Epidemiology and pathogenetic mechanisms of polymorphic light eruption

Polymorphic light eruption (PLE) is a common sun-induced dermatosis presenting with itchy papules, plaques or vesicles on sun-exposed skin sites. In this thesis, epidemiological as well as pathogenetic mechanisms are desribed. By interviewing almost 7000 indoor working Europeans we found a lifetime prevalence of PLE of 18%. There is no evidence of increasing prevalence toward higher latitudes, as was formerly suggested. PLE is regarded an immunological disorder caused by a delayed type hypersensitivity reaction to a de novo photo-induced antigen in the skin. Upon UVB irradiation of the skin, more epidermal Langerhans cells persist in the epidermis of PLE patients and less neutrophilic granulocytes migrate into the epidermis, in contrast to healthy individuals. We show that UV-hardening therapy restores the epidermal cell migration to a normal situation. The reason for the aberrant cell responses in PLE skin remain for as yet unexplained. The presence of higher IL-1a en Il-1b levels in the skin of PLE patients was indicative of a pro-inflammatory situation after UVB irradiation when compared to healthy controls, but does not explain the aberrant cell responses. Our study further shows that the results of artificial UVA nor UVB provocation have any predictive value for the clinical severity of PL