Hepatitis C virus NS3/4A protease blocks IL-28 production

Type I interferons (IFNs), including IFN-α, -β, and -ω, play a critical role in innate immune responses against viral infection. IFN-λ, including IL-29, IL-28A, and IL-28B, recently identified as a new subfamily of IFN named type III IFN, has also been demonstrated to suppress virus replication in vitro and in vivo. However, the molecular mechanisms that regulate the induction of type III IFNs during viral infection remain elusive. Here, we demonstrate that IL-28 (IFN-λ 2/3) IFN production, similar to type I IFN, represents a primary and direct host response to HCV genomic RNA transfection. IL-28 (IFN-λ2/3) induction by HCV genomic RNA was dependent upon the activation of NF-κB and IRF3. We identified a minimal IL-28 promoter region consisting of putative NF-κB and IRF3-binding sites. Furthermore, we showed that HCV infection can inhibit HCV genomic RNA-induced IL-28 expression, and that the viral NS3/4A protease activity was responsible for this inhibitory effect. Our results present important evidence for the control of type III IFN response by HCV, and shed more light on the molecular mechanisms underlying the persistence of HCV infection.     

Emerging roles of interferon-stimulated genes in the innate immune response to hepatitis C virus infection

Infection with hepatitis C virus (HCV), a major viral cause of chronic liver disease, frequently progresses to steatosis and cirrhosis, which can lead to hepatocellular carcinoma. HCV infection strongly induces host responses, such as the activation of the unfolded protein response, autophagy and the innate immune response. Upon HCV infection, the host induces the interferon (IFN)-mediated frontline defense to limit virus replication. Conversely, HCV employs diverse strategies to escape host innate immune surveillance. Type I IFN elicits its antiviral actions by inducing a wide array of IFN-stimulated genes (ISGs). Nevertheless, the mechanisms by which these ISGs participate in IFN-mediated anti-HCV actions remain largely unknown. In this review, we first outline the signaling pathways known to be involved in the production of type I IFN and ISGs and the tactics that HCV uses to subvert innate immunity. Then, we summarize the effector mechanisms of scaffold ISGs known to modulate IFN function in HCV replication. We also highlight the potential functions of emerging ISGs, which were identified from genome-wide siRNA screens, in HCV replication. Finally, we discuss the functions of several cellular determinants critical for regulating host immunity in HCV replication. This review will provide a basis for understanding the complexity and functionality of the pleiotropic IFN system in HCV infection. Elucidation of the specificity and the mode of action of these emerging ISGs will also help to identify novel cellular targets against which effective HCV therapeutics can be developed.     

Innate immune interferon responses to human immunodeficiency virus-1 infection

Type I interferon (IFN) responses represent the canonical host innate immune response to viruses, which serves to upregulate expression of antiviral restriction factors and augment adaptive immune defences. There is clear evidence for type I IFN activity in both acute and chronic HIV-1 infection in vivo, and plasmacytoid dendritic cells have been identified as one important source for these responses, through innate immune detection of viral RNA by Toll-like receptor 7. In addition, new insights into the molecular mechanisms that trigger induction of type I IFNs suggest innate immune receptors for viral DNA may also mediate these responses. It is widely recognised that HIV-1 restriction factors share the characteristic of IFN-inducible expression, and that the virus has evolved to counteract these antiviral mechanisms. However, in some target cells, such as macrophages, IFN can still effectively restrict virus. In this context, HIV-1 shows the ability to evade innate immune recognition and thereby avoid induction of type I IFN in order to successfully establish productive infection. The relative importance of evasion of innate immune detection and evasion of IFN-inducible restriction in the natural history of HIV-1 infection is not known, and the data suggest that type I IFN responses may play a role in both viral control and in the immunopathogenesis of progressive disease. Further study of the relationship between HIV-1 infection and type I IFN responses is required to unravel these issues and inform the development of novel therapeutics or vaccine strategies.     

