Myelin-reactive antibodies mediate the pathology of MBP–PLP fusion protein MP4-induced EAE

Risk Factors from Pregnancy to Adulthood in Multiple Sclerosis Outcome

Multiple sclerosis (MS) is an autoimmune disease characterized by a robust inflammatory response against myelin sheath antigens, which causes astrocyte and microglial activation and demyelination of the central nervous system (CNS). Multiple genetic predispositions and environmental factors are known to influence the immune response in autoimmune diseases, such as MS, and in the experimental autoimmune encephalomyelitis (EAE) model. Although the predisposition to suffer from MS seems to be a multifactorial process, a highly sensitive period is pregnancy due to factors that alter the development and differentiation of the CNS and the immune system, which increases the offspring’s susceptibility to develop MS. In this regard, there is evidence that thyroid hormone deficiency during gestation, such as hypothyroidism or hypothyroxinemia, may increase susceptibility to autoimmune diseases such as MS. In this review, we discuss the relevance of the gestational period for the development of MS in adulthood.

B Cells in Multiple Sclerosis and Virus-Induced Neuroinflammation

Neuroinflammation can be defined as an inflammatory response within the central nervous system (CNS) mediated by a complex crosstalk between CNS-resident and infiltrating immune cells from the periphery. Triggers for neuroinflammation not only include pathogens, trauma and toxic metabolites, but also autoimmune diseases such as neuromyelitis optica spectrum disorders and multiple sclerosis (MS) where the inflammatory response is recognized as a disease-escalating factor. B cells are not considered as the first responders of neuroinflammation, yet they have recently gained focus as a key component involved in the disease pathogenesis of several neuroinflammatory disorders like MS. Traditionally, the prime focus of the role of B cells in any disease, including neuroinflammatory diseases, was their ability to produce antibodies. While that may indeed be an important contribution of B cells in mediating disease pathogenesis, several lines of recent evidence indicate that B cells are multifunctional players during an inflammatory response, including their ability to present antigens and produce an array of cytokines. Moreover, interaction between B cells and other cellular components of the immune system or nervous system can either promote or dampen neuroinflammation depending on the disease. Given that the interest in B cells in neuroinflammation is relatively new, the precise roles that they play in the pathophysiology and progression of different neuroinflammatory disorders have not yet been well-elucidated. Furthermore, the possibility that they might change their function during the course of neuroinflammation adds another level of complexity and the puzzle remains incomplete. Indeed, advancing our knowledge on the role of B cells in neuroinflammation would also allow us to tackle these disorders better. Here, we review the available literature to explore the relationship between autoimmune and infectious neuroinflammation with a focus on the involvement of B cells in MS and viral infections of the CNS.

Obinutuzumab-Induced B Cell Depletion Reduces Spinal Cord Pathology in a CD20 Double Transgenic Mouse Model of Multiple Sclerosis

B cell-depleting therapies have recently proven to be clinically highly successful in the treatment of multiple sclerosis (MS). This study aimed to determine the effects of the novel type II anti-human CD20 (huCD20) monoclonal antibody (mAb) obinutuzumab (OBZ) on spinal cord degeneration in a B cell-dependent mouse model of MS. Double transgenic huCD20xHIGR3 (CD20dbtg) mice, which express human CD20, were immunised with the myelin fusion protein MP4 to induce experimental autoimmune encephalomyelitis (EAE). Both light and electron microscopy were used to assess myelination and axonal pathology in mice treated with OBZ during chronic EAE. Furthermore, the effects of the already established murine anti-CD20 antibody 18B12 were assessed in C57BL/6 wild-type (wt) mice. In both models (18B12/wt and OBZ/CD20dbtg) anti-CD20 treatment significantly diminished the extent of spinal cord pathology. While 18B12 treatment mainly reduced the extent of axonal pathology, a significant decrease in demyelination and increase in remyelination were additionally observed in OBZ-treated mice. Hence, the data suggest that OBZ could have neuroprotective effects on the CNS, setting the drug apart from the currently available type I anti-CD20 antibodies.

