Passive transfer of experimental autoimmune myasthenia by lymph node cells in inbred guinea pigs

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.

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

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

High numbers of autoantigen-reactive mononuclear cells expressing interferon-gamma (IFN-gamma), IL-4 and transforming growth factor-beta (TGF-beta) are present in cord blood

Umbilical cord blood of neonates and peripheral blood of healthy adults were analysed by in situ hybridization for numbers of mononuclear cells (MNC) expressing the cytokines IFN-gamma, TGF-beta and IL-4 mRNA without culture and after culture in the presence of acetylcholine receptor (AChR), myelin basic protein (MBP) and peripheral myelin protein P2. These antigens were chosen since they represent autoantigens in putatively immune-mediated neurological diseases. The numbers of cells expressing cytokine mRNA after 72 h culture in the presence of AChR, MBP and P2 were higher in cord blood than in peripheral blood of healthy adults. IFN-gamma, TGF-beta and IL-4 were always elevated in parallel. In cord blood there was a pronounced reactivity to several of the tested antigens, while such broad reactivity was not found in peripheral blood of healthy adults. No differences in cytokine mRNA expression were found between cord blood and peripheral blood of adults when cells were analysed without culture. The results show a capacity of cord blood cells to react to several autoantigens by the up-regulation of cytokine mRNA expression.

Autoimmunity in neuromuscular disease

A number of confounding factors can be identified from the search for autoimmune mechanisms over the last 2 decades that may be relevant for future studies. (1) An apparently homogeneous clinical disorder may represent more than one disease process and thereby imply antibody/antigen heterogeneity as, for example, in MG with and without detectable anti-AChR antibodies. In some cases, physiologic studies allow the different forms of the disease to be distinguished as in AIDP and acute inflammatory axonal polyneuropathy. (2) A homogeneous disorder (e.g., LEMS) may have at least two different triggering mechanisms (SCLC and an unknown stimulus). (3) Antigen density may be too low to be detected by the immunohistologic techniques available, as initially occurred in MG and LEMS. (4) Autoantibodies may be detected that are irrelevant to the primary disease, such as anti-striated muscle antibodies in MG. (5) Poor antibody cross-reactivity between species may mean that the pathogenic antibody is undetected in binding assays or in experimental passive transfer studies. For example, anti-AChR antibody in MG shows less than 5% reactivity with Torpedo AChR. (6) A poor regenerative capacity of the target antigen may mean that reduction of circulating autoantibodies by either plasma exchange or ISD treatment is not associated with detectable clinical improvement, as may be the case in SSN in which DRG cells appear to be the target. TABLE 5 summarizes the extent to which the data reviewed have established a role for pathogenic antibodies in the light of the postulates for autoimmunity set out earlier and ranks the disorders accordingly. Only in MG with detectable anti-AChR antibody are all the postulates met, including definition of the antigen, experimental passive transfer by the IgG fraction of MG sera, active immunization of experimental animals, and propagation. In both LEMS and the IgM kappa anti-MAG demyelinating neuropathy the antigen is known, although better characterized in LEMS; the epitopes are not yet defined in either. Data relating to passive transfer are more extensive in LEMS, however; systemic passive transfer of anti-MAG has not yet been reported. In neither condition is an animal model available. In the demyelinating neuropathies, the case for autoimmunity is less complete. Neither in AIDP nor in CIDP is the antigen known, and thus the relevance of the different EAN disorders is uncertain. Current evidence thus rests on the demonstration of serum IgM antibodies that react with peripheral nerve myelin and fix complement and on the intraneural passive transfer studies.(ABSTRACT TRUNCATED AT 400 WORDS)

Myasthenia gravis treatment: twelve years experience on 110 patients

The clinical conditions of 110 patients affected by myasthenia gravis (MG) were followed from two to twelve years. Patients with thymectomy showed a statistically higher percentage of clinical remissions than patients without thymectomy. In patients without clinical remission immunosuppressive drugs were prescribed in different schedule; the greater percentage of pharmacological remissions with less adverse effects was obtained with administration of prednisone 50-75 mg/die initially, than gradually reduced to smaller dosage in alternate day, associated to azathioprine. Plasmapheresis, performed in six cases not responders to immunosuppressive drugs, always showed a positive and even prolonged effect.

