Against Acetylcholine Receptor Research Articles

T cell tolerance to AChR, the autoantigen in myasthenia gravis, is mediated primarily by peripheral mechanisms (128.25)

Abstract In myasthenia gravis (MG), a T-cell dependent antibody response is directed against acetylcholine receptor (AChR) at the neuromuscular junction. To study T cell tolerance, we generated a transgenic mouse in which the TAChRα chain is expressed as a self protein. This transgenic was bred to nude mice and thymus transplants were performed to produce progeny expressing TAChRα in the thymus and/or the periphery (muscle). These mice were immunized with the TAChRα dominant epitope, p146–162, and in vitro proliferation of responding T cells was measured. Since AChR is expressed at low levels in the thymus, it was presumed that central tolerance would be important. However, this was not the case; only mice with peripheral expression of TAChRα showed tolerance (a lack of proliferation). Furthermore, CFSE-labeled TAChR specific T cells from a TCR transgenic were adoptively transferred into TAChR transgenic (tolerizing) and non-transgenic recipients. Following immunization, proliferation of the transferred T cells was lower in the TAChR transgenic host. Moreover, when the TAChR transgene was bred to scurfy mice, progeny lacking Tregs (foxp3−/Y) exhibited an increase in serum anti-TAChR Ig. Autoantibodies were not seen in the foxp3+/Y mice or in mice lacking Aire function (which have defective central tolerance). These results are consistent with a primary role for peripheral tolerance in regulating the response to AChR. Supported by an APC Subcontract, a UTHSCSA ERC grant and NIH (T32AG021890, T32DE11438).

Is excitation–contraction coupling impaired in myasthenia gravis?

Objective To investigate whether excitation–contraction (E–C) coupling of muscle is impaired in patients with myasthenia gravis (MG). Methods In 51 patients with generalized MG and 35 normal subjects, compound muscle action potentials (CMAPs) of the abductor pollicis brevis, and movement-related potentials using an accelerometer placed at the thumb tip were simultaneously recorded after median nerve stimulation at the wrist. The E–C coupling time (ECCT) was estimated by a latency difference between CMAP and movement-related potential. Antibodies against acetylcholine receptor (AChR), ryanodine receptor (RyR), and muscle specific receptor tyrosine kinase (MuSK) were measured by immunoassays. Results The mean ECCT was significantly longer in patients with MG (mean ± SEM; 2.79 ± 0.1 ms; p = 0.002) than in normal controls (2.52 ± 0.1 ms). Among MG patients, the mean ECCT was longer for patients with thymoma than for those without it ( P = 0.04), and was shorter for patients treated with FK506 (an immunosuppressant and also an enhancer of RyR related Ca 2+ release) than for those not receiving this treatment ( p = 0.04). ECCT had no significant correlation with anti-AChR, anti-RyR, or anti-MuSK antibodies. Conclusions In MG, E–C coupling appears to be impaired, particularly in patients with thymoma, and FK506 possibly facilitates E–C coupling. Significance The functional implication of impaired E–C coupling is not established, but it may contribute to muscle weakness in patients with MG.

Targeting the Antigen-Binding Site of HLA-Restricting Alleles in Treatment of Autoimmune Disease

In autoimmune disease, production of disease-causing auto-antibodies (Abs) depends on autoreactive T cells that recognize the epitopes of the pathogenic antigen in the context of MHC class II molecules. It is possible that selective inhibition of an antigen-presenting function of disease-associated MHC alleles could lead to suppression of the disease. Myasthenia gravis (MG) is a disabling neuromuscular disease in which autoimmune responses against acetylcholine receptor (AChR), especially against the alpha chain of AChR, cause a postsynaptic defect. HLA linkage of MG has been thus far best detailed for DQB1. Recently, we have shown that certain DQ haplotypes are associated with presentation of AChR alpha-chain peptides in MG. In a mouse model for MG, which can be induced in disease-susceptible C57BL/6 (B6, H-2b) mice by injection with Torpedo AChR, region 62-76 of I-Ab beta chain is involved in the disease mechanism. Monoclonal Abs (mAbs) against synthetic peptide I-Abetab62-76, which localizes at the rim of the antigen-binding site of I-Ab, inhibited in vitro proliferation of disease-associated T cells. Passive transfer of these mAbs as well as vaccination with this peptide strongly suppressed occurrence of clinical MG in B6 mice. In both cases, Ab and T-cell responses against AChR, especially those related to disease pathogenesis, also decreased. mAbs against peptides from the ridge of the antigen-binding region of the correlate DQB1 sequences inhibited in vitro the proliferation of AChR-specific T cells from MG patients. The results indicated that the function of disease-associated MHC alleles may be blocked by directly and selectively targeting the antigen-presenting region on these MHC molecules. The strategy could provide an effective means for immunointervention in other autoimmune and allergic responses.