Contribution of LTi and TH17 cells to B cell aggregate formation in the central nervous system in a mouse model of multiple sclerosis

Background

In a subgroup of patients suffering from progressive multiple sclerosis (MS), which is an inflammation-mediated neurodegenerative disease of the central nervous system (CNS), B cell aggregates were discovered within the meninges. Occurrence of these structures was associated with a more severe disease course and cortical histopathology. We have developed the B cell-dependent MP4-induced experimental autoimmune encephalomyelitis (EAE) as a mouse model to mimic this trait of the human disease. The aim of this study was to determine a potential role of lymphoid tissue inducer (LTi) and T_H17 cells in the process of B cell aggregate formation in the MP4 model.

Methods

We performed flow cytometry of cerebellar and splenic tissue of MP4-immunized mice in the acute and chronic stage of the disease to analyze the presence of CD3⁻CD5⁻CD4⁺RORγt⁺ LTi and CD3⁺CD5⁺CD4⁺RORγt⁺ T_H17 cells. Myelin oligodendrocyte glycoprotein (MOG):35–55-induced EAE was used as B cell-independent control model. We further determined the gene expression profile of B cell aggregates using laser capture microdissection, followed by RNA sequencing.

Results

While we were able to detect LTi cells in the embryonic spleen and adult intestine, which served as positive controls, there was no evidence for the existence of such a population in acute or chronic EAE in neither of the two models. Yet, we detected CD3⁻CD5⁻CD4⁻RORγt⁺ innate lymphoid cells (ILCs) and T_H17 cells in the CNS, the latter especially in the chronic stage of MP4-induced EAE. Moreover, we observed a unique gene signature in CNS B cell aggregates compared to draining lymph nodes of MP4-immunized mice and to cerebellum as well as draining lymph nodes of mice with MOG:35–55-induced EAE.

Conclusion

The absence of LTi cells in the cerebellum suggests that other cells might take over the function as an initiator of lymphoid tissue formation in the CNS. Overall, the development of ectopic lymphoid organs is a complex process based on an interplay between several molecules and signals. Here, we propose some potential candidates, which might be involved in the formation of B cell aggregates in the CNS of MP4-immunized mice.

The enteric nervous system is a potential autoimmune target in multiple sclerosis

Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system (CNS) in young adults that has serious negative socioeconomic effects. In addition to symptoms caused by CNS pathology, the majority of MS patients frequently exhibit gastrointestinal dysfunction, which was previously either explained by the presence of spinal cord lesions or not directly linked to the autoimmune etiology of the disease. Here, we studied the enteric nervous system (ENS) in a B cell- and antibody-dependent mouse model of MS by immunohistochemistry and electron microscopy at different stages of the disease. ENS degeneration was evident prior to the development of CNS lesions and the onset of neurological deficits in mice. The pathology was antibody mediated and caused a significant decrease in gastrointestinal motility, which was associated with ENS gliosis and neuronal loss. We identified autoantibodies against four potential target antigens derived from enteric glia and/or neurons by immunoprecipitation and mass spectrometry. Antibodies against three of the target antigens were also present in the plasma of MS patients as confirmed by ELISA. The analysis of human colon resectates provided evidence of gliosis and ENS degeneration in MS patients compared to non-MS controls. For the first time, this study establishes a pathomechanistic link between the well-established autoimmune attack on the CNS and ENS pathology in MS, which might provide a paradigm shift in our current understanding of the immunopathogenesis of the disease with broad diagnostic and therapeutic implications.

Influence of type I IFN signaling on anti-MOG antibody-mediated demyelination

Background

Antibodies with specificity for myelin oligodendrocyte glycoprotein (MOG) are implicated in multiple sclerosis and related diseases. The pathogenic importance of anti-MOG antibody in primary demyelinating pathology remains poorly characterized.

