Characterization of the murine alpha interferon gene family

Host Restriction Factors and Human Immunodeficiency Virus (HIV-1): A Dynamic Interplay Involving All Phases of the Viral Life Cycle

Mammalian cells have evolved several mechanisms to prevent or block lentiviral infection and spread. Among the innate immune mechanisms, the signaling cascade triggered by type I interferon (IFN) plays a pivotal role in limiting the burden of HIV-1. In the presence of IFN, human cells upregulate the expression of a number of genes, referred to as IFN-stimulated genes (ISGs), many of them acting as antiviral restriction factors (RFs). RFs are dominant proteins that target different essential steps of the viral cycle, thereby providing an early line of defense against the virus. The identification and characterization of RFs have provided unique insights into the molecular biology of HIV-1, further revealing the complex host-pathogen interplay that characterizes the infection. The presence of RFs drove viral evolution, forcing the virus to develop specific proteins to counteract their activity. The knowledge of the mechanisms that prevent viral infection and their viral counterparts may offer new insights to improve current antiviral strategies. This review provides an overview of the RFs targeting HIV-1 replication and the mechanisms that regulate their expression as well as their impact on viral replication and the clinical course of the disease.

ER intrabody-mediated inhibition of interferon α secretion by mouse macrophages and dendritic cells

Interferon α (IFNα) counteracts viral infections by activating various IFNα-stimulated genes (ISGs). These genes encode proteins that block viral transport into the host cell and inhibit viral replication, gene transcription and translation. Due to the existence of 14 different, highly homologous isoforms of mouse IFNα, an IFNα knockout mouse has not yet been established by genetic knockout strategies. An scFv intrabody for holding back IFNα isoforms in the endoplasmic reticulum (ER) and thus counteracting IFNα secretion is reported. The intrabody was constructed from the variable domains of the anti-mouse IFNα rat monoclonal antibody 4EA1 recognizing the 5 isoforms IFNα1, IFNα2, IFNα4, IFNα5, IFNα6.

A soluble form of the intrabody had a K_D of 39 nM to IFNα4. It could be demonstrated that the anti-IFNα intrabody inhibits clearly recombinant IFNα4 secretion by HEK293T cells. In addition, the secretion of IFNα4 was effectively inhibited in stably transfected intrabody expressing RAW 264.7 macrophages and dendritic D1 cells. Colocalization of the intrabody with IFNα4 and the ER marker calnexin in HEK293T cells indicated complex formation of intrabody and IFNα4 inside the ER. Intracellular binding of intrabody and antigen was confirmed by co-immunoprecipitation. Complexes of endogenous IFNα and intrabody could be visualized in the ER of Poly (I:C) stimulated RAW 264.7 macrophages and D1 dendritic cells. Infection of macrophages and dendritic cells with the vesicular stomatitis virus VSV-AV2 is attenuated by IFNα and IFNβ. The intrabody increased virus proliferation in RAW 264.7 macrophages and D1 dendritic cells under IFNβ-neutralizing conditions. To analyze if all IFNα isoforms are recognized by the intrabody was not in the focus of this study. Provided that binding of the intrabody to all isoforms was confirmed, the establishment of transgenic intrabody mice would be promising for studying the function of IFNα during viral infection and autoimmune diseases.

Sources of Type I Interferons in Infectious Immunity: Plasmacytoid Dendritic Cells Not Always in the Driver's Seat

Type I Interferons (IFNs) are hallmark cytokines produced in immune responses to all classes of pathogens. Type I IFNs can influence dendritic cell (DC) activation, maturation, migration, and survival, but also directly enhance natural killer (NK) and T/B cell activity, thus orchestrating various innate and adaptive immune effector functions. Therefore, type I IFNs have long been considered essential in the host defense against virus infections. More recently, it has become clear that depending on the type of virus and the course of infection, production of type I IFN can also lead to immunopathology or immunosuppression. Similarly, in bacterial infections type I IFN production is often associated with detrimental effects for the host. Although most cells in the body are thought to be able to produce type I IFN, plasmacytoid DCs (pDCs) have been termed the natural "IFN producing cells" due to their unique molecular adaptations to nucleic acid sensing and ability to produce high amounts of type I IFN. Findings from mouse reporter strains and depletion experiments in in vivo infection models have brought new insights and established that the role of pDCs in type I IFN production in vivo is less important than assumed. Production of type I IFN, especially the early synthesized IFNβ, is rather realized by a variety of cell types and cannot be mainly attributed to pDCs. Indeed, the cell populations responsible for type I IFN production vary with the type of pathogen, its tissue tropism, and the route of infection. In this review, we summarize recent findings from in vivo models on the cellular source of type I IFN in different infectious settings, ranging from virus, bacteria, and fungi to eukaryotic parasites. The implications from these findings for the development of new vaccination and therapeutic designs targeting the respectively defined cell types are discussed.

Attenuation of interferon regulatory factor 7 activity in local infectious sites of trachea and lung for preventing the development of acute lung injury caused by influenza A virus

The excessive activation of interferon regulatory factor 7 (IRF7) promotes the development of acute lung injury (ALI) caused by influenza A virus (IAV). However, the deficiency of IRF7 increases the susceptibility to deadly IAV infection in both humans and mice. To test whether the attenuation rather than the abolishment of IRF7 activity in local infectious sites could alleviate IAV-induced ALI, we established IAV-infected mouse model and trachea/lung-tissue culture systems, and designed two IRF7-interfering oligodeoxynucleotides, IRF7-rODN M1 and IRF7-rODN A1, based on the mouse and human consensus sequences of IRF7-binding sites of Ifna/IFNA genes, respectively. In the model mice, we found a close relationship between the IAV-induced ALI and the level/activity of IRF7 in local infectious sites, and also found that the reduced IRF7 level or activity in the lungs of mice treated with IRF7-rODN M1 led to decreased mRNA levels of Ifna genes, reduced neutrophil infiltration in the lungs and prolonged survival of mice. Furthermore, we found that the effects of IRF7-rODN M1 on alleviating IAV-induced ALI could be correlated to the reduced translocation of IRF7, caused by the IRF7-rODN M1, from cytosol to nucleus in IAV-infected cells. These data suggest that the proper attenuation of IRF7 activity in local infectious sites could be a novel approach for treating IAV-induced ALI.

Complexities of Type I Interferon Biology: Lessons from LCMV

Over the past decades, infection of mice with lymphocytic choriomeningitis virus (LCMV) has provided an invaluable insight into our understanding of immune responses to viruses. In particular, this model has clarified the central roles that type I interferons play in initiating and regulating host responses. The use of different strains of LCMV and routes of infection has allowed us to understand how type I interferons are critical in controlling virus replication and fostering effective antiviral immunity, but also how they promote virus persistence and functional exhaustion of the immune response. Accordingly, these discoveries have formed the foundation for the development of novel treatments for acute and chronic viral infections and even extend into the management of malignant tumors. Here we review the fundamental insights into type I interferon biology gained using LCMV as a model and how the diversity of LCMV strains, dose, and route of administration have been used to dissect the molecular mechanisms underpinning acute versus persistent infection. We also identify gaps in the knowledge regarding LCMV regulation of antiviral immunity. Due to its unique properties, LCMV will continue to remain a vital part of the immunologists' toolbox.

Interferon β-Mediated Protective Functions of Microglia in Central Nervous System Autoimmunity

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) leading to demyelination and axonal damage. It often affects young adults and can lead to neurological disability. Interferon β (IFNβ) preparations represent widely used treatment regimens for patients with relapsing-remitting MS (RRMS) with therapeutic efficacy in reducing disease progression and frequency of acute exacerbations. In mice, IFNβ therapy has been shown to ameliorate experimental autoimmune encephalomyelitis (EAE), an animal model of MS while genetic deletion of IFNβ or its receptor augments clinical severity of disease. However, the complex mechanism of action of IFNβ in CNS autoimmunity has not been fully elucidated. Here, we review our current understanding of the origin, phenotype, and function of microglia and CNS immigrating macrophages in the pathogenesis of MS and EAE. In addition, we highlight the emerging roles of microglia as IFNβ-producing cells and vice versa the impact of IFNβ on microglia in CNS autoimmunity. We finally discuss recent progress in unraveling the underlying molecular mechanisms of IFNβ-mediated effects in EAE.

