Myasthenia gravis and myasthenic syndromes

Immunological specificity and cross-reactivity of anti-acetylcholine receptor and anti-presynaptic membrane receptor antibodies in myasthenia gravis

Antibodies against acetylcholine receptor (AChR), a protein that binds to alpha-bungarotoxin (alpha-BuTx), are characteristic for myasthenia gravis (MG) and are considered to be of importance in the pathogenesis of the disease. Antibodies against a beta-BuTx binding protein, presynaptic membrane receptor (PsmR), have also been reported in most MG patients. We have analysed the specificity and cross-reactivity of antibodies to bovine AChR and PsmR in sera from 11 patients with MG. More than 90% of antibodies to PsmR were adsorbed specifically by PsmR conjugated affinity chromatography. Similarly, more than 90% of anti-AChR antibodies were absorbed by AChR conjugated affinity chromatography. Specificities of antibodies from affinity chromatography were also confirmed by ELISA and agarose isoelectric focusing. However, the antibodies to PsmR and AChR from MG patients' sera showed about 45-55% cross-reactivity, and there was a high correlation between serum levels of both antibodies. The demonstration of anti-PsmR antibodies could be important in documenting presynaptic damage and understanding the pathogenetic process in MG.

Effect of thymectomy and immunosuppressive therapy on anti-neuroblastoma antibody levels in patients with myasthenia gravis

Antibodies reacting with human neuroblastoma cells (NBL) are distinct from the "classical" anti-acetylcholine receptor (AChR) antibodies in myasthenia gravis (MG). The influence of therapeutic interventions on serum anti-NBL antibody levels was followed in 42 MG patients. Thymectomy alone was performed in 28 patients while immunosuppressive medication was given to 14 patients out of whom 10 also had a thymectomy. In most patients serum anti-NBL antibody titers declined after thymectomy and/or during immunosuppressive treatment, though individual variations in the antibody response could be observed. Sequential examinations of individual patients revealed an association between the clinical severity of MG and anti-NBL antibody levels. No correlation between the treatment-induced changes of anti-NBL and anti-acetylcholine receptor (AChR) antibody titers could be observed during the follow-up period in MG patients positive for both types of antibodies. These findings further emphasize the immunological complexity of MG. Anti-NBL antibodies represent a pathogenic marker of the disease and display a regulation different from that of the anti-AChR antibodies.

Deficiencies in anti-acetylcholine receptor antibody measurement in myasthenia gravis

In a retrospective case note study of 86 patients with myasthenia gravis, 60 had an anti-acetylcholine receptor antibody assay performed by the regional immunology laboratory. Antibody was detected in 38% which compares with 66-93% in other series. Whilst the use of staphylococcal protein A to precipitate the antibody-receptor complex, rather than anti-human immunoglobulin, may be partly responsible for this low sensitivity, other methodological problems are likely to exist. It is suggested that this potentially critical assay becomes a subject for regular audit.

Seronegative myasthenia gravis: clinical features, response to therapy and synthesis of acetylcholine receptor antibodies in vitro

Circulating autoantibodies against the acetylcholine receptor (AChR-Ab) are an important diagnostic tool in myasthenia gravis (MG). Lack of antibodies may cast doubt upon the diagnosis, the immune-mediated mechanism and the nature of the antigen. We examined clinical and laboratory features, response to immunotherapy and production of AChR-Ab in vitro, in 12 seronegative MG patients who were followed up for 2-30 years. It was possible to divide those patients into 2 groups: 7 patients with systemic muscle weakness, with a severe disease and with response to immunosuppressive therapies. The other group of 5 patients was characterized by oculobulbar symptomatology, a relatively benign course and immunotherapy was ineffective in 3 treated patients. Five patients underwent thymectomy and gland histology was normal in all of them. In none of 9 patients examined, were AChR-Ab synthesized in vitro (compared to 65% of seropositive myasthenic patients). Thus seronegative generalized MG is probably an autoimmune disease though the autoantigen is presently unknown and is responsive to immunosuppressive treatment. Seronegative oculobulbar MG might represent a separate disease entity in which immunological mechanisms play no significant role.

