Acetylcholine Receptor In Myasthenia Gravis Research Articles

Efgartigimod in refractory autoimmune myasthenia gravis.

Efgartigimod, a neonatal Fc-receptor inhibitor, has recently been approved as treatment for myasthenia gravis (MG). In this retrospective cohort study, we aimed to systematically assess short- and long-term effectiveness of efgartigimod in patients with refractory MG. Sixteen patients with refractory autoimmune acetylcholine receptor MG were treated with efgartigimod. Data were collected from January 2021 to March 2023 on Myasthenia Gravis Activities of Daily Living (MG-ADL), Quantitative Myasthenia Gravis score (QMG), Myasthenia Gravis Composite score (MGC) and the 15-item revised version of the Myasthenia Gravis Quality of Life questionnaire (MG-QoL15r). A favorable outcome was seen in 56% of patients at the last measurement. Out of 16 patients, 50% were an MG-ADL responder after the first treatment cycle. After 4 weeks, a clinically meaningful improvement compared to baseline was seen on the MG-ADL, QMG, and MGC. There was a statistically significant improvement on the MGQoL15r from baseline to week 4. The improvement was maintained until the last measurement for the MGC and the MGQoL15r. At the last visit, all patients had discontinued 4-weekly dosages, shifting to administration frequencies of 1, 2, or 3 weeks. Drug doses could be decreased for prednisolone (n = 7), azathioprine (n = 2), and intravenous immunoglobulin (n = 9). Frequency of plasma exchange was decreased in nine patients. In patients with refractory MG, efgartigimod was effective for at least half of all patients. Patients required more frequent dosing compared to the ADAPT phase 3 trial. In 80% of the patients concurrent medication could be reduced or discontinued.

Markedly upregulated serum semaphorin 4A as a novel activity marker of myasthenia gravis.

Myasthenia gravis (MG) is an autoantibody-mediated disease of the neuromuscular junction. Semaphorin 4A (Sema4A) is involved in the activation of T cells in various inflammatory disorders. In this study, we aimed to investigate whether Sema4A is involved in the pathogenesis of MG. We measured serum Sema4A concentrations in 30 treatment-naïve MG patients with acetylcholine receptor (AChR) antibodies, 7 with muscle-specific tyrosine kinase (MuSK) antibodies and 21 normal controls. As a result, serum Sema4A levels were significantly higher in patients with AChR antibody-positive MG and MuSK antibody-positive MG than in controls (p ≤ 0.0001 for both MG groups). Serum Sema4A levels were correlated with AChR antibody levels (Spearman's ρ = 0.39, p = 0.03) and MG Foundation of America clinical classification classes (Spearman's ρ = 0.38, p = 0.04) in patients with AChR antibody-positive MG. In conclusion, high serum Sema4A levels may reflect T-cell activation, and this molecule could be a potential marker of disease activity in MG.

Advancements and prospects of novel biologicals for myasthenia gravis: toward personalized treatment based on autoantibody specificities.

Myasthenia gravis (MG) is an antibody-mediated autoimmune disease with a prevalence of 150-250 cases per million individuals. Autoantibodies include long-lived antibodies against the acetylcholine receptor (AChR), mainly of the IgG1 subclass, and IgG4, produced almost exclusively by short-lived plasmablasts, which are prevalent in muscle-specific tyrosine kinase (MuSK) myasthenia gravis. Numerous investigations have demonstrated that MG patients receiving conventional medication today still do not possess satisfactory symptom control, indicating a substantial disease burden. Subsequently, based on the type of the autoantibody and the pathogenesis, we synthesized the published material to date and reached a conclusion regarding the literature related to personalized targeted therapy for MG. Novel agents for AChR MG have shown their efficacy in clinical research, such as complement inhibitors, FcRn receptor antagonists, and B-cell activating factor (BAFF) inhibitors. Rituximab, a representative drug of anti-CD20 therapy, has demonstrated benefits in treatment of MuSK MG patients. Due to the existence of low-affinity antibodies or unidentified antibodies that are inaccessible by existing methods, the treatment for seronegative MG remains complicated; thus, special testing and therapy considerations are necessary. It may be advantageous to initiate the application of novel biologicals at an early stage of the disease. Currently, therapies can also be combined and individualized according to different types of antibodies. With such a wide range of drugs, how to tailor treatment strategies to patients with various conditions and find the most suitable solution for each MG profile are our necessary and urgent aims.

