Interferons, interferon-like cytokines, and their receptors

Interferon-alpha therapy in bcr-abl-negative myeloproliferative neoplasms

Interferon (IFN) was the first cytokine discovered 50 years ago, with a wide range of biological properties, including immunomodulatory, proapoptotic and antiangiogenic activities, that rapidly raised interest in its therapeutic use in malignancies. IFN-receptor characterization was also pivotal in the discovery of the JAK/STAT signaling pathway. Among the large IFN family, mainly one of the type I IFN, IFN-alpha2, is used in therapy. Many clinical trials have shown remarkable efficacy of IFN-alpha in bcr-abl-negative myeloproliferative neoplasms (MPNs), especially polycythemia vera (PV), and essential thrombocythemia (ET). IFN-alpha induces about 80% of hematological responses in those diseases and is able to reduce splenomegaly, as well as relieve pruritus and other constitutional symptoms. Yet its use was limited by toxicity, leading to early treatment discontinuation in about 20% of the patients. However, its lack of leukemogenic potential and its possible use during pregnancy have already made IFN-alpha the drug of choice for younger MPN patients. In addition, several studies have shown a probably selective effect of IFN-alpha on PV and ET clones, as shown by cytogenetic remissions, reversions to polyclonal hematopoiesis, and more recently by induction of JAK2V617F complete molecular remissions in PV which may widen the indications of IFN-alpha in JAK2-mutated MPN.

Inhibition of HBV gene expression and replication by stably expressed interferon-alpha1 via adeno-associated viral vectors

Background

Interferon‐α2 (IFNα2) is routinely used for anti‐hepatitis B virus (HBV) treatment. However, the therapeutic efficiency is unsatisfactory, particularly in East Asia. Such inefficiency might be a result of the short half‐life, relatively low local concentration and strong side‐effects of interferons. Frequent and repeated injection is also a big burden for patients. In the present study, a single dose of vector‐delivered IFNα1 was tested for its anti‐HBV effects.

Methods

Adeno‐associated viral vector (AAV‐IFNα1) was generated to deliver the IFNα1 gene into hepatocytes. IFNα1, hepatitis B surface (HBsAg) and e (HBeAg) antigens were measured by enzyme‐linked immunosorbent assay and/or western blotting. The level of viral DNA was measured by quantitative real‐time polymerase chain reaction.

Results

AAV‐IFNα1 effectively transduced HBV‐producing cells (HepAD38) and mouse hepatocytes, where IFNα1 was expressed in a stable manner. Both intracellular and extracellular HBsAg and HBeAg were significantly reduced in vitro. In the HBV‐producing mice, the concentration of IFNα1 in the liver was eight‐fold higher than that in plasma. Compared with control groups, HBeAg/HBsAg antigen levels were reduced by more than ten‐fold from day 1–5, and dropped to an undetectable level on day 9 in the AAV‐IFNα1 group. Concurrently, the level of viral DNA decreased over 30‐fold for several weeks.

Conclusions

A single dose administration of AAV‐IFNα1 viral vector displayed prolonged transgene expression and superior antiviral effects both in vitro and in vivo. Therefore, the use of AAV‐IFNα1 might be a potential alternative strategy for anti‐HBV therapy. Copyright © 2008 John Wiley & Sons, Ltd.

Fas receptor expression in germinal-center B cells is essential for T and B lymphocyte homeostasis

Fas is highly expressed in activated and germinal center (GC) B cells but can potentially be inactivated by misguided somatic hypermutation. We employed conditional Fas-deficient mice to investigate the physiological functions of Fas in various B cell subsets. B cell-specific Fas-deficient mice developed fatal lymphoproliferation due to activation of B cells and T cells. Ablation of Fas specifically in GC B cells reproduced the phenotype, indicating that the lymphoproliferation initiates in the GC environment. B cell-specific Fas-deficient mice also showed an accumulation of IgG1(+) memory B cells expressing high amounts of CD80 and the expansion of CD28-expressing CD4(+) Th cells. Blocking T cell-B cell interaction and GC formation completely prevented the fatal lymphoproliferation. Thus, Fas-mediated selection of GC B cells and the resulting memory B cell compartment is essential for maintaining the homeostasis of both T and B lymphocytes.

Immune evasion in Kaposi's sarcoma-associated herpes virus associated oncogenesis

A hallmark of herpesviruses is a lifelong persistent infection, which often leads to diseases upon immune suppression of infected host. Kaposi's sarcoma-associated herpesvirus (KSHV), also known as human herpesvirus 8 (HHV8), is etiologically linked to the development of Kaposi's sarcoma (KS), primary effusion lymphoma (PEL), and Multicentric Castleman's disease (MCD). In order to establish a persistent infection, KSHV dedicates a large portion of its genomic information to sabotage almost every aspect of host immune system. Thus, understanding the interplay between KSHV and the host immune system is important in not only unraveling the complexities of viral persistence and pathogenesis, but also discovering novel therapeutic targets. This review summarizes current knowledge of host immune evasion strategies of KSHV and their contributions to KSHV-associated diseases.

Interferon autoantibodies associated with AIRE deficiency decrease the expression of IFN-stimulated genes

Neutralizing autoantibodies to type I, but not type II, interferons (IFNs) are found at high titers in almost every patient with autoimmune polyendocrinopathy candidiasis ectodermal dystrophy (APECED), a disease caused by AIRE gene mutations that lead to defects in thymic T-cell selection. Combining genome-wide expression array with real time RT-PCR assays, we here demonstrate that antibodies against IFN-alpha cause highly significant down-regulation of interferon-stimulated gene expression in cells from APECED patients' blood by blocking their highly dilute endogenous IFNs. This down-regulation was lost progressively as these APECED cells matured in cultures without neutralizing autoantibodies. Most interestingly, a rare APECED patient with autoantibodies to IFN-omega but not IFN-alpha showed a marked increase in expression of the same interferon-stimulated genes. We also report unexpected increases in serum CXCL10 levels in APECED. Our results argue that the breakdown of tolerance to IFNs in AIRE deficiency is associated with impaired responses to them in thymus, and highlight APECED as another autoimmune disease with associated dysregulation of IFN activity.

Genomic-based high throughput screening identifies small molecules that differentially inhibit the antiviral and immunomodulatory effects of IFN-alpha

Multiple lines of evidence suggest that inhibition of Type I Interferons, including IFN-alpha, may provide a therapeutic benefit for autoimmune diseases. Using a chemical genomics approach integrated with cellular and in vivo assays, we screened a small compound library to identify modulators of IFN-alpha biological effects. A genomic fingerprint was developed from both ex vivo patient genomic information and in vitro gene modulation from IFN-alpha cell-based stimulation. A high throughput genomic-based screen then was applied to prioritize 268 small molecule inhibitors targeting 41 different intracellular signaling pathways. Active compounds were profiled further for their ability to inhibit the activation and differentiation of human monocytes using disease-related stimuli. Inhibitors targeting NF-kappaB or Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) signaling emerged as "dissociated inhibitors" because they did not modulate IFN-alpha anti-viral effects against HSV-1 but potently inhibited other immune-related functions. This work describes a novel strategy to identify small molecule inhibitors for the treatment of autoimmune disorders.

