Altered immune responses in pregnant mice.

The immune responses of pregnant mice to alloantigens were studied using the 51chromiun release assay. Four populations of lymphoid effector cells were studied. Control lymphoid cells were from normal, virgin BALB/c females, and BALB/c females specifically immunized to (BALB/c X C3H) F1 spleen cells. Experimental lymphoid cells were from BALB/c females pregnant by BALB/c males (syngeneically pregnant) or C3H males (allogeneically pregnant). Target cells were 51chromiumlabeled phytohemagglutinin-induced lymphoblasts from BALB/c and (BALB/c X C3H) F1 animals. Pooled lymph node and spleen cells from BALB/c females pregnant by C3H males were not cytotoxic for (BALB/c X C3H) F1 target cells. Lymphoid cells were transferred to sublethally irradiated syngeneic recipients that were simultaneously challenged with (BALB/c X C3H) F1 alloantigens. One week later, the spleen cells of the recipient animals were used as effector lymphoid cells. Lymphoid cells from normal, syngeneically pregnant, and allogeneically pregnant animals were equally cytotoxic for (BALB/c X C3H) F, target cells. Lymphoid cells from BALB/c animals specifically immunized to (BALB/c X C3H) F, alloantigens were highly cytotoxic for these target cells. Compared with the unmixed cell populations, mixtures of lymphoid cells from norman and syngeneically or allogeneically pregnant animals were hyporesponsive to alloantigenic challenge. Serum from neither syngeneically pregnant nor allogeneically pregnant animals inhibited the response of normal lymphoid cells to alloantigen. Immunoregulation in pregnancy was discussed.