Immune regulation in myasthenia gravis: evidence for an increased suppressor T-cell population

Alpha interferon treatment in myasthenia gravis: effects on natural killer cell activity

The efficacy of recombinant interferon-alpha (rIFN alpha), on natural killer (NK) cell cytotoxic activity, CD3+, CD4+, CD8+, CD56+, HLA-DR+ lymphocyte counts, anti-acetylcholine receptor antibody (AChR Ab) levels, single fibre electromyography findings (SFEMG) and clinical course were evaluated in patients with myasthenia gravis (MG). During the IFN alpha treatment (3 mu, subcutaneous, 3 times a week), NK cell cytotoxicity and CD4+/8+ ratio increased, NK cell count remarkably decreased, and no significant clinical or SFEMG changes were observed. This preliminary open study in MG patients has demonstrated enhanced NK activity per unit NK cell after IFN alpha therapy. Although lymphocyte phenotypes and NK function approached normal levels during therapy, a higher dose of IFN alpha may be required for a significant clinical response. It has been also concluded that 6 months of IFN alpha therapy seems to be safe in MG, though in patients with malignancy, IFN alpha may cause increased autoimmunity, AChR positivity and MG.

Ocular myasthenia: a protean disorder

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

Characterization of a 58- and a 78-kD monocytic membrane protein with affinity to the acetylcholine receptor in myasthenia gravis patients

The autoimmune disease myasthenia gravis (MG), caused by the effect of specific antibodies, directed towards the nicotinic acetylcholine receptor, is triggered by autoantigen-specific T cells. In order to investigate cellular parts of the immune response in MG, the authors investigated the binding of the nicotinic acetylcholine receptor (AChR) to peripheral blood mononuclear cells (PBMC) from MG patients. AChR binding cells were identified by rosetting experiments using AChR-coated fluorescein beads. Applying this technique, a significant percentage of PBMC (21.2 +/- 7.65%) from MG patients formed rosettes with AChR-coated beads. Membrane preparations of nycodenz- or percoll-separated monocytes from MG patients or T-cell depleted monocytic subpopulations were applied to SDS-PAGE under reducing conditions. Ligand-blotting studies with biotinylated AChRs revealed two cell-membrane proteins with molecular weights of 58- and 78-kD. In parallel the same results were obtained by affinity chromatography of monocytic membrane proteins using AChR-sepharose. A possible interference of anti-AChR IgG was excluded. The 58- and the 78-kD proteins are detectable under reducing conditions by ligand blotting with AChR-biotin, while under non-reducing conditions only the 58-kD protein can be detected. Furthermore, in experiments using Endoglycosidase-H, the 58-kD protein appears to be non-glycosylated, while the 78-kD protein bears carbohydrates. These findings suggest that monocytes which bind the AChR via specific membrane proteins on their surface might act as antigen-presenting cells and may lead to an induction of the T-cell response, in the early phase of the disease.

Changes in peripheral blood lymphocyte subset frequencies in myasthenia gravis patients are related to immunosuppression

Surface antigens on peripheral blood lymphocytes from myasthenia gravis patients were investigated. The expression of DR+ and CD8+/DR+ T lymphocytes was increased and the expression of CD4+ T cells reduced. Neither thymectomy, clinical condition nor anti-acetylcholine receptor antibody titre correlated with any of the changes in peripheral blood lymphocyte subsets observed. However, immunosuppressive therapy correlated with the significant reduction in CD4+ and CD2+/CD4+ T cells in these patients.

