HLA in myasthenia gravis: From superficial correlation to underlying mechanism

Myasthenia gravis (MG) is a rare autoimmune disease characterized by muscle weakness and abnormal fatigability. Like many other autoimmune diseases, genetic contribution to MG has been studied where the HLA system appears to play the most vital role. Although many correlations have been revealed in these studies, the underlying mechanism for them is still in the veil. Based on current evidence, we propose two synergetic mechanisms underlying the MG predisposition via HLA. In brief, the first advocates specific MHC II-peptide patterns that influence the efficacy of antigen presentation, and the second emphasizes the role of classical MHC alleles in shaping the TCR repertoire for MG predisposition. Besides, possible explanations for unresolved or controversial MG-related epidemiological phenomenon or clinical problems are addressed as well. Then, we discuss three factors influencing the effect of HLA on MG: gender discrepancy, inflammatory microenvironment, and epigenetic regulation. Lastly, from a provisional angle, we introduce several precautious treatments for people highly predisposed to MG. Although this is a review focusing on MG, the underlying mechanisms might be applicable in other autoimmune diseases as well.     

Studies on HLA antigens and cellular and humoral autoimmune phenomena in patients with myasthenia gravis.

The HLA phenotype of fifty-four patients with myasthenia gravis (MG) was compared to that of 600 controls. When male and female patients were compared separately with the control group, HLA-B12 was increased in MG males (P less than 0-023) and HLA-A1, B8 in MG females (P less than 0-023). In addition, HLA-A1, B8 was correlated with the early onset type of MG and with a more severe clinical course (Osserman scale IIb-III) in female patients. Cell-mediated immune responses were studied in a twenty-one hospitalized MG patients. Specific cell-mediated immunity to highly purified muscle proteins was investigated using the two-step-leucocyte migration agarose test and general cell-mediated immunity was studied by determining the cutaneous response to four extrinsic antigens. Cellular immune activity to muscle antigens occurred in fourteen out of twenty-one patients (67%) with MG and with one exception, in none of the controls. There was no significant difference in the LIF inducing ability of the different muscle antigens. A statistically significant correlation between HLA-A1 and B8 and either cell-mediated immune reactivity to muscle antigens or humoral autoimmune phenomena or clinical parameters was not found. Only a trend toward an association between HLA-A1 and B8 and a cell-mediated immune response to muscle antigens could be demonstrated. Positive delayed skin reactions to extrinsic antigens were observed with the same frequency as in healthy blood donors.     

HLA class II transgenic mice as models of human diseases

Summary: Predisposition co develop Various autoimmune disorders has been associated with certain HLA class II molecules but there is a lack of information on che pathophysiological rule of HLA genes in conferring susceptibility Various experimental animal models of autoimmune disease have been studied to address the role of immune response genes. To study the interactions involved between class II molecules (DQ and DR) and define the immunologic mechanisms in various diseases, we generated HLA-DR and DQ transgenic mice that lacked endogenous class II molecules. The HLA molecules in these mice arc expressed on the cell surface and can positively select CD4+ T cells expressing Various Vβ T-cell receptors (TCR). A peripheral tolerance is maintained co transgenic HLA molecules thus indicating that these molecules act as self, Mouse co stimulatory and accessory molecules can interact with the HLA-peptide-TCR complex leading to efficient T-cell activation. In this review, we describe immunogenetic models for human diseases using these transgenic mice. Our studies show that HLA class II transgene-restricted T cells recognize the immunodominant antigens and peptide epitopes, similar to HLA class II-restricted human T cells. Thus these mice provide powerful tools to understand the role of HLA class II molecules in predisposition and onset of human diseases and to develop immunotherapy and vaccines.     

HLA class I and class II polymorphisms in Saudi patients with myasthenia gravis

Myasthenia gravis (MG) is a rare autoimmune disease of the neuromuscular junction. MG has been shown to be associated with many HLA antigens in different populations. Here we have analysed the frequency of HLA‐A, B, DR and DQ in a group of Saudi MG patients and compared their results to a group of healthy controls. MG in Saudi patients is found to be associated with HLA‐A*23, B*08, B*18, DRB1*16 and DRB1*13. The strongest association was with HLA‐B*08, which was associated with young age at onset and female gender. Our results are in line with other published results from around the world and warrant fine mapping of the area using microsatellite to map the disease gene.     

