Identification of selectively solubilised syncytiotrophoblast plasma membrane proteins as potential antigenic targets during normal human pregnancy.

Syncytiotrophoblast plasma membranes prepared from term placentae were selectively solubilised in non-ionic detergents. The solubilised proteins and the insoluble residue were tested in an ELISA assay for their ability to function as antigenic targets for anti-trophoblast antibodies present in normal first trimester pregnancy sera. The soluble proteins were fractionated by gel filtration and four major antigen forms were identified. The antigens were reactive with affinity purified anti-trophoblast antibody isolated from maternal sera and hence were termed maternally-recognised trophoblast antigens (MRTA); these were designated MRTA-I (Mr = 400,000 D), MRTA-II (Mr = 142,000), MRTA-III (Mr = 50,000) and MRTA-IV (Mr = 13,000). The relationship between MRTA-I, II, III and IV and antigens identified in maternal sera in the form of immune complexes is discussed.