The role of CD8+ T-cells in lesion formation and axonal dysfunction in multiple sclerosis

Systemic immune derangements are shared across various CNS pathologies and reflect novel mechanisms of immune privilege

Background

The nervous and immune systems interact in a reciprocal manner, both under physiologic and pathologic conditions. Literature spanning various CNS pathologies including brain tumors, stroke, traumatic brain injury and de-myelinating diseases describes a number of associated systemic immunologic changes, particularly in the T-cell compartment. These immunologic changes include severe T-cell lymphopenia, lymphoid organ contraction, and T-cell sequestration within the bone marrow.

Methods

We performed an in-depth systematic review of the literature and discussed pathologies that involve brain insults and systemic immune derangements.

Conclusions

In this review, we propose that the same immunologic changes hereafter termed 'systemic immune derangements', are present across CNS pathologies and may represent a novel, systemic mechanism of immune privilege for the CNS. We further demonstrate that systemic immune derangements are transient when associated with isolated insults such as stroke and TBI but persist in the setting of chronic CNS insults such as brain tumors. Systemic immune derangements have vast implications for informed treatment modalities and outcomes of various neurologic pathologies.

Brain cancer induces systemic immunosuppression through release of non-steroid soluble mediators

Immunosuppression of unknown aetiology is a hallmark feature of glioblastoma and is characterized by decreased CD4 T-cell counts and downregulation of major histocompatibility complex class II expression on peripheral blood monocytes in patients. This immunosuppression is a critical barrier to the successful development of immunotherapies for glioblastoma. We recapitulated the immunosuppression observed in glioblastoma patients in the C57BL/6 mouse and investigated the aetiology of low CD4 T-cell counts. We determined that thymic involution was a hallmark feature of immunosuppression in three distinct models of brain cancer, including mice harbouring GL261 glioma, B16 melanoma, and in a spontaneous model of diffuse intrinsic pontine glioma. In addition to thymic involution, we determined that tumour growth in the brain induced significant splenic involution, reductions in peripheral T cells, reduced MHC II expression on blood leucocytes, and a modest increase in bone marrow resident CD4 T cells. Using parabiosis we report that thymic involution, declines in peripheral T-cell counts, and reduced major histocompatibility complex class II expression levels were mediated through circulating blood-derived factors. Conversely, T-cell sequestration in the bone marrow was not governed through circulating factors. Serum isolated from glioma-bearing mice potently inhibited proliferation and functions of T cells both in vitro and in vivo. Interestingly, the factor responsible for immunosuppression in serum is non-steroidal and of high molecular weight. Through further analysis of neurological disease models, we determined that the immunosuppression was not unique to cancer itself, but rather occurs in response to brain injury. Non-cancerous acute neurological insults also induced significant thymic involution and rendered serum immunosuppressive. Both thymic involution and serum-derived immunosuppression were reversible upon clearance of brain insults. These findings demonstrate that brain cancers cause multifaceted immunosuppression and pinpoint circulating factors as a target of intervention to restore immunity.

The Potential Contribution of Dysfunctional RNA-Binding Proteins to the Pathogenesis of Neurodegeneration in Multiple Sclerosis and Relevant Models

Neurodegeneration in multiple sclerosis (MS) is believed to underlie disease progression and permanent disability. Many mechanisms of neurodegeneration in MS have been proposed, such as mitochondrial dysfunction, oxidative stress, neuroinflammation, and RNA-binding protein dysfunction. The purpose of this review is to highlight mechanisms of neurodegeneration in MS and its models, with a focus on RNA-binding protein dysfunction. Studying RNA-binding protein dysfunction addresses a gap in our understanding of the pathogenesis of MS, which will allow for novel therapies to be generated to attenuate neurodegeneration before irreversible central nervous system damage occurs.

Immunomodulation Mediated by Anti-angiogenic Therapy Improves CD8 T Cell Immunity Against Experimental Glioma

Glioblastoma (GBM) is a lethal cancer of the central nervous system with a median survival rate of 15 months with treatment. Thus, there is a critical need to develop novel therapies for GBM. Immunotherapy is emerging as a promising therapeutic strategy. However, current therapies for GBM, in particular anti-angiogenic therapies that block vascular endothelial growth factor (VEGF), may have undefined consequences on the efficacy of immunotherapy. While this treatment is primarily prescribed to reduce tumor vascularization, multiple immune cell types also express VEGF receptors, including the most potent antigen-presenting cell, the dendritic cell (DC). Therefore, we assessed the role of anti-VEGF therapy in modifying DC function. We found that VEGF blockade results in a more mature DC phenotype in the brain, as demonstrated by an increase in the expression of the co-stimulatory molecules B7-1, B7-2, and MHC II. Furthermore, we observed reduced levels of the exhaustion markers PD-1 and Tim-3 on brain-infiltrating CD8 T cells, indicating improved functionality. Thus, anti-angiogenic therapy has the potential to be used in conjunction with and enhance immunotherapy for GBM.

Brain atrophy in picornavirus-infected FVB mice is dependent on the H-2Db class I molecule

Brain atrophy is a common feature of numerous neurologic diseases in which the role of neuroinflammation remains ill-defined. In this study, we evaluated the contribution of major histocompatibility complex class I molecules to brain atrophy in Theiler's murine encephalomyelitis virus (TMEV)-infected transgenic FVB mice that express the D^b class I molecule. FVB/D^b and wild-type FVB mice were evaluated for changes in neuroinflammation, virus clearance, neuropathology, and development of brain atrophy via T2-weighted MRI and subsequent 3-dimensional volumetric analysis. Significant brain atrophy and hippocampal neuronal loss were observed in TMEV-infected FVB/D^b mice, but not in wild-type FVB mice. Brain atrophy was observed at 1 mo postinfection and persisted through the 4-mo observation period. Of importance, virus-infected FVB/D^b mice elicited a strong CD8 T-cell response toward the immunodominant D^b-restricted TMEV-derived peptide, VP2_121-130, and cleared TMEV from the CNS. In addition, immunofluorescence revealed CD8 T cells near virus-infected neurons; therefore, we hypothesize that class I restricted CD8 T-cell responses promote development of brain atrophy. This model provides an opportunity to analyze the contribution of immune cells to brain atrophy in a system where persistent virus infection and demyelination are not factors in long-term neuropathology.-Huseby Kelcher, A. M., Atanga, P. A., Gamez, J. D., Cumba Garcia, L. M., Teclaw, S. J., Pavelko, K. D., Macura, S. I., Johnson. A. J. Brain atrophy in picornavirus-infected FVB mice is dependent on the H-2D^b class I molecule.

Non-pathogenic tissue-resident CD8+ T cells uniquely accumulate in the brains of lupus-prone mice

Severe lupus often includes psychiatric and neurological sequelae, although the cellular contributors to CNS disease remain poorly defined. Using intravascular staining to discriminate tissue-localized from blood-borne cells, we find substantial accumulation of CD8⁺ T cells relative to other lymphocytes in brain tissue, which correlates with lupus disease and limited neuropathology. This is in contrast to all other affected organs, where infiltrating CD4⁺ cells are predominant. Brain-infiltrating CD8⁺ T cells represent an activated subset of those found in the periphery, having a resident-memory phenotype (CD69⁺CD122⁻PD1⁺CD44⁺CD62L⁻) and expressing adhesion molecules (VLA-4⁺LFA-1⁺) complementary to activated brain endothelium. Remarkably, infiltrating CD8⁺ T cells do not cause tissue damage in lupus-prone mice, as genetic ablation of these cells via β2 m deficiency does not reverse neuropathology, but exacerbates disease both in the brain and globally despite decreased serum IgG levels. Thus, lupus-associated inflammation disrupts the blood-brain barrier in a discriminating way biased in favor of non-pathogenic CD8⁺ T cells relative to other infiltrating leukocytes, perhaps preventing further tissue damage in such a sensitive organ.

