Anti-aquaporin-4 antibody induces astrocytic cytotoxicity in the absence of CNS antigen-specific T cells

Methods for studying mammalian aquaporin biology

Aquaporins (AQPs), transmembrane water-conducting channels, have earned a great deal of scrutiny for their critical physiological roles in healthy and disease cell states, especially in the biomedical field. Numerous methods have been implemented to elucidate the involvement of AQP-mediated water transport and downstream signaling activation in eliciting whole cell, tissue, and organ functional responses. To modulate these responses, other methods have been employed to investigate AQP druggability. This review discusses standard in vitro, in vivo, and in silico methods for studying AQPs, especially for biomedical and mammalian cell biology applications. We also propose some new techniques and approaches for future AQP research to address current gaps in methodology.

The aquaporin-4 water channel and updates on its potential as a drug target for Alzheimer's disease

INTRODUCTION

Although there are several FDA-approved treatments for Alzheimer's disease (AD), only recently have disease-modifying therapies received approval for use in patients. In this narrative review, we examine the history of aquaporin-4 (AQP4) as a therapeutic target for NMOSD (neuromyelitis optica spectrum disorder) and as a potential therapeutic target for AD.

AREAS COVERED

We review the basic science and discovery of AQP4, a transmembrane water-channel essential to regulating water balance in the central nervous system (CNS). We also review the pathogenesis of NMOSD, an autoimmune disease characterized by the destruction of cells that express AQP4. Then, we review how AQP4 is likely involved in the pathogenesis of Alzheimer's disease (AD). Finally, we discuss future challenges with drug design that would modulate AQP4 to potentially slow AD development. The literature search for this article consisted of searching Google Scholar and PubMed for permutations of the keywords 'Alzheimer's disease,' 'aquaporin-4,' 'neuromyelitis optica,' and their abbreviations.

EXPERT OPINION

We place research into AQP4 into context with other recent developments in AD research. A major difficulty with drug development for Alzheimer's is the lack of strategies to cleanly target the early pathogenesis of the disease. Targeting AQP4 may provide such a strategy.

Fahr's syndrome as a manifestation of autoimmune polyendocrine syndrome-1 and its unusual association with neuromyelitis optica spectrum disorder

Fahr's syndrome, also known as bilateral striopallidodendate calcinosis, is a rare inherited neurodegenerative illness characterized by abnormal calcium deposition in several areas of the brain, resulting in a wide range of neuropsychological symptoms. Fahr's syndrome, secondary to autoimmune polyendocrine syndrome type 1, which includes adrenal insufficiency and mucocutaneous candidiasis in addition to hypoparathyroidism, is exceedingly rare. No case report has been documented to date to show the co-occurrence of Fahr's syndrome and neuromyelitis optica spectrum disorder. Here, we discuss the case of a 30-year-old man with a previous history of seizures and symptoms of ectodermal dystrophy presented with seizures, left-sided hemiparesis, dysarthria, and other characteristics indicative of severe hypocalcemia. The neuroimaging findings strongly suggested Fahr's syndrome, with radiographic evidence of Neuromyelitis optica spectrum disorder as longitudinal extensive transverse myelitis in the cervical spinal cord, high titers of serum aquaporin-4 antibodies, and demyelinating neuropathy on nerve conduction studies. This distinct neuropsychological presentation and neuroimaging findings led to the diagnosis of Fahr's syndrome as a result of hypoparathyroidism caused by autoimmune polyendocrine syndrome type 1 with cooccurrence of neuromyelitis optica spectrum disorder. The patient's clinical symptoms improved considerably after he was treated based on a provisional diagnosis. The clinical importance of our case is significant for both neuropsychiatrists and endocrinologists, as autoimmune polyendocrine syndrome should be considered as the etiology of Fahr's syndrome. This case report also aims to report this unusual association of Neuromyelitis optica spectrum disorder with Fahr's syndrome to give the future prospective to know whether this association is incidental or there is a missing link between these two different disorders.

T follicular helper cells contribute to pathophysiology in a model of neuromyelitis optica spectrum disorders

Neuromyelitis optica spectrum disorders (NMOSD) are inflammatory autoimmune disorders of the CNS. IgG autoantibodies targeting the aquaporin-4 water channel (AQP4-IgGs) are the pathogenic effector of NMOSD. Dysregulated T follicular helper (Tfh) cells have been implicated in loss of B cell tolerance in autoimmune diseases. The contribution of Tfh cells to disease activity and therapeutic potential of targeting these cells in NMOSD remain unclear. Here, we established an autoimmune model of NMOSD by immunizing mice against AQP4 via in vivo electroporation. After AQP4 immunization, mice displayed AQP4 autoantibodies in blood circulation, blood-brain barrier disruption, and IgG infiltration in spinal cord parenchyma. Moreover, AQP4 immunization induced motor impairments and NMOSD-like pathologies, including astrocytopathy, demyelination, axonal loss, and microglia activation. These were associated with increased splenic Tfh, Th1, and Th17 cells; memory B cells; and plasma cells. Aqp4-deficient mice did not display motor impairments and NMOSD-like pathologies after AQP4 immunization. Importantly, abrogating ICOS/ICOS-L signaling using anti-ICOS-L antibody depleted Tfh cells and suppressed the response of Th1 and Th17 cells, memory B cells, and plasma cells in AQP4-immunized mice. These findings were associated with ameliorated motor impairments and spinal cord pathologies. This study suggests a role of Tfh cells in the pathophysiology of NMOSD in a mouse model with AQP4 autoimmunity and provides an animal model for investigating the immunological mechanisms underlying AQP4 autoimmunity and developing therapeutic interventions targeting autoimmune reactions in NMOSD.

A real-world study of interleukin-6 receptor blockade in patients with neuromyelitis optica spectrum disorder

Neuromyelitis optica spectrum disorder (NMOSD) is a relapsing autoimmune disease that can cause permanent neurological disabilities. However, the interleukin-6 (IL-6) signaling pathway is a promising therapeutic target for relapse prevention. Therefore, this study evaluated the long-term effectiveness of tocilizumab, a humanized anti-IL-6 receptor antibody, for NMOSD. We enrolled 65 patients with NMOSD who received regular intravenous administration of tocilizumab (8 mg/kg) between October 2017 and January 2022. Then, we retrospectively collected data on the clinical characteristics and baseline glial fibrillary acidic protein (GFAP) and neurofilament light chain levels. The primary outcome was the annualized relapse rate (ARR). Risk factors were assessed using a multivariable logistic regression model. During the median follow-up of 34.1 (interquartile range: 25.5-39.3) months, 23% (15/65) of patients relapsed during tocilizumab treatment, but the median ARR decreased from 1.9 (range 0.12-6.29) to 0.1 (range 0-1.43, p < 0.0001). A prolonged infusion interval (> 4 weeks, odds ratio [OR]: 10.7, 95% confidence interval [CI]: 1.6-71.4, p = 0.014) and a baseline plasma GFAP level of > 220 pg/mL (OR: 20.6, 95% CI 3.3-129.4, p  = 0.001) were risk factors for future relapses. During treatment, the median Expanded Disability Status Scale score significantly decreased in aquaporin-4 antibody-positive and -negative patients, but the pain did not considerably improve. There were no severe safety concerns. Tocilizumab treatment significantly reduced the relapse rate in patients with NMOSD. However, prolonged infusion intervals and high baseline plasma GFAP levels may increase the relapse risk during tocilizumab therapy.

