Abrogation of Cellular Immunity to Antigenically Foreign Mouse Embryonic Cells by a Serum Factor

Abstract

MANY hypotheses have been introduced to explain why the conceptus of an allogeneic mating, which differs genetically and therefore antigenically from its mother, is not rejected by the mother as an allograft^1,2. Two of them deserve particular consideration. First, there may be an anatomical barrier which would separate foetal antigens from maternal immunologically competent cells and also protect the embryo against destruction by sensitized lymphocytes and IgM molecules; preimmunization against paternal antigens does not seem to harm the foetus or alter the normal course of an allogeneic pregnancy^3–5. An interesting possibility is that the presence of a highly sulphated acid mucoprotein on the surface of the trophoblastic cells may serve this function^2,6–8. Second, the mother may be incapable of damaging her foetuses immunologically, either because she is tolerant or because immunological enhancement is operating⁹. Recent claims that the placental membrane is permeable to lymphocytes^10–12 and that the mucoprotein layer is not continuous over the surface of the trophoblast¹³ have raised some doubts about the validity of the first hypothesis, which does not seem to provide the sole explanation why antigenically foreign foetuses are not destroyed.