CD20-mediated B cell depletion in acetylcholine receptor autoantibody-positive myasthenia gravis

Myasthenia gravis (MG) is an autoimmune disorder characterized by muscle weakness and fatigue, mediated in the majority of cases by IgG1 autoantibodies targeting the acetylcholine receptor (AChR). As AChR autoantibodies have been shown to be pathogenic, therapies targeting B cells have been applied in patients with AChR MG for more than a decade. Recently, a phase 2 trial of the CD20-targeting agent, rituximab, in AChR MG unfortunately failed to meet its primary endpoint. Converging data however from non-randomized clinical series, some of which with more participants than the phase 2 trial, support efficacy of rituximab in AChR MG, especially early onset disease. In this opinion article, we summarize both clinical data and mechanistic principles on the use of CD20 depletion therapy in AChR MG, which we believe lend support to the argument that CD20 depletion can still be a useful therapeutic strategy for patients with AChR MG.

Enrichment of serum IgG4 in MuSK myasthenia gravis patients

Muscle-specific kinase (MuSK) myasthenia gravis (MG) is a neuromuscular autoimmune disease belonging to a growing group of IgG4 autoimmune diseases (IgG4-AIDs), in which the majority of pathogenic autoantibodies are of the IgG4 subclass. The more prevalent form of MG with acetylcholine receptor (AChR) antibodies is caused by IgG1–3 autoantibodies. A dominant role for IgG4 in autoimmune disease is intriguing due to its anti-inflammatory characteristics. It is unclear why MuSK autoantibodies are predominantly IgG4. We hypothesized that MuSK MG patients have a general predisposition to generate IgG4 responses, therefore resulting in high levels of circulating IgG4. To investigate this, we quantified serum Ig isotypes and IgG subclasses using nephelometric and turbidimetric assays in MuSK MG and AChR MG patients not under influence of immunosuppressive treatment. Absolute serum IgG1 was increased in both MuSK and AChR MG patients compared to healthy donors. In addition, only MuSK MG patients on average had significantly increased and enriched serum IgG4. Although more MuSK MG patients had elevated serum IgG4, for most the IgG4 serum levels fell within the normal range. Correlation analyses suggest MuSK-specific antibodies do not solely explain the variation in IgG4 levels. In conclusion, although serum IgG4 levels are slightly increased, the levels do not support ubiquitous IgG4 responses in MuSK MG patients as the underlying cause of dominant IgG4 MuSK antibodies.

Heterogeneity of Acetylcholine Receptor Autoantibody-Mediated Complement Activity in Patients With Myasthenia Gravis.

Background and ObjectivesAutoantibodies targeting the acetylcholine receptor (AChR), found in patients with myasthenia gravis (MG), mediate pathology through 3 mechanisms: complement-directed tissue damage, blocking of the acetylcholine binding site, and internalization of the AChR. Clinical assays, used to diagnose and monitor patients, measure only autoantibody binding. Consequently, they are limited in providing association with disease burden, understanding of mechanistic heterogeneity, and monitoring therapeutic response. The objective of this study was to develop a cell-based assay that measures AChR autoantibody–mediated complement membrane attack complex (MAC) formation.MethodsAn HEK293T cell line—modified using CRISPR/Cas9 genome editing to disrupt expression of the complement regulator genes (CD46, CD55, and CD59)—was used to measure AChR autoantibody–mediated MAC formation through flow cytometry.ResultsSerum samples (n = 155) from 96 clinically confirmed AChR MG patients, representing a wide range of disease burden and autoantibody titer, were tested along with 32 healthy donor (HD) samples. AChR autoantibodies were detected in 139 of the 155 (89.7%) MG samples through a cell-based assay. Of the 139 AChR-positive samples, autoantibody-mediated MAC formation was detected in 83 (59.7%), whereas MAC formation was undetectable in the HD group or AChR-positive samples with low autoantibody levels. MAC formation was positively associated with autoantibody binding in most patient samples; ratios (mean fluorescence intensity) of MAC formation to AChR autoantibody binding ranged between 0.27 and 48, with a median of 0.79 and an interquartile range of 0.43 (0.58–1.1). However, the distribution of ratios was asymmetric and included extreme values; 16 samples were beyond the 10–90 percentile, with high MAC to low AChR autoantibody binding ratio or the reverse. Correlation between MAC formation and clinical disease scores suggested a modest positive association (rho = 0.34, p = 0.0023), which included a subset of outliers that did not follow this pattern. MAC formation did not associate with exposure to immunotherapy, thymectomy, or MG subtypes defined by age-of-onset.DiscussionA novel assay for evaluating AChR autoantibody–mediated complement activity was developed. A subset of patients that lacks association between MAC formation and autoantibody binding or disease burden was identified. The assay may provide a better understanding of the heterogeneous autoantibody molecular pathology and identify patients expected to benefit from complement inhibitor therapy.

