Subpopulations of T lymphocytes in myasthenia gravis patients.

Subpopulations of human peripheral blood T lymphocytes were examined in twenty-three myasthenic patients. T lymphocytes bearing receptors for the Fc portion of IgG (T gamma) were significantly increased in a third of the patients examined. T lymphocytes bearing receptors for the Fc portion of IgM (Tmu) were within normal values in all but two patients. Possible implications of these cells in the pathogenesis of myasthenia gravis are discussed.     

Phenotypic characteristics of thymic B lymphocytes in myasthenia gravis

We have found prominent secretion of immunoglobulin and anti-acetylcholine antibodies by thymic lymphocytes (TL) of myasthenics despite a relative paucity of B (surface IgM⁺) cells in such TL. To determine whether there was a surface IgM^– B cell in the TL which could manifest such responses, we compared the frequency of cells expressing the B cell-specific phenotypic marker CD20 (B1⁺), surface IgM (SIgM⁺), surface IgG (SIgG⁺), and surface IgD (SIgD⁺) in TL and autologous blood mononuclear cells in 36 myasthenic patients. B1⁺ cells were significantly more frequent than SIgM⁺ cells in TL (3.2±0.6 vs 0.6±0.2). In double-labeling studies, less than 25% of the B1⁺ cells coexpressed SIgM. Only 0.3% of the TL were SIgD⁺. In contrast, the frequencies of B1⁺ and SIgM⁺ cells in autologous blood were not significantly different (10.7±1.3 vs 8.2±0.8%). About 75% of blood B1⁺ cells co-expressed SIgM. These findings suggest that mast B cells in these TL have undergone isotope switching during priorin vivo differentiation and could manifest the observed humoral responses.     

B and T cell involvement in anti-acetylcholine receptor antibody formation in myasthenia gravis.

The in vitro method of antibody production was applied to ascertain the contribution of B and T cells to the formation of anti-acetylcholine receptor (AChR) antibody. The anti-AChR antibody in the culture supernatant was estimated by radioimmunoassay, and the anti-AChR antibody-forming cells from cultures were detected by autoradiography of the antigen-binding cells. Thymic B cells from myasthenia gravis (MG) patients formed antibody when they were cultured with thymic T cells from MG patients and stimulated with AChR antigen. The antibody formation was more vigorous with thymic B cells, which contained more germinal centres. The antibody was also formed from the B and T cell combination of peripheral blood lymphocytes, although the amount was less than that produced by thymic lymphocytes from MG patients. The antibody produced by lymphocytes from MG patients. The antibody produced by lymphocytes from MG patients was suppressed by the addition of T cells from the culture supernatant of normal individuals, but not by autologous or allogeneic T cells from MG patients. The suppression by T cells from normal individuals was abolished when the cells were treated with mitomycin C. These observations indicated that AChR-specific B cells and helper T cells are active, while the suppressor T cells, which are usually present in normal individuals, are defective in MG patients.     

Ocular myasthenia gravis.

Ocular dysfunction accounts for nearly 70% of the initial manifestations of myasthenia gravis. Since the prevalence rate of myasthenia gravis is two to 10 cases per 100,000 population, it is important for clinicians to be cognizant of this disorder and its varied ocular presentations. The clinical manifestations, diagnosis, treatment, and prognosis of ocular myasthenia gravis are reviewed.     

Clonal expansions of CD4+ B helper T cells in autoimmune myasthenia gravis

The weakness in myasthenia gravis (MG) is mediated by T helper cell (Th)-dependent autoantibodies against neuromuscular epitopes. So far, analyzing Th phenotypes or antigen specificities has yielded very few clues to pathogenesis. Here we adopt an alternative antigen-independent approach, analyzing T cell receptor (TCR) Vbeta usage/expansions in blood from 118 MG patients. We found major expansions (>or= five standard deviations above the mean of 118 healthy, individually age- and sex-matched controls) in diverse Vbeta in 21 patients (17.6%, p<0.001) among CD4+ T cells, and in 45 patients (38.1%, p<0.001) among CD8+ T cells. In informative probands, the expanded CD4+ cells consistently showed a Th cell phenotype (CD57+CXCR5+) and expressed Th1 cytokines. Furthermore, their expression of markers for activation, lymphocyte trafficking and B cell-activating ability persisted for >or=3 years. Surprisingly, we noted a selective decline in the expansions/their CD57 positivity while the probands' MG was improving. CDR3 spectratyping suggested mono- or oligoclonal origins, which were confirmed by the prevalent TCR Vbeta CDR3 sequences of Th cells cloned from repeat bleeds. Thus, our data provide evidence for persistent clonally expanded CD4+ B helper T cell populations in the blood of MG patients. These unexpected CD4+ expansions might hold valuable clues to MG immunopathogenesis.     

Microscopic thymoma and myasthenia gravis.

