Chemokine receptors in the rheumatoid synovium: upregulation of CXCR5

Circulating DNA methylation level of CXCR5 correlates with inflammation in patients with rheumatoid arthritis

OBJECTIVES

To assess the differences in circulating DNA methylation levels of CXCR5 between rheumatoid arthritis (RA) and osteoarthritis (OA) and healthy controls (HC), and the correlation of methylation changes with clinical characteristics of RA patients.

METHODS

Peripheral blood samples were collected from 239 RA patients, 30 patients with OA, and 29 HC. Target region methylation sequencing to the promoter region of CXCR5 was achieved using MethylTarget. The methylation level of cg04537602 and methylation haplotype were compared among the three groups, and the correlation between methylation levels and clinical characteristics of RA patients was performed by Spearman's rank correlation analysis.

RESULTS

The methylation level of cg04537602 was significantly higher in the peripheral blood of RA patients compared with OA patients (p = 1.3 × 10^-3 ) and in the HC group (p = 5.5 × 10^{- 4} ). The sensitivity was enhanced when CXCR5 methylation level combined with rheumatoid factor and anti-cyclic citrullinated peptide with area under curve (AUC) of 0.982 (95% confidence interval 0.970-0.995). The methylation level of cg04537602 in RA was positively correlated with C-reactive protein (CRP) (r = .16, p = .01), and in RA patients aged 60 years and above, cg04537602 methylation levels were positively correlated with CRP (r = .31, p = 4.7 × 10^{- 4} ), tender joint count (r = .21, p = .02), visual analog scales score (r = .21, p = .02), Disease Activity Score in 28 joints (DAS28) using the CRP level DAS28-CRP (r = .27, p = 2.1 × 10^{- 3} ), and DAS28-ESR (r = .22, p = .01). We also observed significant differences of DNA methylation haplotypes in RA patients compared with OA patients and HC, which was consistent with single-loci-based CpG methylation measurement.

CONCLUSION

The methylation level of CXCR5 was significantly higher in RA patients than in OA and HC, and correlated with the level of inflammation in RA patients, our study establishes a link between CXCR5 DNA methylation and clinical features that may help in the diagnosis and disease management of RA patients.

A review of the pleiotropic actions of the IFN-inducible CXC chemokine receptor 3 ligands in the synovial microenvironment

Chemokines are pivotal players in instigation and perpetuation of synovitis through leukocytes egress from the blood circulation into the inflamed articulation. Multitudinous literature addressing the involvement of the dual-function interferon (IFN)-inducible chemokines CXCL9, CXCL10 and CXCL11 in diseases characterized by chronic inflammatory arthritis emphasizes the need for detangling their etiopathological relevance. Through interaction with their mutual receptor CXC chemokine receptor 3 (CXCR3), the chemokines CXCL9, CXCL10 and CXCL11 exert their hallmark function of coordinating directional trafficking of CD4+ TH1 cells, CD8+ T cells, NK cells and NKT cells towards inflammatory niches. Among other (patho)physiological processes including infection, cancer, and angiostasis, IFN-inducible CXCR3 ligands have been implicated in autoinflammatory and autoimmune diseases. This review presents a comprehensive overview of the abundant presence of IFN-induced CXCR3 ligands in bodily fluids of patients with inflammatory arthritis, the outcomes of their selective depletion in rodent models, and the attempts at developing candidate drugs targeting the CXCR3 chemokine system. We further propose that the involvement of the CXCR3 binding chemokines in synovitis and joint remodeling encompasses more than solely the directional ingress of CXCR3-expressing leukocytes. The pleotropic actions of the IFN-inducible CXCR3 ligands in the synovial niche reiteratively illustrate the extensive complexity of the CXCR3 chemokine network, which is based on the intercommunion of IFN-inducible CXCR3 ligands with distinct CXCR3 isoforms, enzymes, cytokines, and infiltrated and resident cells present in the inflamed joints.

CXCL13-CXCR5 axis: Regulation in inflammatory diseases and cancer

Chemokine C-X-C motif ligand 13 (CXCL13), originally identified as a B-cell chemokine, plays an important role in the immune system. The interaction between CXCL13 and its receptor, the G-protein coupled receptor (GPCR) CXCR5, builds a signaling network that regulates not only normal organisms but also the development of many diseases. However, the precise action mechanism remains unclear. In this review, we discussed the functional mechanisms of the CXCL13-CXCR5 axis under normal conditions, with special focus on its association with diseases. For certain refractory diseases, we emphasize the diagnostic and therapeutic role of CXCL13-CXCR5 axis.

The healing myocardium mobilizes a distinct B-cell subset through a CXCL13-CXCR5-dependent mechanism

AIMS

Recent studies have revealed that B cells and antibodies can influence inflammation and remodelling following a myocardial infarction (MI) and culminating in heart failure-but the mechanisms underlying these observations remain elusive. We therefore conducted in mice a deep phenotyping of the post-MI B-cell responses in infarcted hearts and mediastinal lymph nodes, which drain the myocardium. Thereby, we sought to dissect the mechanisms controlling B-cell mobilization and activity in situ.

