Class I antigens of the major histocompatibility complex on cytotrophoblast of human chorion laeve.

Twenty amniochorions from normal, term pregnancies were studied immunohistologically with the use of well-characterized monoclonal antibodies to beta-2-microglobulin (beta 2M) and to common determinant of HLA-A, -B, -C. In the same study, polyclonal antiserum to trophoblast antigens (TA) were employed with double fluorochrome labels to determine if cytotrophoblast in the chorion laeve expressed TA, HLA or both. The results showed that, in the majority of cases, HLA was not identified on trophoblast, but TA were. However, some cytotrophoblast within the amniochorionic mantle were non-reactive with anti-TA serum and were positive with monoclonal antibodies to HLA and beta 2M antigens. Since these structures were identified as cytotrophoblast by a battery of techniques, in this report they are tentatively designated as metatrophoblast. The role of these cells in the materno-trophoblastic relationship in normal human pregnancy has yet to be determined. This is not envisaged as a simple matter, for metatrophoblast can be recognized by anti-beta 2M and anti-HLA (W6/32), but not by anti-HLA (61D2), suggesting that their expression of class I histocompatibility complex (MHC) antigens may be incomplete, or that there may be a contribution of antigens from an extra-embryonic MHC.