Screening of several H-2 congenic mouse strains identified H-2(q) mice as highly susceptible to MOG-induced EAE with minimal adjuvant requirement

Mimicking the brain: Epstein-Barr virus and foreign agents as drivers of neuroimmune attack in multiple sclerosis

T cells have an essential role in adaptive immunity against pathogens and cancer, but failure of thymic tolerance mechanisms can instead lead to escape of T cells with the ability to attack host tissues. Multiple sclerosis (MS) occurs when structures such as myelin and neurons in the central nervous system (CNS) are the target of autoreactive immune responses, resulting in lesions in the brain and spinal cord which cause varied and episodic neurological deficits. A role for autoreactive T cell and antibody responses in MS is likely, and mounting evidence implicates Epstein-Barr virus (EBV) in disease mechanisms. In this review we discuss antigen specificity of T cells involved in development and progression of MS. We examine the current evidence that these T cells can target multiple antigens such as those from pathogens including EBV and briefly describe other mechanisms through which viruses could affect disease. Unravelling the complexity of the autoantigen T cell repertoire is essential for understanding key events in the development and progression of MS, with wider implications for development of future therapies.

Cross-reactive EBNA1 immunity targets alpha-crystallin B and is associated with multiple sclerosis

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system, for which and Epstein-Barr virus (EBV) infection is a likely prerequisite. Due to the homology between Epstein-Barr nuclear antigen 1 (EBNA1) and alpha-crystallin B (CRYAB), we examined antibody reactivity to EBNA1 and CRYAB peptide libraries in 713 persons with MS (pwMS) and 722 matched controls (Con). Antibody response to CRYAB amino acids 7 to 16 was associated with MS (OR = 2.0), and combination of high EBNA1 responses with CRYAB positivity markedly increased disease risk (OR = 9.0). Blocking experiments revealed antibody cross-reactivity between the homologous EBNA1 and CRYAB epitopes. Evidence for T cell cross-reactivity was obtained in mice between EBNA1 and CRYAB, and increased CRYAB and EBNA1 CD4+ T cell responses were detected in natalizumab-treated pwMS. This study provides evidence for antibody cross-reactivity between EBNA1 and CRYAB and points to a similar cross-reactivity in T cells, further demonstrating the role of EBV adaptive immune responses in MS development.

Polymorphic estrogen receptor binding site causes Cd2-dependent sex bias in the susceptibility to autoimmune diseases

Complex autoimmune diseases are sexually dimorphic. An interplay between predisposing genetics and sex-related factors probably controls the sex discrepancy in the immune response, but the underlying mechanisms are unclear. Here we positionally identify a polymorphic estrogen receptor binding site that regulates Cd2 expression, leading to female-specific differences in T cell-dependent mouse models of autoimmunity. Female mice with reduced Cd2 expression have impaired autoreactive T cell responses. T cells lacking Cd2 costimulation upregulate inhibitory Lag-3. These findings help explain sexual dimorphism in human autoimmunity, as we find that CD2 polymorphisms are associated with rheumatoid arthritis and 17-β-estradiol-regulation of CD2 is conserved in human T cells. Hormonal regulation of CD2 might have implications for CD2-targeted therapy, as anti-Cd2 treatment more potently affects T cells in female mice. These results demonstrate the relevance of sex-genotype interactions, providing strong evidence for CD2 as a sex-sensitive predisposing factor in autoimmunity.

Animal Models of Multiple Sclerosis

Animal models with high translational validity are essential tools in understanding disease pathogenesis and in the development of therapeutic strategies. Multiple sclerosis (MS) is an autoimmune demyelinating disease of the central nervous system characterized by progressive neurological deficits and socioeconomic burden. Experimental autoimmune encephalomyelitis (EAE) is the most extensively utilized animal model of MS, with well-characterized rodent and non-human primate variants. The EAE model is typically induced by either active immunization with myelin-derived proteins or peptides in adjuvant or by passive transfer of activated myelin-specific CD4⁺ T lymphocytes. To date, the EAE model has been an essential tool in the development of at least seven U.S. Food and Drug Administration (FDA)-approved immunomodulatory drugs for the treatment of MS, including glatiramer acetate, fingolimod, and natalizumab. However, the translational validity of the EAE model is frequently compromised due to poor study design, inconsistent clinical scoring endpoints, and inappropriate statistical calculations. No single animal model accurately reflects the complexity of human MS pathogenesis. Beyond EAE, multiple additional animal models are described, including Theiler's murine encephalomyelitis virus and cuprizone-induced demyelination, which facilitate the study of pathogen-induced CNS autoimmunity and remyelination, respectively. This overview summarizes several of the most frequently used animal models of MS and highlights key factors that significantly influence the experimental outcome and affect translational validity. © 2021 Wiley Periodicals LLC.

Myelin-specific CD8+ T cells exacerbate brain inflammation in CNS autoimmunity

Multiple sclerosis (MS) is an inflammatory, demyelinating disease of the CNS. Although CD4+ T cells are implicated in MS pathogenesis and have been the main focus of MS research using the animal model experimental autoimmune encephalomyelitis (EAE), substantial evidence from patients with MS points to a role for CD8+ T cells in disease pathogenesis. We previously showed that an MHC class I-restricted epitope of myelin basic protein (MBP) is presented in the CNS during CD4+ T cell-initiated EAE. Here, we investigated whether naive MBP-specific CD8+ T cells recruited to the CNS during CD4+ T cell-initiated EAE engaged in determinant spreading and influenced disease. We found that the MBP-specific CD8+ T cells exacerbated brain but not spinal cord inflammation. We show that a higher frequency of monocytes and monocyte-derived cells presented the MHC class I-restricted MBP ligand in the brain compared with the spinal cord. Infiltration of MBP-specific CD8+ T cells enhanced ROS production in the brain only in these cell types and only when the MBP-specific CD8+ T cells expressed Fas ligand (FasL). These results suggest that myelin-specific CD8+ T cells may contribute to disease pathogenesis via a FasL-dependent mechanism that preferentially promotes lesion formation in the brain.

Independent and inter-dependent immunoregulatory effects of NCF1 and NOS2 in experimental autoimmune encephalomyelitis

Background

Increasing evidence has suggested that a single nucleotide polymorphism in the Ncf1 gene is associated with experimental autoimmune encephalomyelitis (EAE). However, the mechanisms of NCF1-induced immunoregulatory effects remain poorly understood. In this study, we focus on NCF1 deficiency-mediated effects on EAE in NOS2 dependent and independent ways.

Methods

To determine the effects of NCF1 and NOS2 during EAE development, we have established recombinant mouse strains deficient at NCF1 and/or NOS2 in a crossbreeding system. Different strains allow us to examine the entire course of the disease in the Nos2-null mice bearing a Ncf1 gene that encodes a mutated NCF1, deficient in triggering oxidative burst, after immunization with recombinant myelin oligodendrocyte glycoprotein (MOG)_79-96 peptides. The peptide-induced innate and adaptive immune responses were analyzed by flow cytometry.

Results

NCF1-deficient mice developed a reduced susceptibility to EAE, whereas NCF1-NOS2 double-deficient mice developed an enhanced EAE, as compared with NOS2-deficient mice. Flow cytometry analyses show that double deficiencies resulted in an increase of neutrophils in the spleen, accompanied with higher release of interleukin-1β in neutrophils prior to EAE onset. The additional deficiency in NCF1 had no added effect on either interleukin-17 or interferon-γ secretion of T cells during the priming phase.

Conclusions

These studies show that NCF1 and NOS2 interact to regulate peptide-induced EAE.

