Depletion of helper/inducer T cells after thymectomy in myasthenic patients

The effect of thymectomy on autoreactive T- and B-lymphocytes in myasthenia gravis

Eleven patients with myasthenia gravis were followed for three years after thymectomy. Acetylcholine receptor-specific T-cell stimulation was found in 8/11 patients before operation as compared to 2/11 three years after thymectomy. Changes of T-cell antireceptor-reactivity were commonly paralleled by changes in disease severity. The numbers of cells secreting IL-2 upon stimulation with human acetylcholine receptor correlated with those secreting IFN-gamma. T-cell reactivity against a monoclonal acetylcholine receptor antibody did not decrease after thymectomy. Such reactivity could reflect a beneficial immune response counteracting anti-receptor reactivity. The frequency of autoantibody-secreting cells remained unchanged, while the serum concentration of acetylcholine receptor antibodies started to decrease one year after thymectomy. All examined thymus-cell suspensions contained autoreactive T- and B-lymphocytes. There was a preferential enrichment of autoreactive lymphocytes in the thymus in a few patients with recent onset of disease.

Clinical measurement of antibodies against acetylcholine receptor (AchR), SOD and LPO in patients with myasthenia gravis (MG) before and after thymectomy

The antibodies against acetylcholine receptor AchR and levels of SOD and LPO were measured in 11 patients with myasthenia gravis (MG), and the results were compared with normal controls and patients with diseases other than MG. The results showed that the antibodies against AchR were higher as compared with other groups before and after operation. The post-operative level of antibodies was obviously lower than the pre-operative value. An slight increase in SOD and significant decrease in mean value of LPO after surgery were noted. The possible mechanism was discussed.

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.

Antibodies to acetylcholine receptors in myasthenia gravis. In vitro synthesis by peripheral blood lymphocytes before and after thymectomy

Pokeweed mitogen (PWM)-driven in vitro synthesis of antibodies to the acetylcholine receptor (PSA) was studied in non-thymoma patients with myasthenia gravis. In a group of 46 patients, the occurrence of PSA was related to the presence of the thymus or, in operated patients, the absence of a clinical effect of thymectomy. Sixteen patients were followed before and soon after thymectomy. PSA disappeared in all patients, at least temporarily, between 6 weeks and 1 year afterwards, independent of the clinical course and eventual clinical effect of the operation. A recurrence was found only in one of the five patients who derived no benefit from the operation. These findings support the hypothesis that the therapeutic effect of thymectomy can be explained by removal of a source of autoreactive lymphocytes. There was no correlation between the changes in serum levels of a-AChR and clinical improvement, suggesting a minor role of circulating peripheral blood lymphocytes (PBL) and the thymus in the total production of a-AChR.

Surgical treatment of myasthenia gravis and evaluation of its efficacy

This paper reports 30 cases of myasthenia gravis (MG) treated by thymectomy from 1965 to 1990 in our hospital. Of all the 30 cases of MG, peripheral blood lymphocyte subpopulation was determined in 10, and anti-acetylcholine receptor antibody titer in 6, before and after operation. The results demonstrated the efficacy of thymectomy against MG. We considered that with application of hormone before and after operation to regulate immune function of the body, and/or with plasma exchange to remiss symptoms, all the patients with generalized MG may be indicated for treatment by thymectomy. Indication of treatment does not depend on age, sex and the course of the disease. But radical operation, proper anesthesia and appropriate use of antibiotics may ensure safety of the operation and its curative effect.

Spleen cell dialyzable extracts (SCDE) mediated immunotherapy for patients with myasthenia gravis

We studied 14 cases of myasthenia gravis (MG) with regard to their anti-acetylcholine receptor antibody (AChR-Ab) production, peripheral blood CD4+/CD8+ ratio, and responses of peripheral lymphocytes to PHA and PWM stimulations. We found that the clinical severity was not proportional to AChR-Ab level in serum in terms of whole myasthenic population, whereas in one individual patient there was a close correlation between clinical severity and the AChR-Ab level in serum. The CD4+/CD8+ ratio in myasthenic patients was significantly higher than that of normal controls. The responses of T- and B-cells to mitogenic stimulations were impaired in myasthenic patients. The immune abnormalities found in the majority of the patients were restored to about normal after spleen cell dialyzable extracts (SCDE) therapy was applied to all patients. The results implicated that SCDE, working as an immunomodulator, could serve as a promising agent to normalize the abnormal immune functions of MG patients or other autoimmune diseases.

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.

Effect of thymectomy on blood T-cell subsets in myasthenia gravis

We studied peripheral blood mononuclear T-cell subsets in 23 patients with myasthenia gravis who had undergone thymectomy at least one year before study. An increase in the T4+/T8+ (helper-inducer/suppressor-cytotoxic cell) ratio was seen, similar to that previously reported in nonthymectomized patients with myasthenia gravis. Six patients were studied before and after thymectomy and no consistent alteration in the pattern of T-cell subsets was detected. We were not able to demonstrate a quantitative effect of thymectomy on peripheral blood mononuclear T-cell subsets in patients with myasthenia gravis.

Myasthenia gravis: long-term prognostic value of thymus lactate dehydrogenase isoenzyme pattern of hyperplastic thymus and thymoma

Lactate dehydrogenase (LDH) isoenzyme pattern and the percent of H-subunit content were determined in the thymus of 62 patients (55 with hyperplasia, 7 with tumours) after thymectomy. An increase in LDH1 relative activity indicates that in the thymus of patients with myasthenia gravis the ratio of mature differentiated thymocytes was higher than in the thymus of control subjects. LDH isoenzyme profiles of thymus tumours were similar to those described in other neoplasms, except that thymomas with apparent predominance of epithelial cells and with minimal lymphocytic reaction exhibited a marked elevation only in LDH2 relative activity, presumably associated with the specific (secretory) function of epithelial cells. The elevation of H-subunit content, a parameter characteristic of both thymic components (lymphoid and epithelial), correlated closely with a poor clinical condition in patients several years after surgery.

Immunological consequences of dioctyltin dichloride (DOTC)-induced thymic injury

Inbred rats fed diets containing 75 ppm dioctyltin dichloride (DOTC) for 8 or 12 weeks demonstrated marked reduction in thymic weight. This reduction was accompanied by a decrease in the number of W3/25 positive phenotypic circulating lymphocytes and an impaired ability to respond to suboptimal mitogenic stimulation. Responsiveness to alloantigenic stimulation, as measured by mixed leucocyte reactions, was depressed in DOTC-fed animals whereas no effect on natural cytotoxicity in nonimmunized treated or control rats was evident. No difference was found in the ability of treated compared to untreated animals to mount specific antibody responses against sheep red blood cells, and no evidence was found to indicate toxicity to lymphocytes in vivo. The investigation showed that DOTC administration resulted in a selective immunodeficiency.

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.