AChR-specific immunosuppressive therapy of myasthenia gravis

Vaccines and myasthenia gravis: a comprehensive review and retrospective study of SARS-CoV-2 vaccination in a large cohort of myasthenic patients

Introduction

Myasthenia gravis (MG) is an autoimmune disease, for which the risk of exacerbation after vaccines is debated. The aim of this study is to review the available literature concerning safety and efficacy of vaccines in MG. In addition, we also conducted a retrospective research of MG exacerbations and new onset MG after anti-SARS-CoV-2 vaccination in a large cohort of patients.

Methods

A study of the available literature regarding vaccines and MG was carried out through research in the online database “Pubmed”. We also retrospectively collected data from 80 MG patients, who were followed at the Treviso Hospital and completed an anti-SARS-CoV-2 vaccination cycle. For each patient, we recorded MG exacerbations between first and second doses and within a window period of 1 day – 6 weeks after the second dose.

Results

We found 26 relevant articles about influenza, SARS-CoV-2 and other vaccines. No clear associations between most vaccines and MG exacerbations were found. Moreover, cases of new onset post-vaccine MG are mostly anecdotal, except for Japanese encephalitis virus vaccine. Concerning our cohort, 4/80 (5%) MG patients experienced an exacerbation within the post-vaccine window period. In addition, we report a case of new onset post-vaccine MG.

Discussion

Inactivated and subunit vaccines are safe and effective in MG. Although some of them, such as anti-SARS-CoV-2 vaccine, might uncommonly cause MG exacerbations, data from our review suggest that benefits still outweigh by far the potential risks, thus they should be recommended to these patients. Nevertheless, large prospective studies are needed for further investigations.

Receptor clustering and pathogenic complement activation in myasthenia gravis depend on synergy between antibodies with multiple subunit specificities

Myasthenia gravis is an autoimmune disorder defined by muscle weakness and fatigability associated with antibodies against proteins of the neuromuscular junction (NMJ). The most common autoantibody target is the acetylcholine receptor (AChR). Three mechanisms have been postulated by which autoantibodies might interfere with neurotransmission: direct antagonism of the receptor, complement-mediated destruction of the postsynaptic membrane, and enhanced internalization of the receptor. It is very likely that more than one of these mechanisms act in parallel. Dissecting the mechanisms of autoantibody-mediated pathology requires patient-derived, monoclonal antibodies. Using membrane antigen capture activated cell sorting (MACACS), we isolated AChR-specific B cells from patients with myasthenia gravis, and produced six recombinant antibodies. All AChR-specific antibodies were hypermutated, including isotypes IgG₁, IgG₃, and IgG₄, and recognized different subunits of the AChR. Despite clear binding, none of the individual antibodies showed significant antagonism of the AChR measured in an in vitro neuromuscular synapse model, or AChR-dependent complement activation, and they did not induce myasthenic signs in vivo. However, combinations of antibodies induced strong complement activation in vitro, and severe weakness in a passive transfer myasthenia gravis rat model, associated with NMJ destruction and complement activation in muscle. The strongest complement activation was mediated by combinations of antibodies targeting disparate subunits of the AChR, and such combinations also induced the formation of large clusters of AChR on the surface of live cells in vitro. We propose that synergy between antibodies of different epitope specificities is a fundamental feature of this disease, and possibly a general feature of complement-mediated autoimmune diseases. The importance of synergistic interaction between antibodies targeting different subunits of the receptor can explain the well-known discrepancy between serum anti-AChR titers and clinical severity, and has implications for therapeutic strategies currently under investigation.