The model of local axon homeostasis - explaining the role and regulation of microtubule bundles in axon maintenance and pathology

Axons are the slender, cable-like, up to meter-long projections of neurons that electrically wire our brains and bodies. In spite of their challenging morphology, they usually need to be maintained for an organism's lifetime. This makes them key lesion sites in pathological processes of ageing, injury and neurodegeneration. The morphology and physiology of axons crucially depends on the parallel bundles of microtubules (MTs), running all along to serve as their structural backbones and highways for life-sustaining cargo transport and organelle dynamics. Understanding how these bundles are formed and then maintained will provide important explanations for axon biology and pathology. Currently, much is known about MTs and the proteins that bind and regulate them, but very little about how these factors functionally integrate to regulate axon biology. As an attempt to bridge between molecular mechanisms and their cellular relevance, we explain here the model of local axon homeostasis, based on our own experiments in Drosophila and published data primarily from vertebrates/mammals as well as C. elegans. The model proposes that (1) the physical forces imposed by motor protein-driven transport and dynamics in the confined axonal space, are a life-sustaining necessity, but pose a strong bias for MT bundles to become disorganised. (2) To counterbalance this risk, MT-binding and -regulating proteins of different classes work together to maintain and protect MT bundles as necessary transport highways. Loss of balance between these two fundamental processes can explain the development of axonopathies, in particular those linking to MT-regulating proteins, motors and transport defects. With this perspective in mind, we hope that more researchers incorporate MTs into their work, thus enhancing our chances of deciphering the complex regulatory networks that underpin axon biology and pathology.

Tuftsin Combines With Remyelinating Therapy and Improves Outcomes in Models of CNS Demyelinating Disease

Though promoting remyelination in multiple sclerosis (MS) has emerged as a promising therapeutic strategy, it does not address inflammatory signals that continue to induce neuronal damage and inhibit effectiveness of repair mechanisms. Our lab has previously characterized the immunomodulatory tetrapeptide, tuftsin, which induces an anti-inflammatory shift in microglia and macrophages. This targeted anti-inflammatory agent improves physical deficits in experimental autoimmune encephalomyelitis (EAE), an animal model of MS. Here, we sought to determine whether tuftsin is also effective in combination with benztropine, an FDA-approved drug that stimulates remyelination, in both EAE and in the cuprizone model of demyelination. We show that combining these two agents to promote anti-inflammatory and remyelinating mechanisms alleviates symptoms in EAE and lessens pathological hallmarks in both MS models. Importantly, tuftsin is required to transform the inflammatory CNS environment normally present in EAE/MS into one of an anti-inflammatory nature, and benztropine is required in the cuprizone model to improve remyelination. Our data further support tuftsin's beneficial immunomodulatory activity in the context of EAE, and show that when studying remyelination in the absence of an autoimmune insult, tuftsin still activated microglia toward an anti-inflammatory fate, but benztropine was necessary for significant repair of the damaged myelin. Overall, tuftsin effectively combined with benztropine to significantly improve MS-like pathologies in both models.

Clinical and Histopathological Assessment on an Animal Model with Experimental Autoimmune Encephalomyelitis

Multiple sclerosis (MS) is a disease of the Central Nervous System (CNS) which alters over 2 million people, and involves an abnormal autoimmune response directed against the brain, nerves and spinal cord. The antigen or the autoimmune target still remains unknown, a fact for which MS is considered to be an immune mediated disease. The pathology involves mainly the white matter, but the gray matter demyelination plays an important role in its pathogenesis. In 80% of the cases with MS, the disease develops relapses. Experimental autoimmune encephalomyelitis (EAE) is the most used model to study MS and for assessing potential treatments. In the present study we report on the histopathological characterization of an EAE model in C57BL/6 mice immunized by injection with myelin oligodendrocyte glycoprotein, MOG35-55 in complete Freud's adjuvant supplemented with pertussis toxin. On a group of 10 immunized animals and on 5 control animals, we followed the development and grading signs of motor deficiency, and after a survival of 34 days, the study aimed to evaluate the histopathological changes in the telencephalon, brainstem, cervical spinal cord, the optic nerve and retina. We utilized histochemistry, immunohistochemistry, and densitometric image analysis methods to assess myelin loss [Luxol fast blue, immunohistochemistry for the presence of microglia (Iba1) and reactive astrocytes (GFAP)]. Moreover, the study includes a first analysis of the detailed histopathological changes of the optic nerve and retina on an EAE model, all of these as the background for testing drugs with potential therapeutic role in MS.

Mechanisms underlying lesion development and lesion distribution in CNS autoimmunity

It is widely accepted that development of autoimmunity in the central nervous system (CNS) is triggered by autoreactive T cells, that are activated in the periphery and gain the capacity to migrate through endothelial cells at the blood-brain barrier (BBB) into the CNS. Upon local reactivation, an inflammatory cascade is initiated, that subsequently leads to a recruitment of additional immune cells ultimately causing demyelination and axonal damage. Even though the interaction of immune cells with the BBB has been in the focus of research for many years, the exact mechanisms of how immune cells enter and exit the CNS remains poorly understood. In this line, the factors deciding immune cell entry routes, lesion formation, cellular composition as well as distribution within the CNS have also not been elucidated. The following factors have been proposed to represent key determinants for lesion evaluation and distribution: (i) presence and density of (auto) antigens in the CNS, (ii) local immune milieu at sites of lesion development and resolution, (iii) trafficking routes and specific trafficking requirements, especially at the BBB and (iv) characteristics and phenotypes of CNS infiltrating cells and cell subsets (e.g. features of T helper subtypes or CD8 cells). The heterogeneity of lesion development within inflammatory demyelinating diseases remains poorly understood until today, but here especially orphan inflammatory CNS disorders such as neuromyelitis optica spectrum disorder (NMOSD), Rasmussen encephalitis or SUSAC syndrome might give important insights in critical determinants of lesion topography. Finally, investigating the interaction of T cells with the BBB using in vitro approaches or tracking of T cells in vivo in animals or even human patients, as well as the discovery of lymphatic vasculature in the CNS are teaching us new aspects during the development of CNS autoimmunity. In this review, we discuss recent findings which help to unravel mechanisms underlying lesion topography and might lead to new diagnostic or therapeutic approaches in neuroinflammatory disorders including multiple sclerosis (MS).

Scavenger Receptor A Mediates the Clearance and Immunological Screening of MDA-Modified Antigen by M2-Type Macrophages

In this study, we investigated the uptake of malondialdehyde (MDA)-modified myelin oligodendrocyte glycoprotein (MOG) in the context of lipid peroxidation and its implications in CNS autoimmunity. The use of custom-produced fluorescently labeled versions of MOG or MDA-modified MOG enabled us to study and quantify the uptake by different macrophage populations and to identify the responsible receptor, namely SRA. The SRA-mediated uptake of MDA-modified MOG is roughly tenfold more efficient compared to that of the native form. Notably, this uptake is most strongly associated with anti-inflammatory M2-type macrophages. MDA-modified MOG was demonstrated to be resistant to degradation by lysine-dependent proteases in vitro, but the overall digestion fragments appeared to be similar in cell lysates, although their relative abundance appeared to be altered as a result of faster uptake. Accordingly, MDA-modified MOG is processed for presentation by APCs, allowing maximized recall proliferation of MOG_35-55-specific 2D2 T cells in vitro due to higher uptake. However, MDA modification of MOG did not enhance immune priming or disease course in the in vivo MOG-EAE model, but did induce antibody responses to both MOG and MDA adducts. Taken together our results indicate that MDA adducts primarily constitute clearance signals for phagocytes and promote rapid removal of antigen, which is subjected to immunological screening by previously licensed T cells.

