RISK ASSESSMENT FOR THE HARMFUL EFFECTS OF UVB RADIATION ON THE IMMUNOLOGICAL RESISTANCE TO INFECTIOUS-DISEASES

Risk assessment comprises four steps: hazard identification, dose-resp onse assessment, exposure assessment, and risk characterization. In th is study, the effects of increased ultraviolet B (UVB, 280-315 nm) rad iation on immune functions and the immunological resistance to infecti ous diseases in rats were analyzed according to this strategy. In a pa rallelogram approach, nonthreshold mathematical methods were used to e stimate the risk for the human population after increased exposure to UVB radiation. These data demonstrate, using a worst-case strategy (se nsitive individuals, no adaptation), that exposure for approximately 9 0 min (local noon) at 40 degrees N in July might lead to 50% suppressi on of specific T-cell mediated responses to Listeria monocytogenes in humans who were not preexposed to UVB (i.e., not adapted). Additionall y, a 5% decrease in the thickness of the ozone layer might shorten thi s exposure time by approximately 2.5%. These data demonstrate that UVB radiation, at doses relevant to outdoor exposure, may affect the spec ific cellular immune response to Listeria bacteria in humans. Whether this will also lead to a lowered resistance (i.e., increased pathogeni c load) in humans is not known, although it was demonstrated that UVB- induced immunosuppression in rats was sufficient to increase the patho genic load. Epidemiology studies are needed to validate and improve es timates for the potential effects of increased UVB exposure on infecti ous diseases in humans.