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.