Interferon-lambda contributes to innate immunity of mice against influenza A virus but not against hepatotropic viruses

Virus-infected cells secrete a broad range of interferon (IFN) subtypes which in turn trigger the synthesis of antiviral factors that confer host resistance. IFN-α, IFN-β and other type I IFNs signal through a common universally expressed cell surface receptor, whereas IFN-λ uses a distinct receptor complex for signaling that is not present on all cell types. Since type I IFN receptor-deficient mice (IFNAR1^0/0) exhibit greatly increased susceptibility to various viral diseases, it remained unclear to which degree IFN-λ might contribute to innate immunity. To address this issue we performed influenza A virus infections of mice which carry functional alleles of the influenza virus resistance gene Mx1 and which, therefore, develop a more complete innate immune response to influenza viruses than standard laboratory mice. We demonstrate that intranasal administration of IFN-λ readily induced the antiviral factor Mx1 in mouse lungs and efficiently protected IFNAR1^0/0 mice from lethal influenza virus infection. By contrast, intraperitoneal application of IFN-λ failed to induce Mx1 in the liver of IFNAR1^0/0 mice and did not protect against hepatotropic virus infections. Mice lacking functional IFN-λ receptors were only slightly more susceptible to influenza virus than wild-type mice. However, mice lacking functional receptors for both IFN-α/β and IFN-λ were hypersensitive and even failed to restrict usually non-pathogenic influenza virus mutants lacking the IFN-antagonistic factor NS1. Interestingly, the double-knockout mice were not more susceptible against hepatotropic viruses than IFNAR1^0/0 mice. From these results we conclude that IFN-λ contributes to inborn resistance against viral pathogens infecting the lung but not the liver.

The contribution of IFN-λ to innate immunity against virus-induced diseases has remained unclear to date as appropriate mouse models were not available. We now present evidence that IFN-λ is involved in the antiviral defense. Mice lacking functional IFN-λ receptors were only slightly more susceptible to influenza virus than wild-type mice, but intranasal administration of IFN-λ efficiently protected IFN-α/β receptor-deficient mice from lethal influenza virus infection and induced the antiviral factor Mx1 in lungs. Mice lacking functional receptors for both IFN-α/β and IFN-λ were hypersensitive and failed to restrict even usually non-pathogenic influenza virus mutants lacking the IFN-antagonistic factor NS1. By contrast, intraperitoneal application of IFN-λ failed to induce Mx1 in the liver of mice and did not protect against hepatotropic viruses. Furthermore, double-knockout mice were not more susceptible against hepatotropic viruses than IFN-α/β receptor-deficient mice, indicating that IFN-λ contributes to resistance against viral pathogens infecting the lung but not the liver.

Toll-like receptors in skin infections and inflammatory diseases

The skin is the ultimate example of the function of innate immunity, it alerts the host of danger by many systems including sensing pathogen-associated molecule patterns (PAMPs) through Toll-like receptors and other pattern recognition receptors (PRRs), yet normally provides defense without inflammation. The skin responds rapidly to invading microbes by producing antimicrobial peptides or other antimicrobial intermediates before cytokine release results in inflammation. To achieve maximal immune responses for clearing invading microbes, the activation of select PRRs in skin then initiates and shapes adaptive immune responses through the activation of dendritic cells and recruitment of T cell subsets. Importantly, cross-talk between TLRs can influence this system in several ways including augmenting or suppressing the immune response. As a consequence of their pivotal role, TLR responses need to be tightly controlled by associated negative regulators or negative feedback loops to prevent detrimental effects from TLRs overactivation. This review focuses on describing the involvement of TLRs in the development of skin infections and inflammatory diseases, and highlights the potential application of TLR agonists or antagonists in these skin diseases.

Interferon regulatory factor 8 mediates tumor-induced inhibition of antigen processing and presentation by dendritic cells

INTRODUCTION

Suppression of dendritic cells (DCs) is a crucial mechanism by which tumor cells escape immune recognition and elimination. We have recently reported that MHC class I antigen processing machinery (APM) component expression in human DCs is down-regulated by tumor-derived gangliosides. However, the molecular mechanisms underlying this abnormality were not identified. Thus, the aim of this work was to analyze the role of interferon regulatory factor 8 (IRF-8) in APM protein expression and the antigen presenting capacity of DCs developed in the tumor microenvironment.

RESULTS

We demonstrate that the expression of several MHC class I APM components, including delta, MB-1, LMP-10, ERp57, and tapasin, is significantly decreased in murine DCs generated in the presence of prostate cancer cells. APM component down-regulation was associated with decreased ability of DCs to present model antigen to antigen-specific T cells. Notable, impaired antigen-presenting activity of DCs co-cultured with tumor cells was accompanied by decreased levels of IRF-8. Transduction of DCs with the silencing RNA for the IRF-8 gene also led to reduced expression of APM components in DCs and decreased antigen presenting function.

CONCLUSION

Together, our data suggest that tumor-induced inhibition of antigen processing and presenting function of DCs is mediated by IRF-8, a member of the interferon regulatory factor family. These results provide a new molecular target for optimizing the generation of efficient DC vaccines for cancer therapy.

Hypothetical review: thymic aberrations and type-I interferons; attempts to deduce autoimmunizing mechanisms from unexpected clues in monogenic and paraneoplastic syndromes

In sporadic autoimmune disorders, dendritic cells are increasingly being incriminated as agents provocateurs. However, the mechanisms and any 'danger signals' that induce them to autoimmunize remain enigmatic. Here, we focus on unexpected clues from two prototypic/ highly informative autoimmune syndromes, acquired thymoma-associated myasthenia gravis and the monogenic autoimmune polyendocrine syndrome type-1 (APS1), caused by mutations in the AutoImmune Regulator (AIRE). Both involve the thymus, and in both we find early, persistent, highly prevalent and high-titre neutralizing autoantibodies against type-I interferons, regardless of the exact AIRE genotype or the characteristically variable clinical phenotype in APS1. Thus these key innate<-->adaptive immune intermediaries are now implicated in APS1 and paraneoplastic myasthenia as well as in systemic lupus erythematosus and other sporadic autoimmune disorders. The currently accepted notion that autoimmunization proceeds automatically (by 'default') does not explain how, when or where autoimmune responses are initiated against which targets in APS1, or whether exogenous or internal danger signals are involved, or predict whether the primary auto-immunogenic targets are AIRE-dependent. As the parallels between these syndromes must hold novel clues to these puzzles, they demand explanations. To unify these and other findings, we propose that autoimmunization occurs centrally in aberrant thymic environments rendered 'dangerous' by AIRE-deficiency (possibly by excess undegraded nucleic acids/dead cell debris). The ensuing autoreactivity focuses early on the locally abundant type I interferons and then on other peripheral tissue autoantigens that are still expressed despite the absence of AIRE. These ideas raise numerous questions that others may already have the materials to address.

Cigarette smoking products suppress anti-viral effects of Type I interferon via phosphorylation-dependent downregulation of its receptor

While negative effect of smoking on the resistance to viral infections was known, the underlying mechanisms remained unclear. Here we report that products of cigarette smoking compromise the cellular anti-viral defenses by inhibiting the signaling induced by Type I interferon (IFN). Cigarette smoking condensate (but not pure nicotine) stimulated specific serine phosphorylation-dependent ubiquitination and degradation of the IFNAR1 subunit of the Type I IFN receptor leading to attenuation of IFN signaling and decreased resistance to viral infection. This resistance was restored in cells where phosphorylation-dependent degradation of IFNAR1 is abolished. We conclude that smoking compromises cellular anti-viral defenses via degradation of Type I IFN receptor and discuss the significance of this mechanism for efficacy of IFN-based therapies.

