In vivo expression of major histocompatibility complex molecules on oligodendrocytes and neurons during viral infection

Three Types of Demyelination, Perivenous, Confluent, and Perineuronal Nets-Rich in a COVID-19 Patient With Meningoencephalomyelitis

Neurologic symptoms are common in COVID-19, and a variety of neuropathological changes have been reported. One of the important neuropathological findings is demyelination. However, the underlying pathogenesis of demyelination remained poorly understood. We witnessed a case of COVID-19 with distinct types of demyelination in the cerebrum, medulla oblongata, and spinal canal, who died of sepsis. The postmortem examination showed the solitary massive demyelination in the medulla oblongata. The massive lesion was filled with components of perineuronal nets. In the spinal canal, confluent demyelination in bilateral lateral and dorsal funiculi was detected over the entire length from C1 to S5, which was maximum at the level of cervical spinal canal stenosis. Demyelination in the cerebrum was mainly perivenular, and augmented in the area of lacunar infarcts and dilated perivascular spaces. Considering the distribution patterns of the following three types of demyelination, the traces of viral spreading could be highlighted. Discontinuous perivenous demyelination in the cerebrum showed the result of hematogenous spreading. Longitudinal confluent demyelination of the spinal cord should be the picturesque of the trace of axonal spreading. The distribution of demyelination was possibly modified by the underlying diseases, diabetes mellitus, hypertension, and spinal canal stenosis.

T Cells in Tick-Borne Flavivirus Encephalitis: A Review of Current Paradigms in Protection and Disease Pathology

The family Flaviviridae is comprised of a diverse group of arthropod-borne viruses that are the etiological agents of globally relevant diseases in humans. Among these, infection with several of these flaviviruses-including West Nile virus (WNV), Zika virus (ZIKV), Japanese encephalitis virus (JEV), tick-borne encephalitis virus (TBEV), and Powassan virus (POWV)-can result in neuroinvasive disease presenting as meningitis or encephalitis. Factors contributing to the development and resolution of tick-borne flavivirus (TBEV, POWV) infection and neuropathology remain unclear, though many recently undertaken studies have described the virus-host interactions underlying encephalitic disease. With access to neural tissues despite the selectively permeable blood-brain barrier, T cells have emerged as one notable contributor to neuroinflammation. The goal of this review is to summarize the recent advances in tick-borne flavivirus immunology-particularly with respect to T cells-as it pertains to the development of encephalitis. We found that although T cell responses are rarely evaluated in a clinical setting, they are integral in conjunction with antibody responses to restricting the entry of TBFV into the CNS. The extent and means by which they can drive immune pathology, however, merits further study. Understanding the role of the T cell compartment in tick-borne flavivirus encephalitis is instrumental for improving vaccine safety and efficacy, and has implications for treatments and interventions for human disease.

Neuro-immune crosstalk in depressive symptoms of multiple sclerosis

Depressive disorders can occur in up to 50% of people with multiple sclerosis in their lifetime. If left untreated, comorbid major depressive disorders may not spontaneously remit and is associated with an increased morbidity and mortality. Conversely, epidemiological evidence supports increased psychiatric visit as a significant prodromal event prior to diagnosis of MS. Are there common molecular pathways that contribute to the co-development of MS and psychiatric illnesses? We discuss immune cells that are dysregulated in MS and how such dysregulation can induce or protect against depressive symptoms. This is not meant to be a comprehensive review of all molecular pathways but rather a framework to guide future investigations of immune responses in depressed versus euthymic people with MS. Currently, there is weak evidence supporting the use of antidepressant medication in comorbid MS patients. It is our hope that by better understanding the neuroimmune crosstalk in the context of depression in MS, we can enhance the potential for future therapeutic options.

Beyond Myelination: Possible Roles of the Immune Proteasome in Oligodendroglial Homeostasis and Dysfunction

Oligodendroglia play a critical role in CNS homeostasis by myelinating neuronal axons in their mature stages. Dysfunction in this lineage occurs when early stage OPCs are not able to differentiate to replace dying Mature Myelinating Oligodendrocytes. Many hypotheses exist as to why de- and hypo-myelinating disorders and diseases occur. In this review, we present data to show that oligodendroglia can adopt components of the immune proteasome under inflammatory conditions. The works reviewed further reflect that these immune-component expressing oligodendroglia can in fact function as antigen presenting cells, phagocytosing foreign entities and presenting them via MHC II to activate CD4+ T cells. Additionally, we hypothesize, based on the limited literature, that the adoption of immune components by oligodendroglia may contribute to their stalled differentiation in the context of these disorders and diseases. The present review will underline: (1) Mechanisms of neuroinflammation in diseases associated with Immune Oligodendroglia; (2) the first associations between the immune proteasome and oligodendroglia and the subtle distinctions between these works; (3) the suggested functionality of these cells as it is described by current literature; and (4) the hypothesized consequences on metabolism. In doing so we aim to shed light on this fairly under-explored cell type in hopes that study of their functionality may lead to further mechanistic understanding of hypo- and de-myelinating neuroinflammatory disorders and diseases.

Sympathetic Nerves and Innate Immune System in the Spleen: Implications of Impairment in HIV-1 and Relevant Models

The immune and sympathetic nervous systems are major targets of human, murine and simian immunodeficiency viruses (HIV-1, MAIDS, and SIV, respectively). The spleen is a major reservoir for these retroviruses, providing a sanctuary for persistent infection of myeloid cells in the white and red pulps. This is despite the fact that circulating HIV-1 levels remain undetectable in infected patients receiving combined antiretroviral therapy. These viruses sequester in immune organs, preventing effective cures. The spleen remains understudied in its role in HIV-1 pathogenesis, despite it hosting a quarter of the body’s lymphocytes and diverse macrophage populations targeted by HIV-1. HIV-1 infection reduces the white pulp, and induces perivascular hyalinization, vascular dysfunction, tissue infarction, and chronic inflammation characterized by activated epithelial-like macrophages. LP-BM5, the retrovirus that induces MAIDS, is a well-established model of AIDS. Immune pathology in MAIDs is similar to SIV and HIV-1 infection. As in SIV and HIV, MAIDS markedly changes splenic architecture, and causes sympathetic dysfunction, contributing to inflammation and immune dysfunction. In MAIDs, SIV, and HIV, the viruses commandeer splenic macrophages for their replication, and shift macrophages to an M2 phenotype. Additionally, in plasmacytoid dendritic cells, HIV-1 blocks sympathetic augmentation of interferon-β (IFN-β) transcription, which promotes viral replication. Here, we review viral–sympathetic interactions in innate immunity and pathophysiology in the spleen in HIV-1 and relevant models. The situation remains that research in this area is still sparse and original hypotheses proposed largely remain unanswered.

