A tri-modal distribution of age-of-onset in female patients with myasthenia gravis is associated with the gender-related clinical differences.

BACKGROUND: A tri-modal distribution of age-at-onset emerged among females patients with myasthenia gravis (MG) in our database. This finding may be indicative of different gender-based disease mechanisms. METHODS: We retrospectively reviewed the files of 127 MG patients for the clinical, serology and thymus pathology according to their age at disease onset: ≤40 years (early-onset, EOMG), 40-70 years (intermediate-onset, IOMG) and >70 years (late-onset, LOMG). RESULTS: EOMG was more common among females, and IOMG was more common among males. Ocular MG was more common among the male MG patients with an IOMG. Patients with EOMG had lower rates of positive anti-acetylcholine receptor (anti-AChR). IOMG females, but not IOMG males, had lower rates of positive anti-AChR. IOMG and EOMG females had high rates of thymic hyperplasia, while EOMG males had high rates of thymoma. Comorbidity with autoimmune diseases was common among females with IOMG and LOMG. CONCLUSIONS: The prevalence of IOMG was the reason for the trend reversal of MG prevalence between genders. The clinical features of patients with IOMG differed between genders in the rates of positive anti-AChR, follicular hyperplasia of the thymus and comorbidity with autoimmune diseases. This may suggest a different gender-based mechanism of immune intolerance towards AChR and other antigens.

CD4+ FoxP3+ T regulatory cell subsets in myasthenia gravis patients.

Although myasthenia gravis (MG) is a classic autoantibody-mediated disease, T cells are centrally involved in its pathogenesis. In recent years a number of studies have analyzed the role of CD4+ FoxP3+ regulatory T cells (Treg) in the disease with contradictory results. Here, the generation of Treg was significantly reduced in thymoma as compared to thymic hyperplasia and normal thymus tissue (p=0.0002). In the peripheral blood, Treg subsets classified according to CD49d, HELIOS and CD45RA expression changed after thymectomy and in the long-term course of immunosuppression. Compared to healthy volunteers the frequency of CD45RA+FoxP3low Treg was reduced in MG patients in general (p=0.037) and in particular in patients without immunosuppression (p=0.036). In our study, thymectomy and immunosuppressive treatment were associated with changes in Treg subpopulations. The reduced frequency of CD45RA+FoxP3low Treg we observed in MG patients might play a role in MG pathogenesis.

Systemic immunostimulation induces glucocorticoid-mediated thymic involution succeeded by rebound hyperplasia which is impaired in aged recipients.

The thymus is the central organ involved with T-cell development and the production of naïve T cells. During normal aging, the thymus undergoes marked involution, reducing naïve T-cell output and resulting in a predominance of long-lived memory T cells in the periphery. Outside of aging, systemic stress responses that induce corticosteroids (CS), or other insults such as radiation exposure, induce thymocyte apoptosis, resulting in a transient acute thymic involution with subsequent recovery occurring after cessation of the stimulus. Despite the increasing utilization of immunostimulatory regimens in cancer, effects on the thymus and naïve T cell output have not been well characterized. Using both mouse and human systems, the thymic effects of systemic immunostimulatory regimens, such as high dose IL-2 (HD IL-2) with or without agonistic anti-CD40 mAbs and acute primary viral infection, were investigated. These regimens produced a marked acute thymic involution in mice, which correlated with elevated serum glucocorticoid levels and a diminishment of naïve T cells in the periphery. This effect was transient and followed with a rapid thymic "rebound" effect, in which an even greater quantity of thymocytes was observed compared to controls. Similar results were observed in humans, as patients receiving HD IL-2 treatment for cancer demonstrated significantly increased cortisol levels, accompanied by decreased peripheral blood naïve T cells and reduced T-cell receptor excision circles (TRECs), a marker indicative of recent thymic emigrants. Mice adrenalectomized prior to receiving immunotherapy or viral infection demonstrated protection from this glucocorticoid-mediated thymic involution, despite experiencing a substantially higher inflammatory cytokine response and increased immunopathology. Investigation into the effects of immunostimulation on middle aged (7-12 months) and advance aged (22-24 months) mice, which had already undergone significant thymic involution and had a diminished naïve T cell population in the periphery at baseline, revealed that even further involution was incurred. Thymic rebound hyperplasia, however, only occurred in young and middle-aged recipients, while advance aged not only lacked this rebound hyperplasia, but were entirely absent of any indication of thymic restoration. This coincided with prolonged deficits in naïve T cell numbers in advanced aged recipients, further skewing the already memory dominant T cell pool. These results demonstrate that, in both mice and humans, systemic immunostimulatory cancer therapies, as well as immune challenges like subacute viral infections, have the potential to induce profound, but transient, glucocorticoid-mediated thymic involution and substantially reduced thymic output, resulting in the reduction of peripheral naive T cells. This can then be followed by a marked rebound effect with naïve T cell restoration, events that were shown not to occur in advanced-aged mice.

