Apoptosis in acute and chronic central nervous system disease induced by Theiler's murine encephalomyelitis virus

An overall view of the most common experimental models for multiple sclerosis

Multiple sclerosis (MS) is a complex chronic disease with an unknown etiology. It is considered an inflammatory demyelinating and neurodegenerative disorder of the central nervous system (CNS) characterized, in most cases, by an unpredictable onset of relapse and remission phases. The disease generally starts in subjects under 40; it has a higher incidence in women and is described as a multifactorial disorder due to the interaction between genetic and environmental risk factors. Unfortunately, there is currently no definitive cure for MS. Still, therapies can modify the disease's natural history, reducing the relapse rate and slowing the progression of the disease or managing symptoms. The limited access to human CNS tissue slows down. It limits the progression of research on MS. This limit has been partially overcome over the years by developing various experimental models to study this disease. Animal models of autoimmune demyelination, such as experimental autoimmune encephalomyelitis (EAE) and viral and toxin or transgenic MS models, represent the most significant part of MS research approaches. These models have now been complemented by ex vivo studies, using organotypic brain slice cultures and in vitro, through induced Pluripotent Stem cells (iPSCs). We will discuss which clinical features of the disorders might be reproduced and investigated in vivo, ex vivo, and in vitro in models commonly used in MS research to understand the processes behind the neuropathological events occurring in the CNS of MS patients. The primary purpose of this review is to give the reader a global view of the main paradigms used in MS research, spacing from the classical animal models to transgenic mice and 2D and 3D cultures.

Theiler’s virus-induced demyelinating disease as an infectious model of progressive multiple sclerosis

Multiple sclerosis (MS) is a neuroinflammatory and neurodegenerative disease of unknown etiology. However, several studies suggest that infectious agents, e.g., Human Herpes Viruses (HHV), may be involved in triggering the disease. Molecular mimicry, bystander effect, and epitope spreading are three mechanisms that can initiate immunoreactivity leading to CNS autoimmunity in MS. Theiler’s murine encephalomyelitis virus (TMEV)-induced demyelinating disease (TMEV-IDD) is a pre-clinical model of MS in which intracerebral inoculation of TMEV results in a CNS autoimmune disease that causes demyelination, neuroaxonal damage, and progressive clinical disability. Given the spectra of different murine models used to study MS, this review highlights why TMEV-IDD represents a valuable tool for testing the viral hypotheses of MS. We initially describe how the main mechanisms of CNS autoimmunity have been identified across both MS and TMEV-IDD etiology. Next, we discuss how adaptive, innate, and CNS resident immune cells contribute to TMEV-IDD immunopathology and how this relates to MS. Lastly, we highlight the sexual dimorphism observed in TMEV-IDD and MS and how this may be tied to sexually dimorphic responses to viral infections. In summary, TMEV-IDD is an underutilized murine model that recapitulates many unique aspects of MS; as we learn more about the nature of viral infections in MS, TMEV-IDD will be critical in testing the future therapeutics that aim to intervene with disease onset and progression.

Host genetic diversity drives variable central nervous system lesion distribution in chronic phase of Theiler's Murine Encephalomyelitis Virus (TMEV) infection

Host genetic background is a significant driver of the variability in neurological responses to viral infection. Here, we leverage the genetically diverse Collaborative Cross (CC) mouse resource to better understand how chronic infection by Theiler's Murine Encephalomyelitis Virus (TMEV) elicits diverse clinical and morphologic changes in the central nervous system (CNS). We characterized the TMEV-induced clinical phenotype responses, and associated lesion distributions in the CNS, in six CC mouse strains over a 90 day infection period. We observed varying degrees of motor impairment in these strains, as measured by delayed righting reflex, paresis, paralysis, seizures, limb clasping, ruffling, and encephalitis phenotypes. All strains developed neuroparenchymal necrosis and mineralization in the brain, primarily localized to the hippocampal regions. Two of the six strains presented with axonal degeneration with myelin loss of the nerve roots in the lumbar spinal cord. Moreover, we statistically correlated lesion distribution with overall frequencies of clinical phenotypes and phenotype progression to better understand how and where TMEV targets the CNS, based on genetic background. Specifically, we assessed lesion distribution in relation to the clinical progression of these phenotypes from early to late TMEV disease, finding significant relationships between progression and lesion distribution. Finally, we identified quantitative trait loci associated with frequency of lesions in a particular brain region, revealing several loci of interest for future study: lysosomal trafficking regulator (Lyst) and nidogen 1 (Nid1). Together, these results indicate that the genetic background influences the type and severity of clinical phenotypes, phenotypic resilience to TMEV, and the lesion distribution across strains.

Viral mouse models used to study multiple sclerosis: past and present

Multiple sclerosis (MS) is a common inflammatory demyelinating disease of the central nervous system. Although the etiology of MS is unknown, genetics and environmental factors, such as infections, play a role. Viral infections of mice have been used as model systems to study this demyelinating disease of humans. Three viruses that have long been studied in this capacity are Theiler’s murine encephalomyelitis virus, mouse hepatitis virus, and Semliki Forest virus. This review describes the viruses themselves, the infection process, the disease caused by infection and its accompanying pathology, and the model systems and their usefulness in studying MS.

Viral infections and multiple sclerosis

The etiology and pathogenesis of MS is likely to involve multiple factors interacting with each other, and the role of infectious and viral agents is still under debate, however a consistent amount of studies suggests that some viruses are associated with the disease. The strongest documentation has come from the detection of viral nucleic acid or antigen or of an anti-viral antibody response in MS patients. A further step for the study of the mechanism viruses might be involved in can be made using in vitro and in vivo models. While in vitro models, based on glial and neural cell lines from various sources are widely used, in vivo animal models present challenges. Indeed neurotropic animal viruses are currently used to study demyelination in well-established models, but animal models of demyelination by human virus infection have only recently been developed, using animal gammaherpesviruses closely related to Epstein Barr virus (EBV), or using marmosets expressing the specific viral receptor for Human Herpesvirus 6 (HHV-6). The present review will illustrate the main potential mechanisms of MS pathogenesis possibly associated with viral infections and viruses currently used to study demyelination in animal models. Then the viruses most strongly linked with MS will be discussed, in the perspective that more than one virus might have a role, with varying degrees of interaction, contributing to MS heterogeneity.

Neuronal maturation reduces the type I IFN response to orthobunyavirus infection and leads to increased apoptosis of human neurons

BACKGROUND

La Crosse virus (LACV) is the leading cause of pediatric arboviral encephalitis in the USA. LACV encephalitis can result in learning and memory deficits, which may be due to infection and apoptosis of neurons in the brain. Despite neurons being the primary cell infected in the brain by LACV, little is known about neuronal responses to infection.

METHODS

Human cerebral organoids (COs), which contain a spectrum of developing neurons, were used to examine neuronal responses to LACV. Plaque assay and quantitative reverse transcription (qRT) PCR were used to determine the susceptibility of COs to LACV infection. Immunohistochemistry, flow cytometry, and single-cell transcriptomics were used to determine specific neuronal subpopulation responses to the virus.

RESULTS

Overall, LACV readily infected COs causing reduced cell viability and increased apoptosis. However, it was determined that neurons at different stages of development had distinct responses to LACV. Both neural progenitors and committed neurons were infected with LACV, however, committed neurons underwent apoptosis at a higher rate. Transcriptomic analysis showed that committed neurons expressed fewer interferon (IFN)-stimulated genes (ISGs) and genes involved IFN signaling in response to infection compared to neural progenitors. Furthermore, induction of interferon signaling in LACV-infected COs by application of recombinant IFN enhanced cell viability.

