VSV replication in neurons is inhibited by type I IFN at multiple stages of infection

Natural IgG protects against early dissemination of vesicular stomatitis virus

Neonatal Fc receptor (FcRn) recycles immunoglobulin G, and inhibition of FcRn is used clinically for treatment of autoimmune diseases. In this work, using the vesicular stomatitis virus (VSV) mouse infection model system, we determined the role of FcRn during virus infection. While induction of neutralizing antibodies and long-term protection of these antibodies was hardly affected in FcRn deficient mice, FcRn deficiency limited the amount of natural IgG (VSV-specific) antibodies. Lack of natural antibodies (nAbs) limited early control of VSV in macrophages, accelerated propagation of virus in several organs, led to the spread of VSV to the neural tissue resulting in fatal outcomes. Adoptive transfer of natural IgG into FcRn deficient mice limited early propagation of VSV in FcRn deficient mice and enhanced survival of FcRn knockout mice. In line with this, vaccination of FcRn mice with very low dose of VSV prior to infection similarly prevented death after infection. In conclusion we determined the importance of nAbs during VSV infection. Lack of FcRn limited nAbs and thereby enhanced the susceptibility to virus infection.

Infection dynamic of Micropterus salmoides rhabdovirus and response analysis of largemouth bass after immersion infection

Largemouth bass (Micropterus salmoides) is an important economic freshwater aquaculture fish originating from North America. However, the frequent outbreaks of Micropterus salmoides rhabdovirus (MSRV) have seriously limited the healthy development of Micropterus salmoides farming industry. In the present study, a strain of MSRV was isolated and identified from infected largemouth bass by PCR, transmission electron micrograph observation and genome sequences analysis, and tentatively named MSRV-HZ01 strain. Phylogenetic analyses showed that the MSRV-HZ01 presented the highest similarity to MSRV-2021, followed by MSRV-FJ985 and MSRV-YH01. The various tissues of juvenile largemouth bass exhibited significant pathological damage following MSRV-HZ01 immersion infection, and the mortality reached 90%. We also found that intestine was the key organ for MSRV to enter the fish body initially by dynamic analysis of viral infection, and the head kidney was the susceptible tissue of virus. Moreover, the MSRV was also transferred to the external mucosal tissue in later stage of viral infection to achieve horizontal transmission. In addition, the genes of IFN γ and IFN I-C were significantly up-regulated after MSRV infection to exert antiviral functions. The genes of cGAS and Sting might play an important role in the regulation of interferon expression. In conclusion, we investigated the virus infection dynamics and fish response following MSRV immersion infection, which would promote our understanding of the interaction between MSRV and largemouth bass under natural infection.

The role of STING signaling in central nervous system infection and neuroinflammatory disease

The cyclic guanosine monophosphate-adenosine monophosphate (GMP-AMP) synthase-Stimulator of Interferon Genes (cGAS-STING) pathway is a critical innate immune mechanism for detecting the presence of double-stranded DNA (dsDNA) and prompting a robust immune response. Canonical cGAS-STING activation occurs when cGAS, a predominantly cytosolic pattern recognition receptor, binds microbial DNA to promote STING activation. Upon STING activation, transcription factors enter the nucleus to cause the production of Type I interferons, inflammatory cytokines whose primary function is to prime the host for viral infection by producing a number of antiviral interferon-stimulated genes. While the pathway was originally described in viral infection, more recent studies have implicated cGAS-STING signaling in a number of different contexts, including autoimmune disease, cancer, injury, and neuroinflammatory disease. This review focuses on how our understanding of the cGAS-STING pathway has evolved over time with an emphasis on the role of STING-mediated neuroinflammation and infection in the nervous system. We discuss recent findings on how STING signaling contributes to the pathology of pain, traumatic brain injury, and stroke, as well as how mitochondrial DNA may promote STING activation in common neurodegenerative diseases. We conclude by commenting on the current knowledge gaps that should be filled before STING can be an effective therapeutic target in neuroinflammatory disease. This article is categorized under: Neurological Diseases > Molecular and Cellular Physiology Infectious Diseases > Molecular and Cellular Physiology Immune System Diseases > Molecular and Cellular Physiology.

Neuron-intrinsic immunity to viruses in mice and humans

Viral encephalitis is a major neglected medical problem. Host defense mechanisms against viral infection of the central nervous system (CNS) have long remained unclear. The few previous studies of CNS-specific immunity to viruses in mice in vivo and humans in vitro have focused on the contributions of circulating leukocytes, resident microglial cells and astrocytes, with neurons long considered passive victims of viral infection requiring protection from extrinsic antiviral mechanisms. The last decade has witnessed the gradual emergence of the notion that neurons also combat viruses through cell-intrinsic mechanisms. Forward genetic approaches in humans have shown that monogenic inborn errors of TLR3, IFN-α/β, or snoRNA31 immunity confer susceptibility to herpes simplex virus 1 (HSV-1) infection of the forebrain, whereas inborn errors of DBR1 underlie brainstem infections due to various viruses, including HSV-1. The study of human pluripotent stem cell (hPSC)-derived CNS-resident cells has unraveled known (i.e. TLR3-dependent IFN-α/β immunity) and new (i.e. snoRNA31-dependent or DBR1-dependent immunity) cell-intrinsic antiviral mechanisms operating in neurons. Reverse genetic approaches in mice have confirmed that some known antiviral mechanisms also operate in mouse neurons (e.g. TLR3 and IFN-α/β immunity). The search for human inborn errors of immunity (IEIs) underlying various forms of viral encephalitis, coupled with mouse models in vivo, and hPSC-based culture models of CNS and peripheral nervous system cells and organoids in vitro, should shed further light on the cell-specific and tissue-specific mechanisms of host defense against viruses in the human brain.

Combinatorial Approaches for Cancer Treatment Using Oncolytic Viruses: Projecting the Perspectives through Clinical Trials Outcomes

Recent cancer immunotherapy breakthroughs have fundamentally changed oncology and revived the fading hope for a cancer cure. The immune checkpoint inhibitors (ICI) became an indispensable tool for the treatment of many malignant tumors. Alongside ICI, the application of oncolytic viruses in clinical trials is demonstrating encouraging outcomes. Dozens of combinations of oncolytic viruses with conventional radiotherapy and chemotherapy are widely used or studied, but it seems quite complicated to highlight the most effective combinations. Our review summarizes the results of clinical trials evaluating oncolytic viruses with or without genetic alterations in combination with immune checkpoint blockade, cytokines, antigens and other oncolytic viruses as well. This review is focused on the efficacy and safety of virotherapy and the most promising combinations based on the published clinical data, rather than presenting all oncolytic virus variations, which are discussed in comprehensive literature reviews. We briefly revise the research landscape of oncolytic viruses and discuss future perspectives in virus immunotherapy, in order to provide an insight for novel strategies of cancer treatment.

A critical role for MSR1 in vesicular stomatitis virus infection of the central nervous system

Macrophage scavenger receptor 1 (MSR1) plays an important role in host defense to bacterial infections, M2 macrophage polarization, and lipid homeostasis. However, its physiological function in viral pathogenesis remains poorly defined. Herein, we report that MSR1 facilitates vesicular stomatitis virus (VSV) infection in the central nervous system. Msr1-deficient (Msr1^−/−) mice presented reduced morbidity, mortality, and viral loads in the spinal cord following lethal VSV infection, along with normal viremia and innate immune responses, compared to Msr1^+/− littermates and wild-type mice. Msr1 expression was most significantly upregulated in the spinal cord, the predominant target of VSV. Mechanistically, through its extracellular domains, MSR1 interacted with VSV surface glycoprotein and facilitated its cellular entry in a low-density lipoprotein receptor-dependent manner. In conclusion, our results demonstrate that MSR1 serves as a cofactor for VSV cellular entry and facilitates its infection preferentially in the spinal cord.