The thymus in autoimmune Myasthenia Gravis: Paradigm for a tertiary lymphoid organ.

In autoimmune Myasthenia Gravis (MG), a neuromuscular disease generally mediated by autoantibodies against the acetylcholine receptor (AChR), the muscle is the target organ of the autoimmune attack, while the thymus seems to be the primary production site of the autoantibodies. In the majority of patients with anti-AChR antibodies, it is characterized by the presence of germinal centers, which contain B cells that produce anti-AChR antibodies. In this review, we summarize recent results regarding neoangiogenic processes, cell infiltration and modified chemokine expression in the MG thymus, which are typical features of secondary lymphoid organs. The structural and functional changes in the MG thymus therefore allow us to declare it to be an archetype for tertiary lymphoid neogenesis providing optimal settings for the interaction between lymphocytes and antigen presenting cells in order to elicit an immune response. We further discuss factors that may have a key role in the transformation of the MG thymus into a tertiary lymphoid organ, such as IFN type I and dsRNA signaling. These factors could also be of importance in other autoimmune diseases, especially those characterized by tertiary lymphoid neogenesis.

IL-2 and proteoglycans synergistically induce antigen-specific B-cell responses--a possible immune response in the hyperplastic myasthenia thymus.

To understand developmental mechanisms of effector B-cells in the hyperplastic MG thymus, we have evaluated immunological roles of IL-2 and the 100-kDa haemopoietic biglycan, because the number of their producers increases pathologically there. When these two factors were added to an immune system together, the number of antibody-producing cells was markedly increased in a synergistic fashion. Further, IL-2 and the conditioned medium of myoid cells induced immunoglobulin isotype switches, suggesting that new B-cell stimulatory microenvironments were generated in the hyperplastic thymus. In relation to this, we also discuss a new biological feature, an immunomodulator, of conventional biglycan and decorin.

Thymus involvement in early-onset myasthenia gravis.

It has long been established that the thymus plays a central role in autoimmune myasthenia gravis (MG) because of either thymoma or thymic hyperplasia of lymphoproliferative origin. In this review, we discuss thymic changes associated with thymic hyperplasia and their implications in the development of an autoimmune response against the acetylcholine receptor (AChR).The hyperplastic MG thymus displays all the characteristics of tertiary lymphoid organs (TLOs): neoangiogenic processes with high endothelial venule and lymphatic vessel development, chemokine overexpression favoring peripheral cell recruitment, and ectopic germinal center development. As thymic epithelial cells or myoid cells express AChR, a specific antigen presentation can easily occur within the thymus in the presence of recruited peripheral cells, such as B cells and T follicular helper cells. How the thymus turns into a TLO is not known, but local inflammation seems mandatory. Interferon (IFN)-ß is overexpressed in MG thymus and could orchestrate thymic changes associated with MG. Knowledge about how IFN-ß is induced in MG thymus and why its expression is sustained even long after disease onset would be of interest in the future to better understand the etiological and physiopathological mechanisms involved in autoimmune MG.

Clinical features of patients with myasthenia gravis associated with autoimmune diseases.

