The macrolide antibiotic azithromycin improves lung function and prognosis among patients with cystic fibrosis or diffuse panbronchiolitis, independently of bacterial eradication. Anti-inflammatory effects have been implicated, but data from in vivo studies are scarce, and the link between abnormal electrolyte content in airway surface liquid and bronchial infections remains uncertain.In the present study, we treated human airway epithelia on filter supports with azithromycin and monitored transepithelial electrical resistance. We found that azithromycin increased transepithelial electrical resistance of airway epithelia in a dose-dependent manner. Immunocytochemistry and Western blotting showed that addition of azithromycin changed the locations of proteins in cell cultures and induced processing of the tight junction proteins claudin-1 and claudin-4, occludin, and junctional adhesion molecule-A. These effects were reversible, and no effect was seen when cells were treated with penicillin or erythromycin. The data indicate that azithromycin increases the transepithelial electrical resistance of human airway epithelia by changing the processing of tight junction proteins. The results are novel and may help explain the beneficial effects of azithromycin in patients with cystic fibrosis, diffuse panbronchiolitis, and community-acquired pneumonia.

Due to the cellular complexity of the airway epithelium, it is important to carefully define bronchial cell lines that capture the phenotypic traits of a particular cell type. We describe the characterization of a human bronchial epithelial cell line, VA10. It was established by transfection of primary bronchial epithelial cells with retroviral constructs containing the E6 and E7 oncogenes from HPV16. The cell line has been cultured for over 2 yr, a total of 60 passages. Although prolonged culture resulted in increased chromosomal instability, no major phenotypic drift in marker expression was observed. The cells expressed cytokeratins 5, 13, 14, and 17 suggesting a basal-like phenotype. This was further supported by the expression of alpha6beta4 integrins and the basal cell-associated transcription factor p63. The VA10 cell line generated high transepithelial electrical resistance in suspended and air-liquid interface culture, indicating functionally active tight junction (TJ) complexes. Immunocytochemistry showed the typical reticular structures of occludin and TJ-associated F-actin. VA10 produced pseudostratified layer in air-liquid interface culture with expression of p63 restricted to the basal layer. Furthermore, VA10 produced round colonies when cultured in laminin-rich reconstituted basement membrane, and immunostaining of claudin-1 and the basolateral marker beta4 integrin revealed colonies that generated polarization as expected in vivo. These data indicate that VA10 epithelia have the potential to model the bronchial epithelium in vivo and may be useful to study epithelial regeneration and repair and the effect of chemicals and potential drug candidates on TJ molecules in airway epithelia.

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