HLA-DR Antigen on Human Trophoblast*

ABSTRACT: To assess the presence of human leukocyte antigens (HLA) on first trimester human trophoblast cells, frozen sections of villous trophoblast and monolayer cultures of isolated cells from placental villi were prepared and exposed to a mouse monoclonal antibody directed against HLA-DR and then incubated with fluorescein-conjugated goat anti-mouse antibodies. Fluorescence microscopy demonstrated that HLA-DR antigens were present on only the small polygonal epithelioid cells of the monolayer culture. The crescentic staining pattern was consistent with widespread distribution of antigen on the cell membrane. There was no staining over giant multinucleated structures or on fibroblasts of such cell cultures. No HLA-DR was detected when this indirect immunofluorescent technique was applied to tissue sections of villous trophoblast. Existence of high concentrations of hCG in culture supernatants and coincident localization of both hCG and HLA-DR using antibodies conjugated with rhodamine or fluorescein on the polygonal epithelioid cells indicate the trophoblastic origin and expression of HLA-DR antigen under in vitro monolayer culture conditions.