METHODS AND RESULTS

Histological, flow cytometry, and single-cell RNA-sequencing (scRNA-seq) analyses revealed a rapid accumulation of diverse B-cell subsets in infarcted murine hearts, paralleled by mild clonal expansion of germinal centre B cells in the mediastinal lymph nodes. The repertoire of cardiac B cells was largely polyclonal and showed no sign of antigen-driven clonal expansion. Instead, it included a distinct subset exclusively found in the heart, herein termed 'heart-associated B cells' (hB) that expressed high levels of Cd69 as an activation marker, C-C-chemokine receptor type 7 (Ccr7), CXC-chemokine receptor type 5 (Cxcr5), and transforming growth factor beta 1 (Tgfb1). This distinct signature was not shared with any other cell population in the healing myocardium. Moreover, we detected a myocardial gradient of CXC-motif chemokine ligand 13 (CXCL13, the ligand of CXCR5) on Days 1 and 5 post-MI. When compared with wild-type controls, mice treated with a neutralizing CXCL13-specific antibody as well as CXCR5-deficient mice showed reduced post-MI infiltration of B cells and reduced local Tgfb1 expression but no differences in contractile function nor myocardial morphology were observed between groups.

CONCLUSION

Our study reveals that polyclonal B cells showing no sign of antigen-specificity readily infiltrate the heart after MI via the CXCL13-CXCR5 axis and contribute to local TGF-ß1 production. The local B-cell responses are paralleled by mild antigen-driven germinal centre reactions in the mediastinal lymph nodes that might ultimately lead to the production of specific antibodies.

Transcriptional Changes in Regulatory T Cells From Patients With Autoimmune Polyendocrine Syndrome Type 1 Suggest Functional Impairment of Lipid Metabolism and Gut Homing

Autoimmune polyendocrine syndrome type I (APS-1) is a monogenic model disorder of organ-specific autoimmunity caused by mutations in the Autoimmune regulator (AIRE) gene. AIRE facilitates the expression of organ-specific transcripts in the thymus, which is essential for efficient removal of dangerous self-reacting T cells and for inducing regulatory T cells (Tregs). Although reduced numbers and function of Tregs have been reported in APS-I patients, the impact of AIRE deficiency on gene expression in these cells is unknown. Here, we report for the first time on global transcriptional patterns of isolated Tregs from APS-1 patients compared to healthy subjects. Overall, we found few differences between the groups, although deviant expression was observed for the genes TMEM39B, SKIDA1, TLN2, GPR15, FASN, BCAR1, HLA-DQA1, HLA-DQB1, HLA-DRA, GPSM3 and AKR1C3. Of significant interest, the consistent downregulation of GPR15 may indicate failure of Treg gut homing which could be of relevance for the gastrointestinal manifestations commonly seen in APS-1. Upregulated FASN expression in APS-1 Tregs points to increased metabolic activity suggesting a putative link to faulty Treg function. Functional studies are needed to determine the significance of these findings for the immunopathogenesis of APS-1 and for Treg immunobiology in general.

Follicular helper T cells: potential therapeutic targets in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease with joint and systemic inflammation that is accompanied by the production of autoantibodies, such as rheumatoid factor and anti-cyclic citrullinated peptide (anti-CCP) antibodies. Follicular helper T (Tfh) cells, which are a subset of CD4+ T cells, facilitate germinal center (GC) reactions by providing signals required for high-affinity antibody production and the generation of long-lived antibody-secreting plasma cells. Uncontrolled expansion of Tfh cells is observed in various systemic autoimmune diseases. Particularly, the frequencies of circulating Tfh-like (cTfh-like) cells, their subtypes and synovial-infiltrated T helper cells correlate with disease activity in RA patients. Therefore, reducing autoantibody production and restricting excessive Tfh cell responses are ideal ways to control RA pathogenesis. The present review summarizes current knowledge of the involvement of Tfh cells in RA pathogenesis and highlights the potential of these cells as therapeutic targets.

The G Protein-Coupled Receptor (GPR) 15 Counteracts Antibody-Mediated Skin Inflammation

The G protein-coupled receptor 15 (GPR15) has recently been highlighted as an important regulator of T cell trafficking into the gut under physiological and pathophysiological conditions. Additionally, circumstantial evidence has accumulated that GPR15 may also play a role in the regulation of chronic inflammation. However, the (patho)physiological significance of GPR15 has, in general, remained rather enigmatic. In the present study, we have addressed the role of GPR15 in the effector phase of autoantibody-mediated skin inflammation, specifically in the antibody transfer mouse model of bullous pemphigoid-like epidermolysis bullosa acquisita (BP-like EBA). Subjecting Gpr15 ^-/- mice to this model, we have uncovered that GPR15 counteracts skin inflammation. Thus, disease was markedly aggravated in Gpr15 ^-/- mice, which was associated with an increased accumulation of γδ T cells in the dermis. Furthermore, GPR15L, the recently discovered cognate ligand of GPR15, was markedly upregulated in inflamed skin. Collectively, our results highlight GPR15 as counter-regulator of neutrophilic, antibody-mediated cutaneous inflammation. Enhancing the activity of GPR15 may therefore constitute a novel therapeutic principle in the treatment of pemphigoid diseases, such as BP-like EBA.

