A rat cytotrophoblast antigen defined by a monoclonal antibody

A monoclonal antibody that recognizes specifically a cytotrophoblast antigen was obtained. The monoclonal antibody 22H6 was tested on rat choriocarcinoma (in vivo, in vitro), normal placenta, ectoplacental cone, blastocysts, and several normal organs. The antigen was detected on frozen sections and on tissue culture by indirect immunofluorescence. The monoclonal antibody 22H6 reacts with the cytotrophoblasts of rat choriocarcinoma. The giant cells do not display a positive reaction. It is not expressed on other tumors than choriocarcinoma. In adult rats the only cells revealing a positive reaction are the hepatocytes and the epithelial cells lining the small intestine. In the pregnant rat, the antigen is expressed on the cytotrophoblasts of the junctional zone in the placenta, but not on the giant cells. The mab reacts only with the small trophoblast cells of the ectoplacental cone, but not with trophectoderm of blastocyst. The mab has an IgG2b isotype and is not cytotoxic for choriocarcinoma cells in a complement-dependent cytotoxicity test. The described monoclonal antibody is to our knowledge the only known marker of rat benign and malignant cytotrophoblast.