Immunology of the placenta.

The central issues of the immunology of the placenta are poorly defined. As an allograft its success almost certainly depends on the absence of transplantation antigens from syncytiotrophoblast. The placenta is an imperfect immune barrier between mother and fetus. Rhesus isoimmunization is one well-known consequence but maternal graft-versus-host disease is another, although much rarer. The placenta performs an important function by transferring maternal IgG to the fetus and filters out potentially harmful cytotoxic antibodies. However, autoantibodies may, in rare circumstances, cause passively acquired fetal autoimmune disease. Direct maternal immune attack on the placenta is not a clear pathological entity but may occur with placental villitis and pemphigoid gestationis; and may contribute to recurrent abortion of unknown aetiology or to pre-eclampsia.