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The mechanisms whereby narrowband ultraviolet B (UVB) (311–313 nm, TL01) phototherapy are effective in psoriasis may differ from those occurring in broadband UVB phototherapy. In the present study, changes in epidermal cells as a result of TL01 therapy were assessed in the skin of patients with psoriasis. The non-lesional skin of five subjects with plaque psoriasis was biopsied before and after a series of 12 whole-body TL01 treatments. Following appropriate staining of skin sections, the numbers of p53-positive keratinocytes, sunburn cells and Langerhans cells in the epidermis were counted. TL01 therapy induced a threefold increase in the number of p53-positive epidermal cells, a 12-fold increase in sunburn cells and a twofold decrease in Langerhans cells. The increase in epidermal p53 expression and apoptosis of keratinocytes together with the depletion of Langerhans cells in the non-lesional skin of psoriasis patients are likely to contribute to the effectiveness of TL01 phototherapy. [ABSTRACT FROM AUTHOR]