Antigenic analysis of immune complexes formed in normal human pregnancy

Immune complexes, isolated from pregnancy sera by absorption to immobilized protein A, were dissociated and the antigen components separated from the IgG antibodies, which possessed immune reactivity directed against the plasma membrane of the syncytiotrophoblast layer of the placenta. Gel filtration studies demonstrated that five separate antigens could be identified and were of placental origin, as observed by their reactivity in an ELISA with affinity purified anti-trophoblast antibodies isolated from maternal sera. The five antigens of apparent mol. wt 2 X 10(6), 400,000, 150,000, 13,000 and less than 10,000 daltons were designated maternally recognised trophoblast antigens (MRTA), numbers V-IX; the relative proportions of these antigens in the sera were 14%, 68%, 16%, 0.5% and 1%, respectively. Immune complexes were also identified in nulliparous non-pregnant female sera and consisted of the 150,000 and the less than 10,000 daltons antigen components. The relationship between the MRTA present in the immune complexes and the MRTA (numbers I-IV) previously identified as components of the trophoblast plasma membrane is discussed.