Antiviral responses induced by the TLR3 pathway

Antiviral responses are successively induced in virus‐infected animals, and include primary innate immune responses such as type I interferon (IFN) and cytokine production, secondary natural killer (NK) cell responses, and final cytotoxic T lymphocyte (CTL) responses and antibody production. The endosomal Toll‐like receptors (TLRs) and cytoplasmic RIG‐I‐like receptors (RLRs), which recognize viral nucleic acids, are responsible for virus‐induced type I IFN production. RLRs are expressed in most tissues and cells and are primarily implicated in innate immune responses against various viruses through type I IFN production, whereas nucleic acid‐sensing TLRs, TLRs 3, 7, 8 and 9, are expressed on the endosomal membrane of dendritic cells (DCs) and play distinct roles in antiviral immunity. TLR3 recognizes viral double‐stranded RNA taken up into the endosome and serves to protect the host against viral infection by the induction of a range of responses including type I IFN production and DC‐mediated activation of NK cells and CTLs, although the deteriorative role of TLR3 has also been reported in some virus infections. Here, we review the current knowledge on the role of TLR3 during viral infection, and the current understanding of the TLR3‐signalling cascade that operates via the adaptor protein TICAM‐1 (also called TRIF). Copyright © 2011 John Wiley & Sons, Ltd.     

Activation of the interferon-beta promoter during hepatitis C virus RNA replication

In this study we examined the impact of hepatitis C virus (HCV) RNA replication on the innate antiviral response of the host cell. Replication of an HCV subgenomic replicon stimulated the activation of the interferon (IFN)-beta promoter and the production of IFN in human hepatoma cells. Using a variety of functional assays, we found that HCV RNA replication induced the activation and DNA-binding activity of NFkappaB and interferon regulatory factor (IRF)-1. In addition, microscopy experiments revealed a higher frequency of cells containing the nuclear-localized, active form of IRF-3 in HCV replicon cultures versus control cultures. Consistent with these observations, cells harboring the HCV replicon exhibited high basal level expression of a subset of IFN-stimulated antiviral genes. Our results indicate that HCV RNA replication can stimulate cellular antiviral programs that contribute to the assembly and activation of the IFN-beta enhanceosome complex and initiation of the antiviral state. Stable HCV RNA replication in the face of the host antiviral response suggests that HCV may encode one or more proteins capable of overcoming specific antiviral processes, thereby supporting persistent infection.     

Crimean-Congo hemorrhagic fever virus delays activation of the innate immune response

As a first line of defence against virus infection, mammalian cells elicit an innate immune response, characterized by secretion of type I interferons and the up-regulation of interferon stimulated genes. Many viruses down-regulate the innate immune responses in order to enhance their virulence. Crimean-Congo hemorrhagic fever virus (CCHFV), a Nairovirus of the family Bunyaviridae is the causative agent of severe hemorrhagic fever in humans with high mortality. Knowledge regarding the innate immune response against CCHFV is most limited. Interestingly, in this study it is shown that replicating CCHFV delays substantially the IFN response, possibly by interfering with the activation pathway of IRF-3. In addition, it is demonstrated that CCHFV replication is almost insensitive to subsequent treatment with interferon-alpha. Once the virus is replicating, virus replication is more or less insensitive to the antiviral effects induced by the interferon. By using an interferon bioassay, it is shown that infected cells secrete interferon relatively late after infection, that is, 48 hr post-infection. In summary, the results suggest the presence of a virulence factor encoded by CCHFV that delays the host defence in order to allow rapid viral spread in the host.     

Activation of Vgamma9Vdelta2 T cells by non-peptidic antigens induces the inhibition of subgenomic HCV replication

Hepatitis C virus (HCV) has evolved complex strategies to evade host immune responses and establish chronic infection. Since human Vgamma9Vdelta2 T lymphocytes play a critical role in the immune response against viruses, we analyzed their antiviral functions on Huh7 hepatoma cells carrying the subgenomic HCV replicon (Rep60 cells). In a transwell culture system, Rep60 cells were co-cultured with either PBMCs or highly purified gammadelta T cells stimulated by non-peptidic antigens. Vgamma9Vdelta2 T cell activation was associated with a dramatic reduction of HCV RNA levels. Neutralizing antibodies targeting IFN-gamma revealed a critical role for this cytokine in the inhibition of HCV replication. Interestingly, drugs already in clinical use, such as Phosphostim and Zoledronate, known to activate gammadelta T cells, were shown to induce the inhibition of HCV replication mediated by Vgamma9Vdelta2 T cells of HCV patients. Our data suggest that the therapeutic activation of Vgamma9Vdelta2 T lymphocytes may represent an additional strategy to inhibit HCV replication and to restore a Th1-oriented immune response in HCV-infected patients.     

