Intrathecal pathogenic anti-aquaporin-4 antibodies in early neuromyelitis optica

Uncommon inflammatory/immune-related myelopathies

The differential diagnosis for immune-mediated myelopathies is broad. Although clinical manifestations overlap, certain presentations are suggestive of a particular myelopathy etiology. Spine MRI lesion characteristics including the length and location, and the pattern of gadolinium enhancement, help narrow the differential diagnosis and exclude an extrinsic compressive cause. The discovery of specific antibodies that serve as biomarkers of myelitis such as aquaporin-4-IgG and myelin-oligodendrocyte -glycoprotein-IgG (MOG-IgG), has improved our understanding of myelitis pathophysiology and facilitated diagnosis. In this review we will focus on the pathophysiology, clinical presentation, imaging findings and treatment and outcomes of uncommon immune-mediated myelopathies.

Alterations in the Retinal Vascular Network and Structure in MOG Antibody-Associated Disease: An Optical Coherence Tomography Angiography Study

BACKGROUND

To determine retinal vessel density in patients with myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD).

METHODS

Twenty-five patients with MOGAD and 20 healthy participants were enrolled. Patients with MOGAD were divided into myelin oligodendrocyte glycoprotein antibody (MOG-Ab)-positive eyes with a history of optic neuritis (ON; MOG-Ab-ON+ group) or without a history of ON (MOG-Ab-ON- group). Visual function, retinal vessel densities, and thickness were measured.

RESULTS

The retinal nerve fiber layer, parafoveal ganglion cell and inner plexiform layers, and vessel densities in the peripapillary and parafoveal areas were significantly decreased in the MOG-Ab-ON+ eyes compared with healthy eyes and MOG-Ab-ON- eyes (all P < 0.05). An increasing number of ON episodes was associated with greater decreases in these variables (all P < 0.05). Visual field mean deviation was not significantly decreased in patients with a history of 1 or 2 episodes of ON, although the relative decreases in retinal nerve fiber layer thickness, parafoveal ganglion cell and inner plexiform layer thickness, peripapillary vessel density, and parafoveal vessel density reached 33.1%, 23.2%, 17.0%, and 11.5% (all P < 0.05), respectively, in eyes with 2 episodes of ON. The mean deviation was significantly correlated with peripapillary vessel density (P < 0.05) after adjustment for other variables. Best-corrected visual acuity was not significantly correlated with optical coherence tomography variables (all P > 0.05).

CONCLUSIONS

MOG-Ab-associated ON was associated with significant decreases in retinal structure and vessel density, without significant deteriorations in visual function. The peripapillary vessel density might predict the visual outcomes in patients with MOG-Ab-associated ON.

Autoantibodies in neurological disease

The realization that autoantibodies can contribute to dysfunction of the brain has brought about a paradigm shift in neurological diseases over the past decade, offering up important novel diagnostic and therapeutic opportunities. Detection of specific autoantibodies to neuronal or glial targets has resulted in a better understanding of central nervous system autoimmunity and in the reclassification of some diseases previously thought to result from infectious, 'idiopathic' or psychogenic causes. The most prominent examples, such as aquaporin 4 autoantibodies in neuromyelitis optica or NMDAR autoantibodies in encephalitis, have stimulated an entire field of clinical and experimental studies on disease mechanisms and immunological abnormalities. Also, these findings inspired the search for additional autoantibodies, which has been very successful to date and has not yet reached its peak. This Review summarizes this rapid development at a point in time where preclinical studies have started delivering fundamental new data for mechanistic understanding, where new technologies are being introduced into this field, and - most importantly - where the first specifically tailored immunotherapeutic approaches are emerging.

Hope for patients with neuromyelitis optica spectrum disorders - from mechanisms to trials

Neuromyelitis optica spectrum disorder (NMOSD) is a rare inflammatory CNS disease that primarily manifests as relapsing episodes of severe optic neuritis and myelitis. Diagnosis of NMOSD is supported by the detection of IgG autoantibodies that target the aquaporin 4 (AQP4) water channel, which, in the CNS, is an astrocyte-specific protein. AQP4 antibody binding leads to AQP4 internalization, complement-dependent and antibody-dependent cellular cytotoxicity, and water channel dysfunction. Cumulative attack-related injury causes disability in NMOSD, so the prevention of attacks is expected to prevent disability accrual. Until recently, no regulator-approved therapies were available for NMOSD. Traditional immunosuppressant therapies, including mycophenolate mofetil, azathioprine and rituximab, were widely used but their benefits have not been assessed in controlled studies. In 2019 and 2020, five phase II and III randomized placebo-controlled trials of four mechanism-based therapies for NMOSD were published and demonstrated that all four effectively prolonged the time to first relapse. All four drugs were monoclonal antibodies: the complement C5 antibody eculizumab, the IL-6 receptor antibody satralizumab, the B cell-depleting antibody inebilizumab, which targets CD19, and rituximab, which targets CD20. We review the pathophysiology of NMOSD, the rationale for the development of these mechanism-based drugs, the methodology and outcomes of the five trials, and the implications of these findings for the treatment of NMOSD.

Role of Toll-Like Receptors in Neuroimmune Diseases: Therapeutic Targets and Problems

Toll-like receptors (TLRs) are a class of proteins playing a key role in innate and adaptive immune responses. TLRs are involved in the development and progression of neuroimmune diseases via initiating inflammatory responses. Thus, targeting TLRs signaling pathway may be considered as a potential therapy for neuroimmune diseases. However, the role of TLRs is elusive and complex in neuroimmune diseases. In addition to the inadequate immune response of TLRs inhibitors in the experiments, the recent studies also demonstrated that partial activation of TLRs is conducive to the production of anti-inflammatory factors and nervous system repair. Exploring the mechanism of TLRs in neuroimmune diseases and combining with developing the emerging drug may conquer neuroimmune diseases in the future. Herein, we provide an overview of the role of TLRs in several neuroimmune diseases, including multiple sclerosis, neuromyelitis optica spectrum disorder, Guillain-Barré syndrome and myasthenia gravis. Emerging difficulties and potential solutions in clinical application of TLRs inhibitors will also be discussed.

C3 and C4 complement levels in AQP4-IgG-positive NMOSD and in MOGAD

While complement-dependent cytotoxicity (CDC) is a known effector mechanism in aquaporin-4-immunoglobulin (Ig)G-positive (AQP4-IgG+) neuromyelitis optica spectrum disorder (NMOSD), the role of CDC in myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) is less clear. We determined complement C3 and C4 plasma concentrations in patients with clinically stable AQP4-IgG+ NMOSD (n = 16), MOGAD (n = 15), early multiple sclerosis (MS, n = 19) and in healthy controls (HC, n = 18). C4 was lower in AQP4-IgG+ NMOSD than in MOGAD, MS and HC (p < 0.05, pairwise comparisons). C3 was lower in AQP4-IgG+ NMOSD than in MS (p = 0.034). These findings suggest subtle complement consumption in clinically stable AQP4-IgG+ NMOSD, but not in MOGAD.

Cytoprotective IgG antibodies in sera from a subset of patients with AQP4-IgG seropositive neuromyelitis optica spectrum disorder

Neuromyelitis optica spectrum disorder (NMOSD) is an autoimmune inflammatory disease of the central nervous system. Most NMOSD patients are seropositive for immunoglobulin G (IgG) autoantibodies against astrocyte water channel aquaporin-4 (AQP4), called AQP4-IgG. AQP4-IgG binding to aquaporin-4 causes complement-dependent cytotoxicity (CDC), leading to inflammation and demyelination. Here, CDC was measured in AQP4-expressing cells exposed to human complement and heat-inactivated sera from 108 AQP4-IgG seropositive NMOSD subjects and 25 non-NMOSD controls. AQP4-IgG positive sera produced a wide range of CDC, with 50% maximum cytotoxicity produced by as low as 0.2% serum concentration. Unexpectedly, 58 samples produced no cytotoxicity, and of those, four sera were cytoprotective against cytotoxic AQP4-IgG. Cytoprotection was found against different cytotoxic monoclonal AQP4-IgGs and NMOSD patient sera, and in primary astrocyte cultures. Mechanistic studies revealed that the protective factor is an IgG antibody that did not inhibit complement directly, but interfered with binding of cytotoxic AQP4-IgG to AQP4 and consequent C1q binding and complement activation. Further studies suggested that non-pathogenic AQP4-IgG, perhaps with altered glycosylation, may contribute to reduced or ineffectual binding of cytotoxic AQP4-IgG, as well as reduced cell-surface AQP4. The presence of natural cytoprotective antibodies in AQP4-IgG seropositive sera reveals an added level of complexity in NMOSD disease pathogenesis, and suggests the potential therapeutic utility of ‘convalescent’ serum or engineered protective antibody to interfere with pathogenic antibody in AQP4-IgG seropositive NMOSD.

