Lung inflammation and simulated airway resistance in infants with cystic fibrosis.

Cystic fibrosis (CF) is characterized by small airway disease; but central airways may also be affected. We hypothesized that airway resistance estimated from computational fluid dynamic (CFD) methodology in infants with CF was higher than controls and that early airway inflammation in infants with CF is associated with airway resistance. Central airway models with a median of 51 bronchial outlets per model (interquartile range 46,56) were created from chest computed tomography scans of 18 infants with CF and 7 controls. Steady state airflow into the trachea was simulated to estimate central airway resistance in each model. Airway resistance was increased in the full airway models of infants with CF versus controls and in models trimmed to 33 bronchi. Airway resistance was associated with markers of inflammation in bronchoalveolar lavage fluid obtained approximately 8 months earlier but not with markers obtained at the same time. In conclusion, airway resistance estimated by CFD modeling is increased in infants with CF compared to controls and may be related to early airway inflammation.

Association of Antibiotics, Airway Microbiome, and Inflammation in Infants with Cystic Fibrosis.

RATIONALE: The underlying defect in the cystic fibrosis (CF) airway leads to defective mucociliary clearance and impaired bacterial killing, resulting in endobronchial infection and inflammation that contributes to progressive lung disease. Little is known about the respiratory microbiota in the early CF airway and its relationship to inflammation. OBJECTIVES: To examine the bacterial microbiota and inflammatory profiles in bronchoalveolar lavage fluid and oropharyngeal secretions in infants with CF. METHODS: Infants with CF from U.S. and Australian centers were enrolled in a prospective, observational study examining the bacterial microbiota and inflammatory profiles of the respiratory tract. Bacterial diversity and density (load) were measured. Lavage samples were analyzed for inflammatory markers (interleukin 8, unbound neutrophil elastase, and absolute neutrophil count) in the epithelial lining fluid. RESULTS: Thirty-two infants (mean age, 4.7 months) underwent bronchoalveolar lavage and oropharyngeal sampling. Shannon diversity strongly correlated between upper and lower airway samples from a given subject, although community compositions differed. Microbial diversity was lower in younger subjects and in those receiving daily antistaphylococcal antibiotic prophylaxis. In lavage samples, reduced diversity correlated with lower interleukin 8 concentration and absolute neutrophil count. CONCLUSIONS: In infants with CF, reduced bacterial diversity in the upper and lower airways was strongly associated with the use of prophylactic antibiotics and younger age at the time of sampling; less diversity in the lower airway correlated with lower inflammation on bronchoalveolar lavage. Our findings suggest modification of the respiratory microbiome in infants with CF may influence airway inflammation.

Effect of polarized release of CXC-chemokines from wild-type and cystic fibrosis murine airway epithelial cells.

The respiratory epithelium lining the airway relies on mucociliary clearance and a complex network of inflammatory mediators to protect the lung. Alterations in the composition and volume of the periciliary liquid layer, as occur in cystic fibrosis (CF), lead to impaired mucociliary clearance and persistent airway infection. Moreover, the respiratory epithelium releases chemoattractants after infection, inciting airway inflammation. However, characterizing the inflammatory response of primary human airway epithelial cells to infection can be challenging because of genetic heterogeneity. Using well-characterized, differentiated, primary murine tracheal cells grown at an air-liquid interface, which provides an in vitro polarized epithelial model, we compared inflammatory gene expression and secretion in wild-type and ΔF508 CF airway cells after infection with Pseudomonas aeruginosa. The expression of several CXC-chemokines, including macrophage inflammatory protein-2, small inducible cytokine subfamily member 2, lipopolysaccharide-induced chemokine, and interferon-inducible cytokine-10, was markedly increased after infection, and these proinflammatory mediators were asymmetrically released from the airway epithelium, predominantly from the basolateral surface. Equal amounts of CXC-chemokines were released from wild-type and CF cells. Secreted mediators were concentrated in the thin, periciliary fluid layer, and the dehydrated apical microenvironment of CF airway epithelial cells amplified the inflammatory signal, potentially resulting in high chemokine concentration gradients across the epithelium. Consistent with this observation, the enhanced chemotaxis of wild-type neutrophils was detected in CF airway epithelial cultures, compared with wild-type cells. These data suggest that P. aeruginosa infection of the airway epithelium induces the expression and polarized secretion of CXC-chemokines, and the increased concentration gradient across the CF airway leads to an exaggerated inflammatory response.

Cathepsin-G interferes with clearance of Pseudomonas aeruginosa from mouse lungs.

The cystic fibrosis airway is susceptible to Pseudomonas aeruginosa infection, which stimulates an intense inflammatory response leading to airway obstruction and bronchiectasis. Neutrophils migrate into the airway, and once there, release high concentrations of neutral serine proteases during phagocytosis and in death. In particular, neutrophil elastase is central to progression of bronchiectasis by interfering with bacterial clearance and directly perpetuating the inflammatory response in the airway. Using a murine model of endobronchial inflammation, we found that a different neutrophil-derived serine protease, cathepsin G, inhibited the host's ability to clear Pseudomonas from the lung, based on a 1-log reduction in bacteria recovered from cathepsin G-deficient mice. Higher antibody concentrations were found in respiratory epithelial lining fluid from mice lacking cathepsin G, but there was no difference in other opsonins, such as surfactant proteins A and D. Chemokine levels measured in the lung correlated with bacterial burden and not the animal's genotype, indicating that airway inflammation was not affected by the presence (or absence) of specific serine proteases. These findings suggest that cathepsin G interferes with airway defenses, showing that proteases other than neutrophil elastase have roles in the pathogenesis of suppurative airway diseases.