Induction of the morphologic changes of both acute and chronic experimental myasthenia by monoclonal antibody directed against acetylcholine receptor

Summary To investigate pathogenic mechanisms in experimental autoimmune myasthenia gravis (EAMG) and myasthenia gravis (MG), we studied the acute and chronic effects in rats of injection of rat monoclonal antibodies (MCABs) directed against the acetylcholine receptor (AChR). Animals were severely weak 12 h after a single injection, at which time macrophages were found invading endplate regions of muscle and cholinesterase-stained regions were separted from the underlying muscle fibers. Ultrastructural studies showed findings identical to the acute phase of EAMG: degenerating postsynaptic membranes and invasion and phagocytosis of endplate regions by macrophages. Animals receiving sublethal doses of MCAB recovered clinically by 4–5 days after injection. Recovery was accompanied by a progressive decrease in the number of macrophages associated with endplates and reapposition to the myofibers of the cholinesterasestained regions. Animals injected once, or repeatedly over several months, remained clinically and electromyographically normal after recovery from the initial episode of weakness, but their endplate ultrastructure was highly simplified with blunted or absent synaptic folds and shallow or absent secondary synaptic clefts. These studies demonstrate that anti-AChR MCABs can induce the changes of both acute and chronic EAMG. There is good correlation between the inflammatory changes and the acute clinical disease but poor correlation between morphological and clinical parameters in the chronic syndrome. The latter observation suggests that severe ultrastructural changes, similar to those seen in chronic EAMG and MG, cannot account, at least in rats, for the clinical and electrophysiologic abnormalities of MG.Supported in part by grants from the Muscular Dystrophy Association and the National Institutes of Health (NS15462, A19268)     

Antigen presentation and T cell specificity repertoire in determining responsiveness to an epitope important in experimental autoimmune myasthenia gravis

The overall goal of this study was to define, in experimental autoimmune myasthenia gravis (EAMG), immunological differences between helper T cells from two inbred rat strains that explain disease susceptibility on the one hand (in Lewis rats) and disease resistance on the other hand (in Wistar Furth rats). The working hypothesis for these studies was that the T cell compartment in Wistar Furth rats may lack the ability to activate responsiveness by existing B cells that have the potential to produce disease-causing antibodies; this quality may be related to a lack of T cell reactivity toward a determinant(s) associated with the alpha subunit sequence α100–116 of the acetylcholine receptor (AChR) that demonstrates immunodominance in Lewis rats. Results presented below are consistent with the conclusion that there is a deficit in the Wistar Furth (WF) T cell specificity repertoire responsible for unresponsiveness to this important AChR epitope; this deficit exists despite the apparent ability of WF antigen presenting cells to bind and present the α100–116 peptide, and is likely responsible for the inability of Wistar Furth T cells to drive an anti-AChR antibody response with disease-causing potential.     

Characterization of acetylcholine receptor antibodies in a patient with primary biliary cirrhosis

Antibodies against the acetylcholine receptor were found in a patient with primary biliary cirrhosis. The patient had no clinical or electrophysiological evidence of disturbed neuromuscular function. The antibodies were of both IgG and IgM isotype. Following passive transfer, these antibodies showed the same capacity to bind in vivo to mouse muscle receptors as immunoglobulins from patients with myasthenia gravis. The affinity of the antibodies was high and comparable to that found in myasthenia gravis patients.     

VH gene family utilization of anti-acetylcholine receptor antibodies in experimental autoimmune myasthenia gravis

The immunoglobulin heavy chain (V_H) gene family usage in experimental autoimmune myasthenia gravis (EAMG) model was investigated by RNA slot blot hybridization using V_H gene family specific probes. Anti-acetylcholine receptor (AChR) monoclonal antibodies (mAbs) isolated from susceptible C57BL/6 and resistant BALB/c mice were found to be encoded by V_H genes from at least six different families. The Vgam3.8 family was overrepresented in α-bungarotoxin blocking mAbs. Expression of cross-reactive idiotopes by anti-AChR mAbs was irrespective of the V_H gene family usage. Strain dependent differences in susceptibility for EAMG were not reflected in an aberrant V_H gene family usage of anti-AChR mAbs.     