CD318 is a ligand for CD6

It has been proposed that CD6, an important regulator of T cells, functions by interacting with its currently identified ligand, CD166, but studies performed during the treatment of autoimmune conditions suggest that the CD6-CD166 interaction might not account for important functions of CD6 in autoimmune diseases. The antigen recognized by mAb 3A11 has been proposed as a new CD6 ligand distinct from CD166, yet the identity of it is hitherto unknown. We have identified this CD6 ligand as CD318, a cell surface protein previously found to be present on various epithelial cells and many tumor cells. We found that, like CD6 knockout (KO) mice, CD318 KO mice are also protected in experimental autoimmune encephalomyelitis. In humans, we found that CD318 is highly expressed in synovial tissues and participates in CD6-dependent adhesion of T cells to synovial fibroblasts. In addition, soluble CD318 is chemoattractive to T cells and levels of soluble CD318 are selectively and significantly elevated in the synovial fluid from patients with rheumatoid arthritis and juvenile inflammatory arthritis. These results establish CD318 as a ligand of CD6 and a potential target for the diagnosis and treatment of autoimmune diseases such as multiple sclerosis and inflammatory arthritis.

Myelin Oligodendrocyte Glycoprotein: Deciphering a Target in Inflammatory Demyelinating Diseases

Myelin oligodendrocyte glycoprotein (MOG), a member of the immunoglobulin (Ig) superfamily, is a myelin protein solely expressed at the outermost surface of myelin sheaths and oligodendrocyte membranes. This makes MOG a potential target of cellular and humoral immune responses in inflammatory demyelinating diseases. Due to its late postnatal developmental expression, MOG is an important marker for oligodendrocyte maturation. Discovered about 30 years ago, it is one of the best-studied autoantigens for experimental autoimmune models for multiple sclerosis (MS). Human studies, however, have yielded controversial results on the role of MOG, especially MOG antibodies (Abs), as a biomarker in MS. But with improved detection methods using different expression systems to detect Abs in patients' samples, this is meanwhile no longer the case. Using cell-based assays with recombinant full-length, conformationally intact MOG, several recent studies have revealed that MOG Abs can be found in a subset of predominantly pediatric patients with acute disseminated encephalomyelitis (ADEM), aquaporin-4 (AQP4) seronegative neuromyelitis optica spectrum disorders (NMOSD), monophasic or recurrent isolated optic neuritis (ON), or transverse myelitis, in atypical MS and in N-methyl-d-aspartate receptor-encephalitis with overlapping demyelinating syndromes. Whereas MOG Abs are only transiently observed in monophasic diseases such as ADEM and their decline is associated with a favorable outcome, they are persistent in multiphasic ADEM, NMOSD, recurrent ON, or myelitis. Due to distinct clinical features within these diseases it is controversially disputed to classify MOG Ab-positive cases as a new disease entity. Neuropathologically, the presence of MOG Abs is characterized by MS-typical demyelination and oligodendrocyte pathology associated with Abs and complement. However, it remains unclear whether MOG Abs are a mere inflammatory bystander effect or truly pathogenetic. This article provides deeper insight into recent developments, the clinical relevance of MOG Abs and their role in the immunpathogenesis of inflammatory demyelinating disorders.

GM-CSF is not essential for experimental autoimmune encephalomyelitis but promotes brain-targeted disease

Experimental autoimmune encephalomyelitis (EAE) has been used as an animal model of multiple sclerosis to identify pathogenic cytokines that could be therapeutic targets. Granulocyte-macrophage colony-stimulating factor (GM-CSF) is the only cytokine reported to be essential for EAE. We investigated the role of GM-CSF in EAE in C3HeB/FeJ mice that uniquely exhibit extensive brain and spinal cord inflammation. Unexpectedly, GM-CSF-deficient C3HeB/FeJ mice were fully susceptible to EAE because IL-17 activity compensated for the loss of GM-CSF during induction of spinal cord-targeted disease. In contrast, both GM-CSF and IL-17 were needed to fully overcome the inhibitory influence of IFN-γ on the induction of inflammation in the brain. Both GM-CSF and IL-17 independently promoted neutrophil accumulation in the brain, which was essential for brain-targeted disease. These results identify a GM-CSF/IL-17/IFN-γ axis that regulates inflammation in the central nervous system and suggest that a combination of cytokine-neutralizing therapies may be needed to dampen central nervous system autoimmunity.

CD6 as a potential target for treating multiple sclerosis

CD6 was established as a marker of T cells more than three decades ago, and recent studies have identified CD6 as a risk gene for multiple sclerosis (MS), a disease in which autoreactive T cells are integrally involved. Nevertheless, the precise role of CD6 in regulating T-cell responses is controversial and its significance in the pathogenesis of various diseases remains elusive, partly due to the lack of animals engineered to alter expression of the CD6 gene. In this report, we found that CD6 KO mice showed decreased pathogenic T-cell responses, reduced spinal cord T-cell infiltration, and attenuated disease severity in experimental autoimmune encephalomyelitis (EAE), an animal model of MS. CD6-deficient T cells exhibited augmented activation, but also significantly reduced survival and proliferation after activation, leading to overall decreased Th1 and Th17 polarization. Activated CD6-deficient T cells also showed impaired infiltration through brain microvascular endothelial cell monolayers. Furthermore, by developing CD6 humanized mice, we identified a mouse anti-human CD6 monoclonal antibody that is highly effective in treating established EAE without depleting T cells. These results suggest that (i) CD6 is a negative regulator of T-cell activation, (ii) at the same time, CD6 is a positive regulator of activated T-cell survival/proliferation and infiltration; and (iii) CD6 is a potential new target for treating MS and potentially other T-cell-driven autoimmune conditions.

Effects of C2ta genetic polymorphisms on MHC class II expression and autoimmune diseases

Antigen presentation by the MHC-II to CD4⁺ T cells is important in adaptive immune responses. The class II transactivator (CIITA in human and C2TA in mouse) is the master regulator of MHC-II gene expression. It coordinates the transcription factors necessary for the transcription of MHC-II molecules. In humans, genetic variations in CIITA have been associated with differential expression of MHC-II and susceptibility to autoimmune diseases. Here we made use of a C2ta congenic mouse strain (expressing MHC-II haplotype H-2^q ) to investigate the effect of the natural genetic polymorphisms in type I promoter of C2ta on MHC-II expression and function. We demonstrate that an allelic variant in the type I promoter of C2ta resulted in an increased expression of MHC-II on macrophages (72-151% higher mean florescence intensity) and conventional dendritic cells (13-65% higher mean florescence intensity) in both spleen and peripheral blood. The increase in MHC-II expression resulted in an increase in antigen presentation to T cells in vitro and increased T-cell activation. The differential MHC-II expression in B6Q.C2ta, however, did not alter the disease development in models of rheumatoid arthritis (collagen-induced arthritis and human glucose-6-phosphate-isomerase_325-339 -peptide-induced arthritis), or multiple sclerosis (MOG_1-125 protein-induced and MOG_79-96 peptide-induced experimental autoimmune encephalomyelitis). This is the first study to address the role of an allelic variant in type I promoter of C2ta in MHC-II expression and autoimmune diseases; and shows that C2ta polymorphisms regulate MHC-II expression and T-cell responses but do not necessarily have a strong impact on autoimmune diseases.

