RNA interference of avian influenza virus H5N1 by inhibiting viral mRNA with siRNA expression plasmids.

Avian influenza virus H5N1 causes widespread infection in the birds and human respiratory tract, but existing vaccines and drug therapy are of limited value. Here we show that small interfering RNAs (siRNAs) specific for conserved regions of the viral genome can potently inhibit influenza virus production in cell lines, embryonated chicken eggs and BALB/c mice. siRNA expression plasmid pBabe-Super was chosen in the study, which directed the synthesis of small interfering RNAs in cells. The inhibition depended on the presence of a functional antisense strand in the small interfering RNA duplex, suggesting that viral mRNA is the target of RNA interference (RNAi). Among the three small interfering RNA expression plasmids we designed, we found that small interfering RNA for nucleocapsid protein (NP) had a specific effect in inhibiting the accumulation of RNAs in infected cells because of a critical requirement for newly synthesized nucleocapsid proteins in avian influenza viral RNA transcription and replication. The findings reveal that newly synthesized nucleocapsid, polymerase A (PA) and polymerase B1 (PB1) proteins are required for avian influenza virus transcription and replication and provide a basis for the development of small interfering RNAs as prophylaxis and therapy for avian influenza infection in birds and humans.