Deficiency of decay accelerating factor and CD59 leads to crisis in experimental myasthenia

In myasthenia gravis (MG), neuromuscular transmission is disrupted due to the production of autoantibodies against acetylcholine receptors (AChR). In previous work, we showed that decay accelerating factor (DAF or CD55), an intrinsic cell surface complement regulator that disables C3/C5 amplification convertases, protects against receptor loss and muscle weakness. In this study, we examined whether, and if so, to what extent CD59, a downstream intrinsic cell surface regulator that prevents assembly of membrane attack complexes (MACs), contributes to this protection. Twenty-four hours after anti-AChR injection, we found that CD59a −/− mice did not significantly differ from WTs, all Daf1 −/− CD59a −/− mice either died or required euthanasia. At 48 h, Daf1 −/− were significantly weaker than CD59a −/− and WT mice, and for these mice immunohistochemistry revealed marked C9 deposition at postsynaptic junctions, radioimmunoassays showed reductions in AChR levels, and electron microscopy demonstrated massive junctional damage. These data indicate that DAF serves as the initial shield that protects the neuromuscular junction whereas CD59 is a further barrier. They argue that complement inhibitor, particularly if targeted to the receptor, could then have therapeutic value in human MG.

Infantile onset myasthenia gravis with MuSK antibodies

Approximately 80% of patients with myasthenia gravis (MG) show a high antibody (Ab) titer against acetylcholine receptor (AChR). Patients with MG who do not have high titer of anti-AChR are called seronegative MG (SNMG) and their clinical characteristics are shown to be rather different from anti-AChR positive MG in the literature.1 It was recently reported that 70% of sera from generalized SNMG patients contained Ab to a muscle-specific receptor tyrosine kinase (MuSK).2 The frequency of anti-MuSK Ab in generalized SNMG is reportedly from 38% to 47% of cases.3–5 Anti-MuSK MG mainly affects young to middle-aged adults. We describe a case of late infantile onset MG with anti-MuSK Ab. A 29-year-old man first experienced bilateral ptosis after febrile seizures when he was 2 years old. His parents soon noticed abnormal phonation. At age 3 years, the diagnosis of MG was made based on a positive edrophonium test. Treatment was initiated with oral prednisolone. His ocular symptoms responded well to …

Pre- and post-synaptic abnormalities associated with impaired neuromuscular transmission in a group of patients with 'limb-girdle myasthenia'

The properties of neuromuscular junctions (NMJs) were studied in motor-point biopsy samples from eight patients with congenital myasthenic syndromes affecting primarily proximal limb muscles ['limb-girdle myasthenia' (LGM)]. All had moderate to severe weakness of the proximal muscles, without short-term clinical fatigability but with marked variation in strength over periods of weeks or months, with little or no facial weakness or ptosis and no ophthalmoplegia. Most had a characteristic gait and stance. All patients showed decrement of the compound muscle action potential (CMAP) on repetitive stimulation at 3 Hz, and increased jitter and blocking was detected by SFEMG, confirming the presence of impaired neuromuscular transmission. None of the patients had serum antibodies against acetylcholine receptors (AChRs). Two of the patients had similarly affected siblings. Intracellular recording from isolated nerve-muscle preparations revealed that the quantal content (the number of ACh quanta released per nerve impulse) was only approximately 50% of that in controls. However, the quantal size (amplitude of miniature end-plate currents) and the kinetic properties of synaptic potentials and currents were similar to control values. The area of synaptic contact and extent of post-synaptic folding were approximately 50% of control values. Thus, the quantal content per unit area of synaptic contact was normal. The number of AChRs per NMJ was also reduced to approximately 50% of normal, so the local AChR density was normal. Immunolabelling studies revealed qualitatively normal distributions and abundance of each of 14 proteins normally concentrated at the NMJ, including components of the basal lamina, post-synaptic membrane and post-synaptic cytoskeleton. DNA analysis failed to detect mutations in the genes encoding any of the following proteins: AChR subunits, rapsyn, ColQ, ChAT or muscle-specific kinase. Response of these patients to treatment was varied: few showed long-term improvement with pyridostigmine and some even deteriorated with treatments, while others had intolerable side-effects. Several patients showed improvement with 3,4-diaminopyridine, but this was generally only transient. Ephedrine was helpful in half of the patients. We conclude that impaired neuromuscular transmission in these LGM patients results from structural abnormalities of the NMJ, including reduced size and post-synaptic folding, rather from any abnormality in the immediate events of neuromuscular transmission.

