CHARACTERIZATION OF NAIL MATRIX MELANOCYTES WITH ANTI-PEP1, ANTI-PEP8, TMH-1, AND HMB-45 ANTIBODIES

Background: The normal nail matrix contains quiescent melanocytes with a peculiar arrangement and behavior. Objective: Our purpose was to id entify nail matrix melanocytes with antibodies that recognize melanocy tic cells in tissue sections. Methods: We used the polyclonal antibodi es anti-PEP1 and anti-PEP8 and the monoclonal antibody TMH-1, which re cognize melanocytic enzymes, and the monoclonal antibody HMB-45, which reacts with melanoma cells and fetal melanocytes, but not with normal adult melanocytes. Nail matrix specimens were obtained from longitudi nal specimens of eight white patients with ingrown toenails. Specimens from normal adult forearm skin were used as controls. Results: All na il specimens gave similar results. Dendritic melanocytes were more num erous in the distal than in the proximal nail matrix. They were not re stricted to the basal layer, but were also found in the suprabasal lay ers of the nail matrix epithelium. Melanocytes were seen both as singl e dendritic cells among the nail matrix keratinocytes and as small clu sters that appeared irregularly distributed along the length of the na il matrix. Each cluster usually consisted of three to four cells. Conc lusion: Even if normally quiescent, nail matrix melanocytes possess th e key enzymes re- sponsible for the formation of melanin. The suprabas al location of nail matrix melanocytes may be a consequence of the dis tribution of adhesion molecules in the nail epithelium. In fact, in th e nail matrix alpha 2, alpha 3, and beta 1 integrins are not only expr essed on the basal, but also on the fourth to fifth suprabasal layers, with suprabasal expression gradually decreasing from distal to proxim al matrix. The behavior of nail matrix keratinocytes may cause the pec uliar arrangement and behavior of nail matrix melanocytes.