Clonal expansion of IgA-positive plasma cells and axon-reactive antibodies in MS lesions

From diagnosis to treatment: exploring the mechanisms underlying optic neuritis in multiple sclerosis

Multiple sclerosis (MS) is a chronic autoimmune disease affecting the central nervous system, commonly causing sensory disturbances, motor weakness, impaired gait, incoordination and optic neuritis (ON). According to the statistics, up to 50% of MS patients experience vision problems during the disease course, suffering from blurred vision, pain, color vision deficits, and even blindness. Treatments have progressed from corticosteroids to therapies targeted against B/T cells. This review comprehensively and systematically reappraises the diagnostic methods for visual impairment in MS patients. It also summarizes the most recent treatment approaches and effective medications for ON in MS. Finally, we examine the immunoinflammatory mechanisms that underlie lesions in the central nervous system in multiple sclerosis, in order to direct future investigations to confirm these mechanisms in the visual pathway.

Intrathecal Immunoglobulin A Synthesis in Multiple Sclerosis: From Biological Aspects to Clinical Relevance

Intrathecal immunoglobulin A (IgA) synthesis in multiple sclerosis (MS) has long earned little attention, despite a potential significance in disease pathogenesis and prognosis. The presence of IgA-positive plasma cells in MS lesions and along damaged axons suggests a role in disease pathogenesis. Available clinical evidence about a potential positive or negative prognostic role is scarce and inconclusive. Recent observations, however, highlight the migration of immune regulatory IgA-producing plasma cells from the gut to the central nervous system (CNS) in experimental autoimmune encephalitis models. A connection between intrathecal IgA synthesis and the gut-brain axis in MS was further corroborated by the discovery of gut microbiota-specific IgA+ B cells in human CNS during relapse. In this review, we summarize current evidence on the occurrence and immunopathology of intrathecal IgA synthesis in MS, explore its biological implications, and address methodological challenges regarding the detection of IgA as a major limitation and possible source of inconsistencies in clinical studies. By synthesizing these diverse lines of evidence, we highlight the importance of further research and the need for standardized detection methods to clarify the role of IgA in MS pathogenesis, disease progression, and as potential biomarker.

Differential Expression of PACAP/VIP Receptors in the Post-Mortem CNS White Matter of Multiple Sclerosis Donors

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) are two neuroprotective and anti-inflammatory molecules of the central nervous system (CNS). Both bind to three G protein-coupled receptors, namely PAC1, VPAC1 and VPAC2, to elicit their beneficial effects in various CNS diseases, including multiple sclerosis (MS). In this study, we assessed the expression and distribution of PACAP/VIP receptors in the normal-appearing white matter (NAWM) of MS donors with a clinical history of either relapsing-remitting MS (RRMS), primary MS (PPMS), secondary progressive MS (SPMS) or in aged-matched non-MS controls. Gene expression studies revealed MS-subtype specific changes in PACAP and VIP and in the receptors' levels in the NAWM, which were partly corroborated by immunohistochemical analyses. Most PAC1 immunoreactivity was restricted to myelin-producing cells, whereas VPAC1 reactivity was diffused within the neuropil and in axonal bundles, and VPAC2 in small vessel walls. Within and around lesioned areas, glial cells were the predominant populations showing reactivity for the different PACAP/VIP receptors, with distinctive patterns across MS subtypes. Together, these data identify the differential expression patterns of PACAP/VIP receptors among the different MS clinical entities. These results may offer opportunities for the development of personalized therapeutic approaches to treating MS and/or other demyelinating disorders.

Main Role of Antibodies in Demyelination and Axonal Damage in Multiple Sclerosis

Antibodies and oxidative stress are hallmarks of multiple sclerosis (MS) lesions. We aimed to clarify the relation between them, their role in MS patients and to investigate their specificity, comparing MS with classical neurodegenerative diseases (ND). Brain samples from 14 MS cases, 6 with ND and 9 controls (without neurological diseases). Immunohistochemistry assays were used to detect oxidized lipids (EO6), IgG and IgM, oligodendrocytes (Olig2), axons (NF, neurofilament) and cellular (TUNEL) and axonal damage (APP, amyloid precursor protein). We did not observe EO6 in controls. All samples from MS patients showed EO6 in oligodendrocytes and axons within lesions. We did not detect co-localization between EO6 and antibodies. Neither did we between EO6 and TUNEL or APP. 94.4% of TUNEL-positive cells in normal appearing white matter were also stained for IgG and 75.5% for IgM. IgM, but not IgG, co-localized with APP. EO6 was associated with axonal damage in amyotrophic lateral sclerosis (ALS). We did not observe association between antibodies and cellular or axonal damage in ND patients. MS patients showed a higher number of B cells and plasma cells in the lesions and meninges than controls. The number of B cells and plasma cells was associated with the presence of antibodies and with the activity of the lesions. We observed a main role of B lymphocytes in the development of MS lesions. Antibodies contribute to the oligodendrocyte and axonal damage in MS. Oxidative stress was associated with axonal damage in ALS.

Microbiota, IgA and Multiple Sclerosis

Multiple sclerosis (MS) is a neuroinflammatory disease characterized by immune cell infiltration in the central nervous system and destruction of myelin sheaths. Alterations of gut bacteria abundances are present in MS patients. In mouse models of neuroinflammation, depletion of microbiota results in amelioration of symptoms, and gavage with MS patient microbiota exacerbates the disease and inflammation via Th17 cells. On the other hand, depletion of B cells using anti-CD20 is an efficient therapy in MS, and growing evidence shows an important deleterious role of B cells in MS pathology. However, the failure of TACI-Ig treatment in MS highlighted the potential regulatory role of plasma cells. The mechanism was recently demonstrated involving IgA+ plasma cells, specific for gut microbiota and producing IL-10. IgA-coated bacteria in MS patient gut exhibit also modifications. We will focus our review on IgA interactions with gut microbiota and IgA+ B cells in MS. These recent data emphasize new pathways of neuroinflammation regulation in MS.