Objective

The objective of this study is to investigate whether administration of anti-MOG antibody would be sufficient for demyelination and to determine if type I interferon (IFN) signaling plays a similar role in anti-MOG antibody-mediated pathology, as has been shown for neuromyelitis optica-like pathology.

Methods

Purified IgG2a monoclonal anti-MOG antibody and mouse complement were stereotactically injected into the corpus callosum of wild-type and type I IFN receptor deficient mice (IFNAR1-KO) with and without pre-established experimental autoimmune encephalomyelitis (EAE).

Results

Anti-MOG induced complement-dependent demyelination in the corpus callosum of wild-type mice and did not occur in mice that received control IgG2a. Deposition of activated complement coincided with demyelination, and this was significantly reduced in IFNAR1-KO mice. Co-injection of anti-MOG and complement at onset of symptoms of EAE induced similar levels of callosal demyelination in wild-type and IFNAR1-KO mice.

Conclusions

Anti-MOG antibody and complement was sufficient to induce callosal demyelination, and pathology was dependent on type I IFN. Induction of EAE in IFNAR1-KO mice overcame the dependence on type I IFN for anti-MOG and complement-mediated demyelination.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-017-0899-1) contains supplementary material, which is available to authorized users.

Nimodipine fosters remyelination in a mouse model of multiple sclerosis and induces microglia-specific apoptosis

Despite continuous interest in multiple sclerosis (MS) research, there is still a lack of neuroprotective strategies, because the main focus has remained on modulating the immune response. Here we performed in-depth analysis of neurodegeneration in experimental autoimmune encephalomyelitis (EAE) and in in vitro studies regarding the effect of the well-established L-type calcium channel antagonist nimodipine. Nimodipine treatment attenuated clinical EAE and spinal cord degeneration and promoted remyelination. Surprisingly, we observed calcium channel-independent effects on microglia, resulting in apoptosis. These effects were cell-type specific and irrespective of microglia polarization. Apoptosis was accompanied by decreased levels of nitric oxide (NO) and inducible NO synthase (iNOS) in cell culture as well as decreased iNOS and reactive oxygen species levels in EAE. In addition, increased numbers of Olig2+APC+ oligodendrocytes were detected. Overall, nimodipine application seems to generate a favorable environment for regenerative processes and therefore could be a treatment option for MS, because it combines features of immunomodulation with beneficial effects on neuroregeneration.

CEACAM1 mediates B cell aggregation in central nervous system autoimmunity

B cell aggregates in the central nervous system (CNS) have been associated with rapid disease progression in patients with multiple sclerosis (MS). Here we demonstrate a key role of carcinoembryogenic antigen-related cell adhesion molecule1 (CEACAM1) in B cell aggregate formation in MS patients and a B cell-dependent mouse model of MS. CEACAM1 expression was increased on peripheral blood B cells and CEACAM1⁺ B cells were present in brain infiltrates of MS patients. Administration of the anti-CEACAM1 antibody T84.1 was efficient in blocking aggregation of B cells derived from MS patients. Along these lines, application of the monoclonal anti-CEACAM1 antibody mCC1 was able to inhibit CNS B cell aggregate formation and significantly attenuated established MS-like disease in mice in the absence of any adverse effects. CEACAM1 was co-expressed with the regulator molecule T cell immunoglobulin and mucin domain −3 (TIM-3) on B cells, a novel molecule that has recently been described to induce anergy in T cells. Interestingly, elevated coexpression on B cells coincided with an autoreactive T helper cell phenotype in MS patients. Overall, these data identify CEACAM1 as a clinically highly interesting target in MS pathogenesis and open new therapeutic avenues for the treatment of the disease.

Can Antibodies Against Glial Derived Antigens be Early Biomarkers of Hippocampal Demyelination and Memory Loss in Alzheimer's Disease?

