Detection of anti-acetylcholine receptor factors in serum and thymus from patients with myasthenia gravis

Antibody Therapies in Autoimmune Neuromuscular Junction Disorders: Approach to Myasthenic Crisis and Chronic Management

Myasthenia gravis (MG) is a neurological autoimmune disorder characterized by muscle weakness and fatigue. It is a B cell-mediated disease caused by pathogenic antibodies directed against various components of the neuromuscular junction (NMJ). Despite the wide range of adverse effects, current treatment is still based on non-specific immunosuppression, particularly on long-term steroid usage. The increasing knowledge regarding the pathogenic mechanisms of MG has however allowed to create more target-specific therapies. A very attractive therapeutic approach is currently offered by monoclonal antibodies (mAbs), given their ability to specifically and effectively target different immunopathological pathways, such as the complement cascade, B cell-related cluster of differentiation (CD) proteins, and the human neonatal Fc receptor (FcRn). Up to now, eculizumab, a C5-directed mAb, has been approved for the treatment of generalized MG (gMG) and efgartigimod, a FcRn inhibitor, has just been approved by the U.S. Food and Drug Administration for the treatment of anti-acetylcholine receptor (AChR) antibody positive gMG. Other mAbs are currently under investigation with encouraging preliminary results, further enriching the new range of therapeutic possibilities for MG. This review article provides an overview of the present status of mAb-based therapies for MG, which offer an exciting promise for better outcomes by setting the basis of a precision medicine approach.

Improving laboratory diagnostics in myasthenia gravis

Introduction: Myasthenia gravis (MG) is a prototypical autoimmune disease, characterized by pathogenic autoantibodies targeting structures of the neuromuscular junction. Radioimmunoprecipitation assays (RIPAs) represent the gold standard for their detection. However, new methods are emerging to complement, or overcome RIPAs, also with the perspective of eliminating the use of radioactive reagents.Areas covered: We discuss advances in laboratory methods, prompted especially by cell-based assays (CBAs), for the detection of the autoantibodies of MG diagnostics, above all those to the nicotinic acetylcholine receptor (AChR), muscle-specific kinase (MuSK), and low molecular-weight receptor-related low-density lipoprotein-4 (LRP4).Expert opinion: CBA technology makes AChRs aggregate on cell membranes, thus allowing to detect autoantibodies to clustered AChRs, with reduction of seronegative MG cases. The diagnostic relevance of RIPA/CBA-measurable LRP4 antibodies is still unclear, in Caucasian patients at least. Live CBAs for the detection of AChR, MuSK, and LRP4 antibodies might represent an alternative to RIPAs, but first require full validation. CBAs could be used as screening tests, limiting RIPAs for antibody quantification. To this end, ELISAs might be an alternative.Fixation procedures preserving enough degree of antigen conformationality could yield AChR and MuSK CBAs suitable for a wide use in clinical-chemistry laboratories.

Rituximab in Myasthenia Gravis - Where do we stand?

Introduction: Myasthenia gravis (MG) is an antibody-mediated disease with diverse serology and clinical presentation. Currently, MG is managed by untargeted immunomodulatory agents. About 15% patients are refractory to these therapies. Several novel and targeted treatments are on the horizon. Rituximab, a monoclonal antibody, is reported to be highly effective with widespread oof-label usage in MG, particularly in patients with antibody against muscle-specific kinase or refractory disease. However, a recent trial showed negative results. Compared to conventional oral immunosuppressive therapies used in MG, Rituximab has several benefits. Regular hematological monitoring is not required though serious side effects can occur. Current status of Rituximab in MG and newer immunosuppressants is discussed.Areas explored: Biologic features, clinical effectiveness, safety profile, and newer preparations of Rituximab.Expert opinion: Rituximab provides a promising option for management of MG, particularly in patients with muscle-specific kinase antibodies or those with refractory disease. Several knowledge gaps remain due to scarcity of data from randomized controlled studies. Despite lack of regulatory approval Rituximab has found widespread usage in MG. Large, well-designed studies are needed to assess the comparative efficacy of Rituximab and its optimal regimen in MG.

Thymus-derived B cell clones persist in the circulation after thymectomy in myasthenia gravis

Myasthenia gravis (MG) is a neuromuscular, autoimmune disease caused by autoantibodies that target postsynaptic proteins, primarily the acetylcholine receptor (AChR) and inhibit signaling at the neuromuscular junction. The majority of patients under 50 y with AChR autoantibody MG have thymic lymphofollicular hyperplasia. The MG thymus is a reservoir of plasma cells that secrete disease-causing AChR autoantibodies and although thymectomy improves clinical scores, many patients fail to achieve complete stable remission without additional immunosuppressive treatments. We speculate that thymus-associated B cells and plasma cells persist in the circulation after thymectomy and that their persistence could explain incomplete responses to resection. We studied patients enrolled in a randomized clinical trial and used complementary modalities of B cell repertoire sequencing to characterize the thymus B cell repertoire and identify B cell clones that resided in the thymus and circulation before and 12 mo after thymectomy. Thymus-associated B cell clones were detected in the circulation by both mRNA-based and genomic DNA-based sequencing. These antigen-experienced B cells persisted in the circulation after thymectomy. Many circulating thymus-associated B cell clones were inferred to have originated and initially matured in the thymus before emigration from the thymus to the circulation. The persistence of thymus-associated B cells correlated with less favorable changes in clinical symptom measures, steroid dose required to manage symptoms, and marginal changes in AChR autoantibody titer. This investigation indicates that the diminished clinical response to thymectomy is related to persistent circulating thymus-associated B cell clones.