重症肌无力病人乙酰胆碱受体抗体的测定及临床意义

用ＥＬＩＳＡ（固相酶联免疫吸附）法测定１７２例ＭＧ病人血清乙酰胆碱受体抗体（ＡｃｈＲａｂ），结果显著高于健康献血员组和非ＭＧ病人组。不同性别、病程及临床类型与ＡｃｈＲａｂ无相关性，但４１～５０岁组的显著高于其他年龄组。６７例类固醇激素治疗组、２２例大剂量两种球蛋白治疗组、１２例胸腺切除术组及３例ＭＧ危象病人２４次血浆交换疗法（ＰＥ）组，治疗后伴随肌无力症状的好转，ＡｃｈＲａｂ均显著低于治疗前。结果表明：ＡｃｈＲａｂ测定为ＭＧ诊断提供了可靠的实验依据，为类固醇激素、大剂量丙种球蛋白、胸腺切除术和ＰＥ等治疗ＭＧ提供理论依据和疗效评定的实验指标，进一步证实了ＭＧ免疫学发病机理。     

EMG evidence of myopathy and the occurrence of titin autoantibodies in patients with myasthenia gravis

We studied 65 patients with myasthenia gravis (MG). Clinical, neurophysiological, immunological, and histological findings suggested the coexistence of a presumed autoimmune myopathy. The clinical features were persistent pyridostigmine-resistant weakness and atrophy of striated muscles. The myopathy was found more often in patients with late-onset MG than in those with early-onset (37% vs 13%). Patients with myopathy were also prone to have other immune disorders (47% vs 13%). Elevated titres of antibodies against titin were detected more often in patients with electromyography (EMG) evidence of myopathy than in the sera of those without, and only in late-onset MG cases. Copyright Lippincott Williams & Wilkins     

Myasthenogenicity of a human acetylcholine receptor alpha-subunit peptide: morphology and immunology.

Each of 10 rats inoculated with a synthetic peptide comprising residues 125-147 (without a disulfide bond) of human acetylcholine receptor (AChR) alpha-subunit (H alpha) had deposits of IgG and C3 (immune complexes) and showed morphological changes in the fine structure at the motor end-plates 5 weeks after a single immunization. Antibody to the H alpha peptides was elevated 1 week after immunization, but, antibody levels to solubilized human or rat AChR were very low in 8 of the 10 rats. These results suggest that the immune response to peptide H alpha is the myasthenogenic site, which induces morphological change at the end-plates.     

Clinical significance of detection of antibodies to fetal and adult acetylcholine receptors in myasthenia gravis

Objective To evaluate the frequency, distribution and clinical significance of the antibodies to the fetal and/or adult acetylcholine receptor (AChR) in patients with myasthenia gravis (MG). Methods AChR antibodies were detected by cell-based assay in the serum of ocular MG (OMG) (n = 90) and generalized MG (GMG) patients (n = 110). The fetal-type (2α: β: γ: δ) and adult-type (2α: β: ε: δ) AChR were used as antigens, and their relevance to disease presentation was assessed. Results The overall frequencies of anti-adult and anti-fetal AChR antibodies were similar in all 200 patients examined, with 14 having serum specific to the AChR-γ subunit, and 22 to the AChR-ε subunit. The overall sensitivity when using the fetal and adult AChR antibodies was higher than that when using the fetal AChR antibody only (P = 0.015). Compared with OMG patients, the mean age at disease onset and the positive ratio of antibodies to both isoforms of the AChR were significantly higher in patients who subsequently progressed to GMG. Older patients and patients with both anti-fetal and anti-adult AChR antibodies had a greater risk for developing generalized disease [odds ratio (OR), 1.03; 95% confidence interval (CI), 1.01-1.06 and OR, 5.09; 95% CI, 2.23-11.62]. Conclusion Using both fetal-and adult-type AChRs as the antigens may be more sensitive than using either subtype. Patients with serum specific to both isoforms are at a greater risk of progressing to GMG. Patients with disease onset at an advanced age appear to have a higher frequency of GMG conversion.     

