Evidence for two B-cell alloantigen loci in theHLA-D Region

Antigenic determinants recognizable by human antisera (Hon 7 and 2075abs sera) were found in a partially purified antigen preparation obtained from an HLA-D and -DR homozygous cell line (EBV-Wa). Sequential coprecipition tests showed that two determinants detectable with Hon 7 and 2075abs sera (Hon 7 and 2075abs determinants) were present on different molecules. These two antigenic determinants were shown to be allotypic and were expressed predominantly in the B-cell-rich fraction. Family studies showed that both antigenic determinants segregated concordantly with respectiveHLA haplotypes. In the population study, the 2075abs and Hon 7 determinants were shown to be in strong linkage disequilibrium and the 2075abs determinant perfectly correlated with the HLA-DRw4 specificity. The results indicate that the Hon 7 determinant is coded for by a gene distinct from alleles at theHLA-DR locus. Furthermore, the locus (Hon 7) coding for the Hon 7 determinant is suggested to be very closely linked with theHLA-DR locus.