Mechanism of nasal tolerance induced by a recombinant fragment of acetylcholine receptor for treatment of experimental myasthenia gravis

A Recombinant Acetylcholine Receptor α1 Subunit Extracellular Domain Is a Promising New Drug Candidate for Treatment Of Myasthenia Gravis

Background and Aims

Myasthenia gravis (MG) is a T-cell dependent antibody-mediated autoimmune disease in which the nicotinic acetylcholine receptor (AChR) is the major autoantigen, comprising several T and B cell auto-epitopes. We hypothesized that an efficacious drug candidate for antigen-specific therapy in MG should comprise a broad range of these auto-epitopes and be administered in a noninflammatory and tolerogenic context.

Methods

We used a soluble mutated form of the extracellular domain of the α1 chain of the AChR (α1-ECD_m), which represents the major portion of auto-epitopes involved in MG, and investigated, in a well-characterized rat model of experimental autoimmune myasthenia gravis (EAMG) whether its intravenous administration could safely and efficiently treat the autoimmune disease.

Results

We demonstrated that intravenous administration of α1-ECD_m abrogates established EAMG, in a dose and time dependent manner, as assessed by clinical symptoms, body weight, and compound muscle action potential (CMAP) decrement. Importantly, the effect was more pronounced compared to drugs representing current standard of care for MG. The protein had a short plasma half-life, most of what could be recovered was sequestered in the liver, kidneys and spleen. Further, we did not observe any signs of toxicity or intolerability in animals treated with α1-ECD_m.

Conclusion

We conclude that intravenous treatment with α1-ECD_m is safe and effective in suppressing EAMG. α1-ECD_m is in preclinical development as a promising new drug candidate for MG.

Myasthenia Gravis: Autoantibody Specificities and Their Role in MG Management

Myasthenia gravis (MG) is the most common autoimmune disorder affecting the neuromuscular junction, characterized by skeletal muscle weakness and fatigability. It is caused by autoantibodies targeting proteins of the neuromuscular junction; ~85% of MG patients have autoantibodies against the muscle acetylcholine receptor (AChR-MG), whereas about 5% of MG patients have autoantibodies against the muscle specific kinase (MuSK-MG). In the remaining about 10% of patients no autoantibodies can be found with the classical diagnostics for AChR and MuSK antibodies (seronegative MG, SN-MG). Since serological tests are relatively easy and non-invasive for disease diagnosis, the improvement of methods for the detection of known autoantibodies or the discovery of novel autoantibody specificities to diminish SN-MG and to facilitate differential diagnosis of similar diseases, is crucial. Radioimmunoprecipitation assays (RIPA) are the staple for MG antibody detection, but over the past years, using cell-based assays (CBAs) or improved highly sensitive RIPAs, it has been possible to detect autoantibodies in previously SN-MG patients. This led to the identification of more patients with antibodies to the classical antigens AChR and MuSK and to the third MG autoantigen, the low-density lipoprotein receptor-related protein 4 (LRP4), while antibodies against other extracellular or intracellular targets, such as agrin, K_v1.4 potassium channels, collagen Q, titin, the ryanodine receptor and cortactin have been found in some MG patients. Since the autoantigen targeted determines in part the clinical manifestations, prognosis and response to treatment, serological tests are not only indispensable for initial diagnosis, but also for monitoring treatment efficacy. Importantly, knowing the autoantibody profile of MG patients could allow for more efficient personalized therapeutic approaches. Significant progress has been made over the past years toward the development of antigen-specific therapies, targeting only the specific immune cells or autoantibodies involved in the autoimmune response. In this review, we will present the progress made toward the development of novel sensitive autoantibody detection assays, the identification of new MG autoantigens, and the implications for improved antigen-specific therapeutics. These advancements increase our understanding of MG pathology and improve patient quality of life by providing faster, more accurate diagnosis and better disease management.

