Assessment of cellular and humoral immunity of myasthenics

In vivo regulation of experimental autoimmune encephalomyelitis by NK cells: alteration of primary adaptive responses

Innate immune responses provide the host with its first line of defense against infections. Signals generated by subsets of lymphocytes, including NK cells, NKT cells, and APC during this early host response determine the nature of downstream adaptive immune responses. In the present study, we have examined the role of innate NK cells in an autoimmune model through the use of primary immunization with the myelin oligodendrocyte glycoprotein peptide to induce experimental autoimmune encephalomyelitis (EAE). Our studies have shown that in vivo depletion of NK cells can affect the adaptive immune responses, because NK cells were found to regulate the degree of clinical paralysis and to alter immune adaptive responses to the myelin oligodendrocyte glycoprotein peptide. The requirement for NK cells was reflected by changes in the T cell responses and diminished clinical disease seen in mice treated with anti-NK1.1, anti-asialo GM1, and selected Ly49 subtype-depleted mice. In addition to alteration in T cell responses, the maturational status of dendritic cells in lymph nodes was altered both quantitatively and qualitatively. Finally, examination of TCR Vbeta usage of the brain lymphocytes from EAE mice indicated a spectra-type change in receptor expression in NK- depleted mice as compared with non-NK-depleted EAE mice. These findings further establish a recently postulated link between NK cells and the generation of autoreactive T cells.

Antibodies to thymic epithelial cells in myasthenia gravis

The presence of anti-thymus antibodies was investigated in the serum of 36 patients with myasthenia gravis (MG). Using an immunofluorescence technique on frozen thymic sections, we found 45% of patients sera reacting with normal or MG thymuses. Staining was confined to subcapsular and medullary keratin-positive epithelial cells. Thirty-five out of 36 sera from healthy controls and all 15 sera from patients presenting another autoimmune disorder were negative. Antibodies to thymic epithelial cells were almost exclusively detected in patients presenting thymic hyperplasia and did not disappear after thymectomy. They were not clearly associated with antiacetylcholine receptor antibody titer, nor with disease severity. Their strong association to thymic abnormalities highlights the role of the thymus in pathogenesis of MG. The reasons for the appearance of these antibodies, the structure they recognize on thymic epithelial cells and their possible etiological role are discussed.

Myasthenia gravis: the specificities of skeletal muscle and thymus antibodies

Antibodies against skeletal muscle antigens and against thymic myoid cells were examined in sera from 40 patients with myasthenia gravis (MG). Using an indirect immunofluorescence technique, antibodies against the surface of muscle cells were found in 23 sera, and antibodies against muscle cell cross-striations in 28 sera. Antibodies against thymic myoid cells were found in 27 sera, stained cells also occurring in fetal thymus from 14 weeks of gestation and in hyperplastic thymus from MG patients. Sera which stained myoid cells also stained muscle cell cross-striations. Sera from all the 20 patients with thymoma contained antibodies to a citric acid extract of skeletal muscle (CAE) as detected by indirect haemagglutination, whereas sera from 20 comparable patients without thymoma did not contain CAE antibodies. The myoid cell antibodies could be absorbed by homogenized muscle, but not by CAE-coated sheep erythrocytes. Different antibody patterns are seen among different MG patients; close associations were found between cross-striational and myoid cell antibodies, and between CAE-antibodies and a thymoma.

Acetylcholine receptor turnover in myasthenia gravis

Humoral antibodies directed against the acetylcholine receptor are present in most patients with myasthenia gravis. These antibodies accelerate receptor degradation and thus cause a decrease in receptor level and impaired neuromuscular transmission. The stimulus that triggers and sustains the formation of the antibodies has not been identified, but it is possible that the primary antigen may be located on the cell surface of thymic lymphocytes. In some situations the clinical state in myasthenia gravis does not correlate with the antibody titer, suggesting that other factors also influence receptor amount and/or function of other potential regulators that have been investigated. Calcium and agents that increase cyclic AMP appear to increase the formation of the receptor and thus might serve to mitigate the effects of the circulating antibodies. In contrast, cholinergic agonists may cause a further decrease in receptor number, providing an explanation of why myasthenic patients may become resistant to therapy.

Lymphocyte subpopulations and surface membrane immunoglobulins in myasthenia gravis

Lymphocyte subpopulations were studied in 16 myasthenic patients by means of E and EA7s rosettes and surface membrane immunofluorescence. Myasthenic patients showed an increase in lymphocytes with surface IgM an IgD when compared to a control group. In female patients this increase was highly significant, and lymphocytes bearing membrane IgG and IgA were also augmented. No difference was found in male patients when compared with sex-matched controls. These results suggest an activation of the B cell compartment restricted to female patients, and support the hypothesis of different immunopathogenetic mechanisms in this disease.