Lymphocyte subsets of the peripheral blood in myasthenia gravis determined by two-color flow cytometry

Lymphocyte subsets of the peripheral blood in 43 patients with myasthenia gravis (MG) were determined by two-color flow cytometry using a number of monoclonal antibodies. In the MG patients without thymectomy (Tx) and prednisolone (PSL) treatment, lymphocyte counts, B-cells, CD4+ cells and their subsets were normal, but numbers of T-cells, CD8+ cells and CD8+ CD 11-subsets were significantly decreased. Furthermore, proportions of activated cells in T-cells, CD 16+ Leu7- and CD16+ Leu7+ NK subsets were significantly high in the patients. The changes in T-cells, CD8+ cells and activated T-cells were less marked in the MG patients than Sjögren's syndrome (SS) used as a disease control. Contrary to MG patients, lymphocyte counts, CD4+ cells and their subsets were decreased, and the proportions of B-cells were high in SS patients. These results suggest altered immunologic conditions, immunologically active and deficient conditions, in both diseases, although the alterations were more prominent in SS than MG. PSL treatments and Tx significantly altered the lymphocyte profiles: PSL decreased lymphocytes, B-cells, T-cells, CD4+ cells and their subsets, while the proportions of CD8+ cells were increased. The changes were compatible with the known immunosuppressive effects of PSL. After Tx, lymphocytes and B-cells decreased, but the proportions of T-cells, CD8+ cells and their subsets, and NK cells subsets returned toward normal. CD4+ CD8+ cells were not increased in MG patients, and the cells did not decrease after Tx. Some of these observations might be relevant to clinical effects of Tx, although the mechanism responsible for these changes is still unknown.

[Study of circulating lymphocytes by monoclonal antibodies in myasthenia gravis]

A significant decline of CD3 cell detected by rosettes and a significant increased of B cell populations were observed. The total CD3+, helper CD4+ and suppressor CD8+ T-cell subsets showed no significant variation em relation to sex, age thymectomy and corticotherapy by monoclonal antibodies.

Nicotine induces T-suppressor cells: modulation by the nicotinic antagonist D-tubocurarine and myasthenic serum

To further unravel the basic immunoregulatory defect present in myasthenia gravis, we undertook to study nicotinic acetylcholine receptor (AchR) activity on human peripheral blood leukocytes. A biphasic suppressive effect of nicotine was observed on lymphocyte proliferative responses to phytohemagglutinin, concanavalin A, and pokeweed mitogen with peaks at 10(-9) and 10(-5) M. Using a coculture approach, T cells preincubated with nicotine for 24 hr showed enhanced suppressor cell activity. This was partially blocked by serum from myasthenic patients and by the nicotinic antagonist d-tubocurarine. These studies suggest that suppressor T lymphocytes bear functional nicotinic AchR, which may be modulated by myasthenic serum, with possible relevance to the pathogenesis of myasthenia gravis.

In vitro anti-acetylcholine receptor antibody synthesis by myasthenia gravis patient lymphocytes: correlations with thymic histology and thymic epithelial-cell interactions

In vitro anti-acetylcholine receptor antibody (anti-AChR Ab) production by peripheral blood lymphocytes (PBL) and thymic lymphocytes was investigated in 52 patients with myasthenia gravis (MG). There was a positive correlation between in vitro anti-AChR Ab synthesis and in vivo titers. A relationship between the rates of synthesis by PBL and histological abnormalities of the thymus was also observed. Patients with hyperplastic thymus tended to produce the largest amounts in vitro, while those with an involuted thymus produced little or none. Production in thymoma patients is likely to correlate with the histological nature of the thymus associated with the tumor. In vitro Ab synthesis was modulated by the depletion of a cell subset for half of the patients tested. Finally, anti-AChR Ab production by thymocytes but not by PBL is enhanced by the addition of autologous or allogeneic thymic epithelial cells, suggesting a possible role of thymic epithelial cells in the autosensitization against AChR occurring in the thymus.

A double-label flow cytometric analysis of the simultaneous expression of OKT4 and Leu2a antigens on circulating T lymphocytes in myasthenia gravis

A two-color immunofluorescence analysis of circulating abnormal T lymphocytes bearing both helper (T4) and suppressor/cytotoxic (Leu2a) T cell markers (double marker cells) was performed by means of the laser flow cytometry system. The double marker cell level was very low in 6 patients with multiple sclerosis and 12 normal controls studied. Fifteen of 31 patients with myasthenia gravis (MG) showed an elevation of double marker cells without an increase in T6-positive cells. The values were significantly higher in patients with thymoma or thymic hyperplasia than in those with a normal thymus. The double marker cell level was considered to reflect thymic abnormality in MG and to be helpful for determining the indication of thymectomy.

