Tumor necrosis factor receptor-1 is critically involved in the development of experimental autoimmune myasthenia gravis

Rs1800629 polymorphism in TNF-alpha is associated with the susceptibility and initial short-term glucocorticoids efficacy in myasthenia gravis patients

Tumor necrosis factor-alpha (TNF-α) is a potent pro-inflammatory agent involved in various autoimmune and inflammatory diseases including myasthenia gravis (MG). In this study, we enrolled 409 adult MG patients and 487 healthy individuals to investigate the association between TNF-α polymorphism and MG. We found the rs1800629 A allele frequency was significantly higher in the MG group than in the control group. Subgroup analysis revealed that the A allele frequencies were significantly higher in the early-onset subgroup, non-thymoma subgroup, ocular-onset subgroup, and mild severity subgroup than in the control group. To minimize the interactions between clinical features, we used a comprehensive classification and found that the rs1800629 A allele frequency was significantly higher in the non-thymoma AChR-Ab negative subgroup than in the control group. In the analysis of initial short-term glucocorticoids (GC) efficacy in the treatment-naive patients, the rs1800629 A allele frequency was significantly higher in the unresponsive subgroup than in the responsive group and the control group. Logistic regression demonstrated the rs1800629 genotypes in the dominant model and disease duration prior to GC treatment independently contributed to initial short-term GC efficacy. In conclusion, our study revealed that in Chinese adult MG patients, rs1800629 polymorphism in TNF-α was associated with the susceptibility of MG and might indicate the initial short-term GC efficacy.

NKT and NKT-like Cells in Autoimmune Neuroinflammatory Diseases-Multiple Sclerosis, Myasthenia Gravis and Guillain-Barre Syndrome

NKT cells comprise three subsets—type I (invariant, iNKT), type II, and NKT-like cells, of which iNKT cells are the most studied subset. They are capable of rapid cytokine production after the initial stimulus, thus they may be important for polarisation of Th cells. Due to this, they may be an important cell subset in autoimmune diseases. In the current review, we are summarising results of NKT-oriented studies in major neurological autoimmune diseases—multiple sclerosis, myasthenia gravis, and Guillain-Barre syndrome and their corresponding animal models.

Preconditioned mesenchymal stem cells treat myasthenia gravis in a humanized preclinical model

Myasthenia gravis (MG) with anti-acetylcholine receptor (AChR) Abs is an autoimmune disease characterized by severe defects in immune regulation and thymic inflammation. Because mesenchymal stem cells (MSCs) display immunomodulatory features, we investigated whether and how in vitro-preconditioned human MSCs (cMSCs) could treat MG disease. We developed a new humanized preclinical model by subcutaneously grafting thymic MG fragments into immunodeficient NSG mice (NSG-MG model). Ninety percent of the animals displayed human anti-AChR Abs in the serum, and 50% of the animals displayed MG-like symptoms that correlated with the loss of AChR at the muscle endplates. Interestingly, each mouse experiment recapitulated the MG features of each patient. We next demonstrated that cMSCs markedly improved MG, reducing the level of anti-AChR Abs in the serum and restoring AChR expression at the muscle endplate. Resting MSCs had a smaller effect. Finally, we showed that the underlying mechanisms involved (a) the inhibition of cell proliferation, (b) the inhibition of B cell-related and costimulatory molecules, and (c) the activation of the complement regulator DAF/CD55. In conclusion, this study shows that a preconditioning step promotes the therapeutic effects of MSCs via combined mechanisms, making cMSCs a promising strategy for treating MG and potentially other autoimmune diseases.

