Immunosuppressive effects of solar ultraviolet (UV) radiation have been implicated in the risk of non-melanoma and melanoma skin cancers in humans. Previously, we have shown that dietary grape seed proanthocyanidins (GSPs) inhibit photocarcinogenesis in mice and inhibit UV-induced suppression of allergic contact hypersensitivity (CHS) response, a prototypic T-cell-mediated immune response. Studies have shown that UV-induced T regulatory (Treg) cells or suppressor T cells have a role in immune suppression and UV-induced skin carcinogenesis is indicated by the demonstration that depletion of UV-induced T-suppressor cells can inhibit UV-induced carcinogenesis. In our continued efforts to investigate the molecular targets responsible for the prevention of immunosuppression in UV exposed mice by GSPs, we have investigated whether GSPs inhibit UV-induced immunosuppression by inhibiting the development or activity of UV-induced Treg cells in mice. To understand the mechanism, C3H/HeN mice were exposed to UV (150 mJ/cm2) radiation on 4 consecutive days with and without treatment of mice with dietary GSPs, mice were sensitized with 2,4-dinitrofluorobenzene (DNFB) 48 h after the last UV exposure, and then sacrificed 5 days after DNFB sensitization. The flow cytometry analysis of lymph node cells indicated that the numbers of Treg cells were reduced in the mice which were given GSPs in diet compared to non-GSPs-treated UV-exposed mice. We then analyzed effects of dietary GSPs (0.5%, w/w) on secretion of cytokines by Treg cells that were isolated from lymph nodes and spleens of mice that were exposed to UVB (150 mJ/cm2). Our ELISA data showed that in comparison to Treg cells isolated from control mice (GSPs-untreated), Treg cells isolated from mice that received GSPs in diet secreted a significantly higher level of IFNγ, while significantly lower levels of interleukin (IL)-10 and TGF-β, which are immunosuppressive in nature. Finally, we used an adoptive transfer approach, wherein draining lymph nodes were harvested from mice that were exposed to UVB on 4 consecutive days with and without GSPs supplementation in diet and sensitized by DNFB onto the UVB-exposed skin. Treg cells were positively selected using magnetic beads and MACS system and transferred into naïve mice that were subsequently challenged by application of DNFB on the ear skin. Naïve recipients that received Treg cells from GSPs-treated, UVB-irradiated donors exhibited CHS response, whereas no significant CHS was observed in mice which were injected Treg cells from UVB alone-exposed mice compared to control group. These data suggest that dietary GSPs inhibit UVB-induced immunosuppression by suppressing the development as well as the functional activation of Treg cells in UV-exposed mice.

Citation Format: Santosh K. Katiyar, Tripti Singh, Mudit Vaid. Dietary grape seed proanthocyanidins inhibit UV-induced immune suppression by targeting the development of regulatory T cells in mice. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1239. doi:10.1158/1538-7445.AM2014-1239