Prevention of passively transferred experimental autoimmune myasthenia gravis by an in vitro selected RNA aptamer

Myasthenia gravis (MG) and its animal model, experimental autoimmune MG (EAMG), are mainly caused by autoantibodies directed against acetylcholine receptors (AChR) located in the postsynaptic muscle membrane. Previously, we isolated an RNA aptamer with 2′-fluoropyrimidines using in vitro selection techniques that acted as an effective decoy against both a rat monoclonal antibody called mAb198, which recognizes the main immunogenic region on the AChR, and a significant fraction of patient autoantibodies with MG. To investigate the therapeutic potential of the RNA, we tested the ability of the RNA aptamer to protect the receptors in vivo from mAb198. Clinical symptoms of EAMG in rats engendered by passive transfer of mAb198 were efficiently inhibited by a truncated RNA aptamer that was modified with polyethylene glycol, but not by control scrambled RNA. Moreover, the loss of AChR in the animals induced by the antibody was also significantly blocked with the modified RNA aptamer. These results suggested that RNA aptamers could be applied for antigen-specific treatment for autoimmune diseases including MG.

Improvement of RNA Aptamer Activity against Myasthenic Autoantibodies by Extended Sequence Selection

Myasthenia gravis (MG) is mainly engendered by autoantibodies directed against acetylcholine receptors (AChRs) located in the postsynaptic muscle cell membrane. Previously, we isolated an RNA aptamer with 2′-amino pyrimidines using in vitro selection techniques that acted as a decoy against both a rat monoclonal antibody called mAb198, which recognizes the main immunogenic region on the AChR, and patient autoantibodies with MG (1). However, low affinity of this RNA to mAb198 relative to that of AChR might limit potential of the RNA as an inhibitor of the autoantibodies. To improve decoy activity of the RNA aptamer against autoantibodies, here we employed in vitro selection methods with RNA libraries containing extra random nucleotides extended to the 3′ end of previously selected RNA sequences. RNAs isolated in this study showed significant increases in the binding affinities to mAb198 as well as bioactivities protecting AChRs on human cells from both mAb198 and patient autoantibodies, compared with the previous RNA aptamers. These results have important implications for the development of antigen-specific modulation of autoimmune diseases including MG.

Indirect quenching fluororeceptor assay of anti-AChR antibodies.

A fluororeceptor assay (FRA) has been developed for the determination of antibodies against acetylcholine receptor (AChR), employing an antifluorescein serum and fluorescein-labeled AChR. Antiserum raised against rat muscle AChR in rabbit and the labeled AChR are incubated with antifluorescein serum at room temperature. At high levels of anti-AChR, binding of the labeled AChR prevented subsequent binding of the fluorescein groups by antifluorescein, resulting in little change in the signals of the label. Conversely, at low levels of anti-AChR, the free fraction of the labeled AChR is available to be bound by antifluorescein, which markedly reduced fluorescence intensity of the label. Thus, the fluorescence intensity of the assay mixture directly reflects the amount of anti-AChR antibodies in the serum. It is concluded that the availability of fluorescein-labeled AChR and the antibody directed against it permit measurement of anti-AChR antibodies in human myasthenia. The quality of the assay and its preliminary clinical application have been evaluated.

Evidence against chronic antigen-specific T lymphocyte activation in myasthenia gravis.

