*2.9. Syncytium Formation Assay*

The ability of the herb extract and acteoside to block cell to cell spread was evaluated using GFP expression in the cells. HEp2 cells were cultured in 12 well cell culture plates (2.5 <sup>×</sup> 105 cells/well) and incubate for 12 h. Medium was changed to DMEM containing 1% FBS and cells were infected with RSV-GFP (0.1 MOI) for 2 h. Cells were treated with PAE/CTE or acteoside once replacing the medium with DMEM containing 10% FBS. After 48 h incubation cells were washed with cooled PBS and cell images were taken under 400 magnifications. Syncytium formation was quantified with imageJ 1.48 program (https://imagej.net/ImageJ).

#### *2.10. RSV-GFP Challenge Experiment in Mouse Model*

Five-week-old female BALB/c mice were purchased from orient bio (South Korea) and acclimated for three days under experimental condition prior to use. Mice were separated into experimental groups as virus infected, and herb or acteoside treated group (*n* = 5), virus only infected group (*n* = 5) and un infected group (*n* = 2). Mice were anesthetized with ketamine for a short time period, and RSV-GFP 1 <sup>×</sup> 106 Plaque forming unit (PFU) per mice in the total volume 28 <sup>μ</sup>L was infected intranasally. Mice were orally administered 0.5 mg/mL concentration of PAE or CTE at a total volume of 200 μL at 6, 12, 18 and 24 hpi. In the case of acteoside, 80 mg/Kg of body weight/mice was intraperitonially administered to mice at 6 hpi in the total volume of 100 μL. Lung tissues from euthanized mice were collected aseptically at 3- and 5-day post infection (dpi). Lung RSV titration was determined by RSV-G protein mRNA transcription fold quantification. RSV-G protein mRNA level was quantified as described before.