Neuronal Presentation of Antigen and Its Possible Role in Parkinson's Disease

Patients with Parkinson's disease (PD) and other synucleinopathies often exhibit autoimmune features, including CD4+ and some CD8+ T lymphocytes that recognize epitopes derived from alpha-synuclein. While neurons have long been considered to not present antigens, recent data indicate that they can be induced to do so, particularly in response to interferons and other forms of stress. Here, we review literature on neuronal antigen presentation and its potential role in PD. Although direct evidence for CD8+ T cell-mediated neuronal death is lacking in PD, neuronal antigen presentation appears central to the pathology of Rasmussen's encephalitis, a pediatric neurological disorder driven by cytotoxic T cell infiltration and neuroinflammation. Emerging data suggest that T cells enter the brain in PD and other synucleinopathies, where the majority of neuromelanin-containing substantia nigra and locus coeruleus neurons express MHC Class I molecules. In cell culture, CD8+ T cell recognition of antigen:MHC Class I complexes on neuronal membranes leads to cytotoxic responses and neuronal cell death. Recent animal models suggest the possibility of T cell autoreactivity to mitochondrial antigens in PD. It remains unclear if neuronal antigen presentation plays a role in PD or other neurodegenerative disorders, and efforts are underway to better elucidate the potential impact of autoimmune responses on neurodegeneration.

Pro-inflammatory T helper 17 directly harms oligodendrocytes in neuroinflammation

T helper (Th)17 cells are considered to contribute to inflammatory mechanisms in diseases such as multiple sclerosis (MS). However, the discussion persists regarding their true role in patients. Here, we visualized central nervous system (CNS) inflammatory processes in models of MS live in vivo and in MS brains and discovered that CNS-infiltrating Th17 cells form prolonged stable contact with oligodendrocytes. Strikingly, compared to Th2 cells, direct contact with Th17 worsened experimental demyelination, caused damage to human oligodendrocyte processes, and increased cell death. Importantly, we found that in comparison to Th2 cells, both human and murine Th17 cells express higher levels of the integrin CD29, which is linked to glutamate release pathways. Of note, contact of human Th17 cells with oligodendrocytes triggered release of glutamate, which induced cell stress and changes in biosynthesis of cholesterol and lipids, as revealed by single-cell RNA-sequencing analysis. Finally, exposure to glutamate decreased myelination, whereas blockade of CD29 preserved oligodendrocyte processes from Th17-mediated injury. Our data provide evidence for the direct and deleterious attack of Th17 cells on the myelin compartment and show the potential for therapeutic opportunities in MS.

Pro-inflammatory T helper 17 directly harms oligodendrocytes in neuroinflammation

T helper (Th)17 cells are considered to contribute to inflammatory mechanisms in diseases such as multiple sclerosis (MS). However, the discussion persists regarding their true role in patients. Here, we visualized central nervous system (CNS) inflammatory processes in models of MS live in vivo and in MS brains and discovered that CNS-infiltrating Th17 cells form prolonged stable contact with oligodendrocytes. Strikingly, compared to Th2 cells, direct contact with Th17 worsened experimental demyelination, caused damage to human oligodendrocyte processes, and increased cell death. Importantly, we found that in comparison to Th2 cells, both human and murine Th17 cells express higher levels of the integrin CD29, which is linked to glutamate release pathways. Of note, contact of human Th17 cells with oligodendrocytes triggered release of glutamate, which induced cell stress and changes in biosynthesis of cholesterol and lipids, as revealed by single-cell RNA-sequencing analysis. Finally, exposure to glutamate decreased myelination, whereas blockade of CD29 preserved oligodendrocyte processes from Th17-mediated injury. Our data provide evidence for the direct and deleterious attack of Th17 cells on the myelin compartment and show the potential for therapeutic opportunities in MS.

Promoting remyelination through cell transplantation therapies in a model of viral-induced neurodegenerative disease

Multiple sclerosis (MS) is a central nervous system (CNS) disease characterized by chronic neuroinflammation, demyelination, and axonal damage. Infiltration of activated lymphocytes and myeloid cells are thought to be primarily responsible for white matter damage and axonopathy. Several United States Food and Drug Administration-approved therapies exist that impede activated lymphocytes from entering the CNS thereby limiting new lesion formation in patients with relapse-remitting forms of MS. However, a significant challenge within the field of MS research is to develop effective and sustained therapies that allow for axonal protection and remyelination. In recent years, there has been increasing evidence that some kinds of stem cells and their derivatives seem to be able to mute neuroinflammation as well as promote remyelination and axonal integrity. Intracranial infection of mice with the neurotropic JHM strain of mouse hepatitis virus (JHMV) results in immune-mediated demyelination and axonopathy, making this an excellent model to interrogate the therapeutic potential of stem cell derivatives in evoking remyelination. This review provides a succinct overview of our recent findings using intraspinal injection of mouse CNS neural progenitor cells and human neural precursors into JHMV-infected mice. JHMV-infected mice receiving these cells display extensive remyelination associated with axonal sparing. In addition, we discuss possible mechanisms associated with sustained clinical recovery. Developmental Dynamics 248:43-52, 2019. © 2018 Wiley Periodicals, Inc.

Silencing Alpha Synuclein in Mature Nigral Neurons Results in Rapid Neuroinflammation and Subsequent Toxicity

Human studies and preclinical models of Parkinson’s disease implicate the involvement of both the innate and adaptive immune systems in disease progression. Further, pro-inflammatory markers are highly enriched near neurons containing pathological forms of alpha synuclein (α-syn), and α-syn overexpression recapitulates neuroinflammatory changes in models of Parkinson’s disease. These data suggest that α-syn may initiate a pathological inflammatory response, however the mechanism by which α-syn initiates neuroinflammation is poorly understood. Silencing endogenous α-syn results in a similar pattern of nigral degeneration observed following α-syn overexpression. Here we aimed to test the hypothesis that loss of α-syn function within nigrostriatal neurons results in neuronal dysfunction, which subsequently stimulates neuroinflammation. Adeno-associated virus (AAV) expressing an short hairpin RNA (shRNA) targeting endogenous α-syn was unilaterally injected into the substantia nigra pars compacta (SNc) of adult rats, after which nigrostriatal pathology and indices of neuroinflammation were examined at 7, 10, 14 and 21 days post-surgery. Removing endogenous α-syn from nigrostriatal neurons resulted in a rapid up-regulation of the major histocompatibility complex class 1 (MHC-1) within transduced nigral neurons. Nigral MHC-1 expression occurred prior to any overt cell death and coincided with the recruitment of reactive microglia and T-cells to affected neurons. Following the induction of neuroinflammation, α-syn knockdown resulted in a 50% loss of nigrostriatal neurons in the SNc and a corresponding loss of nigrostriatal terminals and dopamine (DA) concentrations within the striatum. Expression of a control shRNA did not elicit any pathological changes. Silencing α-syn within glutamatergic neurons of the cerebellum did not elicit inflammation or cell death, suggesting that toxicity initiated by α-syn silencing is specific to DA neurons. These data provide evidence that loss of α-syn function within nigrostriatal neurons initiates a neuronal-mediated neuroinflammatory cascade, involving both the innate and adaptive immune systems, which ultimately results in the death of affected neurons.

