Human amniochorion: tissue-specific markers, transferrin receptors and histocompatibility antigens

Human amniochorion was studied by immunofluorescence with the use of antisera to human trophoblast, amniotic epithelium and transferrin as well as with monoclonal antibodies to beta 2M and HLA. The results showed that cytotrophoblast of amniochorion, like its counterpart in placenta, manifests a trophoblast-specific membrane marker and lacks beta 2M and HLA. This tissue also did not react with antisera to amniotic epithelium, and unlike its placental counterpart no evidence for transferrin receptors could be obtained. Amniotic epithelium was found to lack trophoblast antigens, beta 2M, HLA and transferrin receptors, but contained a plasma membrane marker not found on any other extra-embryonic tissues. These results show that extra-embryonic cells with characteristic membrane markers fail to manifest histocompatibility antigens, almost as though they were mutually exclusive. This is supported by the observation that transformed amnion epithelial cells lose their unique surface antigens, react with monoclonal anti-beta 2M and acquire transferrin receptors, raising the possibility that the histocompatibility neutrality of extra-embryonic cells is maintained by the normal insertion of specific fetal markers into their plasma membranes.