Clinical Efficacy and Safety of Eculizumab for Treating Myasthenia Gravis

Myasthenia gravis (MG) is an autoimmune disease primarily mediated by acetylcholine receptor antibodies (AChR-Ab), cellular immune dependence, and complement system involvement. Since the AChR on the postsynaptic membrane is destroyed by an immune attack, sufficient endplate potential cannot be generated, resulting in the development of a synaptic transmission disorder at the neuromuscular junction and in muscle weakness. The role of the complement system in MG has been demonstrated in animal models and clinical tests, and it has been determined that complement inhibition in patients with MG can prevent disease induction and reverse its progression. Eculizumab is a humanized monoclonal antibody that inhibits the cleavage of complement protein C5 and prevents autoimmune damage; additionally, it has received subsequent approval by the Federal Drug Administration of the United States for MG treatment. However, various concerns regarding the use of eculizumab persist. In this review, we have discussed the treatment time, cost effectiveness, long-term efficacy, and tolerability of eculizumab for MG treatment. We have also summarized historical information and have presented perspectives on this new therapeutic modality.

Clinical features and outcome of acquired myasthenia gravis in 94 dogs

Background

Factors known to be associated with outcome of acquired myasthenia gravis (MG) in dogs are limited.

Hypothesis/Objectives

Of dogs with MG, advancing age and comorbid neoplasia are associated with poor long‐term prognosis and low rates of remission.

Animals

Ninety‐four client‐owned dogs with MG diagnosed by acetylcholine receptor antibody (AChR Ab) assay between 2001 and 2019 from a university clinic and 3 private clinics in the United States.

Methods

Cases were retrospectively evaluated and data were collected to determine clinical signs, treatment, and response to therapy defined by means of a clinical scoring rubric. Immunological remission was defined as a return of the AChR Ab concentration to <0.6 nmol/L. Multivariable binary logistic regression analysis was used to identify clinical criteria predicting remission.

Results

An anticholinesterase drug was used to treat 90/94 (96%) dogs, which in 63/94 (67%) was the sole treatment; other drugs included immune modulators. Clinical remission (lack of clinical signs ≥4 weeks after treatment cessation) was observed in 29 (31% [95% confidence interval (CI): 22.4‐40.8%]) dogs, clinical response (lack of clinical signs on treatment) in 14 (15% [95% CI: 9.0‐23.6%]) dogs, clinical improvement (on treatment) in 24 (26% [95% CI: 17.8‐35.2%]) dogs, and no clinical improvement in 27 (29% [95% CI: 20.5‐38.6%]) dogs. Immunological remission was observed in 27/46 (59%) dogs, with clinical remission in all 27. Younger age (P = .04) and comorbid endocrine disease (P = .04) were associated with clinical remission. Initial AChR Ab concentration (P = .02) and regurgitation (P = .04) were negatively associated with clinical remission.

Conclusions and Clinical Importance

Clinical remission in MG is less likely in older dogs and dogs presenting with regurgitation or high initial AChR Ab concentration, but more likely in younger dogs and dogs with comorbid endocrine disease.

The mitochondrial biogenesis signaling pathway is a potential therapeutic target for myasthenia gravis via energy metabolism (Review)

Myasthenia gravis (MG) is an autoantibody-mediated autoimmune disease that is characterized by muscle weakness and fatigue. Traditional treatments for MG target the neuromuscular junction (NMJ) or the immune system. However, the efficacy of such treatments is limited, and novel therapeutic options for MG are urgently required. In the current review, a new therapeutic strategy is proposed based on the mitochondrial biogenesis and energy metabolism pathway, as stimulating mitochondrial biogenesis and the energy metabolism might alleviate myasthenia gravis. A number of cellular sensors of the energy metabolism were investigated, including AMP-activated protein kinase (AMPK) and sirtuin 1 (SIRT1). AMPK and SIRT1 are sensors that regulate cellular energy homeostasis and maintain energy metabolism by balancing anabolism and catabolism. Peroxisome proliferator-activated receptor γ coactivator 1α and its downstream transcription factors nuclear respiratory factors 1, nuclear respiratory factors 2, and transcription factor A are key sensors of mitochondrial biogenesis, which can restore mitochondrial DNA and produce new mitochondria. These processes help to control muscle contraction and relieve the symptoms of MG, including muscle weakness caused by dysfunctional NMJ transmission. Therefore, the present review provides evidence for the therapeutic potential of targeting mitochondrial biogenesis for the treatment of MG.