CONCLUSIONS

These findings indicate that neuronal maturation increases the susceptibility of neurons to LACV-induced apoptosis. This susceptibility is likely due, at least in part, to mature neurons being less responsive to virus-induced IFN as evidenced by their poor ISG response to LACV. Furthermore, exogenous administration of recombinant IFN to LACV COs rescued cellular viability suggesting that increased IFN signaling is overall protective in this complex neural tissue. Together these findings indicate that induction of IFN signaling in developing neurons is an important deciding factor in virus-induced cell death.

Facets of Theiler's Murine Encephalomyelitis Virus-Induced Diseases: An Update

Theiler’s murine encephalomyelitis virus (TMEV), a naturally occurring, enteric pathogen of mice is a Cardiovirus of the Picornaviridae family. Low neurovirulent TMEV strains such as BeAn cause a severe demyelinating disease in susceptible SJL mice following intracerebral infection. Furthermore, TMEV infections of C57BL/6 mice cause acute polioencephalitis initiating a process of epileptogenesis that results in spontaneous recurrent epileptic seizures in approximately 50% of affected mice. Moreover, C3H mice develop cardiac lesions after an intraperitoneal high-dose application of TMEV. Consequently, TMEV-induced diseases are widely used as animal models for multiple sclerosis, epilepsy, and myocarditis. The present review summarizes morphological lesions and pathogenic mechanisms triggered by TMEV with a special focus on the development of hippocampal degeneration and seizures in C57BL/6 mice as well as demyelination in the spinal cord in SJL mice. Furthermore, a detailed description of innate and adaptive immune responses is given. TMEV studies provide novel insights into the complexity of organ- and mouse strain-specific immunopathology and help to identify factors critical for virus persistence.

Theiler's Virus-Mediated Immunopathology in the CNS and Heart: Roles of Organ-Specific Cytokine and Lymphatic Responses

Theiler's murine encephalomyelitis virus (TMEV) induces different diseases in the central nervous system (CNS) and heart, depending on the mouse strains and time course, with cytokines playing key roles for viral clearance and immune-mediated pathology (immunopathology). In SJL/J mice, TMEV infection causes chronic TMEV-induced demyelinating disease (TMEV-IDD) in the spinal cord about 1 month post-inoculation (p.i.). Unlike other immunopathology models, both pro- and anti-inflammatory cytokines can play dual roles in TMEV-IDD. Pro-inflammatory cytokines play beneficial roles in viral clearance while they are also detrimental in immune-mediated demyelination. Anti-inflammatory cytokines suppress not only protective anti-viral immune responses but also detrimental autoreactive immune responses. Conversely, in C3H mice, TMEV infection induces a non-CNS disease, myocarditis, with three distinctive phases: phase I, viral pathology with interferon and chemokine responses; phase II, immunopathology mediated by acquired immune responses; and phase III, cardiac fibrosis. Although the exact mechanism(s) by which a single virus, TMEV, induces these different diseases in different organs is unclear, our bioinformatics approaches, especially principal component analysis (PCA) of transcriptome data, allow us to identify the key factors contributing to organ-specific immunopathology. The PCA demonstrated that in vitro infection of a cardiomyocyte cell line reproduced the transcriptome profile of phase I in TMEV-induced myocarditis; distinct interferon/chemokine-related responses were induced in vitro in TMEV-infected cardiomyocytes, but not in infected neuronal cells. In addition, the PCA of the in vivo CNS transcriptome data showed that decreased lymphatic marker expressions were weakly associated with inflammation in TMEV infection. Here, dysfunction of lymphatic vessels is shown to potentially contribute to immunopathology by delaying the clearance of cytokines and immune cells from the inflammatory site, although this can also confine the virus at these sites, preventing virus spread via lymphatic vessels. On the other hand, in the heart, dysfunction of lymphatics was associated with reduced lymphatic muscle contractility provoked by pro-inflammatory cytokines. Therefore, TMEV infection may induce different patterns of cytokine expressions as well as lymphatic vessel dysfunction by rather different mechanisms between the CNS and heart, which might explain observed patterns of organ-specific immunopathology.

Intact interleukin-10 receptor signaling protects from hippocampal damage elicited by experimental neurotropic virus infection of SJL mice

Theiler’s murine encephalomyelitis virus (TMEV) infection represents an experimental mouse model to study hippocampal damage induced by neurotropic viruses. IL-10 is a pleiotropic cytokine with profound anti-inflammatory properties, which critically controls immune homeostasis. In order to analyze IL-10R signaling following virus-induced polioencephalitis, SJL mice were intracerebrally infected with TMEV. RNA-based next generation sequencing revealed an up-regulation of Il10, Il10rα and further genes involved in IL-10 downstream signaling, including Jak1, Socs3 and Stat3 in the brain upon infection. Subsequent antibody-mediated blockade of IL-10R signaling led to enhanced hippocampal damage with neuronal loss and increased recruitment of CD3⁺ T cells, CD45R⁺ B cells and an up-regulation of Il1α mRNA. Increased expression of Tgfβ and Foxp3 as well as accumulation of Foxp3⁺ regulatory T cells and arginase-1⁺ macrophages/microglia was detected in the hippocampus, representing a potential compensatory mechanism following disturbed IL-10R signaling. Additionally, an increased peripheral Chi3l3 expression was found in spleens of infected mice, which may embody reactive regulatory mechanisms for prevention of excessive immunopathology. The present study highlights the importance of IL-10R signaling for immune regulation and its neuroprotective properties in the context of an acute neurotropic virus infection.

Animal models of multiple sclerosis: Focus on experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is a chronic, progressive disorder of the central nervous system (CNS) that affects more than two million people worldwide. Several animal models resemble MS pathology; the most employed are experimental autoimmune encephalomyelitis (EAE) and toxin- and/or virus-induced demyelination. In this review we will summarize our knowledge on the utility of different animal models in MS research. Although animal models cannot replicate the complexity and heterogeneity of the MS pathology, they have proved to be useful for the development of several drugs approved for treatment of MS patients. This review focuses on EAE because it represents both clinical and pathological features of MS. During the past decades, EAE has been effective in illuminating various pathological processes that occur during MS, including inflammation, CNS penetration, demyelination, axonopathy, and neuron loss mediated by immune cells.

Immunoregulation of Theiler's virus-induced demyelinating disease by glatiramer acetate without suppression of antiviral immune responses

While most disease-modifying drugs (DMDs) regulate multiple sclerosis (MS) by suppressing inflammation, they can potentially suppress antiviral immunity, causing progressive multifocal leukoencephalopathy (PML). The DMD glatiramer acetate (GA) has been used for MS patients who are at high risk of PML. We investigated whether GA is safe for use in viral infections by using a model of MS induced by infection with Theiler's murine encephalomyelitis virus (TMEV). Treatment of TMEV-infected mice with GA neither enhanced viral loads nor suppressed antiviral immune responses, while it resulted in an increase in the Foxp3/Il17a ratio and IL-4/IL-10 production. This is the first study to suggest that GA could be safe for MS patients with a proven viral infection.