Myasthenia gravis complement activity is independent of autoantibody titer and disease severity.

Acetylcholine receptor (AChR) autoantibodies, found in patients with autoimmune myasthenia gravis (MG), can directly contribute to disease pathology through activation of the classical complement pathway. Activation of the complement pathway in autoimmune diseases can lead to a secondary complement deficiency resulting in reduced complement activity, due to consumption, during episodes of disease activity. It is not clear whether complement activity in MG patients associates with measurements of disease activity or the titer of circulating pathogenic AChR autoantibodies. To explore such associations, as a means to identify a candidate biomarker, we measured complement activity in AChR MG samples (N = 51) using a CH50 hemolysis assay, then tested associations between these values and both clinical status and AChR autoantibody titer. The majority of the study subjects (88.2%) had complement activity within the range defined by healthy controls, while six patients (11.8%) showed reduced activity. No significant association between complement activity and disease status or AChR autoantibody titer was observed.

Efficacy and safety of different dosages of rituximab for refractory generalized AChR myasthenia gravis: A meta-analysis

BackgroundRituximab (RTX) is a mouse-human chimeric anti-CD20 monoclonal antibody and has been increasingly used for preventing relapses in myasthenia gravis (MG). However, the appropriate dose for maximizing the beneficial effects in refractory MG with acetylcholine receptor (AChR) autoantibody is a long-standing and critical debating question. MethodsWe performed a meta-analysis to evaluate the efficacy and safety of the different doses of RTX in 260 refractory AChR-MG patients. ResultsThe AChR-MG patients were divided into low or routine RTX dose groups. An overall proportion of 77% (p = 0.000) AChR-MG patients demonstrated improved clinical status as indicated by the Myasthenia Gravis Foundation of America post-intervention scale (MGFA-PIS). There were 77.1% patients showed improved clinical status in lower dose of RTX group (p = 0.000) and 76.8% in routine protocol group (p = 0.000). Although we found there was no significant difference in the proportion of AChR-MG patients with improved clinical status or adverse reactions between the two groups, adverse reactions might be lower in the lower dose RTX group. ConclusionMost of refractory MG patients with anti-AChR autoantibody were well responsive and tolerated to RTX treatment. Repeated application of lower dose of RTX was effective and might be more appropriate for refractory AChR-MG patients with potential lower side effects.

The Expression Pattern and Regulatory Mechanism of the G0/G1 Switch Gene 2 (G0S2) in the Pathogenesis and Treatment of AChR Myasthenia Gravis (MG).

