To explore the prophylactic and therapeutic effects of small interfering RNA (siRNA) targeting nucleocapsid protein (NP) gene on influenza A virus (IAV).

On the basis of sequencing IAV, the siRNA targeting NP segment of IAV was synthesized. The changes of IAV loads in the Madin-Darby canine kidney (MDCK) were observed after siRNA transfection and IAV infection or after IAV infection and siRNA transfection.

The virus load was lower or much lower in the siRNA-transfected cells than the transfection agent controls (P<0.05 for 20 pmol siRNA group and 40 pmol siRNA group, and P<0.01 for 80 pmol siRNA group). When the cells were infected with IAV prior to siRNA transfection, the virus load was significantly lower in the siRNA group than the controls (P<0.01) and lower in the siRNA group than the transfection agent group (P<0.05). The immunohistochemical results showed that the expression of NP protein was significantly lower in the siRNA group than the controls (P<0.01), no matter the MDCK cells were firstly transfected with siRNA or infected with IAV.

The production of IAV can be inhibited by siRNAs targeting NP in a dose-dependent manner and can also be inhibited by siRNA targeting NP after the cells were infected with IAV. The inhibition of IAV by siRNA targeting NP is resulted from the interference with NP protein synthesis.