Acquired immune-mediated myasthenia gravis in a cat associated with a cystic thymus

Acquired myasthenia gravis was diagnosed in a five‐year‐old domestic shorthair, neutered, female cat with generalised muscle weakness, tremors, dysphagia and alterations in voice. Radiographs indicated the presence of a mass in the anterior thorax. A response to edrophonium chloride, and raised levels of anti‐acetylcholine receptor antibodies in the serum, confirmed the diagnosis and indicated an immune‐mediated aetiology. Clinical remission occurred following thymectomy and the use of immunosuppressive corticosteroids. This is the first fully‐documented case of acquired feline myasthenia gravis associated with the presence of a thymic abnormality in the United Kingdom. The clinical features, laboratory findings and response to treatment are compared with those reported previously in cats and other species.

The main immunogenic region (MIR) of the nicotinic acetylcholine receptor and the anti-MIR antibodies

Myasthenia gravis (MG) is caused by autoantibodies against the nicotinic acetylcholine receptor (AChR) of the neuromuscular junction. The anti-AChR antibodies are heterogeneous. However, a small region on the extracellular part of the AChR alpha subunit, called the main immunogenic region (MIR), seems to be the major target of the anti-AChR antibodies, but not of the specific T-cells, in experimental animals and possibly in MG patients. The major loop of the overlapping epitopes for all testable anti-MIR monoclonal antibodies (MAbs) was localized within residues 67-76 (WNPADYGGIK for Torpedo and WNPDDYGGVK for human AChR) of the alpha subunit. The N-terminal half of alpha 67-76 is the most critical, Asn68 and Asp71 being indispensable for binding. Yet anti-MIR antibodies are functionally and structurally quite heterogeneous. Anti-MIR MAbs do not affect channel gating, but they are very potent in mediating acceleration of AChR degradation (antigenic modulation) in cell cultures and in transferring experimental MG in animals. Fab fragments of anti-MIR MAbs bound to the AChR prevent the majority of the MG patients' antibodies from binding to and causing loss of the AChR. Whether this inhibition means that most MG antibodies bind on the same small region or is a result of broad steric/allosteric effects is under current investigation.

The main immunogenic region of the acetylcholine receptor. Structure and role in myasthenia gravis

Auto-antibodies to the nicotine acetylcholine receptor (AChR) cause the disease myasthenia gravis (MG). Animals immunized with AChR or receiving anti-AChR antibodies acquire MG symptoms. The majority of the monoclonal antibodies (mAbs) raised in rats against intact AChR bind to a region on the extracellular side of the AChR's alpha-subunit, the main immunogenic region (MIR). The major loop of the overlapping epitopes for several anti-MIR mAbs has been localised between residues 67-76 of the alpha-subunit. Anti-MIR mAbs are very potent in accelerating AChR degradation (antigenic modulation) in muscle cell cultures and transferring experimental MG in animals. Fab fragments of single anti-MIR mAbs when bound to the AChR inhibit two-thirds of the MG patients' antibodies from binding and from inducing antigenic modulation of the AChR. This suggest that the majority of the human MG antibodies are also directed against the MIR. It has however to be verified by direct experiments.

Autoimmune T cell recognition of human acetylcholine receptor: the sites of T cell recognition in myasthenia gravis on the extracellular part of the alpha subunit

Autoimmune T cell lines were prepared from peripheral blood lymphocytes of five myasthenia gravis patients by passage in vitro with an equimolar mixture of 18 overlapping synthetic peptides corresponding to the entire extracellular region (residues alpha 1-210) of the alpha subunit of human acetylcholine receptor (AChR). The proliferative responses of the human AChR-specific T cell lines to each of the individual peptides were determined. It was found that the profiles of the peptides recognized by the T cells were different among the five T cell lines, consistent with genetic control operating at the recognition site level. However, other regulatory influences may play important roles in the triggering of the autoimmune responses. These results suggest that the pathogenesis of this autoimmune disease is variable at the cellular-molecular level.