Suppression by mAbs against DQB1 peptides of in vitro proliferation of AChR-specific T cells from myasthenia gravis patients

It has been indicated that multiple genes, including HLA genes, are collectively involved in the susceptibility to myasthenia gravis (MG). DQB1 alleles represent one of those associated with MG. We have prepared B-cell hybridomas that produce mAbs against peptides corresponding to the tip of the MHC antigen-binding cavity (region 70-90) of alleles DQB1*02, *03, *05 and *06. The mAbs bound to DQ molecules isolated from cells. In the assays using peripheral blood lymphocytes (PBL) from patients with MG, the mAbs against peptides of the correlate HLA DQ sequences inhibited the in vitro proliferation of acetylcholine receptor (AChR)-specific T cells. The results indicate that the function of disease-related MHC alleles may be blocked by directly and selectively targeting the antigen-presenting region on these MHC molecules. The results also suggest that DQ molecules are one of those involved in the restriction of autoimmune anti-AChR responses in MG. The strategy could provide an effective means for immunointervention in MG. It may also potentially be adapted for down-regulation of undesirable immune responses such as in other autoimmune diseases, allergic reactions, or clinical conditions where immune responses to a therapeutic protein develop.     

Suppression by mAbs against DQB1 peptides of in vitro proliferation of AChR-specific T cells from myasthenia gravis patients

It has been indicated that multiple genes, including HLA genes, are collectively involved in the susceptibility to myasthenia gravis (MG). DQB1 alleles represent one of those associated with MG. We have prepared B-cell hybridomas that produce mAbs against peptides corresponding to the tip of the MHC antigen-binding cavity (region 70–90) of alleles DQB1*02, *03, *05 and *06. The mAbs bound to DQ molecules isolated from cells. In the assays using peripheral blood lymphocytes (PBL) from patients with MG, the mAbs against peptides of the correlate HLA DQ sequences inhibited the in vitro proliferation of acetylcholine receptor (AChR)-specific T cells. The results indicate that the function of disease-related MHC alleles may be blocked by directly and selectively targeting the antigen-presenting region on these MHC molecules. The results also suggest that DQ molecules are one of those involved in the restriction of autoimmune anti-AChR responses in MG. The strategy could provide an effective means for immunointervention in MG. It may also potentially be adapted for down-regulation of undesirable immune responses such as in other autoimmune diseases, allergic reactions, or clinical conditions where immune responses to a therapeutic protein develop.     

Antiacetylcholine receptor and antinuclear antibodies in myasthenia gravis. Correlation with HLA, sex and Gm

Sera from 27 subjects with myasthenia gravis (MG) were examined by immunoassay for antibodies to double-stranded DNA (ds-DNA), RNA-nucleoprotein complexes (ENA) and acetylcholine receptor (ACHR). The prevalence of the genetic markers of sex, HLA and Gm were analyzed in relation to various parameters of these autoantibodies. The highest levels of ds-DNA antibodies were associated with HLA B8 as compared to other HLA antigens (p less than 0.05), females as compared with males (p less than 0.05), and females with HLA B8 (p less than 0.05) when both sex and HLA were analyzed concurrently. An association between low titers and HLA B7 (p less than 0.05), with a significant difference between the B8 females and B7 males (p less than 0.05) was also noted. By contrast, no Gm association was noted for antinuclear antibody parameters, but was observed in females between high ACHR antibody titers and the homozygous phenotype (3; 5, 13) (p less than 0.05). This study of MG implicated HLA and sex factors in the production of a broad spectrum of antinuclear antibodies, while the contrasting Gm association noted with ACHR antibody titers was indicative of distinctive immunogenetic influences over autoantibody production in MG.     

