Interferon-λ in the context of viral infections: production, response and therapeutic implications

IFN-λs inhibit Hantaan virus infection through the JAK-STAT pathway and expression of Mx2 protein

Hantaan virus (HTNV), member of the newly defined Hantaviridae family, within the order Bunyavirales, can cause a hemorrhagic fever with renal syndrome with high fatality rates in humans. However, no specific antiviral agents are currently available for HTNV infection approved by the US Food and Drug Administration. Although interferon lambdas (IFN-λs) have been shown to induce an antiviral state against HTNV, the molecular mechanisms remain to be determined. In this study, we found that IFN-λs exerted its anti-HTNV effect by activating Janus kinase/signal transducers and activators of transcription (JAK-STAT) pathway-mediated antiviral immunity in A549 cells. Simultaneously, IFN-λs downregulated suppressor of cytokine signaling proteins, which are the known negative feedback regulators of the JAK-STAT signaling pathway. Additionally, we demonstrated the role of IFN-λs-induced myxovirus resistance 2 (Mx2, also known as MxB) protein as a potential inhibitor for HTNV infection. These findings indicate that IFN-λs play an important role in cellular defenses against HTNV infection at an early stage and that human Mx2 may represent a potential therapeutic target for HTNV infection.

Type III Interferon Restriction by Porcine Epidemic Diarrhea Virus and the Role of Viral Protein nsp1 in IRF1 Signaling

Type III interferons (IFNs) play a vital role in maintaining the antiviral state of the mucosal epithelial surface in the gut, and in turn, enteric viruses may have evolved to evade the type III IFN responses during infection. To study the possible immune evasion of the type III IFN response by porcine epidemic diarrhea virus (PEDV), a line of porcine intestinal epithelial cells was developed as a cell model for PEDV replication. IFN-λ1 and IFN-λ3 inhibited PEDV replication, indicating the anti-PEDV activity of type III IFNs. Of the 21 PEDV proteins, nsp1, nsp3, nsp5, nsp8, nsp14, nsp15, nsp16, open reading frame 3 (ORF3), E, M, and N were found to suppress type III IFN activities, and IRF1 (interferon regulatory factor 1) signaling mediated the suppression. PEDV specifically inhibited IRF1 nuclear translocation. The peroxisome is the innate antiviral signaling platform for the activation of IRF1-mediated IFN-λ production, and the numbers of peroxisomes were found to be decreased in PEDV-infected cells. PEDV nsp1 blocked the nuclear translocation of IRF1 and reduced the number of peroxisomes to suppress IRF1-mediated type III IFNs. Mutational studies showed that the conserved residues of nsp1 were crucial for IRF1-mediated IFN-λ suppression. Our study for the first time provides evidence that the porcine enteric virus PEDV downregulates and evades IRF1-mediated type III IFN responses by reducing the number of peroxisomes.IMPORTANCE Porcine epidemic diarrhea virus (PEDV) is a highly contagious enteric coronavirus that emerged in swine in the United States and has caused severe economic losses. PEDV targets intestinal epithelial cells in the gut, and intestinal epithelial cells selectively induce and respond to the production of type III interferons (IFNs). However, little is known about the modulation of the type III IFN response by PEDV in intestinal epithelial cells. In this study, we established a porcine intestinal epithelial cell model for PEDV replication. We found that PEDV inhibited IRF1-mediated type III IFN production by decreasing the number of peroxisomes in porcine intestinal epithelial cells. We also demonstrated that the conserved residues in the PEDV nsp1 protein were crucial for IFN suppression. This study for the first time shows PEDV evasion of the type III IFN response in intestinal epithelial cells, and it provides valuable information on host cell-virus interactions not only for PEDV but also for other enteric viral infections in swine.

Selective regulation of type II interferon-inducible genes by NPM1/nucleophosmin

Nucleophosmin (NPM1) is a multifunctional nucleolar protein. Here, we analyze the role of NPM1 in gene expression using our previous microarray data and find a relationship between NPM1 and interferon (IFN)-γ-inducible genes. We show that NPM1 selectively regulates the expression of a subset of IFN-γ-inducible genes and directly binds to two important transcription factors in the type II IFN pathway: signal transducer and activator of transcription 1 and interferon regulatory factor 1 (IRF1). Furthermore, NPM1 is found to regulate the IFN-γ-inducible promoter activity of major histocompatibility complex class II transactivator (CIITA), and mutation of the IRF1-binding site on the CIITA promoter abolishes the effect of NPM1. Our results suggest a novel mechanism for IFN-γ-mediated gene expression by NPM1.

Type III Interferon-Mediated Signaling Is Critical for Controlling Live Attenuated Yellow Fever Virus Infection In Vivo

Yellow fever virus (YFV) is an arthropod-borne flavivirus, infecting ~200,000 people worldwide annually and causing about 30,000 deaths. The live attenuated vaccine strain, YFV-17D, has significantly contributed in controlling the global burden of yellow fever worldwide. However, the viral and host contributions to YFV-17D attenuation remain elusive. Type I interferon (IFN-α/β) signaling and type II interferon (IFN-γ) signaling have been shown to be mutually supportive in controlling YFV-17D infection despite distinct mechanisms of action in viral infection. However, it remains unclear how type III IFN (IFN-λ) integrates into this antiviral system. Here, we report that while wild-type (WT) and IFN-λ receptor knockout (λR^-/-) mice were largely resistant to YFV-17D, deficiency in type I IFN signaling resulted in robust infection. Although IFN-α/β receptor knockout (α/βR^-/-) mice survived the infection, mice with combined deficiencies in both type I signaling and type III IFN signaling were hypersusceptible to YFV-17D and succumbed to the infection. Mortality was associated with viral neuroinvasion and increased permeability of the blood-brain barrier (BBB). α/βR^-/- λR^-/- mice also exhibited distinct changes in the frequencies of multiple immune cell lineages, impaired T-cell activation, and severe perturbation of the proinflammatory cytokine balance. Taken together, our data highlight that type III IFN has critical immunomodulatory and neuroprotective functions that prevent viral neuroinvasion during active YFV-17D replication. Type III IFN thus likely represents a safeguard mechanism crucial for controlling YFV-17D infection and contributing to shaping vaccine immunogenicity.IMPORTANCE YFV-17D is a live attenuated flavivirus vaccine strain recognized as one of the most effective vaccines ever developed. However, the host and viral determinants governing YFV-17D attenuation and its potent immunogenicity are still unknown. Here, we analyzed the role of type III interferon (IFN)-mediated signaling, a host immune defense mechanism, in controlling YFV-17D infection and attenuation in different mouse models. We uncovered a critical role of type III IFN-mediated signaling in preserving the integrity of the blood-brain barrier and preventing viral brain invasion. Type III IFN also played a major role in regulating the induction of a potent but balanced immune response that prevented viral evasion of the host immune system. An improved understanding of the complex mechanisms regulating YFV-17D attenuation will provide insights into the key virus-host interactions that regulate host immune responses and infection outcomes as well as open novel avenues for the development of innovative vaccine strategies.

