Amelioration of Influenza Virus Pathogenesis in Chickens Attributed to the Enhanced Interferon-Inducing Capacity of a Virus with a Truncated NS1 Gene

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The dynamic changes in the temporal appearance and quantity of a new class of influenza virus, noninfectious cell-killing particles (niCKP), were compared to defective interfering particles (DIP). After a single high-multiplicity passage in MDCK cells of an egg-derived stock that lacked detectable niCKP or DIP, both classes of particles appeared in large numbers (>5 ؋ 10 8 /ml), and the plaque-forming particle (PFP) titer dropped ϳ60-fold. After two additional serial high-multiplicity passages the DIP remained relatively constant, the DIP/niCKP ratio reached 10:1, and the PFP had declined by about 10,000-fold. Together, the niCKP and DIP subpopulations constituted ca. 20% of the total hemagglutinating particle population in which these noninfectious biologically active particles (niBAP) were subsumed. DIP neither killed cells nor interfered with the cell-killing (apoptosis-inducing) activity of niCKP or PFP (infectious CKP), even though they blocked the replication of PFP. Relative to the UV-target of ϳ13,600 nucleotides (nt) for inactivation of PFP, the UV target for niCKP was ϳ2,400 nt, consistent with one of the polymerase subunit genes, and that for DIP was ϳ350 nt, consistent with the small DI-RNA responsible for DIP-mediated interference. Thus, niCKP and DIP are viewed as distinct particles with a propensity to form during infection at high multiplicities. These conditions are postulated to cause aberrations in the temporally regulated replication of virus and its packaging, leading to the production of niBAP. DIP have been implicated in the virulence of influenza virus, but the role of niCKP is yet unknown.

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

Dynamics of Biologically Active Subpopulations of Influenza Virus: Plaque-Forming, Noninfectious Cell-Killing, and Defective Interfering Particles

Marcus

Ngunjiri

Sekellick

2009

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“…Hemagglutinin (HA) cleavability is a critical determinant of AIV pathogenicity in avian species (61). Other determinants, such as nonstructural (NS) protein and neuraminidase (NA) protein, reportedly regulate the virulence of AIVs (9,29,44). However, waterfowl, known as the natural host for AIVs, do not usually have any symptoms during an HPAIV infection (21), whereas they show neurologic symptoms and death after infection with some of the recently emerged HPAIVs, such as the Asian H5N1 virus (11,46,62).…”

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confidence: 99%

Highly Pathogenic H5N1 Avian Influenza Virus Induces Extracellular Ca ²⁺ Influx, Leading to Apoptosis in Avian Cells

Ueda

Daidoji²,

et al. 2010

In this study, we show that the highly pathogenic H5N1 avian influenza virus (AIV) . Thus, we investigated the molecular mechanisms of apoptosis induced by H5N1-AIV infection. Caspase-dependent and -independent pathways contributed to the cytopathic effects. We further showed that, in the induction of apoptosis, the hemagglutinin of H5N1-AIV played a major role and its cleavage sequence was not critical. We also observed outer membrane permeabilization and loss of the transmembrane potential of the mitochondria of infected DEF, indicating that mitochondrial dysfunction was caused by the H5N1-AIV infection. (

“…Currently, pathogenesis studies of AIVs in chickens clearly indicate that the proteolytic cleavage site of HA (22,25,27) and changes in the NS1 protein (11,33) are important determinants of virulence. Recently it was reported that PA and PB1 gene mutations were responsible for differences between nonpathogenic and highly pathogenic viral clones in ducks (26), and mixtures of polymerase components from different viruses have been found to lead to the attenuation of AIVs in chickens (43).…”

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confidence: 99%

NP, PB1, and PB2 Viral Genes Contribute to Altered Replication of H5N1 Avian Influenza Viruses in Chickens

Wasilenko

Lee

Sarmento

et al. 2008

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The virulence determinants for highly pathogenic avian influenza viruses (AIVs) are considered multigenic, although the best characterized virulence factor is the hemagglutinin (HA) cleavage site. The capability of influenza viruses to reassort gene segments is one potential way for new viruses to emerge with different virulence characteristics. To evaluate the role of other gene segments in virulence, we used reverse genetics to generate two H5N1 recombinant viruses with differing pathogenicity in chickens. Single-gene reassortants were used to determine which viral genes contribute to the altered virulence. Exchange of the PB1, PB2, and NP genes impacted replication of the reassortant viruses while also affecting the expression of specific host genes. Disruption of the parental virus' functional polymerase complexes by exchanging PB1 or PB2 genes decreased viral replication in tissues and consequently the pathogenicity of the viruses. In contrast, exchanging the NP gene greatly increased viral replication and expanded tissue tropism, thus resulting in decreased mean death times. Infection with the NP reassortant virus also resulted in the upregulation of gamma interferon and inducible nitric oxide synthase gene expression. In addition to the impact of PB1, PB2, and NP on viral replication, the HA, NS, and M genes also contributed to the pathogenesis of the reassortant viruses. While the pathogenesis of AIVs in chickens is clearly dependent on the interaction of multiple gene products, we have shown that single-gene reassortment events are sufficient to alter the virulence of AIVs in chickens.