MuSK EAMG: Immunological Characterization and Suppression by Induction of Oral Tolerance

Myasthenia gravis (MG) with antibodies to the muscle-specific receptor tyrosine kinase (MuSK) is a distinct sub-group of MG, affecting 5–8% of all MG patients. MuSK, a receptor tyrosine kinase, is expressed at the neuromuscular junctions (NMJs) from the earliest stages of synaptogenesis and plays a crucial role in the development and maintenance of the NMJ. MuSK-MG patients are more severely affected and more refractory to treatments currently used for MG. Most patients require long-term immunosuppression, stressing the need for improved treatments. Ideally, preferred treatments should specifically delete the antigen-specific autoimmune response, without affecting the entire immune system. Mucosal tolerance, induced by oral or nasal administration of an auto-antigen through the mucosal system, resulting in an antigen-specific immunological systemic hyporesponsiveness, might be considered as a treatment of choice for MuSK-MG. In the present study we have characterized several immunological parameters of murine MuSK-EAMG and have employed induction of oral tolerance in mouse MuSK-EAMG, by feeding with a recombinant MuSK protein one week before disease induction. Such a treatment has been shown to attenuate MuSK-EAMG. Both induction and progression of disease were ameliorated following oral treatment with the recombinant MuSK fragment, as indicated by lower clinical scores and lower anti-MuSK antibody titers.

New Approaches to Targeting B Cells for Myasthenia Gravis Therapy

Current therapies for myasthenia gravis (MG) are limited, and many investigations have recently focused on target-specific therapies. B cell-targeting monoclonal antibody (mAb) therapies for MG are increasingly attractive due to their specificity and efficacy. The targeted B cell biomarkers are mainly the cluster of differentiation (CD) proteins that mediate maturation, differentiation, or survival of pathogenic B cells. Additional B cell-directed therapies include non-specific peptide inhibitors that preferentially target specific B cell subsets. The primary goals of such therapies are to intercept autoantibodies and prevent the generation of an inflammatory response that contributes to the pathogenesis of MG. Treatment of patients with MG using B cell-directed mAbs, antibody fragments, or selective inhibitors have exhibited moderate to high efficacy in early studies, and some of these therapies appear to be highly promising for further drug development. Numerous other biologics targeting various B cell surface molecules have been approved for the treatment of other conditions or are either in clinical trials or preclinical development stages. These approaches remain to be tested in patients with MG or animal models of the disease. This review article provides an overview of B cell-targeted treatments for MG, including those already available and those still in preclinical and clinical development. We also discuss the potential benefits as well as the shortcomings of these approaches to development of new therapies for MG and future directions in the field.

Acetylcholine receptor-specific immunosuppressive therapy of experimental autoimmune myasthenia gravis and myasthenia gravis

Experimental autoimmune myasthenia gravis (EAMG) and myasthenia gravis (MG) are caused by autoantibodies to the extracellular domain of muscle nicotinic acetylcholine receptors (AChRs). Autoantibodies to the cytoplasmic domain of AChRs do not cause EAMG because they cannot bind AChRs in vivo. The ideal MG therapy would quickly and permanently suppress only the pathological autoimmune response to AChRs. We have developed a specific immunosuppressive therapy for EAMG that involves immunizing rats with bacterially expressed cytoplasmic domains of human muscle AChRs. Therapy prevents onset of chronic EAMG, rapidly suppresses ongoing EAMG, and is potent, robust, long lasting, and safe, because the therapeutic antigen cannot induce EAMG. The therapy was developed using incomplete Freund's adjuvant, but is likely to work equally well with alum adjuvants routinely used for human immunizations. Therapeutic mechanisms may involve a combination of antibody-mediated feedback suppression and regulatory T and/or B lymphocytes.

A Novel Approach to Reinstating Tolerance in Experimental Autoimmune Myasthenia Gravis Using a Targeted Fusion Protein, mCTA1-T146

Reinstating tissue-specific tolerance has attracted much attention as a means to treat autoimmune diseases. However, despite promising results in rodent models of autoimmune diseases, no established tolerogenic therapy is clinically available yet. In the experimental autoimmune myasthenia gravis (EAMG) model several protocols have been reported that induce tolerance against the prime disease-associated antigen, the acetylcholine receptor (AChR) at the neuromuscular junction. Using the whole AChR, the extracellular part or peptides derived from the receptor, investigators have reported variable success with their treatments, though, usually relatively large amounts of antigen has been required. Hence, there is a need for better formulations and strategies to improve on the efficacy of the tolerance-inducing therapies. Here, we report on a novel targeted fusion protein carrying the immunodominant peptide from AChR, mCTA1–T146, which given intranasally in repeated microgram doses strongly suppressed induction as well as ongoing EAMG disease in mice. The results corroborate our previous findings, using the same fusion protein approach, in the collagen-induced arthritis model showing dramatic suppressive effects on Th1 and Th17 autoaggressive CD4 T cells and upregulated regulatory T cell activities with enhanced IL10 production. A suppressive gene signature with upregulated expression of mRNA for TGFβ, IL10, IL27, and Foxp3 was clearly detectable in lymph node and spleen following intranasal treatment with mCTA1–T146. Amelioration of EAMG disease was accompanied by reduced loss of muscle AChR and lower levels of anti-AChR serum antibodies. We believe this targeted highly effective fusion protein mCTA1–T146 is a promising candidate for clinical evaluation in myasthenia gravis patients.

