Effects of pregnancy on the maternal lymphoid system in mice.

The effects of pregnancy on the lymphocyte populations in the mouse have been studied. Though cell numbers decreased in the thymus and increased in the lymph nodes draining the parauterine area, no significant changes were seen in the proportions of thymus derived (theta allo-antigen positive) and bone marrow derived (Fc receptor positive) lymphocytes. The humoral response to sheep erythrocytes was suppressed during both syngeneic and allogeneic pregnancies following a decline coincidental with that of thymic mitotic activity. Though the observed immunosuppression could be explained by a selective lymphocyte depletion, it appears more likely to be a nonspecific effect of the steroid milieu of pregnancy.