Inhibited Influenza A Virus Replication Research Articles

Influenza A virus-induced degradation of eukaryotic translation initiation factor 4B contributes to viral replication by suppressing IFITM3 protein expression.

Although alteration in host cellular translation machinery occurs in virus-infected cells, the role of such alteration and the precise pathogenic processes are not well understood. Influenza A virus (IAV) infection shuts off host cell gene expression at transcriptional and translational levels. Here, we found that the protein level of eukaryotic translation initiation factor 4B (eIF4B), an integral component of the translation initiation apparatus, was dramatically reduced in A549 cells as well as in the lung, spleen, and thymus of mice infected with IAV. The decrease in eIF4B level was attributed to lysosomal degradation of eIF4B, which was induced by viral NS1 protein. Silencing eIF4B expression in A549 cells significantly promoted IAV replication, and conversely, overexpression of eIF4B markedly inhibited the viral replication. Importantly, we observed that eIF4B knockdown transgenic mice were more susceptible to IAV infection, exhibiting faster weight loss, shorter survival time, and more-severe organ damage. Furthermore, we demonstrated that eIF4B regulated the expression of interferon-induced transmembrane protein 3 (IFITM3), a critical protein involved in immune defense against a variety of RNA viruses, including influenza virus. Taken together, our findings reveal that eIF4B plays an important role in host defense against IAV infection at least by regulating the expression of IFITM3, which restricts viral entry and thereby blocks early stages of viral production. These data also indicate that influenza virus has evolved a strategy to overcome host innate immunity by downregulating eIF4B protein. Influenza A virus (IAV) infection stimulates the host innate immune system, in part, by inducing interferons (IFNs). Secreted IFNs activate the Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathway, leading to elevated transcription of a large group of IFN-stimulated genes that have antiviral function. To circumvent the host innate immune response, influenza virus has evolved multiple strategies for suppressing the production of IFNs. Here, we show that IAV infection induces lysosomal degradation of eIF4B protein; and eIF4B inhibits IAV replication by upregulating expression of interferon-induced transmembrane protein 3 (IFITM3), a key protein that protects the host from virus infection. Our finding illustrates a critical role of eIF4B in the host innate immune response and provides novel insights into the complex mechanisms by which influenza virus interacts with its host.

Nonstructural protein 1 of influenza A virus interacts with human guanylate-binding protein 1 to antagonize antiviral activity.

Human guanylate-binding protein 1 (hGBP1) is an interferon-inducible protein involved in the host immune response against viral infection. In response to infection by influenza A virus (IAV), hGBP1 transcript and protein were significantly upregulated. Overexpression of hGBP1 inhibited IAV replication in a dose-dependent manner in vitro. The lysine residue at position 51 (K51) of hGBP1 was essential for inhibition of IAV replication. Mutation of K51 resulted in an hGBP1 that was unable to inhibit IAV replication. The viral nonstructural protein 1 (NS1) was found to interact directly with hGBP1. K51 of hGBP1 and a region between residues 123 and 144 in NS1 were demonstrated to be essential for the interaction between NS1 and hGBP1. Binding of NS1 to hGBP1 resulted in a significant reduction in both GTPase activity and the anti-IAV activity of hGBP1. These findings indicated that hGBP1 contributed to the host immune response against IAV replication and that hGBP1-mediated antiviral activity was antagonized by NS1 via binding to hGBP1.

Influenza A Virus Induces Interleukin-27 through Cyclooxygenase-2 and Protein Kinase A Signaling

We previously reported that IL-27, which belongs to the IL-12 family of cytokines, is elevated in the serum of patients infected with influenza A virus (IAV). Here, we show that the expression of IL-27 was significantly up-regulated in A549 human lung epithelial cells and human peripheral blood mononuclear cells infected with IAV. Additionally, IAV triggered IL-27 expression through protein kinase A and cAMP-response element-binding protein signaling, which was mediated by cyclooxygenase-2-derived prostaglandin E(2). IL-27 inhibited IAV replication by STAT1/2/3 phosphorylation and activated antiviral factor protein kinase R phosphorylation. Clinical analysis showed that IL-27 levels were significantly elevated in a cohort of patients infected with IAV compared with healthy individuals and that circulating IL-27 levels were tightly and positively correlated with prostaglandin E(2) levels. These results indicate that IL-27 expression is one host immune factor produced in response to IAV infection and that elevated IL-27 levels inhibit viral replication.

In vitro inhibitory effect of carrageenan oligosaccharide on influenza A H1N1 virus

Carrageenan polysaccharide has been reported to be able to inhibit the infection and replication of many different kinds of viruses. Here, we demonstrated that a 2 kDa κ-carrageenan oligosaccharide (CO-1) derived from the carrageenan polysaccharide, effectively inhibited influenza A (H1N1) virus replication in MDCK cells (selectivity index >25.0). Moreover, the 2 kDa CO-1 inhibited influenza A virus (IAV) replication better than that of 3 kDa and 5 kDa κ-carrageenan oligosaccharides (CO-2 and CO-3). IAV multiplication was suppressed by carrageenan oligosaccharide treatment in a dose-dependent manner. Carrageenan oligosaccharide CO-1 did not bind to the cell surface of MDCK cells but inactivated virus particles after pretreatment. Different to the actions of carrageenan polysaccharide, CO-1 could enter into MDCK cells and did not interfere with IAV adsorption. CO-1 also inhibited IAV mRNA and protein expression after its internalization into cells. Moreover, carrageenan oligosaccharide CO-1 had an antiviral effect on IAV replication subsequent to viral internalization but prior to virus release in one replication cycle. Therefore, inhibition of IAV intracellular replication by carrageenan oligosaccharide might be an alternative approach for anti-influenza A virus therapy.