SJL bone marrow-derived macrophages do not have IRF3 mutations and are highly susceptible to Theiler's virus infection

It is well known that SJL mice are susceptible to Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease while C57BL6 (B6) and B10 mice are resistant, and H-2^s on a B10 background (B10.S) contributes modestly to susceptibility. A recent study linked two IRF3 non-conservative mutations in SJL compared to B10.S mice to resistance to TMEV infection of SJL peritoneal-derived macrophages, an observation of practical interest in light of the central role of IRF3 transcription factor in the type I interferon (IFN) response. However, we did not find these non-conservative mutations among SJL, B10.S, B6 and B10 mice in the IRF3 amino acid sequence, and show SJL bone marrow-derived macrophages infected with TMEV exhibit increased virus RNA replication and infectious virus yields as well as greater IL-6 production than C57Bl strain (including B10.S) cultures.

Theiler's murine encephalomyelitis virus infection of SJL/J and C57BL/6J mice: Models for multiple sclerosis and epilepsy

Mouse models are great tools to study the mechanisms of disease development. Theiler's murine encephalomyelitis virus is used in two distinct viral infection mouse models to study the human diseases multiple sclerosis (MS) and epilepsy. Intracerebral (i.c.) infection of the SJL/J mouse strain results in persistent viral infection of the central nervous system and a MS-like disease, while i.c. infection of the C57BL/6J mouse strain results in acute seizures and epilepsy. Our understanding of how the immune system contributes to the development of two disparate diseases caused by the same virus is presented.

Immunohistochemical insights into Saffold virus infection of the brain of juvenile AG129 mice

Background

Saffold Virus (SAFV) is a human cardiovirus that is suspected of causing infection of the central nervous system (CNS) in children. While recent animal studies have started to elucidate the pathogenesis of SAFV, very little is known about the mechanisms behind it.

Method

In this study, we attempted to elucidate some of the mechanisms of the pathogenesis of SAFV in the brain of a juvenile mouse model by using immunohistochemical methods.

Results

We first showed that SAFV is able to infect both neuronal and glial cells in the brain of 2 week-old AG129 mice. We then showed that SAFV is able to induce apoptosis in both neuronal and glial cells in the brain. Lastly, we showed that SAFV infection does not show any signs of gross demyelination in the brain.

Conclusion

Overall, our results provide important insights into the mechanisms of SAFV in the brain.

Electronic supplementary material

The online version of this article (doi:10.1186/s12985-016-0654-8) contains supplementary material, which is available to authorized users.

Three immune-mediated disease models induced by Theiler's virus: Multiple sclerosis, seizures and myocarditis

Theiler's murine encephalomyelitis virus (TMEV) infection has been used as a viral model for multiple sclerosis (MS), as TMEV can induce chronic inflammatory demyelinating lesions with viral persistence in the spinal cord of SJL/J mice. In contrast, when C57BL/6 mice are infected with TMEV, the mice can clear the virus from the central nervous system (CNS), without viral persistence or demyelination, but develop seizures and hippocampal sclerosis, which has been used as a viral model for seizures/epilepsy. In the two TMEV-induced CNS disease models, not only viral infection, but also immune responses contribute to the pathogenesis. Interestingly, acquired immunity plays an effector role in the MS model, whereas innate immunity appears to contribute to the development of seizures. Recently, we have established the third TMEV-induced disease model, a mouse model for viral myocarditis, using C3H mice. TMEV-induced myocarditis is a triphasic disease, which mimics human myocarditis; phase I, mediated by viral replication in the heart and innate immunity; phase II, mediated by acquired immunity; and phase III, resulted from cardiac fibrosis. The genetic susceptibility to the aforementioned three models (MS, seizures and myocarditis) differs among mouse strains. We have compared and contrasted the three models induced by one single pathogen, TMEV, particularly in regard to the roles of T helper cells and natural killer T cells, which will give an insight into how interactions between the immune system and the host's genetic background determine the tissue tropism of virus and the development of virus-induced organ-specific immunopathology.

Saffold virus, an emerging human cardiovirus

Saffold virus (SAFV) is an emerging human cardiovirus that has been shown to be ubiquitous. Initial studies of SAFV focused on respiratory and gastrointestinal infection; however, it has also recently been associated with diverse clinical symptoms including the endocrine, cardiovascular, and neurological systems. Given the systemic nature of SAFV, and its high prevalence, understanding its pathogenicity and clinical impact is of utmost importance. This comprehensive review highlights and discusses recent developments in epidemiology, human pathogenicity, animal, and molecular studies related to SAFV. It also provides detailed insights into the neuropathogenicity of SAFV. We argue that human studies have been confounded by coinfections and therefore require support from robust molecular and animal research. Thereby, we aim to provide foresight into further research to better understand this emerging virus.

Neuropathogenesis of Zika Virus Infection : Potential Roles of Antibody-Mediated Pathology

Zika virus (ZIKV) is an enveloped, positive-sense, single-stranded RNA virus that belongs to the genus Flavivirus, family Flaviviridae, which includes many human and animal pathogens, such as dengue virus (DENV), West Nile virus, and Japanese encephalitis virus. In the original as well as subsequent experimental and clinical reports, ZIKV seems to have moderate neurotropism (in animal models) and neurovirulence (in human fetuses), but no neuroinvasiveness (in human adults). Intrauterine ZIKV infection (viral pathology) has been linked to an increased incidence of microcephaly, while increased Guillain-Barré syndrome (GBS) following ZIKV infection is likely immune-mediated (immunopathology). Clinically, in ZIKV infection, antibodies against other flaviviruses, such as DENV, have been detected; these antibodies can cross-react with ZIKV without ZIKV neutralization. In theory, such non-neutralizing antibodies are generated at the expense of decreased production of neutralizing antibodies ("antigenic sin"), leading to poor viral clearance, while the non-neutralizing antibodies can also enhance viral replication in Fc receptor (FcR)-bearing cells via antibody-dependent enhancement (ADE). Here, we propose three potential roles of the antibody-mediated pathogenesis of ZIKV infection: 1) cross-reactive antibodies that recognize ZIKV and neural antigens cause GBS; 2) ZIKV-antibody complex is transported transplacentally via neonatal FcR (FcRn), resulting in fetal infection; and 3) ZIKV-antibody complex is taken up at peripheral nerve endings and transported to neurons in the central nervous system (CNS), by which the virus can enter the CNS without crossing the blood-brain barrier.

Correlation of Brain Atrophy, Disability, and Spinal Cord Atrophy in a Murine Model of Multiple Sclerosis

BACKGROUND

Disability progression in multiple sclerosis (MS) remains incompletely understood. Unlike lesional measures, central nervous system atrophy has a strong correlation with disability. Theiler's murine encephalomyelitis virus infection in SJL/J mice is an established model of progressive MS. We utilized in vivo MRI to quantify brain and spinal cord atrophy in this model and analyzed the temporal relationship between atrophy and disability.

METHODS

Infected and control mice were followed for 12 months. Disability was assessed periodically using rotarod assay. Volumetric MRI datasets were acquired at 7 Tesla. Ventricular volume and C4-5 spinal cord cross-sectional area measurements were performed using Analyze 10.

RESULTS

At 3 months, brain atrophy reached statistical significance (P = .005). In contrast, disability did not differ until 4 months post-infection (P = .0005). Cord atrophy reached significance by 9 months (P = 0.009). By 12 months, brain atrophy resulted in 111.8% increased ventricular volume (P = .00003), while spinal cord cross-sectional area was 25.6% reduced (P = .001) among cases.

CONCLUSIONS

Our results suggest that significant brain atrophy precedes and predicts the development of disability, while spinal cord atrophy occurs late and correlates with severe disability. The observed temporal relationship establishes a framework for mechanisms of disability progression and enables further investigations of their underlying substrate.