Experimental models of myasthenia gravis: lessons in autoimmunity and progress toward better forms of treatment

The nicotinic acetylcholine receptor (AChR) is a large membrane protein found in muscle cells. It is involved in the transformation of acetylcholine packets into a membrane depolarization, which thereby leads to a muscle twitch. This large, complex molecule is the target of the autoimmune attack in myasthenia gravis, and much has been learned in the past decade about myasthenia by the induction of autoimmunity to AChR in experimental animals. Experimental autoimmune myasthenia gravis (EAMG) has been produced in a variety of animals by immunization with AChR or AChR-like material, or by the passive transfer of anti-AChR antibodies or lymphocytes from afflicted animals into normal animals. EAMG is a remarkably faithful model of human myasthenia and has provided much information about how the immune response to AChR progresses and how weakness and damage to the neuromuscular junction ensure. EAMG has also allowed the development of a number of revolutionary forms of treatment in which only the abnormal response to AChR is restrained, and other necessary immune functions are left intact. These advances in treatment are not far from being tested in human myasthenia gravis. The experience gained in applying these concepts in EAMG and human myasthenia will be helpful in developing similar forms of treatment for other autoimmune diseases.

Acetylcholine receptor antibody-producing cells in thymus and lymph nodes in myasthenia gravis

Eleven patients with myasthenia gravis (5 with thymoma) were studied and spontaneous production of antibody to acetylcholine receptor (AChR) in vitro was found by thymus cells in 10 (and in all 5 with thymoma) and by lymph node cells in 8 (and in 3 with thymoma). The rate of AChR antibody production by thymus cells was greater than that by lymph node cells (10.7 +/- 11.6 and 1.4 +/- 1.5 fmol/10(6) cells/week, respectively, mean +/- SD, P less than 0.05 by paired t test), although the B-cell population was always smaller in the thymus than in the lymph nodes (9.5 +/- 9.4 and 31 +/- 12.7%, P less than 0.001), suggesting the principal role of the thymus in AChR antibody production. It is suggested that lymph nodes can be one of the main sites of AChR antibody production in myasthenia gravis but the antibody-producing cells may originate in the thymus.

Acetylcholine receptor-specific suppressive T-cell factor from a retrovirally transformed T-cell line

In both experimental and human myasthenia gravis an impairment in the immune regulation leads to an increased synthesis of antibodies against the nicotinic acetylcholine receptor (AcChoR). The present work reports the establishment of an AcChoR-specific suppressive T-cell line obtained by viral transformation of AcChoR-enriched murine T lymphocytes. Enriched T cells from Torpedo AcChoR-primed mice, prestimulated in vitro with antigen, were infected with radiation leukemia viruses and injected intravenously in congeneic recipient mice. Six months later lymphomas were observed in 20% of the injected mice and two of them, of donor origin, were established as permanent continuous cell lines in vitro. One of these lines, named LA41, expresses Thy-1.2, Lyt-2, and I-Jb surface markers. Culture supernatants of LA41 cells suppress the antigen-specific in vitro proliferation of Torpedo AcChoR-primed lymphocytes. This suppression is antigen-specific since the response induced by fetal calf AcChoR and by other antigens is not affected by addition of LA41 culture supernatant in the proliferative assay. LA41 culture supernatant injected in vivo at the time of antigen-priming suppresses also significantly the production of anti-AcChoR antibodies but not the synthesis of antibodies against other antigens--i.e., fetal calf AcChoR or alpha-bungarotoxin. These data show that LA41 cells constitutively produce Torpedo AcChoR-specific suppressor factor.

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.