A rare case of microscopically sized thymoma is described in a 56 year old man suffering from myasthenia gravis. Histological examination of the surgically removed thymus showed the presence of several epithelial thymoma-like islands. As controls, 100 thymuses obtained from consecutive necropsies were sampled: 4% of these cases showed epithelial islands. This case is further proof that "microscopic thymoma" is a true pathological entity and suggests that every thymus removed from myasthenic patients in which there is no macroscopic evidence of thymoma should be examined microscopically on serial sections.     

Experimental autoimmune myasthenia gravis induction in B cell-deficient mice

Experimental autoimmune myasthenia gravis (EAMG) is an animal model for human myasthenia gravis (MG). Autoantibody-induced functional loss of nicotinic acetylcholine receptor (AChR) at the postsynaptic membrane is an important pathogenic feature of both MG and EAMG. To evaluate the extent at which the humoral immune response against AChR operates in the pathogenesis of EAMG, we immunized B cell knockout (muMT) and wild- type C57BL/6 mice with AChR and complete Freund's adjuvant. The ability of AChR-primed lymph node cells to proliferate and secrete IFN-gamma in response to AChR and its dominant peptide alpha146-162 were intact in muMT mice as in wild-type mice. Similar amounts of mRNA for IFN-gamma, IL-4 and IL-10 in AChR-reactive lymph node cells were detected in muMT and wild-type mice. However, muMT mice had no detectable anti-AChR antibodies and remained completely free from clinical EAMG. We conclude that B cells are critically required for the genesis of clinical EAMG, but not for AChR-specific T cell priming.      

B-T lymphocyte interactions in experimental autoimmune myasthenia gravis: autoantibody mediated up-regulation of the response of acetylcholine receptor-specific T lymphocytes.

Twenty-six monoclonal antibodies of five different isotypes and reactive against distinct parts (alpha, beta, gamma, delta-subunits) of the nicotinic acetylcholine receptor (AChR) from Torpedo californica were screened for their capacity to enhance activation of AChR-specific CD4+ autoreactive T cells. The T-cell line (LR) used in this study recognized an epitope (98-116) on the alpha-subunit of Torpedo AChR. Four monoclonal antibodies bearing a gamma 2b isotype and recognizing an epitope on the Torpedo AChR alpha-subunit, especially the main immunogenic region (MIR), were able to enhance T-cell activation in a dose-response manner. Four further gamma 2b isotype monoclonal antibodies, recognizing epitopes other than the AChR alpha-subunit, had no effect. Monoclonal antibodies of other isotypes (IgM, IgG1, IgG2a, IgG2c), irrespective of their subunit specificity, were unable to influence the T-cell response. Thus, the enhancement requires a IgG2b isotype, and both the antibody and the T-cell recognize an epitope on the same subunit. We have previously shown that AChR-specific B cells are directly able to present antigen to AChR-specific T-cell lines in a privileged way. The present data demonstrate that B cells are also capable of enhancing indirectly the immunogenicity of autoantigens via their humoral antibodies.     

Defective T lymphocyte function in nonthymectomized patients with myasthenia gravis

In vitro functional properties of peripheral blood mononuclear cells were evaluated in 29 patients with myasthenia gravis and in 11 healthy controls. Spontaneous cell proliferation was higher in patients than in controls. The production of interleukin-2 and interferon-gamma and the proliferative response to different mitogens were reduced in the patients. A positive correlation was found between the production of interleukin-2 and interferon-gamma. These defects in T cell function were the most pronounced in nonthymectomized patients. Patients with severe disease had a higher percentage of cells bearing the interleukin-2 receptor and a higher spontaneous production of tumor necrosis factor alpha in cell culture than in patients with mild disease. There was no difference between patients and controls in the level of soluble interleukin-2 receptor in cell culture supernatants or in sera. The results indicate a partially suppressed T cell function in myasthenia gravis. This defect was less pronounced in patients studied after thymectomy.     

Heart muscle antibodies in myasthenia gravis.

Myasthenia gravis (MG) may in some patients, especially in those with a thymoma, involve the heart. Using an ELISA, we measured heart muscle antibodies in sera from 75 MG patients and in 173 control sera. Heart muscle antibodies were detected in 29/30 thymoma MG patients, in none of 30 young onset MG patients with thymic hyperplasia and in 7/15 late onset MG patients with thymic atrophy. Among the controls, four sera had a very low concentration of heart muscle antibodies. Absorption studies showed that the heart muscle antibodies cross-react with skeletal muscle, but are unrelated to acetylcholine receptor antibodies.     

T and B lymphocytes in multiple sclerosis.

The percentage and total number of E and EAC rosettes, as indicators of T and B lymphocytes respectively, were studied in the blood of subjects with multiple sclerosis (MS) and normals. MS patients in acute exacerbation were found to have a decrease in E rosettes and an increase in EAC rosettes. The relationship of these findings to the pathogenesis of MS is unclear; several possible pathogenetic implications are considered.