Existence of suppressor cells in the spleen of allogeneic and syngeneic primiparous pregnant mice

Mixed lymphocyte reaction (MLR) and in vitro induction of cytolytic cells against alloantigens were investigated using spleen cells from primiparous mice mated allogeneically or syngeneically. One-way MLR was reduced significantly in degree not only in allogeneic but also in syngeneic pregnant mice. MLR of virgin spleen cells was suppressed when mitomycin C-treated spleen cells taken from syngeneic or allogeneic pregnant mice were added as regulator cells. These suppressive effects disappeared when regulator cells were treated with anti-Thy 1 or anti-Lyt 2 serum plus complement. Generation of cytotoxic lymphocytes from syngeneic or allogeneic pregnancy spleen cells in MLR was depressed compared with that from virgin spleen cells. The addition of pregnancy spleen cells to MLR suppressed in vitro generation of cytotoxic lymphocytes from virgin spleen cells. These results indicated that reduction of in vitro cellular responses of pregnancy spleen cells was due to suppressor cells in the spleens. These cells suppressed non-specifically the reactions to alloantigens and could be detected both in allogeneic and syngeneic primiparous pregnancies.