Figure 3.

Quercetin performed the inhibitory activity in the initial stage of influenza virus infection. (A) The cells were infected with influenza A/Puerto Rico/8/34, and the virus-infected cells were then treated with quercetin in 0–2 h, 2–5 h, 5–8 h, 8–10 h and 0–10 h time intervals respectively. At 10 h post-infection, the viral HA protein was detected by Western blotting; (B) The cells were infected with influenza A/Puerto Rico/8/34, and the cells were then treated with quercetin in 0–2 h, 2–5 h, 5–8 h, 8–10 h and 0–10 h time intervals respectively. The viral HA mRNA was detected by quantitative real-time PCR at 10 h post-infection; (C) Serially diluted compound was added 1 h before virus infection (−1 h p.i.) or 1 h after virus infection (1 h p.i.). The extent of virus infection in the cell was determined at 48 h post-infection using MTT assay; (D) Different modes of treatment, namely co-treatment, pre-treatment of cells and pre-treatment of virus, were conducted to clarify whether the quercetin targets the host cell or the influenza virus. The protection of quercetin to the virus-infected cell was detected at 48 h post-infection by MTT assay.