Seoul virus suppresses NF-κB-mediated inflammatory responses of antigen presenting cells from Norway rats

Hantavirus infection reduces antiviral defenses, increases regulatory responses, and causes persistent infection in rodent hosts. To address whether hantaviruses alter the maturation and functional activity of antigen presenting cells (APCs), rat bone marrow-derived dendritic cells (BMDCs) and macrophages (BMDMs) were generated and infected with Seoul virus (SEOV) or stimulated with TLR ligands. SEOV infected both DCs and macrophages, but copies of viral RNA, viral antigen, and infectious virus titers were higher in macrophages. The expression of MHCII and CD80, production of IL-6, IL-10, and TNF-α, and expression of Ifnβ were attenuated in SEOV-infected APCs. Stimulation of APCs with poly I:C prior to SEOV infection increased the expression of activation markers and production of inflammatory cytokines and suppressed SEOV replication. Infection of APCs with SEOV suppressed LPS-induced activation and innate immune responses. Hantaviruses reduce the innate immune response potential of APCs derived from a natural host, which may influence persistence of these zoonotic viruses in the environment.     

Increased natural cytotoxicity receptor expression and relevant IL-10 production in NK cells from chronically infected viremic HCV patients

Hepatitis C virus (HCV) readily establishes high-level lifelong persistent infection in the majority of immunocompetent adults with failure of HCV-specific CD8+ CTL to clear viral replication. Virus-induced conditioning of innate immune responses is a possible mechanism that may contribute to the impairment of virus-specific CD8+ CTL responses. Here, we analyzed whether triggering of NK cell receptor expression and function is affected during chronic viremic HCV infection. Flow cytometric analysis of purified resting peripheral NK cells showed no evidence of NK cell activation, while analysis of natural cytotoxicity receptors (NCR) showed that NK cells from HCV-infected patients had selective increased expression of NKp30 and NKp46. NK cells had corresponding conserved cytotoxic activity against all targets with the exception of HepG2 hepatoma cells. Freshly separated NK cells from HCV patients showed significant production of IL-10 and normal concentrations of IFN-gamma upon cell-mediated triggering. Thus, increased expression of NKp30 during HCV infection with increased IL-10 production could contribute, once NK cells localize in the liver, to a NK-DC crosstalk leading to skewing of subsequent adaptive immune responses and lack of virus control.     

Roles of Type I and III Interferons in COVID-19

Coronavirus disease 2019 (COVID-19) is an ongoing global pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Type I and III interferon (IFN) responses act as the first line of defense against viral infection and are activated by the recognition of viruses by infected cells and innate immune cells. Dysregulation of host IFN responses has been known to be associated with severe disease progression in COVID-19 patients. However, the reported results are controversial and the roles of IFN responses in COVID-19 need to be investigated further. In the absence of a highly efficacious antiviral drug, clinical studies have evaluated recombinant type I and III IFNs, as they have been successfully used for the treatment of infections caused by two other epidemic coronaviruses, SARS-CoV-1 and Middle East respiratory syndrome (MERS)-CoV. In this review, we describe the strategies by which SARS-CoV-2 evades IFN responses and the dysregulation of host IFN responses in COVID-19 patients. In addition, we discuss the therapeutic potential of type I and III IFNs in COVID-19.     

MDA5/RIG-I and virus recognition

The innate immune system initially recognizes RNA virus infection and evokes antiviral responses by producing type I interferons (IFNs). Toll-like receptors (TLRs) and cytoplasmic retinoic acid-inducible gene I (RIG-I)-like helicases (RLHs) are the two major receptor systems for detecting RNA viruses. The RLH signaling pathways play essential roles in the recognition of RNA viruses in various cells, with the exception of plasmacytoid dendritic cells, which utilize TLRs for virus recognition. The route of infection determines the cell types responsible for type I IFN production. Recent studies have suggested that TLRs are critical for activation of adaptive immune responses against several virus infections, although it may be premature to draw such a conclusion for virus infections in general. In this review, we will discuss recent advances toward clarifying the signaling pathways activated by RLHs and TLRs.     