Functional Evolution of Influenza Virus NS1 Protein in Currently Circulating Human 2009 Pandemic H1N1 Viruses

In 2009, a novel H1N1 influenza virus emerged in humans, causing a global pandemic. It was previously shown that the NS1 protein from this human 2009 pandemic H1N1 (pH1N1) virus was an effective interferon (IFN) antagonist but could not inhibit general host gene expression, unlike other NS1 proteins from seasonal human H1N1 and H3N2 viruses. Here we show that the NS1 protein from currently circulating pH1N1 viruses has evolved to encode 6 amino acid changes (E55K, L90I, I123V, E125D, K131E, and N205S) with respect to the original protein. Notably, these 6 residue changes restore the ability of pH1N1 NS1 to inhibit general host gene expression, mainly by their ability to restore binding to the cellular factor CPSF30. This is the first report describing the ability of the pH1N1 NS1 protein to naturally acquire mutations that restore this function. Importantly, a recombinant pH1N1 virus containing these 6 amino acid changes in the NS1 protein (pH1N1/NSs-6mut) inhibited host IFN and proinflammatory responses to a greater extent than that with the parental virus (pH1N1/NS1-wt), yet virus titers were not significantly increased in cell cultures or in mouse lungs, and the disease was partially attenuated. The pH1N1/NSs-6mut virus grew similarly to pH1N1/NSs-wt in mouse lungs, but infection with pH1N1/NSs-6mut induced lower levels of proinflammatory cytokines, likely due to a general inhibition of gene expression mediated by the mutated NS1 protein. This lower level of inflammation induced by the pH1N1/NSs-6mut virus likely accounts for the attenuated disease phenotype and may represent a host-virus adaptation affecting influenza virus pathogenesis.IMPORTANCE Seasonal influenza A viruses (IAVs) are among the most common causes of respiratory infections in humans. In addition, occasional pandemics are caused when IAVs circulating in other species emerge in the human population. In 2009, a swine-origin H1N1 IAV (pH1N1) was transmitted to humans, infecting people then and up to the present. It was previously shown that the NS1 protein from the 2009 pandemic H1N1 (pH1N1) virus is not able to inhibit general gene expression. However, currently circulating pH1N1 viruses have evolved to encode 6 amino acid changes (E55K, L90I, I123V, E125D, K131E, and N205S) that allow the NS1 protein of contemporary pH1N1 strains to inhibit host gene expression, which correlates with its ability to interact with CPSF30. Infection with a recombinant pH1N1 virus encoding these 6 amino acid changes (pH1N1/NSs-6mut) induced lower levels of proinflammatory cytokines, resulting in viral attenuation in vivo This might represent an adaptation of pH1N1 virus to humans.

Risk of infectious diseases among first-degree relatives of transplant recipients who develop CMV infection: is the infectious phenotype inheritable?

Transplant recipients are at high risk of cytomegalovirus (CMV) infection. Mechanisms explaining the variation in risk of infections are far from fully elucidated. We hypothesised that host genetics explains part of the variation in risk of infection and examined if relatives of recipients with CMV infection have higher rates of severe infections compared to relatives of recipients without this infectious phenotype. In a register-based study, we included first-degree relatives of transplant recipients and examined the risk of hospitalisation due to overall infection or viral infection and risk of death among relatives of recipients who developed CMV infection within the first year of transplantation compared to relatives of recipients without CMV. Analyses were adjusted for sex, age and calendar year. We included 4470 relatives who were followed for 103,786 person-years, median follow-up 24 years [interquartile range (IQR) 12-36]. There were a total of 1360 infection-related hospitalisations in the follow-up period, incidence rate (IR) 13.1/1000 person-years [95% confidence interval (CI), 12.4; 13.8]. 206 relatives were hospitalised with viral infection, IR 1.8/1000 person-years (95% CI, 1.6; 2.0). There was no increased risk of hospitalisation due to infections, IR ratio (IRR) 0.99 (95% CI, 0.88; 1.12), nor specifically viral infections, IRR 0.87 (95% CI, 0.63; 1.19), in relatives of recipients with CMV compared to relatives of recipients without CMV. Also, no difference was seen in analyses stratified by transplant type, family relation and CMV serostatus. The risk of hospitalisation due to infection is not increased among first-degree relatives of transplant recipients with CMV infection compared to relatives of recipients without CMV.

Tick-Borne Viruses and Biological Processes at the Tick-Host-Virus Interface

Ticks are efficient vectors of arboviruses, although less than 10% of tick species are known to be virus vectors. Most tick-borne viruses (TBV) are RNA viruses some of which cause serious diseases in humans and animals world-wide. Several TBV impacting human or domesticated animal health have been found to emerge or re-emerge recently. In order to survive in nature, TBV must infect and replicate in both vertebrate and tick cells, representing very different physiological environments. Information on molecular mechanisms that allow TBV to switch between infecting and replicating in tick and vertebrate cells is scarce. In general, ticks succeed in completing their blood meal thanks to a plethora of biologically active molecules in their saliva that counteract and modulate different arms of the host defense responses (haemostasis, inflammation, innate and acquired immunity, and wound healing). The transmission of TBV occurs primarily during tick feeding and is a complex process, known to be promoted by tick saliva constituents. However, the underlying molecular mechanisms of TBV transmission are poorly understood. Immunomodulatory properties of tick saliva helping overcome the first line of defense to injury and early interactions at the tick-host skin interface appear to be essential in successful TBV transmission and infection of susceptible vertebrate hosts. The local host skin site of tick attachment, modulated by tick saliva, is an important focus of virus replication. Immunomodulation of the tick attachment site also promotes co-feeding transmission of viruses from infected to non-infected ticks in the absence of host viraemia (non-viraemic transmission). Future research should be aimed at identification of the key tick salivary molecules promoting virus transmission, and a molecular description of tick-host-virus interactions and of tick-mediated skin immunomodulation. Such insights will enable the rationale design of anti-tick vaccines that protect against disease caused by tick-borne viruses.

Cross-species antiviral activity of goose interferon lambda against duck plague virus is related to its positive self-regulatory feedback loop

Duck plague virus (DPV) is a virus of the Herpesviridae family that leads to acute disease with a high mortality rate in ducks. Control of the disease contributes to the development of poultry breeding. Type III IFN family (IFN-λs) is a novel member of the IFN family, and goose IFN-λ (goIFN-λ) is a newly identified gene whose antiviral function has only been investigated to a limited extent. Here, the cross-species antiviral activity of goIFN-λ against DPV in duck embryo fibroblasts (DEFs) was studied. We found that pre-treatment with goIFN-λ greatly increased the expression of IFN-λ in both heterologous DEFs and homologous goose embryo fibroblasts (GEFs), while differentially inducing IFNα- and IFN-stimulated genes. Additionally, a positive self-regulatory feedback loop of goIFN-λ was blocked by a mouse anti-goIFN-λ polyclonal antibody, which was confirmed in both homologous GEFs and goose peripheral blood mononuclear cells (PBMCs). The suppression of the BAC-DPV-EGFP by goIFN-λ in DEFs was confirmed by fluorescence microscopy, flow cytometry (FCM) analysis, viral copies and titre detection, which can be rescued by mouse anti-goIFN-λ polyclonal antibody incubation. Finally, reporter gene assays indicated that the cross-species antiviral activity of goIFN-λ against BAC-DPV-EGFP is related to its positive self-regulatory feedback loop and subsequent ISG induction. Our data shed light on the fundamental mechanisms of goIFN-λ antiviral function in vitro and extend the considerable range of therapeutic applications in multiple-poultry disease.