This study is aimed at exploring the expression pattern and methylation level of G0S2 in the peripheral blood mononuclear cells (PBMCs) of myasthenia gravis (MG) patients with positive acetylcholine receptor (AChR) autoantibodies and revealing the relationship between the G0S2 methylation pattern and MG. The relationship between the NFAT family members and G0S2 was explored to reveal the regulatory mechanism of G0S2 in the pathogenesis and treatment of AChR MG. Moreover, we attempted to demonstrate the potential therapeutic mechanism of tacrolimus in AChR MG. The relative G0S2 expression level in the PBMCs of healthy people was compared with that in the PBMCs of AChR MG patients with quantitative real-time PCR (qRT-PCR). The methylation frequency of the G0S2 promoter was detected by bisulfite sequencing PCR (BSP) and pyrosequencing. A dual-luciferase reporter system was used to reveal the relationship between the G0S2 promoter and nuclear factor of activated T cells 5 (NFAT5). The qRT-PCR results showed that G0S2 expression was significantly upregulated in the B cells and CD8+ T cells of AChR MG patients but not in the CD4+ T cells, and these expression differences were significantly associated with a decrease in G0S2 methylation. NFAT5, which was speculated to bind to island 1 (p1) in the G0S2 promoter, may regulate the lymphocyte balance by regulating G0S2 gene expression but failed to affect the methylation of the G0S2 promoter. Tacrolimus therapy-induced methylation and overexpression of NFAT5 could significantly reduce the expression of G0S2 in AChR MG patients. The G0S2 gene was remarkably upregulated in the PBMCs of MG patients. NFAT5 may affect transcription initiation and downregulate G0S2 expression through p1 in the promoter, thus controlling G0S2 gene expression and regulating the lymphocyte balance. Therefore, G0S2 could be an immune regulatory factor in both AChR MG occurrence and treatment with tacrolimus.

Autoimmune Pathology in Myasthenia Gravis Disease Subtypes Is Governed by Divergent Mechanisms of Immunopathology.

Myasthenia gravis (MG) is a prototypical autoantibody mediated disease. The autoantibodies in MG target structures within the neuromuscular junction (NMJ), thus affecting neuromuscular transmission. The major disease subtypes of autoimmune MG are defined by their antigenic target. The most common target of pathogenic autoantibodies in MG is the nicotinic acetylcholine receptor (AChR), followed by muscle-specific kinase (MuSK) and lipoprotein receptor-related protein 4 (LRP4). MG patients present with similar symptoms independent of the underlying subtype of disease, while the immunopathology is remarkably distinct. Here we highlight these distinct immune mechanisms that describe both the B cell- and autoantibody-mediated pathogenesis by comparing AChR and MuSK MG subtypes. In our discussion of the AChR subtype, we focus on the role of long-lived plasma cells in the production of pathogenic autoantibodies, the IgG1 subclass mediated pathology, and contributions of complement. The similarities underlying the immunopathology of AChR MG and neuromyelitis optica (NMO) are highlighted. In contrast, MuSK MG is caused by autoantibody production by short-lived plasmablasts. MuSK MG autoantibodies are mainly of the IgG4 subclass which can undergo Fab-arm exchange (FAE), a process unique to this subclass. In FAE IgG4, molecules can dissociate into two halves and recombine with other half IgG4 molecules resulting in bispecific antibodies. Similarities between MuSK MG and other IgG4-mediated autoimmune diseases, including pemphigus vulgaris (PV) and chronic inflammatory demyelinating polyneuropathy (CIDP), are highlighted. Finally, the immunological distinctions are emphasized through presentation of biological therapeutics that provide clinical benefit depending on the MG disease subtype.

Heterogeneity and shifts in distribution of muscle weakness in myasthenia gravis

The distribution of muscle weakness in myasthenia gravis (MG) patients with acetylcholine receptor (AChR) antibodies is highly variable. As muscle groups respond differently to therapeutic interventions, it is important to acknowledge this variability. We analysed the distribution of muscle weakness in 225 AChR MG patients over time. On the basis of combinations of muscle weakness, seven phenotypes were defined: ‘ocular’ (O), ‘bulbar’ (B), ‘neck/limbs/respiratory’ (NLR), or a combination (O+B, O+NLR, B+NLR and O+B+NLR). MG remained restricted to ocular weakness in 5%, whereas 7% never had ocular weakness. At last follow-up, ocular or bulbar weakness had resolved more frequently than NLR weakness (40%, 38% and 25%; p = 0.003, respectively). Patients with O, B or OB phenotype at baseline had a higher age at onset and were more frequently male than patients with NLR, ONLR, BNLR or OBNLR phenotype (52.7 ± 17.5 vs. 44.0 ± 18.9; p = 0.007 and 64% vs. 37%; p = 0.002, respectively). MG patients have heterogeneous distributions of muscle weakness and frequently shift between phenotypes. The phenotypic variations found in AChR MG suggest that also other factors aside from the AChR antibody mediated immune response are of importance in determining the disease expression in MG.

