Influenza A virus (IAV) infection induces secretion of type I interferon (IFN) and activation of p53, which play essential roles in the host defense against tumor development and viral infection. In this study, we knocked down p53 expression by RNA interference. The expression levels of IFN-stimulated genes (ISGs) including IFN regulatory factor (IRF) 5, IRF9, ISG15, ISG20, guanylate-binding protein 1, retinoic acid-inducible gene-I and 2'-5'-oligoadenylate synthetase 1 were significantly attenuated in response to IAV infection and IFN-alpha stimulation in p53-knockdown cells. This attenuated expression of ISGs was associated with enhanced replication of IAV. Pretreatment of p53-knockdown cells with IFN-alpha failed to inhibit IAV replication, indicating impaired antiviral activity. These findings indicate that p53 plays an essential role in the enhancement of the type I IFN-mediated immune response against IAV infection. (C) 2014 Elsevier Inc. All rights reserved.