Female Balb/c mice 6-12 weeks old were intravenously injected with 100 μg of 5'PPP-RNA, capped 5'-RNA or PBS complexed with in vivo-jetPEI in a volume of 200 μl for 4 days. On day 1, mice were challenged intranasally with a pandemic virus (A/Mexico/4482/09). A separate group of animals that received only 5'PPP-RNA complexed with in vivo-jetPEI without viral challenge were observed to determine changes in body weight and activity. Lungs from control and treated challenged animals were collected on day 4 to determine viral titers using MDCK cells as described earlier.

BACKGROUND: Emergence of drug-resistant strains of influenza viruses, including avian H5N1 with pandemic potential, 1918 and 2009 A/H1N1 pandemic viruses to currently used antiviral agents, neuraminidase inhibitors and M2 Ion channel blockers, underscores the importance of developing novel antiviral strategies. Activation of innate immune pathogen sensor Retinoic Acid Inducible Gene-I (RIG-I) has recently been shown to induce antiviral state. RESULTS: In the present investigation, using real time RT-PCR, immunofluorescence, immunoblot, and plaque assay we show that 5'PPP-containing single stranded RNA (5'PPP-RNA), a ligand for the intracytoplasmic RNA sensor, RIG-I can be used as a prophylactic agent against known drug-resistant avian H5N1 and pandemic influenza viruses. 5'PPP-RNA treatment of human lung epithelial cells inhibited replication of drug-resistant avian H5N1 as well as 1918 and 2009 pandemic influenza viruses in a RIG-I and type 1 interferon dependant manner. Additionally, 5'PPP-RNA treatment also inhibited 2009 H1N1 viral replication in vivo in mice. CONCLUSIONS: Our findings suggest that 5'PPP-RNA mediated activation of RIG-I can suppress replication of influenza viruses irrespective of their genetic make-up, pathogenicity, and drug-sensitivity status.