Systemic lupus erythematosus-myasthenia gravis overlap syndrome: Presentation and treatment depend on prior thymectomy

In this study, we investigated four patients who met the diagnostic criteria for overlapping systemic lupus erythematosus (SLE) and myasthenia gravis (MG) but responded differently to treatment. All patients were acetylcholine receptor (AChR) and antinuclear antibody positive at the time of SLE diagnosis. Two patients presented with SLE who have been effectively treated with cholinesterase inhibitors for MG. These patients developed SLE with photosensitivity, rash, and arthritis post thymectomy, which had been performed 29 years and 40 years earlier, respectively. Two other patients were found to have AChR antibodies and MG in the context on new-onset SLE. These subjects were responsive to hydroxychloroquine and immunosuppression but failed cholinesterase inhibitors. The evolution of these cases is relevant for the role of thymus in lupus pathogenesis during aging and for treatment selection in SLE-MG overlap patients.

Quality of life in patients with MuSK positive myasthenia gravis

It is believed that myasthenia gravis (MG) with antibodies to muscle-specific tyrosine kinase (MuSK) is the most severe form of the disease, especially in the first years of the disease. The aim of our study was to investigate quality of life (QoL) in a population of patients with MuSK MG compared to those with MG who have antibodies to acetylcholine receptor (AChR) in their sera. The study group consisted of 35 MuSK MG patients (28 females and 7 males), while the control group included 38 AChR MG patients matched for gender, age, and duration of the disease. SF-36 questionnaire was used to evaluate the health-related QoL. Following scales were also used: Hamilton's scales for depression and anxiety, the Multidimensional Scale of Perceived Social Support, and the Acceptance of Illness Scale. Physical domain scores of QoL were similarly affected in both MuSK and AChR groups, while mental domain and total SF-36 scores were even better in MuSK MG patients. Social support was better in the MuSK group (77.3 ± 9.3 vs. 70.6 ± 14.1, p < 0.05). SF-36 total score correlated with depression (rho = 0.54, p < 0.01), anxiety (rho = 0.49, p < 0.01), and MSPSS (rho = - 0.35, p < 0.05), and depression was an independent predictor of worse QoL. Besides therapy of weakness, psychiatric treatment and different forms of psychosocial condition should be part of regular therapeutic protocols for MG. Adequate team work of health professionals and family can provide a healthy mental environment in which a MuSK MG patient would feel more comfortable in spite of the disease.

IgG4-mediated autoimmune diseases: a niche of antibody-mediated disorders.

Immunoglobulin 4 (IgG4) is one of four human IgG subclasses and has several unique functional characteristics. It exhibits low affinity for complement and for most Fc receptors. It furthermore has generally high affinity for its antigen, with binding occurring in a monovalent fashion, as IgG4 can exchange Fab-arms with other IgG4 molecules. Because of these characteristics, IgG4 is believed to block its targets and prevent inflammation, which, depending on the setting, can have a protective or pathogenic effect. One example of IgG4 pathogenicity is muscle-specific kinase (MuSK) myasthenia gravis (MG), in which patients develop IgG4 MuSK autoantibodies, resulting in muscle weakness. As a consequence of the distinct IgG4 characteristics, the pathomechanism of MuSK MG is very different from IgG1-and IgG3-mediated autoimmune diseases, such as acetylcholine receptor MG. In recent years, new autoantibodies in a spectrum of autoimmune diseases have been discovered. Interestingly, some were found to be predominantly IgG4. These IgG4-mediated autoimmune diseases share many pathomechanistic aspects with MuSK MG, suggesting that IgG4-mediated autoimmunity forms a separate niche among the antibody-mediated disorders. In this review, we summarize the group of IgG4-mediated autoimmune diseases, discuss the role of IgG4 in MuSK MG, and highlight interesting future research questions for IgG4-mediated autoimmunity.

Autoantibody-producing plasmablasts after B cell depletion identified in muscle-specific kinase myasthenia gravis.