Species Specificity of Type III Interferon Activity and Development of a Sensitive Luciferase-Based Bioassay for Quantitation of Mouse Interferon-λ

The type III interferon (IFN-λ) family includes 4 IFN-λ subtypes in man. In the mouse, only the genes coding for IFN-λ2 and -λ3 are present. Unlike mouse and human type I IFNs (IFN-α/β), which exhibit strong species specificity, type III IFNs were reported to act in a cross-specific manner. We reexamined the cross-specificity and observed that mouse and human IFN-λ exhibit some species specificity, although much less than type I IFNs. Mouse IFN-λ3 displayed clear species specificity, being 25-fold less active in human cells than the closely related mouse IFN-λ2. This specificity likely depends on amino acids in α helices A and F that diverged from other IFN-λ sequences. Human IFN-λ4, in contrast, retained high activity in mouse cells. We next developed a firefly luciferase-based reporter cell line, named Fawa-λ-luc, to detect IFN-λ in biological fluids with high specificity and sensitivity. Fawa-λ-luc cells, derived from mouse epithelial cells that are responsive to IFN-λ, were made nonresponsive to type I IFNs by inactivation of the Ifnar2 gene and strongly responsive to IFN-λ by overexpression of the mouse IFNLR1. This bioassay was as sensitive as a commercially available enzyme-linked immunosorbent assay in detecting mouse IFN-λ in cell culture supernatant, as well as in serum and bronchoalveolar lavage samples of virus-infected mice. The assay also enabled the sensitive detection of human IFN-λ activity, including that of the divergent IFN-λ4 with a bias, however, due to variable activity of IFN-λ subtypes.

Transcriptome Analysis of Infected and Bystander Type 2 Alveolar Epithelial Cells during Influenza A Virus Infection Reveals In Vivo Wnt Pathway Downregulation

Influenza virus outbreaks remain a serious threat to public health. A greater understanding of how cells targeted by the virus respond to the infection can provide insight into the pathogenesis of disease. Here we examined the transcriptional profile of in vivo-infected and uninfected type 2 alveolar epithelial cells (AEC) in the lungs of influenza virus-infected mice. We show for the first time the unique gene expression profiles induced by the in vivo infection of AEC as well as the transcriptional response of uninfected bystander cells. This work allows us to distinguish the direct and indirect effects of infection at the cellular level. Transcriptome analysis revealed that although directly infected and bystander AEC from infected animals shared many transcriptome changes compared to AEC from uninfected animals, directly infected cells produce more interferon and express lower levels of Wnt signaling-associated transcripts, while concurrently expressing more transcripts associated with cell death pathways, than bystander uninfected AEC. The Wnt signaling pathway was downregulated in both in vivo-infected AEC and in vitro-infected human lung epithelial A549 cells. Wnt signaling did not affect type I and III interferon production by infected A549 cells. Our results reveal unique transcriptional changes that occur within infected AEC and show that influenza virus downregulates Wnt signaling. In light of recent findings that Wnt signaling is essential for lung epithelial stem cells, our findings reveal a mechanism by which influenza virus may affect host lung repair.IMPORTANCE Influenza virus infection remains a major public health problem. Utilizing a recombinant green fluorescent protein-expressing influenza virus, we compared the in vivo transcriptomes of directly infected and uninfected bystander cells from infected mouse lungs and discovered many pathways uniquely regulated in each population. The Wnt signaling pathway was downregulated in directly infected cells and was shown to affect virus but not interferon production. Our study is the first to discern the in vivo transcriptome changes induced by direct viral infection compared to mere exposure to the lung inflammatory milieu and highlight the downregulation of Wnt signaling. This downregulation has important implications for understanding influenza virus pathogenesis, as Wnt signaling is critical for lung epithelial stem cells and lung epithelial cell differentiation. Our findings reveal a mechanism by which influenza virus may affect host lung repair and suggest interventions that prevent damage or accelerate recovery of the lung.

Interferon-Mediated Response to Human Metapneumovirus Infection

Human metapneumovirus (HMPV) is one of the leading causes of respiratory diseases in infants and children worldwide. Although this pathogen infects mainly young children, elderly and immunocompromised people can be also seriously affected. To date, there is no commercial vaccine available against it. Upon HMPV infection, the host innate arm of defense produces interferons (IFNs), which are critical for limiting HMPV replication. In this review, we offer an updated landscape of the HMPV mediated-IFN response in different models as well as some of the defense tactics employed by the virus to circumvent IFN response.

Crosstalk between type I and II interferons in regulation of myeloid cell responses during bacterial infection

Type I and type II interferons (IFNα/β and IFNγ) are cytokines that play indispensable roles in directing myeloid cell activity during inflammatory and immune responses. Each IFN type binds a distinct receptor (IFNAR or IFNGR) to transduce signals that reshape gene expression and function of myeloid and other cell types. In the context of murine models and human bacterial infections, production of IFNγ generally promotes resistance while production of IFNα/β is associated with increased host susceptibility. Here, we review mechanisms of crosstalk between type I and II IFNs in myeloid cells and their impact on myeloid cell activation and anti-microbial function.

IFNAR1 Controls Autocrine Type I IFN Regulation of PD-L1 Expression in Myeloid-Derived Suppressor Cells

Tumor cells respond to IFN-γ of activated T cells to upregulate programmed death-ligand 1 (PD-L1) in the tumor microenvironment as an adaptive immune resistance mechanism. Tumor cells also express oncogene-driven PD-L1. PD-L1 is also expressed on myeloid-derived suppressor cells (MDSCs). It is known that both type I and II IFNs upregulate PD-L1 expression in MDSCs. However, the molecular mechanism underlying PD-L1 expression in MDSCs is still largely unknown. We report in this article that MDSCs exhibit constitutive STAT1 phosphorylation in vitro without exogenous IFNs, indicating a constitutive active JAK-STAT signaling pathway in mouse MDSCs in vitro. Furthermore, IFN-α and IFN-β but not IFN-γ are endogenously expressed in the MDSC cell line in vitro and in tumor-induced MDSCs in vivo. Neutralizing type I IFN or inhibiting the JAK-STAT signaling pathway significantly decreased constitutive PD-L1 expression in MDSCs in vitro. However, neither IFN-α expression level nor IFN-β expression level is correlated with PD-L1 expression level in MDSCs; instead, the level of IFN receptor type I (IFNAR1) is correlated with PD-L1 expression levels in MDSCs. Consequently, knocking out IFNAR1 in mice diminished PD-L1 expression in tumor-induced MDSCs. Therefore, we determined that 1) PD-L1 expression in MDSCs is activated by type I IFN through an autocrine manner and 2) the expression level of PD-L1 is controlled at least in part by the IFNAR1 level on MDSCs. Our data indicate that MDSCs may maintain their PD-L1 expression via autocrine type I IFN to exert their suppressive activity in the absence of IFN-γ from the suppressed T cells in the tumor microenvironment.

Anti-IL-10-mediated Enhancement of Antitumor Efficacy of a Dendritic Cell-targeting MIP3α-gp100 Vaccine in the B16F10 Mouse Melanoma Model Is Dependent on Type I Interferons

The chemokine MIP3α (CCL20) binds to CCR6 on immature dendritic cells. Vaccines fusing MIP3α to gp100 have been shown to be effective in therapeutically reducing melanoma tumor burden and prolonging survival in a mouse model. Other studies have provided evidence that interleukin-10 (IL-10) neutralizing antibodies (αIL-10) enhance immunologic melanoma therapies by modulating the tolerogenic tumor microenvironment. In the current study, we have utilized the B16F10 syngeneic mouse melanoma model to demonstrate for the first time that a therapy neutralizing IL-10 enhances the antitumor efficacy of a MIP3α-gp100 DNA vaccine, leading to significantly smaller tumors, slower growing tumors, and overall increases in mouse survival. The additive effects of αIL-10 were not shown to be correlated to vaccine-specific tumor-infiltrating lymphocytes (TILs), total TILs, or regulatory T cells. However, we discovered an upregulation of IFNα-4 transcripts in tumors and a correlation of increased plasmacytoid dendritic cell numbers with reduced tumor burden in αIL-10-treated mice. Interferon α receptor knockout (IFNαR1) mice received no benefit from αIL-10 treatment, demonstrating that the additional therapeutic value of αIL-10 is primarily mediated by type I IFNs. Efficient targeting of antigen to immature dendritic cells with a chemokine-fusion vaccine provides an effective anticancer therapeutic. Combining this approach with an IL-10 neutralizing antibody therapy enhances the antitumor efficacy of the therapy in a manner dependent upon the activity of type I IFNs. This combination of a vaccine and immunomodulatory agent provides direction for future optimization of a novel cancer vaccine therapy.

