Anti-trophoblast antibody responses during normal human pregnancy.

During the course of a normal uncomplicated human pregnancy the mother generates an antibody response directed against determinants present on the plasma membrane of the outer fetal layer of the term placenta, the syncytiotrophoblast. The response, measured by an ELISA that utilises syncytiotrophoblast plasma membrane as the antigenic target, is predominantly IgG in nature, but with a minor contribution from IgM molecules. Maximum responses were observed during the first trimester and the levels gradually declined as the pregnancy progressed. On a population basis, this antibody response profile was mainly restricted to first and second pregnancies, although anti-trophoblast antibody responses could be detected in multiparous women but with a greatly reduced incidence compared with primipara. Mechanisms to account for these observations are discussed. Throughout, the anti-trophoblast antibody levels detected in pregnancy sera were compared with the background levels which were observed in sera obtained from males and nulliparous non-pregnant females.