Does exposure to HLA alloantigens trigger immunoregulatory mechanisms operative in both pregnancy and AIDS?

The complex biological processes responsible for regulating the immune system are presently the subject of considerable interest and study. New insight into this process comes from a variety of observations and it is the purpose of this communication to develop the hypothesis that two seemingly quite disparate observations point to a common biological mechanism bearing on immunoregulation. The observations concern the unique immunologic relationship between mother and fetus and the immunoregulatory abnormalities encountered in HIV-induced acquired immunodeficiency syndrome (AIDS). Exposure to foreign (allo) major histocompatibility complex (MHC) antigens can potentially occur during pregnancy, the transfusion of blood or blood products, or anal insemination. The hypothesis, in its simplest form, states that such MHC alloantigenic exposure triggers a sequence of immunoregulatory mechanisms resulting in immunosuppression and that this response has evolved in placental mammals as a means of protecting the fetus from maternal immune rejection and promoting optimal fetal development.