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.

Neuromyelitis optica spectrum disorders: from pathophysiology to therapeutic strategies

Neuromyelitis optica (NMO) is a chronic inflammatory autoimmune disease of the central nervous system (CNS) characterized by acute optic neuritis (ON) and transverse myelitis (TM). NMO is caused by a pathogenic serum IgG antibody against the water channel aquoporin 4 (AQP4) in the majority of patients. AQP4-antibody (AQP4-ab) presence is highly specific, and differentiates NMO from multiple sclerosis. It binds to AQP4 channels on astrocytes, triggering activation of the classical complement cascade, causing granulocyte, eosinophil, and lymphocyte infiltration, culminating in injury first to astrocyte, then oligodendrocytes followed by demyelination and neuronal loss. NMO spectrum disorder (NMOSD) has recently been defined and stratified based on AQP4-ab serology status. Most NMOSD patients experience severe relapses leading to permanent neurologic disability, making suppression of relapse frequency and severity, the primary objective in disease management. The most common treatments used for relapses are steroids and plasma exchange.Currently, long-term NMOSD relapse prevention includes off-label use of immunosuppressants, particularly rituximab. In the last 2 years however, three pivotal clinical trials have expanded the spectrum of drugs available for NMOSD patients. Phase III studies have shown significant relapse reduction compared to placebo in AQP4-ab-positive patients treated with satralizumab, an interleukin-6 receptor (IL-6R) inhibitor, inebilizumab, an antibody against CD19⁺ B cells; and eculizumab, an antibody blocking the C5 component of complement. In light of the new evidence on NMOSD pathophysiology and of preliminary results from ongoing trials with new drugs, we present this descriptive review, highlighting promising treatment modalities as well as auspicious preclinical and clinical studies.

Inebilizumab for treatment of neuromyelitis optica spectrum disorder

Neuromyelitis optica spectrum disorder (NMOSD) is a rare autoimmune disease characterized by recurrent optic neuritis and transverse myelitis often resulting in severe disability. Anti-AQP4-immunoglobulin G (IgG) is a pathogenic product of CD19-positive plasma cells found in most, but not all, individuals with NMOSD and is associated with immune-mediated neurologic injury. Inebilizumab, an afucosylated humanized IgG1κ, anti-CD19 monoclonal antibody, may target pathogenic CD19-expressing B cells. In a Phase II/III trial, inebilizumab significantly reduced the proportion of participants experiencing an NMOSD attack and was well tolerated versus placebo. Fewer treated participants had worsening disability than those receiving placebo. Inebilizumab was approved in 2020 by the US FDA for treatment of anti-AQP4 antibody positive NMOSD.

Anti-AQP4 autoantibodies promote ATP release from astrocytes and induce mechanical pain in rats

Background

Intractable neuropathic pain is a common symptom of neuromyelitis optica spectrum disorder (NMOSD). However, the underlying mechanism of NMOSD pain remains to be elucidated. In this study, we focused on ATP, which is one of the damage-associated molecular patterns, and also a well-recognized molecule involved in peripheral neuropathic pain.

Methods

We assessed the development of pain symptoms by injecting anti-AQP4 recombinant autoantibodies (rAQP4 IgG) into rat spinal cords. We incubated HEK293 cells expressing AQP4 (HEK-AQP4) and rat astrocytes with rAQP4 IgG and assessed the level of ATP in the supernatant. We performed transcriptome analysis of the spinal cords injected with rAQP4 IgG. Pharmacological inhibition was also applied to investigate the involvement of ATP in the development of neuropathic pain in our rat model. The ATP concentration within the cerebrospinal fluid was examined in patients with NMOSD and other neurological diseases.

Results

Development of mechanical allodynia was confirmed in rAQP4 IgG–treated rats. AQP4-Ab–mediated extracellular ATP release from astrocytes was observed in vitro, and pharmacological inhibition of ATP receptor reversed mechanical allodynia in the rAQP4 IgG–treated rats. Furthermore, transcriptome analysis revealed elevation of gene expressions related to several ATP receptors including P2rx4 and IL1B in the spinal cord of rAQP4 IgG–treated rats. In patients, CSF ATP concentration was significantly higher in the acute and remission phase of NMOSD than in multiple sclerosis or other neurological disorders.

Conclusion

Anti-AQP4 antibody was shown to induce the release of extracellular ATP from astrocytes. The ATP-mediated development of mechanical allodynia was also suggested in rats treated with anti-AQP4 antibody. Our study indicates the pivotal role of ATP in the pain mechanism of NMOSD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02232-w.

Pathogenesis of autoimmune demyelination: from multiple sclerosis to neuromyelitis optica spectrum disorders and myelin oligodendrocyte glycoprotein antibody-associated disease

Autoimmunity plays a significant role in the pathogenesis of demyelination. Multiple sclerosis (MS), neuromyelitis optica spectrum disorders (NMOSD) and myelin oligodendrocyte glycoprotein antibody‐associated disease (MOGAD) are now recognised as separate disease entities under the amalgam of human central nervous system demyelinating disorders. While these disorders share inherent similarities, investigations into their distinct clinical presentations and lesion pathologies have aided in differential diagnoses and understanding of disease pathogenesis. An interplay of various genetic and environmental factors contributes to each disease, many of which implicate an autoimmune response. The pivotal role of the adaptive immune system has been highlighted by the diagnostic autoantibodies in NMOSD and MOGAD, and the presence of autoreactive lymphocytes in MS lesions. While a number of autoantigens have been proposed in MS, recent emphasis on the contribution of B cells has shed new light on the well‐established understanding of T cell involvement in pathogenesis. This review aims to synthesise the clinical characteristics and pathological findings, discuss existing and emerging hypotheses regarding the aetiology of demyelination and evaluate recent pathogenicity studies involving T cells, B cells, and autoantibodies and their implications in human demyelination.

An Experimental Model of Neuromyelitis Optica Spectrum Disorder-Optic Neuritis: Insights Into Disease Mechanisms

Background: Optic neuritis (ON) is a common inflammatory optic neuropathy, which often occurs in neuromyelitis optica spectrum disease (NMOSD). An experimental model of NMOSD-ON may provide insight into disease mechanisms.

Objective: To examine the pathogenicity of autoantibodies targeting the astrocyte water channel aquaporin-4 [aquaporin-4 (AQP4)-immunoglobulin G (AQP4-IgG)] in the optic nerve.

Materials and Methods: Purified IgG from an AQP4-IgG-positive NMOSD-ON patient was together with human complement (C) given to wild-type (WT) and type I interferon (IFN) receptor-deficient mice (IFNAR1-KO) as two consecutive intrathecal injections into cerebrospinal fluid via cisterna magna. The optic nerves were isolated, embedded in paraffin, cut for histological examination, and scored semi-quantitatively in a blinded fashion. In addition, optic nerves were processed to determine selected gene expression by quantitative real-time PCR.

Results: Intrathecal injection of AQP4-IgG+C induced astrocyte pathology in the optic nerve with loss of staining for AQP4 and glial fibrillary acidic protein (GFAP), deposition of C, and demyelination, as well as upregulation of gene expression for interferon regulatory factor-7 (IRF7) and CXCL10. Such pathology was not seen in IFNAR1-KO mice nor in control mice.

Conclusion: We describe induction of ON in an animal model for NMOSD and show a requirement for type I IFN signaling in the disease process.

