History of foreign embryonic isoantigens.

After defining the term 'foreign embryonic isoantigens', the author describes the experimental sequence which has allowed this new fetoprotein class to be identified. Experiments have followed three different directions, namely (i) passive immunization, by which conceptus antibodies raised in another animal species are transferred to the female animal, the effects on the offspring becoming apparent after pregnancy; (ii) laboratory techniques, where the presence of conceptus antibodies in serum from aborting women has been demonstrated by use of analytical techniques or by testing the serum on cultured embryos; and (iii) active isoimmunization, by which the female animal is immunized against a conceptus extract from the same species, and the effects on the offspring are observed after pregnancy. The immunologic basis for autoantigenicity in these fetoproteins, and its significance to materno-fetal medicine, are explained. Finally, some fetoproteins not yet unambiguously classed as foreign embryonic isoantigens are presented.