The Role of Exposomes in the Pathophysiology of Autoimmune Diseases I: Toxic Chemicals and Food

Autoimmune diseases affect 5–9% of the world’s population. It is now known that genetics play a relatively small part in the pathophysiology of autoimmune disorders in general, and that environmental factors have a greater role. In this review, we examine the role of the exposome, an individual’s lifetime exposure to external and internal factors, in the pathophysiology of autoimmune diseases. The most common of these environmental factors are toxic chemicals, food/diet, and infections. Toxic chemicals are in our food, drink, common products, the air, and even the land we walk on. Toxic chemicals can directly damage self-tissue and cause the release of autoantigens, or can bind to human tissue antigens and form neoantigens, which can provoke autoimmune response leading to autoimmunity. Other types of autoimmune responses can also be induced by toxic chemicals through various effects at the cellular and biochemical levels. The food we eat every day commonly has colorants, preservatives, or packaging-related chemical contamination. The food itself may be antigenic for susceptible individuals. The most common mechanism for food-related autoimmunity is molecular mimicry, in which the food’s molecular structure bears a similarity with the structure of one or more self-tissues. The solution is to detect the trigger, remove it from the environment or diet, then repair the damage to the individual’s body and health.

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.

Serum GFAP and NfL as disease severity and prognostic biomarkers in patients with aquaporin-4 antibody-positive neuromyelitis optica spectrum disorder

Background

Neuromyelitis optica spectrum disorder (NMOSD) is a frequently disabling neuroinflammatory syndrome with a relapsing course. Blood-based disease severity and prognostic biomarkers for NMOSD are a yet unmet clinical need. Here, we evaluated serum glial fibrillary acidic protein (sGFAP) and neurofilament light (sNfL) as disease severity and prognostic biomarkers in patients with aquaporin-4 immunoglobulin (Ig)G positive (AQP4-IgG⁺) NMOSD.

Methods

sGFAP and sNfL were determined by single-molecule array technology in a prospective cohort of 33 AQP4-IgG⁺ patients with NMOSD, 32 of which were in clinical remission at study baseline. Sixteen myelin oligodendrocyte glycoprotein IgG-positive (MOG-IgG⁺) patients and 38 healthy persons were included as controls. Attacks were recorded in all AQP4-IgG⁺ patients over a median observation period of 4.25 years.

Results

In patients with AQP4-IgG⁺ NMOSD, median sGFAP (109.2 pg/ml) was non-significantly higher than in MOG-IgG⁺ patients (81.1 pg/ml; p = 0.83) and healthy controls (67.7 pg/ml; p = 0.07); sNfL did not substantially differ between groups. Yet, in AQP4-IgG⁺, but not MOG-IgG⁺ patients, higher sGFAP was associated with worse clinical disability scores, including the Expanded Disability Status Scale (EDSS, standardized effect size = 1.30, p = 0.007) and Multiple Sclerosis Functional Composite (MSFC, standardized effect size = − 1.28, p = 0.01). While in AQP4-IgG⁺, but not MOG-IgG⁺ patients, baseline sGFAP and sNfL were positively associated (standardized effect size = 2.24, p = 0.001), higher sNfL was only non-significantly associated with worse EDSS (standardized effect size = 1.09, p = 0.15) and MSFC (standardized effect size = − 1.75, p = 0.06) in patients with AQP4-IgG⁺ NMOSD. Patients with AQP4-IgG⁺ NMOSD with sGFAP > 90 pg/ml at baseline had a shorter time to a future attack than those with sGFAP ≤ 90 pg/ml (adjusted hazard ratio [95% confidence interval] = 11.6 [1.3–105.6], p = 0.03). In contrast, baseline sNfL levels above the 75^th age adjusted percentile were not associated with a shorter time to a future attack in patients with AQP4-IgG⁺ NMOSD.

Conclusion

These findings suggest a potential role for sGFAP as biomarker for disease severity and future disease activity in patients with AQP4-IgG⁺ NMOSD in phases of clinical remission.

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.

Rodent Models of Optic Neuritis

Optic neuritis (ON) is an inflammatory attack of the optic nerve that leads to visual disability. It is the most common optic neuropathy affecting healthy young adults, most commonly women aged 20-45 years. It can be idiopathic and monophasic or as part of a neurologic disease such as multiple sclerosis with recurrence and cumulative damage. Currently, there is no therapy to repair the damage from optic neuritis. Animal models are an essential tool for the understanding of the pathogenesis of optic neuritis and for the development of potential treatment strategies. Experimental autoimmune encephalomyelitis (EAE) is the most commonly used experimental rodent model for human autoimmune inflammatory demyelinating diseases of the central nervous system (CNS). In this review, we discuss the latest rodent models regarding optic neuritis, focusing on EAE model, and on its recent achievements and developments.

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.

Interaction between food antigens and the immune system: Association with autoimmune disorders

It has been shown that environmental factors such as infections, chemicals, and diet play a major role in autoimmune diseases; however, relatively little attention has been given to food components as the most prevalent modifiers of these afflictions. This review summarizes the current body of knowledge related to different mechanisms and associations between food proteins/peptides and autoimmune disorders. The primary factor controlling food-related immune reactions is the oral tolerance mechanism. The failure of oral tolerance triggers immune reactivity against dietary antigens, which may initiate or exacerbate autoimmune disease when the food antigen shares homology with human tissue antigens. Because the conformational fit between food antigens and a host's self-determinants has been determined for only a few food proteins, we examined evidence related to the reaction of affinity-purified disease-specific antibody with different food antigens. We also studied the reaction of monoclonal or polyclonal tissue-specific antibodies with various food antigens and the reaction of food-specific antibodies with human tissue antigens. Examining the assembled information, we postulated that chemical modification of food proteins by different toxicants in food may result in immune reaction against modified food proteins that cross-react with tissue antigens, resulting in autoimmune reactivity. Because we are what our microbiome eats, food can change the gut commensals, and toxins can breach the gut barrier, penetrating into different organs where they can initiate autoimmune response. Conversely, there are also foods and supplements that help maintain oral tolerance and microbiome homeostasis. Understanding the potential link between specific food consumption and autoimmunity in humans may lay the foundation for further research about the proper diet in the prevention of autoimmune diseases.

Neuromyelitis Optica Spectrum Disorder and Anti-MOG Syndromes

Neuromyelitis optica spectrum disorder (NMOSD) and anti-myelin oligodendrocyte glycoprotein (anti-MOG) syndromes are immune-mediated inflammatory conditions of the central nervous system that frequently involve the optic nerves and the spinal cord. Because of their similar clinical manifestations and habitual relapsing course they are frequently confounded with multiple sclerosis (MS). Early and accurate diagnosis of these distinct conditions is relevant as they have different treatments. Some agents used for MS treatment may be deleterious to NMOSD. NMOSD is frequently associated with antibodies which target aquaporin-4 (AQP4), the most abundant water channel in the CNS, located in the astrocytic processes at the blood-brain barrier (BBB). On the other hand, anti-MOG syndromes result from damage to myelin oligodendrocyte glycoprotein (MOG), expressed on surfaces of oligodendrocytes and myelin sheaths. Acute transverse myelitis with longitudinally extensive lesion on spinal MRI is the most frequent inaugural manifestation of NMOSD, usually followed by optic neuritis. Other core clinical characteristics include area postrema syndrome, brainstem, diencephalic and cerebral symptoms that may be associated with typical MRI abnormalities. Acute disseminated encephalomyelitis and bilateral or recurrent optic neuritis are the most frequent anti-MOG syndromes in children and adults, respectively. Attacks are usually treated with steroids, and relapses prevention with immunosuppressive drugs. Promising emerging therapies for NMOSD include monoclonal antibodies and tolerization.