Targeting Neuromyelitis Optica Pathogenesis: Results from Randomized Controlled Trials of Biologics

Advances in neuromyelitis optica spectrum disorder pathogenesis have allowed the development of targeted drugs. These treatments act on core elements of the disease, including the pro-inflammatory IL-6 pathway (tocilizumab and satralizumab), B cells (rituximab and inebilizumab), and complement (eculizumab). According to recent phase II-III trials, biologics significantly reduced the risk of relapses in aquaporin-4-seropositive patients, whereas results were less striking in the small cohorts of aquaporin-4-seronegative patients. Most adverse events were mild to moderate, with systemic symptoms (headache, arthralgia) or infections (upper respiratory and urinary tracts) being most commonly reported.

B Cells in Neuroinflammation: New Perspectives and Mechanistic Insights

In recent years, the role of B cells in neurological disorders has substantially expanded our perspectives on mechanisms of neuroinflammation. The success of B cell-depleting therapies in patients with CNS diseases such as neuromyelitis optica and multiple sclerosis has highlighted the importance of neuroimmune crosstalk in inflammatory processes. While B cells are essential for the adaptive immune system and antibody production, they are also major contributors of pro- and anti-inflammatory cytokine responses in a number of inflammatory diseases. B cells can contribute to neurological diseases through peripheral immune mechanisms, including production of cytokines and antibodies, or through CNS mechanisms following compartmentalization. Emerging evidence suggests that aberrant pro- or anti-inflammatory B cell populations contribute to neurological processes, including glial activation, which has been implicated in the pathogenesis of several neurodegenerative diseases. In this review, we summarize recent findings on B cell involvement in neuroinflammatory diseases and discuss evidence to support pathogenic immunomodulatory functions of B cells in neurological disorders, highlighting the importance of B cell-directed therapies.

Molecular Level Characterization of Circulating Aquaporin-4 Antibodies in Neuromyelitis Optica Spectrum Disorder

OBJECTIVE

To determine whether distinct aquaporin-4 (AQP4)-IgG lineages play a role in neuromyelitis optica spectrum disorder (NMOSD) pathogenesis, we profiled the AQP4-IgG polyclonal serum repertoire and identified, quantified, and functionally characterized distinct AQP4-IgG lineages circulating in 2 patients with NMOSD.

METHODS

We combined high-throughput sequencing and quantitative immunoproteomics to simultaneously determine the constituents of both the B-cell receptor (BCR) and the serologic (IgG) anti-AQP4 antibody repertoires in the peripheral blood of patients with NMOSD. The monoclonal antibodies identified by this platform were recombinantly expressed and functionally characterized in vitro.

RESULTS

Multiple antibody lineages comprise serum AQP4-IgG repertoires. Their distribution, however, can be strikingly different in polarization (polyclonal vs pauciclonal). Among the 4 serum AQP4-IgG monoclonal antibodies we identified in 2 patients, 3 induced complement-dependent cytotoxicity in a model mammalian cell line (p < 0.01).

CONCLUSIONS

The composition and polarization of AQP4-IgG antibody repertoires may play an important role in NMOSD pathogenesis and clinical presentation. Here, we present a means of coupling both cellular (BCR) and serologic (IgG) antibody repertoire analysis, which has not previously been performed in NMOSD. Our analysis could be applied in the future to clinical management of patients with NMOSD to monitor disease activity over time as well as applied to other autoimmune diseases to facilitate a deeper understanding of disease pathogenesis relative to autoantibody clones.

Short- and Long-Lived Autoantibody-Secreting Cells in Autoimmune Neurological Disorders

As B cells differentiate into antibody-secreting cells (ASCs), short-lived plasmablasts (SLPBs) are produced by a primary extrafollicular response, followed by the generation of memory B cells and long-lived plasma cells (LLPCs) in germinal centers (GCs). Generation of IgG4 antibodies is T helper type 2 (Th2) and IL-4, -13, and -10-driven and can occur parallel to IgE, in response to chronic stimulation by allergens and helminths. Although IgG4 antibodies are non-crosslinking and have limited ability to mobilize complement and cellular cytotoxicity, when self-tolerance is lost, they can disrupt ligand-receptor binding and cause a wide range of autoimmune disorders including neurological autoimmunity. In myasthenia gravis with predominantly IgG4 autoantibodies against muscle-specific kinase (MuSK), it has been observed that one-time CD20⁺ B cell depletion with rituximab commonly leads to long-term remission and a marked reduction in autoantibody titer, pointing to a short-lived nature of autoantibody-secreting cells. This is also observed in other predominantly IgG4 autoantibody-mediated neurological disorders, such as chronic inflammatory demyelinating polyneuropathy and autoimmune encephalitis with autoantibodies against the Ranvier paranode and juxtaparanode, respectively, and extends beyond neurological autoimmunity as well. Although IgG1 autoantibody-mediated neurological disorders can also respond well to rituximab induction therapy in combination with an autoantibody titer drop, remission tends to be less long-lasting and cases where titers are refractory tend to occur more often than in IgG4 autoimmunity. Moreover, presence of GC-like structures in the thymus of myasthenic patients with predominantly IgG1 autoantibodies against the acetylcholine receptor and in ovarian teratomas of autoimmune encephalitis patients with predominantly IgG1 autoantibodies against the N‐methyl‐d‐aspartate receptor (NMDAR) confers increased the ability to generate LLPCs. Here, we review available information on the short-and long-lived nature of ASCs in IgG1 and IgG4 autoantibody-mediated neurological disorders and highlight common mechanisms as well as differences, all of which can inform therapeutic strategies and personalized medical approaches.

Sera from Patients with NMOSD Reduce the Differentiation Capacity of Precursor Cells in the Central Nervous System

INTRODUCTION

AQP4 (aquaporin-4)-immunoglobulin G (IgG)-mediated neuromyelitis optica spectrum disorder (NMOSD) is an inflammatory demyelinating disease that affects the central nervous system, particularly the spinal cord and optic nerve; remyelination capacity in neuromyelitis optica is yet to be determined, as is the role of AQP4-IgG in cell differentiation.

MATERIAL AND METHODS

We included three groups-a group of patients with AQP4-IgG-positive neuromyelitis optica, a healthy group, and a sham group. We analyzed differentiation capacity in cultures of neurospheres from the subventricular zone of mice by adding serum at two different times: early and advanced stages of differentiation. We also analyzed differentiation into different cell lines.

RESULTS AND CONCLUSIONS

The effect of sera from patients with NMOSD on precursor cells differs according to the degree of differentiation, and probably affects oligodendrocyte progenitor cells from NG2 cells to a lesser extent than cells from the subventricular zone; however, the resulting oligodendrocytes may be compromised in terms of maturation and possibly limited in their ability to generate myelin. Furthermore, these cells decrease in number with age. It is very unlikely that the use of drugs favoring the migration and differentiation of oligodendrocyte progenitor cells in multiple sclerosis would be effective in the context of neuromyelitis optica, but cell therapy with oligodendrocyte progenitor cells seems to be a potential alternative.

Difference in the Source of Anti-AQP4-IgG and Anti-MOG-IgG Antibodies in CSF in Patients With Neuromyelitis Optica Spectrum Disorder

Objective

To elucidate the differences in the source and in the level of intrathecal synthesis between anti–aquaporin-4 antibodies (AQP4-IgG) and anti-myelin oligodendrocyte glycoprotein antibodies (MOG-IgG).

Methods

Thirty-eight patients with MOG-IgG–associated disease and 36 with AQP4-IgG–positive neuromyelitis optica spectrum disorders (NMOSD) were studied for the antibody titers in the sera and CSF simultaneously collected in the acute attacks. The quotients between CSF and serum levels of albumin, total immunoglobulin G, and each disease-specific antibody were calculated. Intrathecal production level in each disease-specific antibody was evaluated by calculating the antibody index from these quotients.