The relation of clinical disease to antibody titre, proliferative response and neurophysiology in murine experimental autoimmune myasthenia gravis

Murine myasthenia is a relatively faithful model of the human disease. We studied anti-AChR antibody titres, lymphocyte proliferative response to AChR, characteristic electromyographic (EMG) abnormalities and muscle strength at weekly intervals after immunization of C57B16J mice with Torpedo AChR. The boosting immunization at 1 month after the primary immunization resulted in a progressive increase of anti-AChR IgG antibodies, but caused a marked drop in the proliferative response. Although characteristic EMG abnormalities occurred in nearly all immunized mice, clinical disease appeared very late or not at all. These data parallel findings in human myasthenia.

T-lymphocytes in experimental autoimmune myasthenia gravis. Isolation of T-helper cell lines

The role of T-lymphocytes in Experimental Autoimmune Myasthenia Gravis (EAMG) was investigated. We generated highly purified, acetylcholine receptor (AChR)-specific T-cell populations and subsequently characterized these cell lines with respect to their membrane phenotype and their function. Using a series of mouse monoclonal antibodies directed against rat lymphocyte surface differentiation antigens, the vast majority of line cells was shown to express a leucocyte common antigen, a T-common antigen and a T-helper antigen. Small subpopulations were Ia or T suppressor antigen-positive. Adaptive transfer to sublethally irradiated, thymectomized recipients revealed that 1 X 10(6) AChR-specific line cells could cooperate effectively with 10 X 10(6) AChR-primed, complement (C3) receptor-bearing (B-cell enriched) spleen cells in the production of anti-AChR autoantibodies. Recipients of B-cells along with relevant line cells developed an acute myasthenic syndrome 6-7 days after cell transfer. Electron-microscopical examination revealed the typical features of "acute phase" EAMG with heavy mononuclear infiltration. There was, however, no evidence antibody-independent cytotoxic activity exerted by AChR-specific line cells.

Immunopathology of acetylcholine receptors in myasthenia gravis

It is now clear that the muscular weakness and fatigability seen in MG result from an antibody-mediated immune response to AChR. The mechanisms by which antibodies impair transmission are moderately well understood and detection of antibodies in patient's sera is a reliable diagnostic test for the disease. The spectrum of antibody specificities produced in MG is also beginning to be understood, largely through the use of antibodies produced in the experimental model EAMG. Treatment for MG continues to rely heavily on the symptomatic relief afforded by acetylcholinesterase inhibitors. However, the recent recognition of the autoimmune nature of MG has led to increased emphasis on immunosuppression and antibody removal with some beneficial effects. Despite all that has been learned, the level of ignorance has just been pushed back one step--from the neuromuscular junction to the immune system. What initiates the immune response to AChR in MG and how to specifically suppress this aberrant response remain completely unknown.

Carbamylcholine modulation of E-rosette formation. Effect of plasmapheresis in myasthenia gravis

Myasthenia gravis may result from a reduction of available acetylcholine receptors at the neuromuscular junction, likely secondary to the presence of anti-acetylcholine receptor antibodies. Since T lymphocytes appear to carry a similar nicotinic acetylcholine receptor, we investigated the capacity of T cells from patients with myasthenia gravis to bind sheep erythrocytes. In addition we determined the effect of carbachol, a cholinergic agonist, on E-rosette formation, and the role of myasthenic serum in modulating these responses. Two groups of patients were identified; one with normal numbers of E-rosettes forming cells (E-RFC) and the other with significantly reduced numbers. The majority of patients with myasthenia had a reduced number of carbachol-sensitive T cells. Incubation of their serum (or the IgG fraction) with normal T cells led to a reduction in numbers of E-RFC, particularly of the carbachol-sensitive subset. These effects were blocked by d-tubocurarine and not by atropine. Following plasmapheresis, normal numbers of E-RFC were detected in the patients and the serum inhibitory activity was no longer detected. The data suggest that in parallel to the achievement of some degree of clinical improvement, plasmapheresis may restore some aspects of lymphocyte function.

