Suppressor lymphocytes in myasthenia gravis and effect of adult thymectomy

Immunogenetic heterogeneity and associated autoimmune disorders in myasthenia gravis: a population-based survey in the province of Ferrara, northern Italy

INTRODUCTION

The well-established relationship between myasthenia gravis (MG) and HLA antigens varies among different ethnic groups. In Caucasians B8 and/or DR3 alleles have been found associated with young MG women without thymoma and with high titres of acetylcholine-receptor antibody (AChR Ab). An increased frequency of haplotype HLA-A3, B7 and/or DR2 has been observed in older MG patients with low AChR Ab levels. So far, there is no convincing evidence for an association between a specific haplotype HLA and ocular MG or MG with thymoma. MG subjects often show other concurrent autoimmune disorders suggesting a more general inherited predisposition to autoimmunity. We performed a community-based study to verify the HLA-A, B, C, DR and DQ profile on ethnically homogeneous MG patients and with the aim to estimate the frequency of concurrent autoimmune diseases and to compare HLA phenotypes to autoimmune status in different MG patients groups.

METHODS

Forty-seven patients, living in the province of Ferrara, were followed-up in our neurologic department and typed for HLA Antigens. In addition a set of immunological laboratory tests was performed.

RESULTS

We found a trend towards an increased B8 and DR3 frequencies in total affected population; an association between B8 allele and early onset of generalized MG sustained by thymic hyperplasia. The DR3 allele is statistically associated with the presence of additional autoimmune disorders.

CONCLUSIONS

Our data support the hypothesis of a genetically-based heterogeneity of the disease and show an increased prevalence of associate autoimmune conditions in MG patients.

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.

Asymptomatic oligoclonal CSF IgG and progressive increase of intrathecal IgG synthesis in a patient with myasthenia gravis treated with thymectomy--a 4-years follow-up

A young woman is described who had myasthenia gravis which was favourably influenced by thymectomy. Although there was no evidence for another neurological disease over 7.5 years of clinical observation and computed tomography as well as visual evoked response were normal, CSF studies over 0.5 years prior to and 3.5 years after thymectomy revealed persistent mononuclear pleocytosis, high CSF IgG index, oligoclonal IgG bands in CSF, and increasing IgG synthesis rate within the CNS, reflecting a continuous local humoral immune response. CSF/serum ratios of antibodies to acetylcholine receptors (AChR) were continuously lower than CSF/serum IgG ratios, contradicting intrathecal AChR antibody production. Proportion of total T cells was slightly higher in CSF than peripheral blood, while active T cells were lower in CSF. CSF lymphocytes did not proliferate on PHA stimulation but responded in allogeneic mixed lymphocyte culture. B cells were 4% in CSF and 4.5% in peripheral blood, but 227 IgG, 0 IgA and 0 IgM producing cells were detected among 20 X 10(3) CSF lymphocytes, compared to 5, 4 and 0 in 20 X 10(3) peripheral blood lymphocytes. This patient represents an in vivo 'experiment' regarding influence of thymectomy on CSF compartment constituents. The present study also shows that an individual can be clinically healthy despite continuous and pronounced intrathecal immune response.

Thymectomy-induced decrease in T gamma cells and OKT8+ cells in multiple sclerosis

Studies were performed on lymphocytes from patients with multiple sclerosis before and after thymectomy (group I) and before and after thymectomy and azathioprine therapy (group II), and from matched control patients with multiple sclerosis, control patients with other neurological diseases, and healthy control subjects. Following treatment the percentage of T gamma cells in both group I and group II patients decreased from above the mean normal control levels to below this level; OKT8+ cell numbers in group I became lower than in any of the control groups; the percentage of concanavalin A-induced suppressor activity, which was initially normal, fell in group II and suggestively but not significantly in group I; and total blood lymphocytes in group I decreased from normal to below control levels. Other tests showed no significant changes with therapy. No significant difference in changes in clinical status were observed after one year in the treated patients compared with matched controls.

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

Using monoclonal anti-T-cell antibodies, we have studied peripheral blood T-cell subsets in 53 patients with myasthenia gravis before and after thymectomy (Tx). Before Tx, the mean OKT4/OKT8 ratio was higher in patients than in controls. Furthermore patients showed a high number of cells reacting simultaneously with the OKT4 and OKT8 antibodies. Shortly after surgery, the helper/suppressor ratio was increased in most of the patients, and the doubly reactive subset decreased to normal levels. However, 6 to 12 months after Tx the OKT4/OKT8 ratio was significantly decreased, particularly in patients showing clinical improvement. The percentage of total T cells was slightly but significantly reduced. A group of 14 patients studied more than 2 years after Tx presented very low OKT4/OKT8 ratios. Thymectomy in MG appears to lead to a gradual decrease of the T-helper subset which could contribute to its favorable effect on the course of the disease.

