This grant application seeks to investigate the biological role(s) of the inflammatory molecule, IL-17 (interleukin-17), in the induction of epithelial-mesenchymal transition (EMT). EMT, the conversion of epithelial cells into spindle-shaped fibroblasts, has been increasingly recognized in wound healing and fibrogenesis in fibrotic diseases, such as idiopathic pulmonary fibrosis (IPF) and lung transplant associated obliterative bronchiolitis (OB). IPF is a fatal disease with progressive scarring of the lung tissue with no known causes or effective therapies. Although lung transplantation is the only definitive therapy for many end stage pulmonary diseases including IPF, chronic rejection (OB) sets in resulting in 50% five-year survival rate for lung transplant recipients - the worst of all solid organ transplant recipients. Recent studies demonstrate inflammatory surroundings and dysregulated epithelial repair as a key event responsible for fibrotic diseases such as IPF and OB. It has been observed that type V collagen [col (V)], an autoantigen, has a key role in IPF and this col (V) autoimmunity correlates with localized IL-17 gene expression. A recent study published in Journal of Experimental Medicine has shown an additive fibrotic effect of IL-1? and IL-17. We have observed that neutralizing IL-17A/F protects lungs from developing fibrosis. EMT may be a potential mechanism contributing towards fibrosis and the current proposal offers the excitement for the possibility of discovering IL-17 as a novel promoter of EMT, and a plausible link between inflammation and fibrosis. Our preliminary studies provide a strong rationale for the hypothesis that IL-17 induces EMT in airway epithelial cells. Specifically, we propose: (1) To determine the role of IL-17A or IL-17F or both in the induction of EMT in airway epithelial cells. (2) To determine specific enzymes that trigger and control this event mediated by IL-17A or IL-17F or both. (3) To determine the role of IL-17A or IL-17F or both in the induction of EMT in two experimental mouse models. We will also use mice with fluorescent protein tagged to specific airway cell types and determine their fate in a fibrotic lung. The results of this research promise the identification of a novel biomarker for patients with predisposition to IPF and OB and to demonstrate the feasibility of developing novel treatment strategies for IPF and OB.