Myasthenia gravis (MG) is an antigen-specific autoimmune disease caused by antibodies against acetylcholine receptors (AChR) at the post-synaptic membrane of the neuromuscular junction. Clinical and immunological data imply the involvement of AChR-specific T lymphocytes as helper cells for autoantibody production. Direct data to support this hypothesis, however, remain sparse. In the present study, a large population of MG patients was studied for evidence of peripheral blood T cell activation by several assays. Assays based on non-specific measurements of T cell activation as well as assays of antigen-specific clonal expansion were utilized. Levels of soluble IL-2 receptor in serum were modestly elevated in some patients, suggesting T cell activation. However, peripheral blood cells did not show evidence of IL-2 receptor expression or enhanced reactivity to IL-2 in culture. Clonable T cells selected for hypoxanthine phosphoribosyl transferase (hprt) mutation, another non-antigen-specific marker for T cell activation, were not seen with increased frequency except in patients treated with purine analogs. Antigen-specific T cell activation was measured by proliferation assays using heterologous and autologous sources of AChR. Antigen-restimulated peripheral blood cell cultures were cloned by limiting dilution. The vast majority of patients failed to show convincing evidence of AChR specific T cell activation or clonal expansion; only 2 of 44 patients demonstrated clonable autologous AChR-specific T cells. An alternative hypothesis of T cell involvement in MG is proposed in which T cell activation is discontinuous and predominantly directed at antigens other than AChR.

The Thymus in Myasthenia Gravis

The experimental work discussed here endorses the hypothesis that in the pathogenesis of MG the initial and essential steps take place within the thymus. Most, if not all, thymuses of MG patients contain B cells capable of producing AChR-specific autoantibody along with appropriate stroma elements. This is especially pertinent in hyperplastic thymuses with germinal centers, which characteristically contain cellular complexes formed by AChR-producing MCs and surrounding interdigitating dendritic cells. The source of the myasthenogenic autoantigen is more complex in thymomas. There are data suggesting that thymoma epithelium express a protein that shares certain peptide epitopes with the AChR alpha chain, although there is no further molecular similarity. A unique type of "molecular self mimicry" could be the starter of thymoma-associated MG.

Effect of sera from myasthenia gravis patients and of α-bungarotoxin on acetylcholinesterase during in vitro neuromuscular synaptogenesis

Myasthenia gravis (MG) is mediated by circulating antibodies directed against acetylcholine receptor (AChR) but the antibody titre is poorly correlated with the clinical severity of the disease. We analysed acetylcholinesterase (AChE) activity, molecular forms and distribution during in vitro synaptogenesis, in the presence of sera from MG patient. We observed that the formation of AChE patches is inhibited in proportion to the anti-AChR antibody titre, whatever the clinical severity of the disease. The total activity and the proportion of the different molecular forms were unchanged suggesting that AChE level and distribution are controlled by independent mechanisms. To clarify the relationship between the mechanisms of AChE concentration during synaptogenesis and AChR concentration, we compared the effect of MG sera (receptors are internalised and degraded) and of the acetylcholine antagonist α-bungarotoxin (non-functional receptors are still present in the muscular membrane). In the presence of α-bungarotoxin, the number of AChR clusters, and AChE activity and concentration were equivalent to control values. The comparison of the results obtained with antibodies and α-bungarotoxin suggests that the presence and/or concentration of AChR is a necessary condition for normal concentration of AChE during synaptogenesis.

Specific immunotherapeutic strategy for myasthenia gravis: targeted antigen-presenting cells

The pathogenesis of myasthenia gravis (MG) involves a T cell-dependent antibody-mediated autoimmune response directed against acetylcholine receptors (AChR). Inactivation of AChR-specific T cells should interrupt the immune response, resulting in therapeutic benefit. Since each individual's repertoire of T cells responds to a heterogeneous and unique spectrum of AChR epitopes presented in association with self-major histocompatibility complex (MHC) class II, an individualized approach is required to target all relevant AChR-specific T cells. The individual's own antigen-presenting cells (APC) can be used for this purpose, since they process and present the antigen appropriately, and express the correct MHC class II. A novel method of binding AChR to surface immunoglobulin with a heterobifunctional antibody conjugate allows us to use all B cells as APC. Conjugate-plus-AChR-treated B cells (AChR-APC) effectively targeted AChR-specific T cells, stimulating vigorous proliferative responses in a rat cell culture system. If APCs are ‘fixed’ with cross-linking reagents, they induce long-lasting or permanent ‘anergy’ of the specific T cells. We prepared AChR-APC, allowed them to process AChR in vitro, and fixed them with paraformaldehyde. Pre-culture of these fixed AChR-APC with AChR-specific T cells induced anergy: when restimulated with fresh AChR-APC, the T cells exhibited markedly reduced proliferative responses and IL-2 production, compared with responses of T cells pre-cultured with control fixed B cells. Implications for the design of antigen-specific therapeutic strategies for MG and other immune disorders will be discussed.

