Differential expression patterns of recombination-activating genes in individual mature B cells in juvenile idiopathic arthritis

B Cells on the Stage of Inflammation in Juvenile Idiopathic Arthritis: Leading or Supporting Actors in Disease Pathogenesis?

Juvenile idiopathic arthritis (JIA) is a term that collectively refers to a group of chronic childhood arthritides, which together constitute the most common rheumatic condition in children. The International League of Associations for Rheumatology (ILAR) criteria define seven categories of JIA: oligoarticular, polyarticular rheumatoid factor (RF) negative (RF-), polyarticular RF positive (RF+), systemic, enthesitis-related arthritis, psoriatic arthritis, and undifferentiated arthritis. The ILAR classification includes persistent and extended oligoarthritis as subcategories of oligoarticular JIA, but not as distinct categories. JIA is characterized by a chronic inflammatory process affecting the synovia that begins before the age of 16 and persists at least 6 weeks. If not treated, JIA can cause significant disability and loss of quality of life. Treatment of JIA is adjusted according to the severity of the disease as combinations of non-steroidal anti-inflammatory drugs (NSAIDs), synthetic and/ or biological disease modifying anti-rheumatic drugs (DMARDs). Although the disease etiology is unknown, disturbances in innate and adaptive immune responses have been implicated in JIA development. B cells may have important roles in JIA pathogenesis through autoantibody production, antigen presentation, cytokine release and/ or T cell activation. The study of B cells has not been extensively explored in JIA, but evidence from the literature suggests that B cells might have indeed a relevant role in JIA pathophysiology. The detection of autoantibodies such as antinuclear antibodies (ANA), RF and anti-citrullinated protein antibodies (ACPA) in JIA patients supports a breakdown in B cell tolerance. Furthermore, alterations in B cell subpopulations have been documented in peripheral blood and synovial fluid from JIA patients. In fact, altered B cell homeostasis, B cell differentiation and B cell hyperactivity have been described in JIA. Of note, B cell depletion therapy with rituximab has been shown to be an effective and well-tolerated treatment in children with JIA, which further supports B cell intervention in disease development.

B Cells as a Therapeutic Target in Paediatric Rheumatic Disease

B cells carry out a central role in the pathogenesis of autoimmune disease. In addition to the production of autoantibodies, B cells can contribute to disease development by presenting autoantigens to autoreactive T cells and by secreting pro-inflammatory cytokines and chemokines which leads to the amplification of the inflammatory response. Targeting both the antibody-dependent and antibody-independent function of B cells in adult rheumatic disease has led to the advent of B cell targeted therapies in clinical practice. To date, whether B cell depletion could also be utilized for the treatment of pediatric disease is relatively under explored. In this review, we will discuss the role of B cells in the pathogenesis of the pediatric rheumatic diseases Juvenile Idiopathic Arthritis (JIA), Juvenile Systemic Lupus Erythematosus (JSLE) and Juvenile Dermatomyositis (JDM). We will also explore the rationale behind the use of B cell-targeted therapies in pediatric rheumatic disease by highlighting new case studies that points to their efficacy in JIA, JSLE, and JDM.

Phosphorothioate-modified CpG oligodeoxynucleotides mimic autoantigens and reveal a potential role for Toll-like receptor 9 in receptor revision

Re-expression of recombinase activating genes (RAG) in mature B cells may support autoreactivity by enabling revision of the B-cell receptor (BCR). Recent reports suggest that administration of Toll-like receptor 9 (TLR9) -stimulating CpG oligodeoxynucleotides (ODN) could trigger the manifestation of autoimmune disease and that TLR are involved in the selection processes eliminating autoreactive BCR. The mechanisms involved remain to be elucidated. This prompted us to ask, whether TLR9 could be involved in receptor revision. We found that phosphorothioate-modified CpG ODN (CpG(PTO)) induced expression of Ku70 and re-expression of RAG-1 in human peripheral blood B lymphocytes and Igλ expression in sorted Igκ(+) B cells. Further results revealed unselective binding specificity of CpG(PTO) -induced immunoglobulin and suggested that CpG(PTO) engage and/or mimic IgM receptor signalling, an important prerequisite for the initialization of receptor editing or revision. Altogether, our data describe a potential role for TLR9 in receptor revision and suggest that CpG(PTO) could mimic chromatin-bearing autoantigens by simultaneously engaging the BCR and TLR9 on IgM(+) B cells.

