Project description:A century ago, influenza A virus (IAV) infection caused the 1918 flu pandemic and killed an estimated 20-40 million people. Pandemic IAV outbreaks occur when strains from animal reservoirs acquire the ability to infect and spread among humans. The molecular details of this species barrier are incompletely understood. We combined metabolic pulse labeling and quantitative shotgun proteomics to globally monitor protein synthesis upon infection of human cells with a human- and a bird-adapted IAV strain. While production of host proteins was remarkably similar, we observed striking differences in the kinetics of viral protein synthesis over the course of infection. Most importantly, the matrix protein M1 was inefficiently produced by the bird-adapted strain at later stages. We show that impaired production of M1 from bird-adapted strains is caused by increased splicing of the M segment RNA to alternative isoforms. Experiments with reporter constructs and recombinant influenza viruses revealed that strain-specific M segment splicing is controlled by the 3’ splice site and functionally important for permissive infection. Independent in silico and biochemical evidence shows that avian-adapted M segments have evolved different conserved RNA structure features than human-adapted sequences. Thus, our data identifies M segment RNA splicing as a viral determinant of host range.
Project description:A century ago, influenza A virus (IAV) infection caused the 1918 flu pandemic and killed an estimated 20-40 million people. Pandemic IAV outbreaks occur when strains from animal reservoirs acquire the ability to infect and spread among humans. The molecular details of this species barrier are incompletely understood. We combined metabolic pulse labeling and quantitative shotgun proteomics to globally monitor protein synthesis upon infection of human cells with a human- and a bird-adapted IAV strain. While production of host proteins was remarkably similar, we observed striking differences in the kinetics of viral protein synthesis over the course of infection. Most importantly, the matrix protein M1 was inefficiently produced by the bird-adapted strain at later stages. We show that impaired production of M1 from bird-adapted strains is caused by increased splicing of the M segment RNA to alternative isoforms. Experiments with reporter constructs and recombinant influenza viruses revealed that strain-specific M segment splicing is controlled by the 3’ splice site and functionally important for permissive infection. Independent in silico and biochemical evidence shows that avian-adapted M segments have evolved different conserved RNA structure features than human-adapted sequences. Thus, our data identifies M segment RNA splicing as a viral determinant of host range.
Project description:Ducks and wild aquatic birds are the natural reservoirs of avian influenza viruses. However, the host proteome response that causes disease in vivo during infection by the highly pathogenic avian influenza (HPAI) H5N1 virus is still not well understood. In the present study, we compared the proteome response in Muscovy duck lung tissue during 3 day of infection with either a highly virulent or an avirulent H5N1 virus. During infection, proteins involved in immune response of neutrophils and size of cells were increased markedly in the lung by the virulent strain, while the avirulent strain evoked a distinct response, characterized by an increase in proteins involved in cell movement, maturation of dendritic cells, adhesion of phagocytes, and immune response of macrophages.
Project description:Incursions of new pathogenic viruses into humans from animal reservoirs are occurring with alarming frequency. The molecular underpinnings of immune recognition, host responses, and pathogenesis in this setting arepoorly understood. We studied pandemic influenza viruses to determine the mechanism by which increasing glycosylation during evolution of surface proteins facilitates diminished pathogenicity in adapted viruses. ER stressduring infection with poorly glycosylated pandemic strains activated the unfolded protein response, leading to inflammation, acute lung injury, and mortality. Seasonal strains or viruses engineered to mimic adapted viruses displaying excess glycans on the hemagglutinin did not cause ER stress, allowing preservation of the lungs and survival. We propose that ER stress resultingfrom recognition of non-adapted viruses is utilized to discriminate “non-self” at the level of protein-processing and to activate immune responses, with unintended consequences on pathogenesis. Understanding this mechanism should improve strategies for treating acute lung injury from zoonotic viral infections. Lung transcription analysis of Influenza A virus infected mice.