Circulating AQP4-specific auto-antibodies alone can induce neuromyelitis optica spectrum disorder in the rat

It is well established that the binding of pathogenic aquaporin-4 (AQP4)-specific autoantibodies to astrocytes may initiate a cascade of events culminating in the destruction of these cells and in the formation of large tissue-destructive lesions typical for patients with neuromyelitis optica spectrum disorders (NMOSD). To date, not a single experimental study has shown that the systemic presence of the antibody alone can induce any damage to the central nervous system (CNS), while pathological studies on brains of NMOSD patients suggested that there might be ways for antibody entry and subsequent tissue damage. Here, we systemically applied a highly pathogenic, monoclonal antibody with high affinity to AQP4 over prolonged period of time to rats, and show that AQP4-abs can enter the CNS on their own, via circumventricular organs and meningeal or parenchymal blood vessels, that these antibodies initiate the formation of radically different lesions with AQP4 loss, depending on their mode and site of entry, and that lesion formation is much more efficient in the presence of encephalitogenic T-cell responses. We further demonstrate that the established tissue-destructive lesions trigger the formation of additional lesions by short and far reaching effects on blood vessels and their branches, and that AQP4-abs have profound effects on the AQP4 expression in peripheral tissues which counter-act possible titer loss by antibody absorption outside the CNS. Cumulatively, these data indicate that directly induced pathological changes caused by AQP4-abs inside and outside the CNS are efficient drivers of disease evolution in seropositive organisms.

Effect of CXCR2 Inhibition on Behavioral Outcomes and Pathology in Rat Model of Neuromyelitis Optica

OBJECTIVE

To reduce immune-mediated damage in a rat model of neuromyelitis optica (NMO) by blocking neutrophil migration using SCH527123, a drug that inhibits CXCR2.

BACKGROUND

Neuromyelitis optica is a relapsing autoimmune disease that preferentially targets the optic nerves and spinal cord leading to blindness and paralysis. Part of the immunopathogenesis of this disease is thought to involve neutrophils, which are present within NMO lesions. We tested the effect of blocking neutrophil migration in an NMO rat model.

METHODS

The Lewis rat model of NMO uses a myelin-reactive experimental autoimmune encephalomyelitis (EAE) background with passive transfer of pooled human antibody from patients with aquaporin-4 (AQP4) seropositive NMO at onset of EAE symptoms. We treated rats early in the course of EAE with CXCR2 inhibitor and assessed the extent of neutrophil infiltration into the spinal cord and the extent of AQP4 depletion.

RESULTS

CXCR2 inhibitor decreased neutrophil migration into the spinal cord of AQP4 IgG-treated EAE rats. However, there was no difference in the acute behavioral signs of EAE or the extent and distribution of AQP4 lesions. This suggests that neutrophils are not centrally involved in the immunopathogenesis of the Lewis rat NMO disease model.

CONCLUSIONS

CXCR2 inhibitor blocks neutrophil migration into the spinal cord during EAE but does not significantly reduce inflammation or AQP4 lesions in the Lewis rat model of NMO.

Resolution of inflammation in neuromyelitis optica spectrum disorders

BACKGROUND

Neuromyelitis optica spectrum disorders (NMOSD) are a spectrum of neuroinflammatory disorders associated with autoimmune antibodies against aquaporin-4 (AQP4). Accumulating evidence suggests that inflammation is involved in NMOSD pathogenesis. Resolution of inflammation, which is a highly regulated process mediated by specialized pro-resolving lipid mediators (SPMs) is important to prevent over-responsive inflammation. Deficiency in resolution of inflammation may lead to or accelerates inflammatory diseases. However, whether resolution of inflammation is impaired in NMOSD is not known. The objective of this study was to analyze the levels of SPMs in the serum and cerebrospinal fluid (CSF) of NMOSD patients, and to explore the roles of SPMs in clinical features of NMOSD.

METHODS

Thirty-five patients with NMOSD, 34 patients with multiple sclerosis, and 36 patients with non-inflammatory neurological diseases were enrolled in this study. Pro-resolving mediators including Annexin A1 (ANXA1) and resolvin D1 (RvD1), as well as pro-inflammatory lipid mediator leukotriene B4 (LTB4) levels were analyzed by enzyme-linked immunosorbent assay. Pro- and anti-inflammatory cytokines as well as chemokine levels were analyzed using cytometric beads array (CBA).

RESULTS

Our results showed RvD1 levels were significantly decreased, whereas LTB4 levels were significantly increased in the CSF of NMOSD patients. AQP4-IgG titer was negatively correlated with RvD1 levels in the CSF of NMOSD patients.

CONCLUSIONS

Decreased RvD1 levels indicate impaired resolution of inflammation in NMOSD patients. AQP4-IgG may contribute to increased inflammation and lead to unresolved inflammation in NMOSD.

Critical role of rabphilin-3A in the pathophysiology of experimental lymphocytic neurohypophysitis

Autoimmune hypophysitis (AH) is thought to be an autoimmune disease characterized by lymphocytic infiltration of the pituitary gland. Among AH pathologies, lymphocytic infundibulo-neurohypophysitis (LINH) involves infiltration of the neurohypophysis and/or the hypothalamic infundibulum, causing central diabetes insipidus resulting from insufficiency of arginine vasopressin secretion. The pathophysiological and pathogenetic mechanisms underlying LINH are largely unknown. Clinically, differentiating LINH from other pituitary diseases accompanied by mass lesions, including tumours, has often been difficult, because of similar clinical manifestations. We recently reported that rabphilin-3A is an autoantigen and that anti-rabphilin-3A antibodies constitute a possible diagnostic marker for LINH. However, the involvement of rabphilin-3A in the pathogenesis of LINH remains to be elucidated. This study was undertaken to explore the role of rabphilin-3A in lymphocytic neurohypophysitis and to investigate the mechanism. We found that immunization of mice with rabphilin-3A led to neurohypophysitis. Lymphocytic infiltration was observed in the neurohypophysis and supraoptic nucleus 1 month after the first immunization. Mice immunized with rabphilin-3A showed an increase in the volume of urine that was hypotonic as compared with control mice. Administration of a cocktail of monoclonal anti-rabphilin-3A antibodies did not induce neurohypophysitis. However, abatacept, which is a chimeric protein that suppresses T-cell activation, decreased the number of T cells specific for rabphilin-3A in peripheral blood mononuclear cells (PBMCs). It ameliorated lymphocytic infiltration of CD3+ T cells in the neurohypophysis of mice that had been immunized with rabphilin-3A. Additionally, there was a linear association between the number of T cells specific for rabphilin-3A in PBMCs and the number of CD3+ T cells infiltrating the neurohypophysis. In conclusion, we suggest that rabphilin-3A is a pathogenic antigen, and that T cells specific for rabphilin-3A are involved in the pathogenesis of neurohypophysitis in mice. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Expanding Role of T Cells in Human Autoimmune Diseases of the Central Nervous System

It is being increasingly recognized that a dysregulation of the immune system plays a vital role in neurological disorders and shapes the treatment of the disease. Aberrant T cell responses, in particular, are key in driving autoimmunity and have been traditionally associated with multiple sclerosis. Yet, it is evident that there are other neurological diseases in which autoreactive T cells have an active role in pathogenesis. In this review, we report on the recent progress in profiling and assessing the functionality of autoreactive T cells in central nervous system (CNS) autoimmune disorders that are currently postulated to be primarily T cell driven. We also explore the autoreactive T cell response in a recently emerging group of syndromes characterized by autoantibodies against neuronal cell-surface proteins. Common methodology implemented in T cell biology is further considered as it is an important determinant in their detection and characterization. An improved understanding of the contribution of autoreactive T cells expands our knowledge of the autoimmune response in CNS disorders and can offer novel methods of therapeutic intervention.