Perforin competent CD8 T cells are sufficient to cause immune-mediated blood-brain barrier disruption

Numerous neurological disorders are characterized by central nervous system (CNS) vascular permeability. However, the underlying contribution of inflammatory-derived factors leading to pathology associated with blood-brain barrier (BBB) disruption remains poorly understood. In order to address this, we developed an inducible model of BBB disruption using a variation of the Theiler's murine encephalomyelitis virus (TMEV) model of multiple sclerosis. This peptide induced fatal syndrome (PIFS) model is initiated by virus-specific CD8 T cells and results in severe CNS vascular permeability and death in the C57BL/6 mouse strain. While perforin is required for BBB disruption, the cellular source of perforin has remained unidentified. In addition to CD8 T cells, various innate immune cells also express perforin and therefore could also contribute to BBB disruption. To investigate this, we isolated the CD8 T cell as the sole perforin-expressing cell type in the PIFS model through adoptive transfer techniques. We determined that C57BL/6 perforin^−/− mice reconstituted with perforin competent CD8 T cells and induced to undergo PIFS exhibited: 1) heightened CNS vascular permeability, 2) increased astrocyte activation as measured by GFAP expression, and 3) loss of linear organization of BBB tight junction proteins claudin-5 and occludin in areas of CNS vascular permeability when compared to mock-treated controls. These results are consistent with the characteristics associated with PIFS in perforin competent mice. Therefore, CD8 T cells are sufficient as a sole perforin-expressing cell type to cause BBB disruption in the PIFS model.

Dynamic interaction between astrocytes and infiltrating PBMCs in context of neuroAIDS

HIV-mediated neuropathogenesis is a multifaceted process involving several players, including resident brain cells (neurons, astrocytes, and microglia) and infiltrating cells [peripheral blood mononuclear cells (PBMCs)]. We evaluated the dynamic interaction between astrocytes and infiltrating PBMCs as it impacts HIV in the CNS. We demonstrate that human primary-derived astrocytes (PDAs) predominantly secrete Wnt 1, 2b, 3, 5b, and 10b. Wnts are small secreted glycoproteins that initiate either β-catenin-dependent or independent signal transduction. The Wnt pathway plays a vital role in the regulation of CNS activities including neurogenesis, neurotransmitter release, synaptic plasticity, and memory consolidation. We show that HIV infection of PDAs altered astrocyte Wnt profile by elevating Wnts 2b and 10b. Astrocyte conditioned media (ACM) inhibited HIV replication in PBMCs by 50%. Removal of Wnts from ACM abrogated its ability to suppress HIV replication in PBMCs. Inversely, PBMCs supernatant activated PDAs, as demonstrated by a 10-fold increase in HLA-DR and a 5-fold increase in IFNγ expression, and enhanced astrocyte susceptibility to HIV by 2-fold, which was mediated by IFNγ in a Stat-3-dependent manner. Collectively, these data demonstrate a dynamic interaction between astrocytes and PBMCs, whereby astrocyte-secreted Wnts exert an anti-HIV effect on infected PBMCs and PBMCs, in turn, secrete IFNγ that enhance astrocyte susceptibility to productive HIV infection and mediate their activation.

Low DPP4 expression and activity in multiple sclerosis

Multiple sclerosis (MS) is a prototypic Th1/Th17 chronic autoimmune disease of the central nervous system. Dipeptidyl peptidase 4 (DPP4 or CD26) is a multifunctional molecule involved in autoimmune diseases' pathophysiology. We sought to integrate disparate pieces of data and analyze the plasma levels of sDPP4, DPP activity and DPP4 surface expression on T-cells in 129 MS patients with different clinical forms and 53 healthy controls, across two independent cohorts. Herein, we provide new evidence that sDPP4 concentration and DPP activity are significantly lower in MS patients than controls (p < 0.0001 and p < 0.01, respectively). In contrast, the frequency of circulating CD8(+)DPP4(hi) T-cells (p = 0.02) was increased in MS patients. This is the first study that simultaneously analyzes DPP4 expression and function in a large cohort of MS patients. Our data indicate a putative role for DPP4 in MS pathophysiology and suggest that a deeper understanding of surface versus shed DPP4 biology is warranted.

Tolerogenic vaccines for Multiple sclerosis

Tolerogenic vaccines represent a new class of vaccine designed to re-establish immunological tolerance, restore immune homeostasis, and thereby reverse autoimmune disease. Tolerogenic vaccines induce long-term, antigen-specific, inhibitory memory that blocks pathogenic T cell responses via loss of effector T cells and gain of regulatory T cell function. Substantial advances have been realized in the generation of tolerogenic vaccines that inhibit experimental autoimmune encephalomyelitis in a preclinical setting, and these vaccines may be a prequel of the tolerogenic vaccines that may have therapeutic benefit in Multiple Sclerosis. The purpose here is to provide a snapshot of the current concepts and future prospects of tolerogenic vaccination for Multiple Sclerosis, along with the central challenges to clinical application.

Epitope-specific CD8+ T cells play a differential pathogenic role in the development of a viral disease model for multiple sclerosis

Theiler's virus-induced demyelinating disease has been extensively investigated as a model for persistent viral infection and multiple sclerosis (MS). However, the role of CD8(+) T cells in the development of disease remains unclear. To assess the role of virus-specific CD8(+) T cells in the pathogenesis of demyelinating disease, a single amino acid substitution was introduced into the predominant viral epitope (VP3 from residues 159 to 166 [VP3(159-166)]) and/or a subdominant viral epitope (VP3(173-181)) of susceptible SJL/J mice by site-directed mutagenesis. The resulting variant viruses (N160V, P179A, and N160V/P179A) failed to induce CD8(+) T cell responses to the respective epitopes. Surprisingly, mice infected with N160V or N160V/P179A virus, which lacks CD8(+) T cells against VP3(159-166), did not develop demyelinating disease, in contrast to wild-type virus or P179A virus lacking VP3(173-181)-specific CD8(+) T cells. Our findings clearly show that the presence of VP3(159-166)-specific CD8(+) T cells, rather than viral persistence itself, is strongly correlated with disease development. VP3(173-181)-specific CD8(+) T cells in the central nervous system (CNS) of these virus-infected mice expressed higher levels of transforming growth factor β, forkhead box P3, interleukin-22 (IL-22), and IL-17 mRNA but caused minimal cytotoxicity compared to that caused by VP3(159-166)-specific CD8(+) T cells. VP3(159-166)-specific CD8(+) T cells exhibited high functional avidity for gamma interferon production, whereas VP3(173-181)-specific CD8(+) T cells showed low avidity. To our knowledge, this is the first report indicating that the induction of the IL-17-producing CD8(+) T cell type is largely epitope specific and that this specificity apparently plays a differential role in the pathogenicity of virus-induced demyelinating disease. These results strongly advocate for the careful consideration of CD8(+) T cell-mediated intervention of virus-induced inflammatory diseases.

