The myasthenia gravis thymus: a rare source of human autoantibody-secreting plasma cells for testing potential therapeutics

Targeting autoimmune mechanisms by precision medicine in Myasthenia Gravis

Myasthenia Gravis (MG) is a chronic disabling autoimmune disease caused by autoantibodies to the neuromuscular junction (NMJ), characterized clinically by fluctuating weakness and early fatigability of ocular, skeletal and bulbar muscles. Despite being commonly considered a prototypic autoimmune disorder, MG is a complex and heterogeneous condition, presenting with variable clinical phenotypes, likely due to distinct pathophysiological settings related with different immunoreactivities, symptoms' distribution, disease severity, age at onset, thymic histopathology and response to therapies. Current treatment of MG based on international consensus guidelines allows to effectively control symptoms, but most patients do not reach complete stable remission and require life-long immunosuppressive (IS) therapies. Moreover, a proportion of them is refractory to conventional IS treatment, highlighting the need for more specific and tailored strategies. Precision medicine is a new frontier of medicine that promises to greatly increase therapeutic success in several diseases, including autoimmune conditions. In MG, B cell activation, antibody recycling and NMJ damage by the complement system are crucial mechanisms, and their targeting by innovative biological drugs has been proven to be effective and safe in clinical trials. The switch from conventional IS to novel precision medicine approaches based on these drugs could prospectively and significantly improve MG care. In this review, we provide an overview of key immunopathogenetic processes underlying MG, and discuss on emerging biological drugs targeting them. We also discuss on future direction of research to address the need for patients' stratification in endotypes according with genetic and molecular biomarkers for successful clinical decision making within precision medicine workflow.

Diagnostic value of antibody concentration ratio for treatment-refractory myasthenia gravis

OBJECTIVE

This study aimed to assess the diagnostic potential of the Antibody concentration ratio in identifying treatment-refractory myasthenia gravis (MG).

METHODS

A retrospective analysis was conducted on 116 MG patients who underwent antibody detection at least twice between June 1, 2015, and June 1, 2023. Demographic and clinical characteristics were collated to ascertain their association with refractory MG. The Antibody Concentration Ratio was applied to determine treatment response, using the International Consensus Guidance criteria as the reference standard. The area under nonparametric receiver operating characteristic curve (AUC), sensitivity, specificity, and accuracy were calculated to assess the diagnostic efficacy of the Antibody concentration ratio following consecutive immunotherapy relative to initial antibody concentrations for refractory MG.

RESULTS

19 out of 116 patients were unequivocally diagnosed with refractory MG. A significant correlation was found between the Antibody Concentration Ratio and refractory MG status in treatment-refractory and treatment-responsive patients. Subsequently, the AUC demonstrated the robust diagnostic capability of the Antibody concentration ratio for refractory MG, with an AUC of 0.8709 (95% CI: 0.7995-0.9422, p < 0.0001). The optimal cut-off value stood at 0.8903, exhibiting a sensitivity of 94.74% (95% CI: 75.36%-99.73%), a specificity of 68.04% (95% CI: 58.23%-76.48%), and accuracy of 72.41% (95% CI: 64.28%-80.54%).

CONCLUSION

Elevated Antibody Concentration Ratio is intrinsically linked with refractory MG and exhibits potential as an diagnostic biomarker for the condition.

Jchain-DTR Mice Allow for Diphtheria Toxin-Mediated Depletion of Antibody-Secreting Cells and Evaluation of Their Differentiation Kinetics

Antibody-secreting cells (ASCs) are generated following B cell activation and constitutively secrete antibodies. As such, ASCs are key mediators of humoral immunity whether it be in the context of pathogen exposure, vaccination or even homeostatic clearance of cellular debris. Therefore, understanding basic tenants of ASC biology such as their differentiation kinetics following B cell stimulation is of importance. Towards that aim, we developed a mouse model which expresses simian HBEGF (a.k.a., diphtheria toxin receptor (DTR)) under the control of the endogenous Jchain locus (or J-DTR). ASCs from these mice expressed high levels of cell surface DTR and were acutely depleted following diphtheria toxin treatment. Furthermore, proof-of-principle experiments demonstrated the ability to use these mice to track ASC reconstitution following depletion in 3 distinct organs. Overall, J-DTR mice provide a new and highly effective genetic tool allowing for the study of ASC biology in a wide range of potential applications.

Germinal centers are associated with postthymectomy myasthenia gravis in patients with thymoma

BACKGROUND AND PURPOSE

Germinal centers (GCs) can be observed in the thymic tissues of patients with thymoma-associated myasthenia gravis (MG). Although an association between thymic GCs and MG has been suggested, it is unknown whether the presence of GCs could predict the development of MG after the resection of thymoma, known as postthymectomy MG.

METHODS

We conducted a retrospective analysis of previously nonmyasthenic patients who underwent surgical removal of the thymoma. All available thymic tissue slides were rereviewed by a pathologist to assess for GCs. Patients were classified into GC-positive and GC-negative groups based on the presence of GCs. The incidence of postthymectomy MG was compared between the two groups, and the risk factors for postthymectomy MG were assessed.