IL-10 derived from CD1dhiCD5⁺ B cells regulates experimental autoimmune myasthenia gravis

IL-10-competent subset within CD1d(hi)CD5(+) B cells, also known as B10 cells, has been shown to regulate autoimmune diseases. In our previous study, adoptive transfer of CD1d(hi)CD5(+) B cells expanded in vivo by GM-CSF prevented and suppressed experimental autoimmune myasthenia gravis (EAMG). The goal of this study was to further examine the role and mechanism of IL-10 in the regulatory function of B10 cells in EAMG. We found that only IL-10 competent CD1d(hi)CD5(+) B cells sorted from WT mice, but not IL-10 deficient CD1d(hi)CD5(+) B cells exhibited regulatory function in vitro and in vivo. Adoptive transfer of IL-10 competent CD1d(hi)CD5(+) B cells led to higher frequency of Tregs and B10 cells, and low levels of proinflammatory cytokines and autoantibody production. We conclude that IL-10 production within CD1d(hi)CD5(+) B cells plays an important role in immune regulation of EAMG.

Myasthenia Gravis: paradox versus paradigm in autoimmunity

Myasthenia Gravis (MG) is a paradigm of organ-specific autoimmune disease (AID). It is mediated by antibodies that target the neuromuscular junction. The purpose of this review is to place MG in the general context of autoimmunity, to summarize the common mechanisms between MG and other AIDs, and to describe the specific mechanisms of MG. We have chosen the most common organ-specific AIDs to compare with MG: type 1 diabetes mellitus (T1DM), autoimmune thyroid diseases (AITD), multiple sclerosis (MS), some systemic AIDs (systemic lupus erythematous (SLE), rheumatoid arthritis (RA), Sjogren's syndrome (SS)), as well as inflammatory diseases of the gut and liver (celiac disease (CeD), Crohn's disease (CD), and primary biliary cirrhosis (PBC)). Several features are similar between all AIDs, suggesting that common pathogenic mechanisms lead to their development. In this review, we address the predisposing factors (genetic, epigenetic, hormones, vitamin D, microbiota), the triggering components (infections, drugs) and their interactions with the immune system [1,2]. The dysregulation of the immune system is detailed and includes the role of B cells, Treg cells, Th17 and cytokines. We particularly focused on the role of TNF-α and interferon type I whose role in MG is very analogous to that in several other AIDS. The implication of AIRE, a key factor in central tolerance is also discussed. Finally, if MG is a prototype of AIDS, it has a clear specificity compared to the other AIDS, by the fact that the target organ, the muscle, is not the site of immune infiltration and B cell expansion, but exclusively that of antibody-mediated pathogenic mechanisms. By contrast, the thymus in the early onset subtype frequently undergoes tissue remodeling, resulting in the development of ectopic germinal centers surrounded by high endothelial venules (HEV), as observed in the target organs of many other AIDs.

VAV1 and BAFF, via NFκB pathway, are genetic risk factors for myasthenia gravis

Objective

To identify novel genetic loci that predispose to early-onset myasthenia gravis (EOMG) applying a two-stage association study, exploration, and replication strategy.

Methods

Thirty-four loci and one confirmation loci, human leukocyte antigen (HLA)-DRA, were selected as candidate genes by team members of groups involved in different research aspects of MG. In the exploration step, these candidate genes were genotyped in 384 EOMG and 384 matched controls and significant difference in allele frequency were found in eight genes. In the replication step, eight candidate genes and one confirmation loci were genotyped in 1177 EOMG patients and 814 controls, from nine European centres.

Results

Allele frequency differences were found in four novel loci: CD86, AKAP12, VAV1, B-cell activating factor (BAFF), and tumor necrosis factor-alpha (TNF-α), and these differences were consistent in all nine cohorts. Haplotype trend test supported the differences in allele frequencies between cases and controls. In addition, allele frequency difference in female versus male patients at HLA-DRA and TNF-α loci were observed.

Interpretation

The genetic associations to EOMG outside the HLA complex are novel and of interest as VAV1 is a key signal transducer essential for T- and B-cell activation, and BAFF is a cytokine that plays important roles in the proliferation and differentiation of B-cells. Moreover, we noted striking epistasis between the predisposing VAV1 and BAFF haplotypes; they conferred a greater risk in combination than alone. These, and CD86, share the same signaling pathway, namely nuclear factor-kappaB (NFκB), thus implicating dysregulation of proinflammatory signaling in predisposition to EOMG.