Development of molecular and cellular tools to decipher the type I IFN pathway of the common vampire bat

Though the common vampire bat, Desmodus rotundus, is known as the main rabies virus reservoir in Latin America, no tools are available to investigate its antiviral innate immune system. To characterize the IFN-I pathway, we established an immortalized cell line from a D. rotundus fetal lung named FLuDero. Then we molecularly characterized some of the Toll-like receptors (TLR3, 7, 8 and 9), the three RIG-I-like receptor members, as well as IFNα1 and IFNβ. Challenging the FLuDero cell line with poly (I:C) resulted in an up-regulation of both IFNα1 and IFNβ and the induction of expression of the different pattern recognition receptors characterized. These findings provide evidence of the intact dsRNA recognition machinery and the IFN-I signaling pathway in our cellular model. Herein, we generated a sum of insightful specific molecular and cellular tools that will serve as a useful model to study virus-host interactions of the common vampire bat.

Morphine-potentiated cognitive deficits correlate to suppressed hippocampal iNOS RNA expression and an absent type 1 interferon response in LP-BM5 murine AIDS

Opioid use accelerates neurocognitive impairment in HIV/AIDS patients. We assessed the effect of chronic morphine treatment and LP-BM5/murine AIDS (MAIDS) infection on cognition, cytokine production, and type 1 interferon (IFN) expression in the murine CNS. Morphine treatment decreased expression of pro-inflammatory factors (CCL5, iNOS) and reduced cognitive performance in LP-BM5-infected mice, correlating to increased hippocampal viral load and a blunted type 1 IFN response. In the striatum, morphine reduced viral load while increasing IFN-α RNA expression. Our results suggest that differentially regulated type 1 IFN responses may contribute to distinct regional outcomes in the hippocampus and striatum in LP-BM5/MAIDS.

Tacrolimus interacts with voriconazole to reduce the severity of fungal keratitis by suppressing IFN-related inflammatory responses and concomitant FK506 and voriconazole treatment suppresses fungal keratitis

PURPOSE

To investigate the expression and roles of type I and II interferons (IFNs) in fungal keratitis, as well as the therapeutic effects of tacrolimus (FK506) and voriconazole on this condition.

METHODS

The mRNA and protein expression levels of type I (IFN-α/β) and II (IFN-γ) IFNs, as well as of related downstream inflammatory cytokines (interleukin (IL)-1α, IL-6, IL-12, and IL-17), were detected in macrophages, neutrophils, lymphocytes, and corneal epithelial cells (A6(1) cells) stimulated with zymosan (10 mg/ml) for 8 or 24 h. A fungal keratitis mouse model was generated through intrastromal injection of Aspergillus fumigatus, and the mice were then divided into four groups: group I, the PBS group; group II, the voriconazole group; group III, the FK506 group; and group IV, the voriconazole plus 0.05% FK506 group. Corneal damage was evaluated with clinical scoring and histological examination. In addition, the mRNA and protein expression levels of type I (IFN-α/β) and type II (IFN-γ) IFNs, as well as related inflammatory cytokines, were determined at different time points using quantitative real-time PCR (qRT-PCR) and western blotting.

RESULTS

After zymosan stimulation of mouse neutrophils, lymphocytes, macrophages, and A6(1) cells, the IFN mRNA and protein expression levels were markedly increased until 24 h, peaking at 8 h (p<0.001). The mRNA and protein expression levels of inflammatory cytokines (IL-1α, IL-6, IL-12, and IL-17) were also upregulated after zymosan stimulation. Moreover, type I (IFN-α/β) and type II (IFN-γ) IFN expression levels were increased and positively correlated with the progression of fungal keratitis in vivo. FK506 administered with voriconazole reduced the pathological infiltration of inflammatory cells into the cornea and downregulated the expression levels of IFNs and related inflammatory cytokines.

CONCLUSIONS

In conclusion, this study demonstrated that type I and II IFN levels were markedly increased in fungal keratitis and that FK506 combined with voriconazole decreased the severity of fungal keratitis by suppressing type I and II IFNs and their related inflammatory responses.

Interferon α subtypes in HIV infection

Type I interferons (IFN), which are immediately induced after most virus infections, are central for direct antiviral immunity and link innate and adaptive immune responses. However, several viruses have evolved strategies to evade the IFN response by preventing IFN induction or blocking IFN signaling pathways. Thus, therapeutic application of exogenous type I IFN or agonists inducing type I IFN responses are a considerable option for future immunotherapies against chronic viral infections. An important part of the type I IFN family are 12 IFNα subtypes, which all bind the same receptor, but significantly differ in their biological activities. Up to date only one IFNα subtype (IFNα2) is being used in clinical treatment against chronic virus infections, however its therapeutic success rate is rather limited, especially during Human Immunodeficiency Virus (HIV) infection. Recent studies addressed the important question if other IFNα subtypes would be more potent against retroviral infections in in vitro and in vivo experiments. Indeed, very potent IFNα subtypes were defined and their antiviral and immunomodulatory properties were characterized. In this review we summarize the recent findings on the role of individual IFNα subtypes during HIV and Simian Immunodeficiency Virus infection. This includes their induction during HIV/SIV infection, their antiretroviral activity and the regulation of immune response against HIV by different IFNα subtypes. The findings might facilitate novel strategies for HIV cure or functional cure studies.

Type I Interferon Signaling Is Required for CpG-Oligodesoxynucleotide-Induced Control of Leishmania major, but Not for Spontaneous Cure of Subcutaneous Primary or Secondary L. major Infection

We previously showed that in mice infected with Leishmania major type I interferons (IFNs) initiate the innate immune response to the parasite at day 1 and 2 of infection. Here, we investigated which type I IFN subtypes are expressed during the first 8 weeks of L. major infection and whether type I IFNs are essential for a protective immune response and clinical cure of the disease. In self-healing C57BL/6 mice infected with a high dose of L. major, IFN-α4, IFN-α5, IFN-α11, IFN-α13, and IFN-β mRNA were most prominently regulated during the course of infection. In C57BL/6 mice deficient for IFN-β or the IFN-α/β-receptor chain 1 (IFNAR1), development of skin lesions and parasite loads in skin, draining lymph node, and spleen was indistinguishable from wild-type (WT) mice. In line with the clinical findings, C57BL/6 IFN-β^−/−, IFNAR1^−/−, and WT mice exhibited similar mRNA expression levels of IFN-γ, interleukin (IL)-4, IL-12, IL-13, inducible nitric oxide synthase, and arginase 1 during the acute and late phase of the infection. Also, myeloid dendritic cells from WT and IFNAR1^−/− mice produced comparable amounts of IL-12p40/p70 protein upon exposure to L. major in vitro. In non-healing BALB/c WT mice, the mRNAs of IFN-α subtypes (α2, α4, α5, α6, and α9) were rapidly induced after high-dose L. major infection. However, genetic deletion of IFNAR1 or IFN-β did not alter the progressive course of infection seen in WT BALB/c mice. Finally, we tested whether type I IFNs and/or IL-12 are required for the prophylactic effect of CpG-oligodesoxynucleotides (ODN) in BALB/c mice. Local and systemic administration of CpG-ODN 1668 protected WT and IFN-β^−/− mice equally well from progressive leishmaniasis. By contrast, the protective effect of CpG-ODN 1668 was lost in BALB/c IFNAR1^−/− (despite a sustained suppression of IL-4) and in BALB/c IL-12p35^−/− mice. From these data, we conclude that IFN-β and IFNAR1 signaling are dispensable for a curative immune response to L. major in C57BL/6 mice and irrelevant for disease development in BALB/c mice, whereas IL-12 and IFN-α subtypes are essential for the disease prevention by CpG-ODNs in this mouse strain.