High prevalence of intrathecal IgA synthesis in multiple sclerosis patients

The detection of intrathecal IgA synthesis (IAS) in multiple sclerosis (MS) could be underestimated. To assess it, we develop a highly sensitive assay based on isoelectric focusing (IEF). 151 MS patients and 53 controls with different neurological diseases were recruited. IgA concentration was analyzed using a newly developed in house ELISA. IgA oligoclonal bands to detect IAS were determined by IEF. Most individuals showed an IgA concentration within normal range in serum samples (90.69%) but 31.37% of individuals had a IgA concentration below the normal range in the cerebrospinal fluid (CSF). No significant differences were observed between MS and control groups, neither in CSF nor in serum. The new IEF was more sensitive than those previously described (0.01 mg/dl of IgA), and clearly identified patients with and without IAS, that was not related with IgA concentration. Using IEF, MS patients showed higher percentage of IAS-IEF (43.00%) than the control group (16.98) (p = 0.001). The incidence was especially higher in patients with clinically isolated syndrome (66.00%). The new IFE demonstrated a higher percentage of IAS in MS patients than assumed in the past. The presence of IAS-IEF in MS is higher than in other neurological diseases.

B cells in central nervous system disease: diversity, locations and pathophysiology

B cells represent a relatively minor cell population within both the healthy and diseased central nervous system (CNS), yet they can have profound effects. This is emphasized in multiple sclerosis, in which B cell-depleting therapies are arguably the most efficacious treatment for the condition. In this Review, we discuss how B cells enter and persist in the CNS and how, in many neurological conditions, B cells concentrate within CNS barriers but are rarely found in the parenchyma. We highlight how B cells can contribute to CNS pathology through antibody secretion, antigen presentation and secretion of neurotoxic molecules, using examples from CNS tumours, CNS infections and autoimmune conditions such as neuromyelitis optica and, in particular, multiple sclerosis. Overall, understanding common and divergent principles of B cell accumulation and their effects within the CNS could offer new insights into treating these devastating neurological conditions.

Next Generation Sequencing of Cerebrospinal Fluid B Cell Repertoires in Multiple Sclerosis and Other Neuro-Inflammatory Diseases-A Comprehensive Review

During the last few decades, the role of B cells has been well established and redefined in neuro-inflammatory diseases, including multiple sclerosis and autoantibody-associated diseases. In particular, B cell maturation and trafficking across the blood–brain barrier (BBB) has recently been deciphered with the development of next-generation sequencing (NGS) approaches, which allow the assessment of representative cerebrospinal fluid (CSF) and peripheral blood B cell repertoires. In this review, we perform literature research focusing on NGS studies that allow further insights into B cell pathophysiology during neuro-inflammation. Besides the analysis of CSF B cells, the paralleled assessment of peripheral blood B cell repertoire provides deep insights into not only the CSF compartment, but also in B cell trafficking patterns across the BBB. In multiple sclerosis, CSF-specific B cell maturation, in combination with a bidirectional exchange of B cells across the BBB, is consistently detectable. These data suggest that B cells most likely encounter antigen(s) within the CSF and migrate across the BBB, with further maturation also taking place in the periphery. Autoantibody-mediated diseases, such as neuromyelitis optica spectrum disorder and LGI1 / NMDAR encephalitis, also show features of a CSF-specific B cell maturation and clonal connectivity with peripheral blood. In conclusion, these data suggest an intense exchange of B cells across the BBB, possibly feeding autoimmune circuits. Further developments in sequencing technologies will help to dissect the exact pathophysiologic mechanisms of B cells during neuro-inflammation.

Fantastic IgA plasma cells and where to find them

IgA is produced in large quantities at mucosal surfaces by IgA⁺ plasma cells (PC), protecting the host from pathogens, and restricting commensal access to the subepithelium. It is becoming increasingly appreciated that IgA⁺ PC are not constrained to mucosal barrier sites. Rather, IgA⁺ PC may leave these sites where they provide both host defense and immunoregulatory function. In this review, we will outline how IgA⁺ PC are generated within the mucosae and how they subsequently migrate to their "classical" effector site, the gut lamina propria. From there we provide examples of IgA⁺ PC displacement from the gut to other parts of the body, referencing examples during homeostasis and inflammation. Lastly, we will speculate on mechanisms of IgA⁺ PC displacement to other tissues. Our aim is to provide a new perspective on how IgA⁺ PC are truly fantastic beasts of the immune system and identify new places to find them.

Gut microbiota-specific IgA+ B cells traffic to the CNS in active multiple sclerosis

Changes in gut microbiota composition and a diverse role of B cells have recently been implicated in multiple sclerosis (MS), a central nervous system (CNS) autoimmune disease. Immunoglobulin A (IgA) is a key regulator at the mucosal interface. However, whether gut microbiota shape IgA responses and what role IgA⁺ cells have in neuroinflammation are unknown. Here, we identify IgA-bound taxa in MS and show that IgA-producing cells specific for MS-associated taxa traffic to the inflamed CNS, resulting in a strong, compartmentalized IgA enrichment in active MS and other neuroinflammatory diseases. Unlike previously characterized polyreactive anti-commensal IgA responses, CNS IgA cross-reacts with surface structures on specific bacterial strains but not with brain tissue. These findings establish gut microbiota-specific IgA⁺ cells as a systemic mediator in MS and suggest a critical role of mucosal B cells during active neuroinflammation with broad implications for IgA as an informative biomarker and IgA-producing cells as an immune subset to harness for therapeutic interventions.

Interrelation of Diet, Gut Microbiome, and Autoantibody Production

B cells possess a predominant role in adaptive immune responses via antibody-dependent and -independent functions. The microbiome of the gastrointestinal tract is currently being intensively investigated due to its profound impact on various immune responses, including B cell maturation, activation, and IgA antibody responses. Recent findings have demonstrated the interplay between dietary components, gut microbiome, and autoantibody production. "Western" dietary patterns, such as high fat and high salt diets, can induce alterations in the gut microbiome that in turn affects IgA responses and the production of autoantibodies. This could contribute to multiple pathologies including autoimmune and inflammatory diseases. Here, we summarize current knowledge on the influence of various dietary components on B cell function and (auto)antibody production in relation to the gut microbiota, with a particular focus on the gut-brain axis in the pathogenesis of multiple sclerosis.