Monocyte-Derived Dendritic Cell Differentiation in Inflammatory Arthritis Is Regulated by the JAK/STAT Axis via NADPH Oxidase Regulation

Monocyte-derived Dendritic cells (Mo-DC) are a distinct DC subset, involved in inflammation and infection, they originate from monocytes upon stimulation in the circulation and their activation and function may vary in autoimmune diseases. In this study we investigate the differences in Mo-DC differentiation and function in patients with Rheumatoid (RA) compared to Psoriatic arthritis (PsA). A significant increase in the Mo-DC differentiation marker CD209, paralleled by a corresponding decrease in the monocytic marker CD14, was demonstrated in RA compared to PsA, as early as 1 day post Mo-DC differentiation. RA monocytes ex-vivo were phenotypically different to PsA, displaying a more mature phenotype associated with altered cellular-morphology, early dendrite formation, and a significant increase in the CD40 marker. In addition, SPICE algorithm flow cytometric analysis showed distinct differences in chemokine receptors distribution in HC compared to PsA and RA CD14+ cells in the blood, with increased expression of the chemokine receptors CCR7 and CXCR4 observed in PsA and RA. In addition CD14+ cells at the site of inflammation showed a different chemokine receptor pattern between PsA and RA patients, with higher expression of CXCR3 and CXCR5 in RA when compared to PsA. The early priming observed in RA resulted in monocyte-endocytosis and antigen-uptake mechanisms to be impaired, effects that were not observed in PsA where phagocytosis capacity remained highly functional. Tofacitinib inhibited early Mo-DC differentiation, decreasing both CD209 and CD40 activation markers in RA. Inhibition of Mo-DC differentiation in response to Tofacitinib was mediated via an imbalance in the activation of NADPH-oxidases NOX5 and NOX2. This effect was reversed by NOX5 inhibition, but not NOX2, resulting in suppression of NOX5-dependent ROS production. In conclusion, RA monocytes are already primed ex vivo to become DC, evident by increased expression of activation markers, morphological appearance and impaired endocytosis capacity. Furthermore, we demonstrated for the first time that NOX5 mediates Mo-DC differentiation and function in response to Tofacitinib, which may alter DC functions.

CXCL13 is a differentiation- and hypoxia-induced adipocytokine that exacerbates the inflammatory phenotype of adipocytes through PHLPP1 induction

Hypoxia in adipose tissue is regarded as a trigger that induces dysregulation of the secretory profile in adipocytes. Similarly, local dysregulation of adipocytokine secretion is an initial event in the deleterious effects of obesity on metabolism. We previously reported that CXCL13 is highly produced during adipogenesis, however little is known about the roles of CXCL13 in adipocytes. Here, we found that hypoxia, as modeled by 1% O2 or exposure to the hypoxia-mimetic reagent desferrioxamine (DFO) has strong inductive effects on the expression of CXCL13 and CXCR5, a CXCL13 receptor, in both undifferentiated and differentiated adipocytes and in organ-cultured white adipose tissue (WAT). CXCL13 was also highly expressed in WAT from high fat diet-fed mice. Hypoxic profile, typified by increased expression of interleukin-6 (IL-6) and plasminogen activator inhibitor-1 (PAI-1) and decreased expression of adiponectin, was significantly induced by CXCL13 treatment during adipogenic differentiation. Conversely, the treatment of adipocytes with a neutralizing-antibody against CXCL13 as well as CXCR5 knockdown by specific siRNA effectively inhibited DFO-induced inflammation. The phosphorylation of Akt2, a protective factor of adipose inflammation, was significantly inhibited by CXCL13 treatment during adipogenic differentiation. Mechanistically, CXCL13 induces the expression of PHLPP1, an Akt2 phosphatase, through focal adhesion kinase (FAK) signaling; and correspondingly we show that CXCL13 and DFO-induced IL-6 and PAI-1 expression was blocked by Phlpp1 knockdown. Furthermore, we revealed the functional binding sites of PPARγ2 and HIF1-α within the Cxcl13 promoter. Taken together, these results indicate that CXCL13 is an adipocytokine that facilitates hypoxia-induced inflammation in adipocytes through FAK-mediated induction of PHLPP1 in autocrine and/or paracrine manner.

