Regulation of Th17 cell differentiation and EAE induction by MAP3K NIK.

Th17 cells play an important role in mediating autoimmune diseases, but the molecular mechanism underlying Th17 differentiation is incompletely understood. We show here that NF-kappaB-inducing kinase (NIK), which is known to regulate B-cell maturation and lymphoid organogenesis, is important for the induction of Th17 cells. NIK-deficient naive CD4 T cells are attenuated in the differentiation to Th17 cells, although they are competent in committing to the other effector lineages. Consistently, NIK knockout mice are resistant to experimental autoimmune encephalomyelitis, a disease model that involves the function of Th17 cells. This phenotype was also detected in Rag2 knockout mice reconstituted with NIK-deficient T cells, confirming a T-cell intrinsic defect. We further show that NIK mediates synergistic activation of STAT3 by T-cell receptor and IL-6 receptor signals. NIK deficiency attenuates activation of STAT3 and induction of STAT3 target genes involved in Th17-commitment program. These findings establish NIK as an important signaling factor that regulates Th17 differentiation and experimental autoimmune encephalitis induction.