Organ-specific mechanisms linking innate and adaptive antifungal immunity

Fungal infections remain a significant global health problem in humans. Fungi infect millions of people worldwide and cause from acute superficial infections to life-threatening systemic disease to chronic illnesses. Trying to decipher the complex innate and adaptive immune mechanisms that protect humans from pathogenic fungi is therefore a key research goal that may lead to immune-based therapeutic strategies and improved patient outcomes. In this review, we summarize how the cells and molecules of the innate immune system activate the adaptive immune system to elicit long-term immunity to fungi. We present current knowledge and exciting new advances in the context of organ-specific immunity, outlining the tissue-specific tropisms for the major pathogenic fungi of humans, the antifungal functions of tissue-resident myeloid cells, and the adaptive immune responses required to protect specific organs from fungal challenge.

Differentiated Human SH-SY5Y Cells Provide a Reductionist Model of Herpes Simplex Virus 1 Neurotropism

Neuron-virus interactions that occur during herpes simplex virus (HSV) infection are not fully understood. Neurons are the site of lifelong latency and are a crucial target for long-term suppressive therapy or viral clearance. A reproducible neuronal model of human origin would facilitate studies of HSV and other neurotropic viruses. Current neuronal models in the herpesvirus field vary widely and have caveats, including incomplete differentiation, nonhuman origins, or the use of dividing cells that have neuropotential but lack neuronal morphology. In this study, we used a robust approach to differentiate human SH-SY5Y neuroblastoma cells over 2.5 weeks, producing a uniform population of mature human neuronal cells. We demonstrate that terminally differentiated SH-SY5Y cells have neuronal morphology and express proteins with subcellular localization indicative of mature neurons. These neuronal cells are able to support a productive HSV-1 infection, with kinetics and overall titers similar to those seen in undifferentiated SH-SY5Y cells and the related SK-N-SH cell line. However, terminally differentiated, neuronal SH-SY5Y cells release significantly less extracellular HSV-1 by 24 h postinfection (hpi), suggesting a unique neuronal response to viral infection. With this model, we are able to distinguish differences in neuronal spread between two strains of HSV-1. We also show expression of the antiviral protein cyclic GMP-AMP synthase (cGAS) in neuronal SH-SY5Y cells, which is the first demonstration of the presence of this protein in nonepithelial cells. These data provide a model for studying neuron-virus interactions at the single-cell level as well as via bulk biochemistry and will be advantageous for the study of neurotropic viruses in vitroIMPORTANCE Herpes simplex virus (HSV) affects millions of people worldwide, causing painful oral and genital lesions, in addition to a multitude of more severe symptoms such as eye disease, neonatal infection, and, in rare cases, encephalitis. Presently, there is no cure available to treat those infected or prevent future transmission. Due to the ability of HSV to cause a persistent, lifelong infection in the peripheral nervous system, the virus remains within the host for life. To better understand the basis of virus-neuron interactions that allow HSV to persist within the host peripheral nervous system, improved neuronal models are required. Here we describe a cost-effective and scalable human neuronal model system that can be used to study many neurotropic viruses, such as HSV, Zika virus, dengue virus, and rabies virus.

The Emerging Role of the Major Histocompatibility Complex Class I in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease affecting upper and lower motoneurons (MNs). The etiology of the disease is still unknown for most patients with sporadic ALS, while in 5–10% of the familial cases, several gene mutations have been linked to the disease. Mutations in the gene encoding Cu, Zn superoxide dismutase (SOD1), reproducing in animal models a pathological scenario similar to that found in ALS patients, have allowed for the identification of mechanisms relevant to the ALS pathogenesis. Among them, neuroinflammation mediated by glial cells and systemic immune activation play a key role in the progression of the disease, through mechanisms that can be either neuroprotective or neurodetrimental depending on the type of cells and the MN compartment involved. In this review, we will examine and discuss the involvement of major histocompatibility complex class I (MHCI) in ALS concerning its function in the adaptive immunity and its role in modulating the neural plasticity in the central and peripheral nervous system. The evidence indicates that the overexpression of MHCI into MNs protect them from astrocytes’ toxicity in the central nervous system (CNS) and promote the removal of degenerating motor axons accelerating collateral reinnervation of muscles.

Major Histocompatibility Complex I Expression by Motor Neurons and Its Implication in Amyotrophic Lateral Sclerosis

Neuronal expression of major histocompatibility complex I (MHCI)-related molecules in adults and during CNS diseases is involved in the synaptic plasticity and axonal regeneration with mechanisms either dependent or independent of their immune functions. Motor neurons are highly responsive in triggering the expression of MHCI molecules during normal aging or following insults and diseases, and this has implications in the synaptic controls, axonal regeneration, and neuromuscular junction stability of these neurons. We recently reported that MHCI and immunoproteasome are strongly activated in spinal motor neurons and their peripheral motor axon in a mouse model of familial amyotrophic lateral sclerosis (ALS) during the course of the disease. This response was prominent in ALS mice with slower disease progression in which the axonal structure and function was better preserved than in fast-progressing mice. This review summarizes and discusses our observations in the light of knowledge about the possible role of MHCI in motor neurons providing additional insight into the pathophysiology of ALS.

Lack of Major Histocompatibility Complex Class I Upregulation and Restrictive Infection by JC Virus Hamper Detection of Neurons by T Lymphocytes in the Central Nervous System

The human polyomavirus JC (JCV) infects glial cells in immunosuppressed individuals, leading to progressive multifocal leukoencephalopathy. Polyomavirus JC can also infect neurons in patients with JCV granule cell neuronopathy and JCV encephalopathy. CD8-positive T cells play a crucial role in viral containment and outcome in progressive multifocal leukoencephalopathy, but whether CD8-positive T cells can also recognize JCV-infected neurons is unclear. We used immunohistochemistry to determine the prevalence of T cells in neuron-rich areas of archival brain samples from 77 patients with JCV CNS infections and 94 control subjects. Neurons predominantly sustained a restrictive infection with expression of JCV regulatory protein T antigen (T Ag), whereas glial cells were productively infected and expressed both T Ag and the capsid protein VP1. T cells were more prevalent near JCV-infected cells with intact nuclei expressing both T Ag and VP1 compared with those expressing either protein alone. CD8-positive T cells also colocalized more with JCV-infected glial cells than with JCV-infected neurons. Major histocompatibility complex class I expression was upregulated in JCV-infected areas but could only be detected in rare neurons interspersed with infected glial cells. These results suggest that isolated neurons harboring restrictive JCV infection do not upregulate major histocompatibility complex class I and thus may escape recognition by CD8-positive T cells.

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.

Dual destructive and protective roles of adaptive immunity in neurodegenerative disorders

Inappropriate T cell responses in the central nervous system (CNS) affect the pathogenesis of a broad range of neuroinflammatory and neurodegenerative disorders that include, but are not limited to, multiple sclerosis, amyotrophic lateral sclerosis, Alzheimer’s disease and Parkinson’s disease. On the one hand immune responses can exacerbate neurotoxic responses; while on the other hand, they can lead to neuroprotective outcomes. The temporal and spatial mechanisms by which these immune responses occur and are regulated in the setting of active disease have gained significant recent attention. Spatially, immune responses that affect neurodegeneration may occur within or outside the CNS. Migration of antigen-specific CD4+ T cells from the periphery to the CNS and consequent immune cell interactions with resident glial cells affect neuroinflammation and neuronal survival. The destructive or protective mechanisms of these interactions are linked to the relative numerical and functional dominance of effector or regulatory T cells. Temporally, immune responses at disease onset or during progression may exhibit a differential balance of immune responses in the periphery and within the CNS. Immune responses with predominate T cell subtypes may differentially manifest migratory, regulatory and effector functions when triggered by endogenous misfolded and aggregated proteins and cell-specific stimuli. The final result is altered glial and neuronal behaviors that influence the disease course. Thus, discovery of neurodestructive and neuroprotective immune mechanisms will permit potential new therapeutic pathways that affect neuronal survival and slow disease progression.

