Functional CD40 ligand is expressed by T cells in rheumatoid arthritis

Monocytes, Macrophages, and Their Potential Niches in Synovial Joints - Therapeutic Targets in Post-Traumatic Osteoarthritis?

Synovial joints are complex structures that enable normal locomotion. Following injury, they undergo a series of changes, including a prevalent inflammatory response. This increases the risk for development of osteoarthritis (OA), the most common joint disorder. In healthy joints, macrophages are the predominant immune cells. They regulate bone turnover, constantly scavenge debris from the joint cavity and, together with synovial fibroblasts, form a protective barrier. Macrophages thus work in concert with the non-hematopoietic stroma. In turn, the stroma provides a scaffold as well as molecular signals for macrophage survival and functional imprinting: “a macrophage niche”. These intricate cellular interactions are susceptible to perturbations like those induced by joint injury. With this review, we explore how the concepts of local tissue niches apply to synovial joints. We introduce the joint micro-anatomy and cellular players, and discuss their potential interactions in healthy joints, with an emphasis on molecular cues underlying their crosstalk and relevance to joint functionality. We then consider how these interactions are perturbed by joint injury and how they may contribute to OA pathogenesis. We conclude by discussing how understanding these changes might help identify novel therapeutic avenues with the potential of restoring joint function and reducing post-traumatic OA risk.

The Germinal Center Milieu in Rheumatoid Arthritis: The Immunological Drummer or Dancer?

Rheumatoid Arthritis (RA) is a chronic autoimmune disease characterized by joint inflammation, affecting approximately 1% of the general population. To alleviate symptoms and ameliorate joint damage, chronic use of immunosuppressives is needed. However, these treatments are only partially effective and may lead to unwanted side effects. Therefore, a more profound understanding of the pathophysiology might lead to more effective therapies, or better still, a cure. The presence of autoantibodies in RA indicates that B cells might have a pivotal role in the disease. This concept is further supported by the fact that a diverse antibody response to various arthritis-related epitopes is associated with arthritis development. In this context, attention has focused in recent years on the role of Germinal Centers (GCs) in RA. Since GCs act as the main anatomic location of somatic hypermutations, and, thus, contributing to the diversity and specificity of (auto) antibodies, it has been speculated that defects in germinal center reactions might be crucial in the initiation and maintenance of auto-immune events. In this paper, we discuss current evidence that various processes within GCs can result in the aberrant production of B cells that possess autoreactive properties and might result in the production of RA related autoantibodies. Secondly, we discuss various (pre-)clinical studies that have targeted various GC processes as novel therapies for RA treatment.

The DNA replication regulator MCM6: An emerging cancer biomarker and target

MCM6 is a significant DNA replication regulator that plays a crucial role in sustaining the cell cycle. In many cancer cells, MCM6 expression is enhanced. For example, persistently increased expression of MCM6 promotes the formation, development and progression of hepatocellular carcinoma (HCC). Up- and down-regulation studies have indicated that MCM6 regulates cell cycle, proliferation, metastasis, immune response and the maintenance of the DNA replication system. MCM6 can also regulate downstream signaling such as MEK/ERK thus promoting carcinogenesis. Accordingly, MCM6 may represent a sensitive and specific biomarker to predict adverse progression and poor outcome. Furthermore, inhibition of MCM6 may be an effective cancer treatment. The present review summarizes the latest results on the inactivating and activating functions of MCM6, underlining its function in carcinogenesis. Further studies of the carcinogenic functions of MCM6 may provide novel insight into cancer biology and shed light on new approaches for cancer diagnosis and treatment.

CD40 Ligand Expression Correlates with Resolution of Peritonitis and Mononuclear Cell Recruitment

Background

CD40 belongs to the tumor necrosis factor receptor family and its ligation is a central event in major inflammatory and immune reactions. We have previously demonstrated that CD40 ligation upregulates the secretion of mononuclear chemokines from peritoneal mesothelial cells (PMC), and that blocking the CD40 ligand (CD154) reduced the mononuclear infiltrate in a model of peritonitis.

Objective

To characterize the kinetics of CD154 expression on peritoneal leukocytes and examine the correlation of this occurrence with the mononuclear transition at the resolution phase of peritonitis.

Methods

Leukocytes were collected from the effluent of 11 patients during episodes of peritonitis while undergoing peritoneal dialysis (PD). The effluent was then analyzed by flow cytometry to characterize CD154 expression.

Results

CD154 expression on peritoneal mononuclear cells gradually increased during the resolution phase of peritonitis, peaking first on T cells (CD4+ and CD8+ cells at 20 – 45 hours) and then on macrophages (CD14+ at 20 – 50 hours). The maximal expression of CD154 on macrophages, CD4+ cells, and CD8+ cells during peak hours reached values of 33% ± 23%, 4% ± 3%, and 24% ± 17%, respectively. The increase in CD154 expression was in negative correlation ( r=–0.44, p = 0.032) with total leukocyte numbers and in positive correlation ( r = 0.52, p = 0.009) with the increase of mononuclear cells. Deterioration of peritonitis was associated with a decrease in CD154 levels, while recurrence of peritonitis was related to high CD154 levels.

Conclusion

Our data, which show a positive correlation between CD154 levels and mononuclear dominance, suggest that CD40–CD154 ligation plays an important role in the transition to mononuclear predominance in the late phase of peritonitis.

Mechanistic basis of co-stimulatory CD40-CD40L ligation mediated regulation of immune responses in cancer and autoimmune disorders

Generation of an accurate humoral and a cell mediated adaptive immune responsesare dictated by binding of an antigen to a T- and a B-cell receptor, respectively (first signal) followed by ligation of costimulatory molecules (second signal). CD40, a costimulatory receptor molecule, expressed mainly on antigen presenting cells, some non-immune cells and tumors, binds to CD40 ligand molecule expressed transiently on T-cells and non-immune cells under inflammatory conditions. In the past decade, the CD40-CD40L interaction has emerged as an immune-potentiating system that governs and regulates host immune response against various diseases and pathogens, failing of which results in detrimental patho-physiologies including cancer and autoimmune disorders. CD40-CD40L transduces immune signals intracellularly via TRAF-dependent and independent mechanisms and further downstream by different MAPK pathways and transcription factors such as NF-κB, p38 etc. While CD40 signaling pathway through its cognate interaction between B and T cells promotes activation and proliferation of B-cells, Ig class switching, and generation of B cell memory; however, CD40-CD40L interaction involving other APCs and non-immune cells relay distinct cell signaling resulting in production of a variety of cytokines/chemokines and cell adhesion molecules ultimately conferring host defense against pathogen. In cancer and autoimmune disorders, CD40-CD40L interaction is also responsible for aberrant expression of many disease specific markers, class I/II MHC molecules and other co-stimulatory molecules such as B7 and CD28 in cell- and disease-specific manner. In the present review, the current state of understanding about the CD40-CD40L mediated regulation of immune and non-immune cells is presented. The current paradigm is to target CD40 using agonist anti-CD40 mAbs alone or in synergistic combination with chemotherapy in order to harness or confer anti-tumor and anti-inflammatory immunity.