Myeloperoxidase Peptide-Based Nasal Tolerance in Experimental ANCA-Associated GN

Less toxic treatment options for patients with myeloperoxidase (MPO)-ANCA-associated GN are needed. Using an established murine model of focal necrotizing GN mediated by autoimmunity to MPO (autoimmune anti-MPO GN), we assessed the capacity for nasal tolerance induced by nasal insufflation of the immunodominant nephritogenic MPO peptide (MPO409-428) to attenuate this disease. Compared with mice that received an irrelevant immunodominant ovalbumin (OVA) peptide, OVA323-339, mice that received MPO409-428 were protected from the development of humoral and cell-mediated autoimmunity to full-length MPO and the development of GN. In mice with established anti-MPO autoimmunity, nasal insufflation of MPO409-428 as a therapeutic attenuated anti-MPO GN. To investigate the nature of this induced tolerance, we isolated CD4(+) T cells from the upper airway draining lymph nodes of both OVA323-339- and MPO409-428-tolerized mice. Adoptive transfer of CD4(+) T cells from MPO409-428- but not OVA323-339-tolerized mice to animals with established anti-MPO autoimmunity attenuated the subsequent development of GN, confirming that the immunosuppression induced by these T cells is antigen specific. Ex vivo studies showed that nasal tolerance to MPO is mediated by both conventional and induced T regulatory cells. The strong homology between the pathogenic human MPO B cell epitope recognized by ANCA in patients with acute vasculitis and the nephritogenic murine T cell MPO epitope emphasizes the clinical relevance of this study.

Experimental Autoimmune Myasthenia Gravis (EAMG): from immunochemical characterization to therapeutic approaches

Myasthenia Gravis (MG) is an organ-specific autoimmune disease. In high percentage of patients there are autoantibodies to the nicotinic acetylcholine receptor (AChR) that attack AChR on muscle cells at the neuromuscular junction, resulting in muscle weakness. Experimental Autoimmune Myasthenia Gravis (EAMG) is an experimental model disease for MG. EAMG is induced in several animal species by immunization with acetylcholine receptor (AChR), usually isolated from the electric organ of electric fish, which is a rich source for this antigen. Our lab has been involved for several decades in research of AChR and of EAMG. The availability of an experimental autoimmune disease that mimics in many aspects the human disease, provides an excellent model system for elucidating the immunological nature and origin of MG, for studying various existing treatment modalities and for attempting the development of novel treatment approaches. In this review in honor of Michael Sela and Ruth Arnon, we report first on our early pioneering contributions to research on EAMG. These include the induction of EAMG in several animal species, early attempts for antigen-specific treatment for EAMG, elicitation and characterization of monoclonal antibodies and anti-idiotypic antibodies, measuring humoral and cellular AChR-specific immune responses in MG patient and more. In the second part of the review we discuss more recent studies from our lab towards developing and testing novel treatment approaches for myasthenia. These include antigen-dependent treatments aimed at specifically abrogating the humoral and cellular anti-AChR responses, as well as immunomodulatory approaches that could be used either alone, or in conjunction with antigen-specific treatments, or alternatively, serve as steroid-sparing agents.