CD8 T cell-initiated blood-brain barrier disruption is independent of neutrophil support

Blood-brain barrier (BBB) disruption is a common feature of numerous neurologic disorders. A fundamental question in these diseases is the extent inflammatory immune cells contribute to CNS vascular permeability. We have previously shown that CD8 T cells play a critical role in initiating BBB disruption in the peptide-induced fatal syndrome model developed by our laboratory. However, myelomonocytic cells such as neutrophils have also been implicated in promoting CNS vascular permeability and functional deficit in murine models of neuroinflammatory disease. For this reason, we evaluated neutrophil depletion in a murine model of CD8 T cell-initiated BBB disruption by employing traditionally used anti-granulocyte receptor-1 mAb RB6-8C5 and Ly-6G-specific mAb 1A8. We report that CNS-infiltrating antiviral CD8 T cells express high levels of granulocyte receptor-1 protein and are depleted by treatment with RB6-8C5. Mice treated with RB6-8C5, but not 1A8, display: 1) intact BBB tight junction proteins; 2) reduced CNS vascular permeability visible by gadolinium-enhanced T1-weighted magnetic resonance imaging; and 3) preservation of motor function. These studies demonstrate that traditional methods of neutrophil depletion with RB6-8C5 are broadly immune ablating. Our data also provide evidence that CD8 T cells initiate disruption of BBB tight junction proteins and CNS vascular permeability in the absence of neutrophil support.

Is multiple sclerosis an autoimmune disease?

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS) with varied clinical presentations and heterogeneous histopathological features. The underlying immunological abnormalities in MS lead to various neurological and autoimmune manifestations. There is strong evidence that MS is, at least in part, an immune-mediated disease. There is less evidence that MS is a classical autoimmune disease, even though many authors state this in the description of the disease. We show the evidence that both supports and refutes the autoimmune hypothesis. In addition, we present an alternate hypothesis based on virus infection to explain the pathogenesis of MS.

Reduction in healthcare and societal resource utilization associated with cladribine tablets in patients with relapsing-remitting multiple sclerosis: analysis of economic data from the CLARITY Study

BACKGROUND

Multiple sclerosis (MS) is a common, chronic, neurodegenerative condition associated with substantial healthcare and societal economic burden. Disease-modifying MS treatments have the potential to reduce health resource utilization (HRU), thereby reducing the attendant socioeconomic burden.

OBJECTIVE

This study aimed to compare health and societal resource use and productivity in patients with relapsing-remitting MS (RRMS) receiving cladribine tablets versus placebo over 96 weeks in the CLARITY study.

METHODS

The CLARITY study was a 96-week, randomized, double-blind, placebo-controlled study in patients with RRMS. HRU data, societal resource use and productivity data were collected at baseline and during scheduled patient visits, at 6-month intervals. The recall period for the HRU questionnaire was 3 months. The study was carried out at 155 sites across 32 countries worldwide. The intent-to-treat population comprised 1326 patients with RRMS randomized to cladribine 3.5 mg/kg (n = 433) or 5.25 mg/kg (n = 456) tablets or placebo (n = 437). Patient subgroups with high baseline disease activity were identified based on criteria of ≥2 relapses in the previous year (n = 392); ≥1 T1 gadolinium-enhancing (Gd+) lesion (n = 413); and ≥2 relapses in the previous year plus ≥1 T1 Gd+ lesion (n = 138). Cladribine tablets were administered in two (3.5 mg/kg group) or four (5.25 mg/kg group) short courses given at 4-week intervals at the start of a 48-week treatment period, followed by another two courses at the start of a subsequent 48-week re-treatment period. Interferon-β rescue therapy was permitted from week 24. Intravenous corticosteroids were available for the treatment of neurological relapses. HRU outcomes included mean number of hospital days and emergency room (ER), clinic and home visits during each study period. Societal resource use and productivity outcomes included mean number of hours and days of paid assistance, mean patient and carer work days missed, and self-reported productivity.

RESULTS

The mean number of hospital days per patient over 96 weeks was lower in the cladribine tablets groups (3.5 mg/kg group: -3.19 days; 5.25 mg/kg group: -1.54 days [both p < 0.01]) versus placebo. Likewise the mean number of ER visits was lower in both cladribine tablet groups compared with placebo (3.5 mg/kg group: -0.09 visits; 5.25 mg/kg group: -0.11 visits [both p < 0.01]), and the mean number of clinic visits was also lower in both cladribine tablet groups (3.5 mg/kg group: -0.68 visits; 5.25 mg/kg group: -0.66 visits [both p = 0.01]). Furthermore, treatment with cladribine tablets was associated with reduced mean numbers of missed work days for patients (3.5 mg/kg group: -2.42 days [p < 0.01]; 5.25 mg/kg group: -0.60 days [p = 0.50]). Corticosteroid use was lower amongst patients in the cladribine tablet groups than in the placebo group. The reduction in hospital days following treatment with cladribine tablets was also observed in patients with high disease activity at study baseline.

CONCLUSION

This study provides evidence that the efficacy of cladribine tablets observed during the CLARITY study was associated with a reduced consumption of healthcare resources and a decreased need for medical and societal support.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT00213135; EudraCT number: 2004-005148-28.

Degenerate T-cell recognition of peptides on MHC molecules creates large holes in the T-cell repertoire

The cellular immune system screens peptides presented by host cells on MHC molecules to assess if the cells are infected. In this study we examined whether the presented peptides contain enough information for a proper self/nonself assessment by comparing the presented human (self) and bacterial or viral (nonself) peptides on a large number of MHC molecules. For all MHC molecules tested, only a small fraction of the presented nonself peptides from 174 species of bacteria and 1000 viral proteomes ([Formula: see text]0.2%) is shown to be identical to a presented self peptide. Next, we use available data on T-cell receptor-peptide-MHC interactions to estimate how well T-cells distinguish between similar peptides. The recognition of a peptide-MHC by the T-cell receptor is flexible, and as a result, about one-third of the presented nonself peptides is expected to be indistinguishable (by T-cells) from presented self peptides. This suggests that T-cells are expected to remain tolerant for a large fraction of the presented nonself peptides, which provides an explanation for the "holes in the T-cell repertoire" that are found for a large fraction of foreign epitopes. Additionally, this overlap with self increases the need for efficient self tolerance, as many self-similar nonself peptides could initiate an autoimmune response. Degenerate recognition of peptide-MHC-I complexes by T-cells thus creates large and potentially dangerous overlaps between self and nonself.

