Background: The normal nail matrix contains quiescent melanocytes with a peculiar arrangement and behavior. Objective: Our purpose was to identify nail matrix melanocytes with antibodies that recognize melanocytic cells in tissue sections. Methods: We used the polyclonal antibodies anti-PEP1 and anti-PEP8 and the monoclonal antibody TMH-1, which recognize 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 longitudinal specimens of eight white patients with ingrown toenails. Specimens from normal adult forearm skin were used as controls. Results: All nail specimens gave similar results. Dendritic melanocytes were more numerous in the distal than in the proximal nail matrix. They were not restricted to the basal layer, but were also found in the suprabasal layers of the nail matrix epithelium. Melanocytes were seen both as single dendritic cells among the nail matrix keratinocytes and as small clusters that appeared irregularly distributed along the length of the nail matrix. Each cluster usually consisted of three to four cells. Conclusion: Even if normally quiescent, nail matrix melanocytes possess the key enzymes responsible for the formation of melanin. The suprabasal location of nail matrix melanocytes may be a consequence of the distribution of adhesion molecules in the nail epithelium. In fact, in the nail matrix α2, α3, and β1 integrins are not only expressed on the basal, but also on the fourth to fifth suprabasal layers, with suprabasal expression gradually decreasing from distal to proximal matrix. The behavior of nail matrix keratinocytes may cause the peculiar arrangement and behavior of nail matrix melanocytes.
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