Myasthenia Gravis: Autoantibody Specificities and Their Role in MG Management

Myasthenia gravis (MG) is the most common autoimmune disorder affecting the neuromuscular junction, characterized by skeletal muscle weakness and fatigability. It is caused by autoantibodies targeting proteins of the neuromuscular junction; ~85% of MG patients have autoantibodies against the muscle acetylcholine receptor (AChR-MG), whereas about 5% of MG patients have autoantibodies against the muscle specific kinase (MuSK-MG). In the remaining about 10% of patients no autoantibodies can be found with the classical diagnostics for AChR and MuSK antibodies (seronegative MG, SN-MG). Since serological tests are relatively easy and non-invasive for disease diagnosis, the improvement of methods for the detection of known autoantibodies or the discovery of novel autoantibody specificities to diminish SN-MG and to facilitate differential diagnosis of similar diseases, is crucial. Radioimmunoprecipitation assays (RIPA) are the staple for MG antibody detection, but over the past years, using cell-based assays (CBAs) or improved highly sensitive RIPAs, it has been possible to detect autoantibodies in previously SN-MG patients. This led to the identification of more patients with antibodies to the classical antigens AChR and MuSK and to the third MG autoantigen, the low-density lipoprotein receptor-related protein 4 (LRP4), while antibodies against other extracellular or intracellular targets, such as agrin, K_v1.4 potassium channels, collagen Q, titin, the ryanodine receptor and cortactin have been found in some MG patients. Since the autoantigen targeted determines in part the clinical manifestations, prognosis and response to treatment, serological tests are not only indispensable for initial diagnosis, but also for monitoring treatment efficacy. Importantly, knowing the autoantibody profile of MG patients could allow for more efficient personalized therapeutic approaches. Significant progress has been made over the past years toward the development of antigen-specific therapies, targeting only the specific immune cells or autoantibodies involved in the autoimmune response. In this review, we will present the progress made toward the development of novel sensitive autoantibody detection assays, the identification of new MG autoantigens, and the implications for improved antigen-specific therapeutics. These advancements increase our understanding of MG pathology and improve patient quality of life by providing faster, more accurate diagnosis and better disease management.

The correlation of neutrophil-to-lymphocyte ratio with the presence and short-time curative effect of myasthenia gravis in children: a retrospectively study

OBJECTIVES

This study aimed to investigate the influence of neutrophil-to-lymphocyte ratio (NLR) on the severity and short-time curative effect of myasthenia gravis (MG) in children.

METHODS

Data of 132 MG children were retrospectively analyzed, and data of 140 healthy controls (HC group) in the same period were collected. The data of both groups were compared and analyzed.

RESULTS

NLR of MG group was significantly higher than that of HC group (Z = 2.644, p = 0.008). According to NLR level, patients were divided into 3 groups: N1 (NLR < 1.03), N2 (NLR 1.03-2.17), and N3 (NLR > 2.17). Significant differences in white blood cell counts, course of disease, uric acid, albumin and the time of hospital stay among the 3 groups were observed (p < 0.05, 0.01). The results of logistic regression revealed that NLR (adjusted OR = 3.874, 95% CI 1.359-11.045, p = 0.011) was the risk factor of MG, and it was risk factor of higher QMG during admission (adjusted OR = 2.989, 95% CI 1.247-7.160, p = 0.014) as well. Using the NLR level for the MG diagnostic test, the area under the receiver operating characteristic (ROC) curve was 0.765 [95%CI (0.710-0.820), p = 0.000], with a cut-off value of 1.39, sensitivity of 0.833, and specificity of 0.479. Cox regression analysis suggested that NLR (N1: Wald = 9.262, p = 0.010, N2: HR = 12.267, 95%CI 2.432-61.863, p = 0.000, and N3: HR = 8.142, 95%CI 1.209-77.754, p = 0.032) was associated with poor efficacy at discharge. Elevated NLR was considered as an independent risk factor of poor outcomes during discharge.

