A NOVEL, ANTIGEN-PRESENTING FUNCTION OF MELANOCYTES AND ITS POSSIBLE RELATIONSHIP TO HYPOPIGMENTARY DISORDERS

It is now well established that cultured human melanocytes are capable of expressing immunologically important cell surface molecules and th at they can produce cytokines. Not all cells with the ability to expre ss MHC class II molecules are capable of effective Ag presentation. Ho wever, the dendritic nature of melanocytes, their strategic position w ithin the skin, and their phagocytic capacity seem to suggest a role f or these cells in processing and presenting Ag. This study demonstrate s that cultured normal human skin melanocytes can present peptide Ag, and process and present the mycobacterial HSP65 kDa protein and whole Mycobacterium leprae sonicate to CD4+ cytotoxic proliferative T cell c lones in an Ag-specific and HLA-class II-restricted manner. T cell sti mulation was dependent on costimulatory signals, i.e., LFA-3/CD2 and L FA-1/ICAM-1. Besides eliciting a T cell proliferative response, our st udies further demonstrate that melanocytes can function as target cell s for T cell-mediated cytotoxicity. The described Ag-processing and -p resenting functions of melanocytes, taken together with in vivo behavi or of melanocytes in hypopigmentation, provide new clues for the etiop athogenesis of melanin pigmentary disorders.