Myasthenia gravis

Myasthenia Gravis is a disorder of neuromuscular function resulting from an immunologically based premature destruction of acetylcholine receptors. The disease is characterized clinically by variable weakness accentuated by repetitive muscular activity and usually responding to the administration of acetylcholinesterase inhibitors. Myasthenia Gravis is a complex disease and requires understanding of the many facets of its natural history and immunological basis to ensure optimal individual patient management. The long-term goal is control of the immunological imbalance; treatment regimens include thymectomy, corticosteroids, azathioprine, and plasmapheresis. The common use of acetylcholinesterase inhibitors provides symptomatic relief during variable daily muscular activity. Disability due to myasthenia gravis is to a large extent reversible and death is preventable. Early recognition of myasthenia gravis and appropriate treatment are often rewarded by remission that may be permanent.

Oculo-bulbar myasthenic symptoms as the sole sign of tumour involving or compressing the brain stem

Four patients with tumours involving or compressing the brain stem are described whose initial clinical symptoms of fluctuating paresis of the external ocular muscles and/or the pharyngeal muscles without other neurological deficits led to the primary diagnosis of focal myasthenia. The combination of an unusual clinical pattern, involvement of muscles of only one ocular nerve or severe dysphagia/dysarthria without extension of the myasthenic symptoms, should lead to further investigation to exclude other reasons of a focal myasthenic syndrome such as a brain-stem tumour.

Immunodominant regions for T helper-cell sensitization on the human nicotinic receptor alpha subunit in myasthenia gravis

In myasthenia gravis an autoimmune response against the nicotinic acetylcholine receptor (AChR) occurs. The alpha subunit of the AChR contains both the epitope(s) that dominates the antibody response (main immunogenic region) and epitopes involved in T helper cell sensitization. In this study, overlapping synthetic peptides corresponding to the complete AChR alpha-subunit sequence were used to propagate polyclonal AChR-specific T helper cell lines from four myasthenic patients of different HLA types. Response of the T helper lines to the individual peptides was studied. Four immunodominant sequence segments were identified--i.e., residues 48-67, 101-120, 304-322, and 419-437. These regions did not include residues known to form the main immunogenic region or the cholinergic binding site, and they frequently contained sequence motifs that have been proposed to be related to T-epitope formation.

[Diagnosis and treatment of myasthenia gravis: study of an inpatient population]

Between 1974 and 1987 we have examined 50 patients with the diagnosis of myasthenia gravis. Female preponderance (2.5: 1) was found. Also, it was observed that most of the patients were aged between 20 and 49 years. Beside the clinical examination, the following tests were performed: (1) edrofonium test, (2) supramaximal repetitive nerve stimulation, (3) serum acetylcholine antibodies titers and (4) intraperitoneal passive transference of patient's sera to mice and recording of meepp's amplitude in the phrenic-diaphragm preparation in vitro. These four tests gave positive values for myasthenia in 90 to 100% of the cases. Thymus radiological examination was carried out by pneumomediastinography, which proved to correlate with the histological picture of the gland, and computed tomography, which disclosed some discrepances with the histology. Treatment was based on anticholinesterase drugs, corticosteroids and thymectomy, being the corticosteroids the most valuable therapeutical tool. Nine patients treated with steroids disclosed transitory worsening of their signs and symptoms at very early stages after onset of corticosteroid therapy, 6 of them had a disfavorable course in their follow-up. This observation seem to have value in the early prognosis of the disease.

Thymectomy in juvenile myasthenia gravis

The long-term results of thymectomy in 24 children with generalized myasthenia gravis are reviewed. Sixteen had complete remission and another seven were improved. This compares favorably with reported spontaneous remission rates of 30%. Because of the low morbidity in recent reports and the possibility that early thymectomy is more beneficial, we recommend thymectomy at the onset of juvenile generalized myasthenia gravis.