Nitration of MOG diminishes its encephalitogenicity depending on MHC haplotype

Post-translational modifications of autoantigens are hypothesized to affect their immunogenicity. We here report that nitration of tyrosine 40 in Myelin Oligodendrocyte Glycoprotein (MOG) abrogates its encephalitogenicity both at protein and peptide levels in the experimental autoimmune encephalomyelitis (EAE) model in H2^b C57BL/6 mice. Furthermore, nitrated MOG displays inferior antigen-specific proliferation of 2D2 splenocytes in vitro. Conversely, H2^q DBA1 mice remain fully susceptible to EAE induction using nitrated MOG as the dominant epitope of H2^q mice is unaltered. Molecular modeling analysis of the MOG_35-55/H2-IA^b complex and bioinformatics peptide binding predictions indicate that the lack of T cell reactivity towards nitrated MOG can be attributed to the inability of murine H2-IA^b to efficiently present the altered peptide ligand of MOG_35-55 because the nitrated tyrosine 40 cannot be accommodated in the p1 anchor pocket. In conclusion we demonstrate nitration as a relevant determinant affecting T cell recognition of carrier antigen depending on MHC haplotype. Our data have implications for understanding the role of post-translationally modified antigen in autoimmunity.

BAFF-secreting neutrophils drive plasma cell responses during emergency granulopoiesis

Harris and collaborators show that neutropenia results in increased formation of plasma cells and elevated antibody production.

Prolonged infections or adjuvant usage can trigger emergency granulopoiesis (EG), leading to dysregulation in neutrophil blood counts. However, the impact of EG on T and B cell function remains largely unknown. In this study, to address this question, we used a mouse model of neutropenia and studied immune activation after adjuvant administration. The initial neutropenic state fostered an environment of increased dendritic cell activation and T cell–derived IL-17 production. Interestingly, neutropenic lysozyme 2–diphtheria toxin A mice exhibited striking EG and amplified neutrophil recruitment to the lymph nodes (LNs) that was dependent on IL-17–induced prostaglandin activity. The recruited neutrophils secreted a B cell–activating factor that highly accelerated plasma cell generation and antigen-specific antibody production. Reduction of neutrophil functions via granulocyte colony-stimulating factor neutralization significantly diminished plasma cell formation, directly linking EG with the humoral immune response. We conclude that neutrophils are capable of directly regulating T cell–dependent B cell responses in the LN.

Modelling MS: Chronic-Relapsing EAE in the NOD/Lt Mouse Strain

Modelling complex disorders presents considerable challenges, and multiple sclerosis (MS) is no exception to this rule. The aetiology of MS is unknown, and its pathophysiology is poorly understood. Moreover, the last two decades have witnessed a dramatic revision of the long-held view of MS as an inflammatory demyelinating white matter disease. Instead, it is now regarded as a global central nervous system (CNS) disorder with a neurodegenerative component. Currently, there is no animal model recapitulating MS immunopathogenesis. Available models are based on autoimmune-mediated demyelination, denoted experimental autoimmune encephalomyelitis (EAE) or virally or chemically induced demyelination. Of these, the EAE model has been the most commonly used. It has been extensively improved since its first description and now exists as a number of variants, including genetically modified and humanized versions. Nonetheless, EAE is a distinct disease, and each variant models only certain facets of MS. Whilst the search for more refined MS models must continue, it is important to further explore where mechanisms underlying EAE provide proof-of-principle for those driving MS pathogenesis. EAE variants generated with the myelin component myelin oligodendrocyte glycoprotein (MOG) have emerged as the preferred ones, because in this particular variant disease is associated with both T- and B-cell effector mechanisms, together with demyelination. MOG-induced EAE in the non-obese diabetic (NOD) mouse strain exhibits a chronic-relapsing EAE clinical profile and high disease incidence. We describe the generation of this variant, its contribution to the understanding of MS immune and pathogenetic mechanisms and potential for evaluation of candidate therapies.

Immunodominant T-cell epitopes of MOG reside in its transmembrane and cytoplasmic domains in EAE

Objective:

Studies evaluating T-cell recognition of myelin oligodendrocyte glycoprotein (MOG) in multiple sclerosis (MS) and its model, experimental autoimmune encephalomyelitis (EAE), have focused mostly on its 117 amino acid (aa) extracellular domain, especially peptide (p) 35-55. We characterized T-cell responses to the entire 218 aa MOG sequence, including its transmembrane and cytoplasmic domains.

Methods:

T-cell recognition in mice was examined using overlapping peptides and intact full-length mouse MOG. EAE was evaluated by peptide immunization and by adoptive transfer of MOG epitope-specific T cells. Frequency of epitope-specific T cells was examined by ELISPOT.

Results:

Three T-cell determinants of MOG were discovered in its transmembrane and cytoplasmic domains, p119–132, p181–195, and p186–200. Transmembrane MOG p119-132 induced clinical EAE, CNS inflammation, and demyelination as potently as p35-55 in C57BL/6 mice and other H-2^b strains. p119-128 contained its minimal encephalitogenic epitope. p119-132 did not cause disease in EAE-susceptible non-H-2^b strains, including Biozzi, NOD, and PL/J. MOG p119-132–specific T cells produced Th1 and Th17 cytokines and transferred EAE to wild-type recipient mice. After immunization with full-length MOG, a significantly higher frequency of MOG-reactive T cells responded to p119-132 than to p35-55, demonstrating that p119-132 is an immunodominant encephalitogenic epitope. MOG p181-195 did not cause EAE, and MOG p181-195–specific T cells could not transfer EAE into wild-type or highly susceptible T- and B-cell–deficient mice.

Conclusions:

Transmembrane and cytoplasmic domains of MOG contain immunodominant T-cell epitopes in EAE. A CNS autoantigen can also contain nonpathogenic stimulatory T-cell epitopes. Recognition that a myelin antigen contains multiple encephalitogenic and nonencephalitogenic determinants may have implications for therapeutic development in MS.

Cytokine-regulated neutrophil recruitment is required for brain but not spinal cord inflammation during experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is an autoimmune disease in which inflammatory lesions lead to tissue injury in the brain and/or spinal cord. The specific sites of tissue injury are strong determinants of clinical outcome in MS, but the pathways that determine whether damage occurs in the brain or spinal cord are not understood. Previous studies in mouse models of MS demonstrated that IFN-γ and IL-17 regulate lesion localization within the brain; however, the mechanisms by which these cytokines mediate their effects have not been identified. In the present study, we show that IL-17 promoted, but IFN-γ inhibited, ELR(+) chemokine-mediated neutrophil recruitment to the brain, and that neutrophil infiltration was required for parenchymal tissue damage in the brain. In contrast, IFN-γ promoted ELR(+) chemokine expression and neutrophil recruitment to the spinal cord. Surprisingly, tissue injury in the spinal cord did not exhibit the same dependence on neutrophil recruitment that was observed for the brain. Our results demonstrate that the brain and spinal cord exhibit distinct sensitivities to cellular mediators of tissue damage, and that IL-17 and IFN-γ differentially regulate recruitment of these mediators to each microenvironment. These findings suggest an approach toward tailoring therapies for patients with distinct patterns of neuroinflammation.