Autoimmune Pathology in Myasthenia Gravis Disease Subtypes Is Governed by Divergent Mechanisms of Immunopathology

Myasthenia gravis (MG) is a prototypical autoantibody mediated disease. The autoantibodies in MG target structures within the neuromuscular junction (NMJ), thus affecting neuromuscular transmission. The major disease subtypes of autoimmune MG are defined by their antigenic target. The most common target of pathogenic autoantibodies in MG is the nicotinic acetylcholine receptor (AChR), followed by muscle-specific kinase (MuSK) and lipoprotein receptor-related protein 4 (LRP4). MG patients present with similar symptoms independent of the underlying subtype of disease, while the immunopathology is remarkably distinct. Here we highlight these distinct immune mechanisms that describe both the B cell- and autoantibody-mediated pathogenesis by comparing AChR and MuSK MG subtypes. In our discussion of the AChR subtype, we focus on the role of long-lived plasma cells in the production of pathogenic autoantibodies, the IgG1 subclass mediated pathology, and contributions of complement. The similarities underlying the immunopathology of AChR MG and neuromyelitis optica (NMO) are highlighted. In contrast, MuSK MG is caused by autoantibody production by short-lived plasmablasts. MuSK MG autoantibodies are mainly of the IgG4 subclass which can undergo Fab-arm exchange (FAE), a process unique to this subclass. In FAE IgG4, molecules can dissociate into two halves and recombine with other half IgG4 molecules resulting in bispecific antibodies. Similarities between MuSK MG and other IgG4-mediated autoimmune diseases, including pemphigus vulgaris (PV) and chronic inflammatory demyelinating polyneuropathy (CIDP), are highlighted. Finally, the immunological distinctions are emphasized through presentation of biological therapeutics that provide clinical benefit depending on the MG disease subtype.

Therapies Directed Against B-Cells and Downstream Effectors in Generalized Autoimmune Myasthenia Gravis: Current Status

Myasthenia gravis is a rare, heterogeneous, classical autoimmune disease characterized by fatigable skeletal muscle weakness, which is directly mediated by autoantibodies targeting various components of the neuromuscular junction, including the acetylcholine receptor, muscle specific tyrosine kinase, and lipoprotein-related protein 4. Subgrouping of myasthenia gravis is dependent on the age of onset, pattern of clinical weakness, autoantibody detected, type of thymic pathology, and response to immunotherapy. Generalized immunosuppressive therapies are effective in all subgroups of myasthenia gravis; however, approximately 15% remain refractory and more effective treatments with improved safety profiles are needed. In recent years, successful utilization of targeted B-cell therapies in this disease has triggered renewed focus in unraveling the underlying immunopathology in attempts to identify newer therapeutic targets. While myasthenia gravis is predominantly B-cell mediated, T cells, T cell-B cell interactions, and B-cell-related factors are increasingly recognized to play key roles in its immunopathology, particularly in autoantibody production, and novel therapies have focused on targeting these specific immune system components. This overview describes the current understanding of myasthenia gravis immunopathology before discussing B-cell-related therapies, their therapeutic targets, and the rationale and evidence for their use. Several prospective studies demonstrated efficacy of rituximab in various myasthenia gravis subtypes, particularly that characterized by antibodies against muscle-specific tyrosine kinase. However, a recent randomized control trial in patients with acetylcholine receptor antibodies was negative. Eculizumab, a complement inhibitor, has recently gained regulatory approval for myasthenia gravis based on a phase III trial that narrowly missed its primary endpoint while achieving robust results in all secondary endpoints. Zilucoplan is a subcutaneously administered terminal complement inhibitor that recently demonstrated significant improvements in functional outcome measures in a phase II trial. Rozanolixizumab, CFZ533, belimumab, and bortezomib are B-cell-related therapies that are in the early stages of evaluation in treating myasthenia gravis. The rarity of myasthenia gravis, heterogeneity in its clinical manifestations, and variability in immunosuppressive regimens are challenges to conducting successful trials. Nonetheless, these are promising times for myasthenia gravis, as renewed research efforts provide novel insights into its immunopathology, allowing for development of targeted therapies with increased efficacy and safety.

B cells in the pathophysiology of myasthenia gravis

Myasthenia gravis (MG) is an archetypal autoimmune disease. The pathology is characterized by autoantibodies to the acetylcholine receptor (AChR) in most patients or to muscle-specific tyrosine kinase (MuSK) in others and to a growing number of other postsynaptic proteins in smaller subsets. A decrease in the number of functional AChRs or functional interruption of the AChR within the muscle end plate of the neuromuscular junction is caused by pathogenic autoantibodies. Although the molecular immunology underpinning the pathology is well understood, much remains to be learned about the cellular immunology contributing to the production of autoantibodies. This Review documents research concerning the immunopathology of MG, bringing together evidence principally from human studies with an emphasis on the role of adaptive immunity and B cells in particular. Proposed mechanisms for autoimmunity, which take into account that different types of MG may incorporate divergent immunopathology, are offered. Muscle Nerve 57: 172-184, 2018.

Myf5 and Myogenin in the development of thymic myoid cells - Implications for a murine in vivo model of myasthenia gravis

Myasthenia gravis (MG) is caused by autoantibodies against the neuromuscular junction of striated muscle. Most MG patients have autoreactive T- and B-cells directed to the acetylcholine receptor (AChR). To achieve immunologic tolerance, developing thymocytes are normally eliminated after recognition of self-antigen-derived peptides. Presentation of muscle-specific antigens is likely achieved through two pathways: on medullary thymic epithelial cells and on medullary dendritic cells cross-presenting peptides derived from a unique population of thymic myoid cells (TMC). Decades ago, it has been hypothesized that TMC play a key role in the induction of immunological tolerance towards skeletal muscle antigens. However, an experimental model to address this postulate has not been available. To generate such a model, we tested the hypothesis that the development of TMC depends on myogenic regulatory factors. To this end, we utilized Myf5-deficient mice, which lack the first wave of muscle cells but form normal skeletal muscles later during development, and Myogenin-deficient mice, which fail to form differentiated myofibers. We demonstrate for the first time that Myf5- and Myogenin-deficient mice showed a partial or complete, respectively, loss of TMC in an otherwise regularly structured thymus. To overcome early postnatal lethality of muscle-deficient, Myogenin-knockout mice we transplanted Myogenin-deficient fetal thymuses into Foxn1(nu/nu) mice that lack their own thymus anlage. We found that the transplants are functional but lack TMC. In combination with established immunization strategies (utilizing AChR or Titin), this model should enable us in the future testing the hypothesis that TMC play an indispensable role in the development of central tolerance towards striated muscle antigens.

Ocular myasthenia gravis

PURPOSE OF REVIEW

To review ocular myasthenia gravis (OMG), a localized form of myasthenia gravis clinically involving only the extraocular, levator palpebrae superioris, and orbicularis oculi muscles.

RECENT FINDINGS

Ocular manifestations can masquerade as a variety of ocular motility disorders, including central nervous system disorders and peripheral cranial nerve palsies. While sparing the pupils, the diagnosis and management can be challenging.