Antiviral activity and possible mechanisms of action of pentagalloylglucose (PGG) against influenza A virus

Influenza A virus (IAV) infection is a major public health threat leading to significant morbidity and mortality. The emergence of drug-resistant virus strains highlights the urgent need to develop novel antiviral drugs with alternative modes of action. Pentagalloylglucose (PGG), a naturally occurring polyphenolic compound, possesses a broad spectrum of biological activities. In this study, we found that PGG has anti-influenza-virus activity, and investigated its possible mechanism(s) of action in vitro. Both pre-incubation of virus prior to infection and post-exposure of infected cells with PGG significantly inhibited virus yields. Influenza-virus-induced hemagglutination of chicken red blood cells was inhibited by PGG treatment, suggesting that PGG can inhibit IAV infection by interacting with the viral hemagglutinin. PGG did not affect viral protein synthesis or nuclear transport of viral nucleoprotein (NP) but greatly reduced plasma membrane accumulation of NP protein at the late stage of the replication cycle. Furthermore, PGG significantly reduced virus budding and progeny virus release from infected cells. This study revealed for the first time that PGG can inhibit IAV replication with a dual mode of action and offers new insights into its underlying mechanisms of antiviral action.

Influenza A virus replication is inhibited in IFN-λ2 and IFN-λ3 transfected or stimulated cells

Interferons lambda (IFN-λ) are the most recently defined members of the class III cytokine family. To investigate whether IFN-λ2 and IFN-λ3 displayed antiviral activity against influenza A virus (IAV), a number of cell lines induced with IFNs – as well as two established cell lines (A549-IFN-λ2 and A549-IFN-λ3) – were infected with IAV. Our results indicate that IFN-λ2 has statistically significant antiviral activity in A549-IFN-λ2 ( P = 0.0028) although less so than IFN-λ3, which reduced viral titer to 10% ( P < 0.0001). The reverse was observed for cells treated with IFNs, with IFN-λ2-treated A549 cells inhibiting IAV infection more efficiently than IFN-λ3-treated A549 cells. The antiviral effect on IFN-stimulated cells was most apparent on Vero cells (compared with MDCK and HeLa). Both IFNs significantly inhibited IAV replication and inhibition was observed in a dose-dependent manner, with an optimal IFN concentration of 20 ng/ml. IFN-λ2 was more potent than IFN-λ3 on Vero cells while IFN-λ3 appeared more efficient than IFN-λ2 on MDCK and HeLa cells.

Influenza A virus facilitatesStreptococcus pneumoniaetransmission and disease

Streptococcus pneumoniae (the pneumococcus) kills approximately 1.6 million people annually. Pneumococcal infections predominantly manifest as pneumonia, sepsis, meningitis, and otitis media. S. pneumoniae is also a member of the normal nasopharyngeal flora, colonizing up to 80% of children. Infection with influenza A virus (IAV) has been associated with both pneumococcal disease and transmission. However, to date no animal model has been available to investigate the role of IAV in the spread of S. pneumoniae. Here we investigate pneumococcal-influenza synergism with a particular focus on the role of IAV on pneumococcal transmission. Infant mice were colonized with S. pneumoniae and subsequently infected with IAV 3 d later. Using this novel model we show increased pneumococcal colonization and disease in the presence of IAV. Notably, in vivo imaging showed that IAV was essential for the transmission of S. pneumoniae from colonized ("index") mice to their naive cohoused littermates ("contacts"). Transmission occurred only when all mice were infected with IAV and was prevented when an IAV-neutralizing antibody was used to inhibit IAV replication in either index mice or contact mice. Together, these data provide novel insights into pneumococcal-influenza synergism and may indicate a previously unappreciated role of IAV in the spread of S. pneumoniae.

Expression of mouse beta-defensin-3 in MDCK cells and its anti-influenza-virus activity

Influenza (flu) pandemics have presented a threat to human health in the past century. Because of outbreaks of avian flu in humans in some developing countries in recent years, humans are more eager to find a way to control flu. Mammalian beta-defensins (beta-defensins) are associated primarily with mucosal and skin innate immunity. Previous studies have demonstrated antimicrobial properties of a variety of defensin peptides. We have identified the presence of mouse beta-defensin 1, 2, and 3 genes (Mbd-1, 2, and 3) in trachea and lung tissues by RT-PCR before and after infection with influenza virus. We constructed a eukaryotic expression plasmid containing Mbd-3, pcDNA 3.1(+)/MBD-3, and the plasmid was introduced into Madin-Darby canine kidney (MDCK) cells by transfection. The expression of Mbd-3 in MDCK cells was verified by immunofluorescence test, RT-PCR, and Western blot. The pcDNA 3.1(+)/MBD-3 plasmid was injected into mice to observe its effect against influenza A virus (IAV) in vivo. Mouse beta-defensin genes could be expressed in trachea and lung tissues before IAV infection, but expression of Mbd-2 and Mbd-3 was increased significantly after IAV infection. The survival rate of mice with MBD-3 against IAV challenge was 71.43%, and MDCK cells with MBD-3 could clearly inhibit IAV replication. The results demonstrated that mouse beta-defensins possess anti-influenza virus activity, suggesting that mouse beta-defensins might be used as agents to prevent and treat influenza.