Impairment of graft versus host reactivity in pregnant mice.

The popliteal lymph node (PLN) assay for graft versus host (GVH) reactivity has been used to analyse specific features associated with the immunological aspects of the materno-fetal relationship. GVH responses induced following the injection of maternal lymphocytes into F1 hybrid recipients is a particularly relevant model for testing the cellular reactivity of maternal lymphocytes against F1 hybrid determinants since every allogeneic pregnancy could initiate a naturally occurring mother versus F1 allograft reaction. Experiments monitored sequentially the effects of the pregnancy environment and multiparity on maternal cell-mediated immunity. The PLN assay performed within the confines of pregnant F1 hosts indicated that GVH reactivity was significantly suppressed during the mid and late stages of gestation with suppression being greatest in allogeneic combinations. In addition cells obtained from pregnant donors were less efficient than normal cells at GVH induction when transferred to virgin F1 recipients. The suppressive effect was maximal at mid-gestation; however, in this situation, the genotype of the paternal strain had no significant effect on the degree of immunosuppression observed. Multiparity in allogeneic combinations induced anti-paternal humoral immunity but an equivalent increase in GVH reactivity was not detected. These results support the concept of pregnancy-associated suppression of cell-mediated immunity. The nature of the suppressive effect is discussed.