Nerve stimulation test in murine experimental autoimmune myasthenia gravis

Use of the mouse model of myasthenia gravis (murine EAMG), ideally suited for immunological study, has been hampered by the relatively mild character of the disease and by the extended time and effort required for inducing severe disease. Electromyographic measurement of the compound action potential after repetitive stimuli, the nerve stimulation test, was evaluated for its ability to diagnose neuromuscular transmission defects in mice immunized with Torpedo acetylcholine receptor. With the combination of provocative maneuvers and raising of the body temperature, EAMG could be diagnosed in nearly all immunized animals a few weeks after immunization, whereas clinical evaluation of muscle weakness was positive in less than half of immunized mice months after the first immunization. Thus, EMG provides a means of objective evaluation of the disease and attempts at its experimental modification.

Recent advances in the molecular mechanisms of human and animal models of myasthenia gravis

The receptor-channel molecule is a dynamic system which exists in multiple conformations and that is the way we should think of it when we study antibody interaction with the molecule. The results presented here suggest that some antibodies may affect receptor function by occupying sites other than the receptor site. Some of these sites may by exposed only in certain conformations, and occupation of some site by antibodies may effect conformational changes. These small but perhaps important differences in cholinergic channel properties of the myasthenic muscle from the normal one are revealed by studying the effect of myasthenic sera on drug interactions with the channel sites. The sera of myasthenics are able to react with certain channel conformations and are able to affect the interaction of channel antagonists such as H12HTX and QNB. The sera appear to act preferentially with the open conformation of the channel. As a consequence of such an effect, important conformational changes of the channel may fail to occur upon activation.

Experimental autoimmune myasthenia gravis

Injection of animals with purified acetylcholine receptor in complete Freund's adjuvant causes development of antibodies which crossreact with receptors in muscle. The crossreacting antibodies impair neuromuscular transmission. Animals with experimental autoimmune myasthenia gravis (EAMG) are excellent models for studying the complex mechanisms by which the autoimmune response to receptor in myasthenia gravis causes muscle weakness. This review first briefly describes the discovery of EAMG. Then, to provide the necessary perspective, receptor structure and function and properties of anti-receptor antibodies are discussed, followed by a brief review of the pathological mechanisms in EAMG.

Identification of two serum components regulating the expression of T-lymphocyte function in childhood myasthenia gravis

We studied serums and cells from nine children with myasthenia gravis to determine whether there were alterations in the distribution or function of different T-lymphocyte subpopulations. The low numbers of E-rosette-forming T lymphocytes and their failure to respond to antigen by producing normal suppressor T cells were correlated with the presence of an IgG antibody directed toward the theophylline-sensitive T-cell subset; this activity could be blocked by d-tubocurarine. Incubation of normal T lymphocytes with serum from patients rendered the cells "myasthenia-like" when assayed for E-rosettes and for antigen-induced suppressor-cell function. A second, non-IgG factor found in patients' serums had activity like that of thymic hormone and induced T-cell maturation in normal bone marrow. This factor was not inhibited by d-tubocurarine; its activity was strongest in the two patients most severely affected, and it disappeared after thymectomy in both these patients. We conclude that in childhood myasthenia gravis there may be two independent serum factors; one an IgG antibody directed at a subset of T lymphocytes, blocked by d-tubocurarine and apparently unaffected by thymectomy, and the other a thymus factor that induces T-lymphocyte maturation.

The immunopathology of myasthenia gravis

Experimental autoimmune myasthenia gravis, induced by immunization with solubilized acetylcholine receptors, has proven an excellent animal model for the study of myasthenia gravis. The role of the thymus in myasthenia gravis is not yet known. Its content of skeletal muscle elements and acetylcholine receptors and the presence of germinal centers in myasthenia gravis suggest that the thymus could be a site of autoimmunization. An effector role has not been demonstrated for T cells in the pathogenesis of experimental autoimmune or clinical myasthenia gravis, but helper T cells participate in the rat's autoantibody response to acetylcholine receptors. Antibodies and lymphocytes reactive with acetylcholine receptors are demonstrable in the peripheral blood of patients with myasthenia gravis and appear to be specific for this disease. Parallel studies of both experimental autoimmune and clinical myasthenia gravis have provided evidence for an autoimmune basis for the pathophysiology in myasthenia gravis. Antiacetylcholine receptor antibodies appear to play a central role in impairing neuromuscular transmission. Numerous antibody specificities have been described, but none seems to be directed at the acetylcholine binding site of the receptor. Addition of antiacetylcholine receptor antibodies to cultured muscle cells, in the absence of complement, causes redistribution of the receptors on the membranes of myotubes, accelerated receptor degradation, apparent impairment of ionophore function, and loss of sensitivity to acetylcholine. In vivo complement appears to be an important mediator of antiacetylcholine receptor antibody pathogenicity. Its presence is essential for the passive transfer of experimental autoimmune myasthenia gravis with antibodies. In muscle biopsy specimens from patients with myasthenia gravis, IgG and C3 have been demonstrated on the postsynaptic membrane and on degenerated fragments of membrane in the synaptic cleft. This suggests that complement activation in vivo is associated with focal lysis of the postsynaptic membrane. A causal relationship appears to exist between the binding of antibody to acetylcholine receptors, the reduction in muscle acetylcholine receptors, and impairment of neuromuscular transmission.