The epigenetic landscape of B lymphocyte tolerance to self

Despite frequent exposures to a variety of potential triggers, including antigens produced by pathogens or commensal microbiota, B-lymphocytes are able to mount highly protective responses to a variety of threats, while remaining tolerant to self-components. A number of cytokines, signaling pathways and transcription factors have been characterized to elucidate the mechanisms underlying B cell tolerance to self. It is, however, unclear how the signals received by B-lymphocytes are converted into complex and sustained patterns of gene expression that can allow production of protective antibodies and maintain immune tolerance to self-components. Mounting evidence now suggests an important role for epigenetic mechanisms in modulating and transmitting signals for B lymphocyte tolerization to self-antigens. It is likely that a better insight into epigenetic regulation of B cell tolerance will lead to development of gene-specific therapeutic approaches that optimize host defense mechanisms to exogenous threats, while preventing development and/or progression of autoimmune inflammatory diseases.

Abatacept in difficult-to-treat juvenile idiopathic arthritis

Juvenile idiopathic arthritis (JIA) is the most common chronic rheumatic disease in children and an important cause of short-term and long-term disability. Gene changes in the immune system can predispose to JIA and regulation of the immune system is crucial in the pathogenesis. The goal of therapy is complete disease control using disease-modifying antirheumatic drugs (DMARDS). Activated T-cells may play a role in the immunopathology of JIA. Therefore, targeting T-cell activation is a rational approach for the treatment of JIA. Abatacept (ABA), a selective co-stimulation modulator, has been shown to be effective in treating all JIA subtypes and is generally safe and well tolerated in JIA. Neutralizing antibodies were found in 6/9 (67%) of seropositive patients, but anti-ABA antibodies did not appear to be associated with disease flare, serious adverse events, acute infusional adverse events, hypersensitivity, autoimmune disorders, or low ABA serum concentrations. Anti-ABA antibodies were more frequent when ABA concentrations were below therapeutic levels. Although information on ABA in JIA is still limited, available data suggest a potential role in difficult to treat JIA patients previously treated with other biologic agents and for non-responders to TNF-blockade.

Juvenile idiopathic arthritis

Juvenile idiopathic arthritis is a heterogeneous group of diseases characterised by arthritis of unknown origin with onset before age of 16 years. Pivotal studies in the past 5 years have led to substantial progress in various areas, ranging from disease classification to new treatments. Gene expression profiling studies have identified different immune mechanisms in distinct subtypes of the disease, and can help to redefine disease classification criteria. Moreover, immunological studies have shown that systemic juvenile idiopathic arthritis is an acquired autoinflammatory disease, and have led to successful studies of both interleukin-1 and interleukin-6 blockade. In other forms of the disease, synovial inflammation is the consequence of a disturbed balance between proinflammatory effector cells (such as T-helper-17 cells), and anti-inflammatory regulatory cells (such as FOXP3-positive regulatory T cells). Moreover, specific soluble biomarkers (S100 proteins) can guide individual treatment. Altogether these new developments in genetics, immunology, and imaging are instrumental to better define, classify, and treat patients with juvenile idiopathic arthritis.

Epigenetics in lupus

Accumulating epidemiological, clinical, and experimental evidence supports the conclusion of a critical role of epigenetic factors in immune programming. This understanding provides the basis for elucidating how the intricate interactions of the genome, epigenome, and transcriptome shape immune responses and maintain immune tolerance to self-antigens. Deciphering the precise contribution of epigenetic factors to autoimmunity, and in particular to lupus, has become an active research area. On one hand, it is well established that environmental factors have an impact on the epigenome and, therefore, on the transcriptional and translational machinery of specific cell types; on the other, the environment also plays an important role in the severity of lupus and other autoimmunity diseases. Determining how epigenetics "connects" the environment to cell biology and to autoreactivity will be key for advancing our understanding in this field and, possibly, for developing novel preventive strategies.

