Topographical expression of class I major histocompatibility complex antigens on human amniotic epithelium

The expression of class I major histocompatibility complex (MHC) antigens on different regions of human amnion was studied by the avidin-biotin-complex immunoperoxidase (ABC) technique using monoclonal antibodies. In contrast to previous reports, the use of higher affinity monoclonal antibodies and the sensitive immunoperoxidase method has allowed the identification of class I MHC antigens on the amniotic epithelium. The level of expression is different between cells from various parts of the amnion, with the amniotic epithelium from the edge of the placenta consistently showing the strongest reactivity. Some of the class I MHC antigens expressed by the amnion are similar to those expressed by extravillous trophoblast cells in that both show much weaker or no reactivity with the monoclonal antibody 61D2.