Depression of cellular immune response during syngeneic pregnancy as measured by the graft-versus-host reaction.

The cellular immune response during the course of intrastrain pregnancies was evaluated in primiparous and multiparous BALB/c females by the graft-versus-host (GVH) activity of the splenic and lymph nodal lymphocytes. Splenic lymphocytes of both primiparous and multiparous pregnant mice had a GVH activity lower than that of the virgin mice. This immune deficit was more evident in multiparous than in primiparous females and occurred at the 6th day and during the last week of pregnancy. A similar although less pronounced phenomenon was found when lymph nodes instead of spleen of multiparous females were used at the source of cells in GVH reaction. The immune deficit was less marked when spleen and lymph node cells of pregnant mice were compared with similar cells of pseudopregnant females. Incubation of virgin BALB/c spleen lymphocytes in the serum of multiparous pregnant mice as compared to normal virgin serum caused a reduction of the GVH activity; incubation of the cells in pseudopregnant serum also inhibited the immune response, but to a lesser extent than the incubation in multiparous sera.