B-cell pathology in juvenile idiopathic arthritis

Juvenile Idiopathic Arthritis (JIA) is the most common cause of chronic arthritis in childhood and adolescents and encompasses a heterogeneous group of different diseases. Due to the promising results of B-cell depleting therapies in rheumatoid arthritis the role of B-cells in autoimmune diseases has to be discussed in a new context. Additionally, experiments in mouse models have shed new light on the antibody-independent role of B-cells in the development of autoimmune diseases. In this review we will discuss the importance of B-cells in the pathogenesis of JIA appraising the question for an immunological basis of B-cell targeted therapy in JIA.

Do B cells play a role in the pathogenesis of juvenile idiopathic arthritis?

Juvenile idiopathic arthritis (JIA) is the most common cause of chronic arthritis in childhood and adolescents and encompasses a heterogeneous group of diseases. The role of B cells (BC) in autoimmune diseases has been put in a new perspective due to the promising results of BC depleting therapies in RA. Experiments in mouse models have shed new light on the Ab-independent role of BC in the pathogenesis of autoimmune diseases. We discuss whether BC play a role in the pathogenesis of JIA appraising the question for an immunological basis of BC directed therapy.

The kappa immunoglobulin light chain repertoire of peripheral blood B cells in patients with juvenile rheumatoid arthritis

The frequent appearance of antinuclear antibodies in patients with juvenile rheumatoid arthritis (JRA) indicates a loss of tolerance in B cell differentiation and/or activation. In this analysis, we were interested whether particular changes in the immunoglobulin light chain repertoire might exist in early-onset pauciarticular arthritis (EOPA) patients thereby potentially revealing distinct molecular patterns, which characterize defects in central tolerance mechanisms as well as an autoreactive peripheral B cell repertoire. Using single cell sorting and single cell PCR the distribution of Vkappa Jkappa rearrangements has been analyzed in individual naïve B cells of patients with EOPA-JRA and healthy individuals. The immunoglobulin kappa light chain repertoire of peripheral blood B cells in EOPA patients seems to be skewed to a decreased use of downstream Vkappa gene segments indicating increased events of secondary V(D)J-recombination. Another prominent molecular pattern in JRA B cells seem to be a restricted combination of Vkappa Jkappa rearrangements based on the predominant utilization of the Jkappa 1 and 2 gene segment. The current study indicates disturbances in the peripheral B cell pool in juvenile rheumatoid arthritis. The peripheral blood B cell pool of JRA patients did show molecular changes in the kappa light chain repertoire which, in part, could be a sequel of secondary V(D)J-recombination and of a molecular bias during immunoglobulin rearrangement in the bone marrow. Thus, B cell tolerance might be broken by more than one pathogenic mechanism.

[Concepts on the pathogenesis of juvenile idiopathic arthritis]

There are various explanations for the development of juvenile idiopathic arthritis (JIA).Gene changes in the immune system can predispose to JIA and regulation of the immune system is crucial in the pathogenesis. The adaptive, acquired immune system probably plays a central role. Thus, in the case of JIA a conspicuous population of highly activated T-cells can be found in the synovia. B-cells are also involved, as indicated by positive ANA titers in JIA patients. Regulatory T-cells (Tregs) attempt to prevent the expansion of autoreactive T-cells.However, the natural or the innate immune system also plays a role. Thus a disorder of the inflammasome could underlie the cause of JIA with systemic onset. The interaction between congenital and adaptive immune system shows that a distinct spatial and temporal separation between the two immune systems is becoming increasingly difficult. An infection- and virus-related immune reaction could also be the cause of JIA. Proinflammatory cytokines are of proven significance in pathogenesis in terms of how they are released under stress, for example. New genomic and proteomic techniques are able to produce individualized profiles for each patient and allow for increasingly fine separation between subtypes, thus improving therapeutic possibilities.

