Rhinovirus and Bacteria Synergistically Induce IL-17C Release from Human Airway Epithelial Cells To Promote Neutrophil Recruitment.

Virus-bacteria coinfections are associated with more severe exacerbations and increased risk of hospital readmission in patients with chronic obstructive pulmonary disease (COPD). The airway epithelium responds to such infections by releasing proinflammatory and antimicrobial cytokines, including IL-17C. However, the regulation and role of IL-17C is not well understood. In this study, we examine the mechanisms regulating IL-17C production and its potential role in COPD exacerbations. Human bronchial epithelial cells (HBE) obtained from normal, nontransplanted lungs or from brushings of nonsmokers, healthy smokers, or COPD patients were exposed to bacteria and/or human rhinovirus (HRV). RNA and protein were collected for analysis, and signaling pathways were assessed with pharmacological agonists, inhibitors, or small interfering RNAs. HBE were also stimulated with IL-17C to assess function. HRV-bacterial coinfections synergistically induced IL-17C expression. This induction was dependent on HRV replication and required NF-κB-mediated signaling. Synergy was lost in the presence of an inhibitor of the p38 MAP kinase pathway. HBE exposed to IL-17C show increased gene expression of CXCL1, CXCL2, NFKBIZ, and TFRC, and release CXCL1 protein, a neutrophil chemoattractant. Knockdown of IL-17C significantly reduced induction of CXCL1 in response to HRV-bacterial coinfection as well as neutrophil chemotaxis. HBE from healthy smokers release less IL-17C than cells from nonsmokers, but cells from COPD patients release significantly more IL-17C compared with either nonsmokers or healthy smokers. These data suggest that IL-17C may contribute to microbial-induced COPD exacerbations by promoting neutrophil recruitment.

Human ß-defensin-2 production upon viral and bacterial co-infection is attenuated in COPD.

Viral-bacterial co-infections are associated with severe exacerbations of COPD. Epithelial antimicrobial peptides, including human ß-defensin-2 (HBD-2), are integral to innate host defenses. In this study, we examined how co-infection of airway epithelial cells with rhinovirus and Pseudomonas aeruginosa modulates HBD-2 expression, and whether these responses are attenuated by cigarette smoke and in epithelial cells obtained by bronchial brushings from smokers with normal lung function or from COPD patients. When human airway epithelial cells from normal lungs were infected with rhinovirus, Pseudomonas aeruginosa, or the combination, co-infection with rhinovirus and bacteria resulted in synergistic induction of HBD-2 (p<0.05). The combination of virus and flagellin replicated this synergistic increase (p<0.05), and synergy was not seen using a flagella-deficient mutant Pseudomonas (p<0.05). The effects of Pseudomonas aeruginosa were mediated via interactions of flagellin with TLR5. The effects of HRV-16 depended upon viral replication but did not appear to be mediated via the intracellular RNA helicases, retinoic acid-inducible gene-I or melanoma differentiation-associated gene-5. Cigarette smoke extract significantly decreased HBD-2 production in response to co-infection. Attenuated production was also observed following co-infection of cells obtained from healthy smokers or COPD patients compared to healthy controls (p<0.05). We conclude that co-exposure to HRV-16 and Pseudomonas aeruginosa induces synergistic production of HBD-2 from epithelial cells and that this synergistic induction of HBD-2 is reduced in COPD patients. This may contribute to the more severe exacerbations these patients experience in response to viral-bacterial co-infections.