Effect of maternal-fetal histoincompatibility on the weight of the feto-placental unit in mice: the role of minor histocompatibility antigens.

Female mice from four congenic strains were bred to males of the same four strains to determine the effect of maternal-fetal disparity at major histocompatibility complex (MHC) and the effect of non-MHC minor histocompatibility antigens on the weight of the feto-placental unit. An increase in feto-placental weights was found in all three of the four strains that could be evaluated when mother and fetus differed at multiple minor histocompatibility loci, irrespective of whether disparity at the MHC was present. No increase in feto-placental weights was found when mother and fetus differed at the MHC alone. The fact that these results were found in all strains studied suggests that the effect of maternal-fetal disparity at multiple minor histocompatibility antigens (minor HA) on the weight of the feto-placental unit is biologically significant. We conclude that if the increase in weight of the feto-placental unit results from immunostimulation, then minor histocompatibility antigens are the primary target of the maternal immune response to the histocompatibility antigens of the fetus.