Glycoprotein P3.58, associated with tumor progression in malignant melanoma, is a novel leukocyte activation antigen.

The P3.58 antigen is defined by monoclonal antibodies (MAbs) selected to discriminate between benign and malignant melanocytic cells. Its expression in malignant cells has been shown to correlate with an increased risk of metastasis. A survey of a wide range of tissues revealed that, on normal tissue, expression of P3.58 antigen is restricted to a subset of cells involved in the immune response. The antigen was found not only on certain endothelia, but also on activated macrophages in vivo and in vitro and as well as on activated B lymphocytes. A comparison with known B-lymphocyte and leukocyte activation antigens indicated that P3.58 is a novel leukocyte activation antigen. Biochemical analysis of the P3.58 antigen isolated from cells of different histogenic origin indicated that different molecular forms of the antigen exist, apparently depending on the cell type of origin. P3.58 molecules precipitated from tunicamycin-treated cells were identical in all cell types, suggesting that the variation observed is due to variable N-glycosylation.