Inhibition of NF-κB activity by the porcine epidemic diarrhea virus nonstructural protein 1 for innate immune evasion

Porcine epidemic diarrhea virus emerged in the US is known to suppress the type I interferons response during infection. In the present study using porcine epithelial cells, we showed that PEDV inhibited both NF-κB and proinflammatory cytokines. PEDV blocked the p65 activation in infected cells and suppressed the PRD II-mediated NF-κB activity. Of the total of 22 viral proteins, nine proteins were identified as NF-κB antagonists, and nsp1 was the most potent suppressor of proinflammatory cytokines. Nsp1 interfered the phosphorylation and degradation of IκBα, and thus blocked the p65 activation. Mutational studies demonstrated the essential requirements of the conserved residues of nsp1 for NF-κB suppression. Our study showed that PEDV inhibited NF-κB activity and nsp1 was a potent NF-κB antagonist for suppression of both IFN and early production of pro-inflammatory cytokines.

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PEDV inhibits type I IFNs and NF-κB-mediated pro-inflammatory cytokines.

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PEDV blocks p65 nuclear translocation in virus-infected cells.

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Among 22 viral proteins, nsp1, nsp3, nsp5, nsp7, nsp14, nsp15, nsp16, ORF3, and E are NF-κB antagonists.

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Nsp1 suppresses pro-inflammatory cytokines and p65 activation by blocking IκBα phosphorylation.

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The conserved residues of nsp1 are crucial for NF-κB suppression.

The dynamic changes of interferon lambdas related genes and proteins in JAK/STAT pathway in both acute and chronic HIV-1 infected patients

BACKGROUND

Host immune responses during acute HIV-1 infection can influence the viral setpoint, which is a predictor of disease progression. Interferon (IFN)-lambdas are newly classified type III interferons, which use JAK-STAT pathway. Currently, the dynamics of IFN-lambdas related genes and proteins expression in the signaling pathway have not been well elaborated, especially in acute HIV-1-infected patients.

OBJECTIVES

To evaluate the dynamic changes of IFN-lambdas related genes and proteins in JAK/STAT pathway in acute HIV-1-infected patients, and analyze their correlation with CD4 T cell counts and HIV-1 viral loads.

STUDY DESIGN

Real-time PCR and flow cytometry methods were used to evaluate the dynamic changes of IFN-lambdas related genes and proteins in JAK/STAT pathway in both acute and chronic HIV-1-infected patients.

RESULTS

The IFN-alpha receptors (R), IFN-gamma R, IFN-lambdas R and STAT1 mRNA and protein levels increased in acute HIV-1-infected patients (p < 0.01), in addition, Mx1 mRNA levels in acute HIV-1-infected patients are higher than those in HIV-negative subjects. IFN-lambdas R and IFN-alpha R mRNA levels are inversely correlated with CD4+ T-cell counts, but are positively correlated with viral loads.

CONCLUSIONS

The dynamic changes of IFNs related genes in JAK-STAT pathway in acute HIV-1 infection will deepen our understanding of the roles of IFN-lambdas in HIV pathogenesis.

Dendritic Cell-Airway Epithelial Cell Cross-Talk Changes with Age and Contributes to Chronic Lung Inflammatory Diseases in the Elderly

Age-associated dysregulated immune and inflammatory responses are one of the major factors responsible for the prevalence of chronic respiratory diseases in the older population. Pulmonary dendritic cells (DCs) are present below the airway epithelial cells (AECs) and are critical in initiating effective immune responses to harmful pathogens while maintaining tolerance against harmless antigens. The interaction between DCs and AECs plays a crucial role in lung immunity at homeostasis and during infections. The functions of both DCs and AECs are impacted with age. The present report reviews how the potential crosstalk between pulmonary DCs and AECs is dysregulated in the elderly impairing the capacity to maintain tolerance at the respiratory surfaces, which results in severe and chronic respiratory inflammatory diseases. We also discuss how such DC-AECs crosstalk will provide insight into the mechanisms underlying the increased susceptibility of the elderly to pulmonary inflammatory diseases.

IL28B genetic variation and cytomegalovirus-specific T-cell immunity in allogeneic stem cell transplant recipients

A single nucleotide polymorphism (SNP), 3 kbp upstream of the IL28B gene (rs12979860; C/T), has been shown to influence the dynamics of cytomegalovirus (CMV) replication in allogeneic stem cell transplant recipients (Allo-SCT). We investigated whether this SNP had any effect on the dynamics of CMV-specific T-cell immunity in these patients. CMV pp65/IE-1 IFN-γ CD8+ and CD4+ T cells were enumerated by flow cytometry in 85 patients with no prior CMV DNAemia (group A) and in 57 after the onset of CMV DNAemia (group B). Donor IL28B genotype was determined by real-time PCR and plasma levels of IL-28B were quantitated by ELISA. CMV-specific T-cell counts and plasma IL-28B levels in patients in group A were not significantly different among the IL28B genotype groups. Patients harboring the donor IL28B T/T genotype appeared to expand CMV-specific IFN-γ CD8+ cells to a higher level in response to viral replication than their C/T and C/C counterparts. Fewer patients in the T/T group received pre-emptive antiviral therapy (P = 0.05). Overall, a significant inverse correlation was observed between median IL-28B levels measured prior to the CMV DNAemia onset and the level of CMV-specific CD8+ T cells enumerated after detection of CMV DNAemia (σ = -0.471; P = 0.013). In summary, the data suggested that the protective effect attributed to the rs12979860 SNP minor T allele could be mediated, at least in part, by eliciting robust CMV-specific T-cell responses. J. Med. Virol. 89:685-695, 2017. © 2016 Wiley Periodicals, Inc.

Expression of Ifnlr1 on Intestinal Epithelial Cells Is Critical to the Antiviral Effects of Interferon Lambda against Norovirus and Reovirus

Lambda interferon (IFN-λ) has potent antiviral effects against multiple enteric viral pathogens, including norovirus and rotavirus, in both preventing and curing infection. Because the intestine includes a diverse array of cell types, however, the cell(s) upon which IFN-λ acts to exert its antiviral effects is unclear. Here, we sought to identify IFN-λ-responsive cells by generation of mice with lineage-specific deletion of the receptor for IFN-λ, Ifnlr1 We found that expression of IFNLR1 on intestinal epithelial cells (IECs) in the small intestine and colon is required for enteric IFN-λ antiviral activity. IEC Ifnlr1 expression also determines the efficacy of IFN-λ in resolving persistent murine norovirus (MNoV) infection and regulates fecal shedding and viral titers in tissue. Thus, the expression of Ifnlr1 by IECs is necessary for the response to both endogenous and exogenous IFN-λ. We further demonstrate that IEC Ifnlr1 expression is required for the sterilizing innate immune effects of IFN-λ by extending these findings in Rag1-deficient mice. Finally, we assessed whether our findings pertained to multiple viral pathogens by infecting mice specifically lacking IEC Ifnlr1 expression with reovirus. These mice phenocopied Ifnlr1-null animals, exhibiting increased intestinal tissue titers and enhanced reovirus fecal shedding. Thus, IECs are the critical cell type responding to IFN-λ to control multiple enteric viruses. This is the first genetic evidence that supports an essential role for IECs in IFN-λ-mediated control of enteric viral infection, and these findings provide insight into the mechanism of IFN-λ-mediated antiviral activity.IMPORTANCE Human noroviruses (HNoVs) are the leading cause of epidemic gastroenteritis worldwide. Type III interferons (IFN-λ) control enteric viral infections in the gut and have been shown to cure mouse norovirus, a small-animal model for HNoVs. Using a genetic approach with conditional knockout mice, we identified IECs as the dominant IFN-λ-responsive cells in control of enteric virus infection in vivo Upon murine norovirus or reovirus infection, Ifnlr1 depletion in IECs largely recapitulated the phenotype seen in Ifnlr1^-/- mice of higher intestinal tissue viral titers and increased viral shedding in the stool. Moreover, IFN-λ-mediated sterilizing immunity against murine norovirus requires the capacity of IECs to respond to IFN-λ. These findings clarify the mechanism of action of this cytokine and emphasize the therapeutic potential of IFN-λ for treating mucosal viral infections.