LFMM 2: Fast and Accurate Inference of Gene-Environment Associations in Genome-Wide Studies

Gene-environment association (GEA) studies are essential to understand the past and ongoing adaptations of organisms to their environment, but those studies are complicated by confounding due to unobserved demographic factors. Although the confounding problem has recently received considerable attention, the proposed approaches do not scale with the high-dimensionality of genomic data. Here, we present a new estimation method for latent factor mixed models (LFMMs) implemented in an upgraded version of the corresponding computer program. We developed a least-squares estimation approach for confounder estimation that provides a unique framework for several categories of genomic data, not restricted to genotypes. The speed of the new algorithm is several order faster than existing GEA approaches and then our previous version of the LFMM program. In addition, the new method outperforms other fast approaches based on principal component or surrogate variable analysis. We illustrate the program use with analyses of the 1000 Genomes Project data set, leading to new findings on adaptation of humans to their environment, and with analyses of DNA methylation profiles providing insights on how tobacco consumption could affect DNA methylation in patients with rheumatoid arthritis. Software availability: Software is available in the R package lfmm at https://bcm-uga.github.io/lfmm/.

Route to Rheumatoid Arthritis by Macrophage-Derived Microvesicle-Coated Nanoparticles

The targeted delivery of therapeutics to sites of rheumatoid arthritis (RA) has been a long-standing challenge. Inspired by the intrinsic inflammation-targeting capacity of macrophages, a macrophage-derived microvesicle (MMV)-coated nanoparticle (MNP) was developed for targeting RA. The MMV was efficiently produced through a novel method. Cytochalasin B (CB) was applied to relax the interaction between the cytoskeleton and membrane of macrophages, thus stimulating MMV secretion. The proteomic profile of the MMV was analyzed by iTRAQ (isobaric tags for relative and absolute quantitation). The MMV membrane proteins were similar to those of macrophages, indicating that the MMV could exhibit bioactivity similar to that of RA-targeting macrophages. A poly(lactic- co-glycolic acid) (PLGA) nanoparticle was subsequently coated with MMV, and the inflammation-mediated targeting capacity of the MNP was evaluated both in vitro and in vivo. The in vitro binding of MNP to inflamed HUVECs was significantly stronger than that of the red blood cell membrane-coated nanoparticle (RNP). Compared with bare NP and RNP, MNP showed a significantly enhanced targeting effect in vivo in a collagen-induced arthritis (CIA) mouse model. The targeting mechanism was subsequently revealed according to the proteomic analysis, indicating that Mac-1 and CD44 contributed to the outstanding targeting effect of the MNP. A model drug, tacrolimus, was encapsulated in MNP (T-RNP) and significantly suppressed the progression of RA in mice. The present study demonstrates MMV as a promising and rich material, with which to mimic macrophages, and demonstrates that MNP is an efficient biomimetic vehicle for RA targeting and treatment.

Novel DNA Methylation Sites Influence GPR15 Expression in Relation to Smoking

Smoking is a major risk factor for cardiovascular diseases and has been implicated in the regulation of the G protein-coupled receptor 15 (GPR15) by affecting CpG methylation. The G protein-coupled receptor 15 is involved in angiogenesis and inflammation. An effect on GPR15 gene regulation has been shown for the CpG site CpG3.98251294. We aimed to analyze the effect of smoking on GPR15 expression and methylation sites spanning the GPR15 locus. DNA methylation of nine GPR15 CpG sites was measured in leukocytes from 1291 population-based individuals using the EpiTYPER. Monocytic GPR15 expression was measured by qPCR at baseline and five-years follow up. GPR15 gene expression was upregulated in smokers (beta (ß) = −2.699, p-value (p) = 1.02 × 10⁻⁷⁷) and strongly correlated with smoking exposure (ß = −0.063, p = 2.95 × 10⁻³⁴). Smoking cessation within five years reduced GPR15 expression about 19% (p = 9.65 × 10⁻⁵) with decreasing GPR15 expression over time (ß = 0.031, p = 3.81 × 10⁻⁶). Additionally, three novel CpG sites within GPR15 affected by smoking were identified. For CpG3.98251047, DNA methylation increased steadily after smoking cessation (ß = 0.123, p = 1.67 × 10⁻³) and strongly correlated with changes in GPR15 expression (ß = 0.036, p = 4.86 × 10⁻⁵). Three novel GPR15 CpG sites were identified in relation to smoking and GPR15 expression. Our results provide novel insights in the regulation of GPR15, which possibly linked smoking to inflammation and disease progression.

