Diversion of CD4(+) T cell development from regulatory T helper to effector T helper cells alters the contact hypersensitivity response

Cutaneous sensitization to reactive haptens and subsequent challenge results in a T cell-mediated response, contact hypersensitivity (CHS). Recent results from this laboratory have indicated that hapten sensitization induces two populations of reactive T cells: CD8(+) T cells producing interferon (IFN)-gamma which mediate the response and CD4(+) T cells producing interleukin (IL)-4 and IL-10 which negatively regulate the magnitude and duration of the response. Since CD4(+) T cell development to either IFN-gamma- (Th1) or IL-4/IL-10- (Th2)-producing cells is dependent upon the cytokine environment during antigen priming, we hypothesized that CD4(+) T cell induction in a Th1-promoting environment would not only alter the CD4(+) T cell cytokine-producing phenotype but also the course of the CHS response. Administration of the Th1-promoting cytokine IL-12 during hapten sensitization resulted in a CHS response of greater magnitude following challenge and extended the duration of the response. In hapten-sensitized mice depleted of CD8(+) T cells, treatment with IL-12 induced effector CD4(+) T cells. Histological examination of challenged ear tissue from these mice indicated minimal edema and an acute mononuclear cell infiltration more typical of classical delayed-type hypersensitivity than CHS. Hapten-primed CD4(+) T cells from IL-12 treated, sensitized mice produced IFN-gamma, but not IL-4 in response to T cell receptor-mediated stimulation. Use of neutralizing anti-IFN-gamma antibody indicated that IL-12 not only directly promoted Th1 development but also indirectly inhibited Th2 development through stimulation of IFN-gamma production al the rime of hapten sensitization. Overall, these results demonstrate that diversion of CD4(+) T cell development to Th1 effector cells rather than to Th2 cells alters the efferent nature of CHS and removes a primary regulatory mechanism of the immune response.