Paramyxovirus Infection Regulates T Cell Responses by BDCA-1 + and BDCA-3 + Myeloid Dendritic Cells

Abstract Respiratory syncytial virus (RSV) and human Metapneumovirus (hMPV), viruses belonging to the family Paramyxoviridae, are the most important causes of lower respiratory tract infection in young children. Infections with RSV and hMPV are clinically indistinguishable, and both RSV and hMPV infection have been associated with aberrant adaptive immune responses. Myeloid Dendritic cells (mDCs) play a pivotal role in shaping adaptive immune responses during infection; however, few studies have examined how interactions of RSV and hMPV with individual mDC subsets (BDCA-1 + and BDCA-3 + mDCs) affect the outcome of anti-viral responses. To determine whether RSV and hMPV induce virus-specific responses from each subset, we examined co-stimulatory molecules and cytokines expressed by BDCA-1 + and BDCA-3 + mDCs isolated from peripheral blood after infection with hMPV and RSV, and examined their ability to stimulate T cell proliferation and differentiation. Our data show that RSV and hMPV induce virus-specific and subset-specific patterns of co-stimulatory molecule and cytokine expression. RSV, but not hMPV, impaired the capacity of infected mDCs to stimulate T cell proliferation. Whereas hMPVinfected BDCA-1 + and BDCA-3 + mDCs induced expansion of Th17 cells, in response to RSV, BDCA-1 + mDCs induced expansion of Th1 cells and BDCA-3 + mDCs induced expansion of Th2 cells and Tregs. These results demonstrate a virusspecific and subset-specific effect of RSV and hMPV infection on mDC function, suggesting that these viruses may induce different adaptive immune responses

Oxidative stress in Nipah virus-infected human small airway epithelial cells

Nipah virus (NiV) is a zoonotic emerging pathogen that can cause severe and often fatal respiratory disease in humans. The pathogenesis of NiV infection of the human respiratory tract remains unknown. Reactive oxygen species (ROS) produced by airway epithelial cells in response to viral infections contribute to lung injury by inducing inflammation and oxidative stress; however, the role of ROS in NiV-induced respiratory disease is unknown. To investigate whethe

Human Metapneumovirus Glycoprotein G Inhibits Innate Immune Responses

Human metapneumovirus (hMPV) is a leading cause of acute respiratory tract infection in infants, as well as in the elderly and immunocompromised patients. No effective treatment or vaccine for hMPV is currently available. A recombinant hMPV lacking the G protein (rhMPV-ΔG) was recently developed as a potential vaccine candidate and shown to be attenuated in the respiratory tract of a rodent model of infection. The mechanism of its attenuation, as well as the role of G protein in modulation of hMPV-induced cellular responses in vitro, as well as in vivo, is currently unknown. In this study, we found that rhMPV-ΔG-infected airway epithelial cells produced higher levels of chemokines and type I interferon (IFN) compared to cells infected with rhMPV-WT. Infection of airway epithelial cells with rhMPV-ΔG enhanced activation of transcription factors belonging to the nuclear factor (NF)-κB and interferon regulatory factor (IRF) families, as revealed by increased nuclear translocation and/or phosphorylation of these transcription factors. Compared to rhMPV-WT, rhMPV-ΔG also increased IRF- and NF-κB-dependent gene transcription, which was reversely inhibited by G protein expression. Since RNA helicases have been shown to play a fundamental role in initiating viral-induced cellular signaling, we investigated whether retinoic induced gene (RIG)-I was the target of G protein inhibitory activity. We found that indeed G protein associated with RIG-I and inhibited RIG-I-dependent gene transcription, identifying an important mechanism by which hMPV affects innate immune responses. This is the first study investigating the role of hMPV G protein in cellular signaling and identifies G as an important virulence factor, as it inhibits the production of important immune and antiviral mediators by targeting RIG-I, a major intracellular viral RNA sensor

Human Metapneumovirus Inhibits IFN-β Signaling by Downregulating Jak1 and Tyk2 Cellular Levels

Human metapneumovirus (hMPV), a leading cause of respiratory tract infections in infants, inhibits type I interferon (IFN) signaling by an unidentified mechanism. In this study, we showed that infection of airway epithelial cells with hMPV decreased cellular level of Janus tyrosine kinase (Jak1) and tyrosine kinase 2 (Tyk2), due to enhanced proteosomal degradation and reduced gene transcription. In addition, hMPV infection also reduced the surface expression of type I IFN receptor (IFNAR). These inhibitory mechanisms are different from the ones employed by respiratory syncytial virus (RSV), which does not affect Jak1, Tyk2 or IFNAR expression, but degrades downstream signal transducer and activator of transcription proteins 2 (STAT2), although both viruses are pneumoviruses belonging to the Paramyxoviridae family. Our study identifies a novel mechanism by which hMPV inhibits STAT1 and 2 activation, ultimately leading to viral evasion of host IFN responses

