Antiviral activity of R. Officinalis extract against hRSV. (A) Anti-hRSV effects of extracts of A. altissima, C. atratum, and R. officinalis. A549 cells (5 × 104 cells/well) were infected with hRSV A2 (1000 pfu) and treated with different concentrations of total extracts or vehicle (DMSO). Expression of hRSV fusion (F) protein was assessed by microneutralization assay using an anti-F antibody. The assay was performed in duplicate and data represent means ± SD. (B) Viral yield-reduction assay. A549 cells were treated with vehicle or 20 μg/ml of the indicated compounds 1 hour prior to hRSV infection (0.5 MOI). Viruses were harvested 3 days after infection and titrated by plaque assay. Data represent number of plaques (means ± SD). * p < 0.05 versus vehicle. ** p < 0.01 versus vehicle.