Molecular Basis of Efficient Replication and Pathogenicity of H9N2 Avian Influenza Viruses in Mice

Abstract

H9N2 subtype avian influenza viruses (AIVs) have shown expanded host range and can infect mammals, such as humans and swine. To date the mechanisms of mammalian adaptation and interspecies transmission of H9N2 AIVs remain poorly understood. To explore the molecular basis determining mammalian adaptation of H9N2 AIVs, we compared two avian field H9N2 isolates in a mouse model: one (A/chicken/Guangdong/TS/2004, TS) is nonpathogenic, another one (A/chicken/Guangdong/V/2008, V) is lethal with efficient replication in mouse brains. In order to determine the basis of the differences in pathogenicity and brain tropism between these two viruses, recombinants with a single gene from the TS (or V) virus in the background of the V (or TS) virus were generated using reverse genetics and evaluated in a mouse model. The results showed that the PB2 gene is the major factor determining the virulence in the mouse model although other genes also have variable impacts on virus replication and pathogenicity. Further studies using PB2 chimeric viruses and mutated viruses with a single amino acid substitution at position 627 [glutamic acid (E) to lysine, (K)] in PB2 revealed that PB2 627K is critical for pathogenicity and viral replication of H9N2 viruses in mouse brains. All together, these results indicate that the PB2 gene and especially position 627 determine virus replication and pathogenicity in mice. This study provides insights into the molecular basis of mammalian adaptation and interspecies transmission of H9N2 AIVs.

Matriptase, HAT, and TMPRSS2 Activate the Hemagglutinin of H9N2 Influenza A Viruses

“…Orthologs of matriptase have been identified in all vertebrate genomes examined to date (47), and proteolytic activation of H9-782 and H9-2061 in MDCK-II cells suggests that matriptase may support HA activation in several hosts. Some H9N2 strains were reported to cause lethal infections in mice with virus replication in the lung and the brain (11,20). Matriptase has recently been shown to be expressed in neural progenitor cells and neurons (52).…”

“…H9N2 viruses show a high genetic compatibility with other subtypes and have undergone extensive reassortments and rapid evolution in diverse host species worldwide (15)(16)(17)(18). Many H9N2 isolates have acquired human viruslike receptor specificity with preferential binding to ␣2,6-linked sialic acids (19) and are able to replicate efficiently in human airway epithelial cells, mice, and ferrets without prior adaptation, indicating that they have already adapted to mammalian hosts (11,(20)(21)(22). In general, H9N2 viruses are defined as LPAIV.…”

“…In addition, coinfections with bacteria or infectious bronchitis virus (IBV) have been shown to exacerbate disease in chickens (23,(25)(26)(27). Moreover, some H9N2 strains cause significant morbidity and mortality in experimentally infected mice (11,20).…”

PB2 subunit of avian influenza virus subtype H9N2: a pandemic risk factor

“…A particularly important determinant of host range appears to be the PB2 (polymerase basic 2) subunit of the polymerase, as numerous adaptive mutations have been observed in this protein (Subbarao et al, 1993(Subbarao et al, , 1998Gabriel et al, 2005;Labadie et al, 2007;Bussey et al, 2010;Wang et al, 2012;Czudai-Matwich et al, 2014;Zhang et al, 2014;Li et al, 2015). Amongst these, mutation E627K in the PB2 subunit of the polymerase complex has been known for a long time to play a prominent role in the adaptation of avian viruses of various subtypes to mammalian hosts (Subbarao et al, 1993(Subbarao et al, , 1998Li et al, 2012;Zhang et al, 2014). Another important determinant of mammalian specificity is the adaptive mutation D701N also observed with different viruses (Gabriel et al, 2005;Li et al, 2005;Steel et al, 2009).…”

High Pathogenicity of Influenza A (H10N8) Virus in Mice

“…[11][12][13] These results suggest that PB2-E627K in H10N8 virus is critical for the high pathogenicity in mammals. The H10N8 virus, as a novel avian-origin influenza A virus, demonstrated higher virulence than the reported H10 subtype influenza viruses as H346-1 was proved to be fatal in human and mouse.…”