Role of NK and NKT cells in the immunopathogenesis of HCV-induced hepatitis

Natural killer (NK) cells constitute the first line of host defense against invading pathogens. They usually become activated in an early phase of a viral infection. Liver is particularly enriched in NK cells, which are activated by hepatotropic viruses such as hepatitis C virus (HCV). The activated NK cells play an essential role in recruiting virus-specific T cells and in inducing antiviral immunity in liver. They also eliminate virus-infected hepatocytes directly by cytolytic mechanisms and indirectly by secreting cytokines, which induce an antiviral state in host cells. Therefore, optimally activated NK cells are important in limiting viral replication in this organ. This notion is supported by the observations that interferon treatment is effective in HCV-infected persons in whom it increases NK cell activity. Not surprisingly, HCV has evolved multiple strategies to counter host's NK cell response. Compromised NK cell functions have been reported in chronic HCV-infected individuals. It is ironic that activated NK cells may also contribute toward liver injury. Further studies are needed to understand the role of these cells in host defense and in liver pathology in HCV infections. Recent advances in understanding NK cell biology have opened new avenues for boosting innate and adaptive antiviral immune responses in HCV-infected individuals.     

Innate immune responses in hepatitis C virus infection

Hepatitis C virus (HCV) is a major causative agent of chronic hepatitis and hepatocellular carcinoma worldwide and thus poses a significant public health threat. A hallmark of HCV infection is the extraordinary ability of the virus to persist in a majority of infected people. Innate immune responses represent the front line of defense of the human body against HCV immediately after infection. They also play a crucial role in orchestrating subsequent HCV-specific adaptive immunity that is pivotal for viral clearance. Accumulating evidence suggests that the host has evolved multifaceted innate immune mechanisms to sense HCV infection and elicit defense responses, while HCV has developed elaborate strategies to circumvent many of these. Defining the interplay of HCV with host innate immunity reveals mechanistic insights into hepatitis C pathogenesis and informs approaches to therapy. In this review, we summarize recent advances in understanding innate immune responses to HCV infection, focusing on induction and effector mechanisms of the interferon antiviral response as well as the evasion strategies of HCV.     

Impact of alloimmune T cell responses on hepatitis C virus replication in liver transplant recipients

We investigated the influence of alloimmune T cell responses on hepatitis C virus (HCV) replication in HCV-infected patients after liver transplantation (LT). To monitor the immune-status in 27 HCV-infected LT recipients, we routinely performed mixed lymphocyte reaction (MLR) assays within 4 weeks after LT. HCV RNA titers in most patients fluctuated in inverse proportion to the stimulation index (SI) of anti-donor reactive T cells early after LT. Two weeks after LT, recipients with high HCV RNA titers (>1000 KIU/mL) displayed a significantly lower SI for anti-donor reactive T cells than recipients with low HCV RNA titers did (<1000 KIU/mL). An in vitro transwell assay mimicking the anatomical features of the interaction between HCV-infected hepatocytes and alloreactive T cells in allograft livers demonstrated that interferon (IFN)-γ was necessary to suppress HCV replication. This study proves the significant impact of alloimmune T cell responses on HCV replication in HCV-infected LT recipients.     

Cell-type-specific innate immune response to oncolytic newcastle disease virus

Abstract Virotherapy of cancer exploits the potential of naturally occurring and engineered oncolytic viruses to selectively replicate in and cause cytotoxicity to tumor cells without affecting healthy normal cells. The tumor selectivity of Newcastle disease virus (NDV), a member of the family Paramyxoviridae, depends on the differential type I interferon (IFN) response. Further understanding of the key mechanisms and immune effector molecules involved will aid in augmenting the oncolytic properties of NDV. Here we report on the infection kinetics and innate immune responses to a recombinant LaSota strain of NDV (rLaSota eGFP) in human tumor and normal cells. We observed varying replicative fit and cytotoxicity of rLaSota eGFP depending on the tumor cell type, with severely restricted replication in normal cells. The absence of retinoic acid-inducible gene I (RIG-I), a cytosolic RNA sensor, determined sensitivity to NDV. Productive NDV infection with a moderate IFN-α induction in human multiple myeloma cells suggested a role for IFN-independent mechanisms or lack of type I IFN reinforcement by RIG-I. Proinflammatory cytokines and chemokines were altered differentially in infected normal and tumor cells. Our results suggest that tumor selectivity is dependent on variations in the cellular antiviral response to infection with NDV and RIG-I expression.     

