*3.3. Synergistic Anti-RSV E*ff*ect of PAE and CTE in HEp2 Cells*

Next, synergistic anti-RSV effect of PAE and CTE were determined in HEp2 cells. HEp2 cells were infected with RSV-GFP (0.1MOI) for 2 h in DMEM containing 1% FBS. Then cells were treated with PAE, CTE along or as a combination (1:1) in DMEM containing 10% FBS. At 48 hpi GFP absorbance were taken, and the virus titer was determined by standard plaque assay. GFP expression level was significantly reduced with the increasing dose either PAE, CTE along or combination treatment (Figure 3A). However, there was no significant difference observed in combined herb extract treatment compared to individual herb extract treatment at the same final dose treatment. Furthermore, a similar result was observed in the virus replication quantification by standard plaque assay (Figure 3B). Therefore, this data demonstrates that PAE or CTE does not enhance anti-RSV activity synergistically.

**Figure 2.** The therapeutic effect of PAE and CTE against RSV-GFP infection. HEp2 cells were seeded into 12 well cell culture plates and left for 12 h. Medium was changed with DMEM containing 1% FBS and cells were infected with RSV-GFP (0.1MOI) for 2 h. (**A**,**B**) RSV-GFP infected cells were treated with 50 μg/mL PAE or CTE at different times after post infection as indicated or left untreated, and GFP expression level was measured at 48 hpi. (**C**,**D**) Virus titer was measured from both supernatant and cells by standard plaque assay at 48 hpi and expressed as PFU. (**E**,**F**) Cells were treated with 50 μg/mL PAE or CTE, and GFP expression level was measured at different time after virus infection as indicated. GFP absorbance and virus titer expressed as mean ± SD. Error bars indicate the range of values obtained from counting duplicate in three independent experiments (\* *p* < 0.05, \*\* *p* < 0.01 and \*\*\* *p* < 0.001 regarded as significant difference).