Model-based analysis of interferon-beta induced signaling pathway

MOTIVATION

Interferon-beta induced JAK-STAT signaling pathways contribute to mucosal immune recognition and an anti-viral state. Though the main molecular mechanisms constituting these pathways are known, neither the detailed structure of the regulatory network, nor its dynamics has yet been investigated. The objective of this work is to build a mathematical model for the pathway that would serve two purposes: (1) to reproduce experimental results in simulation of both early and late response to Interferon-beta stimulation and (2) to explain experimental phenomena generating new hypotheses about regulatory mechanisms that cannot yet be tested experimentally.

RESULTS

Experimentally determined time dependent changes in the major components of this pathway were used to build a mathematical model describing pathway dynamics in the form of ordinary differential equations. The experimental results suggested existence of unknown negative control mechanisms that were tested numerically using the model. Together, experimental and numerical data show that the epithelial JAK-STAT pathway might be subjected to previously unknown dynamic negative control mechanisms: (1) activation of dormant phosphatases and (2) inhibition of nuclear import of IRF1.

Human interleukin-10 gene transfer is protective in a rat model of Parkinson's disease

In Parkinson's disease (PD) chronic inflammation occurs in the substantia nigra (SNc) concurrently with dopaminergic neurodegeneration. In models of PD, microglial activation precedes neurodegeneration in the SNc, suggesting that the underlying pathogenesis involves a complex response in the nigrostriatal pathway, and that the innate immune system plays a significant role. We have investigated the neuroprotective effect of an adeno-associated viral type-2 (AAV2) vector containing the complementary DNA (cDNA) for human interleukin-10 (hIL-10) in the unilateral 6-hydroxydopamine (6-OHDA) rat model of PD. AAV2-hIL-10 reduced the 6-OHDA-induced loss of tyrosine hydroxylase (TH)-positive neurons in the SNc, and also reduced loss of striatal dopamine (DA). Pretreatment with AAV2-hIL-10 reduced glial activation in the SNc but did not attenuate striatal release of the inflammatory cytokine IL-1beta. Assessment of rotational behavior in response to apomorphine challenge showed absence of asymmetry, confirming protection of dopaminergic innervation of the lesioned striatum. At baseline, 6-OHDA-lesioned animals displayed a deficit in contralateral forelimb use, but pretreatment with AAV2-hIL-10 reduced this forelimb akinesia. Transcriptional analyses revealed alteration of a few genes by AAV2-hIL-10; these alterations may contribute to neuroprotection. This study supports the need for further investigations relating to gene therapies aimed at reducing neuroinflammation in early PD.

IFNalpha and IFNlambda differ in their antiproliferative effects and duration of JAK/STAT signaling activity

Interferon (IFN)lambda, also known as IL-28A, IL-28B or IL-29, is a new type III IFN, which like type I IFN(alpha/beta), activates common elements of the JAK/STAT signaling pathway and exhibits antiproliferative activity. Currently, IFNalpha is used in the treatment of certain forms of cancer, but its antitumor effects are limited and associated with high toxicity. In this study, we determined whether IFNlambda induced the same level of cell growth inhibition relative to IFNalpha. To this effect HaCaT cells, which are typically growth inhibited by IFNalpha, underwent apoptosis in response to IFNlambda. Next, in contrast to IFNalpha stimulation, IFNlambda prolonged the duration of activated STAT1 and STAT2. Furthermore, the kinetics of IFN-stimulated genes was different as IFNlambda induced a delayed but stronger induction of IFN-responsive genes. Components of the JAK/STAT pathway remained essential for the antiproliferative effects of IFNalpha and IFNlambda. IFNlambda-induced persistence of STAT activation required de novo protein synthesis and was in part due to a delay in STAT2 inactivation. Thus our data demonstrate that the duration of IFNlambda signaling is different from that of IFNalpha, and that IFNlambda could be a suitable cytokine to evaluate for cancer therapy.

The function of the human interferon-beta 1a glycan determined in vivo

Recombinant human interferon-beta (rhIFN-beta) is the leading therapeutic intervention shown to change the cause of relapsing-remitting multiple sclerosis, and both a nonglycosylated and a significantly more active glycosylated variant of rhIFN-beta are used in treatment. This study investigates the function of the rhIFN-beta1a glycan moiety and its individual carbohydrate residues, using the myxovirus resistance (Mx) mRNA as a biomarker in Mx-congenic mice. We showed that the Mx mRNA level in blood leukocytes peaked 3 h after s.c. administration of rhIFN-beta1a. In addition, a clear dose-response relationship was confirmed, and the Mx response was shown to be receptor-mediated. Using specific glycosidases, different glycosylation analogs of rhIFN-beta1a were obtained, and their activities were determined. The glycosylated rhIFN-beta1a showed significantly higher activity than its deglycosylated counterpart, due to a protein stabilization/solubilization effect of the glycan. It is interesting to note that the terminating sialic acids were essential for these effects. Conclusively, the structure/bioactivity relationship of rhIFN-beta1a was determined in vivo, and it provided a novel insight into the role of the rhIFN-beta1a glycan and its carbohydrate residues. The possibilities of improving the pharmacological properties of rhIFN-beta1a using glycoengineering are discussed.

The DEAD-box helicase DDX3X is a critical component of the TANK-binding kinase 1-dependent innate immune response

TANK-binding kinase 1 (TBK1) is of central importance for the induction of type-I interferon (IFN) in response to pathogens. We identified the DEAD-box helicase DDX3X as an interaction partner of TBK1. TBK1 and DDX3X acted synergistically in their ability to stimulate the IFN promoter, whereas RNAi-mediated reduction of DDX3X expression led to an impairment of IFN production. Chromatin immunoprecipitation indicated that DDX3X is recruited to the IFN promoter upon infection with Listeria monocytogenes, suggesting a transcriptional mechanism of action. DDX3X was found to be a TBK1 substrate in vitro and in vivo. Phosphorylation-deficient mutants of DDX3X failed to synergize with TBK1 in their ability to stimulate the IFN promoter. Overall, our data imply that DDX3X is a critical effector of TBK1 that is necessary for type I IFN induction.

IFN-beta provides immuno-protection in the retina by inhibiting ICAM-1 and CXCL9 in retinal pigment epithelial cells

The retinal pigment epithelial (RPE) cell is a potent regulatory cell that facilitates normal physiologic processes and plays a critical role in a variety of retinal diseases. We evaluated IFN-beta production in human RPE cells through TLR signaling and investigated the effects of IFN-beta on RPE cells. RPE cells treated with poly(I:C) or infected with an RNA virus produce IFN-beta. Kinetic studies revealed that IFN-beta levels continue to increase over a 48-h period and this was associated with the up-regulation of IRF-7 gene expression, a known positive feedback molecule for IFN-beta production. Microarray analysis revealed that in IFN-beta treated cells, 480 genes of 22,283 genes were up or down-regulated by >2-fold. We hypothesize that IFN-beta induction during TLR signaling in the retina is an immunosuppressive factor produced to limit immunopathologic damage. Cytokine activation of RPE cells results in the production of the chemokines, CXCL9 and CXCL10, and the adhesion molecule, ICAM-1. Pretreatment of RPE cells with IFN-beta resulted in inhibition of ICAM-1 production and elimination of CXCL9 production. This treatment did not alter CXCL10 production. Anti-IFN-beta Ab blocked the inhibitory action of IFN-beta. Real time PCR analysis revealed that IFN-beta treatment inhibited gene expression of sICAM-1 and CXCL9. The results indicate a critical role for RPE cell derived IFN-beta in the down-regulation of CXCL9 and ICAM-1 expression in the retina and suggest that the inhibition of CXCL9 is an immuno-suppressive mechanism that protects the retina from excessive inflammation.