Cortactin autoantibodies in myasthenia gravis

Myasthenia gravis (MG) is an autoimmune disease characterized by muscle weakness, fatigability, and autoantibodies against protein antigens of the muscle endplate. Antibodies against acetylcholine receptor (AChR), and less frequently against muscle-Specific Kinase (MuSK) or lipoprotein related protein 4 (LRP4) occur in patients with seropositive MG (SPMG). However, about 10% of patients do not have detectable autoantibodies despite evidence suggesting that the disorder is immune mediated; this disorder is known as seronegative MG (SNMG). Using a protein array approach we identified cortactin (a protein that acts downstream from agrin/MuSK promoting AChR clustering) as potential new target antigen in SNMG. We set up an ELISA assay and screened sera from patients with SPMG, SNMG, other autoimmune diseases and controls. Results were validated by immunoblot. We found that 19.7% of patients with SNMG had antibodies against cortactin whereas only 4.8% of patients with SPMG were positive. Cortactin antibodies were also found in 12.5% of patients with other autoimmune disorders but only in 5.2% of healthy controls. We conclude that the finding of cortactin antibodies in patients with SNMG, suggests an underlying autoimmune mechanism, supporting the use of immune therapy.     

Complicating autoimmune diseases in myasthenia gravis: a review

Abstract

Myasthenia gravis (MG) is a rare autoimmune disease of skeletal muscle endplates. MG subgroup is relevant for comorbidity, but usually not accounted for. MG patients have an increased risk for complicating autoimmune diseases, most commonly autoimmune thyroid disease, systemic lupus erythematosus and rheumatoid arthritis. In this review, we present concomitant autoimmune disorders associated with the different MG subgroups, and show how this influences treatment and prognosis. Concomitant MG should always be considered in patients with an autoimmune disorder and developing new neuromuscular weakness, fatigue or respiratory failure. When a second autoimmune disorder is suspected, MG should be included as a differential diagnosis.     

HLA genotypes in Turkish patients with myasthenia gravis: comparison with multiple sclerosis patients on the basis of clinical subtypes and demographic features

The nature and intensity of the association of myasthenia gravis (MG) with distinct human leukocyte antigens (HLA) haplotypes differ between ethnic populations. The aims of the present study were to examine the relationship between HLA class I and II haplotypes and MG; to show the HLA associations with various MG subsets; and to investigate the association between MG and clinical subgroups of multiple sclerosis (MS) regarding HLA haplotypes. A total of 66 patients with MG were enrolled onto the study. The mean age at onset was 42.01 years. A total of 122 clinically definite MS patients and 188 healthy subjects were examined as control groups. The present study clearly showed associations with HLA-DR3, -B8, -A1, and -A2 in MG. In patients with early-onset MG, associations with HLA-DR3, -B8, and -A2 were stronger. When compared with MS, in the MG group, there was still a strong association with -B8, -DR3, and -A1. In subgroup analysis, there was no difference between MG and primary progressive MS patients. On the basis of the presence of anti-AChR antibodies, there was a statistically significant association with HLA-DR3. On the basis of presence of thymoma, no HLA allele showed clear associations in MG patients with thymoma. This is the first study to examine the relationship between HLA haplotypes and MG in the Turkish population and to compare MG with another autoimmune disease, MS, on the basis of the HLA haplotypes. Further investigations with a larger population are required to explain this finding.     

Genetic basis of myasthenia gravis – A comprehensive review

Myasthenia gravis (MG) is a rare autoimmune disease characterized by the production of autoantibodies against proteins of the postsynaptic membrane in the neuromuscular junction. The estimated number of MG patients is steadily increasing, and it had more than doubled in the last 20 years. Monozygotic MG twin concordance is estimated to be about 35% supporting the central role of environmental factors in MG etiology. Epigenetics, presume to be the mechanistic link between environmental and genetic risk factors in disease development, provides support for specific microRNAs associated with MG. Genetic studies have mainly pointed at specific HLA alleles implicated in MG susceptibility, however recently both TNFAIP3-interacting protein 1 (TNIP1) and tyrosine phosphatase non-receptor 22 (PTPN22) were indicated to be associated with MG in a GWAS study. A gender bias was observed for SNPs in the HLA-locus, suggesting female-specific alleles have an increase risk for MG. Moreover, sex hormones play a pivotal role in the gender bias in autoimmunity in general and in MG in particular. Hence the genetic basis of gender bias might be highly pertinent to MG and deserves further characterization. Pathway-based analyses that combine information across multiple genes into a limited number of molecular networks have been found to be a powerful approach. Both regulatory T-cell (Treg) differentiation and NF-κB signaling pathway have been shown to have relevance to MG pathophysiology. Hence studies centered around two pathways might be a fruitful approach to identify additional polymorphisms associated with myasthenia gravis.     