MuSK-Ab与血清学双阴性MG患者的检测及临床表现

目的探讨肌肉特异性酪氨酸激酶抗体(Mu SK-Ab)及血清学双阴性(d SN-MG)重症肌无力(MG)患者的临床特征。方法采用ELISA法检测108例MG患者、80例对照组的乙酰胆碱受体抗体(AchR-Ab)及Mu SK-Ab水平,并分析各型的临床特点。结果 108例MG患者中:AchR-Ab单阳性共计57例(占52.8%);AchRAb阴性的MG患者中Mu SK-Ab阳性的患者有5例(占10%),分型均为全身型。1例患者为AchR-Ab和Mu SK-Ab双阳性(d SP-MG)。共有45例血清双阴性MG(d SN-MG),占41.7%。胸腺异常者仅占24.4%且均未发生肌无力危象。除此之外,我们在疾病对照组中发现2例AchR-Ab阳性,1例Mu SK-Ab阳性。结论贵州省MG患者AchRAb及Mu SK-Ab阳性率同中国大陆、台湾地区的研究结果类似,低于欧美人种。Mu SK-Ab阳性的患者临床分型较重。d SN-MG也占有较大比例,其年龄组成及胸腺情况与其他两组均有差异。     

Experimental myasthenia gravis: Isolation and quantitative assay of anti-acetylcholine receptor antibody protein concentration in sera of rabbits immunized with Narke acetylcholine receptor

Antibody to acetylcholine receptor from Narke electroplax japonica was isolated from serum of rabbits with experimental autoimmune myasthenia gravis by affinity chromatography on a column of torpedo AChR-agarose conjugates. Sixty-three to eight hundred and ninety-six micrograms of antibody protein were obtained per milliliter myasthenic serum. Serum concentrations of antibody protein correlated with the intensity of the disease and were in exact proportion to the antibody titers of the same samples measured by double immunoprecipitant method. This study showed that anti-AChR antibody played a major role in experimental autoimmune myasthenia gravis and provided the first direct, quantitative evidence that the titers measured by Lindstrom's method could be quite a reliable index of antibody protein concentration in the serum of experimental myasthenia gravis subjects.     

Congenital myasthenic syndrome with novel pathogenic variants in the COLQ gene associated with the presence of antibodies to acetylcholine receptors

Congenital myasthenic syndrome (CMS) is a heterogeneous group of inherited disorder which does not associate with anti-acetylcholine receptor (AChR) antibody. The presence of AChR autoantibody is pathogenic and highly sensitive and specific for autoimmune myasthenia gravis (MG). We describe 2 children from unrelated families who presented with hypotonia, ptosis and fatigability in early infancy with anti-AChR antibodies detected via ELISA on 2 separate occasions in the sera. Both were treated as refractory autoimmune MG due to poor clinical response to acetylcholinesterase inhibitor and immunotherapy. In view of the atypical clinical features, genetic studies of CMS were performed and both were confirmed to have novel pathogenic mutations in the COLQ gene. To the best of our knowledge, the presence of anti-AChR antibody in COLQ-related CMS has never been reported in the literature. The clinical presentation of early onset phenotype, and refractoriness to acetylcholinesterase inhibitor and immunotherapy should prompt CMS as a differential diagnosis.     

