Reactivity of human trophoblast with an antibody to the HLA class II antigen, HLA-DP.

Cytotrophoblast cells in term amniochorion and in first trimester chorionic villi were shown by immunohistology of frozen tissue sections to bind B7/21, an antibody specific for the MHC Class II antigen, HLA-DP. This binding was shown to be specific, as adsorption of the B7/21 antibody with a B cell line expressing HLA-DP prevented subsequent binding to trophoblast. When tested with a variety of other antibodies reacting with HLA-DR, HLA-DQ or the common sequences of HLA-DR, -DQ and -DP, trophoblast was negative, thus confirming previous reports. The significance of this unique pattern of reactivity of trophoblast is discussed.