CONCLUSION

NLR could reflect disease severity and short time curative effect in children with MG to some extent. It may also be a potential marker in indicating diagnosis and severity of MG in children.

Effects of Mitophagy on Regulatory T Cell Function in Patients With Myasthenia Gravis

Objective: This study was conducted to determine whether regulatory T cells (CD4⁺CD25⁺T, Tregs) show abnormal mitophagy as well as the function of Tregs in patients with myasthenia gravis (MG).

Methods: CD4⁺T cells and CD4⁺CD25⁺Treg cells were obtained from 15 patients with MG (MG group) and 15 controls (N group). Tregs from the MG group were subjected to rapamycin-induced culture for 48 h (Rapa group) and 3-methyladenine-induced culture for 48 h (3-MA group). The levels of mitophagy in Tregs were then observed through electron and confocal microscopy. Expression of the autophagy-related protein LC3-II was detected by western blotting, and mitochondrial function in each group was evaluated by flow cytometry. Inhibition of Treg cell proliferation was detected by flow cytometry.

Results: Mitophagy in the MG group was lower than that in the N group; it was higher in the Rapa group compared to that in the MG group and lowered in the 3-MA group than in the MG group. Expression of the autophagy-related protein LC3-II was lower in the MG group than in the N group, higher in the Rapa group than in the MG group, and lower in the 3-MA group than in the MG group. The mitochondrial membrane potential was lower in the MG group compared to that in the N group; it was higher in the Rapa group than in the MG group and lowered in the 3-MA group than in the MG group. Inhibition of Treg proliferation was lower in the MG group than in the N group; it was higher in the Rapa group than in the MG group and lowered in the 3-MA group than in the MG group.

Conclusion: The decreased mitochondrial membrane potential and mitophagy in Tregs in the MG group may be related to a decreased inhibition of Treg proliferation. The mitochondrial membrane potential was increased after adding the autophagy agent Rapa to enhance mitophagy, and the proliferation inhibition function of Tregs was also enhanced. The autophagy agent 3-MA down-regulated mitophagy, which decreased the mitochondrial membrane potential and inhibitory effect of Tregs. These results reveal the possible cellular immune mechanism of Treg dysfunction in MG.

Autoantibody Specificities in Myasthenia Gravis; Implications for Improved Diagnostics and Therapeutics

Myasthenia gravis (MG) is an autoimmune disease characterized by muscle weakness and fatiguability of skeletal muscles. It is an antibody-mediated disease, caused by autoantibodies targeting neuromuscular junction proteins. In the majority of patients (~85%) antibodies against the muscle acetylcholine receptor (AChR) are detected, while in 6% antibodies against the muscle-specific kinase (MuSK) are detected. In ~10% of MG patients no autoantibodies can be found with the classical diagnostics for AChR and MuSK antibodies (seronegative MG, SN-MG), making the improvement of methods for the detection of known autoantibodies or the discovery of novel antigenic targets imperative. Over the past years, using cell-based assays or improved highly sensitive immunoprecipitation assays, it has been possible to detect autoantibodies in previously SN-MG patients, including the identification of the low-density lipoprotein receptor-related protein 4 (LRP4) as a third MG autoantigen, as well as AChR and MuSK antibodies undetectable by conventional methods. Furthermore, antibodies against other extracellular or intracellular targets, such as titin, the ryanodine receptor, agrin, collagen Q, K_v1.4 potassium channels and cortactin have been found in some MG patients, which can be useful biomarkers. In addition to the improvement of diagnosis, the identification of the patients' autoantibody specificity is important for their stratification into respective subgroups, which can differ in terms of clinical manifestations, prognosis and most importantly their response to therapies. The knowledge of the autoantibody profile of MG patients would allow for a therapeutic strategy tailored to their MG subgroup. This is becoming especially relevant as there is increasing progress toward the development of antigen-specific therapies, targeting only the specific autoantibodies or immune cells involved in the autoimmune response, such as antigen-specific immunoadsorption, which have shown promising results. We will herein review the advances made by us and others toward development of more sensitive detection methods and the identification of new antibody targets in MG, and discuss their significance in MG diagnosis and therapy. Overall, the development of novel autoantibody assays is aiding in the more accurate diagnosis and classification of MG patients, supporting the development of advanced therapeutics and ultimately the improvement of disease management and patient quality of life.