Innate immune responses to HIV infection in the central nervous system

Human immunodeficiency virus (HIV) invades the brain early during infection and generates a chronic inflammatory microenvironment that can eventually result in neurological disease, even in the absence of significant viral replication. Thus, HIV-1 infection of the brain has been characterized both as a neuroimmunological and neurodegenerative disorder. While the brain and central nervous system (CNS) have historically been regarded as immune privileged or immunologically quiescent, newer concepts of CNS immunity suggest an important if not defining role for innate immune responses generated by glial cells. Innate immunity may be the first line of defense against HIV infection of the brain and CNS, with multiple cellular elements providing responses that can be anti-viral and neuroprotective, but also potentially neurotoxic, impairing neurogenesis and promoting neuronal apoptosis. To investigate the effects of HIV exposure on neurogenesis and neuronal survival, we have studied the responses of human neuroepithelial progenitor (NEP) cells, which undergo directed differentiation into astrocytes and neurons in vitro. We identified a group of genes that were differentially expressed in NEP-derived cells during virus exposure. This included genes that are strongly related to interferon-induced responses and antigen presentation. Moreover, we observed that the host factor apolipoprotein E influences the innate immune response expressed by these cells, with a more robust response in the apolipoprotein E3/E3 genotype cultures compared to the apolipoprotein E3/E4 counterparts. Thus, neuroepithelial progenitors and their differentiated progeny recognize HIV and respond to it by mounting an innate immune response with a vigor that is influenced by the host factor apolipoprotein E.

The similar expression pattern of MHC class I molecules in human and mouse cerebellar cortex

The major histocompatibility complex (MHC) class I molecules are considered to be important in the immune system. However, the results reported in the past decade indicate that they also play important roles in the central nervous system. Here we examined the expression of MHC I and β2-microglobulin (β2m) in human and mouse cerebellar cortex. The results show that MHC I molecules are expressed both in human and mouse cerebellar cortex during brain development. The expression of H-2K(b)/D(b) is gradually increased with the development of mouse cerebellar cortex, but finally decreased to a very low level. Similarly, the expression of HLA-B/C genes is increased in developing human cerebellar cortex, but decreased after birth. The spatial and temporal expression of β2m overlaps mostly with that of HLA-B/C molecules, and they are co-expressed in Purkinje cells. Our findings provide a fundamental basis to reveal the functions of neuronal MHC class I molecules in the development of human cerebellum.

IL-25 prevents T cell-mediated neurotoxicity by decreasing LFA-1 expression

Autoimmune diseases such as multiple sclerosis (MS) are thought to develop due to a dysregulation in the normal T(H)1-T(H)17/T(H)2 immune system balance, where pro-inflammatory responses with a T(H)1/T(H)17 prevalence develop. Some therapeutic treatments in MS promote a shift toward a TH2-prevalent environment and this has been shown to be protective. However, not all patients respond to current immunomodulatory treatments in MS so that new immunomodulatory drugs that can promote a shift of the immune system into an anti-inflammatory T(H)2 status are needed. IL-25 is a cytokine of the IL-17 family with powerful anti-inflammatory properties. This study demonstrates that IL-25 exerts neuroprotective functions by reducing T cell-mediated killing of human fetal neurons. The mechanism of action of this IL-25-mediated neuroprotective effect appears to be linked to reduction in the expression of the adhesion molecule LFA-1, which is relevant in stabilizing the immune synapse during cytotoxicity.

Development of transgenic mice expressing a coronavirus-specific public CD4 T cell receptor

Mice that are transgenic (Tg) for T cell receptor (TCR) expression are used extensively to analyze longitudinal T cell responses during effector and memory phases of the T cell response. Generation of TCR Tg mice generally requires T cell stimulation and cloning in vitro prior to amplification, processes which introduce biases into selection of the TCR that is ultimately chosen for TCR Tg mouse generation. Here we describe an alternative approach that involves no T cell stimulation or propagation in vitro. We generated mice that were transgenic for a TCR responding to a CD4 T cell epitope (epitope M133) that is immunodominant in mice infected with a neurotropic coronavirus, the JHM strain of mouse hepatitis virus. The CD4 T cell response to epitope M133 is of particular interest because it may be pathogenic, protective or regulatory, depending upon the physiological setting. We applied an iterative process in which we identified a TCR-β chain expressed by all mice that were examined (‘public sequence’). This TCR-β chain was introduced into bone marrow cells with a lentivirus vector, generating TCR-β retrogenic mice. A TCR-α chain that paired with this TCR-β was then identified and used to generate a second set of TCR (α/β) retrogenic mice. After demonstrating that these cells were functional and responded to epitope M133, these TCR chains were used to generate an epitope M133-specific TCR Tg mouse. This method should be generally useful for engineering TCR Tg mice without introduction of bias caused by in vitro manipulation and propagation.

Possible involvement of TLRs and hemichannels in stress-induced CNS dysfunction via mastocytes, and glia activation

In the central nervous system (CNS), mastocytes and glial cells (microglia, astrocytes and oligodendrocytes) function as sensors of neuroinflammatory conditions, responding to stress triggers or becoming sensitized to subsequent proinflammatory challenges. The corticotropin-releasing hormone and glucocorticoids are critical players in stress-induced mastocyte degranulation and potentiation of glial inflammatory responses, respectively. Mastocytes and glial cells express different toll-like receptor (TLR) family members, and their activation via proinflammatory molecules can increase the expression of connexin hemichannels and pannexin channels in glial cells. These membrane pores are oligohexamers of the corresponding protein subunits located in the cell surface. They allow ATP release and Ca²⁺ influx, which are two important elements of inflammation. Consequently, activated microglia and astrocytes release ATP and glutamate, affecting myelinization, neuronal development, and survival. Binding of ligands to TLRs induces a cascade of intracellular events leading to activation of several transcription factors that regulate the expression of many genes involved in inflammation. During pregnancy, the previous responses promoted by viral infections and other proinflammatory conditions are common and might predispose the offspring to develop psychiatric disorders and neurological diseases. Such disorders could eventually be potentiated by stress and might be part of the etiopathogenesis of CNS dysfunctions including autism spectrum disorders and schizophrenia.

