Ultraviolet radiation induced suppression of Mantoux reactions in humans

The effects of low dose ultraviolet (UV) radiation on delayed type hypersensitivity responses to tuberculin purified protein derivative were investigated in 17 healthy, Mantoux-positive volunteers. Suberythemal and erythemal doses of solar simulated UV from a fluorescent lamp source were delivered to the subjects' lower backs daily for five consecutive days. Mantoux testing with intradermally injected purified protein derivative was then performed at both the irradiated sites and an adjacent, unirradiated site, and the Mantoux induced erythema was quantitated 72 h later with a reflectance erythema meter. In comparison with the unirradiated Mantoux sites, Mantoux induced erythema was significantly reduced at the irradiated test sites. In six subjects, we compared the effects of chronic versus short term UV irradiation on the Mantoux reaction. These volunteers were irradiated on one side of their lower backs with the 5 d UV protocol, and on the other side of their backs for 4 or 5 wk. In all but one subject, the short irradiation protocol induced greater suppression of Mantoux responses than prolonged UV exposure. We conclude that even suberythemal doses of UV significantly reduce delayed type hypersensitivity responses to purified protein derivative, and that an adaptive mechanism appears to counteract the immunosuppressive effects of chronic irradiation.