B cells promote induction of experimental autoimmune encephalomyelitis by facilitating reactivation of T cells in the central nervous system

The efficacy of rituximab treatment in multiple sclerosis has renewed interest in the role of B cells in CNS autoimmunity. In this study, we show that B cells are the predominant MHC class II(+) subset in the naive CNS in mice, and they constitutively express proinflammatory cytokines. Incidence of experimental autoimmune encephalomyelitis induced by adoptive transfer was significantly reduced in C3HeB/Fej μMT (B cell-deficient) mice, suggesting an important role for CNS B cells in initiating inflammatory responses. Initial T cell infiltration of the CNS occurred normally in μMT mice; however, lack of production of T cell cytokines and other immune mediators indicated impaired T cell reactivation. Subsequent recruitment of immune cells from the periphery driven by this initial T cell reactivation did not occur in μMT mice. B cells required exogenous IL-1β to reactivate Th17 but not Th1 cells in vitro. Similarly, reactivation of Th1 cells infiltrating the CNS was selectively impaired compared with Th17 cells in μMT mice, causing an increased Th17/Th1 ratio in the CNS at experimental autoimmune encephalomyelitis onset and enhanced brain inflammation. These studies reveal an important role for B cells within the CNS in reactivating T cells and influencing the clinical manifestation of disease.

The influence of T cell Ig mucin-3 signaling on central nervous system autoimmune disease is determined by the effector function of the pathogenic T cells

Multiple sclerosis (MS) is an inflammatory, demyelinating disease of the CNS mediated by self-reactive, myelin-specific T cells. Both CD4(+) and CD8(+) T cells play important roles in the pathogenesis of MS. MS is studied using experimental autoimmune encephalomyelitis (EAE), an animal model mediated by myelin-specific T cells. T cell Ig mucin-3 (Tim-3) is a cell surface receptor expressed on CD4(+) IFN-γ-secreting Th1 cells, and triggering Tim-3 signaling ameliorated EAE by inducing death in pathogenic Th1 cells in vivo. This suggested that enhancing Tim-3 signaling might be beneficial in patients with MS. However, Tim-3 is also expressed on activated CD8(+) T cells, microglia, and dendritic cells, and the combined effect of manipulating Tim-3 signaling on these cell types during CNS autoimmunity is unknown. Furthermore, CD4(+) IL-17-secreting Th17 cells also play a role in MS, but do not express high levels of Tim-3. We investigated Tim-3 signaling in EAE models that include myelin-specific Th17, Th1, and CD8(+) T cells. We found that preventing Tim-3 signaling in CD4(+) T cells altered the inflammatory pattern in the CNS due to differential effects on Th1 versus Th17 cells. In contrast, preventing Tim-3 signaling during CD8(+) T cell-mediated EAE exacerbated disease. We also analyzed the importance of Tim-3 signaling in EAE in innate immune cells. Tim-3 signaling in dendritic cells and microglia did not affect the manifestation of EAE in these models. These results indicate that the therapeutic efficacy of targeting Tim-3 in EAE is dependent on the nature of the effector T cells contributing to the disease.

Laquinimod, a quinoline-3-carboxamide, induces type II myeloid cells that modulate central nervous system autoimmunity

Laquinimod is a novel oral drug that is currently being evaluated for the treatment of relapsing-remitting (RR) multiple sclerosis (MS). Using the animal model for multiple sclerosis, experimental autoimmune encephalomyelitis (EAE), we examined how laquinimod promotes immune modulation. Oral laquinimod treatment reversed established RR-EAE and was associated with reduced central nervous system (CNS) inflammation, decreased Th1 and Th17 responses, and an increase in regulatory T cells (Treg). In vivo laquinimod treatment inhibited donor myelin-specific T cells from transferring EAE to naive recipient mice. In vivo laquinimod treatment altered subpopulations of myeloid antigen presenting cells (APC) that included a decrease in CD11c⁺CD11b⁺CD4⁺ dendritic cells (DC) and an elevation of CD11b^hiGr1^hi monocytes. CD11b⁺ cells from these mice exhibited an anti-inflammatory type II phenotype characterized by reduced STAT1 phosphorylation, decreased production of IL-6, IL-12/23 and TNF, and increased IL-10. In adoptive transfer, donor type II monocytes from laquinimod-treated mice suppressed clinical and histologic disease in recipients with established EAE. As effects were observed in both APC and T cell compartments, we examined whether T cell immune modulation occurred as a direct effect of laquinimod on T cells, or as a consequence of altered APC function. Inhibition of Th1 and Th17 differentiation was observed only when type II monocytes or DC from laquinimod-treated mice were used as APC, regardless of whether myelin-specific T cells were obtained from laquinimod-treated or untreated mice. Thus, laquinimod modulates adaptive T cell immune responses via its effects on cells of the innate immune system, and may not influence T cells directly.

A reversible form of axon damage in experimental autoimmune encephalomyelitis and multiple sclerosis

In multiple sclerosis, a common inflammatory disease of the central nervous system, immune-mediated axon damage is responsible for permanent neurological deficits. How axon damage is initiated is not known. Here we use in vivo imaging to identify a previously undescribed variant of axon damage in a mouse model of multiple sclerosis. This process, termed 'focal axonal degeneration' (FAD), is characterized by sequential stages, beginning with focal swellings and progressing to axon fragmentation. Notably, most swollen axons persist unchanged for several days, and some recover spontaneously. Early stages of FAD can be observed in axons with intact myelin sheaths. Thus, contrary to the classical view, demyelination-a hallmark of multiple sclerosis-is not a prerequisite for axon damage. Instead, focal intra-axonal mitochondrial pathology is the earliest ultrastructural sign of damage, and it precedes changes in axon morphology. Molecular imaging and pharmacological experiments show that macrophage-derived reactive oxygen and nitrogen species (ROS and RNS) can trigger mitochondrial pathology and initiate FAD. Indeed, neutralization of ROS and RNS rescues axons that have already entered the degenerative process. Finally, axonal changes consistent with FAD can be detected in acute human multiple sclerosis lesions. In summary, our data suggest that inflammatory axon damage might be spontaneously reversible and thus a potential target for therapy.

A single nucleotide polymorphism in Tyk2 controls susceptibility to experimental allergic encephalomyelitis

Genes controlling immunopathologic diseases of differing etiopathology may also influence susceptibility to autoimmune disease. B10.D1-H2(q)/SgJ mice with a 2538 G-->A missense mutation in the tyrosine kinase-2 gene (Tyk2) are susceptible to Toxoplasma gondii yet resistant to autoimmune arthritis, unlike the wild-type B10.Q/Ai substrain. To understand whether Tyk2 is also important in a second autoimmune model, experimental allergic encephalomyelitis (EAE) was induced in B10.D1-H2(q)/SgJ (Tyk2(A)) and B10.Q/Ai (Tyk2(G)) mice with the myelin oligodendrocyte glycoprotein peptide 79-96. B10.D1-H2(q)/SgJ mice were resistant to EAE whereas B10.Q/Ai mice were susceptible, and a single copy of the Tyk2(G) allele conferred EAE susceptibility in F(1) hybrids. Furthermore, EAE resistance in B10.D1-H2(q)/SgJ mice was overridden when pertussis toxin (PTX) was used to mimic the effects of environmental factors derived from infectious agents. Numerous cytokines and chemokines were increased when PTX was included in the immunization protocol. However, only RANTES, IL-6, and IFN-gamma increased significantly with both genetic compensation and PTX treatment. These data indicate that Tyk2 is a shared autoimmune disease susceptibility gene whose genetic contribution to disease susceptibility can be modified by environmental factors. Single nucleotide polymorphisms like the one that distinguishes Tyk2 alleles are of considerable significance given the potential role of gene-by-environment interactions in autoimmune disease susceptibility.