We investigated the incidence and clinical features of patients with myasthenia gravis (MG) associated with autoimmune diseases. Associated autoimmune diseases were found in 28 of 142 consecutive Japanese MG patients (19.7%), amongst which Graves' disease (7.7%) and Hashimoto's thyroiditis (4.2%) were predominant. The clinical features of MG patients with Graves' disease were different from those of MG patients without autoimmune diseases in terms of age at onset of MG symptoms (35.5 +/- 4.0 years and 49.0 +/- 1.7 years; P < 0.05), positivity for the anti-acetylcholine receptor antibody (44.4% and 89.8%; P < 0.05), and association with thymic hyperplasia (72.7 and 17.9%; P < 0.05). The therapeutic outcome of MG patients with Graves' disease and that of those without autoimmune diseases were not significantly different. Further studies should be performed to investigate whether MG associated with Graves' disease is a distinct subtype of MG.

PD-L1, PD-1, CD4, and CD8 expression in neoplastic and nonneoplastic thymus.

The checkpoint protein programmed cell death ligand-1 protein (PD-L1) binds to its receptor (PD-1) activating the PD-L1/PD-1 pathway, an important therapeutic target. There is limited information regarding PD-L1 and PD-1 expression in thymic lesions. Sections from nonneoplastic thymi (n = 20), thymomas World Health Organization types A, AB, B1, B2, and B3 (n = 38) and thymic squamous cell carcinoma (n = 8) were stained for PD-L1 (clone SP142; Spring BioScience), PD-1 (MRQ22; Cell Marque), CD4 (clone SPO32; Cell Marque), and CD8 (JCB117; Ventana). Immunoreactivity for each antibody was classified as focal or diffuse and scored as follows: 0, negative; 1%-5%, 1+; 6%-20%, 2+; and >20%, 3+. The proportions of cases expressing PD-L1, PD-1, CD4, and C8 at score ≥1+ were compared by diagnosis, using χ2 statistics. PD-L1 was expressed in 90% of nonneoplastic thymi, 92% of thymomas, and 50% of carcinomas, with significantly higher scores (P < .01) in B2 and B3 thymomas and carcinomas than in AB and B1 thymomas; PD-L1 was diffuse in most B2 and B3 thymomas and focal in carcinomas. PD-1 was focally expressed, and mostly with scores 1+, in 55% of nonneoplastic thymi, 63% of thymomas, and 37.5% of carcinomas. CD4+ and CD8+ cells were diffusely distributed with scores 3+ in all lesions other than B3 thymomas and carcinomas. The latter showed CD4+ cells mostly at the interface between neoplastic cells and stroma. PD-L1 and PD-1 are not expressed in similar locations and cellular proportions in thymic lesions, raising a question as to whether the PD-L1/PD-1 pathway is an actionable therapeutic target in these lesions.

[Thymus CT scan and thymoma associated antibodies in myasthenia gravis with thymoma].

OBJECTIVE: To investigate the clinical significance of the serum anti-titin, anti-ryanodine receptor (RyR) antibody level and thymus CT scan in the diagnosis of myasthenia gravis with thymoma. METHODS: Totally 32 patients with myasthenia gravis who had received thymectomy were included in the study. Abnormalities were shown under CT scan of thymus in all these patients. The relationships were studied among the pathological diagnosis, CT findings, and serum level of thymoma associated antibodies: anti-titin and anti-RyR antibodies. RESULTS: The pathological diagnosis of thymoma was made in 21 patients and thymus hyperplasia in 11 patients after operation. The sensitivity of CT scan in the diagnosis of thymomas was 90.5%, the specificity of serum thymoma associated antibodies in the diagnosis of thymoma was 100%. CONCLUSION: The thymoma-associated antibodies test is helpful in the differential diagnosis of thymomas and thymus hyperplasia; when combined with CT scan, it may achieve high sensitivity in the diagnosis of the thymoma.

Graves' Patient with Thymic Expression of Thyrotropin Receptors and Dynamic Changes in Thymic Hyperplasia Proportional to Graves' Disease Activity.