Monoclonal antibody analysis of blood T-cell subsets in myasthenia gravis

Analysis of peripheral blood T -cell subsets and B-cells in patients with myasthenia gravis was performed using monoclonal antibodies and antibody against surface immunoglobulins (SIg) in an immunofluorescent technique. We found a modest but significant decrease in percentages of OKT3- and OKT8-positive cells (thought to represent total T-cells and T-suppressor/cytotoxic cells, respectively) in myasthenics as a group. The percentage of OKT3-positive cells was significantly decrease in patients with late-onset disease (greater than 35 years old), while the percentage of OKT8-positive cells was significantly reduced in those with early-onset myasthenia (greater than 35 years old). Both thymectomized and nonthymectomized patients exhibited a decreased percentage of OKT3-positive cells. No significant difference was found between the percentages of SIg-positive cells in myasthenics and controls. Our results suggest that only modest imbalances of circulating immunoregulatory lymphocytes occur in myasthenia gravis; however, it is conceivable that the small differences observed in this study may reflect pathogenetically important reductions in a functionally distinct lymphocyte subpopulation.

Effect of corticosteroids on the thymus in myasthenia gravis

The weight and histological appearance of the thymus from patients with myasthenia gravis were studied. Nine patients treated with corticosteroids were compared with 10 patients not treated with corticosteroids before thymectomy. The thymuses of corticosteroid-treated patients were found to have significantly increased fat and connective tissue, decreased germinal centers, and poorer corticomedullary differentiation than those of untreated patients. The glandular weight and degree of myoepithelial stroma were the same in both groups. The changes following corticosteroid treatment mimic those following aging or acute stress, with retention of the myoepithelial stroma but depletion of thymic lymphoid elements. In myasthenic patients not undergoing thymectomy, the possibility remains that persistent myoepithelial tissue can adversely affect the prognosis.

Evaluation of T cell subsets in myasthenia gravis using anti-T cell monoclonal antibodies

Functional T cell subsets have been evaluated in the peripheral blood of patients with myasthenia gravis using monoclonal anti-T cell antibodies and a suppressor cell assay based on the suppression of the mixed-lymphocyte reaction by concanavalin A-activated lymphocytes. A significant decline of suppressor cells was found in a large proportion of patients, both by direct count using the anti-suppressor-cytotoxic T cell antibody (OKT8) and by the suppressor assay. Patients also showed an increase in immature T cells defined by their simultaneous reaction with the anti-helper cell (OKT4) and anti-suppressor cell (OKT8) antibody. Thymectomy tended to enhance the deficit in suppressor cells, and to induce the disappearance of double-labelled cells.

Clinical and immunological associations in myasthenia gravis. 1: Autoantibodies

Associations between female sex, HLA B8, positive anti-thyroid microsomal antibody and, to a lesser extent, antinuclear antibody were seen in 34 patients with myasthenia gravis. This supports the concept that the disease is heterogeneous. Anti-DNA antibodies, which were present in 62% of the patients, did not show such associations.

Clinical and immunological associations in myasthenia gravis. 2. Cell-mediated immunity

Myasthenic patients showed low absolute T cell counts and low spontaneous and phytohaemagglutinin-induced lymphocyte transformation responses. The abnormalities were particularly associated with late onset disease and female sex, but not with HLA phenotype or autoantibody production. Serum factors inhibitory to lymphocyte transformation occurred in some patients.

Thymic lymphocytes bear a surface antigen which cross-reacts with acetylcholine receptor

Acetylcholine receptor (AChR) is a major antigen in the neuromuscular disease myasthenia gravis and it is clear today that the basic defect in this disease is brought about by an autoimmune attack on acetylcholine receptors at the neuromuscular junctions. The involvement of the thymus and its role in myasthenia have been widely investigated but are still poorly understood. A high incidence of thymic abnormalities is observed in patients with myasthenia and thymectomy is beneficial in many cases. Immunological studies have demonstrated the presence of humoral as well as cellular immune responses towards thymic tissues in myasthenic patients. There were also some reports that animals immunized with thymic extracts develop a partial defect in neuromuscular transmission. In spite of all these observations, the nature and origin of the association between the thymus and the neuromuscular junction in myasthenia gravis are still not known. We have previously demonstrated an immunological cross-reactivity, both humoral and cellular, between a thymic component and AChR; such a cross-reactivity could provide a molecular explanation for the involvement of the thymus in myasthenia gravis. In this study, we demonstrate, by using immunofluorescence and radioimmunological techniques, that thymic lymphocytes bear a surface antigen which binds specifically to antibodies against nicotinic AChR and is thus defined as an 'AChR-like' antigen. A preliminary report of this study has been published.

Lymphocyte subpopulations and IgG concentrations in cerebrospinal fluid and blood from patients with myasthenia gravis

Twelve patients with myasthenia gravis (MG) were examined for cerebrospinal fluid (CSF) T lymphocytes and for peripheral blood lymphocyte subpopulations (E-, EAET-, EA- and EAC-rosette-forming cells). The patients had a significantly increased percentage of CSF T cells (88.2 +/- 8.7%) when compared with controls (78.0 +/- 9.1%). Absolute concentrations of CSF T cells were not significantly increased. In peripheral blood no significant change in lymphocyte subpopulations was observed, but there was a slight leucocytosis in the patient group. The patients had increased CSF IgG concentrations, CSF IgG to protein ratio, and CSF to serum IgG ratio, indicating an intrathecal production of IgG. No oligoclonal bands could be demonstrated in the agarose gel electrophoresis. The two patients with thymoma had anti-muscle antibodies in CSF and serum, with ratios of 1:256 and 1:1024, respectively. Serum IgG levels were increased, but not significantly, in the patient group. These results suggest an involvement also of the central nervous system in some patients with MG.