MuSK IgG4 autoantibodies cause myasthenia gravis by inhibiting binding between MuSK and Lrp4

Myasthenia gravis (MG) is a severely debilitating autoimmune disease that is due to a decrease in the efficiency of synaptic transmission at neuromuscular synapses. MG is caused by antibodies against postsynaptic proteins, including (i) acetylcholine receptors, the neurotransmitter receptor, (ii) muscle-specific kinase (MuSK), a receptor tyrosine kinase essential for the formation and maintenance of neuromuscular synapses, and (iii) low-density lipoprotein receptor-related protein 4 (Lrp4), which responds to neural Agrin by binding and stimulating MuSK. Passive transfer studies in mice have shown that IgG4 antibodies from MuSK MG patients cause disease without requiring complement or other immune components, suggesting that these MuSK antibodies cause disease by directly interfering with MuSK function. Here we show that pathogenic IgG4 antibodies to MuSK bind to a structural epitope in the first Ig-like domain of MuSK, prevent binding between MuSK and Lrp4, and inhibit Agrin-stimulated MuSK phosphorylation. In contrast, these IgG4 antibodies have no direct effect on MuSK dimerization or MuSK internalization. These results provide insight into the unique pathogenesis of MuSK MG and provide clues toward development of specific treatment options.

Current and emerging treatments for the management of myasthenia gravis

Myasthenia gravis is an autoimmune neuromuscular disorder. There are several treatment options, including symptomatic treatment (acetylcholinesterase inhibitors), short-term immunosuppression (corticosteroids), long-term immunosuppression (azathioprine, cyclosporine, cyclophosphamide, methotrexate, mycophenolate mofetil, rituximab, tacrolimus), rapid acting short-term immunomodulation (intravenous immunoglobulin, plasma exchange), and long-term immunomodulation (thymectomy). This review explores in detail these different treatment options. Potential future treatments are also discussed.

Current and emerging therapies for the treatment of myasthenia gravis

Myasthenia gravis (MG) is an autoimmmune disease in which autoantibodies to different antigens of the neuromuscular junction cause the typical weakness and fatigability. Treatment includes anticholinesterase drugs, immunosuppression, immunomodulation, and thymectomy. The autoimmune response is maintained under control by corticosteroids frequently associated with immunosuppressive drugs, with improvement in the majority of patients. In case of acute exacerbations with bulbar symptoms or repeated relapses, modulation of autoantibody activity by plasmapheresis or intravenous immunoglobulins provides rapid improvement. Recently, techniques removing only circulating immunoglobulins have been developed for the chronic management of treatment-resistant patients. The rationale for thymectomy relies on the central role of the thymus. Despite the lack of controlled studies, thymectomy is recommended as an option to improve the clinical outcome or promote complete remission. New videothoracoscopic techniques have been developed to offer the maximal surgical approach with the minimal invasiveness and hence patient tolerability. The use of biological drugs such as anti-CD20 antibodies is still limited but promising. Studies performed in the animal model of MG demonstrated that several more selective or antigen-specific approaches, ranging from mucosal tolerization to inhibition of complement activity or cellular therapy, might be feasible. Investigation of the transfer of these therapeutic approaches to the human disease will be the challenge for the future.

Mucosal tolerance induced by an immunodominant peptide from rat alpha3(IV)NC1 in established experimental autoimmune glomerulonephritis

Experimental autoimmune glomerulonephritis (EAG), an animal model of Goodpasture's disease, can be induced in Wistar Kyoto (WKY) rats by immunization with the noncollagenous domain of the alpha 3 chain of type IV collagen, alpha3(IV)NC1. Recent studies have identified an immunodominant peptide, pCol (24-38), from the N-terminus of rat alpha3(IV)NC1; this peptide contains the major B- and T-cell epitopes in EAG and can induce crescentic nephritis. In this study, we investigated the mechanisms of mucosal tolerance in EAG by examining the effects of the nasal administration of this peptide after the onset of disease. A dose-dependent effect was observed: a dose of 300 microg had no effect, a dose of 1000 microg resulted in a moderate reduction in EAG severity, and a dose of 3000 microg produced a marked reduction in EAG severity accompanied by diminished antigen-specific, T-cell proliferative responses. These results demonstrate that mucosal tolerance in EAG can be induced by nasal administration of an immunodominant peptide from the N-terminus of alpha3(IV)NC1 and should be of value in designing new therapeutic strategies for patients with Goodpasture's disease and other autoimmune disorders.