SUMMARY

Because several diagnostic and treatment options are available for OMG, clinicians must decide the sequence and combination based on the level of disease activity and patient disability.

Reflections on the "intrathymic pathogenesis" of myasthenia gravis

The beneficial effects of thymectomy argue for a causal role of the thymus in myasthenia gravis (MG). The MG thymus contains acetylcholine receptor (AChR), which is expressed by myoid cells (whole AChR), and by medullary thymic epithelial cells (AChR subunits). The myoid cells are closely associated with antigen-presenting dendritic cells, helper T cells, and antibody-producing B cells in lymphoid follicles ("lymphofollicular hyperplasia"). Thus, all the cellular components required to initiate and maintain an autoimmune response to AChR are present in the MG thymus. It is unlikely that the cellular alterations in the thymus are secondary to an ongoing peripheral immune response, because they are absent in experimental autoimmune myasthenia gravis.

Acetylcholine receptor antibody: clinical and experimental aspects

Anti-acetylcholine (ACh) receptor antibody is the specific antibody in myasthenia gravis (MG). Groups of patients distinguished by thymic pathology and age of onset have shown differences in sex and HLA antigen incidence and in anti-ACh receptor antibody levels. Group differences in the characteristics of this antibody, including the percentage of kappa and gamma light chains, IgG subclass and reactivity with other ACh receptor preparations, were detected only in patients with ocular MG. This group alone showed a possible association with Gm allotype in Caucasians; the anti-ACh receptor antibody had a greater proportion of kappa light chain and better reactivity with human ocular ACh receptor than did generalized MG. The results indicate heterogeneity of this disease. Thymic cells from myasthenic patients with thymic hyperplasia spontaneously synthesize anti-ACh receptor antibody in culture and, after irradiation to abrogate antibody production and any suppressor effects, can selectively enhance the synthesis of anti-ACh receptor antibody by autologous blood lymphocytes in co-culture. The cell types that underlie these responses have been investigated by deleting cell subsets by complement-mediated lysis using monoclonal antibodies. Neither cortical (NA1/34+) thymocytes nor mature T cells (MBG6+) are essential for antibody production in vitro by thymic cells. The enhancement of antibody production by irradiated thymic cells may depend on antigen-presenting cells not expressing the HLA-DR surface marker, or possibly antigen-specific helper T cells, or both.

Sensitivity to vecuronium in seropositive and seronegative patients with myasthenia gravis

Patients with myasthenia gravis (MG) are hypersensitive to nondepolarizing neuromuscular blocking drugs. Although antibodies to the acetylcholine receptor (AChR) often are observed in MG patients, 10% to 30% of patients do not show an anti-AChR antibody. Little is known about differences in sensitivity to nondepolarizing neuromuscular blocking drugs between MG patients with and without anti-AChR antibody. Hypothesizing that seronegative patients are as sensitive to vecuronium as seropositive patients, we assessed sensitivity in seropositive and seronegative MG patients and in non-MG patients (n = 8 each). During anesthesia with sevoflurane (2.5%) and nitrous oxide (60%) in oxygen, neuromuscular transmission was monitored by measuring the twitch tension of the adductor pollicis muscle with supramaximal stimulation. After baseline measurements, 10 microg/kg IV dose increments of vecuronium were administered sequentially until blockade exceeded 90%. The degree of blockade and onset time after the initial 10 microg/kg of vecuronium were assessed, and doses required to exceed 90% blockade were recorded. In addition, effective doses of 50% and 95% for vecuronium were calculated from a single data point. Both types of MG patients showed increased sensitivity to vecuronium compared with non-MG patients.

IMPLICATIONS

Hypothesizing that seronegative patients are as sensitive to vecuronium as seropositive patients, we assessed sensitivity in seropositive and seronegative myasthenia gravis (MG) patients and in non-MG patients. They were, indeed, both equally sensitive to vecuronium.

Difference in sensitivity to vecuronium between patients with ocular and generalized myasthenia gravis

Patients with myasthenia gravis show sensitivity to non-depolarizing neuromuscular blocking drugs, but little is known about differences in this sensitivity between types of myasthenia. In 10 patients with ocular myasthenia gravis and 10 with generalized myasthenia gravis, twitch tension was monitored in the adductor pollicis muscle by supramaximal train-of-four stimulation of the ulnar nerve during anaesthesia with sevoflurane 2.5% and nitrous oxide 60%. After baseline measurement, an initial dose of vecuronium 10 microg kg(-1) was given. When the twitch height stabilized (maximum block after the first 10 microg kg(-1)), the next incremental dose of 10 microg kg(-1) was given and repeated until block, defined as [1-(first twitch/baseline first twitch)] x 100 reached 90%. Maximum block after the first dose of vecuronium in ocular patients was significantly less than that in generalized patients (median 51 vs 91%; P<0.05). Onset of block after the first dose of vecuronium was significantly slower in ocular than in generalized myasthenic patients (mean 300 vs 200 s; P<0.05). Doses required to attain a block of 90% or more were significantly higher in ocular than in generalized patients (median 20 vs 10 microg kg(-1); P<0.05). Clinicians should consider the type of disease according to the Osserman classification when using non-depolarizing neuromuscular. blocking drugs in patients with myasthenia gravis.

Inadequate response to H2-receptor antagonists. Absence of parietal cell cAMP-stimulating autoantibodies

In peptic ulcer patients with adequate (AR; N = 16) and inadequate response (IR; N = 20) to H2-receptor antagonists, the presence of parietal cell cAMP-stimulating autoantibodies was studied. Serum Ig fractions from these patients and 10 control subjects were examined to test whether they could stimulate cAMP production in a gastric cell line model. The human cell line HGT-1 was found to be a sensitive in vitro model for the cAMP stimulation assay as histamine (10 microM) increased by 11-fold the production of cAMP. Neither IgG (4 mg/ml) nor IgG-free Ig fractions (1 mg/ml) isolated from the blood of AR or IR affected cAMP production in the HGT-1 cells. The results obtained with the cAMP stimulation assay were confirmed by indirect immunofluorescence measurements based on frozen sections of rat stomach and kidney. No specific staining of rat parietal cells could be observed with patient sera. In addition, human gastric biopsies of the oxyntic mucosa from the same patients were studied for immunoreactive cell populations to assess organ-specific autoimmune processes. Biopsy specimens from AR and IR showed increased lymphocytic infiltrates, usually associated with gastritis. However, no significant differences in location of various cell populations between AR and IR could be observed. Our findings do not support a recent hypothesis that poor response to treatment with H2-receptor antagonists is due to the presence of autoantibodies.

