c-jun controls the ability of IL-12 to induce IL-10 production from human memory CD4+ T cells.

IL-12p70 is an immunoregulatory cytokine that has been shown to induce IL-10 production from CD4+ T cells, yet the underlying cellular mechanisms controlling this process are poorly understood. In the present study, we demonstrate that IL-12p70 induces IL-10 production from human memory CD4+ T cells via a PI3K-dependent signaling mechanism. Specifically, stimulation of human memory CD4+ T cells in the presence of IL-12p70 lead to increased PI3K activity and the subsequent phosphorylation and inactivation of the downstream constitutively active serine/threonine kinase, glycogen synthase kinase-3beta (GSK3beta). Inhibition of PI3K prevented the inactivation of GSK3beta by IL-12p70, as well as the subsequent ability of IL-12p70 to augment IL-10 levels by memory CD4+ T cells. Moreover, ectopic expression of a constitutively active form of GSK3beta abrogated the ability of IL-12p70 to increase IL-10 production by TCR-stimulated CD4+ T cells. In contrast, direct inhibition of GSK3 mimicked the effect of IL-12p70 on IL-10 production by memory CD4+ T cells. Analysis of downstream transcription factors identified that the ability of IL-12p70 to inactivate GSK3beta lead to increased levels of c-jun. The ability of IL-12p70 to inactivate GSK3beta and induce c-jun levels was required for IL-12 to augment IL-10 production by human memory CD4+ T cells, since small interfering RNA-mediated gene silencing of c-jun abrogated this process. These studies identify the cellular mechanism by which IL-12 induces IL-10 production from human memory CD4+ T cells.