Results

Eleven of the 38 patients with MOG-IgG were positive for the antibody only in the CSF, while no patient with AQP4-IgG showed CSF-restricted AQP4-IgG. Blood-brain barrier compromise as shown by raised albumin quotients was seen in 75.0% of MOG-IgG–positive cases and 43.8% of AQP4-IgG–positive cases. Moreover, MOG-IgG quotients were >10 times higher than AQP4-IgG quotients (effect size r = 0.659, p < 0.0001). Elevated antibody index (>4.0) was confirmed in 12 of 21 with MOG-IgG, whereas it was seen only in 1 of 16 with AQP4-IgG (φ = 0.528, p < 0.0001). The CSF MOG-IgG titers (ρ = 0.519, p = 0.001) and antibody indexes for MOG-IgG (ρ = 0.472, p = 0.036) correlated with the CSF cell counts but not with clinical disability.

Conclusions

Intrathecal production of MOG-IgG may occur more frequently than that of AQP4-IgG. This finding implies the different properties of B-cell trafficking and antibody production between MOG-IgG–associated disease and AQP4-IgG–positive NMOSD.

Serum Glial Fibrillary Acidic Protein: A Neuromyelitis Optica Spectrum Disorder Biomarker

Objective

Blood tests to monitor disease activity, attack severity, or treatment impact in neuromyelitis optica spectrum disorder (NMOSD) have not been developed. This study investigated the relationship between serum glial fibrillary acidic protein (sGFAP) concentration and NMOSD activity and assessed the impact of inebilizumab treatment.

Methods

N‐MOmentum was a prospective, multicenter, double‐blind, placebo‐controlled, randomized clinical trial in adults with NMOSD. sGFAP levels were measured by single‐molecule arrays (SIMOA) in 1,260 serial and attack‐related samples from 215 N‐MOmentum participants (92% aquaporin 4‐immunoglobulin G‐seropositive) and in control samples (from healthy donors and patients with relapsing–remitting multiple sclerosis).

Results

At baseline, 62 participants (29%) exhibited high sGFAP concentrations (≥170 pg/ml; ≥2 standard deviations above healthy donor mean concentration) and were more likely to experience an adjudicated attack than participants with lower baseline concentrations (hazard ratio [95% confidence interval], 3.09 [1.6–6.1], p = 0.001). Median (interquartile range [IQR]) concentrations increased within 1 week of an attack (baseline: 168.4, IQR = 128.9–449.7 pg/ml; attack: 2,160.1, IQR = 302.7–9,455.0 pg/ml, p = 0.0015) and correlated with attack severity (median fold change from baseline [FC], minor attacks: 1.06, IQR = 0.9–7.4; major attacks: 34.32, IQR = 8.7–107.5, p = 0.023). This attack‐related increase in sGFAP occurred primarily in placebo‐treated participants (FC: 20.2, IQR = 4.4–98.3, p = 0.001) and was not observed in inebilizumab‐treated participants (FC: 1.1, IQR = 0.8–24.6, p > 0.05). Five participants (28%) with elevated baseline sGFAP reported neurological symptoms leading to nonadjudicated attack assessments.

Interpretation

Serum GFAP may serve as a biomarker of NMOSD activity, attack risk, and treatment effects. ANN NEUROL 2021;89:895–910

Recent Advances in Neuromyelitis Optica Spectrum Disorder: Pathogenesis, Mechanisms and Potential Treatments

Neuromyelitis optica spectrum disorder (NMOSD) is an acute or subacute demyelinating disease that affects mainly the optic nerve and spinal cord. A major proportion of NMOSD cases have a relationship with autoimmunity to aquaporin 4 (AQP4) found on the central nervous system. NMOSD can occur repeatedly, causing symptoms such as decreased vision and weakness of limbs. The main goal of current therapy is to relieve acute symptoms and prevent recurrence of the disease. Without timely and appropriate treatment, the recurrence and disability rates are high. In the present work, we review recent advances in the diagnosis and treatment of patients with NMOSD, as well as the pathogenesis and mechanisms of AQP4-IgG-seropositive NMOSD.

Targeting interleukin-6 to treat neuromyelitis optica spectrum disorders: Implications from immunology, the FcRn pathway and clinical experience

Neuromyelitis optica spectrum disorder (NMOSD) is a rare disease of the central nervous system (CNS) that is associated with poor outcomes for patients. Until recently, when complement inhibitors were approved, there was no approved therapy. Most recently, clinical trials of interleukin-6 (IL-6) blockade showed a therapeutic benefit for NMOSD. In this review, we introduce the immunological basis of IL-6 blockade in NMOSD and summarize current knowledge about the clinical use of the IL-6 receptor inhibitors tocilizumab and satralizumab. The aim of extending the half-life of monoclonal antibodies (mAbs) has been actualized by successful clinical translation for Satralizumab, achieved via the neonatal Fc receptor (FcRn) pathway. The basic principles of FcRn are highlighted in this review together with the potential therapeutic benefits of this emerging technology.

Affinity maturation is required for pathogenic monovalent IgG4 autoantibody development in myasthenia gravis

Pathogenic muscle-specific tyrosine kinase (MuSK)–specific IgG4 autoantibodies in autoimmune myasthenia gravis (MG) are functionally monovalent as a result of Fab-arm exchange. The development of these unique autoantibodies is not well understood. We examined MG patient–derived monoclonal autoantibodies (mAbs), their corresponding germline-encoded unmutated common ancestors (UCAs), and monovalent antigen-binding fragments (Fabs) to investigate how affinity maturation contributes to binding and immunopathology. Mature mAbs, UCA mAbs, and mature monovalent Fabs bound to MuSK and demonstrated pathogenic capacity. However, monovalent UCA Fabs bound to MuSK but did not have measurable pathogenic capacity. Affinity of the UCA Fabs for MuSK was 100-fold lower than the subnanomolar affinity of the mature Fabs. Crystal structures of two Fabs revealed how mutations acquired during affinity maturation may contribute to increased MuSK-binding affinity. These findings indicate that the autoantigen drives autoimmunity in MuSK MG through the accumulation of somatic mutations such that monovalent IgG4 Fab-arm–exchanged autoantibodies reach a high-affinity threshold required for pathogenic capacity.

Neuromyelitis Optica Spectrum Disorder Treatment-Current and Future Prospects

Neuromyelitis optica (NMO) is an immune-mediated demyelinative disorder of the central nervous system affecting mainly the optical nerves and the spinal cord. The recurrent course of the disease, with exacerbations and incomplete remissions, causes accumulating disability, which has a profound impact upon patients’ quality of life. The discovery of antibodies against aquaporin 4 (AQP4) and their leading role in NMO etiology and the formulation of diagnostic criteria have improved appropriate recognition of the disease. In recent years, there has been rapid progress in understanding the background of NMO, leading to an increasing range of treatment options. On the basis of a review of the relevant literature, the authors present currently available therapeutic strategies for NMO as well as ongoing research in this field, with reference to key points of immune-mediated processes involved in the background of the disease.

Blood-brain barrier resealing in neuromyelitis optica occurs independently of astrocyte regeneration

Approximately 80% of neuromyelitis optica spectrum disorder (NMOSD) patients harbor serum anti-aquaporin-4 autoantibodies targeting astrocytes in the CNS. Crucial for NMOSD lesion initiation is disruption of the blood-brain barrier (BBB), which allows the entrance of Abs and serum complement into the CNS and which is a target for new NMOSD therapies. Astrocytes have important functions in BBB maintenance; however, the influence of their loss and the role of immune cell infiltration on BBB permeability in NMOSD have not yet been investigated. Using an experimental model of targeted NMOSD lesions in rats, we demonstrate that astrocyte destruction coincides with a transient disruption of the BBB and a selective loss of occludin from tight junctions. It is noteworthy that BBB integrity is reestablished before astrocytes repopulate. Rather than persistent astrocyte loss, polymorphonuclear leukocytes (PMNs) are the main mediators of BBB disruption, and their depletion preserves BBB integrity and prevents astrocyte loss. Inhibition of PMN chemoattraction, activation, and proteolytic function reduces lesion size. In summary, our data support a crucial role for PMNs in BBB disruption and NMOSD lesion development, rendering their recruitment and activation promising therapeutic targets.

