Molecular identification of the antigens recognized by monoclonal antibody JT95 specific for thyroid carcinomas

JT95 is a monoclonal antibody (MAb) raised against the membrane fraction of differentiated thyroid carcinoma. JT95 specifically reacts to differentiated thyroid carcinoma, but not to benign thyroid tumor, normal tissue or other cancers. In this study, we purified the antigen by affinity-chromatography using MAb JT95 from spent culture medium of cell line SW1736, which was derived from a human thyroid carcinoma. The antigen was a glycoprotein having a molecular weight of 250,000 and its partial sequences obtained by peptide sequencing coincided with fibronectin. However, MAb JT95 reacted to the fibronectin purified from SW1736 but not to normal fibronectin, indicating modification of fibronectin was responsible for its antigenicity. Furthermore, immunochemical analysis of glycolipids extracted from SW1736 cells demonstrated that a second antigen was displayed on ganglioside. These results show that MAb JT95 recognized a novel antigenic epitope on a glycochain carried by both fibronectin and by a ganglioside produced by thyroid carcinoma cells.