Pathogenesis of acute and chronic central nervous system infection with variants of mouse hepatitis virus, strain JHM

Host response to Aplysia Abyssovirus 1 in nervous system and gill

The California sea hare (Aplysia californica) is a model for age associated cognitive decline. Recent researched identified a novel nidovirus, Aplysia Abyssovirus 1, with broad tropism enriched in the Aplysia nervous system. This virus is ubiquitous in wild and maricultured, young and old animals without obvious pathology. Here we re-evaluated gene expression data from several previous studies to investigate differential expression in the nervous system and gill in response to virus and aging as well as the mutational spectrum observed in the viral sequences obtained from these datasets. Viral load and age were highly correlated, indicating persistent infection. Upregulated genes in response to virus were enriched for immune genes and signatures of ER and proteostatic stress, while downregulated genes were enriched for mitochondrial metabolism. Differential expression with respect to age suggested increased iron accumulation and decreased glycolysis, fatty acid metabolism, and proteasome function. Interaction of gene expression trends associated with viral infection and aging suggest that viral infection likely plays a role in aging in the Aplysia nervous system. Mutation analysis of viral RNA identified signatures suggesting ADAR and AID/APOBEC like deaminase act as part of Aplysia anti-viral defense.

Neurotropic murine coronavirus mediated demyelination: Factors dampening pathogenesis

Virus infections and autoimmune responses are implicated as primary triggers of demyelinating diseases. Specifically, the association of Epstein-Barr virus (EBV) infection with development of multiple sclerosis (MS) has re-ignited an interest in virus induced autoimmune responses to CNS antigens. Nevertheless, demyelination may also be caused by immune mediated bystander pathology in an attempt to control direct infection in the CNS. Tissue damage as a result of anti-viral responses or low level viral persistence may lead to immune activation manifesting in demyelinating lesions, axonal damage and clinical symptoms. This review focuses on the neurotropic mouse coronavirus induced demyelination model to highlight how immune responses activated during the acute phase pave the way to dampen pathology and promote repair. We specifically discuss the role of immune dampening factors programmed cell death ligand 1 (PD-L1) and interleukin (IL)-10, as well as microglia and triggering receptor expressed on myeloid cells 2 (Trem2), in limiting demyelination independent of viral persistence.

Cystatin F attenuates neuroinflammation and demyelination following murine coronavirus infection of the central nervous system

BACKGROUND

Cystatin F is a secreted lysosomal cysteine protease inhibitor that has been implicated in affecting the severity of demyelination and enhancing remyelination in pre-clinical models of immune-mediated demyelination. How cystatin F impacts neurologic disease severity following viral infection of the central nervous system (CNS) has not been well characterized and was the focus of this study. We used cystatin F null-mutant mice (Cst7-/-) with a well-established model of murine coronavirus-induced neurologic disease to evaluate the contributions of cystatin F in host defense, demyelination and remyelination.

METHODS

Wildtype controls and Cst7-/- mice were intracranially (i.c.) infected with a sublethal dose of the neurotropic JHM strain of mouse hepatitis virus (JHMV), with disease progression and survival monitored daily. Viral plaque assays and qPCR were used to assess viral levels in CNS. Immune cell infiltration into the CNS and immune cell activation were determined by flow cytometry and 10X genomics chromium 3' single cell RNA sequencing (scRNA-seq). Spinal cord demyelination was determined by luxol fast blue (LFB) and Hematoxylin/Eosin (H&E) staining and axonal damage assessed by immunohistochemical staining for SMI-32. Remyelination was evaluated by electron microscopy (EM) and calculation of g-ratios.

RESULTS

JHMV-infected Cst7-/- mice were able to control viral replication within the CNS, indicating that cystatin F is not essential for an effective Th1 anti-viral immune response. Infiltration of T cells into the spinal cords of JHMV-infected Cst7-/- mice was increased compared to infected controls, and this correlated with increased axonal damage and demyelination associated with impaired remyelination. Single-cell RNA-seq of CD45 + cells enriched from spinal cords of infected Cst7-/- and control mice revealed enhanced expression of transcripts encoding T cell chemoattractants, Cxcl9 and Cxcl10, combined with elevated expression of interferon-g (Ifng) and perforin (Prf1) transcripts in CD8 + T cells from Cst7-/- mice compared to controls.

CONCLUSIONS

Cystatin F is not required for immune-mediated control of JHMV replication within the CNS. However, JHMV-infected Cst7-/- mice exhibited more severe clinical disease associated with increased demyelination and impaired remyelination. The increase in disease severity was associated with elevated expression of T cell chemoattractant chemokines, concurrent with increased neuroinflammation. These findings support the idea that cystatin F influences expression of proinflammatory gene expression impacting neuroinflammation, T cell activation and/or glia cell responses ultimately impacting neuroinflammation and neurologic disease.