RESULTS

Of the 196 previously nonmyasthenic patients who underwent thymoma resection, 21 were GC-positive, whereas 175 were GC-negative. Postthymectomy MG developed in 11 (5.6%) patients and showed a higher incidence in the GC-positive group than in the GC-negative group (33.3% vs. 2.3%, p < 0.001). No postoperative radiotherapy and the presence of GCs were risk factors for postthymectomy MG in the univariate analysis. In multivariate analysis, invasive thymoma (hazard ratio [HR] = 9.835, 95% confidence interval [CI] = 1.358-105.372), postoperative radiotherapy (HR = 0.160, 95% CI = 0.029-0.893), and presence of GCs (HR = 15.834, 95% CI = 3.742-67.000) were significantly associated with postthymectomy MG.

CONCLUSIONS

Thymic GCs may be a significant risk factor for postthymectomy MG. Even in patients with thymoma who do not show clinical symptoms of MG, postthymectomy MG should be considered, especially if thymic GCs are observed.

An interleukin 6 responsive plasma cell signature is associated with disease progression in systemic sclerosis interstitial lung disease

Systemic sclerosis (SSc) interstitial lung disease (ILD) is among the leading causes of SSc-related morbidity and mortality. Tocilizumab (TCZ, anti-IL6RA) has demonstrated a reduced rate of pulmonary function decline in two phase 2/3 trials (faSScinate and focuSSced) in SSc-ILD patients. We performed transcriptome analysis of skin biopsy samples collected in the studies to decipher gene networks that were potentially associated with clinical responses to TCZ treatment. One module correlated with disease progression showed pharmacodynamic changes with TCZ treatment, and was characterized by plasma cell (PC) genes. PC signature gene expression levels were also significantly increased in both fibrotic SSc and IPF lungs compared to controls. scRNAseq analyses confirmed that PC signature genes were co-expressed in CD38 and CD138 expressing PC subsets in SSc lungs. These data provide insights into the potential role of PC in disease progression and mechanisms of action of TCZ in fibrotic interstitial lung diseases.

Thymus antibody-secreting cells possess an interferon gene signature and are preferentially expanded in young female mice

Antibody-secreting cells (ASCs) are key contributors to humoral immunity through immunoglobulin production and the potential to be long-lived. ASC persistence has been recognized in the autoimmune thymus (THY); however, only recently has this population been appreciated in healthy THY tissue. We showed that the young female THY was skewed toward higher production of ASCs relative to males. However, these differences disappeared with age. In both sexes, THY ASCs included Ki-67⁺ plasmablasts which required CD154(CD40L) signals for their propagation. Single cell RNA-sequencing revealed that THY ASCs were enriched for an interferon responsive transcriptional signature relative to those from bone marrow and spleen. Flow cytometry confirmed that THY ASCs had increased levels of Toll-like receptor 7 as well as CD69 and major histocompatibility complex class II. Overall, we identified fundamental aspects of THY ASC biology which may be leveraged for future in depth studies of this population in both health and disease.

Thymus antibody-secreting cells: once forgotten but not lost

Antibody-secreting cells are essential contributors to the humoral response. This is due to multiple factors which include: 1) the ability to secrete thousands of antibodies per second, 2) the ability to regulate the immune response and 3) the potential to be long-lived. Not surprisingly, these cells can be found in numerous sites within the body which include organs that directly interface with potential pathogens (e.g., gut) and others that provide long-term survival niches (e.g., bone marrow). Even though antibody-secreting cells were first identified in the thymus of both humans and rodents in the 1960s, if not earlier, only recently has this population begun to be extensively investigated. In this article, we provide an update regarding the current breath of knowledge pertaining to thymus antibody-secreting cells and discuss the potential roles of these cells and their impact on health.

Novel pathophysiological insights in autoimmune myasthenia gravis

PURPOSE OF REVIEW

This review summarizes recent insights into the immunopathogenesis of autoimmune myasthenia gravis (MG). Mechanistic understanding is presented according to MG disease subtypes and by leveraging the knowledge gained through the use of immunomodulating biological therapeutics.

RECENT FINDINGS

The past two years of research on MG have led to a more accurate definition of the mechanisms through which muscle-specific tyrosine kinase (MuSK) autoantibodies induce pathology. Novel insights have also emerged from the collection of stronger evidence on the pathogenic capacity of low-density lipoprotein receptor-related protein 4 autoantibodies. Clinical observations have revealed a new MG phenotype triggered by cancer immunotherapy, but the underlying immunobiology remains undetermined. From a therapeutic perspective, MG patients can now benefit from a wider spectrum of treatment options. Such therapies have uncovered profound differences in clinical responses between and within the acetylcholine receptor and MuSK MG subtypes. Diverse mechanisms of immunopathology between the two subtypes, as well as qualitative nuances in the autoantibody repertoire of each patient, likely underpin the variability in therapeutic outcomes. Although predictive biomarkers of clinical response are lacking, these observations have ignited the development of assays that might assist clinicians in the choice of specific therapeutic strategies.

SUMMARY

Recent advances in the understanding of autoantibody functionalities are bringing neuroimmunologists closer to a more detailed appreciation of the mechanisms that govern MG pathology. Future investigations on the immunological heterogeneity among MG patients will be key to developing effective, individually tailored therapies.

