Class I antigens of the major histocompatibility complex on cytotrophoblast of the human placental basal plate.

The lack of class I antigens of the major histocompatibility complex (MHC) on syncytiotrophoblast has been proposed as an explanation for the survival of the allogeneic fetus. These antigens, however, have recently been detected on nonvillous trophoblastic columns of the early human placenta. By using a combination of immunofluorescence techniques to identify trophoblast, we have studied transplantation antigens of the cytotrophoblastic shell present in the basal plate of normal full-term human placentae. With the use of two different monoclonal antibodies to a common determinant of HLA (clones W6/32 and 61D2), it was shown that this subset of trophoblast does express class 1 MHC antigens. However, while these cells reacted uniformly with W6/32, only rare reactivity with 61D2 was found. Reactivity of polyclonal antisera to beta 2-microglobulin correlated with that seen using W6/32. These results are similar to those recently observed in a subset of trophoblast of the amniochorion to which the term "metatrophoblast" has been given.