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Ultraviolet radiation effects on immunologic function.

Studies over the past two decades have established that exposure to ultraviolet radiation (UVR) has profound effects on immunity. Most of this work was done in animal models with limited data from human studies. Exposure to UVR inhibits the induction of contact hypersensitivity in mice systemically at high doses and locally at low doses, associated with the appearance of transferable T suppressor cells. In some strains of mice, chronic UVR exposure results in the occurrence of highly immunogenic cutaneous malignancies which are rejected upon transplantation to syngeneic recipients. However, within the primary host the tumor is protected from destruction, at least in part, by the appearance of T suppressor cells. Syngeneic animals exposed to large doses of UVR also permit the growth of these transplanted tumors and this phenomenon also results, at least in part, from the presence of suppressor cells. Interestingly, these suppressor cells appear to recognize UVR-induced regressor tumors as a class within a given mouse strain, suggesting that they recognize shared determinants. The mechanisms of these examples of UVR-induced immunosuppression are not completely clear, but perhaps relate to changes in Langerhans cell function and/or epidermal cell release of cytokines induced by UVR. Exposure to UVR in vitro alters the ability of epidermal cells and Langerhans cells to present some antigens. Keratinocytes alter their secretion of specific cytokines after exposure to UVR and are induced to produce immunosuppressive factors. Immunosuppressed patients also have increased rates of skin cancer, suggesting immunologic involvement in regulation of cutaneous oncogenesis in humans.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1998

Risk assessment for the harmful effects of UVB radiation on the immunological resistance to infectious diseases.

Risk assessment comprises four steps: hazard identification, dose-response assessment, exposure assessment, and risk characterization. In this study, the effects of increased ultraviolet B(UVB, 280-315 nm) radiation on immune functions and the immunological resistance to infectious diseases in rats were analyzed according to this strategy. In a parallelogram approach, nonthreshold mathematical methods were used to estimate the risk for the human population after increased exposure to UVB radiation. These data demonstrate, using a worst-case strategy (sensitive individuals, no adaptation), that exposure for approximately 90 min (local noon) at 40 degrees N in July might lead to 50% suppression of specific T-cell mediated responses to Listeria monocytogenes in humans who were not preexposed to UVB (i.e., not adapted). Additionally, a 5% decrease in the thickness of the ozone layer might shorten this exposure time by approximately 2.5%. These data demonstrate that UVB radiation, at doses relevant to outdoor exposure, may affect the specific cellular immune response to Listeria bacteria in humans. Whether this will also lead to a lowered resistance (i.e.,increased pathogenic load) in humans is not known, although it was demonstrated that UVB-induced immunosuppression in rats was sufficient to increase the pathogenic load. Epidemiology studies are needed to validate and improve estimates for the potential effects of increased UVB exposure on infectious diseases in humans.

Animals↗
PubMed1996

Risk assessment for the harmful effects of UVB radiation on the immunological resistance to infectious diseases.

Risk assessment comprises four steps: hazard identification, dose-response assessment, exposure assessment, and risk characterization. According this scheme, we have analysed the effects of UVB radiation on basal immune functions in rats and man, and the immunological resistance to infectious diseases in rats. Non-threshold mathematical methods were used in order to estimate the risk for the human population after increased exposure to UVB radiation. These data demonstrate that UVB radiation, at doses relevant to outdoors exposure, may affect the immunological resistance to infectious diseases in human individuals. This study may also provide a basis for a strategy to assess the risk of adverse effects of exposure to immunotoxic agents.

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