Immunoactive products of murine placenta. II.--Afferent suppression of maternal cell-mediated immunity by supernatants from short-term cultures of murine trophoblast-enriched cell suspensions.

Supernatants from short-term cultures of mid-term murine trophoblast cells were assayed for their in vitro regulatory potential. They markedly inhibited cell-mediated lympholysis and mixed lymphocyte reaction in a non-specific, non-restricted fashion. By contrast, the mitogenic response to optimal doses of ConA was unaffected, while the plaque-forming cell response to sheep red blood cells was either unmodified or slightly enhanced. These data suggest that placenta-derived cells secrete factors which selectively impair some cell-mediated immune responses. It is suggested that these factors play an important role in the lack of generation of cytolytic T lymphocytes towards paternal alloantigens expressed on the trophoblast during allopregnancy.