Thymic hyperplasia is frequently observed in Graves' disease. However, detectable massive enlargement of the thymus is rare, and the mechanism of its formation has remained elusive. This case showed dynamic changes in thymic hyperplasia on serial computed tomography images consistent with changes in serum thyrotropin receptor (TSH-R) antibodies and thyroid hormone levels. Furthermore, the patient's thymic tissues underwent immunohistochemical staining for TSH-R, which demonstrated the presence of thymic TSH-R. The correlation between serum TSH-R antibody levels and thymic hyperplasia sizes and the presence of TSH-R in her thymus suggest that TSH-R antibodies could have a pathogenic role in thymic hyperplasia.

Cellular aspects of myasthenia gravis.

Several cellular aspects were investigated in a large series of patients with MG. First, non-Ag-specific proliferation was tested by measuring the response to r-IL2. Thymocytes from most MG patients showed hyperactivity to r-IL2. Peripheral blood lymphocytes (PBL) from some patients also showed a high response to r-IL2. These responding patients were generally those tested before thymectomy, presenting a high anti-AChR Ab titer and a severe form of the disease. Second, Ag-specific proliferation of MG PBL was assayed using 8 synthetic peptides corresponding to selected domains of torpedo or human AChR. Only 2 peptides gave a positive response in a significant number of patients, essentially in those presenting high anti-AChR Ab titer. The first is located near the alpha-bungarotoxin binding site and the second is in a cytoplasmic domain, according to models predicting the AChR transmembrane orientation. The positive results were essentially obtained with the human peptides; the corresponding torpedo peptides were positive in very few patients. Both human and torpedo peptides which include a part of the alpha-bungarotoxin binding site were negative. Finally, although morphological abnormalities were clearly visible in thymic hyperplasia, no correlation could be established between the thymus type and the cellular proliferation either to r-IL2, or to the peptides. Overall, our data indicate that cell-dependent mechanisms participate in the pathogenesis of MG, but the level of their involvement deserves further investigation.

Myasthenia gravis: monoclonal antihuman acetylcholine receptor antibodies used to analyze antibody specificities and responses to treatment.

We investigated the heterogeneity of serum antibodies to acetylcholine receptor (AChR) by competition with nine antihuman monoclonal antibodies in a cross-sectional study of 36 patients with myasthenia gravis (MG), and in three who showed clinical improvement associated with decrease in total anti-AChR following immunologic treatment. Two specificities were more prevalent in patients without thymoma, an done of these was more prevalent in cases beginning before age 40. Some specificities were stable during serial studies, whereas other fluctuated. We found evidence of three groups of antibody specificities that had different control mechanisms and may define different regions of the receptor.

Linkage of HLA to myasthenia gravis and genetic heterogeneity depending on anti-titin antibodies.

BACKGROUND: MG is an autoimmune disease of the neuromuscular junction. MG with thymus hyperplasia has been associated with, but not genetically linked to, the HLA-DR3 haplotype. OBJECTIVE: To re-evaluate the association of HLA with MG in 656 patients with generalized disease and to test linkage of HLA to MG with thymus hyperplasia. METHOD: Patients were genotyped for HLA-DRB1. Data analysis included case-control comparisons after subgrouping patients by thymus histopathology. The transmission of parental alleles to MG offspring with thymus hyperplasia was studied in simplex families using the transmission/disequilibrium test (TDT) as a test of linkage. RESULTS: MG with thymus hyperplasia was positively associated with DR3 (OR = 4.5, p = 1 x 10(-6)) and negatively associated with DR7 (OR = 0.28, p = 1 x 10(-6)), based on both case-control comparisons and TDT. No association was detected with thymomas. Conversely, patients who lacked thymus anomalies but expressed anti-titin antibodies (ATA) had an increase of DR7 (OR = 2.08, p = 4 x 10(-3)) and a decrease of DR3 (OR = 0.33, p = 9 x 10(-3)). CONCLUSIONS: The authors established linkage of HLA to MG and thymus hyperplasia, defining the MYAS1 locus. Moreover, DR3 and DR7, or closely linked genes, have opposing effects on MG phenotypes. Nonthymomatous patients with ATA may be a pathogenetically distinct subset of MG patients.

Immunohistological studies of the thymus in myasthenia gravis. Correlation with clinical state and thymocyte culture responses.