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MSR1 contributes to VSV pathogenesis in mice

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MSR1 is highly upregulated and facilitates VSV infection in the central nervous system

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MSR1 facilitates cellular entry of VSV in an LDLR family-dependent manner

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MSR1 interacts with VSV glycoprotein G via its extracellular domains

Host-virus interaction and viral evasion

With each infectious pandemic or outbreak, the medical community feels the need to revisit basic concepts of immunology to understand and overcome the difficult times brought about by these infections. Regarding viruses, they have historically been responsible for many deaths, and such a peculiarity occurs because they are known to be obligate intracellular parasites that depend upon the host's cell machinery for their replication. Successful infection with the production of essential viral components requires constant viral evolution as a strategy to manipulate the cellular environment, including host internal factors, the host's nonspecific and adaptive immune responses to viruses, the metabolic and energetic state of the infected cell, and changes in the intracellular redox environment during the viral infection cycle. Based on this knowledge, it is fundamental to develop new therapeutic strategies for controlling viral dissemination, by means of antiviral therapies, vaccines, or antioxidants, or by targeting the inhibition or activation of cell signaling pathways or metabolic pathways that are altered during infection. The rapid recovery of altered cellular homeostasis during viral infection is still a major challenge. Here, we review the strategies by which viruses evade the host's immune response and potential tools used to develop more specific antiviral therapies to cure, control, or prevent viral diseases.

Interferon Regulatory Factor 7 Attenuates Chronic Gammaherpesvirus Infection

Gammaherpesviruses are ubiquitous pathogens that establish lifelong infections and are associated with a variety of malignancies, including lymphomas. Interferon regulatory factor 7 (IRF-7) is an innate immune transcription factor that restricts acute replication of diverse viruses, including murine gammaherpesvirus 68 (MHV68). Importantly, very little is known about the role of IRF-7 during chronic virus infections. In this study, we demonstrate that IRF-7 attenuates chronic infection by restricting establishment of gammaherpesvirus latency in the peritoneal cavity and, to a lesser extent, viral reactivation in the spleen. Despite the classical role of IRF-7 as a stimulator of type I interferon (IFN) transcription, there were no global effects on the expression of IFN-induced genes (ISGs) in the absence of IRF-7, with only a few ISGs showing attenuated expression in IRF-7-deficient peritoneal cells. Further, IRF-7 expression was dispensable for the induction of a virus-specific CD8 T cell response. In contrast, IRF-7 expression restricted latent gammaherpesvirus infection in the peritoneal cavity under conditions where the viral latent reservoir is predominantly hosted by peritoneal B cells. This report is the first demonstration of the antiviral role of IRF-7 during the chronic stage of gammaherpesvirus infection.IMPORTANCE The innate immune system of the host is critical for the restriction of acute viral infections. In contrast, the role of the innate immune network during chronic herpesvirus infection remains poorly defined. Interferon regulatory factor 7 (IRF-7) is a transcription factor with many target genes, including type I interferons (IFNs). In this study, we show that the antiviral role of IRF-7 continues into the chronic phase of gammaherpesvirus infection, wherein IRF-7 restricts the establishment of viral latency and viral reactivation. This study is, to our knowledge, the first to define the role of IRF-7 in chronic virus infection.

Usp18 Expression in CD169+ Macrophages is Important for Strong Immune Response after Vaccination with VSV-EBOV

Ebola virus epidemics can be effectively limited by the VSV-EBOV vaccine (Ervebo) due to its rapid protection abilities; however, side effects prevent the broad use of VSV-EBOV as vaccine. Mechanisms explaining the efficient immune activation after single injection with the VSV-EBOV vaccine remain mainly unknown. Here, using the clinically available VSV-EBOV vaccine (Ervebo), we show that the cell-intrinsic expression of the interferon-inhibitor Usp18 in CD169⁺ macrophages is one important factor modulating the anti-Ebola virus immune response. The absence of Usp18 in CD169⁺ macrophages led to the reduced local replication of VSV-EBOV followed by a diminished innate as well as adaptive immune response. In line, CD169-Cre^+/ki x Usp18^fl/fl mice showed reduced innate and adaptive immune responses against the VSV wildtype strain and died quickly after infection, suggesting that a lack of Usp18 makes mice more susceptible to the side effects of the VSV vector. In conclusion, our study shows that Usp18 expression in CD169⁺ macrophages is one important surrogate marker for effective vaccination against VSV-EBOV, and probably other VSV-based vaccines also.

Upregulated expression of the antioxidant sestrin 2 identified by transcriptomic analysis of Japanese encephalitis virus-infected SH-SY5Y neuroblastoma cells

Japanese encephalitis virus (JEV) exerts a profound burden of viral encephalitis. We have investigated the differentially expressed transcripts in the neuronal transcriptome during JEV infection by RNA sequencing (RNA-Seq) of virus-infected SH-SY5Y human neuroblastoma cells. Gene ontology analysis revealed significant enrichment from two main pathways: endoplasmic reticulum (ER)-nucleus signaling (P value: 5.75E-18; false discovery rate [FDR] 3.11E-15) and the ER unfolded protein response (P value: 7.58E-18; FDR 3.11E-15). qPCR validation showed significant upregulation and differential expression (P < 0.01) of ER stress-signaling transcripts (SESN2, TRIB3, DDIT3, DDIT4, XBP1, and ATF4) at 24 h post-infection for both low (LN) and high (HN) neurovirulence JEV strains. Immunoblot analysis following JEV infection of SH-SY5Y cells showed an increase in levels of SESN2 protein following JEV infection. Similarly, Zika virus (MR766) infection of SH-SY5Y showed a titer-dependent increase in ER stress-signaling transcripts; however, this was absent or diminished for DDIT4 and ATF4, respectively, suggestive of differences in the induction of stress-response transcripts between flaviviruses. Interestingly, SLC7A11 and SLC3A2 mRNA were also both deregulated in JEV-infected SH-SY5Y cells and encode the two constituent subunits of the plasma membrane xCT amino acid antiporter that relieves oxidative stress by export of glutamate and import of cystine. Infection of SH-SY5Y and HEK293T cells by the JEV HN strain Sw/Mie/40/2004 lead to significant upregulation of the SLC7A11 mRNA to levels comparable to DDIT3. Our findings suggest upregulation of antioxidants including SESN2 and, also, the xCT antiporter occurs to counteract the oxidative stress elicited by JEV infection.

Innate Immune Responses and Viral-Induced Neurologic Disease

Multiple sclerosis (MS) is a disease of the central nervous system (CNS) characterized by chronic neuroinflammation, axonal damage, and demyelination. Cellular components of the adaptive immune response are viewed as important in initiating formation of demyelinating lesions in MS patients. This notion is supported by preclinical animal models, genome-wide association studies (GWAS), as well as approved disease modifying therapies (DMTs) that suppress clinical relapse and are designed to impede infiltration of activated lymphocytes into the CNS. Nonetheless, emerging evidence demonstrates that the innate immune response e.g., neutrophils can amplify white matter damage through a variety of different mechanisms. Indeed, using a model of coronavirus-induced neurologic disease, we have demonstrated that sustained neutrophil infiltration into the CNS of infected animals correlates with increased demyelination. This brief review highlights recent evidence arguing that targeting the innate immune response may offer new therapeutic avenues for treatment of demyelinating disease including MS.

Tumor Necrosis Factor-Mediated Survival of CD169+ Cells Promotes Immune Activation during Vesicular Stomatitis Virus Infection

Innate immune activation is essential to mount an effective antiviral response and to prime adaptive immunity. Although a crucial role of CD169⁺ cells during vesicular stomatitis virus (VSV) infections is increasingly recognized, factors regulating CD169⁺ cells during viral infections remain unclear. Here, we show that tumor necrosis factor is produced by CD11b⁺ Ly6C⁺ Ly6G⁺ cells following infection with VSV. The absence of TNF or TNF receptor 1 (TNFR1) resulted in reduced numbers of CD169⁺ cells and in reduced type I interferon (IFN-I) production during VSV infection, with a severe disease outcome. Specifically, TNF triggered RelA translocation into the nuclei of CD169⁺ cells; this translocation was inhibited when the paracaspase MALT-1 was absent. Consequently, MALT1 deficiency resulted in reduced VSV replication, defective innate immune activation, and development of severe disease. These findings indicate that TNF mediates the maintenance of CD169⁺ cells and innate and adaptive immune activation during VSV infection.IMPORTANCE Over the last decade, strategically placed CD169⁺ metallophilic macrophages in the marginal zone of the murine spleen and lymph nodes (LN) have been shown to play a very important role in host defense against viral pathogens. CD169⁺ macrophages have been shown to activate innate and adaptive immunity via "enforced virus replication," a controlled amplification of virus particles. However, the factors regulating the CD169⁺ macrophages remain to be studied. In this paper, we show that after vesicular stomatitis virus infection, phagocytes produce tumor necrosis factor (TNF), which signals via TNFR1, and promote enforced virus replication in CD169⁺ macrophages. Consequently, lack of TNF or TNFR1 resulted in defective immune activation and VSV clearance.