Differential regulation of central nervous system autoimmunity by T(H)1 and T(H)17 cells

Multiple sclerosis is an inflammatory, demyelinating disease of the central nervous system (CNS) characterized by a wide range of clinical signs. The location of lesions in the CNS is variable and is a crucial determinant of clinical outcome. Multiple sclerosis is believed to be mediated by myelin-specific T cells, but the mechanisms that determine where T cells initiate inflammation are unknown. Differences in lesion distribution have been linked to the HLA complex, suggesting that T cell specificity influences sites of inflammation. We demonstrate that T cells that are specific for different myelin epitopes generate populations characterized by different T helper type 17 (T(H)17) to T helper type 1 (T(H)1) ratios depending on the functional avidity of interactions between TCR and peptide-MHC complexes. Notably, the T(H)17:T(H)1 ratio of infiltrating T cells determines where inflammation occurs in the CNS. Myelin-specific T cells infiltrate the meninges throughout the CNS, regardless of the T(H)17:T(H)1 ratio. However, T cell infiltration and inflammation in the brain parenchyma occurs only when T(H)17 cells outnumber T(H)1 cells and trigger a disproportionate increase in interleukin-17 expression in the brain. In contrast, T cells showing a wide range of T(H)17:T(H)1 ratios induce spinal cord parenchymal inflammation. These findings reveal critical differences in the regulation of inflammation in the brain and spinal cord.

Bioluminescence in vivo imaging of autoimmune encephalomyelitis predicts disease

Background

Experimental autoimmune encephalomyelitis is a widely used animal model to understand not only multiple sclerosis but also basic principles of immunity. The disease is scored typically by observing signs of paralysis, which do not always correspond with pathological changes.

Methods

Experimental autoimmune encephalomyelitis was induced in transgenic mice expressing an injury responsive luciferase reporter in astrocytes (GFAP-luc). Bioluminescence in the brain and spinal cord was measured non-invasively in living mice. Mice were sacrificed at different time points to evaluate clinical and pathological changes. The correlation between bioluminescence and clinical and pathological EAE was statistically analyzed by Pearson correlation analysis.

Results

Bioluminescence from the brain and spinal cord correlates strongly with severity of clinical disease and a number of pathological changes in the brain in EAE. Bioluminescence at early time points also predicts severity of disease.

Conclusion

These results highlight the potential use of bioluminescence imaging to monitor neuroinflammation for rapid drug screening and immunological studies in EAE and suggest that similar approaches could be applied to other animal models of autoimmune and inflammatory disorders.

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.

Malondialdehyde modification of myelin oligodendrocyte glycoprotein leads to increased immunogenicity and encephalitogenicity

Self proteins may become autoantigenic through structural modification. We studied malondialdehydation of recombinant rat (rr) myelin oligodendrocyte glycoprotein (MOG), an autoantigen in multiple sclerosis. Malondialdehyde (MDA) modification changed protein weight and charge, the location of these adducts being mapped by Fourier transform ion cyclotron resonance. Molecular modelling revealed significant differences in the MDA-rrMOG three-dimensional structure. DBA/1 mice immunised with MDA-rrMOG developed greater proliferative responses and more severe experimental autoimmune encephalomyelitis than mice immunised with unmodified rrMOG. MDA-rrMOG was taken up more effectively by antigen-presenting cells (APC), at least partially through scavenger receptors. Exposure to MDA-rrMOG led to increased expression of IL-23, IL-12 and IL-12R, indicating a role not only for increased antigen uptake but also for activation of APC. We thus provide biochemical, structural, immunological and clinical data that suggest that the post-translationally modified form of this myelin autoantigen is a more relevant form of the molecule.

Differential upregulation of heme oxygenase-1 (HSP32) in glial cells after oxidative stress and in demyelinating disorders

Oxidative stress is implicated in the pathogenesis of demyelinating disorders and inflammatory responses. Heme oxygenase-1 (HO-1; HSP32) is a small heat shock protein (HSP) with enzymatic activity, which is inducible by oxidative stress. In this study we analyzed autopsy and biopsy brain samples of patients with multiple sclerosis (MS) and ADEM (acute disseminated leucoencephalomyelits) and spinal cord lesions of mouse EAE (experimental autoimmune encephalomyelitis), which was actively induced by immunization with myelin oligodendrocyte glycoprotein (MOG35-55) peptide, for the presence of HO-1. HO-1 was observed in glial cells during different stages: (1) during acute phases of mainly inflammatory diseases (EAE and ADEM) expression of HO-1 was prominent in microglia/macrophages and astrocytes, and upregulation correlated with inflammation, and (2) in early MS lesions HO-1 was expressed in oligodendrocytes. Furthermore, in glial cell cultures, we can show that upregulation of HO-1 in oligodendrocytes was paralleled by severe morphological damage. Oligodendrocytes underwent apoptotic cell death at a concentration of hydrogen peroxide (50-200 microM) which did not affect astrocytes or microglia. Using oligodendroglial OLN-93 cells, we demonstrate that oxidative stress led to mitochondrial impairment and the disorganization of the microtubule network. Zinc protoporphyrin, an inhibitor of HO-1, augmented the cytotoxic consequences of hydrogen peroxide in OLN-93 cells. Hence, the presence of HO-1 in EAE, ADEM, and MS points to the involvement of oxidative stress and a role of HO-1 in the pathogenesis of the diseases. The data suggest that stress-induced HO-1 initially plays a protective role, while its chronic upregulation, might contribute to oligodendroglial cell death rather than providing protection.

Native myelin oligodendrocyte glycoprotein promotes severe chronic neurological disease and demyelination in Biozzi ABH mice

Myelin oligodendrocyte glycoprotein (MOG) is a powerful encephalitogen for experimental autoimmune demyelination. However, the use of MOG peptides or recombinant proteins representing part of the protein fails to fully address the possible pathogenic role of the full-length myelin-derived protein expressing post-translational modifications. Immunization of mice with central nervous system tissues from wild-type (WT) and MOG-deficient (MOG(-/-)) mice demonstrates that MOG in myelin is necessary for the development of chronic demyelinating experimental autoimmune encephalomyelitis (EAE) in mice. While immunization with WT spinal cord homogenate (SCH) resulted in a progressive EAE phenotype, MOG(-/-) SCH induced a mild self-limiting acute disease. Following acute EAE with MOG(-/-) SCH, mice developed T cell responses to recombinant mouse MOG (rmMOG), indicating that MOG released from myelin is antigenic; however, the lack of chronic disease indicates that such responses were not pathogenic. Chronic demyelinating EAE was observed when MOG(-/-) SCH was reconstituted with a dose of rmMOG comparable to MOG in myelin (2.5% of total white matter-derived protein). These data reveal that while immunization with the full-length post-translational modified form of MOG in myelin promotes the development of a more chronic autoimmune demyelinating neurological disease, MOG (and/or other myelin proteins) released from myelin during ongoing disease do not induce destructive autoimmunity.

Co-infection with Trypanosoma brucei brucei prevents experimental autoimmune encephalomyelitis in DBA/1 mice through induction of suppressor APCs

The immune system has co-evolved with the infectious agents that challenge it, and in response pathogens have developed different mechanisms to subvert host immunity. A wealth of evidence suggests that infections are important components in the development of a functional immune system, and understanding the modulation of the host immune system by pathogens may offer new therapeutic strategies in a non-infectious setting. We investigated how infection with the protozoan parasite Trypanosoma brucei brucei (Tbb) modulates the autoimmune response to recombinant myelin oligodendrocyte glycoprotein (rMOG) in DBA/1 mice. Mice harbouring a Tbb infection did not develop experimental autoimmune encephalomyelitis (EAE) induced by immunization with rMOG in CFA, an animal model for the human autoimmune disease multiple sclerosis. Additionally, mice infected with the parasite at the time of immunization or 1 week later developed less severe EAE than uninfected controls. Protected mice displayed a markedly diminished rMOG-specific proliferation and IFNgamma production in lymph node cells and had correspondingly low titres of serum anti-rMOG IgG. Antigen-presenting cells (APCs) from spleens of Tbb-infected mice presented rMOG less efficiently to rMOG-specific T cells in vitro than did splenic APCs from uninfected mice and could also inhibit antigen-specific proliferation in control in vitro cultures. This suppressive effect is at least in part due to increased release of IL-10. Transfer of splenic APCs from Tbb-infected mice into mice immunized with rMOG-CFA 7 days previously abrogated disease significantly. These findings indicate that infections can prevent autoimmunity and that APCs might be used as immunomodulants.

