Immunohistochemical analysis of malignant melanomas and nevocellular nevi with monoclonal antibodies to distinct monomorphic determinants of HLA antigens.

Using an indirect immunoperoxidase technique, 20 nevocellular nevi, 5 dysplastic nevi, 14 primary cutaneous melanomas, and 24 metastatic melanomas were tested with a panel of monoclonal antibodies to monomorphic determinants of Class I (HLA-A,B,C) and Class II (la-like) major histocompatibility complex antigens. Class I HLA and beta 2-microglobulins were not detected on the majority of nevus cells but were expressed by 3 of 5 dysplastic nevi, by the majority of tumor cells in 12 of 14 primary cutaneous melanomas, and in 13 of 24 metastases. The different expression of Class I HLA and beta 2-microglobulins in primary and metastatic lesions suggests that loss of these antigens may be associated with progression of malignancy. Class II HLA were not detected in common nevi but were locally present in 1 of 5 dysplastic nevi, 7 of 14 cases of primary cutaneous melanoma, and all 24 cases of metastatic lesions tested. These findings suggest that increase in Class II HLA expression may be associated with progression of malignancy. The staining patterns obtained with monoclonal antibodies to distinct determinants of Class I HLA and Class II HLA were superimposable within each type of antigen. Therefore, the discrepancies in the literature about the expression of histocompatibility antigens by lesions of melanocytic origin are not likely to reflect the different specificity of the antibodies used by the various investigators.