The brain parenchyma has a type I interferon response that can limit virus spread

The brain has a tightly regulated environment that protects neurons and limits inflammation, designated "immune privilege." However, there is not an absolute lack of an immune response. We tested the ability of the brain to initiate an innate immune response to a virus, which was directly injected into the brain parenchyma, and to determine whether this response could limit viral spread. We injected vesicular stomatitis virus (VSV), a transsynaptic tracer, or naturally occurring VSV-derived defective interfering particles (DIPs), into the caudate-putamen (CP) and scored for an innate immune response and inhibition of virus spread. We found that the brain parenchyma has a functional type I interferon (IFN) response that can limit VSV spread at both the inoculation site and among synaptically connected neurons. Furthermore, we characterized the response of microglia to VSV infection and found that infected microglia produced type I IFN and uninfected microglia induced an innate immune response following virus injection.

Antibody-Dependent Enhancement of Dengue Virus Infection in Primary Human Macrophages; Balancing Higher Fusion against Antiviral Responses

The dogma is that the human immune system protects us against pathogens. Yet, several viruses, like dengue virus, antagonize the hosts’ antibodies to enhance their viral load and disease severity; a phenomenon called antibody-dependent enhancement of infection. This study offers novel insights in the molecular mechanism of antibody-mediated enhancement (ADE) of dengue virus infection in primary human macrophages. No differences were observed in the number of bound and internalized DENV particles following infection in the absence and presence of enhancing concentrations of antibodies. Yet, we did find an increase in membrane fusion activity during ADE of DENV infection. The higher fusion activity is coupled to a low antiviral response early in infection and subsequently a higher infection efficiency. Apparently, subtle enhancements early in the viral life cycle cascades into strong effects on infection, virus production and immune response. Importantly, and in contrast to other studies, the antibody-opsonized virus particles do not trigger immune suppression and remain sensitive to interferon. Additionally, this study gives insight in how human macrophages interact and respond to viral infections and the tight regulation thereof under various conditions of infection.

Abortively Infected Astrocytes Appear To Represent the Main Source of Interferon Beta in the Virus-Infected Brain

Interferon beta (IFN-β) is a key component of cellular innate immunity in mammals, and it constitutes the first line of defense during viral infection. Studies with cultured cells previously showed that almost all nucleated cells are able to produce IFN-β to various extents, but information about the in vivo sources of IFN-β remains incomplete. By applying immunohistochemistry and employing conditional-reporter mice that express firefly luciferase under the control of the IFN-β promoter in either all or only distinct cell types, we found that astrocytes are the main producers of IFN-β after infection of the brain with diverse neurotropic viruses, including rabies virus, Theiler's murine encephalomyelitis virus, and vesicular stomatitis virus. Analysis of a panel of knockout mouse strains revealed that sensing of viral components via both RIG-I-like helicases and Toll-like receptors contributes to IFN induction in the infected brain. A genetic approach to permanently mark rabies virus-infected cells in the brain showed that a substantial number of astrocytes became labeled and, therefore, must have been infected by the virus at least transiently. Thus, our results strongly indicate that abortive viral infection of astrocytes can trigger pattern recognition receptor signaling events which result in secretion of IFN-β that confers antiviral protection.

IMPORTANCE

Previous work indicated that astrocytes are the main producers of IFN after viral infection of the central nervous system (CNS), but it remained unclear how astrocytes might sense those viruses which preferentially replicate in neurons. We have now shown that virus sensing by both RIG-I-like helicases and Toll-like receptors is involved. Our results further demonstrate that astrocytes get infected in a nonproductive manner under these conditions, indicating that abortive infection of astrocytes plays a previously unappreciated role in the innate antiviral defenses of the CNS.

Retargeting Oncolytic Vesicular Stomatitis Virus to Human T-Cell Lymphotropic Virus Type 1-Associated Adult T-Cell Leukemia

Adult T cell leukemia/lymphoma (ATL) is an aggressive cancer of CD4/CD25(+) T lymphocytes, the etiological agent of which is human T-cell lymphotropic virus type 1 (HTLV-1). ATL is highly refractory to current therapies, making the development of new treatments a high priority. Oncolytic viruses such as vesicular stomatitis virus (VSV) are being considered as anticancer agents since they readily infect transformed cells compared to normal cells, the former appearing to exhibit defective innate immune responses. Here, we have evaluated the efficacy and safety of a recombinant VSV that has been retargeted to specifically infect and replicate in transformed CD4(+) cells. This was achieved by replacing the single VSV glycoprotein (G) with human immunodeficiency virus type 1 (HIV-1) gp160 to create a hybrid fusion protein, gp160G. The resultant virus, VSV-gp160G, was found to only target cells expressing CD4 and retained robust oncolytic activity against HTLV-1 actuated ATL cells. VSV-gp160G was further noted to be highly attenuated and did not replicate efficiently in or induce significant cell death of primary CD4(+) T cells. Accordingly, VSV-gp160G did not elicit any evidence of neurotoxicity even in severely immunocompromised animals such as NOD/Shi-scid, IL-2Rγ-c-null (NSG) mice. Importantly, VSV-gp160G effectively exerted potent oncolytic activity in patient-derived ATL transplanted into NSG mice and facilitated a significant survival benefit. Our data indicate that VSV-gp160G exerts potent oncolytic efficacy against CD4(+) malignant cells and either alone or in conjunction with established therapies may provide an effective treatment in patients displaying ATL.

IMPORTANCE

Adult T cell leukemia (ATL) is a serious form of cancer with a high mortality rate. HTLV-1 infection is the etiological agent of ATL and, unfortunately, most patients succumb to the disease within a few years. Current treatment options have failed to significantly improve survival rate. In this study, we developed a recombinant strain of vesicular stomatitis virus (VSV) that specifically targets transformed CD4(+) T cells through replacement of the G protein of VSV with a hybrid fusion protein, combining domains from gp160 of HIV-1 and VSV-G. This modification eliminated the normally broad tropism of VSV and restricted infection to primarily the transformed CD4(+) cell population. This effect greatly reduced neurotoxic risk associated with VSV infection while still allowing VSV to effectively target ATL cells.

Neuronal Interferon Signaling Is Required for Protection against Herpes Simplex Virus Replication and Pathogenesis

Interferon (IFN) responses are critical for controlling herpes simplex virus 1 (HSV-1). The importance of neuronal IFN signaling in controlling acute and latent HSV-1 infection remains unclear. Compartmentalized neuron cultures revealed that mature sensory neurons respond to IFNβ at both the axon and cell body through distinct mechanisms, resulting in control of HSV-1. Mice specifically lacking neural IFN signaling succumbed rapidly to HSV-1 corneal infection, demonstrating that IFN responses of the immune system and non-neuronal tissues are insufficient to confer survival following virus challenge. Furthermore, neurovirulence was restored to an HSV strain lacking the IFN-modulating gene, γ34.5, despite its expected attenuation in peripheral tissues. These studies define a crucial role for neuronal IFN signaling for protection against HSV-1 pathogenesis and replication, and they provide a novel framework to enhance our understanding of the interface between host innate immunity and neurotropic pathogens.

Herpes simplex virus type 1 (HSV-1) is a ubiquitous virus that can cause cold sores, blindness, and even death from encephalitis. There is no vaccine against HSV, and although antiviral drugs can control HSV-1, it persists because it establishes lifelong latent infections in neurons. Humans with deficiencies in innate immunity have significant problems controlling HSV infections. In this study we therefore sought to elucidate the role of neuronal innate immunity in the control of viral infection. Sensory neurons, in which HSV resides, have projection which that extend long distances to innervate the skin, the initial site of HSV infection. We found that neurons can respond to interferon beta, a molecule that strongly stimulates innate immunity and inhibits virus growth, at both the cell body and at the end of these long projections. Moreover, we found that this interferon response of neurons is critical for controlling HSV infection in vivo and that the interferon responses of non-neuronal cells are insufficient to provide protection. Our results have important implications for understanding how the nervous system defends itself against virus infections.

