Immunosuppressive properties of murine trophoblast

The modification of the immunological response by murine trophoblast cells of different sources was investigated using the mixed lymphocyte reaction (MLR) and the cell mediated lympholysis (CML) test. MLR between C57BL (H-2b) stimulator splenocytes (mitomycin C treated in the unidirectional MLR) and BALB/c (H-2d) responder lymph node cells were markedly suppressed by trophoblast of ectoplacental cone (EPC) and placental origin. The same in vitro effect was observed with supernatants (SN) of trophoblast cells and with supernatants of blastocysts. Addition of anti-progesterone serum (APS), anti-testosterone serum (RAT), and anti-immunoglobulin serum (RAHIg) in serial dilutions to the trophoblast-MLR system revealed that the immunosuppressive effect of trophoblast giant cells and trophoblast giant cell culture supernatants can be abolished with APS. Identical results were obtained with APS added to immunosuppressive doses of progesterone. CML between C57BL responder lymph node cells and mitomycin C-treated BALB/c stimulator spleen cells was also markedly suppressed when trophoblast of EPC origin was added. A similar suppression of cytotoxic T-cell induction was seen when progesterone was added to the system. The immunosuppressive action of trophoblast as detected in vitro is likely to play an important role in the maintainance of pregnancy by protecting the semiallogeneic conceptus against immune aggression by the maternal immune system.