Immunogenetic heterogeneity and associated autoimmune disorders in myasthenia gravis: a population-based survey in the province of Ferrara, northern Italy

Introduction - The well-established relationship between myasthenia gravis (MG) and HLA antigens varies among different ethnic groups. In Caucasians B8 and/or DR3 alleles have been found associated with young MG women without thymoma and with high titres of acetylcholine-receptor antibody (AChR Ab). An increased frequency of haplotype HLA-A3, B7 and/or DR2 has been observed in older MG patients with low AChR Ab levels. So far, there is no convincing evidence for an association between a specific haplotype HLA and ocular MG or MG with thymoma. MG subjects often show other concurrent autoimmune disorders suggesting a more general inherited predisposition to autoimmunity. We performed a community-based study to verify the HLA-A, B, C, DR and DQ profile on ethnically homogeneous MG patients and with the aim to estimate the frequency of concurrent autoimmune diseases and to compare HLA phenotypes to autoimmune status in different MG patients groups. Methods - Forty-seven patients, living in the province of Ferrara, were followed-up in our neurologic department and typed for HLA Antigens. In addition a set of immunological laboratory tests was performed. Results - We found a trend towards an increased B8 and DR3 frequencies in total affected population; an association between B8 allele and early onset of generalized MG sustained by thymic hyperplasia. The DR3 allele is statistically associated with the presence of additional autoimmune disorders. Conclusions - Our data support the hypothesis of a genetically-based heterogeneity of the disease and show an increased prevalence of associate autoimmune conditions in MG patients.     

放射免疫法定量检测乙酰胆碱受体抗体与重症肌无力患者临床特征的相关性

目的探讨乙酰胆碱受体抗体(AChR-Ab)与重症肌无力(MG)临床特征的相关性。方法采用放射免疫法检测115例MG患者及92例对照组(非MG神经系统疾病患者42例,健康体检者50名)血清AChRAb浓度,应用临床绝对评分记录MG患者病情严重程度。分析各组血清AChR-Ab浓度的差异,以及AChR-Ab浓度与MG患者临床特征的相关性。采用ROC工作特征曲线探讨AChR-Ab诊断MG的敏感度和特异度。结果MG患者血清AChR-Ab浓度中位数(四分位数间距,下同)为3.45(39.38)nmol/L,较非MG神经系统疾病患者[0(0)nmol/L]和健康体检者[0(0)nmol/L]增高(P0.01)。全身型MG(GMG)患者AChR-Ab浓度[25.45(46.14)nmol/L]较眼肌型MG(OMG)患者[0.58(3.56)nmol/L]增高(P0.01)。用ROC曲线法分析显示,以血清AChR-Ab浓度≥0.50nmol/L作为诊断MG界值时灵敏度为72.17%,特异度为100%,曲线下面积(AUC)=0.895(95%CI:0.849~0.941)。AChR-Ab浓度与发病年龄、病程及改良Osserman分型呈正相关(r=0.220,P0.05;r=0.184,P0.05;r=0.382,P0.01),但相关性较弱(均r0.5),与临床绝对记分无相关性(r=0.147,P0.05)。结论用放射免疫法检测血清AChR-Ab浓度诊断MG的灵敏度和特异度均高,有助于减少MG的漏诊率及误诊率,值得临床推广。     

Possible implications of dysregulated nicotinic acetylcholine receptor diffusion and nanocluster formation in myasthenia gravis

Myasthenia gravis is a rare and invalidating disease affecting the neuromuscular junction of voluntary muscles. The classical form of this autoimmune disease is characterized by the presence of antibodies against the most abundant protein in the neuromuscular junction, the nicotinic acetylcholine receptor. Other variants of the disease involve autoimmune attack of non-receptor scaffolding proteins or enzymes essential for building or maintaining the integrity of this peripheral synapse. This review summarizes the participation of the above proteins in building the neuromuscular junction and the destruction of this cholinergic synapse by autoimmune aggression in myasthenia gravis. The review also covers the application of a powerful biophysical technique, superresolution optical microscopy, to image the nicotinic receptor in live cells and follow its motional dynamics. The hypothesis is entertained that anomalous nanocluster formation by antibody crosslinking may lead to accelerated endocytic internalization and elevated turnover of the receptor, as observed in myasthenia gravis.     

