Chicken interferon α (ChIFN-α) and ChIFN-β are type I IFNs that are important antiviral cytokines in the innate immune system. In the present study, we identified the virus-induced expression of ChIFN-α and ChIFN-β in chicken fibroblast DF-1 cells and systematically evaluated the antiviral activities of recombinant ChIFN-α and ChIFN-β by cytopathic-effect (CPE) inhibition assays. We found that ChIFN-α exhibited stronger antiviral activity than ChIFN-β in terms of inhibiting the replication of vesicular stomatitis virus, Newcastle disease virus and avian influenza virus, respectively. To elucidate the mechanism of differential antiviral activities between the two ChIFNs, we measured the relative mRNA levels of IFN-stimulated genes (ISGs) in IFN-treated DF-1 cells by real-time PCR. ChIFN-α displayed greater induction potency than ChIFN-β on several ISGs encoding antiviral proteins and MHC-I, whereas ChIFN-α was less potent than ChIFN-β for inducing ISGs involved in signaling pathways. In conclusion, ChIFN-α and ChIFN-β presented differential induction potency on various sets of ISGs, and the stronger antiviral activity of ChIFN-α is likely attributed to the greater expression levels of downstream antiviral ISGs.

Influenza A virus (IAV) is an important pathogen that has a wide range of hosts and represents a threat to the health of humans and several animal species. IAV infection can induce the transcription of many genes in the host. In the present study, we demonstrated for the first time that three different strains of H1N1 IAV induce the expression of an IFN-stimulated gene, ISG20. We determined the antiviral activity of ISG20 against IAV because ISG20 inhibited viral protein expression and reduced the progeny viral titer dependent upon its exonuclease activity. To elucidate the detailed mechanism of ISG20, we further demonstrated that ISG20 impairs the polymerase activity and inhibits both the replication and transcription levels of the M1 and NP genes. Notably, we identified that ISG20 colocalizes and interacts with NP during IAV infection, while exonuclease-inactive mutant ISG20 lacked association with NP, indicating that ISG20 inhibits IAV replication by interacting with NP. Together, these data provide a detailed explanation for the specific antiviral action of ISG20 and suggest that ISG20 may act as a promising antiviral drug candidate against IAV.