IFN-λ Inhibits Drug-Resistant HIV Infection of Macrophages

Type III interferons (IFN-λs) have been demonstrated to inhibit a number of viruses, including HIV. Here, we further examined the anti-HIV effect of IFN-λs in macrophages. We found that IFN-λs synergistically enhanced anti-HIV activity of antiretrovirals [azidothymidine (AZT), efavirenz, indinavir, and enfuvirtide] in infected macrophages. Importantly, IFN-λs could suppress HIV infection of macrophages with the drug-resistant strains, including AZT-resistant virus (A012) and reverse transcriptase inhibitor-resistant virus (TC49). Mechanistically, IFN-λs were able to induce the expression of several important anti-HIV cellular factors, including myxovirus resistance 2 (Mx2), a newly identified HIV post-entry inhibitor and tetherin, a restriction factor that blocks HIV release from infected cells. These observations provide additional evidence to support the potential use of IFN-λs as therapeutics agents for the treatment of HIV infection.

Evolutionary Origin of the Interferon-Immune Metabolic Axis: The Sterol-Vitamin D Link

In vertebrate animals, the sterol metabolic network is emerging as a central player in immunity and inflammation. Upon infection, flux in the network is acutely moderated by the interferon (IFN) response through direct molecular and bi-directional communications. How sterol metabolism became linked to IFN control and for what purpose is not obvious. Here, we deliberate on the origins of these connections based on a systematic review of the literature. A narrative synthesis of publications that met eligibility criteria allowed us to trace an evolutionary path and functional connections between cholesterol metabolism and immunity. The synthesis supports an ancestral link between toxic levels of cholesterol-like products and the vitamin D receptor (VDR). VDR is an ancient nuclear hormone receptor that was originally involved in the recognition and detoxification of xenobiotic marine biotoxins exhibiting planar sterol ring scaffolds present in aquatic environments. Coadaptation of this receptor with the acquisition of sterol biosynthesis and IFNs in vertebrate animals set a stage for repurposing and linking a preexisting host-protection mechanism of harmful xenobiotics to become an important regulator in three key interlinked biological processes: bone development, immunity, and calcium homeostasis. We put forward the hypothesis that sterol metabolites, especially oxysterols, have acted as evolutionary drivers in immunity and may represent the first example of small-molecule metabolites linked to the adaptive coevolution and diversification of host metabolic and immune regulatory pathways.

Downregulation of autophagy-related gene ATG5 and GABARAP expression by IFN-λ1 contributes to its anti-HCV activity in human hepatoma cells

Type-III interferon (IFN-λ), the most recently discovered family of IFNs, shares common features with type I IFNs, but also has many distinctive activities. It is not clear that whether IFN-λ has additional antiviral mechanisms. In this study, we investigated the effects of IFN-λ on autophagy, a cellular process closely related to hepatitis C virus (HCV) infection in human hepatoma Huh7 cells. Our results showed that IFN-λ1 treatment inhibit autophagic activity in Huh7 cells, as evidenced by the decreased expression of microtubule-associated protein 1 light chain 3B (LC3B)-II and conversion of LC3B-I to LC3B-II, decreased formation of GFP-LC3 puncta and accumulation of autophagosomes. IFN-λ1 could also inhibit HCV-induced or tunicamycin (a known inducer of autophagy with similar mechanism to HCV infection) -induced LC3B-II expression and autophagosome formation. Through PCR array, real time RT PCR, and western blot, two autophagy-related genes, ATG5 and GABARAP, were identified and verified to be down-regulated by IFN-λ1 treatment, either in HCV-uninfected Huh7 cells or in HCV JFH-1-infected cells. Overexpression of ATG5 and/or GABARAP could partly recover the IFN-λ1-inhibited HCV replication. Mechanism research demonstrated that IFN-λ1 could induce the expression of miR-181a and miR-214 (targeting ATG5 and GABARAP respectively), by which down-regulates ATG5 and GABARAP expression. Taken together, our results indicate that suppression of the autophagy response by IFN-λ1 contributes to IFN-λ1 anti-HCV activity. The results also provide a theoretical basis for improving the effectiveness of IFN treatment of HCV infection through inhibition of the HCV-induced autophagy response.

IFN-λ: A New Inducer of Local Immunity against Cancer and Infections

IFN-λ is the newly established type III IFN with unique immunomodulatory functions. In contrast to the IFN-α/β family and to some extent IFN-γ, IFN-λ is apparently acting in specific areas of the body to activate resident immune cells and induces a local immunity, instrumental in preventing particular infections and also keeping transformed cells under control. Mucosal areas of lung and gastrointestinal tracts are now under scrutiny to elucidate the immune mechanisms triggered by IFN-λ and leading to viral protection. New evidence also indicates the crucial role of IFN-λ in promoting innate immunity in solid cancer models. Based on its unique biological activities among the IFN system, new immunotherapeutic approaches are now emerging for the treatment of cancer, infection, and autoimmune diseases. In the present review, we highlight the recent advances of IFN-λ immunomodulatory functions. We also discuss the perspectives of IFN-λ as a therapeutic agent.

NS1 Protein Mutation I64T Affects Interferon Responses and Virulence of Circulating H3N2 Human Influenza A Viruses

Influenza NS1 protein is the main viral protein counteracting host innate immune responses, allowing the virus to efficiently replicate in interferon (IFN)-competent systems. In this study, we analyzed NS1 protein variability within influenza A (IAV) H3N2 viruses infecting humans during the 2012-2013 season. We also evaluated the impact of the mutations on the ability of NS1 proteins to inhibit host innate immune responses and general gene expression. Surprisingly, a previously unidentified mutation in the double-stranded RNA (dsRNA)-binding domain (I64T) decreased NS1-mediated general inhibition of host protein synthesis by decreasing its interaction with cleavage and polyadenylation specificity factor 30 (CPSF30), leading to increased innate immune responses after viral infection. Notably, a recombinant A/Puerto Rico/8/34 H1N1 virus encoding the H3N2 NS1-T64 protein was highly attenuated in mice, most likely because of its ability to induce higher antiviral IFN responses at early times after infection and because this virus is highly sensitive to the IFN-induced antiviral state. Interestingly, using peripheral blood mononuclear cells (PBMCs) collected at the acute visit (2 to 3 days after infection), we show that the subject infected with the NS1-T64 attenuated virus has diminished responses to interferon and to interferon induction, suggesting why this subject could be infected with this highly IFN-sensitive virus. These data demonstrate the importance of influenza virus surveillance in identifying new mutations in the NS1 protein, affecting its ability to inhibit innate immune responses and, as a consequence, the pathogenicity of the virus.

