Immunohistochemical demonstration of S-100 protein and melanoma-associated antigens in melanocytic nevi.

Thirty-nine melanocytic nevi of varying histologic structure and stages of development were examined for the presence of S-100 protein and melanoma-associated antigens (MAA) by the indirect immunoperoxidase technique, using a polyclonal anti-serum to S-100 protein and monoclonal antibodies to MAA. S-100 protein and MAA were found in the cells of all types of nevi, including dysplastic and congenital nevi. While S-100 protein was present in nevus cells at the epidermodermal junction and at all levels of the dermis, the melanoma-directed monoclonal antibodies BM 24-2, NKI/C-3, Mel-1, and Mel-2 reacted most prominently with the superficial (A-type) nevus cells; the B- and C-type cells being negative in these cells. An exception to this rule was melanoma-monoclonal antibody 34.1 which reacted with nevus cells at all levels; deep C-cells often being more intensely stained than the subepidermal A-cells. The cells of the different nevus cell layers, known to differ morphologically and enzymatically, are, thus, also different in their expression of MAA. Our data suggest that for most antibodies these variations may be due to differences in the metabolic activities of nevus cells at various distances from the epidermis.