Effector and regulatory B cells in Multiple Sclerosis

The role of B cells in the pathogenesis of Multiple Sclerosis (MS), an autoimmune neurodegenerative disease, is becoming eminent in recent years, but the specific contribution of the distinct B cell subsets remains to be elucidated. Several B cell subsets have shown regulatory, anti-inflammatory capacities in response to stimuli in vitro, as well as in the animal model of MS: Experimental Autoimmune Encephalomyelitis (EAE). However, the functional role of the B regulatory cells (Bregs) in vivo and specifically in the human disease is yet to be clarified. In the present review, we have summarized the updated information on the roles of effector and regulatory B cells in MS and the immune-modulatory effects of MS therapeutic agents on their phenotype and function.

B-lymphocyte-mediated delayed cognitive impairment following stroke

Each year, 10 million people worldwide survive the neurologic injury associated with a stroke. Importantly, stroke survivors have more than twice the risk of subsequently developing dementia compared with people who have never had a stroke. The link between stroke and the later development of dementia is not understood. There are reports of oligoclonal bands in the CSF of stroke patients, suggesting that in some people a B-lymphocyte response to stroke may occur in the CNS. Therefore, we tested the hypothesis that a B-lymphocyte response to stroke could contribute to the onset of dementia. We discovered that, in mouse models, activated B-lymphocytes infiltrate infarcted tissue in the weeks after stroke. B-lymphocytes undergo isotype switching, and IgM, IgG, and IgA antibodies are found in the neuropil adjacent to the lesion. Concurrently, mice develop delayed deficits in LTP and cognition. Genetic deficiency, and the pharmacologic ablation of B-lymphocytes using an anti-CD20 antibody, prevents the appearance of delayed cognitive deficits. Furthermore, immunostaining of human postmortem tissue revealed that a B-lymphocyte response to stroke also occurs in the brain of some people with stroke and dementia. These data suggest that some stroke patients may develop a B-lymphocyte response to stroke that contributes to dementia, and is potentially treatable with FDA-approved drugs that target B cells.

Toward biomarkers in multiple sclerosis: new advances

Multiple sclerosis is an autoimmune disease that commonly affects young adults. If initially characterized by acute relapses, it is later followed by only incomplete remission. Over years, progressive disability and irreversible deficit lead to chronic neurological deficits in the majority of patients. The clinical course is protracted and unpredictable, and no biological marker is useful in predicting the evolution of autoaggression and disability. It is difficult to diagnose and to monitor disease progression after the initial symptoms or even during the major clinical manifestations, and it is difficult to treat. In this review, the authors report recent advances in the field, focusing on the search of new antigens as a marker of the disease, in their relevance to the pathophysiology and diagnosis of the disease.

The experimental autoimmune encephalomyelitis (EAE) model of MS: utility for understanding disease pathophysiology and treatment

While no single model can exactly recapitulate all aspects of multiple sclerosis (MS), animal models are essential in understanding the induction and pathogenesis of the disease and to develop therapeutic strategies that limit disease progression and eventually lead to effective treatments for the human disease. Several different models of MS exist, but by far the best understood and most commonly used is the rodent model of experimental autoimmune encephalomyelitis (EAE). This 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. Mouse models are most frequently used because of the inbred genotype of laboratory mice, their rapid breeding capacity, the ease of genetic manipulation, and availability of transgenic and knockout mice to facilitate mechanistic studies. Although not all therapeutic strategies for MS have been developed in EAE, all of the current US Food and Drug Administration (FDA)-approved immunomodulatory drugs are effective to some degree in treating EAE, a strong indicator that EAE is an extremely useful model to study potential treatments for MS. Several therapies, such as glatiramer acetate (GA: Copaxone), and natalizumab (Tysabri), were tested first in the mouse model of EAE and then went on to clinical trials. Here we discuss the usefulness of the EAE model in understanding basic disease pathophysiology and developing treatments for MS as well as the potential drawbacks of this model.

Intrathecal immune reset in multiple sclerosis: exploring a new concept

Multiple sclerosis impairment is mainly driven by the progressive phase, whose pathology remains elusive. No drug has yet been able to halt this phase so therapeutic management remains challenging. It was recently demonstrated that late disability correlates with the spreading of cortical subpial lesions, and tertiary lymphoid organs (TLO) were identified in close apposition with these lesions. TLO are of crucial importance since they are able to mount a complete local immune response, as observed in the intrathecal compartment from the moment MS is diagnosed (i.e. oligoclonal bands). This article examines the consequences of this intrathecal response: giving a worst clinical prognostic value and bearing arguments for possible direct brain toxicity, intrathecal secretion should be targeted by drugs abating both B-lymphocytes and plasma cells. Another consequence is that intrathecal secretion has value as a surrogate marker of the persistence of an ongoing intrathecal immune reaction after treatment. Although it is still unsure which mechanism or byproduct secreted by TLO triggers cortical lesions, we propose to target TLO components as a new therapeutic avenue in progressive MS. Whereas it was long considered that the inability of therapies to penetrate the blood-brain-barrier was a crucial obstacle, our proposed strategy will take advantage of the properties of the BBB to safely reset the intrathecal immune system in order to halt the slow axonal burning underlying secondary MS. We review the literature in support of the rationale for treating MS with intrathecal drugs dedicated to clearing the local immune response. Since many targets are involved, achieving this goal may require a combination of monoclonal antibodies targeting each cell sub-type. Hope might be rekindled with a one-shot intrathecal multi-drug treatment in progressive MS.

Rituximab in relapsing and progressive forms of multiple sclerosis: a systematic review

BACKGROUND

Rituximab is an anti-CD20 monoclonal antibody approved for non Hodgkin lymphoma and rheumatoid arthritis. It is being considered for the treatment of MS.

OBJECTIVES

To evaluate the efficacy and safety of rituximab for MS treatment.

DATA COLLECTION

Studies were selected if they were clinical trials, irrespective of the dosage or combination therapies.