Intensive Care Management of the Neuromuscular Patient

Neuromuscular emergencies are a distinct group of acute neurological diseases with distinct characteristic presentations. Patients who suffer from this group of diseases are at immediate risk of losing protection of their native airway as well as aspirating orogastric contents. This is secondary to weakness of the muscles of the oropharynx and respiratory muscles. Although some neuromuscular emergencies such as myasthenia gravis or Guillain-Barré syndrome are well understood, others such as critical illness myopathy and neuropathy are less well characterized. In this chapter, we have discussed the pathophysiology, diagnostic evaluation, and management options in patients who are admitted to the intensive care unit. We have also emphasized the importance of a thorough understanding of the use of pharmacological anesthetic agents in this patient population.

Advances in autoimmune myasthenia gravis management

INTRODUCTION

Myasthenia gravis (MG) is an autoimmune neuromuscular disorder with no cure and conventional treatments limited by significant adverse effects and variable benefit. In the last decade, therapeutic development has expanded based on improved understanding of autoimmunity and financial incentives for drug development in rare disease. Clinical subtypes exist based on age, gender, thymic pathology, autoantibody profile, and other poorly defined factors, such as genetics, complicate development of specific therapies. Areas covered: Clinical presentation and pathology vary considerably among patients with some having weakness limited to the ocular muscles and others having profound generalized weakness leading to respiratory insufficiency. MG is an antibody-mediated disorder dependent on autoreactive B cells which require T-cell support. Treatments focus on elimination of circulating autoantibodies or inhibition of effector mechanisms by a broad spectrum of approaches from plasmapheresis to B-cell elimination to complement inhibition. Expert commentary: Standard therapies and those under development are disease modifying and not curative. As a rare disease, clinical trials are challenged in patient recruitment. The great interest in development of treatments specific for MG is welcome, but decisions will need to be made to focus on those that offer significant benefits to patients.

Treatment of experimental autoimmune myasthenia gravis rats with FTY720 and its effect on Th1/Th2 cells

Myasthenia gravis (MG) is an autoimmune neurological disease that is characterized by the expression of anti-acetylcholine receptor (AChR) antibodies. The immune response at AChRs of neuromuscular junction is disrupted in patients with MG, which manifests as skeletal muscle fatigue and is aggravated following periods of activity and alleviated following rest. Although a novel immune suppressant FTY720 drug, which exhibits strong immune suppression efficacy and minor adverse effects, is available, its role and mechanism in MG have not been elucidated. The aim of this study was to investigate the role of FTY720 in MG. A total of 60 healthy female Lewis rats were randomly assigned into 4 groups: Control group, Model group of experimental autoimmune myasthenia gravis (EAMG), 0.5 mg/kg FTY720-treatment EAMG group and 1.0 mg/kg FTY720‑treatment EAMG group. Body weight and symptoms were examined; Lennon score was used to evaluate improvement of clinical symptoms. Reverse transcription‑quantitative polymerase chain reaction and ELISA were used to test the mRNA and protein expression levels, respectively, of the helper T (Th)1 and Th2 cell cytokines, including interleukin (IL)‑2, interferon (IFN)‑γ, IL‑4 and IL‑6 in thymus tissue and serum. FTY720 treatment improved rat MG symptoms, increased body weight and decreased Lennon score. FTY720 treatments also reduced tissue and serum levels of IL‑2, IFN‑γ and IL‑6, but not IL‑4 expression levels. FTY720 suppressed the inflammatory response and improved EAMG symptoms by inhibiting the secretion of inflammatory factors.

