Myasthenia gravis

Role of complement in myasthenia gravis

Myasthenia gravis is a prototypic neuroimmune disorder with autoantibodies targeting the acetylcholine receptor complex at the neuromuscular junction. Patients present with mainly ocular muscle weakness and tend to have a generalized muscle weakness later in the clinical course. The weakness can be severe and fatal when bulbar muscles are heavily involved. Acetylcholine receptor antibodies are present in the majority of patients and are of IgG1 and IgG3 subtypes which can activate the complement system. The complement involvement plays a major role in the neuromuscular junction damage and the supporting evidence in the literature is described in this article. Complement therapies were initially studied and approved for paroxysmal nocturnal hemoglobinuria and in the past decade, those have also been studied in myasthenia gravis. The currently available randomized control trial and real-world data on the efficacy and safety of the approved and investigational complement therapies are summarized in this review.

The clinical utility of neostigmine administration in the diagnosis of acquired myasthenia gravis

OBJECTIVE

To assess the clinical utility of neostigmine methylsulfate administration in the diagnosis of suspected acquired myasthenia gravis (MG) in dogs and cats.

DESIGN

Retrospective study (2017-2019).

SETTING

Five university teaching hospitals and 2 private referral hospitals.

ANIMALS

Twenty-two dogs and 3 cats. Criteria for inclusion were clinical signs consistent with acquired MG, performance of a neostigmine challenge and acetylcholine receptor antibody titers.

INTERVENTIONS

None.

MEASUREMENTS & MAIN RESULTS

The route of neostigmine administration was recorded. Response to neostigmine challenge was determined via sequential evaluation of muscle strength and ambulation following administration of neostigmine methylsulfate. Response to neostigmine challenge was compared to acetylcholine receptor antibody titers, which were used as the biochemical gold standard in this study. Sixteen out of 22 dogs were diagnosed with acquired MG. Thirteen of 16 had a strong positive response to neostigmine challenge whereas 3 of 16 had no response. Two out of 3 dogs with polymyositis also had a strong positive response to neostigmine challenge. Weak positive results were seen with intracranial neoplasia (n = 1) and a dog with dilated cardiomyopathy and coxofemoral joint disease (n = 1). One cat was diagnosed with acquired MG and had a positive response to neostigmine challenge. Two cats had no response to neostigmine challenge and were diagnosed with alternate conditions. Two cats were premedicated with glycopyrrolate, one of which had a mild adverse response to neostigmine challenge (sialorrhea and mild transient tremors). Three out of 22 dogs had minimal adverse effects (sialorrhea and 1 dog with muscle tremors).

CONCLUSIONS

The neostigmine challenge appears to be safe and viable alternative to the previously utilized edrophonium challenge, particularly when weak positive responses are considered negative for acquired MG. Polymyositis cases may have a false positive response to neostigmine challenge.

Possible participation of colloid antigen 2 and abhormone (IgG with hormone activity) for the etiology of Graves' disease

The theory that antibody (Ab) directed against the TSH receptor (TSHR) (TSHRAb) is the causal factor of Graves' disease seems unlikely. Corticosteroids have not had a curative effect on the hyperthyroidism of Graves' disease despite their effectiveness for other autoimmune diseases. Two kinds of TSHRAb, thyroid-stimulating Ab (TSAb) and thyroid-blocking Ab (TBAb), are known as causal factors of hyperthyroidism and hypothyroidism, respectively. Previously, we reported that TSAb may be thyroid stimulating animal IgG-like hormone and TBAb may be the precursor of TSAb. In this paper we suggested that TBAb (precursor) converts to TSAb (active form) via the action of the protease, colloid antigen 2 (CA2). We speculate that the conversion of TBAb to TSAb is controlled by two factors: the protease and an anti-protease Ab. When anti-protease Ab levels are high, the patient exhibits hypothyroidism due to the increase in TBAb levels caused by neutralization of the protease. When anti-protease Ab levels are negative, the patient's hypothyroidism disappeared by the negative serum TBAb due to increased protease. An immunoglobulin G (IgG) with enzyme activity is known as an abzyme, which may be an undeveloped form. IgG with hormone activity may be likewise called an abhormone, which could also be an undeveloped form. The tumor marker CEA is a known member of the IgG supergene family. Many ancestral versions of proteins may have been produced as an IgG form. Possible participation of colloid antigen 2 and abhormone for the etiology of Graves' disease is suggested.

Removal of antiacetylcholine receptor antibodies by protein-A immunoadsorption in myasthenia gravis

Myasthenia Gravis is an autoimmune disease in which autoantibodies to the acetylcholine receptor interfere with neuromuscular transmission. Plasma exchange is effective in temporarily relieving the symptoms of the disease, but for repeated use the lack of selectivity and need for replacement fluids (which increases the risk of contracting viral diseases) are important drawbacks. Staphylococcal protein A, a potent ligand for immunoglobulins, that interacts negligibly with other plasma proteins, appears to be an optimal candidate for removing antiacetylcholine receptor antibodies, which are mostly IgG. We treated three patients with severe immunosuppression-resistant myasthenia gravis with protein A immunoadsorption. Neurological impairment significantly improved in all patients. After immunoadsorption of 1.5-2 plasma volumes per session, the mean percentage reductions for serum IgG and specific autoantibodies were 71% and 82% respectively. No major side effects occurred. Protein A immunoadsorption appears to be a safe, efficient and effective alternative to plasmaexchange for selected myasthenic patients requiring prolonged apheresis.

Two-year outcome of thymectomy with or without immunosuppressive treatment in nonthymomatous myasthenia gravis and its effect on regulatory T cells

BACKGROUND

Myasthenia gravis (MG) is the autoimmune disorder in which the thymus is considered the pathogenic organ. Thymectomy (TE) is a therapeutic option for MG and often ameliorates clinical symptoms.

METHODS

We evaluated clinical features and outcomes after TE in patients without thymoma and the influence of TE with or without concomitant immunotherapy on the CD4(+)CD25(+) regulatory T cell subpopulation of lymphocytes in peripheral blood in defined followed groups of nonthymomatous MG patients.

RESULTS

A total of 46 patients with generalized MG who underwent transsternal TE were identified. Neurologic outcomes after TE were favorable for the majority of patients mainly from the group treated with corticosteroids or combined immunosuppressive treatment. TEs with immunosuppressive treatment in MG patients were associated with increased percentages of CD4(+)CD25(+) cells (p<0.001). No significant change in the postoperative levels of CD4(+)CD25(+) cells was observed in thymectomized patients who preoperatively only received pyridostigmine. Also their clinical response to TE after 2 years of follow-up was worst of all followed groups.

CONCLUSIONS

The exact mechanism by which TE ameliorates symptoms of MG is yet not clear. These observations indicate that increased percentages of CD4(+)CD25(+) T cells in MG may be related to disease stability and that TE and synergistic effect with concomitant, continuing immunotherapy augmented the proportion of CD4(+)CD25(+) T cells. On the basis of our observations TE alone is not enough to increase the number of circulating CD4(+)CD25(+) regulatory T cells and to establish complete stable remission.

