Antigen expression by trophoblast populations in the human placenta and their possible immunobiological relevance.

Antigen expression by villous and extravillous human trophoblast populations at discrete anatomical sites has been reviewed. The various different antigenic phenotypes have been highlighted using a panel of monoclonal antibodies reactive with characteristic trophoblast membrane antigens, a trophoblast-leucocyte common antigen, class I MHC antigens, epithelial cell cytokeratin and epithelial membrane markers. This approach has allowed three separate fetal trophoblast populations to be identified within term amniochorionic membranes, and also has facilitated further definition of trophoblast populations in maternal uterine tissues. Furthermore, antigenic alterations have been noted in the maternal uterine gland epithelium in pregnancy leading to the expression of a trophoblastic phenotype, thereby suggesting a mechanism of extrinsic regulation of gene expression in these tissues. The possible involvement in the immunoregulatory control of maternal responses in pregnancy of MHC-linked gene products expressed by trophoblast has been discussed.