Twenty-eight years after the discovery of the CFTR gene, the causes of cystic fibrosis (CF) airway disease remain controversial, we still lack answers to many critical questions, our therapies are inadequate, and CF remains a life limiting and too often lethal disease. A major impediment to progress has been lack of CF animal models with a lung disease phenotype resembling humans with CF. We developed pigs with targeted alterations of the CFTR gene. CF pigs spontaneously develop the hallmark features of CF lung disease, including airway infection, inflammation, airway wall remodeling, mucus accumulation, and airway obstruction. Within hours of birth, CF pigs fail to eradicate bacteria as effectively as wild-type pigs. At least two host defense defects, reduced antimicrobial activity in airway surface liquid (ASL) and impaired mucociliary transport (MCT) contribute. Both were caused by abnormally acidic airway liquid. In this Program three highly accomplished investigators will use CF pigs to answer fundamental questions about CF lung disease. Together, the three projects will discover how loss of CFTR function affects: a) submucosal gland function, the properties of mucus, and MCT; b) ASL pH and proton secretion via ATP12A; and, c) small airways function, a likely site of CF disease pathogenesis. The Project Leaders and their teams have an outstanding track record of collaborative CF research, and here they sharpen their focus to a common goal. Their highly creative research is supported by five cores that provide innovative infrastructure and services. By further educating CF pathogenesis, it will accelerate discovery of novel therapies for this lethal disease.