BACKGROUND

Alzheimer's disease (AD) is known to exhibit well characterized pathologies including the extracellular accumulation of amyloid plaques, intra-axonal presence of neurofibrillary tangles, and glial hypertrophy. Nevertheless, the nature of myelin pathology in AD has not been well studied. Recent studies on animal models of AD, however, revealed focal demyelination within amyloid-β plaques in hippocampus.

OBJECTIVES

In a view of this finding, we decided to assess humoral response against proteins of myelin sheath in AD, in the hope of identifying early biomarkers of memory loss and neuropathological process characteristic of AD.

METHODS

We assessed antibodies levels against proteins of the myelin sheath: myelin oligodendrocyte glycoprotein (MOG), myelin basic protein (MBP), myelin-associated glycoprotein (MAG), and proteolipoprotein (PLP) in sera of 26 AD patients and 26 healthy controls, using commercially available ELISA system (Mediagnost, Germany).

RESULTS

In the AD patient subgroup, significantly higher titers were observed for all types of assessed IgG autoantibodies compared to healthy control subjects (anti-MOG, anti-MAG, anti-MBP, anti-PLP). The titers of most of the investigated IgM antibodies were also higher in AD patients (p <  0.05), with the exception of anti-MAG IgM antibodies (p >  0.05).

CONCLUSION

The study provides the evidence for the significantly increased production of autoantibodies against proteins of myelin sheath in AD. These results can be of importance in the light of emerging data from animal models of AD, indicating early demyelination of hippocampal region. Further studies on larger population are necessary to confirm whether these autoantibodies could serve as early biomarkers of AD in humans.

Hypersensitivity Responses in the Central Nervous System

Immune-mediated tissue damage or hypersensitivity can be mediated by autospecific IgG antibodies. Pathology results from activation of complement, and antibody-dependent cellular cytotoxicity, mediated by inflammatory effector leukocytes include macrophages, natural killer cells, and granulocytes. Antibodies and complement have been associated to demyelinating pathology in multiple sclerosis (MS) lesions, where macrophages predominate among infiltrating myeloid cells. Serum-derived autoantibodies with predominant specificity for the astrocyte water channel aquaporin-4 (AQP4) are implicated as inducers of pathology in neuromyelitis optica (NMO), a central nervous system (CNS) demyelinating disease where activated neutrophils infiltrate, unlike in MS. The most widely used model for MS, experimental autoimmune encephalomyelitis, is an autoantigen-immunized disease that can be transferred to naive animals with CD4⁺ T cells, but not with antibodies. By contrast, NMO-like astrocyte and myelin pathology can be transferred to mice with AQP4–IgG from NMO patients. This is dependent on complement, and does not require T cells. Consistent with clinical observations that interferon-beta is ineffective as a therapy for NMO, NMO-like pathology is significantly reduced in mice lacking the Type I IFN receptor. In MS, there is evidence for intrathecal synthesis of antibodies as well as blood–brain barrier (BBB) breakdown, whereas in NMO, IgG accesses the CNS from blood. Transfer models involve either direct injection of antibody and complement to the CNS, or experimental manipulations to induce BBB breakdown. We here review studies in MS and NMO that elucidate roles for IgG and complement in the induction of BBB breakdown, astrocytopathy, and demyelinating pathology. These studies point to significance of T-independent effector mechanisms in neuroinflammation.

Four different synthetic peptides of proteolipid protein induce a distinct antibody response in MP4-induced experimental autoimmune encephalomyelitis

Here we studied the autoantibody specificity elicited by proteolipid protein (PLP) in MP4-induced experimental autoimmune encephalomyelitis, a mouse model of multiple sclerosis (MS). In C57BL/6 (B6) mice, antibodies were induced by immunization with one of the two extracellular and by the intracellular PLP domain. Antibodies against extracellular PLP were myelin-reactive in oligodendrocyte cultures and induced mild spinal cord demyelination upon transfer into B cell-deficient J(H)T mice. Remarkably, also antibodies against intracellular PLP showed binding to intact oligodendrocytes and were capable of inducing myelin pathology upon transfer into J(H)T mice. In MP4-immunized mice peptide-specific T(H)1/T(H)17 responses were mainly directed against the extracellular PLP domains, but also involved the intracellular epitopes. These data suggest that both extracellular and intracellular epitopes of PLP contribute to the pathogenesis of MP4-induced EAE already in the setting of intact myelin. It remains to be elucidated if this concept also applies to MS itself.

