Acetylcholine receptors and myasthenia gravis

Recent years have seen considerable progress in understanding the nature of the molecular events involved in neuromuscular transmission. The acetylcholine receptor (AChR) has been purified to homogeneity and acetylcholine-induced ion transport has been reconstituted by incorporation of pure AChR into artificial membranes. Immunization against purified AChR induces a condition, clinically and physiologically similar to the human disease myasthenia gravis, which is due to circulating anti-AChR antibodies. This model, experimental autoimmune myasthenia gravis, is proving useful for investigating the role of genetic factors in determining the immune response to AChRs and for testing various experimental approaches to specific treatment. Myasthenia gravis is an autoimmune disease in which there is loss of acetylcholine receptors at the neuromuscular junction. Anti-AChR antibodies can be detected in the majority of patients and they cause loss of AChR by a variety of mechanisms. Anti-AChR antibody is heterogeneous and not restricted in idiotype. The role of the thymus in MG is still uncertain, but recent experiments implicate the presence of a cell type in MG thymus which may be involved in autosensitization to AChR.     

Comparative Study of Clinical Effects Between Plasma Adsorption and Double Filtration Plasmapheresis in Patients with Myasthenia Gravis

Abstract: Plasma exchange (PE) has been one of the most powerful treatments for patients with myasthenia gravis (MG) since Pinching et al. reported its clinical usefulness in 1976, despite the need for supplemental human plasma. However, new apheresis techniques, e.g., plasma adsorption (PA) and double filtration plasmapheresis (DFPP), which do not need human plasma, were developed and have been introduced for clinical use in MG. We compared the effects of these plasma purification therapies in patients with MG and found that DFPP improved such subjective symptoms as chest compression and general fatigue better than PA while both of them could decrease the serum level of acetylcholine receptor (AChR) antibodies and relieve objective muscle weakness to a similar degree. It may be that DFPP can remove some circulating pathogenic factors other than AChR antibodies more efficiently than PA.—     

Immunoadsorption in Myasthenia Gravis Based on Specific Ligands Mimicking the Immunogenic Sites of the Acetylcholine Receptor

Abstract: A specific system for antibody removal from blood circulation in myasthenia gravis (MG) patients was devised by use of the immunoadsorbent bound to an acetylcholine receptor (AChR) peptide that was synthesized corresponding to the sequence of residues 183‐200 of the AChR alpha‐subunit (alpha 183‐200), antibodies which prevent the binding of ACh to AChR. The alpha 183‐200 peptide was confirmed to be immunogenic for induction of an animal model of the disease and for reactivity with MG autoantibodies. We then made use of these results for immunoadsorption therapy through the antigen‐antibody reaction on the molecular level, having given patients relief from myasthenic weakness. The greatest care was taken for the selection of an antigenic region in the molecular structure among various myasthenogenic domains of AChR and for the antigenic conformation of synthetic peptide as the adsorbent to react with antibodies raised against the native protein.     

Robotic thymectomy for myasthenia gravis surgical techniques and outcomes

Myasthenia gravis (MG) is an autoimmune disorder in which antibodies are produced against post-synaptic acetylcholine receptors, thereby causing impairment of neuromuscular transmission. Diagnosis of MG is confirmed with the AChR antibody test and via an Electromyography. Although medical treatment with acetylcholinesterase inhibitors remains the main treatment of MG, in recent years thymectomy has become an integral part of the treatment algorithm. Numerous factors such as the Patient’s age, presence of AChR antibodies, or MuSK antibody, the severity of disease affect the decision of preforming the thymectomy. Historically thymectomy was preformed via sternotomy associated with significant morbidity. Advancement in the minimally invasive approaches to thymic resection has led to more acceptance of thymectomy in the management of MG. Among these approaches, robotic thymectomy is gaining popularity across the globe due to the unique advantages of the robotic platform like 3D visibility, enhanced dexterity, and wrist like articulating movements of instruments. This has led to less post-operative pain and morbidity; faster recovery and shorter hospital stay. Successful treatment of MG requires a multi-modality approach, which has led to the formation of MG teams in most academic centers, comprising of a specialist neurologist, intensivist, and thoracic surgeon. In this article, we describe the techniques and outcomes of the robotic thymectomy for MG.     

Modulation of experimental myasthenia gravis by IVIg

Myasthenia Gravis (MG) is an autoimmune disease mediated by antibodies directed against the acetylcholine receptor (AChR). Treatment by IVIg is effective in acute forms of myasthenia gravis. In order to determine the in vivo effects of the various fractions of human immunoglobulins, we used an experimental model of myasthenia gravis in SCID mice. To this end, thymic cells from MG patients are transferred to these mice according to a well defined protocol. When establishing of the model, we noticed the appearance of anti-AChR antibodies and the loss of AChR expression at the muscle level. After treatment with IVIgG or IVIgM, the mice displayed a lower anti-AChR antibody titer compared to control mice (albumin treated) and the loss of the AChR number at the muscle was significantly reduced. These results obtained from one MG patient indicate that the human immunoglobulin preparations induce significant effects on pathogenic parameters in the SCID mouse model. Therefore this model is interesting to approach the mechanisms of action of human immunoglobulins and deserves further investigation.     