Contrasting roles for CD4 vs. CD8 T-cells in a murine model of virally induced "T1 black hole" formation

MRI is sensitive to tissue pathology in multiple sclerosis (MS); however, most lesional MRI findings have limited correlation with disability. Chronic T1 hypointense lesions or "T1 black holes" (T1BH), observed in a subset of MS patients and thought to represent axonal damage, show moderate to strong correlation with disability. The pathogenesis of T1BH remains unclear. We previously reported the first and as of yet only model of T1BH formation in the Theiler's murine encephalitis virus induced model of acute CNS neuroinflammation induced injury, where CD8 T-cells are critical mediators of axonal damage and related T1BH formation. The purpose of this study was to further analyze the role of CD8 and CD4 T-cells through adoptive transfer experiments and to determine if the relevant CD8 T-cells are classic epitope specific lymphocytes or different subsets. C57BL/6 mice were used as donors and RAG-1 deficient mice as hosts in our adoptive transfer experiments. In vivo 3-dimensional MRI images were acquired using a 7 Tesla small animal MRI system. For image analysis, we used semi-automated methods in Analyze 9.1; transfer efficiency was monitored using FACS of brain infiltrating lymphocytes. Using a peptide depletion method, we demonstrated that the majority of CD8 T-cells are classic epitope specific cytotoxic cells. CD8 T-cell transfer successfully restored the immune system's capability to mediate T1BH formation in animals that lack adaptive immune system, whereas CD4 T-cell transfer results in an attenuated phenotype with significantly less T1BH formation. These findings demonstrate contrasting roles for these cell types, with additional evidence for a direct pathogenic role of CD8 T-cells in our model of T1 black hole formation.

miR-155 modulates microglia-mediated immune response by down-regulating SOCS-1 and promoting cytokine and nitric oxide production

Innate immunity constitutes the first line of defence against both external and endogenous threats in the brain, and microglia cells are considered key mediators of this process. Recent studies have shown that microRNAs (miRNAs) may play a determinant role in the regulation of gene expression during innate immune responses. The major goal of this work was to investigate the contribution of a specific miRNA - miR-155 - to the modulation of the microglia-mediated immune response. For this purpose, in vitro studies were performed in N9 microglia cells to evaluate changes in the levels of this miRNA following microglia activation. A strong up-regulation of miR-155 expression was observed following microglia exposure to lipopolysaccharide, which was consistent with a decrease in the levels of the suppressor of cytokine signalling 1 (SOCS-1) protein, a key inhibitor of the inflammatory process and a predicted target of miR-155. The miR-155 knockdown by anti-miRNA oligonucleotides up-regulated SOCS-1 mRNA and protein levels and significantly decreased the production of nitric oxide and the expression of inflammatory cytokines and inducible nitric oxide synthase. Finally, treatment of neuronal primary cultures with conditioned medium obtained from microglia cells, in which miR-155 was inhibited before cell activation, decreased inflammatory-mediated neuronal cell death. Overall, our results show that miR-155 has a pro-inflammatory role in microglia and is necessary for the progression of the immune response through the modulation of SOCS-1, suggesting that, in a chronic inflammatory context, miR-155 inhibition can have a neuroprotective effect.

Cladribine: mode of action and implications for treatment of multiple sclerosis

Multiple sclerosis (MS) is an inflammatory neurodegenerative disease of the central nervous system. The inflammation is driven significantly by autoreactive lymphocytes, which recruit cells of the innate immune system such as macrophages that contribute to subsequent tissue damage, ultimately resulting in demyelination and axonal damage that are characteristic in MS lesions. Cladribine (2-chlorodeoxyadenosine [2-CdA]) is a synthetic chlorinated deoxyadenosine analog that is biologically active in selected cell types and provides targeted and sustained reduction of circulating T and B lymphocytes implicated in the pathogenesis of MS. The biologic activity of cladribine depends on the preferential accumulation of cladribine phosphates in cell types with a high intracellular ratio of deoxycytidine kinase to 5'-nucleotidases. Cladribine-phosphates interfere with DNA synthesis and repair through incorporation into DNA and through inhibition of enzymes involved in DNA metabolism, including DNA polymerase and ribonucleotide reductase. This in turn leads to DNA strand breaks and ultimately cell death. This review explores the mechanism of action of cladribine further, in the context of recent clinical data, after completion of the phase III, 96-week, placebo-controlled CLARITY study. In this study, cladribine tablets demonstrated significant efficacy on clinical and neuroimaging outcomes in relapsing-remitting MS.

The HLA Region and Autoimmune Disease: Associations and Mechanisms of Action

The HLA region encodes several molecules that play key roles in the immune system. Strong association between the HLA region and autoimmune disease (AID) has been established for over fifty years. Association of components of the HLA class II encoded HLA-DRB1-DQA1-DQB1 haplotype has been detected with several AIDs, including rheumatoid arthritis, type 1 diabetes and Graves' disease. Molecules encoded by this region play a key role in exogenous antigen presentation to CD4+ Th cells, indicating the importance of this pathway in AID initiation and progression. Although other components of the HLA class I and III regions have also been investigated for association with AID, apart from the association of HLA-B*27 with ankylosing spondylitis, it has been difficult to determine additional susceptibility loci independent of the strong linkage disequilibrium (LD) with the HLA class II genes. Recent advances in the statistical analysis of LD and the recruitment of large AID datasets have allowed investigation of the HLA class I and III regions to be re-visited. Association of the HLA class I region, independent of known HLA class II effects, has now been detected for several AIDs, including strong association of HLA-B with type 1 diabetes and HLA-C with multiple sclerosis and Graves' disease. These results provide further evidence of a possible role for bacterial or viral infection and CD8+ T cells in AID onset. The advances being made in determining the primary associations within the HLA region and AIDs will not only increase our understanding of the mechanisms behind disease pathogenesis but may also aid in the development of novel therapeutic targets in the future.

Atacicept: targeting B cells in multiple sclerosis

Multiple sclerosis (MS) has traditionally been considered to be a T-cell-mediated disease. However, there is an increasing body of evidence for the involvement of B cells and autoantibodies in the pathology of this disease, providing a rationale for treatments directed against B cells. In this paper we summarize evidence for the key role of B cells in the immunopathology of MS and review data supporting the use of a novel B-cell targeted therapy, atacicept, in this condition. Atacicept is a human recombinant fusion protein that comprises the binding portion of a receptor for both BLyS (B-Lymphocyte Stimulator) and APRIL (A PRoliferation-Inducing Ligand), two cytokines that have been identified as important regulators of B-cell maturation, function and survival. Atacicept has shown selective effects on cells of the B-cell lineage, acting on mature B cells and blocking plasma cells and late stages of B-cell development while sparing B-cell progenitors and memory cells. The efficacy of atacicept in animal models of autoimmune disease and the biological activity of atacicept in patients with systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) has been demonstrated. Clinical studies were initiated to investigate the safety, tolerability and efficacy of atacicept in patients with MS. An unexpected increase in inflammatory activity in one of the trials, however, led to suspension of all atacicept trials in MS.

Rapid formation of extended processes and engagement of Theiler's virus-infected neurons by CNS-infiltrating CD8 T cells

A fundamental question in neuroimmunology is the extent to which CD8 T cells actively engage virus-infected neurons. In the Theiler's murine encephalomyelitis virus (TMEV) model of multiple sclerosis, an effective central nervous system (CNS)-infiltrating antiviral CD8 T cell response offers protection from this demyelinating disease. However, the specific CNS cell types engaged by these protective CD8 T cells in TMEV-resistant strains remains unknown. We used confocal microscopy to visualize the morphology, migration, and specific cellular interactions between adoptively transferred CD8 T cells and specific CNS cell types. Adoptively transferred GFP+ CD8+ splenocytes migrated to the brain and became 93% specific for the immunodominant virus epitope D(b):VP2(121-130). These CD8 T cells also polarized T cell receptor, CD8 protein, and granzyme B toward target neurons. Furthermore, we observed CD8 T cells forming cytoplasmic processes up to 45 μm in length. Using live tissue imaging, we determined that these T cell-extended processes (TCEPs) could be rapidly formed and were associated with migratory behavior through CNS tissues. These studies provide evidence that antiviral CD8 T cells have the capacity to engage virus-infected neurons in vivo and are the first to document and measure the rapid formation of TCEPs on these brain-infiltrating lymphocytes using live tissue imaging.

