[Mouse monoclonal antibody (FKH1) detecting human melanoma-associated antigens: production, partial characterization...

A mouse monoclonal antibody, FKH1, was produced to detect cytoplasmic melanoma-associated antigen. FKH1 was raised using cultured human melanoma cell line KHm-6 as immunogen. Reactivity of this antibody was assessed by immunohistochemical techniques. Positive reactions were seen against 5 human melanoma cell lines and cultured human epidermal melanocyte. It stained cytoplasm of melanoma cells in a diffuse and granular pattern with indirect immunofluorescence. Immunoelectron microscopy showed diffuse distribution of immuno-reactant in the cytoplasm of KHm-1 cells excluding melanosomes and other subcellular organelles. In immunoblotting, FKH1 bound with proteins having molecular weight of 71 kd and 55 kd extracted from KHm-6 cells. Reactivity against frozen and alcohol-fixed paraffin-embedded melanocytic tumors was also tested with indirect immunofluorescence or ABC (avidin biotin peroxidase complex) techniques. All cases of frozen sections from benign and malignant melanocytic tumors including 2 cases of amelanotic melanoma showed positive staining with FKH1. In fixed tissues, reactivity was 16/19 (84.2%) in malignant melanoma and 30/44 (68.2%) in other melanocytic tumors. FKH1 did not react against normal melanocytes, C-type nevus cell, intradermal nevus pigmentosus with neuroid structure and neurofibroma. It was demonstrated that FKH1 recognized proliferative melanocytes originated from melanoblast or melanoblastic nevoblast. FKH1 failed to stain normal human peripheral nerves and nonmelanocytic tumors except APUDoma and malignant Merkel cell tumor. In halo nevus, nevus cells were clearly distinguished from intermingling inflammatory cell infiltrate. It was suggested that FKH1 is a useful monoclonal antibody in diagnosing human malignant melanoma, particularly in evaluating tumor thickness of Breslow more precisely.