Comparison between double-filtration plasmapheresis and immunoadsorption plasmapheresis in the treatment of patients with myasthenia gravis

Two techniques for plasmapheresis are used in the treatment of myasthenia gravis (MG): immunoadsorption (IA) and double filtration (DR). This controlled study evaluated the differences between these techniques in clinical effects and serological changes. Five patients with generalized MG (clinical states IIb and III) were enrolled; each patient received IA and DF plasmapheresis on separate occasions. Immunosorba TR-350 with an affinity to acetylcholine receptor antibodies (AchRAb) was used for IA, while Evaflux 4A was used as the plasma fractionator for DF. Each course of treatment consisted of five sessions of apheresis. MG score, titers of AchRAb, immunoglobulins (IG), and plasma biochemistry were assessed by blinded examiners before and immediately after the entire course of treatment. Both treatments effectively ameliorated symptoms of MG. There were no significant changes in MG score between the two groups (IA vs. DF: 2.2 vs. 2.6, P>0.5). IA had a higher clearance rate of AchRAb than DF (66 % vs. 54 %, P<0.05), while DF removed more IgA (72 % vs. 21 %, P< 0.05) and IgM (89 % vs. 57 %, P<0.01) than did IA. Although IA removed AchRAb more effectively than DF, the clinical effects between these two treatments were similar. The titers of AchRAb cannot reflect the clinical severity. Some circulating factors other than AchRAb may contribute to the pathogenesis of MG. Received: 10 September 1999, Received in revised form: 7 February 2000, Accepted: 24 February 2000     

Content and release of acetylcholinesterase in skeletal muscle of rats with experimental autoimmune myasthenia gravis

The effects of experimental autoimmune myasthenia gravis (EAMG) on acetylcholinesterase (AChE) were investigated in diaphragms of adult female Lewis rats. Both total AChE activity per muscle and release of enzyme activity during a 3-h incubation in vitro were measured. Two groups of myasthenic animals were used. Acute EAMG was induced by intravenous injection 48 h earlier with a syngeneic monoclonal autoantibody against the nicotinic acetylcholine receptor (AChR) of rat skeletal muscle; age- and weight-matched controls received a monoclonal anti-AChR antibody nonreactive with mammalian muscle. Chronic EAMG was induced by immunization 4 weeks earlier with AChR purified from Torpedo electroplax; controls received only adjuvants. When preparations from rats with acute or chronic EAMG were compared with the appropriate controls, no statistically significant differences in content or release of AChE activity were detected. Neither was there any change in the relative amounts of the various molecular forms of AChE in samples from animals with chronic EAMG. We conclude that the structural and functional changes arising in EAMG are highly specific for the acetylcholine receptor and associated elements of the neuromuscular junction, but have little impact on the biology of AChE.     

Corticosteroid treatment of experimental autoimmune encephalomyelitis in the Lewis rat results in loss of Vβ8.2 and myelin basic protein-reactive cells from the spinal cord, with increased total T-cell apoptosis but reduced apoptosis of Vβ8.2 cells

We have studied the effects of corticosteroid treatment on the numbers of lymphocytes obtained from the spinal cords of Lewis rats with acute experimental autoimmune encephalomyelitis (EAE) induced by inoculation with myelin basic protein (MBP) and adjuvants. Flow cytometric studies showed that treatment with dexamethasone (4 mg/kg) 8–12 h prior to study on day 14 after inoculation resulted in a reduction in the numbers of CD5⁺, TCRαβ⁺ and Vβ8.2⁺ cells in the spinal cord. Limiting dilution analysis indicated that dexamethasone treatment 12 h prior to study on day 12 after inoculation reduced the frequencies of MBP-reactive and interleukin-2-responsive lymphocytes in the spinal cord to low levels, but reduced the frequency of concanavalin-A-responsive lymphocytes to a lesser extent. Using propidium iodide staining of nuclear chromatin we also studied lymphocyte apoptosis. Greater numbers of apoptotic cells were found in the cells extracted from the spinal cords of rats, examined on day 14, that had been treated 1–12 h previously with dexamethasone, than in saline-treated controls. This increased level of apoptosis was observed in the CD5⁺ and TCRαβ⁺ cell populations. At 1–4 h after dexamethasone treatment there was a reduction in the selective apoptosis of Vβ8.2⁺ cells that normally occurs during spontaneous recovery from EAE. Therefore apoptosis of Vβ38.2⁺ cells cannot explain the reduction in the numbers of Vβ8.2⁺ cells and MBP-reactive cells in the CNS after dexamethasone treatment. By 8–12 h after dexamethasone treatment the selectivity of the apoptotic process was restored. These studies suggest that a reduction in the number of T-lymphocytes in the central nervous system contributes to the beneficial effects of corticosteroids in EAE.     