Lymphocyte populations in patients with myasthenia gravis. Influence of thymectomy and immunosuppressive drugs

The T/B peripheral blood lymphocyte ratio was evaluated in 51 patients with myasthenia gravis by means of the rosette test and HTLA. Total T cells and T gamma and Tmu were decreased while B lymphocytes were increased. E-active rosettes were also above the normal range. The previous thymectomy and/or immunosuppressive treatment restored the T lymphocytes identified by HTLA to normal range while those identified by E rosettes were still reduced. This difference may be due to the different stages of T lymphocyte maturation.

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.

Changes in human T lymphocytes after thymectomy and during senescence

Peripheral lymphocytes from individuals who had been thymectomized in adult life for myasthenia gravis (MG) or for other, nonimmunological reasons showed a moderate decrease in proliferative response capacity to several T-cell mitogens as compared to lymphocytes from normal individuals. The decrease of the response to mitogens and allogeneic lymphocytes was 20-30% within 5 years after thymectomy and about 50% more than 15 years after thymectomy. A comparable decrease in lymphocyte proliferative response capacity was found in healthy aged humans (68-97 years old). Analysis of T lymphocytes from both aged and thymectomized individuals with monoclonal (OKT) antibodies showed a similar pattern: the proportion of T lymphocytes binding OKT6, OKT10, or OKI1 were found. A biochemical parameter for human T-cell differentiation, the lactate dehydrogenase (LDH) isoenzyme pattern, showed a significantly lower H/M ratio in the group of elderly people compared to young individuals. Furthermore, among patients thymectomized for MG, a significant correlation was observed between the LDH isoenzyme pattern of the T lymphocytes and the proliferative response to mitogens of these cells. In contrast, in healthy thymectomized individuals the LDH isoenzyme pattern appeared to be normal. These findings indicate that, after thymectomy or involution of the thymus, at least part of the peripheral blood T lymphocytes have properties different from those of the cells of young individuals. These cells might represent immature and/or not fully differentiated lymphocytes.

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.

Defective mitogenic responses in myasthenia gravis and multiple sclerosis

Using in vitro lymphocyte proliferation induced by the phytomitogen concanavalin A (Con A), we investigated immune function and regulation in patients with myasthenia gravis (MG) and multiple sclerosis (MS). Unfractionated peripheral blood mononuclear cells of normal individuals responded to a wide range of ConA concentrations; the T cell fraction responded to a lesser degree and only to high concentrations. These findings suggest the presence of two receptors for ConA, one of high affinity present on a non-T cell accessory cell and the other of low affinity present on T cells. Contrasting defects in the level of response of unfractionated lymphocytes and T cells were found in patients with MG and MS. The peak response of T cells in the MG patients was 22.6 +/- 9.6 X 10(3) cpm (mean +/- SEM) compared with 54.6 +/- 6.5 X 10(3) for controls (p less than 0.05), while the response of unfractionated lymphocytes did not differ from that in controls. For MS patients, the unfractionated lymphocyte response was diminished: 56.3 +/-2.8 X 10(3) cpm versus 70.5 +/- 4.5 X 10(3) for controls (p less than 0.05), while the T cell response was normal. These results indicate a defect in the direct T cell response in MG; in contract, in MS the response requiring T cell-accessory cell interaction is abnormal.

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.

The effect of anti-thymocyte antiserum in progressive myasthenia gravis

The therapeutic effect of goat anti-human thymocyte antiserum globulin (ATG) was assessed in ten patients with myasthenia gravis. Five patients had undergone prior thymectomy. All subjects had far-advanced, debilitating and progressing disease poorly responsive to classic anticholinesterase therapy. Prolonged, low dose ATG therapy was used with 1.0-2.6 grams/protein administered intramuscularly over a 28-73 period. Depression of cellular immunity was observed with anti-thymocyte antiserum was more profound in patients with a prior thymectomy. Therapeutic responses of varying degrees were noted in 8 out of 10 patients. Completion of a course of ATG and discontinuation of the drug did not lead to acute relapse states. Follow-up examinations for over five years have been maintained. A mean remission period of approximately two years was observed. It is suggested that this therapy deserves further evaluation. Subjects with prior thymectomy and progressive disease may represent the most ideal candidates.