[Atacicept: a new B lymphocyte-targeted therapy for multiple sclerosis]

Multiple sclerosis (MS) has traditionally been considered to be a T cell-mediated disease. However, there is an increasing body of evidence for the involvement of B cells and autoantibodies in the pathology of this disease, providing a rationale for treatment strategies directed against B cells. This paper summarizes the evidence for a key role of B cells in the immunopathology of MS and reviews data supporting the use of a novel B cell-targeted therapy, atacicept, for this condition. Atacicept is a human recombinant fusion protein that comprises the binding portion of a receptor for both BLyS (B Lymphocyte Stimulator) and APRIL (A PRoliferation-Inducing Ligand), two cytokines that have been identified as important regulators of B cell maturation, function and survival. Atacicept has shown selective effects on cells of the B cell lineage, acting on mature B cells and blocking plasma cells and late stages of B cell development while sparing B cell progenitors and memory cells. The efficacy of atacicept in animal models of autoimmune disease and the biological activity of atacicept in patients with systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) has been demonstrated. Ongoing clinical studies are investigating the safety, tolerability and efficacy of atacicept in patients with MS, SLE and RA.

Inflammation in neurodegenerative diseases

Neurodegeneration, the slow and progressive dysfunction and loss of neurons and axons in the central nervous system, is the primary pathological feature of acute and chronic neurodegenerative conditions such as Alzheimer's disease and Parkinson's disease, neurotropic viral infections, stroke, paraneoplastic disorders, traumatic brain injury and multiple sclerosis. Despite different triggering events, a common feature is chronic immune activation, in particular of microglia, the resident macrophages of the central nervous system. Apart from the pathogenic role of immune responses, emerging evidence indicates that immune responses are also critical for neuroregeneration. Here, we review the impact of innate and adaptive immune responses on the central nervous system in autoimmune, viral and other neurodegenerative disorders, and discuss their contribution to either damage or repair. We also discuss potential therapies aimed at the immune responses within the central nervous system. A better understanding of the interaction between the immune and nervous systems will be crucial to either target pathogenic responses, or augment the beneficial effects of immune responses as a strategy to intervene in chronic neurodegenerative diseases.

CD8 T cell-initiated vascular endothelial growth factor expression promotes central nervous system vascular permeability under neuroinflammatory conditions

Dysregulation of the blood-brain barrier (BBB) is a hallmark feature of numerous neurologic disorders as diverse as multiple sclerosis, stroke, epilepsy, viral hemorrhagic fevers, cerebral malaria, and acute hemorrhagic leukoencephalitis. CD8 T cells are one immune cell type that have been implicated in promoting vascular permeability in these conditions. Our laboratory has created a murine model of CD8 T cell-mediated CNS vascular permeability using a variation of the Theiler's murine encephalomyelitis virus system traditionally used to study multiple sclerosis. Previously, we demonstrated that CD8 T cells have the capacity to initiate astrocyte activation, cerebral endothelial cell tight junction protein alterations and CNS vascular permeability through a perforin-dependent process. To address the downstream mechanism by which CD8 T cells promote BBB dysregulation, in this study, we assess the role of vascular endothelial growth factor (VEGF) expression in this model. We demonstrate that neuronal expression of VEGF is significantly upregulated prior to, and coinciding with, CNS vascular permeability. Phosphorylation of fetal liver kinase-1 is significantly increased early in this process indicating activation of this receptor. Specific inhibition of neuropilin-1 significantly reduced CNS vascular permeability and fetal liver kinase-1 activation, and preserved levels of the cerebral endothelial cell tight junction protein occludin. Our data demonstrate that CD8 T cells initiate neuronal expression of VEGF in the CNS under neuroinflammatory conditions, and that VEGF may be a viable therapeutic target in neurologic disease characterized by inflammation-induced BBB disruption.

IFNbeta-1a therapy for multiple sclerosis expands regulatory CD8+ T cells and decreases memory CD8+ subset: a longitudinal 1-year study

The beneficial effects of interferon beta-1a (IFNbeta-1a) in multiple sclerosis (MS) remain only partially understood. CD8(+) T cells are key cells in MS pathogenesis that contribute to axonal damage in MS, whereas CD4(+) regulatory T cells (T(Reg)) and CD8(+) regulatory/suppressor T cells (Ts) play an important role in protecting against subsequent MS activity. We analysed ex vivo changes on T(Reg) and on the different subsets of CD4(+) and CD8(+) T lymphocytes, before IFNbeta-1a (Rebif) therapy and at 3, 6, and 12 months after treatment, in 23 MS patients and in 26 healthy controls. IFNbeta-1a significantly increased the proportions of CD4(+) T(Reg) and regulatory CD8(+) T cells (Tr). Memory CD8(+) T cells were significantly decreased after 1 year of treatment, maybe reflecting down-regulation of abnormally persistent systemic activation in MS patients. After 1 year of IFNbeta-1a, a direct correlation was observed between plasmacytoid dendritic cells and effector CD8(+) T cells.

Increased numbers of IL-7 receptor molecules on CD4+CD25-CD107a+ T-cells in patients with autoimmune diseases affecting the central nervous system

Background

High content immune profiling in peripheral blood may reflect immune aberrations associated with inflammation in multiple sclerosis (MS) and other autoimmune diseases affecting the central nervous system.

Methods and Findings

Peripheral blood mononuclear cells from 46 patients with multiple sclerosis (MS), 9 patients diagnosed with relapsing remitting MS (RRMS), 13 with secondary progressive multiple sclerosis (SPMS), 9 with other neurological diseases (OND) and well as 15 healthy donors (HD) were analyzed by 12 color flow cytometry (TCRαβ, TCRγδ, CD4, CD8α, CD8β, CD45RA, CCR7, CD27, CD28, CD107a, CD127, CD14) in a cross-sectional study to identify variables significantly different between controls (HD) and patients (OND, RRMS, SPMS). We analyzed 187 individual immune cell subsets (percentages) and the density of the IL-7 receptor alpha chain (CD127) on 59 individual immune phenotypes using a monoclonal anti-IL-7R antibody (clone R34.34) coupled to a single APC molecule in combination with an APC-bead array. A non-parametric analysis of variance (Kruskal-Wallis test) was conducted in order to test for differences among the groups in each of the variables. To correct for the multiplicity problem, the FDR correction was applied on the p-values. We identified 19 variables for immune cell subsets (percentages) which allowed to segregate healthy individuals and individuals with CNS disorders. We did not observe differences in the relative percentage of IL-7R-positive immune cells in PBMCs. In contrast, we identified significant differences in IL-7 density, measured on a single cell level, in 2/59 variables: increased numbers of CD127 molecules on TCRαβ+CD4+CD25 (intermed) T-cells and on TCRαβ+CD4+CD25−CD107a+ T-cells (mean: 28376 Il-7R binding sites on cells from HD, 48515 in patients with RRMS, 38195 in patients with SPMS and 33692 IL-7 receptor binding sites on cells from patients with OND).

Conclusion

These data show that immunophenotyping represents a powerful tool to differentiate healthy individuals from individuals suffering from neurological diseases and that the number of IL-7 receptor molecules on differentiated TCRαβ+CD4+CD25−CD107a+ T-cells, but not the percentage of IL-7R-positive cells, segregates healthy individuals from patients with neurological disorders.