Efficacy and safety of tacrolimus treatment for neuromyelitis optica spectrum disorder

Neuromyelitis optica spectrum disorder (NMOSD) is a severe inflammatory autoimmune disease that mainly involves the optic nerves and spinal cord, causing blindness and paralysis. Although some immunosuppressants such as rituximab and azathioprine have proven to be effective in relapse prevention, the high costs or intolerable adverse events preclude their wide application. Thus, we have conducted a retrospective study in 25 NMOSD patients who were treated with tacrolimus, an immunosuppressant with high efficacy and good tolerance in other autoimmune diseases, to assess its efficacy and safety in NMOSD treatment during the last five years (2011-2016). The results revealed that tacrolimus could reduce the relapse rate by 86.2% and improve the Expanded Disability Status Scale (EDSS) scores (4.5 vs 2.3; P < 0.001) significantly. Relapses in tacrolimus treatment were associated with serum titers of aquaporin 4 antibody (AQP4-IgG) (P = 0.028). Further Cox proportional analysis demonstrated that patients with high titers of AQP4-IgG (≥1:64) had a significantly higher risk of relapse than those with low titers after tacrolimus therapy (HR:5.665; CI₉₅: 1.012-31.705; P = 0.048). Tacrolimus tended to be superior to azathioprine (29 patients) in terms of efficacy and safety during the same period. Our study suggests that tacrolimus may be another promising immunosuppressant for NMOSD.

Neuromyelitis Spectrum Disorders

The understanding of neuromyelitis optica spectrum disorder (NMOSD) has evolved substantially since its initial description over a century ago. The discovery in 2004 of a pathogenic autoantibody biomarker targeting aquaporin 4 IgG revolutionized diagnosis and therapeutic development. Although NMOSD resembles multiple sclerosis (MS), differences were identified and articulated in the late 1990s. New diagnostic criteria incorporating the biomarker as well as better understanding of the clinical and radiologic features of NMOSD now permit accurate diagnosis and differentiation from MS. Aquaporin 4 IgG-associated NMOSD is now regarded as an immune astrocytopathy with lytic and nonlytic effects on astrocytes. A second autoantibody, myelin oligodendrocyte glycoprotein IgG, which targets myelin rather than astrocytes, leads to an NMOSD syndrome with clinical and radiologic features that overlap but are distinct from those of aquaporin 4 IgG-associated NMOSD and MS. We review current understanding of the clinical aspects, pathophysiology, and treatment of NMOSD.

Variable sensitivity to complement-dependent cytotoxicity in murine models of neuromyelitis optica

Background

Studies of neuromyelitis optica (NMO), an autoimmune disease of the central nervous system (CNS), have demonstrated that autoantibodies against the water channel aquaporin-4 (AQP4) induce astrocyte damage through complement-dependent cytotoxicity (CDC). In developing experimental models of NMO using cells, tissues or animals from mice, co-administration of AQP4-IgG and normal human serum, which serves as the source of human complement (HC), is required. The sensitivity of mouse CNS cells to HC and CDC in these models is not known.

Methods

We used HC and recombinant monoclonal antibodies (rAbs) against AQP4 to investigate CDC on mouse neurons, astrocytes, differentiated oligodendrocytes (OLs), and oligodendrocyte progenitors (OPCs) in the context of purified monocultures, neuroglial mixed cultures, and organotypic cerebellar slices.

Results

We found that murine neurons, OLs, and OPCs were sensitive to HC in monocultures. In mixed murine neuroglial cultures, HC-mediated toxicity to neurons and OLs was reduced; however, astrocyte damage induced by an AQP-specific rAb #53 and HC increased neuronal and oligodendroglial loss. OPCs were resistant to HC toxicity in neuroglial mixed cultures. In mouse cerebellar slices, damage to neurons and OLs following rAb #53-mediated CDC was further reduced, but in contrast to neuroglial mixed cultures, astrocyte damage sensitized OPCs to complement damage. Finally, we established that some injury to neurons, OLs, and OPCs in cell and slice cultures resulted from the activation of HC by anti-tissue antibodies to mouse cells.

Conclusions

Murine neurons and oligodendroglia demonstrate variable sensitivity to activated complement based on their differentiation and culture conditions. In organotypic cultures, the protection of neurons, OLs, and OPCs against CDC is eliminated by targeted astrocyte destruction. The activation of human complement proteins on mouse CNS cells necessitates caution when interpreting the results of mouse experimental models of NMO using HC.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0767-4) contains supplementary material, which is available to authorized users.

A research update on the potential roles of aquaporin 4 in neuroinflammation

The presence of aquaporins (AQPs) in the brain has led to intense research on the underlying roles of this family of proteins under both normal and pathological conditions. Aquaporin 4 (AQP4) is the major water-channel membrane protein expressed in the central nervous system (CNS), primarily in astrocytes. Emerging evidence suggests that AQP4 could play an important role in water and ion homeostasis in the brain, and it has been studied in various brain pathological conditions. However, far less is known about the potential for AQP4 to influence neuroinflammation and, furthermore, its potential role in neurodegenerative disorders such as Alzheimer's disease (AD). It has been suggested that the pathogenesis of many clinical diseases, such as neuromyelitis optica (NMO), multiple sclerosis (MS) and brain injuries, is related to the regulation of AQP4 expression. Investigating the effects of AQP4 on microglia and astrocytes could be important to understand its role in the pathogenesis of neuroinflammation. Although the exact roles of non-steroidal anti-inflammatory drugs (NSAIDs) in protection against the detrimental effects of neuroinflammation remain unclear, research into the possible neuroprotective effects of AQP4 against neuroinflammation regulation seems to be important for future investigations.

Autoimmune AQP4 channelopathies and neuromyelitis optica spectrum disorders

Neuromyelitis optica (NMO) spectrum disorders (SD) represent an evolving group of central nervous system (CNS)-inflammatory autoimmune demyelinating diseases unified by a pathogenic autoantibody specific for the aquaporin-4 (AQP4) water channel. It was historically misdiagnosed as multiple sclerosis (MS), which lacks a distinguishing biomarker. The discovery of AQP4-IgG moved the focus of CNS demyelinating disease research from emphasis on the oligodendrocyte and myelin to the astrocyte. NMO is recognized today as a relapsing disease, extending beyond the optic nerves and spinal cord to include brain (especially in children) and skeletal muscle. Brain magnetic resonance imaging abnormalities, identifiable in 60% of patients at the second attack, are consistent with MS in 10% of cases. NMOSD-typical lesions (another 10%) occur in AQP4-enriched regions: circumventricular organs (causing intractable nausea and vomiting) and the diencephalon (causing sleep disorders, endocrinopathies, and syndrome of inappropriate antidiuresis). Advances in understanding the immunobiology of AQP4 autoimmunity have necessitated continuing revision of NMOSD clinical diagnostic criteria. Assays that selectively detect pathogenic AQP4-IgG targeting extracellular epitopes of AQP4 are promising prognostically. When referring to AQP4 autoimmunity, we suggest substituting the term "autoimmune aquaporin-4 channelopathy" for the term "NMO spectrum disorders." Randomized clinical trials are currently assessing the efficacy and safety of newer immunotherapies. Increasing therapeutic options based on understanding the molecular pathogenesis is anticipated to improve the outcome for patients with AQP4 channelopathy.