Acetylcholine receptor-specific immunosuppressive therapy of experimental autoimmune myasthenia gravis and myasthenia gravis

Experimental autoimmune myasthenia gravis (EAMG) and myasthenia gravis (MG) are caused by autoantibodies to the extracellular domain of muscle nicotinic acetylcholine receptors (AChRs). Autoantibodies to the cytoplasmic domain of AChRs do not cause EAMG because they cannot bind AChRs in vivo. The ideal MG therapy would quickly and permanently suppress only the pathological autoimmune response to AChRs. We have developed a specific immunosuppressive therapy for EAMG that involves immunizing rats with bacterially expressed cytoplasmic domains of human muscle AChRs. Therapy prevents onset of chronic EAMG, rapidly suppresses ongoing EAMG, and is potent, robust, long lasting, and safe, because the therapeutic antigen cannot induce EAMG. The therapy was developed using incomplete Freund's adjuvant, but is likely to work equally well with alum adjuvants routinely used for human immunizations. Therapeutic mechanisms may involve a combination of antibody-mediated feedback suppression and regulatory T and/or B lymphocytes.

A Novel Approach to Reinstating Tolerance in Experimental Autoimmune Myasthenia Gravis Using a Targeted Fusion Protein, mCTA1-T146

Reinstating tissue-specific tolerance has attracted much attention as a means to treat autoimmune diseases. However, despite promising results in rodent models of autoimmune diseases, no established tolerogenic therapy is clinically available yet. In the experimental autoimmune myasthenia gravis (EAMG) model several protocols have been reported that induce tolerance against the prime disease-associated antigen, the acetylcholine receptor (AChR) at the neuromuscular junction. Using the whole AChR, the extracellular part or peptides derived from the receptor, investigators have reported variable success with their treatments, though, usually relatively large amounts of antigen has been required. Hence, there is a need for better formulations and strategies to improve on the efficacy of the tolerance-inducing therapies. Here, we report on a novel targeted fusion protein carrying the immunodominant peptide from AChR, mCTA1–T146, which given intranasally in repeated microgram doses strongly suppressed induction as well as ongoing EAMG disease in mice. The results corroborate our previous findings, using the same fusion protein approach, in the collagen-induced arthritis model showing dramatic suppressive effects on Th1 and Th17 autoaggressive CD4 T cells and upregulated regulatory T cell activities with enhanced IL10 production. A suppressive gene signature with upregulated expression of mRNA for TGFβ, IL10, IL27, and Foxp3 was clearly detectable in lymph node and spleen following intranasal treatment with mCTA1–T146. Amelioration of EAMG disease was accompanied by reduced loss of muscle AChR and lower levels of anti-AChR serum antibodies. We believe this targeted highly effective fusion protein mCTA1–T146 is a promising candidate for clinical evaluation in myasthenia gravis patients.

The correlation of neutrophil-to-lymphocyte ratio with the presence and activity of myasthenia gravis

Though the pathogenesis of myasthenia gravis (MG) is not fully understood, the role of inflammation has been well appreciated in the development of MG. We aimed to investigate the role of neutrophil-to-lymphocyte ratio (NLR) in MG patients and the relationship between the NLR and the activity of the disease. A total number of 172 MG patients and 207 healthy controls (HC) were enrolled in this study. The MG patients were divided into tertiles according to NLR (low NLR < 1.58, n = 57; intermediate NLR 1.58-2.33, n = 57 and high NLR > 2.33, n = 58). The disease activity assessment was performed according to the standard criteria established by the Myasthenia Gravis Foundation of America. Patients with MG had significantly higher NLR when compared with the HC group (P < 0.0001). The NLR levels were higher in the MG patients with severe disease activity than those with mild disease activity (P < 0.001), meanwhile, median NLR was statistically higher in MG patients with myasthenic crisis (MC) than those without MC (P < 0.001). Incidences of severe disease activity and MC were both higher in the high NLR group, compared to low and intermediate NLR groups (both P < 0.001). Multivariate logistic regression analysis suggested that elevated NLR was an independent predictor of severe disease activity (odds ratio = 13.201, CI% = 1.418-122.938, P = 0.023). These results indicate that NLR may be a simple and useful potential marker in indicating disease activity in patients with MG.