Assessment of CD40 and CD40L expression in rheumatoid arthritis patients, association with clinical features and DAS28

The predominance of the effector mechanisms by CD4 + T cells is a characteristic of inflammatory autoimmune diseases such as rheumatoid arthritis (RA). The CD40/CD40L costimulatory pathway contributes to these pathogenic mechanisms by promoting autoantibody production and inflammation. Aberrant expression of CD40 and CD40L in RA patients has been shown, the latter prevailing in females. However, contrasting results have emerged regarding the clinical associations of these findings. We determined the association of CD40 and CD40L expression with the clinical activity evaluated through DAS28 in RA patients. A total of 38 female RA patients and 10 age- and sex-matched control subjects were included. CD40 and CD40L mRNA expression was quantified by real-time qPCR, cell surface proteins were determined by flow cytometry, and protein soluble forms were determined by ELISA. The expansion of a CD4 + T cell subpopulation expressing CD40 was identified in the RA group. In addition, high frequencies of CD4 + CD40L + T cells expressing high levels of CD40L, increased levels of sCD40L and overexpression of CD40L mRNA were observed in these patients. Moreover, there was a gradual increase in CD40L when data were stratified according to DAS28, except for very active patients. No correlation was observed between the levels of mRNA, cell surface protein and soluble protein of CD40 and CD40L with the clinical features of RA patients. There is an altered expression of CD40L in female RA patients in association with clinical activity assessed by DAS28, these findings support the evidence that suggests CD40L as a marker of clinical activity.

Effects of BI 655064, an antagonistic anti-CD40 antibody, on clinical and biomarker variables in patients with active rheumatoid arthritis: a randomised, double-blind, placebo-controlled, phase IIa study

OBJECTIVE

To evaluate the safety, efficacy and therapeutic mechanism of BI 655064, an antagonistic anti-CD40 monoclonal antibody, in patients with rheumatoid arthritis (RA) and an inadequate response to methotrexate (MTX-IR).

METHODS

In total, 67 patients were randomised to receive weekly subcutaneous doses of 120 mg BI 655064 (n=44) or placebo (n=23) for 12 weeks. The primary endpoint was the proportion of patients who achieved 20% improvement in American College of Rheumatology criteria (ACR20) at week 12. Safety was assessed in patients who received at least one dose of study drug.

RESULTS

At week 12, the primary endpoint was not met, with 68.2% of patients treated with BI 655064 achieving an ACR20 vs 45.5% with placebo (p=0.064); using Bayesian analysis, the posterior probability of seeing a difference greater than 35% was 42.9%. BI 655064 was associated with greater changes in CD40-CD40L pathway-related markers, including reductions in inflammatory and bone resorption markers (interleukin-6, matrix metalloproteinase-3, receptor activator of nuclear factor-κB ligand), concentration of autoantibodies (immunoglobulin [Ig]G rheumatoid factor [RF], IgM RF, IgA RF) and CD95+ activated B-cell subsets. No serious adverse events (AEs) related to BI 655064 treatment or thromboembolic events occurred; reported AEs were mainly of mild intensity.

CONCLUSION

Although blockade of the CD40-CD40L pathway with BI 655064 in MTX-IR patients with RA resulted in marked changes in clinical and biological parameters, including reductions in activated B-cells, autoantibody production and inflammatory and bone resorption markers, with a favourable safety profile, clinical efficacy was not demonstrated in this small phase IIa study.

TRIAL REGISTRATION NUMBER

NCT01751776.

PTPN22 1858C>T polymorphism is associated with increased CD154 expression and higher CD4+ T cells percentage in rheumatoid arthritis patients

BACKGROUND

CD40 is a costimulatory molecule for B cells, and CD154 is a marker of CD4+ T cells activation. CD40-CD154 interaction promotes pro-inflammatory cytokines secretion and autoantibodies production. PTPN22 gene encodes LYP protein, an inhibitor of T- and B-cell activation. PTPN22 1858C>T polymorphism confers rheumatoid arthritis (RA) susceptibility. Hence, we evaluate the relationship between 1858C>T polymorphism with CD40 and CD154 expression and IFN-γ secretion in RA patients.

METHODS

PTPN22 1858C>T polymorphism was genotyped in 315 RA patients and 315 control subjects (CS) using PCR-RFLP method. Later, we selected only ten anti-CCP-positive RA patients, naïve to disease-modifying antirheumatic drugs and ten CS, all with known 1858C>T PTPN22 genotype. The CD40 and CD154 membrane expressions were determined by flow cytometry in peripheral B and T cells, correspondingly.

RESULTS

The B cells percentage and mCD40 expression were similar between RA and CS (P > 0.05) and we did not find an association between these variables and the 1858C>T polymorphism. The CD4+ T cells percentage was higher in RA patients than CS (P = 0.003), and in the RA group, the CD4+ T cells percentage and mCD154 expression were higher in the 1858 T allele carriers (P = 0.008 and P = 0.032, respectively). The IFN-γ levels were lower in RA patients carrying the PTPN22 risk allele (P = 0.032).

CONCLUSION

The PTPN22 1858 T risk allele is associated with increased CD4+ T cells percentage and high mCD154 expression in RA patients, which could favor the pro-inflammatory cytokine release and the establishment of the inflammatory response at the seropositive RA.

Updating osteoimmunology: regulation of bone cells by innate and adaptive immunity

Osteoimmunology encompasses all aspects of the cross-regulation of bone and the immune system, including various cell types, signalling pathways, cytokines and chemokines, under both homeostatic and pathogenic conditions. A number of key areas are of increasing interest and relevance to osteoimmunology researchers. Although rheumatoid arthritis has long been recognized as one of the most common autoimmune diseases to affect bone integrity, researchers have focused increased attention on understanding how molecular triggers and innate signalling pathways (such as Toll-like receptors and purinergic signalling pathways) related to pathogenic and/or commensal microbiota are relevant to bone biology and rheumatic diseases. Additionally, although most discussions relating to osteoimmune regulation of homeostasis and disease have focused on the effects of adaptive immune responses on bone, evidence exists of the regulation of immune cells by bone cells, a concept that is consistent with the established role of the bone marrow in the development and homeostasis of the immune system. The active regulation of immune cells by bone cells is an interesting emerging component of investigations that seek to understand how to control immune-associated diseases of the bone and joints.

Co-stimulatory and Co-inhibitory Pathways in Autoimmunity

The immune system is guided by a series of checks and balances, a major component of which is a large array of co-stimulatory and co-inhibitory pathways that modulate the host response. Although co-stimulation is essential for boosting and shaping the initial response following signaling through the antigen receptor, inhibitory pathways are also critical for modulating the immune response. Excessive co-stimulation and/or insufficient co-inhibition can lead to a breakdown of self-tolerance and thus to autoimmunity. In this review, we will focus on the role of co-stimulatory and co-inhibitory pathways in two systemic (systemic lupus erythematosus and rheumatoid arthritis) and two organ-specific (multiple sclerosis and type 1 diabetes) emblematic autoimmune diseases. We will also discuss how mechanistic analysis of these pathways has led to the identification of potential therapeutic targets and initiation of clinical trials for autoimmune diseases, as well as outline some of the challenges that lie ahead.

