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 HLA 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 daughter; (2) significantly increased sharing of maternal class I HLA antigens between the firstborn son and his brothers from higher birth orders, as compared to his sisters; and (3) HLA-A2 antigen, which is known to be involved in HLA restricted cytotoxic reactions in the recognition of minor histocompatibility antigens, was inherited in subsequent deliveries of sons as compared to daughters in a significantly higher frequency from the paternal than from maternal HLA haplotype. The results suggest that sharing of identical maternal HLA haplotypes between brothers may aid to decrease the degree of maternal sensitization to fetal antigens, and lack of HLA-2 antigen in maternal cells from sons as compared to daughters may avoid maternal HLA-A2 restricted cytotoxic reactions toward the male fetus.