A COLQ missense mutation in Labrador Retrievers having congenital myasthenic syndrome

Congenital myasthenic syndromes (CMSs) are heterogeneous neuromuscular disorders characterized by skeletal muscle weakness caused by disruption of signal transmission across the neuromuscular junction (NMJ). CMSs are rarely encountered in veterinary medicine, and causative mutations have only been identified in Old Danish Pointing Dogs and Brahman cattle to date. Herein, we characterize a novel CMS in 2 Labrador Retriever littermates with an early onset of marked generalized muscle weakness. Because the sire and dam share 2 recent common ancestors, CMS is likely the result of recessive alleles inherited identical by descent (IBD). Genome-wide SNP profiles generated from the Illumina HD array for 9 nuclear family members were used to determine genomic inheritance patterns in chromosomal regions encompassing 18 functional candidate genes. SNP haplotypes spanning 3 genes were consistent with autosomal recessive transmission, and microsatellite data showed that only the segment encompassing COLQ was inherited IBD. COLQ encodes the collagenous tail of acetylcholinesterase, the enzyme responsible for termination of signal transduction in the NMJ. Sequences from COLQ revealed a variant in exon 14 (c.1010T>C) that results in the substitution of a conserved amino acid (I337T) within the C-terminal domain. Both affected puppies were homozygous for this variant, and 16 relatives were heterozygous, while 288 unrelated Labrador Retrievers and 112 dogs of other breeds were wild-type. A recent study in which 2 human CMS patients were found to be homozygous for an identical COLQ mutation (c.1010T>C; I337T) provides further evidence that this mutation is pathogenic. This report describes the first COLQ mutation in canine CMS and demonstrates the utility of SNP profiles from nuclear family members for the identification of private mutations.

Titin antibody positive myasthenia gravis patients have a cellular immune response against the main immunogenic region of titin

Some myasthenia gravis (MG) patients have antibodies against non-acetylcholine receptor (AChR) epitopes of skeletal muscle including titin. Peripheral blood lymphocytes from 11 MG patients and 13 blood-donors were tested for lymphocyte proliferation after stimulation with the titin peptide MGT-30, which represents the main immunogenic region. Four out of seven titin antibody positive patients had significant stimulation defined as a stimulation index (SI) above 2. Neither of the four titin antibody negative patients nor the 13 blood-donors had SI above 2 (p = 0.001). Mean SI was significantly higher for T-cells from titin antibody positive MG patients, SI = 2.2 ± 0.8, compared to titin antibody negative patients, SI = 0.9 ± 0.2 (p = 0.01), and blood-donors, SI = 0.8 ±0.3 (p > 0.0005). After MGT-30 stimulation, IL-4 was detected in the blood lymphocyte culture supernatant from four of the five MG patients examined, but from none of the eight blood-donors. Thus, MG patients with anti-titin antibodies have a T-cell mediated immune reaction against titin.

Overview of myasthenia gravis

Myasthenia gravis is an antibody-mediated disorder of neuromuscular transmission that is characterized by weakness and fatigue of voluntary muscles. Weakness may be ocular, bulbar, or generalized. Diagnostic evaluation of patients consists of bedside assessment, antibody testing, and electrophysiologic studies. Various therapeutic options are available, which consist of anticholinesterase inhibitors for symptomatic management, immunosuppressive agents as maintenance therapy, and thymectomy. Plasmapheresis and intravenous immunoglobulin are used in patients in crisis or those with rapidly worsening or refractory symptoms. In our article, we elaborate on key aspects of the epidemiology, pathogenesis, diagnostic evaluation, and therapeutic options for patients with myasthenia gravis.

A comparison of epitope repertoires associated with myasthenia gravis in humans and nonhuman hosts

Here we analyzed the molecular targets associated with myasthenia gravis (MG) immune responses, enabled by an immune epitope database (IEDB) inventory of approximately 600 MG-related epitopes derived from 175 references. The vast majority of epitopes were derived from the α-subunit of human AChR suggesting that other MG-associated autoantigens should be investigated further. Human α-AChR was mostly characterized in humans, whereas reactivity primarily to T. californica AChR was examined in animal models. While the fine specificity of T-cell response was similar in the two systems, substantial antibody reactivity to the C-terminus was detected in the nonhuman system, but not in humans. Further analysis showed that the reactivity of nonhuman hosts to the C-terminus was eliminated when data were restricted to hosts tested in the context of autoimmune disease (spontaneous or induced), demonstrating that the epitopes recognized in humans and animals were shared when disease was present. Finally, we provided data subsets relevant to particular applications, including those associated with HLA typing or restriction, sets of epitopes recognized by monoclonal antibodies, and epitopes associated with modulation of immunity or disease. In conclusion, this analysis highlights gaps, differences, and similarities in the epitope repertoires of humans and animal models.

Thymus, thymoma and myasthenia gravis

Myasthenia gravis is an autoimmune disease. An autoantibody directed toward acetylcholine receptor (AChR) causes the destruction of the postsynaptic membrane and a reduction of the number of AChRs at neuromuscular junctions. A very puzzling, but interesting characteristic of myasthenia gravis is that many of the patients have an abnormality in their thymus. Many have a hyperplastic thymus with germinal centers, while others have a thymic tumor. How is the abnormality of the thymus related to myasthenia gravis? This review will summarize the existing evidence and try to find the missing link between the thymus and myasthenia gravis. The review will also comment on two distinct populations of myasthenia gravis patients without thymoma. The autoimmunity found in elderly patients is nonspecific and initiated via a different mechanism from the initiation of myasthenia gravis in younger patients.

The autoimmune model of schizophrenia

Schizophrenia is of mysterious causation. It is not infectious, not congenital, but shows familial aggregation, the Mendelian genetics indicating involvement of multiple codominant genes with incomplete penetrance. This is the pattern for autoimmune diseases, such as Graves' disease of the thyroid, where forbidden clones of B lymphocytes develop, and cause thyrotoxicosis by secreting autoantibodies that react with the thyroid gland's receptor for thyroid-stimulating hormone from the pituitary gland. In 1982, Knight postulated that autoantibodies affecting the function of neurons in the limbic region of the brain are a possible cause of schizophrenia. Today, this is even more probable, with genes predisposing to schizophrenia having being found to be immune response genes, one in the MHC and two for antibody light chain V genes. Immune response genes govern the immune repertoire, dictating the genetic risk of autoimmune diseases. The simplest test for an autoimmune basis of schizophrenia would be trial of immunosuppression with prednisone in acute cases. The urgent research need is to find the microbial trigger, as done by Ebringer for rheumatoid arthritis and for ankylosing spondylitis. This could lead to prophylaxis of schizophrenia by vaccination against the triggering microbe.