Prevention of allograft tolerance by bacterial infection with Listeria monocytogenes

Exposure to certain viruses and parasites has been shown to prevent the induction of transplantation tolerance in mice via the generation of cross-reactive memory T cell responses or the induction of bystander activation. Bacterial infections are common in the perioperative period of solid organ allograft recipients in the clinic, and correlations between bacterial infections and acute allograft rejection have been reported. However, whether bacterial infections at the time of transplantation have any effect on the generation of transplantation tolerance remains to be established. We used the Gram-positive intracellular bacterium Listeria monocytogenes (LM) as a model pathogen because its effects on immune responses are well described. Perioperative LM infection prevented cardiac and skin allograft acceptance induced by anti-CD154 and donor-specific transfusion in mice. LM-mediated rejection was not due to the generation of cross-reactive T cells and was largely independent of signaling via MyD88, an adaptor for most TLRs, IL-1, and IL-18. Instead, transplant rejection following LM infection was dependent on the expression of the phagosome-lysing pore former listeriolysin O and on type I IFN receptor signaling. Our results indicate that bacterial exposure at the time of transplantation can antagonize tolerogenic regimens by enhancing alloantigen-specific immune responses independently of the generation of cross-reactive memory T cells.

[An integrated biological model for interferon signaling pathway and its gene polymorphisms]

To construct a systemic structural model for interferon (IFN) signaling pathways with gene's single nucleotide polymorphisms (SNPs) information, it is visual to investigate the effects of gene-gene interaction on IFN signaling path-ways. The genes function information was retrieved from Pubmed and Embase database. The IFN signaling pathways were constructed by applying Teranode Design Suite (TDS) biological software. The SNPs information of genes in pathways was retrieved by using SNP Trawler biological software. The biological systemic structural model for IFN signaling pathways, involving in genetic information, particularly their SNPs information, was constructed successfully. It contained JAK-STAT, MAPK-p38 and PI3K pathways, through which IFNs play variable biological roles. Type-I-IFN makes an important role in against viral infection, cell proliferation and immunoregulation by these three pathways. However, the biological activities of type-II-IFN are through JAK-STAT and MAPK-p38 pathways, and type-III-IFN is only through PI3K pathway. These pathways contained 98 genes and 19 693 SNPs information, which consist of a complicate gene-gene interactional network. In conclusion, this software model not only helps us intensively research the effects of SNPs on IFN biological roles and predict IFN therapeutic effect, but also set up a good foundation for translational medicine, discovering new target of drugs and developing new drugs.

Antagonizing activity of vaccinia virus E3L against human interferons in Huh7 cells

The E3L protein of vaccinia virus (VV) is well known for its capacity to evade cellular innate antiviral immunity related to interferon (IFN), for example PKR and RNaseL mediated antiviral activities. However, due to the limited range of cells that support VV E3L deletion mutant replication, the full capacity of E3L inhibiting the innate immune response induced by IFNs remains to be examined. In this report, the inhibition activity of VV E3L against a wide spectrum of human IFNs, including type I IFNs (12 IFN-alpha subtypes, IFN-beta, and IFN-omega), and type II IFN (gamma), was comparatively examined using the Copenhagen strain E3L deletion mutant and its revertant control virus in a human hepatoma cell line, Huh7. Deletion of the E3L open reading frame rendered the mutant VV sensitive to all types of IFNs, while the revertant VV was strongly resistant to these treatments. Furthermore, we show that the inhibition of VV E3L deletion mutant by IFN occurs at the stage of intermediate gene translation, while the expression of early genes and transcription of intermediate genes are largely unaffected. Using specific siRNAs to suppress the classical IFN-induced antiviral pathways, we found that PKR is the key factor modulated by E3L, while the RNaseL and MxA pathways play limited roles in this Huh7 cell system. Thus, our data demonstrates that VV E3L can mediate strong inhibition activity against all human type I and type II IFNs, mainly through modulation of the PKR pathway in Huh7 cells.

Biological characterisation of a recombinant Atlantic salmon type I interferon synthesized in Escherichia coli

Type I (alpha/beta) interferons (IFNs) are a family of cytokines that stimulate the expression of numerous proteins that mediate an antiviral state in uninfected cells. Two Atlantic salmon (Salmo salar) IFN-alpha (SasaIFN-alpha1 & 2) genes have previously been cloned and both were found to contain a putative N-linked glycosylation site. Recombinant SasaIFN-alpha1 (rSasaIFN-alpha1) produced in eukaryotic systems has repeatedly been shown to confer antiviral properties. However, different IFN-alpha subtypes may exhibit differential antiviral activities and be subject to glycosylation. To evaluate the potential therapeutic impact of a rSasaIFN-alpha, the mature form of the SasaIFN-alpha2 protein was produced in a high-level Escherichia coli expression system. Expression of the rSasaIFN-alpha2 was detected by SDS-PAGE and Western blot, and its identity was confirmed by mass spectrometry. In the homologous Chinook salmon embryonic (CHSE-214) cell line, the rSasaIFN-alpha2 incited early expression of the IFN-induced Mx protein and exhibited high antiviral activity of about 2.8 x 10(6) U mg(-1) against infectious pancreatic necrosis virus (IPNV). Conversely, antiviral protection by rSasaIFN-alpha2 was not observed in a heterologous Japanese flounder embryo (HINAE) cell line. Hence, a biologically active form of rSasaIFN-alpha2 was successfully produced using a glycosylation-deficient prokaryotic system and purified to homogeneity, suggesting that glycosylation is not required for its antiviral activity.

Cytosolic DNA recognition for triggering innate immune responses

The detection of microbial components by pattern recognition receptors (PRRs) and the subsequent triggering of innate immune responses constitute the first line of defense against infections. Recently, much attention has been focused on cytosolic nucleic acid receptors; the activation of these receptors commonly evokes a robust innate immune response, the hallmark of which is the induction of type I interferon (IFN) genes. In addition to receptors for RNA, receptors that detect DNA exposed in the cytosol and activate innate immune responses have long been thought to exist. Recently, DAI (DLM-1/ZBP1) has been identified as a candidate cytosolic DNA sensor. Cytosolic signaling by DNA-activated DAI (DLM-1/ZBP1) signaling results in activation of the two pathways of gene transcription critical to innate immune responses, the IRF and NF-kappaB pathways. In this review, we summarize our current view of activation mechanism and immunological roles of DAI (DLM-1/ZBP1) and related molecules. In addition, we also discuss the issue of self vs. non-self DNA recognition by DAI (DLM-1/ZBP1) and other DNA sensors in terms of the possible involvement in autoimmune abnormalities.

A critical role for type I IFN-dependent NK cell activation in innate immune elimination of adenoviral vectors in vivo

Recombinant adenoviruses have been used widely for gene therapy due to their high transduction efficiency in vivo. However, the attendant innate immune response to adenoviral vectors has limited their applications for in vivo gene therapy. Recent studies have shown that adenoviruses activate the innate immunity through both Toll-like receptor-dependent (TLR-dependent) and TLR-independent pathways, leading to the production of type I interferons (IFNs) and other inflammatory cytokines. Furthermore, type I IFNs play a pivotal role in innate immune elimination of adenoviral vectors in vivo. It remains to be defined how type I IFNs regulate innate immune clearance of adenoviral vectors. In this study, we showed in vivo that natural killer (NK) cells were activated and accumulated in the liver upon intravenous administration of adenoviral vectors, leading to the loss of adenoviral genome and the reduction of transgene expression. We further demonstrated that type I IFNs were critical for the activation of NK cells. This was achieved by direct action of type I IFNs on NK cells. Overall, our observations reveal a critical role for type I IFN-dependent NK cell activation in innate immune elimination of adenoviral vectors in vivo and may help design effective strategies to improve the outcome of adenovirus-mediated gene therapy.

