An immunohistochemical study of UV-induced skin lesions in actinic prurigo. Resistance of langerhans cells to UV light.

Actinic prurigo is an inflammatory disease of the skin that appears to be mediated by an abnormal immune response. Cell adhesion molecules play a key role in the induction of the immune response as well as in the pathogenesis of inflammation. We investigated the expression of cell adhesion and activation molecules, as well as the density of Langerhans cells in skin from patients with actinic prurigo. Skin biopsies from ultraviolet light-induced lesions, and non-irradiated areas from 10 actinic prurigo patients were studied; in addition, several spontaneous skin lesions were studied. Skin biopsies from normal individuals were used as controls. The expression of ICAM-1, ICAM-3, LFA-3, CD2, LFA-1, VLA-4, CD1a, VCAM-1, CD69, and activated b1 integrins were assessed by immunostaining. An increased expression of LFA-1, LFA-2, ICAM-3, VLA-4, and activated b1 integrins was observed in the cell infiltrate of actinic prurigo lesions and an up-regulated expression of ICAM-1 was detected in keratinocytes from these specimens. Interestingly, the number of Langerhans cells (CD1a + ) in actinic prurigo skin was not significantly affected by ultraviolet irradiation, a phenomenon that was not observed in normal controls. The increased expression of adhesion molecules in the cell infiltrate of actinic prurigo, indicates that these cells are activated and suggests that they are involved in the skin damage seen in these patients. The resistance of Langerhans cells from patients with actinic prurigo to ultraviolet light may have an important role in the pathogenesis of this condition. The involvement of keratinocytes in the pathogenesis of actinic prurigo is suggested by the expression of ICAM-1 on these cells.