Possible sex-correlated transmission of maternal class I HLA haplotypes.

Forty-seven alleles of class I HLA-AB loci (14 for locus A and 33 for locus B) were identified in 787 participants in two groups of unrelated families. Group I included parents and children typed for bone marrow transplantation. Group II included families typed for renal transplantation. Before statistical evaluation, the A locus alleles were grouped into eight classes according to broad specificity, and the B locus alleles were grouped according to HLA epitopes into two classes. Significant differences in HLA-AB haplotype frequencies were found between male and female offspring. When families with children of both sexes were analysed, the frequencies of maternally inherited HLA-AB haplotypes were found to be significantly different in brothers and sisters. The results suggest the possibility that the transmission of specific AB haplotypes from mother to offspring may be correlated to children's sex. The major histocompatibility complex has been shown to be involved in the expression of H-Y male-specific minor histocompatibility antigens. The possible selection in the transmission of specific maternal HLA-AB haplotypes to male offspring may contribute to the avoidance of maternal cytotoxic reactions toward the male foetus.