Defects of immunoregulatory mechanisms in myasthenia gravis: role of IL-17

International audienceDeficient immunoregulation is consistently observed in autoimmune diseases. Here, we summarize the abnormalities of the T cell response in autoimmune myasthenia gravis (MG) by focusing on activation markers, inflammatory features, and imbalance between the different T cell subsets, including Th17 and regulatory T cells (T(reg) cells). In the thymus from MG patients, T(reg) cell numbers are normal while their suppressive function is severely defective, and this defect could not be explained by contaminating effector CD127(low) T cells. A transcriptomic analysis of T(reg) cell and conventional T cell (T(conv) ; CD4(+) CD25(-) cells) subsets pointed out an upregulation of Th17-related genes in MG cells. Together with our previous findings of an inflammatory signature in the MG thymus and an overproduction of IL-1 and IL-6 by MG thymic epithelial cells (TEC), these data strongly suggest that T cell functions are profoundly altered in the thymic pathological environment. In this short review we discuss the mechanisms of chronic inflammation linked to the pathophysiology of MG disease

The chemokine CXCL13 is a key molecule in autoimmune myasthenia gravis

Myasthenia gravis (MG) is associated with ectopic germinal centers in the thymus. Thymectomy and glucocorticoids are the main treatments but they induce operative risks and side effects, respectively. The aim of this study was to propose new therapies more efficient for MG. We hypothesized that molecules dysregulated in MG thymus and normalized by glucocorticoids may play a key role in thymic pathogenesis. Using gene chip analysis, we identified 88 genes complying with these criteria, the most remarkable being the B-cell chemoattractant (CXCL13). Its expression was increased in thymus and sera of glucocorticoid-untreated patients and decreased in response to treatment in correlation with clinical improvement. Normal B cells were actively chemoattracted by thymic extracts from glucocorticoid-untreated patients, an effect inhibited by anti-CXCL13 antibodies. In the thymus, CXCL13 was preferentially produced by epithelial cells and overproduced by epithelial cells from MG patients. Altogether, our results suggest that a high CXCL13 production by epithelial cells could be responsible for germinal center formation in MG thymus. Furthermore, they show that this gene is a main target of corticotherapy. Thus, new therapies targeting CXCL13 could be of interest for MG and other autoimmune diseases characterized by ectopic germinal center formation

The thymic theme of acetylcholinesterase splice variants in myasthenia gravis

International audienceAbstract Cholinergic signaling and acetylcholinesterase (AChE) influence immune response and inflammation. Autoimmune myasthenia gravis (MG) is mediated by antibodies to the acetylcholine receptor and current therapy is based on anti-AChE drugs. MG is associated with thymic hyperplasia, showing signs of inflammation. The objectives of this study were to analyze the involvement of AChE variants in thymic hyperplasia. We found lower hydrolytic activities in the MG thymus compared with adult controls, accompanied by translocation of AChE-R from the cytoplasm to the membrane and increased expression of the signaling protein kinase PKC-βII. To explore possible causal association of AChE-R changes with thymic composition and function, we used an AChE-R transgenic model and showed smaller thymic medulla compared with strain-matched controls, indicating that AChE-R overexpression interferes with thymic differentiation mechanisms. Interestingly, AChE-R transgenic mice showed increased numbers of CD4+CD8+ cells that were considerably more resistant in vitro to apoptosis than normal thymocytes, suggesting possibly altered positive selection. We further analyzed microarray data of MG thymic hyperplasia compared with healthy controls and found continuous and discrete changes in AChE-annotated GO categories. Together, these findings show that modified AChE gene expression and properties are causally involved in thymic function and development

Integrative analysis of methylome and transcriptome in human blood identifies extensive sex- and immune cell-specific differentially methylated regions