Myasthenia gravis and the tops and bottoms of AChRs: antigenic structure of the MIR and specific immunosuppression of EAMG using AChR cytoplasmic domains

The main immunogenic region (MIR), against which half or more of the autoantibodies to acetylcholine receptors (AChRs) in myasthenia gravis (MG) or experimental autoimmune MG (EAMG) are directed, is located at the extracellular end of alpha1 subunits. Rat monoclonal antibodies (mAbs) to the MIR efficiently compete with MG patient autoantibodies for binding to human muscle AChRs. Antibodies bound to the MIR do not interfere with cholinergic ligand binding or AChR function, but target complement and trigger antigenic modulation. Rat mAbs to the MIR also bind to human ganglionic AChR alpha3 subunits, but MG patient antibodies do not. By making chimeras of alpha1 subunits with alpha7 subunits or ACh binding protein, the structure of the MIR and its functional effects are being investigated. Many mAbs to the MIR bind only to the native conformation of alpha1 subunits because they bind to sequences that are adjacent only in the native structure. The MIR epitopes recognized by these mAbs are not recognized by most patient antibodies whose epitopes must be nearby. The presence of the MIR epitopes in alpha1/alpha7 chimeras greatly promotes AChR expression and sensitivity to activation. EAMG can be suppressed by treatment with denatured, bacterially expressed mixtures of extracellular and cytoplasmic domains of human alpha1, beta1, gamma, delta, and epsilon subunits. A mixture of only the cytoplasmic domains not only avoids the potential liability of provoking formation antibodies to pathologically significant epitopes on the extracellular surface, but also potently suppresses the development of EAMG.

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.

Vaccines against myasthenia gravis

Myasthenia gravis (MG) is an autoimmune disease mediated by antibodies to nicotinic acetylcholine receptor (AChR) interfering with the neuromuscular transmission. Experimental autoimmune MG serves as an excellent animal model to study possible therapeutic modalities for MG. This review will focus on the different ways to turn off the autoimmune response to AChR, which results in suppression of myasthenia. This paper will describe the use of fragments or peptides derived from the AChR, antigen-presenting cells and anti-T cell receptor antibodies, and will discuss the underlying mechanisms of action. Finally, the authors propose new promising therapeutic prospects, including treatment based on the modulation of regulatory T cells, which have recently been found to be functionally defective in MG patients.

Induction of partial immune tolerance to factor VIII through prior mucosal exposure to the factor VIII C2 domain

BACKGROUND

The development of anti-factor VIII (FVIII) neutralizing antibodies (inhibitors) is a significant obstacle to FVIII replacement therapy.

OBJECTIVE

As mucosal administration of an antigen may induce immune tolerance we have evaluated the efficacy of mucosal antigen exposure to achieve tolerance to FVIII.

METHODS

We investigated the effects of oral and nasal administration of the purified FVIII C2 domain (FVIII-C2) to FVIII-deficient BALB/c mice prior to FVIII protein challenge. Mice received oral or nasal doses of FVIII-C2, followed by a subcutaneous challenge of either FVIII-C2 or FVIII. The development of anti-FVIII inhibitors, cytokine production by splenocytes in vitro, and adoptive transfer assays were analyzed.

RESULTS AND CONCLUSIONS

Mucosal administration of FVIII-C2 decreases the titer of anti-FVIII-C2 inhibitors after FVIII-C2 challenge, and decreases the percentage of FVIII-C2 specific antibodies after challenge with full-length FVIII. Tolerance induction to FVIII-C2 is associated with increased IL-10 production by splenocytes in vitro, and can be adoptively transferred to naïve mice. This study is the first to demonstrate that tolerance to the FVIII-C2 domain can be induced via the mucosal route. Based on these results, the potential use of FVIII-specific mucosal tolerance induction as an immunotherapy treatment for anti-FVIII inhibitor development warrants further investigation.

CD4+ T and B cells cooperate in the immunoregulation of Experimental Autoimmune Myasthenia Gravis

C57Bl6 mice (B6 mice) immunized with Torpedo acetylcholine receptor (TAChR) in Freund's adjuvants (FA) develop Experimental Autoimmune Myasthenia Gravis (EAMG). In mouse EAMG Th2 cytokines may be protective. Aluminum hydroxide (Alum) was used to immunize B6 mice to the TAChR and prime CD4+ T and B cells secreting Th2 cytokines. Mice immunized with TAChR/Alum developed anti-AChR CD4+ T cells response, but minimal antibody levels and symptoms. TAChR/Alum treatments prior immunization with TAChR/FA protected mice from EAMG. Cell transfer experiments demonstrated that B and CD4+ T cells mediated the protective effect by causing intense reduction of complement-fixing anti-TAChR IgG subclasses.

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.

