Class I MHC expression in the yellow baboon

MHC class I molecules play a crucial role in the immune response to pathogens and vaccines and in self/non-self recognition, Therefore, characterization of MNC class I gene expression of Papio subspecies is a prerequisite for studies of immunology and transplantation in the baboon (Papio hamadryas). To elucidate MHC class I expression and variation within Papio subspecies and to further investigate the evolution of A and B loci in Old World primates, we have characterized the expressed class I repertoire of the yellow baboon (Papio hamadryas cynocephalus) by cDNA library screening. A total of nine distinct MHC class I cDNAs were isolated from a spleen cDNA library, The four A alleles and four B alleles obtained represent four distinct loci indicating that a duplication of the A and B loci has taken place in the lineage leading to these Old World primates. No HLA-C homologue/orthologue was found. In addition a single, nonclassical homologue of HLA-E was characterized. Examination of nucleotide and extrapolated protein sequences indicates that alleles at the two B loci are much more diversified than the alleles at the A loci. One of the A loci in particular appears to display very limited polymorphism in both Papio hamadryas cynocephalas and Papio hamadryas anubis subspecies. The failure to detect a homologue of HLA-C in the baboon provides additional evidence for the more recent origin of this locus in the Pongidae and Hominidae. Further comparative analysis with MHC sequences among the primate species reveals specific patterns of divergence and conservation within class I molecules of the yellow baboon.