Experimental models of spontaneous autoimmune disease in the central nervous system

Multiple sclerosis and the intestine: Chasing the microbial offender

Multiple sclerosis (MS) affects more than 2.8 million people worldwide but the distribution is not even. Although over 200 gene variants have been associated with susceptibility, studies of genetically identical monozygotic twin pairs suggest that the genetic make-up is responsible for only about 20%-30% of the risk to develop disease, while the rest is contributed by milieu factors. Recently, a new, unexpected player has entered the ranks of MS-triggering or facilitating elements: the human gut microbiota. In this review, we summarize the present knowledge of microbial effects on formation of a pathogenic autoreactive immune response targeting the distant central nervous system and delineate the approaches, both in people with MS and in MS animal models, which have led to this concept. Finally, we propose that a tight combination of investigations of human patients with studies of suitable animal models is the best strategy to functionally characterize disease-associated microbiota and thereby contribute to deciphering pathogenesis of a complex human disease.

Delimiting MOGAD as a disease entity using translational imaging

The first formal consensus diagnostic criteria for myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) were recently proposed. Yet, the distinction of MOGAD-defining characteristics from characteristics of its important differential diagnoses such as multiple sclerosis (MS) and aquaporin-4 antibody seropositive neuromyelitis optica spectrum disorder (NMOSD) is still obstructed. In preclinical research, MOG antibody-based animal models were used for decades to derive knowledge about MS. In clinical research, people with MOGAD have been combined into cohorts with other diagnoses. Thus, it remains unclear to which extent the generated knowledge is specifically applicable to MOGAD. Translational research can contribute to identifying MOGAD characteristic features by establishing imaging methods and outcome parameters on proven pathophysiological grounds. This article reviews suitable animal models for translational MOGAD research and the current state and prospect of translational imaging in MOGAD.

Gene Expression in Spontaneous Experimental Autoimmune Encephalomyelitis Is Linked to Human Multiple Sclerosis Risk Genes

Recent genome-wide association studies have identified over 230 genetic risk loci for multiple sclerosis. Current experimental autoimmune encephalomyelitis (EAE) models requiring active induction of disease may not be optimally suited for the characterization of the function of these genes. We have thus used gene expression profiling to study whether spontaneous opticospinal EAE (OSE) or MOG-induced EAE mirrors the genetic contribution to the pathogenesis of multiple sclerosis more faithfully. To this end, we compared gene expression in OSE and MOG EAE models and analyzed the relationship of both models to human multiple sclerosis risk genes and T helper cell biology. We observed stronger gene expression changes and an involvement of more pathways of the adaptive immune system in OSE than MOG EAE. Furthermore, we demonstrated a more extensive enrichment of human MS risk genes among transcripts differentially expressed in OSE than was the case for MOG EAE. Transcripts differentially expressed only in diseased OSE mice but not in MOG EAE were significantly enriched for T helper cell-specific transcripts. These transcripts are part of immune-regulatory pathways. The activation of the adaptive immune system and the enrichment of both human multiple sclerosis risk genes and T helper cell-specific transcripts were also observed in OSE mice showing only mild disease signs. These expression changes may, therefore, be indicative of processes at disease onset. In summary, more human multiple sclerosis risk genes were differentially expressed in OSE than was observed for MOG EAE, especially in T_H1 cells. When studying the functional role of multiple sclerosis risk genes and pathways during disease onset and their interactions with the environment, spontaneous OSE may thus show advantages over MOG-induced EAE.

Imaging the execution phase of neuroinflammatory disease models

In vivo imaging of the rodent spinal cord has advanced our understanding of how resident cells of the central nervous system (CNS) respond to neuroinflammation. By combining two-photon imaging and experimental autoimmune encephalomyelitis (EAE), the most widely used rodent model of multiple sclerosis (MS), it has been possible, for example, to study how axons degenerate when confronted with inflammatory cells, how oligodendrocytes get damaged in inflammatory lesions, and how immune cells themselves adapt their phenotype and functionality to the changing lesion environment. Similar approaches are now increasingly used to study other forms of neuroinflammation, such as antibody/complement-mediated neuromyelitis optica spectrum disease (NMOSD). To tackle the most pressing open questions in the field, new biosensors and indicator mice that report the metabolic state and interaction of cells in neuroinflammatory lesions are being developed. Moreover, the field is moving towards new anatomical sites of inflammation, such as the cortical gray matter, but also towards longer observation intervals to reveal the chronic perturbations and adaptations that characterize advanced stages of MS.