Detection of the anti-Hu antibody in the serum of patients with small cell lung cancer--a quantitative western blot analysis

We looked for the presence of the anti-Hu antibody in the sera from 50 normal subjects; 44 patients with small cell lung cancer, not associated with paraneoplastic disease; and 25 patients with small cell lung cancer associated with paraneoplastic sensory neuropathy, encephalomyelitis, or both. Using the avidin-biotin immunoperoxidase method and a highly sensitive quantitative Western blot analysis, the anti-Hu antibody was not detected in the 50 normal human sera. Seven of the 44 patients with small cell lung cancer but no paraneoplastic syndrome had detectable levels (average titer, 76 U/ml) of anti-Hu antibody on Western blot. These levels are significantly lower than the average titer of the 25 patients who had small cell lung cancer and paraneoplastic sensory neuropathy or encephalomyelitis (average titer, 4,592 U/ml). In the group with nonparaneoplastic small cell lung cancer (low anti-Hu titer) there was a predominance of women (5 women: 2 men), and all patients had "limited" disease when diagnosed. In the antibody-negative group the sex ratio was 16 women to 21 men and 51% of the patients had "extensive" disease. None of the 7 patients with a low-titer anti-Hu antibody developed a paraneoplastic syndrome by the time of writing. The anti-Hu antibody appears, when present, to be a good marker for small cell lung cancer and, when present at high titer, for small cell lung cancer associated with a paraneoplastic syndrome.

EMG evaluation of the floppy infant: differential diagnosis and technical aspects

Electromyographic examination of the newborn and young infant provides a relatively uncommon challenge to most electromyographers. The usual reason for referral for electromyographic studies in the newborn and young infant is to evaluate a floppy baby. The electromyographer must not only be aware of important differences in normal physiologic parameters but must also be familiar with a spectrum of diseases that are not typically encountered in the adult. The results of electromyography must also be correlated with the normal maturation of neuromuscular function. Although the most common pathophysiologic mechanisms affecting the peripheral motor unit are infantile motor neuron disease and the congenital myopathies, a large number of other disease entities warrant careful consideration.

Sensitivity to vecuronium in myasthenia gravis: a dose-response study

A cumulative dose plus infusion technique and integrated EMG monitoring of the first dorsal interosseous muscle were used to determine the potency of vecuronium in 20 normal patients and in ten patients with myasthenia gravis under thiamylal, N2O, O2, fentanyl anaesthesia. The mean (+/- SEM) values for ED50, ED90, and ED95 in the normal patients were 19 +/- 1, 31 +/- 1 and 36 +/- 2 micrograms.kg-1, respectively. Myasthenic patients showed increased sensitivity to vecuronium, the mean values for ED50, ED90, and ED95 were 10 +/- 2, 17 +/- 2 and 20 +/- 3 micrograms.kg-1, being 50, 55 and 56 per cent of normal, respectively. We did not demonstrate a difference in sensitivity to vecuronium between those myasthenic patients who received pyridostigmine preoperatively and those who did not, nor among those chronically treated with corticosteroids, compared with those who were not.

Results of an open trial of cyclosporine in a group of steroido-dependent myasthenic subjects

9 subjects with myasthenia gravis, chronically treated with prednisone, underwent an open clinical trial with cyclosporine, an immunosuppressive and immunomodulator drug. Preliminary results after one year of treatment show that cyclosporine induces a further improvement of myasthenic symptoms, and that prednisone may be reduced or discontinued without relapse of clinical symptoms. Side effects of cyclosporine are very frequent and largely influence the treatment.

Experience with intravenous immunoglobulin in myasthenia gravis

Myasthenia gravis (MG) is an acquired autoimmune disorder of neuromuscular transmission associated with a deficiency of acetylcholine receptor at the neuromuscular junction. Current therapeutic strategies are aimed at increasing the amount of acetylcholine at the neuromuscular junction or at addressing the abnormal immune response. Therapies influencing the immune response include thymectomy, corticosteroids, nonsteroidal immunosuppression, and plasmapheresis. Unfortunately, whether used alone or in combination the toxicities of these agents can be quite significant; thus, an agent with a distinct and more favorable side effect profile might be useful in MG. Intravenous immunoglobulin has such potential.

Anti-neuroblastoma antibodies in myasthenia gravis: clinical and immunological correlations

Forty-four of 109 myasthenia gravis (MG) patients (40%) had serum antibodies against human neuroblastoma cells (NBL). Anti-NBL antibodies were most frequent in the sera of MG patients who had either a hyperplastic thymus or a thymoma, clinically mild to moderately severe generalized MG, and a long disease duration (greater than or equal to 11 years). No correlation between individual anti-NBL antibody and anti-acetylcholine receptor (AChR) antibody titers was observed. Seven of the 19 patients negative for anti-AChR antibodies (37%) had anti-NBL antibodies in their sera. These findings provide further evidence for immunological heterogeneity in MG. In addition to the typical autoantibodies to the AChR, autoimmunization against neural antigens can frequently be detected in these patients.