The Emerging Role of Microglia in Neuromyelitis Optica

Neuromyelitis optica (NMO) is an autoantibody-triggered neuro-inflammatory disease which preferentially attacks the spinal cord and optic nerve. Its defining autoantibody is specific for the water channel protein, aquaporin-4 (AQP4), which primarily is localized at the end-feet of astrocytes. Histopathology studies of early NMO lesions demonstrated prominent activation of microglia, the resident immune sentinels of the central nervous system (CNS). Significant microglial reactivity is also observed in NMO animal models induced by introducing AQP4-IgG into the CNS. Here we review the potential roles for microglial activation in human NMO patients as well as different animal models of NMO. We will focus primarily on the molecular mechanisms underlying microglial function and microglia-astrocyte interaction in NMO pathogenesis. Understanding the role of microglia in NMO pathology may yield novel therapeutic approaches for this disease.

Targeting the complement system in neuromyelitis optica spectrum disorder

INTRODUCTION

Neuromyelitis optica spectrum disorder (NMOSD) is characterized by central nervous system inflammation and demyelination. In AQP4-IgG seropositive NMOSD, circulating immunoglobulin G (IgG) autoantibodies against astrocyte water channel aquaporin-4 (AQP4) cause tissue injury. Compelling evidence supports a pathogenic role for complement activation following AQP4-IgG binding to AQP4. Clinical studies supported the approval of eculizumab, an inhibitor of C5 cleavage, in AQP4-IgG seropositive NMOSD.

AREAS COVERED

This review covers in vitro, animal models, and human evidence for complement-dependent and complement-independent tissue injury in AQP4-IgG seropositive NMOSD. Complement targets are discussed, including complement proteins, regulators and anaphylatoxin receptors, and corresponding drug candidates.

EXPERT OPINION

Though preclinical data support a central pathogenic role of complement activation in AQP4-IgG seropositive NMOSD, they do not resolve the relative contributions of complement-dependent vs. complement-independent disease mechanisms such as antibody-dependent cellular cytotoxicity, T cell effector mechanisms, and direct AQP4-IgG-induced cellular injury. The best evidence that complement-dependent mechanisms predominate in AQP4-IgG seropositive NMOSD comes from eculizumab clinical data. Various drug candidates targeting distinct complement effector mechanisms may offer improved safety and efficacy. However, notwithstanding the demonstrated efficacy of complement inhibition in AQP4-IgG seropositive NMOSD, the ultimate niche for complement inhibition is not clear given multiple drug options with alternative mechanisms of action.Abbreviations: AAV2, Adeno-associated virus 2; ADCC, antibody-dependent cellular cytotoxicity; ANCA, antineutrophilic cytoplasmic autoantibody; AQP4, aquaporin-4; AQP4-IgG, AQP4-immunoglobulin G; C1-INH, C1-esterase inhibitor; C3aR, C3a receptor; C4BP, C4 binding protein; C5aR, C5a receptor; CDC, complement-dependent cytotoxicity; CFHR1, complement factor H related 1; CNS, central nervous system; EAE, experimental autoimmune encephalomyelitis; EndoS, endoglycosidase S; FHL-1, factor-H-like protein 1; GFAP, glial fibrillary acidic protein; Iba-1, ionized calcium-binding adaptor protein-1; IgG, immunoglobulin G; IVIG, intravenous human immunoglobulin G; MAC, membrane attack complex; MBL, maltose-binding lectin; MBP, myelin basic protein; MOG, myelin oligodendrocyte glycoprotein; NK cell, natural killer cell; NMOSD, neuromyelitis optica spectrum disorder; OAP, orthogonal arrays of particles; PNH, paroxysmal nocturnal hemoglobinuria.

Connexins in neuromyelitis optica: a link between astrocytopathy and demyelination

Neuromyelitis optica, a rare neuroinflammatory demyelinating disease of the CNS, is characterized by the presence of specific pathogenic autoantibodies directed against the astrocytic water channel aquaporin 4 (AQP4) and is now considered as an astrocytopathy associated either with complement-dependent astrocyte death or with astrocyte dysfunction. However, the link between astrocyte dysfunction and demyelination remains unclear. We propose glial intercellular communication, supported by connexin hemichannels and gap junctions, to be involved in demyelination process in neuromyelitis optica. Using mature myelinated cultures, we demonstrate that a treatment of 1 h to 48 h with immunoglobulins purified from patients with neuromyelitis optica (NMO-IgG) is responsible for a complement independent demyelination, compared to healthy donors' immunoglobulins (P < 0.001). In parallel, patients' immunoglobulins induce an alteration of connexin expression characterized by a rapid loss of astrocytic connexins at the membrane followed by an increased size of gap junction plaques (+60%; P < 0.01). This was co-observed with connexin dysfunction with gap junction disruption (-57%; P < 0.001) and increased hemichannel opening (+17%; P < 0.001), associated with glutamate release. Blocking connexin 43 hemichannels with a specific peptide was able to prevent demyelination in co-treatment with patients compared to healthy donors' immunoglobulins. By contrast, the blockade of connexin 43 gap junctions with another peptide was detrimental for myelin (myelin density -48%; P < 0.001). Overall, our results suggest that dysregulation of connexins would play a pathogenetic role in neuromyelitis optica. The further identification of mechanisms leading to connexin dysfunction and soluble factors implicated, would provide interesting therapeutic strategies for demyelinating disorders.

Inhibition of ERK1/2 phosphorylation attenuates spinal cord injury induced astrocyte activation and inflammation through negatively regulating aquaporin-4 in rats

The extracellular signal-regulated kinase (ERK) pathway has been reported to play a pivotal role in mediating spinal cord injury (SCI) progression. The present study aimed to investigate the effects of phosphorylated ERK1/2 (p-ERK1/2) inhibition on SCI-induced astrocyte activation and inflammation and its possible mechanism in rats. Here, female Sprague-Dawley rats were randomly assigned to four groups: (1) Sham group, (2) SCI group, (3) TGN-020 group (aquaporin-4, AQP4, blocking agent), (4) PD98059 group (ERK blocking agent). A well SCI model was established by compressing the thoracic vertebra 10 level (weight 35 g, time 5 min) in rats. Western blotting and immunofluorescence staining were used to measure the expression of associated proteins after SCI. HE staining and Nissl staining were performed to detect the morphological changes of spinal cords and the number of surviving neurons following SCI, respectively. The Basso-Beattie-Bresnahan open-field rating scale was used to evaluate functional locomotor recovery following SCI in rats. Our results demonstrated that SCI significantly induced the upregulation of aquaporin-4, p-ERK1/2, glial fibrillary acidic protein, proliferating cell nuclear antigen, and proinflammatory cytokines (tumor necrosis factor-α, interleukin-6 and interleukin-1β). However, treatment with TGN-020 or PD98059 could effectively inhibit astrocyte proliferation and proinflammatory cytokine release, preserve the number of surviving ventral horn neurons, and subsequently improve the locomotor function of rats after SCI. Interestingly, the SCI-induced elevation of AQP4 expression was downregulated by p-ERK1/2 inhibition, suggesting that blocking ERK1/2 phosphorylation could attenuate astrocyte activation and inflammatory processes through negative regulation of AQP4. Therefore, p-ERK1/2 blockade may be employed as a therapeutic target for SCI.

Astrocytes in rare neurological conditions: Morphological and functional considerations

Astrocytes are a population of central nervous system (CNS) cells with distinctive morphological and functional characteristics that differ within specific areas of the brain and are widely distributed throughout the CNS. There are mainly two types of astrocytes, protoplasmic and fibrous, which differ in morphologic appearance and location. Astrocytes are important cells of the CNS that not only provide structural support, but also modulate synaptic activity, regulate neuroinflammatory responses, maintain the blood-brain barrier, and supply energy to neurons. As a result, astrocytic disruption can lead to widespread detrimental effects and can contribute to the pathophysiology of several neurological conditions. The characteristics of astrocytes in more common neuropathologies such as Alzheimer's and Parkinson's disease have significantly been described and continue to be widely studied. However, there still exist numerous rare neurological conditions in which astrocytic involvement is unknown and needs to be explored. Accordingly, this review will summarize functional and morphological changes of astrocytes in various rare neurological conditions based on current knowledge thus far and highlight remaining neuropathologies where astrocytic involvement has yet to be investigated.