Merits and complexities of modeling multiple sclerosis in non-human primates: implications for drug discovery

INTRODUCTION

The translation of scientific discoveries made in animal models into effective treatments for patients often fails, indicating that currently used disease models in preclinical research are insufficiently predictive for clinical success. An often-used model in the preclinical research of autoimmune neurological diseases, multiple sclerosis in particular, is experimental autoimmune encephalomyelitis (EAE). Most EAE models are based on genetically susceptible inbred/SPF mouse strains used at adolescent age (10-12 weeks), which lack exposure to genetic and microbial factors which shape the human immune system. Areas covered: Herein, the authors ask whether an EAE model in adult non-human primates from an outbred conventionally-housed colony could help bridge the translational gap between rodent EAE models and MS patients. Particularly, the authors discuss a novel and translationally relevant EAE model in common marmosets (Callithrix jacchus) that shares remarkable pathological similarity with MS. Expert opinion: The MS-like pathology in this model is caused by the interaction of effector memory T cells with B cells infected with the γ1-herpesvirus (CalHV3), both present in the pathogen-educated marmoset immune repertoire. The authors postulate that depletion of only the small subset (<0.05%) of CalHV3-infected B cells may be sufficient to limit chronic inflammatory demyelination.

Toll-Like Receptor 2 Mediates In Vivo Pro- and Anti-inflammatory Effects of Mycobacterium Tuberculosis and Modulates Autoimmune Encephalomyelitis

Mycobacteria display pro- and anti-inflammatory effects in human and experimental pathology. We show here that both effects are mediated by Toll-like receptor 2 (Tlr2), by exploiting a previously characterized Tlr2 variant (Met82Ile). Tlr2 82ile promoted self-specific proinflammatory polarization as well as expansion of ag-specific FoxP3(+) Tregs, while Tlr2 82met impairs the expansion of Tregs and reduces the production of IFN-γ and IL-17 proinflammatory cytokines. Preferential dimerization with Tlr1 or Tlr6 could not explain these differences. In silico, we showed that Tlr2 variant Met82Ile modified the binding pocket for peptidoglycans and participated directly to a putative binding pocket for sugars and cadherins. The distinct pro- and anti-inflammatory actions impacted severity, extent of remission, and distribution of the lesions within the central nervous system of experimental autoimmune encephalomyelitis. Thus, Tlr2 has a janus function in vivo as mediator of the role of bacterial products in balancing pro- and anti-inflammatory immune responses.

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.

Treg cells mediate recovery from EAE by controlling effector T cell proliferation and motility in the CNS

Regulatory T cells are crucial in controlling various functions of effector T cells during experimental autoimmune encephalomyelitis. While regulatory T cells are reported to exert their immunomodulatory effects in the peripheral immune organs, their role within the central nervous system (CNS) during experimental autoimmune encephalomyelitis is unclear. Here, by combining a selectively timed regulatory T cells depletion with 2-photon microscopy, we report that regulatory T cells exercise their dynamic control over effector T cells in the CNS. Acute depletion of regulatory T cells exacerbated experimental autoimmune encephalomyelitis severity which was accompanied by increased pro-inflammatory cytokine production and proliferation of effector T cells. Intravital microscopy revealed that, in the absence of regulatory T cells, the velocity of effector T cells was decreased with simultaneous increase in the proportion of stationary phase cells in the CNS. Based on these data, we conclude that regulatory T cells mediate recovery from experimental autoimmune encephalomyelitis by controlling cytokine production, proliferation and motility of effector T cells in the CNS.