Variation in the major histocompatibility complex [MHC] gene family in schizophrenia: associations and functional implications

Schizophrenia is a chronic debilitating neuropsychiatric disorder with a complex genetic contribution. Although multiple genetic, immunological and environmental factors are known to contribute to schizophrenia susceptibility, the underlying neurobiological mechanism(s) is yet to be established. The immune system dysfunction theory of schizophrenia is experiencing a period of renewal due to a growth in evidence implicating components of the immune system in brain function and human behavior. Current evidence indicates that certain immune molecules such as Major Histocompatibility Complex (MHC) and cytokines, the key regulators of immunity and inflammation are directly involved in the neurobiological processes related to neurodevelopment, neuronal plasticity, learning, memory and behavior. However, the strongest support in favor of the immune hypothesis has recently emerged from on-going genome wide association studies advocating MHC region variants as major determinants of one's risk for developing schizophrenia. Further identification of the interacting partners and receptors of MHC molecules in the brain and their role in down-stream signaling pathways of neurotransmission have implicated these molecules as potential schizophrenia risk factors. More recently, combined brain imaging and genetic studies have revealed a relationship between genetic variations within the MHC region and neuromorphometric changes during schizophrenia. Furthermore, MHC molecules play a significant role in the immune-infective and neurodevelopmental pathogenetic pathways, currently hypothesized to contribute to the pathophysiology of schizophrenia. Herein, we review the immunological, genetic and expression studies assessing the role of the MHC in conferring risk for developing schizophrenia, we summarize and discuss the possible mechanisms involved, making note of the challenges to, and future directions of, immunogenetic research in schizophrenia.

Immune heterogeneity in neuroinflammation: dendritic cells in the brain

Dendritic cells (DC) are critical to an integrated immune response and serve as the key link between the innate and adaptive arms of the immune system. Under steady state conditions, brain DC’s act as sentinels, continually sampling their local environment. They share this function with macrophages derived from the same basic hemopoietic (bone marrow-derived) precursor and with parenchymal microglia that arise from a unique non-hemopoietic origin. While multiple cells may serve as antigen presenting cells (APCs), dendritic cells present both foreign and self-proteins to naïve T cells that, in turn, carry out effector functions that serve to protect or destroy. The resulting activation of the adaptive response is a critical step to resolution of injury or infection and is key to survival. In this review we will explore the critical roles that DCs play in the brain’s response to neuroinflammatory disease with emphasis on how the brain’s microenvironment impacts these actions.

MHC class I in activity-dependent structural and functional plasticity

Members of the major histocompatibility complex (MHC) class I family of proteins are well known for their central role in the adaptive immune system, where they present self and non-self peptides for immune surveillance. Although the brain has been long considered immune privileged, in part because of an apparent lack of neuronal MHC class I, it has since been shown that MHC class I proteins are expressed by normal, uninfected neurons. Moreover, expression of MHC class I is unusually dynamic in the developing and adult brain, and MHC class I levels in neurons can be regulated by endogenous and exogenous electrical activity. Unexpectedly, several recent studies find that MHC class I is required for distinct activity-dependent events during brain development, adult plasticity, and in response to injury. Together, these studies indicate a novel role for MHC class I proteins in translating electrical activity into changes in synaptic strength and neuronal connectivity in vivo.

Granule-derived granzyme B mediates the vulnerability of human neurons to T cell-induced neurotoxicity

Multiple sclerosis (MS) is considered an autoimmune disease of the CNS and is characterized by inflammatory cells infiltrating the CNS and inducing demyelination, axonal loss, and neuronal death. Recent evidence strongly suggests that axonal and neuronal degeneration underlie the progression of permanent disability in MS. In this study, we report that human neurons are selectively susceptible to the serine-protease granzyme B (GrB) isolated from cytotoxic T cell granules. In vitro, purified human GrB induced neuronal death to the same extent as the whole activated T cell population. On the contrary, activated T cells isolated from GrB knockout mice failed to induce neuronal injury. We found that following internalization through various parts of neurons, GrB accumulated in the neuronal soma. Within the cell body, GrB diffused out of endosomes possibly through a perforin-independent mechanism and induced subsequent activation of caspases and cleavage of α-tubulin. Inhibition of caspase-3, a well-known substrate for GrB, significantly reduced GrB-mediated neurotoxicity. We demonstrated that treatment of neurons with mannose-6-phosphate prevented GrB entry and inhibited GrB-mediated neuronal death, suggesting mannose-6-phosphate receptor-dependent endocytosis. Together, our data unveil a novel mechanism by which GrB induces selective neuronal injury and suggest potential new targets for the treatment of inflammatory-mediated neurodegeneration in diseases such as MS.

Chronic progressive multiple sclerosis - pathogenesis of neurodegeneration and therapeutic strategies

Multiple sclerosis (MS) is an inflammatory, autoimmune, demyelinating disease of the central nervous system (CNS) that usually starts as a relapsing-remitting disease. In most patients the disease evolves into a chronic progressive phase characterized by continuous accumulation of neurological deficits. While treatment of relapsing-remitting MS (RRMS) has improved dramatically over the last decade, the therapeutic options for chronic progressive MS, both primary and secondary, are still limited. In order to find new pharmacological targets for the treatment of chronic progressive MS, the mechanisms of the underlying neurodegenerative process that becomes apparent as the disease progresses need to be elucidated. New animal models with prominent and widespread progressive degenerative components of MS have to be established to study both inflammatory and non-inflammatory mechanisms of neurodegeneration. Here, we discuss disease mechanisms and treatment strategies for chronic progressive MS.

Characterization of signaling function and expression of HLA class I molecules in medulloblastoma

Although known for the important function in the immune system, MHC class I molecules are increasingly ascribed an alternative role in modifying signal transduction. In medulloblastoma, HLA class I molecules are associated with poor prognosis, and can induce ERK1/2 activation upon engagement with ligands that bind to incompletely assembled complexes (so called open conformers). We here demonstrate that ERK1/2 activation in medulloblastoma can occur in the absence of endogenously synthesized β2m, formally excluding involvement of closed HLA class conformation. In addition, several experimental observations suggest that heterogeneity of HLA class I expression may be a reflection of the status of original cells before transformation, rather than a consequence of immune-based selection of HLA-loss mutants. These results contribute to our understanding of an immune system-independent role of HLA class I in the pathology of medulloblastoma, and cancer in general.

Long-term gliosis and molecular changes in the cervical spinal cord of the rhesus monkey after traumatic brain injury

Recovery of fine motor skills after traumatic brain injury (TBI) is variable, with some patients showing progressive improvements over time while others show poor recovery. We therefore studied possible cellular mechanisms accompanying the recovery process in a non-human primate model system, in which the lateral frontal motor cortex areas controlling the preferred upper limb were unilaterally lesioned, and the animals eventually regained fine hand motor function. Immunohistochemical staining of the cervical spinal cord, the site of compensatory sprouting and degeneration of corticospinal axons, showed profound increases in immunoreactivities for major histocompatibility complex class II molecule (MHC-II) and extracellular signal-regulated kinases (ERK1/2) up to 12 months post lesion, particularly within the lateral corticospinal tract (LCST). Double immunostaining demonstrated that phosphorylated ERK1/2 colocalized within the MCH-II + microglia, suggesting a trophic role of long-term microglia activation after TBI at the site of compensatory sprouting. Active sprouting was observed in the LCST as well as in the spinal gray matter of the lesioned animals, as illustrated by increases in growth associated protein 43. Upregulation of Nogo receptor and glutamate transporter expression was also observed in this region after TBI, suggesting possible mechanisms for controlling aberrant sprouting and/or synaptic formation en route and interstitial glutamate concentration changes at the site of axon degeneration, respectively. Taken together, these changes in the non-human primate spinal cord support a long-term trophic/tropic role for reactive microglia, in particular, during functional and structural recovery after TBI.