A cytokine protein-protein interaction network for identifying key molecules in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease of the synovial joints. Though the current RA therapeutics such as disease-modifying antirheumatic drugs (DMARDs), nonsteroidal anti-inflammatory drugs (NSAIDs) and biologics can halt the progression of the disease, none of these would either dramatically reduce or cure RA. So, the identification of potential therapeutic targets and new therapies for RA are active areas of research. Several studies have discovered the involvement of cytokines in the pathogenesis of this disease. These cytokines induce signal transduction pathways in RA synovial fibroblasts (RASF). These pathways share many signal transducers and their interacting proteins, resulting in the formation of a signaling network. In order to understand the involvement of this network in RA pathogenesis, it is essential to identify the key transducers and their interacting proteins that are part of this network. In this study, based on a detailed literature survey, we have identified a list of 12 cytokines that induce signal transduction pathways in RASF. For these cytokines, we have built a signaling network using the protein-protein interaction (PPI) data that was obtained from public repositories such as HPRD, BioGRID, MINT, IntAct and STRING. By combining the network centrality measures with the gene expression data from the RA related microarrays that are available in the open source Gene Expression Omnibus (GEO) database, we have identified 24 key proteins of this signaling network. Two of these 24 are already drug targets for RA, and of the remaining, 12 have direct PPI links to some of the current drug targets of RA. Therefore, these key proteins seem to be crucial in the pathogenesis of RA and hence might be treated as potential drug targets.

RNA sequencing to predict response to TNF-α inhibitors reveals possible mechanism for nonresponse in smokers

BACKGROUND

Several studies have employed microarray-based profiling to predict response to tumor necrosis factor-alpha inhibitors (TNFi) in rheumatoid arthritis (RA); yet efforts to validate these targets have failed to show predictive abilities acceptable for clinical practice.

METHODS

The eighty most extreme responders and nonresponders to TNFi therapy were selected from the observational BiOCURA cohort. RNA sequencing was performed on mRNA from peripheral blood mononuclear cells (PBMCs) collected before initiation of treatment. The expression of pathways as well as individual gene transcripts between responders and nonresponders was investigated. Promising targets were technically replicated and validated in n = 40 new patients using qPCR assays.

RESULTS

Before therapy initiation, nonresponders had lower expression of pathways related to interferon and cytokine signaling, while also showing higher levels of two genes, GPR15 and SEMA6B (p = 0.02). The two targets could be validated, however, additional analyses revealed that GPR15 and SEMA6B did not independently predict response, but were rather dose-dependent markers of smoking (p < 0.0001).

CONCLUSIONS

The study did not identify new transcripts ready to use in clinical practice, yet GPR15 and SEMA6B were recognized as candidate explanatory markers for the reduced treatment success in RA smokers.

Toxicological effects of irregularly shaped and spherical microplastics in a marine teleost, the sheepshead minnow (Cyprinodon variegatus)

The increasing global contamination of plastics in marine environments is raising public concerns about the potential hazards of microplastics to environmental and human health. Microplastics formed by the breakdown of larger plastics are typically irregular in shape. The objective of this study was to compare the effects of spherical or irregular shapes of microplastics on changes in organ distribution, swimming behaviors, gene expression, and enzyme activities in sheepshead minnow (Cyprinodon variegatus). Both types of microplastics accumulated in the digestive system, causing intestinal distention. However, when compared to spherical microplastics, irregular microplastics decreased swimming behavior (i.e., total distance travelled and maximum velocity) of sheepshead minnow. Both microplastics generated cellular reactive oxygen species (ROS), while ROS-related molecular changes (i.e., transcriptional and enzymatic characteristics) differed. This study provides toxicological insights into the impacts of environmentally relevant (fragmented) microplastics on fish and improves our understanding of the environmental effects of microplastics in the ecosystem.

An initial investigation into endothelial CC chemokine expression in the human rheumatoid synovium

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Comparison of the presence of 26 of the CC-chemokines in RA synovial ECs.

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The chemokines CCL7, CCL14, CCL16 and CCL22 were established as being present at RA synovial ECs for the first time.

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CCL8, CCL14, CCL19 and CCL22 are significantly increased in RA compared to non-RA.

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Synovial fluid CCL7 may be a novel RA disease marker.

Rheumatoid arthritis (RA) is a destructive and chronic autoimmune inflammatory disease. Synovial inflammation is a major feature of RA and is associated with leukocyte recruitment. Leukocytes cross the endothelial cells (ECs) into the synovial tissue and fluid and this migration is mediated via a range of chemokines and adhesion molecules on the ECs. As important mediators of leukocyte extravasation, a number of chemokines from each of the chemokine families have been established as expressed in the RA joint.

However, as little information is available on which chemokines are expressed/presented by the ECs themselves, the purpose of the study was to ascertain which of the CC chemokines were localised in RA ECs.

Immunofluoresence was used to assess the presence of the CC-family chemokines in RA synovial ECs using von-Willebrand factor (VWF) as a pan-endothelial marker and a range of human chemokine antibodies. The percentage of VWF positive vessels which were positive for the chemokines was determined. The presence of the four most highly expressed novel chemokines were further investigated in non-RA synovial ECs and the sera and synovial fluid (SF) from patients with RA and osteoarthritis (OA). Statistical analysis of immunofluorescence data was carried out by Student’s t-test. For analysis of ELISA data, Kruskal-Wallis ANOVA followed by Dunn’s multiple comparison test was utilised to analyse differences in sera and SF levels for each chemokine between RA and OA. Spearman rank correlations of sera and SF chemokine levels with a range of clinical variables were also performed.