Human immunodeficiency virus enhances hepatitis C virus replication by differential regulation of IFN and TGF family genes

HIV co‐infection significantly impacts the natural history of hepatitis C virus (HCV) by increasing plasma HCV viral load, accelerating liver disease progression, and reducing rates of HCV clearance. Cytokines play an important role in regulating hepatic inflammation and fibrogenesis during chronic HCV infection, yet the impact of HIV on cytokine expression is unknown. In this study, an HCV continuous infection cell culture system was modified to permit co‐infection with HIV to test the hypothesis that virus‐induced disregulation of immune‐response genes, particularly interferons and TGF‐β, may create a permissive environment for the initial establishment of HIV/HCV co‐infection in the host. CCR5‐expressing Huh‐7.5 hepatoma cells were transduced with human CD4 antigen to allow HIV infection in vitro. Co‐infection of CD4⁺ Huh‐7.5 cells with HIV and HCV or co‐culture of HIV‐infected CD4⁺ Huh‐7.5 cells and HCV‐infected Huh‐7.5 cells increased the level of HCV RNA compared to HCV mono‐infection. Quantitative gene expression analysis revealed HIV‐induced up regulation of most tested IFN family genes when compared to HCV or co‐infection. HCV infection induced up regulation of many TGF family genes that were subsequently down‐regulated in the presence of HIV or HIV/HCV. Interestingly, co‐infection resulted in down regulation of several IFN genes and significant up regulation of TGF‐β genes leading to an overall enhancement of HCV replication. These data suggest that HIV infection may influence HCV replication in vitro by increasing levels of HCV RNA, possibly through the differential regulation of endogenous IFN and TGF family genes. J. Med. Virol. 84:1344–1352, 2012. © 2012 Wiley Periodicals, Inc.     

B cells are the predominant mediators of early systemic viral dissemination during rectal LCMV infection

Determining the magnitude of local immune response during mucosal exposure to viral pathogens is critical to understanding the mechanism of viral pathogenesis. We previously showed that vaginal inoculation of lymphocytic choriomeningitis virus (LCMV) fails to induce a robust innate immune response in the lower female reproductive tract (FRT), allowing high titer viral replication and a delay in T-cell-mediated viral control. Despite this immunological delay, LCMV replication remained confined mainly to the FRT and the draining iliac lymph node. Here, we show that rectal infection with LCMV triggers type I/III interferon responses, followed by innate immune activation and lymphocyte recruitment to the colon. In contrast to vaginal exposure, innate immunity controls LCMV replication in the colon, but virus rapidly disseminates systemically. Virus-induced inflammation promotes the recruitment of LCMV target cells to the colon followed by splenic viral dissemination by infected B cells, and to a lesser extent by CD8 T cells. These findings demonstrate major immunological differences between vaginal and rectal exposure to the same viral pathogen, highlighting unique risks associated with each of these common routes of sexual viral transmission.     

Differences in Type I interferon response in human lung epithelial cells infected by highly pathogenic H5N1 and low pathogenic H11N1 avian influenza viruses

Influenza A virus infection induces type I interferons (IFNs α/β) which activate host antiviral responses through a cascade of IFN signaling events. Herein, we compared highly pathogenic H5N1 and low pathogenic H11N1 avian influenza viruses isolated from India, for their replication kinetics and ability to induce IFN-β and interferon-stimulating genes (ISGs). The H5N1 virus showed a higher replication rate and induced less IFN-β and ISGs compared to the H11N1 virus when grown in the human lung epithelial A549 cells, reflecting the generation of differential innate immune responses during infection by these viruses. The non-structural 1 (NS1) protein, a major IFN-antagonist, known to help the virus in evading host innate immune response was compared from both the strains using bioinformatics tools. Analyses revealed differences in the composition of the NS1 proteins from the two strains that may have an impact on the modulation of the innate immune response. Intriguingly, H5N1 virus attenuated IFN-β response in a non-NS1 manner, suggesting the possible involvement of other viral proteins (PB2, PA, PB1/PB1-F2) of H5N1 in synergy with NS1. Preliminary analyses of the above proteins of the two strains by sequence comparison show differences in charged residues. The insight gained will be useful in designing experimental studies to elucidate a probable role of the polymerase protein(s) in association with NS1 in inhibiting the IFN signaling and understanding the molecular mechanism governing the difference.