Tumor necrosis factor-α blockade treatment decreased CD154 (CD40-ligand) expression in rheumatoid arthritis

Contexts

CD154 (commonly referred to as CD40-ligand) is a critical T cell factor that participates in the pathogenesis of autoimmune and is over-expressed in rheumatoid arthritis (RA). TNF-α blockade treatment had dramatic efficacy in RA.

Objective

To investigate whether TNF-α blockade treatment can inhibit CD154 expression in RA.

Methods

Blood samples were collected from 33 patients with rheumatoid arthritis before and 3 months after TNF-α blockade treatment. Clinical serological data determined by standard assays and T cell CD154 expression levels determined by flow cytometry were statistically analyzed for these two time points.

Results

The percentage of CD154 expression on gated CD4+ T cells of PBMCs from RA patients after 3 months TNF-α blockade treatment was significantly lower than before treatment (2.94 ± 3.21% vs. 7.21 ± 5.64%; p = 0.0001). The disease activity and anti-CCP antibody levels were also significantly reduced after TNF-α blockade treatment. The CD154 expression levels were positively correlated with disease activity index DAS28, and CRP. The post-stimulated CD154 expression percentage of purified CD4+ T cells between baseline and after TNF-α blockade treatment was not significantly different (p = 0.221). Baseline CD154 levels were positively correlated with treatment-induced changes in DAS28 (p = 0.014; r2 = 0.187).

Conclusions

TNF-α blockade treatment significantly decreased the CD154 expression on CD4+ T cells, disease activity and anti-CCP antibody simultaneously in RA patients. However TNF-α blockade did not impair T cell capacity to express CD154 after stimulation. These results suggest that decreased CD154 expression after TNF-α blockade may be due to decreased RA disease activity but not direct inhibition of CD154 responsiveness of T cells.

CD40L-Dependent Pathway Is Active at Various Stages of Rheumatoid Arthritis Disease Progression

The inflammatory CD40-CD40L pathway is implicated in various autoimmune diseases, but the activity status of this pathway in various stages of rheumatoid arthritis (RA) progression is unknown. In this study, we used gene signatures of CD40L stimulation derived from human immature dendritic cells and naive B cells to assess the expression of CD40-downstream genes in synovial tissues from anti-citrullinated protein Ab-positive arthralgia, undifferentiated arthritis (UA), early RA, and established RA cohorts in comparison with healthy donors. Interestingly, the expression of CD40LG and active full-length CD40 was increased in the disease tissues, whereas that of a dominant-negative CD40 isoform was decreased. Gene set variation analysis revealed that CD40L-responsive genes in immature dendritic cells and naive B cells were significantly enriched in synovial tissues from UA, early RA, and established RA patients. Additionally, CD40L-induced naive B cell genes were also significantly enriched in synovial tissues from arthralgia patients. In our efforts to characterize downstream mediators of CD40L signaling, we have identified GPR120 and KDM6B as novel components of the pathway. In conclusion, our data suggest that therapeutic CD40-CD40L blocking agents may prove efficacious not only in early and established RA, but also in inhibiting the progression of the disease from arthralgia or UA to RA.

Regulatory role of cytosolic phospholipase A2 alpha in the induction of CD40 in microglia

Background

The aberrant expression of CD40, a co-stimulatory receptor found on the antigen-presenting cells, is involved in the pathogenesis of various degenerative diseases. Our previous study demonstrated that the reduction of cytosolic phospholipase A₂ alpha (cPLA₂α) protein overexpression and activation in the spinal cord of a mouse model of ALS, hmSOD1 G93A, inhibited CD40 upregulation in microglia. The present study was designed to determine whether cPLA₂α has a direct, participatory role in the molecular events leading to CD40 induction.

Methods

Cultures of primary mouse microglia or BV-2 microglia cell line exposed to lipopolysaccharide (LPS) or interferon gamma (IFNγ) for different periods of time, in order to study the role of cPLA₂α in the events leading to CD40 protein induction.

Results

Addition of LPS or IFNγ caused a significant upregulation of cPLA₂α and of CD40, while prevention of cPLA₂α upregulation by a specific oligonucleotide antisense (AS) prevented the induction of CD40, suggesting a role of cPLA₂α in the induction of CD40. Addition of LPS to microglia caused an immediate activation of cPLA₂α detected by its phosphorylated form, while addition of IFNγ induced cPLA₂α activation at a later time scale (4 h). The activation of cPLA₂α is mediated by ERK activity. Suppression of cPLA₂α activity inhibited superoxide production by NOX2-NADPH oxidase and activation of NF-κB detected by the phosphorylation of p65 on serine 536 at 15 min by LPS and at 4 h by IFNγ. Inhibition of NOX2 prevented NF-κB activation and CD40 induction but did not affect cPLA₂α activation, suggesting cPLA₂α is located upstream to NOX2 and NF-κB. The activation of cPLA₂ by LPS was mediated by both adaptor proteins downstream to LPS receptor; TRIF and MyD88, while the activation of cPLA₂α by IFNγ was mediated by the secreted TNF-α at 4 h. The early activation of STAT1α (detected by phospho-serine727 and phoshpo-tyrosine701) by IFNγ and the late activation of STAT1α by LPS were not affected in the presence of cPLA₂α inhibitors, indicating that STAT1α is not under cPLA₂α regulation.

Conclusions

Our results show for the first time that cPLA₂ upregulates CD40 protein expression induced by either LPS or IFNγ, and this regulatory effect is mediated via the activation of NOX2-NADPH oxidase and NF-κB. Cumulatively, our results indicate that cPLA₂α may serve as a pivotal amplifier of the inflammatory response in the CNS.

Cellular and Molecular Mechanisms of Autoimmunity and Lupus Nephritis

Autoimmunity involves immune responses directed against self, which are a result of defective self/foreign distinction of the immune system, leading to proliferation of self-reactive lymphocytes, and is characterized by systemic, as well as tissue-specific, inflammation. Numerous mechanisms operate to ensure the immune tolerance to self-antigens. However, monogenetic defects or genetic variants that weaken immune tolerance render susceptibility to the loss of immune tolerance, which is further triggered by environmental factors. In this review, we discuss the phenomenon of immune tolerance, genetic and environmental factors that influence the immune tolerance, factors that induce autoimmunity such as epigenetic and transcription factors, neutrophil extracellular trap formation, extracellular vesicles, ion channels, and lipid mediators, as well as costimulatory or coinhibitory molecules that contribute to an autoimmune response. Further, we discuss the cellular and molecular mechanisms of autoimmune tissue injury and inflammation during systemic lupus erythematosus and lupus nephritis.

Cardiovascular disease in patients with rheumatoid arthritis

The risk of cardiovascular disease (CVD) in patients with rheumatoid arthritis (RA) is 1.5-2-fold higher than age- and sex-matched individuals from the general population. This excess risk is attributed to the systemic chronic inflammation which is a hallmark of RA. Challenges to optimizing CV risk management in RA include the need for improved methods to predict CV risk, and defining the target risk factor(s) to reduce CV risk. Lessons learned from RA studies can also inform CV risk prevention in the general population, where inflammation also has an important role in the pathogenesis of atherosclerosis.

