STRUCTURAL HETEROGENEITY IN HLA-B70, A HIGH-FREQUENCY ANTIGEN OF BLACK POPULATIONS

Although the B70 antigen exhibits allele frequencies of 8-23% in Afric an and American black populations, it remains poorly defined. Cloning and sequencing of cDNA encoding B70 antigens from six cell lines has i dentified a group of three closely related alleles: B1503, B*1509 and B1510, that form a subgroup of the B15 family. The sequences of thes e alleles and, in particular, B1503, are close to that of the HLA-B c onsensus consistent with the difficulty in their serological definitio n. The products of the three alleles correspond to three electrophoret ically detected variants of the B70 antigen and some correlation with the B71 and B72 subspecificities of the B70 antigen can be made. A fou rth allele, B7901 previously described by Choo et al. (J. Immunol. 14 7: 174-180, 1991) that was not serologically typed as B70, differs by a single nucleotide substitution from B1510. The sensitivity of alloa ntibodies to single differences in peptide binding residues suggest a role for bound peptides in the HLA-B70 alloantigenic specificities. Th e heavy chains encoded by the four alleles differ at four peptide bind ing residues of the antigen recognition site, the evolutionary modific ation of which can be explained in terms of interallelic recombination events.