J774a 1 cell line

The mouse monocyte macrophage (J774A.1 cell line) was purchased from Procell Life Science and Technology Co., Ltd. (Wuhan, China) and cultured into high-glucose DMEM medium (No.11965118, ThermoFisher Scientific, Waltham, MA, USA) containing 10% fetal bovine serum (No.35-079-CV, Corning, Somerville, MA, USA) and 1% antibiotic penicillin-streptomycin (No. YM-S1033, Corning, USA) at 37 °C under 5% CO₂. The mouse-adapted IAV PR8 strain (strain A/Puerto Rico/8/1934 (H1N1)) was propagated in 9-day-old chicken embryos at 35 °C for 48 h, then at 4 °C for 12 h and stored in the refrigerator at −80 °C in our laboratory. The titer of the virus was 10^−5.4/0.1 mL in J774A.1 cell using 50% tissue culture infectious dose (TCID₅₀) as standard. The SBE solution is provided by Shanghai Kaibao Pharmaceutical Co., Ltd. (No.1808320, Shanghai, China) and obtained by methanol extraction under ultrasonication from dried Scutellaria baicalensis roots. Before experiments, the SBE solution was filtered by 0.22 µm micro membranes and the major components were identified using ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF MS).