Non-canonical NF-κB signaling in rheumatoid arthritis: Dr Jekyll and Mr Hyde?

The nuclear factor-κB (NF-κB) family of transcription factors is essential for the expression of pro-inflammatory cytokines, but can also induce regulatory pathways. NF-κB can be activated via two distinct pathways: the classical or canonical pathway, and the alternative or non-canonical pathway. It is well established that the canonical NF-κB pathway is essential both in acute inflammatory responses and in chronic inflammatory diseases, including rheumatoid arthritis (RA). Although less extensively studied, the non-canonical NF-κB pathway is not only central in lymphoid organ development and adaptive immune responses, but is also thought to play an important role in the pathogenesis of RA. Importantly, this pathway appears to have cell type-specific functions and, since many different cell types are involved in the pathogenesis of RA, it is difficult to predict the net overall contribution of the non-canonical NF-κB pathway to synovial inflammation. In this review, we describe the current understanding of non-canonical NF-κB signaling in various important cell types in the context of RA and consider the relevance to the pathogenesis of the disease. In addition, we discuss current drugs targeting this pathway, as well as future therapeutic prospects.

Are polymorphisms of the immunoregulatory factor CD40LG implicated in acute transfusion reactions?

The CD40 ligand (CD40L/CD154), a member of TNF superfamily, is notably expressed on activated CD4+ T-cells and stimulated platelets. CD40L is linked to a variety of pathologies and to acute transfusion reactions (ATR). Mutations in this gene (CD40LG) lead to X-linked hyper-IgM syndrome. Some CD40LG polymorphisms are associated with variable protein expression. The rationale behind this study is that CD40L protein has been observed to be involved in ATR. We wondered whether genetic polymorphisms are implicated. We investigated genetic diversity in the CD40LG using DHPLC and capillary electrophoresis for screening and genotyping (n = 485 French and Tunisian blood donors). We identified significant difference in the CD40LG linkage pattern between the two populations. Variant minor alleles were significantly over-represented in Tunisian donors (P<0.0001 to 0.0270). We found higher heterogeneity in the Tunisian, including three novel low frequency variants. As there was not a particular pattern of CD40LG in single apheresis donors whose platelet components induced an ATR, we discuss how this information may be useful for future disease association studies on CD40LG.

Regulatory B cells are inversely associated with disease activity in rheumatoid arthritis

PURPOSE

The function of regulatory B lymphocytes is known to be abnormal in inflammatory diseases. However, a recent study indicates that IL-10+ B cells seem to be expanded in rheumatoid arthritis (RA). Therefore, the state of IL-10+ B cells in the peripheral blood from RA patients and healthy controls were investigated.

MATERIALS AND METHODS

CD19+ cells in peripheral blood mononuclear cells were purified from blood samples of RA patients and age and gender-matched healthy controls, and stimulated with CD40 ligand and CpG for 48 hours. Then, intracellular IL-10 in CD19+ cells was analyzed using flow cytometry.

RESULTS

There was no significant difference in the proportion of IL-10+ B cells between 10 RA patients and 10 healthy controls (RA, 0.300±0.07 vs. healthy control 0.459±0.07, p=0.114). The proportion of induced IL-10+ B cells to total B cells in RA patients was significantly higher than those in controls (RA, 4.44±3.44% vs. healthy control 2.44±1.64%, p=0.033). However, the proportion of IL-10+ B cells to total B cells correlated negatively with disease activity in RA patients (r=-0.398, p=0.040). Erythrocyte sedimentation rate or C-reactive protein or medication was not associated with the proportion of IL-10+ B cells.

CONCLUSION

The proportion of induced IL-10+ B cell increased in RA patients compared to healthy control, however, negatively correlated with disease activity in RA.

Immune checkpoint receptors in regulating immune reactivity in rheumatic disease

Immune checkpoint regulators are critical modulators of the immune system, allowing the initiation of a productive immune response and preventing the onset of autoimmunity. Co-inhibitory and co-stimulatory immune checkpoint receptors are required for full T-cell activation and effector functions such as the production of cytokines. In autoimmune rheumatic diseases, impaired tolerance leads to the development of diseases such as rheumatoid arthritis, systemic lupus erythematosus, and Sjogren's syndrome. Targeting the pathways of the inhibitory immune checkpoint molecules CD152 (cytotoxic T lymphocyte antigen-4) and CD279 (programmed death-1) in cancer shows robust anti-tumor responses and tumor regression. This observation suggests that, in autoimmune diseases, the converse strategy of engaging these molecules may alleviate inflammation owing to the success of abatacept (CD152-Ig) in rheumatoid arthritis patients. We review the preclinical and clinical developments in targeting immune checkpoint regulators in rheumatic disease.

Human genetics in rheumatoid arthritis guides a high-throughput drug screen of the CD40 signaling pathway

Although genetic and non-genetic studies in mouse and human implicate the CD40 pathway in rheumatoid arthritis (RA), there are no approved drugs that inhibit CD40 signaling for clinical care in RA or any other disease. Here, we sought to understand the biological consequences of a CD40 risk variant in RA discovered by a previous genome-wide association study (GWAS) and to perform a high-throughput drug screen for modulators of CD40 signaling based on human genetic findings. First, we fine-map the CD40 risk locus in 7,222 seropositive RA patients and 15,870 controls, together with deep sequencing of CD40 coding exons in 500 RA cases and 650 controls, to identify a single SNP that explains the entire signal of association (rs4810485, P = 1.4×10⁻⁹). Second, we demonstrate that subjects homozygous for the RA risk allele have ∼33% more CD40 on the surface of primary human CD19+ B lymphocytes than subjects homozygous for the non-risk allele (P = 10⁻⁹), a finding corroborated by expression quantitative trait loci (eQTL) analysis in peripheral blood mononuclear cells from 1,469 healthy control individuals. Third, we use retroviral shRNA infection to perturb the amount of CD40 on the surface of a human B lymphocyte cell line (BL2) and observe a direct correlation between amount of CD40 protein and phosphorylation of RelA (p65), a subunit of the NF-κB transcription factor. Finally, we develop a high-throughput NF-κB luciferase reporter assay in BL2 cells activated with trimerized CD40 ligand (tCD40L) and conduct an HTS of 1,982 chemical compounds and FDA–approved drugs. After a series of counter-screens and testing in primary human CD19+ B cells, we identify 2 novel chemical inhibitors not previously implicated in inflammation or CD40-mediated NF-κB signaling. Our study demonstrates proof-of-concept that human genetics can be used to guide the development of phenotype-based, high-throughput small-molecule screens to identify potential novel therapies in complex traits such as RA.