Achieving antigen-specific tolerance in diabetes: regulating specifically

Autoreactive T cells that escape negative selection in the thymus do not normally cause productive immune responses to self-antigens because of a number of regulatory mechanisms. Studies with anti-CD3 monoclonal antibodies (mAbs) have suggested that immune regulatory mechanisms are induced by drug treatments that are able to stop on-going unwanted immune responses, such as type 1 diabetes, involving induction of regulatory T cells. TGF-beta dependent and independent mechanisms have been described involving CD4(+) as well as CD8(+) T cells. The challenge is now to apply these mechanisms in an antigen-specific manner and so that lasting tolerance to the autoimmune responses can be maintained. We discuss recent data concerning the mechanisms of anti-CD3 mAb treatment and the ways in which our understanding of these mechanisms can be used to develop adoptive immune therapy with regulatory T cells to treat patients with type 1 diabetes or other autoimmune diseases.

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.

Nasal Administration of Recombinant Rat α3(IV)NC1 Prevents the Development of Experimental Autoimmune Glomerulonephritis in the WKY Rat

Experimental autoimmune glomerulonephritis (EAG), an animal model of Goodpasture's disease, can be induced in Wistar Kyoto (WKY) rats by immunization with either collagenase-solubilized rat glomerular basement membrane (GBM) or the recombinant NC1 domain of the alpha3 chain of type IV collagen [alpha3(IV)NC1]. EAG is characterized by circulating and deposited anti-glomerular basement membrane antibodies, focal necrotizing glomerulonephritis with crescent formation, and glomerular infiltration by T cells and macrophages. Previous studies have demonstrated that oral administration of collagenase-solubilized GBM to WKY rats prevented the development of EAG. Nasal administration of specific autoantigens has been reported to be more effective than oral administration in other models of autoimmune disease. The main aim of this study was to investigate further the concept of mucosal tolerance in EAG by examining the effect of nasal administration of recombinant rat alpha3(IV)NC1. Groups of WKY rats with EAG, induced by immunization with recombinant rat alpha3(IV)NC1, were given alpha3(IV)NC1 nasally on 3 consecutive days before immunization, at total cumulative doses of 25, 100, or 250 microg per rat. A dose-dependent effect was observed on the development of EAG. A dose of 25 microg had no effect on disease; 100 microg resulted in a moderate reduction in the severity of nephritis; and 250 microg led to a marked reduction in circulating and deposited antibodies, albuminuria, severity of glomerular abnormalities, and numbers of glomerular CD8+ T cells and macrophages. In addition, there was a reduction in the proliferative response of splenocytes from rats in the high dose group (250 microg) to alpha3(IV)NC1 in vitro. The results from this study clearly demonstrate for the first time that mucosal tolerance in EAG can be induced by nasal administration of recombinant rat alpha3(IV)NC1 and that this approach is effective in the prevention of crescentic glomerulonephritis. Further work using new antigen-specific treatment strategies may provide a novel approach to the treatment of patients with anti-glomerular basement membrane disease.

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.

Suppression of Myasthenia Gravis by Antigen-Specific Mucosal Tolerance and Modulation of Cytokines and Costimulatory Factors

We have shown that mucosal administration of recombinant fragments corresponding to the human acetylcholine receptor (AChR) alpha subunit suppresses chronic ongoing experimental autoimmune myasthenia gravis (EAMG) in rats. Treated animals exhibit a Th1 to Th2/Th3 shift in their cytokine profile and downregulation of costimulatory factors. However, application of a xenogeneic recombinant fragment may have limitations when considered as a possible approach for the treatment of MG in humans. We therefore tested the potential of a syngeneic fragment and of long synthetic peptides to suppress EAMG. We found that a syngeneic fragment corresponding to the extracellular region of the rat AChR alpha subunit was as effective as the formerly described human xenogeneic fragment in suppressing ongoing EAMG. This is encouraging in view of the potential use of mucosally administered recombinant AChR fragments for the treatment of MG in humans. However, in severely affected individuals, this antigen-specific approach may need to be supported by direct modulation of cytokines and costimulatory factors known to be involved in the pathogenesis of EAMG. To test the potential of this approach, myasthenic rats were injected by antibodies either to the proinflammatory cytokine IL-18 or to the costimulatory factor CD40L. These treatments act via different mechanisms, but both lead to the alleviation of clinical symptoms even when given at the chronic phase of EAMG. We suggest that antagonists to key cytokines and/or costimulatory factors be used to augment antigen-specific treatments of myasthenia such as mucosal administration of AChR recombinant fragments.