MAIN RESULTS

Four studies with a total of 599 patients were included. One assessed the efficacy of rituximab for primary progressive (PP) MS while the other three focused on relapsing-remitting (RR) MS. In the PPMS study, rituximab delayed time to confirmed disease progression (CDP) in pre-planned sub-group analyses. The increase in T2 lesion volume was lower in the rituximab group at week 96 compared with placebo. For the RRMS studies, an open-label phase I study found that rituximab reduced the annualized relapse rate to 0.25 from pre-therapy baseline to week 24, while in the randomized placebo-controlled phase II trial, annualized relapse rates were 0.37 in the rituximab group and 0.84 in the placebo group (p = 0.04) at week 24. Rituximab dramatically reduced the number of gadolinium-enhancing lesions on brain MRI scans for both RRMS studies. Off-label rituximab as an add-on therapy in patients with breakthrough disease on first-line agents was associated with an 88% reduction when comparing the mean number of gadolinium-enhancing lesions prior to and after the treatment. Although frequent adverse events classified as mild or moderate occurred in up to 77% of the patients, there were no grade 4 infusion-related adverse events. AUTHOR’S CONCLUSION: Despite the frequent mild/moderate adverse events related to the drug, rituximab appears overall safe for up to 2 years of therapy and has a substantial impact on the inflammatory disease activity (clinical and/or radiological) of RRMS. The effect of rituximab on disease progression in PPMS appears to be marginal.

Rituximab in relapsing and progressive forms of multiple sclerosis: a systematic review

Background

Rituximab is an anti-CD20 monoclonal antibody approved for non Hodgkin lymphoma and rheumatoid arthritis. It is being considered for the treatment of MS.

Objectives

To evaluate the efficacy and safety of rituximab for MS treatment.

Data collection

Studies were selected if they were clinical trials, irrespective of the dosage or combination therapies.

Main results

Four studies with a total of 599 patients were included. One assessed the efficacy of rituximab for primary progressive (PP) MS while the other three focused on relapsing-remitting (RR) MS. In the PPMS study, rituximab delayed time to confirmed disease progression (CDP) in pre-planned sub-group analyses. The increase in T2 lesion volume was lower in the rituximab group at week 96 compared with placebo. For the RRMS studies, an open-label phase I study found that rituximab reduced the annualized relapse rate to 0.25 from pre-therapy baseline to week 24, while in the randomized placebo-controlled phase II trial, annualized relapse rates were 0.37 in the rituximab group and 0.84 in the placebo group (p = 0.04) at week 24. Rituximab dramatically reduced the number of gadolinium-enhancing lesions on brain MRI scans for both RRMS studies. Off-label rituximab as an add-on therapy in patients with breakthrough disease on first-line agents was associated with an 88% reduction when comparing the mean number of gadolinium-enhancing lesions prior to and after the treatment. Although frequent adverse events classified as mild or moderate occurred in up to 77% of the patients, there were no grade 4 infusion-related adverse events.

Author’s conclusion

Despite the frequent mild/moderate adverse events related to the drug, rituximab appears overall safe for up to 2 years of therapy and has a substantial impact on the inflammatory disease activity (clinical and/or radiological) of RRMS. The effect of rituximab on disease progression in PPMS appears to be marginal.

The sonic hedgehog pathway mediates brain plasticity and subsequent functional recovery after bone marrow stromal cell treatment of stroke in mice

Bone marrow stromal cells (MSCs) improve neurologic recovery after middle cerebral artery occlusion (MCAo). To examine whether in vivo blockage of the endogenous sonic hedgehog (Shh) pathway affects grafted MSC-induced neurologic benefits, MCAo mice were administered: vehicle (control); cyclopamine (CP)- a specific Shh pathway inhibitor; MSC; and MSC and cyclopamine (MSC-CP). Neurologic function was evaluated after MCAo. Electron microscopy and immunofluorescence staining were employed to measure synapse density, protein expression of tissue plasminogen activator (tPA), and Shh in parenchymal cells in the ischemic boundary zone (IBZ), respectively. Marrow stromal cell treatment significantly enhanced functional recovery after ischemia, concurrent with increases of synaptophysin, synapse density, and myelinated axons along the IBZ, and significantly increased tPA and Shh expression in astrocytes and neurons compared with control. After treatment with MSC-CP or CP, the above effects were reversed. Co-culture of MSCs with cortical neurons confirmed the effect of Shh on MSC-mediated neurite outgrowth. Our data support the hypothesis that the Shh pathway mediates brain plasticity via tPA and thereby functional recovery after treatment of stroke with MSCs.

Pathology of demyelinating diseases

There has been significant progress in our understanding of the pathology and pathogenesis of central nervous system inflammatory demyelinating diseases. Neuropathological studies have provided fundamental new insights into the pathogenesis of these disorders and have led to major advances in our understanding of multiple sclerosis (MS) heterogeneity, the substrate of irreversible progressive disability in MS, the relationship between inflammation and neurodegeneration in MS, the neuroimaging correlates of MS lesions, and the pathogenesis of other central nervous system inflammatory disorders, including neuromyelitis optica, acute disseminated encephalomyelitis, and Balo's concentric sclerosis. Herein, we review the pathological features of these central nervous system inflammatory demyelinating disorders and discuss neuropathological studies that have yielded novel insights into potential mechanisms involved in the formation of the demyelinated lesion.

Multiple binding partners

GAPDH interacts with a plethora of diverse cellular proteins. The network of interacting partners, or interactome, is presented for GAPDH with the interacting molecules grouped into specific functional and structural categories. By organizing the binding partners in this way, certain common structural features are beginning to surface, such as acidic dipeptide sequences that are found in several of these binding proteins. Additionally, the consensus sequences for target polynucleotides are being brought to light. The categories, which are presented according to function, offer an opportunity for research into the corresponding structural correlates to these interactions. Recent discoveries of interacting proteins have revealed novel relationships that are generating emerging mechanisms. Proteins that are associated with age-related neurodegenerative diseases appear to be particularly prone to binding GAPDH, suggesting that GAPDH may be playing a role in these diseases. Neurodegenerative diseases that are discussed are the conformational diseases of aging, suggesting that GAPDH may be a global sensor for cellular conformational stress. In addition to GAPDH's oxidoreductase activity, several other enzymatic functions have been discovered, including peroxidase, nitrosylase, mono-ADP-ribosylase and kinase activities.