Spinal motoneuron synaptic plasticity after axotomy in the absence of inducible nitric oxide synthase

Background

Astrocytes play a major role in preserving and restoring structural and physiological integrity following injury to the nervous system. After peripheral axotomy, reactive gliosis propagates within adjacent spinal segments, influenced by the local synthesis of nitric oxide (NO). The present work investigated the importance of inducible nitric oxide synthase (iNOS) activity in acute and late glial responses after injury and in major histocompatibility complex class I (MHC I) expression and synaptic plasticity of inputs to lesioned alpha motoneurons.

Methods

In vivo analyses were carried out using C57BL/6J-iNOS knockout (iNOS^-/-) and C57BL/6J mice. Glial response after axotomy, glial MHC I expression, and the effects of axotomy on synaptic contacts were measured using immunohistochemistry and transmission electron microscopy. For this purpose, 2-month-old animals were sacrificed and fixed one or two weeks after unilateral sciatic nerve transection, and spinal cord sections were incubated with antibodies against classical MHC I, GFAP (glial fibrillary acidic protein - an astroglial marker), Iba-1 (an ionized calcium binding adaptor protein and a microglial marker) or synaptophysin (a presynaptic terminal marker). Western blotting analysis of MHC I and nNOS expression one week after lesion were also performed. The data were analyzed using a two-tailed Student's t test for parametric data or a two-tailed Mann-Whitney U test for nonparametric data.

Results

A statistical difference was shown with respect to astrogliosis between strains at the different time points studied. Also, MHC I expression by iNOS^-/- microglial cells did not increase at one or two weeks after unilateral axotomy. There was a difference in synaptophysin expression reflecting synaptic elimination, in which iNOS^-/- mice displayed a decreased number of the inputs to alpha motoneurons, in comparison to that of C57BL/6J.

Conclusion

The findings herein indicate that iNOS isoform activity influences MHC I expression by microglial cells one and two weeks after axotomy. This finding was associated with differences in astrogliosis, number of presynaptic terminals and synaptic covering of alpha motoneurons after lesioning in the mutant mice.

T-cell subsets of the encephalitis induced by the superantigen Staphylococcal Enterotoxin A (SEA) in the Lewis rat: an immunohistochemical investigation

In the present investigation, T-cell subsets of the previously described superantigen-induced encephalitis [9] have been investigated in 16 Lewis rats in comparison with four controls. Three days after intracerebral injection of Staphylococcal Enterotoxin A (SEA) or saline, 1.5 x 10(7) ConA-activated splenocytes were loaded i.v. animals were sacrificed after 0.5, 3 or 5 days, followed by immunohistochemical investigation of CD3, CD4 and CD8. Pronounced perivascular cuffing was identified 0.5 days after splenocyte injection and declined thereafter. The majority of the perivascular round cells consisted of CD8+ T-cells (65%) and CD4+ T-cells (10%). Less than 20% of the perivascular round cells were CD3+. The reduced expression of CD3 relative to e.g. CD8 is presumably due to the previous superantigenic stimulus. The presented data may be of relevance for the pathogenesis of infectious or autoimmune encephalitis, e.g. in multiple sclerosis.

Major histocompatibility complex class I expression and glial reaction influence spinal motoneuron synaptic plasticity during the course of experimental autoimmune encephalomyelitis

Recent studies have shown that major histocompatibility complex class I (MHC I) expression directly influences the stability of nerve terminals. Also, the acute phase of experimental autoimmune encephalomyelitis (EAE) has shown a significant impact on inputs within the spinal cord. Therefore, the present work investigated the synaptic covering of motoneurons during the induction phase of disease and progressive remissions of EAE. EAE was induced in C57BL/6J mice, which were divided into four groups: normal, peak disease, first remission, and second remission. The animals were killed and their lumbar spinal cords processed for in situ hybridization (IH), immunohistochemistry, and transmission electron microscopy (TEM). The results indicated an increase in glial reaction during the peak disease. During this period, the TEM analysis showed a reduction in the synaptic covering of the motoneurons, corresponding to a reduction in synaptophysin immunolabeling and an increase in the MHC I expression. The IH analysis reinforced the immunolabeling results, revealing an increased expression of MHC I mRNA by motoneurons and nonneuronal cells during the peak disease and first remission. The results observed in both remission groups indicated a return of the terminals to make contact with the motoneuron surface. The ratio between excitatory and inhibitory inputs increased, indicating the potential for development of an excitotoxic process. In conclusion, the results presented here indicate that MHC I up-regulation during the course of EAE correlates with the periods of synaptic plasticity induced by the infiltration of autoreactive immune cells and that synaptic plasticity decreases after recurrent peaks of inflammation.

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

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

Neurons under viral attack: victims or warriors?

When the central nervous system (CNS) is under viral attack, defensive antiviral responses must necessarily arise from the CNS itself to rapidly and efficiently curb infections with minimal collateral damage to the sensitive, specialized and non-regenerating neural tissue. This presents a unique challenge because an intact blood-brain barrier (BBB) and lack of proper lymphatic drainage keeps the CNS virtually outside the radar of circulating immune cells that are at constant vigilance for antigens in peripheral tissues. Limited antigen presentation skills of CNS cells in comparison to peripheral tissues is because of a total lack of dendritic cells and feeble expression of major histocompatibility complex (MHC) proteins in neurons and glia. However, research over the past two decades has identified immune effector mechanisms intrinsic to the CNS for immediate tackling, attenuating and clearing of viral infections, with assistance pouring in from peripheral circulation in the form of neutralizing antibodies and cytotoxic T cells at a later stage. Specialized CNS cells, microglia and astrocytes, were regarded as sole sentinels of the brain for containing a viral onslaught but neurons held little recognition as a potential candidate for protecting itself from the proliferation and pathogenesis of neurotropic viruses. Accumulating evidence however indicates that extracellular insult causes neurons to express immune factors characteristic of lymphoid tissues. This article aims to comprehensively analyze current research on this conditional alteration in the protein expression repertoire of neurons and the role it plays in CNS innate immune response to counter viral infections.

