[The immunosuppressive activity of human syncytiotrophoblast]

Enzyme treatment and mechanical tearing were used to separate syncytiotrophoblast from human placentae in this study. The normal fresh placentae were digested in a collagenase solution and then forced through a stainless steel mesh (mesh no. 60 = 0.301 mm). Smears of syncytiotrophoblast suspensions were stained with Wright's as well as PAS-hemotoxylin. It has given an isolation of 90-95% pure syncytiotrophoblast as obtained by our technique. The viability of the syncytiotrophoblast in the culture at onset and at harvesting was over 90%. The supernatants from short-term cultures of pure syncytiotrophoblast suppressed remarkably the maternal and fetal lymphocyte transformation to phytohemagglutinin and the one-way mixed lymphocyte culture. This effect is not antigen-specific, non-MHC restricted, and not due to non-specific toxic effects of dying cells. Our preliminary results, similar to that reported in the literatures indicate that the direct suppression by syncytiotrophoblasts and their products might play an important role in the protection of the fetus from rejection by the maternal immune system.