Myasthenia gravis: signs, symptoms, diagnosis, immunology, and current therapy

Myasthenia gravis is a neuromuscular disease that presents clinically as fluctuating weakness of one or more skeletal muscle groups. Weakness becomes more severe with exercise and improves with rest. The disease is caused by an autoimmune reaction at or near the post-synaptic nicotinic acetylcholine receptor. The results of this immune reaction are the lytic destruction of the post-synaptic membrane and a reduction in the number of acetylcholine receptors. Myasthenia gravis can be diagnosed by repetitive exercise of the involved muscles, administration of edrophonium (Tensilon), electrophysiologic testing, or demonstration of anti-acetylcholine receptor antibodies. When the myasthenic weakness is mild or limited to the extraocular muscles, it may be treated with acetylcholinesterase inhibitors. When the weakness is more severe and/or more generalized, immunotherapy is most often indicated. Prednisone or prednisone plus thymectomy is the most frequently used form of immunotherapy. Azathioprine, 6-mercaptopurine, plasmapheresis, or gamma globulin injections are other immunotherapeutic options that may be useful in selected patients. A large number of drugs may precipitate or exacerbate myasthenic weakness.

Immune disease and HLA associations with myasthenia gravis

In the late 1950's laboratory and clinical evidence suggested that myasthenia gravis was an autoimmune disorder. Since then a voluminous literature has developed documenting the many immunological abnormalities that occur in this condition. Recent findings point to a central disorder of immunoregulation. It is postulated that the disease occurs as a result of host genetic and environmental influences-the latter being, as yet unidentified and possibly a virus.

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.

Thymic hyperplasia and neoplasia: a review of current concepts

Although the term thymic hyperplasia is used most commonly to indicate the occurrence of germinal centers in the thymus, cognizance must be taken of the fact that such centers may occur in apparently normal thymuses in both children and adults. A concept of thymic compartmentalization is proposed with origin of germinal centers in the perivascular space (extraparenchymal compartment) of the thymus. These germinal centers contain a high percentage of B lymphocytes in contrast to the true thymic parenchyma. Although the significance of germinal centers in the thymus parenchyma. Although the significance of germinal centers in the thymus in myasthenia gravis remains controversial, removal of nonneoplastic thymus in this condition is of proven therapeutic value. A variety of neoplasms originating in the thymus have previously been lumped together under the single term "thymoma." It is apparent, however, that thymoma, thymic carcinoid, various lymphomas, and germ cell tumors that arise in the thymus differ not only pathologically but also in their clinical behavior. Thymoma is regarded as an epithelial neoplasm and ultrastucturally is characterized by many desmosomes and tonofilaments. The lymphocytes do not behave in a malignant manner, and lymphomas of the thymus should be sharply separated from true thymoma. Poorly differentiated thymic carcinoma and histiocytic lymphoma may be distinguishable only by the electron microscopic demonstration of desmosomes and filaments in the thymic carcinoma. The evidence that Hodgkin's disease of the thymus ("granulomatous thymoma") is not a variant of thymoma appears overwhelming. Lymphoblastic lymphoma of the thymus is a distinctive neoplasm that is especially prevalent in teenage males. High levels of terminal transferase characterize the lymphoblasts and there is a striking tendency for leukemia to occur. Thymic carcinoid is usually nonfunctional, although one-third of the reported cases are associated with Cushing's syndrome. On light microscopy a ribbon pattern and punctate necroses are characteristic of thymic carcinoids. Electron microscopic demonstration of many dense core granules is invaluable in establishing this diagnosis. An important clue to the diagnosis of thymic seminoma (a neoplasm that shows the same radiosensitivity as its testicular counterpart) is the frequent presence of epithelioid and giant cell granulomas and germinal centers. Separation of the various thymic neoplasms described not only is justifiable on pathologic grounds but is often essential for appropriate patient investigation and treatment.

Thymic lymphocytes in myasthenia gravis

Lymphocytes from the thymus glands of myasthenic patients and controls were characterized in terms of their percentages of B- and T-cells and their ability to stimulate the proliferation of autologous peripheral blood lymphocytes. Percentages of B- and T-cells were the same in the thymuses of myasthenic and control subjects. Autologous peripheral lymphocyte stimulation by thymocytes was observed in only 1 of 3 myasthenic patients, and this was with a thymus gland containing a thymoma. These results thus differ from those of other investigators.