T cells facilitate recovery from Venezuelan equine encephalitis virus-induced encephalomyelitis in the absence of antibody

Venezuelan equine encephalitis virus (VEEV) is a mosquito-borne RNA virus of the genus Alphavirus that is responsible for a significant disease burden in Central and South America through sporadic outbreaks into human and equid populations. For humans, 2 to 4% of cases are associated with encephalitis, and there is an overall case mortality rate of approximately 1%. In mice, replication of the virus within neurons of the central nervous system (CNS) leads to paralyzing, invariably lethal encephalomyelitis. However, mice infected with certain attenuated mutants of the virus are able to control the infection within the CNS and recover. To better define what role T cell responses might be playing in this process, we infected B cell-deficient microMT mice with a VEEV mutant that induces mild, sublethal illness in immune competent mice. Infected microMT mice rapidly developed the clinical signs of severe paralyzing encephalomyelitis but were eventually able to control the infection and recover fully from clinical illness. Recovery in this system was T cell dependent and associated with a dramatic reduction in viral titers within the CNS, followed by viral persistence in the brain. Further comparison of the relative roles of T cell subpopulations within this system revealed that CD4(+) T cells were better producers of gamma interferon (IFN-gamma) than CD8(+) T cells and were more effective at controlling VEEV within the CNS. Overall, these results suggest that T cells, especially CD4(+) T cells, can successfully control VEEV infection within the CNS and facilitate recovery from a severe viral encephalomyelitis.

Immune control of mammalian gamma-herpesviruses: lessons from murid herpesvirus-4

Many acute viral infections can be controlled by vaccination; however, vaccinating against persistent infections remains problematic. Herpesviruses are a classic example. Here, we discuss their immune control, particularly that of gamma-herpesviruses, relating the animal model provided by murid herpesvirus-4 (MuHV-4) to human infections. The following points emerge: (i) CD8(+) T-cell evasion by herpesviruses confers a prominent role in host defence on CD4(+) T cells. CD4(+) T cells inhibit MuHV-4 lytic gene expression via gamma-interferon (IFN-gamma). By reducing the lytic secretion of immune evasion proteins, they may also help CD8(+) T cells to control virus-driven lymphoproliferation in mixed lytic/latent lesions. Similarly, CD4(+) T cells specific for Epstein-Barr virus lytic antigens could improve the impact of adoptively transferred, latent antigen-specific CD8(+) T cells. (ii) In general, viral immune evasion necessitates multiple host effectors for optimal control. Thus, subunit vaccines, which tend to prime single effectors, have proved less successful than attenuated virus mutants, which prime multiple effectors. Latency-deficient mutants could make safe and effective gamma-herpesvirus vaccines. (iii) The antibody response to MuHV-4 infection helps to prevent disease but is suboptimal for neutralization. Vaccinating virus carriers with virion fusion complex components improves their neutralization titres. Reducing the infectivity of herpesvirus carriers in this way could be a useful adjunct to vaccinating naive individuals with attenuated mutants.

Pathogenic MOG-reactive CD8+ T cells require MOG-reactive CD4+ T cells for sustained CNS inflammation during chronic EAE

XIncreasing evidence supports a role for CD8+ T cells in multiple sclerosis. In an attempt to isolate the contribution of CD8+ T cells in a murine model of MS, we immunized mice with a dominant CD8 epitope MOG37-46, a truncated version of MOG35-55. The data presented here show mild disease induced with MOG37-46, characterized by lower clinical scores, a decrease in CNS infiltration and a decrease in microglial activation. CD8+ T cells reactive to MOG37-46 are pro-inflammatory and traffic to the CNS; however, the presence of CD4+ T cells elicits more severe disease and sustained inflammation of the CNS.

Target-dependent B7-H1 regulation contributes to clearance of central nervous system infection and dampens morbidity

The neurotropic coronavirus JHM strain of mouse hepatitis virus persists in oligodendroglia despite the presence of virus-specific CD8 T cells. Expression of programmed death 1 (PD-1) and B7-H1 were studied during acute and persistent infection to examine whether this negative regulatory mechanism contributes to CNS viral persistence. The majority of CNS-infiltrating CD8 T cells expressed PD-1, with the highest levels on virus-specific CD8 T cells. Moreover, despite control of infectious virus, CD8 T cells within the CNS of persistently infected mice maintained high PD-1 expression. Analysis of virus-susceptible target cells in vivo revealed that B7-H1 expression was regulated in a cell type-dependent manner. Oligodendroglia and microglia up-regulated B7-H1 following infection; however, although B7-H1 expression on oligodendroglia was prominent and sustained, it was significantly reduced and transient on microglia. Infection of mice deficient in the IFN-gamma or IFN-alpha/beta receptor demonstrated that B7-H1 expression on oligodendroglia is predominantly regulated by IFN-gamma. Ab blockade of B7-H1 on oligodendroglia in vitro enhanced IFN-gamma secretion by virus-specific CD8 T cells. More efficient virus control within the CNS of B7-H1-deficient mice confirmed inhibition of CD8 T cell function in vivo. Nevertheless, the absence of B7-H1 significantly increased morbidity without altering demyelination. These data are the first to demonstrate glia cell type-dependent B7-H1 regulation in vivo, resulting in adverse effects on antiviral CD8 T cell function. However, the beneficial role of PD-1:B7-H1 interactions in limiting morbidity highlights the need to evaluate tissue-specific intervention strategies.

Perivascular spaces and the two steps to neuroinflammation

Immune cells enter the central nervous system (CNS) from the circulation under normal conditions for immunosurveillance and in inflammatory neurologic diseases. This review describes the distinct anatomic features of the CNS vasculature that permit it to maintain parenchymal homeostasis and which necessitate specific mechanisms for neuroinflammation to occur. We review the historical evolution of the concept of the blood-brain barrier and discuss distinctions between diffusion/transport of solutes and migration of cells from the blood to CNS parenchyma. The former is regulated at the level of capillaries, whereas the latter takes place in postcapillary venules. We summarize evidence that entry of immune cells into the CNS parenchyma in inflammatory conditions involves 2 differently regulated steps: transmigration of the vascular wall into the perivascular space and progression across the glia limitans into the parenchyma.

Expression profile of interferon stimulated genes in central nervous system of mice infected with dengue virus Type-1

Dengue virus (DENV) infection can cause a self-limiting disease (dengue fever) or a more severe clinical presentation known as dengue hemorrhagic fever (DHF)/dengue shock syndrome (DSS). Furthermore, data from recent dengue epidemics in Brazil indicate that the neurological manifestations are becoming more prevalent. However, the neuropathogenesis of dengue are not well understood. The balance between viral replication efficiency and innate immunity--in opposition during the early stages of infection--determines the clinical outcome of DENV infection. In this study, we investigated the effects of DENV infection on the transcription profile of the central nervous system (CNS) of mice. We observed in infected mice the up-regulation of 151 genes possibly involved in neuropathogenesis of dengue. Conversely, they may have a protective effect. Ingenuity Systems software analysis demonstrated, that the main pathways modulated by DENV infection in the mouse CNS are involved in interferon signaling and antigen presentation.