Efficacy of a Virus-Like Nanoparticle As Treatment for a Chronic Viral Infection Is Hindered by IRAK1 Regulation and Antibody Interference

Although vaccination has been an effective way of preventing infections ever since the eighteenth century, the generation of therapeutic vaccines and immunotherapies is still a work in progress. A number of challenges impede the development of these therapeutic approaches such as safety issues related to the administration of whole pathogens whether attenuated or inactivated. One safe alternative to classical vaccination methods gaining recognition is the use of nanoparticles, whether synthetic or naturally derived. We have recently demonstrated that the papaya mosaic virus (PapMV)-like nanoparticle can be used as a prophylactic vaccine against various viral and bacterial infections through the induction of protective humoral and cellular immune responses. Moreover, PapMV is also very efficient when used as an immune adjuvant in an immunotherapeutic setting at slowing down the growth of aggressive mouse melanoma tumors in a type I interferon (IFN-I)-dependent manner. In the present study, we were interested in exploiting the capacity of PapMV of inducing robust IFN-I production as treatment for the chronic viral infection model lymphocytic choriomeningitis virus (LCMV) clone 13 (Cl13). Treatment of LCMV Cl13-infected mice with two systemic administrations of PapMV was ineffective, as shown by the lack of changes in viral titers and immune response to LCMV following treatment. Moreover, IFN-α production following PapMV administration was almost completely abolished in LCMV-infected mice. To better isolate the mechanisms at play, we determined the influence of a pretreatment with PapMV on secondary PapMV administration, therefore eliminating potential variables emanating from the infection. Pretreatment with PapMV led to the same outcome as an LCMV infection in that IFN-α production following secondary PapMV immunization was abrogated for up to 50 days while immune activation was also dramatically impaired. We showed that two distinct and overlapping mechanisms were responsible for this outcome. While short-term inhibition was partially the result of interleukin-1 receptor-associated kinase 1 degradation, a crucial component of the toll-like receptor 7 signaling pathway, long-term inhibition was mainly due to interference by PapMV-specific antibodies. Thus, we identified a possible pitfall in the use of virus-like particles for the systemic treatment of chronic viral infections and discuss mitigating alternatives to circumvent these potential problems.

Toll-Like Receptor 4, but Not Neutrophil Extracellular Traps, Promote IFN Type I Expression to Enhance Th2 Responses to Nippostrongylus brasiliensis

The induction of Th2 responses is thought to be multifactorial, and emerge from specific pathways distinct from those associated with antagonistic antibacterial or antiviral Th1 responses. Here, we show that the recognition of non-viable Nippostrongylus brasiliensis (Nb) in the skin induces a strong recruitment of monocytes and neutrophils and the release of neutrophil extracellular traps (NETs). Nb also activates toll-like receptor 4 (TLR4) signaling with expression of Ifnb transcripts in the skin and the development of an IFN type I signature on helminth antigen-bearing dendritic cells in draining lymph nodes. Co-injection of Nb together with about 10,000 Gram-negative bacteria amplified this TLR4-dependent but NET-independent IFN type I response and enhanced the development of Th2 responses. Thus, a limited activation of antibacterial signaling pathways is able to boost antihelminthic responses, suggesting a role for bacterial sensing in the optimal induction of Th2 immunity.

Type I interferon is required for T helper (Th) 2 induction by dendritic cells

Type 2 inflammation is a defining feature of infection with parasitic worms (helminths), as well as being responsible for widespread suffering in allergies. However, the precise mechanisms involved in T helper (Th) 2 polarization by dendritic cells (DCs) are currently unclear. We have identified a previously unrecognized role for type I IFN (IFN‐I) in enabling this process. An IFN‐I signature was evident in DCs responding to the helminth Schistosoma mansoni or the allergen house dust mite (HDM). Further, IFN‐I signaling was required for optimal DC phenotypic activation in response to helminth antigen (Ag), and efficient migration to, and localization with, T cells in the draining lymph node (dLN). Importantly, DCs generated from Ifnar1^−/− mice were incapable of initiating Th2 responses in vivo. These data demonstrate for the first time that the influence of IFN‐I is not limited to antiviral or bacterial settings but also has a central role to play in DC initiation of Th2 responses.

Advances in anti-viral immune defence: revealing the importance of the IFN JAK/STAT pathway

Interferon-alpha (IFN-α) is a potent anti-viral cytokine, critical to the host immune response against viruses. IFN-α is first produced upon viral detection by pathogen recognition receptors. Following its expression, IFN-α embarks upon a complex downstream signalling cascade called the JAK/STAT pathway. This signalling pathway results in the expression of hundreds of effector genes known as interferon stimulated genes (ISGs). These genes are the basis for an elaborate effector mechanism and ultimately, the clearance of viral infection. ISGs mark an elegant mechanism of anti-viral host defence that warrants renewed research focus in our global efforts to treat existing and emerging viruses. By understanding the mechanistic role of individual ISGs we anticipate the discovery of a new "treasure trove" of anti-viral mediators that may pave the way for more effective, targeted and less toxic anti-viral therapies. Therefore, with the aim of highlighting the value of the innate type 1 IFN response in our battle against viral infection, this review outlines both historic and recent advances in understanding the IFN-α JAK/STAT pathway, with a focus on new research discoveries relating to specific ISGs and their potential role in curing existing and future emergent viral infections.

Involvement of NK Cells in IL-28B-Mediated Immunity against Influenza Virus Infection

IL-28B is a member of the newly discovered type III IFN family and exhibits unique antiviral properties compared with other family members. NK cells play a critical role in defending against viruses; however, little is known about the role of IL-28B in NK cell function. In a mouse model of influenza A virus (mouse adapted influenza A/PR/8/34 strain) infection, long-term overexpression of IL-28B induced by hepatocyte-specific gene delivery exerted a strong antiviral effect in the presence of NK cells. In IL-28B-overexpressing wild-type mice, the percentages and absolute numbers of NK cells in the spleen, liver, and lung were markedly increased, with higher proliferation and accelerated NK cell maturation based on phenotypes staining with CD11b and CD27 or CD11b and KLRG1. Furthermore, the effect of IL-28B on NK cells was macrophage dependent, as confirmed in an in vitro coculture assay and in in vivo macrophage- or alveolar macrophage-depletion experiments. Transwell studies demonstrated that CFSE-labeled NK cell proliferation was driven, in a dose-dependent manner, by unknown soluble factor(s) secreted by IL-28B-stimulated alveolar macrophages, without requiring direct cell-cell contact. An understanding of the NK cell-promoting features of IL-28B will facilitate future clinical application of this cytokine.

Lung epithelial cells have virus-specific and shared gene expression responses to infection by diverse respiratory viruses

The severity of respiratory viral infections is partially determined by the cellular response mounted by infected lung epithelial cells. Disease prevention and treatment is dependent on our understanding of the shared and unique responses elicited by diverse viruses, yet few studies compare host responses to viruses from different families while controlling other experimental parameters. Murine models are commonly used to study the pathogenesis of respiratory viral infections, and in vitro studies using murine cells provide mechanistic insight into the pathogenesis observed in vivo. We used microarray analysis to compare changes in gene expression of murine lung epithelial cells infected individually by three respiratory viruses causing mild (rhinovirus, RV1B), moderate (coronavirus, MHV-1), and severe (influenza A virus, PR8) disease in mice. RV1B infection caused numerous gene expression changes, but the differential effect peaked at 12 hours post-infection. PR8 altered an intermediate number of genes whose expression continued to change through 24 hours. MHV-1 had comparatively few effects on host gene expression. The viruses elicited highly overlapping responses in antiviral genes, though MHV-1 induced a lower type I interferon response than the other two viruses. Signature genes were identified for each virus and included host defense genes for PR8, tissue remodeling genes for RV1B, and transcription factors for MHV-1. Our comparative approach identified universal and specific transcriptional signatures of virus infection that can be used to distinguish shared and virus-specific mechanisms of pathogenesis in the respiratory tract.