Project description:Zoonotic influenza A viruses of avian origin can cause severe disease in individuals, or even global pandemics, and thus pose a threat to human populations. Waterfowl and shorebirds are believed to be the reservoir for all influenza A viruses, but this has recently been challenged by the identification of novel influenza A viruses in bats. The major bat influenza A virus envelope glycoprotein, haemagglutinin, does not bind the canonical influenza A virus receptor, sialic acid or any other glycan, despite its high sequence and structural homology with conventional haemagglutinins. This functionally uncharacterized plasticity of the bat influenza A virus haemagglutinin means the tropism and zoonotic potential of these viruses has not been fully determined. Here we show, using transcriptomic profiling of susceptible versus non-susceptible cells in combination with genome-wide CRISPR-Cas9 screening, that the major histocompatibility complex class II (MHC-II) human leukocyte antigen DR isotype (HLA-DR) is an essential entry determinant for bat influenza A viruses. Genetic ablation of the HLA-DR α-chain rendered cells resistant to infection by bat influenza A virus, whereas ectopic expression of the HLA-DR complex in non-susceptible cells conferred susceptibility. Expression of MHC-II from different bat species, pigs, mice or chickens also conferred susceptibility to infection. Notably, the infection of mice with bat influenza A virus resulted in robust virus replication in the upper respiratory tract, whereas mice deficient for MHC-II were resistant. Collectively, our data identify MHC-II as a crucial entry mediator for bat influenza A viruses in multiple species, which permits a broad vertebrate tropism.
Project description:The circulation of seasonal influenza A viruses (IAVs) in humans relies on effective evasion and subversion of the host immune response. While the evolution of seasonal H1N1 and H3N2 viruses to avoid humoral immunity is well characterized, relatively little is known about the evolution of innate immune antagonism phenotypes in these viruses. Numerous studies have established that only a small subset of infected cells are responsible for initiating the type I and type III interferon (IFN) response during IAV infection, emphasizing the importance of single cell studies to accurately characterize the IFN response during infection. We developed a flow cytometry-based method to examine transcriptional changes in IFN and interferon stimulated gene (ISG) expression at the single cell level. We observed that NS segments derived from seasonal H3N2 viruses are more efficient at antagonizing IFN signaling but less effective at suppressing IFN induction, compared to the pdm2009 H1N1 lineage. We compared a collection of NS segments spanning the natural history of the current seasonal IAV lineages, and demonstrate long periods of stability in IFN antagonism potential, punctuated by occasional phenotypic shifts. Altogether, our data reveal significant differences in how seasonal and pandemic H1N1 and H3N2 viruses antagonize the human IFN response at the single cell level.
Project description:Parasitic elements of the viral population which are unable to replicate on their own yet rise to high frequencies, defective interfering particles are found in a variety of different viruses. Their presence is associated with a loss of population fitness, both through the depletion of key cellular resources and the stimulation of innate immunity. For influenza A virus, these particles contain large internal deletions in the genomic segments which encode components of the heterotrimeric polymerase. Using a library-based approach, we comprehensively profile the growth and replication of defective species, demonstrating they possess an advantage during genome replication, and that exclusion during packaging reshapes population composition in a manner consistent with their final, observed, distribution in natural populations. We find that innate immunity is not linked to the size of a deletion; however, replication of defective segments can enhance their immunostimulatory properties. Overall, our results address several key questions in defective influenza A virus biology, and the methods we have developed to answer those questions may be broadly applied to other defective viruses.
Project description:Human disease caused by highly pathogenic avian influenza (HPAI) H5N1 can lead to a rapidly progressive viral pneumonia leading to acute respiratory distress syndrome. There is increasing evidence suggests a role for virus-induced cytokine dysregulation in contributing to the pathogenesis of human H5N1 disease. The key target cells for the virus in the lung are the alveolar epithelium and alveolar macrophages, and previous data has shown that compared to seasonal human influenza viruses, equivalent infecting doses of H5N1 viruses markedly up-regulate pro-inflammatory cytokines in both primary cell types in vitro. The dysregulation of H5N1-induced host responses is therefore important for understanding the viral pathogenesis. We used microarrays to analyze and compare the gene expression profiles in primary human macrophages after influenza A virus infection.
Project description:Periodic outbreaks of highly pathogenic avian H5N1 influenza viruses and the current H1N1 pandemic highlight the need for a more detailed understanding of influenza virus pathogenesis. To investigate the host transcriptional response induced by pathogenic influenza viruses, we used a functional-genomics approach to compare gene expression profiles in lungs from wild-type 129S6/SvEv and interferon receptor (IFNR) knockout mice infected with either the fully reconstructed H1N1 1918 pandemic virus (1918) or the highly pathogenic avian H5N1 virus Vietnam/1203/04 (VN/1203).