Abstract
To identify soluble cell surface melanoma‐associated antigens (MAA), human melanoma cells in culture were radioiodinated by the lactoper‐oxidase 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.