The role of Acinetobacter in the pathogenesis of multiple sclerosis examined by using Popper sequences

Multiple sclerosis (MS) is an autoimmune neurological disorder. The role of 'Acinetobacter' has been examined using the method of Karl Popper and involves nine "Popper sequences". (1) The frequency of MS increases with latitudes in the Northern Hemisphere, and the reverse is found in the Southern Hemisphere. (2) Sinusitis is found frequently at colder latitudes. (3) Sinusitis occurs frequently in patients with MS. (4) Specific sequences of bovine myelin when injected into experimental animals will produce a neurological disorder resembling MS which is called "experimental allergic encephalomyelitis". (5) Computer analysis of myelin shows molecular mimicry with sequences found in Acinetobacter. (6) Antibodies to Acinetobacter bacteria are found in MS patients. (7) Acinetobacter bacteria are located on human skin and in the nasal sinuses. (8) IgA antibodies are preferentially elevated in the sera of MS patients, thereby suggesting the trigger microbe is acting across a mucosal surface probably located in the nasal sinuses. (9) Only Acinetobacter bacteria and no other microbes evoke statistically significant titres of antibodies in MS patients. These nine Popper sequences suggest that MS is most probably caused by infections with Acinetobacter bacteria in the nasal sinuses, and this could have therapeutic implications.

Citrullination of CNS proteins in the pathogenesis of multiple sclerosis

Multiple sclerosis is a chronic immune-mediated disease of the CNS. Although it is a predominantly T-cell mediated condition, B cells and autoreactive antibodies play an important role in its pathogenesis, with the presence of oligoclonal immunoglobulins in the cerebrospinal fluid being an important diagnostic indicator. The target of these immunoglobulins has not yet been fully characterized. However, post-translational modifications of CNS-specific proteins are thought to contribute to their production through the generation of novel epitopes. One post-translational modification in particular, the conversion of the amino acid arginine to the nonstandard amino acid, citrulline, has been increasingly described in the literature as a factor in the pathogenesis of this condition. In this article, we summarize and discuss the current knowledge on citrullination in multiple sclerosis, the importance of this in relation to its pathogenesis and, potentially, its diagnosis.

Peptide reactivity between multiple sclerosis (MS) CSF IgG and recombinant antibodies generated from clonally expanded plasma cells in MS CSF

We employed 19 recombinant antibodies (rAbs) generated from clonally expanded plasma cells, and native IgG from cerebrospinal fluid (CSF) of three multiple sclerosis (MS) patients for panning with phage displayed random peptide libraries. Specific peptide epitopes/mimotopes were identified and characterized. Importantly, peptide-antibody interactions were shared by rAbs and native IgG from the same patient. Three peptides strongly interacted with at least one other MS CSF, but not to inflammatory CNS controls. Database searches revealed several protein candidates including stress proteins, cell surface proteins, and neuronal proteins. Peptides derived from the candidate proteins were recognized by rAbs. Identification of peptide epitopes/mimotopes in MS may provide clues regarding disease-relevant antigens.

Local delivery of recombinant human bone morphogenetic protein-2 increases axonal regeneration and the expression of tau protein after facial nerve injury

This study explored the function and possible mechanism of bone morphogenetic protein-2 (BMP-2) in the healing of injured peripheral nerves in vivo. Rabbit facial nerves were injured by clamping and then treated with recombinant human BMP-2 (rhBMP-2) or phosphate-buffered saline (control) by injecting once during surgery and twice a day post-injury for 7 days. Facial nerve fragments within 5 mm of the clamping point were examined at different times post-surgery. Axon structures visualized by Bielschowsky staining were similar in experimental and control nerves 2 and 6 weeks post-injury. At 4 weeks post-injury, cross-section images of facial nerves showed that axons treated with rhBMP-2 were denser and thicker, and levels of tau protein were increased. It is concluded from these data that rhBMP-2 may affect injured facial nerve regeneration by inducing more neurons to return to embryonic patterns of tau gene expression.

A case for regulatory B cells in controlling the severity of autoimmune-mediated inflammation in experimental autoimmune encephalomyelitis and multiple sclerosis

Multiple sclerosis (MS) is considered to be a T cell-mediated autoimmune disease that results in the presence of inflammatory lesions/plaques associated with mononuclear cell infiltrates, demyelination and axonal damage within the central nervous system (CNS). To date, FDA approved therapies in MS are thought to largely function by modulation of the immune response. Since autoimmune responses require many arms of the immune system, the direct cellular mechanisms of action of MS therapeutics are not definitively known. The mouse model of MS, experimental autoimmune encephalomyelitis (EAE), has been instrumental in deciphering the mechanism of action of MS drugs. In addition, EAE has been widely used to study the contribution of individual components of the immune system in CNS autoimmunity. In this regard, the role of B cells in EAE has been studied in mice deficient in B cells due to genetic ablation and following depletion with a B cell-targeted monoclonal antibody (mAb) (anti-CD20). Both strategies have indicated that B cells regulate the extent of EAE clinical disease and in their absence disease is exacerbated. Thus a new population of "regulatory B cells" has emerged. One reoccurring component of regulatory B cell function is the production of IL-10, a pleiotropic cytokine with potent anti-inflammatory properties. B cell depletion has also indicated that B cells, in particular antibody production, play a pathogenic role in EAE. B cell depletion in MS using a mAb to CD20 (rituximab) has shown promising results. In this review, we will discuss the current thinking on the role of B cells in MS drawing from knowledge gained in EAE studies and clinical trials using therapeutics that target B cells.

