Prevention of ultraviolet radiation-induced immunosuppression by (-)-epigallocatechin-3-gallate in mice is mediated through interleukin 12-dependent DNA repair.

Abstract

Solar UV radiation-induced immunosuppression is considered to be a risk factor for melanoma and nonmelanoma skin cancers. We previously have shown that topical application of (-)-epigallocatechin-3-gallate (EGCG) prevents UV-induced immunosuppression in mice. We studied whether prevention of UV-induced immunosuppression by EGCG is mediated through interleukin 12 (IL-12)-dependent DNA repair. IL-12 knockout (KO) mice on C3H/HeN background and DNA repair-deficient cells from xeroderma pigmentosum complementation group A (XPA) patients were used in this study. The effect of EGCG was determined on UV-induced suppression of contact hypersensitivity and UV-induced DNA damage in the form of cyclobutane pyrimidine dimers (CPD) in mice and XPA-deficient cells using immunohistochemistry and dot-blot analysis. Topical treatment with EGCG prevented UV-induced suppression of the contact hypersensitivity in wild-type (WT) mice but did not prevent it in IL-12 KO mice. Injection of anti-IL-12 monoclonal antibody to WT mice blocked the preventive effect of EGCG on UV-induced immunosuppression. EGCG reduced or repaired UV-induced DNA damage in skin faster in WT mice as shown by reduced number of CPDs(+) cells and reduced the migration of CPD(+) antigen-presenting cells from the skin to draining lymph nodes. In contrast, this effect of EGCG was not seen in IL-12 KO mice. Further, EGCG was able to repair UV-induced CPDs in XPA-proficient cells obtained from healthy person but did not repair in XPA-deficient cells, indicating that nucleotide excision repair mechanism is involved in DNA repair. These data identify a new mechanism by which EGCG prevents UV-induced immunosuppression, and this may contribute to the chemopreventive activity of EGCG in prevention of photocarcinogenesis.