CHIMPANZEE MHC CLASS-I A-LOCUS ALLELES ARE RELATED TO ONLY ONE OF THE6 FAMILIES OF HUMAN A-LOCUS ALLELES

There are nearly 50 alleles at the highly polymorphic HLA-A class I lo cus that fall into six distinct families. To determine the allelic rep ertoire and the mechanism of generation of diversity of the A locus in primates we have analyzed A locus alleles from 28 apparently unrelate d chimpanzees (Pan troglodytes) and bonobos (Pan paniscus). We have, t herefore, compared the sequences of 19 HLA-A homologues from chimpanze es and bonobos to 42 HLA-A sequences. HLA-A homologues were well prese rved in chimpanzees and bonobos with very few new substitutions presen t in the A locus alleles of both species of chimpanzee. Surprisingly, all chimpanzees and bonobos expressed A locus alleles related to only one of the six families of human HLA-A alleles. This suggests that the common ancestor of these two species either passed through a genetic bottleneck or that selection has favored the maintenance of the HLA-A1 , -A3, -A11 family in chimpanzees.