Antigens expressed by myelinating glia cells induce peripheral cross-tolerance of endogenous CD8+ T cells

Auto-reactivity of T cells is largely prevented by central and peripheral tolerance. Nevertheless, immunization with certain self-antigens emulsified in CFA induces autoimmunity in rodents, suggesting that tolerance to some self-antigens is not robust. To investigate the fate of nervous system-specific CD8(+) T cells, which only recently came up as being important contributors for MS pathogenesis, we developed a mouse model that allows inducible expression of lymphocytic choriomeningitis virus-derived CD8(+) T-cell epitopes specifically in oligodendrocytes and Schwann cells, the myelinating glia of the nervous system. These transgenic CD8(+) T-cell epitopes induced robust tolerance of endogenous auto-reactive T cells, which proved thymus-independent and was mediated by cross-presenting bone-marrow-derived cells. Immunohistological staining of secondary lymphoid organs demonstrated the presence of glia-derived antigens in DC, suggesting that peripheral tolerance of CD8(+) T cells results from uptake and presentation by steady state DC.

VEGF and angiogenesis in acute and chronic MOG((35-55)) peptide induced EAE

An increased expression of vascular endothelial growth factor (VEGF) is associated with demyelinated lesions in both multiple sclerosis (MS) and its model (EAE), implicating changes in vasculature as a potential component of CNS plaque formation. The purpose of this study was to investigate the vascular changes in acute and chronic EAE in C57BL/6 mice induced with myelin oligodendrocyte glycoprotein (MOG ((35-55))) peptide. We investigated the functional contribution of VEGF to acute and chronic EAE by treating immunized mice with SU5416 (Semaxinib), a potent and selective inhibitor of VEGF receptor 2 (VEGFR2). Animals received seven daily injections of SU5416 (50 mg/kg) or vehicle beginning on the day after disease onset (acute study) or on day 45 post-immunization (chronic study). Spinal cord sections were collected on the day of sacrifice. Modulation of angiogenic gene expression was determined using RNA isolated from 4 acute and 4 non-immunized controls. MOG peptide induction produced extensive demyelination, immune cell infiltration, tissue laminin deposits, and axonal loss in lesions. VEGF expression was extensively increased in the acute mice, which correlated positively with clinical score. In the acute study, SU5416 treatment produced a significant clinical improvement versus vehicle controls (p<0.001), with less demyelination (-37%) and cellular infiltration (-23%) in the spinal cord (p<0.05). Treated animals also had significantly fewer blood vessels per section than controls (56.1+/-6.1 v. 81.6+/-11.5, p<0.05), and significantly reduced laminin abnormalities (28.9% of lesion area v. 46.8%, p<0.05). There was no improvement in clinical score or tissue pathology, and no difference in vessel number or lesion laminin expression, when SU5416 was administered during the chronic disease (all p>0.05). In the acute study only, VEGF staining correlated with demyelination and the extent of cellular infiltration in both control (r=0.723, r=0.665) and treated (r=0.681, r=0.487) animals (all p<0.05). Laminin staining in lesion areas was strongly correlated with tissue pathology for all animals in both the acute and chronic study (all p<0.001). Vascular alterations in MOG peptide-induced EAE in the mouse are accompanied by increased lesion-specific levels of VEGF, extensive laminin deposits in the tissue and altered transcription of numerous angiogenic factors. In the microarray studies, acute mice showed a significant increase in several angiogenic RNA transcripts, six of which were verified by RT-PCR, alanyl aminopeptidase, caspase 8, Hif1a, MMP-19, plasminogen activator inhibitor, and thrombospondin1.

Evaluating epigenetic landmarks in the brain of multiple sclerosis patients: a contribution to the current debate on disease pathogenesis

The evidence suggesting a role of epigenetics in the definition of complex trait diseases is rapidly increasing. The gender prevalence of multiple sclerosis, the low level concordance in homozygous twins and the linkage to several genetic loci, suggest an epigenetic component to the definition of this demyelinating disorder. While the immune etio-pathogenetic mechanism of disease progression has been well characterized, still relatively little is known about the initial events contributing to onset and progression of the demyelinating lesion. This article addresses the challenging question of whether loss of the mechanisms of epigenetic regulation of gene expression in the myelinating cells may contribute to the pathogenesis of multiple sclerosis, by affecting the repair process and by modulating the levels of enzymes involved in neo-epitope formation. The role of altered post-translational modifications of nucleosomal histones and DNA methylation in white matter oligodendroglial cells are presented in terms of pathogenetic concepts and the relevance to therapeutic intervention is then discussed.

Blood CD8+ T cell responses against myelin determinants in multiple sclerosis and healthy individuals

Patients with multiple sclerosis (MS) display significant peripheral blood CD8(+) T cell receptor biases, suggesting clonal selection. Our objective was to identify relevant myelin-derived peptides capable of eliciting responses of fresh blood CD8+ T cells in MS patients. We focused our analysis on the HLA supertypes (HLA-A3, -A2, -B7, -B27, -B44) predominant in a patient cohort. Three myelin protein (MBP, PLP and MOG) sequences were screened for HLA binding motifs and peptides were tested for their binding to HLA molecules. The cellular responses of 27 MS patients and 19 age- and sex-matched healthy controls (HC) were tested in IFN-gamma ELISPOT assays only detecting pre-committed CD8+ T cells. Sixty-nine new epitopes elicited positive responses, with MOG-derived peptides being the most immunogenic and peptides binding to HLA-A3 being the most frequent. However, MS patients and HC displayed the same frequency of autoreactive cells. The epitopes inducing the strongest responses were not those with the highest HLA binding, suggesting an effective thymic selection in MS patients. Our data extend the concept that the frequency of myelin-reactive T cells in MS patient blood is not increased compared to HC. The description of this set of myelin-derived peptides (MHC class I restricted, recognized by CD8+ T cells) offers new tools to explore the CD8+ cell role in MS.

Induction of blood brain barrier tight junction protein alterations by CD8 T cells

Disruption of the blood brain barrier (BBB) is a hallmark feature of immune-mediated neurological disorders as diverse as viral hemorrhagic fevers, cerebral malaria and acute hemorrhagic leukoencephalitis. Although current models hypothesize that immune cells promote vascular permeability in human disease, the role CD8 T cells play in BBB breakdown remains poorly defined. Our laboratory has developed a novel murine model of CD8 T cell mediated central nervous system (CNS) vascular permeability using a variation of the Theiler's virus model of multiple sclerosis. In previous studies, we observed that MHC class II^−/− (CD4 T cell deficient), IFN-γR^−/−, TNF-α^−/−, TNFR1^−/−, TNFR2^−/−, and TNFR1/TNFR2 double knockout mice as well as those with inhibition of IL-1 and LTβ activity were susceptible to CNS vascular permeability. Therefore, the objective of this study was to determine the extent immune effector proteins utilized by CD8 T cells, perforin and FasL, contributed to CNS vascular permeability. Using techniques such as fluorescent activated cell sorting (FACS), T1 gadolinium-enhanced magnetic resonance imaging (MRI), FITC-albumin leakage assays, microvessel isolation, western blotting and immunofluorescent microscopy, we show that in vivo stimulation of CNS infiltrating antigen-specific CD8 T cells initiates astrocyte activation, alteration of BBB tight junction proteins and increased CNS vascular permeability in a non-apoptotic manner. Using the aforementioned techniques, we found that despite having similar expansion of CD8 T cells in the brain as wildtype and Fas Ligand deficient animals, perforin deficient mice were resistant to tight junction alterations and CNS vascular permeability. To our knowledge, this study is the first to demonstrate that CNS infiltrating antigen-specific CD8 T cells have the capacity to initiate BBB tight junction disruption through a non-apoptotic perforin dependent mechanism and our model is one of few that are useful for studies in this field. These novel findings are highly relevant to the development of therapies designed to control immune mediated CNS vascular permeability.