IgG4 Autoantibodies in Organ-Specific Autoimmunopathies: Reviewing Class Switching, Antibody-Producing Cells, and Specific Immunotherapies

Organ-specific autoimmunity is often characterized by autoantibodies targeting proteins expressed in the affected tissue. A subgroup of autoimmunopathies has recently emerged that is characterized by predominant autoantibodies of the IgG4 subclass (IgG4-autoimmune diseases; IgG4-AID). This group includes pemphigus vulgaris, thrombotic thrombocytopenic purpura, subtypes of autoimmune encephalitis, inflammatory neuropathies, myasthenia gravis and membranous nephropathy. Although the associated autoantibodies target specific antigens in different organs and thus cause diverse syndromes and diseases, they share surprising similarities in genetic predisposition, disease mechanisms, clinical course and response to therapies. IgG4-AID appear to be distinct from another group of rare immune diseases associated with IgG4, which are the IgG4-related diseases (IgG4-RLD), such as IgG4-related which have distinct clinical and serological properties and are not characterized by antigen-specific IgG4. Importantly, IgG4-AID differ significantly from diseases associated with IgG1 autoantibodies targeting the same organ. This may be due to the unique functional characteristics of IgG4 autoantibodies (e.g. anti-inflammatory and functionally monovalent) that affect how the antibodies cause disease, and the differential response to immunotherapies of the IgG4 producing B cells/plasmablasts. These clinical and pathophysiological clues give important insight in the immunopathogenesis of IgG4-AID. Understanding IgG4 immunobiology is a key step towards the development of novel, IgG4 specific treatments. In this review we therefore summarize current knowledge on IgG4 regulation, the relevance of class switching in the context of health and disease, describe the cellular mechanisms involved in IgG4 production and provide an overview of treatment responses in IgG4-AID.

Bortezomib: a proteasome inhibitor for the treatment of autoimmune diseases

Autoimmune diseases (ADs) are conditions in which the immune system cannot distinguish self from non-self and, as a result, tissue injury occurs primarily due to the action of various inflammatory mediators. Different immunosuppressive agents are used for the treatment of patients with ADs, but some clinical cases develop resistance to currently available therapies. The proteasome inhibitor bortezomib (BTZ) is an approved agent for first-line therapy of people with multiple myeloma. BTZ has been shown to improve the symptoms of different ADs in animal models and ameliorated symptoms in patients with systemic lupus erythematous, rheumatoid arthritis, myasthenia gravis, neuromyelitis optica spectrum disorder, Chronic inflammatory demyelinating polyneuropathy, and autoimmune hematologic diseases that were nonresponsive to conventional therapies. Proteasome inhibition provides a potent strategy for treating ADs. BTZ represents a proteasome inhibitor that can potentially be used to treat AD patients resistant to conventional therapies.

Biological mechanisms of ectopic lymphoid structure formation and their pathophysiological significance

Ectopic lymphoid structures (ELS) or tertiary lymphoid organs are structures with the organization similar to the one of secondary lymphoid organs, formed in non-lymphoid tissues. They are considered to be an important site for the lymphocytic physiological and pathological role in conditions such are chronic infections, autoimmune diseases, cancer, and allograft rejection. Although similar to the secondary lymphoid tissues, the initiation of ELS formation is not preprogramed and requires chronic inflammation, expression of homeostatic chemokines, and lymphotoxin beta receptor activation. Importantly, while ELS formation may be considered beneficiary in antimicrobial and antitumor immunity, the persistence of these active lymphoid structures within the tissue increase the chance for development of autoimmunity and lymphoma. This paper is providing an overview of biological mechanisms involved in ELS formation, as well as the overview of the pathophysiological role of these structures. In addition, the paper discusses the possibility to therapeutically target ELS formation, bearing in mind their bivalent nature and role in different pathophysiological conditions.

Autoimmune Pathology in Myasthenia Gravis Disease Subtypes Is Governed by Divergent Mechanisms of Immunopathology

Myasthenia gravis (MG) is a prototypical autoantibody mediated disease. The autoantibodies in MG target structures within the neuromuscular junction (NMJ), thus affecting neuromuscular transmission. The major disease subtypes of autoimmune MG are defined by their antigenic target. The most common target of pathogenic autoantibodies in MG is the nicotinic acetylcholine receptor (AChR), followed by muscle-specific kinase (MuSK) and lipoprotein receptor-related protein 4 (LRP4). MG patients present with similar symptoms independent of the underlying subtype of disease, while the immunopathology is remarkably distinct. Here we highlight these distinct immune mechanisms that describe both the B cell- and autoantibody-mediated pathogenesis by comparing AChR and MuSK MG subtypes. In our discussion of the AChR subtype, we focus on the role of long-lived plasma cells in the production of pathogenic autoantibodies, the IgG1 subclass mediated pathology, and contributions of complement. The similarities underlying the immunopathology of AChR MG and neuromyelitis optica (NMO) are highlighted. In contrast, MuSK MG is caused by autoantibody production by short-lived plasmablasts. MuSK MG autoantibodies are mainly of the IgG4 subclass which can undergo Fab-arm exchange (FAE), a process unique to this subclass. In FAE IgG4, molecules can dissociate into two halves and recombine with other half IgG4 molecules resulting in bispecific antibodies. Similarities between MuSK MG and other IgG4-mediated autoimmune diseases, including pemphigus vulgaris (PV) and chronic inflammatory demyelinating polyneuropathy (CIDP), are highlighted. Finally, the immunological distinctions are emphasized through presentation of biological therapeutics that provide clinical benefit depending on the MG disease subtype.

