Polymorphic light eruption--an immunopathological study of provoked lesions.

Polymorphic light eruption (PLE) lesions were induced in 26 patients after an average of 60 J total body UVA irradiation. Using the criteria of the French literature, that make a distinction between PLE and benign summer light eruption (BSLE), the group of 26 patients with PLE was divided into 12 patients with BSLE and 14 patients with PLE, on the basis of historical criteria. Biopsies were taken and compared immunohistochemically with biopsies from 15 unirradiated normal control subjects, in order to find evidence in support of the hypothesis that PLE involves a delayed-type hypersensitivity reaction. The provoked lesions showed: ICAM-1 expression on the keratinocytes of the basal and suprabasal cell layers in 18 of 25 patients, i.e. 72%; HLA-DR expression on the keratinocytes of the basal, squamous and granular cell layer in 13 of 25 patients, i.e. 52%; and OKM5 expression on the keratinocytes of the granular cell layer in 13 of 26 patients, i.e. 50% of the cases. The control samples showed no such antigen expression on the keratinocytes, except for two cases where weak and very localized ICAM-1 positivity was observed; one of these also had a slight localized positivity for HLA-DR and OKM5. The results of the phototesting procedures and the immunohistochemical investigations were similar in both BSLE and PLE. This suggests that they are the same condition, and the term BSLE should therefore probably be discarded. The results of our investigations support the theory of an immunological basis for PLE.