The Impact of Innate Components on Viral Pathogenesis in the Neurotropic Coronavirus Encephalomyelitis Mouse Model

Recognition of viruses invading the central nervous system (CNS) by pattern recognition receptors (PRRs) is crucial to elicit early innate responses that stem dissemination. These innate responses comprise both type I interferon (IFN-I)-mediated defenses as well as signals recruiting leukocytes to control the infection. Focusing on insights from the neurotropic mouse CoV model, this review discusses how early IFN-I, fibroblast, and myeloid signals can influence protective anti-viral adaptive responses. Emphasis is placed on three main areas: the importance of coordinating the distinct capacities of resident CNS cells to induce and respond to IFN-I, the effects of select IFN-stimulated genes (ISGs) on host immune responses versus viral control, and the contribution of fibroblast activation and myeloid cells in aiding the access of T cells to the parenchyma. By unraveling how the dysregulation of early innate components influences adaptive immunity and viral control, this review illustrates the combined effort of resident CNS cells to achieve viral control.

Ablation of microglia following infection of the central nervous system with a neurotropic murine coronavirus infection leads to increased demyelination and impaired remyelination

Intracranial inoculation of susceptible mice with a glial-tropic strain of mouse hepatitis virus (JHMV), a murine coronavirus, results in an acute encephalomyelitis followed by viral persistence in white matter tracts accompanied by chronic neuroinflammation and demyelination. Microglia are the resident immune cell of the central nervous system (CNS) and are considered important in regulating events associated with neuroinflammation as well as influencing both white matter damage and remyelination. To better understand mechanisms by which microglia contribute to these immune-mediated events, JHMV-infected mice with established demyelination were treated with the small molecular inhibitor of colony stimulating factor 1 receptor (CSF1R), PLX5622, to deplete microglia. Treatment with PLX5622 did not affect viral replication within the CNS yet the severity of demyelination was increased and remyelination impaired compared to control mice. Gene expression analysis revealed that targeting microglia resulted in altered expression of genes associated with immune cell activation and phagocytosis of myelin debris. These findings indicate that microglia are not critical in viral surveillance in persistently JHMV-infected mice yet restrict white matter damage and remyelination, in part, by influencing phagocytosis of myelin debris.

Connecting Neuroinflammation and Neurodegeneration in Multiple Sclerosis: Are Oligodendrocyte Precursor Cells a Nexus of Disease?

The pathology in neurodegenerative diseases is often accompanied by inflammation. It is well-known that many cells within the central nervous system (CNS) also contribute to ongoing neuroinflammation, which can promote neurodegeneration. Multiple sclerosis (MS) is both an inflammatory and neurodegenerative disease in which there is a complex interplay between resident CNS cells to mediate myelin and axonal damage, and this communication network can vary depending on the subtype and chronicity of disease. Oligodendrocytes, the myelinating cell of the CNS, and their precursors, oligodendrocyte precursor cells (OPCs), are often thought of as the targets of autoimmune pathology during MS and in several animal models of MS; however, there is emerging evidence that OPCs actively contribute to inflammation that directly and indirectly contributes to neurodegeneration. Here we discuss several contributors to MS disease progression starting with lesion pathology and murine models amenable to studying particular aspects of disease. We then review how OPCs themselves can play an active role in promoting neuroinflammation and neurodegeneration, and how other resident CNS cells including microglia, astrocytes, and neurons can impact OPC function. Further, we outline the very complex and pleiotropic role(s) of several inflammatory cytokines and other secreted factors classically described as solely deleterious during MS and its animal models, but in fact, have many neuroprotective functions and promote a return to homeostasis, in part via modulation of OPC function. Finally, since MS affects patients from the onset of disease throughout their lifespan, we discuss the impact of aging on OPC function and CNS recovery. It is becoming clear that OPCs are not simply a bystander during MS progression and uncovering the active roles they play during different stages of disease will help uncover potential new avenues for therapeutic intervention.

The Role of Extracellular Vesicles in Demyelination of the Central Nervous System

It is being increasingly demonstrated that extracellular vesicles (EVs) are deeply involved in the physiology of the central nervous system (CNS). Processes such as synaptic activity, neuron-glia communication, myelination and immune response are modulated by EVs. Likewise, these vesicles may participate in many pathological processes, both as triggers of disease or, on the contrary, as mechanisms of repair. EVs play relevant roles in neurodegenerative disorders such as Alzheimer’s or Parkinson’s diseases, in viral infections of the CNS and in demyelinating pathologies such as multiple sclerosis (MS). This review describes the involvement of these membrane vesicles in major demyelinating diseases, including MS, neuromyelitis optica, progressive multifocal leukoencephalopathy and demyelination associated to herpesviruses.

Environmental Nanoparticles, SARS-CoV-2 Brain Involvement, and Potential Acceleration of Alzheimer's and Parkinson's Diseases in Young Urbanites Exposed to Air Pollution

Alzheimer's and Parkinson's diseases (AD, PD) have a pediatric and young adult onset in Metropolitan Mexico City (MMC). The SARS-CoV-2 neurotropic RNA virus is triggering neurological complications and deep concern regarding acceleration of neuroinflammatory and neurodegenerative processes already in progress. This review, based on our MMC experience, will discuss two major issues: 1) why residents chronically exposed to air pollution are likely to be more susceptible to SARS-CoV-2 systemic and brain effects and 2) why young people with AD and PD already in progress will accelerate neurodegenerative processes. Secondary mental consequences of social distancing and isolation, fear, financial insecurity, violence, poor health support, and lack of understanding of the complex crisis are expected in MMC residents infected or free of SARS-CoV-2. MMC residents with pre-SARS-CoV-2 accumulation of misfolded proteins diagnostic of AD and PD and metal-rich, magnetic nanoparticles damaging key neural organelles are an ideal host for neurotropic SARS-CoV-2 RNA virus invading the body through the same portals damaged by nanoparticles: nasal olfactory epithelium, the gastrointestinal tract, and the alveolar-capillary portal. We urgently need MMC multicenter retrospective-prospective neurological and psychiatric population follow-up and intervention strategies in place in case of acceleration of neurodegenerative processes, increased risk of suicide, and mental disease worsening. Identification of vulnerable populations and continuous effort to lower air pollution ought to be critical steps.

