Autoimmune inflammation from the Th17 perspective

Recent studies demonstrated an IL-17-producer CD4(+) T cell subpopulation, termed Th17, distinct from Th1 and Th2. It represents a different pro-inflammatory Th-cell lineage. This notion is supported by gene-targeted mice studies. Mice lacking TL-23 (p19(-/-)) do not develop experimental autoimmune encephalomyelitis (EAE) or collagen-induced arthritis (CIA), while knockout mice for the Th1 cytokine IL-12 (p35(-/-)) strongly develop both autoimmune diseases. Disease resistance by IL-23 knockout mice correlates well with the absence of IL-17-producing CD4+ T lymphocytes in target organs despite normal presence of antigen-specific-IFN-gamma-producing Th1 cells. This finding may thus explain previous contradictory reports showing that anti-IFN-gamma-treated mice, IFN-gamma- or IFNR-deficient mice develop CIA or EAE. TGF-beta, IL-6 and IL-1 are the differentiation factors of Th17 cells. IL-23 is dispensable for this function, but necessary for Th17 expansion and survival. The master regulator that directs the differentiation program of Th17 cells is the orphan nuclear receptor ROR gamma t. IL-27, a member of the IIL12/IL-23 family, potently inhibits Th17 development. Evidence suggesting rheumatoid arthritis and multiple sclerosis as primarily IL-17 autoimmune inflammatory-mediated diseases is rapidly accumulating. The IL-17/23 axis of inflammation and related molecules may rise as therapeutic targets for treating these and perhaps other autoimmune diseases. (c) 2006 Elsevier B.V. All rights reserved.