Ncf1 (p47phox) polymorphism determines oxidative burst and the severity of arthritis in rats and mice

Identifying genes that regulate polygenic diseases influenced by the environment such as rheumatoid arthritis (RA), has so far proven to be difficult. By using an alternative approach, i.e., linkage analysis using relevant animal models we succeeded in finding the Ncf1 gene residing in the Pia4 quantitative trait locus to be responsible for the severity of pristane induced arthritis in rats. The influence of another mutation in the mouse Ncf1 gene showed the same association between decreased oxidative burst and enhanced arthritis. In this case the mutation affected a splice site giving a non-detectable oxidative burst response and enhanced collagen induced arthritis as well as myelin oligodendrocyte protein induced experimental autoimmune encephalomyelitis. These findings open up new possibilities for new treatments for autoimmune diseases, i.e., RA, targeting the NADPH oxidase pathway.

Differential macrophage expression of IL-12 and IL-23 upon innate immune activation defines rat autoimmune susceptibility

Rodents typically demonstrate strain-specific susceptibilities to induced autoimmune models such as experimental arthritis and encephalomyelitis. A common feature of the local pathology of these diseases is an extensive infiltration of activated macrophages (MPhi). Different functional activation states can be induced in MPhi during innate immune activation, and it is this differential activation that might be important in susceptibility/resistance to induction or perpetuation of autoimmunity. In this study, we present an extensive, comparative analysis of the activation phenotypes of MPhi derived from autoimmune-susceptible and autoimmune-resistant rat strains to describe a cellular phenotype that defines the disease phenotype. We included investigation of receptor function, intracellular signaling pathways, cytokines, and other soluble mediators released after activation of cells using a panel of stimuli embracing many activation routes. We report that activation of MPhi from the autoimmune-susceptible strain was associated with alternative activation indicated by induction of arginase activity, a lower production of classical proinflammatory mediators, and a high production of interleukin (IL)-23, and MPhi from the autoimmune-resistant strains were associated with a higher production of proinflammatory mediators, a classical activation phenotype, and preferential induction of IL-12. These MPhi phenotypes thus reflect disparate, genetic cellular programs that define autoimmune susceptibility.

Methotrexate ameliorates T cell dependent autoimmune arthritis and encephalomyelitis but not antibody induced or fibroblast induced arthritis

OBJECTIVE

To investigate the mode of action of methotrexate (MTX) in different types of models for rheumatoid arthritis (RA) and multiple sclerosis (MS).

METHODS

Models for RA and MS were selected known to have different pathogenesis--that is, fibroblast induced arthritis in SCID mice, collagen induced arthritis (CIA), anticollagen II antibody induced arthritis (CAIA), and experimental autoimmune encephalomyelitis (EAE) in (Balb/c x B10.Q)F1 and B10.Q mice, and Pristane induced arthritis in DA rats (PIA). The MTX treatment was started 1 day after the onset of disease and continued for 14 days to compare effects on the different models.

RESULTS

All models known to be critically dependent on T cell activation (CIA, PIA, and EAE) were effectively down regulated by titrated doses of MTX. In contrast, no effects were seen on fibroblast induced arthritis or CAIA. No effects were seen on the levels of anticollagen II antibodies in the CIA experiment.

CONCLUSION

The data show that MTX has strong ameliorative effect on both classical models of RA, like CIA and PIA, but also on a model for MS, EAE. It also suggests that MTX operates only in diseases which are preceded by, and dependent on, T cell activation. A comparison of CAIA and CIA suggested that MTX operates independently of arthritogenic antibodies. These results demonstrate that different animal models reflect the complexity of the corresponding human diseases and suggest that several models should be used for effective screening of new therapeutic agents.

Enhanced autoimmunity, arthritis, and encephalomyelitis in mice with a reduced oxidative burst due to a mutation in the Ncf1 gene

The Ncf1 gene was recently identified as a strong regulator of severe arthritis in rat. This finding was surprising, because the disease-promoting allele mediated a lower level of reactive oxygen species in NADPH oxidase-expressing cells. We have now investigated a splice mutation of the Ncf1 gene in B10.Q mice, causing a truncated and nonfunctional Ncf1 protein. We found that the mutated Ncf1 led to a more severe and chronic relapsing collagen-induced arthritis. Enhanced IgG and delayed-type hypersensitivity responses against type II collagen were seen, indicating increased activity of autoreactive T cells. Interestingly, female Ncf1-mutated mice spontaneously developed severe arthritis during the postpartum period. The arthritis was accompanied by an increased antibody response to type II collagen, with the same fine specificity as in collagen-induced arthritis. The enhancing effect of the mutated Ncf1 could also be shown to be more general in that it enhanced myelin oligodendrocyte glycoprotein protein-induced experimental autoimmune encephalomyelitis, a model for multiple sclerosis. These results show that Ncf1, a gene important for oxidative burst, regulates the susceptibility and severity of both arthritis and encephalomyelitis and modulates, directly or indirectly, the level of T cell-dependent autoimmune responses.

Comparing the pathogenesis of experimental autoimmune encephalomyelitis in CD4-/- and CD8-/- DBA/1 mice defines qualitative roles of different T cell subsets

Experimental autoimmune encephalomyelitis (EAE) was induced with myelin oligodendrocyte glycoprotein (MOG(1-125)) in CD4(-/-) and CD8(-/-) DBA/1 mice. Both gene-deleted mice developed clinical signs of EAE, albeit milder than in wild-type mice, suggesting that both CD4(+) and CD8(+) cells participate in disease development. Demyelination and inflammation in the central nervous system was reduced in the absence of CD8(+) T cells. Antibody depletion of CD4(+) cells completely protected CD8(-/-) mice from MOG-induced EAE while depletion of CD8(+) cells in CD4(-/-) mice resulted in fewer EAE incidence compared to that in control antibody-treated mice. Antibody depletion of CD4(+) cells in wild-type mice protected from EAE, but not depletion of CD8(+) cells, although demyelination was reduced on removal of CD8(+) T cells. Immunization with immunodominant MOG(79-96) peptide led to EAE only in the presence of pertussis toxin (PT) in the inoculum. PT also triggered an earlier onset and more severe EAE in CD8(-/-) mice. We interpret our findings such that in an ontogenic lack of CD4(+) T cells, EAE is mediated by CD8(+) and elevated levels of alphabetaCD4(-)CD8(-) cells, and that CNS damage is partly enacted by the activity of CD8(+) T cells.