In frozen sections of thymus from 9 out of 12 myasthenia gravis patients, the medulla contained follicles of B lymphocytes with germinal centres showing the same immunofluorescence staining pattern as is seen normally in reactive lymphoid tissues. Only 1 similar follicle was seen in 9 normal thymus samples. There was a positive association between the extent of germinal centres, plasma anti-acetylcholine receptor (AChR) titre, and spontaneous anti-AChR production by thymocytes in vitro. These thymic changes were not universally found, and are thus probably not central to the initiation of myasthenia. Between the follicles, in 9 cases, there was an apparent increase in interdigitating cells with closely associated 'inducer' (OKT4+)T lymphocytes. Thymic antigen presenting cells--either here or in the germinal centres--could be involved in breaking self-tolerance, or in perpetuating the autoimmune response, and it may be their removal that is therapeutic.

Rabbit antiserum to a citric acid extract of human skeletal muscle staining thymomas from myasthenia gravis patients.

Rabbit antiserum to a citric acid extract of human skeletal muscle (CA) stained both the cell membrane and the cross-striational bands of skeletal muscle cells. The rabbit antiserum also stained the cell membrane of epithelial thymoma cells from myasthenia gravis (MG) patients. Normal and hyperplastic thymus tissue were not stained, apart from scattered myoid thymic cells. Absorption of the antiserum with CA abolished staining of the thymoma, indicating that human skeletal muscle and epithelial thymoma cells possess common antigens.

Studies on the thymus from patients with multiple sclerosis and myasthenia gravis.

The thymus glands which were excised for therapy (myasthenia gravis; MG) or experimental therapy (multiple sclerosis; MS) were compared to thymic biopsies from patients undergoing cardiac surgery. There was no difference in the weight or total cells of MG and MS thymuses or of the cell density of control, of MG or MS glands. Only 1 of 25 MS thymuses was hyperplastic, as were 2 of 9 of the MG thymuses and none of the controls. Several differences were noted for thymic lymphocyte proliferation to mitogenes in MS patients and to antigens in MS and MG patients. Ms thymuses had a decreased stimulation index to antithymocyte globulin and to optimal concentrations of pokeweed mitogen. Myasthenia gravis thymuses showed a significantly increased stimulation of myelin basic protein. The % B and % T cell counts were normal for the MS patients. No differences were noted in the incidence of mixed lymphocyte reactions between thymocytes and peripheral lymphocytes in the three groups. Fresh thymic lymphocytes did not suppress concanavalin A stimulated lymphocyte proliferation. It is not known if the differences in lymphocyte proliferation between MS, MG, and control thymuses represent a primary or secondary change.

Myasthenia gravis: immunohistological heterogeneity in microenvironmental organization of hyperplastic and neoplastic thymuses suggesting different mechanisms of tolerance breakdown.

Four samples of thymoma obtained from patients affected by myasthenia gravis have been immunohistologically analysed on cryostat sections using a panel of antisera and monoclonal antibodies specific for antigens which define different stages of intrathymic lymphocyte differentiation and antigens specific for different types of thymic epithelial cells (cortical, medullary). When the thymoma samples were compared to age-matched normal thymuses and hyperplastic thymuses obtained from patients with myasthenia gravis some evident microenvironmental differences could be demonstrated using these reagents. In all the thymoma samples in fact the neoplastic lobules appeared as grossly enlarged cortical-type areas, formed by accumulations of T lymphocytes exhibiting the cortical immature phenotype (TdT+, T6+, etc.) within a network of putatively neoplastic epithelial cells characterized by cortical phenotype as defined by reactivity with various monoclonal antibodies (RFD4-, MR3+). These 'cortical' epithelia showed some abnormal features such as lack or irregular distribution of HLA-DR and enhanced keratin expression. Small areas of 'medullary' differentiation could be observed in 3/4 thymoma samples. In thymic hyperplasia, on the other hand, the cortical areas appeared somewhat compressed (but comparable to those observed in normal age-matched samples) by enlarged medullary areas. The expansion of medullary areas was due to the infiltration of 'peripheral' lymphoid tissue intruding through the extraparenchymal zone and forming organized B and T areas. These observations are discussed in the light of the clinical heterogeneity observed in myasthenia gravis.

