MODE OF INHERITANCE OF HLA HAPLOTYPES LOCUS A,B IN SIBLINGS OF DIFFERENT SEXES

METHOD: Forty-eight parents and 172 children were typed for class I HL A antigens, locus A,B. RESULTS: Although the number of cases is small, we observed: (1) a significantly decreased number of sons born after a first delivery of a son, as compared to a first delivery of a daught er; (2) significantly increased sharing of maternal class I HLA antige ns between the firstborn son and his brothers from higher birth orders , as compared to his sisters; and (3) HLA-A2 antigen, which is known t o be involved in HLA restricted cytotoxic reactions in the recognition of minor histocompatibility antigens, was inherited in subsequent del iveries of sons as compared to daughters in a significantly higher fre quency from the paternal than from maternal HLA haplotype. The results suggest that sharing of identical maternal HLA haplotypes between bro thers may aid to decrease the degree of maternal sensitization to feta l antigens, and lack of HLA-2 antigen in maternal cells from sons as c ompared to daughters may avoid maternal HLA-A2 restricted cytotoxic re actions toward the male fetus.