Role of complement in the pathogenesis of experimental autoimmune myasthenia gravis

An acute phase of experimental autoimmune myasthenia gravis (EAMG) occurs transiently early in the immune response of Lewis rats to nicotinic acetylcholine receptors (AChR) when Bordetella pertussis is used as adjuvant. It is characterized by a destructive cellular attack directed at the postsynaptic membranes of muscle. Acute EAMG can be passively transferred to normal rats by IgG from serum of rats with chronic EAMG. In the present study, acute EAMG, induced either by passive transfer of syngeneic antibodies or by active immmunization, was inhibited in rats depleted of complement by treatment with cobra venom factor (CoF). Furthermore, passive transfer of antibodies in excess of the muscle's content of AChR was without any measurable effect in rats treated with CoF. Although 60% of the muscle's AChR was complexed with antibody, there was no reduction in the muscle's content of AChR, and neuromuscular transmission was not compromised as judged electromyographically by curare sensitivity. These data imply that redistribution, accelerated degradation, and impairment of the ionophore function of AChR, effects of antibodies described in vitro on extrajunctional AChR, do not play a significant role in vivo in impairing neuromuscular transmission in an intact neuromuscular junction. Complement appears to be a critical mediator of anti-AChR antibodies' pathogenicity in vivo.

Myasthenia gravis: a personal view of pathogenesis and mechanism, part 1

A review of our current knowledge of the etiology and pathogenesis of myasthenia gravis is presented, with particular emphasis on the immunological aspects of the disease. Part 1, published in this issue, deals with the clinical and genetic features of myasthenia gravis which led to the autoimmune theory of the etiology of this disease. Various theories in this field are reviewed, and recent advances in our knowledge of the acetylcholine receptor protein, and its immunology, are examined. Part 2, which will appear in the March/April issue, provides a review of the dysfunction of physiology, pharmacology, and structure of the neuromuscular junction in myasthenia gravis, and the part played by the autoimmune process.

Streptococcal-induced cell-mediated-immune destruction of cardiac myofibers in vitro

We have demonstrated that T lymphocytes from the spleens of adult guinea pigs sensitized to group A streptococcal antigens are cytotoxic for cultured fetal guinea pig heart cells. Lymphocyte cytotoxicity, measured by 51Cr release from target cells, was stimulated by sensitization in vivo with group A whole cells, cell walls, and purified protoplast membranes emulsified with complete Freund's adjuvant (CFA). Sensitization with group C streptococcal antigens in CFA or CFA alone produced lymphocytes with little or no specific cytotoxic activity. Target cells of cultured fetal skeletal muscle, liver, or skin were relatively refractory to effector cell cytotoxicity. The presence of antigenic determinants on the membranes of cultured myofibers, cross-reacting with group A streptococcal cellular antigens, was confirmed by immunofluorescence. These data are discussed in terms of a model for poststreptococcal rheumatic myocarditis in which cell-mediated autoimmune mechanisms may participate.