Specific Immunoadsorbent for Myasthenia Gravis Treatment: Development of Synthetic Peptide Designed to Remove Antiacetylcholine Receptor Antibody

Abstract: We have developed Medisorba MG, a new immunoadsorbent column for myasthenia gravis (MG). The a 183–200 segment of the Torpedo Californica acetylcholine receptor (AChR) is recognized as the acetylcholine binding site by the blocking antibody, which is one of the anti-AChR antibodies involved in the pathogenesis of MG. As a specific affinity ligand to remove the blocking antibody, Torpedoα 183–200 was synthesized and immobilized covalently to porous cellulose beads. This immunoadsorbent showed specific removal of the blocking antibody without reducing IgG and albumin levels significantly in clinical evaluation and in vitro study. Clinical improvement was found in 78% of the cases, and no adverse effects were observed in any case. The Medisorba MG column has been confirmed as a useful device for the treatment of MG.     

重症肌无力患者妊娠期临床特点及预后分析

目的:探讨重症肌无力（MG）患者妊娠前后肌无力症状的变化及MG对妊娠预后的影响。方法:回顾性研究2013年1月至2018年10月28例就诊于解放军总医院第八医学中心MG患者38例次妊娠分娩的临床资料。比较妊娠前与妊娠不同时期MG严重程度评分、血乙酰胆碱受体（AChR）抗体变化及药物的使用情况,并分析妊娠后MG不同转归（...     

Myasthenia gravis and hepatitis C virus infection

SUMMARY. Chronic hepatitis C virus (HCV) infections are often associated with extrahepatic immunological manifestations, including various autoimmune disorders. The aims of this study were to determine the prevalence of HCV markers in patients with myasthenia gravis (MG) and to determine any relationship with HCV infection. Eighty-three patients with MG, 40 men aged 20–93 years and 43 women aged 13–87 years (mean age 54 years) were studied. The MG patients were positive for antibody to acetylcholine receptor, in addition, their sera was analysed for antibody to HCV (HCVAb) and HCV RNA. HCVAb was detected in two of the 83 patients (2.4%). Four patients were repeatedly HCV RNA positive. They were infected by HCV genotype 1 (one patient), HCV genotype 2a (two patients) and an undetermined HCV genotype in one patient. They received plasmapheresis or intravenous immunoglobulin treatment. Among the four patients, one was infected after the onset of MG without receiving a blood transfusion or using intravenous drugs. The other three had chronic hepatitis C which was discovered at the same time as MG and only one patient had been exposed to blood products. The prevalence of HCV markers in patients with MG (4.8%) was higher than that reported for the general French population, about 1%. This prevalence is similar to that occurring in patients exposed to plasmapheresis or intravenous immunoglobulin. In conclusion, HCV appears to play little, if any, role in causing MG. The higher prevalence of infection among MG patients may be related to transmission in the course of therapy.     

Immunochemical characterization of anti-acetylcholine receptor antibodies in primary biliary cirrhosis

Although the presence of anti-mitochondrial antibodies is the main characteristic of primary biliary cirrhosis (PBC), other autoantibodies have been described in this disease. This study employs immunoblot methods to test whether the sera of PBC patients also contain antibodies directed against nicotinic acetylcholine receptors (AChR). We show that the majority of patients' sera indeed react with AChR just as sera of myasthenic patients do. In contrast, however, these anti-AChR antibodies do not lead to significant clinical symptoms of myasthenia. In all cases studied, PBC sera recognized a protein with the molecular weight of the alpha-chain of acetylcholine receptor (40 kDa). In addition, with both liver mitochondria and AChR-rich membranes as antigens, PBC sera reacted with proteins with apparent molecular weights around 68 kDa and the same pI values. This protein is not present in purified AChR preparations. These data suggest structural, if not functional, relationships between membrane components of liver mitochondria and muscle endplates.     

Prevention of experimental autoimmune myasthenia gravis by manipulation of the immune network with a complementary peptide for the acetylcholine receptor.