Acquired immune-mediated myasthenia gravis in a cat

Acquired myasthenia gravis was diagnosed in a four‐year‐old castrated male Somali in which the presenting signs consisted of progressive lameness, weakness, generalised muscle tremors, an inability to blink and voice loss. Clinical testing with edrophonium chloride, electrophysiology, immunocytochemistry and serum immunological techniques confirmed the diagnosis of myasthenia gravis and proved its immune‐mediated nature. Clinical remission was achieved following long term immunosuppression with corticosteroids.

AAEE Minimonograph #33: electrodiagnostic approach to defects of neuromuscular transmission

Clinical testing for neuromuscular dysfunction is supported by an extensive amount of excellent basic information about normal and abnormal subcellular physiology and ultrastructure. This information provides an essential frame of reference for describing the rationale of single-fiber electromyography (SFEMG). SFEMG in turn helps to explain the more conventional clinical testing of neuromuscular function by repetitive nerve stimulation (RNS). Electrical findings in myasthenia gravis, Lambert-Eaton myasthenic syndrome, and botulinum intoxication are discussed from the subcellular level via the cellular level (SFEMG) to the integrated responses of whole muscle (RNS) as a rational means of understanding the technique of clinical repetitive nerve stimulation.

Neurological autoimmune disease and the trimolecular complex of T-lymphocytes

T-lymphocytes recognize antigen in a trimolecular complex: The T-cell receptor binds to a processed fragment of antigen that itself is bound to a major histocompatibility complex (MHC) molecule on the surface of an antigen-presenting cell. The trimolecular complex controls antigen-specific T-cell activation in normal and abnormal immune reactions. Recent progress in myasthenia gravis (MG) and experimental autoimmune encephalomyelitis (EAE) exemplifies this, leading to the following conclusions: (1) Autoimmune T cells may act by interfering with immunoregulation (as in MG) or by directly mediating autoimmune damage (as in EAE), or both. (2) In both diseases, the autoimmune T cells are clonally heterogeneous but recognize only a limited number of epitopes on the autoantigen (acetylcholine receptor in MG; myelin basic protein in EAE). Many of these epitopes can be defined as short peptide fragments of antigen, bound to a particular type of MHC molecule. (3) The MHC determines which peptides are recognized by autoimmune T cells in a given patient or inbred animal strain. (4) The discovery of the limited repertoire of autoimmune T cells has allowed considerable progress in the immunotherapy of EAE, using either monoclonal antibodies or cytotoxic T cells directed against clonotypic determinants on the autoaggressive T cells. (5) One obstacle to this approach in human disease is the polymorphism of the MHC in the species and the commensurate heterogeneity of autoimmune T cells.

[Familial myasthenia gravis: a case report in identical twins]

To the best of our knowledge this is the seventh case report of monozygotic twins both affected by myasthenia gravis (MG). The monozygotism was proven by sex identity, blood group and HLA determinations ('O' Rh+, A2, A19.2, B40, CW3). One paternal aunt was also affected and the three cases have high titles of anti-acetylcholine receptor antibodies and anti-striated muscle antibodies, which indicate an acquired form of MG. After several myasthenic crises the twins are now doing well with corticosteroid therapy. The paternal aunt has a more benign form of MG, with ocular and limb involvement (grade IIa of Osserman) and was submitted to thymectomy. The authors discuss the use of corticosteroid for the infantile form of MG instead of thymectomy, based on the immaturity of the immune system in the young age. The use of other immunosuppressive drugs is not advisable because of potential hazardous development of neoplasms.