Suppression of interferon (IFN)-inducible genes and IFN-mediated functional responses in BCR-ABL-expressing cells

The interferons (IFNs) are cytokines that play key roles in host defense against viral infections and immune surveillance against cancer. We report that BCR-ABL transformation of hematopoietic cells results in suppression of IFN-dependent responses, including transcription of IFN-inducible genes and generation of IFN-mediated antiviral effects. BCR-ABL transformation suppresses expression of several IFN-regulated genes containing IFN-sensitive response element (ISRE) or GAS elements in their promoters, including Isg15, Irf1, Irf9, and Ifit2 (interferon-induced protein with tetratricopeptide repeats 2). Suppression of transcription of ISRE-containing genes is also seen in cells expressing various BCR-ABL kinase domain mutants, including T315I, H396P, Y253F, and E255K, but not kinase-defective BCR-ABL. Such effects are associated with impaired IFN-dependent phosphorylation of Stat1 on Tyr(701) and Stat3 on Tyr(705) and defective binding of Stat complexes to ISRE or GAS elements. Beyond suppression of Stat activities, BCR-ABL inhibits IFN-inducible phosphorylation/activation of the p38 MAPK, suggesting a dual mechanism by which this abnormal fusion protein blocks IFN transcriptional responses. The inhibitory activities of BCR-ABL ultimately result in impaired IFNalpha-mediated protection against encephalomyocarditis virus infection and reversal of IFN-dependent growth suppression. Altogether, our data provide evidence for a novel mechanism by which BCR-ABL impairs host defenses and promotes malignant transformation, involving dual suppression of IFN-activated signaling pathways.

STAT1 signaling in CD8 T cells is required for their clonal expansion and memory formation following viral infection in vivo

Recent advances have shown that direct type I IFN signaling on T cells is required for their efficient expansion in response to viral infections in vivo. It is not clear which intracellular signaling molecule is responsible for this effect. Although STAT1 has been shown to mediate many of the type I IFN-dependent biological effects, its role in T cells remains uncertain in vivo. In this study, we demonstrated that STAT1 signaling in CD8 T cells was required for their efficient expansion by promoting the survival of activated CD8 T cells upon vaccinia viral infection in vivo, suggesting that the direct effect of type I IFNs on CD8 T cells is mediated by STAT1. Furthermore, effector CD8 T cells that lack STAT1 signaling did not survive the contraction phase to differentiate into long-lived memory cells. These results identify a critical role for type I IFN-STAT1 signaling in multiple stages of CD8 T cell response in vivo and suggest that strategies to activate type I IFN-STAT1 signaling pathway may enhance vaccine potency.

T helper cell type 1 (Th1), Th2 and Th17 responses to myelin basic protein and disease activity in multiple sclerosis

Autoreactive T cells are thought to play an essential role in the pathogenesis of multiple sclerosis (MS). We examined the stimulatory effect of human myelin basic protein (MBP) on mononuclear cell (MNC) cultures from 22 patients with MS and 22 sex-matched and age-matched healthy individuals, and related the patient responses to disease activity, as indicated by magnetic resonance imaging. The MBP induced a dose-dependent release of interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha) and interleukin-10 (IL-10) by patient-derived MNCs. The patients' cells produced higher amounts of IFN-gamma and TNF-alpha, and lower amounts of IL-10, than cells from healthy controls (P<0.03 to P<0.04). Five patients with MS and no controls, displayed MBP-induced CD4+ T-cell proliferation. These high-responders exhibited enhanced production of IL-17, IFN-gamma, IL-5 and IL-4 upon challenge with MBP, as compared with the remaining patients and the healthy controls (P<0.002 to P<0.01). A strong correlation was found between the MBP-induced CD4+ T-cell proliferation and production of IL-17, IFN-gamma, IL-5 and IL-4 (P<0.0001 to P<0.01) within the patient group, and the production of IL-17 and IL-5 correlated with the number of active plaques on magnetic resonance images (P=0.04 and P=0.007). These data suggest that autoantigen-driven CD4+ T-cell proliferation and release of IL-17 and IL-5 may be associated with disease activity. Larger studies are needed to confirm this.

IFN-lambda (IFN-lambda) is expressed in a tissue-dependent fashion and primarily acts on epithelial cells in vivo

Interferons (IFN) exert antiviral, immunomodulatory and cytostatic activities. IFN-alpha/beta (type I IFN) and IFN-lambda (type III IFN) bind distinct receptors, but regulate similar sets of genes and exhibit strikingly similar biological activities. We analyzed to what extent the IFN-alpha/beta and IFN-lambda systems overlap in vivo in terms of expression and response. We observed a certain degree of tissue specificity in the production of IFN-lambda. In the brain, IFN-alpha/beta was readily produced after infection with various RNA viruses, whereas expression of IFN-lambda was low in this organ. In the liver, virus infection induced the expression of both IFN-alpha/beta and IFN-lambda genes. Plasmid electrotransfer-mediated in vivo expression of individual IFN genes allowed the tissue and cell specificities of the responses to systemic IFN-alpha/beta and IFN-lambda to be compared. The response to IFN-lambda correlated with expression of the alpha subunit of the IFN-lambda receptor (IL-28R alpha). The IFN-lambda response was prominent in the stomach, intestine and lungs, but very low in the central nervous system and spleen. At the cellular level, the response to IFN-lambda in kidney and brain was restricted to epithelial cells. In contrast, the response to IFN-alpha/beta was observed in various cell types in these organs, and was most prominent in endothelial cells. Thus, the IFN-lambda system probably evolved to specifically protect epithelia. IFN-lambda might contribute to the prevention of viral invasion through skin and mucosal surfaces.

Poly I:C induces Mx transcription and promotes an antiviral state against sole aquabirnavirus in the flatfish Senegalese sole (Solea senegalensis Kaup)

Mx is an interferon-induced protein that protects against viral infections. In this study the absolute number of Mx transcripts after poly I:C injection (a synthetic dsRNA) or sole aquabirnavirus (solevirus) inoculation in Senegalese sole (Solea senegalensis Kaup) has been quantified. Mx expression profiles differed clearly in both experimental conditions; the induction response was faster and more intense after poly I:C injection than after solevirus inoculation. Moreover, pre-injection of soles with poly I:C prior to solevirus infection eliminated the induction of Mx expression associated with this virus. To evaluate the possible interference of poly I:C treatments on solevirus replication, the mRNA levels of the virus capsid protein (VP2) were determined by RT-PCR. VP2 transcripts were hardly detected in poly I:C pre-injected animals from 12 to 72 h after solevirus inoculation. All these data suggest that poly I:C is able to induce an antiviral state that interferes with solevirus replication, and support the suitability of Mx expression analysis as a marker to study the defensive response against solevirus.