重症肌无力的免疫耐受治疗

重症肌无力（MG）是累及神经一肌肉接头突触后膜上乙酰胆碱受体（AChR）的自身免疫性疾病,其发病的关键在于自我耐受的破坏,导致自身AChR出现异常的细胞免疫应答和体液免疫应答。这种抗AChR抗体的产生是T细胞依赖性的,故AChR特异性的T细胞就是MG特异性治疗的潜在靶位。随着免疫学的发展,MG免疫耐受治疗有可能会特异性地和有效地防止或阻断MG的发生与进展。     

Anti-p110 autoantibodies identify a subtype of "seronegative" myasthenia gravis with prominent oculobulbar involvement

Myasthenia gravis (MG) is an autoimmune disease characterized by muscle weakness and pathogenetic autoantibodies directed against the nicotinic acetylcholine receptor (seropositive myasthenia gravis; SPMG). Nearly 15% to 20% of MG patients do not have these antibodies (seronegative myasthenia gravis; SNMG), but several evidence indicate that these patients have circulating pathogenic autoantibodies directed against other muscle antigens. Using the TE671 rhabdomyosarcoma cell line as an antigen source, we analyzed sera from 63 SNMG and 26 SPMG patients and 26 healthy blood donors by FACS analysis. We found that 40 of 63 SNMG patients and only 1 of 26 SPMG patients had IgG binding to the TE671 cell line. None of the sera bound to the unrelated MRC5 cell line. To identify the antigen, we analyzed sera immunoreactivity in more detail by immunoprecipitation of biotinylated membrane proteins from TE671 cells. When the immunoprecipitated proteins were separated by SDS-PAGE electrophoresis and then transferred to nitrocellulose membranes, we found that SNMG IgG identify a band corresponding to a protein with a molecular weight of 110 kDa (P110), which is not recognized by seropositive MG sera. This anti-P110 immunoreactivity is significantly associated with a distinct clinical picture characterized by a prominent involvement of ocular and bulbar muscles, with frequent respiratory problems (p < 0.005), and is recognized by a specific antimuscle specific kinase (MuSK) antiserum. In a recent article, the presence of anti-MuSK antibodies was described in SNMG. Our results confirm the presence of these antibodies in SNMG and suggest that anti-P110/MuSK autoantibodies identify a subtype of SNMG in which the different pathogenesis induces the distinct clinical picture.     

The different roles of the thymus in the pathogenesis of the various myasthenia gravis subtypes

The thymus plays distinct roles in the pathogenesis of the different Myasthenia gravis (MG) subtypes. Inflammatory, neoplastic and age-related alterations of the thymus are of pivotal relevance for the initiation of anti-acetylcholine receptor (AChR) autoimmunity in early onset MG, thymoma-associated MG and, likely, late onset MG, respectively. By contrast, the thymus is presumably not related to MG that is due to autoantibodies to the muscle specific kinase, MuSK. Finally, the role of the thymus is still obscure in MG defined by antibodies against the agrin receptor LRP4 and in MG without all of the above autoantibdies (triple sero-negative MG) since these MG subtypes have been described only recently and thymectomy has not been their standard treatment. This review aims to give an update on intrathymic mechanisms of tolerance breakdown in MG, including abnormal T cell selection and activation, the role of thymic myoid cells, the autoimmune regulator (AIRE) and regulatory T cells.     

