The Role of Neutrophils in Cystic Fibrosis Pathogenesis - ABSTRACT Cystic fibrosis (CF) is a life-threatening genetic disorder, caused by mutations in the gene that encodes cystic fibrosis transmembrane-conductance regulator (CFTR), a cAMP-activated chloride channel. This disease affects multiple organ systems, including the lung, intestine and other epithelium-lined organs. The most destructive pathologies are characterized to be chronic bacterial infection, persistent neutrophilic inflammation and mucopurulent duct obstruction. As bacterial infection and neutrophilic inflammation are highly related to innate immune cells, neutrophils should be a major player in the disease pathogenesis. However, the prevailing belief holds that CF is a disorder resulting from the malfunction of epithelial cells, and all the clinical consequences stem from this epithelial anomaly. As a result, the significance of neutrophils in the disease process has been underappreciated. Our previous research discovered that CFTR is pre-made and pre-stored in the secretory vesicles within mature neutrophils, and is critically needed for transporting chloride to the phagosomes to produce hypochlorous acid (HOCl or bleach) for neutrophil anti-microbial function. However, it is unknown when the CFTR protein is made during neutrophil differentiation. Moreover, when infection occurs in the lung, neutrophils are mobilized from the circulation to the lung lumen. Under this condition, how neutrophils acquire chloride to support their essential host defense function has never been elucidated. Furthermore, lung health is collectively protected by multiple types of cells, including permanent lung-resident cells, such as pulmonary epithelial cells and tissue macrophages, and transient lung-recruited immune cells, notably neutrophils and monocytes/macrophages. The exact contribution of CF neutrophils to the overall CF infection and inflammation in this system is undetermined. To fill these gaps in knowledge, we have laid out a detailed plan in this application to address the following outstanding questions: 1) how CFTR is expressed during neutrophil steady-state or infection-precipitated emergency granulopoiesis, 2) whether chloride acquisition by neutrophils on an epithelial surface is limited by epithelial CFTR function, and 3) to what extent the CF neutrophil defect contributes to the CF infection and inflammation. This research will produce unprecedented data to refine the current paradigm of CF disease. New insights will be provided to establish the critical role of neutrophils in the disease pathogenesis. Novel therapeutic targets may be revealed for developing innovative and effective treatments to combat established infection and inflammation in CF.
