Discrimination between benign and malignant cells of melanocytic lineage by two novel antigens, a glycoprotein with a molecular weight of 113,000 and a protein with a molecular weight of 76,000

The present study describes two novel antigens, a glycoprotein with a molecular weight of 113,000 and a protein with a molecular weight of 76,000, which are associated with the transformed phenotype of melanocytes. The monoclonal antibodies (MoAb) MUC18 and MUC54, raised against human malignant melanoma, were selected for differential reactivity with normal and neoplastic cells of melanocyte lineage. The antigen defined by MoAb MUC18 is a membrane bound monomeric sialylated glycoprotein with an apparent molecular weight of 113,000. In contrast to the broad reactivity with melanomas, isolated nevus nests were stained in only 1 of 55 nevi investigated. No staining of MoAb MUC18 was observed in a large variety of surgically removed normal and tumor tissues except for smooth muscle cells of the blood vessel wall and hair follicles. MoAb MUC54 immunoprecipitated a cytoplasmic monomeric protein with an apparent molecular weight of 76,000. By immunoperoxidase staining, the antigen was demonstrated on a large number of melanomas and in addition on 1 of 36 nevocellular, 3 of 4 Spitz, and 5 of 14 dysplastic nevi. The Mr 76,000 protein was found in a number of epithelial tissues and various types of neoplasms. Both antibodies presented in this study define structural changes in the antigenic profile of melanocytes occurring during carcinogenesis.