Myasthenia Gravis: Pathogenic Effects of Autoantibodies on Neuromuscular Architecture

Myasthenia gravis (MG) is an autoimmune disease of the neuromuscular junction (NMJ). Autoantibodies target key molecules at the NMJ, such as the nicotinic acetylcholine receptor (AChR), muscle-specific kinase (MuSK), and low-density lipoprotein receptor-related protein 4 (Lrp4), that lead by a range of different pathogenic mechanisms to altered tissue architecture and reduced densities or functionality of AChRs, reduced neuromuscular transmission, and therefore a severe fatigable skeletal muscle weakness. In this review, we give an overview of the history and clinical aspects of MG, with a focus on the structure and function of myasthenic autoantigens at the NMJ and how they are affected by the autoantibodies' pathogenic mechanisms. Furthermore, we give a short overview of the cells that are implicated in the production of the autoantibodies and briefly discuss diagnostic challenges and treatment strategies.

Characterization of the thymus in Lrp4 myasthenia gravis: Four cases

Myasthenia gravis (MG) is an autoimmune disease of the neuromuscular junction. Most patients have pathogenic autoantibodies against the acetylcholine receptor (AChR). In the last years a novel subpopulation of MG patients has been described that harbors antibodies against low-density lipoprotein receptor-related protein 4 (Lrp4), another postsynaptic neuromuscular antigen. In early-onset AChR MG (EOMG), the thymus plays an important role in immunopathogenesis, and early thymectomy is beneficial. It is still unknown if the thymus plays any role in Lrp4-MG. In this pilot study, we compared thymus samples from four patients with Lrp4-MG (one pre-treated with immunosuppressive drugs), four non-MG controls and five EOMG patients (not pretreated with immunosuppressive drugs). Immunohistochemistry of the Lrp4-MG thymi revealed normal architecture, with normal numbers and distribution of B-cells, lymphoid follicles and Hassall's corpuscles. Primary CD23⁺ lymphoid follicles were similarly infrequent in Lrp4-MG and control thymic sections. In none of the control or Lrp4-MG thymi did we find secondary follicles with CD10⁺ germinal centers. These were evident in 2 of the 5 EOMG thymi, where primary lymphoid follicles were also more frequent on average, thus showing considerable heterogeneity between patients. Even if characteristic pathological thymic changes were not observed in the Lrp4 subgroup, we cannot exclude a role for the thymus in Lrp4-MG pathogenesis, since one Lrp4-MG patient went into clinical remission after thymectomy alone (at one year follow-up) and one more improved after thymectomy in combination with immunosuppressive therapy.

Tertiary Lymphoid Structures: Autoimmunity Goes Local

Tertiary lymphoid structures (TLS) are frequently observed in target organs of autoimmune diseases. TLS present features of secondary lymphoid organs such as segregated T and B cell zones, presence of follicular dendritic cell networks, high endothelial venules and specialized lymphoid fibroblasts and display the mechanisms to support local adaptive immune responses toward locally displayed antigens. TLS detection in the tissue is often associated with poor prognosis of disease, auto-antibody production and malignancy development. This review focuses on the contribution of TLS toward the persistence of the inflammatory drive, the survival of autoreactive lymphocyte clones and post-translational modifications, responsible for the pathogenicity of locally formed autoantibodies, during autoimmune disease development.

Tertiary Lymphoid Structures Among the World of Noncanonical Ectopic Lymphoid Organizations

Tertiary lymphoid structures (TLOs), also known as ectopic lymphoid structures, are associated with chronic infections and inflammatory diseases. Despite their association with pathology, these structures are actually a normal, albeit transient, component of the immune system and facilitate local immune responses that are meant to mitigate inflammation and resolve infection. Many of the mechanisms controlling the formation and function of tertiary lymphoid structures have been identified, in part by experimentally triggering their formation using defined stimuli under controlled conditions. Here, we introduce the experimental and pathological conditions in which tertiary lymphoid tissues are formed, describe the mechanisms linked to their formation, and discuss their functions in the context of both infection and inflammation.

Spontaneous germinal centers and autoimmunity

Germinal centers (GCs) are dynamic microenvironments that form in the secondary lymphoid organs and generate somatically mutated high-affinity antibodies necessary to establish an effective humoral immune response. Tight regulation of GC responses is critical for maintaining self-tolerance. GCs can arise in the absence of purposeful immunization or overt infection (called spontaneous GCs, Spt-GCs). In autoimmune-prone mice and patients with autoimmune disease, aberrant regulation of Spt-GCs is thought to promote the development of somatically mutated pathogenic autoantibodies and the subsequent development of autoimmunity. The mechanisms that control the formation of Spt-GCs and promote systemic autoimmune diseases remain an open question and the focus of ongoing studies. Here, we discuss the most current studies on the role of Spt-GCs in autoimmunity.

