DOPA-NEGATIVE MELANOCYTES IN THE OUTER ROOT SHEATH OF HUMAN HAIR-FOLLICLES EXPRESS PREMELANOSOMAL ANTIGENS BUT NOT A MELANOSOMAL ANTIGEN ORTHE MELANOSOME-ASSOCIATED GLYCOPROTEINS TYROSINASE, TRP-1, AND TRP-2

It is believed that DOPA-negative melanocytes in the outer root sheath of the human hair follicle are activated, become identifiable by DOPA staining, and migrate into the epidermis during the repigmenting phas e of vitiligo. These cells are difficult to identify, however, and oth erwise have not been characterized. These cells are readily identified by immunofluorescence, immunohistochemistry, and immunoelectronmicros copy using the antibodies NKI/beteb and A4F11, which recognize premela nosome-related antigens. The majority of the outer root sheath melanoc ytes were found in the mid to the upper portion of the hair follicle. Double staining revealed that these cells were distinct from HLA-DR-be aring dendritic cells. Further immunohistochemical investigation using alpha-PEP-7, alpha-PEP-1, or TMH-1 and alpha-PEP-8 antibodies reveale d that outer root sheath melanocytes cannot be identified by antibodie s to tyrosinase, TRP-1, or TRP-2, respectively. These cells also did n ot react with HMB45 antibody, which recognizes a melanosome-associated cytoplasmic antigen, We believe that the inactive outer root sheath m elanocytes contain some of the early structural proteins but not any o f the enzymatic proteins necessary for melanogenesis. Therefore, activ ation is the process whereby outer root sheath melanocytes acquire all of the structural and enzymatic proteins necessary for melanogenesis.