Nodal and extranodal plasmacytomas expressing immunoglobulin a: an indolent lymphoproliferative disorder with a low risk of clinical progression

Plasmacytomas expressing immunoglobulin A are rare and not well characterized. In this study, 9 cases of IgA-positive plasmacytoma presenting in lymph node and 3 in extranodal sites were analyzed by morphology, immunohistochemistry, and polymerase chain reaction examination of immunoglobulin heavy and κ light chain genes. Laboratory features were correlated with clinical findings. There were 7 males and 5 females; age range was 10 to 66 years (median, 32 y). Six of the patients were younger than 30 years of age, 5 of whom had nodal disease. About 67% (6 of 9) of the patients with nodal disease had evidence of immune system dysfunction, including human immunodeficiency virus infection, T-cell deficiency, autoantibodies, arthritis, Sjögren syndrome, and decreased B cells. An IgA M-spike was detected in 6 of 11 cases, and the M-protein was nearly always less than 30 g/L. All patients had an indolent clinical course without progression to plasma cell myeloma. Histologically, nodal IgA plasmacytomas showed an interfollicular or diffuse pattern of plasma cell infiltration. The plasma cells were generally of mature Marschalko type with little or mild pleomorphism and exclusive expression of monotypic IgA. There was an equal expression of κ and λ light chains (ratio 6:6). Clonality was showed in 9 of 12 cases: by polymerase chain reaction in 7 cases, by cytogenetic analysis in 1 case, and by immunofixation in 1 case. Clonality did not correlate with pattern of lymph node infiltration. Our results suggest that IgA plasmacytomas may represent a distinct form of extramedullary plasmacytoma characterized by younger age at presentation, frequent lymph node involvement, and low risk of progression to plasma cell myeloma.

Inhibition of glyceraldehyde-3-phosphate dehydrogenase activity by antibodies present in the cerebrospinal fluid of patients with multiple sclerosis

We have previously shown that B cells and Abs reactive with GAPDH and antitriosephosphate isomerase (TPI) are present in lesions and cerebrospinal fluid (CSF) in multiple sclerosis (MS). In the current study, we studied the effect of anti-GAPDH and anti-TPI CSF IgG on the glycolytic enzyme activity of GAPDH and TPI after exposure to intrathecal IgG from 10 patients with MS and 34 patients with other neurologic diseases. The degree of inhibition of GAPDH activity by CSF anti-GAPDH IgG in the seven MS samples tested varied from 13 to 98%, which seemed to correlate with the percentage of anti-GAPDH IgG in the CSF IgG (1-45%). Inhibition of GAPDH activity (18 and 23%) by CSF IgG was seen in two of the 34 patients with other neurologic diseases, corresponding to the low percentage of CSF anti-GAPDH IgG (1 and 8%). In addition, depletion of anti-GAPDH IgG from CSF IgG, using immobilized GAPDH, removed the inhibitory effect of the IgG on GAPDH. No inhibition of GAPDH activity was seen with CSF samples not containing anti-GAPDH IgG. No inhibition of TPI activity was seen with any purified CSF IgG sample. These findings demonstrate an increased percentage of anti-GAPDH Abs in the CSF of patients with MS that can inhibit GAPDH glycolytic enzyme activity and may contribute to neuroaxonal degeneration.

B-cell depletion with rituximab in relapsing-remitting multiple sclerosis

BACKGROUND

There is increasing evidence that B lymphocytes are involved in the pathogenesis of multiple sclerosis, and they may be a therapeutic target. Rituximab, a monoclonal antibody, selectively targets and depletes CD20+ B lymphocytes.

METHODS

In a phase 2, double-blind, 48-week trial involving 104 patients with relapsing-remitting multiple sclerosis, we assigned 69 patients to receive 1000 mg of intravenous rituximab and 35 patients to receive placebo on days 1 and 15. The primary end point was the total count of gadolinium-enhancing lesions detected on magnetic resonance imaging scans of the brain at weeks 12, 16, 20, and 24. Clinical outcomes included safety, the proportion of patients who had relapses, and the annualized rate of relapse.

RESULTS

As compared with patients who received placebo, patients who received rituximab had reduced counts of total gadolinium-enhancing lesions at weeks 12, 16, 20, and 24 (P<0.001) and of total new gadolinium-enhancing lesions over the same period (P<0.001); these results were sustained for 48 weeks (P<0.001). As compared with patients in the placebo group, the proportion of patients in the rituximab group with relapses was significantly reduced at week 24 (14.5% vs. 34.3%, P=0.02) and week 48 (20.3% vs. 40.0%, P=0.04). More patients in the rituximab group than in the placebo group had adverse events within 24 hours after the first infusion, most of which were mild-to-moderate events; after the second infusion, the numbers of events were similar in the two groups.

CONCLUSIONS

A single course of rituximab reduced inflammatory brain lesions and clinical relapses for 48 weeks. This trial was not designed to assess long-term safety or to detect uncommon adverse events. The data provide evidence of B-cell involvement in the pathophysiology of relapsing-remitting multiple sclerosis. (ClinicalTrials.gov number, NCT00097188 [ClinicalTrials.gov].).

Resistance is futile: antineuronal autoimmunity in multiple sclerosis

For many years, loss of myelin was considered to be the major cause of neurological dysfunction in multiple sclerosis (MS), a chronic inflammatory, demyelinating disease of the central nervous system. This 'myelinocentric' view of MS was revised recently, after recognition that axonal damage, rather than demyelination, provides a better correlate to clinical symptoms. Nonetheless, current views of MS pathogenesis remain focused on the role of myelin-specific autoimmunity, and the potential contribution of autoimmune responses to axonal and neuronal antigens is ignored. Drawing on experience gained from work with other neurodegenerative diseases, we hypothesize that autoimmunity, particularly pathogenic antibodies to neuronal and axonal antigens, plays a significant role in the development of axonal pathology in MS. This concept offers a new perspective of disease pathogenesis and therapeutic approaches to prevent irreversible axonal loss and chronic disability in MS.

B cells and autoantibodies in the pathogenesis of multiple sclerosis and related inflammatory demyelinating diseases

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system (CNS). The mainstream view is that MS is caused by an autoimmune attack of the CNS myelin by myelin-specific CD4 T cells, and this perspective is supported by extensive work in the experimental autoimmune encephalomyelitis (EAE) model of MS as well as immunological and genetic studies in humans. However, it is important to keep in mind that other cell populations of the immune system are also essential in the complex series of events leading to MS, as exemplified by the profound clinical efficacy of B cell depletion with Rituximab. This review discusses the mechanisms by which B cells contribute to the pathogenesis of MS and dissects their role as antigen-presenting cells (APCs) to T cells with matching antigen specificity, the production of proinflammatory cytokines and chemokines, as well as the secretion of autoantibodies that target structures on the myelin sheath and the axon. Mechanistic dissection of the interplay between T cells and B cells in MS may permit the development of B cell based therapies that do not require depletion of this important cell population.

