Human respiratory syncytial virus (RSV) is the leading cause of acute lower respiratory infections in infants and Toll-like receptors (TLRs) are the first line of host defense against such infections. In this study, we aimed to elucidate the antiviral effect of TLR3 against RSV infection. The human TLR3 gene was either transiently or stably overexpressed in A549 cells and they were infected with the Long strain of RSV. In both cases, RSV production determined by plaque assay was modestly but significantly decreased in the TLR3-overexpressed cells compared with control cells. Less interferon (IFN)-β, measured by ELISA, was produced in the supernatant of the TLR3- overexpressed cells. Neutralization of IFN-β in the supernatant of the TLR3-overexpressed cells failed to increase RSV production to the same level as controls. These results indicate that TLR3 has modest anti-RSV activity and IFN-β seems not to be a significant mediator of this activity
