Ultraviolet-A light prolongs survival and improves immune function in (New Zealand black x New Zealand white)F1 hybrid mice.

Although ultraviolet (UV) light is generally harmful to patients with systemic lupus erythematosus, most clinical and immunologic studies of UV exposure have evaluated the effects of UV-B (280-320 nm). The long-wavelength UV-A band (320-400 nm), however, is less toxic than UV-B and has different immunologic actions. Therefore, we studied the effect of UV-A irradiation on survival and immunologic function in the (New Zealand black x New Zealand white)F1 hybrid mouse model of systemic lupus erythematosus. Twenty-one (New Zealand black x New Zealand white)F1 mice were treated with 3.5 joules/cm2/day of UV-A light for 5 days each week, beginning at age 10 weeks. A control group consisted of 20 untreated animals. All UV-A-irradiated mice survived to 32 weeks, compared with 12 of 20 mice in the nonirradiated group (P = 0.0013). Splenomegaly was significantly decreased in the irradiated mice (P less than 0.03). Mice that received UV-A treatment combined with depilation had significantly improved lymphocyte responses to phytohemagglutinin and lipopolysaccharide and significantly decreased levels of anti-DNA antibodies compared with mice that received neither treatment. Reductions in spleen size and anti-DNA antibody titer were significantly correlated with improved parameters of lymphocyte function. These results suggest that a relatively small dose of UV-A exerts significant therapeutic action in murine lupus, perhaps through an effect on immunologic regulation.