Abstract
Despite increased morbidity associated with secondary respiratory viral infections in cystic fibrosis (CF) patients with chronic Pseudomonas aeruginosa infection, the underlying mechanisms are not well understood. Here, we investigated the effect of P. aeruginosa infection on the innate immune responses of bronchial epithelial cells to rhinovirus (RV) infection. CF cells sequentially infected with mucoid P. aeruginosa (MPA) and RV showed lower levels of interferons (IFNs) and higher viral loads than those of RV-infected cells. Unlike results for CF cells, normal bronchial epithelial cells coinfected with MPA/RV showed higher IFN expression than RV-infected cells. In both CF and normal cells, the RV-stimulated IFN response requires phosphorylation of Akt and interferon response factor 3 (IRF3). Preinfection with MPA inhibited RV-stimulated Akt phosphorylation and decreased IRF3 phosphorylation in CF cells but not in normal cells. Compared to normal, unstimulated CF cells or normal cells treated with CFTR inhibitor showed increased reactive oxygen species (ROS) production. Treatment of CF cells with antioxidants prior to MPA infection partially reversed the suppressive effect of MPA on the RV-stimulated IFN response. Together, these results suggest that MPA preinfection inhibits viral clearance by suppressing the antiviral response particularly in CF cells but not in normal cells. Further, increased oxidative stress in CF cells appears to modulate the innate immune responses to coinfection.