B cells in the pathophysiology of myasthenia gravis

Myasthenia gravis (MG) is an archetypal autoimmune disease. The pathology is characterized by autoantibodies to the acetylcholine receptor (AChR) in most patients or to muscle-specific tyrosine kinase (MuSK) in others and to a growing number of other postsynaptic proteins in smaller subsets. A decrease in the number of functional AChRs or functional interruption of the AChR within the muscle end plate of the neuromuscular junction is caused by pathogenic autoantibodies. Although the molecular immunology underpinning the pathology is well understood, much remains to be learned about the cellular immunology contributing to the production of autoantibodies. This Review documents research concerning the immunopathology of MG, bringing together evidence principally from human studies with an emphasis on the role of adaptive immunity and B cells in particular. Proposed mechanisms for autoimmunity, which take into account that different types of MG may incorporate divergent immunopathology, are offered. Muscle Nerve 57: 172-184, 2018.

Tertiary lymphoid organs in systemic autoimmune diseases: pathogenic or protective?

Tertiary lymphoid organs are found at sites of chronic inflammation in autoimmune diseases such as systemic lupus erythematosus and rheumatoid arthritis. These organized accumulations of T and B cells resemble secondary lymphoid organs and generate autoreactive effector cells. However, whether they contribute to disease pathogenesis or have protective functions is unclear. Here, we discuss how tertiary lymphoid organs can generate potentially pathogenic cells but may also limit the extent of the response and damage in autoimmune disease.

Dysregulation of B Cell Repertoire Formation in Myasthenia Gravis Patients Revealed through Deep Sequencing

Myasthenia gravis (MG) is a prototypical B cell-mediated autoimmune disease affecting 20-50 people per 100,000. The majority of patients fall into two clinically distinguishable types based on whether they produce autoantibodies targeting the acetylcholine receptor (AChR-MG) or muscle specific kinase (MuSK-MG). The autoantibodies are pathogenic, but whether their generation is associated with broader defects in the B cell repertoire is unknown. To address this question, we performed deep sequencing of the BCR repertoire of AChR-MG, MuSK-MG, and healthy subjects to generate ∼518,000 unique V_H and V_L sequences from sorted naive and memory B cell populations. AChR-MG and MuSK-MG subjects displayed distinct gene segment usage biases in both V_H and V_L sequences within the naive and memory compartments. The memory compartment of AChR-MG was further characterized by reduced positive selection of somatic mutations in the V_H CDR and altered V_H CDR3 physicochemical properties. The V_L repertoire of MuSK-MG was specifically characterized by reduced V-J segment distance in recombined sequences, suggesting diminished V_L receptor editing during B cell development. Our results identify large-scale abnormalities in both the naive and memory B cell repertoires. Particular abnormalities were unique to either AChR-MG or MuSK-MG, indicating that the repertoires reflect the distinct properties of the subtypes. These repertoire abnormalities are consistent with previously observed defects in B cell tolerance checkpoints in MG, thereby offering additional insight regarding the impact of tolerance defects on peripheral autoimmune repertoires. These collective findings point toward a deformed B cell repertoire as a fundamental component of MG.

Clinical features of patients with Myasthenia gravis from the Henan province, China

INTRODUCTION

Myasthenia gravis (MG) occurs globally, and many studies have indicated that there are regional differences in epidemiology, biomarkers, and prognosis of MG.

METHODS

A total of 478 patients with MG who visited hospitals in the Henan Province between January 2010 and February 2014 were included. Age, gender, age at onset, serum antibody, thymus pathology, treatment information, and Myasthenia Gravis Foundation of America (MGFA) classification were assessed.

RESULTS

Compared with previous reports from other areas, we found some differences in MG patients from Henan. The proportion of childhood MG in our study was lower than other reports of Oriental patients with MG. There seems to be an association between onset age, muscle involvement, and acetylcholine receptor antibody levels. Thymectomy improved the symptoms in 78.5% of thymectomy-treated patients.

CONCLUSIONS

These differences are likely related to geographical, environmental, and ethnic differences. Understanding these differences will help us to define more specific treatment.

Increased expression of Toll-like receptors 7 and 9 in myasthenia gravis thymus characterized by active Epstein-Barr virus infection

Considerable data implicate the thymus as the main site of autosensitization to the acetylcholine receptor in myasthenia gravis (MG), a B-cell-mediated autoimmune disease affecting the neuromuscular junction. We recently demonstrated an active Epstein-Barr virus (EBV) infection in the thymus of MG patients, suggesting that EBV might contribute to the onset or maintenance of the autoimmune response within MG thymus, because of its ability to activate and immortalize autoreactive B cells. EBV has been reported to elicit and modulate Toll-like receptor (TLR) 7- and TLR9-mediated innate immune responses, which are known to favor B-cell dysfunction and autoimmunity. Aim of this study was to investigate whether EBV infection is associated with altered expression of TLR7 and TLR9 in MG thymus. By real-time PCR, we found that TLR7 and TLR9 mRNA levels were significantly higher in EBV-positive MG compared to EBV-negative normal thymuses. By confocal microscopy, high expression levels of TLR7 and TLR9 proteins were observed in B cells and plasma cells of MG thymic germinal centers (GCs) and lymphoid infiltrates, where the two receptors co-localized with EBV antigens. An increased frequency of Ki67-positive proliferating B cells was found in MG thymuses, where we also detected proliferating cells expressing TLR7, TLR9 and EBV antigens, thus supporting the idea that EBV-associated TLR7/9 signaling may promote abnormal B-cell activation and proliferation. Along with B cells and plasma cells, thymic epithelium, plasmacytoid dendritic cells and macrophages exhibited enhanced TLR7 and TLR9 expression in MG thymus; TLR7 was also increased in thymic myeloid dendritic cells and its transcriptional levels positively correlated with those of interferon (IFN)-β. We suggested that TLR7/9 signaling may be involved in antiviral type I IFN production and long-term inflammation in EBV-infected MG thymuses. Our overall findings indicate that EBV-driven TLR7- and TLR9-mediated innate immune responses may participate in the intra-thymic pathogenesis of MG.

