Effects of acute and chronic exposure to natural sunlight and UVB on CD4/CD8 ratio and circulating pro-inflammatory and anti-inflammatory cytokine levels in mice

Abstract

Abstract Solar ultraviolet radiation (UVR) constitutes a significant hazard to the skin because of its direct carcinogenic action and its immunosuppressive action, which are mostly attributed to its ultraviolet B (UVB) component. Evidence suggests that ultraviolet A (UVA) in natural sunlight might neutralize the damaging effect of UVB. We aimed at evaluating the systemic immunological impacts of exposure to either natural sunlight (sun UVR) or UVB. The experiment included five groups of mice: unexposed control group; two groups in which animals were daily exposed to 30 min of sun UVR for either 4 days (acute exposure) or 20 days (chronic exposure); and two groups in which animals were daily exposed to 20 min of UVB for either 4 days or 20 days. In all groups, plasma tumor necrosis factor-alpha (TNF-α), interleukin-10 (IL-10), IL-12, interferon gamma (IFN-γ), and transforming growth factor-beta (TGF-β) were measured using enzyme-linked immunosorbent assay (ELISA). Circulating CD4, CD8, and CD4/CD8 ratio were evaluated by fluorescent flow cytometry. CD4/CD8 ratios were significantly altered in groups exposed to sun UVR. Circulating pro-inflammatory and anti-inflammatory cytokines increased significantly in all forms of exposure. Except for TNF-α, the increase of which was more prominent in acute exposure, chronic exposure resulted in higher cytokine concentrations compared with acute exposure, but the difference reached significance only in IL-10 and IFN-γ. In conclusion, exposure to sun UVR or UVB results in significant changes in plasma cytokine levels that can be used to monitor the systemic immunological effect of UVR exposure. Except for its effect on CD4/CD8 ratio, the systemic immunological impact of exposure to natural sunlight did not differ from exposure to UVB, which argues against the neutralizing effect of its UVA component.