Histocompatibility Antigens on Mouse Blastocysts and Ectoplacental Cones

Blastocysts and ectoplacental cones were transferred under the kidney capsule of allogeneic control and preimmunized recipient mice. Whereas the blastocysts failed to develop in immunized recipients, the outgrowth of ectoplacental cones was not affected by the preimmunization. The immunity against allogeneic blastocysts could be adoptively transferred by sensitized lymphoid cells but not by immune serum, which indicates that the immune reaction is based upon a cell-mediated mechanism. In vitro experiments showed that the trophoblast cells grown from ectoplacental cones as well as placental trophoblastic giant cells were not affected by sensitized peritoneal or lymphoid cells which had a strong cytotoxic effect on allogeneic mouse embryo fibroblasts. It is suggested that these trophoblastic giant cells may act as an anatomical barrier against immune aggression during pregnancy.