Immunocytology of body cavity fluids: MOC-31, a monoclonal antibody discriminating between mesothelial and epithelial cells

This study was designed to assess whether monoclonal antibody MOC-31, which recognizes a membrane glycoprotein of 40-kd molecular weight present on epithelial cells and not on mesothelial cells, is a useful adjunct in the differential diagnosis of reactive pleural or ascitic fluids and adenocarcinoma. A panel of antibodies against carcinoembryonic antigen, epithelial membrane antigen, vimentin (antivimentin), keratin 18 (RGE-53), and cytokeratins of several molecular weights (AE1/AE3) was employed for comparison. Ninety-eight cases were selected based on the availability of pleural and peritoneal biopsy specimens for histologic confirmation. All cases with adenocarcinoma stained MOC-31 positive, including three cases that had not been identified by morphologic criteria. All cases of reactive mesothelial hyperplasia were negative, as well as five cases of malignant mesothelioma. One case of squamous cell carcinoma was also negative. Anti-carcinoembryonic antigen only identified half of the carcinoma cases, and anti-epithelial membrane antigen and both anticytokeratin antibodies were positive in the majority of tumor cells as well as in the mesothelial cells. This study indicates that monoclonal antibody MOC-31 is a highly sensitive and reliable reagent in the differential diagnosis between mesothelial and epithelial cells.