Investigation of chimeric reads using the MinION

Following a nanopore sequencing run of PCR products of three amplicons less than 1kb, an abundance of reads failed quality control due to template/complement mismatch. A BLAST search demonstrated that some of the failed reads mapped to two different genes -- an unexpected observation, given that PCR was carried out separately for each amplicon. A further investigation was carried out specifically to search for chimeric reads, using separate barcodes for each amplicon and trying two different ligation methods prior to sample loading. Despite the separation of ligation products, chimeric reads formed from different amplicons were still observed in the base-called sequence. The long-read nature of nanopore sequencing presents an effective tool for the discovery and filtering of chimeric reads. We have found that at least 1.7% of reads prepared using the Nanopore LSK002 2D Ligation Kit include post-amplification chimeric elements. This finding has potential implications for other amplicon sequencing technologies, as the process is unlikely to be specific to the sample preparation used for nanopore sequencing.

Investigation of chimeric reads using the MinION

Following a nanopore sequencing run of PCR products of three amplicons less than 1kb, an abundance of reads failed quality control due to template/complement mismatch. A BLAST search demonstrated that some of the failed reads mapped to two different genes -- an unexpected observation, given that PCR was carried out separately for each amplicon. A further investigation was carried out specifically to search for chimeric reads, using separate barcodes for each amplicon and trying two different ligation methods prior to sample loading. Despite the separation of ligation products, chimeric reads formed from different amplicons were still observed in the base-called sequence.The long-read nature of nanopore sequencing presents an effective tool for the discovery and filtering of chimeric reads. We have found that at least 1.7% of reads prepared using the Nanopore LSK002 2D Ligation Kit include post-amplification chimeric elements. This finding has potential implications for other amplicon sequencing technologies, as the process is unlikely to be specific to the sample preparation used for nanopore sequencing.

Getting "Inside" Type I IFNs: Type I IFNs in Intracellular Bacterial Infections

Type I interferons represent a unique and complex group of cytokines, serving many purposes during innate and adaptive immunity. Discovered in the context of viral infections, type I IFNs are now known to have myriad effects in infectious and autoimmune disease settings. Type I IFN signaling during bacterial infections is dependent on many factors including whether the infecting bacterium is intracellular or extracellular, as different signaling pathways are activated. As such, the repercussions of type I IFN induction can positively or negatively impact the disease outcome. This review focuses on type I IFN induction and downstream consequences during infection with the following intracellular bacteria: Chlamydia trachomatis, Listeria monocytogenes, Mycobacterium tuberculosis, Salmonella enterica serovar Typhimurium, Francisella tularensis, Brucella abortus, Legionella pneumophila, and Coxiella burnetii. Intracellular bacterial infections are unique because the bacteria must avoid, circumvent, and even co-opt microbial "sensing" mechanisms in order to reside and replicate within a host cell. Furthermore, life inside a host cell makes intracellular bacteria more difficult to target with antibiotics. Because type I IFNs are important immune effectors, modulating this pathway may improve disease outcomes. But first, it is critical to understand the context-dependent effects of the type I IFN pathway in intracellular bacterial infections.

In Vivo Conditions Enable IFNAR-Independent Type I Interferon Production by Peritoneal CD11b+ Cells upon Thogoto Virus Infection

Type I interferons (IFNs) crucially contribute to host survival upon viral infections. Robust expression of type I IFNs (IFN-α/β) and induction of an antiviral state critically depend on amplification of the IFN signal via the type I IFN receptor (IFNAR). A small amount of type I IFN produced early upon virus infection binds the IFNAR and activates a self-enhancing positive feedback loop, resulting in induction of large, protective amounts of IFN-α. Unexpectedly, we found robust, systemic IFN-α expression upon infection of IFNAR knockout mice with the orthomyxovirus Thogoto virus (THOV). The IFNAR-independent IFN-α production required in vivo conditions and was not achieved during in vitro infection. Using replication-incompetent THOV-derived virus-like particles, we demonstrate that IFNAR-independent type I IFN induction depends on viral polymerase activity but is largely independent of viral replication. To discover the cell type responsible for this effect, we used type I IFN reporter mice and identified CD11b(+) F4/80(+) myeloid cells within the peritoneal cavity of infected animals as the main source of IFNAR-independent type I IFN, corresponding to the particular tropism of THOV for this cell type.

IMPORTANCE

Type I IFNs are crucial for the survival of a host upon most viral infections, and, moreover, they shape subsequent adaptive immune responses. Production of protective amounts of type I IFN critically depends on the positive feedback amplification via the IFNAR. Unexpectedly, we observed robust IFNAR-independent type I IFN expression upon THOV infection and unraveled molecular mechanisms and determined the tissue and cell type involved. Our data indicate that the host can effectively use alternative pathways to induce type I IFN responses if the classical feedback amplification is not available. Understanding how type I IFN can be produced in large amounts independently of IFNAR-dependent enhancement will identify mechanisms which might contribute to novel therapeutic strategies to fight viral pathogens.

A functional polymorphism in IFNAR1 gene is associated with susceptibility and severity of HFMD with EV71 infection

Enterovirus 71 (EV71), one of the major pathogens of Hand, foot and mouth disease (HFMD), results in millions of infections and hundreds of deaths each year in Southeast Asia. Biased infection and variable clinical manifestations of EV71 HFMD indicated that host genetic background played an important role in the occurrence and development of the disease. We identified the mRNA profiles of EV71 HFMD patients, which type I interferon (IFN) pathway related genes were down-regulated. Four single nucleotide polymorphisms (SNPs) of type I IFN receptor 1 (IFNAR1) were chosen to analyze their relationships to EV71 infection. We found that genotype GG of promoter variant rs2843710 was associated with the susceptibility and severity to EV71 HFMD. In addition, we assessed the regulatory effects of rs2843710 to IFN stimulated genes (ISGs), and found that the expressions of IFNAR1, OAS1 and MX1 were significantly lower in patients with rs2843710 genotype GG. And rs2843710 allele G showed weaker transcriptional activity compared with allele C. Our study indicated that rs2843710 of IFNAR1 was associated with the susceptibility and severity of EV71 HFMD in Chinese Han populations, acting as a functional polymorphism by regulating ISGs expression, such as OAS1 and MX1.

Differential Biological Activities of Swine Interferon-α Subtypes

Interferons (IFNs) play a crucial role in the host's immune response and other homeostatic control actions. Three IFN types and several IFN families within the types allow for a plethora of regulatory actions. The number of distinct IFN molecules is highest among type I IFNs and, in particular, within the IFN-α family. In pigs, there are 17 IFN-α subtypes with different antiviral activities and different expression profiles; however, no data are available about biological properties other than the antiviral effector activities. Therefore, 16 porcine IFN-α genes were cloned, expressed in mammalian Chinese hamster ovary cells, and characterized for antiviral, anti-inflammatory, and MHC-modulating activities at a pre-established level of 10 IU/mL. Antiviral activity: IFN-α2, -α5, -α9, and -α10 showed the highest level of activity in a pseudorabies virus yield reduction assay. On the contrary, little, if any, activity was shown by IFN-α3, -α7, -α13, -α4, and -α15. Anti-inflammatory activity: With the exception of IFNs-α2, -α7, -α9, and -α11, all IFN-α subtypes had significant anti-inflammatory control activity in an interleukin-8 (IL-8) yield reduction assay. Gene expression analyses showed that some IFN-α subtypes can significantly downregulate the expression of IL-8, tumor necrosis factor α (TNF-α), IL-6, Toll-like receptor 4 (TLR4), βD1, and nuclear factor-κB (NF-kB) genes, while maintaining or upregulating the expression of βD4. Immunomodulation: A significant upregulation of class I and/or class II MHC was induced by all the IFNs under study, with the exception of IFNs-α11, -α15, and -α16, which instead significantly downregulated class I MHC. Our results indicate that gene duplications in the porcine IFN-α family underlie diverse effector and regulatory activities, being therefore instrumental in host survival and environmental adaptation. This role of IFN-α could be founded on fine-tuning and regulation of pro- and anti-inflammatory control actions after exposure to both infectious and noninfectious environmental stressors.