A novel hypothesis for the etiology of Graves' disease: TSAb may be thyroid stimulating animal IgG-like hormone and TBAb may be the precursor of TSAb

There are doubtful points about the theory that autoimmunity with auto-antibody (Ab) to TSH receptor (R) causes hyperthyroidism in Graves' disease (GD). A main doubtful point is no curative effect of corticosteroid on Graves' hyperthyroidism in spite of curative effect of corticosteroid for all autoimmune diseases. Recently we demonstrated the immunological similarity of TSAb and TBAb-IgG to animal IgGs, except for human (h)IgG, by neutralization and purification of TSAb and TBAb-IgG using (1) heterophilic Ab to animal IgG in GD sera and (2) experimentally generated anti-animal IgG Abs [such as dog (d), bovine (b), porcine (p), and rabbit (rb)]. Furthermore, greater immunological similarity of Fab- and F(ab')(2)-portion of TSAb- and TBAb-IgG to bovine Fab, compared to hFab, was demonstrated using goat anti-bovine F(ab')(2) Ab. Existence of b and p TSH-like portions in the LATS-IgG molecule (probably Fab portion) was suggested by a previous report of neutralization of LATS activity by anti-b- or anti-p-TSH Ab. We suggested the existence of a mammalian animal-TSH-like structure, excepting hTSH, in the TSAb-IgG molecule (probably Fab portion), by discovery of anti-mammalian TSH Ab (such as d, b, p, guinea-pig, rat, whale, except h) in sera of GD. Lately, similar TSHR binding of H- and L-chain of human stimulating monoclonal TSHR Ab (M22)-Fab with TSH-α and-β subunit was reported. This evidence suggests that Fab portion of TSAb has a structure like mammalian TSH, but not hTSH. IgG-λ type of d, horse, b, p, goat, ovine is 95% and IgG-κ type is 5%, while human κ and λ chain is 60:40. Previous report that LATS (TSAb)-IgG composed of predominant λ type is supporting evidence that TRAb-IgG has immunological similarity with these animal IgGs compared to hIgG. We speculate that TSAb-IgG may be referred as a mermaid consisted in face (Fab) and trunk-leg (Fc). Face may be a kind of hormone with animal TSH-like structure and trunk-leg has animal IgG-like structure (in spite of no antibody function). There are many reports for co-existence of TSAb and TBAb-IgG in sera of GD. We reported conversion from TBAb (non-thyroid stimulating type IgG) to TSAb by co-incubation of anti-hIgG Ab (containing anti-animal IgG Ab as a cross-reaction) with TBAb-bound porcine thyroid cells. Thus, we suggest that TBAb may be the precursor form of TSAb.

Harnessing regulatory T cells for the therapy of lupus and other autoimmune diseases

Regulatory T cells (Tregs) maintain immunological homeostasis and prevent autoimmunity. The depletion or functional alteration of Tregs may lead to the development of autoimmune diseases. Tregs consist of different subpopulations of cells, of which CD4(+)CD25(+)Foxp3(+) cells are the most well characterized. However, CD8 Tregs also constitute a major cell population that has been shown to play an important role in autoimmune diseases. This review will discuss the role of Tregs in autoimmune diseases in general and specifically in systemic lupus erythematosus (SLE). SLE is a multisystem autoimmune disease characterized by the production of autoantibodies against nuclear components and by the deposition of immune complexes in the kidneys as well as in other organs. Abnormalities in Tregs were reported in SLE patients and in animal models of the disease. Current treatment of SLE is based on immunosuppressive drugs that are nonspecific and may cause adverse effects. Therefore, the development of novel, specific, side effect-free therapeutic means that will induce functional Tregs is a most desirable goal. Our group and others have designed and utilized tolerogenic peptides that ameliorate SLE manifestations in murine models. Here, we demonstrate the role of CD4 and CD8 Tregs, as well as the interaction between the two subsets of cells and the mechanism of action of the tolerogenic peptides. We also discuss their therapeutic potential for the treatment of SLE.

Maintenance of immune tolerance to a neo-self acetylcholine receptor antigen with aging: implications for late-onset autoimmunity

Age-related changes in immune regulation are likely to account for the age-associated increase in serum autoantibody levels and in certain autoimmune disorders, such as myasthenia gravis (MG). To demonstrate directly a loss of immune tolerance in older individuals, responses to the acetylcholine receptor, the autoantigen in MG, were assessed in transgenic mice expressing the Torpedo californica acetylcholine receptor (TAChR) alpha-chain as a neo-self Ag. T cells from young transgenic mice had been shown to be tolerant to p146-162, the TAChR alpha-chain peptide that dominated young nontransgenic T cell responses in vitro. The immunodominance of p146-162 was not lost with age; fine specificity was preserved. Moreover, T cell tolerance to p146-162, as well as to other epitopes of the TAChR alpha-chain extracellular domain, was maintained in old transgenic mice. Even multiple TAChR immunizations coupled with the MG-enhancing cytokine, IL-12, did not break tolerance. In addition, T cells exhibiting CD4 upregulation, an early activation marker, were reduced in frequency equivalently in old and young transgenic animals, suggesting that immune regulation in this model was not impacted by aging. Moreover, B cell tolerance was also maintained with age. The persistence of immune tolerance was accompanied by an increase in the proportion of T regulatory cells; it is speculated that this may compensate for deficiencies in central tolerance that occur owing to thymic involution. In summary, our study reveals, for the first time, that some immune tolerance mechanisms do survive aging; this suggests that certain late-onset autoimmune disorders may be induced by a specific insult that disrupts immune homeostasis.

Biological implications of thymectomy for myasthenia gravis

Myasthenia gravis (MG) is an autoimmune disease mediated by autoantibodies to the striated muscle tissue. It is often treated by thymectomy. We review recent studies to investigate the biological implications of thymectomy. In anti-acetylcholine receptor antibody (anti-AchR Ab)-positive patients without a thymoma, abnormal germinal center formation in the thymus seems to play an essential role in the pathogenesis of MG. Specific differentiation of B cells producing anti-AchR Ab takes place uniquely in the thymus, and thymectomy is thought to assist in terminating the provision of high-affinity anti-AchR antibody-producing cells to peripheral organs. Thymectomy is not indicated for anti-AchR Ab-negative MG patients who are antimuscle specific kinase antibody (anti-MuSK Ab)-positive, although some anti-MuSK Ab-negative patients may benefit from the procedure. A thymoma can be considered as an acquired thymus with insufficient function of negative selection. The resection of a thymoma is thought to terminate the production of self-reactive T cells. Thus, the biological implications of thymectomy for MG have been partially revealed. Nevertheless, additional studies are needed to elucidate the ontogeny of T cells that recognize AchR and the mechanism of the activation of anti-AchR antibodies producing B cells.

Sequence and structural features of RNA aptamer against myasthenic autoantibodies

Myasthenia gravis (MG) is mainly caused by autoantibodies to postsynaptic nicotinic acetylcholine receptors (AChRs). Previously, we isolated an RNA aptamer with 2'-amino pyrimidines that inhibited both a rat monoclonal antibody, which recognizes the main immunogenic region on the AChR, and MG patient autoantibodies from down-modulating AChRs on human cells. In this study, secondary configuration and binding motif of the aptamer were characterized, and moreover, various mutant aptamer forms were generated to figure out sequence and structure requirements of the aptamer. Then, we found that intrinsic structure formation and sequence composition of the selected RNA aptamer specific to the antibody are required for the aptamer activity to inhibit the myasthenic autoantibody-mediated destruction of cell surface AChRs. Noticeably, we identified 47-mer minimized aptamer version, which can efficiently protect cells from the effects of the autoantibodies and could be optimally applicable for MG therapy.

