Evaluation of human chorionic trophoblast cells and placental macrophages as stimulators of maternal lymphocyte proliferation in vitro.

Dispersed cell suspensions of human chorion membrane and placentae were obtained by enzyme digestion and the cells examined for HLA expression and for the ability to stimulate immune cell proliferation in vitro. Chorion cells with the characteristics of trophoblast were HLA-A, B, C and Ia negative following tissue digestion whereas placental cells, primarily Fc gamma R positive macrophages, were HLA-A, B, C positive and were frequently Ia positive. When chorion and placental cell suspensions were used as stimulator cells in one-way mixed cell cultures (MCC) with maternal mononuclear leukocytes (MNL) as responder cells, chorion cells were not normally stimulatory (mean stimulation index (SI), 2.7) whereas placental cells usually were (mean SI, 11.5). No evidence for active suppression by chorion cells was obtained in a group of experiments designed to detect suppressive activity. The results support the concept of the trophoblast layer as an immunologically inert barrier between the mother and the fetus.