Ultraviolet radiation causes less immunosuppression in patients with polymorphic light eruption than in controls.

It is hypothesized that polymorphic light eruption is characterized by a partial failure of ultraviolet radiation-induced immunosuppression, resulting in a delayed-type hypersensitivity response to photo-induced antigens. We aimed to study the susceptibility of PLE patients to UVR-induced immunosuppression, by measuring the strength of sensitization to 2,4-dinitrochlorobenzene after UVR exposure, and to diphenylcyclopropenone without UVR exposure, in subjects with PLE and controls. Thirteen PLE patients and 11 controls were exposed to 1 minimum erythema dose (MED) of UVR delivered from Waldmann UV-6 bulbs to the upper inner arm. Twenty-four hours later at the same site they were exposed to a sensitizing dose of 2,4-dinitrochlorobenzene. One week later they were exposed to a sensitizing dose of diphenylcyclopropenone at a nonirradiated site. Three weeks later all subjects were challenged with four doses of 2,4-dinitrochlorobenzene and four doses of diphenylcyclopropenone. The resulting increase in skin thickness was measured with Harpenden callipers and summed over the four doses, to give a single value representing the reactivity of the subject to 2,4-dinitrochlorobenzene (Sigma DN) and diphenylcyclopropenone (Sigma DP). Among all subjects, there was a very strong correlation between Sigma DN and Sigma DP (Pearson correlation 0.56, p=0.004). The strength of the reaction to 2,4-dinitrochlorobenzene relative to the reaction to diphenylcyclopropenone was significantly greater among PLE patients than controls (p=0.04 independent samples t test of Sigma DP-Sigma DN). We conclude that induction of sensitization by 2,4-dinitrochlorobenzene is suppressed less by UVR in patients with PLE than in healthy controls.