[Effect of major histocompatibility complex disparity on reproductive performance]

From the viewpoint of transplantation immunology, the fetus is a allograft which bears antigens incompatible with the mother. So immunological rejection reaction has been considered as one possible mechanism of abortion. To investigate this possibility, we applied some immunological procedures to rat and mouse. The results were as follows: 1) Prior active immunization with allogeneic placental cells or spleen cells emulsified with Freund's complete adjuvant increased the rate of abortion in the rat. But this effect was not manifested in the cases to which these cells were administered without the adjuvant. 2) Prior active immunization with major histocompatibility complexes had no deleterious effect on gestation in either the rat or the mouse. 3) Compared with inbred mating, decrease in the incidence of abortion, increase in fetal weight and increase in litter size were noticed in outbred mating in the rat. The latter two were statistically significant but the former was not significant. These results suggest that the major histocompatibility complex disparity between the fetus and mother does not have a deleterious but a beneficial effect on reproductive performance. Some possible immunological mechanisms of abortion are discussed.