Chemokine detection varied, the least abundant being CCL27 which was present in 8.3% of RA blood vessels and the most abundant being CCL19 which was present in 80%. Of the 26 chemokines studied, 19 have not been previously observed in RA ECs. Four of these novel chemokines, namely CCL7, CCL14, CCL16 and CCL22 were present on ≥60% of vessels. CCL14 and CCL22 were shown to be increased in RA ECs compared to non-RA ECs, p = 0.0041 and p = 0.014 respectively. EC chemokines CCL7, CCL14, CCL16 and CCL22 also occurred in RA synovial fluid and sera as established by ELISA. CCL7 was shown to be significantly increased in sera and SF from RA patients compared to that from osteoarthritis (OA) patients (p < 0.01), and to have a highly significant correlation with the level of anti-CCP (R = 0.93, p = 0.001). Less abundant chemokines shown to be present in RA ECs were CCL1-3, CCL5, CCL10-13, CCL15, CCL17, CCL18, CCL20, CCL21 and CCL23-28.

In conclusion, this initial study is the first to show the presence of a number of CC chemokines in RA ECs. It provides evidence that further validation and investigation into the presence and functionality of these novel chemokines expressed at RA synovial ECs may be warranted.

Roles of T follicular helper cells in the pathogenesis of adenoidal hypertrophy combined with secretory otitis media

The aim of this study was to investigate the roles of T follicular helper (Tfh) cells in secretory otitis media (SOM) combined with adenoidal hypertrophy (AH).Patients with AH or AH combined with SOM admitted to the Yancheng No. 1 People's Hospital from December 2012 to December 2014 were included. Fourteen age-matched healthy individuals received physical examinations in the hospital served as control. The venous Tfh was determined using flow cytometry, and CD3 + CD4 + CXCR5 + T lymphocytes were defined as Tfh cells. Serum inflammatory factors including IL-8, IL-1b, IL-6, IL-10, TNF, IL-12p70, IL-21, and IgE were determined using commercial kits.Compared with the AH group, the number of CD4 + CXCR5 + T cells in peripheral blood of the AH combined with SOM group showed significant increase. Statistical differences were noticed in the number of the number of CD4 + CXCR5 + T cells in moderate and severe AH groups compared with that of the control group. Statistical differences were identified in the proportion of CD4 + CXCR5 + T cells in the adenoidal tissues between the AH combined with SOM group and AH group (P < .05). For the CD4 + CXCR5 + T cells in adenoidal tissues, no statistical differences were noticed between the moderate and severe AH groups (P > .05). The number of CD4 + CXCR5 + T cells was positively correlated to the serum IL-21. Nevertheless, no correlation was noticed between CD4 + CXCR5 + T cell and serum IL-8, IL-6, IL-10, and IgE.Tfh is involved in the AH combined with SOM in children. Besides, serum IL-21, IL-8, IL-6, IL-10, and IgE may be involved in the onset of SOM in children.

B-cell phenotype and IgD-CD27- memory B cells are affected by TNF-inhibitors and tocilizumab treatment in rheumatoid arthritis

Background

The use of TNF-inhibitors and/or the IL-6 receptor antagonist, tocilizumab, in rheumatoid arthritis (RA) have pleiotropic effects that also involve circulating B-cells. The main goal of this study was to assess the effect of TNF-inhibitors and tocilizumab on B-cell phenotype and gene expression in RA.

Methods

Blood samples were collected from untreated early RA (ERA) patients, established RA patients under methotrexate treatment, established RA patients before and after treatment with TNF-inhibitors and tocilizumab, and healthy donors. B-cell subpopulations were characterized by flow cytometry and B-cell gene expression was analyzed by real-time PCR on isolated B-cells. Serum levels of BAFF, CXCL13 and sCD23 were determined by ELISA.

Results

The frequency of total CD19+ B cells in circulation was similar between controls and all RA groups, irrespective of treatment, but double negative (DN) IgD-CD27- memory B cells were significantly increased in ERA and established RA when compared to controls. Treatment with TNF-inhibitors and tocilizumab restored the frequency of IgD-CD27- B-cells to normal levels, but did not affect other B cell subpopulations. TACI, CD95, CD5, HLA-DR and TLR9 expression on B-cells significantly increased after treatment with either TNF-inhibitors and/ or tocilizumab, but no significant changes were observed in BAFF-R, BCMA, CD69, CD86, CXCR5, CD23, CD38 and IgM expression on B-cells when comparing baseline with post-treatment follow-ups. Alterations in B-cell gene expression of BAFF-R, TACI, TLR9, FcγRIIB, BCL-2, BLIMP-1 and β2M were found in ERA and established RA patients, but no significant differences were observed after TNF-inhibitors and tocilizumab treatment when comparing baseline and follow-ups. Serum levels of CXCL13, sCD23 and BAFF were not significantly affected by treatment with TNF-inhibitors and tocilizumab.

