Evolution of the immune system

L.A. Moran lamoran at gpu.utcs.utoronto.ca
Thu Dec 3 08:19:53 EST 1992

I can't resist commenting on the following conference notice.



      Host defense mechanisms have been evolving since the first 
      organisms encountered one another hundreds of millions of years 
      ago. All multi-cellular organisms face the survival necessity of 
      distinguishing between self and nonself in response to parasitism 
      or infection with microbial pathogens. Studies of ancient defense
      systems have extensive implications for understanding the evolution
      of immunity and problems of human health and disease."

Yes, it would be wonderful to study ancient defense systems but unfortunately
they only exist in organisms that are now extinct (by definition). Until time
travel becomes feasible (don't hold your breath) we will have to content
ourselves with the study of modern organisms that are the product of three
billion years of evolution. I know that studies of defense mechanisms in many
organisms could lead to a better understanding of all of them, what I object
to is the implication that human defense mechanisms are advanced and modern
while others are ancient and primitive. We would all do well to remember that
evolution is best represented by a branching bush and not by a ladder with
vertebrates on the top.

The defense mechanisms employed by bacteriophage and viruses are very 
sophisticated and have been studied intensely. However, it is unlikely that
they are evolutionarily related to the immune system in mammals. Similarly,
the mechansisms employed by plants, arthropods and other invertebrates have
evolved over a period of hundreds millions of years from the time of the last
common ancestor of these organisms and vertebrates. Given that there is such
variety within vertebrates and that the immune systems are so sloppy it
doesn't seem very likely that there is much of an evolutionary history to
detect. Very few of the molecules of the vertebrate immune system have an
evolutionary history that predates the origin of chordates, this suggests
that most of the vertebrate immune system is fairly new on the scene.

Laurence A. Moran (Larry)

P.S. Parts of this posting are deliberately provocative in order to generate

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