Neurofascin as a novel target for autoantibody-mediated axonal injury

Axonal injury is considered the major cause of disability in patients with multiple sclerosis (MS), but the underlying effector mechanisms are poorly understood. Starting with a proteomics-based approach, we identified neurofascin-specific autoantibodies in patients with MS. These autoantibodies recognize the native form of the extracellular domains of both neurofascin 186 (NF186), a neuronal protein concentrated in myelinated fibers at nodes of Ranvier, and NF155, the oligodendrocyte-specific isoform of neurofascin. Our in vitro studies with hippocampal slice cultures indicate that neurofascin antibodies inhibit axonal conduction in a complement-dependent manner. To evaluate whether circulating antineurofascin antibodies mediate a pathogenic effect in vivo, we cotransferred these antibodies with myelin oligodendrocyte glycoprotein-specific encephalitogenic T cells to mimic the inflammatory pathology of MS and breach the blood-brain barrier. In this animal model, antibodies to neurofascin selectively targeted nodes of Ranvier, resulting in deposition of complement, axonal injury, and disease exacerbation. Collectively, these results identify a novel mechanism of immune-mediated axonal injury that can contribute to axonal pathology in MS.

Microfluorimetry defines early axonal damage in a rat model of optic neuritis: a novel method targeting early CNS autoimmunity

Autoimmune optic neuritis is a common early manifestation of multiple sclerosis (MS), yet early therapeutic interventions for MS often have high ocular toxicity associated with increased risks for glaucoma, cataract, or retinopathy. This need to discover better early treatment options prompted our development of a sensitive and reliable means to quantify the broad range of pathologies that potentially develop very early in autoimmune optic neuritis. Tissue microfluorimetry was used to measure seven established markers for human MS pathology in normal and autoimmune optic nerves 13 days after antigen exposure, in a Brown Norway rat model of myelin oligodendrocyte glycoprotein (MOG) peptide (35-55)-induced autoimmune optic neuritis. Optic neuritis rats demonstrated early and significant pathologic changes in five established indices for neuroinflammation, immune infiltration, and demyelination that accurately modeled pathologies characteristic of MS. Two indices of MS-like axon damage advanced significantly within 13 days of antigen exposure. Fluorimetrically measured immunoreactivity (-ir) was significantly decreased for paranodin (PN, the requisite axonal paranodal junction protein) and significantly increased for amyloid precursor protein (APP), indicating loss of paranodal junctions and impaired fast axonal transport, respectively. Measurements showing decreased PN-ir with increased APP-ir quantitatively defined a pattern of early axonal damage in autoimmune optic neuritis.

Immunization with neurofilament light protein induces spastic paresis and axonal degeneration in Biozzi ABH mice

Axonal damage is the major cause of irreversible neurologic disability in patients with multiple sclerosis. Although axonal damage correlates with antibodies against neurofilament light (NF-L) protein, a major component of the axonal cytoskeleton, the possible pathogenic role of autoimmunity to axonal antigens such as NF-L has so far been ignored. Here we show that Biozzi ABH mice immunized with NF-L protein develop neurologic disease characterized by spastic paresis and paralysis concomitant with axonal degeneration and inflammation primarily in the dorsal column of the spinal cord. The inflammatory central nervous system lesions were dominated by F4/80+ macrophages/microglia and relatively low numbers of CD4+ and CD8+ T-cells. In splenocyte cultures, proliferation to NF-L was observed in CD4+ T-cells accompanied by the production of the proinflammatory cytokine interferon-gamma. Elevated levels of circulating antibodies recognizing recombinant mouse NF-L were present in the serum, and immunoglobulin deposits were observed within axons in spinal cord lesions of mice exhibiting clinical disease. These data provide evidence that autoimmunity to NF-L protein induces axonal degeneration and clinical neurologic disease in mice, indicating that autoimmunity to axonal antigens, as described in multiple sclerosis, may be pathogenic rather than acting merely as a surrogate marker for axonal degeneration.

Triosephosphate isomerase- and glyceraldehyde-3-phosphate dehydrogenase-reactive autoantibodies in the cerebrospinal fluid of patients with multiple sclerosis

Our previous results revealed that Igs in lesions and single chain variable fragment Abs (scFv-Abs) generated from clonal B cells in the cerebrospinal fluid (CSF) from patients with multiple sclerosis (MS) bind to axons in MS brains. To study the axonal Ags involved in MS, we identified the glycolytic enzymes, triosephosphate isomerase (TPI) and GAPDH, using Igs from the CSF and scFv-Abs generated from clonal B cells in the CSF and in lesions from MS patients. Elevated levels of CSF-Abs to TPI were observed in patients with MS (46%), clinically isolated syndrome (CIS) suggestive of MS (40%), other inflammatory neurological diseases (OIND; 29%), and other noninflammatory neurological diseases (ONIND; 31%). Levels of GAPDH-reactive Abs were elevated in MS patients (60%), in patients with CIS (10%), OIND (14%), and ONIND (8%). The coexistence of both autoantibodies was detected in 10 MS patients (29%), and 1 CIS patient (3%), but not in patients with OIND/ONIND. Two scFv-Abs generated from the CSF and from lesions of a MS brain showed immunoreactivity to TPI and GAPDH, respectively. The findings suggest that TPI and GAPDH may be candidate Ags for an autoimmune response to neurons and axons in MS.