A current challenge in human genetics is to follow-up “hits” from genome-wide association studies (GWAS) to guide drug discovery for complex traits. Previously, we identified a common variant in the CD40 locus as associated with risk of rheumatoid arthritis (RA). Here, we fine-map the CD40 signal of association through a combination of dense genotyping and exonic sequencing in large patient collections. Further, we demonstrate that the RA risk allele is a gain-of-function allele that increases the amount of CD40 on the surface of primary human B lymphocyte cells from healthy control individuals. Based on these observations, we develop a high-throughput assay to recapitulate the biology of the RA risk allele in a system suitable for a small molecule drug screen. After a series of primary screens and counter screens, we identify small molecules that inhibit CD40-mediated NF-kB signaling in human B cells. While this is only the first step towards a more comprehensive effort to identify CD40-specific inhibitors that may be used to treat RA, our study demonstrates a successful strategy to progress from a GWAS to a drug screen for complex traits such as RA.

CD154: the atherosclerotic risk factor in rheumatoid arthritis?

Atherosclerosis, now regarded as a chronic inflammatory disease of the arterial wall, and its clinical manifestations have increasingly been associated with rheumatoid arthritis (RA), supporting the notion that autoimmune diseases and vascular disorders share common etiological features. Indeed, evidence pertaining to this matter indicates that inflammation and its multiple components are the driving force behind the pathogenesis of these disorders. Interestingly, CD154 and its receptors have emerged as major players in the development of RA and atherosclerosis, which raises the possibility that this axis may represent an important biological link between both complications. Indeed, CD154 signaling elicits critical inflammatory responses that are common to the pathogenesis of both diseases. Here, we provide an overview of the traditional and disease-related interrelations between RA and vascular abnormalities, while focusing on CD154 as a potential mediator in the development of atherosclerotic events in RA patients.

Interleukin-6 production in CD40-engaged fibrocytes in thyroid-associated ophthalmopathy: involvement of Akt and NF-κB

PURPOSE

CD40-CD40 ligand (CD40L) interactions appear to play pathogenic roles in autoimmune disease. Here we quantify CD40 expression on fibrocytes, circulating, and bone marrow-derived progenitor cells. The functional consequences of CD40 ligation are determined since these may promote tissue remodeling linked with thyroid-associated ophthalmopathy (TAO).

METHODS

CD40 levels on cultivated fibrocytes and orbital fibroblasts (GOFB) from patients with Graves' disease (GD), as well as fibrocyte abundance, were determined by flow cytometry. CD40 mRNA expression was evaluated by real-time PCR, whereas response to CD40 ligation was measured by Luminex and RT-PCR. Protein kinase B (Akt) and nuclear factor (NF)-kappa B (NF-κB) signaling were determined by Western blot and immunofluorescence.

RESULTS

Basal CD40 expression on fibrocytes is greater than that on GOFB. IFN-γ upregulates CD40 in both cell types and its actions are mediated at the pretranslational level. Fibrocytes produce high levels of cytokines, including interleukin-6 (IL-6), TNF-α, IL-8, MCP-1, and RANTES (Regulated on Activation, Normal T Cell Expressed and Secreted) in response to CD40L. IL-6 induction results from an increase in steady state IL-6 mRNA, and is mediated through Akt and NF-κB activation. Circulating CD40(+)CD45(+)Col1(+) fibrocytes are far more frequent in vivo in donors with TAO compared with healthy subjects.

CONCLUSIONS

Particularly high levels of functional CD40 are displayed by fibrocytes. CD40L-provoked signaling results in the production of several cytokines. Among these, IL-6 expression is mediated through Akt and NF-κB pathways. The frequency of circulating CD40(+) fibrocytes is markedly increased in patients with TAO, suggesting that this receptor might represent a therapeutic target for TAO.

A novel role of the scaffolding protein JLP in tuning CD40-induced activation of dendritic cells

Receptor internalization is a common mechanism underlying surface receptor down-regulation (and thus receptor signaling) upon its engagement with the cognate ligand. Tight regulation of surface CD40 expression is critical in regulating different functional properties of dendritic cell (DC). Engagement of CD40 on mature DC and the cognate CD40 ligand on T cell activates c-Jun N-terminal MAPK, p38 and ERK1/2 MAPK pathways in mature DC. JNK-associated leucine zipper protein (JLP) is a scaffolding protein that interacted with p38 and JNK. The molecular mechanism underlying CD40 internalization and its physiological impact on DC functions remained unclear. Here we reported that the engagement of CD40 on the LPS-activated DC down-regulated the surface expression of CD40. We examined the role of the JLP protein in DC differentiation, and in the regulation of DC function(s) in vitro. In contrast to the abundant JLP expression observed in immortal cell lines, primary immature DC expressed low levels of the JLP proteins. The induction of the JLP protein expression was observed in the LPS-mature DC that were activated by CD40 ligation, and also in the poly I:C stimulated DC. JLP-silenced DC was impaired in regulating CD40 surface expression upon LPS stimulation and CD40 induced receptor internalization. Such aberrant change in the regulation of surface CD40 expression was associated with an augmented capacity of the JLP-silenced DC in IL-12 production. Collectively, our data identified a novel role of a scaffolding protein JLP in the regulation of surface CD40 expression and fine-tuning of DC function.

CD40L demethylation in CD4(+) T cells from women with rheumatoid arthritis

We have previously demonstrated that DNA demethylation of CD40L on the X chromosome is responsible for female susceptibility to systemic lupus erythematosus (SLE). It is unknown whether aberrant methylation of the CD40L gene also contributes to the higher incidence of rheumatoid arthritis (RA) in females. In this study, we used real-time RT-PCR and flow cytometry to compare CD40L expression levels, and bisulfite sequencing to assess the methylation status of the CD40L promoter region. The results show that CD40L is upregrulated in CD4(+) T cells of female patients with RA. In addition, the CD40L promoter region in CD4(+) T cells from female RA patients was found to be demethylated, which corresponded with increased CD40L mRNA expression. These findings suggest that DNA demethylation contributes to CD40L expression in RA CD4(+) T cells and may in part explain the female preponderance of this disease.

Preformed CD40L is stored in Th1, Th2, Th17, and T follicular helper cells as well as CD4+ 8- thymocytes and invariant NKT cells but not in Treg cells

CD40L is essential for the development of adaptive immune responses. It is generally thought that CD40L expression in CD4⁺ T cells is regulated transcriptionally and made from new mRNA following antigen recognition. However, imaging studies show that the majority of cognate interactions between effector CD4⁺ T cells and APCs in vivo are too short to allow de novo CD40L synthesis. We previously showed that Th1 effector and memory cells store preformed CD40L (pCD40L) in lysosomal compartments and mobilize it onto the plasma membrane immediately after antigenic stimulation, suggesting that primed CD4⁺ T cells may use pCD40L to activate APCs during brief encounters. Indeed, our recent study showed that pCD40L is sufficient to mediate selective activation of cognate B cells and trigger DC activation in vitro. In this study, we show that pCD40L is present in Th1 and follicular helper T cells developed during infection with lymphocytic choriomeningitis virus, Th2 cells in the airway of asthmatic mice, and Th17 cells from the CNS of animals with experimental autoimmune encephalitis (EAE). pCD40L is nearly absent in both natural and induced Treg cells, even in the presence of intense inflammation such as occurs in EAE. We also found pCD40L expression in CD4 single positive thymocytes and invariant NKT cells. Together, these results suggest that pCD40L may function in T cell development as well as an unexpectedly broad spectrum of innate and adaptive immune responses, while its expression in Treg cells is repressed to avoid compromising their suppressive activity.

