Immunologic mechanisms in the maternal-fetal relationship.

Until recently, the immunologic tolerance between a mother and her allogeneic fetus has been a highly speculative and poorly understood phenomenon. New data indicate that maternal acceptance of the fetal allograft necessitates a specific, protective immune response. This specific recognition apparently involves unique placental antigens with genes that are closely linked to HLA loci. Lack of recognition of these antigens, as in matings between partners with similar HLA profiles, may result in repeated spontaneous abortions caused by unsuppressed rejection mechanisms.