Ocular myasthenia: a protean disorder

Ocular myasthenia is a localized form of myasthenia clinically involving only the extraocular, levator palpebrae superioris, and/or orbicularis oculi muscles. Ocular manifestations can masquerade as a variety of ocular motility disorders, including cranial nerve and gaze palsies. A history of variable and fatiguable muscle weakness suggests this diagnosis, which may be confirmed by the edrophonium (Tensilon) test and acetylcholine receptor antibody titer. Anticholinesterases, corticosteroids and other immunosuppressive agents, and other therapeutic modalities, including thymectomy and plasmapheresis, are used in treatment. As the pathophysiology of myasthenia has been elucidated in recent years, newer treatment strategies have evolved, resulting in a much more favorable prognosis than several decades ago. This review provides historical background, pathophysiology, immuno-genetics, diagnostic testing, and treatment options for ocular myasthenia, as well as a discussion of drug-induced myasthenic syndromes.

T-helper epitopes on human nicotinic acetylcholine receptor in myasthenia gravis

The synthesis of AChR antibodies requires intervention of AChR-specific Th cells. Because of the paucity of anti-AChR Th cells in the blood of myasthenia gravis (MG) patients, direct studies of these autoimmune cells in the blood are seldom possible. Propagation in vitro of anti-AChR T cells from MG patients by cycles of stimulation with AChR antigens selectively enriches and expands the autoimmune T-cell clones, allowing investigation of their function and epitope specificity. Torpedo electroplax AChR was initially used for propagation of anti-AChR T-cell lines. Those studies demonstrated the feasibility of in vitro propagation of AChR-specific T cells. These are bona fide CD4+ Th cells, which stimulate production in vitro of anti-AChR antibodies by B cells of myasthenic patients and recognize equally well denatured and native AChR, suggesting the usefulness of synthetic human AChR sequences as antigens for propagation of the autoimmune Th cells. We used pools of overlapping synthetic peptides, corresponding to the complete sequences of the human AChR alpha-, beta-, gamma-, and delta-subunits, to propagate AChR-specific Th cells from the blood of MG patients. The AChR sequence regions forming epitopes recognized by the autoimmune T cells were determined by challenging the lines with individual synthetic peptides, 20 residues long, screening the AChR subunit sequences. Although each line had an individual pattern of epitope recognition--as expected from their different HLA-DR haplotype--some peptides were recognized by most of all the CD4+ T-cell lines, irrespective of their DR haplotype. The existence of immunodominant regions of the AChR sequence was verified by investigating the response of unselected CD4+ cells from the blood of a relatively large number of MG patients to the individual peptides screening the human alpha-, gamma-, and delta-subunit sequences. Those studies confirmed that each patient has an individual pattern of peptide recognition. The studies also identified a large number of T epitopes of the human AChR and verified the existence of sequence regions immunodominant for T-helper sensitization, because a limited number of sequence regions, including all those immunodominant for the T-helper lines, were recognized by most patients. Anti-AChR CD4+ T lines could be propagated from some healthy controls only for a brief period of time. They recognized AChR sequences poorly, suggesting a low affinity of their T-cell receptors for the corresponding AChR epitopes.(ABSTRACT TRUNCATED AT 400 WORDS)

Ten years experience with therapeutic apheresis in a community hospital

A retrospective study was carried out on 2,500 therapeutic hemapheresis procedures performed at a community teaching hospital from 1980 to 1990. Seventy-six percent of the procedures consisted of plasmapheresis (PE). The most frequently treated conditions were myasthenia gravis (MG), Guillain-Barré syndrome (GB), hyperviscosity (HV), and thrombotic thrombocytopenia purpura (TTP). Therapeutic results and clinical implications for these four conditions are discussed.

A non-immunogenic myasthenia gravis model and its application in a study of transsynaptic regulation at the neuromuscular junction

A non-immunological model for myasthenia gravis was developed in rats: 'toxin-induced myasthenia gravis'. Rats were injected once every 48 h with 3-5 micrograms alpha-bungarotoxin for periods of up to 5 weeks. This treatment caused weakness, especially of facial muscles. Respiration, however, was unaffected. Miniature endplate potentials and 125I-alpha-bungarotoxin binding in the extensor digitorum longus muscles were severely reduced. Acetylcholine release evoked by electrical and chemical (50 mM KCl) stimulation was higher in diaphragms from alpha-bungarotoxin-treated rats than in those from control animals. Histological investigation of the tibialis anterior muscle provided no evidence that the endplates were enlarged. It is concluded that the activity of acetylcholine receptors influences the rate of transmitter release in the neuromuscular junction and it is suggested that a transsynaptic regulation process may be active in myasthenia gravis. The present animal model for myasthenia gravis seems very suitable for studying such a regulation of transmitter release.

Conformational modification enhances myasthenogenicity in synthetic peptide of acetylcholine receptor alpha-subunit

The induction of myasthenia gravis depends on linked recognition of antigenic sites of acetylcholine receptor (AChR) by B-cells and T-cells. The former is conformationally restrained, and the latter is under the MHC class II restriction. We synthesized an artificially formed peptide (model peptide) by coupling the alpha 190-195 selected as B-cell site and cholinergic binding site and the alpha-107-116 selected as T-cell site and agretope with the intervening chain segment aligned as Asn-Pro-Gly-Gly (NPGG) to adopt beta-turn conformation. This model peptide, alpha 107-116-NPGG-alpha 190-195, was potently immunogenic in Lewis rats to provoke anti-peptide antibody reactive with native AChR and to induce the animal model of immunopharmacologic blockade of acetylcholine (ACh)-binding site. Low immunogenicity compared with this was found when using natural peptides predicted as sequences of B-cell site or T-cell site and the peptide synthesized by linking both without intervention of NPGG. The alpha 190-195 had no function of cholinergic binding either as a single segment or as part of the conformation-modified peptides; results suggest that the conformation modified for high immunogenicity does not assume the bioactive conformation for ACh-binding.

