S100A9 activates TLR4/MyD88 pathway and activation of TLR4/MyD88 pathway is essential for IAV-induced pro-inflammatory response.

<p>Primary bone marrow derived macrophages (BMDM) isolated from wild-type (WT) and TLR4 knockout (KO) mice were incubated with purified recombinant mouse S100A9 protein (5 ug/mL). The medium supernatant was collected to assess levels of mouse IL-6 (<b>A</b>) and mouse TNF-α(TNF) (<b>B</b>) by ELISA. (<b>C</b>) IL-6 production from S100A9 protein treated WT and MyD88 KO BMDMs. (<b>D</b>) BMDM isolated from WT, TLR4 KO and MyD88 KO mice were infected with IAV (2 MOI). At 12 h and 24 h post-infection time-period, medium supernatant was collected to assess levels of mouse IL-6 by ELISA. (<b>E</b>) TNF production from IAV infected WT and TLR4 KO BMDMs. The values represent the mean ± standard deviation from three independent experiments performed in triplicate, *p<0.05 using a Student's t test. Veh; cells incubated with HBSS buffer (vehicle control).