A Local Antigen-Driven Humoral Response Is Present in the Inflammatory Myopathies

The inflammatory myopathies are putative autoimmune disorders characterized by muscle weakness and the presence of intramuscular inflammatory infiltrates. Although inclusion body myositis and polymyositis have been characterized as cytotoxic CD8(+) T cell-mediated diseases, we recently demonstrated high frequencies of CD138(+) plasma cells in the inflamed muscle tissue of patients with these diseases. To gain a deeper understanding of the role these B cell family members play in the disease pathology, we examined the molecular characteristics of the H chain portion of the Ag receptor. Biopsies of muscle tissue were sectioned and tissue regions and individual cells were isolated through laser capture microdissection. Ig H chain gene transcripts isolated from the sections, regions, and cells were used to determine the variable region gene sequences. Analysis of these sequences revealed clear evidence of affinity maturation in that significant somatic mutation, isotype switching, receptor revision, codon insertion/deletion, and oligoclonal expansion had occurred within the B and plasma cell populations. Moreover, analysis of tissue regions isolated by laser capture microdissection revealed both clonal expansion and variation, suggesting that local B cell maturation occurs within muscle. In contrast, sequences from control muscle tissues and peripheral blood revealed none of these characteristics found in inflammatory myopathy muscle tissue. Collectively, these data demonstrate that Ag drives a B cell Ag-specific response in muscle in patients with dermatomyositis, inclusion body myositis, and polymyositis. These findings highlight the need for a revision of the current paradigm of exclusively T cell-mediated intramuscular Ag-specific autoimmunity in inclusion body myositis and polymyositis.

The heat-shock protein 90 inhibitor 17-allylamino-17-demethoxygeldanamycin suppresses glial inflammatory responses and ameliorates experimental autoimmune encephalomyelitis

The heat-shock response (HSR), a highly conserved cellular response, is characterized by rapid expression of heat-shock proteins (HSPs), and inhibition of other synthetic activities. The HSR can attenuate inflammatory responses, via suppression of transcription factor activation. A HSR can be induced pharmacologically by HSP90 inhibitors, through activation of the transcription factor Heat Shock Factor 1 (HSF1). In the present study we characterized the effects of 17-allylamino-17-demethoxygeldanamycin (17-AAG), a less toxic derivative of the naturally occurring HSP90 inhibitor geldanamycin, on glial inflammatory responses and the development of experimental autoimmune encephalomyelitis. In primary enriched glial cultures, 17-AAG dose dependently reduced lipopolysaccharide-dependent expression and activity of inducible nitric oxide synthase, attenuated interleukin (IL)-1beta expression and release, increased inhibitor of kappaB protein levels, and induced HSP70 expression. 17-AAG administration to mice immunized with myelin oligodendrocyte glycoprotein peptide prevented disease onset when given at an early time, and reduced clinical symptoms when given during ongoing disease. T cells from treated mice showed a reduced response to immunogen re-stimulation, and 17-AAG reduced CD3- and CD28-dependent IL-2 production. Together, these data suggest that HSP90 inhibitors could represent a new approach for therapeutic intervention in autoimmune diseases such as multiple sclerosis.

The neurobiology of multiple sclerosis: genes, inflammation, and neurodegeneration

The autoimmune model of multiple sclerosis (MS) pathogenesis provided for many years a useful but incomplete conceptual framework for understanding the complex array of factors that lead to the loss of immune homeostasis, myelin and axonal injury, and progressive neurological symptoms. The availability of novel tools in molecular neurogenetics and increasingly sophisticated neuroimaging technologies, together with the revitalization of MS neuropathology, has created a new paradigm for the multidisciplinary study of this disease. This is reflected by the growing resolution of the MS genomic map, discovery of delicate inflammatory networks that are perturbed in MS, identification of mediators of demyelination, and recognition that cumulative axonal loss and neuronal injury are the histological correlates of neurological disability. Together, these advances have set the stage for the development of therapeutic approaches designed to target the demyelinating and neurodegenerative components of the disease and promote repair.

Complex gene-gene interactions in multiple sclerosis: a multifactorial approach reveals associations with inflammatory genes

The complex inheritance involved in multiple sclerosis (MS) risk has been extensively investigated, but our understanding of MS genetics remains rudimentary. In this study, we explore 51 single nucleotide polymorphisms (SNPs) in 36 candidate genes from the inflammatory pathway and test for gene-gene interactions using complementary case-control, discordant sibling pair, and trio family study designs. We used a sample of 421 carefully diagnosed MS cases and 96 unrelated, healthy controls; discordant sibling pairs from 146 multiplex families; and 275 trio families. We used multifactor dimensionality reduction to explore gene-gene interactions. Based on our analyses, we have identified several statistically significant models including both main effect models and two-locus, three-locus, and four-locus epistasis models that predict MS disease risk with between approximately 61% and 85% accuracy. These results suggest that significant epistasis, or gene-gene interactions, may exist even in the absence of statistically significant individual main effects.

Monoclonal antibodies to distinct regions of human myelin proteolipid protein simultaneously recognize central nervous system myelin and neurons of many vertebrate species

Myelin proteolipid protein (PLP), the major protein of mammalian CNS myelin, is a member of the proteolipid gene family (pgf). It is an evolutionarily conserved polytopic integral membrane protein and a potential autoantigen in multiple sclerosis (MS). To analyze antibody recognition of PLP epitopes in situ, monoclonal antibodies (mAbs) specific for different regions of human PLP (50-69, 100-123, 139-151, 178-191, 200-219, 264-276) were generated and used to immunostain CNS tissues of representative vertebrates. mAbs to each region recognized whole human PLP on Western blots; the anti-100-123 mAb did not recognize DM-20, the PLP isoform that lacks residues 116-150. All of the mAbs stained fixed, permeabilized oligodendrocytes and mammalian and avian CNS tissue myelin. Most of the mAbs also stained amphibian, teleost, and elasmobranch CNS myelin despite greater diversity of their pgf myelin protein sequences. Myelin staining was observed when there was at least 40% identity of the mAb epitope and known pgf myelin proteins of the same or related species. The pgf myelin proteins of teleosts and elasmobranchs lack 116-150; the anti-100-123 mAb did not stain their myelin. In addition to myelin, the anti-178-191 mAb stained many neurons in all species; other mAbs stained distinct neuron subpopulations in different species. Neuronal staining was observed when there was at least approximately 30% identity of the PLP mAb epitope and known pgf neuronal proteins of the same or related species. Thus, anti-human PLP epitope mAbs simultaneously recognize CNS myelin and neurons even without extensive sequence identity. Widespread anti-PLP mAb recognition of neurons suggests a novel potential pathophysiologic mechanism in MS patients, i.e., that anti-PLP antibodies associated with demyelination might simultaneously recognize pgf epitopes in neurons, thereby affecting their functions.