Myasthenia gravis (MG) and experimental autoimmune myasthenia gravis (EAMG) are caused, in part, by the production of autoantibodies against the main immunogenic region, amino acids 61-76, of the alpha chain of the acetylcholine receptor (AChR). Theoretically, induction of anti-idiotypic (Id) antibodies (Abs) should be a highly specific treatment for the disease by virtue of their potential ability to neutralize Abs to the AChR. We have tested this idea by attempting to evoke such anti-Id Abs by immunization with a peptide (termed RhCA 67-16) encoded by RNA complementary to the Torpedo AChR main immunogenic region and determining whether such treatment will prevent the development of EAMG. Immunization with RhCA 67-16, but not a control peptide termed PBM 9-1, was found to elicit the production of anti-Id Abs that blocked recognition of native Torpedo AChR by its Ab. This anti-Id Ab activity was ablated by incubation of the anti-RhCA 67-16 serum with RhCA 67-16, but PBM 9-1, prior to the assay for Ab binding to AChR. The anti-Id Ab-inducing activity of RhCA 67-16 was confirmed by the ability to produce a rat monoclonal Ab to RhCA 67-16 that showed anti-Id activity for polyclonal rat Ab reactive with AChR residues 67-76. Most importantly, RhCA 67-16 immunization also prevented the development of EAMG in Lewis rats challenged with Torpedo AChR (25% incidence versus 90% in the controls) and diminished the AChR Ab levels in animals injected with low doses of AChR. Our results suggest a therapy for MG and perhaps other autoimmune diseases through the induction of anti-Id Abs by peptide immunogens.     

Concurrent inflammatory myopathy and myasthenia gravis with or without thymic pathology: A case series and literature review

Objectives

The association of myasthenia gravis (MG) and inflammatory myositis (IM) is rare and typically only one of the diseases is present. The management of the 2 diseases differs, therefore it is important to recognize the concomitant presentation. Here, we report a case series of 7 patients with co-existing MG and IM with review of the literature.

Myasthenia gravis: MuSK MG,late-onset MG and ocular MG

Myasthenia gravis (MG) is an autoimmune disease of the neuromuscular junction which affects all striated muscles, resulting in fluctuating weakness. Approaching MG as a disease with subgroups having different clinical, serological and genetic features is crucial in predicting the progression and planning treatment. Three relatively less frequently seen subtypes of MG are the subject of this review: MG with anti-MuSK antibodies (MuSK MG), non-thymomatous late-onset MG (LOMG), and ocular MG (OMG). In addition to reviewing the literature, mainly from a clinical point of view, our experience in each of the subgroups, based on close to 600 patients seen over a 10 year period, is related. MuSK MG is a severe disease with predominant bulbar involvement. It is more common in women and in early-onset patients. With the use of high dose corticosteroids, azathioprine and more recently rituximab, outcome is favorable, though the patients usually require higher maintenance doses of immunosuppressives. LOMG with onset ≥ 50 years of age is more common in men and ocular onset is common. Frequency of anti-AChR and anti-titin antibodies are high. Although it can be severe in some patients, response to treatment is usually very good. OMG is reported to be more frequent in men in whom the disease has a later onset. Anti-AChR antibodies are present in about half of the patients. Generalization is less likely when symptoms remain confined to ocular muscles for 2 years. Low dose corticosteroids are usually sufficient. Thyroid disease is the most common autoimmune disease accompanying all three subgroups.Key words: Myasthenia gravis, MuSK MG, Late-onset MG, Ocular MG     

Lambert-Eaton myasthenic syndrome: diagnosis and treatment

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder of neuromuscular and autonomic transmission in which IgG autoantibodies lead to presynaptic voltage-gated calcium channel (VGCC) loss, or as a paraneoplastic disorder in association with small cell lung carcinoma (SCLC). Recent results strongly suggest that the antibodies to P/Q-type VGCC are the principal pathogenic factors in LEMS. Here, we present diagnosis and treatment of LEMS patients. Proximal weakness, depressed tendon reflexes, autonomic symptoms, and electrical posttetanic potentiation together are essential to accurately diagnose LEMS. The diagnosis is established immunologically by the presence of anti-P/Q-type VGCC antibodies, detected using the (125)I-omega-conotoxin MVIIC radioimmunoassay, which will be present in 85% of LEMS patients. The drug 3,4-diaminopyridine with anti-cholinesterase inhibitor is most effective in LEMS patients with or without SCLC. In LEMS with SCLC, specific tumor therapy will often improve the neurological disorder. In some cases plasmapheresis or intravenous immunoglobulin may be indicated.     

Antibodies to calcium channel and synaptotagmin in Lambert-Eaton myasthenic syndrome

In the Lambert-Eaton myasthenic syndrome (LEMS), an autoimmune disease that is often associated with lung cancer and characterized by reduced quantal release of acetylcholine from the motor nerve terminal, our studies to search for the target of LEMS antibodies have brought the voltage-gated calcium channel (VGCC) into relief. Among multiple types of VGCCs, the P/Q-type was highly recognized by LEMS antibodies. Using synthetic peptides or recombinant proteins as antigens, the study specified the S5-S6 linker regions in 3 of 4 domains as immunodominant sites in the molecular structure of P/Q-type VGCC alpha1 subunit. Synaptotagmin, one of the functionally VGCC-associated synaptic proteins, was also found to be an immunogen in the pathogenesis of LEMS.     

