Abstract
The 2009 pandemic influenza A virus (IAV) H1N1 strain (H1N1pdm09) has widely spread and is circulating in humans and swine together with other human and avian IAVs. This fact raises the concern that reassortment between H1N1pdm09 and co-circulating viruses might lead to an increase of H1N1pdm09 pathogenicity in different susceptible host species. Herein, we explored the potential of different NS segments to enhance the replication dynamics, pathogenicity and host range of H1N1pdm09 strain A/Giessen/06/09 (Gi-wt). The NS segments were derived from (i) human H1N1- and H3N2 IAVs, (ii) highly pathogenic- (H5- or H7-subtypes) or (iii) low pathogenic avian influenza viruses (H7- or H9-subtypes). A significant increase of growth kinetics in A549 (human lung epithelia) and NPTr (porcine tracheal epithelia) cells was only noticed in vitro for the reassortant Gi-NS-PR8 carrying the NS segment of the 1918-descendent A/Puerto Rico/8/34 (PR8-wt, H1N1), whereas all other reassortants showed either reduced or comparable replication efficiencies. Analysis using ex vivo tracheal organ cultures of turkeys (TOC-Tu), a species susceptible to IAV H1N1 infection, demonstrated increased replication of Gi-NS-PR8 compared to Gi-wt. Also, Gi-NS-PR8 induced a markedly higher expression of immunoregulatory and pro-inflammatory cytokines, chemokines and interferon-stimulated genes in A549 cells, THP-1-derived macrophages (dHTP) and TOC-Tu. In vivo, Gi-NS-PR8 induced an earlier onset of mortality than Gi-wt in mice, whereas, 6-week-old chickens were found to be resistant to both viruses. These data suggest that the specific characteristics of the PR8 NS segments can impact on replication, virus induced cellular immune responses and pathogenicity of the H1N1pdm09 in different avian and mammalian host species.
Highlights
Throughout the last century and in the recent past, influenza A viruses (IAVs) have led to drastic outbreaks and pandemics in poultry and humans, respectively (Lai et al, 2016)
In order to investigate whether the NS segment of other IAV strains would improve propagation of H1N1pdm09 and/or expand the host range we analyzed the impact of NS reassortment between the pandemic H1N1pdm09 (A/Giessen/06/09, Gi-wt) and other IAVs (HPAIV, LPAIV) on its replication efficiency in human and porcine cells
Only the NS segment of PR8 enhanced the replication efficiency of the reassortant Gi-virus, while the NS segment of Victoria/H3N2 interfered with the replication efficiency of the reassortant Gi-virus and the other NS segments either did not affect or even reduced replication efficiencies of H1N1pdm09
Summary
Throughout the last century and in the recent past, influenza A viruses (IAVs) have led to drastic outbreaks and pandemics in poultry and humans, respectively (Lai et al, 2016). In 2009, the world was confronted with the first pandemic of this century caused by the swine-originated H1N1-type IAV (H1N1pdm09) (Lessler et al, 2009) This pandemic IAV strain evolved following multiple reassortment events including genomic segments from two swine IAV strains [North American classical swine viruses (HA, NP, and NS) and Eurasian avian-like swine viruses (NA, M)], one human strain [North American human H3N2 viruses (PB1)], and one avian strain [North American avian viruses (PB2, PA)] (Neumann et al, 2009). As H1N1pdm is circulating in mammals and birds together with seasonal IAVs (H1N1- and H3N2-type), and occasionally with 2013/H7N9- and H5N1-type highly pathogenic avian influenza virus (HPAIV) (Reid et al, 2012; Abdelwhab et al, 2016; Zhu et al, 2016), H1N1pdm genome reassortment and evolution, resulting in variants of unknown virulence for mammalian and avian species, is a possible event. Gene segments highly related to those of the 1918 pandemic virus can be found in circulating avian IAVs, suggesting that 1918-like variants may emerge in the future (Watanabe et al, 2014)
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