Organ-specific protective role of NKT cells in virus-induced inflammatory demyelination and myocarditis depends on mouse strain

Theiler's murine encephalomyelitis virus (TMEV) can induce demyelination or myocarditis in susceptible mouse strains. A deficiency of NKT cells exacerbated TMEV-induced demyelinating disease (TMEV-IDD) in SJL/J and BALB/c mice. In C57BL/6 background, however, NKT-cell-deficient Jα18 KO mice remained as resistant to TMEV-IDD as wild-type mice. Echocardiography and histology showed that Jα18 KO mice developed more severe myocarditis (greater T cell infiltration and fibrosis) than wild-type mice, suggesting a protective role of NKT cells in myocarditis in C57BL/6 mice. Jα18 KO mice had higher cardiac viral RNA and anti-viral antibody titers, but had lower lymphoproliferation and IL-4 and IL-10 production.

Targeting insulin-like growth factor 1 leads to amelioration of inflammatory demyelinating disease

In patients with multiple sclerosis (MS) and in mice with experimental autoimmune encephalomyelitis (EAE), proliferating autoreactive T cells play an important role in the pathogenesis of the disease. Due to the importance of these myelin-specific T cells, these cells have been therapeutic targets in a variety of treatments. Previously we found that Lenaldekar (LDK), a novel small molecule, could inhibit exacerbations in a preclinical model of MS when given at the start of an EAE exacerbation. In those studies, we found that LDK could inhibit human T cell recall responses and murine myelin responses in vitro. In these new studies, we found that LDK could inhibit myelin specific T cell responses through the insulin-like growth factor-1 receptor (IGF-1R) pathway. Alteration of this pathway led to marked reduction in T cell proliferation and expansion. Blocking this pathway could account for the observed decreases in clinical signs and inflammatory demyelinating disease, which was accompanied by axonal preservation. Our data indicate that IGF-1R could be a potential target for new therapies for the treatment of autoimmune diseases where autoreactive T cell expansion is a requisite for disease.

Transcriptomic meta-analysis of multiple sclerosis and its experimental models

Background

Multiple microarray analyses of multiple sclerosis (MS) and its experimental models have been published in the last years.

Objective

Meta-analyses integrate the information from multiple studies and are suggested to be a powerful approach in detecting highly relevant and commonly affected pathways.

Data sources

ArrayExpress, Gene Expression Omnibus and PubMed databases were screened for microarray gene expression profiling studies of MS and its experimental animal models.

Study eligibility criteria

Studies comparing central nervous system (CNS) samples of diseased versus healthy individuals with n >1 per group and publically available raw data were selected.

Material and Methods

Included conditions for re-analysis of differentially expressed genes (DEGs) were MS, myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis (EAE) in rats, proteolipid protein-induced EAE in mice, Theiler’s murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD), and a transgenic tumor necrosis factor-overexpressing mouse model (TNFtg). Since solely a single MS raw data set fulfilled the inclusion criteria, a merged list containing the DEGs from two MS-studies was additionally included. Cross-study analysis was performed employing list comparisons of DEGs and alternatively Gene Set Enrichment Analysis (GSEA).

Results

The intersection of DEGs in MS, EAE, TMEV-IDD, and TNFtg contained 12 genes related to macrophage functions. The intersection of EAE, TMEV-IDD and TNFtg comprised 40 DEGs, functionally related to positive regulation of immune response. Over and above, GSEA identified substantially more differentially regulated pathways including coagulation and JAK/STAT-signaling.

Conclusion

A meta-analysis based on a simple comparison of DEGs is over-conservative. In contrast, the more experimental GSEA approach identified both, a priori anticipated as well as promising new candidate pathways.

Apoptosis induction influences reovirus replication and virulence in newborn mice

Apoptosis is a type of controlled cell death that is essential for development and tissue homeostasis. It also serves as a robust host response against infection by many viruses. The capacity of neurotropic viruses to induce apoptosis strongly correlates with virulence. However, the precise function of apoptosis in viral infection is not well understood. Reovirus is a neurotropic virus that induces apoptosis in a variety of cell types, including central nervous system neurons, leading to fatal encephalitis in newborn mice. To determine the effect of apoptosis on reovirus replication in the host, we generated two otherwise isogenic viruses that differ in a single amino acid in viral capsid protein μ1 that segregates with apoptotic capacity. Apoptosis-proficient and apoptosis-deficient viruses were compared for replication, dissemination, tropism, and tissue injury in newborn mice and for the capacity to spread to uninfected littermates. Our results indicate that apoptotic capacity enhances reovirus replication in the brain and consequent neurovirulence but reduces transmission efficiency. The replication advantage of the apoptosis-proficient strain is limited to the brain and correlates with enhanced infectivity of neurons. These studies reveal a new cell type-specific determinant of reovirus virulence.

Viral models of multiple sclerosis: neurodegeneration and demyelination in mice infected with Theiler's virus

Multiple sclerosis (MS) is a complex inflammatory disease of unknown etiology that affects the central nervous system (CNS) white matter, and for which no effective cure exists. Indeed, whether the primary event in MS pathology affects myelin or axons of the CNS remains unclear. Animal models are necessary to identify the immunopathological mechanisms involved in MS and to develop novel therapeutic and reparative approaches. Specifically, viral models of chronic demyelination and axonal damage have been used to study the contribution of viruses in human MS, and they have led to important breakthroughs in our understanding of MS pathology. The Theiler's murine encephalomyelitis virus (TMEV) model is one of the most commonly used MS models, although other viral models are also used, including neurotropic strains of mouse hepatitis virus (MHV) that induce chronic inflammatory demyelination with similar histological features to those observed in MS. This review will discuss the immunopathological mechanisms involved in TMEV-induced demyelinating disease (TMEV-IDD). The TMEV model reproduces a chronic progressive disease due to the persistence of the virus for the entire lifespan in susceptible mice. The evolution and significance of the axonal damage and neuroinflammation, the importance of epitope spread from viral to myelin epitopes, the presence of abortive remyelination and the existence of a brain pathology in addition to the classical spinal cord demyelination, are some of the findings that will be discussed in the context of this TMEV-IDD model. Despite their limitations, viral models remain an important tool to study the etiology of MS, and to understand the clinical and pathological variability associated with this disease.

The antiapoptotic protein Mcl-1 controls the type of cell death in Theiler's virus-infected BHK-21 cells

Theiler's murine encephalomyelitis virus (TMEV) results in a persistent central nervous system infection (CNS) and immune-mediated demyelination in mice. TMEV largely persists in macrophages (Ms) in the CNS, and infected Ms in vitro undergo apoptosis, whereas the infection of other rodent cells produces necrosis. We have found that necrosis is the dominant form of cell death in BeAn virus-infected BHK-21 cells but that ~20% of cells undergo apoptosis. Mcl-1 was highly expressed in BHK-21 cells, and protein levels decreased upon infection, consistent with onset of apoptosis. In infected BHK-21 cells in which Mcl-1 expression was knocked down using silencing RNAs there was a 3-fold increase in apoptotic cell death compared to parental cells. The apoptotic program switched on by BeAn virus is similar to that in mouse Ms, with hallmarks of activation of the intrinsic apoptotic pathway in a tumor suppressor protein p53-dependent manner. Infection of stable Mcl-1-knockdown cells led to restricted virus titers and increased physical to infectious particle (PFU) ratios, with additional data suggesting that a late step in the viral life cycle after viral RNA replication, protein synthesis, and polyprotein processing is affected by apoptosis. Together, these results indicate that Mcl-1 acts as a critical prosurvival factor that protects against apoptosis and allows high yields of infectious virus in BHK-21 cells.

