Melanosomal antigenic expression on the cell surface and intracellular subunits within melanogenic compartments of pigment cells: analysis by antimelanosome-associated monoclonal antibody.

Antimelanosome-associated monoclonal antibody has recognized the common antigenic determinant of melanosomes and cell surface of pigment cells, and it is suggested that melanosomes play a significant role as an antigen in progressive depigmentary disorders, in which melanocytes are selectively altered and disappear presumably by auto-antibodies in vivo. Mouse myeloma cells were fused with spleen cells from BALB/c mice immunized with a melanosomal fraction separated from human melanotic melanoma cells (Mm-1-JCK). The monoclonal antibody (MoAb) A4F11 has been found to react with premelanosomes, melanosomes, and probably with Golgi-associated endoplasmic reticulum lysosomes, but not with mitochondria, nuclei, and cytosol from human melanoma cells, by immunoelectron microscopy using the saponin permeation method, which was carried out together with indirect radioimmunoassay and quantitative absorption assay. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting using melanosome preparations have revealed the antigen(s) reactive with the MoAb A4F11 in 3 bands corresponding to Mr 50,000, 18,000, and 17,000. Cell binding assay has shown the reactivity of the MoAb A4F11 with the cell surface of human normal melanocytes and melanoma cells, but not with other mammalian melanoma cells or with human nonpigment cells examined. Indirect immunofluorescence on cultured cells and frozen sections has revealed distinct granular reactivity not only with human melanotic melanoma, but also with junctional and intradermal nevi, cultured malignant blue nevus cells, as well as normal melanocytes. The above evidence has indicated the presence of an antigenic determinant common to the intracellular melanogenic compartments and to the cell surface of human pigment cells, regardless of their oncogenic differentiation status.