*2.5. Determination of E*ff*ective Concentration (EC50) of Extracts and Acteoside*

HEp2 cells were grown in 24-well cell culture plates (1.25 <sup>×</sup> <sup>10</sup><sup>5</sup> cells/well) and incubated at 37 ◦C in a 5% CO2 atmosphere. After 12 h, the medium was replaced with DMEM containing 1% FBS and cells were infected with RSV-GFP (0.1 MOI) for 2 h. Then cells were washed with PBS once, and the medium was replaced with DMEM containing 10% FBS. Cells were treated with indicated concentrations of herb extracts or acteoside. The experiment was performed in triplicate. GFP expression was measured 48 hpi with the Glomax multi-detection system (Promega, Fitchburg, WI, USA) according to the manufacturer's instructions. The EC50 values were then calculated as the extract concentration yielding 50% GFP expression.