Myasthenia gravis (MG) is a B cell-mediated autoimmune disorder of neuromuscular transmission. Pathogenic autoantibodies to muscle-specific tyrosine kinase (MuSK) can be found in patients with MG who do not have detectable antibodies to the acetylcholine receptor (AChR). MuSK MG includes immunological and clinical features that are generally distinct from AChR MG, particularly regarding responsiveness to therapy. B cell depletion has been shown to affect a decline in serum autoantibodies and to induce sustained clinical improvement in the majority of MuSK MG patients. However, the duration of this benefit may be limited, as we observed disease relapse in MuSK MG patients who had achieved rituximab-induced remission. We investigated the mechanisms of such relapses by exploring autoantibody production in the reemerging B cell compartment. Autoantibody-expressing CD27+ B cells were observed within the reconstituted repertoire during relapse but not during remission or in controls. Using two complementary approaches, which included production of 108 unique human monoclonal recombinant immunoglobulins, we demonstrated that antibody-secreting CD27hiCD38hi B cells (plasmablasts) contribute to the production of MuSK autoantibodies during relapse. The autoantibodies displayed hallmarks of antigen-driven affinity maturation. These collective findings introduce potential mechanisms for understanding both MuSK autoantibody production and disease relapse following B cell depletion.

Hinge-deleted IgG4 blocker therapy for acetylcholine receptor myasthenia gravis in rhesus monkeys

Autoantibodies against ion channels are the cause of numerous neurologic autoimmune disorders. Frequently, such pathogenic autoantibodies have a restricted epitope-specificity. In such cases, competing antibody formats devoid of pathogenic effector functions (blocker antibodies) have the potential to treat disease by displacing autoantibodies from their target. Here, we have used a model of the neuromuscular autoimmune disease myasthenia gravis in rhesus monkeys (Macaca mulatta) to test the therapeutic potential of a new blocker antibody: MG was induced by passive transfer of pathogenic acetylcholine receptor-specific monoclonal antibody IgG1-637. The effect of the blocker antibody (IgG4Δhinge-637, the hinge-deleted IgG4 version of IgG1-637) was assessed using decrement measurements and single-fiber electromyography. Three daily doses of 1.7 mg/kg IgG1-637 (cumulative dose 5 mg/kg) induced impairment of neuromuscular transmission, as demonstrated by significantly increased jitter, synaptic transmission failures (blockings) and a decrease in the amplitude of the compound muscle action potentials during repeated stimulations (decrement), without showing overt symptoms of muscle weakness. Treatment with three daily doses of 10 mg/kg IgG4Δhinge-637 significantly reduced the IgG1-637-induced increase in jitter, blockings and decrement. Together, these results represent proof-of principle data for therapy of acetylcholine receptor-myasthenia gravis with a monovalent antibody format that blocks binding of pathogenic autoantibodies.

Rituximab treatment of myasthenia gravis: A systematic review

Rituximab is a chimeric mouse/human anti-CD20 monoclonal immunoglobulin. We reviewed the efficacy and safety of rituximab in 169 myasthenia gravis (MG) patients from case reports and series. Antibodies to the acetylcholine receptor (AChR) were present in 59% and muscle-specific tyrosine kinase (MuSK) in 34%. Modified Myasthenia Gravis Foundation of America postintervention scale of minimal manifestations (MM) or better occurred in 44%, and combined pharmacologic and chronic stable remission in 27% overall; MM or better was achieved in 72% of MuSK MG and 30% of AChR MG (P < 0.001). Posttreatment relapses decreased more in MuSK MG (P = 0.05). Response predictors were MuSK MG, less severe disease, and younger age at treatment. Among a responder subset, 26% of AChR and 82% of MuSK MG patients showed decreased posttreatment antibody titers. Rituximab was generally well tolerated. Detectable serum rituximab and depleted CD20+ B-cells were observed up to 20 and 16 weeks, respectively, after 4 weekly infusions. Muscle Nerve 56: 185-196, 2017.

Electrophysiological findings in patients with low density lipoprotein receptor related protein 4 positive myasthenia gravis.

