IL-10 Controls Ultraviolet-Induced Carcinogenesis in Mice1

UV radiation-induced immunosuppression contributes significantly to the development of UV-induced skin cancer by inhibiting protective immune responses. IL-10 has been shown to be a key mediator of UV-induced immunosuppression. To investigate the role of IL-10 during photocarcinogenesis, groups of IL-10+/+, IL-10+/−, and IL-10−/− mice were chronically irradiated with UV. IL-10+/+ and IL-10+/− mice developed skin cancer to similar extents, whereas IL-10−/− mice were protected against the induction of skin malignancies by UV. Because UV is able to induce regulatory T cells, which play a role in the suppression of protective immunity, UV-induced regulatory T cell function was analyzed. Splenic regulatory T cells from UV-irradiated IL-10−/− mice were unable to confer immunosuppression upon transfer into naive recipients. UV-induced CD4+CD25+ T cells from IL-10−/− mice showed impaired suppressor function when cocultured with conventional CD4+CD25− T cells. CD4+CD25− T cells from IL-10−/− mice produced increased amounts of IFN-γ and enhanced numbers of CD4+TIM-3+ T cells were detectable within UV-induced tumors in IL-10−/− mice, suggesting strong Th1-drived immunity. Mice treated with CD8+ T cells from UV-irradiated IL-10−/− mice rejected a UV tumor challenge significantly faster, and augmented numbers of granzyme A+ cells were detected within injected UV tumors in IL-10−/− animals, suggesting marked antitumoral CTL responses. Together, these findings indicate that IL-10 is critically involved in antitumoral immunity during photocarcinogenesis. Moreover, these results point out the crucial role of Th1 responses and UV-induced regulatory T cell function in the protection against UV-induced tumor development.