[Myasthenia gravis: treatment with thymectomy, corticoids and plasmapheresis]

This paper reviews a 12 year experience with myasthenia gravis management (surgical and drug therapy). A total of 27 patients were submitted to thymectomy, and 12 out of 13 showed fairly good results with this only form of therapy (15.3% with complete remission, 46.15% with marked improvement and 30.7% with moderate improvement). The other 14 need either a combination of surgery and plasmapheresis or corticosteroids with the cummulative results of: 14.8% of remission (4 out of 27), 74% of improvement (20 out of 27), 7.4% of worsening (2 out of 27) and 3.7% without change (1 out of 27). Two other patients not submitted to surgery showed either a stable state of their symptoms or a mildly worsening. Another eight patients not submitted to surgery could not be bollowed up. The authors also conclude by the validity of the use of plasmapheresis in myasthenic crises leading to a transient relief of the symptoms and suggest the use of corticosteroids as a second choice, due to their undesirable side effects and difficulty in their reduction and elimination without worsening the symptoms. Other immunosuppressive drugs could be used in cases in which those above cited therapies showed unsuitable results.

An immunodominant site of acetylcholine receptor in experimental myasthenia mapped with T lymphocyte clones and synthetic peptides

Myasthenia gravis (MG) is an autoimmune disease of man caused by antibodies directed against the acetylcholine receptor (AChR). In the experimental model of MG in mice, murine experimental autoimmune myasthenia gravis (EAMG), an anti-AChR immune response is induced by immunization with Torpedo AChR, and anti-AChR antibodies. AChR-sensitized T cells, and neuromuscular dysfunction result. The production of antibodies to AChR is thymus-dependent. In order to define the epitopes of the AChR identified by AChR-specific T cells, we generated T cell populations and T cell hybridoma clones and tested their reactivity to synthetic uniform-sized overlapping peptides representing the entire extracellular portion of the alpha-chain of the AChR. The predominant reactivity of the T cell clones and the parent lines was to a peptide corresponding to residues 146-162 of Torpedo AChR. This data is consistent with a highly limited recognition of AChR determinants in murine EAMG by AChR-specific T cells.

Humoral factors in inflammatory disorders of the central and peripheral nervous system

The immune-mediated disorders of the central and peripheral nervous systems all involve humoral mechanisms in which immunoglobulin, complement and/or other mediators are implicated. The disorders can be characterized by pattern of disease activity, site of immunoglobulin synthesis, humoral mechanism of injury, and presence of one or more concurrent cellular mechanisms of injury. Control of the humoral responses is presumably T-cell dependent. While these disorders should be viewed as having both humoral and cellular components, the specific components of each disorder might predict the response to specific therapeutic approaches.

Isolation and characterization of nicotinic acetylcholine receptor-like protein from fetal calf thymus

A nicotinic acetylcholine receptor-like protein (AChR-LP) was isolated from fetal calf thymus by affinity chromatography using cobrotoxin-Sepharose after alkaline extraction and solubilization with Triton X-100. The AChR-LP had a specificity of 1.61 +/- 1.12 nmol of alpha-bungarotoxin binding sites per mg of protein. The isoelectric point, sedimentation coefficient and amino acid composition of the purified AChR-LP were very similar to those of muscle and electric organ AChRs. Upon SDS-polyacrylamide gel electrophoresis purified thymus AChR-LP preparations contained up to 6 polypeptide bands of molecular weights of 40,000, 43,000, 51,000, 56,000, 58,000, and 66,000, respectively. The peptides of 40,000, 51,000, 56,000, and 66,000 dalton cross-reacted with the four subunits of Torpedo californica and fetal calf muscle AChR.

Familial autoimmune myasthenia gravis with different pathogenetic antibodies

Two cases of familial myasthenia gravis are reported. One patient is a typical case of autoimmune myasthenia with positive anti acetylcholine receptor antibodies, while in the second patient the impairment of neuromuscular transmission is likely to be due to antibodies directed against determinants other than the acetylcholine receptors.

Plasma from myasthenia gravis patients reduces acetylcholine receptor agonist-induced Na+ flux into TE671 cell line

Plasma from myasthenia gravis patients was tested for its ability to inhibit agonist-induced 22Na+ influx into the TE671 cell line that expresses human acetylcholine receptors. Reduced 22Na+ influx correlated weakly with the total anti-acetylcholine receptor antibody level in the plasma, and was also related to the presence of antibody directed against the agonist binding site, as detected by inhibition of 125I-alpha-bungarotoxin binding. However, in some cases there was inhibition of 22Na+ flux without evident anti-alpha-bungarotoxin binding site antibody. We conclude that in most patients antibodies that interfere with 22Na+ influx do so by blocking the agonist binding site. However, in some cases antibodies may be directed at the Na+ ion channel or some important functional determinant.