Induction of class I antigen processing components in oligodendroglia and microglia during viral encephalomyelitis

Glia exhibit differential susceptibility to CD8 T cell mediated effector mechanisms during neurotropic coronavirus infection. In contrast to microglia, oligodendroglia are resistant to CD8 T cell perforin‐mediated viral control in the absence of IFNγ. Kinetic induction of MHC Class I expression by microglia and oligodendroglia in vivo was thus analyzed to assess responses to distinct inflammatory signals. Flow cytometry demonstrated delayed Class I surface expression by oligodendroglia compared with microglia. Distinct kinetics of Class I protein upregulation correlated with cell type specific transcription patterns of genes encoding Class I heavy chains and antigen processing components. Microglia isolated from naïve mice expressed high levels of these mRNAs, whereas they were near detection limits in oligodendroglia; nevertheless, Class I protein was undetectable on both cell types. Infection induced modest mRNA increases in microglia, but dramatic transcriptional upregulation in oligodendroglia coincident with IFNα or IFNγ mRNA increases in infected tissue. Ultimately mRNAs reached similar levels in both cell types at their respective time points of maximal Class I expression. Expression of Class I on microglia, but not oligodendroglia, in infected IFNγ deficient mice supported distinct IFN requirements for Class I presentation. These data suggest an innate immune preparedness of microglia to present antigen and engage CD8 T cells early following infection. The delayed, yet robust, IFNγ dependent capacity of oligodendroglia to express Class I suggests strict control of immune interactions to avoid CD8 T cell recognition and potential presentation of autoantigen to preserve myelin maintenance. © 2008 Wiley‐Liss, Inc.

MHC I expression and synaptic plasticity in different mice strains after axotomy

The success of axonal regeneration has been attributed to a co-operation between the severed neurons and the surrounding environment, including non-neuronal cells and the extracellular matrix. Important differences regarding the regeneration potential after injury have been described among inbred mice strains. To date, there is only limited knowledge of how such variation can be linked with the genetic background. It has recently been demonstrated that MHC class I molecules have an influence on the spinal cord synaptic plasticity elicited by a peripheral lesion, and the regenerative capacity following such a lesion. Therefore, in the present work we compared the MHC I expression after axotomy in three isogenic mice strains, namely C57BL/6J, Balb/cJ, and A/J, and investigated the fine ultrastructure of the synaptic elimination process that follows such lesion. The results show that C57BL/6J mice, that have a comparatively poor regenerative potential, display a lower upregulation of MHC I in the spinal cord, coupled with a slower synaptic stripping. On the other hand, A/J mice, which have been shown to have a stronger axonal regrowth potential, showed a clear upregulation of MHC I and a sharp acute loss of afferents, at 1 week after lesion. Our results suggest that a more prominent expression of MHC I in the first week after lesion may positively influence the regenerative outcome associated with a more effective axonal regrowth.

Antiviral CD8 T cells recognize borna disease virus antigen transgenically expressed in either neurons or astrocytes

Borna disease virus (BDV) can persistently infect the central nervous system (CNS) of mice. The infection remains nonsymptomatic as long as antiviral CD8 T cells do not infiltrate the infected brain. BDV mainly infects neurons which reportedly carry few, if any, major histocompatibility complex class I molecules on the surface. Therefore, it remains unclear whether T cells can recognize replicating virus in these cells or whether cross-presentation of viral antigen by other cell types is important for immune recognition of BDV. To distinguish between these possibilities, we used two lines of transgenic mice that strongly express the N protein of BDV in either neurons (Neuro-N) or astrocytes (Astro-N). Since these animals are tolerant to the neo-self-antigen, we adoptively transferred T cells with specificity for BDV N. In nontransgenic mice persistently infected with BDV, the transferred cells accumulated in the brain parenchyma along with immune cells of host origin and efficiently induced neurological disease. Neurological disease was also observed if antiviral T cells were injected into the brains of Astro-N or Neuro-N but not nontransgenic control mice. Our results demonstrate that CD8 T cells can recognize foreign antigen on neurons and astrocytes even in the absence of infection or inflammation, indicating that these CNS cell types are playing an active role in immune recognition of viruses.

CD4 T cells contribute to virus control and pathology following central nervous system infection with neurotropic mouse hepatitis virus

Replication of the neurotropic mouse hepatitis virus strain JHM (JHMV) is controlled primarily by CD8(+) T-cell effectors utilizing gamma interferon (IFN-gamma) and perforin-mediated cytotoxicity. CD4(+) T cells provide an auxiliary function(s) for CD8(+) T-cell survival; however, their direct contribution to control of virus replication and pathology is unclear. To examine a direct role of CD4(+) T cells in viral clearance and pathology, pathogenesis was compared in mice deficient in both perforin and IFN-gamma that were selectively reconstituted for these functions via transfer of virus-specific memory CD4(+) T cells. CD4(+) T cells from immunized wild-type, perforin-deficient, and IFN-gamma-deficient donors all initially reduced virus replication. However, prolonged viral control by IFN-gamma-competent donors suggested that IFN-gamma is important for sustained virus control. Local release of IFN-gamma was evident by up-regulation of class II molecules on microglia in recipients of IFN-gamma producing CD4(+) T cells. CD4(+) T-cell-mediated antiviral activity correlated with diminished clinical symptoms, pathology, and demyelination. Both wild-type donor CD90.1 and recipient CD90.2 CD4(+) T cells trafficked into the central nervous system (CNS) parenchyma and localized to infected white matter, correlating with decreased numbers of virus-infected oligodendrocytes in the CNS. These data support a direct, if limited, antiviral role for CD4(+) T cells early during acute JHMV encephalomyelitis. Although the antiviral effector mechanism is initially independent of IFN-gamma secretion, sustained control of CNS virus replication by CD4(+) T cells requires IFN-gamma.

Vacuolar degeneration affecting brain macrophages/microglia in variant CJD: a report on two cases

We present the neuropathology of two cases of variant Creutzfeldt-Jakob disease (vCJD) showing significant vacuolar degenerative alterations specifically affecting brain macrophages/microglia within the thalamus and, to a lesser extent, within the neocortical grey matter. Vacuolar degeneration in these cells was extensive, and likely to be associated with the development of a uniform sub-type of 'spongiform' vacuole seen in vCJD. The extensive morphological alterations described here closely resemble those very recently reported by Zucconi and colleagues, in response to experimental copper deficiency induced through dietary restriction, but could not be detected in cases of sporadic CJD examined. The significance of these novel findings are discussed in relation to copper homeostasis, loss of function of cellular prion protein and aberrant lysosomal catabolism within brain macrophages/microglia. This type of vacuolation may constitute a component of the overall profile of spongiform changes associated with vCJD.

Distinct regulation of MHC molecule expression on astrocytes and microglia during viral encephalomyelitis

The potential interplay of glial cells with T cells during viral induced inflammation was assessed by comparing major histocompatibility complex molecule upregulation and retention on astrocytes and microglia. Transgenic mice expressing green fluorescent protein under control of the astrocyte‐specific glial fibrillary acidic protein promoter were infected with a neurotropic coronavirus to facilitate phenotypic characterization of astrocytes and microglia using flow cytometry. Astrocytes in the adult central nervous system up‐regulated class I surface expression, albeit delayed compared with microglia. Class II was barely detectable on astrocytes, in contrast to potent up‐regulation on microglia. Maximal MHC expression in both glial cell types correlated with IFN‐γ levels and lymphocyte accumulation. Despite a decline of IFN‐γ concomitant to virus clearance, MHC molecule expression on glia was sustained. These data demonstrate distinct regulation of both class I and class II expression by microglia and astrocytes in vivo following viral induced inflammation. Furthermore, prolonged MHC expression subsequent to viral clearance implies a potential for ongoing presentation. © 2007 Wiley‐Liss, Inc.