Experimental allergic neuritis induced by a basic neuritogenic protein (P1L) of human peripheral nerve origin

Experimental allergic neuritis (EAN) in the peripheral nervous system, without involvement of the central nervous system, was produced in laboratory animals by the injection of a basic neuritogenic protein, P1L, purified from human peripheral nerves. The animals manifested a positive skin test with P1L, and their lymphocytes were found to be transformed in vitro in the presence of this protein several days before the appearance of the clinical signs. Passive transfer of the disease was performed with lymph node cells from donor guinea pigs immunized with P1L protein. EAN, the experimental model for the human disease Guillaain-Barré syndrome, was shown to be a transient disease and could be suppressed by the administration of hydrocortisone.

Studies of human myasthenia gravis: electrophysiological and ultrastructural evidence compatible with antibody attachment to acetylcholine receptor complex

Neuromuscular junctions from patients with early onset and chronic myasthenia gravis were examined by electrophysiological and ultrastructural techniques. Acetylcholine (AcCh) sensitivities were reduced by 34-63% in early onset myasthenia and 60-80% in chronic myasthenia. Ultrastructural analysis revealed that virtually all junctional folds of the early onset patients were intact but that the AcCh-receptor-rich crests of these folds were uniformly covered by an attached layer of 30 X 70 A particles arranged in small tufts or rosettes. In chronic myasthenic endplates, however, junctional fold crests were destroyed, apparently being replaced by vesicular membrane debris similarly labeled by tufts of 30 X 70 A particles. Thus, the initial reduction in junctional AcCh sensitivity observed in early onset myasthenia gravis may be attributed at least in part to in situ masking or inactivation of AcCh receptors, whereas the marked decrease in AcCh sensitivity observed in the chronic myasthenic patient may represent a combination of two factors: (a) in situ masking of AcCh receptors and (b) destruction of the receptor-containing crests of the junctional folds. These observations are compatible with an autoimmune etiology of myasthenia gravis initially involving an apparent antibody attachment to one or more components of the functional AcCh receptor complex, followed by systematic destruction and removal of junctional folds by both humoral and cell-mediated autoimmune responses.

Pathological mechanisms in experimental autoimmune myasthenia gravis. II. Passive transfer of experimental autoimmune myasthenia gravis in rats with anti-acetylcholine recepotr antibodies

Passive transfer of experimental autoimmune myasthenia gravis (EAMG) was achieved using the gamma globulin fraction and purified IgG from sera of rats immunized with Electrophus electricus (eel) acetylcholine receptor (AChR). This demonstrates the critical role of anti-AChR antibodies in impairing neuromuscular transmission in EAMG. Passive transfer of anti-AChR antibodies from rats with chronic EAMG induced signs of the acute phase of EAMG in normal recipient rats, including invasion of the motor end-plate region by mononuclear inflammatory cells. Clinical, eletrophysiological, histological, and biochemical signs of acute EAMG were observed by 24 h after antibody transfer. Recipient rats developed profound weakness and fatigability, and the posture characteristic of EAMG. Striking weight loss was attributable to dehydration. Recipient rats showed large decreases in amplitude of muscle responses to motor nerve stimulation, and repetitive nerve stimulation induced characteristic decrementing responses. End-plate potentials were not detectable in many muscle fibers, and the amplitudes of miniature end-plate potentials were reduced in the others. Passively transferred EAMG more severely affected the forearm muscles than diaphragm muscles, though neuromuscular transmission was impaired and curare sensitivity was increased in both muscles. Some AChR extracted from the muscles of rats with passively transferred EAMG was found to be complexed with antibody, and the total yield of AChR per rat was decreased. The quantitative decrease in AChR approximately paralleled in time the course of clinical and electrophysiological signs. The amount of AChR increased to normal levels and beyond at the time neuromuscular transmission was improving. The excess of AChR extractable from muscle as the serum antibody level decreased probably represented extrajunctional receptors formed in response to functional denervation caused by phagocytosis of the postsynaptic membrane by macrophages. The amount of antibody required to passively transfer EAMG was less than required to bind all AChR molecules in a rat's musculature. The effectiveness of samll amounts of antibody was probably amplified by the activation of complement and by the destruction of large areas of postsynaptic membrane by phagocytic cells. A self-sustaining autoimmune response to AChR was not provoked in animals with passively transferred EAMG.