Investigating the Antigen Specificity of Multiple Sclerosis Central Nervous System-Derived Immunoglobulins

The central nervous system (CNS) of patients with multiple sclerosis (MS) is the site where disease pathology is evident. Damaged CNS tissue is commonly associated with immune cell infiltration. This infiltrate often includes B cells that are found in multiple locations throughout the CNS, including the cerebrospinal fluid (CSF), parenchyma, and the meninges, frequently forming tertiary lymphoid structures in the latter. Several groups, including our own, have shown that B cells from distinct locations within the MS CNS are clonally related and display the characteristics of an antigen-driven response. However, the antigen(s) driving this response have yet to be conclusively defined. To explore the antigen specificity of the MS B cell response, we produced recombinant human immunoglobulin (rIgG) from a series of expanded B cell clones that we isolated from the CNS tissue of six MS brains. The specificity of these MS-derived rIgG and control rIgG derived from non-MS tissues was then examined using multiple methodologies that included testing individual candidate antigens, screening with high-throughput antigen arrays and evaluating binding to CNS-derived cell lines. We report that while several MS-derived rIgG recognized particular antigens, including neurofilament light and a protocadherin isoform, none were unique to MS, as non-MS-derived rIgG used as controls invariably displayed similar binding specificities. We conclude that while MS CNS resident B cells display the characteristics of an antigen-driven B cell response, the antigen(s) driving this response remain at large.

Proteasome inhibition with bortezomib depletes plasma cells and specific autoantibody production in primary thymic cell cultures from early-onset myasthenia gravis patients

Bortezomib is a potent inhibitor of proteasomes currently used to eliminate malignant plasma cells in multiple myeloma patients. It is also effective in depleting both alloreactive plasma cells in acute Ab-mediated transplant rejection and their autoreactive counterparts in animal models of lupus and myasthenia gravis (MG). In this study, we demonstrate that bortezomib at 10 nM or higher concentrations killed long-lived plasma cells in cultured thymus cells from nine early-onset MG patients and consistently halted their spontaneous production not only of autoantibodies against the acetylcholine receptor but also of total IgG. Surprisingly, lenalidomide and dexamethasone had little effect on plasma cells. After bortezomib treatment, they showed ultrastructural changes characteristic of endoplasmic reticulum stress after 8 h and were no longer detectable at 24 h. Bortezomib therefore appears promising for treating MG and possibly other Ab-mediated autoimmune or allergic disorders, especially when given in short courses at modest doses before the standard immunosuppressive drugs have taken effect.

Ectopic lymphoid-like structures in infection, cancer and autoimmunity

Ectopic lymphoid-like structures often develop at sites of inflammation where they influence the course of infection, autoimmune disease, cancer and transplant rejection. These lymphoid aggregates range from tight clusters of B cells and T cells to highly organized structures that comprise functional germinal centres. Although the mechanisms governing ectopic lymphoid neogenesis in human pathology remain poorly defined, the presence of ectopic lymphoid-like structures within inflamed tissues has been linked to both protective and deleterious outcomes in patients. In this Review, we discuss investigations in both experimental model systems and patient cohorts to provide a perspective on the formation and functions of ectopic lymphoid-like structures in human pathology, with particular reference to the clinical implications and the potential for therapeutic targeting.

Artery Tertiary Lymphoid Organs Contribute to Innate and Adaptive Immune Responses in Advanced Mouse Atherosclerosis

Tertiary lymphoid organs emerge in tissues in response to nonresolving inflammation. Recent research characterized artery tertiary lymphoid organs in the aorta adventitia of aged apolipoprotein E–deficient mice. The atherosclerosis-associated lymphocyte aggregates are organized into distinct compartments, including separate T-cell areas harboring conventional, monocyte-derived, lymphoid, and plasmacytoid dendritic cells, as well as activated T-cell effectors and memory cells; B-cell follicles containing follicular dendritic cells in activated germinal centers; and peripheral niches of plasma cells. Artery tertiary lymphoid organs show marked neoangiogenesis, aberrant lymphangiogenesis, and extensive induction of high endothelial venules. Moreover, newly formed lymph node–like conduits connect the external lamina with high endothelial venules in T-cell areas and also extend into germinal centers. Mouse artery tertiary lymphoid organs recruit large numbers of naïve T cells and harbor lymphocyte subsets with opposing activities, including CD4 + and CD8 + effector and memory T cells, natural and induced CD4 + regulatory T cells, and memory B cells at different stages of differentiation. These data suggest that artery tertiary lymphoid organs participate in primary immune responses and organize T- and B-cell autoimmune responses in advanced atherosclerosis. In this review, we discuss the novel concept that pro- and antiatherogenic immune responses toward unknown arterial wall–derived autoantigens may be organized by artery tertiary lymphoid organs and that disruption of the balance between pro- and antiatherogenic immune cell subsets may trigger clinically overt atherosclerosis.

