PNL2, a New Monoclonal Antibody Directed against a Fixative-Resistant Melanocyte Antigen

We report the production of a new monoclonal antibody, PNL2, directed against a fixative resistant melanocyte antigen. The analysis of PNL2 immunostaining on a broad range of normal or malignant human tissues and on various melanocytic lesions revealed its high specificity. PNL2 gave a strong cytoplasmic staining of skin and oral mucosae melanocytes, and staining of granulocytes when used at high concentration. PNL2 stained all intra-epidermal nevi irrespective of their histologic type, but common intradermal nevi and the dermal component of compound nevi were largely non-reactive as only scattered nevus cells in the papillary dermis were labeled. PNL2 labeled more than 70% of the neoplastic cells in all primary melanomas irrespective of their histologic type. However, PNL2 did not label desmoplastic melanomas. All metastatic melanomas were also stained but the percentage of labeled cells was occasionally lower than the primary tumor. PNL2, as anti–Melan A and HMB-45 antibodies, stained most of the clear cell sarcoma cells, and a few cells in angiomyolipomas and lymphangioleiomyomatosis. None of the other non-melanocytic lesions tested were labeled. Proteomic approaches showed that the immunoaffinity purified PNL2-binding complexes isolated from melanoma cell lines comprise at least TAP1, Clathrin 17 and prealbumin proteins, but not the gp100 recognized by HMB-45. In conclusion, this new monoclonal antibody, PNL2, is directed against a new fixative resistant melanocyte associated antigen. This antigen is chemically resistant and thus allows immunostaining after melanin bleaching or decalcification. We also demonstrate that it is different from Melan A and from gp100, even if PNL2 and HMB-45 staining patterns are sometimes similar.