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 α-bungarotoxin (α-BuTx), are characteristic for myasthenia gravis (MG) and are considered to be of importance in the pathogenesis of the disease. Antibodies against a β-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.

Suppression of immune responses to acetylcholine receptor by interleukin 2-fusion toxin: in vivo and in vitro studies

The pathogenesis of the autoimmune disease, myasthenia gravis (MG), involves an antibody-mediated attack against acetylcholine receptors (AChRs). Since the relevant antibody response is T cell dependent, a therapeutic strategy aimed at T lymphocytes actively participating in the immune reaction to AChR should result in relatively selective suppression of AChR antibody. During an active immune response, T cells express receptors for interleukin 2 (IL2). In this study, we have used a genetically engineered fusion protein comprised of the binding region of IL2 and the toxic portion of diphtheria toxin (DAB 486-IL2), to attempt to treat an experimental animal model of MG in rodents. We examined the effects of treatment with DAB 486-IL2 in vivo on primary, ongoing, and secondary antibody responses to purified Torpedo AChR. Treatment of mice with intraperitoneal injections of DAB 486-IL2 beginning at the time of immunization inhibited the primary AChR antibody response by 50% during the treatment period. Ongoing and secondary antibody responses to AChR were not suppressed in vivo by treatment with DAB 486-IL2. In comparison, DAB 486-IL2 was far more potent in suppressing antibody responses and lymphoproliferation in cell culture. At a dose comparable to that given in vivo, cellular proliferation and antibody production were virtually eliminated in a secondary response in vitro. The suppressive effects of DAB 486-IL2 was much more pronounced when it was given at the time of initial antigen stimulation, as compared with its effect when given during an already established antibody response. These findings suggest that the effect of the fusion toxin on AChR antibody production was due predominantly to inhibition of T cells rather than B cells.

High recombinant interleukin-2 sensitivity of peripheral blood lymphocytes from patients with Myasthenia Gravis: Correlations with clinical parameters

Myasthenia Gravis (MG) is an autoimmune disorder of neuromuscular transmission associated with antibodies (Ab) against acetylcholine receptor (AChR). Autoantibody production is a T-cell-dependent phenomenon perhaps caused by aberrant immunoregulation. So far, a possible role for immunoregulatory molecules has not been investigated in the pathogenesis of MG. Since interleukin-2 (IL-2) is able to induce peripheral blood mononuclear cell (PBMC) proliferation without a previous activating signal and to upregulate IL-2-receptor expression, we have evaluated the activation state of PBMC in patients with MG, by cytofluorographic analysis of CD25 expression and by testing their sensitivity to recombinant IL-2 (rIL-2) without any known previous stimulation. We found no significant difference in CD25 expression in a large group of patients compared to controls. However, proliferative responses to rIL-2 were significantly higher in MG patients than in controls. In MG, as in controls, this response was time- and dose-dependent, was inhibited by an anti-IL-2 receptor Ab and correlated with an increased percentage of CD25 + T cells after rIL-2 exposure. The response was greater in patients with a high anti-AChR Ab titer and a severe form of the disease, and in patients tested before thymectomy. Thus blood T cells in MG showed functional signs of preactivation (high sensitivity to rIL-2 alone) without detectable CD25 expression on fresh cells, raising the possibility of aberrant IL-2 receptor regulation and/or expression in MG T cells. Decreased sensitivity to rIL-2 after thymectomy, associated with general clinical improvement, suggests a role for activated cells originating from the thymus in the pathogenesis of MG, and is of clinical relevance in patient follow-up. Our findings also provide a new approach in the study of MG pathogenesis: the search for aberrant immunoregulation mechanisms linked to defects in lymphokine circuits.