CD154: an immunoinflammatory mediator in systemic lupus erythematosus and rheumatoid arthritis

Systemic lupus erythematosus and rheumatoid arthritis are two major chronic inflammatory autoimmune diseases with significant prevalence rates among the population. Although the etiology of these diseases remains unresolved, several evidences support the key role of CD154/CD40 interactions in initiating and/or propagating these diseases. The discovery of new receptors (αIIbβ3, α5β1, and αMβ2) for CD154 has expanded our understanding about the precise role of this critical immune mediator in the physiopathology of chronic inflammatory autoimmune diseases in general, and in systemic lupus erythematosus and rheumatoid arthritis in particular. This paper presents an overview of the interaction of CD154 with its various receptors and outlines its role in the pathogenesis of systemic lupus erythematosus and rheumatoid arthritis. Moreover, the potential usefulness of various CD154-interfering agents in the treatment and prevention of these diseases is also discussed.

Cyclosporine-resistant, Rab27a-independent mobilization of intracellular preformed CD40 ligand mediates antigen-specific T cell help in vitro

CD40L is critically important for the initiation and maintenance of adaptive immune responses. It is generally thought that CD40L expression in CD4(+) T cells is regulated transcriptionally and made from new mRNA following Ag recognition. However, recent studies with two-photon microscopy revealed that most cognate interactions between effector CD4(+) T cells and APCs are too short for de novo synthesis of CD40L. Given that effector and memory CD4(+) T cells store preformed CD40L (pCD40L) in lysosomal compartments and that pCD40L comes to the cell surface within minutes of antigenic stimulation, we and others have proposed that pCD40L might mediate T cell-dependent activation of cognate APCs during brief encounters in vivo. However, it has not been shown that this relatively small amount of pCD40L is sufficient to activate APCs, owing to the difficulty of separating the effects of pCD40L from those of de novo CD40L and other cytokines in vitro. In this study, we show that pCD40L surface mobilization is resistant to cyclosporine or FK506 treatment, while de novo CD40L and cytokine expression are completely inhibited. These drugs thus provide a tool to dissect the role of pCD40L in APC activation. We find that pCD40L mediates selective activation of cognate but not bystander APCs in vitro and that mobilization of pCD40L does not depend on Rab27a, which is required for mobilization of lytic granules. Therefore, effector CD4(+) T cells deliver pCD40L specifically to APCs on the same time scale as the lethal hit of CTLs but with distinct molecular machinery.

Sustained T cell Rap1 signaling is protective in the collagen-induced arthritis model of rheumatoid arthritis

OBJECTIVE

Defective activation of T cell receptor-proximal signaling proteins, such as the small GTPase Rap1, is thought to contribute to the pathologic behavior of rheumatoid arthritis (RA) synovial T cells. This study was undertaken to determine whether maintaining Rap1 signaling in murine T cells modifies disease onset or severity in collagen-induced arthritis (CIA).

METHODS

CIA experiments were conducted using wild-type and RapV12-transgenic mice, which express an active mutant of Rap1 in the T cell compartment. Mice were assessed using macroscopic, microscopic, and radiologic measures, and serum levels of anticollagen antibodies were measured by enzyme-linked immunosorbent assay. Phenotypic and functional characterization of wild-type and RapV12-transgenic T cells under homeostatic conditions and during disease onset was performed by flow cytometry.

RESULTS

Disease incidence and severity, synovial infiltration, joint destruction, and anticollagen antibody production were significantly reduced in RapV12-transgenic mice. Although the numbers and percentages of CD3+, CD4+, and CD8+ (naive, effector, and memory) T cells, Treg cells, and Th17 cells were equivalent in wild-type and RapV12-transgenic mice, a significant decrease in the percentage of tumor necrosis factor α-secreting CD8+ T cells was observed in RapV12-transgenic mice during CIA. RapV12-transgenic T cells also inefficiently expressed inducible costimulator and CD40L costimulatory proteins involved in B cell immunoglobulin class switching.

CONCLUSION

Our findings indicate that maintenance of T cell Rap1 signaling in murine T cells reduces disease incidence and severity in CIA, which are associated with specific defects in T cell effector function. Therefore, the restoration of Rap1 function in RA synovial T cells may have therapeutic benefit in RA.

The balancing act of autoimmunity: central and peripheral tolerance versus infection control

Genetic associations with autoimmune disease are enriched in immune response regulators. The immune system in individuals at genetic risk of autoimmunity must balance pressures on the innate and adaptive immune system, most notably infection control, with those of maintaining self-tolerance or controlling autoimmune inflammation. In spite of multiple tolerance mechanisms, inflammation becomes chronic in autoimmune disease, and complete resolution is difficult. This article proposes a perspective on the pathogenesis of autoimmunity-focusing on rheumatoid arthritis and type 1 diabetes-integrating clinical advances and animal models with the role that colonizing micro-organisms play in the balance between tolerance and autoimmunity.

The Toll-like receptor 4 ligands Mrp8 and Mrp14 are crucial in the development of autoreactive CD8+ T cells

Mechanisms linking innate immunity and autoimmune responses are poorly understood. Myeloid-related protein-8 (Mrp8) and Mrp14 are damage-associated molecular pattern molecules (DAMPs) highly upregulated in various autoimmune disorders. We show in a mouse autoimmune model that local Mrp8 and Mrp14 production is essential for the induction of autoreactive CD8+ T cells and the development of systemic autoimmunity. This effect is mediated via Toll-like receptor 4 (TLR4) signaling leading to increased interleukin-17 (IL-17) expression. Notably, expression of Mrp8 and Mrp14 was upregulated in cutaneous lupus erythematosus, and stimulation of CD8+ T cells from individuals with lupus erythematosus with MRP proteins resulted in an upregulation of IL-17, suggesting a key role for MRP8 and MRP14 for the development of autoreactive lymphocytes during human autoimmunity as well. These results demonstrate a link between local expression of DAMP molecules and the development of systemic autoimmunity.

Local B cells and IgE production in the oesophageal mucosa in eosinophilic oesophagitis

BACKGROUND

Eosinophilic oesophagitis (EO) is an emerging yet increasingly prevalent disorder characterised by a dense and selective eosinophilic infiltration of the oesophageal wall. While EO is considered an atopic disease primarily triggered by food antigens, disparities between standard allergen testing and clinical responses to exclusion diets suggest the participation of distinct antigen-specific immunoglobulin E (IgE) in the pathophysiology of EO.

AIM

To find evidence for a local IgE response.