Clonal heterogeneity of thymic B cells from early-onset myasthenia gravis patients with antibodies against the acetylcholine receptor

Myasthenia gravis (MG) with antibodies against the acetylcholine receptor (AChR-MG) is considered as a prototypic autoimmune disease. The thymus is important in the pathophysiology of the disease since thymus hyperplasia is a characteristic of early-onset AChR-MG and patients often improve after thymectomy. We hypothesized that thymic B cell and antibody repertoires of AChR-MG patients differ intrinsically from those of control individuals. Using immortalization with Epstein-Barr Virus and Toll-like receptor 9 activation, we isolated and characterized monoclonal B cell lines from 5 MG patients and 8 controls. Only 2 of 570 immortalized B cell clones from MG patients produced antibodies against the AChR (both clones were from the same patient), suggesting that AChR-specific B cells are not enriched in the thymus. Surprisingly, many B cell lines from both AChR-MG and control thymus samples displayed reactivity against striated muscle proteins. Striational antibodies were produced by 15% of B cell clones from AChR-MG versus 6% in control thymus. The IgVH gene sequence analysis showed remarkable similarities, concerning VH family gene distribution, mutation frequency and CDR3 composition, between B cells of AChR-MG patients and controls. MG patients showed clear evidence of clonal B cell expansion in contrast to controls. In this latter aspect, MG resembles multiple sclerosis and clinically isolated syndrome, but differs from systemic lupus erythematosus. Our results support an antigen driven immune response in the MG thymus, but the paucity of AChR-specific B cells, in combination with the observed polyclonal expansions suggest a more diverse immune response than expected.

Innate immunity in myasthenia gravis thymus: pathogenic effects of Toll-like receptor 4 signaling on autoimmunity

The thymus is the main site of immune sensitization to AChR in myasthenia gravis (MG). In our previous studies we demonstrated that Toll-like receptor (TLR) 4 is over-expressed in MG thymuses, suggesting its involvement in altering the thymic microenvironment and favoring autosensitization and autoimmunity maintenance processes, via an effect on local chemokine/cytokine network. Here, we investigated whether TLR4 signaling may favor abnormal cell recruitment in MG thymus via CCL17 and CCL22, two chemokines known to dictate immune cell trafficking in inflamed organs by binding CCR4. We also investigated whether TLR4 activation may contribute to immunodysregulation, via the production of Th17-related cytokines, known to alter effector T cell (Teff)/regulatory T cell (Treg) balance. We found that CCL17, CCL22 and CCR4 were expressed at higher levels in MG compared to normal thymuses. The two chemokines were mainly detected around medullary Hassall's corpuscles (HCs), co-localizing with TLR4(+) thymic epithelial cells (TECs) and CCR4(+) dendritic cells (DCs), that were present in higher number in MG thymuses compared to controls. TLR4 stimulation in MG TECs increased CCL17 and CCL22 expression and induced the production of Th17-related cytokines. Then, to study the effect of TLR4-stimulated TECs on immune cell interactions and Teff activation, we generated an in-vitro imaging model by co-culturing CD4(+) Th1/Th17 AChR-specific T cells, naïve CD4(+)CD25(+) Tregs, DCs and TECs from Lewis rats. We observed that TLR4 stimulation led to a more pronounced Teff activatory status, suggesting that TLR4 signaling in MG thymic milieu may affect cell-to-cell interactions, favoring autoreactive T-cell activation. Altogether our findings suggest a role for TLR4 signaling in driving DC recruitment in MG thymus via CCL17 and CCL22, and in generating an inflammatory response that might compromise Treg function, favoring autoreactive T-cell pathogenic responses.

Thymus, thymoma and myasthenia gravis

Myasthenia gravis is an autoimmune disease. An autoantibody directed toward acetylcholine receptor (AChR) causes the destruction of the postsynaptic membrane and a reduction of the number of AChRs at neuromuscular junctions. A very puzzling, but interesting characteristic of myasthenia gravis is that many of the patients have an abnormality in their thymus. Many have a hyperplastic thymus with germinal centers, while others have a thymic tumor. How is the abnormality of the thymus related to myasthenia gravis? This review will summarize the existing evidence and try to find the missing link between the thymus and myasthenia gravis. The review will also comment on two distinct populations of myasthenia gravis patients without thymoma. The autoimmunity found in elderly patients is nonspecific and initiated via a different mechanism from the initiation of myasthenia gravis in younger patients.

Tertiary lymphoid organs in infection and autoimmunity

The lymph nodes (LNs) and spleen have an optimal structure that allows the interaction between T cells, B cells and antigen-presenting dendritic cells (DCs) on a matrix made up by stromal cells. Such a highly organized structure can also be formed in tertiary lymphoid organs (TLOs) at sites of infection or chronic immune stimulation. This review focuses on the molecular mechanisms of TLO formation and maintenance, the controversies surrounding the nature of the inducing events, and the functions of these structures in infection, transplantation and autoimmunity.