IL-4 receptor as a bridge between the immune system and muscle in experimental myasthenia gravis I: up-regulation of muscle IL-15 by IL-4

The study reported below describes increased expression of IL-4 receptor in cultured rat myocytes following exposure to an antibody reactive with the acetylcholine receptor (AChR). In addition, upon up-regulation of IL-4R, myocytes demonstrated an increased responsiveness to IL-4 by producing increased levels of IL-15. Moreover, following passive transfer of AChR antibody into Lewis rats, both the increased IL-4R expression and IL-15 production were also observed in intact skeletal muscle, co-localizing in particular individual muscle fibers; the same muscle fibers also produced the chemokine MCP-1 to which IL-4-producing T cells were attracted. A model is proposed in which these muscle activities participate in disease progression in experimental myasthenia gravis.

Immunological function of thymoma and pathogenesis of paraneoplastic myasthenia gravis

Thymoma and thymic carcinoma are the representative tumors arising from the thymic epithelium. Thymoma is well known for association with autoimmune diseases including myasthenia gravis, suggesting its biological activity. Herein, recent progress in research of thymoma is reviewed with reference to its immunological function. Myasthenia gravis is frequently associated with WHO type B1 and B2 thymomas. These types of thymomas hold a significant number of CD4(+)CD8(+) double-positive T cells, and at the same time, the neoplastic epithelial cells express HLA-DR molecules at a slightly reduced level compared with the normal thymus. The impaired expression of HLA-DR molecules in neoplastic epithelial cells of thymomas possibly affects positive selection of CD4(+)CD8(-) single-positive T cells and may result in alteration of its repertoire. The function of thymoma neoplastic cells as the cortical epithelium of the thymus and the morphological resemblance of thymomas to the cortex suggest that thymoma is of cortical epithelial origin; this might imply that thymoma lacks the functional medulla where professional antigen-presenting cells are engaged in negative selection. These findings suggest that thymoma generates autoreactive T cells causing autoimmunity. Further investigation on immunological function of thymoma is supposed to elucidate the pathogenesis of thymoma-related autoimmunity and the high affinity of thymoma with myasthenia gravis. In addition, studying the biology of thymoma is also expected to contribute to further understanding of T-cell development and immunological tolerance in the human, because thymoma can be considered an acquired thymus.

HLA class II transgenic mice mimic human inflammatory diseases

Population studies have shown that among all the genetic factors linked with autoimmune disease development, MHC class II genes on chromosome 6 accounts for majority of familial clustering in the common autoimmune diseases. Despite the highly polymorphic nature of HLA class II genes, majority of autoimmune diseases are linked to a limited set of class II-DR or -DQ alleles. Thus a more detailed study of these HLA-DR and -DQ alleles were needed to understand their role in genetic predisposition and pathogenesis of autoimmune diseases. Although in vitro studies using class-II restricted CD4 T cells and purified class II molecules have helped us in understanding some aspects of HLA class-II association with disease, it is difficult to study the role of class II genes in vivo because of heterogeneity of human population, complexity of MHC, and strong linkage disequilibrium among different class II genes. To overcome this problem, we pioneered the generation of HLA-class II transgenic mice to study role of these molecule in inflammatory disease. These HLA class II transgenic mice were used to develop novel in vivo disease model for common autoimmune diseases such as rheumatoid arthritis, multiple sclerosis, insulin-dependent diabetes mellitus, myasthenia gravis, celiac disease, autoimmune relapsing polychondritis, autoimmune myocarditis, thyroiditis, uveitis, as well as other inflammatory disease such as allergy, tuberculosis and toxic shock syndrome. As the T-cell repertoire in these humanized HLA transgenic mice are shaped by human class II molecules, they show the same HLA restriction as humans, implicate potential triggering mechanism and autoantigens, and identify similar antigenic epitopes seen in human. This review describes the value of these humanized transgenic mice in deciphering role of HLA class II molecules in immunopathogenesis of inflammatory diseases.

The role of CD8+CD28 regulatory cells in suppressing myasthenia gravis-associated responses by a dual altered peptide ligand

Myasthenia gravis (MG) and experimental autoimmune MG are T cell-dependent antibody-mediated autoimmune diseases. A dual altered peptide ligand (APL), composed of the tandemly arranged two single amino acid analogs of two myasthenogenic peptides, p195-212 and p259-271, down-regulated in vitro and in vivo MG-associated T cell responses. In the present study, we investigated the role of CD8(+)CD28(-) regulatory cells in the mechanism of action of the dual APL. We demonstrated that treatment of mice with the dual APL concomitant with immunization with a myasthenogenic peptide resulted in an increased population of CD8(+)CD28(-) cells that express forkhead box P3 (Foxp3). The dual APL inhibited the proliferation of lymph node (LN) cells of the Torpedo acetylcholine receptor-immunized WT C57BL/6 mice, whereas the inhibition was abrogated in CD8(-/-) knockout mice. Moreover, the dual APL did not inhibit the secretion of IFN-gamma by LN cells from CD8(-/-) mice immunized with Torpedo acetylcholine receptor. However, the mRNA expression of IL-10 and TGF-beta by LN cells from CD8(-/-) mice was up-regulated similarly to that of the WT mice. Furthermore, the dual APL elevated the proapoptotic markers caspases 3 and caspase 8, whereas it down-regulated the antiapoptotic marker Bcl-xL in both CD8(-/-) and WT mice. Finally, the dual APL-induced CD4(+)CD25(+)Foxp3(+) cells were up-regulated in CD8(-/-) mice to a similar extent to that observed in the WT mice. Thus, we suggest that CD8(+)CD28(-) regulatory cells play a partial role in the mechanism of action by which the dual APL suppresses experimental autoimmune MG-associated T cell responses.

Curcumin and autoimmune disease

The immune system has evolved to protect the host from microbial infection; nevertheless, a breakdown in the immune system often results in infection, cancer, and autoimmune diseases. Multiple sclerosis, rheumatoid arthritis, type 1 diabetes, inflammatory bowel disease, myocarditis, thyroiditis, uveitis, systemic lupus erythromatosis, and myasthenia gravis are organ-specific autoimmune diseases that afflict more than 5% of the population worldwide. Although the etiology is not known and a cure is still wanting, the use of herbal and dietary supplements is on the rise in patients with autoimmune diseases, mainly because they are effective, inexpensive, and relatively safe. Curcumin is a polyphenolic compound isolated from the rhizome of the plant Curcuma longa that has traditionally been used for pain and wound-healing. Recent studies have shown that curcumin ameliorates multiple sclerosis, rheumatoid arthritis, psoriasis, and inflammatory bowel disease in human or animal models. Curcumin inhibits these autoimmune diseases by regulating inflammatory cytokines such as IL-1beta, IL-6, IL-12, TNF-alpha and IFN-gamma and associated JAK-STAT, AP-1, and NF-kappaB signaling pathways in immune cells. Although the beneficial effects of nutraceuticals are traditionally achieved through dietary consumption at low levels for long periods of time, the use of purified active compounds such as curcumin at higher doses for therapeutic purposes needs extreme caution. A precise understanding of effective dose, safe regiment, and mechanism of action is required for the use of curcumin in the treatment of human autoimmune diseases.