Severely exacerbated neuromyelitis optica rat model with extensive astrocytopathy by high affinity anti-aquaporin-4 monoclonal antibody

Introduction

Neuromyelitis optica (NMO), an autoimmune astrocytopathic disease associated with anti-aquaporin-4 (AQP4) antibody, is characterized by extensive necrotic lesions preferentially involving the optic nerves and spinal cord. However, previous in-vivo experimental models injecting human anti-AQP4 antibodies only resulted in mild spinal cord lesions compared to NMO autopsied cases. Here, we investigated whether the formation of severe NMO-like lesions occurs in Lewis rats in the context of experimental autoimmune encephalomyelitis (EAE), intraperitoneally injecting incremental doses of purified human immunoglobulin-G from a NMO patient (hIgG_NMO) or a high affinity anti-AQP4 monoclonal antibody (E5415A), recognizing extracellular domain of AQP4 made by baculovirus display method.

Results

NMO-like lesions were observed in the spinal cord, brainstem, and optic chiasm of EAE-rats with injection of pathogenic IgG (hIgG_NMO and E5415A), but not in control EAE. Only in higher dose E5415A rats, there were acute and significantly severer clinical exacerbations (tetraparesis or moribund) compared with controls, within half day after the injection of pathogenic IgG. Loss of AQP4 was observed both in EAE rats receiving hIgG_NMO and E5415A in a dose dependent manner, but the ratio of AQP4 loss in spinal sections became significantly larger in those receiving high dose E5415A up to about 50 % than those receiving low-dose E5415A or hIgG_NMO less than 3 %. These lesions were also characterized by extensive loss of glial fibrillary acidic protein but relatively preserved myelin sheaths with perivascular deposition of IgG and C5b-9, which is compatible with post mortem NMO pathology. In high dose E5415A rats, massive neutrophil infiltration was observed especially at the lesion edge, and such lesions were highly vacuolated with partial demyelination and axonal damage. In contrast, such changes were absent in EAE rats receiving low-dose E5415A and hIgG_NMO.

Conclusions

In the present study, we established a severe experimental NMO rat model with highly clinical exacerbation and extensive tissue destructive lesions typically observed in NMO patients, which has not adequately been realized in in-vivo rodent models. Our data suggest that the pathogenic antibodies could induce immune mediated astrocytopathy with mobilized neutrophils, resulted in early lesion expansion of NMO lesion with vacuolation and other tissue damages. (350/350)

Electronic supplementary material

The online version of this article (doi:10.1186/s40478-015-0259-2) contains supplementary material, which is available to authorized users.

Highly encephalitogenic aquaporin 4-specific T cells and NMO-IgG jointly orchestrate lesion location and tissue damage in the CNS

In neuromyelitis optica (NMO), astrocytes become targets for pathogenic aquaporin 4 (AQP4)-specific antibodies which gain access to the central nervous system (CNS) in the course of inflammatory processes. Since these antibodies belong to a T cell-dependent subgroup of immunoglobulins, and since NMO lesions contain activated CD4⁺ T cells, the question arose whether AQP4-specific T cells might not only provide T cell help for antibody production, but also play an important role in the induction of NMO lesions. We show here that highly pathogenic, AQP4-peptide-specific T cells exist in Lewis rats, which recognize AQP4_268–285 as their specific antigen and cause severe panencephalitis. These T cells are re-activated behind the blood–brain barrier and deeply infiltrate the CNS parenchyma of the optic nerves, the brain, and the spinal cord, while T cells with other AQP4-peptide specificities are essentially confined to the meninges. Although AQP4_268–285-specific T cells are found throughout the entire neuraxis, they have NMO-typical “hotspots” for infiltration, i.e. periventricular and periaqueductal regions, hypothalamus, medulla, the dorsal horns of spinal cord, and the optic nerves. Most remarkably, together with NMO-IgG, they initiate large astrocyte-destructive lesions which are located predominantly in spinal cord gray matter. We conclude that the processing of AQP4 by antigen presenting cells in Lewis rats produces a highly encephalitogenic AQP4 epitope (AQP4_268–285), that T cells specific for this epitope are found in the immune repertoire of normal Lewis rats and can be readily expanded, and that AQP4_268–285-specific T cells produce NMO-like lesions in the presence of NMO-IgG.

Experimental models of neuromyelitis optica: current status, challenges and future directions

Neuromyelitis optica (NMO) is a recurrent inflammatory disease that predominantly attacks the opticnerves and spinal cord. NMO-IgG, the specific autoantibody present in the vast majority of NMO patients, targets the astrocytic water channel protein aquaporin 4 (AQP4), and differentiates NMO from multiple sclerosis. The growing clinical and research interest in NMO makes it urgent to produce an animal model of NMO. The pathogenic effect of anti-AQP4 antibodies derived from the serum of patients paves the way to generating an experimental model based on the anti-AQP4-mediated astrocyte damage. In this review, we discuss the contribution of experimental models to the understanding of the pathogenesis of the disease and drug development. Key questions raised by the existing models are also discussed.

Neuromyelitis optica and the evolving spectrum of autoimmune aquaporin-4 channelopathies: a decade later

The discovery of AQP4-IgG (a pathogenic antibody that targets the astrocytic water channel aquaporin-4), as the first sensitive and specific biomarker for any inflammatory central nervous system demyelinating disease (IDD), has shifted emphasis from the oligodendrocyte and myelin to the astrocyte as a central immunopathogenic player. Neuromyelitis optica (NMO) spectrum disorders (SDs) represent an evolving spectrum of IDDs extending beyond the optic nerves and spinal cord to include the brain (especially in children) and, rarely, muscle. NMOSD typical brain lesions are located in areas that highly express the target antigen, AQP4, including the circumventricular organs (accounting for intractable nausea and vomiting) and the diencephalon (accounting for sleep disorders, endocrinopathies, and syndrome of inappropriate antidiuresis). Magnetic resonance imaging brain abnormalities fulfill Barkoff criteria for multiple sclerosis in up to 10% of patients. As the spectrum broadens, the importance of highly specific assays that detect pathogenic AQP4-IgG targeting extracellular epitopes of AQP4 cannot be overemphasized. The rapid evolution of our understanding of the immunobiology of AQP4 autoimmunity necessitates continuing revision of NMOSD diagnostic criteria. Here, we describe scientific advances that have occurred since the discovery of NMO-IgG in 2004 and review novel targeted immunotherapies. We also suggest that NMOSDs should now be considered under the umbrella term autoimmune aquaporin-4 channelopathy.

Neuromyelitis optica and the evolving spectrum of autoimmune aquaporin-4 channelopathies: a decade later

The discovery of AQP4-IgG (a pathogenic antibody that targets the astrocytic water channel aquaporin-4), as the first sensitive and specific biomarker for any inflammatory central nervous system demyelinating disease (IDD), has shifted emphasis from the oligodendrocyte and myelin to the astrocyte as a central immunopathogenic player. Neuromyelitis optica (NMO) spectrum disorders (SDs) represent an evolving spectrum of IDDs extending beyond the optic nerves and spinal cord to include the brain (especially in children) and, rarely, muscle. NMOSD typical brain lesions are located in areas that highly express the target antigen, AQP4, including the circumventricular organs (accounting for intractable nausea and vomiting) and the diencephalon (accounting for sleep disorders, endocrinopathies, and syndrome of inappropriate antidiuresis). Magnetic resonance imaging brain abnormalities fulfill Barkoff criteria for multiple sclerosis in up to 10% of patients. As the spectrum broadens, the importance of highly specific assays that detect pathogenic AQP4-IgG targeting extracellular epitopes of AQP4 cannot be overemphasized. The rapid evolution of our understanding of the immunobiology of AQP4 autoimmunity necessitates continuing revision of NMOSD diagnostic criteria. Here, we describe scientific advances that have occurred since the discovery of NMO-IgG in 2004 and review novel targeted immunotherapies. We also suggest that NMOSDs should now be considered under the umbrella term autoimmune aquaporin-4 channelopathy.

