Sherif E. Gabriel

The airway epithelium occupies a critical environmental interface, protecting the host from a wide variety of inhaled insults, including chemical and particulate pollutants and pathogens. The coordinated regulation of ion and water transport, mucous secretion, and cilia beating underlies mucociliary clearance. Physical trapping and removal of harmful substances, in combination with baseline or inducible secretion of antimicrobial factors, antioxidants, and protease inhibitors and recruitment of nonspecific inflammatory cells (neutrophils, monocytes), constitutes airway innate host defense.

The effect of the number of cystic fibrosis (CF) alleles on cholera toxin (CT)-induced intestinal secretion was examined in the CF mouse model. CF mice that expressed no CF transmembrane conductance regulator (CFTR) protein did not secrete fluid in response to CT. Heterozygotes expressed 50 percent of the normal amount of CFTR protein in the intestinal epithelium and secreted 50 percent of the normal fluid and chloride ion in intestinal epithelium and secreted 50 percent of the normal fluid and chloride ion and fluid secretion suggests that CF heterozygotes might possess a selective advantage of resistance to cholera.

The cystic fibrosis transmembrane conductance regulator (CFTR) gene encodes an adenosine 3',5'-monophosphate (cyclic AMP)-activated chloride channel. In cystic fibrosis (CF) patients, loss of CFTR function because of a genetic mutation results in defective cyclic AMP-mediated chloride secretion across epithelia. Because of their potential role as an animal model for CF, mice with targeted disruption of the murine CFTR gene [CFTR(-/-)] were tested for abnormalities in epithelial chloride transport. In both freshly excised tissue from the intestine and in cultured epithelia from the proximal airways, the cyclic AMP-activated chloride secretory response was absent in CFTR(-/-) mice as compared to littermate controls. Thus, disruption of the murine CFTR gene results in the chloride transport abnormalities predicted from studies of human CF epithelia.