From classic to spontaneous and humanized models of multiple sclerosis: impact on understanding pathogenesis and drug development

Multiple sclerosis (MS), a demyelinating disease of the central nervous system (CNS), presents as a complex disease with variable clinical and pathological manifestations, involving different pathogenic pathways. Animal models, particularly experimental autoimmune encephalomyelitis (EAE), have been key to deciphering the pathophysiology of MS, although no single model can recapitulate the complexity and diversity of MS, or can, to date, integrate the diverse pathogenic pathways. Since the first EAE model was introduced decades ago, multiple classic (induced), spontaneous, and humanized EAE models have been developed, each recapitulating particular aspects of MS pathogenesis. The advances in technologies of genetic ablation and transgenesis in mice of C57BL/6J background and the development of myelin-oligodendrocyte glycoprotein (MOG)-induced EAE in C57BL/6J mice yielded several spontaneous and humanized EAE models, and resulted in a plethora of EAE models in which the role of specific genes or cell populations could be precisely interrogated, towards modeling specific pathways of MS pathogenesis/regulation in MS. Collectively, the numerous studies on the different EAE models contributed immensely to our basic understanding of cellular and molecular pathways in MS pathogenesis as well as to the development of therapeutic agents: several drugs available today as disease modifying treatments were developed from direct studies on EAE models, and many others were tested or validated in EAE. In this review, we discuss the contribution of major classic, spontaneous, and humanized EAE models to our understanding of MS pathophysiology and to insights leading to devising current and future therapies for this disease.

Microbial view of central nervous system autoimmunity

Not much is known about the initial events leading to the development of the central nervous system (CNS)-specific autoimmune disorder Multiple Sclerosis (MS). Environmental factors are suspected to trigger the pathogenic events in people with genetic disease susceptibility. Historically, many infectious microbes were linked to MS, but no infection has ever been demonstrated to be the cause of the disease. Recent emerging evidence from animal models of MS suggests a causal link with resident commensal bacteria. Microbial organisms may trigger the activation of CNS-specific, auto-aggressive lymphocytes either through molecular mimicry or via bystander activation. In addition, several gut microbial metabolites and bacterial products may interact with the immune system to modulate CNS autoimmunity.

Immune regulation of multiple sclerosis

Multiple sclerosis (MS) is considered a prototype inflammatory autoimmune disorder of the central nervous system (CNS). The etiology of this disease remains unknown, but an interplay between as yet unidentified environmental factors and susceptibility genes appears most likely. In consequence, these factors trigger a cascade, involving an inflammatory response within the CNS that results in demyelination, oligodendrocyte death, axonal damage, gliosis, and neurodegeneration. How these complex traits translate into the clinical presentation of the disease is a focus of ongoing research. The central hypothesis is that T lymphocytes with receptors for CNS myelin components are driving the disease. The initial activation of autoreactive lymphocytes is thought to take place in the systemic lymphoid organs, most likely through molecular mimickry or nonspecifically through bystander activation. These autoreactive lymphocytes can migrate to the CNS where they become reactivated upon encountering their target antigen, initiating an autoimmune inflammatory attack. This ultimately leads to demyelination and axonal damage. This chapter focuses on the role of T and B lymphocytes in the immunopathogenesis of MS.

Remote control-triggering of brain autoimmune disease in the gut

Converging evidence indicates that multiple sclerosis, an inflammatory demyelinating disease of the central nervous system, is caused by brain-specific, self-reactive T lymphocytes. These are normal components embedded in the human immune system throughout healthy life. Only upon activation in the periphery, the T cells assume properties that enable them to break through the vascular blood-brain barrier and to invade the brain white matter. While activation has been traditionally associated with microbial infections, recently, studies of animal models revealed a critical role of the commensal gut flora as a key triggering factor. These findings may pave the way to new strategies to treat MS and other human autoimmune diseases, and commend a reevaluation of dietary approaches.

Endothelial TWIK-related potassium channel-1 (TREK1) regulates immune-cell trafficking into the CNS