Absence of IL-4, and not suppression of the Th2 response, prevents development of experimental autoimmune Graves' disease

In autoimmune Graves' disease (GD), autoantibodies bind to the thyrotropin receptor (TSHR) and cause hyperthyroidism. We studied the effects of fms-like tyrosine kinase receptor 3 ligand (Flt3-L) or GM-CSF treatment on the development of experimental autoimmune GD (EAGD) in mice, a slowly progressing Ab-mediated organ-specific autoimmune disease of the thyroid induced by immunization with syngeneic cells expressing TSHR. Flt3-L and GM-CSF treatment resulted in up-regulation of CD8a(+) and CD8a(-) dendritic cells, and skewing of cytokine and immune responses to TSHR in favor of Th1 and Th2, respectively. However, this skewing did not persist until the later stages, and thus failed to affect the course or severity of the disease. To determine whether the total absence of either IL-4 or IFN-gamma could affect the development of EAGD, we immunized wild-type, IFN-gamma(-/-) and IL-4(-/-) BALB/c mice with TSHR. Nearly 100% of the wild-type and IFN-gamma(-/-) mice developed EAGD with optimal TSHR-specific immune responses, while IL-4(-/-) mice completely resisted disease and showed delayed and suboptimal pathogenic Ab response. These data demonstrated that skewing immune responses to TSHR, using either Flt3-L or GM-CSF, in favor of Th1 or Th2, respectively, may not be sufficient to alter the course of the disease, while the complete absence of IL-4, but not IFN-gamma, can prevent the development of EAGD.

Autoimmune diseases involving nicotinic receptors

The antibody-mediated autoimmune response to alpha1 muscle nicotinic acetylcholine receptors that causes myasthenia gravis is one of the best characterized autoimmune diseases. Antibody-mediated autoimmune responses to neuronal nicotinic receptors are just beginning to be discovered and characterized. One of these causes dysautonomia through antibodies to alpha 3 nicotinic receptors of autonomic ganglia. Another causes pemphigus through antibodies to alpha 9 nicotinic receptors in skin. Other autoimmune responses to nicotinic receptors may be discovered as the many functional roles of nicotinic receptors are revealed.

Nasal administration of CTB-insulin induces active tolerance against autoimmune diabetes in non-obese diabetic (NOD) mice

Nasal administration of beta cell-derived auto-antigens has been reported to suppress the development of autoimmune diabetes. We investigated the tolerogenic effects of insulin conjugated to the B subunit of cholera toxin (CTB). Nasal administration of 1 micro g of CTB-insulin significantly delayed the incidence of diabetes in comparison to CTB treated mice. However, administration of 4 or 8 micro g of the conjugate had no protective effect. Protection induced by CTB-insulin was transferred to naive recipients by splenic CD4+ T cells. This result favours an active cellular mechanism of regulation, which was lost using higher (4-8 micro g) or lower (0.1-0.5 micro g) amounts of the conjugate. When co-administered with diabetogenic T cells, splenic T cells from CTB-insulin-treated mice reduced the lymphocytic infiltration of the islets. Reverse transcription-polymerase chain reaction analysis of recipients' pancreatic glands revealed an increase of TGF-beta and IL-10 transcripts after donor mice tolerization, while levels of IFN-gamma and IL-4 RNAs were unchanged. We observed a significant increase of T cell proliferation after unspecific stimulation in the spleen and pancreatic lymph nodes 24 h after CTB-insulin administration in -comparison to control treatment. Higher amounts of IL-4 and IFN-gamma were noticed in pancreatic lymph nodes of tolerized mice upon in vitro stimulation. Antigen-specific unresponsiveness after immunization and upon subsequent in vitro exposure to homologous antigen was obtained in nasally treated animals. Our results underlined the importance of nasal mucosa as an inducing site of tolerance and provided evidence for similar mechanisms of action to what has been described for the oral route, which favoured a CTB-insulin specific effect.

