title: HLA-A and B polymorphisms predate the divergence of humans and chimpanzees.
abstract: Major histocompatibility complex (MHC) glycoproteins bind processed fragments of proteins and present them to the receptors of T lymphocytes. The extraordinary polymorphism of class I MHC molecules in man (HLA-A, B and C) and mouse (H-2 K, D and L) poses many questions concerning their diversification and evolution. Comparison of allelic sequences within a species suggests diversity is generated by the assortment of point mutations into varied combinations by mechanisms of recombination and gene conversion. We have now compared class I MHC alleles in two closely related species: humans (Homo sapiens) and chimpanzees (Pan troglodytes). Chimpanzee homologues of HLA-A, HLA-B and a non-classical gene have been identified. No features distinguishing human and chimpanzee alleles could be found. Individual HLA-A or B alleles are more closely related to individual chimpanzee alleles than to other HLA-A or B alleles. These results show that a considerable proportion of contemporary HLA-A and B polymorphism existed before divergence of the chimpanzee and human lines. The stability of the polymorphism indicates that hyper-mutational mechanisms are not necessary to account for HLA-A, B and C diversity.
authors.affiliation: Department of Cell Biology, Stanford University Medical School, California 94305.
authors.forename: D A
authors.initials: DA
authors.lastname: Lawlor
authors.forename: F E
authors.initials: FE
authors.lastname: Ward
authors.forename: P D
authors.initials: PD
authors.lastname: Ennis
authors.forename: A P
authors.initials: AP
authors.lastname: Jackson
authors.forename: P
authors.initials: P
authors.lastname: Parham
mesh_terms: D000483:Alleles; D000818:Animals; D001483:Base Sequence; D002417:Cattle; D005805:Genes, MHC Class I; D006801:Humans; D051379:Mice; D002679:Pan troglodytes / Q000235:genetics*; D011110:Polymorphism, Genetic; D011817:Rabbits; D012689:Sequence Homology, Nucleic Acid; D013552:Swine