Mechanisms of Autoantibody-Induced Pathology

Autoantibodies are frequently observed in healthy individuals. In a minority of these individuals, they lead to manifestation of autoimmune diseases, such as rheumatoid arthritis or Graves' disease. Overall, more than 2.5% of the population is affected by autoantibody-driven autoimmune disease. Pathways leading to autoantibody-induced pathology greatly differ among different diseases, and autoantibodies directed against the same antigen, depending on the targeted epitope, can have diverse effects. To foster knowledge in autoantibody-induced pathology and to encourage development of urgently needed novel therapeutic strategies, we here categorized autoantibodies according to their effects. According to our algorithm, autoantibodies can be classified into the following categories: (1) mimic receptor stimulation, (2) blocking of neural transmission, (3) induction of altered signaling, triggering uncontrolled (4) microthrombosis, (5) cell lysis, (6) neutrophil activation, and (7) induction of inflammation. These mechanisms in relation to disease, as well as principles of autoantibody generation and detection, are reviewed herein.

Pemphigus

Pemphigus is a group of IgG-mediated autoimmune diseases of stratified squamous epithelia, such as the skin and oral mucosa, in which acantholysis (the loss of cell adhesion) causes blisters and erosions. Pemphigus has three major subtypes: pemphigus vulgaris, pemphigus foliaceus and paraneoplastic pemphigus. IgG autoantibodies are characteristically raised against desmoglein 1 and desmoglein 3, which are cell-cell adhesion molecules found in desmosomes. The sites of blister formation can be physiologically explained by the anti-desmoglein autoantibody profile and tissue-specific expression pattern of desmoglein isoforms. The pathophysiological roles of T cells and B cells have been characterized in mouse models of pemphigus and patients, revealing insights into the mechanisms of autoimmunity. Diagnosis is based on clinical manifestations and confirmed with histological and immunochemical testing. The current first-line treatment is systemic corticosteroids and adjuvant therapies, including immunosuppressive agents, intravenous immunoglobulin and plasmapheresis. Rituximab, a monoclonal antibody against CD20⁺ B cells, is a promising therapeutic option that may soon become first-line therapy. Pemphigus is one of the best-characterized human autoimmune diseases and provides an ideal paradigm for both basic and clinical research, especially towards the development of antigen-specific immune suppression treatments for autoimmune diseases.

Structural insights into the molecular mechanisms of myasthenia gravis and their therapeutic implications

The nicotinic acetylcholine receptor (nAChR) is a major target of autoantibodies in myasthenia gravis (MG), an autoimmune disease that causes neuromuscular transmission dysfunction. Despite decades of research, the molecular mechanisms underlying MG have not been fully elucidated. Here, we present the crystal structure of the nAChR α1 subunit bound by the Fab fragment of mAb35, a reference monoclonal antibody that causes experimental MG and competes with ~65% of antibodies from MG patients. Our structures reveal for the first time the detailed molecular interactions between MG antibodies and a core region on nAChR α1. These structures suggest a major nAChR-binding mechanism shared by a large number of MG antibodies and the possibility to treat MG by blocking this binding mechanism. Structure-based modeling also provides insights into antibody-mediated nAChR cross-linking known to cause receptor degradation. Our studies establish a structural basis for further mechanistic studies and therapeutic development of MG.

DOI:http://dx.doi.org/10.7554/eLife.23043.001

Myasthenia gravis is a disease that causes chronic weakness in muscles. It affects more than 20 in every 100,000 people and diagnosis is becoming more common due to increased awareness of the disease. However, most current treatments only temporarily relieve symptoms so there is a need to develop more effective therapies.