IMPORTANCE

Influenza A and B viruses are one of the most common causes of respiratory infections in humans, causing 1 billion infections and between 300,000 and 500,000 deaths annually. Influenza virus surveillance to identify new mutations in the NS1 protein affecting innate immune responses and, as a consequence, the pathogenicity of the circulating viruses is highly relevant. Here, we analyzed amino acid variability in the NS1 proteins from human seasonal viruses and the effect of the mutations in innate immune responses and virus pathogenesis. A previously unidentified mutation in the dsRNA-binding domain decreased NS1-mediated general inhibition of host protein synthesis and the interaction of the protein with CPSF30. This mutation led to increased innate immune responses after viral infection, augmented IFN sensitivity, and virus attenuation in mice. Interestingly, using PBMCs, the subject infected with the virus encoding the attenuating mutation induced decreased antiviral responses, suggesting why this subject could be infected with this virus.

Effects of lactoferrin on the production of interferon-λ by the human intestinal epithelial cell line HT-29

We examined the in-vitro effects of bovine lactoferrin (LF) on the production of interferon-λ (IFN-λ), an antiviral cytokine important for the defense of enterocytes, using the human intestinal epithelial cell line HT-29. HT-29 cell cultures were treated with LF for 1 h, and the cultures were stimulated with polyinosinic-polycytidylic acid (poly I:C). LF increased the concentration of IFN-λ in the culture supernatant after stimulation in a dose-dependent manner. A similar increase in the concentration of IFN-λ was observed in the supernatant of cells washed between treatment with LF and stimulation with poly I:C. At 6 and 24 h after stimulation with poly I:C (early and late phases, respectively) treated cultures contained significantly higher concentrations of IFN-λ1 in the culture supernatant, and significantly higher IFN-λ1 and IFN-λ2 mRNA levels, than controls. These results suggest that LF activates the innate cellular immunity of the enterocytes to double-stranded RNA and increases the production of IFN-λ.

Synergistic production of TNFα and IFNα by human pDCs incubated with IFNλ3 and IL-3

In this study, we investigated whether IFNλ3 and IL-3 reciprocally influence their capacity to activate various functions of human plasmacytoid dendritic cells (pDCs). In fact, we preliminarily observed that IFNλ3 upregulates the expression of the IL-3Rα (CD123), while IL-3 augments the expression of IFNλR1 in pDCs. As a result, we found that combination of IFNλ3 and IL-3 induces a strong potentiation in the production of TNFα, IFNα, as well as in the expression of Interferon-Stimulated Gene (ISG) mRNAs by pDCs, as compared to either IFNλ3 or IL-3 alone. In such regard, we found that endogenous IFNα autocrinally promotes the expression of ISG mRNAs in IL-3-, but not in IFNλ3 plus IL-3-, treated pDCs. Moreover, we uncovered that the production of IFNα by IFNλ3 plus IL-3-treated pDCs is mostly dependent on endogenously produced TNFα. Altogether, our data demonstrate that IFNλ3 and IL-3 collaborate to promote, at maximal levels, discrete functional responses of human pDCs.

Mumps Virus Induces Protein-Kinase-R-Dependent Stress Granules, Partly Suppressing Type III Interferon Production

Stress granules (SGs) are cytoplasmic granular aggregations that are induced by cellular stress, including viral infection. SGs have opposing antiviral and proviral roles, which depend on virus species. The exact function of SGs during viral infection is not fully understood. Here, we showed that mumps virus (MuV) induced SGs depending on activation of protein kinase R (PKR). MuV infection strongly induced interferon (IFN)-λ1, 2 and 3, and IFN-β through activation of IFN regulatory factor 3 (IRF3) via retinoic acid inducible gene-I (RIG-I) and the mitochondrial antiviral signaling (MAVS) pathway. MuV-induced IFNs were strongly upregulated in PKR-knockdown cells. MuV-induced SG formation was suppressed by knockdown of PKR and SG marker proteins, Ras-GTPase-activating protein SH3-domain-binding protein 1 and T-cell-restricted intracellular antigen-1, and significantly increased the levels of MuV-induced IFN-λ1. However, viral titer was not altered by suppression of SG formation. PKR was required for induction of SGs by MuV infection and regulated type III IFN (IFN-λ1) mRNA stability. MuV-induced SGs partly suppressed type III IFN production by MuV; however, the limited suppression was not sufficient to inhibit MuV replication in cell culture. Our results provide insight into the relationship between SGs and IFN production induced by MuV infection.

Rotavirus Strategies Against the Innate Antiviral System

"Rotaviruses represent the most important etiological agents of acute, severe gastroenteritis in the young of many animal species, including humans." This statement, variations of which are a common beginning in articles about rotaviruses, reflects the fact that these viruses have evolved efficient strategies for evading the innate immune response of the host and for successfully replicating in the population. In this review, we summarize what is known about the defense mechanisms that host cells employ to prevent rotavirus invasion and the countermeasures that these viruses have successfully developed to surpass cellular defenses. Rotaviruses use at least two viral multifunctional proteins to directly interact with, and prevent the activation of, the interferon system, and they use at least one other protein to halt the protein synthesis machinery and prevent the expression of most of the transcriptional antiviral program of the cell. Characterization of the confrontation between rotaviruses and their host cells has allowed us to learn about the virus-host coevolution that prevents the damaging effects of the innate immune response.

Dengue virus infection induces interferon-lambda1 to facilitate cell migration

A marked increase in the rate of dengue virus (DENV) infection has resulted in more than 212 deaths in Taiwan since the beginning of 2015, mostly from fatal outcomes such as dengue hemorrhagic fever and dengue shock syndrome. The pathogenic mechanisms of these fatal manifestations are poorly understood. Cytokines induce an overwhelming immune reaction and thus have crucial roles. Interferon-lambda (IFN-λ), a newly identified IFN subtype, has antiviral effects, but its immunologic effects in DENV infection have not been investigated. In the present study, we show that DENV infection preferentially induced production of IFN-λ1 in human dendritic cells (DCs) and human lung epithelial cells. Virus nonstructural 1 (NS1) glycoprotein was responsible for the effect. DENV-induced production of IFN-λ1 was dependent on signaling pathways involving toll-like receptor (TLR)-3, interferon regulation factor (IRF)-3, and nuclear factor-kappaB (NF-κB). Blocking interaction between IFN-λ1 and its receptor IFN-λR1 through siRNA interference reduced DENV-induced DC migration towards the chemoattractants CCL19 and CCL21, by inhibiting CCR7 expression. Furthermore, IFN-λ1 itself induced CCR7 expression and DC migration. Our study presents the first evidence of the mechanisms and effects of IFN-λ1 induction in DENV-infected DCs and highlights the role of this cytokine in the immunopathogenesis of DENV infection.

Gene-disease association with human IFNL locus polymorphisms extends beyond hepatitis C virus infections

Interferon (IFN) lambda (IFN-λ or type III IFN) gene polymorphisms were discovered in the year 2009 to have a strong association with spontaneous and treatment-induced clearance of hepatitis C virus (HCV) infection in human hosts. This landmark discovery also brought renewed interest in type III IFN biology. After more than half a decade since this discovery, we now have reports that show that genetic association of IFNL gene polymorphisms in humans is not limited only to HCV infections but extends beyond, to include varied diseases such as non-alcoholic fatty liver disease, allergy and several other viral diseases including that caused by the human immunodeficiency virus. Notably, all these conditions have strong involvement of host innate immune responses. After the discovery of a deletion polymorphism that leads to the expression of a functional IFN-λ4 as the prime 'functional' variant, the relevance of other polymorphisms regulating the expression of IFN-λ3 is in doubt. Herein, I seek to critically address these issues and review the current literature to provide a framework to help further understanding of IFN-λ biology.

