The effects of 3 daily, 7-min exposures to artificial ultraviolet light (UVL), designed to simulate natural sunlight, on epidermal Langerhans cells (LC) and melanocytes were studied in 17 healthy Australian volunteers of differing skin pigmentation. Six were of Celtic, 6 of Asian and 5 of Aboriginal descent. LC were visualized using the immunofluorescence method for HLA-DR and T6 antigens, and the histochemical method for ATPase. UVL induced a transient reduction in the LC population density and an increase in the number of melanocytes in all subject groups. The reduction in number of immunocompetent LC or the disruption of their surface markers was greatest in the Celtic subjects, who had the fairest skin, and least in the Aboriginal and Asian subjects, who had the darkest skin. However, neither the inherently dark skin pigmentation nor the UVL-induced increase in pigmentation were sufficient to prevent the depletion of immunocompetent epidermal LC. Non-dendritic, rounded cells and very large dendritic, non-LC, which were present in the epidermis of some subjects, were stimulated to increase in number by exposure to UVL. The identity and function of these cells is uncertain and they require further investigation.
