Tn antigen is expressed on leukosialin from T-lymphoid cells

Various T-lymphoid cells were labeled with [3H] glucosamine and then cell lysates were prepared from them. The Tn antigen was immunoprecipitated and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by fluorography. The Tn antigen was found to be expressed on leukosialin, a major glycoprotein of T-lymphoid cells. The carbohydrate moieties of leukosialin were isolated from Jurkat and Molt 4 cells by alkaline borohydride treatment. The leukosialin in both cases predominantly contained single N-acetylgalactosamine residues, consistent with expression of the Tn antigen. Tryptic glycopeptides containing antigenic sites were isolated using an MLS 128 immunoaffinity column and purified by gel filtration and reverse phase column chromatographies. Sequence analyses revealed that all the glycopeptides obtained contained three consecutive residues of N-acetylgalactosamine-Ser/Thr, supporting the idea that the epitopic structure is a cluster of N-acetylgalactosamine-Ser/Thr.