Coxsackievirus counters the host innate immune response by blocking type III interferon expression

Type I IFNs play an important role in the immune response to enterovirus infections. Their importance is underscored by observations showing that many enteroviruses including coxsackie B viruses (CVBs) have developed strategies to block type I IFN production. Recent studies have highlighted a role for the type III IFNs (also called IFNλs) in reducing permissiveness to infections with enteric viruses including coxsackievirus. However, whether or not CVBs have measures to evade the effects of type III IFNs remains unknown. By combining virus infection studies and different modes of administrating the dsRNA mimic poly I : C, we discovered that CVBs target both TLR3- and MDA5/RIG-I-mediated type III IFN expression. Consistent with this, the cellular protein expression levels of the signal transduction proteins TRIF and IPS1 were reduced and no hyperphosphorylation of IRF-3 was observed following infection with the virus. Notably, decreased expression of full-length TRIF and IPS1 and the appearance of cleavage products was observed upon both CVB3 infection and in cellular protein extracts incubated with recombinant 2Apro, indicating an important role for the viral protease in subverting the cellular immune system. Collectively, our study reveals that CVBs block the expression of type III IFNs, and that this is achieved by a similar mechanism as the virus uses to block type I IFN production. We also demonstrate that the virus blocks several intracellular viral recognition pathways of importance for both type I and III IFN production. The simultaneous targeting of numerous arms of the host immune response may be required for successful viral replication and dissemination.

Cytokine Profiles in Human Metapneumovirus Infected Children: Identification of Genes Involved in the Antiviral Response and Pathogenesis

Human metapneumovirus (hMPV) causes severe airway infection in children that may be caused by an unfavorable immune response. The nature of the innate immune response to hMPV in naturally occurring infections in children is largely undescribed, and it is unknown if inflammasome activation is implicated in disease pathogenesis. We examined nasopharynx aspirates and blood samples from hMPV-infected children without detectable co-infections. The expression of inflammatory and antiviral genes were measured in nasal airway secretions by relative mRNA quantification while blood plasma proteins were determined by a multiplex immunoassay. Several genes were significantly up-regulated at mRNA and protein level in the hMPV infected children. Most apparent was the expression of the chemokine IP-10, the pro-inflammatory cytokine IL-18 in addition to the interferon inducible gene ISG54. Interestingly, children experiencing more severe disease, as indicated by a severity index, had significantly more often up-regulation of the inflammasome-associated genes IL-1β and NLRP3. Overall, our data point to cytokines, particularly inflammasome-associated, that might be important in hMPV mediated lung disease and the antiviral response in children with severe infection. Our study is the first to demonstrate that inflammasome components are associated with increased illness severity in hMPV-infected children.

Murine gammaherpesvirus targets type I IFN receptor but not type III IFN receptor early in infection

The innate immune response represents a primary line of defense against invading viral pathogens. Since epithelial cells are the primary site of gammaherpesvirus replication during infection in vivo and there are no information on activity of IFN-III signaling against gammaherpesviruses in this cell type, in present study, we evaluated the expression profile and virus-host interactions in mouse mammary epithelial cell (NMuMG) infected with three strains of murine gammaherpesvirus, MHV-68, MHV-72 and MHV-4556. Studying three strains of murine gammaherpesvirus, which differ in nucleotide sequence of some structural and non-structural genes, allowed us to compare the strain-dependent interactions with host organism. Our results clearly demonstrate that: (i) MHV-68, MHV-72 and MHV-4556 differentially interact with intracellular signaling and dysregulate IFN signal transduction; (ii) MHV-68, MHV-72 and MHV-4556 degrade type I IFN receptor in very early stages of infection (2-4hpi), but not type III IFN receptor; (iii) type III IFN signaling might play a key role in antiviral defense of epithelial cells in early stages of murine gammaherpesvirus replication; (iv) NMuMG cells are an appropriate model for study of not only type I IFN signaling, but also type III IFN signaling pathway. These findings are important for better understanding of individual virus-host interactions in lytic as well as in persistent gammaherpesvirus replication and help us to elucidate IFN-III function in early events of virus infection.

TLR3 Signaling Promotes the Induction of Unique Human BDCA-3 Dendritic Cell Populations

Conventional and plasmacytoid dendritic cells (cDCs and pDCs) are the two populations of DCs that can be readily identified in human blood. Conventional DCs have been subdivided into CD1c⁺, or blood dendritic cells antigen (BDCA) 1 and CD141⁺, or BDCA-3, DCs, each having both unique gene expression profiles and functions. BDCA-3 DCs express high levels of toll-like receptor 3 and upon stimulation with Poly I:C secrete IFN-β, CXCL10, and IL-12p70. In this article, we show that activation of human BDCA-3 DCs with Poly I:C induces the expression of activation markers (CD40, CD80, and CD86) and immunoglobulin-like transcript (ILT) 3 and 4. This Poly I:C stimulation results in four populations identifiable by flow cytometry based on their expression of ILT3 and ILT4. We focused our efforts on profiling the ILT4⁻ and ILT4⁺ DCs. These ILT-expressing BDCA-3 populations exhibit similar levels of activation as measured by CD40, CD80, and CD86; however, they exhibit differential cytokine secretion profiles, unique gene signatures, and vary in their ability to prime allogenic naïve T cells. Taken together, these data illustrate that within a pool of BDCA-3 DCs, there are cells poised to respond differently to a given input stimulus with unique output of immune functions.

Design and evaluation of novel interferon lambda analogs with enhanced antiviral activity and improved drug attributes

Type III interferons (IFNs) (also called IFN-λ: IFN-λ1, IFN-λ2, IFN-λ3, and IFN-λ4) are critical players in the defense against viral infection of mucosal epithelial cells, where the activity of type I IFNs is weak, and unlike type I IFNs that are associated with severe and diverse side effects, type III IFNs cause minimal side effects due to the highly restricted expression of their receptors, and thus appear to be promising agents for the treatment and prevention of respiratory and gastrointestinal viral infection. However, the antiviral potency of natural type III IFNs is weak compared to type I and, although IFN-λ3 possesses the highest bioactivity among the type III IFNs, IFN-λ1, instead of IFN-λ3, is being developed as a therapeutic drug due to the difficulty to express IFN-λ3 in the prokaryotic expression system. Here, to develop optimal IFN-λ molecules with improved drug attributes, we designed a series of IFN-λ analogs by replacing critical amino acids of IFN-λ1 with the IFN-λ3 counterparts, and vice versa. Four of the designed analogs were successfully expressed in Escherichia coli with high yield and were easily purified from inclusion bodies. Interestingly, all four analogs showed potent activity in inducing the expression of the antiviral genes MxA and OAS and two of them, analog-6 and -7, displayed an unexpected high potency that is higher than that of type I IFN (IFN-α2a) in activating the IFN-stimulated response element (ISRE)-luciferase reporter. Importantly, both analog-6 and -7 effectively inhibited replication of hepatitis C virus in Huh-7.5.1 cells, with an IC50 that is comparable to that of IFN-α2a; and consistent with the roles of IFN-λ in mucosal epithelia, both analogs potently inhibited replication of H3N2 influenza A virus in A549 cells. Together, these studies identified two IFN-λ analogs as candidates to be developed as novel antiviral biologics.