Single-Cell RNA Sequencing Reveals the Diversity of the Immunological Landscape following Central Nervous System Infection by a Murine Coronavirus

Intracranial (i.c.) infection of susceptible C57BL/6 mice with the neurotropic JHM strain of mouse hepatitis virus (JHMV) (a member of the Coronaviridae family) results in acute encephalomyelitis and viral persistence associated with an immune-mediated demyelinating disease. The present study was undertaken to better understand the molecular pathways evoked during innate and adaptive immune responses as well as the chronic demyelinating stage of disease in response to JHMV infection of the central nervous system (CNS). Using single-cell RNA sequencing analysis (scRNAseq) on flow-sorted CD45-positive (CD45+) cells enriched from brains and spinal cords of experimental mice, we demonstrate the heterogeneity of the immune response as determined by the presence of unique molecular signatures and pathways involved in effective antiviral host defense. Furthermore, we identify potential genes involved in contributing to demyelination as well as remyelination being expressed by both microglia and macrophages. Collectively, these findings emphasize the diversity of the immune responses and molecular networks at defined stages following viral infection of the CNS.IMPORTANCE Understanding the immunological mechanisms contributing to both host defense and disease following viral infection of the CNS is of critical importance given the increasing number of viruses that are capable of infecting and replicating within the nervous system. With this in mind, the present study was undertaken to evaluate the molecular signatures of immune cells within the CNS at defined times following infection with a neuroadapted murine coronavirus using scRNAseq. This approach has revealed that the immunological landscape is diverse, with numerous immune cell subsets expressing distinct mRNA expression profiles that are, in part, dictated by the stage of infection. In addition, these findings reveal new insight into cellular pathways contributing to control of viral replication as well as to neurologic disease.

Microglia influence host defense, disease, and repair following murine coronavirus infection of the central nervous system

The present study examines functional contributions of microglia in host defense, demyelination, and remyelination following infection of susceptible mice with a neurotropic coronavirus. Treatment with PLX5622, an inhibitor of colony stimulating factor 1 receptor (CSF1R) that efficiently depletes microglia, prior to infection of the central nervous system (CNS) with the neurotropic JHM strain of mouse hepatitis virus (JHMV) resulted in increased mortality compared with control mice that correlated with impaired control of viral replication. Single cell RNA sequencing (scRNASeq) of CD45+ cells isolated from the CNS revealed that PLX5622 treatment resulted in muted CD4+ T cell activation profile that was associated with decreased expression of transcripts encoding MHC class II and CD86 in macrophages but not dendritic cells. Evaluation of spinal cord demyelination revealed a marked increase in white matter damage in PLX5622-treated mice that corresponded with elevated expression of transcripts encoding disease-associated proteins Osteopontin (Spp1), Apolipoprotein E (Apoe), and Triggering receptor expressed on myeloid cells 2 (Trem2) that were enriched within macrophages. In addition, PLX5622 treatment dampened expression of Cystatin F (Cst7), Insulin growth factor 1 (Igf1), and lipoprotein lipase (Lpl) within macrophage populations which have been implicated in promoting repair of damaged nerve tissue and this was associated with impaired remyelination. Collectively, these findings argue that microglia tailor the CNS microenvironment to enhance control of coronavirus replication as well as dampen the severity of demyelination and influence repair.

Fine Tuning the Cytokine Storm by IFN and IL-10 Following Neurotropic Coronavirus Encephalomyelitis

The central nervous system (CNS) is vulnerable to several viral infections including herpes viruses, arboviruses and HIV to name a few. While a rapid and effective immune response is essential to limit viral spread and mortality, this anti-viral response needs to be tightly regulated in order to limit immune mediated tissue damage. This balance between effective virus control with limited pathology is especially important due to the highly specialized functions and limited regenerative capacity of neurons, which can be targets of direct virus cytolysis or bystander damage. CNS infection with the neurotropic strain of mouse hepatitis virus (MHV) induces an acute encephalomyelitis associated with focal areas of demyelination, which is sustained during viral persistence. Both innate and adaptive immune cells work in coordination to control virus replication. While type I interferons are essential to limit virus spread associated with early mortality, perforin, and interferon-γ promote further virus clearance in astrocytes/microglia and oligodendrocytes, respectively. Effective control of virus replication is nonetheless associated with tissue damage, characterized by demyelinating lesions. Interestingly, the anti-inflammatory cytokine IL-10 limits expansion of tissue lesions during chronic infection without affecting viral persistence. Thus, effective coordination of pro- and anti-inflammatory cytokines is essential during MHV induced encephalomyelitis in order to protect the host against viral infection at a limited cost.

