The carcinogenic potential of UV radiation (the primary cause of nonmelanoma skin cancer) is associated with its ability to suppress cell-mediated immune responses. Previous studies have shown that this UV-induced immune suppression is caused by the secretion of immunosuppressive cytokines such as IL-10. Because the effects of IL-10 on the immune response are countered by IL-12, we injected irradiated mice with IL-12 to determine whether it could overcome UV-induced immune suppression. Administration of IL-12 blocked the suppression of delayed-in-time hypersensitivity reactions observed in UV-irradiated animals. Moreover, IL-12 prevented the induction of suppressor T cells, in that adoptive transfer of spleen cells from UV-irradiated mice treated with IL-12 had no effect on the immune response of the recipient mice, whereas transfer of spleen cells from UV-irradiated mice treated with the vehicle inhibited the immune response. In addition, IL-12 neutralized the activity of UV-induced suppressor T cells. Although the adoptive transfer of UV-induced suppressor T cells from irradiated mice suppressed the immune response of the recipient mice, treatment of the recipient mice with IL-12 following the adoptive transfer overcame the immune suppression. The results of these experiments demonstrate that IL-12 can overcome UV-induced immune suppression by preventing the induction of, as well as neutralizing the activity of pre-formed suppressor T cells.

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