The effect of avian influenza virus NS1 allele on virus replication and innate gene expression in avian cells

The NS1 gene encoded by Type A influenza virus circulates as two alleles, the A and B allele. The immunomodulatory properties of the NS1 A allele have been thoroughly examined; however, comparisons of allele function have been predominantly made in mammalian systems. Here we show that counter to the current understanding of allele function in mammals, the two alleles similarly regulate elements of the type I interferon (IFN) signaling pathway, including the interferon-inducible genes Mx and 2'-5' oligoadenylate synthase (2'-5' OAS), and IL-6, which share the same induction pathway as the interferons in embryo fibroblasts from chickens, turkeys or ducks. Replication of two reassortant viruses demonstrated that the B allele virus replicates more and to higher titers than the A allele virus in duck cells; however, the A allele virus replicates more in the cells from chickens and turkeys. Finally, chimeric constructs were used to identify a region of the NS1 gene that conferred the statistically significant differences in expression and replication observed between the alleles.