Once initiated, viral encephalitis-induced seizures are consistent no matter the treatment or lack of interleukin-6

Theiler's murine encephalomyelitis virus infection of C57BL/6 mice results in acute behavioral seizures in 50% of the mice. Treatment of infected mice with minocycline or infection of interleukin (IL)-6-deficient chimeric mice results in a significant decrease in the number of mice developing seizures. However, in those mice that do develop seizures, the pathological changes (neuronal cell loss, inflammation [perivascular cuffing, gliosis, activated microglia/macrophages]), and the numbers of virus infected cells in minocycline-treated or IL-6-deficient chimeric mice are very similar. Therefore, once seizures develop, the pathological changes are consistent regardless of the treatment or genetic background.

Theiler's virus infection: Pathophysiology of demyelination and neurodegeneration

Multiple sclerosis (MS) has been suggested to be an autoimmune demyelinating disease of the central nervous system (CNS), whose primary target is either myelin itself, or myelin-forming cells, the oligodendrocytes. Although axonal damage occurs in MS, it is regarded as a secondary event to the myelin damage. Here, the lesion develops from the myelin (outside) to the axons (inside) "Outside-In model". The Outside-In model has been supported by an autoimmune model for MS, experimental autoimmune (allergic) encephalomyelitis (EAE). However, recently, (1) EAE-like disease has also been shown to be induced by immune responses against axons, and (2) immune responses against axons and neurons as well as neurodegeneration independent of inflammatory demyelination have been reported in MS, which can not be explained by the Outside-In model. Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease (TMEV-IDD) is a viral model for MS. In TMEV infection, axonal injury precedes demyelination, where the lesion develops from the axons (inside) to the myelin (outside) "Inside-Out model". The initial axonal damage could result in the release of neuroantigens, inducing autoimmune responses against myelin antigens, which potentially attack the myelin from outside the nerve fiber. Thus, the Inside-Out and Outside-In models can make a "vicious" immunological cycle or initiate an immune cascade.

The L-coding region of the DA strain of Theiler's murine encephalomyelitis virus causes dysfunction and death of myelin-synthesizing cells

The DA strain and other members of the TO subgroup of Theiler's murine encephalomyelitis virus (TMEV) induce an early transient subclinical neuronal disease followed by a chronic progressive inflammatory demyelination, with persistence of the virus in the central nervous system (CNS) for the life of the mouse. Although TMEV-induced demyelinating disease (TMEV-IDD) is thought to be immune mediated, there is also evidence that supports a role for the virus in directly inducing demyelination. In order to clarify the function of DA virus genes, we generated a transgenic mouse that had tamoxifen-inducible expression of the DA L-coding region in oligodendrocytes (and Schwann cells), a cell type in which the virus is known to persist. Tamoxifen-treated young transgenic mice usually developed an acute progressive fatal paralysis, with abnormalities of the oligodendrocytes and Schwann cells and demyelination, but without significant lymphocytic infiltration; later treatment led to transient weakness with demyelination and persistent expression of the recombined transgene. These findings demonstrate that a high level of expression of DA L can cause the death of myelin-synthesizing cells and death of the mouse, while a lower level of L expression (which can persist) can lead to cellular dysfunction with survival. The results suggest that expression of DA L plays an important role in the pathogenesis of TMEV-IDD. Virus-induced infection and death of oligodendrocytes may play a part in the demyelination of other diseases in which an immune-mediated mechanism has been stressed, including multiple sclerosis.

The virology and developments toward control of human enterovirus 71

Enterovirus 71 (EV71), a member of the Enterovirus genus in the Picornaviridae family, was first recognized as a dermotrophic virus that usually cause mild, self-limiting hand-foot-and-mouth disease (HFMD). However, EV71 infection can sometimes induce a variety of severe neurological complications and even death. Current large outbreaks of EV71 make this virus being a major public health issue. Intense effort has been made to address its underlying pathogenesis and to develop effective means for combating EV71 infections. Here, we aimed to provide an overview of cellular mechanisms underlying EV71 infection and to assess potential agents for prevention and treatment of EV71 infections.

Apoptotic and antiapoptotic activity of L protein of Theiler's murine encephalomyelitis virus

Cellular apoptosis induced by viral genes can play a critical role in determining virulence as well as viral persistence. This form of cell death has been of interest with respect to Theiler's murine encephalomyelitis virus (TMEV) because the GDVII strain and members of the GDVII subgroup are highly neurovirulent, while the DA strain and members of the TO subgroup induce a chronic progressive inflammatory demyelination with persistence of the virus in the central nervous system. The TMEV L protein has been identified as important in the pathogenesis of Theiler's virus-induced demyelinating disease (TMEV-IDD). We now show that DA L is apoptotic following transfection of L expression constructs or following DA virus infection of HeLa cells; the apoptotic activity depends on the presence of the serine/threonine domain of L, especially a serine at amino acid 57. In contrast, GDVII L has little apoptotic activity following transfection of L expression constructs in HeLa cells and is antiapoptotic following GDVII infection of HeLa cells. Of note, both DA and GDVII L cleave caspase-3 in BHK-21 cells, although neither implements the full apoptotic machinery in this cell type as manifested by the induction of terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL) staining. The differences in apoptotic activities of DA and GDVII L in varied cell types may play an important role in TMEV subgroup-specific disease phenotypes.

Coxsackievirus B3-induced cellular protrusions: structural characteristics and functional competence

Virus-induced alterations in cell morphology play important roles in the viral life cycle. To examine the intracellular events of coxsackievirus B3 (CVB3) infection, green monkey kidney (GMK) cells were either inoculated with the virus or transfected with the viral RNA. Various microscopic and flow cytometric approaches demonstrated the emergence of CVB3 capsid proteins at 8 h posttransfection, followed by morphological transformation of the cells. The morphological changes included formation of membranous protrusions containing viral capsids, together with microtubules and actin. Translocation of viral capsids into these protrusions was sensitive to cytochalasin D, suggesting the importance of actin in the process. Three-dimensional (3D) live-cell imaging demonstrated frequent contacts between cellular protrusions and adjacent cells. Markedly, in spite of an increase in the cellular viral protein content starting 8 h postinfection, no significant decrease in cell viability or increase in the amount of early apoptotic markers was observed by flow cytometry by 28 h postinfection. Comicroinjection of viral RNA and fluorescent dextran in the presence of neutralizing virus antibody suggested that these protrusions mediated the spread of infection from one cell to another prior to virus-induced cell lysis. Altogether, the CVB3-induced cellular protrusions could function as a hitherto-unknown nonlytic mechanism of cell-to-cell transmission exploited by enteroviruses.

The anti-apoptotic protein L(*) of Theiler's murine encephalomyelitis virus (TMEV) contains a mitochondrial targeting signal

L(*) protein of TMEV is out-of-frame with the viral polyprotein from an alternative initiation codon AUG, 13 nucleotides downstream from the authentic polyprotein AUG. Anti-apoptotic activity of L(*) was demonstrated by both 'loss of function' and 'gain of function' experiments. However, the precise mechanism(s) of anti-apoptotic activity of L(*) remains to be clarified. In this study, L(*) was demonstrated to be localized to mitochondria. It was also shown by the GFP fusion protein that N-terminal sequence of L(*) may contain a mitochondrial targeting signal (MTS). Surprisingly, L(*)((5-70))-GFP and L(*)((41-70))-GFP were localized to mitochondria although L(*)((1-70))-GFP was distributed in the cytosol, suggesting L(*) has an MTS between amino acid (AA) positions 41 and 70, and that L(*)((1-4)) inhibits its mitochondrial targeting. Furthermore, L(*)((1-70))-GFP was localized to the mitochondria by co-expression of L(*)((65-156)), indicating that L(*)((65-156)) suppresses the inhibition of mitochondrial targeting by L(*)((1-4)). These results suggest that the intra- or inter-molecular interaction of L(*) regulates its mitochondrial localization. It is also suggested that L(*) may inhibit the intrinsic apoptosis through the localization to mitochondria.