Pathogenic aquaporin-4 reactive T cells are sufficient to induce mouse model of neuromyelitis optica

Introduction

Neuromyelitis Optica (NMO) is an autoimmune disease primarily targeting the spinal cord and optic nerve leading to paralysis and blindness. The discovery of an antibody against the astrocytic water channel, aquaporin-4 (AQP4), in the majority of patients, has led to the presumption that the antibody was necessary for disease pathogenesis. The potential role of T cells in the central nervous system, however, has not been thoroughly examined.

Results

We generated an anti-AQP4 antibody seronegative model of NMO using pathogenic AQP4-reactive T cells in mice by immunizing AQP4 null mice with peptides corresponding to the second extracellular loop of AQP4, loop C. When polarized to a Th17 phenotype and transferred to wild-type mice, these cells caused tail and limb weakness. Histology showed demyelination and T cell infiltration in the spinal cord, optic nerve and brain. Animals receiving cells re-stimulated in culture with non-specific proteins resulted in no behavioral disease, indicating that specific targeting of AQP4 is essential for this phenotype.

Conclusions

In summary, we show that AQP4-reactive T cells are sufficient to trigger an NMO-like disease in mice, independent of antibodies, indicating that pathogenic AQP4-reactive T cells may play a similar role in humans.

Experimental models of neuromyelitis optica

For a long time, the most important inflammatory demyelinating diseases of the central nervous system (CNS), for example, multiple sclerosis (MS) and neuromyelitis optica (NMO), were extremely hard to differentiate, often with severe consequences for affected patients. This changed with the discovery of NMO‐immunoglobulin G (IgG), a specific autoantibody which was detected in the vast majority of NMO patients, and with the demonstration that this autoantibody targets aquaporin 4 (AQP4), a water channel found on astrocytes in the CNS. These findings paved the way for the generation of experimental models of NMO. This chapter will discuss the contribution of experimental models to NMO research and what key questions remain to be addressed.

The pathology of an autoimmune astrocytopathy: lessons learned from neuromyelitis optica

Neuromyelitis optica (NMO) is a disabling autoimmune astrocytopathy characterized by typically severe and recurrent attacks of optic neuritis and longitudinally extensive myelitis. Until recently, NMO was considered an acute aggressive variant of multiple sclerosis (MS), despite the fact that early studies postulated that NMO and MS may be two distinct diseases with a common clinical picture. With the discovery of a highly specific serum autoantibody (NMO-IgG), Lennon and colleagues provided the first unequivocal evidence distinguishing NMO from MS and other central nervous system (CNS) inflammatory demyelinating disorders. The target antigen of NMO-IgG was confirmed to be aquaporin-4 (AQP4), the most abundant water channel protein in the CNS, mainly expressed on astrocytic foot processes at the blood-brain barrier, subpial and subependymal regions. Pathological studies demonstrated that astrocytes were selectively targeted in NMO as evidenced by the extensive loss of immunoreactivities for the astrocytic proteins, AQP4 and glial fibrillary acidic protein (GFAP), as well as perivascular deposition of immunoglobulins and activation of complement even within lesions with a relative preservation of myelin. In support of these pathological findings, GFAP levels in the cerebrospinal fluid (CSF) during acute NMO exacerbations were found to be remarkably elevated in contrast to MS where CSF-GFAP levels did not substantially differ from controls. Additionally, recent experimental studies showed that AQP4 antibody is pathogenic, resulting in selective astrocyte destruction and dysfunction in vitro, ex vivo and in vivo. These findings strongly suggest that NMO is an autoimmune astrocytopathy where damage to astrocytes exceeds both myelin and neuronal damage. This chapter will review recent neuropathological studies that have provided novel insights into the pathogenic mechanisms, cellular targets, as well as the spectrum of tissue damage in NMO.

Neuromyelitis optica: clinical features, immunopathogenesis and treatment

The term 'neuromyelitis optica' ('Devic's syndrome', NMO) refers to a syndrome characterized by optic neuritis and myelitis. In recent years, the condition has raised enormous interest among scientists and clinical neurologists, fuelled by the detection of a specific serum immunoglobulin (Ig)G reactivity (NMO-IgG) in up to 80% of patients with NMO. These autoantibodies were later shown to target aquaporin-4 (AQP4), the most abundant water channel in the central nervous system (CNS). Here we give an up-to-date overview of the clinical and paraclinical features, immunopathogenesis and treatment of NMO. We discuss the widening clinical spectrum of AQP4-related autoimmunity, the role of magnetic resonance imaging (MRI) and new diagnostic means such as optical coherence tomography in the diagnosis of NMO, the role of NMO-IgG, T cells and granulocytes in the pathophysiology of NMO, and outline prospects for new and emerging therapies for this rare, but often devastating condition.

Biology of AQP4 and anti-AQP4 antibody: therapeutic implications for NMO

The water channel aquaporin-4 (AQP4) is the target of the immunoglobulin G autoantibody (AQP4-IgG) in neuromyelitis optica (NMO). AQP4 is expressed in foot processes of astrocytes throughout the central nervous system, as well as in skeletal muscle and epithelial cells in kidney, lung and gastrointestinal organs. Phenotype analysis of AQP4 knockout mice indicates the involvement of AQP4 in water movement into and out of the brain, astrocyte migration, glial scar formation and neuroexcitatory phenomena. AQP4 monomers form tetramers in membranes, which further aggregate to form supramolecular assemblies called orthogonal arrays of particles. AQP4-IgG is pathogenic in NMO by a mechanism involving complement- and cell-mediated astrocyte cytotoxicity, which produces an inflammatory response with oligodendrocyte injury and demyelination. AQP4 orthogonal arrays are crucial in NMO pathogenesis, as they increase AQP4-IgG binding to AQP4 and greatly enhance complement-dependent cytotoxicity. Novel NMO therapeutics are under development that target AQP4-IgG or AQP4, including aquaporumab monoclonal antibodies and small molecules that block AQP4-IgG binding to AQP4, and enzymatic inactivation strategies to neutralize AQP4-IgG pathogenicity.

Immunopathogenesis of neuromyelitis optica

Neuromyelitis optica (NMO, Devic's syndrome) is a clinical syndrome characterized by optic neuritis and (mostly longitudinally extensive) myelitis. If untreated, NMO usually takes a relapsing course and often results in blindness and tetra- or paraparesis. The discovery of autoantibodies to aquaporin-4, the most abundant water channel in the CNS, in 70-80% of patients with NMO (termed NMO-IgG or AQP4-Ab) and subsequent investigations into the pathogenic impact of this new reactivity have led to the recognition of NMO as an autoimmune condition and as a disease entity in its own right, distinct from classic multiple sclerosis. Here, we comprehensively review the current knowledge on the role of NMO-IgG/AQP4-Ab, B cells, T cells, and the innate immune system in the pathogenesis of NMO.