Neurons versus herpes simplex virus: the innate immune interactions that contribute to a host-pathogen standoff

Herpes simplex virus (HSV) is a prevalent neurotropic virus, which establishes lifelong latent infections in the neurons of sensory ganglia. Despite our long-standing knowledge that HSV predominately infects sensory neurons during its life cycle, little is known about the neuronal antiviral response to HSV infection. Recent studies show that while sensory neurons have impaired intrinsic immunity to HSV infection, paracrine IFN signaling can potentiate a potent antiviral response. Additionally, antiviral autophagy plays an important role in neuronal control of HSV infection. Here we review the literature of antiviral signaling and autophagy in neurons, the mechanisms by which HSV can counteract these responses, and postulate how these two pathways may synergize to mediate neuronal control of HSV infection and yet result in lifelong persistence of the virus.

Oncolytic adenoviruses: A potent form of tumor immunovirotherapy

The therapeutic efficacy of oncolytic viruses including adenovirus has been thought to depend mostly on direct viral destruction of tumor cells. However, this view has changed with the discovery that oncolysis can also induce innate and antigen-specific adaptive immunity against the tumor. Here we summarize our findings from cancer patients.

Intrinsic innate immunity fails to control herpes simplex virus and vesicular stomatitis virus replication in sensory neurons and fibroblasts

Herpes simplex virus 1 (HSV-1) establishes lifelong latent infections in the sensory neurons of the trigeminal ganglia (TG), wherein it retains the capacity to reactivate. The interferon (IFN)-driven antiviral response is critical for the control of HSV-1 acute replication. We therefore sought to further investigate this response in TG neurons cultured from adult mice deficient in a variety of IFN signaling components. Parallel experiments were also performed in fibroblasts isolated concurrently. We showed that HSV-1 replication was comparable in wild-type (WT) and IFN signaling-deficient neurons and fibroblasts. Unexpectedly, a similar pattern was observed for the IFN-sensitive vesicular stomatitis virus (VSV). Despite these findings, TG neurons responded to IFN-β pretreatment with STAT1 nuclear localization and restricted replication of both VSV and an HSV-1 strain deficient in γ34.5, while wild-type HSV-1 replication was unaffected. This was in contrast to fibroblasts in which all viruses were restricted by the addition of IFN-β. Taken together, these data show that adult TG neurons can mount an effective antiviral response only if provided with an exogenous source of IFN-β, and HSV-1 combats this response through γ34.5. These results further our understanding of the antiviral response of neurons and highlight the importance of paracrine IFN-β signaling in establishing an antiviral state.

IMPORTANCE

Herpes simplex virus 1 (HSV-1) is a ubiquitous virus that establishes a lifelong latent infection in neurons. Reactivation from latency can cause cold sores, blindness, and death from encephalitis. Humans with deficiencies in innate immunity have significant problems controlling HSV infections. In this study, we therefore sought to elucidate the role of neuronal innate immunity in the control of viral infection. Using neurons isolated from mice, we found that the intrinsic capacity of neurons to restrict virus replication was unaffected by the presence or absence of innate immunity. In contrast, neurons were able to mount a robust antiviral response when provided with beta interferon, a molecule that strongly stimulates innate immunity, and that HSV-1 can combat this response through the γ34.5 viral gene. Our results have important implications for understanding how the nervous system defends itself against virus infections.

RNA viruses and microRNAs: challenging discoveries for the 21st century

RNA viruses represent the predominant cause of many clinically relevant viral diseases in humans. Among several evolutionary advantages acquired by RNA viruses, the ability to usurp host cellular machinery and evade antiviral immune responses is imperative. During the past decade, RNA interference mechanisms, especially microRNA (miRNA)-mediated regulation of cellular protein expression, have revolutionized our understanding of host-viral interactions. Although it is well established that several DNA viruses express miRNAs that play crucial roles in their pathogenesis, expression of miRNAs by RNA viruses remains controversial. However, modulation of the miRNA machinery by RNA viruses may confer multiple benefits for enhanced viral replication and survival in host cells. In this review, we discuss the current literature on RNA viruses that may encode miRNAs and the varied advantages of engineering RNA viruses to express miRNAs as potential vectors for gene therapy. In addition, we review how different families of RNA viruses can alter miRNA machinery for productive replication, evasion of antiviral immune responses, and prolonged survival. We underscore the need to further explore the complex interactions of RNA viruses with host miRNAs to augment our understanding of host-virus interplay.

Understanding and altering cell tropism of vesicular stomatitis virus

Vesicular stomatitis virus (VSV) is a prototypic nonsegmented negative-strand RNA virus. VSV's broad cell tropism makes it a popular model virus for many basic research applications. In addition, a lack of preexisting human immunity against VSV, inherent oncotropism and other features make VSV a widely used platform for vaccine and oncolytic vectors. However, VSV's neurotropism that can result in viral encephalitis in experimental animals needs to be addressed for the use of the virus as a safe vector. Therefore, it is very important to understand the determinants of VSV tropism and develop strategies to alter it. VSV glycoprotein (G) and matrix (M) protein play major roles in its cell tropism. VSV G protein is responsible for VSV broad cell tropism and is often used for pseudotyping other viruses. VSV M affects cell tropism via evasion of antiviral responses, and M mutants can be used to limit cell tropism to cell types defective in interferon signaling. In addition, other VSV proteins and host proteins may function as determinants of VSV cell tropism. Various approaches have been successfully used to alter VSV tropism to benefit basic research and clinically relevant applications.

Engagement of soluble resistance-related calcium binding protein (sorcin) with foot-and-mouth disease virus (FMDV) VP1 inhibits type I interferon response in cells

Foot-and-mouth disease (FMD) is an acute, highly contagious animal disease caused by FMD virus (FMDV). Although FMDV-induced immunosuppression in host has been well established, the exact molecular mechanism for such induction is not very clear. We report here the identification of FMDV VP1 as an interferon-suppressor by interacting with soluble resistance-related calcium binding protein (sorcin). We found that VP1 suppressed tumor necrosis factor (TNF)-α or Sendai virus (SeV)-induced type I interferon response in HEK293T cells, and that this suppression could be completely abolished by knockdown of sorcin by shRNA. Furthermore, overexpression of sorcin inhibited type I interferon response. Conversely, TNF- or SeV-induced type I interferon response increased when sorcin knocked down, leading to inhibition of vesicular stomatitis virus (VSV) replication. Thus, VP1-induced suppression of type I interferon is mediated by interacting with sorcin, a protein that appears to regulate cell response to viral infections.

Mechanism of action of inhibition of allergic immune responses by a novel antedrug TLR7 agonist

Triggering innate immune responses through TLRs is expected to be a novel therapeutic strategy for the treatment of allergic diseases. TLR agonists are able to modulate Th2 immune responses through undefined mechanisms. We investigated the mechanism of action of the suppression of Th2 immune responses with a novel antedrug TLR7 agonist. The antedrug is rapidly metabolized by plasma esterases to an acid with reduced activity to limit systemic responses. Topical administration of this compound inhibited features of the allergic airway inflammatory response in rat and murine allergic airways model. Type I IFN played a role in the suppression of Th2 cytokines produced from murine splenocytes. Inhibition of Th2 immune responses with the antedrug TLR7 agonist was shown to be via a type I IFN-dependent mechanism following short-term exposure to the compound, although there might be type I IFN-independent mechanisms following long-term exposure. We have demonstrated that local type I IFN signaling and plasmacytoid dendritic cells, but not Th1 immune responses, are required for in vivo efficacy against murine airway Th2-driven eosinophilia. Furthermore, migration of dendritic cell subsets into the lung was related to efficacy and is dependent on type I IFN signaling. Thus, the mechanism of action at the cytokine and cellular level involved in the suppression of Th2 allergic responses has been characterized, providing a potential new approach to the treatment of allergic disease.

Molecular mechanisms involved in antibody-dependent enhancement of dengue virus infection in humans

Dengue is the most common arthropod-borne viral infection in humans with ∼50 million cases annually worldwide. In recent decades, a steady increase in the number of severe dengue cases has been seen. Severe dengue disease is most often observed in individuals that have pre-existing immunity against heterotypic dengue subtypes and in infants with low levels of maternal dengue antibodies. The generally accepted hypothesis explaining the immunopathogenesis of severe dengue is called antibody-dependent enhancement of dengue infection. Here, circulating antibodies bind to the newly infecting virus but do not neutralize infection. Rather, these antibodies increase the infected cell mass and virus production. Additionally, antiviral responses are diminished allowing massive virus particle production early in infection. The large infected cell mass and the high viral load are prelude for severe disease development. In this review, we discuss what is known about the trafficking of dengue virus in its human host cells, and the signalling pathways activated after virus detection, both in the absence and presence of antibodies against the virus. This review summarizes work that aims to better understand the complex immunopathogenesis of severe dengue disease.