IFN-lambda therapy: current status and future perspectives

Interferon-lambda (IFN-λ), the most recently described type III IFN, plays a crucial part by acting on specific cell types, controlling viral infections and establishing robust innate immunity against cancer. In contrast to IFN-α or IFN-γ, IFN-λ has a restricted cell response pattern, which could make this new IFN a better choice for disease targeting and reducing adverse events. Although IFN-λ is considered to have pivotal roles in cancer, viral infections and autoimmune diseases, clinical trials have only been conducted for treatment of chronic hepatitis C virus infection. In this review, we discuss the current and the potential clinical applications of IFN-λ in the context of current IFN therapy.

Effects of type 1 diabetes-associated IFIH1 polymorphisms on MDA5 function and expression

Recent evidence has highlighted the role of the innate immune system in type 1 diabetes (T1D) pathogenesis. Specifically, aberrant activation of the interferon response prior to seroconversion of T1D-associated autoantibodies supports a role for the interferon response as a precipitating event toward activation of autoimmunity. Melanoma differentiation-associated protein 5 (MDA5), encoded by IFIH1, mediates the innate immune system's interferon response to certain viral species that form double-stranded RNA (dsRNA), the MDA5 ligand, during their life cycle. Extensive research has associated single nucleotide polymorphisms (SNPs) within the coding region of IFIH1 with T1D. This review discusses the different risk and protective IFIH1 alleles in the context of recent structural and functional analysis that relate to MDA5 regulation of interferon responses. These studies have provided a functional hypothesis for IFIH1 T1D-associated SNPs' effects on MDA5-mediated interferon responses as well as supporting the genome-wide association (GWA) studies that first associated IFIH1 with T1D.

Endogenously produced TNF-α contributes to the expression of CXCL10/IP-10 in IFN-λ3-activated plasmacytoid dendritic cells

The interplay between IFN-λs and dendritic cells is becoming increasingly relevant, particularly in light of their key role in inducing the antiviral state, including in hepatitis C virus infection. In this work, we have analyzed extensively how human plasmacytoid dendritic cells respond to IFN-λ3. We report that plasmacytoid dendritic cells incubated with IFN-λ3 prolong their survival; alter their expression pattern of surface HLA-DRα, CD123, CD86, and CD303; and time dependently produce IFN-α, CXCL10/IFN-γ-induced protein 10, and even modest quantities of TNF-α. Nevertheless, endogenously produced TNF-α, but not IFN-α, was found to be essential for driving the expression of CXCL10/IFN-γ-induced protein 10 in IFN-λ3-treated plasmacytoid dendritic cells, as revealed by neutralizing experiments by use of adalimumab, etanercept, and infliximab. We also observed that based on the kinetics and levels of IFN-α and CXCL10/IFN-γ-induced protein 10 produced by their IFN-λ3-treated plasmacytoid dendritic cells, healthy donors could be categorized into 2 and 3 groups, respectively. In particular, we identified a group of donors whose plasmacytoid dendritic cells produced modest quantities of CXCL10/IFN-γ-induced protein 10; another one whose plasmacytoid dendritic cells produced elevated CXCL10/IFN-γ-induced protein 10 levels, already after 18 h, declining thereafter; and a 3rd group characterized by plasmacytoid dendritic cells releasing very high CXCL10/IFN-γ-induced protein 10 levels after 42 h only. Finally, we report that in plasmacytoid dendritic cells, equivalent concentrations of IFN-λ3 and IFN-λ1 promote survival, antigen modulation, and cytokine production in a comparable manner and without acting additively/synergistically. Altogether, data not only extend the knowledge on the biologic effects that IFN-λs exert on plasmacytoid dendritic cells but also add novel light to the networking between IFN-λs and plasmacytoid dendritic cells in fighting viral diseases.

Guarding the frontiers: the biology of type III interferons

Type III interferons (IFNs) or IFN-λs regulate a similar set of genes as type I IFNs, but whereas type I IFNs act globally, IFN-λs primarily target mucosal epithelial cells and protect them against the frequent viral attacks that are typical for barrier tissues. IFN-λs thereby help to maintain healthy mucosal surfaces through immune protection, without the significant immune-related pathogenic risk associated with type I IFN responses. Type III IFNs also target the human liver, with dual effects: they induce an antiviral state in hepatocytes, but specific IFN-λ4 action impairs the clearance of hepatitis C virus and could influence inflammatory responses. This constitutes a paradox that has yet to be resolved.

Interferon-λ: Immune Functions at Barrier Surfaces and Beyond

When type III interferon (IFN-λ; also known as interleukin-28 [IL-28] and IL-29) was discovered in 2003, its antiviral function was expected to be analogous to that of type I IFNs (IFN-α and IFN-β) via the induction of IFN-stimulated genes (ISGs). Although IFN-λ stimulates expression of antiviral ISGs preferentially in cells of epithelial origin, recent studies have defined additional antiviral mechanisms in other cell types and tissues. Viral infection models using mice lacking IFN-λ signaling and SNP associations with human disease have expanded our understanding of the contribution of IFN-λ to the antiviral response at anatomic barriers and the immune response beyond these barriers. In this review, we highlight recent insights into IFN-λ functions, including its ability to restrict virus spread into the brain and to clear chronic viral infections in the gastrointestinal tract. We also discuss how IFN-λ modulates innate and adaptive immunity, autoimmunity, and tumor progression and its possible therapeutic applications in human disease.

Interferon-λ restricts West Nile virus neuroinvasion by tightening the blood-brain barrier

Although interferon-λ [also known as type III interferon or interleukin-28 (IL-28)/IL-29] restricts infection by several viruses, its inhibitory mechanism has remained uncertain. We used recombinant interferon-λ and mice lacking the interferon-λ receptor (IFNLR1) to evaluate the effect of interferon-λ on infection with West Nile virus, an encephalitic flavivirus. Cell culture studies in mouse keratinocytes and dendritic cells showed no direct antiviral effect of exogenous interferon-λ, even though expression of interferon-stimulated genes was induced. We observed no differences in West Nile virus burden between wild-type and Ifnlr1(-/-) mice in the draining lymph nodes, spleen, or blood. We detected increased West Nile virus infection in the brain and spinal cord of Ifnlr1(-/-) mice, yet this was not associated with a direct antiviral effect in mouse neurons. Instead, we observed an increase in blood-brain barrier permeability in Ifnlr1(-/-) mice. Treatment of mice with pegylated interferon-λ2 resulted in decreased blood-brain barrier permeability, reduced West Nile virus infection in the brain without affecting viremia, and improved survival against lethal virus challenge. An in vitro model of the blood-brain barrier showed that interferon-λ signaling in mouse brain microvascular endothelial cells increased transendothelial electrical resistance, decreased virus movement across the barrier, and modulated tight junction protein localization in a protein synthesis- and signal transducer and activator of transcription 1 (STAT1)-independent manner. Our data establish an indirect antiviral function of interferon-λ in which noncanonical signaling through IFNLR1 tightens the blood-brain barrier and restricts viral neuroinvasion and pathogenesis.

Is the third interferon a charm?

IFNλ restores blood-brain barrier integrity after disruption by West Nile virus, reducing virus invasion of the brain and increasing survival of infected mice (Lazear et al., this issue).

