Analysis of the anti-hRSV activity of carnosic acid. A549 cells (A) and HEp-2 cells (B) were treated with different concentrations of carnosic acid. Cells were infected with hRSV A2 virus (MOI 0.5) for 48 hours, followed by RNA preparation and RT-qPCR. The relative amount of RNA for hRSV F, NS2 and SH protein were determined by RT-qPCR. Data represent means ± SD. ** p < 0.01 versus Mock-treated (Mock). A.U.: Arbitrary unit. (C) The effect of carnosic acid on influenza A virus replication was tested in A549 cells in a similar manner. Cells were infected with influenza A/PR8 virus (MOI 0.01) for 24 hours and the relative amount of RNA for influenza A virus NP and P protein were determined by RT-qPCR. A.U.: Arbitrary unit. (D) Inhibition of progeny virus production by carnosic acid. A549 cells were treated with the indicated compounds 1 hour prior to hRSV infection (MOI 0.1). Two and four days after infection, progeny viruses were harvested and titrated by plaque assay. All the experiments were performed in triplicate and data represent number of plaques (means ± SD). N/D.: not detected. *** p < 0.001 versus Mock-treated (Mock).