Innate immune response during herpes simplex virus encephalitis and development of immunomodulatory strategies

Herpes simplex viruses are large double-stranded DNA viruses. These viruses have the ability to establish a lifelong latency in sensory ganglia and to invade and replicate in the CNS. Apart from relatively benign mucosal infections, HSV is responsible for severe illnesses including HSV encephalitis (HSE). HSE is the most common cause of sporadic, potentially fatal viral encephalitis in Western countries. If left untreated, the mortality rate associated with HSE is approximately 70%. Despite antiviral therapy, the mortality is still higher than 30%, and almost 60% of surviving individuals develop neurological sequelae. It is suggested that direct virus-related and indirect immune-mediated mechanisms contribute to the damages occurring in the CNS during HSE. In this manuscript, we describe the innate immune response to HSV, the development of HSE in mice knock-out for proteins of the innate immune system as well as inherited deficiencies in key components of the signaling pathways involved in the production of type I interferon that could predispose individuals to develop HSE. Finally, we review several immunomodulatory strategies aimed at modulating the innate immune response at a critical time after infection that were evaluated in mouse models and could be combined with antiviral therapy to improve the prognosis of HSE. In conclusion, the cerebral innate immune response that develops during HSE is a "double-edged sword" as it is critical to control viral replication in the brain early after infection, but, if left uncontrolled, may also result in an exaggerated inflammatory response that could be detrimental to the host.

The Interferon-Inducible Mouse Apolipoprotein L9 and Prohibitins Cooperate to Restrict Theiler's Virus Replication

Apolipoprotein L9b (Apol9b) is an interferon-stimulated gene (ISG) that has antiviral activity and is weakly expressed in primary mouse neurons as compared to other cell types. Here, we show that both Apol9 isoforms (Apol9b and Apol9a) inhibit replication of Theiler’s murine encephalomyelitis virus (TMEV) but not replication of vesicular stomatitis virus (VSV), Murid herpesvirus-4 (MuHV-4), or infection by a lentiviral vector. Apol9 genes are strongly expressed in mouse liver and, to a lesser extent, in pancreas, adipose tissue and intestine. Their expression is increased by type I interferon and viral infection. In contrast to genuine apolipoproteins that are involved in lipid transport, ApoL9 has an intracytoplasmic localization and does not seem to be secreted. The cytoplasmic localization of ApoL9 is in line with the observation that ApoL9 inhibits the replication step of TMEV infection. In contrast to human ApoL6, ApoL9 did not sensitize cells to apoptosis, in spite of the presence of a conserved putative BH3 domain, required for antiviral activity. ApoL9a and b isoforms interact with cellular prohibitin 1 (Phb1) and prohibitin 2 (Phb2) and this interaction might contribute to ApoL9 antiviral activity. Knocking down Phb2 slightly increased TMEV replication, irrespective of ApoL9 overexpression. The antiviral activity of prohibitins against TMEV contrasts with the pro-viral activity of prohibitins observed for VSV and reported previously for Dengue 2 (DENV-2), Chikungunya (CHIKV) and influenza H5N1 viruses. ApoL9 is thus an example of ISG displaying a narrow antiviral range, which likely acts in complex with prohibitins to restrict TMEV replication.

Selective Blockade of Interferon-α and -β Reveals Their Non-Redundant Functions in a Mouse Model of West Nile Virus Infection

Although type I interferons (IFNs) were first described almost 60 years ago, the ability to monitor and modulate the functional activities of the individual IFN subtypes that comprise this family has been hindered by a lack of reagents. The major type I IFNs, IFN-β and the multiple subtypes of IFN-α, are expressed widely and induce their effects on cells by interacting with a shared heterodimeric receptor (IFNAR). In the mouse, the physiologic actions of IFN-α and IFN-β have been defined using polyclonal anti-type I IFN sera, by targeting IFNAR using monoclonal antibodies or knockout mice, or using Ifnb^-/- mice. However, the corresponding analysis of IFN-α has been difficult because of its polygenic nature. Herein, we describe two monoclonal antibodies (mAbs) that differentially neutralize murine IFN-β or multiple subtypes of murine IFN-α. Using these mAbs, we distinguish specific contributions of IFN-β versus IFN-α in restricting viral pathogenesis and identify IFN-α as the key mediator of the antiviral response in mice infected with West Nile virus. This study thus suggests the utility of these new reagents in dissecting the antiviral and immunomodulatory roles of IFN-β versus IFN-α in murine models of infection, immunity, and autoimmunity.

Expression of porcine fusion protein IRF7/3(5D) efficiently controls foot-and-mouth disease virus replication

Several studies have demonstrated that the delivery of type I, II, or III interferons (IFNs) by inoculation of a replication-defective human adenovirus 5 (Ad5) vector expressing IFNs can effectively control foot-and-mouth disease (FMD) in cattle and swine during experimental infections. However, relatively high doses are required to achieve protection. In this study, we identified the functional properties of a porcine fusion protein, poIRF7/3(5D), as a biotherapeutic and enhancer of IFN activity against FMD virus (FMDV). We showed that poIRF7/3(5D) is a potent inducer of type I IFNs, including alpha IFN (IFN-α), IFN-β, and IFN-ω but not type III IFN (interleukin-28B), without inducing cytotoxicity. Expression of poIRF7/3(5D) significantly and steadily reduced FMDV titers by up to 6 log10 units in swine and bovine cell lines. Treatment with an IFN receptor inhibitor (B18R) combined with an anti-IFN-α antibody neutralized the antiviral activity in the supernatants of cells transduced with an Ad5 vector expressing poIRF7/3(5D) [Ad5-poIRF7/3(5D)]. However, several transcripts with known antiviral function, including type I IFNs, were still highly upregulated (range of increase, 8-fold to over 500-fold) by poIRF7/3(5D) in the presence of B18R. Furthermore, the sera of mice treated with Ad5-poIRF7/3(5D) showed antiviral activity that was associated with the induction of high levels of IFN-α and resulted in complete protection against FMDV challenge at 6, 24, or 48 h posttreatment. This study highlights for the first time the antiviral potential of Ad5-poIRF7/3(5D) in vitro and in vivo against FMDV.

IMPORTANCE

FMD remains one of the most devastating diseases that affect livestock worldwide. Effective vaccine formulations are available but are serotype specific and require approximately 7 days before they are able to elicit protective immunity. We have shown that vector-delivered IFN is an option to protect animals against many FMDV serotypes as soon as 24 h and for about 4 days postadministration. Here we demonstrate that delivery of a constitutively active transcription factor that induces the production of endogenous IFNs and potentially other antiviral genes is a viable strategy to protect against FMD.

An essential role for IFN-β in the induction of IFN-stimulated gene expression by LPS in macrophages

TLR agonists such as LPS and poly(I:C) induce expression of type I IFNs, such as IFN-α and -β, by macrophages. To examine the role of IFN-β in the induction of ISGs by LPS, we compared the ability of LPS to induce ISGF3 activity and ISG expression in bone marrow-derived macrophages from WT and Ifnb1(-/-) mice. We found that LPS treatment activated ISGF3 and induced expression of ISGs such as Oas1, Mx1, Ddx58 (RIG-I), and Ifih1 (MDA5) in WT macrophages, but not in macrophages derived from Ifnb1(-/-) mice or Ifnar1(-/-) mice. The inability of LPS to induce activation of ISGF3 and ISG expression in Ifnb1(-/-) macrophages correlated with the failure of LPS to induce activation of STAT1 and -2 in these cells. Consistent with these findings, LPS treatment also failed to induce ISG expression in bone marrow-derived macrophages from Stat2 KO mice. Although activation of ISGF3 and induction of ISG expression by LPS was abrogated in Ifnb1(-/-) and Ifnar1(-/-) macrophages, activation of NF-κB and induction of NF-κB-responsive genes, such as Tnf (TNF-α) and Il1b (IL-1β), were not affected by deletion of either the IFN-β or IFN-αR1 genes. These findings demonstrate that induction of ISGF3 activity and ISG expression by LPS is critically dependent on intermediate production of IFN-β and autocrine signaling through type I IFN receptors.

The bacterial pathogen Listeria monocytogenes and the interferon family: type I, type II and type III interferons

Interferons (IFNs) are secreted proteins of the cytokine family that regulate innate and adaptive immune responses to infection. Although the importance of IFNs in the antiviral response has long been appreciated, their role in bacterial infections is more complex and is currently a major focus of investigation. This review summarizes our current knowledge of the role of these cytokines in host defense against the bacterial pathogen Listeria monocytogenes and highlights recent discoveries on the molecular mechanisms evolved by this intracellular bacterium to subvert IFN responses.