青蒿素对实验性自身免疫性重症肌无力大鼠R97-116抗体及细胞因子的影响

目的探讨青蒿素(artemisinin)对实验性自身免疫性重症肌无力(EAMG)大鼠R97-116抗体及干扰素γ(IFN-γ)、白细胞介素17(IL-17)表达水平的影响。方法采用鼠源AChRα亚基97-116肽段免疫方法建立EAMG大鼠模型,将造模成功的大鼠20只随机分为青蒿素小、中、大剂量组和EAMG对照组。青蒿素小、中、大剂量组分别给予15、30、45mg/(kg·d)青蒿素溶液灌胃治疗,1次/d,模型对照组给予等浓度二甲基亚砜水溶液灌胃。评测各组大鼠体质量和临床症状,采用流式细胞术检测淋巴结单个核细胞悬液细胞因子IFN-γ、IL-17水平,ELISA法检测血清抗R97-116IgG/IgG1/IgG2b水平。结果青蒿素中、高剂量组大鼠体质量高于对照组(P0.05);青蒿素各剂量组大鼠临床评分低于对照组(P0.05)。青蒿素各治疗组IFN-γ、IL-17水平均低于对照组(P0.01)。青蒿素15mg/(kg·d)剂量组血清IgG、IgG1、IgG2b水平与对照组比较差异无统计学意义(P0.05);30mg/(kg·d)剂量组血清IgG(P0.05)、IgG1(P0.01)、IgG2b(P0.01)水平低于对照组;45mg/(kg·d)剂量组血清IgG(P0.05)、IgG1(P0.01)水平低于对照组。结论青蒿素能改善EAMG大鼠临床症状,对EAMG大鼠具有免疫调节作用,其机制可能与其通过直接或间接降低血清抗R97-116抗体水平、抑制淋巴结单个核细胞分泌IFN-γ和IL-17促炎性因子有关。     

Glial cell activation and altered metabolic profile in the spinal-trigeminal axis in a rat model of multiple sclerosis associated with the development of trigeminal sensitization

Trigeminal neuralgia is often an early symptom of multiple sclerosis (MS), and it generally does not correlate with the severity of the disease. Thus, whether it is triggered simply by demyelination in specific central nervous system areas is currently questioned. Our aims were to monitor the development of spontaneous trigeminal pain in an animal model of MS, and to analyze: i) glial cells, namely astrocytes and microglia in the central nervous system and satellite glial cells in the trigeminal ganglion, and ii) metabolic changes in the trigeminal system. The subcutaneous injection of recombinant MOG_1-125 protein fragment to Dark Agouti male rats led to the development of relapsing-remitting EAE, with a first peak after 13 days, a remission stage from day 16 and a second peak from day 21. Interestingly, orofacial allodynia developed from day 1 post injection, i.e. well before the onset of EAE, and worsened over time, irrespective of the disease phase. Activation of glial cells both in the trigeminal ganglia and in the brainstem, with no signs of demyelination in the latter tissue, was observed along with metabolic alterations in the trigeminal ganglion. Our data show, for the first time, the spontaneous development of trigeminal sensitization before the onset of relapsing-remitting EAE in rats. Additionally, pain is maintained elevated during all stages of the disease, suggesting the existence of parallel mechanisms controlling motor symptoms and orofacial pain, likely involving glial cell activation and metabolic alterations which can contribute to trigger the sensitization of sensory neurons.