The blood-brain barrier (BBB) is an integral part of the neurovascular unit (NVU). The NVU is comprised of endothelial cells that are interconnected by tight junctions resting on a parenchymal basement membrane ensheathed by pericytes, smooth muscle cells and a layer of astrocyte end feet. Circulating blood cells, such as leukocytes, complete the NVU. BBB disruption is common in several neurological diseases, but the molecular mechanisms involved remain largely unknown. We analyzed the role of TWIK-related potassium channel-1 (TREK1, encoded by KCNK2) in human and mouse endothelial cells and the BBB. TREK1 was downregulated in endothelial cells by treatment with interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α). Blocking TREK1 increased leukocyte transmigration, whereas TREK1 activation had the opposite effect. We identified altered mitogen-activated protein (MAP) kinase signaling, actin remodeling and upregulation of cellular adhesion molecules as potential mechanisms of increased migration in TREK1-deficient (Kcnk2(-/-)) cells. In Kcnk2(-/-) mice, brain endothelial cells showed an upregulation of the cellular adhesion molecules ICAM1, VCAM1 and PECAM1 and facilitated leukocyte trafficking into the CNS. Following the induction of experimental autoimmune encephalomyelitis (EAE) by immunization with a myelin oligodendrocyte protein (MOG)35-55 peptide, Kcnk2(-/-) mice showed higher EAE severity scores that were accompanied by increased cellular infiltrates in the central nervous system (CNS). The severity of EAE was attenuated in mice given the amyotrophic lateral sclerosis drug riluzole or fed a diet enriched with linseed oil (which contains the TREK-1 activating omega-3 fatty acid α-linolenic acid). These beneficial effects were reduced in Kcnk2(-/-) mice, suggesting TREK-1 activating compounds may be used therapeutically to treat diseases related to BBB dysfunction.

The Primate EAE Model Points at EBV-Infected B Cells as a Preferential Therapy Target in Multiple Sclerosis

The remarkable clinical efficacy of anti-CD20 monoclonal antibodies (mAb) in relapsing-remitting multiple sclerosis points at the critical involvement of B cells in the disease. However, the exact pathogenic contribution of B cells is poorly understood. In this publication we review new data on the role of CD20+ B cells in a unique experimental autoimmune encephalomyelitis (EAE) model in common marmosets (Callithrix jacchus), a small-bodied neotropical primate. We will also discuss the relevance of these data for MS. Different from rodent EAE models, but similar to MS, disease progression in marmosets can develop independent of autoantibodies. Progressive disease is mediated by MHC class Ib (Caja-E) restricted cytotoxic T cells, which are activated by γ-herpesvirus-infected B cells and cause widespread demyelination of cortical gray matter. B-cell directed monoclonal antibody therapies (anti-CD20 versus anti-BLyS and anti-APRIL) have a variable effect on EAE progression, which we found associated with variable depletion of the Epstein Barr virus (EBV)-like γ-herpesvirus CalHV3 from lymphoid organs. These findings support an important pathogenic role of CD20+ B cell in MS, especially of the subset infected with EBV.

Modeling the heterogeneity of multiple sclerosis in animals

Multiple sclerosis (MS) is an inflammatory, demyelinating disease of the central nervous system (CNS) manifested with varying clinical course, pathology, and inflammatory patterns. There are multiple animal models that reflect different aspects of this heterogeneity. Collectively, these models reveal a balance between pathogenic and regulatory CD4(+) T cells, CD8(+) T cells, and B cells that influences the incidence, timing, and severity of CNS autoimmunity. In this review we discuss experimental autoimmune encephalomyelitis (EAE) models that have been used to study the pathogenic and regulatory roles of these immune cells; models that recapitulate different aspects of the disease seen in patients with MS, and questions remaining for future studies.

Integrative continuum: accelerating therapeutic advances in rare autoimmune diseases

Autoimmune diseases are chronic, life threatening, and of burgeoning public health concern. They rank among the 10 most common causes of death in women, and some have incidence rates surpassing those of heart disease and cancer. Emerging information regarding molecular and cellular mechanisms affords opportunities for the discovery of novel therapeutic strategies or the repurposing of FDA-approved pharmacologic agents. Yet, obstacles to drug development amplify as an inverse function of the incidence of rare autoimmune disease; challenges include heterogeneous clinical presentation, paucity of definitive biomarkers, and poorly validated measures of therapeutic response. An integrative continuum model to address these challenges is being applied to neuromyelitis optica (NMO)-a potentially devastating neurodegenerative process that has had limited therapeutic options. This model links target discovery with pharmacologic application to accelerate improved clinical efficacy. The application of such innovative strategies may help researchers overcome barriers to therapeutic advances in NMO and other rare autoimmune diseases.