Human but not mouse hepatocytes respond to interferon-lambda in vivo

The type III interferon (IFN) receptor is preferentially expressed by epithelial cells. It is made of two subunits: IFNLR1, which is specific to IFN-lambda (IFN-λ) and IL10RB, which is shared by other cytokine receptors. Human hepatocytes express IFNLR1 and respond to IFN-λ. In contrast, the IFN-λ response of the mouse liver is very weak and IFNLR1 expression is hardly detectable in this organ. Here we investigated the IFN-λ response at the cellular level in the mouse liver and we tested whether human and mouse hepatocytes truly differ in responsiveness to IFN-λ. When monitoring expression of the IFN-responsive Mx genes by immunohistofluorescence, we observed that the IFN-λ response in mouse livers was restricted to cholangiocytes, which form the bile ducts, and that mouse hepatocytes were indeed not responsive to IFN-λ. The lack of mouse hepatocyte response to IFN-λ was observed in different experimental settings, including the infection with a hepatotropic strain of influenza A virus which triggered a strong local production of IFN-λ. With the help of chimeric mice containing transplanted human hepatocytes, we show that hepatocytes of human origin readily responded to IFN-λ in a murine environment. Thus, our data suggest that human but not mouse hepatocytes are responsive to IFN-λ in vivo. The non-responsiveness is an intrinsic property of mouse hepatocytes and is not due to the mouse liver micro-environment.

Inefficient type I interferon-mediated antiviral protection of primary mouse neurons is associated with the lack of apolipoprotein l9 expression

We examined the antiviral response promoted by type I interferons (IFN) in primary mouse neurons. IFN treatment of neuron cultures strongly upregulated the transcription of IFN-stimulated genes but conferred a surprisingly low resistance to infection by neurotropic viruses such as Theiler's murine encephalomyelitis virus (TMEV) or vesicular stomatitis virus (VSV). Response of primary mouse neurons to IFN treatment was heterogeneous, as many neurons failed to express the typical IFN response marker Mx1 after IFN treatment. This heterogeneous response of primary neurons correlated with a low level of basal expression of IFN-stimulated genes, such as Stat1, that are involved in signal transduction of the IFN response. In addition, transcriptomic analysis identified 15 IFN-responsive genes whose expression was low in IFN-treated primary neurons compared to that of primary fibroblasts derived from the same mice (Dhx58, Gvin1, Sp100, Ifi203 isoforms 1 and 2, Irgm2, Lgals3bp, Ifi205, Apol9b, Ifi204, Ifi202b, Tor3a, Slfn2, Ifi35, Lgals9). Among these genes, the gene coding for apolipoprotein L9b (Apol9b) displayed antiviral activity against Theiler's virus when overexpressed in L929 cells or in primary neurons. Accordingly, knocking down Apol9b expression in L929 cells increased viral replication. Therefore, we identified a new antiviral protein induced by interferon, ApoL9b, whose lack of expression in primary neurons likely contributes to the high sensitivity of these cells to viral infection.

IMPORTANCE

The type I interferon (IFN) response is an innate immune defense mechanism that is critical to contain viral infection in the host until an adaptive immune response can be mounted. Neurons are a paradigm for postmitotic, highly differentiated cells. Our data show that primary mouse neurons that are exposed to type I interferon remain surprisingly susceptible to viral infection. On one hand, the low level of basal expression of some factors in neurons might prevent a rapid response of these cells. On the other hand, some genes that are typically activated by type I interferon in other cell types are expressed at much lower levels in neurons. Among these genes is the gene encoding apolipoprotein L9, a protein that proved to have antiviral activity against the neurotropic Theiler's murine encephalomyelitis virus. Our data suggest important functional differences in the IFN response mounted by specific cell populations.

Anti-CD20-interferon-β fusion protein therapy of murine B-cell lymphomas

Type I interferons (IFNα/β) are cytokines with a broad spectrum of antitumor activities including antiproliferative, proapoptotic, and immunostimulatory effects, and are potentially useful in the treatment of B-cell malignancies and other cancers. To improve antitumor potency and diminish the systemic side effects of IFN, we recently developed anti-CD20-IFNα fusion proteins with in vitro and in vivo efficacy against both mouse and human lymphomas expressing CD20. As IFNβ binds more tightly to the IFNα/β receptor (IFNAR) and has more potent antitumor activities, we have now constructed an anti-CD20 fusion protein with murine IFNβ (mIFNβ). Anti-CD20-mIFNβ was more potent than recombinant mIFNβ and anti-CD20-mIFNα in inhibiting the proliferation of a mouse B-cell lymphoma expressing human CD20 (38C13-huCD20). Growth inhibition was accompanied by caspase-independent apoptosis and DNA fragmentation. The efficacy of anti-CD20-mIFNβ required the physical linkage of mIFNβ to anti-CD20 antibody. Importantly, anti-CD20-mIFNβ was active against tumor cells expressing low levels of IFNAR (38C13-huCD20 IFNAR). In vivo, established 38C13-huCD20 tumors were largely insensitive to rituximab or a nontargeted mIFNβ fusion protein, yet treatment with anti-CD20-mIFNβ eradicated 83% of tumors. Anti-CD20-mIFNβ was also more potent in vivo against 38C13-huCD20 than anti-CD20-mIFNα, curing 75% versus 25% of tumors (P=0.001). Importantly, although anti-CD20-mIFNα could not eradicate 38C13-huCD20 IFNAR tumors, anti-CD20-mIFNβ treatment prolonged survival (P=0.0003), and some animals remained tumor-free. Thus, antibody fusion proteins targeting mIFNβ to tumors show promise as therapeutic agents, especially for use against tumors resistant to the effects of mIFNα.

Deficiency of the myeloid differentiation primary response molecule MyD88 leads to an early and rapid development of Helicobacter-induced gastric malignancy

Approximately 50% of the world's population is infected with Helicobacter pylori, leading to chronic inflammation, which increases the risk for gastric adenocarcinoma. MyD88 is a key adaptor molecule in inflammatory pathways involved in interleukin 1 (IL-1)/IL-18/Toll-like receptor signaling and has been shown to have divergent effects in carcinogenesis. The role of MyD88 in Helicobacter-induced gastric malignancy is unknown. Using a mouse model of Helicobacter-induced gastric cancer, we assessed the role of MyD88 in cancer development by evaluating gastric histopathology, apoptosis, proliferation, and cytokine expression. Infection of MyD88-deficient (Myd88(-/-)) mice with Helicobacter resulted in early and rapid advancement to gastric dysplasia as early as 25 weeks postinfection. The progression of Helicobacter-induced disease to precancerous and cancerous lesions in the absence of MyD88 signaling was accompanied by increased gastric epithelial apoptosis and proliferation. In addition, inflammatory cytokines, including tumor necrosis factor alpha (TNF-α), gamma interferon (IFN-γ), IL-6, and IL-1β were highly expressed in association with the development of gastric dysplasia. These data suggest that MyD88 signaling retards development and progression to cancer during Helicobacter infection. This is the first study to show evidence of MyD88 protection in an infection-driven inflammation-associated cancer model.

IFN-ε is constitutively expressed by cells of the reproductive tract and is inefficiently secreted by fibroblasts and cell lines

Type-I interferons (IFNs) form a large family of cytokines that primarily act to control the early development of viral infections. Typical type-I IFN genes, such as those encoding IFN-α or IFN-β are upregulated by viral infection in many cell types. In contrast, the gene encoding IFN-ε was reported to be constitutively expressed by cells of the female reproductive tract and to contribute to the protection against vaginal infections with herpes simplex virus 2 and Chlamydia muridarum. Our data confirm the lack of induction of IFN-ε expression after viral infection and the constitutive expression of IFN-ε by cells of the female but also of the male reproductive organs. Interestingly, when expressed from transfected expression plasmids in 293T, HeLa or Neuro2A cells, the mouse and human IFN-ε precursors were inefficiently processed and secretion of IFN-ε was minimal. Analysis of chimeric constructs produced between IFN-ε and limitin (IFN-ζ) showed that both the signal peptide and the mature moiety of IFN-ε contribute to poor processing of the precursor. Immunofluorescent detection of FLAG-tagged IFN-ε in transfected cells suggested that IFN-ε and chimeric proteins were defective for progression through the secretory pathway. IFN-ε did not, however, act intracellularly and impart an antiviral state to producing cells. Given the constitutive expression of IFN-ε in specialized cells and the poor processing of IFN-ε precursor in fibroblasts and cell lines, we hypothesize that IFN-ε secretion may require a co-factor specifically expressed in cells of the reproductive organs, that might secure the system against aberrant release of this IFN.

