Respiratory syncytial virus infection up-regulates TLR7 expression by inducing oxidative stress via the Nrf2/ARE pathway in A549 cells.
In order to better understand the early pathways of the pathogenesis of, and immune response to, RSV, herein, we explored the relationship between TLR7 expression and oxidative stress induction following RSV infection in A549 cells. We studied the intervening effects of the Nrf2/ARE pathway agonist butylated hydroxyanisole (BHA) and inhibitor trigonelline (TRI) on TLR7 modulation or oxidative stress induction. For comparison purposes, we set up seven treatment groups in this study, including RSV-treated cells, BHA + RSV-treated cells, TRI + RSV-treated cells, normal cell controls, inactivated RSV controls, BHA controls and TRI controls. We measured changes in TLR7, IL-6, TNF-α mRNA using RT-PCR and IL-6, TNF-α and IL-1β protein using ELISA as well as TLR7, Nrf2 and HO-1 protein using Western blot in A549 cells from the different treatment groups. We also assessed changes in cell proliferation and measured changes in ·OH and NO in A549 cells from the different treatment groups. The results indicate that TLR7 up-regulation is related to RSV infection and the induction of oxidative stress and that TLR7 expression was mediated by the anti-inflammatory effects of Nrf2/ARE pathway inhibitors or agonists. Our experiments may help elucidate the underlying pathology of RSV infection and suggest potential therapeutic targets for drug development and the prevention of RSV-induced human diseases.