AU cell-surface antigen of human malignant melanoma: solubilization and partial characterization.

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Abstract
AU antigen was defined by reactions of sera from patient AU with cell-surface antigens of cultured autologous melanoma cells (SK-MEL-28). Past studies established that no available cell type other than AU melanoma expressed AU antigen. By using antibody inhibition tests for antigen detection, limited papain digestion of AU melanoma cells resulted in the solubilization of AU antigen along with .beta.2-microglobulin (.beta.2m) and HLA allogeneic and xenogeneic specificities. Comparable papain treatment of other melanoma and nonmelanoma cell lines solubilized .beta.2m and HLA, but did not result in the release of antigen with AU reactivity. Maximum yield of AU antigen from AU melanoma cells was obtained after very short (5-15 min) digestion times in contrast to the more prolonged proteolysis required for maximum HLA and .beta.2m release. AU antigen was not immunoprecipitated by rabbit antiserum against .beta.2m or HLA under conditions leading to partial or complete removal of .beta.2m and HLA. At least a proportion of the molecules with AU determinants appear to be glycoproteins, as indicated by specific affinity for Lens culinaris hemagglutinin (LcH). After affinity chromatography on LcH-agarose, the specific activity of AU antigen was increased 50-fold. As determined by gel filtration chromatography, AU antigen has a MW in the range of 20,000-50,000.

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