The disease occurs when the immune system produces molecules called antibodies that bind to and destroy a receptor protein called nAChR. This receptor is normally found at the junctions between nerve cells and muscle cells, and its destruction disrupts communication between the nervous system and the muscle. However, it is not known exactly how these antibodies bind to nAChR, partly due to the lack of a detailed three-dimensional structure of the antibodies and nAChR together.

The human nAChR protein is made up of several subunits, including one called alpha1 that is the primary target of Myasthenia gravis antibodies. Noridomi et al. used a technique known as X-ray crystallography to generate a highly detailed three-dimensional model of the structure of the alpha1 subunit with an antibody from rats that acts as in a similar way to human Myasthenia gravis antibodies. The structure reveals the points of contact between the antibodies and a core region of the nAChR alpha1 subunit and suggests that many different Myasthenia gravis antibodies may bind to nAChR in the same way.

These findings may aid the development of drugs that bind to and disable Myasthenia gravis antibodies to relieve the symptoms of the disease.

DOI:http://dx.doi.org/10.7554/eLife.23043.002

Serum uric acid levels in patients with myasthenia gravis are inversely correlated with disability

Uric acid (UA), the final product of purine metabolism, has been reported to be reduced in patients with various neurological disorders and is considered to be a possible indicator for monitoring the disability and progression of multiple sclerosis. However, it remains unclear whether there is a close relationship between UA and myasthenia gravis (MG), or whether UA is primarily deficient or secondarily reduced because of its peroxynitrite scavenging activity. We investigated the correlation between serum UA levels and the clinical characteristics of MG. We assessed 338 serum UA levels obtained in 135 patients with MG, 47 patients with multiple sclerosis, and 156 healthy controls. In addition, we compared serum UA levels when MG patients were stratified according to disease activity and classifications performed by the Myasthenia Gravis Foundation of America, age of onset, duration, and thymus histology (by means of MRI or computed tomography). MG patients had significantly lower serum UA levels than the controls (P<0.001). Moreover, UA levels in patients with MG were inversely correlated with disease activity and disease progression (P=0.013). However, UA levels did not correlate significantly with disease duration, age of onset, and thymus histology. Our findings suggest that serum level of UA was reduced in patients with MG and serum UA might be considered a surrogate biomarker of MG disability and progression.

Low serum albumin concentrations are associated with disease severity in patients with myasthenia gravis

Serum albumin (S-Alb) is a widely used biomarker of nutritional status and disease severity in patients with autoimmune diseases. We investigated the correlation between S-Alb and the severity of myasthenia gravis (MG).A total number of 166 subjects were recruited in the study. Subjects were divided into 3 groups (T1 to T3) by S-Alb levels: T1: 21.1 to 38.4 g/L, T2: 38.5 to 41.5 g/L, T3: 41.6 to 48.9 g/L. Regression analysis was performed to determine the correlation of initial albumin concentrations and the severity of disease of MG.Lower levels of S-Alb were observed in subjects with increased disease severity than those with slight disease severity, meanwhile, incidence of myasthenia crisis increased in the lower albumin tertiles (P < 0.001). The disease severity assessment was performed according to the criteria established by the Myasthenia Gravis Foundation of America. After adjusting for age, sex, body mass index (BMI), and duration of disease, it showed that higher S-Alb concentrations were associated with lower disease severity. Odds ratios (ORs) of T2 to T3 were 0.241 (95% CI: 0.103-0.566, P < 0.001), 0.140 (95% CI: 0.054-0.367, P < 0.001) when compared with subjects in the T1, respectively. When subjects were stratified into hypoalbuminemia and normal albumin groups, we found that the association between S-Alb and MG remained significant in the hypoalbuminemia group only (OR: 0.693, 95% CI: 0.550-0.874, P = 0.002) after further adjustment for age, sex, BMI, and duration of disease.This is the first study to demonstrate that S-Alb was independently associated with MG severity. In patients with low S-Alb, S-Alb concentration could be a potential biomarker for MG disability.