Inflammation and epstein-barr virus infection are common features of myasthenia gravis thymus: possible roles in pathogenesis

The thymus plays a major role in myasthenia gravis (MG). Our recent finding of a persistent Epstein-Barr (EBV) virus infection in some MG thymuses, combined with data showing that the thymus is in a proinflammatory state in most patients, supports a viral contribution to the pathogenesis of MG. Aim of this study was to gain further evidence for intrathymic chronic inflammation and EBV infection in MG patients. Transcriptional profiling by low density array and real-time PCR showed overexpression of genes involved in inflammatory and immune response in MG thymuses. Real-time PCR for EBV genome, latent (EBER1, EBNA1, LMP1) and lytic (BZLF1) transcripts, and immunohistochemistry for LMP1 and BZLF1 proteins confirmed an active intrathymic EBV infection, further supporting the hypothesis that EBV might contribute to onset or perpetuation of the autoimmune response in MG. Altogether, our results support a role of inflammation and EBV infection as pathogenic features of MG thymus.

Mucocutaneous candidiasis and autoimmunity against cytokines in APECED and thymoma patients: clinical and pathogenetic implications

Much has been learnt about the mechanisms of thymic self-tolerance induction from work on both the rare autosomal recessive disease autoimmune polyendocrinopathy candidiasis ectodermal dystrophy (APECED) and the autoimmune regulator (AIRE) protein mutated in this disease. Normally, AIRE drives low-level expression of huge numbers of peripheral tissue-specific antigens (TSAgs) in medullary thymic epithelial cells (mTECs), leading to the deletion of TSAg-reactive thymocytes maturing nearby. The very recently discovered neutralizing autoantibodies (autoAbs) against Th17-related cells and cytokines in two autoimmunity-related syndromes associated with AIRE-mutant thymi or AIRE-deficient thymomas help to explain the chronic mucocutaneous candidiasis (CMC) seen in both syndromes. The surprising parallels between these syndromes also demand new hypotheses and research into the consequences of AIRE deficiency and the ensuing autoimmunizing pathways, and suggest more appropriate treatment regimens as discussed in this review.

Local renal autoantibody production in lupus nephritis

Autoantibodies are central to the pathogenesis of several autoimmune diseases including systemic lupus erythematosus. Plasma cells secrete these autoantibodies, but the anatomical sites of these cells are not well defined. Here, we found that although dsDNA-specific plasma cells in NZB/W mice were present in spleen and bone marrow, a large number were in the kidneys and their number correlated with the serum dsDNA-IgG titer. We observed renal plasma cells only in mice with nephritis, where they located mainly to the tubulointerstitium of the cortex and outer medulla. These cells had the phenotypic characteristics of fully differentiated plasma cells and, similar to long-lived bone marrow plasma cells, they were not in cell cycle. In patients with lupus nephritis, plasma cells were often present in the medulla in those with the most severe disease, especially combined proliferative and membranous lupus nephritis. The identification of the kidney as a major site of autoreactive plasma cells has implications for our understanding of the pathogenesis of lupus nephritis and for strategies to deplete autoreactive plasma cells, a long-standing therapeutic aim.

Thymoma and paraneoplastic myasthenia gravis

Paraneoplastic autoimmune diseases associate occasionally with small cell lung cancers and gynecologic tumors. However, myasthenia gravis (MG) occurs in at least 30% of all patients with thymomas (usually present at MG diagnosis). These epithelial neoplasms almost always have numerous admixed maturing polyclonal T cells (thymocytes). This thymopoiesis-and export of mature CD4(+)T cells-particularly associates with MG, though there are rare/puzzling exceptions in apparently pure epithelial WHO type A thymomas. Other features potentially leading to inefficient self-tolerance induction include defective epithelial expression of the autoimmune regulator (AIRE) gene and/or of major histocompatibility complex class II molecules in thymomas, absence of myoid cells, failure to generate FOXP3(+) regulatory T cells, and genetic polymorphisms affecting T-cell signaling. However, the strong focus on MG/neuromuscular targets remains unexplained and suggests some biased autoantigen expression, T-cell selection, or autoimmunization within thymomas. There must be further clues in the intriguing serological and cellular parallels in some patients with late-onset MG but without thymomas-and in others with AIRE mutations-and in the contrasts with early-onset MG, as discussed here.

Factors associated with response to calcineurin inhibitors in myasthenia gravis

The objective was to assess which clinical factors of patients with myasthenia gravis (MG) are associated with responsiveness to calcineurin inhibitors (CNIs, cyclosporine and tacrolimus). We retrospectively analyzed the 6-month effects of CNIs in 62 MG patients. We excluded the influence of other immune treatments and determined factors associated with response to CNIs. The frequency of patients who achieved neither a > or =3-point reduction in quantitative MG score nor a > or =25% reduction in daily dose of prednisolone (poor responders) reached 35.5% (22/62) and 64.5% (40/62), respectively, compared with patients who achieved at least one of these improvements (responders). Neither dose nor blood concentration of CNIs differed between groups. Multivariate logistic regression analysis revealed time since onset of disease [odds ratio (OR) = 0.85, P = 0.005] and presence of thymoma (OR = 5.56, P = 0.05) as clinical factors that predict response to CNIs. As for MG-related autoantibody status, an autoantibody against a voltage-gated potassium channel, Kv1.4, was associated with response (OR = 9.01, P = 0.04) and showed a correlation with the presence of thymoma (P < 0.01). In MG, the early stages of disease and thymoma-associated MG are responsive to treatment with CNIs.