Prophylactic effect of probiotics on the development of experimental autoimmune myasthenia gravis

Probiotics are live bacteria that confer health benefits to the host physiology. Although protective role of probiotics have been reported in diverse diseases, no information is available whether probiotics can modulate neuromuscular immune disorders. We have recently demonstrated that IRT5 probiotics, a mixture of 5 probiotics, could suppress diverse experimental disorders in mice model. In this study we further investigated whether IRT5 probiotics could modulate the progression of experimental autoimmune myasthenia gravis (EAMG). Myasthenia gravis (MG) is a T cell dependent antibody mediated autoimmune disorder in which acetylcholine receptor (AChR) at the neuromuscular junction is the major auto-antigen. Oral administration of IRT5 probiotics significantly reduced clinical symptoms of EAMG such as weight loss, body trembling and grip strength. Prophylactic effect of IRT5 probiotics on EMAG is mediated by down-regulation of effector function of AChR-reactive T cells and B cells. Administration of IRT5 probiotics decreased AChR-reactive lymphocyte proliferation, anti-AChR reactive IgG levels and inflammatory cytokine levels such as IFN-γ, TNF-α, IL-6 and IL-17. Down-regulation of inflammatory mediators in AChR-reactive lymphocytes by IRT5 probiotics is mediated by the generation of regulatory dendritic cells (rDCs) that express increased levels of IL-10, TGF-β, arginase 1 and aldh1a2. Furthermore, DCs isolated from IRT5 probiotics-fed group effectively converted CD4⁺ T cells into CD4⁺Foxp3⁺ regulatory T cells compared with control DCs. Our data suggest that IRT5 probiotics could be applicable to modulate antibody mediated autoimmune diseases including myasthenia gravis.

Complement and cytokine based therapeutic strategies in myasthenia gravis

Myasthenia gravis (MG) is a T cell-dependent and antibody-mediated disease in which the target antigen is the skeletal muscle acetylcholine receptor (AChR). In the last few decades, several immunological factors involved in MG pathogenesis have been discovered mostly by studies utilizing the experimental autoimmune myasthenia gravis (EAMG) model. Nevertheless, MG patients are still treated with non-specific global immunosuppression that is associated with severe chronic side effects. Due to the high heterogeneity of AChR epitopes and antibody responses involved in MG pathogenesis, the specific treatment of MG symptoms have to be achieved by inhibiting the complement factors and cytokines involved in anti-AChR immunity. EAMG studies have clearly shown that inhibition of the classical and common complement pathways effectively and specifically diminish the neuromuscular junction destruction induced by anti-AChR antibodies. The inborn or acquired deficiencies of IL-6, TNF-α and TNF receptor functions are associated with the lowest EAMG incidences. Th17-type immunity has recently emerged as an important contributor of EAMG pathogenesis. Overall, these results suggest that inhibition of the complement cascade and the cytokine networks alone or in combination might aid in development of future treatment models that would reduce MG symptoms with highest efficacy and lowest side effect profile.

Suppression of Experimental Autoimmune Myasthenia Gravis by Intravenous Immunoglobulin and Isolation of a Disease-Specific IgG Fraction

Intravenous immunoglobulin (IVIG) administration has been beneficially used for the treatment of a variety of autoimmune diseases including myasthenia gravis (MG). We have demonstrated that IVIG administration in experimental autoimmune MG (EAMG) results in suppression of disease that is accompanied by decreased Th1 cell and B cell proliferation. Chromatography of pooled human immunoglobulins (IVIGs) on immobilized IgG, isolated from rats with EAMG, results in a complete depletion of the suppressive activity of the IVIG. Moreover, the eluate from this EAMG-specific antibody column retains the immunosuppressive activity of IVIG. This study supports the notion that the therapeutic effect of IVIGs is mediated by an antigen-specific anti-immunoglobulin (anti-idiotypic) activity that is essential for its suppressive activity.

Myasthenia gravis: past, present, and future

Myasthenia gravis (MG) is an autoimmune syndrome caused by the failure of neuromuscular transmission, which results from the binding of autoantibodies to proteins involved in signaling at the neuromuscular junction (NMJ). These proteins include the nicotinic AChR or, less frequently, a muscle-specific tyrosine kinase (MuSK) involved in AChR clustering. Much is known about the mechanisms that maintain self tolerance and modulate anti-AChR Ab synthesis, AChR clustering, and AChR function as well as those that cause neuromuscular transmission failure upon Ab binding. This insight has led to the development of improved diagnostic methods and to the design of specific immunosuppressive or immunomodulatory treatments.