Human reproductive failure II: immunogenetic and interacting factors

Studies in humans suggest that reproductive failure may be influenced by immunological factors or by genes encoding immunological factors and regulatory mechanisms controlling immunological expression. Using molecular methods, immunological factors can be clearly studied in an immunogenetic context. One example, the major histocompatibility complex (MHC), known as the human leukocyte antigens (HLA) in humans and MHC in other mammals, affects many different stages of reproduction. Studies in some outbred, and in closely related, human populations indicate that HLA, or HLA-linked, genes and HLA regulatory factors affect gamete development, embryo cleavage, blastocyst and trophoblast formation, implantation, fetal development and survival. Studies in non-human mammals indicate that MHC, or MHC-linked, genes such as the grc complex, Ped/Qa-2, t haplotypes and MHC regulatory factors, have similar reproductive effects. Human reproductive failure may also be a consequence of disruption of interacting factors, including interactions between HLA antigens, cytokines and natural killer (NK) cells. In this review, we highlight the importance of immunogenetic and interacting factors in human reproductive failure. We argue that studies in closely related human populations and animal models may contribute to a better understanding of the ways in which immunogenetic and interacting factors are involved in human reproduction.     

Genetic control of autoantibody expression in autoimmune myasthenia gravis: role of the self-antigen and of HLA-linked loci

Autoantibodies against the muscle acetylcholine receptor (AChR) play an essential role in the pathophysiology of autoimmune myasthenia gravis (MG). Their serum titers, however, vary considerably among patients. Our aim was to investigate whether their variation might be explained by genetic factors. Using different methods, we have obtained strong evidence for a three-locus association influencing autoantibody titers in MG patients with thymus hyperplasia or with a normal thymus. Two of the loci, one encoding the AChR alpha-subunit, the other encoding the alpha-chain of the class II antigen-presentation molecule, HLA-DQ, demonstrated interaction to determine high autoantibody titers. The third locus was associated with the 8.1 ancestral HLA haplotype. It exerted an additive effect and it is postulated to have a nonantigen specific immunoregulatory function. Our study demonstrates for the first time that polymorphism of an autoantigen gene may quantitatively modify the immune response against it. Altogether, the data lend support to a three-gene model to explain autoantibody expression in a subset of MG patients.     

Complement associated pathogenic mechanisms in myasthenia gravis

The complement system is profoundly involved in the pathogenesis of acetylcholine receptor (AChR) antibody (Ab) related myasthenia gravis (MG) and its animal model experimental autoimmune myasthenia gravis (EAMG). The most characteristic finding of muscle pathology in both MG and EAMG is the abundance of IgG and complement deposits at the nerve–muscle junction (NMJ), suggesting that AChR-Ab induces muscle weakness by complement pathway activation and consequent membrane attack complex (MAC) formation. This assumption has been supported with EAMG resistance of complement factor C3 knockout (KO), C4 KO and C5 deficient mice and amelioration of EAMG symptoms following treatment with complement inhibitors such as cobra venom factor, soluble complement receptor 1, anti-C1q, anti-C5 and anti-C6 Abs. Moreover, the complement inhibitor decay accelerating factor (DAF) KO mice exhibit increased susceptibility to EAMG. These findings have brought forward improvisation of novel therapy methods based on inhibition of classical and common complement pathways in MG treatment.     

Ectopic germinal centers,BAFF and anti-B-cell therapy in myasthenia gravis

Myasthenia gravis (MG) is an autoimmune disease mediated by antibodies directed to molecules of the endplate of the neuromuscular junction. B cells play a major role in MG disease since they produce the pathogenic antibodies and therapies targeting B cells are effective. The aim of this article was to review the role of B cells in myasthenia gravis. We will first describe what we know about B cells in this disease and examine the involvement of the B cells in the thymus of MG patients. We will detail the role of factors associated with B-cell function such as BAFF. Finally, we will discuss the effects of therapy targeting B cells.     

Daunomycin treatment prevents clinical expression of experimental autoimmune myasthenia gravis

Myasthenia gravis (MG) is an autoimmune neuromuscular disease, characterized by muscle weakness and electrophysiological abnormality. No treatment which would reliably induce permanent clinical remission of MG is yet available. The therapeutic efficacy and toxic effect of daunomycin (Dm), an antibiotic of the rhodomycin group, was evaluated in murine experimental autoimmune MG. Low dosage Dm treatment effectively prevented the development of muscle weakness and its associated electrophysiological abnormality, without inducing detectable toxicity and global immunosuppression.