Neuropathogenesis of Theiler's murine encephalomyelitis virus infection, an animal model for multiple sclerosis

Theiler's murine encephalomyelitis virus (TMEV) infection of mice is an experimental model for multiple sclerosis (MS). TMEV induces a biphasic disease in susceptible mouse strains. During the acute phase, 1 week after infection, TMEV causes polioencephalomyelitis characterized by infection and apoptosis of neurons in the gray matter of the brain. During the chronic phase, about 1 month after infection, virus infects glial cells and macrophages, and induces inflammatory demyelination with oligodendrocyte apoptosis and axonal degeneration in the white matter of the spinal cord. Although antibody, CD4(+), and CD8(+) T cell responses against TMEV capsid proteins play important roles in neuropathogenesis, infectious virus with persistence is necessary to induce demyelination; in general, adoptive transfer of antibody or T cells alone did not induce central nervous system (CNS) disease. The TMEV model can be useful for testing new therapeutic strategies specifically as a viral model for MS. Therapies targeting adhesion molecules, axonal degeneration, and immunosuppression can be beneficial for pure autoimmune CNS demyelinating diseases, such as experimental autoimmune encephalomyelitis, but could be detrimental in virus-induced demyelinating diseases, such as progressive multifocal leukoencephalopathy.

Activation of tumor suppressor protein p53 is required for Theiler's murine encephalomyelitis virus-induced apoptosis in M1-D macrophages

Theiler's murine encephalomyelitis virus (TMEV) is a highly cytolytic picornavirus that persists in the mouse central nervous system (CNS) largely in macrophages with infection maintained by macrophage-to-macrophage spread. Infected macrophages in the CNS undergo apoptosis. We recently showed that M1-D macrophages infected with the low-neurovirulence TMEV BeAn virus became apoptotic through the mitochondrial pathway that is Bax mediated. Our present analyses of the molecular events and signaling pathway(s) culminating in the mitochondrial outer membrane permeabilization that initiates the caspase cascade and apoptosis of BeAn virus-infected M1-D macrophages revealed activation of p38 mitogen-activated protein kinase by 2 to 3 h postinfection (p.i.), followed by phosphorylation of tumor suppressor protein p53 Ser 15 at 3 to 6 h p.i., stabilizing p53 levels until 6 h p.i. Activated p53 upregulated the transcription of proapoptotic puma and noxa genes at 2 to 4 h p.i. and their BH3-only protein expression, followed by the loss of detectable prosurvival Mcl-1 and A1 proteins at 4 to 10 h p.i. Degradation of the prosurvival proteins is known to release Bax, which forms homo-oligomers and translocates into and permeabilizes the mitochondrial outer membrane. Inhibition of phospho-p38 by two specific inhibitors, SB203580 and BIRB796, led to a significant decrease in apoptosis at 10 h p.i., with no effect on virus titers (only SB203580 tested). Together, these data indicate that p53 activation is required for the induction of apoptosis in infected M1-D cells.

Apoptosis of hippocampal pyramidal neurons is virus independent in a mouse model of acute neurovirulent picornavirus infection

Many viruses, including picornaviruses, have the potential to infect the central nervous system (CNS) and stimulate a neuroinflammatory immune response, especially in infants and young children. Cognitive deficits associated with CNS picornavirus infection result from injury and death of neurons that may occur due to direct viral infection or during the immune responses to virus in the brain. Previous studies have concluded that apoptosis of hippocampal neurons during picornavirus infection is a cell-autonomous event triggered by direct neuronal infection. However, these studies assessed neuron death at time points late in infection and during infections that lead to either death of the host or persistent viral infection. In contrast, many neurovirulent picornavirus infections are acute and transient, with rapid clearance of virus from the host. We provide evidence of hippocampal pathology in mice acutely infected with the Theiler's murine encephalomyelitis picornavirus. We found that CA1 pyramidal neurons exhibited several hallmarks of apoptotic death, including caspase-3 activation, DNA fragmentation, and chromatin condensation within 72 hours of infection. Critically, we also found that many of the CA1 pyramidal neurons undergoing apoptosis were not infected with virus, indicating that neuronal cell death during acute picornavirus infection of the CNS occurs in a non-cell-autonomous manner. These observations suggest that therapeutic strategies other than antiviral interventions may be useful for neuroprotection during acute CNS picornavirus infection.

Antiapoptotic activity of the cardiovirus leader protein, a viral "security" protein

Apoptosis is a common antiviral defensive mechanism that potentially limits viral reproduction and spread. Many viruses possess apoptosis-suppressing tools. Here, we show that the productive infection of HeLa cells with encephalomyocarditis virus (a cardiovirus) was not accompanied by full-fledged apoptosis (although the activation of caspases was detected late in infection) but rather elicited a strong antiapoptotic state, as evidenced by the resistance of infected cells to viral and nonviral apoptosis inducers. The development of the antiapoptotic state appeared to depend on a function(s) of the viral leader (L) protein, since its mutational inactivation resulted in the efflux of cytochrome c from mitochondria, the early activation of caspases, and the appearance of morphological and biochemical signs of apoptosis in a significant proportion of infected cells. Infection with both wild-type and L-deficient viruses induced the fragmentation of mitochondria, which in the former case was not accompanied with cytochrome c efflux. Although the exact nature of the antiapoptotic function(s) of cardioviruses remains obscure, our results suggested that it includes previously undescribed mechanisms operating upstream and possibly downstream of the mitochondrial level, and that L is involved in the control of these mechanisms. We propose that cardiovirus L belongs to a class of viral proteins, dubbed here security proteins, whose roles consist solely, or largely, in counteracting host antidefenses. Unrelated L proteins of other picornaviruses as well as their highly variable 2A proteins also may be security proteins. These proteins appear to be independent acquisitions in the evolution of picornaviruses, implying multiple cases of functional (though not structural) convergence.

Apoptosis in animal models of virus-induced disease

Apoptosis is associated with virus-induced human diseases of the central nervous system, heart and liver, and causes substantial morbidity and mortality. Although virus-induced apoptosis is well characterized in individual cells in cell culture, virus-induced apoptosis in vivo and the role of apoptosis in virus-induced disease is not well established. This review focuses on animal models of virus-induced diseases of the central nervous system, heart and liver that provide insights into the role of apoptosis in pathogenesis, the pathways involved and the potential therapeutic implications.