Neuromyelitis optica pathology in rats following intraperitoneal injection of NMO-IgG and intracerebral needle injury

Introduction

Animal models of neuromyelitis optica (NMO) are needed for drug testing and evaluation of NMO disease pathogenesis mechanisms.

Results

We describe a novel passive-transfer model of NMO in which rats made seropositive for human anti-aquaporin-4 (AQP4) immunoglobulin G antibody (NMO-IgG) by intraperitoneal (IP) injections were subject to intracerebral needle injury. Following a single IP injection, NMO-IgG distributed rapidly to peripheral AQP4-expressing cells (kidney collecting duct, gastric glands, airways, skeletal muscle) and area postrema in brain, but not elsewhere in the central nervous system; however, no pathology was seen in brain, spinal cord, optic nerve or peripheral tissues. After testing various maneuvers to produce NMO-IgG-dependent pathology in brain, we found that transient puncture of brain parenchyma with a 28-gauge needle in NMO-IgG seropositive rats produced robust NMO pathology around the needle track, with loss of AQP4 and glial fibrillary acidic protein, granulocyte and macrophage infiltration, centrovascular deposition of activated complement, and blood–brain barrier disruption, with demyelination by 5 days. Pathology was not seen in rats receiving control (non-NMO) human IgG or in NMO-IgG-seropositive rats made complement-deficient by cobra venom factor. Interestingly, at 1 day a reversible, multifocal astrocytopathy was seen with loss of AQP4 and GFAP (but not myelin) in areas away from the needle track.

Conclusions

NMO-IgG-seropositivity alone is not sufficient to cause NMO pathology in rats, but a single intracerebral needle insertion, without pre-existing inflammation or infusion of pro-inflammatory factors, was sufficient to produce robust NMO pathology in seropositive rats.

Autocrine MMP-2/9 secretion increases the BBB permeability in neuromyelitis optica

OBJECTIVE

Pathological breakdown of the blood-brain barrier (BBB) is thought to constitute the beginning of the disease process in neuromyelitis optica (NMO). In the current study, we investigated possible molecular mechanisms responsible for the breakdown of BBB using NMO sera.

METHODS

We analysed the effects of sera obtained from anti-aquaporin 4 (AQP4) antibody-positive NMO spectrum disorder (NMOSD) patients, multiple sclerosis (MS) patients and control subjects on the production of claudin-5, matrix-metalloproteinases (MMPs)-2/9, and vascular cell adhesion protein-1 (VCAM-1) in human brain microvascular endothelial cells (BMECs). We also examined whether immunoglobulin G (IgG) purified from NMOSD sera influences the claudin-5 or VCAM-1 protein expression.

RESULTS

The disturbance of BBB properties in BMECs following exposure to NMOSD sera was restored after adding the MMP inhibitor, GM6001. The secretion of MMP-2/9 by BMECs significantly increased after applying the NMOSD sera. The sera from NMOSD patients also increased both the MMP-2/9 secretion and the VCAM-1 protein level by BMECs. The IgG purified from NMOSD sera did not influence the BBB properties or the amount of MMP-2/9 proteins, although it did increase the amount of VCAM-1 proteins in BMECs. Reduction in anti-AQP4 antibody titre was not correlated with a reduction in VCAM-1 expression.

CONCLUSIONS

The autocrine secretion of MMP-2/9 by BMECs induced by humoral factors, other than IgG, in sera obtained from NMOSD patients potentially increases BBB permeability. IgG obtained from NMOSD sera, apart from anti-AQP4 antibodies, affect the BBB by upregulating VCAM, thereby facilitating the entry of inflammatory cells into the central nervous system.

Unique neuromyelitis optica pathology produced in naïve rats by intracerebral administration of NMO-IgG

Animal models of neuromyelitis optica (NMO) are needed for elucidation of disease mechanisms and for testing new therapeutics. Prior animal models of NMO involved administration of human anti-aquaporin-4 immunoglobulin G antibody (NMO-IgG) to rats with pre-existing neuroinflammation, or to naïve mice supplemented with human complement. We report here the development of NMO pathology following passive transfer of NMO-IgG to naïve rats. A single intracerebral infusion of NMO-IgG to adult Lewis rats produced robust lesions around the needle track in 100 % of rats; at 5 days there was marked loss of aquaporin-4 (AQP4), glial fibrillary acidic protein (GFAP) and myelin, granulocyte and macrophage infiltration, vasculocentric complement deposition, blood-brain barrier disruption, microglial activation and neuron death. Remarkably, a distinct 'penumbra' was seen around lesions, with loss of AQP4 but not of GFAP or myelin. No lesions or penumbra were seen in rats receiving control IgG. The size of the main lesion with loss of myelin was greatly reduced in rats made complement-deficient by cobra venom factor or administered NMO-IgG lacking complement-dependent cytotoxicity (CDC) effector function. However, the penumbra was seen under these conditions, suggesting a complement-independent pathogenesis mechanism. The penumbra was absent with NMO-IgG lacking both CDC and antibody-dependent cellular cytotoxicity (ADCC) effector functions. Finally, lesion size was significantly reduced after macrophage depletion with clodronate liposomes. These results: (i) establish a robust, passive-transfer model of NMO in rats that does not require pre-existing neuroinflammation or complement administration; (ii) implicate ADCC as responsible for a unique type of pathology also seen in human NMO; and (iii) support a pathogenic role of macrophages in NMO.

Autoimmune epilepsies

In patients with immune-associated disorders of the gray central nervous system matter (including recurrent seizures), antibodies against intracellular antigens have been discovered since the 1980s/1990s. In recent years, new antibodies against surface antigens have also been discovered. In two respects, these antibodies are even more interesting than the ones to intracellular antigens as, first, they promise a better response to immunotherapy; and, second, these antibodies contribute greatly to the understanding of the disease mechanisms. Whereas in encephalitides with antibodies against intracellular antigens, a cytotoxic T-cell-mediated response seems to be responsible for neuronal cell loss, in encephalitides with autoantibodies against surface antigens these antibodies are probably the relevant pathogenic agents in the associated disease conditions. On the one hand, antibodies to the NR1 subunit of N-methyl-D-aspartate receptors have been suggested to cause internalization and loss of these receptors without any cell destruction. This mechanism can explain the reversible functional effects caused by these antibodies. On the other hand, antibody- and complement-mediated destructive, and the irreversible effects of antibodies against the voltage-gated potassium channel antigens have been noted. These emerging findings make it plausible that immunological therapies, preferably early after characterization of the antibodies, offer opportunities to restore the health of affected patients.

Acute disseminated encephalomyelitis, transverse myelitis, and neuromyelitis optica

PURPOSE OF REVIEW

This review defines current clinical criteria for diagnosis, differential diagnosis, and clinical evaluation of acute disseminated encephalomyelitis, transverse myelitis, and neuromyelitis optica, and summarizes principles of treatment.

RECENT FINDINGS

Consensus criteria for transverse myelitis and acute disseminated encephalomyelitis have been proposed. A specific biomarker, aquaporin-4 autoantibody, has been discovered for neuromyelitis optica that allows for early and accurate diagnosis even in the absence of cardinal findings of optic neuritis and myelitis. The antibody is pathogenic and is facilitating an understanding of the pathophysiology of neuromyelitis optica and development of antigen-specific treatments.

SUMMARY

Clinical and radiologic findings combined with serologic findings may permit classification of syndromes of transverse myelitis and acute disseminated encephalomyelitis in ways that may predict risk of relapse, type of relapse, and prognosis. Treatment, especially to prevent relapse, is dependent on the specific disease context in which syndromes such as transverse myelitis occur.