Characterization of antigenic structures in auto-immune atrophic gastritis with pernicious anaemia. The parietal cell H,K-ATPase and the chief cell pepsinogen are the two major antigens

Using isolated cells and subcellular fractions from pig gastric mucosa, antigenic structures with specific binding of IgG from sera of patients with auto-immune atrophic gastritis were characterized by means of immunoblotting and enzyme-linked immunosorbent assay. In immunoblotting experiments using mucosal cells as the antigen source, two dominating bands of 94 and 41 kDa were found. The two major antigens were identified as the H,K-ATPase (94 kDa), which constitutes the parietal cell acid pump, and pepsinogen (41 kDa) located in the chief cells. There was also a small but significant binding of antibodies to a preparation of Na,K-ATPase, an enzyme which is about 60% homologous to H,K-ATPase. Commercial preparations of hog gastric pepsinogen and pepsin bound pernicious anaemia IgG with equal efficacy. When sera from seven patients with the diagnosis pernicious anaemia were tested, all were found to contain auto-antibodies against H,K-ATPase as well as pepsinogen. In intact, isolated H,K-ATPase-containing vesicles the cytosolic part of the ATPase molecule is facing the outside of the vesicles. Both intact and trypsinized vesicles were incubated with patient sera and with a monoclonal antibody against H,K-ATPase. Pernicious anaemia IgG was found to bind to a cytosolic, trypsin-resistant structure, but the binding of the monoclonal antibody was lost upon trypsinization. The present results indicate that intracellular structures of the gastric mucosa, due to cell damage, may be exposed to immune-competent cells, which do not recognize these structures as 'self'.

Participation of nicotinic receptor in hormone release from isolated rat islets of Langerhans

Pancreatic hormone release is generally thought to be regulated through adrenergic as well as muscarinic receptors. We have previously observed possible nicotinic involvement in insulin release. In the present study, we incubated isolated rat islets for 60 min with various concentrations of atropine (a muscarinic receptor blocker), alpha-bungarotoxin (alpha-Btx, a nicotinic receptor blocker), and anti-acetylcholine receptor antibody (IgG) (anti-Ach.R.Ab) obtained from a patient with myasthenia gravis. Atropine suppressed insulin release, and alpha-Btx and anti-Ach.R.Ab potentiated it; atropine did not suppress glucagon release, while alpha-Btx and anti-Ach.R.Ab raised it. None of these agents influenced somatostatin release. These observations suggest that muscarinic as well as nicotinic receptors influence insulin release, as nicotinic receptors do glucagon release. Neither nicotinic nor muscarinic receptors seem to regulate somatostatin release.

Snake envenomation. Incidence, clinical presentation and management

Snake envenomation is a major cause of death and disability in the developing countries, particularly India and Southeast Asia. Species variation in venom components, yield, and lethality leads to quite different clinical presentations and mortality. Venomous snakes are divided into 5 families. Bites of the Viperidae, Crotalidae and Colubridae usually cause primarily local effects and bleeding; the Elapidae most commonly cause neurological symptoms, particularly paralysis; while the Hydrophidae cause paralysis and myolysis. Venoms are complex mixtures of enzymes, peptides and metalloproteins. 26 enzymes have been identified, and 10 of those are found in most venoms. Components have been identified that act as procoagulants, anticoagulants, hyaluronidases, RNases, DNases, postsynaptic toxins and presynaptic toxins. Other peptides induce capillary leak syndrome, haemolysis and shock. The clinical results of envenomation vary widely, and there may be no envenomation with a bite. Syndromes reported include oedema, haemolysis, shock, bleeding, pituitary failure, renal failure, myonecrosis, and combinations of the above. First aid measures that have been proposed include tourniquets, constricting bands, tight crepe bandages, incision and suction, cryotherapy, and high voltage electric shock. None of these has been shown to be effective except usage of a crepe bandage for Australian elapid bite. Tourniquets or cryotherapy, if used for extended periods may lead to gangrene. The most important first aid measure is rapid transport to comprehensive medical care. There is some controversy about medical treatment in the United States, but less in other countries. Supportive measures routinely required include intravenous fluids, tetanus prophylaxis and antibiotics. Anticholinergics may be useful in elapid bite. Intubation and ventilation may be necessary. Unproven surgical approaches include excision of envenomated tissues and fasciotomy. The former is disfiguring, the latter should be reserved for those patients with demonstrated increased intracompartmental pressure. More than 100 antivenins are produced by about 36 laboratories worldwide. The products are effective, but carry a high risk of serum sickness and a lesser risk of anaphylaxis. A more effective and less reactive product is under development.

Myasthenogenic significance of synthetic alpha-subunit peptide 183-200 of Torpedo californica and human acetylcholine receptor

Synthetic peptides of the Torpedo californica and human acetylcholine receptor alpha-subunit, Gly183-Asp200, were studied. Both peptides bound alpha-bungarotoxin to a significant extent, and inhibited toxin-binding with Torpedo or human acetylcholine receptor. The human peptide was, however, less potent than the Torpedo peptide. One can assume, therefore, that this sequence participates in cholinergic binding. The Torpedo alpha 183-200 segment was immunogenic in the induction of experimental autoimmune myasthenia gravis in rats, accompanied by elevation of anti-peptide and anti-rat acetylcholine receptor blocking antibody and reduced amplitudes of miniature end-plate potentials. Sera did not accelerate the degradation of rat acetylcholine receptor. Thus, one may interpret this to be the animal model induced by an immunopharmacological blockade of the acetylcholine-binding site. Furthermore, this Torpedo peptide was antigenic in the detection of antibody in human myasthenic sera. The human alpha 183-200 segment had neither of these 2 properties, although the corresponding anti-peptide antibody was elicited in immunized rats. It is feasible that the synthetic segment of this human sequence may not be maintained in such a conformation to be immunogenic.

