2.2. Cell Viability Assay
The cytotoxic effects of AS-IV (Solarbio, CAS:84687-43-4, HPLC≥98%, Beijing, China) on A549 cells were detected by Cell Counting Kit-8 (CCK-8, CK04, Dojindo, Japan). In brief, the A549 cells were seeded in 96-well plates at a density of 1 × 104 cells per well, and AS-IV was diluted to the following concentrations: 1000, 500, 250, 125, 62.5, 31.2 and 0μ M added to the cells. After 72h, 10 μ L CCK-8 was added to each well immediately and continued to incubate for 2h. The cell viability was calculated by reading the optical density (OD) value at 450nm with a microplate reader (Thermo Fisher Scientific). The effect of AS-IV on the viability of A549 cells infected with the influenza virus was also detected by the cck8 method. A549 cells were seeded in 96-well plates with partitions, and the experiment was set as the negative control group (NC), IAV group, and IAV+ AS-IV group. 2 h after virus infection, the cells were cleaned with PBS solution twice, and then AS-IV solution was added to IAV+ AS-IV group, and maintenance medium was added to the other groups. OD values were determined after continuous culture for 24 h.