Reactive oxygen species and IRF1 stimulate IFNα production by proximal tubules during ischemic AKI

We previously reported that expression of the transcription factor interferon regulatory factor 1 (IRF1) is an early, critical maladaptive signal expressed by renal tubules during murine ischemic acute kidney injury (AKI). We now show that IRF1 mediates signals from reactive oxygen species (ROS) generated during ischemic AKI and that these signals ultimately result in production of α-subtypes of type I interferons (IFNαs). We found that genetic knockout of the common type I IFN receptor (IFNARI-/-) improved kidney function and histology during AKI. There are major differences in the spatial-temporal production of the two major IFN subtypes, IFNβ and IFNαs: IFNβ expression peaks at 4 h, earlier than IFNαs, and continues at the same level at 24 h; expression of IFNαs also increases at 4 h but continues to increase through 24 h. The magnitude of the increase in IFNαs relative to baseline is much greater than that of IFNβ. We show by immunohistology and study of isolated cells that IFNβ is produced by renal leukocytes and IFNαs are produced by renal tubules. IRF1, IFNαs, and IFNARI were found on the same renal tubules during ischemic AKI. Furthermore, we found that ROS induced IFNα expression by renal tubules in vitro. This expression was inhibited by small interfering RNA knockdown of IRF1. Overexpression of IRF1 resulted in the production of IFNαs. Furthermore, we found that IFNα stimulated production of maladaptive proinflammatory CXCL2 by renal tubular cells. Altogether our data support the following autocrine pathway in renal tubular cells: ROS > IRF1 > IFNα > IFNARI > CXCL2.

IFN-α subtypes: distinct biological activities in anti-viral therapy

During most viral infections, the immediate host response is characterized by an induction of type I IFN. These cytokines have various biological activities, including anti-viral, anti-proliferative and immunomodulatory effects. After induction, they bind to their IFN-α/β receptor, which leads to downstream signalling resulting in the expression of numerous different IFN-stimulated genes. These genes encode anti-viral proteins that directly inhibit viral replication as well as modulate immune function. Thus, the induction of type I IFN is a very powerful tool for the host to fight virus infections. Many viruses evade this response by various strategies like the direct suppression of IFN induction or inhibition of the IFN signalling pathway. Therefore, the therapeutic application of exogenous type I IFN or molecules that induce strong IFN responses should be of great potential for future immunotherapies against viral infections. Type I IFN is currently used as a treatment in chronic hepatitis B and C virus infection, but as yet is not widely utilized for other viral infections. One reason for this restricted clinical use is that type I IFN belongs to a multigene family that includes 13 different IFN-α subtypes and IFN-β, whose individual anti-viral and immunomodulatory properties have so far not been investigated in detail to improve IFN therapy against viral infections in humans. In this review, we summarize the recent achievements in defining the distinct biological functions of type I IFN subtypes in cell culture and in animal models of viral infection as well as their clinical usage in chronic hepatitis virus infections.

Antiviral immune responses of bats: a review

Despite being the second most species-rich and abundant group of mammals, bats are also among the least studied, with a particular paucity of information in the area of bat immunology. Although bats have a long history of association with rabies, the emergence and re-emergence of a number of viruses from bats that impact human and animal health has resulted in a resurgence of interest in bat immunology. Understanding how bats coexist with viruses in the absence of disease is essential if we are to begin to develop therapeutics to target viruses in humans and susceptible livestock and companion animals. Here, we review the current status of knowledge in the field of bat antiviral immunology including both adaptive and innate mechanisms of immune defence and highlight the need for further investigations in this area. Because data in this field are so limited, our discussion is based on both scientific discoveries and theoretical predictions. It is hoped that by provoking original, speculative or even controversial ideas or theories, this review may stimulate further research in this important field. Efforts to understand the immune systems of bats have been greatly facilitated in recent years by the availability of partial genome sequences from two species of bats, a megabat, Pteropus vampyrus, and a microbat, Myotis lucifugus, allowing the rapid identification of immune genes. Although bats appear to share most features of the immune system with other mammals, several studies have reported qualitative and quantitative differences in the immune responses of bats. These observations warrant further investigation to determine whether such differences are associated with the asymptomatic nature of viral infections in bats.

Molecular cloning and functional characterization of two duplicated two-cysteine containing type I interferon genes in rock bream Oplegnathus fasciatus

Two type I interferon (IFN) genes, designated as rbIFN1 and rbIFN2, have been cloned and characterized in rock bream. They are both comprised of 5 exons and 4 introns, and are closely linked on the rock bream chromosome in a unique head-to-head configuration. Both genes encode 183 amino acid (aa) precursor with a putative 17 aa signal peptide in the N-terminal. Only one amino acid divergence is present between two IFNs. Compared with the type I IFNs in higher vertebrates, two rock bream IFNs possess conserved alpha helical structure and share approximately 20% identity in aa sequence. The highest aa sequence homology (83.2%) was found with European seabass IFNs. Phylogenetic analysis grouped two rock bream IFNs into the subgroup-d of two-cysteine containing IFNs. The gene synteny analysis revealed that they are orthologous with the zebrafish IFNφ4 on chromosome-12 and paralogous to each other, which are likely derived from a gene duplication event followed by an inversion. A number of cis-regulatory elements associated with immune response including 15 IRF and 6 NF-κB binding sites are predicted in the shared 4.5 kb 5'-flanking region. Highest constitutive expression of two IFNs was detected in blood cells and skin. Their expression in blood cells and head kidney was up-regulated by lipopolysaccharide, poly I:C, Edwardsiella tarda, Streptococcus iniae and iridovirus. Furthermore, recombinant rbIFN1 protein produced by E. coli induced a rapid and transient expression of the interferon inducible Mx gene in head kidney cells. These results suggest that two duplicated type I IFN genes are involved in rock bream host response to both viral and bacterial pathogens.

Interferon-alpha subtype 11 activates NK cells and enables control of retroviral infection

The innate immune response mediated by cells such as natural killer (NK) cells is critical for the rapid containment of virus replication and spread during acute infection. Here, we show that subtype 11 of the type I interferon (IFN) family greatly potentiates the antiviral activity of NK cells during retroviral infection. Treatment of mice with IFN-α11 during Friend retrovirus infection (FV) significantly reduced viral loads and resulted in long-term protection from virus-induced leukemia. The effect of IFN-α11 on NK cells was direct and signaled through the type I IFN receptor. Furthermore, IFN-α11-mediated activation of NK cells enabled cytolytic killing of FV-infected target cells via the exocytosis pathway. Depletion and adoptive transfer experiments illustrated that NK cells played a major role in successful IFN-α11 therapy. Additional experiments with Mouse Cytomegalovirus infections demonstrated that the therapeutic effect of IFN-α11 is not restricted to retroviruses. The type I IFN subtypes 2 and 5, which bind the same receptor as IFN-α11, did not elicit similar antiviral effects. These results demonstrate a unique and subtype-specific activation of NK cells by IFN-α11.

The innate immune response mediated by cells such as natural killer (NK) cells can contribute to immunity against viral infections. NK cells can kill virus-infected cells and thus inhibit virus replication and spread during acute infection. However, in infections with retroviruses, like HIV, these cells are not sufficient to prevent pathology. Here, we describe a new strategy to augment natural killer cell responses during virus infections by using a subtype of the type I interferon family as antiviral drug. This therapy strongly activated NK cells and enabled them to control retrovirus as well as herpes virus infections in mice. The new approach might have great potential for the treatment of many infectious and tumor diseases in which natural killer cells play a significant role in immunity.