Effect on Virulence and Pathogenicity of H5N1 Influenza A Virus through Truncations of NS1 eIF4GI Binding Domain

To study the effect of NS1 eIF4GI binding domain on virulence and pathogenicity of H5N1 influenza A virus, 5 recombinant H5N1 viruses encoding eIF4GI binding domain—truncated NS1 proteins and parental NS1 (NS1-wt) were generated by an 8-plasmid—based reverse genetics system. The results indicated that the recombinants with the addition of 5-amino acid and the deletion position of 85–89 in NS1-wt were attenuated in replication in vitro and in vivo, compared with the recombinant wild-type virus rNS1-wt, whereas the deletion position 85–94 or the entire eIF4GI binding domain in NS1-wt displayed a significantly attenuated phenotype in chicken and mice. We also showed that the eIF4GI binding domain—truncated mutants were impaired in their ability to inhibit interferon production in vitro, and they did not replicate as efficiently as the parental recombinant strain in embryonated hen eggs, in Madin-Darby Canine Kidney cells, or in vivo in chickens and in a mouse model. Therefore, these attenuated NS1-truncated viruses may have a great potential as live attenuated vaccine candidates against H5N1 influenza A virus.