Conclusions

In RA patients, the use of TNF-inhibitors and/ or tocilizumab treatment affects B-cell phenotype and IgD-CD27- memory B cells in circulation, but not B-cell gene expression levels.

T cell specific Cxcr5 deficiency prevents rheumatoid arthritis

The chemokine receptor CXCR5 is primarily expressed on B cells and Tfh cells and facilitates their migration towards B cell follicles. In the present study we investigated the role of the CXCL13/CXCR5 axis in the pathogenesis of rheumatoid arthritis (RA) and specifically addressed the impact of CXCR5-mediated T and B cell migration in this disease. Employing collagen-induced arthritis (CIA) we identify CXCR5 as an absolutely essential factor for the induction of inflammatory autoimmune arthritis. Cxcr5-deficient mice and mice selectively lacking Cxcr5 on T cells were completely resistant to CIA, showed impaired germinal center responses and failed to mount an IgG1 antibody response to collagen II. Selective ablation of CXCR5 expression in B cells also led to suppression of CIA owing to diminished GC responses in secondary lymphoid organs (SLO) and impaired anti-collagen II antibody production. Chimeric mice harboring Cxcr5-proficient and Cxcr5-deficient immune cells revealed SLO and not the synovial tissue as the compartment where CXCR5-mediated cell migration induces autoimmune inflammation in arthritis. Thus our data demonstrate that CXCR5-mediated co-localization of Tfh cells and B cells in SLOs is absolutely essential for the induction of RA and identify CXCR5 and Tfh cells as promising therapeutic targets for the treatment of RA.

Secretion of pro-inflammatory cytokines and chemokines and loss of regulatory signals by fibroblast-like synoviocytes in juvenile idiopathic arthritis

PURPOSE

The goal is to investigate the specific contribution of fibroblast-like synoviocytes (FLS) to the inflammatory milieu of the synovium in juvenile idiopathic arthritis (JIA) through detection of secreted proteins.

EXPERIMENTAL DESIGN

Expression of 89 cytokines and chemokines is determined on unprocessed synovial fluid from controls and JIA patients using antibody arrays. Supernatants from pure cell cultures of FLS grown from synovial fluids or tissues from JIA and controls are also examined for protein expression. Ingenuity Pathway Analysis (IPA) is revealed top pathways and upstream regulators of significant proteins.

RESULTS

Protein studies is revealed that JIA FLS release pro-inflammatory cytokines and chemokines, including IL-4, IL-6, IL-17, CXCL1, and CXCL6, and lose expression of important regulator signals, such as IL-10 and TIMP2. Of the 84 proteins differentially expressed between controls and JIA in the synovial fluid, 1/3 (29 proteins) are differentially expressed in the cell culture supernatants of JIA and control FLS. ELISA of cell culture supernatants and synovial fluid confirmed seven key proteins.

CONCLUSION AND CLINICAL RELEVANCE

JIA FLS are central to perpetuation of inflammation in JIA, including trafficking of inflammatory cells and effects on the extracellular matrix. These cells express key disease-specific chemokines that, with further refinement, may allow us to tailor therapy appropriately.

Activation of GPR15 and its involvement in the biological effects of smoking

Smoking is one of the most significant modifiable environmental risk factors for many diseases. Smoking causes excessive mortality worldwide. Despite decades of long research, there has not been a clear understanding regarding the molecular mechanism that makes smoking harmful to health. Some recent studies have found that smoking influences most significantly the expression and methylation of GPR15. GPR15 is an orphan receptor that is involved in the regulation of the innate immunity and the T-cell trafficking in the intestinal epithelium. Further studies have confirmed that GPR15 is very strongly involved in smoking and smoking-induced molecular changes. Therefore, the altered expression and epigenetic regulation of GPR15 could have a significant role in the health impact of smoking. Impact statement The review describes an orphan receptor GPR15 that has recently been found to be influenced by smoking. This makes GPR15 very sensitive and adequate biomarker for smoking and smoking studies. Also, activation of GPR15 by smoking could help to explain its effects on health.

Analysis of CXCR5+Th17 cells in relation to disease activity and TNF inhibitor therapy in Rheumatoid Arthritis

Th17 and TfH cells are thought to promote tissue inflammation and autoantibody production, respectively, in autoimmune diseases including rheumatoid arthritis (RA). TfH cells that co-express Th17 markers (CXCR5⁺Th17) encompass both of these pathogenic functions, and are increased in some human autoimmune settings including juvenile dermatomyositis. We investigated CXCR5⁺Th17 cells in RA subjects with stable or active disease and before and after TNF inhibitor therapy. CXCR5⁺Th17 cell frequency was increased in RA compared to healthy controls, but other helper T cell subsets were not different. CXCR5⁺Th17 cells correlated with disease activity in subjects with active RA prior to initiation of TNF inhibitor therapy. Baseline CXCR5⁺Th17 cells also correlated with numbers of swollen joints as late as one year post-therapy. CXCR5⁺Th17 cell frequencies were unaltered by TNF blockade and in fact remained remarkably stable within individuals. We conclude that CXCR5⁺Th17 cells are not a direct target of TNF blockade and therefore cannot serve as a biomarker of current disease activity. However, basal CXCR5⁺Th17 cell frequency may indicate underlying differences in disease phenotype between patients and predict ultimate success of TNF inhibitor therapy.