Selective regulation of CD8 effector T cell migration by the p110 gamma isoform of phosphatidylinositol 3-kinase

Chemokine-mediated T cell migration is essential to an optimal immune response. The p110gamma isoform of PI3K is activated by G protein-coupled receptors and regulates neutrophil and macrophage chemotaxis. We used p110gamma-deficient mice to examine the role of p110gamma in CD8 T cell migration and activation in response to viral challenge. Naive CD8 T cell migration in response to CCL21 in vitro and trafficking into secondary lymphoid organs in vivo was unaffected by the loss of p110gamma. Furthermore, loss of p110gamma did not affect CD8 T cell proliferation and effector cell differentiation in vitro in response to anti-CD3 stimulation or in vivo in response to vaccinia virus (VV) challenge. However, there was reduced migration of p110gamma knockout (p110gamma(-/-)) CD8 effector T cells into the peritoneum following i.p. challenge with VV. The role of p110gamma in CD8 effector T cell migration was intrinsic to T cells, as p110gamma(-/-) CD8 effector T cells exhibited impaired migration into the inflamed peritoneum following secondary transfer into wild-type recipients. In addition, p110gamma(-/-) CD8 effector T cells exhibited impaired migration in vitro in response to inflammatory chemoattractants. Although wild-type mice efficiently cleared VV at high viral doses, infection of p110gamma knockout mice resulted in visible illness and death less than a week after infection. Thus, p110gamma is dispensable for constitutive migration of naive CD8 T cells and subsequent activation and differentiation into effector CD8 T cells, but plays a central role in the migration of effector CD8 T cells into inflammatory sites.

Erythropoietin: a potent inducer of peripheral immuno/inflammatory modulation in autoimmune EAE

Background

Beneficial effects of short-term erythropoietin (EPO) therapy have been demonstrated in several animal models of acute neurologic injury, including experimental autoimmune encephalomyelitis (EAE)-the animal model of multiple sclerosis. We have found that EPO treatment substantially reduces the acute clinical paralysis seen in EAE mice and this improvement is accompanied by a large reduction in the mononuclear cell infiltration and downregulation of glial MHC class II expression within the inflamed CNS. Other reports have recently indicated that peripherally generated anti-inflammatory CD4⁺Foxp3⁺ regulatory T cells (Tregs) and the IL17-producing CD4+ T helper cell (Th17) subpopulations play key antagonistic roles in EAE pathogenesis. However, no information regarding the effects of EPO therapy on the behavior of the general mononuclear-lymphocyte population, Tregs or Th17 cells in EAE has emerged.

Methods and Findings

We first determined in vivo that EPO therapy markedly suppressed MOG specific T cell proliferation and sharply reduced the number of reactive dendritic cells (CD11c positive) in EAE lymph nodes during both inductive and later symptomatic phases of MOG_35–55 induced EAE. We then determined the effect in vivo of EPO on numbers of peripheral Treg cells and Th17 cells. We found that EPO treatment modulated immune balance in both the periphery and the inflamed spinal cord by promoting a large expansion in Treg cells, inhibiting Th17 polarization and abrogating proliferation of the antigen presenting dendritic cell population. Finally we utilized tissue culture assays to show that exposure to EPO in vitro similarly downregulated MOG-specific T cell proliferation and also greatly suppressed T cell production of pro-inflammatory cytokines.

Conclusions

Taken together, our findings reveal an important new locus whereby EPO induces substantial long-term tissue protection in the host through signaling to several critical subsets of immune cells that reside in the peripheral lymphatic system.

Multiple sclerosis: pathogenesis and MR imaging features of T1 hypointensities in a [corrected] murine model

PURPOSE

To prospectively determine how T1 hypointensities (T1 black holes) on brain magnetic resonance (MR) images are generated by the immune system by using a Theiler murine encephalitis virus-induced model of multiple sclerosis and high-field-strength MR imaging.

MATERIALS AND METHODS

All animal protocols and experiments were approved by the institutional animal care and use committee. Volumetric MR imaging studies were conducted at 7 T in six C57BL/6 mice and in immune differentiation marker (recombination activation gene [RAG]-1)-, immune cell (CD4, CD8)-, and immune effector molecule (Fas ligand, perforin)-deficient mice (six mice in each group) to determine which immune cell types and effector molecules lead to T1 hypointensities. The main outcome measure was the total T1 black hole volume per animal, as determined with volumetric analysis, and was analyzed statistically by using software.

RESULTS

Compared with C57BL/6 mice, RAG-1-deficient mice showed a significant (P = .003) decrease in total T1 black hole volume, suggesting a clear role for the adaptive immune system. While CD4-deficient mice did not show a significant decrease in T1 black hole volume (P = .33), CD8-deficient mice did (P = .003). Perforin-deficient mice showed a significant reduction of T1 black hole volume (P = .002), whereas Fas ligand-deficient mice did not (P = .77).

CONCLUSION

The data suggest that CD8 T cells utilizing perforin effector molecules are responsible for T1 black hole formation.

Pro-inflammatory functions of astrocytes correlate with viral clearance and strain-dependent protection from TMEV-induced demyelinating disease

Intracerebral infection of susceptible strains of mice, e.g. SJL/J, with Theiler's murine encephalomyelitis virus (TMEV) leads to a persistent CNS infection accompanied by development of a chronic-progressive inflammatory CNS autoimmune demyelinating disease which is clinically and pathologically similar to human multiple sclerosis. In contrast, resistant strains of mice, e.g. C57BL/6 (B6), effectively clear TMEV from the CNS and do not develop demyelinating disease. Although CD8(+) T cells are crucial for viral clearance in B6 mice, SJL mice also mount potent CD8(+) T cell responses against virus, thus the reason for the viral persistence in the CNS in these mice is unclear. Here, we examined innate anti-viral responses of CNS-resident astrocytes as a potential determinant of viral persistence and disease susceptibility. We demonstrate that B6 astrocytes produce significantly higher levels of cytokines, chemokines and adhesion molecules in response to TMEV infection, or stimulation with IFN-gamma and TNF-alpha or poly I:C than SJL mice. In addition, TMEV more effectively induces MHC I molecules on B6 astrocytes than SJL, corresponding with an increased ability to activate TMEV-specific CD8(+) T cells directly ex vivo. These results suggest that enhanced anti-viral responses of B6 astrocytes contribute to the ability of these mice to clear TMEV from the CNS and therefore to their resistance to the development of autoimmune demyelinating disease.

CNS T-cell lymphoma: an under-recognized entity?