Commensal gut flora and brain autoimmunity: a love or hate affair?

Multiple sclerosis (MS) and other chronic inflammatory autoimmune diseases represent major public health challenges in industrialised Western society. MS results from an autoimmune attack against myelin structures by self-reactive lymphocytes, which are normal components of the healthy immune repertoire. The nature of the triggers that convert the innocuous self-reactive lymphocytes into an autoaggressive phenotype is poorly understood. In the past, it was primarily suspected that pathogenic infections trigger MS. However, so far, none of the incriminated pathogenic microbes were firmly associated with the disease. A growing body of evidence in animal models of MS implicates the gut microbiota in the induction of central nervous system (CNS) autoimmunity. The mammalian gut harbors a diverse population of microbial organisms which are essential for our well being. There is an increasing understanding that the gut microbiota not only modulates the local immune functions but also affects the systemic immune system. We are only just beginning to understand the nature of the interactions of the gut microbiota with the host's immune system especially in the context of autoimmune diseases. This review will address the influence of intestinal microbiota on immune homeostasis and on the development of autoimmune responses at sites distal to the intestine with a particular emphasis placed on a discussion about CNS autoimmunity.

IL-17 producing T cells in mouse models of multiple sclerosis and rheumatoid arthritis

Multiple Sclerosis (MS) and Rheumatoid Arthritis (RA) are amongst the most common autoimmune diseases in the northern hemisphere. There is mounting evidence that in both afflictions, not only environmental and genetic factors influence disease, but cellular components such as autoreactive T cells also contribute to pathology. Animal models are key in the study and subsequent therapeutic development for human autoimmune diseases. As patient material is often difficult to obtain and in some cases--as in MS, where the central nervous system (CNS) is concerned--even not accessible, animal models provide a multifaceted tool to explore disease-underlying mechanisms. The pro-inflammatory T cell cytokine IL-17 has recently moved to center stage due to its crucial role in autoimmune diseases including MS and RA. A plethora of studies in animal models has sustained the relevance of this cytokine pathway for the development of autoimmunity and shed light on its cellular sources and patho-mechanisms. This review addresses the role of IL-17 producing T lymphocytes, in particular CD4(+) and γδ T cells, in three commonly used mouse models for MS and RA, namely experimental autoimmune encephalomyelitis (EAE), collagen-induced arthritis (CIA), and antigen-induced arthritis (AIA). Comparing and combining knowledge gained from different animal models will broaden our understanding of the IL-17 biology and facilitate the translation to the human diseases.

New methods for multiple sclerosis drug discovery

INTRODUCTION

MS is a heterogeneous disorder that requires the development of better diagnostics to identify disease subtypes enabling appropriate therapeutic intervention at an early stage of the disease. Accumulating evidence indicates that members of the inhibitor of apoptosis (IAP) family play an important role in the pathogenesis of MS by reducing the apoptotic elimination of autoreactive immune cells.

AREAS COVERED

The authors describe improved animal modeling strategies to identify compounds that have immunomodulatory, neurorestorative and neuroprotective properties. In addition, the authors propose new approaches to better model cognitive dysfunction in MS, which will aid the development of novel therapeutics for this complex disorder. The paper provides the reader with an appreciation for the diagnostic and therapeutic potential of apoptosis-related proteins for MS.

EXPERT OPINION

Recent evidence suggests that increased resistance of autoreactive immune cells to apoptotic elimination is a contributing factor to both disease susceptibility and progression in MS. This occurs, at least in part, because of elevated levels of the IAP family of anti-apoptotic genes that display distinct expression profiles associated with different subtypes of MS. The authors believe that the detection and targeting of members of the IAP family can provide better drugs for MS. Particularly, the authors feel that the overexpression of IAPs in animal models can provide novel insights into MS for both its pathogenesis and the discovery of new lead compounds.

B cells in spontaneous autoimmune diseases of the central nervous system

B cells and their secreted products participate in the intricate network of pathogenic and regulatory immune responses. In human autoimmune diseases like rheumatoid arthritis, systemic lupus erythematosus and type 1 diabetes, a role for B cells and antibodies is well established. However, in multiple sclerosis (MS), despite the presence of autoantibodies, B cells were less considered as a major participant of autoimmune processes, until recently. Several lines of evidence now indicate a more active role for B cells in disease pathogenesis. In this review, we discuss the diverse roles of B cells in autoimmune diseases with particular focus on multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE) as well as the recently generated spontaneous EAE mouse models.