Adsorption column for myasthenia gravis treatment: Medisorba MG-50

Adsorption column Medisorba MG-50 (Kuraray Medical Inc.) for the treatment of myasthenia gravis (MG) is introduced. The adsorbent in this column is composed of cellulose beads as carrier material and covalent-bound synthetic peptide as a ligand that has a specific affinity to the pathogenic anti-acetylcholine receptor antibody of MG. The amino acid sequence of the peptide is modified from the segment of alpha 183-200 of the torpedo acetylcholine receptor (AChR) protein, and the segment is the acetylcholine binding site on AChR and the target site of anti-AChR antibody. The adsorbent showed specific adsorption characteristics to the anti-ACHR antibody (blocking antibody) in vitro. Clinically, MG-50 is used in plasma-perfusion therapy, and it is recognized that MG-50 specifically reduces blocking antibody titer and improves MG symptoms. MG-50 is approved in Japan.     

Oral administration of a dual analog of two myasthenogenic T cell epitopes down-regulates experimental autoimmune myasthenia gravis in mice

Myasthenia gravis (MG) and experimental autoimmune MG (EAMG) are T cell-regulated, antibody-mediated autoimmune diseases. The major autoantigen in MG is the nicotinic acetylcholine receptor (AChR). Two peptides, representing sequences of the human AChR alpha-subunit, p195-212 and p259-271, were previously shown to be immunodominant T cell epitopes in MG patients as well as, respectively, in SJL and BALB/c mice. A dual analog (termed Lys-262-Ala-207) composed of the tandemly arranged two single amino acid analogs of p195-212 and p259-271 was shown to inhibit, in vitro and in vivo, MG-associated autoimmune responses. Furthermore, the dual analog could down-regulate myasthenogenic manifestations in mice with EAMG that was induced by inoculation of a pathogenic T cell line. In the present study, the ability of the dual analog to treat EAMG induced in susceptible C57BL/6 mice by native Torpedo AChR was evaluated. Mice that were diagnosed to have clinical symptoms of EAMG were treated with the dual analog by oral administration, 500 microg per mouse three times a week for 5-8 weeks. Treatment with the dual analog down-regulated the clinical manifestations of the ongoing disease as assessed by the clinical score, grip strength (measured by a grip strength meter), and electromyography. The effects on the clinical EAMG correlated with a reduced production of anti-AChR antibody as well as a decrease in the secretion of interleukin-2 and, more dramatically, interferon-gamma, in response to AChR triggering. Thus, the dual analog is an efficient immunomodulator of EAMG in mice and might be of specific therapeutic potential for MG.     

重症肌无力全身表现及发病机制探讨

６４４例重症肌无力（ＭＧ）患者合并多种免疫有关性疾病，并且有多种自身抗体阳性，同时发现了一些骨骼肌以外受损害的表现，伴锥体束征者（ＰＳ）１１例，伴发癫痫４例，原因未明的周围神经病变３例，部分重症肌无力病人伴有血清ＡＬＴ增高，１４例ＭＧ患者的超声心动图，射血指数，２例心脏核素扫描，均未见明显异常。ＭＧ病人的骨骼肌以外损伤的表现，一般不需要特殊处理，随着重症肌无力的好转，绝大部分能够好转，其发病机制可能与乙酰胆碱受体抗体（ＡＣｈＲＡｂ）有关，或者是免疫泛化产生的其他免疫因素的作用，由此可见ＭＧ可能是一种主要累及神经肌肉接头处突触后膜上ＡＣｈＲ的全身性自身免疫性疾病。     

Semiquantitative measurement of acetylcholine receptor at the motor end-plate in myasthenia gravis

OBJECTIVE: The purpose of this study was to investigate whether this semiquantitative measurement of the motor end-plate acetylcholine receptors (AChRs) can be used to confirm the diagnosis of myasthenia gravis (MG), and in particular ocular MG. METHODS: Motor point biopsies were performed from the biceps brachii muscles. Measurement of AChRs was made in peroxidase-labeled alpha-bungarotoxin stained muscle specimens. PATIENTS: Twenty patients with ocular MG, 37 with generalized MG, 5 with Lambert-Eaton myasthenic syndrome, 3 with botulism, 8 with amyotrophic lateral sclerosis, and 8 controls were included in this study. RESULTS: AChRs were decreased in all patients with generalized MG and in 80% of ocular MG including patients without detectable circulating anti-AChR antibodies, as compared with the control subjects. CONCLUSION: This method is useful to confirm the diagnosis of MG, in particular ocular MG without detectable anti-AChR antibodies.