The aim was to determine the electrophysiological profile of our cohort of low density lipoprotein receptor related protein 4 (LRP4) positive myasthenia gravis (MG) patients. A repetitive nerve stimulation (RNS) test and jitter analysis using a concentric needle electrode were performed in 17 LRP4 positive MG patients. The results were compared to 31 muscle-specific tyrosine kinase (MuSK) positive and 28 acetylcholine receptor (AChR) positive MG patients. The RNS test was negative in almost all patients belonging to the LRP4/seronegative and LRP4/MuSK groups. It was positive most frequently in the AChR MG patients, especially those without anti-LRP4 antibodies. The presence of anti-LRP4 antibodies was connected to lower decrement values, whilst the independent presence of anti-AChR or anti-MuSK antibodies was connected to higher decrement values. Lowest jitter was recorded in patients with LRP4/seronegative MG. The highest percentage of pathological jitter analysis test results was present in MuSK and AChR MG patients. The isolate presence of anti-LRP4 antibodies did not influence the mean consecutive difference values, whilst mean consecutive difference values were higher in the presence of anti-AChR or anti-MuSK antibodies. Low density lipoprotein receptor related protein 4 positive patients make a distinct MG subgroup with rarely detected pathological electrophysiological test results. The lack of influence of anti-LRP4 antibodies on the different electrophysiological parameters brings into question the pathogenic role of anti-LRP4 antibodies in MG.

Myopathic changes detected by quantitative electromyography in patients with MuSK and AChR positive myasthenia gravis

Myopathic changes are frequent a electrophysiological finding in patients with muscle specific tyrosine kinase (MuSK) positive myasthenia gravis (MG). The aim of this study was to explore the importance of quantitative electromyography (EMG) in the detection of myopathic changes in MuSK MG patients. Classical and quantitative EMG were performed in 31 MuSK and 28 acetylcholine receptor (AChR) positive MG patients, matched by sex, age, disease duration and severity. Classical EMG revealed the presence of myopathic changes more frequently in MuSK MG compared to AChR MG patients, especially in the facial muscles. Quantitative EMG registered myopathic lesions more frequently than classical EMG, but the frequency was similar between MuSK and AChR MG patients. Quantitative EMG revealed myopathic changes in the majority of both MuSK and AChR positive MG patients. This examination is sensitive, but it cannot be used to differentiate between MG patients belonging to the different disease groups. It should not be used in isolation. Rather, it should complement classical EMG in the detection of myopathic changes.

Increased expression of Toll-like receptors 7 and 9 in myasthenia gravis thymus characterized by active Epstein–Barr virus infection

Considerable data implicate the thymus as the main site of autosensitization to the acetylcholine receptor in myasthenia gravis (MG), a B-cell-mediated autoimmune disease affecting the neuromuscular junction. We recently demonstrated an active Epstein–Barr virus (EBV) infection in the thymus of MG patients, suggesting that EBV might contribute to the onset or maintenance of the autoimmune response within MG thymus, because of its ability to activate and immortalize autoreactive B cells. EBV has been reported to elicit and modulate Toll-like receptor (TLR) 7- and TLR9-mediated innate immune responses, which are known to favor B-cell dysfunction and autoimmunity. Aim of this study was to investigate whether EBV infection is associated with altered expression of TLR7 and TLR9 in MG thymus. By real-time PCR, we found that TLR7 and TLR9 mRNA levels were significantly higher in EBV-positive MG compared to EBV-negative normal thymuses. By confocal microscopy, high expression levels of TLR7 and TLR9 proteins were observed in B cells and plasma cells of MG thymic germinal centers (GCs) and lymphoid infiltrates, where the two receptors co-localized with EBV antigens. An increased frequency of Ki67-positive proliferating B cells was found in MG thymuses, where we also detected proliferating cells expressing TLR7, TLR9 and EBV antigens, thus supporting the idea that EBV-associated TLR7/9 signaling may promote abnormal B-cell activation and proliferation. Along with B cells and plasma cells, thymic epithelium, plasmacytoid dendritic cells and macrophages exhibited enhanced TLR7 and TLR9 expression in MG thymus; TLR7 was also increased in thymic myeloid dendritic cells and its transcriptional levels positively correlated with those of interferon (IFN)-β. We suggested that TLR7/9 signaling may be involved in antiviral type I IFN production and long-term inflammation in EBV-infected MG thymuses. Our overall findings indicate that EBV-driven TLR7- and TLR9-mediated innate immune responses may participate in the intra-thymic pathogenesis of MG.