Animal models of multiple sclerosis--potentials and limitations

Experimental autoimmune encephalomyelitis (EAE) is still the most widely accepted animal model of multiple sclerosis (MS). Different types of EAE have been developed in order to investigate pathogenetic, clinical and therapeutic aspects of the heterogenic human disease. Generally, investigations in EAE are more suitable for the analysis of immunogenetic elements (major histocompatibility complex restriction and candidate risk genes) and for the study of histopathological features (inflammation, demyelination and degeneration) of the disease than for screening of new treatments. Recent studies in new EAE models, especially in transgenic ones, have in connection with new analytical techniques such as microarray assays provided a deeper insight into the pathogenic cellular and molecular mechanisms of EAE and potentially of MS. For example, it was possible to better delineate the role of soluble pro-inflammatory (tumor necrosis factor-α, interferon-γ and interleukins 1, 12 and 23), anti-inflammatory (transforming growth factor-β and interleukins 4, 10, 27 and 35) and neurotrophic factors (ciliary neurotrophic factor and brain-derived neurotrophic factor). Also, the regulatory and effector functions of distinct immune cell subpopulations such as CD4+ Th1, Th2, Th3 and Th17 cells, CD4+FoxP3+ Treg cells, CD8+ Tc1 and Tc2, B cells and γδ+ T cells have been disclosed in more detail. The new insights may help to identify novel targets for the treatment of MS. However, translation of the experimental results into the clinical practice requires prudence and great caution.

Mucopolysaccharidosis IIIB, a lysosomal storage disease, triggers a pathogenic CNS autoimmune response

Background

Recently, using a mouse model of mucopolysaccharidosis (MPS) IIIB, a lysosomal storage disease with severe neurological deterioration, we showed that MPS IIIB neuropathology is accompanied by a robust neuroinflammatory response of unknown consequence. This study was to assess whether MPS IIIB lymphocytes are pathogenic.

Methods

Lymphocytes from MPS IIIB mice were adoptively transferred to naïve wild-type mice. The recipient animals were then evaluated for signs of disease and inflammation in the central nervous system.

Results

Our results show for the first time, that lymphocytes isolated from MPS IIIB mice caused a mild paralytic disease when they were injected systemically into naïve wild-type mice. This disease is characterized by mild tail and lower trunk weakness with delayed weight gain. The MPS IIIB lymphocytes also trigger neuroinflammation within the CNS of recipient mice characterized by an increase in transcripts of IL2, IL4, IL5, IL17, TNFα, IFNα and Ifi30, and intraparenchymal lymphocyte infiltration.

Conclusions

Our data suggest that an autoimmune response directed at CNS components contributes to MPS IIIB neuropathology independent of lysosomal storage pathology. Adoptive transfer of purified T-cells will be needed in future studies to identify specific effector T-cells in MPS IIIB neuroimmune pathogenesis.

Trafficking of immune cells in the central nervous system

The CNS is an immune-privileged environment, yet the local control of multiple pathogens is dependent on the ability of immune cells to access and operate within this site. However, inflammation of the distinct anatomical sites (i.e., meninges, cerebrospinal fluid, and parenchyma) associated with the CNS can also be deleterious. Therefore, control of lymphocyte entry and migration within the brain is vital to regulate protective and pathological responses. In this review, several recent advances are highlighted that provide new insights into the processes that regulate leukocyte access to, and movement within, the brain.

Experimental autoimmune encephalomyelitis in the common marmoset, a bridge between rodent EAE and multiple sclerosis for immunotherapy development

The attrition rate of new drugs for central nervous system diseases including multiple sclerosis (MS) is very high. A widely recognized bottleneck in the selection of promising central nervous system drug candidates from the development pipeline is the lack of sufficiently predictive animal models. Here, we review how the experimental autoimmune encephalomyelitis (EAE) model in the Neotropical primate "common marmoset" can help to bridge the gap between rodent EAE models and MS. The EAE model in the marmoset closely resembles MS in the clinical as well as pathological presentation and can be used for fundamental research into immunopathogenic mechanisms and for therapy development. We discuss recent insights arising from this model, both on novel therapeutics and immunopathogenesis.