Role of hydrogen sulfide in paramyxovirus infections

Hydrogen sulfide (H2S) is an endogenous gaseous mediator that has gained increasing recognition as an important player in modulating acute and chronic inflammatory diseases. However, its role in virus-induced lung inflammation is currently unknown. Respiratory syncytial virus (RSV) is a major cause of upper and lower respiratory tract infections in children for which no vaccine or effective treatment is available. Using the slow-releasing H2S donor GYY4137 and propargylglycin (PAG), an inhibitor of cystathionine-γ-lyase (CSE), a key enzyme that produces intracellular H2S, we found that RSV infection led to a reduced ability to generate and maintain intracellular H2S levels in airway epithelial cells (AECs). Inhibition of CSE with PAG resulted in increased viral replication and chemokine secretion. On the other hand, treatment of AECs with the H2S donor GYY4137 reduced proinflammatory mediator production and significantly reduced viral replication, even when administered several hours after viral absorption. GYY4137 also significantly reduced replication and inflammatory chemokine production induced by human metapneumovirus (hMPV) and Nipah virus (NiV), suggesting a broad inhibitory effect of H2S on paramyxovirus infections. GYY4137 treatment had no effect on RSV genome replication or viral mRNA and protein synthesis, but it inhibited syncytium formation and virus assembly/release. GYY4137 inhibition of proinflammatory gene expression occurred by modulation of the activation of the key transcription factors nuclear factor κB (NF-κB) and interfero

Protective Role of Nuclear Factor Erythroid 2-Related Factor 2 Against Respiratory Syncytial Virus and Human Metapneumovirus Infections

The pathogenesis of respiratory syncytial virus (RSV) infections is characterized by lower airway obstruction driven at great extent by the exuberant production of inflammatory cytokines. We have previously shown that RSV infection in vitro and in vivo results in production of reactive oxygen species along with reduction in the expression of antioxidant enzymes (AOEs), which are involved in maintaining the cellular oxidant–antioxidant balance. These events were associated with the concomitant reduction in nuclear factor erythroid 2-related factor 2 (Nrf2), a key transcription factor that controls AOE expression. The objective of the current study was to establish the role of Nrf2 in shaping innate immune responses, clinical disease, airway inflammation, and viral replication in established experimental models of intranasal RSV and human metapneumovirus (hMPV) infections, by employing mice genetically deficient for the Nrf2 gene. Compared to control wild type (WT), mice genetically deficient in Nrf2 (Nrf2 KO) developed enhanced clinical disease, airway inflammation and pathology, and significantly greater lung viral titers following experimental infection with either RSV or hMPV. In particular, compared to control mice, RSV-infected Nrf2 KO mice lost more body weight and had increased airway obstruction at time points characterized by a remarkable increase in inflammatory cytokines and airway neutrophilia. Airway levels of AOEs and enzymes that regulate synthesis of the endogenous hydrogen sulfide (H2S) pathway, which we showed to play an important antiviral function, were also decreased in RSV-infected Nrf2 KO compared to WT. In conclusion, these results suggest that Nrf2 is a critical regulator of innate, inflammatory, and disease-associated responses in the airways of mice infected with viruses that are members of the Pneumoviridae family. Importantly, the results of this study suggest that Nrf2-dependent genes, including those controlling the cellular antioxidant and H2S-generating enzymes and cytokines can affect several aspects of the antiviral response, such as airway neutrophilia, clinical disease, airway obstruction, and viral replication

Human Metapneumovirus Antagonism of Innate Immune Responses

 Human metapneumovirus (hMPV) is a recently identified RNA virus belonging to the Paramyxoviridae family, which includes several major human and animal pathogens. Epidemiological studies indicate that hMPV is a significant human respiratory pathogen with worldwide distribution. It is associated with respiratory illnesses in children, adults, and immunocompromised patients, ranging from upper respiratory tract infections to severe bronchiolitis and pneumonia. Interferon (IFN) represents a major line of defense against virus infection, and in response, viruses have evolved countermeasures to inhibit IFN production as well as IFN signaling. Although the strategies of IFN evasion are similar, the specific mechanisms by which paramyxoviruses inhibit IFN responses are quite diverse. In this review, we will present an overview of the strategies that hMPV uses to subvert cellular signaling in airway epithelial cells, the major target of infection, as well as in primary immune cells

Role of Hydrogen Sulfide in NRF2- and Sirtuin-Dependent Maintenance of Cellular Redox Balance

Hydrogen sulfide (H2S) has arisen as a critical gasotransmitter signaling molecule modulating cellular biological events related to health and diseases in heart, brain, liver, vascular systems and immune response. Three enzymes mediate the endogenous production of H2S: cystathione β-synthase (CBS), cystathione γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3-MST). CBS and CSE localizations are organ-specific. 3-MST is a mitochondrial and cytosolic enzyme. The generation of H2S is firmly regulated by these enzymes under normal physiological conditions. Recent studies have highlighted the role of H2S in cellular redox homeostasis, as it displays significant antioxidant properties. H2S exerts antioxidant effects through several mechanisms, such as quenching reactive oxygen species (ROS) and reactive nitrogen species (RNS), by modulating cellular levels of glutathione (GSH) and thioredoxin (Trx-1) or increasing expression of antioxidant enzymes (AOE), by activating the transcription factor nuclear factor (erythroid-derived 2)-like 2 (NRF2). H2S also influences the activity of the histone deacetylase protein family of sirtuins, which plays an important role in inhibiting oxidative stress in cardiomyocytes and during the aging process by modulating AOE gene expression. This review focuses on the role of H2S in NRF2 and sirtuin signaling pathways as they are related to cellular redox homeostasis