Single-cell approaches to investigate B cells and antibodies in autoimmune neurological disorders

Autoimmune neurological disorders, including neuromyelitis optica spectrum disorder, anti-N-methyl-D-aspartate receptor encephalitis, anti-MOG antibody-associated disorders, and myasthenia gravis, are clearly defined by the presence of autoantibodies against neurological antigens. Although these autoantibodies have been heavily studied for their biological activities, given the heterogeneity of polyclonal patient samples, the characteristics of a single antibody cannot be definitively assigned. This review details the findings of polyclonal serum and CSF studies and then explores the advances made by single-cell technologies to the field of antibody-mediated neurological disorders. High-resolution single-cell methods have revealed abnormalities in the tolerance mechanisms of several disorders and provided further insight into the B cells responsible for autoantibody production. Ultimately, several factors, including epitope specificity and binding affinity, finely regulate the pathogenic potential of an autoantibody, and a deeper appreciation of these factors may progress the development of targeted immunotherapies for patients.

Novel insights into pathophysiology and therapeutic possibilities reveal further differences between AQP4-IgG- and MOG-IgG-associated diseases

PURPOSE OF REVIEW

This review summarizes recent insights into the pathogenesis and therapeutic options for patients with MOG- or AQP4-antibodies.

RECENT FINDINGS

Although AQP4-IgG are linked to NMOSD, MOG-IgG-associated diseases (MOGAD) include a broader clinical spectrum of autoimmune diseases of the central nervous system (CNS). Details of membrane assembly of AQP4-IgG required for complement activation have been uncovered. Affinity-purified MOG-IgG from patients were shown to be pathogenic by induction of demyelination when the blood--brain barrier (BBB) was breached and by enhancement of activation of cognate T cells. A high-affinity AQP4-IgG, given peripherally, could induce NMOSD-like lesions in rats in the absence of BBB breach. Circulating AQP4-specific and MOG-specific B cells were identified and suggest differences in origin of MOG-antibodies or AQP4-antibodies. Patients with MOG-IgG show a dichotomy concerning circulating MOG-specific B cells; whether this is related to differences in clinical response of anti-CD20 therapy remains to be analyzed. Clinical trials of AQP4-IgG-positive NMOSD patients showed success with eculizumab (preventing cleavage of complement factor C5, thereby blocking formation of chemotactic C5a and membrane attack complex C9neo), inebilizumab (depleting CD19 + B cells), and satralizumab (anti-IL-6R blocking IL-6 actions).

SUMMARY

New insights into pathological mechanisms and therapeutic responses argue to consider NMOSD with AQP4-IgG and MOGAD as separate disease entities.

B Cells and Antibodies as Targets of Therapeutic Intervention in Neuromyelitis Optica Spectrum Disorders

The first description of neuromyelitis optica by Eugène Devic and Fernand Gault dates back to the 19th century, but only the discovery of aquaporin-4 autoantibodies in a major subset of affected patients in 2004 led to a fundamentally revised disease concept: Neuromyelits optica spectrum disorders (NMOSD) are now considered autoantibody-mediated autoimmune diseases, bringing the pivotal pathogenetic role of B cells and plasma cells into focus. Not long ago, there was no approved medication for this deleterious disease and off-label therapies were the only treatment options for affected patients. Within the last years, there has been a tremendous development of novel therapies with diverse treatment strategies: immunosuppression, B cell depletion, complement factor antagonism and interleukin-6 receptor blockage were shown to be effective and promising therapeutic interventions. This has led to the long-expected official approval of eculizumab in 2019 and inebilizumab in 2020. In this article, we review current pathogenetic concepts in NMOSD with a focus on the role of B cells and autoantibodies as major contributors to the propagation of these diseases. Lastly, by highlighting promising experimental and future treatment options, we aim to round up the current state of knowledge on the therapeutic arsenal in NMOSD.

Specific Induction of Double Negative B Cells During Protective and Pathogenic Immune Responses

Double negative (DN) (CD19+CD20lowCD27-IgD-) B cells are expanded in patients with autoimmune and infectious diseases; however their role in the humoral immune response remains unclear. Using systematic flow cytometric analyses of peripheral blood B cell subsets, we observed an inflated DN B cell population in patients with variety of active inflammatory conditions: myasthenia gravis, Guillain-Barré syndrome, neuromyelitis optica spectrum disorder, meningitis/encephalitis, and rheumatic disorders. Furthermore, we were able to induce DN B cells in healthy subjects following vaccination against influenza and tick borne encephalitis virus. Transcriptome analysis revealed a gene expression profile in DN B cells that clustered with naïve B cells, memory B cells, and plasmablasts. Immunoglobulin VH transcriptome sequencing and analysis of recombinant antibodies revealed clonal expansion of DN B cells that were targeted against the vaccine antigen. Our study suggests that DN B cells are expanded in multiple inflammatory neurologic diseases and represent an inducible B cell population that responds to antigenic stimulation, possibly through an extra-follicular maturation pathway.

Emerging Targeted Therapies for Neuromyelitis Optica Spectrum Disorders

Neuromyelitis optica spectrum disorder (NMOSD) is an autoimmune, inflammatory disorder of the central nervous system that typically presents with recurrent episodes of optic neuritis, longitudinally extensive myelitis, brainstem, diencephalic, and cerebral syndromes. Up to 80% of NMOSD patients have a circulating pathogenic autoantibody that targets the water channel aquaporin-4 (AQP4-IgG). The discovery of AQP4-IgG transformed our understanding of the pathogenesis of the disease and its possible treatment targets. Monoclonal antibodies targeting terminal complement (eculizumab), CD19 (inebilizumab), and the interleukin-6 receptor (satralizumab) have demonstrated efficacy in NMOSD attack prevention in recent phase 3 trials and have gained subsequent regulatory approval in the USA and other countries. We aim to review the evidence supporting the efficacy of these new drugs.

Neuromyelitis optica

Neuromyelitis optica (NMO; also known as Devic syndrome) is a clinical syndrome characterized by attacks of acute optic neuritis and transverse myelitis. In most patients, NMO is caused by pathogenetic serum IgG autoantibodies to aquaporin 4 (AQP4), the most abundant water-channel protein in the central nervous system. In a subset of patients negative for AQP4-IgG, pathogenetic serum IgG antibodies to myelin oligodendrocyte glycoprotein, an antigen in the outer myelin sheath of central nervous system neurons, are present. Other causes of NMO (such as paraneoplastic disorders and neurosarcoidosis) are rare. NMO was previously associated with a poor prognosis; however, treatment with steroids and plasma exchange for acute attacks and with immunosuppressants (in particular, B cell-depleting agents) for attack prevention has greatly improved the long-term outcomes. Recently, a number of randomized controlled trials have been completed and the first drugs, all therapeutic monoclonal antibodies, have been approved for the treatment of AQP4-IgG-positive NMO and its formes frustes.

Lupus and NMOSD: The Blending of Humoral Autoimmunity

Systemic lupus erythematous (SLE) is a chronic autoimmune disease that can target any organ of the body. It may coexist with other autoimmune neurologic conditions such as neuromyelitis optica spectrum disorder (NMOSD). NMOSD, previously known as Devic's disease, is an autoimmune inflammatory disorder of the central nervous system (CNS) that targets the spinal cord, optic nerves, and certain brain regions. Most current evidence suggests that NMOSD is best described as a CNS astrocytopathy. While these diseases share several immunosuppressive treatment options, timely diagnosis of NMOSD is critical as patients may benefit from treatment tailored specifically to NMOSD as opposed to SLE. Steroids, plasmapheresis, intravenous immunoglobulin, cyclophosphamide, azathioprine, mycophenolate mofetil, and rituximab are used to treat both SLE and NMOSD. However, there are several new therapies (inebilizumab, eculizumab, and satralizumab) recently approved specifically for use in NMOSD. In this case series, we report on three patients with coexisting SLE and NMOSD. We describe a 31-year-old woman who suffered an NMOSD flare after 11 years of clinical remission in the context of receiving an influenza vaccination; her SLE remained quiescent on hydroxychloroquine. Next, we describe a 52-year-old woman with emergence of neurologically devastating seropositive NMOSD in the setting of active treatment for SLE with intravenous cyclophosphamide, oral steroids, and hydroxychloroquine. Last, we describe a 48-year-old woman with emergence of seronegative NMOSD in the setting of SLE that was well-controlled on azathioprine and hydroxychloroquine. These cases illustrate the importance of accurate diagnosis and targeted treatment of NMOSD when coexisting with SLE.

