The in vitro immunoregulatory properties of cultured murine trophoblast are not unique to this tissue.

Primary cultures of murine trophoblast (ectoplacental cone and mid-term placenta) and their supernatants were found to inhibit in vitro lymphocyte proliferative responses to concanavalin A (77-87%) and allo-antigen (52-84%). However, cultures and cell-conditioned media from non-trophoblastic tissues (embryonic sac, adult lung and liver, and B16 melanoma line) produced similar results. In all cases, the inhibitory effects were not due to reduced cell viability. Addition of anti-progesterone serum to the ectoplacental cone-lymphocyte co-cultures, at a concentration known to bind the available trophoblast-derived progesterone, did not overcome the observed suppression. The results clearly demonstrate that a range of cultured cell types, and their conditioned media, will suppress immune responses in vitro. We conclude that cultured trophoblast is not an appropriate model for studies of placental immunoregulation.