Monoclonal antibody B72.3 reacts with a core region structure of O-linked carbohydrates.

Monoclonal antibody (moAb) B72.3 appears to be exceptional among the many mouse moAbs reactive with human tumor cells in its degree of tumor specificity. The antigen recognized was characterized as a mucin-like molecule. We report here that B72.3 reacts strongly with ovine submaxillary mucin and that reactivity is abolished by desialylation, suggesting that the determinant recognized is the disaccharide N-acetylneuraminic acid alpha (2----6)-N-acetylgalactosamine, linked to serine or threonine, which might be designated sialylated Tn. A variety of human mucin preparations, including human salivary mucins, and other glycoproteins containing O-linked or N-linked carbohydrates were nonreactive. The data suggest that the determinant recognized is a core structure which is normally not exposed due to chain elongation at C-3 of the N-acetylgalactosamine, which appears to be less frequent in carcinoma cells than in normal cells.