Neuromyelitis optica (Devic's syndrome)

Neuromyelitis optica (NMO) is an inflammatory demyelinating disease of the central nervous system that selectively targets the optic nerve and spinal cord, although it may also target certain areas of the brain. The majority of cases are associated with relapses. A specific biomarker, an autoantibody that targets aquaporin-4, is present in the majority of patients and facilitates the diagnosis. Detection of this biomarker in serum has enabled recognition of an expanded spectrum of clinical disorders that previously would not have met diagnostic criteria for NMO. Aquaporin-4 IgG1 autoantibodies are pathogenic and produce lesions of the brain when injected intracerebrally or systemically. The clinical course of NMO is dominated by acute attacks. Progressive worsening of disability, as occurs in prototypic multiple sclerosis, is distinctly unusual. Corticosteroids and plasma exchange are useful for management of acute attacks. Several treatments used to prevent attacks of multiple sclerosis are ineffective in this condition; effective immunotherapies include azathioprine, mycophenolate mofetil and rituximab.

Connexin 43 astrocytopathy linked to rapidly progressive multiple sclerosis and neuromyelitis optica

BACKGROUND

Multiple sclerosis (MS) and neuromyelitis optica (NMO) occasionally have an extremely aggressive and debilitating disease course; however, its molecular basis is unknown. This study aimed to determine a relationship between connexin (Cx) pathology and disease aggressiveness in Asian patients with MS and NMO.

METHODS/PRINCIPAL FINDINGS

Samples included 11 autopsied cases with NMO and NMO spectrum disorder (NMOSD), six with MS, and 20 with other neurological diseases (OND). Methods of analysis included immunohistochemical expression of astrocytic Cx43/Cx30, oligodendrocytic Cx47/Cx32 relative to AQP4 and other astrocytic and oligodendrocytic proteins, extent of demyelination, the vasculocentric deposition of complement and immunoglobulin, and lesion staging by CD68 staining for macrophages. Lesions were classified as actively demyelinating (n=59), chronic active (n=58) and chronic inactive (n=23). Sera from 120 subjects including 30 MS, 30 NMO, 40 OND and 20 healthy controls were examined for anti-Cx43 antibody by cell-based assay. Six NMO/NMOSD and three MS cases showed preferential loss of astrocytic Cx43 beyond the demyelinated areas in actively demyelinating and chronic active lesions, where heterotypic Cx43/Cx47 astrocyte oligodendrocyte gap junctions were extensively lost. Cx43 loss was significantly associated with a rapidly progressive disease course as six of nine cases with Cx43 loss, but none of eight cases without Cx43 loss regardless of disease phenotype, died within two years after disease onset (66.7% vs. 0%, P=0.0090). Overall, five of nine cases with Cx43 loss and none of eight cases without Cx43 loss had distal oligodendrogliopathy characterized by selective myelin associated glycoprotein loss (55.6% vs. 0.0%, P=0.0296). Loss of oligodendrocytic Cx32 and Cx47 expression was observed in most active and chronic lesions from all MS and NMO/NMOSD cases. Cx43-specific antibodies were absent in NMO/NMOSD and MS patients.

CONCLUSIONS

These findings suggest that autoantibody-independent astrocytic Cx43 loss may relate to disease aggressiveness and distal oligodendrogliopathy in both MS and NMO.

Passively transferred human NMO-IgG exacerbates demyelination in mouse experimental autoimmune encephalomyelitis

BACKGROUND

Neuromyelitis optica (NMO) is a devastating inflammatory disorder of the optic nerves and spinal cord characterized by frequently recurring exacerbations of humoral inflammation. NMO is associated with the highly specific NMO-IgG biomarker, an antibody that binds the aquaporin-4 water channel. Aquaporin-4 is present on glial endfeet in the central nervous system (CNS). In humans, the NMO-IgG portends more frequent exacerbations and a worse long-term clinical outcome.

METHODS

We tested the longer-term outcome of mice with EAE injected with NMO-IgG and followed them for 60 days. Clinical exams and pathology of the spinal cord and optic nerves were compared to mice that received control human IgG.

RESULTS

Passively transferred human NMO-IgG leads to more severe neurology disability over two months after onset of disease. Clinical worsening is associated with an increased concentration of large demyelinating lesions primarily to subpial AQP4-rich regions of the spinal cord.

CONCLUSIONS

NMO-IgG is pathogenic in the context of EAE in mice.

Aquaporin 4 molecular mimicry and implications for neuromyelitis optica

Neuromyelitis optica (NMO) is associated with antibodies to aquaporin 4 (AQP4). We hypothesized that antibodies to AQP4 can be triggered by exposure to environmental proteins. We compared human AQP4 to plant and bacterial proteins to investigate the occurrence of significantly similar structures and sequences. High similarity to a known epitope for NMO-IgG, AQP4(207-232), was observed for corn ZmTIP4-1. NMO and non-NMO sera were assessed for reactivity to AQP4(207-232) and the corn peptide. NMO patient serum showed reactivity to both peptides as well as to plant tissue. These findings warrant further investigation into the role of the environment in NMO etiology.

Myelin oligodendrocyte glycoprotein induces aquaporin-4 autoantibodies in mouse experimental autoimmune encephalomyelitis

To investigate whether AQP4 autoantibodies (AQP4-Ab) are causative for neuromyelitis optica (NMO), the production of AQP4-Ab and clinical experimental autoimmune encephalomyelitis (EAE) was investigated in mice administered with mouse AQP4 antigen or myelin oligodendrocyte glycoprotein (MOG35-55) alone, and in combination. Eight- to twelve-week-old female C57BL/6 mice were randomly immunized with encephalitogenic mixture containing 300 μg of MOG35-55 or AQP4 antigen alone, and in combination in complete Freund's adjuvant supplemented with H37Ra M. tuberculosis. The incidence of EAE, Weaver 15 scores, and body weight was evaluated. ELISA was used to detect serum mouse AQP4-Ab. Mice injected with MOG35-55 and MOG33-35 plus AQP4 antigen began to show EAE symptoms 12 days after immunization. The incidence of EAE was 91.6%, and 62.5%, for MOG35-55 alone and MOG33-35 plus AQP4 antigen groups, respectively, while AQP4 antigen alone didn't develop EAE. In all but the control group, serum AQP4-Ab levels were increased, and correlated positively with Weaver 15 score (rs=0.713, p=0.000) and negatively with body weight changes (rs=-0.415, p=0.011). Injection of human NMO sera positive for AQP4-Ab exacerbated MOG-induced EAE. Our results suggest that AQP4-Ab can be produced in MOG-induced MS model, and itself is not sufficient for the development of EAE, implying that NMO might be a subtype or transition from MS.

Neuromyelitis optica preceded by hyperCKemia and a possible association with coxsackie virus group A10 infection

We report the case of a 48-year-old woman presenting with an elevated serum creatine kinase level (hyperCKemia) associated with an initial attack of neuromyelitis optica (NMO). The patient initially showed general fatigue with fever. Laboratory findings showed hyperCKemia and subsequently she developed a slight weakness of both lower limbs and reduced vision. Autoantibodies against aquaporin 4 were found in her serum, and a retrospective examination of viral titers indicated a possible coxsackie virus group A10 infection. The present case suggests that hyperCKemia-mediated disease onset is involved in some patients with NMO, and furthermore, it may be related to muscular destruction associated with viral infection.