Specificity of reagents directed to the Thomsen-Friedenreich antigen and their capacity to bind to the surface of human carcinoma cell lines.

The Thomsen-Friedenreich antigen (T-antigen) is a cryptic disaccharide structure on human erythrocytes and is supposed to be expressed in an unhidden form on carcinoma cells. We tested the ability of four anti-T reagents (i.e., peanut agglutinin, human and rabbit anti-T antisera, and monoclonal anti-T antibodies) to agglutinate neuraminidase treated human erythrocytes and compared their capacity to bind to the surface of human carcinoma cell lines or neuraminidase treated lymphocytes. We found that all of the reagents strongly agglutinated neuraminidase treated erythrocytes. In contrast, only peanut agglutinin and the monoclonal antibody bound to the surface of carcinoma cell lines and to neuraminidase treated lymphocytes. Peanut agglutinin was inhibited by D-galactose and is known to be specific for the T-disaccharide. The determinants on erythrocytes, lymphocytes, and carcinoma cells, recognized by peanut agglutinin, are resistant to trypsin treatment. The monoclonal antibody was specifically inhibited by phenyl-beta-D-galactoside. The binding sites on erythrocytes and lymphocytes for the monoclonal antibody can be removed by treatment with trypsin or Pronase. On the other hand, the binding sites on carcinoma cells are resistant to trypsin but can be removed with Pronase. In contrast to the peanut agglutinin binding sites on carcinoma cells the structures recognized by the monoclonal antibody cannot be further increased by neuraminidase treatment. Human and rabbit anti-T antisera did not bind to tumor cell surface or to neuraminidase treated lymphocytes. Hemagglutination of human anti-T could be inhibited by asialofetuin; the specificity of rabbit anti-T could not be established in this study. Hemagglutination with both antisera is resistant to trypsin but partially sensitive to Pronase treatment. These results indicate that each of the reagents has a distinct specificity and recognizes different antigenic determinants on different molecules. Only peanut agglutinin and monoclonal anti-T antibodies are able to detect common structures on the surface of neuraminidase treated erythrocytes and carcinoma cell lines.