Mucosa-associated lymphoid tissue of the thymus hyperplasia vs lymphoma.

In the thymus, the relationship between lymphofollicular hyperplasia and mucosa-associated lymphoid tissue (MALT)-type lymphoma is uncertain. We analyzed 14 cases with a diagnosis of thymic follicular hyperplasia in patients with connective tissue disease (n = 2), myasthenia gravis (n = 11), or both (n = 1). In 11 cases, well-defined reactive lymphoid follicles were surrounded by a continuous layer of medullary epithelial cells. A polyclonal rearrangement of the immunoglobulin heavy chain gene (IgH) was observed. In 3 cases, ill-defined lymphoid follicles with sheets of centrocytic-like B cells disrupting the medullary cytokeratin epithelial network were observed on certain sections. These cells expressed the phenotypic features of memory B cells with CD20, CD79a, and bcl-2 positivity and CD5, CD10, CD23, and bcl-6 negativity, and a monoclonal rearrangement of the IgH gene was detected. Appropriate sampling, cytokeratin staining, and molecular analyses may help to identify early MALT-type lymphoma developing in the setting of thymic lymphofollicular hyperplasia.

The role of humoral and cellular immune factors in neuromuscular block in myasthenia gravis.

The neuromuscular block of myasthenia gravis appears to be due to decreased and abnormal responsiveness of the motor end plates to transmitter, and perhaps a decreased number of functioning end plates. The presence in myasthenic patients of serum globulins that bind to a bariety of cellular and subcellular components, and of thymic abnormalities, has encourage the search for humoral and cellular immune factors that may be responsible for the anatomic and functional defects. Attempts to demonstrate neuromuscular blocking activity in the serum have been inconclusive. While 30% to 48% of myasthenic patients have globulins that react with muscle membrane, striations, ribonucleporotein, and thymic epithelial cells, these globulins have not been shown to react with the end plate or acetylcholine receptor, or to impair neuromuscular transmission. Antinuclear, rheumatoid, antimitochondrial antithyroid, anti-smooth-muscle, and anti-gastric-parietal cell factors are found in the serum of 3% to 16% of myasthenic patients, but these are much more commonly present in other diseases. However, antibodies to acetylcholine receptor from electric tissue, which were recently reported in the serum of three fourths of myasthenic patients, may prove to be more directly related to the neuromuscular block. While the majority of myasthenic patients have thymic abnormalities, including thymoma in 9% of patients and hyperplastic thymus in 66% of patients, the remaining 25% of patients have normal, involuted, or undetectable thymus. Thymectomy has a favorable effect in about two thirds of myasthenic patients, but about one third of patients have no benefit. Thirty-two patients have been described who developed myasthenia gravis after total thymectomy and presumably in the absence of the thymus. Thymus lymphocytes of myasthenic patients have some differences from those of normal subjects, including a greater proportion of B cells, but their significance is not known. Attempts to demonstrate neuromuscular blocking activity in the thymus of myasthenic patients have been inconclusive. Blood lymphocytes of myasthenic patients also have some differences from those of normal subjects, including a lower proportion of T cells. The proportion of both T and B cells increased following thymectomy. While studies on the immunological reactivity of lymphocytes from myasthenic patients have shown some differences from those of normal subjects, neuromuscular blocking activity has not been demonstrated in these cells or in their extracts. There is increasing evidence that the neuromuscular block of myasthenia gravis is due to alteration of the acetylcholine receptor. The recent reports of antibodies to acetylcholine receptor in the serum of myasthenic patients suggests that these may be responsible for the neuromuscular block, but such action, and the cause of antibody release, remain to be determined.

Myasthenia gravis, thymectomy, and antiacetycholine receptor antibody.

The antiacetylcholine receptor antibody was titered in the serum of 63 patients with myasthenia gravis (MG) and 20 control healthy subjects. The titer was significantly high in 92% of MG patients in contrast with none of the controls and no correlation was found with the thymus pathology and the severity of the disease. The titer decreased after thymectomy almost steadily with the improvement of the myasthenic signs. The role of the antibody in the pathogenesis of the disease is discussed.