Intravenous immunoglobulin suppresses experimental myasthenia gravis: Immunological mechanisms

Intravenous immunoglobulin (IVIG) administration has been beneficially used in the treatment of several autoimmune disorders including myasthenia gravis (MG), although its mechanism of action is still not clear. To study the optimal conditions of IVIG treatment and delineate its mechanism of action we established a suitable model in rat experimental autoimmune MG (EAMG). We show that IVIG has a suppressive effect on the clinical symptoms of ongoing EAMG that is associated with decreased AChR-specific cellular and humoral immune reactivity. Costimulatory factors and cytokine profile analyses suggest that IVIG immunomodulation in EAMG involves suppression of B and Th1-type T cell responses with no generation of T-regulatory cells. Our data contribute to the understanding of the immunological mechanisms underlying IVIG treatment in MG and in other autoimmune disorders.

Overexpression of phosphodiesterases in experimental autoimmune myasthenia gravis: suppression of disease by a phosphodiesterase inhibitor

Myasthenia gravis (MG) and experimental autoimmune MG (EAMG) are T cell-dependent antibody-mediated autoimmune disorders, in which the nicotinic acetylcholine receptor (AChR) is the major autoantigen. DNA microarray analysis revealed increased levels of several phosphodiesterase (PDE) subtypes in lymph node cells (LNC) and muscles of EAMG rats compared with healthy controls. Quantitative real-time PCR analysis indicated that EAMG is characterized by an increase of PDE subtypes 1, 3, 4, and 7 in LNC and of PDE subtypes 2, 3, 4, and 7 in muscles. Pentoxifylline (PTX), a general PDE inhibitor, inhibited the progression of EAMG when treatment started at either the acute or chronic stages of disease. This suppression was associated with down-regulation of humoral and cellular AChR-specific responses, as well as down-regulation of PDE4, TNF-alpha, IL-18, IL-12, and IL-10 in LNC and of PDEs 1, 4, 7, and TNF-alpha in muscles. The expression of Foxp3, a transcription factor essential for CD4+CD25+ regulatory T cell function, was increased in splenocytes although the number of these cells remained unchanged. PTX also reduced the expression of the endopeptidase cathepsin-l, a marker of muscle damage, in EAMG muscles. This study demonstrates the involvement of PDE regulation in EAMG pathogenesis and suggests that PDE inhibitors may be considered for immunotherapy of MG.

IL-1 receptor antagonist-mediated therapeutic effect in murine myasthenia gravis is associated with suppressed serum proinflammatory cytokines, C3, and anti-acetylcholine receptor IgG1

In myasthenia gravis (MG), TNF and IL-1beta polymorphisms and high serum levels of these proinflammatory cytokines have been observed. Likewise, TNF and IL-1beta are critical for the activation of acetylcholine receptor (AChR)-specific T and B cells and for the development of experimental autoimmune myasthenia gravis (EAMG) induced by AChR immunization. We tested the therapeutic effect of human recombinant IL-1 receptor antagonist (IL-1ra) in C57BL/6 mice with EAMG. Multiple daily injections of 0.01 mg of IL-1ra administered for 2 wk following two AChR immunizations decreased the incidence and severity of clinical EAMG. Furthermore, IL-1ra treatment of mice with ongoing clinical EAMG reduced the clinical symptoms of disease. The IL-1ra-mediated suppression of clinical disease was associated with suppressed serum IFN-gamma, TNF-alpha, IL-1beta, IL-2, IL-6, C3, and anti-AChR IgG1 without influencing total serum IgG. Therefore, IL-1ra could be used as a nonsteroidal drug for the treatment of MG.

