Development and characterization of a mouse monoclonal antibody, MoAb HMSA-1, against a melanosomal fraction of human malignant melanoma.

To characterize the biological property unique to melanocytes and to utilize this property to establish laboratory diagnostic tools for malignant melanoma, monoclonal antibody (MoAb) human melanosome-associated antigen-1 (HMSA-1), a mouse monoclonal antibody, was developed against purified melanosomal fractions of human melanoma. MoAb HMSA-1 belongs to an IgG1 (kappa) subclass. Fractionation of cell organelles combined with enzyme linked immunosorbent assay analysis indicated that the antigen(s) reactive with MoAb HMSA-1 is localized in melanosome and endoplasmic reticulum fractions and that it is related to melanosomal protein and its precursor forms. The localization of the antigen in the melanosome and endoplasmic reticulum was also confirmed by immunoelectron microscopy. Characteristically, MoAb HMSA-1 reacted with formalin-fixed and paraffin-processed tissues of melanocytic nevi and malignant melanoma, including amelanotic lesions. It did not react with normal melanocytes, normal tissues and organs from fetuses and adults, or most non-melanocytic tumors. Thus MoAb HMSA-1 identifies the differentiation antigen for the melanosome-associated property in neoplastic melanocytes and is a useful adjunct for immunohistological diagnosis of melanocytic lesions on routine paraffin sections.