Suppression of human T-cell colony formation during pregnancy

Abstract

THE human fetus, as a natural allograft, escapes destruction by the maternal immune system. As a possible mechanism, Alexander¹ proposed a rapid shedding of transplantation antigens by embryonic cells, resulting in a blindfolding of the otherwise fully functional maternal immune system. Other investigators have reported a suppressive activity of lymphoid cells from human cord blood on the proliferation of maternal lymphocytes^2,3. Suppressor T cells are induced by α-fetoprotein in mice⁴, and the elevated levels of α-fetoprotein during pregnancy have been shown to exert an immunosuppressive influence in mice^5,6 and in man⁷. Olding⁸ demonstrated a soluble factor from mitogen stimulated lymphoid cells of human newborns suppressing the proliferation of maternal lymphocytes. These observations point out that the embryo might protect itself by release of soluble factors, acting either themselves as lymphocyte suppressive agents, and/or by the induction of suppressor cells. However, no direct evidence has so far been presented to show the presence and action of T-cell suppressor cells in the immune system of pregnant women. Such an experiment would have to use components of the immune system of pregnant women solely, and therein demonstrate an immune suppression as compared to non-pregnant individuals. We present here results indicating that the ability of T cells from pregnant women to proliferate in soft agar cultures is strongly inhibited, regardless of the source of the serum being used in the assay, thus pointing rather to a cell-mediated suppressor mechanism.