A Dual Altered Peptide Ligand Inhibits Myasthenia Gravis Associated Responses by Inducing Phosphorylated Extracellular-regulated Kinase 1,2 that Upregulates CD4+CD25+Foxp3+Cells

Myasthenia gravis (MG) and its animal model experimental autoimmune MG (EAMG), are T-cell dependent, antibody-mediated autoimmune disorders. A dual altered peptide ligand (APL) composed of the tandemly arranged two single amino acids analogs of two myasthenogenic peptides, p195-212 and p259-271, was demonstrated to downregulate, in vitro and in vivo, MG-associated autoimmune responses. Upregulation of regulatory CD4(+)CD25(+) cells plays a key role in the mechanism of action of the dual APL. The objectives of the present study were to address the involvement of extracellular-regulated kinase (ERK)1,2 in the mechanisms by which the dual APL-induced CD4(+)CD25(+) cells suppress MG-associated autoimmune responses. We demonstrate here that administration of the dual APL increased activated ERK1,2 in the CD4(+)CD25(+)-enriched population. Further, inhibition of ERK1,2 by its inhibitor, U0126, in dual APL-induced CD4(+)CD25(+) cells, abrogated their ability to suppress interferon (IFN)-gamma secretion by lymph node (LN) cells of mice that were immunized with the myasthenogenic peptide. Moreover, inhibition of ERK1,2 in the dual APL-induced regulatory CD4(+)CD25(+) cells, resulted in downregulation of the forkhead box p3 (Foxp3) gene and protein expression levels, as well as in the downregulation of CD4(+)CD25(+) development, suggesting that the active suppression exerted by the dual APL via CD4(+)CD25(+) cells depends on ERK1,2 activity.

Muscle-derived nitric oxide synthase expression, differences associated with muscle fiber-type, and disease susceptibility in a rat model of myasthenia gravis

Reports from this laboratory suggested that expression of skeletal muscle-derived, inducible nitric oxide synthase (iNOS), is associated with resistance of a particular rat strain to the autoimmune model of myasthenia gravis (MG). The study reported below demonstrates a similar association between iNOS induction in skeletal muscle and disease-resistance when comparing different skeletal muscles originating from the same rat strain. Thus, soleus muscles, shown previously to be relatively resistant to disease even when obtained from disease-susceptible Lewis rats, were observed to express high levels of iNOS following exposure to antibody reactive with the nicotinic acetylcholine receptor (AChR). Increased iNOS expression appears to be associated with slow-twitch, type 1 fibers and would explain the relatively high iNOS expression in soleus muscles since they are dominated by this fiber type, compared to disease-susceptible EDL muscles which are dominated by fast-twitch, type 2 fibers.

A 50-kDa ERK-like protein is up-regulated by a dual altered peptide ligand that suppresses myasthenia gravis-associated responses

Myasthenia gravis (MG) and its animal model, experimental autoimmune MG (EAMG), are T cell-dependent antibody-mediated autoimmune diseases. A dual altered peptide ligand (APL) that is composed of the tandemly arranged two single amino acid analogues of two myasthenogenic peptides, p195-212 and p259-271, down-regulated in vitro and in vivo MG-associated autoreactive responses. The dual APL was shown to exert its beneficial effects by up-regulating ERK1,2 in CD4(+)CD25(+) regulatory cells. In this study, we investigated a novel 50-kDa ERK-like protein (ERK-50) that is up-regulated significantly in addition to ERK1,2 after treatment with the dual APL. We report here that ERK-50 was up-regulated in LN cells and in LN-derived T cells of mice that were immunized with the myasthenogenic peptides and treated with the dual APL. Moreover, ERK-50 was up-regulated in dual-APL- treated mice that were immunized with the Torpedo acetylcholine receptor. ERK-50 was demonstrated to be recognized by antibodies directed against the C and N termini of ERK1, against the C terminus of ERK2, and against general ERK. The 50-kDa ERK was shown to be stimulated by Con A, and inhibition of MEK1 down-regulated the 50-kDa ERK as was shown for ERK1,2. However, 4beta-phorbol 12-myristate 13-acetate (TPA) did not stimulate ERK-50. Finally, the activated ERK-50 was up-regulated in the dual-APL-induced CD4(+)CD25(+) regulatory cells. Thus, ERK-50 is suggested to be a novel ERK isoform, being up-regulated in response to treatment with the dual APL.

A dual altered peptide ligand down-regulates myasthenogenic T cell responses and reverses experimental autoimmune myasthenia gravis via up-regulation of Fas-FasL-mediated apoptosis

Myasthenia gravis (MG) and experimental autoimmune MG (EAMG) are T cell-dependent, antibody-mediated autoimmune diseases. A dual altered peptide ligand (APL) that is composed of the tandemly arranged two single amino acid analogues of two myasthenogenic peptides, p195-212 and p259-271, was demonstrated to down-regulate in vitro and in vivo MG-associated autoreactive responses. The aims of this study were to investigate the possible role of Fas-FasL-mediated apoptosis in the down-regulatory mechanism of the dual APL. We demonstrate here the effect of the dual APL on expression of key molecules involved in the Fas-FasL pathway, in a p195-212-specific T cell line, in mice immunized with Torpedo acetylcholine receptor and in mice afflicted with EAMG (induced with the latter). In vitro and in vivo results show that the dual APL up-regulated expression of Fas and FasL on the CD4 cells. Expression of the pro-apoptotic molecules, caspase 8 and caspase 3, was significantly up-regulated, while anti-apoptotic cFLIP and Bcl-2 were down-regulated upon treatment with the dual APL. The dual APL also increased phosphorylation of the mitogen-activated protein kinases, c-Jun-NH2-terminal kinase and p-38, known to play a role in the regulation of FasL expression. Further, in the T cell line incubated with the dual APL as well as in mice of the SJL inbred strain immunized with the myasthenogenic peptide and treated concomitantly with the dual APL, the percentage of apoptotic cells increased. Results strongly indicate that up-regulation of apoptosis via the Fas-FasL pathway is one of the mechanisms by which the dual APL reverses EAMG manifestations in C57BL/6 mice.