METHODS

Endoscopic biopsies of the distal oesophagus of atopic and non-atopic EO and control individuals (CTL) were processed for immunohistochemistry and immunofluorescence to assess the presence of B cells, mast cells, and IgE-bearing cells. Oesophageal RNA was analysed for the expression of genes involved in B cell activation, class switch recombination to IgE and IgE production, including germline transcripts (GLTs), activation-induced cytidine deaminase (AID), IgE heavy chain (Cepsilon) and mature IgE mRNA using polymerase chain reaction and microarray analysis.

RESULTS

Regardless of atopy, EO showed increased density of B cells (p<0.05) and of IgE-bounded mast cells compared to CTL. Both EO and CTL expressed muGLT, epsilonGLT, gamma4GLT, AID, Cepsilon and IgE mRNA. However, the frequency of expression of total GLTs (p = 0.002), epsilonGLT (p = 0.024), and Cepsilon (p = 0.0003) was significantly higher in EO than in CTL, independent of the atopic status.

CONCLUSION

These results support the heretofore unproven occurrence of both local immunoglobulin class switching to IgE and IgE production in the oesophageal mucosa of EO patients. Sensitisation and activation of mast cells involving local IgE may therefore critically contribute to disease pathogenesis.

CD40 and autoimmunity: the dark side of a great activator

CD40 is a tumor necrosis factor receptor superfamily member expressed by immune and non-immune cells. CD40:CD154 interactions mediate T-dependent B cell responses and efficient T cell priming. Thus, CD40 is a likely candidate to play roles in autoimmune diseases in which activated T and B cells cause pathology. Diseases in which CD40 plays a pathogenic role include autoimmune thyroiditis, type 1 diabetes, inflammatory bowel disease, psoriasis, multiple sclerosis, rheumatoid arthritis, and systemic lupus erythematosus. This review discusses the role of CD40:CD154 interaction in human and mouse autoimmunity, human polymorphisms associated with disease incidence, and disrupting CD40:CD154 interactions as an autoimmune therapy.

CD40/CD40L signaling and its implication in health and disease

CD40, a transmembrane receptor of the tumor necrosis factor gene superfamily is expressed on a variety of cells, such as monocytes, B-cells, antigen presenting cells, endothelial, smooth muscle cells, and fibroblasts. The interaction between CD40 and CD40 ligand (CD40L) enhances the expression of cytokines, chemokines, matrix metalloproteinases, growth factors, and adhesion molecules, mainly through the stimulation of nuclear factor kappa B. The aim of this review is to summarize the molecular and cellular characteristics of CD40 and CD40L, the mechanisms that regulate their expression, the cellular responses they stimulate and finally their implication in the pathophysiology of inflammatory and autoimmune diseases.

Characterization of effector T cells in dry eye disease

PURPOSE

Dry eye disease (DED) is associated with ocular surface inflammation that is thought to be mediated primarily by CD4 T cells. The purpose of this study was to investigate whether this T cell-mediated immune response is generated in the lymphoid compartment and to characterize the functional phenotype of the T cells activated in DED.

METHODS

DED was induced in female C57BL/6 mice by exposure to a desiccating environment in the controlled environment chamber and to systemic scopolamine. T cells from regional draining lymph nodes (LNs) of DED mice and normally sighted mice were analyzed for surface activation markers (CD69 and CD154), chemokine and cytokine receptors, and proliferation potential.

RESULTS

Draining LNs of DED mice showed increased frequencies of CD69- and CD154-expressing T cells with higher proliferative capacity. In addition, these LN T cells primarily showed a helper T-cell (Th)1 phenotype, expressing significantly higher levels of IFN-gamma and IL-12Rbeta2 but not IL-4R. Similarly, the LNs of DED mice showed significantly increased frequencies of T cells expressing CXCR3 and CCR5, but not CCR4, suggesting a bias toward a Th1 phenotype.

CONCLUSIONS

These data demonstrate that a Th1-type immune response is induced in the regional LNs of DED mice. The identification of specific cytokine/chemokine receptors overexpressed by these T cells may signify potential novel targets/strategies for the treatment of DED.

A novel paradigm for dendritic cells as effectors of cartilage destruction

OBJECTIVE

Dendritic cells (DCs) are enriched in RA synovium and have been implicated in the pathogenesis of RA primarily through their ability to present autoantigen and activate T cells. However, whether DCs play an effector role in cartilage destruction is unknown. The aim of this study was to investigate whether DCs can induce collagen release from cartilage and the mechanism involved.

METHODS

Human monocyte-derived DCs (mDCs) were activated with CD40 ligand (CD40L) to mimic DC-T-cell interaction, and supernatants were incubated with cartilage explants. Hydroxyproline was assessed as a measure of collagen release and collagenolytic activity was measured by a bioassay using tritiated collagen. TNF-alpha in DC supernatants was measured by specific ELISA.

RESULTS

Supernatants from CD40L-activated mDCs, but not unstimulated mDCs, strongly induced the destruction of cartilage collagen. mDC supernatants did not contain collagenases but did induce collagenolytic activity in cartilage explants. Neutralization of TNF-alpha in mDC supernatants completely abolished collagenolysis.

CONCLUSIONS

This study shows that mDCs, upon CD40-ligation, induce cartilage collagen degradation through an indirect mechanism via the production of TNF-alpha. Our data suggest a potential important role for mDC-derived TNF-alpha in RA, which is in line with the previously reported observations that DCs are a major source of TNF-alpha in early autoimmune lesions and that anti-TNF-alpha therapeutics effectively suppress joint damage in RA patients. We propose that DCs can act as effectors in cartilage destruction, adding a new aspect to the functional role of DCs in RA pathogenesis.

Mature antigen-experienced T helper cells synthesize and secrete the B cell chemoattractant CXCL13 in the inflammatory environment of the rheumatoid joint

OBJECTIVE

Synovial B cells play a critical role in rheumatoid arthritis (RA), being involved in autoantibody synthesis, T cell activation, and cytokine production. CXCL13 is a B cell chemoattractant that is instrumental in synovial B cell organization; the regulatory determinants of CXCL13 in inflammation are poorly characterized. This study was undertaken to investigate the functional involvement of synovial T cells in the ectopic expression of CXCL13 in RA.

METHODS

CXCL13 production and regulation were addressed using immunohistochemistry, in situ hybridization, quantitative polymerase chain reaction, multicolor flow cytometry, and enzyme-linked immunosorbent assay, by in situ-ex vivo analysis and in vitro functional assays with rheumatoid synovial tissue and primary cells.

RESULTS

CXCL13 messenger RNA and protein expression and spontaneous CXCL13 secretion were detected in RA synovial fluid T cells but were not detected (or were detected only occasionally) in peripheral blood T cells. Analysis of tissue expression confirmed cytoplasm localization of CXCL13 in T lymphocytes infiltrating B cell follicles and small perivascular aggregates. Multicolor characterizations in synovial fluid demonstrated CXCL13 expression in antigen-experienced T helper cells, frequently characterized by terminal differentiation and the lack of the follicular helper T cell markers CXCR5 and BCL6 protein. In vitro functional assays revealed the enhancing effect of T cell receptor-CD28 engagement on CXCL13 production and secretion in primary cells.

