Signal transduction and Th17 cell differentiation

IkappaBzeta regulates T(H)17 development by cooperating with ROR nuclear receptors

Interleukin (IL)-17-producing helper T (T(H)17) cells are a distinct T-cell subset characterized by its pathological role in autoimmune diseases. IL-6 and transforming growth factor-beta (TGF-beta) induce T(H)17 development, in which the orphan nuclear receptors, RORgammat and RORalpha, have an indispensable role. However, in the absence of IL-6 and TGF-beta, the ectopic expression of RORgammat or RORalpha leads to only a modest IL-17 production. Here we identify a nuclear IkappaB family member, IkappaBzeta (encoded by the Nfkbiz gene), as a transcription factor required for T(H)17 development in mice. The ectopic expression of IkappaBzeta in naive CD4(+) T cells together with RORgammat or RORalpha potently induces T(H)17 development, even in the absence of IL-6 and TGF-beta. Notably, Nfkbiz(-/-) mice have a defect in T(H)17 development and a resistance to experimental autoimmune encephalomyelitis (EAE). The T-cell-intrinsic function of IkappaBzeta was clearly demonstrated by the resistance to EAE of the Rag2(-/-) mice into which Nfkbiz(-/-) CD4(+) T cells were transferred. In cooperation with RORgammat and RORalpha, IkappaBzeta enhances Il17a expression by binding directly to the regulatory region of the Il17a gene. This study provides evidence for the transcriptional mechanisms underlying T(H)17 development and points to a molecular basis for a novel therapeutic strategy against autoimmune disease.

IL-6 promotes NK cell production of IL-17 during toxoplasmosis

Previous studies have implicated T cell production of IL-17 in resistance to Toxoplasma gondii as well as the development of immune-mediated pathology during this infection. Analysis of C57BL/6 and C57BL/6 RAG(-/-) mice challenged with T. gondii-identified NK cells as a major innate source of IL-17. The ability of soluble Toxoplasma Ag to stimulate NK cells to produce IL-17 was dependent on the presence of accessory cells and the production of IL-6, IL-23, and TGF-beta. In contrast, these events were inhibited by IL-2, IL-15, and IL-27. Given that IL-6 was one of the most potent enhancers of NK cell production of IL-17, further studies revealed that only a subset of NK cells expressed both chains of the IL-6R, IL-6 upregulated expression of the Th17-associated transcription factor RORgammat, and that IL-6(-/-) mice challenged with T. gondii had a major defect in NK cell production of IL-17. Together, these data indicate that many of the same cytokines that regulate Th17 cells are part of a conserved pathway that also control innate production of IL-17 and identify a major role for IL-6 in the regulation of NK cell responses.