Trehalose-mediated autophagy impairs the anti-viral function of human primary airway epithelial cells

Human rhinovirus (HRV) is the most common cause of acute exacerbations of chronic lung diseases including asthma. Impaired anti-viral IFN-λ1 production and increased HRV replication in human asthmatic airway epithelial cells may be one of the underlying mechanisms leading to asthma exacerbations. Increased autophagy has been shown in asthmatic airway epithelium, but the role of autophagy in anti-HRV response remains uncertain. Trehalose, a natural glucose disaccharide, has been recognized as an effective autophagy inducer in mammalian cells. In the current study, we used trehalose to induce autophagy in normal human primary airway epithelial cells in order to determine if autophagy directly regulates the anti-viral response against HRV. We found that trehalose-induced autophagy significantly impaired IFN-λ1 expression and increased HRV-16 load. Inhibition of autophagy via knockdown of autophagy-related gene 5 (ATG5) effectively rescued the impaired IFN-λ1 expression by trehalose and subsequently reduced HRV-16 load. Mechanistically, ATG5 protein interacted with retinoic acid-inducible gene I (RIG-I) and IFN-β promoter stimulator 1 (IPS-1), two critical molecules involved in the expression of anti-viral interferons. Our results suggest that induction of autophagy in human primary airway epithelial cells inhibits the anti-viral IFN-λ1 expression and facilitates HRV infection. Intervention of excessive autophagy in chronic lung diseases may provide a novel approach to attenuate viral infections and associated disease exacerbations.

Leukocyte-derived IFN-α/β and epithelial IFN-λ constitute a compartmentalized mucosal defense system that restricts enteric virus infections

Epithelial cells are a major port of entry for many viruses, but the molecular networks which protect barrier surfaces against viral infections are incompletely understood. Viral infections induce simultaneous production of type I (IFN-α/β) and type III (IFN-λ) interferons. All nucleated cells are believed to respond to IFN-α/β, whereas IFN-λ responses are largely confined to epithelial cells. We observed that intestinal epithelial cells, unlike hematopoietic cells of this organ, express only very low levels of functional IFN-α/β receptors. Accordingly, after oral infection of IFN-α/β receptor-deficient mice, human reovirus type 3 specifically infected cells in the lamina propria but, strikingly, did not productively replicate in gut epithelial cells. By contrast, reovirus replicated almost exclusively in gut epithelial cells of IFN-λ receptor-deficient mice, suggesting that the gut mucosa is equipped with a compartmentalized IFN system in which epithelial cells mainly respond to IFN-λ that they produce after viral infection, whereas other cells of the gut mostly rely on IFN-α/β for antiviral defense. In suckling mice with IFN-λ receptor deficiency, reovirus replicated in the gut epithelium and additionally infected epithelial cells lining the bile ducts, indicating that infants may use IFN-λ for the control of virus infections in various epithelia-rich tissues. Thus, IFN-λ should be regarded as an autonomous virus defense system of the gut mucosa and other epithelial barriers that may have evolved to avoid unnecessarily frequent triggering of the IFN-α/β system which would induce exacerbated inflammation.

Virus-induced interferon consists of two distinct families of molecules, IFN-α/β and IFN-λ. IFN-α/β family members are key antiviral molecules that confer protection against a large number of viruses infecting a wide variety of cell types. By contrast, IFN-λ responses are largely confined to epithelial cells due to highly restricted expression of the cognate receptor. Interestingly, virus resistance of the gut epithelium is not dependent on IFN-α/β but rather relies on IFN-λ, questioning the prevailing view that receptors for IFN-α/β are expressed ubiquitously. Here we demonstrate that the IFN-α/β system is unable to compensate for IFN-λ deficiency during infections with epitheliotropic viruses because intestinal epithelial cells do not express functional receptors for IFN-α/β. We further demonstrate that virus-infected intestinal epithelial cells are potent producers of IFN-λ, indicating that the gut mucosa possesses a compartmentalized IFN system in which epithelial cells predominantly respond to IFN-λ, whereas other cells of the gut mainly rely on IFN-α/β for antiviral defense. We suggest that IFN-λ may have evolved as an autonomous virus defense system of the gut mucosa to avoid unnecessarily frequent triggering of the IFN-α/β system which, due to its potent activity on immune cells, would induce exacerbated inflammation.

Activation of Type I and Type III Interferons in Chronic Hepatitis C

Infection with hepatitis C virus (HCV) results in chronic and progressive liver disease. Persistency rates add up to 85%. Despite recognition of the virus by the human host in peripheral blood and in the liver, immune response appears to be ineffective in clearing infection. The ability to spontaneously eradicate the virus as well as the outcome of infection upon therapy with human recombinant interferon-α (IFN-α) was found to correlate most closely with genetic variations within the region encoding the IFN-λ genes, as revealed by genome-wide association studies on main ethnic populations in 2009. This review summarizes the induction of type I and type III IFN genes and their effectors, the IFN-stimulated genes. It focusses on the in vivo situation in chronic HCV infection in man both in the peripheral blood compartment and in the liver. It also addresses the impact of genetic polymorphisms in the region of type III IFN genes on their activation. Finally, it discusses how antiviral drugs (i.e. IFN-α, ribavirin and the direct-acting antivirals) may complementarily control the activation of endogenous IFNs and succeed in combatting infections.

Human keratinocytes restrict chikungunya virus replication at a post-fusion step

Transmission of chikungunya virus (CHIKV) to humans is initiated by puncture of the skin by a blood-feeding Aedes mosquito. Despite the growing knowledge accumulated on CHIKV, the interplay between skin cells and CHIKV following inoculation still remains unclear. In this study we questioned the behavior of human keratinocytes, the predominant cell population in the skin, following viral challenge. We report that CHIKV rapidly elicits an innate immune response in these cells leading to the enhanced transcription of type I/II and type III interferon genes. Concomitantly, we show that despite viral particles internalization into Rab5-positive endosomes and efficient fusion of virus and cell membranes, keratinocytes poorly replicate CHIKV as attested by absence of nonstructural proteins and genomic RNA synthesis. Accordingly, human keratinocytes behave as an antiviral defense against CHIKV infection rather than as a primary targets for initial replication. This picture significantly differs from that reported for Dengue and West Nile mosquito-borne viruses.

Transcriptomic profiling facilitates classification of response to influenza challenge

Abstract

Despite increases in vaccination coverage, reductions in influenza-related mortality have not been observed. Better vaccines are therefore required and influenza challenge studies can be used to test the efficacy of new vaccines. However, this requires the accurate post-challenge classification of subjects by outcome, which is limited in current methods that use artificial thresholds to assign ‘symptomatic’ and ‘asymptomatic’ phenotypes. We present data from an influenza challenge study in which 22 healthy adults (11 vaccinated) were inoculated with H3N2 influenza (A/Wisconsin/67/2005). We generated genome-wide gene expression data from peripheral blood taken immediately before the challenge and at 12, 24 and 48 h post-challenge. Variation in symptomatic scoring was found amongst those with laboratory confirmed influenza. By combining the dynamic transcriptomic data with the clinical parameters this variability can be reduced. We identified four subjects with severe laboratory confirmed influenza that show differential gene expression in 1103 probes 48 h post-challenge compared to the remaining subjects. We have further reduced this profile to six genes (CCL2, SEPT4, LAMP3, RTP4, MT1G and OAS3) that can be used to define these subjects. We have used this gene set to predict symptomatic infection from an independent study. This analysis gives further insight into host-pathogen interactions during influenza infection. However, the major potential value is in the clinical trial setting by providing a more quantitative method to better classify symptomatic individuals post influenza challenge.

Key message

Differential gene expression signatures are seen following influenza challenge.

Expression of six predictive genes can classify response to influenza challenge.

The genomic influenza response classification replicates in an independent dataset.

Electronic supplementary material

The online version of this article (doi:10.1007/s00109-014-1212-8) contains supplementary material, which is available to authorized users.