Macrophages in murine uterus are immunosuppressive.

The mechanisms by which the fetal allograft is protected from a maternal anti-fetal immune response are not understood. This study was designed to examine the possibility that tissues near the developing fetus contain immunoregulatory cells and to begin the process of identification of those cells. Dispersed uterine cell suspensions from pregnant Swiss/Webster mice consistently inhibited the responses of normal murine spleen cells to the polyclonal mitogen phytohemagglutinin (PHA). These suspensions contained few lymphocytes (mean 1%), but abundant macrophages (mean 28%), identified by morphology and Fc gamma-receptor expression. Depletion of Fc gamma-receptor-positive cells restored spleen cell (SC) responses to PHA to near normal levels and partial depletion of adherent cells provided varying degrees of relief of the observed suppression. Adherent cells (greater than 95% macrophages) recovered from plastic surfaces were highly immunosuppressive. Suppressor cells appeared to interfere with both early and late stages of spleen cell proliferative responses. The results suggest that cells with some characteristics of macrophages within tissues near the maternal-fetal interface may create a local environment prohibitive to maternal lymphocyte proliferation.