Polymorphic light eruption: an immunopathological study of evolving lesions

SUMMARY Polymorphic light eruption (PLE) papules were successfully induced on previously affected sites in 11 out of 14 patients with PLE 4–20 h after single exposures to suberythemogenic doses of solar simulated radiation. Histological examination of biopsies performed 1 h, 5 h, 24 h, 72 h and 144 h post‐irradiation revealted onset within 5 h of perivascular cellular infiltration. The infiltrate was dominated by lymphocytes in both early and established lesions, without evident epidermal pathology. Immunohistochemistry demonstrated a predominance of CD4 + cells in lesions up to 72 h post‐induction, but later biopsies were dominated by a CD8 + infiltrate. Significantly increased numbers of dermal macrophages and CD1b + cells were detected 1 h and 5 h post‐irradiation, respectively. These findings are consistent with a delayed type hypersensitivity response underlying the pathogenesis of polymorphic light eruption.