Glucocorticoid receptors of mononuclear leukocytes from myasthenia gravis patients

The present study was performed to analyse glucocorticoid receptor (GR) binding in peripheral blood mononuclear leukocytes (MNL) from 39 myasthenia gravis (MG) patients (unoperated patients (n = 13), thymectomized patients (n = 14) and patients receiving glucocorticoids: thymectomized (n = 11) and unoperated (n = 6]. A whole cell binding assay with 3(H) dexamethasone was used. GR mean values were significantly higher in the MNL of MG patients (thymectomized or not) not receiving glucocorticoid than in the MNL of healthy donors. Affinity was within the normal range. Sex, age or clinical forms of illness did not influence the results. In patients receiving prednisone (Pd) the GR values were significantly lower than in MG patients without Pd therapy, independent of Pd dose or time of administration. No differences in receptor binding between normal subjects and MG patients receiving Pd have been found.

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.

Myasthenia gravis and myasthenic syndromes

More than a decade ago myasthenic symptoms were observed in rabbits immunized with acetylcholine receptor (AChR) [119] and AChR deficiency was found at the neuromuscular junction in human myasthenia gravis (MG) [36]. By 1977 the autoimmune character of MG and the pathogenic role of AChR antibodies had been established by several measures. These included the demonstration of circulating AChR antibodies in nearly 90% of patients with MG [87], passive transfer with IgG of several features of the disease from human to mouse [149], localization of immune complexes (IgG and complement) on the postsynaptic membrane [30], and the beneficial effects of plasmapheresis [20, 123]. Substantial subsequent progress has occurred in understanding the structure and function of AChR and its interaction with AChR antibodies. The relationships of the concentration, specificities, and functional properties of the antibodies to the clinical state in MG have been carefully analyzed, and the mechanisms by which AChR antibodies impair neuromuscular transmission have been further investigated. The clinical classification of MG has been refined, the role of the thymus gland in the disease has been further clarified, and new information has become available on transient neonatal MG. The prognosis for generalized MG is improving, but there is still no consensus on its optimal management. Novel therapeutic approaches to MG are now being explored in animal models. Recognition of the autoimmune origin of acquired MG also implied that myasthenic disorders occurring in a genetic or congenital setting had a different cause. As a result, a number of congenital myasthenic syndromes have come to be recognized and investigated. Finally, an acquired disorder of neuromuscular transmission different from MG, the Lambert-Eaton myasthenic syndrome, has also been shown to have an autoimmune basis. In this syndrome, active zone particles of the presynaptic membrane are direct or indirect targets of the pathogenic autoantibodies.

A case of myasthenia gravis associated with optic neuritis

A case of myasthenia gravis is described in association with optic neuritis in which brain-stem auditory and somatosensory evoked potentials were normal. CSF contained alkaline oligoclonal IgG bands. Blood lymphocyte subpopulations showed a decreased number of T-suppressor cells.

Pathogenesis of Mooren's ulcer: some new concepts

Mooren's ulcer is a chronic, painful corneal ulceration of unknown aetiology. Recent histological and immunological studies suggest an autoimmune basis. It is now becoming clear that the immune system plays an intricate role in maintaining homoeostasis in health and disease. Regulation of the immune response appears to involve a subset of peripheral blood T lymphocytes known as suppressor cells. A qualitative or quantitative deficiency of suppressor cells may therefore be responsible for chronic inflammation, autoimmune disease, and immunodeficiency states. To explain the reported immunological aberrations the number of suppressor T cells in addition to other immunological parameters were studied in a patient with bilateral Mooren's ulcers. A deficiency of suppressor T cells was found in the peripheral blood. This deficit in the immunoregulatory mechanism explains some of the immunological abnormalities reported in previous studies. Furthermore this study provides additional evidence for an autoimmune aetiology. In the light of these findings the possibility of a new line of treatment has been raised.

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.