Protective molecular mimicry in experimental myasthenia gravis

Protein databases were searched for microbial sequences that bear amino acid similarities with identified T- or B-cell epitopes within the human alpha-subunit of acetylcholine receptor (AChR). One peptide, derived from Haemophilus influenzae, exhibits 50% homology to an identified T-cell epitope of AChR alpha-subunit. This peptide was shown to have a protective effect in experimental autoimmune myasthenia gravis (EAMG). Pretreatment of rats with the mimicry peptide attenuated the induction and progression of EAMG. These effects were accompanied by a reduced T-cell response to AChR, diminished IL-2, IL-12, IFN-gamma and IL-4 levels, as well as decreased humoral response to self-AChR.

Adoptive protection from experimental myasthenia gravis with T cells from mice treated nasally with acetylcholine receptor epitopes

Nasal administration of synthetic CD4(+) epitopes of the acetylcholine receptor (AChR) prevents experimental myasthenia gravis (EMG) in C57Bl/6 mice, but not in IL4-deficient C57Bl/6 (IL4(-/-)) mice. Here we verify that nasal tolerance requires IL4, by showing that CD4(+) cells from C57Bl/6 mice treated nasally with a pool of AChR CD4(+) epitopes protected IL4(-/-) mice from EMG and caused a reduced production of anti-AChR antibody. CD4(+) cells from C57Bl/6 mice treated with unrelated peptides or sham-treated did not induce protection. CD4(+) cells from C57Bl/6 mice treated with just one AChR peptide protected IL4(-/-) mice from EMG without affecting antibody synthesis.

Suppression of experimental myasthenia gravis, a B cell-mediated autoimmune disease, by blockade of IL-18

Interleukin-18 (IL-18) is a pleiotropic proinflammatory cytokine that plays an important role in interferon gamma (IFN-gamma) production and IL-12-driven Th1 phenotype polarization. Increased expression of IL-18 has been observed in several autoimmune diseases. In this study we have analyzed the role of IL-18 in an antibody-mediated autoimmune disease and elucidated the mechanisms involved in disease suppression mediated by blockade of IL-18, using experimental autoimmune myasthenia gravis (EAMG) as a model. EAMG is a T cell-regulated, antibody-mediated autoimmune disease in which the nicotinic acetylcholine receptor (AChR) is the major autoantigen. Th1- and Th2-type responses are both implicated in EAMG development. We show that treatment by anti-IL-18 during ongoing EAMG suppresses disease progression. The protective effect can be adoptively transferred to naive recipients and is mediated by increased levels of the immunosuppressive Th3-type cytokine TGF-beta and decreased AChR-specific Th1-type cellular responses. Suppression of EAMG is accompanied by down-regulation of the costimulatory factor CD40L and up-regulation of CTLA-4, a key negative immunomodulator. Our results suggest that IL-18 blockade may potentially be applied for immunointervention in myasthenia gravis.

Blockade of CD40 Ligand Suppresses Chronic Experimental Myasthenia Gravis by Down-Regulation of Th1 Differentiation and Up-Regulation of CTLA-4

Myasthenia gravis (MG) and experimental autoimmune MG (EAMG) are T cell-dependent Ab-mediated autoimmune disorders, in which the nicotinic acetylcholine receptor (AChR) is the major autoantigen. Th1-type cells and costimulatory factors such as CD40 ligand (CD40L) contribute to disease pathogenesis by producing proinflammatory cytokines and by activating autoreactive B cells. In this study we demonstrate the capacity of CD40L blockade to modulate EAMG, and analyze the mechanism underlying this disease suppression. Anti-CD40L Abs given to rats at the chronic stage of EAMG suppress the clinical progression of the autoimmune process and lead to a decrease in the AChR-specific humoral response and delayed-type hypersensitivity. The cytokine profile of treated rats suggests that the underlying mechanism involves down-regulation of AChR-specific Th1-regulated responses with no significant effect on Th2- and Th3-regulated AChR-specific responses. EAMG suppression is also accompanied by a significant up-regulation of CTLA-4, whereas a series of costimulatory factors remain unchanged. Adoptive transfer of splenocytes from anti-CD40L-treated rats does not protect recipient rats against subsequently induced EAMG. Thus it seems that the suppressed progression of chronic EAMG by anti-CD40L treatment does not induce a switch from Th1 to Th2/Th3 regulation of the AChR-specific immune response and does not induce generation of regulatory cells. The ability of anti-CD40L treatment to suppress ongoing chronic EAMG suggests that blockade of CD40L may serve as a potential approach for the immunotherapy of MG and other Ab-mediated autoimmune diseases.