Axonal degeneration as a self-destructive defense mechanism against neurotropic virus infection

Theiler's murine encephalomyelitis virus (TMEV) and other neurotropic virus infections result in degeneration of each component of the neuron: apoptosis of the cell body, axonal (Wallerian) degeneration, and dendritic and synaptic pathology. In general, axonal degeneration is detrimental for hosts. However, axonal degeneration can be beneficial in the case of infection with neurotropic viruses that spread in the CNS using axonal transport. C57BL/Wld(S) (Wld(S), Wallerian degeneration slow mutant) mice are protected from axonal degeneration. Wld(S) mice infected with the neurovirulent GDVII strain of TMEV are more resistant to virus infection than wild-type mice, suggesting that axonal preservation contributes to the resistance. By contrast, infection with the less virulent Daniels strain of TMEV results in high levels of virus propagation in the CNS, suggesting that prolonged survival of axons in Wld(S) mice favors virus spread. Thus, axonal degeneration might be a beneficial self-destruct mechanism that limits the spread of neurotropic viruses, in the case of less virulent virus infection. We hypothesize that neurons use 'built-in' self-destruct protection machinery (compartmental neurodegeneration) against neurotropic virus infection, since the CNS is an immunologically privileged site. Early induction of apoptosis in the neuronal cell body limits virus replication. Wallerian degeneration of the axon prevents axonal transport of virus. Dendritic and synaptic degeneration blocks virus transmission at synapses. Thus, the balance between neurodegeneration and virus propagation may be taken into account in the future design of neuroprotective therapy.

Regulatory role of CD1d in neurotropic virus infection

The GDVII strain of Theiler's murine encephalomyelitis virus (TMEV) causes an acute fatal polioencephalomyelitis in mice. Infection of susceptible mice with the DA strain of TMEV results in an acute polioencephalomyelitis followed by chronic immune-mediated demyelination with virus persistence in the central nervous system (CNS); DA virus infection is used as an animal model for multiple sclerosis. CD1d-restricted natural killer T (NKT) cells can contribute to viral clearance and regulation of autoimmune responses. To investigate the role of CD1d in TMEV infection, we first infected CD1d-deficient mice (CD1(-/-)) and wild-type BALB/c mice with GDVII virus. Wild-type mice were more resistant to virus than CD1(-/-) mice (50% lethal dose titers: wild-type mice, 10 PFU; CD1(-/-) mice, 1.6 PFU). Wild-type mice had fewer viral antigen-positive cells with greater inflammation in the CNS than CD1(-/-) mice. Second, an analysis of DA virus infection in CD1(-/-) mice was conducted. Although both wild-type and CD1(-/-) mice had similar clinical signs during the first 2 weeks after infection, CD1(-/-) mice had an increase in neurological deficits over those observed in wild-type mice at 3 to 5 weeks after infection. Although wild-type mice had no demyelination, 20 and 60% of CD1(-/-) mice developed demyelination at 3 and 5 weeks after infection, respectively. TMEV-specific lymphoproliferative responses, interleukin-4 (IL-4) production, and IL-4/gamma interferon ratios were higher in CD1(-/-) mice than in wild-type mice. Thus, CD1d-restricted NKT cells may play a protective role in TMEV-induced neurological disease by alteration of the cytokine profile and virus-specific immune responses.

TGF-beta1 suppresses T cell infiltration and VP2 puff B mutation enhances apoptosis in acute polioencephalitis induced by Theiler's virus

GDVII and DA strains of Theiler's murine encephalomyelitis virus (TMEV) differ in VP2 puff B. One week after GDVII virus infection, SJL/J mice had large numbers of TUNEL+ apoptotic cells with a relative lack of T cell infiltration in the brain. DA viruses with mutation in puff B induced higher levels of apoptosis than wild-type DA virus, but levels of inflammation in brains were similar between DA and DA virus mutants. The difference in inflammation among TMEVs could be due to TGF-beta1 expression that was seen only in GDVII virus infection and negatively correlated with CD3+ T cell infiltration.

Molecular mimicry in multiple sclerosis

One of the most common demyelinating central nervous system (CNS) diseases in humans is multiple sclerosis (MS). The disease can be very debilitating with vision loss, motor and sensory disturbances, and cognitive impairment. The clinical course may present as a relapsing-remitting disease course, a progressive disease course, or a combination thereof. The etiology of MS is unknown. Though many viruses have been shown to be associated with MS, no one virus has ever been demonstrated to be the cause of MS. In addition, MS is thought to have an autoimmune component. Molecular mimicry is one hypothesis put forth which could reconcile the diverse pathology and etiology of MS. Molecular mimicry occurs when peptides from pathogens share sequence or structural similarities with self-antigens. Infection with various pathogens, each with its individual molecular mimic to a CNS antigen, may explain the inability of investigators to link one specific virus to MS. Molecular mimicry may be mediated through human leukocyte antigen class I- and class II-restricted T cells and antibodies, which may explain the diversity in phenotype. Aspects of molecular mimicry will be discussed in relation to each of these immune system components. Examples of various molecular mimics will be discussed with a particular focus on the CNS and MS. Molecular mimicry alone may not be able to induce disease; priming of the immune system by infection with a pathogen that carries a molecular mimic to self may have to be followed by a later nonspecific immunologic challenge in order for disease to be initiated. Recent research into this priming and triggering of disease will be discussed in relation to an animal model for MS.

MMP-12, MMP-3, and TIMP-1 are markedly upregulated in chronic demyelinating theiler murine encephalomyelitis

Theiler murine encephalomyelitis (TME) represents a highly relevant viral model for multiple sclerosis. Matrix metalloproteinases (MMPs) degrade extracellular matrix molecules and are involved in demyelination processes. To elucidate their impact on demyelination in TME, spinal cords of TME virus (TMEV)-infected SJL/J mice were taken at 9 different time points postinfection (pi) ranging from 1 hour to 196 days pi and investigated for the expression of TMEV, MMP-2, -3, -7, -9, -10, -11, -12, -13, -14, -15, -24, and TIMP-1 to -4 by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). High TMEV RNA levels were detectable throughout the observation period using RT-qPCR. In addition, TMEV RNA was visualized within demyelinated lesions by in situ hybridization. MMP-3 mRNA was significantly upregulated at 1 day pi and again in the late phase of infection. TIMP-1 mRNA was significantly elevated throughout the observation period. MMP-12 mRNA was most prominently upregulated in the late phase of infection and MMP-12 protein was localized in intralesional microglia/macrophages and astrocytes by immunohistochemistry. In summary, in early TMEV infection, MMP-3 and TIMP-1 mRNA upregulation might be directly virus-induced, whereas persistent TMEV infection directly or indirectly stimulated MMP-12 production in microglia/macrophages and astrocytes and might account for ongoing demyelination in TME.

Leader (L) and L* proteins of Theiler's murine encephalomyelitis virus (TMEV) and their regulation of the virus' biological activities

Theiler's murine encephalomyelitis virus (TMEV) is divided into two subgroups on the basis of their different biological activities. GDVII subgroup strains produce fatal poliomyelitis in mice without virus persistence or demyelination. In contrast, TO subgroup strains induce demyelinating disease with virus persistence in the spinal cords of weanling mice. Two proteins, whose open reading frames are located in the N-terminus of the polyprotein, recently have been reported to be important for TMEV biological activities. One is leader (L) protein and is processed from the most N-terminus of the polyprotein; its function is still unknown. Although the homology of capsid proteins between DA (a representative strain of TO subgroup) and GDVII strains is over 94% at the amino acid level, that of L shows only 85%. Therefore, L is thought to be a key protein for the subgroup-specific biological activities of TMEV. Various studies have demonstrated that L plays important roles in the escape of virus from host immune defenses in the early stage of infection. The second protein is a 17–18 kDa protein, L*, which is synthesized out-of-frame with the polyprotein. Only TO subgroup strains produce L* since GDVII subgroup strains have an ACG rather than AUG at the initiation site and therefore do not synthesize L*. 'Loss and gain of function' experiments demonstrate that L* is essential for virus growth in macrophages, a target cell for TMEV persistence. L* also has been demonstrated to be necessary for TMEV persistence and demyelination. Further analysis of L and L* will help elucidate the pathomechanism(s) of TMEV-induced demyelinating disease.