Autonomic dysfunction in Lambert-Eaton myasthenic syndrome

Autonomic symptoms were observed in 6 patients with clinically and electrophysiologically documented Lambert-Eaton myasthenic syndrome (LEMS). Of the 6 patients, 2 were extensively investigated in the laboratory. In contrast to previous reports which recognized only cholinergic dysautonomia, abnormalities of sympathetic as well as parasympathetic function were evident. Of the 6 patients, 4 had small cell lung cancer (SCLC). In one male patient, chemotherapy for SCLC resulted in an early improvement of autonomic dysfunction and the electrophysiological defect, documenting simultaneous regression of dysautonomia and LEMS. In addition, the patients with SCLC and LEMS had a survival thus far of 3-13 years suggesting that a subgroup of SCLC patients have a better prognosis.

Localization of the main immunogenic region of human muscle acetylcholine receptor to residues 67-76 of the alpha subunit

The majority of antibodies to the acetylcholine receptor (AcChoR), both in the human disease myasthenia gravis and in its experimental models, are directed against an extracellular area of the AcChoR alpha subunit called the main immunogenic region (MIR). We have studied the binding of anti-AcChoR monoclonal antibodies (mAbs) to 26 synthetic peptides corresponding to the hydrophilic parts of the human AcChoR alpha subunit. The binding sites for eight anti-MIR mAbs and for eight anti-alpha-subunit, non-anti-MIR mAbs were localized. Anti-MIR mAbs bound to one peptide corresponding to residues 63-80 of the human alpha subunit. A second panel of peptides corresponding to the various parts of the alpha-subunit segment 63-80 was synthesized. Anti-MIR antibodies bound to a peptide that contained the alpha-subunit sequence 67-76. Thus, a main constituent loop of the MIR is localized between residues 67 and 76 of the alpha subunit.

Anti AChR antibody: relevance to diagnosis and clinical aspects of myasthenia gravis

227 sera from myasthenic patients were tested for the presence of anti-AChR antibodies (anti-AChR Abs) by mean of a fetal calf receptor (Fc-AChR); 73.5% of cases proved positive with this method. Significant correlations were found between presence of anti-Fc-AChr Abs and various clinical aspects such as: clinical stage and duration of disease; moreover significantly higher than the median titers were found among younger patients (i.e. age less than 40 yrs).

Amphipathic segment of the nicotinic receptor alpha subunit contains epitopes recognized by T lymphocytes in myasthenia gravis

Autoimmune helper T lymphocytes were selected from the blood of two myasthenic patients of different HLA-DR type, using acetylcholine receptor (AChR) from Torpedo californica. These polyclonal T cell lines were tested for reactivity with three synthetic peptides corresponding to the NH2-terminal region of the human AChR alpha subunit. This segment is a good candidate for T cell epitopes since it has a propensity to form an amphipathic alpha helix. The peptides elicited 10-30% of the response induced by native Torpedo AChR. Different peptides were recognized by the autoreactive T cells of the two patients. These results suggest that the NH2-terminal region of the AChR alpha chain contains T cell-stimulating epitopes, and that the T cell autoimmune response in myasthenia gravis, like the B cell response, is heterogeneous.

Passive transfer of myasthenia gravis by immunoglobulins: lack of correlation between AChR with antibody bound, acetylcholine receptor loss and transmission defect

The effects of serum Ig from 7 myasthenia gravis patients on neuromuscular transmission was investigated by passive transfer to mice. A protocol of 60 mg/day for 3 days produced mouse serum levels of anti-mouse AChR that were similar to those in the MG patients, and resulted in corresponding levels (2-76%) of mouse muscle AChR with antibody bound in situ. However, AChR loss was only greater than 20% with one MG preparation. Nevertheless, there was a marked neuromuscular defect in mice injected with 3 preparations which did not necessarily correlate with the degree of AChR loss or the amount of AChRs with antibody bound in situ. We conclude that in some MG patients part of the defect in neuromuscular transmission may result from antibodies binding to other components of the neuromuscular junction.

