Quantitative and morphologic changes of Langerhans' cells after ultraviolet A irradiation of human epidermis.

Three different surface markers (OKT6, HLA-DR, and adenosinetriphosphatase) were compared to identify Langerhans' cells, and the changes in number and morphology of these cells were studied at different intervals after irradiation of human skin by a 2.5-fold minimal erythema dose of ultraviolet A. Morphologic alteration and decreased surface-marker reactivity became evident on day 2 and were most pronounced on day 3 or day 4 (injury phase). The recovery phase started between day 4 and 1 week and was complete by 3 weeks. HLA-DR+/OKT6- (DR+T6-) cells were present at all time intervals. The ratio of these cells to the sum of DR+T6- and DR+T6+ cells was 0.3% before irradiation, reached a peak of 65.4% at day 4, and decreased to 0.6% by 3 weeks.