ISG15 inhibits Nedd4 ubiquitin E3 activity and enhances the innate antiviral response

Interferons regulate diverse immune functions through the transcriptional activation of hundreds of genes involved in anti-viral responses. The interferon-inducible ubiquitin-like protein ISG15 is expressed in cells in response to a variety of stress conditions like viral or bacterial infection and is present in its free form or is conjugated to cellular proteins. In addition, protein ubiquitination plays a regulatory role in the immune system. Many viruses modulate the ubiquitin (Ub) pathway to alter cellular signaling and the antiviral response. Ubiquitination of retroviral group-specific antigen precursors and matrix proteins of the Ebola, vesicular stomatitis, and rabies viruses by Nedd4 family HECT domain E3 ligases is an important step in facilitating viral release. We found that Nedd4 is negatively regulated by ISG15. Free ISG15 specifically bound to Nedd4 and blocked its interaction with Ub-E2 molecules, thus preventing further Ub transfer from E2 to E3. Furthermore, overexpression of ISG15 diminished the ability of Nedd4 to ubiquitinate viral matrix proteins and led to a decrease in the release of Ebola VP40 virus-like particles from the cells. These results point to a mechanistically novel function of ISG15 in the enhancement of the innate anti-viral response through specific inhibition of Nedd4 Ub-E3 activity. To our knowledge, this is the first example of a Ub-like protein with the ability to interfere with Ub-E2 and E3 interaction to inhibit protein ubiquitination.

Interferon type I responses in primary and secondary infections

The mammalian host responds to a microbial infection with a rapid innate immune reaction that is dominated by type I interferon (IFN-I) release. Most cells of vertebrates can respond to microbial attack with IFN-I production, but the cell type responsible for most of the systemic IFN-I release is thought to be plasmacytoid dendritic cells (pDCs). Besides its anti-microbial and especially anti-viral properties IFN-I also exerts a regulatory role on many facets of the sequential adaptive immune response. One of these is being the recently described partial, systemic activation of the vast majority of B and T lymphocytes in mice, irrespective of antigen reactivity. The biological significance of this partial activation of lymphocytes is at present speculative. Secondary infections occurring within a short time span of a primary infection fail to elicit a similar lymphocyte activation response due to a refractory period in systemic IFN-I production. This period of exhaustion in IFN-I responses is associated with an increased susceptibility of the host to secondary infections. The latter correlates with well-established clinical observations of heightened susceptibility of patients to secondary microbial infections after viral episodes.

Interferon-Induced Effector Proteins and Hepatitis C Virus Replication

Hepatitis C virus (HCV) is a small, enveloped RNA virus that is often capable of establishing a persistent infection, which may lead to chronic liver disease, cirrhosis, hepatocellular carcinoma, and eventually death. For more than 20 years, hepatitis C patients have been treated with interferon-alpha (IFN-α). Current treatment usually consists of polyethylene glycol-conjugated IFN-α that is combined with ribavirin, but even the most advanced IFN-based therapies are still ineffective in eliminating the virus from a large proportion of individuals. Therefore, a better understanding of the IFN-induced innate immune response is urgently needed. By using selectable self-replicating RNAs (replicons) and, more recently, recombinant full-length genomes, many groups have tried to elucidate the mechanism(s) by which IFNs inhibit HCV replication. This chapter attempts to summarize the current state of knowledge in this interesting field of HCV research.

Ligand-independent pathway that controls stability of interferon alpha receptor

Ligand-specific negative regulation of cytokine-induced signaling relies on down regulation of the cytokine receptors. Down regulation of the IFNAR1 sub-unit of the Type I interferon (IFN) receptor proceeds via lysosomal receptor proteolysis, which is triggered by ubiquitination that depends on IFNAR1 serine phosphorylation. While IFN-inducible phosphorylation, ubiquitination, and degradation requires the catalytic activity of the Tyk2 Janus kinase, here we found the ligand- and Tyk2-independent pathway that promotes IFNAR1 phosphorylation, ubiquitination, and degradation when IFNAR1 is expressed at high levels. A major cellular kinase activity that is responsible for IFNAR1 phosphorylation in vitro does not depend on either ligand or Tyk2 activity. Inhibition of ligand-independent IFNAR1 degradation suppresses cell proliferation. We discuss the signaling events that might lead to ubiquitination and degradation of IFNAR1 via ligand-dependent and independent pathways and their potential physiologic significance.

Type I IFN are host modulators of strain-specific Listeria monocytogenes virulence

Type I IFN (IFN-I) increase the sensitivity of cells and mice to lethal infection with Listeria monocytogenes. Therefore the amount of IFN-I produced during infection might be an important factor determining Listeria virulence. Two commonly used strains of L. monocytogenes, EGD and LO28, were identified as, respectively, low and high inducers of IFN-I synthesis in infected macrophages. Increased IFN-I production resulted from the stronger ability of the LO28 strain to trigger the IRF3 signalling pathway and correlated with an increased sensitization of macrophages to lethal infection. In contrast, stimulation of NFkappaB, MAPK, or inflammasome signalling by the LO28 and EGD strains did not differ significantly. The LO28 strain was more virulent in wild-type (wt) C57/BL6 mice than the EGD strain whereas both strains were similarly virulent in IFN-I receptor-deficient C57/BL6 mice. Together our data suggest that isolates of wt L. monocytogenes differ in their ability to trigger the IRF3 signalling pathway and IFN-I production, and that the amount of IFN-I produced during infection is an important determinant of Listeria virulence.

LTHREADER: prediction of extracellular ligand-receptor interactions in cytokines using localized threading

Identification of extracellular ligand-receptor interactions is important for drug design and the treatment of diseases. Difficulties in detecting these interactions using high-throughput experimental techniques motivate the development of computational prediction methods. We propose a novel threading algorithm, LTHREADER, which generates accurate local sequence-structure interface alignments and integrates various statistical scores and experimental binding data to predict interactions within ligand-receptor families. LTHREADER uses a profile of secondary structure and solvent accessibility predictions with residue contact maps to guide and constrain alignments. Using a decision tree classifier and low-throughput experimental data for training, it combines information inferred from statistical interaction potentials, energy functions, correlated mutations, and conserved residue pairs to predict interactions. We apply our method to cytokines, which play a central role in the development of many diseases including cancer and inflammatory and autoimmune disorders. We tested our approach on two representative families from different structural classes (all-alpha and all-beta proteins) of cytokines. In comparison with the state-of-the-art threader RAPTOR, LTHREADER generates on average 20% more accurate alignments of interacting residues. Furthermore, in cross-validation tests, LTHREADER correctly predicts experimentally confirmed interactions for a common binding mode within the 4-helical long-chain cytokine family with 75% sensitivity and 86% specificity with 40% gain in sensitivity compared to RAPTOR. For the TNF-like family our method achieves 70% sensitivity with 55% specificity with 70% gain in sensitivity. LTHREADER combines information from multiple complex templates when such data are available. When only one solved structure is available, a localized PSI-BLAST approach also outperforms standard threading methods with 25%-50% improvements in sensitivity.

Independent and cooperative antiviral actions of beta interferon and gamma interferon against herpes simplex virus replication in primary human fibroblasts

Type I and type II interferons (IFNs) act in synergy to inhibit the replication of a variety of viruses, including herpes simplex virus (HSV). To understand the mechanism of this effect, we have analyzed the transcriptional profiles of primary human fibroblast cells that were first treated with IFN-beta1, IFN-gamma, or a combination of both and then subsequently infected with HSV-1. We have identified two types of synergistic activities in the gene expression patterns induced by IFN-beta1 and IFN-gamma that may contribute to inhibition of HSV-1 replication. The first is defined as "synergy by independent action," in which IFN-beta1 and IFN-gamma induce distinct gene categories. The second, "synergy by cooperative action," is a term that describes the positive interaction between IFN-beta1 and IFN-gamma as defined by a two-way analysis of variance. This form of synergy leads to a much higher level of expression for a subset of genes than is seen with either interferon alone. The cooperatively induced genes by IFN-beta1 and IFN-gamma include those involved in apoptosis, RNA degradation, and the inflammatory response. Furthermore, the combination of IFN-beta1 and IFN-gamma induces significantly more apoptosis and inhibits HSV-1 gene expression and DNA replication significantly more than treatment with either interferon alone. Taken together, these data suggest that IFN-beta1 and IFN-gamma work both independently and cooperatively to create an antiviral state that synergistically inhibits HSV-1 replication in primary human fibroblasts and that cooperatively induced apoptosis may play a role in the synergistic effect on viral replication.

