Active suppression of host-vs-graft reaction in pregnant mice. IV. Local suppressor cells in decidua and uterine blood.

The mammalian fetus bears a wide variety of antigens against which the maternal immune system can respond. Although some of these antigens are transplantation antigens, the type of immune response mounted by the mother seems incapable of mediating graft rejection. We have previously demonstrated suppressor cells in the lymph nodes draining the uterus (DLN) that regulate the immune response in allogeneically pregnant C3H/HeJ and CBA/J mice. The suppressor cells were shown to be small lymphocytes (sedimenting at 3 mm/h at unit gravity) resistant to anti-T cell serum + complement that elaborated a soluble suppressor activity and selectively inhibited the generation of cytotoxic T lymphocytes (CTL) reactive with paternal alloantigens. Suppression could be induced in the DLN by syngeneic pregnancy or pseudopregnancy, and behaved as an anatomically localized activity during pregnancy. We now report that during first allogeneic pregnancy, the most potent suppressor cell activity is found in lymphocytes in uterine venous blood and in decidual lymphocytes. This suppressor cell population also sediments at 3 mm/h and is associated with production of a soluble suppressor factor. Substantial suppressor cell activity can also be obtained from the deciduomata of pseudopregnant mice. Local suppressor cell activity within the uterus may play an important role in ensuring the immunological success of the fetal allograft.