Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: Promilla on 06/12/2014 14:48:11
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Hi everyone.
So I was recently thinking about immune system. We know a lot about it, and we are aware that it is redicously sophisticated, but there is still a lot to learn (so I guess it might be even more complcated than what we know). Apart from gene shuffling, which provides huge number of B cells, there is also a number of cytokines, different T cells, etc. I was wondering - for one would it be possible to come up with much simpler immune system, which would have similar efficiency in protecting us against pathogens? And two - how on Earther did we evolve such a complex system? Do other animals (from primates, dogs, to fruit flies) have similar immune systems?
Thanks a lot.
Best,
Promilla
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It is possible to have a simpler immune system. For example, we could have penicillin in our blood. Oh... yes, that is an immune molecule made by yeast and molds. The problem is that the diseases would quickly adapt to the penicillin (as already is happening), and the immune system would be ineffective.
Think of how much work scientists put into developing new, novel drugs, and we have relatively few independent classes of antibiotics developed de-novo. Each one only good until the next antibiotic resistance gene develops. The effectiveness of our immune system is extraordinary, to the point where even with the most advanced science, a person can't live without it.
All mammals have similar immune systems, although each mammal would express a different set of antigens, so if you put human tissue into a mouse, the mouse would quickly reject it. Thus, for research of human cancers in mice, a special immune compromised breed of mice was developed.
Drosophila (fruit flies) (http://en.wikipedia.org/wiki/Drosophila_melanogaster#Immunity) have what is known as an innate immune system (http://en.wikipedia.org/wiki/Innate_immune_system). Humans share some aspects of the Drosophila innate immune system, but essentially have an adaptive immune system layered on top of it. Perhaps there is a difference in the growth of the organisms... save the individual vs save the colony or species.
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Thanks CliffordK.
You are probably right. It's just so surprising that evolution came up with such a complex system, with just a one task in mind - to protect as against pathogens. I am wondering - since the bacterial are evolving on much faster rate than human beings - does it mean they will always be ahead of our immune system?
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"One task in mind" is wrong! Those organisms that do not have an immune response, tend to get extinguished. But there has to be a balance because a virus thet killed all its hosts would itself become extinct.
It may be more profitable to consider complex animals as ecosystems within which a number of semiautonomous subspecies coexist. Some are pretty obvious - gut flora and fauna, for instance, can flourish in another host and may be recognisable as species. But suppose a phagocyte, for instance, evolved from a species that found life in a mammalian body so comfortable that it lost any ability to survive outside or do anything except eat bacteria. Next trick is to modify the mammalian DNA to allow the "ecosystem" to manufacture phagocytes - a friendly and persistent version of viral reproduction.
So there's a completely different approach to evolution - the triumph of collaboration and assimilation.
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http://www.britannica.com/EBchecked/topic/283636/immune-system/215595/Immune-capacity-among-invertebrates
Here is an article about the evolution of the immune system written at a basic, reader friendly level that describes where in the evolutionary tree certain features first appear, such as simple discrimination of self vs non self, phagocytic cells, lymphoid tissues, immunoglobulins, and the complement cascade.
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Your immune system is pretty extraordinary in fighting off diseases.
As far as always being one step behind... Perhaps that is a way of looking at what happens when a novel disease is presented to your immune system, and it adapts to fight the disease. Then you retain immunity either for an extended period of time, or perhaps even forever. But, that is only the diseases that you've heard about. There are many zoonotic diseases that do not infect humans, or are not pathogenic with humans. A few may infect humans, but can not be passed from human to human.
Likewise, some diseases such as Malaria are difficult to study in animals because they have no natural animal host, and the animal immune systems fight them off better than the human immune systems. Or, HIV/AIDS that is only marginally infectious to closely related primates.
The worst diseases are the ones that may be considered "flora" to one species, and pathogenic to another.
Consider E-Coli. There are actually a number of related E-Coli species. Some are normal (minor) gut flora in humans. There is a class called entero-toxogenic e-coli. Essentially a variety of toxin producing E-Coli that I think has become flora in a group of individuals, but visitors end up with "traveler's diarrhea" on exposure. Entero-hemolytic E-Coli seems to be far more pathogenic to humans than to cattle and other carriers of the disease.
In a sense, Ebola is also a dead-end disease in humans. Typically it ravages a small community, then dies out. It only endures in animals, some of which may have developed immunity to the disease, and reinfects humans from animal carriers. Likewise rabies would die out if humans were the only carriers.
There are many natural adaptations to disease in humans. For example, the sickle cell gene is thought to reduce the severity of malaria in heterozygous carriers, but unfortunately is very damaging in homozygous carriers. Likewise, the heterozygous cystic fibrosis gene may reduce the lethality of typhoid fever or cholera. Unfortunately it is lethal when homozygous.
Chicken Pox has a unique adaptation in that a large portion of the children infected with chickenpox become life-long non infectious carriers of the disease which occasionally remanifests itself in adults (from the original childhood infection) as shingles which once again are infectious.
There is a lot of concern about bird flu, but it may require a step where humans become infected and pass it back to the birds before it truly evolves to be problematic for humans.
Birds --> Humans ==> Birds....---> Birds... ----> Humans
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You can consider it one step behind, but there is also a kind of cost/ benefit balance between vigilance and tolerance, protecting against non-self invaders vs and damage from friendly fire when the immune system over reacts to foreign proteins or microorganisms that aren't really destructive.