<div><p>The relationship between DNA methylation and gene expression is complex and elusive. To further elucidate these relations, we performed an integrative analysis of the methylome and transcriptome of 4 circulating immune cell subsets (B cells, monocytes, CD4⁺, and CD8⁺ T cells) from healthy females. Additionally, in light of the known sex bias in the prevalence of several immune-mediated diseases, the female datasets were compared with similar public available male data sets. Immune cell-specific differentially methylated regions (DMRs) were found to be highly similar between sexes, with an average correlation coefficient of 0.82; however, numerous sex-specific DMRs, shared by the cell subsets, were identified, mainly on autosomal chromosomes. This provides a list of highly interesting candidate genes to be studied in disorders with sexual dimorphism, such as autoimmune diseases. Immune cell-specific DMRs were mainly located in the gene body and intergenic region, distant from CpG islands but overlapping with enhancer elements, indicating that distal regulatory elements are important in immune cell specificity. In contrast, sex-specific DMRs were overrepresented in CpG islands, suggesting that the epigenetic regulatory mechanisms of sex and immune cell specificity may differ. Both positive and, more frequently, negative correlations between subset-specific expression and methylation were observed, and cell-specific DMRs of both interactions were associated with similar biological pathways, while sex-specific DMRs were linked to networks of early development or estrogen receptor and immune-related molecules. Our findings of immune cell- and sex-specific methylome and transcriptome profiles provide novel insight on their complex regulatory interactions and may particularly contribute to research of immune-mediated diseases.</p></div

Methylome and transcriptome profiling in Myasthenia Gravis monozygotic twins.

OBJECTIVE: To identify novel genetic and epigenetic factors associated with Myasthenia gravis (MG) using an identical twins experimental study design. METHODS: The transcriptome and methylome of peripheral monocytes were compared between monozygotic (MZ) twins discordant and concordant for MG, as well as with MG singletons and healthy controls, all females. Sets of differentially expressed genes and differentially methylated CpGs were validated using RT-PCR for expression and target bisulfite sequencing for methylation on additional samples. RESULTS: >100 differentially expressed genes and approximately 1800 differentially methylated CpGs were detected in peripheral monocytes between MG patients and controls. Several transcripts associated with immune homeostasis and inflammation resolution were reduced in MG patients. Only a relatively few genes differed between the discordant healthy and MG co-twins, and both their expression and methylation profiles demonstrated very high similarity. INTERPRETATION: This is the first study to characterize the DNA methylation profile in MG, and the expression profile of immune cells in MZ twins with MG. Results suggest that numerous small changes in gene expression or methylation might together contribute to disease. Impaired monocyte function in MG and decreased expression of genes associated with inflammation resolution could contribute to the chronicity of the disease. Findings may serve as potential new predictive biomarkers for disease and disease activity, as well as potential future targets for therapy development. The high similarity between the healthy and the MG discordant twins, suggests that a molecular signature might precede a clinical phenotype, and that genetic predisposition may have a stronger contribution to disease than previously assumed

Central role of macrophages and nucleic acid release in Myasthenia Gravis thymus

International audienceObjective: Myasthenia gravis (MG) is a neuromuscular disease mediated by antibodies against the acetylcholine receptor (AChR). The thymus plays a primary role in AChR-MG and is characterized by a type I interferon (IFN) signature linked to IFN-β. We investigated if AChR-MG was characterized by an IFN-I signature in the blood, and further investigated the chronic thymic IFN-I signature.Methods: Serum levels of IFN-β and IFN-α subtypes, and mRNA expression for IFN-I subtypes and IFN-stimulated genes in PBMCs were analyzed. The contribution of endogenous nucleic acids in thymicexpression of IFN-I subtypes was investigated in human thymic epithelial cell cultures and the mouse thymus. By immunohistochemistry, thymic CD68+ and CD163+ macrophages were analyzed in AChR-MG.To investigate the impact of a decrease in thymic macrophages, mice were treated with an anti-CSF1R antibody. Results: No IFN-I signature was observed in the periphery emphasizing that the IFN-I signature is restricted to the MG thymus. Molecules mimicking endogenous dsDNA signalization (Poly(dA:dT) and 2’3’-cGAMP), or dexamethasone-induced necrotic thymocytes increased IFN-β and α-AChR expression by thymic epithelial cells, and in the mouse thymus. A significant decrease in thymic macrophages was demonstrated in AChR-MG. In mice, a decrease in thymic macrophages led to an increase of necrotic thymocytes associated with IFN-β and α-AChR expression. Interpretation: These results suggest that the decrease of thymic macrophages in AChR-MG impairs the elimination of apoptotic thymocytes favoring the release of endogenous nucleic acids from necrotic thymocytes. In this inflammatory context, thymic epithelial cells may overexpress IFN-β, which specifically induces α-AChR, resulting in self-sensitization and thymic changes leading to AChR-MG