Clinical correlations of antibodies that bind, block, or modulate human acetylcholine receptors in myasthenia gravis

Acetylcholine receptor (AChR) binding and AChR modulating antibodies were found with approximately the same frequency (86%) in 349 patients with myasthenia gravis (MG). However, the total yield of positive serological results was significantly improved (90%) by assaying AChR modulating antibodies when AChR binding antibodies were not detected, because in 27 patients (8%) only one of the two tests was positive. The immunoprecipitation test for AChR blocking antibodies yielded fewer positive results (52%), but there was a significant correlation between the degree of AChR blockade and generalization of muscle weakness. In no patient was this the only positive test, because the test for AChR modulating antibodies in this study detected both AChR blocking and modulating antibodies. Human muscle AChR was used as antigen in all tests. False positive results were rare and were attributed to unexplained antibodies to 125I-alpha-Bgt (AChR binding antibody assay) and recent general anesthesia using muscle relaxants (AChR blocking and AChR modulating antibody assays). Unexplained positive results, documented previously in 5% of patients with the Lambert-Eaton myasthenic syndrome and amyotrophic lateral sclerosis (ALS), were found in this study in two of 22 patients with ALS, but in none of 427 patients with miscellaneous neurological diseases. Patients with severe generalized MG and/or thymoma tended to have higher titers of AChR binding antibodies and greater AChR modulating antibody activity. However, some patients with severe muscle weakness had low titers of antibodies, and some patients in remission or with only ocular manifestations had high titers. These seemingly paradoxical results reflect heterogeneity in the specificities, affinities, and isotypes of anti-AChR antibodies. To effect pathogenicity, antibodies must have access in vivo to extracellular antigenic sites on the AChR. One would anticipate that antibodies with greatest pathophysiological potential would be of an IgG with greatest pathophysiological potential would be of an IgG subclass that activates complement, or of a specificity that competes for acetylcholine's binding site on the receptor or readily cross-links two AChR molecules to trigger receptor modulation (e.g., by binding to sites on the duplicated alpha-subunit). In patients with suspected MG who lack serological evidence of anti-AChR antibodies, motor endplate biopsy is required for microelectrophysiological, immunochemical, and ultrastructural studies to establish with certainty whether or not the condition is acquired MG.

Anti-acetylcholine antibodies and the pathogenesis of myasthenia gravis

Using an ELISA system, antibodies recognizing conjugated acetylcholine (ACh) were detected in sera of patients suffering from myasthenia gravis. The mean antibody level was three times higher in sera from myasthenic than from control patients. No correlation was found between anti-ACh antibody levels and anti-ACh receptor (AChR) titer. Also, the anti-ACh antibody titers were independent of sex and age of patients. Competition experiments demonstrated that the most immunoreactive compounds were choline-glutaryl-bovine serum albumin (BSA) and choline-succinyl-BSA. Antibodies present in the sera of myasthenic patients recognized an antigenic determinant mimicking conjugated ACh. The antibody affinity and specificity were sufficiently high for the detection of ACh in locust brain.

Positive response to edrophonium in patients with neurotoxic envenoming by cobras (Naja naja philippinensis). A placebo-controlled study

To study the ability of anticholinesterase drugs to reverse the potentially fatal paralytic effects of cobra venom, we conducted a placebo-controlled, double-blind crossover trial of intravenous edrophonium (Tensilon) in 10 adults with neurotoxic envenoming caused by bites of the Philippine cobra (Naja naja philippinensis). There was significantly more improvement in ptosis and endurance of upward gaze after edrophonium than after placebo. Five minutes after injection, the mean difference (+/- SD) in the percentage of the iris that was uncovered was 39 +/- 5.47 (70 vs. 31 percent; P less than 0.01), and the mean difference in the number of seconds of upward gaze was 33.1 +/- 9.29 (39.7 vs. 6.6 seconds; P less than 0.01). The expiratory and inspiratory pressures, forced vital capacity, and ability to cough, speak, and swallow also improved after edrophonium. In both the patients who were studied electromyographically, pretreatment and postplacebo responses were typical of myasthenia gravis and became normal after edrophonium. We conclude that anticholinesterases are beneficial in the management of neurotoxic envenoming by Asian cobras (Naja naja), and we recommended a test of edrophonium in any patient with signs of neurotoxic envenoming after snakebite.

Clinical correlates of enzyme-immunoassay versus radioimmunoassay measurements of antibody against acetylcholine receptor in patients with myasthenia gravis

Antibody against human nicotinic acetylcholine receptor [Ab(AcChR)] was measured in the sera obtained from 55 patients with myasthenia gravis (MG) using both radioimmunoassay (RIA) and enzyme-linked immunosorbent assay (ELISA). By at least one assay, 91% of the patients had elevated Ab(AcChR). We found no correlation between the amount of Ab(AcChR) measured by RIA and that measured by ELISA. Patient subpopulations defined by ELISA- or RIA-measured Ab(AcChR) were associated with different disease durations. All of those who had high Ab(AcChR) levels by both assays had experienced symptoms for less than 2 years. 87% of those with high Ab(AcChR) levels by ELISA had had MG for less than 4 years. Those patients with high Ab(AcChR) only by RIA had a mean disease duration of over 8 years. With regard to correlations of Ab(AcChR) with patient age and sex, females under 50 years of age had high levels of Ab(AcChR) by RIA, but had lower levels by ELISA, whereas men over 50 had high Ab(AcChR) levels by ELISA. Using either assay, no relationship was established between concentrations of Ab(AcChR) and the patient's functional status, previous thymectomy, or current therapy. In this study, 16% of the MG patients with elevated Ab(AcChR) would have been considered within the non-disease range of Ab(AcChR) had only the RIA been performed, thus recommending the routine use of both assays for diagnostic purposes.

Kinetic studies on neurotoxin-binding inhibitory antibodies in myasthenia gravis

A method for measuring antibodies which inhibit the binding of 125I-alpha-bungarotoxin to the acetylcholine receptor was developed. The procedure allows the detection of inhibitory activity in 70% of sera from the patients with myasthenia gravis. Kinetic analysis showed that (1) a linear dose-response exists between logarithmic concentrations of any test serum and inhibitory activity, (2) the slope of the inhibition line is identical among various myasthenic sera and, (3) the slope of line induced by various cholinergic ligands was comparable to that obtained by myasthenic sera. The inhibitory activity correlated with the titer of anti-acetylcholine receptor antibody measured by an immunoprecipitation method (r = 0.76, p less than 0.01).