Expression of the long form of human FLIP by retroviral gene transfer of hemopoietic stem cells exacerbates experimental autoimmune encephalomyelitis

Subsidence of inflammation and clinical recovery in experimental autoimmune encephalomyelitis (EAE) is postulated to involve apoptosis of inflammatory cells. To test this concept, we examined the effects of overexpressing the long form of human FLICE-inhibitory protein, a potent inhibitor of death receptor-mediated apoptosis, in myelin oligodendrocyte glycoprotein-induced EAE in DBA/1 mice. We found that overexpression of the long form of human FLICE-inhibitory protein by retroviral gene transfer of hemopoietic stem cells led to a clinically more severe EAE in these mice compared with control mice receiving the retroviral vector alone. The exacerbated disease was evident by an enhanced and prolonged inflammatory reaction in the CNS of these animals compared with control mice. The acute phase of EAE was characterized by a massive infiltration of macrophages and granulocytes and a simultaneous increase in TNF-alpha production in the CNS. In the chronic phase of the disease, there was a prolonged inflammatory response in the form of persistent CD4(+) T and B cells in the CNS and a peripheral Th1 cytokine bias caused by elevated levels of IFN-gamma and reduced levels of IL-4 in the spleen. Our findings demonstrate that death receptor-mediated apoptosis can be important in the pathogenesis of EAE and further emphasize the need for effective apoptotic elimination of inflammatory cells to achieve disease remission.

Autoreactive T cells promote post-traumatic healing in the central nervous system

In general, autoimmune responses are considered harmful to the host. In the best-defined model of autoimmune disease, murine experimental allergic encephalomyelitis (EAE), for example, brain-protein-specific autoimmune responses of both major classes, type-1 and type-2, have been implicated in causing brain pathology. We induced type-1 and type-2 autoimmunity to myelin oligodendrocyte protein (MOG) in C57.BL/6 mice. Instead of using pertussis toxin (PTX) to open the blood-brain barrier (BBB), which is the classic procedure, we set an aseptic cerebral injury (ACI) to see what the consequences of pre-primed, autoreactive type-1 and type-2 memory T cells gaining access to the brain in the course of sterile tissue injury would be. Neither of these autoimmune response types induced pathology; on the contrary, both accelerated re-vascularization and post-traumatic healing. The data suggest that induction of either type-1 or type-2 autoimmune responses is not inherently noxious to the host, but can have beneficial effects on tissue repair. Autoimmune pathology may develop only if molecules of microbial origin such as pertussis toxin additionally induce the "infectious nonself/danger" reaction in the antigen-presenting cells (APC) of the target organ itself.

High immunogenicity of intracellular myelin oligodendrocyte glycoprotein epitopes

Multiple sclerosis (MS) is an inflammatory and demyelinating disease of the CNS with associated axonal loss. There is strong evidence for an autoimmune pathogenesis driven by myelin-specific T cells. Myelin oligodendrocyte glycoprotein (MOG) induces a type of experimental autoimmune encephalomyelitis in animals which is very MS-like since there are demyelinating CNS lesions and axonal loss. This underscores the potential role of MOG in MS pathogenesis. We performed a T cell reactivity pattern analysis of MS patients at the onset of relapse or progression of neurological deficits and controls that were stratified for the genetic risk factor HLA-DRB1*1501. For the first time, we show that there is an HLA-DR-restricted promiscuous dominant epitope for CD4(+) T cells within the transmembrane/intracellular part of MOG comprising aa 146-154 (FLCLQYRLR). Surprisingly, controls had broader T cell reactivity patterns toward MOG peptides compared with MS patients, and the transmembrane and intracellular parts of MOG were much more immunogenic compared with the extracellular part. Measurements of in vitro binding affinities revealed that HLA-DRB1*1501 molecules bound MOG 146-154 with intermediate and HLA-DRB1*0401 molecules with weak affinities. The binding of MOG 146-154 was comparable or better than myelin basic protein 85-99, which is the dominant myelin basic protein epitope in context with HLA-DRB1*1501 molecules in MS patients. This is the first study in which the data underscore the need to investigate the pathogenic or regulatory role of the transmembrane and intracellular part of MOG for MS in more detail.

Fc receptors are critical for autoimmune inflammatory damage to the central nervous system in experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is simulated by various forms of experimental autoimmune encephalomyelitis, in which T cells, antibodies, cytokines and complementary factors interact with the central nervous system (CNS) myelin proteins and lead to inflammatory damage. We investigated the role of Fc receptors (FcRs), which link the cellular and humoral branches of the immune system, in myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE), using two different FcRgamma knockout DBA/1 mice. The first knockout were the FcRgamma chain-deficient mice, which lack FcgammaRI, FcgammaRIII and Fc(epsilon)RI, while the second knockout mice lack only FcgammaRII. The lack of FcgammaRII enhanced the disease susceptibility with associated increased CNS demyelination. While FcRgamma+/+ DBA/1 mice also developed pronounced CNS infiltration and myelin destruction, FcRgamma-/- littermates were protected despite initial peripheral autoimmune responses to MOG. In vitro analyses revealed equivalent potentials of fluid phase phagocytosis of myelin and MOG in bone-marrow macrophages derived from both FcRgamma+/+ and FcRgamma-/- mice, while MOG-immunoglobulin (Ig)G immune complexes were only internalized by FcRgamma+/+ macrophages. This was associated with cellular activation in FcRgamma+/+ but not FcRgamma-/- macrophages, as assessed by the activation of intracellular mitogen activated protein (MAP)-kinase signalling elements. We propose that protection from EAE in FcRgamma-deficient mice is due to the inefficient antigen processing/presentation of myelin proteins during the induction of secondary immune responses locally in the CNS, which leads to demyelination. This demonstrates the importance of FcR in the promotion of autoimmune inflammation of the CNS and highlights the therapeutic possibility of treatment of MS with FcR-directed modalities.

T- and B-cell responses to myelin oligodendrocyte glycoprotein in experimental autoimmune encephalomyelitis and multiple sclerosis

The identification of myelin oligodendrocyte glycoprotein (MOG) as a target for autoantibody-mediated demyelination in experimental autoimmune encephalomyelitis (EAE) resulted in the re-evaluation of the role of B cell responses to myelin autoantigens in the immunopathogenesis of multiple sclerosis. MOG is a central nervous system specific myelin glycoprotein that is expressed preferentially on the outermost surface of the myelin sheath. Although MOG is only a minor component of CNS myelin it is highly immunogenic, inducing severe EAE in both rodents and primates. In rat and marmoset models of MOG-induced EAE demyelination is antibody-dependent and reproduces the immunopathology seen in many cases of MS. In contrast, in mice inflammation in the CNS can result in demyelination in the absence of a MOG-specific B cell response, although if present this will enhance disease severity and demyelination. Clinical studies indicate that autoimmune responses to MOG are enhanced in many CNS diseases and implicate MOG-specific B cell responses in the immunopathogenesis of multiple sclerosis. This review provides a summary of our current understanding of MOG as a target autoantigen in EAE and MS, and addresses the crucial question as to how immune tolerance to MOG may be maintained in the healthy individual.

Immune responses against the myelin/oligodendrocyte glycoprotein in experimental autoimmune demyelination

Myelin/oligodendrocyte glycoprotein (MOG) is a surface-exposed antigen of myelin and an important target for autoimmune responses which mediate inflammatory demyelination in the central nervous system. Experimentally, MOG induces strong pathogenic T cell responses in many strains of laboratory animals. Immunological studies in humans also identify MOG as a surprisingly prevalent antigenic molecule among the myelin proteins. In addition, the encephalitogenic properties of MOG are linked to the induction of antibody responses which have been demonstrated to directly promote central nervous system demyelination, a hallmark neuropathological feature in disorders such as human multiple sclerosis. Factors responsible for autoimmunity to MOG likely include genetic influences as well as other mechanisms, which are the subject of intense investigation. This article reviews experimental data currently available on specificity and pathogenic roles of T cell and antibody responses against MOG, which have implications relevant to multiple sclerosis and related disorders.