Real-time reverse transcription-PCR of influenza viral Nucleoprotein (NP) RNA levels normalized to beta-actin. MDCK cells were infected with influenza viruses A/PR/8/34 (H1N1) (1 × 106 PFU). After 1 h, viruses were removed. MDCK cells were treated with dandelion extracts (2.5 mg/ml) or untreated with drugs. Total RNA extraction was performed at 16 h after influenza virus infection and the levels of intracellular influenza viral RNA were measured. Influenza viral RNA levels normalized to beta-actin. (* p < 0.01). Mock-infected cells were also analyzed.