Interferons at age 50: past, current and future impact on biomedicine

The family of interferon (IFN) proteins has now more than reached the potential envisioned by early discovering virologists: IFNs are not only antivirals with a spectrum of clinical effectiveness against both RNA and DNA viruses, but are also the prototypic biological response modifiers for oncology, and show effectiveness in suppressing manifestations of multiple sclerosis. Studies of IFNs have resulted in fundamental insights into cellular signalling mechanisms, gene transcription and innate and acquired immunity. Further elucidation of the multitude of IFN-induced genes, as well as drug development strategies targeting IFN production via the activation of the Toll-like receptors (TLRs), will almost certainly lead to newer and more efficacious therapeutics. Our goal is to offer a molecular and clinical perspective that will enable IFNs or their TLR agonist inducers to reach their full clinical potential.

A recombinant CHSE-214 cell line expressing an Mx1 promoter-reporter system responds to both interferon type I and type II from salmonids and represents a versatile tool to study the IFN-system in teleost fish

A transgenic cell line for the detection of salmon interferons (IFNs) has been established. It is based on a CHSE-214 cell line containing a reporter construct expressing firefly luciferase under the control of the rainbow trout promoter for the IFN-induced Mx1 gene. This cell line, named CHSE-Mx10, showed IFN-induced luciferase expression after more than 80 passages, confirming the stability of this cell line. Interestingly, the Mx promoter was shown to respond to both salmon IFN-alpha/beta and trout IFN-gamma in a dose-dependent manner, while there was no response to TNF-alpha and IL-1beta. IFN-alpha/beta activity could be measured at a range of 9-150 U/ml, and IFN-gamma showed activity between 10 and 100 ng/ml. The reproducibility of both responses was good. The CHSE-Mx10 reporter system constitutes a versatile tool to study the induction and regulation of IFN signaling in teleost fish. A preliminary study presented herein suggests that both infectious pancreas necrosis virus (IPNV) and salmon pancreas disease virus (SPDV) may block activation of the Mx promoter in CHSE-Mx10 stimulated with IFN-alpha/beta.

Pathogenesis and immune responses in gnotobiotic calves after infection with the genogroup II.4-HS66 strain of human norovirus

We previously characterized the pathogenesis of two host-specific bovine enteric caliciviruses (BEC), the GIII.2 norovirus (NoV) strain CV186-OH and the phylogenetically unassigned NB strain, in gnotobiotic (Gn) calves. In this study we evaluated the Gn calf as an alternative animal model to study the pathogenesis and host immune responses to the human norovirus (HuNoV) strain GII.4-HS66. The HuNoV HS66 strain caused diarrhea (five/five calves) and intestinal lesions (one/two calves tested) in the proximal small intestine (duodenum and jejunum) of Gn calves, with lesions similar to, but less severe than, those described for the Newbury agent 2 (NA-2) and NB BEC. Viral capsid antigen was also detected in the jejunum of the proximal small intestine of one of two calves tested by immunohistochemistry. All inoculated calves shed virus in feces (five/five calves), and one/five had viremia. Antibodies and cytokine (proinflammatory, tumor necrosis factor alpha [TNF-alpha]; Th1, interleukin-12 [IL-12] and gamma interferon [IFN-gamma]; Th2, IL-4; Th2/T-regulatory, IL-10) profiles were determined in serum, feces, and intestinal contents (IC) of the HuNoV-HS66-inoculated calves (n = 5) and controls (n = 4) by enzyme-linked immunosorbent assay in the acute (postinoculation day 3 [PID 3]) and convalescent (PID 28) stages of infection. The HuNoV-HS66-specific antibody and cytokine-secreting cells (CSCs) were quantitated by ELISPOT in mononuclear cells of local and systemic tissues at PID 28. Sixty-seven percent of the HuNoV-HS66-inoculated calves seroconverted, and 100% coproconverted with immunoglobulin A (IgA) and/or IgG antibodies to HuNoV-HS66, at low titers. The highest numbers of antibody-secreting cells (ASC), both IgA and IgG, were detected locally in intestine, but systemic IgA and IgG ASC responses also occurred in the HuNoV-HS66-inoculated calves. In serum, HuNoV-HS66 induced higher peaks of TNF-alpha and IFN-gamma at PIDs 2, 7, and 10; of IL-4 and IL-10 at PID 4; and of IL-12 at PIDs 7 and 10, compared to controls. In feces, cytokines increased earlier (PID 1) than in serum and TNF-alpha and IL-10 were elevated acutely in the IC of the HS66-inoculated calves. Compared to controls, at PID 28 higher numbers of IFN-gamma and TNF-alpha CSCs were detected in mesenteric lymph nodes (MLN) or spleen and Th2 (IL-4) CSCs were elevated in intestine; IL-10 CSCs were highest in spleen. Our study provides new data confirming HuNoV-HS66 replication and enteropathogenicity in Gn calves and reveals important and comprehensive aspects of the host's local (intestine and MLN) and systemic (spleen and blood) immune responses to HuNoV-HS66.

Experimental coronavirus retinopathy (ECOR): retinal degeneration susceptible mice have an augmented interferon and chemokine (CXCL9, CXCL10) response early after virus infection

Mouse hepatitis virus induces a biphasic disease in BALB/c mice that consists of an acute retinitis followed by progression to a chronic retinal degeneration with autoimmune reactivity. Retinal degeneration resistant CD-1 mice do not develop the late phase. What host factors contribute to the distinct responses to the virus are unknown. Herein, we show that IFN-α, IFN-β and IFN-γ act in concert as part of the innate immune response to the retinal infection. At day 2, high serum levels of IFN-γ, CXCL9 and CXCL10, were detected in BALB/c mice. Moreover, elevated levels of CXCL9 and CXCL10 gene expression were detected in retinal tissue. Although IFN-γ and the chemokines were detected in CD-1 mice, they were at significantly lower levels compared to BALB/c mice. These augmented innate responses observed correlated with the development of autoimmune reactivity and retinal degeneration and thus may contribute to the pathogenic processes.

Maturation-dependent responses of human neuronal cells to western equine encephalitis virus infection and type I interferons

Innate cell-autonomous antiviral responses are essential first lines of defense against central nervous system infections but may also contribute to neuropathogenesis. We investigated the relationships between innate immunity and neuronal differentiation using an in vitro culture system with human cell lines to analyze cellular responses to the neurotropic alphavirus western equine encephalitis virus. Human neuronal cells displayed a maturation-dependent reduction in virus-induced cytopathology that was independent of autocrine interferon alpha or beta activity. In addition, maturation was associated with enhanced responsiveness to exogenous stimuli, such that differentiated neurons required five- to ten-fold less type I interferon to suppress viral replication or virus-induced cytopathology compared to immature cells, although this enhanced responsiveness extended to only a subset of unique type I interferons. These results demonstrate that maturation-dependent changes in human neuronal cells may be key determinants in the innate immune response to infections with neurotropic alphaviruses.