Brain antibody sequence evaluation (BASE): an easy-to-use software for complete data analysis in single cell immunoglobulin cloning

Background

Repertoire analysis of patient-derived recombinant monoclonal antibodies is an important tool to study the role of B cells in autoimmune diseases of the human brain and beyond. Current protocols for generation of patient-derived recombinant monoclonal antibody libraries are time-consuming and contain repetitive steps, some of which can be assisted with the help of software automation.

Results

We developed BASE, an easy-to-use software for complete data analysis in single cell immunoglobulin cloning. BASE consists of two modules: aBASE for immunological annotations and cloning primer lookup, and cBASE for plasmid sequence identity confirmation before expression. Comparing automated BASE analysis with manual analysis we confirmed the validity of BASE output: identity between manual and automated aBASE analysis was 100% for all outputs, except for immunoglobulin isotype determination. In this case, aBASE yielded correct results in 96% of cases, whereas 4% of cases required manual confirmation. cBASE automatically concluded expression recommendations in 89.8% of cases, 91.8% of which were identical to manually derived results and none of them were false-positive.

Conclusions

BASE offers an easy-to-use software solution suitable for complete Ig sequence data analysis and tracking during recombinant mAb cloning from single cells. Plasmid sequence identity confirmation by cBASE offers functionality not provided by existing software solutions in the field and will help to reduce time-consuming steps of the monoclonal antibody generation workflow. BASE can be installed locally or accessed online at Code Ocean.

The B cell immunobiology that underlies CNS autoantibody-mediated diseases

A rapidly expanding and clinically distinct group of CNS diseases are caused by pathogenic autoantibodies that target neuroglial surface proteins. Despite immunotherapy, patients with these neuroglial surface autoantibody (NSAb)-mediated diseases often experience clinical relapse, high rates of long-term morbidity and adverse effects from the available medications. Fundamentally, the autoantigen-specific B cell lineage leads to production of the pathogenic autoantibodies. These autoantigen-specific B cells have been consistently identified in the circulation of patients with NSAb-mediated diseases, accompanied by high serum levels of autoantigen-specific antibodies. Early evidence suggests that these cells evade well-characterized B cell tolerance checkpoints. Nearer to the site of pathology, cerebrospinal fluid from patients with NSAb-mediated diseases contains high levels of autoantigen-specific B cells that are likely to account for the intrathecal synthesis of these autoantibodies. The characteristics of their immunoglobulin genes offer insights into the underlying immunobiology. In this Review, we summarize the emerging knowledge of B cells across the NSAb-mediated diseases. We review the evidence for the relative contributions of germinal centres and long-lived plasma cells as sources of autoantibodies, discuss data that indicate migration of B cells into the CNS and summarize insights into the underlying B cell pathogenesis that are provided by therapeutic effects.

Interleukin-6 in neuromyelitis optica spectrum disorder pathophysiology

Neuromyelitis optica spectrum disorder (NMOSD) is a rare autoimmune disorder that preferentially affects the spinal cord and optic nerve. Most patients with NMOSD experience severe relapses that lead to permanent neurologic disability; therefore, limiting frequency and severity of these attacks is the primary goal of disease management. Currently, patients are treated with immunosuppressants. Interleukin-6 (IL-6) is a pleiotropic cytokine that is significantly elevated in the serum and the CSF of patients with NMOSD. IL-6 may have multiple roles in NMOSD pathophysiology by promoting plasmablast survival, stimulating the production of antibodies against aquaporin-4, disrupting blood-brain barrier integrity and functionality, and enhancing proinflammatory T-lymphocyte differentiation and activation. Case series have shown decreased relapse rates following IL-6 receptor (IL-6R) blockade in patients with NMOSD, and 2 recent phase 3 randomized controlled trials confirmed that IL-6R inhibition reduces the risk of relapses in NMOSD. As such, inhibition of IL-6 activity represents a promising emerging therapy for the management of NMOSD manifestations. In this review, we summarize the role of IL-6 in the context of NMOSD.

Mitochondrial DNA enhance innate immune responses in neuromyelitis optica by monocyte recruitment and activation

Although recent studies indicate the involvement of monocytes in accelerating the lesion formation of neuromyelitis optica spectrum disorder (NMOSD), the precise mechanism of the innate immune system activation remains elusive. Thus, in this study, we aimed to clarify the mechanisms of NMOSD pathogenesis from the viewpoint of innate immunity activation. We established anti-AQP4 recombinant autoantibodies (Ab) from plasmablasts in NMOSD patient's CSF. Human astrocytes treated with anti-AQP4 Ab produced a significant amount of CCL2 and contributed to the efficient recruitment of monocytes. Moreover, mitochondrial DNA (mtDNA), which activated monocytes via Toll-like receptor 9 (TLR9), was released from astrocytes treated with anti-AQP4 Ab. MtDNA further enhanced CCL2 production by monocytes, and it was demonstrated that mtDNA concentration correlated with the efficiency of monocyte recruitment in the CSF of NMOSD patients. In conclusion, these observations highlight that mtDNA which was released from astrocytes damaged by anti-AQP4 Ab has a central role in establishing the inflammatory loop of monocyte recruitment and activation via an innate immunity pathway.

High-throughput investigation of molecular and cellular biomarkers in NMOSD

Objective

To identify candidate biomarkers associated with neuromyelitis optica spectrum disorder (NMOSD) using high-throughput technologies that broadly assay the concentrations of serum analytes and frequencies of immune cell subsets.

Methods

Sera, peripheral blood mononuclear cells (PBMCs), and matched clinical data from participants with NMOSD and healthy controls (HCs) were obtained from the Collaborative International Research in Clinical and Longitudinal Experience Study NMOSD biorepository. Flow cytometry panels were used to measure the frequencies of 39 T-cell, B-cell, regulatory T-cell, monocyte, natural killer (NK) cell, and dendritic cell subsets in unstimulated PBMCs. In parallel, multiplex proteomics assays were used to measure 46 serum cytokines and chemokines in 2 independent NMOSD and HC cohorts. Multivariable regression models were used to assess molecular and cellular profiles in NMOSD compared with HC.

Results

NMOSD samples had a lower frequency of CD16⁺CD56⁺ NK cells. Both serum cohorts and multivariable logistic regression revealed increased levels of B-cell activating factor associated with NMOSD. Interleukin 6, CCL22, and CCL3 were also elevated in 1 NMOSD cohort of the 2 analyzed. Multivariable linear regression of serum analyte levels revealed a correlation between CX3CL1 (fractalkine) levels and the number of days since most recent disease relapse.

Conclusions

Integrative analyses of cytokines, chemokines, and immune cells in participants with NMOSD and HCs provide congruence with previously identified biomarkers of NMOSD and highlight CD16⁺CD56⁺ NK cells and CX3CL1 as potential novel biomarker candidates.

