The antiviral activity of Thuja orientalis folium against Influenza A virus

• Thuja orientalis folium inhibits influenza A viral infection. • Thuja orientalis folium significantly inhibits influenza viral binding and entry to the cells by modulating hemagglutinin. • Thuja orientalis folium represses the neuraminidase activity of the influenza virus. • Thuja orientalis folium contains a strong virucidal effect at the early phase of viral infection. Thuja orientalis Folium (TOF) has been prescribed traditionally as an expectorant for inflammatory airway disease. In this study, we evaluated the anti-influenza A virus (IAV) activity of TOF by detecting GFP expressed by influenza A virus (A/PR/8/34-GFP) infection. The fluorescence microscopy and fluorescence-activated cell sorting analysis showed that TOF potently inhibited IAV infection, dose-dependently. Consistently, immunofluorescence and Q-PCR analysis results confirmed TOF significantly represses IAV protein and RNA expression. TOF inhibited IAV infection at the binding and entry step upon viral infection and interferes with HA protein. Further, TOF exhibited a virucidal effect and inhibited the neuraminidase activity of IAV. Additionally, TOF prevented the cytopathic effect caused by H1N1 and H3N2 IAV infection. Amentoflavone among the constituents in TOF exerted the strongest anti-IAV effect. Myricetin, quercetin, and quercitrin also inhibited IAV infection. However, the potent anti-IAV effect of TOF may be related to the synergistic effect of constituents, not by a single specific compound. Our results suggest TOF exhibits a significant inhibitory effect against IAV infection at multi-stages via the blockage of viral attachment and entry, inhibition of neuraminidase, and induction of virucidal effects.