Molecular mechanisms of the anti-inflammatory functions of interferons

Interferons are pleiotropic cytokines with important proinflammatory functions required in defence against infections with bacteria, viruses and multicellular parasites. In recent years, fundamental functions of interferons in other processes such as cancer immunosurveillance, immune homeostasis and immunosuppression have been established. In addition, anti-inflammatory roles of interferons are well-documented in several inflammatory disease models in the mouse, most importantly in experimental autoimmune encephalomyelitis that resembles multiple sclerosis in humans. While the beneficial effects of interferons in such disease models are known, the molecular mechanisms remain poorly understood. Only recently a few molecular principles for the anti-inflammatory properties of interferons at the cellular level have been revealed. They include the ability of interferons to reduce the expression of the receptors for the inflammation-related cytokines IL-1 and IL-4, or to increase the expression of the potent anti-inflammatory genes tristetraprolin and Twist. However, the individual contribution of these anti-inflammatory responses to the overall beneficial effects of interferons in inflammatory diseases is still an open question. Also, the reason for the apparently limited number of tissues that are susceptible to the anti-inflammatory functions of interferons remains enigmatic. This review summarizes the present knowledge of the anti-inflammatory effects of interferons, and describes the currently known molecular mechanisms that may help explain the benefits of interferon signalling in several inflammatory diseases.

Comparable potency of IFNalpha2 and IFNbeta on immediate JAK/STAT activation but differential down-regulation of IFNAR2

Type I IFNs (interferons) (IFNalpha/beta) form a family of related cytokines that control a variety of cellular functions through binding to a receptor composed of IFNAR (IFNalpha receptor subunit) 1 and 2. Among type I IFNs, the alpha2 and beta subtypes exhibit a large difference in their binding affinities to IFNAR1, and it was suggested that high concentrations of IFNAR1 may compensate for its low intrinsic binding affinity for IFNalpha2. We tested whether receptor-proximal signalling events are sensitive to IFNAR1 surface concentration by investigating the relationship between relative IFNAR1/IFNAR2 surface levels and IFNalpha2 and IFNbeta signalling potencies in several cell lines. For this, we monitored the activation profile of JAK (Janus kinase)/STAT (signal transducer and activator of transcription) proteins, measured basal and ligand-induced surface decay of each receptor subunit and tested the effect of variable IFNAR1 levels on IFNalpha2 signalling potency. Our data show that the cell-surface IFNAR1 level is indeed a limiting factor for assembly of the functional complex, but an increased concentration of it does not translate into an IFNalpha/beta differential JAK/STAT signalling nor does it change the dynamics of the engaged receptor. Importantly, however, our data highlight a differential effect upon routing of IFNAR2. Following binding of IFNalpha2, IFNAR2 is internalized, but, instead of being routed towards degradation as it is when complexed to IFNbeta, it recycles back to the cell surface. These observations suggest strongly that the stability and the intracellular lifetime of the ternary complex account for the differential control of IFNAR2. Moreover, the present study opens up the attractive possibility that endosomal-initiated signalling may contribute to IFNalpha/beta differential bioactivities.

Innate recognition of viruses

Virus infection elicits potent responses in all cells intended to contain virus spread before intervention by the adaptive immune system. Central to this process is the virus-elicited production of type I interferons (IFNs) and other cytokines. The sensors involved in coupling recognition of viruses to the induction of the type I IFN genes have only recently been uncovered and include endosomal and cytosolic receptors for RNA and DNA. Here, we review their properties and discuss how their ability to recognize the unusual presence of atypical nucleic acids in particular subcellular compartments is used by the body to detect virus presence.

Transcriptional networks in plasmacytoid dendritic cells stimulated with synthetic TLR 7 agonists

Background

Plasmacytoid Dendritic Cells (pDC) comprise approximately 0.2 to 0.8% of the blood mononuclear cells and are the primary type 1 interferon (IFN), producing cells, secreting high levels of IFN in response to viral infections. Plasmacytoid dendritic cells express predominantly TLRs 7 & 9, making them responsive to ssRNA and CpG DNA. The objective of this study was to evaluate the molecular and cellular processes altered upon stimulation of pDC with synthetic TLR 7 and TLR 7/8 agonists. To this end, we evaluated changes in global gene expression upon stimulation of 99.9% pure human pDC with the TLR7 selective agonists 3M-852A, and the TLR7/8 agonist 3M-011.

Results

Global gene expression was evaluated using the Affymetrix U133A GeneChip^® and selected genes were confirmed using real time TaqMan^® RTPCR. The gene expression profiles of the two agonists were similar indicating that changes in gene expression were solely due to stimulation through TLR7. Type 1 interferons were among the highest induced genes and included IFNB and multiple IFNα subtypes, IFNα2, α5, α6, α8, α1/13, α10, α14, α16, α17, α21. A large number of chemokines and co-stimulatory molecules as well as the chemokine receptor CCR7 were increased in expression indicating maturation and change in the migratory ability of pDC. Induction of an antiviral state was shown by the expression of several IFN-inducible genes with known anti-viral activity. Further analysis of the data using the pathway analysis tool MetaCore gave insight into molecular and cellular processes impacted. The analysis revealed transcription networks that show increased expression of signaling components in TLR7 and TLR3 pathways, and the cytosolic anti-viral pathway regulated by RIG1 and MDA5, suggestive of optimization of an antiviral state targeted towards RNA viruses. The analysis also revealed increased expression of a network of genes important for protein ISGylation as well as an anti-apoptotic and pro-survival gene expression program.

Conclusion

Thus this study demonstrates that as early as 4 hr post stimulation, synthetic TLR7 agonists induce a complex transcription network responsible for activating pDC for innate anti-viral immune responses with optimized responses towards RNA viruses, increased co-stimulatory capacity, and increased survival.

Interferon-based therapy of hepatitis C

In 2007, the world celebrated the 50th anniversary of the discovery of interferon (IFN). The first clinical trial of recombinant IFN-alpha in patients with chronic hepatitis C was published in 1986. This article reviews the classification of IFNs, IFN production during viral infections, IFN signaling pathways and the mechanisms of their antiviral and immunomodulatory properties. Hepatitis C virus infection treatment is currently based on the combination of pegylated IFN-alpha and ribavirin. The pegylated IFN-alpha molecules are described, as well as the putative mechanisms of action of ribavirin. Current treatment guidelines are discussed and new results suggesting that the treatment schedule should be tailored to the early virological response during therapy are presented. Finally, insights into new hepatitis C drug developments are given.

Historical developments in the research of interferon receptors

Interferons (IFNs) were discovered 50 years ago independently by Isaacs and Lindemann and by Nagata and Kojima. When it was later realized that IFNs are active at very low concentrations, research began to determine how their powerful effects were generated from such a small initial signal. It has since been established that interferons, as well as all other cytokines, employ cell surface receptors to translate their presence in the serum to a potent cellular response to a viral infection. These receptor complexes are composed of multiple distinct glycosylated transmembrane polypeptides, a number of protein tyrosine kinases, and interact transiently with a large variety of other proteins including transcription factors, phosphatases, signaling repressors, and adaptor proteins coupling the receptor to alternative signaling pathways. Three major receptor complexes exist that are exclusive to each of three major classes of interferon. Even though the effects of each major class of interferon vary physiologically, each receptor complex interacts with its ligand in similar ways and activates similar signaling cascades. In this mini-review, we take a historical perspective at the major events in the characterization of interferon receptors, discussing interesting results that still need to be explained.