Overexpression of IFN-Induced Protein 10 and Its Receptor CXCR3 in Myasthenia Gravis

Myasthenia gravis (MG) and its animal model, experimental autoimmune MG (EAMG), are autoimmune disorders in which the acetylcholine receptor (AChR) is the major autoantigen. Microarray technology was used to identify new potential drug targets for treatment of myasthenia that would reduce the need for the currently used nonspecific immunosuppression. The chemokine IFN-gamma-inducible protein 10 (IP-10; CXCL10), a CXC chemokine, and its receptor, CXCR3, were found to be overexpressed in lymph node cells of EAMG rats. Quantitative real-time PCR confirmed these findings and revealed up-regulated mRNA levels of another chemoattractant that activates CXCR3, monokine induced by IFN-gamma (Mig; CXCL9). TNF-alpha and IL-1beta, which act synergistically with IFN-gamma to induce IP-10, were also up-regulated. These up-regulations were observed in immune response effector cells, namely, lymph node cells, and in the target organ of the autoimmune attack, the muscle of myasthenic rats, and were significantly reduced after suppression of EAMG by mucosal tolerance induction with an AChR fragment. The relevance of IP-10/CXCR3 signaling in myasthenia was validated by similar observations in MG patients. A significant increase in IP-10 and CXCR3 mRNA levels in both thymus and muscle was observed in myasthenic patients compared with age-matched controls. CXCR3 expression in PBMC of MG patients was markedly increased in CD4(+), but not in CD8(+), T cells or in CD19(+) B cells. Our results demonstrate a positive association of IP-10/CXCR3 signaling with the pathogenesis of EAMG in rats as well as in human MG patients.

Myasthenia gravis: clinical, immunological, and therapeutic advances

We give an update on clinical, immunological, and therapeutic advances in the field of myasthenia gravis, including a summary of suggested therapeutic recommendations.

Etanercept treatment in corticosteroid-dependent myasthenia gravis

The authors report a prospective pilot trial of etanercept in corticosteroid-dependent autoimmune myasthenia gravis. Eleven patients were enrolled, with eight completing the 6-month trial. Two patients were withdrawn owing to disease worsening, and one patient was withdrawn because of an erythematous skin rash. Six of the eight patients who completed the trial improved, based on quantitative measures of muscle strength and lowering of corticosteroid requirement.

Immunosuppression of rat myasthenia gravis by oral administration of a syngeneic acetylcholine receptor fragment

A syngeneic rat recombinant fragment of the extracellular domain of the acetylcholine receptor (AChR) alpha-subunit (Ralpha1-205), administered orally, suppresses ongoing experimental autoimmune myasthenia gravis (EAMG) in rats. The underlying mechanism is a shift from Th1 to Th2 regulation as evidenced by downregulated mRNA expression levels of IFN-gamma and TNF-alpha, upregulated IL-10, changes in anti-AChR IgG isotypes and diminished Th1 signaling via CD28/CTLA-4:B7. Unlike the xenogeneic fragment, the syngeneic Ralpha1-205 does not induce elevation in TGF-beta and elicitation of autoregulatory cells. The ability to suppress EAMG by a non-immunogenic syngeneic fragment of AChR is encouraging and may in the future be applied for the treatment of myasthenia gravis in humans.

Protective potential of experimental autoimmune myasthenia gravis in Lewis rats by IL-10-modified dendritic cells

Dendritic cells (DC) are usually regarded as antigen-presenting cells (APC) involved in T cell activation, but DC also directly or indirectly affect B cell function, antibody synthesis and isotype switch. In this study, we explore potential of DC-based immunotherapy in ongoing experimental autoimmune myasthenia gravis (EAMG) in Lewis rats, which is mediated by anti-acetylcholine receptor (AChR) antibodies. Spleen DC were isolated from onset of Lewis rat EAMG on day 39 post immunization (p.i.), exposed in vitro to IL-10 and then injected intraperitoneally into ongoing EAMG Lewis rats at dose of 1 x 10(6) cells/rat on day 5 p.i. with AChR + complete Freund's adjuvant. IL-10-modified DC resulted in lower clinical scores, less body weight loss, lower numbers of anti-AChR IgG antibody-secreting cells and lower affinity of anti-AChR antibodies in rats receiving IL-10-modified DC, accompanied with lower expression of CD80 and CD86 and lower lymphocyte proliferation among lymph node mononuclear cells compared with control EAMG rats. Lower levels of IL-10 and IFN-gamma were also found in the supernatants of AChR-stimulated lymph node MNC culture in rats receiving IL-10-modified DC. These results demonstrate that IL-10-modified DC induced hypo-responsiveness by down-regulating co-stimulatory molecules, and reduced production of anti-AChR antibodies possibly by inhibiting IL-10 production. Importantly, this procedure that autologous DC from EAMG were adopted to treat ongoing EAMG is more close to clinical trial in human, encouraging future evaluation in human myasthenia gravis.