Extended JAK activation and delayed STAT1 dephosphorylation contribute to the distinct signaling profile of CNS neurons exposed to interferon-gamma

Although interferon-gamma (IFN-γ) plays a critical role in the noncytolytic elimination of many neurotropic viral infections, the signaling response to this cytokine has not been extensively characterized in primary CNS neurons. We previously demonstrated that the IFN-γ response at the signaling and gene expression levels is temporally extended in primary mouse hippocampal neurons, as compared to the transient response of primary mouse embryonic fibroblasts (MEF). We hypothesize that the protracted kinetics of STAT1 phosphorylation in IFN-γ-treated neurons are due to extended receptor activation and/or delayed STAT1 dephosphorylation in the nucleus. Here, we show that in response to IFN-γ, the Janus kinases (JAK1/JAK2) associated with the neuronal IFN-γ receptor complex remain active for an extended period as compared to MEF. Experimental inactivation of JAK1/JAK2 in neurons after IFN-γ treatment did not reverse the extended STAT1 phosphorylation phenotype. These results suggest that the extended kinetics of neuronal IFN-γ signaling are a product of distinct negative feedback mechanisms operating at both the receptor and within the nucleus.

B cell maintenance of subcapsular sinus macrophages protects against a fatal viral infection independent of adaptive immunity

Neutralizing antibodies have been thought to be required for protection against acutely cytopathic viruses, such as the neurotropic vesicular stomatitis virus (VSV). Utilizing mice that possess B cells but lack antibodies, we show here that survival upon subcutaneous (s.c.) VSV challenge was independent of neutralizing antibody production or cell-mediated adaptive immunity. However, B cells were absolutely required to provide lymphotoxin (LT) α1β2, which maintained a protective subcapsular sinus (SCS) macrophage phenotype within virus draining lymph nodes (LNs). Macrophages within the SCS of B cell-deficient LNs, or of mice that lack LTα1β2 selectively in B cells, displayed an aberrant phenotype, failed to replicate VSV, and therefore did not produce type I interferons, which were required to prevent fatal VSV invasion of intranodal nerves. Thus, although B cells are essential for survival during VSV infection, their contribution involves the provision of innate differentiation and maintenance signals to macrophages, rather than adaptive immune mechanisms.

Interferon-induced tetherin restricts vesicular stomatitis virus release in neurons

Tetherin, a recently identified interferon (IFN)-inducible, type 2 transmembrane protein, has been shown to be a cellular antiviral restriction factor that retains newly formed virions in infected cells. Thus, tetherin plays an important role in the innate cell-autonomous immune response. The aim of this study was to examine the antiviral activities of tetherin in vesicular stomatitis virus infections of murine neuronal cells. Both IFN-β and IFN-γ induce the expression of tetherin mRNA and protein. Tetherin knockdown experiments were carried out by transfection of tethrin shRNA into murine neuroblastoma cells using a vector containing the pCMV-driven tGFP gene. The efficiency of transfection was monitored through GFP expression by the transfected cells. Selected transfected cells were used for further mRNA and protein analysis, fluorescent immunocytolocalization, and viral infection to study the impact of tetherin knockdown. Our research indicates that tetherin is expressed on the outer face of the plasma membrane of murine neuroblastoma cells, its expression can be induced with both IFN-γ and IFN-β, and tetherin restricts progeny virus release up to 100-fold in mammalian neurons, thus contributing to a potent antiviral state within the host cell.

The type I interferon response bridles rabies virus infection and reduces pathogenicity

Rabies virus (RABV) is a neurotropic virus transmitted by the bite of an infected animal that triggers a fatal encephalomyelitis. During its migration in the nervous system (NS), RABV triggers an innate immune response, including a type I IFN response well known to limit viral infections. We showed that although the neuroinvasive RABV strain CVS-NIV dampens type I IFN signaling by inhibiting IRF3 phosphorylation and STAT2 translocation, an early and transient type I IFN response is still triggered in the infected neuronal cells and NS. This urged us to investigate the role of type I IFN on RABV infection. We showed that primary mouse neurons (DRGs) of type I IFN(α/β) receptor deficient mice (IFNAR(-/-) mice) were more susceptible to RABV than DRGs of WT mice. In addition, exogenous type I IFN is partially efficient in preventing and slowing down infection in human neuroblastoma cells. Intra-muscular inoculation of type I IFNAR deficient mice [IFNAR(-/-) mice and NesCre ((+/-)) IFNAR ((flox/flox)) mice lacking IFNAR in neural cells of neuroectodermal origin only] with RABV reveals that the type I IFN response limits RABV dissemination in the inoculated muscle, slows down invasion of the spinal cord, and delays mortality. Thus, the type I IFN which is still produced in the NS during RABV infection is efficient enough to reduce neuroinvasiveness and pathogenicity and partially protect the host from fatal infection.

Restricted growth of U-type infectious haematopoietic necrosis virus (IHNV) in rainbow trout cells may be linked to casein kinase II activity

Previously, we demonstrated that a representative M genogroup type strain of infectious haematopoietic necrosis virus (IHNV) from rainbow trout grows well in rainbow trout-derived RTG-2 cells, but a U genogroup type strain from sockeye salmon has restricted growth, associated with reduced genome replication and mRNA transcription. Here, we analysed further the mechanisms for this growth restriction of U-type IHNV in RTG-2 cells, using strategies that assessed differences in viral genes, host immune regulation and phosphorylation. To determine whether the viral glycoprotein (G) or non-virion (NV) protein was responsible for the growth restriction, four recombinant IHNV viruses were generated in which the G gene of an infectious IHNV clone was replaced by the G gene of U- or M-type IHNV and the NV gene was replaced by NV of U- or M-type IHNV. There was no significant difference in the growth of these recombinants in RTG-2 cells, indicating that G and NV proteins are not major factors responsible for the differential growth of the U- and M-type strains. Poly I:C pretreatment of RTG-2 cells suppressed the growth of both U- and M-type IHNV, although the M virus continued to replicate at a reduced level. Both viruses induced type 1 interferon (IFN1) and the IFN1 stimulated gene Mx1, but the expression levels in M-infected cells were significantly higher than in U-infected cells and an inhibitor of the IFN1-inducible protein kinase PKR, 2-aminopurine (2-AP), did not affect the growth of U- or M-type IHNV in RTG-2 cells. These data did not indicate a role for the IFN1 system in the restricted growth of U-type IHNV in RTG-2 cells. Prediction of kinase-specific phosphorylation sites in the viral phosphoprotein (P) using the NetPhosK program revealed differences between U- and M-type P genes at five phosphorylation sites. Pretreatment of RTG-2 cells with a PKC inhibitor or a p38MAPK inhibitor did not affect the growth of the U- and M-type viruses. However, 100 μm of the casein kinase II (CKII) inhibitor, 5,6-dichloro-1-β-d-ribofuranosylbenzimidazole (DRB), reduced the titre of the U type 8.3-fold at 24 h post-infection. In contrast, 100 μm of the CKII inhibitor reduced the titre of the M type only 1.3-fold at 48 h post-infection. Our data suggest that the different growth of U- and M-type IHNV in RTG-2 cells may be linked to a differential requirement for cellular protein kinases such as CKII for their growth.

Interferon-induced cell membrane proteins, IFITM3 and tetherin, inhibit vesicular stomatitis virus infection via distinct mechanisms

Tetherin and IFITM3 are recently identified interferon-induced cellular proteins that restrict infections by retroviruses and filoviruses and of influenza virus and flaviviruses, respectively. In our efforts to further explore their antiviral activities against other viruses and determine their antiviral mechanisms, we found that the two antiviral proteins potently inhibit the infection of vesicular stomatitis virus (VSV), a prototype member of the Rhabdoviridae family. Taking advantage of this well-studied virus infection system, we show that although both tetherin and IFITM3 are plasma membrane proteins, tetherin inhibits virion particle release from infected cells, while IFITM3 disrupts an early event after endocytosis of virion particles but before primary transcription of incoming viral genomes. Furthermore, we demonstrate that both the N-terminal 21 amino acid residues and C-terminal transmembrane region of IFITM3 are required for its antiviral activity. Collectively, our work sheds light on the mechanisms by which tetherin and IFITM3 restrict infection with rhabdoviruses and possibly other pathogenic viruses.