Virus tropism, distribution, persistence and pathology in the corpus callosum of the Semliki Forest virus-infected mouse brain: a novel system to study virus-oligodendrocyte interactions

The temporal course of cellular pathology in virus-infected oligodendrocytes in vivo is not well defined. Here we study these events in the mouse brain using a novel system in which large numbers of oligodendrocytes can be reproducibly infected. In the mouse, following extraneural inoculation, the A7(74) strain of the alphavirus Semliki Forest virus (SFV) is efficiently neuroinvasive and central nervous system (CNS) infection leads to predominantly perivascular lesions of immune-mediated demyelination. This study demonstrates that direct intracerebral inoculation with SFV A7(74) or the SFV1 vector results in dramatic, selective and widespread infection of the major white matter tract of the brain, the corpus callosum. Mature oligodendrocytes are the predominant cell type infected. Subsequent events are complex; early virus-induced necrotic death of infected cells is followed by apoptotic death of adjacent apparently uninfected cells. A strong inflammatory response and considerable myelin loss are evident from 10 days and virus-positive cells are not observed after this time. In contrast, in athymic nu/nu mice, in the absence of T-cell responses, no inflammatory infiltrates are observed and virus-infected cells persist for over 30 days with extensive vacuolation but less demyelination. The change from an early destructive to a potentially persistent infection of oligodendrocytes is likely to reflect activation of innate immune responses. Activation of peripheral innate defences by inoculation of poly I : C prior to CNS virus infection abrogates the widespread corpus callosum infection. This widespread infection of the corpus callosum provides a novel in vivo system in which to study virus-oligodendrocyte interactions.

Sex-dependent effects of chronic restraint stress during early Theiler's virus infection on the subsequent demyelinating disease in CBA mice

Chronic restraint stress, administered during early infection with Theiler's virus, was found to exacerbate the acute CNS viral infection in male and female mice. During the subsequent demyelinating phase of disease (a model of multiple sclerosis), the effect of stress on disease progression was sex-dependent. Previously stressed male mice had less severe behavioral signs of the chronic phase, better rotarod performance and decreased inflammatory lesions of the spinal cord, while the opposite pattern was observed in females. In addition, mice in all groups developed autoantibodies to MBP, PLP139-151 and MOG33-55.

Antibody association with a novel model for primary progressive multiple sclerosis: induction of relapsing-remitting and progressive forms of EAE in H2s mouse strains

Multiple sclerosis (MS) can be divided into 4 clinical forms: relapsing-remitting (RR), primary progressive (PP), secondary progressive (SP), and progressive relapsing (PR). Since PP-MS is notably different from the other forms of MS, both clinically and pathologically, the question arises whether PP-MS is immunologically similar to the other forms. The pathogenesis of the PP-MS remains unclear, partly due to a lack of highly relevant animal models. Using an encephalitogenic peptide from myelin oligodendrocyte glycoprotein (MOG)92-106, we have established animal models that mimic different forms of MS in 2 strains of H-2s mice, SJL/J and A.SW. We induced experimental allergic encephalomyelitis (EAE) using MOG92-106 in the presence or absence of supplemental Bordetella pertussis (BP). Although, SJL/J mice developed RR-EAE whether BP was given or not, A.SW mice developed PP-EAE without BP and SP-EAE with BP. Histologically, SJL/J mice developed mild demyelinating disease with T cell infiltration, while A.SW mice developed large areas of plaque-like demyelination with immunoglobulin deposition and neutrophil infiltration, but with minimal T cell infiltration. In A.SW mice without BP, high titer serum anti-MOG antibody was detected and the anti-MOG IgG2a/IgG1 ratio correlated with survival times of mice. We hypothesized that, in A.SW mice, a Th2 response favors production of myelinotoxic antibodies, leading to progressive forms with early death. Our new models indicate that a single encephalitogen could induce either RR-, PP-, or SP- forms of demyelinating disease in hosts with immunologically different humoral immune responses.

Exacerbation of viral and autoimmune animal models for multiple sclerosis by bacterial DNA

Theiler's murine encephalomyelitis virus (TMEV) infection and relapsing-remitting experimental allergic encephalomyelitis (R-EAE) have been used to investigate the viral and autoimmune etiology of multiple sclerosis (MS), a possible Th1-type mediated disease. DNA immunization is a novel vaccination strategy in which few harmful effects have been reported. Bacterial DNA and oligodeoxynucleotides, which contain CpG motifs, have been reported to enhance immunostimulation. Our objectives were two-fold: first, to ascertain whether plasmid DNA, pCMV, which is widely used as a vector in DNA immunization studies, could exert immunostimulation in vitro; and second, to test if pCMV injection could modulate animal models for MS in vivo. We demonstrated that this bacterially derived DNA could induce interleukin (IL)-12, interferon (IFN)gamma, (Th1-promoting cytokines), and IL-6 production as well as activate NK cells. Following pCMV injections, SJL/J mice were infected with TMEV or challenged with encephalitogenic myelin proteolipid protein (PLP) peptides. pCMV injection exacerbated TMEV-induced demyelinating disease in a dose-dependent manner. Exacerbation of the disease did not correlate with the number of TMEV-antigen positive cells but did with an increase in anti-TMEV antibody. pCMV injection also enhanced R-EAE with increased IFNgamma and IL-6 responses. These results caution the use of DNA vaccination in MS patients and other possible Th1-mediated diseases.

Caspase-3 and -7 mediate apoptosis of human Chang's conjunctival cells induced by enterovirus 70

Enterovirus 70 (EV70) is the major etiological agent of acute hemorrhagic conjunctivitis (AHC). EV70 m.o.i.- (multiplicity of infection) and time-dependently induced apoptosis in human Chang's conjunctival (HCC) cells. UV- or heat-inactivated EV70 did not induce apoptosis. EV70-induced apoptosis was inhibited by cycloheximide and methoxysuccinyl-Ala-Ala-Pro-Val-chloromethylketone (MPCMK), but not actinomycin D and guanidine.HCl (although guanidine.HCl inhibited the apoptosis induced by EV70 infection at 0.5 PFU/cell for 18 h). EV70 infection induced activation of caspase-3 and -7 and degradation of the constitutively activated caspase-6. EV70-induced apoptotic DNA ladders and activated caspase-3 and -7, correlated with virus release. Caspase inhibitor IX (Z-VD-FMK) inhibited EV70-induced apoptosis and virus release, but not intracellular viral production. The results suggest that infectious virus and the syntheses of viral proteins especially EV70 proteases, but not viral genome RNA, are required for caspase-3 and -7-mediated EV70-induced apoptosis, and that apoptosis through cell lysis promotes EV70 release from HCC cells.

Inhibitory activity of bovine lactoferrin against echovirus induced programmed cell death in vitro

Lactoferrin is a glycoprotein and plays an important role in defence against pathogens. Although the antiviral activity of lactoferrin is one of the major biological functions of such protein, the mechanism of action is still under debate. The effect of lactoferrin on echovirus 6 infection in vitro was analysed and results showed that (i) cells infected with echovirus 6, died as a result of apoptosis and that (ii) programmed cell death was inhibited by lactoferrin treatment. In this report, we demonstrate that lactoferrin can exert its anti-enteroviral activity by preventing viral-induced apoptosis.