Central nervous system infiltrates are characterized by features of ongoing B cell-related immune activity in MP4-induced experimental autoimmune encephalomyelitis

In multiple sclerosis (MS) lymphoid follicle-like aggregates have been reported in the meninges of patients. Here we investigated the functional relevance of B cell infiltration into the central nervous system (CNS) in MP4-induced experimental autoimmune encephalomyelitis (EAE), a B cell-dependent mouse model of MS. In chronic EAE, B cell aggregates were characterized by the presence of CXCL13(+) and germinal center CD10(+) B cells. Germline transcripts were expressed in the CNS and particularly related to TH17-associated isotypes. We also observed B cells with restricted VH gene usage that differed from clones found in the spleen. Finally, we detected CNS-restricted spreading of the antigen-specific B cell response towards a myelin and a neuronal autoantigen. These data imply the development of autonomous B cell-mediated autoimmunity in the CNS in EAE - a concept that might also apply to MS itself.

Protective effect of tanreqing injection on axon myelin damage in the brain of mouse model for experimental autoimmune encephalomyelitis

OBJECTIVE

To evaluate the effect of Tanreqing injection on axon myelin in the mouse brain of experimental autoimmune encephalomyelitis (EAE).

METHODS

An EAE model was established by myelin oligodendrocyte glycoprotein (MOG)35-55 immunization in C57BL/6 mice. Mice were randomly divided into the following groups: normal, model, prednisone acetate (PA) (6 mg/kg), Tanreqing high dose (5.14 mL/kg), Tanreqing low dose (2.57 mL/kg). On the day of immunization, both Tanreqing groups were treated by intraperitoneal injection, with the PA group treated by intragastrical perfusion after T cell response, and the other groups treated with saline. Changes in body weight, neurological deficit score, incidence rate, mortality rate, and course of disease were observed for all mice. Brain tissue was isolated and stained with hematoxylin-eosin, and pathological investigations performed to evaluate axon myelin damage by transmission electron microscopy (TEM). Myelin basic protein and microtubule associated protein-2 were analyzed by immunohistochemistry.

RESULTS

Tanreqing injection significantly prolonged EAE latency and decreased the neurological deficit score, alleviated infiltration of inflammatory cells in the focus area, up-regulated hippocampal MBP expression at the acute stage and the remission stage, and increased microtubule associated protein-2 expression in the EAE brain to varying degrees in the acute stage. TEM analysis indicated that Tanreqing injection alleviates myelin damage in the EAE mouse and maintains the integrity of circular layer structures and alleviates axon mitochondrial swelling.

CONCLUSION

Tanreqing injection alleviates EAE symptoms.

Critical role of activation induced cytidine deaminase in experimental autoimmune encephalomyelitis

Multiple Sclerosis (MS) is a neurodegenerative autoimmune disorder caused by chronic inflammation and demyelination within the central nervous system (CNS). Clinical studies in MS patients have demonstrated efficacy with B cell targeted therapies such as anti-CD20. However, the exact role that B cells play in the disease process is unclear. Activation Induced cytidine deaminase (AID) is an essential enzyme for the processes of antibody affinity maturation and isotype switching. To evaluate the impact of affinity maturation and isotype switching, we have interrogated the effect of AID-deficiency in an animal model of MS. Here, we show that the severity of experimental autoimmune encephalomyelitis (EAE) induced by the extracellular domain of human myelin oligodendrocyte glycoprotein (MOG1-125) is significantly reduced in Aicda deficient mice, which, unlike wild-type mice, lack serum IgG to myelin associated antigens. MOG specific T cell responses are comparable between wild-type and Aicda knockout mice suggesting an active role for antigen experienced B cells. Thus affinity maturation and/or class switching are critical processes in the pathogenesis of EAE.

