Identification and solubilization of iodinated cell surface human melanoma associated antigens.

To identify soluble cell surface melanoma-associated antigens (MAA), human melanoma cells in culture were radioiodinated by the lactoperoxidase technique and solubilized in non-ionic detergent (NP-40). Labelled MAA were identified by a quantitative double-antibody antigen binding assay and unrelated labelled macromolecules by trichloroacetic acid precipitation. Detergent solubilized 95% of the macromolecule-associated radioactivity. Approximately 8%, presumably MAA, was bound specifically by anti-melanoma serum. In contrast, anti-melanoma serum bound specifically only 0.5 to 1.5% of the acid precipitable radioactivity in control cells iodinated in a similar manner. Specificity was further studied by quantitative serum absorption. Two different melanoma lines were equally effective in inhibiting specific binding of iodinated melanoma lysate, whereas 50-100 times more normal fresh lymphocytes, liver and spleen cells, cultured HeLa or colon adenocarcinoma cells, and 8 times more cultured fetal cells were required to produce similar reductions in specific binding. These studies demonstrate that cell surface human melanoma antigens that differ qualitatively and/or quantitatively from those on normal or malignant allogeneic tissues can be solubilized and identified. These antigens are shared with other melanomas, and some are also present on fetal cells.