Autoantibody to the gastrin receptor in pernicious anemia

We examined serum IgG fractions from 20 patients with pernicious anemia and 25 control subjects for their capacity to inhibit binding of [125I]15-leu human gastrin-17 to parietal-cell-enriched gastric mucosal cells. IgG fractions from six patients reduced gastrin binding by 45.6 +/- 12.2 per cent, as compared with a reduction of 1.8 +/- 0.7 per cent by fractions from the 25 controls. The fractions from these six patients also reduced gastrin-stimulated [14C]aminopyrine uptake by gastric cells (an index of gastric acid secretory activity in vitro) by 50.2 +/- 8.4 per cent (mean +/- S.D.), as compared with 9.2 +/- 4.1 per cent for the controls. IgG fractions from six other patients that did not reduce gastrin binding also inhibited gastrin-stimulated [14C]aminopyrine uptake, by 48.1 +/- 9.1 per cent. These reductions in gastrin binding and aminopyrine uptake were abolished by absorption of the IgG fractions with suspensions of viable gastric mucosal cells but not by absorption with liver or kidney cells. The IgG fractions did not inhibit [3H]histamine binding or histamine-stimulated [14C]aminopyrine uptake. These results suggest that serum IgG from some patients with pernicious anemia contains autoantibodies to the gastrin receptor.

A molecular hypothesis concerning the pathogenesis of myasthenia gravis

The purine enzyme, adenosine deaminase, is essential for the maturation of lymphocytes, cell growth and normal immune function. Since adenosine deaminase has the highest activity in the thymus and in T lymphocytes, it is hypothesized that a defective or altered enzyme may be a cause of myasthenia gravis, a lymphoid dyscrasia. It is proposed that the alteration is on the non-catalytic portion of adenosine deaminase concerned with the normal immune function of T lymphocytes. Lymphocytes, particularly suppressor T lymphocytes containing a defective adenosine deaminase will function improperly. They will lose their normal immune regulatory function, allowing immunoglobulin-producing B lymphocytes to produce autoantibodies against the nicotinic acetylcholine receptor, with resultant induction and perpetuation of the autoimmune state. In an attempt to compensate for the defect, there may be hypertrophy of the thymus and lymphoid system, with overproduction of a defective adenosine deaminase. Since many of the functions of thymosin, the alleged active principle in thymus are identical to those of adenosine deaminase, it is postulated that thymosin may be a subunit of adenosine deaminase.

A practical enzyme immunoassay for anti-acetylcholine receptor antibodies in myasthenia gravis

A practical enzyme immunoassay (EIA) has been developed for the measurement of anti-acetylcholine receptor (AChR) antibodies in sera from patients with myasthenia gravis (MG). This system is based on the double antibody technique, using denervated rat muscle AChR labeled with horseradish peroxidase-linked alpha-bungarotoxin (HRP-alpha BGT). This method has the following advantages compared to conventional radioimmunoassay (RIA): (1) HRP-alpha BGT is more stable than [125I]alpha BGT and can be used for at least one year without any loss of the binding activity to AChR and enzymatic activity, (2) the procedure avoids the use of radioactive isotopes, and (3) the equipment for our EIA is more economical than that for RIA.

Myasthenia gravis with thymoma: analysis of and postoperative prognosis for 65 patients with thymomatous myasthenia gravis

Sixty-five patients with thymomatous myasthenia gravis were investigated. Thymomas were present in 44% of the male patients and 19% of the female patients with myasthenia gravis. The incidence of thymomatous disease in male patients was higher than in female patients in all age groups. Eighty percent of men more than 50 years old and women more than 60 years old had myasthenia gravis with thymoma. Germinal center formation in the thymus of patients with thymomatous myasthenia gravis was positive in 91% and was high grade. The prognosis for patients undergoing extended thymectomy of thymomatous myasthenia gravis was significantly better than in those having transsternal simple thymectomy, but it was worse than the prognosis for patients with nonthymomatous myasthenia gravis. No increase in the rate of remission or palliation was seen one year after thymectomy. It is concluded that early thymectomy is effective in control of myasthenia gravis in thymomatous myasthenia gravis.

Analysis of false negative results in the immunoassay for anti-acetylcholine receptor antibodies in myasthenia gravis

Possible causes for the failure of immunoassays to detect anti-acetylcholine receptor activity in serum from confirmed myasthenia gravis (MG) patients were investigated. A more sensitive assay, using Protein A to trap immune complexes (ARIA), was applied to 65 MG sera which were negative in the usual assay and to 42 normal human sera. Normal and negative MG sera had antibody (Ab) activity in the same range (50-70 pM). Titers present in 70% of normal sera appeared to be specific antireceptor antibodies as defined by tests for antigen specificity. Thus, higher sensitivity assays did not improve discrimination of MG from normals. In a second group of 108 MG sera studied, 48 were negative by the usual assay criteria in a rat acetylcholine receptor immunoassay. Further detailed analysis of this negative group showed that 3/48 had IgG3 antibody not detectable in the test, 14/48 had Ab's recognizing human receptor determinants exclusively, 29/48 had toxin blocking Ab's not determined by immunoassays, and 6/48 were negative in all tests. The results indicate that the exclusive occurrence of toxin-blocking antibodies in MG subjects is a major factor contributing to false negatives in the ARIA test. Estimates of the amount of Ab's with this functionality indicated that they are present in very much smaller amounts than other classes of anti-receptor Ab's. Degree of blocking activity in patient serum showed a fair correlation with severity of disease. Thus, blocking antibodies appear capable of causing all degrees of disease severity in the absence of other types of antireceptor Ab's. The development of a sensitive and quantitative in vitro assay for blocking antibodies combined with the usual immunoassay would be a major improvement for a MG diagnostic test, with greater than 94% positivity predicted.

Enzyme-linked immunosorbent assay for antibody against the nicotinic acetylcholine receptor in human myasthenia gravis

Antibody against acetylcholine receptor (AChR) of human skeletal muscle was measured using enzyme-linked immunosorbent assay and found in 23 (74%) of 31 Japanese patients with generalized myasthenia gravis. In 15 patients with generalized myasthenia gravis who had not undergone thymectomy and who were not receiving adrenocorticosteroids, the antibody was found in 13 (87%). Antibody was also found in 13 (54%) of 24 patients with myasthenia gravis against AChR fractions obtained from fetal calf thymus. Based on the subunit structures of the AChR protein, the double precipitation assay using iodine 125-alpha-bungarotoxin is also capable of detecting antibody against the toxin binding site, by cross reactivity. This is among the first reports of experiments in which enzyme-linked immunosorbent assay was used to measure the antibodies in human myasthenia gravis and provides evidence of anti-AChR antibody against antigens from fetal calf thymus.