Viral-induced suppression of self-reactive T cells: Lessons from neurotropic coronavirus-induced demyelination

Genetic and environmental factors, i.e. infections, have been proposed to contribute to disease induction and relapsing events in multiple sclerosis (MS), an autoimmune demyelinating disease of the central nervous system (CNS). While research has mainly focused on virus associated autoimmune activation, less is known about prevention of autoimmunity, especially following resolving infections associated with CNS tissue damage. This review discusses novel insights on control of self-reactive (SR) T cells activated during neurotropic coronavirus-induced demyelination. A new concept is introduced that SR T cells can be dampened by distinct regulatory mechanisms in the periphery and the CNS, thereby preventing autoimmune disease.

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Virus-induced demyelination activates myelin specific T cells.

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Virus-induced regulatory mechanisms limit pathogenic self-reactive R CD4 T cells.

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Self-reactive CD4 T cells are controlled by distinct mechanisms in the CLN and CNS.

Pharmacological approaches to intervention in hypomyelinating and demyelinating white matter pathology

White matter disease afflicts both developing and mature central nervous systems. Both cell intrinsic and extrinsic dysregulation result in profound changes in cell survival, axonal metabolism and functional performance. Experimental models of developmental white matter (WM) injury and demyelination have not only delineated mechanisms of signaling and inflammation, but have also paved the way for the discovery of pharmacological approaches to intervention. These reagents have been shown to enhance protection of the mature oligodendrocyte cell, accelerate progenitor cell recruitment and/or differentiation, or attenuate pathological stimuli arising from the inflammatory response to injury. Here we highlight reports of studies in the CNS in which compounds, namely peptides, hormones, and small molecule agonists/antagonists, have been used in experimental animal models of demyelination and neonatal brain injury that affect aspects of excitotoxicity, oligodendrocyte development and survival, and progenitor cell function, and which have been demonstrated to attenuate damage and improve WM protection in experimental models of injury. The molecular targets of these agents include growth factor and neurotransmitter receptors, morphogens and their signaling components, nuclear receptors, as well as the processes of iron transport and actin binding. By surveying the current evidence in non-immune targets of both the immature and mature WM, we aim to better understand pharmacological approaches modulating endogenous oligodendroglia that show potential for success in the contexts of developmental and adult WM pathology. This article is part of the Special Issue entitled 'Oligodendrocytes in Health and Disease'.

MicroRNA-155 enhances T cell trafficking and antiviral effector function in a model of coronavirus-induced neurologic disease

BACKGROUND

MicroRNAs (miRNAs) are noncoding RNAs that modulate cellular gene expression, primarily at the post-transcriptional level. We sought to examine the functional role of miR-155 in a model of viral-induced neuroinflammation.

METHODS

Acute encephalomyelitis and immune-mediated demyelination were induced by intracranial injection with the neurotropic JHM strain of mouse hepatitis virus (JHMV) into C57BL/6 miR-155 (+/+) wildtype (WT) mice or miR-155 (-/-) mice. Morbidity and mortality, viral load and immune cell accumulation in the CNS, and spinal cord demyelination were assessed at defined points post-infection. T cells harvested from infected mice were used to examine cytolytic activity, cytokine activity, and expression of certain chemokine receptors. To determine the impact of miR-155 on trafficking, T cells from infected WT or miR-155 (-/-) mice were adoptively transferred into RAG1 (-/-) mice, and T cell accumulation into the CNS was assessed using flow cytometry. Statistical significance was determined using the Mantel-Cox log-rank test or Student's T tests.

RESULTS

Compared to WT mice, JHMV-infected miR-155 (-/-) mice developed exacerbated disease concomitant with increased morbidity/mortality and an inability to control viral replication within the CNS. In corroboration with increased susceptibility to disease, miR-155 (-/-) mice had diminished CD8(+) T cell responses in terms of numbers, cytolytic activity, IFN-γ secretion, and homing to the CNS that corresponded with reduced expression of the chemokine receptor CXCR3. Both IFN-γ secretion and trafficking were impaired in miR-155 (-/-) , virus-specific CD4(+) T cells; however, expression of the chemokine homing receptors analyzed on CD4(+) cells was not affected. Except for very early during infection, there were not significant differences in macrophage infiltration into the CNS between WT and miR-155 (-/-) JHMV-infected mice, and the severity of demyelination was similar at 14 days p.i. between WT and miR-155 (-/-) JHMV-infected mice.

CONCLUSIONS

These findings support a novel role for miR-155 in host defense in a model of viral-induced encephalomyelitis. Specifically, miR-155 enhances antiviral T cell responses including cytokine secretion, cytolytic activity, and homing to the CNS in response to viral infection. Further, miR-155 can play either a host-protective or host-damaging role during neuroinflammation depending on the disease trigger.

Self-reactive CD4(+) T cells activated during viral-induced demyelination do not prevent clinical recovery

Background

Microbial infections have been implicated in initiating and enhancing severity of autoimmune diseases including the demyelinating disease multiple sclerosis (MS). Nevertheless, the incidence of both acute and persisting viral infections without evidence of autoimmune sequelae suggests that this process is well controlled. The conditions promoting or stemming self-reactive (SR) T cells following viral-induced tissue damage thus need to be better defined. Using a non-fatal viral mouse model of encephalomyelitis associated with demyelination and disability, yet ultimate clinical improvement, this study set out to monitor uptake and presentation of endogenous myelin antigens, as well as induction and fate of SR T cells.