Myasthenia gravis. A well-understood neuromuscular disorder

Myasthenia gravis is a disorder of neuromuscular function caused by autoimmunity to acetylcholine receptors and the postsynaptic region of the neuromuscular junction. Clinically, it is manifest by abnormal weakness and fatigability of skeletal muscle. Distribution and severity of weakness vary among patients. Most cases can be treated effectively with a combination of anticholinesterase inhibitors and glucocorticoids. Thymectomy is often recommended.

Treatment of experimental autoimmune myasthenia gravis in rabbits with leupeptin, a protease inhibitor

We injected 12 New Zealand white rabbits intraperitoneally with 15 mg/kg Leupeptin on alternative days for about 4 months. After 1 week of Leupeptin treatment, they were challenged with purified acetylcholine receptor (AChR) from Torpedo californica in Freund's complete adjuvant. All control animals died within 60 days. Six animals treated with Leupeptin did not develop EAMG in spite of repeated AChR injections. Three animals developed clinical signs of EAMG after 65 days. The clinical course was short in the one that survived and prolonged in the 2 that finally died. All animals (Leupeptin-treated and controls) had circulating anti-AChR antibodies. Among the survivors, titers were slightly lower and EMG repetitive stimulation tests were normal. Leupeptin (0.02-200 mM) did not prevent curaremimetic [3H]toxin binding to AChR in membranes or in solution, nor dissociate AChR-toxin-antibody complexes. Immune response to antigens other than receptor remained intact in Leupeptin-treated animals. Leupeptin was not toxic at the doses given. The mechanism of this protection is not well understood. Leupeptin seems to decelerate the turnover rate of AChR induced by anti-AChR antibodies and/or to decrease the complement-mediated immune attack against the muscle end-plate.

[Myasthenia gravis. Clinical and therapeutic evaluation of 55 cases]

It is reported the study of 55 myasthenia gravis cases, with a review of the symptoms and signals, comparing initial symptoms ant those found at the time of the first evaluation. The mean age of the patients was 31.05 +/- 18.46 and the mean time of follow-up 5.88 +/- 5.47 years. Also the results of the diagnostic tests is reported, as well as the results of the treatment. The patients were treated with anticholinesterasics, corticosteroids, azathioprine, plasma-exchange and thymectomy. A statistical analysis with the chi-square test was unable to show a difference between the above procedures, regarding the definitive resolution of the disease. From the 55 cases, 9 (16.6%) had total remission, 41 (74.5%) remained with symptoms and need some kind of treatment, and 5 (9.09%) died (three patients with thymoma, one patient with congenital myasthenia gravis, severe kyphoscoliosis and pulmonary restriction, and one patient during the thymectomy procedure). It was found a relation between the signs of respiratory insufficiency, myasthenic crisis and thymoma only in the group of patients who died. A review about the diagnostic methods and treatment in the current days is made.

Human x human hybridomas from patients with myasthenia gravis: possible tools for idiotypic therapy for myasthenia

Hybridomas secreting monoclonal antibodies directed against the nicotinic acetylcholine receptor have been developed from rats with experimental autoimmune myasthenia gravis and from a patient with myasthenia gravis. Rat monoclonal antibodies were characterized by their ability to bind to electroblotted acetylcholine receptor subunits. Of 34 tested, 22 bound to the alpha subunit. Three bound to other subunits, and the remainder appeared to bind only to the native molecule. The human monoclonal antibodies were analyzed with respect to their binding to membrane-bound and solubilized acetylcholine receptor. Many bound with greater affinity to the membrane-bound form of the antigen. Two rat monoclonal antibodies capable of passively transferring experimental autoimmune myasthenia gravis, and with reactivities to the alpha subunit of the acetylcholine receptor, were employed to produce isogeneic monoclonal antiidiotypic antibodies. When they were injected prior to immunization with acetylcholine receptor, two of the antiidiotypic antibodies directed against framework determinants prevented the development of experimental autoimmune myasthenia gravis. This observation raises the possibility that the human monoclonal antibodies will be useful in the development of idiotypic treatment of the human disease.