Anti-TNF-alpha antibodies suppress the development of experimental autoimmune myasthenia gravis

To understand the role of TNF-alpha in the induction of experimental autoimmune myasthenia gravis (EAMG) and detect a possible effect of anti-TNF-alpha antibodies in the treatment of EAMG, anti-TNF-alpha antibodies were administrated intraperitoneally to Lewis rats twice per week for 5 weeks from the day of immunization with Torpedo AChR and complete Freund's adjuvant (CFA). Administration of anti-TNF-alpha antibodies resulted in lower incidence of EAMG, and in delayed onset and only mild muscle weakness compared with control EAMG rats. These mild clinical signs were accompanied by lower AChR-specific lymphocyte proliferation, down-regulated IFN-gamma and IL-10, and up-regulated TGF-beta. The lower levels of anti-AChR IgG, Ig2a and IgG2b and decreased anti-AChR IgG affinity were found in rats treated with anti-TNF-alpha antibodies. These results demonstrate that anti-TNF-alpha antibodies can suppress the induction and development of EAMG.

Tumor necrosis factor receptor p55 and p75 deficiency protects mice from developing experimental autoimmune myasthenia gravis

The precise pathogenic role of proinflammatory cytokines belonging to the tumor necrosis factor (TNF) family has not been investigated yet in antibody-mediated myasthenia gravis (MG) and experimental autoimmune myasthenia gravis (EAMG). In this study we report that TNF receptor p55(-/-) p75(-/-) mice were resistant to the development of clinical EAMG induced by acetylcholine receptor (AChR) immunizations. The resistance was associated with reduced serum levels of IgG, IgG(1), IgG(2a), and IgG(2b) anti-AChR antibody isotypes. However, IgM anti-AChR antibodies were not reduced, suggesting defective anti-AChR IgG class switching in TNF receptor p55(-/-) p75(-/-) mice. We thus demonstrate the genetic evidence for the role of TNF receptor p55 and p75 in EAMG pathogenesis, and their requirement for the generation of anti-AChR IgG antibodies.

Treatment of experimental autoimmune myasthenia gravis with recombinant human tumor necrosis factor receptor Fc protein

Lymphotoxin-alpha (TNF-beta) and TNF receptor p55 gene knockout mice are resistant to the development of antibody and complement mediated experimental autoimmune myasthenia gravis (EAMG), suggesting a possible role of TNF in mediating EAMG. Therefore, we tested the hypothesis that blocking the functional interaction of TNF with their receptors by soluble recombinant human TNFR:Fc would suppress the ongoing clinical EAMG. Recombinant human TNFR:Fc administered daily for 2 weeks to C57BL6 mice with ongoing clinical EAMG significantly improved clinical EAMG when compared with placebo-treated mice. A clinical trial of selected myasthenia gravis patients with recombinant human TNFR:Fc could be attempted.

Effector lymphocytes in autoimmunity

Autoimmune diseases result from complex interactions among different T- and B-lymphocyte subpopulations that target a rapidly growing number of autoantigens on different cell types. The etiology of most spontaneous autoimmune disorders, and both the kinetics and hierarchy of the underlying autoimmune responses are poorly understood. However, important advances have been made in recent years in our understanding of how autoreactive lymphocytes cause tissue damage, including the discovery that granzyme B binds to a cell surface receptor on target cells. This review is an attempt to summarize recent developments in this area.