Role of Immunity in Control of Fertility

Abstract

It has been known for a long time that in outbred animals there was a specific immunological problem in breeding, due to the evolution of mixed histocompatibility antigens (MHC antigens). These antigens are very important in the defence against viruses and tumours (Opelz, Mickey and Terasaki, 1974). They are present on the surface of nucleated cells, and vary from individual to individual. Individuals may, therefore, recognise these antigens as foreign, and mount immunological attack on cells carrying them. This is the basis of the rejection of transplanted organs in animals and man. It is clear that a similar mechanism should operate in pregnancy in mammals, leading to maternal recognition of the MHC antigens of the fetoplacental unit which were derived from the father. The mother would then be expected to reject the ‘foreign tissue’ which was in direct contact with her own tissues. Indeed the trophoblastic villi in primates dip directly into the maternal blood, so that syncytiotrophoblast cells are direclty accessible to maternal cells and antibodies which might affect them (Boyd and Hamilton, 1970, Redman et al., 1984). Thus, it was for some decades an enigma: why did the mother not reject her offspring if she was antigenically different from the father? Several possible mechanisms were suggested, and most have been shown to be inoperative.