Regulation of airway innate and adaptive immune responses: The IL-17 paradigm

IL-17 is a proinflammatory cytokine produced by immune cells. Its significance in host defense and disease development has been demonstrated in various infection and autoimmune models. Recently, additional studies have shown that IL-17 is also important in modulating airway immune response in several aspects. Along with the well-established Th1/Th2 model, new discoveries regarding the Th17 lineage and IL-17 functions have added an extra twist to the already complicated cytokine network that regulates airway immunity. The IL-17 receptor is expressed on blood cells, as well as on structural cells such as the epithelial cells in the airway. Therefore, the effect of IL-17 on airway immunity is very broad, covering both the innate and the adaptive aspects. In this review, we summarize the findings of recent studies on IL-17 signaling and function in pulmonary immune response, and the implications of IL-17 in disease pathogenesis.