Methods

Activation and central nervous system (CNS) recruitment of myelin-specific CD4 T cells was analyzed by flow cytometry during encephalomyelitis induced by a glia tropic murine coronavirus. Potential antigen-presenting cells (APC) ingesting myelin were characterized by flow cytometry and their ability to activate SR T cells tested by co-culture with carboxyfluorescein succinimidyl ester (CFSE)-labeled myelin-specific CD4 T cells. Endogenous SR T cell kinetics was analyzed within both cervical lymph nodes and CNS by Enzyme-Linked ImmunoSpot (ELISPOT) following viral infection.

Results

The data demonstrate the presence of APC capable of activating SR T cells in both draining lymph nodes and the CNS temporally correlating with overt demyelination. While both the CNS-infiltrating myeloid population and microglia ingested myelin, only CNS-infiltrating APC were capable of presenting endogenous myelin antigen to SR T cells ex vivo. Finally, SR T cell activation from the endogenous T cell repertoire was most notable when infectious virus was controlled and paralleled myelin damage. Although SR T cell accumulation peaked in the persistently infected CNS during maximal demyelination, they were not preferentially retained. Their gradual decline, despite ongoing demyelination, suggested minimal re-stimulation and pathogenic function in vivo consistent with the lack of autoimmune symptoms.

Conclusions

The results demonstrate the potential for CNS tissue destruction to induce and recruit SR T cells to the injury site and support a host suppressive mechanism limiting development of autoimmunity.

Optic Neuritis: A Model for the Immuno-pathogenesis of Central Nervous System Inflammatory Demyelinating Diseases

Evidence for the tenuous regulation between the immune system and central nervous system (CNS) can be found with examples of interaction between these organ systems gone awry. Multiple sclerosis (MS) is the prototypical inflammatory disease of the CNS and is characterized by widely distributed inflammatory demyelinating plaques that can involve the brain, spinal cord and/or optic nerves. Optic neuritis (ON), inflammatory injury of the optic nerve that frequently occurs in patients with MS, has been the focus of intense study in part given the readily accessible nature of clinical outcome measures. Exploring the clinical and pathological features of ON in relation to other inflammatory demyelinating conditions of the CNS, namely MS and neuromyelitis optica, provides an opportunity to glean common and distinct mechanisms of disease. Emerging data from clinical studies along with various animal models involving ON implicate innate and adaptive immune responses directed at glial targets, including myelin oligodendrocyte glycoprotein and aquaporin 4. Resolution of inflammation in ON is commonly observed both clinically and experimentally, but persistent nerve injury is also one emerging hallmark of ON. One hypothesis seeking evaluation is that, in comparison to other sites targeted in MS, the optic nerve is a highly specialized target within the CNS predisposing to unique immunologic processes that generate ON. Overall, ON serves as a highly relevant entity for understanding the pathogenesis of other CNS demyelinating conditions, most notably MS.

Promoting remyelination: utilizing a viral model of demyelination to assess cell-based therapies

Multiple sclerosis (MS) is a chronic inflammatory disease of the CNS. While a broad range of therapeutics effectively reduce the incidence of focal white matter inflammation and plaque formation for patients with relapse-remitting forms of MS, a challenge within the field is to develop therapies that allow for axonal protection and remyelination. In the last decade, growing interest has focused on utilizing neural precursor cells (NPCs) to promote remyelination. To understand how NPCs function in chronic demyelinating environments, several excellent pre-clinical mouse models have been developed. One well accepted model is infection of susceptible mice with neurotropic variants of mouse hepatitis virus (MHV) that undergo chronic demyelination exhibiting clinical and histopathologic similarities to MS patients. Combined with the possibility that an environmental agent such as a virus could trigger MS, the MHV model of demyelination presents a relevant mouse model to assess the therapeutic potential of NPCs transplanted into an environment in which inflammatory-mediated demyelination is established.

Distinct Immune Responses in Resistant and Susceptible Strains of Mice during Neurovirulent Alphavirus Encephalomyelitis

Susceptibility to alphavirus encephalomyelitis is dependent on a variety of factors, including the genetic background of the host. Neuroadapted Sindbis virus (NSV) causes uniformly fatal disease in adult C57BL/6 (B6) mice, but adult BALB/c (Bc) mice recover from infection. In B6 mice, fatal encephalomyelitis is immune mediated rather than a direct result of virus infection. To identify the immunological determinants of host susceptibility to fatal NSV-induced encephalomyelitis, we compared virus titers and immune responses in adult B6 and Bc mice infected intranasally with NSV. B6 mice had higher levels of virus replication, higher levels of type I interferon (IFN), and slower virus clearance than did Bc mice. B6 mice had more neuronal apoptosis, more severe neurologic disease, and higher mortality than Bc mice. B6 mice had more infiltration of inflammatory cells and higher levels of IL1b, IL-6, TNFa, Csf2, and CCL2 mRNAs and interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-α), IFN-γ, and C-C motif ligand 2 (CCL2) protein in brains than Bc mice. However, Bc mice had more brain antibody at day 7 and a higher percentage of CD4(+) T cells. CD4(+) T cells in the brains of Bc mice included fewer Th17 cells and more regulatory T cells (Tregs) producing IL-10 than B6 mice, accompanied by higher levels of Il2 and Cxcl10 mRNAs. In the absence of IL-10, resistant Bc mice became susceptible to fatal encephalomyelitis after NSV infection. These studies demonstrate the importance of the immune response and its regulation in determining host survival during alphavirus encephalomyelitis.