Characterization of retinoic acid-inducible gene-I expression in primary murine glia following exposure to vesicular stomatitis virus

Vesicular stomatitis virus (VSV) is a negative-sense single-stranded RNA virus that closely resembles its deadly cousin, rabies virus. In mice, VSV elicits a rapid and severe T cell-independent encephalitis, indicating that resident glial cells play an important role in the initiation of central nervous system (CNS) inflammation. Recently, retinoic acid-inducible gene I (RIG-I)-like helicases have been shown to function as intracellular pattern recognition receptors for replicative viral RNA motifs. In the present study, we demonstrate that the expression of two members of this RIG-I-like receptor family (RLR), RIG-I and melanoma differentiation-associated antigen 5 (MDA5), are elevated in mouse brain tissue following intranasal administration of VSV. Using isolated cultures of primary murine glial cells, we demonstrate that microglia and astrocytes constitutively express both RIG-I and MDA5 transcripts and protein. Importantly, we show that such expression is elevated following challenge with VSV or another negative-sense RNA virus, Sendai virus. The authors provide evidence that such induction is indirect and secondary to the production of soluble mediators by infected cells. Circumstantial evidence for the functional nature of RLR expression in glial cells comes from the observation that microglia express the RLR downstream effector molecule, interferon promoter stimulator-1, and demonstrate diminished levels of the negative RLR regulator, laboratory of genetics and physiology 2, following viral challenge. These findings raise the exciting possibility that RLR molecules play important roles in the detection of viral CNS pathogens and the initiation of protective immune responses or, alternatively, the progression of damaging inflammation within the brain.

Rabies virus infection induces type I interferon production in an IPS-1 dependent manner while dendritic cell activation relies on IFNAR signaling

As with many viruses, rabies virus (RABV) infection induces type I interferon (IFN) production within the infected host cells. However, RABV has evolved mechanisms by which to inhibit IFN production in order to sustain infection. Here we show that RABV infection of dendritic cells (DC) induces potent type I IFN production and DC activation. Although DCs are infected by RABV, the viral replication is highly suppressed in DCs, rendering the infection non-productive. We exploited this finding in bone marrow derived DCs (BMDC) in order to differentiate which pattern recognition receptor(s) (PRR) is responsible for inducing type I IFN following infection with RABV. Our results indicate that BMDC activation and type I IFN production following a RABV infection is independent of TLR signaling. However, IPS-1 is essential for both BMDC activation and IFN production. Interestingly, we see that the BMDC activation is primarily due to signaling through the IFNAR and only marginally induced by the initial infection. To further identify the receptor recognizing RABV infection, we next analyzed BMDC from Mda-5−/− and RIG-I−/− mice. In the absence of either receptor, there is a significant decrease in BMDC activation at 12h post infection. However, only RIG-I−/− cells exhibit a delay in type I IFN production. In order to determine the role that IPS-1 plays in vivo, we infected mice with pathogenic RABV. We see that IPS-1−/− mice are more susceptible to infection than IPS-1+/+ mice and have a significantly increased incident of limb paralysis.

Rabies virus (RABV) is a neurotropic RNA virus responsible for the deaths of the at least 40,000 to 70,000 individuals globally each year. However, the innate immune response induced by both wildtype and vaccine strains of RABV is not well understood. In this study, we assessed the pattern recognition receptors involved in the host immune response to RABV in bone marrow derived dendritic cells (DC). Our studies revealed that Toll like receptor (TLR) signaling is not required to induce innate responses to RABV. On the other hand, we see that IPS-1, the adaptor protein for RIG-I like receptor (RLR) signaling, is essential for induction of innate immune responses. Furthermore, we found that RIG-I and Mda-5, both RLRs, are able to induce DC activation and type I interferon production. This finding is significant as we can target unused pattern recognition receptors with recombinant RABV vaccine strains to elicit a varied, and potentially protective, immune response. Lastly, we show that IPS-1 plays an important role in mediating the pathogenicity of RABV and preventing RABV associated paralysis. Overall, this study illustrates that RLRs are essential for recognition of RABV infection and that the subsequent host cell signaling is required to prevent disease.

A confocal and electron microscopic comparison of interferon beta-induced changes in vesicular stomatitis virus infection of neuroblastoma and nonneuronal cells

Vesicular stomatitis virus (VSV) replication is highly sensitive to interferon (IFN)-induced antiviral responses. Pretreatment of sensitive cultured cells with IFNbeta results in a 10(4)-fold reduction in the release of infectious VSV particles. However, differences exist between the mechanisms of reduced infectious particle titers in cell lines of neuroblastoma and nonneuronal lineage. In L929-fibroblast-derived cells, using immunofluorescence confocal microscopy, infection under control conditions reveals the accumulation of VSV matrix, phosphoprotein (P), and nucleocapsid (N) proteins over time, with induced cellular morphological changes indicative of cytopathic effects (CPEs). Upon observing L929 cells that had been pretreated with IFNbeta, neither detectable VSV proteins nor CPEs were seen, consistent with type I IFN antiviral protection. When using the same techniques to observe VSV infections of NB41A3 cells, a neuroblastoma cell line, aside from similar viral progression in the untreated control cells, IFNbeta-treated cells illustrated a severely attenuated VSV infection. Attenuated VSV progression was observed through detection of VSV matrix, P, and N proteins in isolated cells during the first 8 h of infection. However, by 18-24 h postinfection all neuroblastomas had succumbed to the viral infection. Finally, upon closer inspection of IFNbeta-treated NB41A3 cells, no detectable changes in VSV protein localization were identified compared with untreated, virally infected neuroblastomas. Next, to extend our study to test our hypothesis that virion assembly is compromised within type I IFN-treated neuroblastoma cells, we employed electron microscopy to examine our experimental conditions at the ultrastructural level. Using VSV-specific antibodies in conjunction with immuno-gold reagents, we observed several similarities between the two cell lines, such as identification of viroplasmic regions containing VSV N and P proteins and signs of stress-induced CPEs of VSV-infected cells, which had either been mock-treated or pretreated with interferon-beta (IFNbeta). One difference we observed between nonneuronal and neuroblastoma cells was more numerous actively budding VSV virions across untreated L929 plasma membranes compared with untreated NB41A3 cells. Additionally, IFNbeta-treated, VSV-infected L929 cells exhibited neither cytoplasmic viroplasm nor viral protein expression. In contrast, IFNbeta-treated, VSV-infected NB41A3 cells showed evidence of VSV infection at a very low frequency as well as small-scale viroplasmic regions that colocalized with viral N and P proteins. Finally, we observed that VSV viral particles harvested from untreated VSV-infected L929 and NB41A3 cells were statistically similar in size and shape. A portion of VSV virions from IFNbeta-treated, virally infected NB41A3 cells were similar in size and shape to virus from both untreated cell types. However, among the sampling of virions, pleomorphic viral particles that were identified from IFNbeta-treated, VSV-infected NB41A3 cells were different enough to suggest a misassembly mechanism as part of the IFNbeta antiviral state in neuroblastoma cells.

IFN-beta-induced alteration of VSV protein phosphorylation in neuronal cells

Vesicular stomatitis virus (VSV) replication is highly sensitive to interferon (IFN)-induced antiviral responses. VSV infection of well-known cell lines pretreated with IFN-beta results in a 10(4)-fold reduction in the release of infectious particles, with a concomitant abrogation in viral transcript and/or protein levels. However, in cell lines of neuronal lineage only a threefold reduction in viral transcript and protein levels was observed, despite the same 10(4)-fold reduction in released infectious virions, suggesting an assembly defect. Examination of VSV matrix (M) protein ubiquitination yielded no differences between mock- and IFN-beta-treated neuronal cells. Further analysis of potential post-translational modification events, by scintillation and two-dimensional electrophoretic methods, revealed IFN-beta-induced alterations in M protein and phosphoprotein (P) phosphorylation. Hypophosphorylated P protein was demonstrated by reduced (32)P counts, normalized by (35)S-cysteine/methionine incorporation, and by a shift in isoelectric focusing. Hypophosphorylation of VSV P protein was found to occur in neuronal cell lysates, but not within budded virions from the same IFN-beta-treated cells. In contrast, hyperphosphorylation of VSV M protein was observed in both cell lysates and viral particles from IFN-beta-treated neuronal cells. Hyperphosphorylated M protein was demonstrated by increased (32)P counts relative to (35)S-cysteine/methionine normalization, and by altered isoelectric focusing in protein populations from cell and viral lysates. Hyperphosphorylated VSV M protein was found to inhibit its association with VSV nucleocapsid, suggesting a possible mechanism for type I IFN-mediated misassembly through disruption of the interactions between ribonucleoprotein cores, and hyperphosphorylated M protein bound to the plasma membrane inner leaflet.

