Respiratory Syncytial Virus Induces TLR3 Protein and Protein Kinase R, Leading to Increased Double-Stranded RNA Responsiveness in Airway Epithelial Cells

Respiratory syncytial virus (RSV) preferentially infects airway epithelial cells, causing bronchiolitis, upper respiratory infections, asthma exacerbations, chronic obstructive pulmonary disease exacerbations, and pneumonia in immunocompromised hosts. A replication intermediate of RSV is dsRNA. This is an important ligand for both the innate immune receptor, TLR3, and protein kinase R (PKR). One known effect of RSV infection is the increased responsiveness of airway epithelial cells to subsequent bacterial ligands (i.e., LPS). In this study, we examined a possible role for RSV infection in increasing amounts and responsiveness of another TLR, TLR3. These studies demonstrate that RSV infection of A549 and human tracheobronchial epithelial cells increases the amounts of TLR3 and PKR in a time-dependent manner. This leads to increased NF-kappaB activity and production of the inflammatory cytokine IL-8 following a later exposure to dsRNA. Importantly, TLR3 was not detected on the cell surface at baseline but was detected on the cell surface after RSV infection. The data demonstrate that RSV, via an effect on TLR3 and PKR, sensitizes airway epithelial cells to subsequent dsRNA exposure. These findings are consistent with the hypothesis that RSV infection sensitizes the airway epithelium to subsequent viral and bacterial exposures by up-regulating TLRs and increasing their membrane localization.