Some immunoregulatory aspects of pregnancy in rats

The success of the majority of pregnancies, despite the allograft character of the fetus, is principally due to trophoblastic mechanisms, but some ancillary immunoregulatory processes in the mother are probably also involved. In order to analyze this, adult female rats, both virgin and parous by syngeneic and allogeneic males, were grafted with skin from histoincompatible donors, and the median survival time registered and hemagglutinin assays performed. Multiple allogeneic pregnancies prolonged graft survival and impaired hemagglutinin responses. Another group of experiments, where female virgin rats were mated with allogeneic males after removal of paraaortic lymphnodes and the spleen, and then challenged by skin grafts, pointed to a role played by the lymphnodes in suppressing hemagglutinin formation. Trophoblast cones from allogeneic conceptuses were implanted beneath the renal capsule of another group of animals, and this led to a slight prolongation of the survival of subsequently grafted skin and to a moderate depression of hemagglutinin responses. Further, viable cells and serum from animals that had gone through one or more allogeneic pregnancies were transferred to normal syngeneic hosts; after skin grafting, the hemagglutinin response and graft rejection were suppressed most when spleen cells were used. The results of these experiments are discussed.