Modeling multiple sclerosis in laboratory animals

Inflammatory demyelinating disease of the central nervous system is one of the most frequent causes of neurological disability in young adults. While in situ analysis and in vitro models do shed some light onto the processes of tissue damage and cellular interactions, the development of neuroinflammation and demyelination is a far too complex process to be adequately modeled by simple test tube systems. Thus, animal models using primarily genetically modified mice have been proven to be of paramount importance. In this chapter, we discuss recent advances in modeling brain diseases focusing on murine models and report on new tools to study the pathogenesis of complex diseases such as multiple sclerosis.

EAE: an immunologist's magic eye

EAE comes in many shapes and colors. Individual variants of EAE present a baffling complexity of different aspects and traits, clinical, immunological, and structural. But, embedded in this seemingly chaotic image, the educated eye will discern patterns that retrace fundamental features of immune response, in particular, autoimmunity and self-tolerance. EAE and its variants thus can be likened to an autostereogram, i.e. they are an immunologist's magic eye.

Multiple sclerosis: human model for EAE?

Concepts of the pathogenesis of MS are based on evidence from the animal model, EAE. Yet, the relationship between human MS and EAE is far from being a one-way road: many paths lead from the bedside back to animals in the laboratory.

Spontaneous relapsing-remitting EAE in the SJL/J mouse: MOG-reactive transgenic T cells recruit endogenous MOG-specific B cells

We describe new T cell receptor (TCR) transgenic mice (relapsing-remitting [RR] mice) carrying a TCR specific for myelin oligodendrocyte glycoprotein (MOG) peptide 92-106 in the context of I-A(s). Backcrossed to the SJL/J background, most RR mice spontaneously develop RR experimental autoimmune encephalomyelitis (EAE) with episodes often altering between different central nervous system tissues like the cerebellum, optic nerve, and spinal cord. Development of spontaneous EAE depends on the presence of an intact B cell compartment and on the expression of MOG autoantigen. There is no spontaneous EAE development in B cell-depleted mice or in transgenic mice lacking MOG. Transgenic T cells seem to expand MOG autoreactive B cells from the endogenous repertoire. The expanded autoreactive B cells produce autoantibodies binding to a conformational epitope on the native MOG protein while ignoring the T cell target peptide. The secreted autoantibodies are pathogenic, enhancing demyelinating EAE episodes. RR mice constitute the first spontaneous animal model for the most common form of multiple sclerosis (MS), RR MS.

Multiple system atrophy: a primary oligodendrogliopathy

To this day, the cause of multiple system atrophy (MSA) remains stubbornly enigmatic. A growing body of observations regarding the clinical, morphological, and biochemical phenotypes of MSA has been published, but the interested student is still left without a clue as to its underlying cause. MSA has long been considered a rare cousin of Parkinson's disease and cerebellar degeneration; it is rich in acronyms but poor in genetic and environmental leads. Because of the worldwide research efforts conducted over the last two decades and the discovery of the alpha-synuclein-encoding SNCA gene as a cause of rare familial Parkinson's disease, the MSA field has seen advances on three fronts: the identification of its principal cellular target, that is, oligodendrocytes; the characterization of alpha-synuclein-rich glial cytoplasmic inclusions as a suitable marker at autopsy; and improved diagnostic accuracy in living patients resulting from detailed clinicopathological studies. The working model of MSA as a primary glial disorder was recently strengthened by the finding of dysregulation in the metabolism of myelin basic protein and p25alpha, a central nervous system-specific phosphoprotein (also called tubulin polymerization promoting protein, TPPP). Intriguingly, in early cases of MSA, the oligodendrocytic changes in myelin basic protein and p25alpha processing were recorded even before formation of glial cytoplasmic inclusions became detectable. Here, we review the evolving concept that MSA may not just be related to Parkinson's disease but also share traits with the family of demyelinating disorders. Although these syndromes vary in their respective cause of oligodendrogliopathy, they have in common myelin disruption that is often followed by axonal dysfunction.