Intracranial administration of P gene siRNA protects mice from lethal Chandipura virus encephalitis

Background

In parts of India, Chandipura Virus (CHPV) has emerged as an encephalitis causing pathogen in both epidemic and sporadic forms. This pediatric disease follows rapid course leading to 55–75% mortality. In the absence of specific treatment, effectiveness of RNA interference (RNAi) was evaluated.

Methods and Findings

Efficacy of synthetic short interfering RNA (siRNA) or short hairpin RNA (shRNA) in protecting mice from CHPV infection was assessed. The target genes were P and M genes primarily because important role of the former in viral replication and lethal nature of the latter. Real time one step RT-PCR and plaque assay were used for the assessment of gene silencing. Using pAcGFP1N1-CHPV-P, we showed that P-2 siRNA was most efficient in reducing the expression of P gene in-vitro. Both quantitative assays documented 2logs reduction in the virus titer when P-2, M-5 or M-6 siRNAs were transfected 2hr post infection (PI). Use of these siRNAs in combination did not result in enhanced efficiency. P-2 siRNA was found to tolerate four mismatches in the center. As compared to five different shRNAs, P-2 siRNA was most effective in inhibiting CHPV replication. An extended survival was noted when mice infected intracranially with 100 LD₅₀ CHPV were treated with cationic lipid complexed 5 µg P-2 siRNA simultaneously. Infection with 10LD₅₀ and treatment with two doses of siRNA first, simultaneously and second 24 hr PI, resulted in 70% survival. Surviving mice showed 4logs less CHPV titers in brain without histopathological changes or antibody response. Gene expression profiles of P-2 siRNA treated mice showed no interferon response. First dose of siRNA at 2hr or 4hr PI with second dose at 24hr resulted in 40% and 20% survival respectively suggesting potential application in therapy.

Conclusions

The results highlight therapeutic potential of siRNA in treating rapid and fatal Chandipura encephalitis.

Peripheral immunization blocks lethal actions of vesicular stomatitis virus within the brain

Vesicular stomatitis virus (VSV) is the prototype virus for 75 or more negative-strand RNA viruses in the rhabdovirus family. Some of these viruses, including VSV, can cause neurological impairment or death upon brain infection. VSV has shown promise in the prevention and treatment of disease as a vaccine vector and an oncolytic virus, but infection of the brain remains a concern. Three VSV variants, the wild-type-related VSV-G/GFP and two attenuated viruses, VSV-CT1 and VSV-CT9-M51, were compared for neuroinvasiveness and neuromorbidity. In nonimmunized mice, direct VSV-G/GFP injection into the brain invariably resulted in lethal encephalitis; in contrast, partial survival was seen after direct injection of the attenuated VSV strains. In addition, both attenuated VSV strains showed significantly reduced neuroinvasiveness after intranasal inoculation of young postnatal day 16 mice. Of the three tested variants, VSV-CT9-M51 generated the lowest degree of neuropathology. Despite its attenuated state, peripheral inoculations of VSV-CT9-M51 targeted and killed human glioblastoma implanted into the mouse brain. Importantly, we show here that intranasal or intramuscular immunization prevents the lethal effects of subsequent VSV-G/GFP, VSV-CT1, and VSV-CT9-M51 injections into the brain. These results indicate that attenuated recombinant viruses show reduced neurovirulence and that peripheral immunization blocks the lethal actions of all VSVs tested.

Local type I IFN receptor signaling protects against virus spread within the central nervous system

Several neurotropic viruses such as vesicular stomatitis virus (VSV) induce peripheral neutralizing Ab responses and still can infect cells within the CNS. To address whether local type I IFN receptor (IFNAR) triggering plays a role in controlling virus replication within the brain, we generated mice with a cell type-specific IFNAR deletion in neuroectodermal cells of the CNS (NesCre(+/-)IFNAR(flox/flox)). Intranasal VSV infection with 10(3) PFU was well tolerated by wild-type mice, whereas conventional IFNAR(-/-) mice died within 2-3 days. In contrast, brain-specific NesCre(+/-)IFNAR(flox/flox) mice survived until day 5-6 and then became hemiplegic and died. Terminally ill NesCre(+/-)IFNAR(flox/flox) mice showed 10- to 100-fold higher virus loads in the brain than IFNAR(-/-) mice, whereas little or no virus was found in other organs. In wild-type animals, virus could be reisolated only from the olfactory bulb until day 6 where also STAT1 activation as a measure of IFNAR triggering was detected. Virus infection was found exclusively in glomerular structures of the olfactory bulb, whereas surrounding cells that showed STAT1 phosphorylation as a measure of IFNAR trigging were free of virus. Our data indicate that upon intranasal VSV instillation, early and localized IFNAR triggering in the glomerular layer of the olfactory bulb is critically required to prevent viral spread over the entire CNS and thus confers survival.

Interferon-beta expressed by a rabies virus-based HIV-1 vaccine vector serves as a molecular adjuvant and decreases pathogenicity

Type I interferon is important in anti-viral responses and in coordinating the innate immune response. Here we explore the use of interferon-beta to adjuvant the response to a rabies virus (RV) vaccine vector expressing both HIV-1 Gag and IFN-beta. Viral load and immune responses of immunized mice were analyzed over time. Our results indicate that the RV expressing IFN-beta (IFN+) is highly attenuated when compared to control RV and demonstrate that the expression of IFN-beta reduces viral replication approximately 100-fold. Despite the decrease in replication, those mice immunized with the IFN+ RV had a significantly greater number of activated CD8+ T cells. The increased activation of CD8+ T cells was dependent on IFN-beta signaling, as we saw no difference following infection of IFNAR-/- mice. Although mice immunized with IFN+ have a greater primary immune response than controls, immunized mice that were challenged with vaccinia-expressing Gag had no significant difference in the number or functionality of CD8+ T cells. The increased CD8+ T cell activation in the presence of IFN-beta, even with greatly reduced viral replication, indicates the beneficial effect of IFN-beta for the host.

Early steps of the virus replication cycle are inhibited in prostate cancer cells resistant to oncolytic vesicular stomatitis virus

Vesicular stomatitis virus (VSV) is currently being studied as a candidate oncolytic virus for tumor therapies due to its potent tumoricidal activity. Previous studies have demonstrated that VSV selectively infects tumor cells due to defects in their antiviral pathways. These defects make them more susceptible to VSV-induced killing than normal cells. However, some cancer cells display differential sensitivity to VSV. Specifically, LNCaP prostate cancer cells are sensitive to infection with VSV, while PC3 prostate cancer cells are relatively resistant to VSV. This suggests that tumor cells vary in the extent to which they develop defects in antiviral pathways and, thus, permit virus replication. The goal of these studies was to identify the step(s) of the viral replication cycle that is inhibited in PC3 cells. Results showed that although attachment of VSV was not significantly different among cell types, penetration was delayed by 10 to 30 min in PC3 cells relative to LNCaP cells. Primary transcription was delayed by 6 to 8 h in PC3 cells relative to LNCaP cells. Similarly, both secondary transcription and viral protein synthesis rates were delayed by about 6 to 8 h. The progressively increasing delay suggests that more than one step is affected in PC3 cells. Analysis of cellular gene expression showed that in contrast to LNCaP cells, PC3 cells constitutively expressed numerous antiviral gene products, which may enhance their resistance to VSV. These data indicate that the use of VSV for oncolytic virus therapy for prostate tumors may require prescreening of tumors for their level of susceptibility.

