The HLA-B12 and -B40 cross-reactive groups and their serological relationships.

The serological analysis of 82 broad HLA-B antisera, produced by pregnancy alone, containing reactivity against HLA-B12 and/or B40 positive cells and up to nine additional specificities was performed, using highly selected lymphocyte panels. The HLA typing of 76 of the antiserum donors and 75 of their husbands showed that the antisera were stimulated in response to one of 10 different HLA-B antigens. It also showed the influence of serum donor HLA-B antigens on the reaction range of the antiserum produced, as well as significant HLA-B antigen frequency disturbances within various groups of the antiserum donors. Fifteen HLA-B specificities were found to comprise the B12 cross-reactive group and its related cross-reactions, with bidirectional cross-reactivity occurring between Bw44, Bw45, Bw49 and Bw50 (unidirectional between Bw44 and Bw50). Seventeen specificities were observed in the B40 cross-reactive group and its related cross-reactions, with bidirectional cross-reactivity occurring between Bw41, Bw50, Bw60 and Bw61. Antisera were studied that showed; (1) cross-reactivity between Bw44, Bw45 and Bw60 stimulated antisera and both subdivisions of the B12 and B40 antigens; (2) cross-reactivity between B13, Bw44, Bw49, Bw60 and Bw61 stimulated antisera and Bw47; and (3) cross-reactivity between Bw44, Bw49, Bw60 and Bw61 stimulated antisera and B13, with bidirectional cross-reactivity occurring between B13, Bw60 and Bw61 and between B13 and Bw44. Bidirectional cross-reactivity was also observed between B37 and Bw44 and between B7 and Bw60. HLA-Bw48 was shown to be included within the reaction range of both B7 and Bw60 stimulated antisera. Preferential cross-reactivity with one of two antigen subdivisions was extensively observed and occurred exclusively between antigens of the same Bw4/Bw6 association as the antiserum stimulating specificity. The results are discussed within the framework of the existence of multiple shared antigenic determinants.