The lambda gene immunoglobulin repertoire of human neonatal B cells

The dynamics of immunoglobulin rearrangements and selection, which depend on age, antigen exposure and tolerance functions, are only partly understood. Thus, we analyzed and compared the lambda chain immunoglobulin repertoire of individual IgD+ human neonatal B cells with the adult peripheral B cell VlambdaJlambda repertoire. Some Vlambda genes, 4C, 2A2, 2B2, 5A, 1G and 4B, were overexpressed in the non-productive neonatal repertoire, whereas other Vlambda genes (2E, 2A2, 3H, 2B2, 1C and 1G) were overexpressed in the productive repertoire. The adult B cell repertoire revealed nearly the same predominance of genes in the non-productive and productive repertoire. A comparison of the non-productive and productive repertoire indicated that the genes 3H and 1C were positively selected, whereas the genes 4C, 2A1, 3I, 5A, 9A, 4A and 4B were negatively selected. All four functional Jlambda genes were used in both repertoires. Jlambda2/3 was used mainly. Insertions of non-templated nucleotides at the VlambdaJlambda-junction by the enzyme TdT were less frequent as compared to the adult, but the CDR3 length was the same. Comparison of CD5+IgD+ and CD5-IgD+ B cells revealed no differences between neonatal productive rearrangements. However, the genes 1C and 1G were used more often in the non-productive repertoire of CD5+ B cells, whereas gene 4B was used significantly more frequent in CD5- B cells. These data provide evidence that the primary usage and subsequent selection of Vlambda genes in the neonate are surprisingly comparable with the adult. This suggests that selection into the productive Vlambda repertoire in principal might be driven mainly by autoantigens in the newborn, as well as in adulthood, since newborns have not been exposed to exogenous antigens.

Overexpression of activation-induced cytidine deaminase in B cells is associated with production of highly pathogenic autoantibodies

Defective receptor editing or defective B cell checkpoints have been associated with increased frequency of multireactive autoantibodies in autoimmune disease. However, Ig somatic hypermutation and/or class switch recombination may be mechanisms enabling the development of pathogenic multireactive autoantibodies. In this study, we report that, in the BXD2 mouse model of autoimmune disease, elevated expression of activation-induced cytidine deaminase (AID) in recirculating follicular CD86(+) subsets of B cells and increased germinal center B cell activity are associated with the production of pathogenic multireactive autoantibodies. CD4 T cells from BXD2 mice that expressed increased levels of CD28 and an increased proliferative response to anti-CD3 and anti-CD28 stimulation are required for this process. Inhibition of the CD28-CD86 interaction in BXD2 mice with AdCTLA4-Ig resulted in normalization of AID in the B cells and suppression of IgG autoantibodies. This treatment also prevented the development of germinal center autoantibody-producing B cells, suggesting that an optimal microenvironment enabling AID function is important for the formation of pathogenic autoantibodies. Taken together, our data indicate that AID expression in B cells is a promising therapeutic target for the treatment of autoimmune diseases and that suppression of this gene may be a molecular target of CTLA4-Ig therapy.

Subversion of B lymphocyte tolerance by hydralazine, a potential mechanism for drug-induced lupus

Accumulating evidence indicates that epigenetic alterations contribute to exacerbated activation or deregulation of the mechanisms that maintain tolerance to self-antigens in patients with lupus, a systemic autoimmune disease that can be triggered by medications taken to treat a variety of conditions. Here, we tested the effect of hydralazine, an antihypertensive drug that triggers lupus, on receptor editing, a chief mechanism of B lymphocyte tolerance to self-antigens. Using mice expressing transgenic human Igs, we found that hydralazine impairs up-regulation of RAG-2 gene expression and reduces secondary Ig gene rearrangements. Receptor editing was also partially abolished in a dose-dependent manner by a specific inhibitor of MEK1/2. Adoptive transfer of bone marrow B cells pretreated with hydralazine or with a MEK inhibitor to naïve syngeneic mice resulted in autoantibody production. We conclude that, by disrupting receptor editing, hydralazine subverts B lymphocyte tolerance to self and contributes to generation of pathogenic autoreactivity. We also postulate that inhibition of the Erk signaling pathway contributes to the pathogenesis of hydralazine-induced lupus and idiopathic human lupus.