Systemic vesicular stomatitis virus selectively destroys multifocal glioma and metastatic carcinoma in brain

Metastatic tumors and malignant gliomas make up the majority of cancers in the brain. They are invariably fatal and there is currently no cure. From in vitro comparisons of a number of viruses, we selected one that appeared the best in selectively killing glioblastoma cells. This replication-competent virus, the glioma-adapted vesicular stomatis virus strain VSVrp30a, was used for in vivo tests with the underlying view that infection of tumor cells will lead to an increase in the number of viruses subsequently released to kill additional tumor cells. Intravenous injection of VSVrp30a expressing a green fluorescent protein reporter, rapidly targeted and destroyed multiple types of human and mouse tumors implanted in the mouse brain, including glioblastoma and mammary tumors. When tumors were implanted both in the brain and peripherally, emulating systemic cancer metastasis, tumors inside and outside the brain were simultaneously infected. Intranasal inoculation, leading to olfactory nerve transport of the virus into the brain, selectively infected and killed olfactory bulb tumors. Neither control cortical wounds nor transplanted normal mouse or human cells were targeted, indicating viral tumor selectivity. Control viruses, including pseudorabies, adeno-associated, or replication-deficient VSV, did not infect the brain tumor. Confocal laser time-lapse imaging through a cranial window showed that intravenous VSV infects the tumor at multiple sites and kills migrating tumor cells. Disrupted tumor vasculature, suggested by dye leakage, may be the port of entry for intravenously delivered VSV. Quantitative PCR analysis of how VSVrp30a selectively infected tumor cells suggested multiple mechanisms, including cell surface binding and internalization.

NKG2D receptor signaling enhances cytolytic activity by virus-specific CD8+ T cells: evidence for a protective role in virus-induced encephalitis

Inoculation with the neurotropic JHM strain of mouse hepatitis virus (JHMV) into the central nervous system (CNS) of mice results in an acute encephalitis associated with an immune-mediated demyelinating disease. During acute disease, infiltrating CD8(+) T cells secrete gamma interferon (IFN-gamma) that controls replication in oligodendrocytes, while infected astrocytes and microglia are susceptible to perforin-mediated lysis. The present study was undertaken to reveal the functional contributions of the activating NKG2D receptor in host defense and disease following JHMV infection. NKG2D ligands RAE-1, MULT1, and H60 were expressed within the CNS following JHMV infection. The immunophenotyping of infiltrating cells revealed that NKG2D was expressed on approximately 90% of infiltrating CD8(+) T cells during acute and chronic disease. Blocking NKG2D following JHMV infection resulted in increased mortality that correlated with increased viral titers within the CNS. Anti-NKG2D treatment did not alter T-cell infiltration into the CNS or the generation of virus-specific CD8(+) T cells, and the expression of IFN-gamma was not affected. However, cytotoxic T-lymphocyte (CTL) activity was dependent on NKG2D expression, because anti-NKG2D treatment resulted in a dramatic reduction in lytic activity by virus-specific CD8(+) T cells. Blocking NKG2D during chronic disease did not affect either T-cell or macrophage infiltration or the severity of demyelination, indicating that NKG2D does not contribute to virus-induced demyelination. These findings demonstrate a functional role for NKG2D in host defense during acute viral encephalitis by selectively enhancing CTL activity by infiltrating virus-specific CD8(+) T cells.

Peripheral, but not central nervous system, type I interferon expression in mice in response to intranasal vesicular stomatitis virus infection

Type I interferon (IFN) is critical for resistance of mice to infection with vesicular stomatitis virus (VSV). Wild type (wt) VSV infection did not induce type I IFN production in vitro or in the central nervous system (CNS) of mice; however IFN-beta was detected in lungs, spleen, and serum within 24 h. The M protein mutant VSV, T1026R1 (also referred to as M51R), induced type I IFN production in vitro and in the CNS, with poor expression in spleens. In addition, VSV T1026R1 was not pathogenic to mice after intranasal infection, illustrating the importance of IFN in controlling VSV replication in the CNS. Experiments with chemical sympathectomy, sRAGE, and neutralizing antibody to VSV were performed to investigate the mechanism(s) utilized for induction of peripheral IFN; neither sRAGE infusion nor chemical sympathectomy had an effect on peripheral IFN production. In contrast, administration of neutralizing antibody (Ab) readily blocked the response. Infectious VSV was transiently present in lungs and spleens at 24 h post infection. The results are consistent with VSV traffic from the olfactory neuroepithelium to peripheral lymphoid organs hematogenously or via lymphatic circulation. These results suggest that VSV replicates to high titers in the brains of mice because of the lack of IFN production in the CNS after intranasal VSV infection. In contrast, replication of VSV in peripheral organs is controlled by the production of large amounts of IFN.

Altered levels of STAT1 and STAT3 influence the neuronal response to interferon gamma

As immune responses in the CNS are highly regulated, cell-specific differences in IFNgamma signaling may be integral in dictating the outcome of host cell responses. In comparing the response of IFNgamma-treated primary neurons to control MEF, we observed that neurons demonstrated lower basal expression of both STAT1 and STAT3, the primary signal transducers responsible for IFNgamma signaling. Following IFNgamma treatment of these cell populations, we noted muted and delayed STAT1 phosphorylation, no detectable STAT3 phosphorylation, and a 3-10-fold lower level of representative IFNgamma-responsive gene transcripts. Moreover, in response to a brief pulse of IFNgamma, a steady increase in STAT1 phosphorylation and IFNgamma gene expression over 48 h was observed in neurons, as compared to rapid attenuation in MEF. These distinct response kinetics in IFNgamma-stimulated neurons may reflect modifications in the IFNgamma negative feedback loop, which may provide a mechanism for the cell-specific heterogeneity of responses to IFNgamma.

Interferon- alpha and - beta restrict polyomavirus JC replication in primary human fetal glial cells: implications for progressive multifocal leukoencephalopathy therapy

One of the major limitations of highly active antiretroviral therapy is its inability to inhibit the replication of polyomavirus JC (JCV), the etiologic agent of progressive multifocal leukoencephalopathy (PML), an acquired immunodeficiency syndrome-defining illness. We previously demonstrated the induction of interferon (IFN)-stimulated genes (ISGs) by JCV. In the present study, we characterize the specific viral events required to induce ISGs and the potential antiviral effects of type I IFN on JCV replication in human fetal glial cells in the presence and absence of type I IFNs. Productive JCV replication was essential for the induction of the antiviral host response. JCV replication at all steps was significantly inhibited in the presence of IFN, and neutralizing anti-IFN antibody rescued the inhibitory effect of IFN. These results support the use of IFN as an adjunct therapy for patients with PML. Because IFN cannot cross the blood-brain barrier to achieve its direct antiviral effect, intrathecal administration of IFN is warranted.

Synergistic roles of antibody and interferon in noncytolytic clearance of Sindbis virus from different regions of the central nervous system

Sindbis virus (SINV) is an alphavirus that causes infection of neurons and encephalomyelitis in adult immunocompetent mice. Recovery can occur without apparent neurological damage. To better define the factors facilitating noncytolytic clearance of SINV in different regions of the central nervous system (CNS) and the roles of innate and adaptive immune responses at different times during infection, we have characterized SINV infection and clearance in the brain, brain stem, and spinal cords of severe combined immunodeficiency (SCID) and C57BL/6 (wild-type [WT]) mice and mice deficient in beta interferon (IFN-beta) (BKO), antibody (muMT), IFN-gamma (GKO), IFN-gamma receptor (GRKO), and both antibody and IFN-gamma (muMT/GKO). WT mice cleared infectious virus by day 8, while SCID mice had persistent virus replication at all sites. For 3 days after infection, BKO mice had higher titers at all sites than WT mice, despite similar IFN-alpha production, but cleared virus similarly. GKO and GRKO mice cleared infectious virus from all sites by days 8 to 10 and, like WT mice, displayed transient reactivation at 12 to 22 days. muMT mice did not clear virus from the brain, and clearance from the brain stem and lumbar spinal cord was delayed, followed by reactivation. Eighty-one days after infection, muMT/GKO mice had not cleared virus from any site, but titers were lower than for SCID mice. These studies show that IFN-beta is independently important for early control of CNS virus replication, that antiviral antibody is critical for clearance from the brain, and that both antibody and IFN-gamma contribute to prevention of reactivation after initial clearance.