Down-regulation of T cell responses to AChR and reversal of EAMG manifestations in mice by a dual altered peptide ligand via induction of CD4+CD25+ regulatory cells

A dual altered peptide ligand (APL) composed of the tandemly arranged two single amino acid analogs of two myasthenogenic peptides, p195-212 and p259-271 was demonstrated to down-regulate in vitro and in vivo myasthenia gravis (MG) associated autoreactive responses. In this study, we demonstrate the suppressive properties of the dual APL following immunization with the whole Torpedo AChR (TAChR) and in mice with established experimental autoimmune MG (EAMG). The dual APL acts by up-regulating CD4+ CD25+ cells expressing characteristic regulatory markers along with an associated increase in levels of IL-10 and TGF-beta. The latter cytokine plays a key role in the ameliorating effects of the dual APL.

Modulation of immune responses and suppression of experimental autoimmune myasthenia gravis by surgical denervation of the spleen

Critical interactions between the nervous system and the immune system during experimental autoimmune myasthenia gravis (EAMG) were examined in an animal model for human MG after immunization of adult female Lewis rats with Torpedo acetylcholine receptor (AChR) and complete Freund's adjuvant. Immunized rats depicted marked clinical severity of the disease. Using enzyme-linked immunospot (ELISPOT) assay and in situ hybridization techniques, immune responses in these animals were examined and showed elevated numbers of anti-AChR IgG secreting B cells and AChR reactive interferon (IFN)-gamma-secreting cells, enhanced mRNA expression of the proinflammatory cytokines IFN-gamma and tumour necrosis factor (TNF)-alpha as Th1 subset and the anti-inflammatory cytokines interleukin (IL)-4 and IL-10 as a Th2 subset, and transforming growth factor (TGF)-beta as a Th3 cytokine. Corticosterone and prostaglandin E(2) (PGE(2)) levels were measured by radioimmunoassay and illustrated increased production after immunization. Surgical denervation of the spleen reduced significantly the clinical severity of the disease, suppressed the numbers of IgG and IFN-gamma-secreting cells, down-regulated the mRNA expression for cytokines and reduced corticosterone and PGE(2) production. As controls, sham-operated rats were used and showed results as the EAMG non-denervated control rats. The data present herein, and for the first time, substantial effects of the nervous system on immune responses that may influence the outcome of EAMG. These effects were not dependent on cytokine inhibitory mediators such as prostaglandins or stress hormones. IL-10 and TGF-beta, the two potent immunosuppressive cytokines, were also suppressed, indicating a general suppression by splenic denervation. More investigations are initiated at our laboratories to understand the evident neural control over the immune system during challenges leading to the break of tolerance and development of autoimmunity, which may assist in innovative therapeutic approaches.

Titin and ryanodine receptor antibodies in myasthenia gravis

Some myasthenia gravis (MG) patients have antibodies against skeletal muscle antigens in addition to the acetylcholine receptor (AChR). Two major antigens for non-AchR antibodies in MG are the Ca(2+) release channel of the sarcoplasmic reticulum, the ryanodine receptor (RyR) and titin, a gigantic filamentous muscle protein essential for muscle structure, function and development. RyR and titin antibodies are found mainly in thymoma MG patients and in a few late-onset MG patients and correlate with a severe MG disease. The presence of titin antibodies, which bind to key regions near the A/I junction and in the central I-band, correlates with myopathy. The immunosuppressant (FK506), which enhances Ca(2+) release from the RyR, seems to have a symptomatic effect on MG patients with RyR antibodies. The RyR antibodies recognize a region near the N-terminus important for channel regulation and inhibit Ca(2+) release in vitro. However, evidence that antibodies against the intracellular antigens RyR and titin are pathogenic in vivo is still missing.

Immunomodulatory vaccines against autoimmune diseases

Vaccines are for healthy people, to prevent them from becoming ill. Such prophylactic vaccines have been a great success. Therapeutic vaccines become more and more important, especially as life expectancy increases. Efforts to develop vaccines against such diseases as cancer, AIDS, hepatitis, tuberculosis, Alzheimer disease, and mad cow disease have not yet reached the stage where they can be successfully used on a daily basis. However, significant progress has been made in the realm of autoimmune diseases, resulting (at least in one case) in an immunomodulatory vaccine against multiple sclerosis that was developed in the author's laboratory, and that is in daily use by about 100,000 patients. The drug or therapeutic vaccine against the exacerbating-remitting type of multiple sclerosis is a copolymer of four amino acid residues, denoted Copaxone, which are related to myelin basic protein. This paper discusses Copaxone as well as a candidate immunomodulatory vaccine against myasthenia gravis, a peptide derived from the nicotinic acetylcholine receptor. Copolymer 1 (Cop 1, glatiramer acetate, Copaxone) is a synthetic amino acid random copolymer that is immunologically cross-reactive with myelin basic protein and suppresses experimental allergic encephalomyelitis in several animal species. Cop 1 slows the progression of disability and reduces the relapse rate in exacerbating-remitting multiple sclerosis patients. Cop 1 is a potent inducer of T helper 2 (Th2) regulatory cells in mice and humans; and Th2 cells are found in both the brains and spinal cords of Cop 1-treated mice and humans. MG and experimental autoimmune MG are T cell-regulated, antibody-mediated autoimmune diseases. Two peptides, representing sequences of the human AChR-alpha-subunit, p195-212 and p259-271, are immunodominant T-cell epitopes in MG patients and two strains of mice. Altered peptide ligand, composed of the randomly arranged two single amino acid analogs inhibits in vitro and in vivo MG-associated autoimmune responses. The active suppression is mediated by the CD4+ CD25+ immunoregulatory cells and is associated with the downregulation of Th1-type cytokines and upregulation of the secretion of IL-10 and the immunosuppressive cytokine transforming growth factor beta.

CDR3 Spectratyping Analysis of the TCR Repertoire in Myasthenia Gravis

Because myasthenia gravis (MG) is an autoimmune disease mediated by Abs specific for the acetylcholine receptor, helper T cells play a role in Ab production. In this study, we have performed large-scale cross-sectional and longitudinal TCR studies by CDR3 spectratyping using PBL and thymus tissues from MG patients. We found that there was no preferential usage of any particular TCR beta-chains that was identical among MG patients. However, the longitudinal study clearly demonstrated that one or more TCR Vbeta expansions persisted frequently in MG patients. Importantly, persistent TCR expansions correlated with clinical severity and high anti-acetylcholine receptor Ab titer. Finally, examinations of T cells expressing CXCR5, i.e., follicular B-helper T cells, revealed that spectratype expansions in MG patients were detected mainly in the CD4+ CXCR5+ T cell populations, whereas CD8+ T cells were the major source of clonal expansion in healthy subjects. These findings suggest that persistent clonal expansions of T cells in MG patients are associated with the development and maintenance of MG. Close examination of pathogenic T cells in MG provides useful information to elucidate the pathogenesis and to estimate the disease status.

