Skin exposure to chronic but not acute UV radiation affects peripheral T-cell function

Ultraviolet (UV) radiation (UVR) produces deleterious effects that may finally lead to carcinogenesis. These adverse effects include tissue inflammation, free radical formation with consequent oxidation of proteins and lipids, DNA damage, and immune function suppression. The aim of this study was to evaluate the effects of UVR at the local and systemic levels following acute (4 consecutive days with 0.5 minimal erythema dose [MED]) or chronic (20 consecutive days with 0.25 MED) exposure. Locally, histological alterations and epidermal T-cell populations were studied. Systemically, inguinal lymph-node and spleen T cells were analyzed with respect to proliferative response and cytokine production against a nonspecific mitogen. Lymph-node T-cell populations were also characterized. Our results indicated that while both acute and chronic UVR produced epidermal hyperplasia and a decrease in epidermal T-cell density, acute UVR increased T-cell proliferative response, while chronic UVR produced the opposite effect, shifting the cytokine production toward a Th2/Treg profile. Therefore, even though acute irradiation produced a direct effect on skin, it did not correlate with a marked modification of overall T-cell response, which is in contrast to marked effects in chronically irradiated animals. These findings may contribute to understanding the clinical relevance of occupational UVR exposure, typically related to outdoor activities, which is associated with nonmelanoma skin carcinogenesis.