Disappearance of epidermal Langerhans cells during PUVA therapy

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Abstract
The numbers and morphological appearance of epidermal Langerhans cells (LC) were studied in 25 patients with psoriasis receiving treatment with 8-methoxypsoralen and long wavelength UV irradiation (UV-A) (PUVA). After a single exposure, LC showed loss of fine dendritic processes. Repeated treatments resulted in a reduction of the number of LC from the mean pretreatment value of 713/mm2 to less than 60/mm2 after 7 treatments. The number of LC remained low while treatment continued for up to 4 wk. This finding may explain the impaired contact hypersensitivity observed in patients with psoriasis receiving PUVA therapy.