Maternal immune response to pregnancy

The pregnant female is exposed to a variety of potentially immunogenic foreign antigens on her allogenic intra-uterine conceptus. The extent to which maternal antibodies and cell-mediated immune responses to these antigens are relevant to the paradoxical survival of the fetal allograft is not clearly established. The key to the maintenance of pregnancy lies in the trophoblast. This tissue prevents significant entry of maternal lymphocytes to the fetus and is most likely to protected from maternal immune rejection by features of its cell surface molecular structure and/or its synthesis of factors that render it insusceptible to antibody- or cell-mediated immune lysis in vivo. An alternative, or complementary, protective system, involving maternal recognition and immunoregulatory processes that deviate responses away from the expected rejection reactions, may also operate but has not yet been convincingly demonstrated. Such a mechanism is unlikely to involve the classically defined histocompatibility classically defined histocompatibility antigen system, at least in human pregnancy, where there is an absence of Class I antigens from the trophoblast but increasing evidence of trophoblast-associated antigens and related immune responses. It remains to be established whether unexplained recurrent miscarriage in women and spontaneous abortion in animal models is caused by failure of maternal immunoregulatory control or by non-immunological factors. This is relevant to the validity of immunotherapeutic approaches to the prevention of early fetal loss.