookofbacteriology.net/antiphago.html

http://textbookofbacteriology.net/antiimmuno.html

http://www.sciencedaily.com/releases/2010/04/100425151159.htm

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

http://www.ncbi.nlm.nih.gov/pubmed/15231256

http://www.sciencedaily.com/releases/2011/11/111117144009.htm

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CCoQFjAB&url=http%3A%2F%2Fassets.cambridge.org%2F97805218%2F01737%2Fsample%2F9780521801737ws.pdf&ei=_N5lUPu4D8-GyQGEy4GAAQ&usg=AFQjCNEKYTv8woZ0L40EEdezU3UKyIXmCA

http://phys.org/news193846665.html

Bacteriocins –

http://www.foodsafetynews.com/2011/09/a-lantibiotic-steps-up-to-kill-harmful-bacteria/#.UGXgahhf13I

http://www.sciencedirect.com/science/article/pii/S2211546312000034

see Pubmed (http://www.ncbi.nlm.nih.gov/pubmed) for more information on these defenses.

Wednesday, June 8, 2016

Immune To Evolution

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.

Every animal 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.

Plant PTI (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 evidence suggests 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

http://www.youtube.com/watch?v=qvyUwamNu9A

http://www.ehow.com/facts_6867421_do-oysters-protect-themselves_.html

http://archive.fieldmuseum.org/pearls/making.html

http://www2.vims.edu/bridge/search/bridge1output_menu.cfm?q=mollusc

plant defense/immune responses –

http://www.canopyintheclouds.com/teach/lessons/ecology-plant-defense.php

http://rd.springer.com/article/10.1007/s10763-011-9297-9

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&ved=0CEYQFjAG&url=http%3A%2F%2Fpurple.niagara.edu%2Fwje%2FBio123%2FLab%25204%2520Plant%2520Defense%2520Compounds2005.pdf&ei=kFNXUKrlG4HByQHp4YCQCQ&usg=AFQjCNEf7ydz1CHsfBpgCPD40_oxZDgt-A

http://www.botany.org/plantimages/plantdefensemechanisms.php

http://www.scoop.it/t/effectors-and-plant-immunity

http://www.goldiesroom.org/video_archive.htm

http://www.clfs.umd.edu/classroom/CBMG688R/Ref4_07defense.htm

http://www.cornell.edu/outreach/programs/program_view.cfm?ProgramID=1021

https://ag.purdue.edu/btny/pages/teachingresources.aspx

http://www.abc.net.au/science/articles/2012/06/12/3522493.htm

http://today.agrilife.org/2011/06/16/plants-teach-humans-about-fighting-diseases/

http://bcs.whfreeman.com/thelifewire/content/chp40/40020.html

Wednesday, June 1, 2016

The Dirt On Staying Healthy

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!

Triclosan can 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?

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/