The incidence of CNS lymphoma has increased significantly in the past 30 years, primarily in the elderly and immunocompromised. While T-cell lymphomas comprise 15-20% of systemic lymphomas, they comprise less than 4% of primary CNS lymphomas, suggesting that they may be under-recognized compared to their systemic counterparts. To investigate this, we studied brain biopsies from three patients who were diagnosed with T-cell lymphoma confined to the brain. They had enhancing lesions by MRI, arising in the cerebellum and brainstem in one and temporal lobe in two. We compared these to biopsies from three patients who had reactive lymphoid infiltrates and who had clinical signs/symptoms and radiographic findings that were indistinguishable from the lymphoma group. Biopsies from both the lymphoma group and reactive group showed considerable cytomorphologic heterogeneity. Although one lymphoma case contained large atypical cells, the other two contained small, mature lymphocytes within a heterogeneous infiltrate of neoplastic and reactive inflammatory cells. Surface marker aberrancies were present in two lymphoma cases, but this alone could not reliably diagnose T-cell lymphoma. The proliferation index was not useful for differentiating lymphoma from reactive infiltrates. In five of the six cases the diagnosis was most influenced by clonality studies for T-cell receptor-gamma gene rearrangements. We conclude that because of the high degree of overlap in cytomorphologic and immunophenotypic features between T-cell lymphoma and reactive infiltrates, T-cell lymphoma may not be recognized unless studies for T-cell receptor gene rearrangements are performed for CNS lesions composed of a polymorphous but predominantly T-cell infiltrate.

Passive induction of experimental allergic encephalomyelitis

Experimental allergic encephalomyelitis (EAE) is a widely used animal model of the human demyelinating disease multiple sclerosis. EAE is initiated by immunization with myelin antigens in adjuvant or by adoptive transfer of myelin-specific T cells, resulting in inflammatory infiltrates and demyelination in the central nervous system. Induction of EAE in rodents typically results in ascending flaccid paralysis with inflammation primarily targeting the spinal cord. This protocol describes passive induction of EAE by adoptive transfer of T cells isolated from mice primed with myelin antigens into naïve mice. The advantages of using this method versus active induction of EAE are discussed.

Active induction of experimental allergic encephalomyelitis

This protocol details a method to actively induce experimental allergic encephalomyelitis (EAE), a widely used animal model for studies of multiple sclerosis. EAE is induced by stimulating T-cell-mediated immunity to myelin antigens. Active induction of EAE is accomplished by immunization with myelin antigens emulsified in adjuvant. This protocol focuses on induction of EAE in mice; however, the same principles apply to EAE induction in other species. EAE in rodents is manifested typically as ascending flaccid paralysis with inflammation targeting the spinal cord. However, more diverse clinical signs can occur in certain strain/antigen combinations in rodents and in other species, reflecting increased inflammation in the brain.

T cell tolerance to the skin: a central role for central tolerance

T cell tolerance to self-antigens is believed to be achieved in a two-step process. The first step, called central tolerance, takes place in the thymus. The second step takes place outside the thymus in secondary lymphoid organs. One may ask why two mechanisms are needed to insure T cell tolerance. These two mechanisms share redundant functions and dysfunctions, leading to T cell-mediated autoimmune syndromes. By reviewing the literature on relevant animal models for T cell tolerance and our own recent findings, we are providing evidences that only central tolerance is acting for the skin.

Minocycline Down-regulates MHC II Expression in Microglia and Macrophages through Inhibition of IRF-1 and Protein Kinase C (PKC)α/βII

Experimental allergic encephalomyelitis, an autoimmune disorder mediated by T cells, results in demyelination, inflammation, and axonal loss in the central nervous system (CNS). Microglia play a critical role in major histocompatibility complex class II (MHC II)-dependent antigen presentation and in reactivation of CNS-infiltrated encephalitogenic T cells. Minocycline, a tetracycline anti-biotic, has profound anti-inflammatory properties and is experimentally used for treatment of many CNS disorders; however, the mechanisms involved in minocycline effects remain unknown. We show that administration of minocycline for 2 weeks ameliorated clinical severity of experimental allergic encephalomyelitis, an effect that partially involves the down-regulation of MHC II proteins in the spinal cord. Therefore, we sought to elucidate the molecular mechanisms of minocycline inhibitory effects on MHC II expression in microglia. Although complex, the co-activator class II transactivator (CIITA) is a key regulator of MHC II expression. Here we show that minocycline inhibited interferongamma (IFNgamma)-induced CIITA and MHC II mRNA. Interestingly, however, it was without effect on STAT1 phosphorylation or IRF-1 expression, transcription factors that are activated by IFNgamma and necessary for CIITA expression. Further experiments revealed that MHC II expression is down-regulated in the presence of the PKC(alpha) inhibitor Gö6976. Minocycline inhibited IFNgamma-induced PKC(alpha/betaII) phosphorylation and the nuclear translocation of both PKC(alpha/betaII) and IRF-1 that subsequently inhibits CIITA expression. Our present data delineate a molecular pathway of minocycline action that includes inhibitory effects on PKC(alpha/betaII) and transcription factors that regulate the expression of critical inflammatory genes such as MHC II. Such a fundamental mechanism may underlie the pleiotropic effects of minocycline in CNS inflammatory disorders.

Selective retention of herpes simplex virus-specific T cells in latently infected human trigeminal ganglia

Primary infection with herpes simplex virus 1 (HSV-1) and varicella zoster virus (VZV) results in lifelong latent infections of neurons in sensory ganglia such as the trigeminal ganglia (TG). It has been postulated that T cells retained in TG inhibit reactivation of latent virus. The acquisition of TG specimens of individuals within hours after death offered the unique opportunity to characterize the phenotype and specificity of TG-resident T cells in humans. High numbers of activated CD8(+) T cells expressing a late effector memory phenotype were found to reside in latently infected TG. The T cell infiltrate was oligoclonal, and T cells selectively clustered around HSV-1 but not VZV latently infected neurons. Neuronal damage was not observed despite granzyme B expression by the neuron-interacting CD8(+) T cells. The TG-resident T cells, mainly CD8(+) T cells, were directed against HSV-1 and not to VZV, despite neuronal expression of VZV proteins. The results implicate that herpesvirus latency in human TG is associated with a local, persistent T cell response, comprising activated late effector memory CD8(+) T cells that appear to control HSV-1 latency by noncytolytic pathways. In contrast, T cells do not seem to be directly involved in controlling VZV latency in human TG.

Increased citrullination of histone H3 in multiple sclerosis brain and animal models of demyelination: a role for tumor necrosis factor-induced peptidylarginine deiminase 4 translocation

Modification of arginine residues by citrullination is catalyzed by peptidylarginine deiminases (PADs), of which five are known, generating irreversible protein structural modifications. We have shown previously that enhanced citrullination of myelin basic protein contributed to destabilization of the myelin membrane in the CNS of multiple sclerosis (MS) patients. We now report increased citrullination of nucleosomal histones by PAD4 in normal-appearing white matter (NAWM) of MS patients and in animal models of demyelination. Histone citrullination was attributable to increased levels and activity of nuclear PAD4. PAD4 translocation into the nucleus was attributable to elevated tumor necrosis factor-alpha (TNF-alpha) protein. The elevated TNF-alpha in MS NAWM was not associated with CD3+ or CD8+ lymphocytes, nor was it associated with CD68+ microglia/macrophages. GFAP, a measure of astrocytosis, was the only cytological marker that was consistently elevated in the MS NAWM, suggesting that TNF-alpha may have been derived from astrocytes. In cell cultures of mouse and human oligodendroglial cell lines, PAD4 was predominantly cytosolic but TNF-alpha treatment induced its nuclear translocation. To address the involvement of TNF-alpha in targeting PAD4 to the nucleus, we found that transgenic mice overexpressing TNF-alpha also had increased levels of citrullinated histones and elevated nuclear PAD4 before demyelination. In conclusion, high citrullination of histones consequent to PAD4 nuclear translocation is part of the process that leads to irreversible changes in oligodendrocytes and may contribute to apoptosis of oligodendrocytes in MS.