CONCLUSION

Our findings define a new functional property of synovial T cells, demonstrating their active involvement in the local production of B cell chemoattractants, and support a direct contribution of the adaptive immune system and antigen-dependent signals in the mechanisms of B cell localization in RA.

Therapeutic interventions targeting CD40L (CD154) and CD40: the opportunities and challenges

CD40 was originally identified as a receptor on B-cells that delivers contact-dependent T helper signals to B-cells through interaction with CD40 ligand (CD40L, CD154). The pivotal role played by CD40-CD40L interaction is illustrated by the defects in B-lineage cell development and the altered structures of secondary lymphoid tissues in patients and engineered mice deficient in CD40 or CD40L. CD40 signaling also provides critical functions in stimulating antigen presentation, priming of helper and cytotoxic T-cells and a variety of inflammatory reactions. As such, dysregulations in the CD40-CD40L costimulation pathway are prominently featured in human diseases ranging from inflammatory conditions to systemic autoimmunity and tissue-specific autoimmune diseases. Moreover, studies in CD40-expressing cancers have provided convincing evidence that the CD40-CD40L pathway regulates survival of neoplastic cells as well as presentation of tumor-associated antigens to the immune system. Extensive research has been devoted to explore CD40 and CD40L as drug targets. A number of anti-CD40L and anti-CD40 antibodies with diverse biological effects are in clinical development for treatment of cancer and autoimmune diseases. This chapter reviews the role of CD40-CD40L costimulation in disease pathogenesis, the characteristics of therapeutic agents targeting this pathway and status of their clinical development.

High avidity autoreactive T cells with a low signalling capacity through the T-cell receptor: central to rheumatoid arthritis pathogenesis?

Self-reactive T cells with low signalling capacity through the T-cell receptor were recently observed in the SKG mouse model of rheumatoid arthritis (RA) and have been linked to a spontaneous mutation in the ZAP-70 signal transduction molecule. Here we hypothesize that similar mechanisms also drive RA, associated with an abnormal innate and adaptive immune response driven by nuclear factor-κB activation and tumour necrosis factor secretion. Similar to the essential role played by pathogens in SKG mice, we propose that HLA-associated immunity to chronic viral infection is a key factor in the immune dysregulation and joint inflammation that characterize RA.

Elevated serum levels of soluble CD154 in children with juvenile idiopathic arthritis

OBJECTIVE

Cytokines play important roles in mediating inflammation in autoimmunity. Several cytokines are elevated in serum and synovial fluid samples from children with Juvenile Idiopathic Arthritis (JIA). Soluble CD154 (sCD154) is elevated in other autoimmune disorders, but has not been characterized in JIA. Our objectives were to determine if sCD154 is elevated in JIA, and to examine correlations between sCD154 and other inflammatory cytokines.

METHODS

Serum from 77 children with JIA and 81 pediatric controls was analyzed for interleukin (IL)1beta, IL2, IL4, IL5, IL6, IL8, IL10, IL12, IL13, sCD154, interferon-gamma (IFNgamma), soluble IL2 receptor (sIL2R), and tumor necrosis factor-alpha (TNFalpha), using the Luminex Multi-Analyte Profiling system. Differences in levels of cytokines between cases and controls were analyzed. Logistic regression was also performed.

RESULTS

sCD154 was significantly elevated in cases compared to controls (p < 0.0001). IL1beta, IL5, IL6, IL8, IL13, IFNgamma, sIL2R, and TNFalpha were also significantly elevated in JIA. Levels of sCD154 were highly correlated with IL1beta, IL6, IL8, and TNFalpha (p < 0.0001). Logistic regression analysis suggested that IL6 (odds ratio (OR): 1.4, p < 0.0001), sCD154 (OR: 1.1, p < 0.0001), and TNFalpha (OR: 1.1, p < 0.005) were positively associated with JIA, while IL10 (OR: 0.5, p < 0.002) was protective. sCD154 was elevated in all JIA subtypes, with highest levels among more severe subtypes. IL1beta, IL6, IL8, sIL2R and TNFalpha were also elevated in several JIA subtypes.

CONCLUSION

Serum levels of sCD154, IL1beta, IL6, IL8, sIL2R and TNFalpha are elevated in most JIA subtypes, suggesting a major role for sCD154, and these cytokines and cytokine receptors in the pathogenesis of JIA.

Withdrawal: Leptin induces CD40 expression through the activation of Akt in murine dendritic cells

Increasing evidence suggests a regulatory role for leptin, an adipocyte-derived hormone, in immunity. Although recent studies indicated an essential role of leptin signaling in dendritic cell (DC) maturation, the molecular mechanisms by which leptin modulates DC functional maturation remained unclear. In this study, we showed that leptin induced CD40 expression in murine DC and significantly up-regulated their immunostimulatory function in driving T cell proliferation. Moreover, leptin markedly enhanced lipopolysaccharide-mediated DC activation. Using pharmacological inhibitors for Akt, STAT-1alpha, or NF-kappaB and the dominant negative forms of Akt and IkappaB kinase alpha/beta/gamma, as well as small interfering RNA for STAT-1alpha, we showed that Akt, STAT-1alpha, and NF-kappaB were important for the leptinor lipopolysaccharide-induced CD40 expression. Coimmunoprecipitation analysis revealed that leptin promoted immune complex formation between Akt and the IkappaB kinase subunits as well as STAT-1alpha. Blocking the activity of Akt demonstrated a crucial role for Akt in translocation of STAT-1alpha and NF-kappaB to the nucleus and activation of the CD40 promoter. Further analysis with chromatin immunoprecipitation assay confirmed that leptin recruited STAT-1alpha, NF-kappaBp65, and RNA polymerase II to the CD40 promoter and enhanced histone 4 acetylation in a time-dependent manner. Thus, our results have elucidated the molecular mechanisms underlying leptin-induced CD40 expression and DC maturation.

Preformed CD40 ligand exists in secretory lysosomes in effector and memory CD4+ T cells and is quickly expressed on the cell surface in an antigen-specific manner

CD40 ligand (CD40L) is an essential effector cytokine for macrophage activation, dendritic cell licensing, and T-cell-dependent antibody responses. Although CD40L is known to be made de novo following antigen recognition, several reports have described surface mobilization of preformed, intracellular CD40L in certain CD4(+) effector T cells. Here we show that rapid surface expression of preformed CD40L following antigen recognition is a general property of both effector and memory CD4(+) T cells, including in vitro and in vivo activated T-cell-receptor transgenic T cells, memory phenotype CD4(+) T cells from pathogen-free naive mice, and polyclonal virus-specific effector and memory T cells. Intracellular CD40L is stored in secretory lysosomes, and colocalizes more strongly with Fas ligand than with CTLA-4, two other molecules that are delivered to the cell surface following antigen recognition. Stimulated surface expression of preformed CD40L is found in memory CD4(+) T cells from CD40-deficient mice, indicating that it does not depend on CD40-induced internalization for delivery to the secretory compartment. We suggest that delivery of preformed CD40L to antigen-presenting cells (APCs) could enable antigen-specific activation of APCs in transient interactions that are too brief to permit de novo synthesis of CD40L.