IMPORTANCE

Mosquito-borne alphavirus infections are an important cause of encephalomyelitis in humans. The severity of disease is dependent both on the strain of the virus and on the age and genetic background of the host. A neurovirulent strain of Sindbis virus causes immune-mediated fatal encephalomyelitis in adult C57BL/6 mice but not in BALB/c mice. To determine the host-dependent immunological mechanisms underlying the differences in susceptibility between these two strains of mice, we compared their immune responses to infection. Resistance to fatal disease in BALB/c mice was associated with better antibody responses, more-rapid virus clearance, fewer Th17 cells, and more-potent regulatory T cell responses than occurred in susceptible C57BL/6 mice. In the absence of interleukin-10, a component of the regulatory immune response, resistant mice became susceptible to lethal disease. This study demonstrates the importance of the immune response and its regulation for host survival during alphavirus encephalomyelitis.

Two-photon imaging of remyelination of spinal cord axons by engrafted neural precursor cells in a viral model of multiple sclerosis

Neural precursor cells (NPCs) offer a promising approach for treating demyelinating diseases. However, the cellular dynamics that underlie transplanted NPC-mediated remyelination have not been described. Using two-photon imaging of a newly developed ventral spinal cord preparation and a viral model of demyelination, we describe the motility and intercellular interactions of transplanted mouse NPCs expressing green fluorescent protein (GFP) with damaged axons expressing yellow fluorescent protein (YFP). Our findings reveal focal axonal degeneration that occurs in the ventral side of the spinal cord within 1 wk following intracranial instillation with the neurotropic JHM strain of mouse hepatitis virus (JHMV). Axonal damage precedes extensive demyelination and is characterized by swelling along the length of the axon, loss of YFP signal, and transected appearance. NPCs engrafted into spinal cords of JHMV-infected mice exhibited diminished migration velocities and increased proliferation compared with transplanted cells in noninfected mice. NPCs preferentially accumulated within areas of axonal damage, initiated direct contact with axons, and subsequently expressed the myelin proteolipid protein gene, initiating remyelination. These findings indicate that NPCs transplanted into an inflammatory demyelinating microenvironment participate directly in therapeutic outcome through the wrapping of myelin around damaged neurons.

Human neural precursor cells promote neurologic recovery in a viral model of multiple sclerosis

Using a viral model of the demyelinating disease multiple sclerosis (MS), we show that intraspinal transplantation of human embryonic stem cell-derived neural precursor cells (hNPCs) results in sustained clinical recovery, although hNPCs were not detectable beyond day 8 posttransplantation. Improved motor skills were associated with a reduction in neuroinflammation, decreased demyelination, and enhanced remyelination. Evidence indicates that the reduced neuroinflammation is correlated with an increased number of CD4⁺CD25⁺FOXP3⁺ regulatory T cells (Tregs) within the spinal cords. Coculture of hNPCs with activated T cells resulted in reduced T cell proliferation and increased Treg numbers. The hNPCs acted, in part, through secretion of TGF-β1 and TGF-β2. These findings indicate that the transient presence of hNPCs transplanted in an animal model of MS has powerful immunomodulatory effects and mediates recovery. Further investigation of the restorative effects of hNPC transplantation may aid in the development of clinically relevant MS treatments.

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Spinal cord transplantation of hNPCs results in recovery in a viral model of MS

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hNPC-mediated recovery occurs in the absence of engrafted cells

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hNPCs are immunomodulatory through increasing the frequency of Tregs in the CNS

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hNPCs increase Treg frequency via a TGF-β1- and TGF-β2-dependent pathway

Protective role of Toll-like Receptor 3-induced type I interferon in murine coronavirus infection of macrophages

Toll-like Receptors (TLRs) sense viral infections and induce production of type I interferons (IFNs), other cytokines, and chemokines. Viral recognition by TLRs and other pattern recognition receptors (PRRs) has been proven to be cell-type specific. Triggering of TLRs with selected ligands can be beneficial against some viral infections. Macrophages are antigen-presenting cells that express TLRs and have a key role in the innate and adaptive immunity against viruses. Coronaviruses (CoVs) are single-stranded, positive-sense RNA viruses that cause acute and chronic infections and can productively infect macrophages. Investigation of the interplay between CoVs and PRRs is in its infancy. We assessed the effect of triggering TLR2, TLR3, TLR4, and TLR7 with selected ligands on the susceptibility of the J774A.1 macrophage cell line to infection with murine coronavirus (mouse hepatitis virus, [MHV]). Stimulation of TLR2, TLR4, or TLR7 did not affect MHV production. In contrast, pre-stimulation of TLR3 with polyinosinic-polycytidylic acid (poly I:C) hindered MHV infection through induction of IFN-β in macrophages. We demonstrate that activation of TLR3 with the synthetic ligand poly I:C mediates antiviral immunity that diminishes (MHV-A59) or suppresses (MHV-JHM, MHV-3) virus production in macrophages.