The chemokine CXCL13 is a key molecule in autoimmune myasthenia gravis

Myasthenia gravis (MG) is associated with ectopic germinal centers in the thymus. Thymectomy and glucocorticoids are the main treatments but they induce operative risks and side effects, respectively. The aim of this study was to propose new therapies more efficient for MG. We hypothesized that molecules dysregulated in MG thymus and normalized by glucocorticoids may play a key role in thymic pathogenesis. Using gene chip analysis, we identified 88 genes complying with these criteria, the most remarkable being the B-cell chemoattractant (CXCL13). Its expression was increased in thymus and sera of glucocorticoid-untreated patients and decreased in response to treatment in correlation with clinical improvement. Normal B cells were actively chemoattracted by thymic extracts from glucocorticoid-untreated patients, an effect inhibited by anti-CXCL13 antibodies. In the thymus, CXCL13 was preferentially produced by epithelial cells and overproduced by epithelial cells from MG patients. Altogether, our results suggest that a high CXCL13 production by epithelial cells could be responsible for germinal center formation in MG thymus. Furthermore, they show that this gene is a main target of corticotherapy. Thus, new therapies targeting CXCL13 could be of interest for MG and other autoimmune diseases characterized by ectopic germinal center formation.

Estrogen enhances susceptibility to experimental autoimmune myasthenia gravis by promoting type 1-polarized immune responses

Myasthenia gravis (MG) is an organ-specific autoimmune disease caused in most cases by autoantibodies against the nicotinic acetylcholine receptor (AChR). It is now well documented that many autoimmune diseases, including MG, are more prevalent in women than in men, and that fluctuations in disease severity occur during pregnancy. These observations raise the question of the potential role of sex hormones, such as estrogens, as mediators of sex differences in autoimmunity. In the present study, we have analyzed the effect of 17beta-estradiol (E2) on the pathogenesis of experimental autoimmune myasthenia gravis (EAMG), an animal model of MG. We show that treatment with E2 before Ag priming is necessary and sufficient to promote AChR-specific Th1 cell expansion in vivo. This time-limited exposure to E2 enhances the production of anti-AChR IgG2a(b) (specific for b allotype; e.g., B6) and IgG2b, but not IgG1, and significantly increases the severity of EAMG in mice. Interestingly, the E2-mediated augmentation in AChR-specific Th1 response correlates with an enhanced production of IL-12 by splenic APCs through the recruitment of CD8alpha(+) dendritic cells. These data provide the first evidence that estrogen enhances EAMG, and sheds some light on the role of sex hormones in immune responses and susceptibility to autoimmune disease in women.

Suppression of myasthenogenic responses of a T cell line by a dual altered peptide ligand by induction of CD4+CD25+ regulatory cells

Myasthenia gravis is a T cell-dependent, antibody-mediated autoimmune disease. A dual altered peptide ligand (APL) that is composed of the tandemly arranged two single amino acid analogs of two myasthenogenic peptides, p195-212 and p259-271, was demonstrated to down-regulate in vitro and in vivo myasthenia gravis-associated autoreactive responses. The aims of this study were to demonstrate the suppressive properties and to elucidate the mechanism of action of the dual APL on a T cell line specific to the myasthenogenic peptide p195-212. We demonstrate here that incubation of cells of the line with the dual APL resulted in the inhibition of proliferation and secretion of IL-2 and IFN-gamma triggered by p195-212. In contrast, secretion of TGF-beta and IL-10 was upregulated. The dual APL induced the generation of CD4+CD25+ cells that were characterized by the expression of CD45Rb(low), cytotoxic T lymphocyte-associated antigen-4, TGF-beta, CD62L, Foxp3, and neuropilin. In addition, the dual APL-treated cells were capable of inhibiting the proliferation response of the line when the two sets of cells were cocultured. The role of CD4+CD25+ cells was further confirmed by demonstrating that the suppression was abrogated by blocking/neutralization of CD25. Thus, the dual APL acts by inducing the formation of CD4+CD25+ regulatory cells. By using a T cell line, we could show that the immunosuppressive CD4+CD25+ cells were indeed induced by the dual APL and are not part of the naturally occurring regulatory cells.

Isolation and characterization of human anti-acetylcholine receptor monoclonal antibodies from transgenic mice expressing human immunoglobulin loci

The isolation of human antibodies against muscle acetylcholine receptor (AChR), the autoantigen involved in myasthenia gravis (MG), is important for the development of therapeutically useful reagents. Monovalent antibody fragments from monoclonal antibodies against the main immunogenic region (MIR) of AChR protect the receptor from the destructive activity of MG autoantibodies. Human anti-AChR alpha-subunit antibody fragments with therapeutic potential have been isolated using phage display antibody libraries. An alternative approach for obtaining human mAb has been provided by the development of humanized mice. In this report, we show that immunization of transgenic mouse strains with the extracellular domain of the human AChR alpha-subunit results in antibody responses and isolation of hybridomas producing human mAb. Four specific IgM mAb were isolated and analyzed. mAb170 recognized the native receptor the best and was capable of inducing AChR antigenic modulation, suggesting its specificity for a pathogenic epitope. Moreover, the recombinant antigen-binding (Fab) fragment of this mAb competed with an anti-MIR mAb, revealing that its antigenic determinant lies in or near the MIR. Finally, Fab170 was able to compete with MG autoantibodies and protect the AChR against antigenic modulation induced by MG sera. This approach will be useful for isolating additional mAb with therapeutic potential against the other AChR subunits.

Immunomodulation by a dual altered peptide ligand of autoreactive responses to the acetylcholine receptor of peripheral blood lymphocytes of patients with myasthenia gravis

Myasthenia gravis (MG) is a T cell-dependent, antibody-mediated autoimmune disease. A dual altered peptide ligand (APL) that is composed of the tandemly arranged two single amino acid analogs of two myasthenogenic peptides was demonstrated to downregulate in vitro and in vivo murine MG associated autoreactive responses. Furthermore, treatment with the dual APL ameliorated the clinical manifestations of an established experimental autoimmune MG in mice. This study was undertaken in order to investigate the ability of the dual APL to immunomodulate MG-associated responses of peripheral blood lymphocytes (PBL) of patients with MG to the native autoantigen acetylcholine receptor (AChR). PBL of 22 of 27 patients with MG tested responded by proliferation to torpedo AChR. The proliferative responses of PBL of 21 of 22 responders were significantly inhibited by the dual APL. The inhibition was specific because a control peptide did not inhibit these proliferative responses. The dual APL also downregulated the levels of the secreted pathogenic cytokine IFN-gamma in supernatants of stimulated PBL of 80% of the tested patients. The latter inhibitions correlated with an upregulated production of the immunosuppressive cytokine, tumor growth factor beta. Thus, the results of our study demonstrate that the dual APL is capable of downregulating in vitro autoreactive responses of patients with MG and suggest that this peptide is a potential candidate for a novel specific treatment of patients with MG.

