Lack of applicability of the Enterocyte Chloride ion secretion paradigm to the Pathology of Cystic Fibrosis

This review examines of the concept of a defective chloride channel in epithelial cells being a major cause of cystic fibrotic pathophysiology. The central concept of the defective chloride ion channel paradigm is that faulty CFTR protein or failed delivery of CFTR protein to the mucosal membrane of epithelial cells is the basis of cystic fibrosis. Defective placement or function of CFTR prevents hydration of bronchial mucus that is normally caused by epithelial cells; these are capable through chloride ion secretion of transporting fluid to the mucosal surface. This concept relies heavily on a paradigm taken from intestinal physiology-namely that the intestinal epithelial cell secretes chloride ion and fluid and that this has conferred heterozygote selective advantage in carriers of the cystic fibrosis gene. This present review examines the evidence for that hypothesis and assembles evidence from past studies that it is the smooth muscle cell that is of greater relevance. This review does not aim to provide an overview of current research into cystic fibrosis. The intention is to provide an overview of past research that led to the concept of a failure of epithelial cells to hydrate bronchial mucus because of compromised CFTR function. It is important to present all past evidence for aspects of the chloride secretion hypothesis and its associated heterozygote advantage concept so that the important evidential milestones can be re-assessed