Changes in the NS1 gene of avian influenza viruses isolated in Thailand affect expression of type I interferon in primary chicken embryonic fibroblast cells

The non-structural protein 1 (NS1) of avian influenza virus was defined as one of the virulent factors. To understand the effect of NS1 protein of influenza virus H5N1 isolated in Thailand on type I (α/β) interferon (IFN) synthesis, five reverse genetic viruses were constructed and used as models. The viruses were generated using NS genomic segment from A/Peurto Rico/8/1934 (H1N1) and four avian influenza viruses isolated from the first outbreak in Thailand. All the viruses have the rest of the genome from A/Peurto Rico/8/1934 (H1N1). The constructed viruses were named (1) NS1 PR8/34, (2) NS1 wild type, (3) NS1 L15FD53G, (4) NS1 N171I and (5) NS1 E71K, respectively. The type I (α/β) IFN gene expression in control and infected primary chicken embryonic fibroblast cells were analyzed by quantitative polymerase chain reaction. The results show that the inhibition of IFN-β gene expression by NS1 wild type infected cells is stronger than NS1 N171I, NS1 E71K, NS1 PR8/34 and NS1 L15FD53G, respectively. The data suggest that the difference of amino acid sequence of NS1 protein contributes to the IFN-β antagonist. In contrast, the difference of the NS1 protein does not influence in the IFN-α antagonistic activity.