Myasthenia Gravis in the Cat

Myasthenia gravis (MG) was diagnosed in four cats--one had an apparently congenital form and three had the acquired autoimmune form. All four cats were examined because of episodes of weakness including gait abnormalities, voice change, neck ventroflexion, and regurgitation. Palpebral reflexes were absent in all cats. Administration of edrophonium chloride resulted in transient resolution of clinical signs in all four cats. Three cats were tested for the presence of serum autoantibodies against acetylcholine receptor (AChR) by radioimmunoassay. Two cats with acquired MG had anti-AChR antibody titers of 10.5 and 96.8 nmol/l (normal, less than or equal to 0.03 nmol/l). Antibodies were not detected in the cat with presumptive congenital MG. All four cats were treated with pyridostigmine bromide. Two cats with acquired MG were euthanatized because of clinical deterioration. The third cat with acquired MG has been asymptomatic since 2 months after diagnosis. The cat with presumed congenital MG is alive 3 years after diagnosis.

Specificity of the T cell immune response to acetylcholine receptor in experimental autoimmune myasthenia gravis. Response to subunits and synthetic peptides.

Myasthenia gravis (MG) and its animal model, experimental autoimmune MG (EAMG), are T cell-dependent diseases mediated by antibodies against acetylcholine receptor (AChR) on skeletal muscle. Most of the antibodies are directed toward conformation-dependent epitopes on the AChR, whereas T cells recognize denatured AChR. In search of T cell epitopes in EAMG, we tested 24 synthetic peptides covering 62% of the alpha-subunit sequence of Torpedo californica electric organ AChR in the T cell proliferation assay with lymph node cells from rats immunized with AChR. In Lewis rats, 2 of these peptides, [Tyr 100]alpha 100-116 and [Gly 89, Tyr 90]alpha 73-90, strongly stimulated T cells and, of these, [Tyr 100]alpha 100-116 was much more potent; 4 other peptides were weakly mitogenic and 18 were ineffective. None of the 24 synthetic peptides alone stimulated anti-AChR production and, when added to cultures along with AChR, [Tyr 100]alpha 100-116 and [Gly 89, Tyr 90]alpha 73-90 suppressed antibody production. Of twelve cloned T cell lines specific to AChR, 4 responded to [Tyr 100]alpha 100-116, indicating the importance of the epitope in alpha 101-116 in Lewis rats. In three other strains of rats whose responses to AChR and its subunits were similar to those in the Lewis rat, neither [Tyr 100]alpha 100-116 nor [Gly 89, Tyr 90]alpha 73-90 was stimulatory. Instead, completely different sets of peptides stimulated their T cells. When peptides were used as immunogens, each strain (except Lewis rats) responded only to the peptides that stimulated AChR-immune T cells from the same strain. Genetically restricted T cell recognition of AChR peptides in rats suggests that T cells from MG patients with different major histocompatibility haplotypes may recognize different AChR peptides.

Thymic hyperplasia in myasthenia gravis: immunohistological abnormalities and responsiveness to recombinant IL2.

Myasthenia Gravis (MG) is an autoimmune disorder of neuromuscular transmission characterized by the presence of autoantibodies directed against acetylcholine receptor (AChR), which are detected in more than 85 % of patients’ sera (1). The role of the thymus in MG has been strongly suggested by the favorable clinical effects of thymectomy and by the high incidence of thymic abnormalities (15–20 % thymomas and 50 % hyperplastic thymuses) (2).KeywordsDouble Label ExperimentThymic HyperplasiaThymic LymphocyteThymic AbnormalityHigh Proliferative ResponseThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

MYASTHENIA GRAVIS WITHOUT ACETYLCHOLINE-RECEPTOR ANTIBODY: A DISTINCT DISEASE ENTITY

Immunoglobulin preparations from eight patients with clinical features of myasthenia gravis, in whom no serum antibody against acetylcholine receptor (AChR) could be detected, were injected intraperitoneally into mice. Neuromuscular transmission was significantly impaired compared with mice receiving control human immunoglobulin. No antibody bound to the mouse AChR was detected, but there was a small loss (9·4%) of AChR in the mouse diaphragms. Mice injected with myasthenic AChR-antibody-positive immunoglobulin and mice growing hybridoma cells secreting monoclonal AChR antibody showed similar impairment of neuromuscular transmission, but 75% and 94%, respectively, of their muscle AChR had antibody bound and AChR losses were 47% and 60%. The results suggest that a pathogenetic immunoglobulin antibody interferes with neuromuscular transmission in these AChR-antibody-negative patients by binding to non-AChR determinants at the neuromuscular junction. This form of myasthenia is immunologically and physiologically distinct from the AChR-antibody-positive form.