Functional relevance of T helper 17 (Th17) cells and the IL-17 cytokine family in inflammatory bowel disease.

The recent discovery and characterization of T helper 17 cells (Th17) and their signature cytokines (IL-17) represents a hallmark in T-cell immunobiology by providing a new distinctive pathway for the communication between adaptive and innate immunity. From the six members of the IL-17 cytokine family presently known, at least two have evident proinflammatory qualities and are involved in several chronic inflammatory disorders, including inflammatory bowel disease (IBD). IL-17A and IL-17F are abundantly found in inflamed IBD mucosa, suggesting their pivotal role in IBD. However, the precise implication of IL-17 cytokine family members in IBD pathogenesis and the mechanisms regulating their secretion are incompletely understood. Importantly, recent findings suggest that beyond IL-17 production-Th17 cells may secret a plethora of other effector cytokines such as IL-21, IL-22, and IL-9- which is in part induced by its own IL-9 production. However, the use of anti-IL-17 therapeutic strategies in experimental models of chronic inflammation results in disease-ameliorating effects suggesting their potential use in IBD patients. In this review article we discuss the latest findings on the role of Th17 cells and IL-17 family members in IBD immunopathology, as well as research perspectives.