The complement system contributes to the pathology of experimental autoimmune encephalomyelitis by triggering demyelination and modifying the antigen-specific T and B cell response

So far, studies of the human autoimmune disease multiple sclerosis (MS) have largely been hampered by the absence of a pathogenic B cell component in its animal model, experimental autoimmune encephalomyelitis (EAE). To overcome this shortcoming, we have previously introduced the myelin basic protein (MBP)-proteolipid protein (PLP) MP4-induced EAE, which is B cell and autoantibody-dependent. Here we show that MP4-immunized wild-type C57BL/6 mice displayed a significantly lower disease incidence when their complement system was transiently depleted by a single injection of cobra venom factor (CVF) prior to immunization. Considering the underlying pathomechanism, our data suggest that the complement system is crucial for MP4-specific antibodies to trigger CNS pathology. Demyelinated lesions in the CNS were colocalized with complement depositions. In addition, B cell deficient JHT mice reconstituted with MP4-reactive serum showed significantly attenuated clinical and histological EAE after depletion of complement by CVF. The complement system was also critically involved in the generation of the MP4-specific T and B cell response: in MP4-immunized wild-type mice treated with CVF the MP4-specific cytokine and antibody response was significantly attenuated compared to untreated wild-type mice. Taken together, we propose two independent mechanisms by which the complement system can contribute to the pathology of autoimmune encephalomyelitis. Our data corroborate the role of complement in triggering antibody-dependent demyelination and antigen-specific T cell immunity and also provide first evidence that the complement system can modify the antigen-specific B cell response in EAE and possibly MS.

Tertiary lymphoid organ development coincides with determinant spreading of the myelin-specific T cell response

While the role of T cells has been studied extensively in multiple sclerosis (MS), the pathogenic contribution of B cells has only recently attracted major attention, when it was shown that B cell aggregates can develop in the meninges of a subset of MS patients and were suggested to be correlates of late-stage and more aggressive disease in this patient population. However, whether these aggregates actually exist has subsequently been questioned and their functional significance has remained unclear. Here, we studied myelin basic protein (MBP)-proteolipid protein (PLP)-induced experimental autoimmune encephalomyelitis (EAE), which is one of the few animal models for MS that is dependent on B cells. We provide evidence that B cell aggregation is reflective of lymphoid neogenesis in the central nervous system (CNS) in MBP-PLP-elicited EAE. B cell aggregation was present already few days after disease onset. With disease progression CNS B cell aggregates increasingly displayed the phenotype of tertiary lymphoid organs (TLOs). Our results further imply that these TLOs were not merely epiphenomena of the disease, but functionally active, supporting intrathecal determinant spreading of the myelin-specific T cell response. Our data suggest that the CNS is not a passive "immune-privileged" target organ, but rather a compartment, in which highly active immune responses can perpetuate and amplify the autoimmune pathology and thereby autonomously contribute to disease progression.

B cells in MS: Why, where and how?

Multiple sclerosis (MS) is a chronic disease of the central nervous system (CNS), in which auto-aggressive lymphocytes participate in inflammation that causes myelin destruction. Although T lymphocytes have been viewed as important culprits in the inflammatory cascade that results in MS, clinical trial results and animal model data support a role for B lymphocytes in MS pathology. In spite of these encouraging results, the mechanism behind why B cell depletion might be effective for MS treatment remains unknown. Herein we summarize the state of our knowledge for how B cells and their antibody products may influence the initiation and or propagation of MS, drawing from human studies and animal model data.