Highly activated cytotoxic CD8 T cells express protective IL-10 at the peak of coronavirus-induced encephalitis

Acute viral encephalitis requires rapid pathogen elimination without significant bystander tissue damage. In this article, we show that IL-10, a potent anti-inflammatory cytokine, is produced transiently at the peak of infection by CD8 T cells in the brains of coronavirus-infected mice. IL-10(+)CD8 and IL-10(-)CD8 T cells interconvert during acute disease, possibly based on recent Ag exposure. Strikingly, IL-10(+)CD8 T cells were more highly activated and cytolytic than IL-10(-)CD8 T cells, expressing greater levels of proinflammatory cytokines and chemokines, as well as cytotoxic proteins. Even though these cells are highly proinflammatory, IL-10 expressed by these cells was functional. Furthermore, IL-10 produced by CD8 T cells diminished disease severity in mice with coronavirus-induced acute encephalitis, suggesting a self-regulatory mechanism that minimizes immunopathological changes.

The human microbiome in multiple sclerosis: pathogenic or protective constituents?

The human microbiome is comprised of commensal and pathogenic microorganisms, which exert diverse effects in close proximity to the site of intection as well as in remote tissues through immune-mediated mechanisms. Multiple infectious agents have been implicated in the pathogenesis of multiple sclerosis (MS) with variable findings depending on the agent, techniques, and disease phenotype. Herein, the contributions of individual infectious agents to MS and their effects on the immune and nervous systems are reviewed, focusing on herpes viruses, coronaviruses, retroviruses, and synchronic infections. While infectious agents are often assumed to be pathogenic, their effects might also be beneficial to the host in the long-term, depending on age and the type of immunogen/pathogen exposure, as proposed by the hygiene hypothesis. The human microbiome has potential impact on future diagnostic and therapeutic issues in MS.

Regulatory T cells inhibit T cell proliferation and decrease demyelination in mice chronically infected with a coronavirus

Mice infected with the neurotropic JHM strain of mouse hepatitis virus (JHMV) develop acute and chronic demyelinating diseases with histopathological similarities to multiple sclerosis. The process of demyelination is largely immune-mediated, as immunodeficient mice (RAG1(-/-) mice) do not develop demyelination upon infection; however, demyelination develops if these mice are reconstituted with either JHMV-immune CD4 or CD8 T cells. Because myelin destruction is a consequence of the inflammatory response associated with virus clearance, we reasoned that decreasing the amount of inflammation would diminish clinical disease and demyelination. Given that regulatory T cells (Tregs) have potent anti-inflammatory effects, we adoptively transferred Tregs into infected C57BL/6 and RAG1(-/-) mice. In both instances, transfer of Tregs decreased weight loss, clinical scores, and demyelination. Transferred Tregs were not detected in the CNS of infected RAG1(-/-) mice, but rather appeared to mediate their effects in the draining cervical lymph nodes. We show that Tregs dampen the inflammatory response mediated by transferred JHMV-immune splenocytes in infected RAG1(-/-) mice by decreasing T cell proliferation, dendritic cell activation, and proinflammatory cytokine/chemokine production, without inducing apoptosis. By extension, decreasing inflammation, whether by Treg transfer or by otherwise enhancing the anti-inflammatory milieu, could contribute to improved clinical outcomes in patients with virus-induced demyelination.

Central neuroinvasion and demyelination by inflammatory macrophages after peripheral virus infection is controlled by SHP-1

SHP-1 is a protein tyrosine phosphatase that negatively regulates cytokine signaling and inflammatory gene expression. Mice genetically lacking SHP-1 (me/me) display severe inflammatory demyelinating disease following intracranial inoculation with the BeAn strain of Theiler's murine encephalomyelitis virus (TMEV) compared to infected wild-type mice. Furthermore, SHP-1-deficient mice show a profound and predominant infiltration of blood-derived macrophages into the CNS following intracerebral injection of TMEV, and these macrophages are concentrated in areas of demyelination in brain and spinal cord. In the present study we investigated the role of SHP-1 in controlling CNS inflammatory demyelination following a peripheral instead of an intracerebral inoculation of TMEV. Surprisingly, we found that while wild-type mice were entirely refractory to intraperitoneal (IP) infection by TMEV, in agreement with previous studies, all SHP-1-deficient mice displayed profound macrophage neuroinvasion and macrophage-mediated inflammatory demyelination. Moreover, SHP-1 deficiency led to increased expression of inflammatory molecules in macrophages, serum, and CNS following IP infection with TMEV. Importantly, pharmacological depletion of peripheral macrophages significantly decreased both paralysis and CNS viral loads in SHP-1-deficient mice. In addition, peripheral MCP-1 neutralization attenuated disease severity, decreased macrophage infiltration into the CNS, and decreased monocyte numbers in the blood of SHP-1-deficient mice, implicating MCP-1 as an important mediator of monocyte migration between multiple tissues. These results demonstrate that peripheral TMEV infection results in a unique evolution of macrophage-mediated demyelination in SHP-1-deficient mice, implicating SHP-1 in the control of neuroinvasion of inflammatory macrophages and neurotropic viruses into the CNS.

