Evolution of the immune system

Thu Dec 10 09:10:58 EST 1992

Larry says (ref.1)
>There is very little evidence for functional organization of genes that are
>not evolutionarily related (in eukaryotes). For example, the genes for
>beta-2 microglobulin, t-cell receptors, and class I molecules are on different
>chromosomes. There is a chaperone that has been shown to be required for
>assembly of class I molecules and beta-2 microglobulin (p88), the gene for
>this protein does not seem to map to the same chromosome as the MHC locus.
>Furthermore the genes that encode enzymes of many metabolic pathways are
>unlinked. (Homeotic genes in Drosophila may be one exception that proves
>the rule.)
    It does not follow that because many genes which are functionally related
are not linked, that functional relationships never require close linkage.
One obvious example are meiotic drive loci, often within inversions, where the
drive gene and its target are closely linked. If two proteins must be finely
tuned to each other then linkage is likely to found. Let us anthropomorphize a
bit. Most of us go the the barber round the corner on a regular basis, but if
we travel elsewhere and have need of a barber we can usually find one who will
give us a passable haircut. However, this is not OK for some public figures,
who, I am told, have their own personal barber in their retinue wherever they
go. The barber and target are so finely tuned that only close linkage is
acceptable for proper function. What these proper functions might be in
biochemical terms is a matter for speculation. One example, as mentioned
previously,might be found in the debate in the August 1992 Bionet.immunology
files (ref.2).
>The TCP-1 gene (t-complex polypeptide-1) encodes a protein that might function
>as a chaperone. It is related to proteins in yeast and archaebacteria and
>forms complexes that are similar to those formed by chaperonins (groEL,
>hsp60). There is very weak similarity between the TCP-1 genes and chaperonins
>suggesting that they could be related by evolution. One role of TCP-1 is
>thought to be in the assembly of spindle but there are undoubtedly many
>other roles consistant with a chaperone function. There is no evidence that
>I am aware of for a role in immunology and even if there were such evidence
>it would not be the most important role of this protein (recall that it is
>found in yeast and archaebacteria, and also Drosophila).
   Yeast, archaebacteria, Drosophila and Man all need an intracellular system
of discrimination between self and not-self (ref. 2).
>I realize that immunology is an exiting and important discipline but it is
>wise to remember that organisms do a lot of other interesting and important
   Larry, you and I are here because our species has won so far in the war
which we call evolution. There is nothing more important than being good at
warfare if you want to survive in the sort of struggle which biological evol-
ution imposes. Than means weapons at the intracellular level, the cellular
level and at the organismic level. Above all it means distinguishing self from
          Sincerely,  Don Forsdyke
1. Moran, L. (1992) Bionet.immunology 1208, 1706gmt
2. Forsdyke, D. (1992) Bionet.immunology 817, 1757edt

P.S. Thank you Sean Davidson for your helpful contribution to this debate.

3. Davidson, S. (1992) Bionet.immunology 1209, 1308gmt

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