HL-A, fertility and natural selection.

The antibodies occasionally produced in gravid females usually cause no adverse effects and the mother may become hyporesponsive. Exceptions may occur in some cases of abortion where frequency of antibodies appears to be unduly high. Sperm antigens in the mouse include T locus alleles as well as H-2 and H-Y. The T locus is involved in differentiation. T locus alleles are expressed on early but not late embryos. A search for similar factors in man is in progress. The antigenic differences between sperm and mother and between foetus and mother may be important in natural selection. It is possible that the union of sperm with ovum is non-random and that the ovum can select "compatible" sperm through recognition of cell surface markers present on sperm. Immunologic differences between mother and foetus may cause local "graft-versus-host" reactions in the placenta. This leads to increased placental size and may be a factor in hybrid vigour as well as a protective device.