PURIFICATION AND CHARACTERIZATION OF A HUMAN SIALOGLYCOPROTEIN ANTIGEN EXPRESSED IN IMMATURE THYMOCYTES AND FETAL TISSUES

The monoclonal antibody UN1 was previously produced in our laboratory on the basis of selective reactivity with human thymocytes and has bee n classified as unclustered by the 5th and 6th International Workshop and Conference on Human Leukocyte Differentiation Antigens. The antige n recognized by mAb UNI was found to be expressed on the cell surface of immature human thymocytes, a subpopulation of peripheral T lymphocy tes and on several fetal tissues including thymus. The UN1 antigen is purified from children's thymus by ion-exchange and affinity chromatog raphy. Two-dimensional electrophoresis shows that the purified antigen displays microheterogeneity appearing as multiple spots over a pi ran ge 4.4-5.0 at 100-120 kDa. Treatment with neuraminidase results in a r etarded migration in SDS-PAGE, an increase in isoelectric point and a reduction in carbohydrate content, indicating a substantial content of sialic acid. Glycosidase digestion and lectin-binding analysis indica te that the carbohydrate residues are essentially O-linked. A prelimin ary analysis has detected the UN1 antigen in human breast carcinoma ti ssues but not in normal breast. The biochemical features and the patte rn of expression of the UN1 antigen indicate that this molecule may ha ve the characteristics typical of the family of cell-membrane-associat ed mucin-like glycoproteins; a number of these molecules are thought t o have a role in cell-cell interaction, tumor progression and metastas is.