Evidence for the presence of immunoreactive acetylcholine receptors on human thymus cells

Triton extracts from thymuses and thymomas from either normal subjects or MG patients specifically bind [125I] alpha-bungarotoxin (alpha Bgt). This binding is saturable (apparent Ks = 5.9 X 10(-9) M) and can be inhibited by cold alpha Bgt, acetylcholine or nicotinic agonists. These results demonstrate the presence on human thymus cells of acetylcholine receptor (ACh.R), 2.8% for normal human thymus in regard of ACh.R concentration in human muscle. Normal human thymic extracts were used as an antigen source in the radioimmunoassay for the detection of anti-ACh.R antibodies in positive MG patients' sera. 72% of these sera were also positive with the thymic antigen. The demonstration of ACh.R in human thymus brings further support to the hypothesis of intrathymic autosensitivity against ACh.R as a major factor in MG pathogenesis.

Immunisation with Torpedo acetylcholine receptor

Acetylcholine mediates the transfer of information between neurons in the electric organ of, for example, Torpedo as well as in vertebrate skeletal muscle. The nicotinic acetylcholine receptor complex translates the binding of acetylcholine into ion permeability changes. This leads to an action potential in the muscle fibre. The nicotinic acetylcholine receptor protein has been purified from Torpedo by use of affinity chromatography. The receptor is an intrinsic membrane glycoprotein composed of five polypeptide chains. When various animals are immunised with the receptor they demonstrate clinical signs of severe muscle weakness coincident with high antibody titres in their sera. The symptoms resemble those found in the autoimmune neuromuscular disease myasthenia gravis in humans. This animal model has constituted a unique model for studying autoimmune diseases. This paper reviews some of the work using Torpedo acetylcholine receptor in order to increase the understanding of the motor nervous system function and myasthenia gravis. It is now known that the nicotinic acetylcholine receptor protein is the antigen involved in myasthenia gravis. The mechanism of immune damage involves a direct block of the receptor function. This depends on the presence of antibodies which crosslink the postsynaptic receptors leading to their degradation. The questions to be answered in the future are; (a) what initiates or triggers the autoimmune response, (b) how do the antibodies cause the symptoms--is there a steric hindrance of the interaction of acetylcholine and the receptor, (c) why is there not a strict relationship between antibody titre and severity of symptoms, and (d) why are some muscles affected and other spared? With help of the experimental model, answers to these questions may result in improved strategies for the treatment of the autoimmune disease myasthenia gravis.

Voice change in the pediatric patient. A differential diagnosis

This paper reviews the causes of voice change in the infant and child. Symptoms of dysphonia can be very early evidence of a serious problem, either within the larynx or resulting from a systemic disease. The need to investigate the cause of voice disturbances is stressed. The large number of diseases in which voice change occurs makes a complete examination of the child, both local and systemic, absolutely necessary in order to arrive at a specific diagnosis. The mechanism of voice change is described in each category of the numerous causes of dysphonia.

Depletion of helper/inducer T cells after thymectomy in myasthenic patients

Using monoclonal anti-T-cell antibodies, we have studied peripheral blood T-cell subsets in 53 patients with myasthenia gravis before and after thymectomy (Tx). Before Tx, the mean OKT4/OKT8 ratio was higher in patients than in controls. Furthermore patients showed a high number of cells reacting simultaneously with the OKT4 and OKT8 antibodies. Shortly after surgery, the helper/suppressor ratio was increased in most of the patients, and the doubly reactive subset decreased to normal levels. However, 6 to 12 months after Tx the OKT4/OKT8 ratio was significantly decreased, particularly in patients showing clinical improvement. The percentage of total T cells was slightly but significantly reduced. A group of 14 patients studied more than 2 years after Tx presented very low OKT4/OKT8 ratios. Thymectomy in MG appears to lead to a gradual decrease of the T-helper subset which could contribute to its favorable effect on the course of the disease.

Immunology of myasthenia gravis

Anti-acetylcholine-receptor antibody is demonstrable in more than 90 per cent of patients with myasthenia gravis. Serum antibody titers do not show a direct correlation with disease severity, although in certain patients antibody levels increase in association with disease activity. Impairment of neuromuscular transmission results from the loss of junctional receptors, either as a result of receptor internalization or destruction of junctional folds containing the acetylcholine receptor. Myasthenia gravis manifests immunologic, genetic, and clinical similarities to rheumatic syndromes, suggesting a generic immune dysfunction common to these disorders.

Bilateral intracavernous carotid aneurysms mimicking a prolactin-secreting pituitary tumor

The triad of hyperprolactinemia, ophthalmoplegia, and radiologic abnormalities of the sell turcica suggest a tumor in the area of the pituitary gland. A new association--bilateral intracavernous carotid aneurysms--is presented. Two elderly women had extraocular muscle palsies and elevated serum prolactin levels of 71 and 32 ng/ml (normal: less than 20 ng/ml). In the former, a high-resolution computed tomography scan made after contrast medium injection was incorrectly interpreted as demonstrating a pituitary tumor; cerebral arteriography revealed bilateral aneurysms. In the other patient, a computed tomography scan after contrast medium injection demonstrated the bilateral aneurysms, and these were confirmed by radionuclide angiography.

Immunohistochemical and enzyme histochemical contributions to the problem concerning the role of the thymus in the pathogenesis of myasthenia gravis

Normal fetal and postnatal thymuses, as well as thymuses from patients with myasthenia gravis (MG), were investigated by immunohistochemical and enzyme histochemical techniques and their morphology reviewed. Intrathymic B-cells, detected by ATPase activity, were found to be markedly increased in number in MG thymuses. They were scattered in the medulla and accumulated around the junctional and medullary vessels and Hassall's corpuscles (HCs). Large epithelial cells, singly or within HCs, were found to be unevenly distributed in the medulla of all the thymuses examined. The striated muscle-like nature of some of these cells was revealed by the presence of myoglobin in their cytoplasm. In myasthenics these cells and small developing HCs characteristically surrounded lymph follicles and were in direct contact with the expanded cap of the follicle mantle, without interposition of reticulin fibres. The close association of immune reactive foci (lymphoid follicles, junctional and medullary vessels, and HCs) with structures involved in autoimmune responses in the thymus (muscle-like and true myoid cells, HCs) strongly suggests that the autoimmune reactions against AChR (acetylcholine receptor) and other muscular components, which constitute the basic defects in myasthenia gravis, may begin in the thymus.