Down-regulation of myasthenogenic T cell responses by a dual altered peptide ligand via CD4+CD25+-regulated events leading to apoptosis

The myasthenogenic peptides p195-212 and p259-271 are sequences of the human acetylcholine receptor and were shown to induce myasthenia gravis-associated immune responses in mice. A dual altered peptide ligand (APL) composed of the two APLs of the myasthenogenic peptides inhibited, in vitro and in vivo, those responses. The aims of this study were to elucidate the events that follow the in vivo treatment with the dual APL and to characterize the cell population that is induced by the latter. We demonstrate here that s.c. administration of the dual APL up-regulates CD4+CD25+ regulatory T cells that are characterized by up-regulated expression of cytotoxic T lymphocyte-associated antigen 4, intracellular and membranal TGF-beta, and Foxp3. Administration of the dual APL to mice concomitant with the immunization with either of the myasthenogenic peptides resulted also in the up-regulation of c-Jun-NH2-terminal kinase activity and of Fas signaling pathway molecules as determined by measuring Fas, Fas ligand, and caspase 8. Thus, our results suggest that the suppression of myasthenia gravis-associated T cell responses exerted by the dual APL is mediated by the CD4+CD25+ immunoregulatory T cell function via TGF-beta or cytotoxic T lymphocyte-associated antigen 4, which further stimulate a cascade of events that up-regulates apoptosis.

Therapeutic vaccines in autoimmunity

Similarly to prophylactic vaccines whose purpose is to prevent infectious diseases, therapeutic vaccines against autoimmune diseases are based on their similarity to the putative causes of the disease. We shall describe here two such examples: a copolymer of amino acids related to myelin basic protein, in the case of multiple sclerosis, and a peptide derived from the nicotinic acetylcholine receptor (AChR), in the case of myasthenia gravis (MG). Copolymer 1 (Cop 1, glatiramer acetate, Copaxone) is a synthetic amino acid random copolymer, immunologically cross-reactive with myelin basic protein and suppresses experimental allergic encephalomyelitis in several animal species. Cop 1 slows the progression of disability and reduces relapse rate in exacerbating-remitting multiple sclerosis patients. It was approved by the Food and Drug Administration in 1996, and today is used by tens of thousands of patients. Cop 1 is a potent inducer of T helper 2 (Th2) regulatory cells in mice and humans, and Th2 cells are found both in the brains and spinal cords of Cop 1-treated mice. MG and experimental autoimmune MG are T cell-regulated, antibody-mediated autoimmune diseases. Two peptides, representing sequences of the human AChR alpha-subunit, p195-212 and p259-271, are immunodominant T cell epitopes in MG patients and in two strains of mice. Altered peptide ligand, composed of the tandemly arranged two single amino acid analogs, inhibits in vitro and in vivo MG-associated autoimmune responses. The active suppression is mediated by the CD4(+)CD25(+) immunoregulatory cells and is associated with the down-regulation of Th1-type cytokines and the up-regulation of the secretion of IL-10 and the immunosuppressive cytokine, transforming growth factor beta.

Pathogenesis of myositis and myasthenia associated with titin and ryanodine receptor antibodies

Some myasthenia gravis (MG) patients have antibodies against skeletal muscle antigens in addition to the acetylcholine receptor (AChR). Two major antigens for these antibodies are the Ca(2+) release channel of the sarcoplasmic reticulum, the ryanodine receptor (RyR), and titin, a gigantic filamentous muscle protein essential for muscle structure, function, and development. RyR and titin antibodies are found in MG patients with a thymoma and in a proportion of late-onset MG, and they correlate with severe MG disease. The RyR antibodies recognize a region near the N-terminus important for channel regulation. They inhibit Ca(2+) release from sarcoplasmic reticulum in vitro. There is electrophysiological evidence for a disordered excitation-contraction coupling in MG patients. The presence of titin antibodies, which bind to key regions near the A/I junction and in the central I-band, correlates with myopathy in MG patients. However, so far, there is no direct evidence that antibodies against the intracellular antigens RyR and titin are pathogenic in vivo.

The immunologic role of thymectomy in the treatment of myasthenia gravis: implication of thymus-associated B-lymphocyte subset in reduction of the anti-acetylcholine receptor antibody titer

BACKGROUND AND PURPOSE

Thymectomy is generally accepted as the major option of treatment for myasthenia gravis. To elucidate the biological role of thymectomy in the treatment of myasthenia gravis, the immunologic characteristics of the thymus was studied in association with the postoperative kinetics of the anti-acetylcholine receptor antibody titer.

MATERIALS AND METHODS

Thirty-four patients with nonthymomatous myasthenia gravis who had positive anti-acetylcholine receptor antibody titer and undergoing extended thymectomy were subjected to the study. Reduction of anti-acetylcholine receptor antibody titer was evaluated in terms of the proportion of anti-acetylcholine receptor antibody titer at 1 year after thymectomy to that before the operation. The numbers of B lymphocytes (CD19(+) cells) and the germinal center B lymphocytes (CD19(+)CD38(high) cells) present in 1 g of the thymic tissue were calculated by flow cytometry.

RESULTS

The proportion of anti-acetylcholine receptor antibody titer at 1 year after thymectomy ranged from 27.5% to 150%. The numbers of B lymphocytes and the germinal center B lymphocytes in 1 g of the thymic tissue ranged from 0.19 x 10(6)/g to 162.8 x 10(6)/g and from 0.09 x 10(6)/g to 33.4 x 10(6)/g, respectively. The proportion of anti-acetylcholine receptor antibody titer at 1 year after thymectomy had a significant inverted correlation with the number of B lymphocytes (P =.002) as well as that of the germinal center B lymphocytes (P =.007).

CONCLUSION

Effectiveness of thymectomy was dependent on predominance of B lymphocytes and the germinal center B lymphocytes in the thymus, suggesting that one of the biological roles of thymectomy in the treatment of myasthenia gravis is removing the thymus-associated germinal centers.

T Cells and Cytokines in the Pathogenesis of Acquired Myasthenia Gravis

Although the symptoms of myasthenia gravis (MG) and experimental MG (EAMG) are caused by autoantibodies, CD4(+) T cells specific for the target antigen, the nicotinic acetylcholine receptor, and the cytokines they secrete, have an important role in these diseases. CD4(+) T cells have a pathogenic role, by permitting and facilitating the synthesis of high-affinity anti-AChR antibodies. Th1 CD4(+) cells are especially important because they drive the synthesis of anti-AChR complement-fixing IgG subclasses. Binding of those antibodies to the muscle AChR at the neuromuscular junction will trigger the complement-mediated destruction of the postsynaptic membrane. Thus, IL-12, a crucial cytokine for differentiation of Th1 cells, is necessary for development of EAMG. Th2 cells secrete different cytokines, with different effects on the pathogenesis of EAMG. Among them, IL-10, which is a potent growth and differentiation factor for B cells, facilitates the development of EAMG. In contrast, IL-4 appears to be involved in the differentiation of AChR-specific regulatory CD4(+) T cells, which can prevent the development of EAMG and its progression to a self-maintaining, chronic autoimmune disease. Studies on the AChR-specific CD4(+) cells commonly present in the blood of MG patients support a crucial role of CD4(+) T cells in the development of MG. Circumstantial evidence supports a pathogenic role of IL-10 also in human MG. On the other hand, there is no direct or circumstantial evidence yet indicating a role of IL-4 in the modulatory or immunosuppressive circuits in MG.