Achieving a golden mean: mechanisms by which coronaviruses ensure synthesis of the correct stoichiometric ratios of viral proteins

In retroviruses and the double-stranded RNA totiviruses, the efficiency of programmed -1 ribosomal frameshifting is critical for ensuring the proper ratios of upstream-encoded capsid proteins to downstream-encoded replicase enzymes. The genomic organizations of many other frameshifting viruses, including the coronaviruses, are very different, in that their upstream open reading frames encode nonstructural proteins, the frameshift-dependent downstream open reading frames encode enzymes involved in transcription and replication, and their structural proteins are encoded by subgenomic mRNAs. The biological significance of frameshifting efficiency and how the relative ratios of proteins encoded by the upstream and downstream open reading frames affect virus propagation has not been explored before. Here, three different strategies were employed to test the hypothesis that the -1 PRF signals of coronaviruses have evolved to produce the correct ratios of upstream- to downstream-encoded proteins. Specifically, infectious clones of the severe acute respiratory syndrome (SARS)-associated coronavirus harboring mutations that lower frameshift efficiency decreased infectivity by >4 orders of magnitude. Second, a series of frameshift-promoting mRNA pseudoknot mutants was employed to demonstrate that the frameshift signals of the SARS-associated coronavirus and mouse hepatitis virus have evolved to promote optimal frameshift efficiencies. Finally, we show that a previously described frameshift attenuator element does not actually affect frameshifting per se but rather serves to limit the fraction of ribosomes available for frameshifting. The findings of these analyses all support a "golden mean" model in which viruses use both programmed ribosomal frameshifting and translational attenuation to control the relative ratios of their encoded proteins.

Insertion of the CXC chemokine ligand 9 (CXCL9) into the mouse hepatitis virus genome results in protection from viral-induced encephalitis and hepatitis

The role of the CXC chemokine ligand 9 (CXCL9) in host defense following infection with mouse hepatitis virus (MHV) was determined. Inoculation of the central nervous system (CNS) of CXCL9-/- mice with MHV resulted in accelerated and increased mortality compared to wild type mice supporting an important role for CXCL9 in anti-viral defense. In addition, infection of RAG1-/- or CXCL9-/- mice with a recombinant MHV expressing CXCL9 (MHV-CXCL9) resulted in protection from disease that correlated with reduced viral titers within the brain and NK cell-mediated protection in the liver. Survival in MHV-CXCL9-infected CXCL9-/- mice was associated with reduced viral burden within the brain that coincided with increased T cell infiltration. Similarly, viral clearance from the livers of MHV-CXCL9-infected mice was accelerated but independent of increased T cell or NK cell infiltration. These observations indicate that CXCL9 promotes protection from coronavirus-induced neurological and liver disease.

In vivo potential effects of adenovirus type 5 E1A and E1B on lung carcinogenesis and lymphoproliferative inflammation

Triggering uncontrolled cellular proliferation, chronic inflammation, and/or disruption of p53 activity is critical for tumorigenesis initiated by latent viral oncogenes. The adenovirus type 5 (Ad5) early genes E1A and E1B can maintain lifelong latency in the lungs of patients with chronic pulmonary diseases. To determine the in vivo effects of the latent Ad5 E1A and E1B oncogenes, we have examined the influence of Ad5 E1A and E1B gene products on mouse lung carcinogenesis and inflammation by generation and characterization of lung-specific transgenic mouse models. Here, we show that either the Ad5 E1A 243-amino-acid (aa) protein or the E1B 58-kDa protein was dominantly expressed in the transgenic lung. Preferential expression of Ad5 E1A 243-aa protein alone was not sufficient to induce lung carcinogenesis but resulted in low-grade cellular proliferation and high-grade lymphoproliferative inflammation in the lung. The presence of Ad5 E1B dramatically enhanced the expression of the E1A 243-aa protein, in addition to impairing p53 and apoptosis response, resulting in uncontrolled cellular proliferation, lymphoproliferative inflammation, and metastatic carcinomas in the lung after a period of latency. Our studies may provide clues to understanding the potential in vivo biological effects of Ad5 E1A and E1B latent in the lung and a new scope for assessing in vivo functions of viral genes latent in the infection target tissue.

Role of IFN-gamma responsiveness in CD8 T-cell-mediated viral clearance and demyelination in coronavirus-infected mice

Immunocompetent, but not RAG1(-/-) mice infected with MHV-JHM develop demyelination. Transferred CD8 T cell-enriched splenocytes reconstitute demyelination, and this ability is dependent on donor IFN-gamma. We used IFN-gammaR1(-/-) mice to examine the target of IFN-gamma in CD8 T cell-mediated demyelination. In IFN-gammaR1(-/-)RAG1(-/-) recipients, demyelination is decreased, but not eliminated, while viral titers are significantly increased when compared to IFN-gammaR1(+/+)RAG1(-/-) recipients. IFN-gammaR1(-/-) CD8 T cells retain virus-specific effector function regardless of IFN-gammaR1 expression. Although IFN-gammaR1 responsiveness is critical for maximal demyelination, increased levels of infectious virus coupled with adoptive transfer of CD8 T cells may result in myelin destruction independent of IFN-gammaR1 expression.