Cystic fibrosis (CF) patients are hypersusceptible to chronic Pseudomonas aeruginosa lung infections. Cultured human airway epithelial cells expressing the ΔF508 allele of the cystic fibrosis transmembrane conductance regulator (CFTR) were defective in uptake of P. aeruginosa compared with cells expressing the wild-type allele. Pseudomonas aeruginosa lipopolysaccharide (LPS)-core oligosaccharide was identified as the bacterial ligand for epithelial cell ingestion; exogenous oligosaccharide inhibited bacterial ingestion in a neonatal mouse model, resulting in increased amounts of bacteria in the lungs. CFTR may contribute to a host-defense mechanism that is important for clearance of P. aeruginosa from the respiratory tract.Among the most serious manifestations of CF are chronic pulmonary infections with the bacterium P. aeruginosa. The basis for hypersusceptibility of CF patients to this bacterium is not well understood, and the role of mutant CFTR, if any, is not clear. Binding and internalization of respiratory pathogens by epithelial cells followed by desquamation could be an important mechanism for clearing bacteria from the lung. This mechanism has been shown to be important in protecting against bladder infections (1).To investigate whether the most common and severe CFTR mutation (ΔF508) affected uptake of P. aeruginosa, we performed bacterial invasion assays (2) with four cell lines: CFT1, an airway epithelial cell line derived from a CF patient homozygous for ΔF508 CFTR and that is transformed with human papilloma virus 18 E6/E7; CFT1-ΔF508, which expresses a third copy of ΔF508 CFTR introduced by a retrovirus; CFT1-LC3, which expresses a control gene (β-galactosidase) introduced by the same retrovirus; and CFT1-LCFSN, which expresses a functional wild-type human CFTR gene (3). We tested a standard laboratory strain of P. aeruginosa, designated PAOI, and two nonmucoid, LPSsmooth clinical isolates from CF patients (4). Compared with CFT1-LCFSN cells, the three lines expressing ΔF508 CFTR internalized significantly fewer bacterial cells (Fig. 1A). The ΔF508 mutation causes inefficient processing of CFTR, a defect that is partially corrected if the cells are grown at 26°C (5). When epithelial cells were cultured for 72 hours at 26°C there were no longer significant differences in uptake of the P. aeruginosa strains by the cells expressing wild-type or mutant CFTR (Fig. 1B). Because the overall uptake of bacteria at 26°C was low, we performed additional experiments with cells grown for 72 hours at 26°C in which the invasion assay was performed at 37°C for 3 hours, conditions under which surface expression of mutant ΔF508 CFTR is maintained (5). No significant difference in bacterial cell uptake was measured (Fig. 1C), and overall amounts of internalization approached those of the CFT1-LCFSN cells at 37°C. Returning cells expressing ΔF508 CFTR to 37°C for 24 hours after growth for 72 hours at 26°C removes CFTR from the cell surface (5); under these conditions internalization of the bacterial strains ...

The cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride ion channel, but its relationship to the primary clinical manifestation of CF, chronic Pseudomonas aeruginosa pulmonary infection, is unclear. We report that CFTR is a cellular receptor for binding, endocytosing, and clearing P. aeruginosa from the normal lung. Murine cells expressing recombinant human wild-type CFTR ingested 30-100 times as many P. aeruginosa as cells lacking CFTR or expressing mutant ⌬F508 CFTR protein.Purified CFTR inhibited ingestion of P. aeruginosa by human airway epithelial cells. The first extracellular domain of CFTR specifically bound to P. aeruginosa and a synthetic peptide of this region inhibited P. aeruginosa internalization in vivo, leading to increased bacterial lung burdens. CFTR clears P. aeruginosa from the lung, indicating a direct connection between mutations in CFTR and the clinical consequences of CF.

Homozygous mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) cause cystic fibrosis (CF). In the heterozygous state, increased resistance to infectious diseases may maintain mutant CFTR alleles at high levels in selected populations. Here we investigate whether typhoid fever could be one such disease. The disease is initiated when Salmonella typhi enters gastrointestinal epithelial cells for submucosal translocation. We found that S. typhi, but not the related murine pathogen S. typhimurium, uses CFTR for entry into epithelial cells. Cells expressing wild-type CFTR internalized more S. typhi than isogenic cells expressing the most common CFTR mutation, a phenylalanine deleted at residue 508 (delta508). Monoclonal antibodies and synthetic peptides containing a sequence corresponding to the first predicted extracellular domain of CFTR inhibited uptake of S. typhi. Heterozygous deltaF508 Cftr mice translocated 86% fewer S. typhi into the gastrointestinal submucosa than wild-type Cftr mice; no translocation occurred in deltaF508 Cftr homozygous mice. The Cftr genotype had no effect on the translocation of S. typhimurium. Immunoelectron microscopy revealed that more CFTR bound to S. typhi in the submucosa of Cftr wild-type mice than in deltaF508 heterozygous mice. We conclude that diminished levels of CFTR in heterozygotes may decrease susceptibility to typhoid fever.