Recent developments in MOG-IgG associated neurological disorders

In the past few years, acquired demyelinating syndromes of the central nervous system associated with antibodies against myelin oligodendrocyte glycoprotein (MOG) have evolved into a new inflammatory disease entity distinct from neuromyelitis optica spectrum disorders or multiple sclerosis. The meticulous clinical description of patients with MOG IgG antibodies (MOG-IgG) has been achieved by development and use of highly specific cell-based assays. MOG-IgG associated disorders comprise a wide spectrum of syndromes ranging from acute disseminated encephalomyelitis predominantly in children to optic neuritis or myelitis mostly in adults. In recent studies, phenotype of MOG-IgG associated disorders has further broadened with the description of cases of brainstem encephalitis, encephalitis with seizures and overlap syndromes with other types of autoimmune encephalitis. In this review, we provide an overview of current knowledge of MOG-IgG associated disorders, describe the clinical presentations identified, highlight differences from neuromyelitis optica spectrum disorders and multiple sclerosis, summarize clinical outcome and concepts of immune treatment, depict the underlying mechanisms of antibody pathogenicity and provide the methodological essentials of MOG-IgG assays.

Study of B Cell Repertoire in Patients With Anti-N-Methyl-D-Aspartate Receptor Encephalitis

Anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis is the most common antibody-mediated encephalitis. There are several studies on B cell repertoire of anti-NMDAR encephalitis in Caucasians. Here, the cerebrospinal fluid (CSF) samples of 12 Chinese patients with first-episode anti-NMDAR encephalitis were collected to investigate the B cell receptor (BCR) binding to NMDAR by single cell amplification of BCR and Sanger sequencing. BCR data of healthy persons, and of patients with anti-leucine-rich glioma inactivated 1 (anti-LGI1) encephalitis, multiple sclerosis (MS), and neuromyelitis optica spectrum disorder (NMOSD) from the public databases were used as control. A heavy chain common clone IGHV1-18^*04,IGHD1-26^*01/ IGHD2-2^*03/IGHD2-8^*01, IGHJ3^*02_(CDR3) ARVGSKYGFETFDI was found in 11 of 12 enrolled patients but not in the comparison data set. In addition, 4 shared clonotypes were found among these patients, and three of them contained the common clone. This study also revealed that the antibody gene family usage preference between patients and healthy controls were different, while they had similar antibody mutation rate. Our findings may have potential clinical implications for the diagnosis of anti-NMDAR encephalitis.

Differential Effects of MS Therapeutics on B Cells-Implications for Their Use and Failure in AQP4-Positive NMOSD Patients

B cells are considered major contributors to multiple sclerosis (MS) pathophysiology. While lately approved disease-modifying drugs like ocrelizumab deplete B cells directly, most MS medications were not primarily designed to target B cells. Here, we review the current understanding how approved MS medications affect peripheral B lymphocytes in humans. These highly contrasting effects are of substantial importance when considering these drugs as therapy for neuromyelitis optica spectrum disorders (NMOSD), a frequent differential diagnosis to MS, which is considered being a primarily B cell- and antibody-driven diseases. Data indicates that MS medications, which deplete B cells or induce an anti-inflammatory phenotype of the remaining ones, were effective and safe in aquaporin-4 antibody positive NMOSD. In contrast, drugs such as natalizumab and interferon-β, which lead to activation and accumulation of B cells in the peripheral blood, lack efficacy or even induce catastrophic disease activity in NMOSD. Hence, we conclude that the differential effect of MS drugs on B cells is one potential parameter determining the therapeutic efficacy or failure in antibody-dependent diseases like seropositive NMOSD.

Tanshinone IIA alleviates brain damage in a mouse model of neuromyelitis optica spectrum disorder by inducing neutrophil apoptosis

Background

Neuromyelitis optica spectrum disorder (NMOSD), an autoimmune astrocytopathic disease associated with the anti-aquaporin-4 (AQP4) antibody, is characterized by extensive necrotic lesions primarily located on the optic nerves and spinal cord. Tanshinone IIA (TSA), an active natural compound extracted from Salvia miltiorrhiza Bunge, has profound immunosuppressive effects on neutrophils.

Objective

The present study aimed to evaluate the effect of TSA on NMOSD mice and explore the underlying mechanisms. Mice were initially administered TSA (pre-TSA group, n = 20) or vehicle (vehicle group, n = 20) every 8 h for 3 days, and then NMOSD model was induced by intracerebral injection of NMOSD-immunoglobulin G (NMO-IgG) and human complement (hC). In addition, post-TSA mice (n = 10) were administered equal dose of TSA at 8 h and 16 h after model induction. At 24 h after intracerebral injection, histological analysis was performed to assess the inhibitory effects of TSA on astrocyte damage, demyelination, and neuroinflammation in NMOSD mice, and western blotting was conducted to clarify the effect of TSA on the NF-κB and MAPK signaling pathways. Furthermore, flow cytometry and western blotting were conducted to verify the proapoptotic effects of TSA on neutrophils in vitro.

Results

There was a profound reduction in astrocyte damage and demyelination in the pre-TSA group and post-TSA group. However, prophylactic administration of TSA induced a better effect than therapeutic treatment. The number of infiltrated neutrophils was also decreased in the lesions of NMOSD mice that were pretreated with TSA. We confirmed that prophylactic administration of TSA significantly promoted neutrophil apoptosis in NMOSD lesions in vivo, and this proapoptotic effect was mediated by modulating the caspase pathway in the presence of inflammatory stimuli in vitro. In addition, TSA restricted activation of the NF-κB signaling pathway in vivo.

Conclusion

Our data provide evidence that TSA can act as a prophylactic agent that reduces NMO-IgG-induced damage in the mouse brain by enhancing the resolution of inflammation by inducing neutrophil apoptosis, and TSA may serve as a promising therapeutic agent for neutrophil-associated inflammatory disorders, such as NMOSD.

Comparative Analysis of T-Cell Responses to Aquaporin-4 and Myelin Oligodendrocyte Glycoprotein in Inflammatory Demyelinating Central Nervous System Diseases

Autoantibodies against aquaporin-4 (AQP4-Ab) and myelin oligodendrocyte glycoprotein (MOG-Ab) are associated with rare central nervous system inflammatory demyelinating diseases like neuromyelitis optica spectrum disorders (NMOSD). Previous studies have shown that not only antibodies, but also autoreactive T-cell responses against AQP4 are present in NMOSD. However, no study has yet analyzed the presence of MOG reactive T-cells in patients with MOG antibodies. Therefore, we compared AQP4 and MOG specific peripheral T-cell response in individuals with AQP4-Ab (n = 8), MOG-Ab (n = 10), multiple sclerosis (MS, n = 8), and healthy controls (HC, n = 14). Peripheral blood mononuclear cell cultures were stimulated with eight AQP4 and nine MOG peptides selected from previous studies and a tetanus toxoid peptide mix as a positive control. Antigen-specific T-cell responses were assessed using the carboxyfluorescein diacetate succinimidyl ester proliferation assay and the detection of granulocyte macrophage colony-stimulating factor (GM-CSF), interferon (IFN)-ɤ and interleukin (IL)-4, IL-6, and IL-17A in cell culture supernatants. Additionally, human leukocyte antigen (HLA)-DQ and HLA-DR genotyping of all participants was performed. We classified a T-cell response as positive if proliferation (measured by a cell division index ≥3) was confirmed by the secretion of at least one cytokine. Reactivity against AQP4 peptides was observed in many groups, but the T-cell response against AQP4 p156-170 was present only in patients with AQP4-Ab (4/8, 50%) and absent in patients with MOG-Ab, MS and HC (corrected p = 0.02). This AQP4 p156-170 peptide specific T-cell response was significantly increased in participants with AQP4-Ab compared to those without [Odds ratio (OR) = 59.00, 95% confidence interval-CI 2.70–1,290.86]. Moreover, T-cell responses against at least one AQP4 peptide were also more frequent in participants with AQP4-Ab (OR = 11.45, 95% CI 1.24–106.05). We did not observe any significant differences for the other AQP4 peptides or any MOG peptide. AQP4-Ab were associated with HLA DQB1^*02 (OR = 5.71, 95% CI 1.09–30.07), DRB1^*01 (OR = 9.33, 95% CI 1.50–58.02) and DRB1^*03 (OR = 6.75, 95% CI = 1.19–38.41). Furthermore, HLA DRB1^*01 was also associated with the presence of AQP4 p156-170 reactive T-cells (OR = 31.67, 95% CI 1.30–772.98). To summarize, our findings suggest a role of AQP4-specific, but not MOG-specific T-cells, in NMOSD.