Smoking-induced expression of the GPR15 gene indicates its potential role in chronic inflammatory pathologies

Despite the described clear epigenetic effects of smoking, the effect of smoking on genome-wide gene expression in the blood is obscure. We therefore studied the smoking-induced changes in the gene-expression profile of the peripheral blood. RNA was extracted from the whole blood of 48 individuals with a detailed smoking history (24 never-smokers, 16 smokers, and 8 ex-smokers). Gene-expression profiles were evaluated with RNA sequencing, and results were analyzed separately in 24 men and 24 women. In the male smokers, 13 genes were statistically significantly (false-discovery rate <0.1) differentially expressed; in female smokers, 5 genes. Although most of the differentially expressed genes were different between the male and female smokers, the G-protein-coupled receptor 15 gene (GPR15) was differentially expressed in both male and female smokers compared with never-smokers. Analysis of GPR15 methylation identified significantly greater hypomethylation in smokers compared with that in never-smokers. GPR15 is the chemoattractant receptor that regulates T-cell migration and immunity. Up-regulation of GPR15 could explain to some extent the health hazards of smoking with regard to chronic inflammatory diseases.

LPA Promotes T Cell Recruitment through Synthesis of CXCL13

Lysophosphatidic acid (LPA) is a bioactive phospholipid playing an important role in various inflammatory diseases by inducing expression and secretion of many inflammatory cytokines/chemokines. Here we report in a murine air pouch model of inflammation that LPA induced CXCL13 secretion in a time-dependent manner and with exacerbation of the response when LPA was administered after a pretreatment with TNF-α, a key inflammatory cytokine. LPA mediates recruitment of leukocytes, including that of CD3⁺ cells into unprimed and TNF-α-primed air pouches. CXCL13 neutralization using a blocking antibody injected into air pouches prior to administration of LPA into TNF-α-primed air pouches decreased CD3⁺ cell influx. Our data highlight that LPA-mediated CXCL13 secretion plays a role in T cell recruitment and participates in regulation of the inflammatory response.

T Cell Migration in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation in joints, associated with synovial hyperplasia and with bone and cartilage destruction. Although the primacy of T cell-related events early in the disease continues to be debated, there is strong evidence that autoantigen recognition by specific T cells is crucial to the pathophysiology of rheumatoid synovitis. In addition, T cells are key components of the immune cell infiltrate detected in the joints of RA patients. Initial analysis of the cytokines released into the synovial membrane showed an imbalance, with a predominance of proinflammatory mediators, indicating a deleterious effect of Th1 T cells. There is nonetheless evidence that Th17 cells also play an important role in RA. T cells migrate from the bloodstream to the synovial tissue via their interactions with the endothelial cells that line synovial postcapillary venules. At this stage, selectins, integrins, and chemokines have a central role in blood cell invasion of synovial tissue, and therefore in the intensity of the inflammatory response. In this review, we will focus on the mechanisms involved in T cell attraction to the joint, the proteins involved in their extravasation from blood vessels, and the signaling pathways activated. Knowledge of these processes will lead to a better understanding of the mechanism by which the systemic immune response causes local joint disorders and will help to provide a molecular basis for therapeutic strategies.

CXCL13 antibody for the treatment of autoimmune disorders

BACKGROUND

Homeostatic B Cell-Attracting chemokine 1 (BCA-1) otherwise known as CXCL13 is constitutively expressed in secondary lymphoid organs by follicular dendritic cells (FDC) and macrophages. It is the only known ligand for the CXCR5 receptor, which is expressed on mature B cells, follicular helper T cells (Tfh), Th17 cells and regulatory T (Treg) cells. Aberrant expression of CXCL13 within ectopic germinal centers has been linked to the development of autoimmune disorders (e.g. Rheumatoid Arthritis, Multiple Sclerosis, Systemic Lupus Erythematosis). We, therefore, hypothesized that antibody-mediated disruption of the CXCL13 signaling pathway would interfere with the formation of ectopic lymphoid follicles in the target organs and inhibit autoimmune disease progression. This work describes pre-clinical development of human anti-CXCL13 antibody MAb 5261 and includes therapeutic efficacy data of its mouse counterpart in murine models of autoimmunity.

RESULTS

We developed a human IgG1 monoclonal antibody, MAb 5261 that specifically binds to human, rodent and primate CXCL13 with an affinity of approximately 5 nM and is capable of neutralizing the activity of CXCL13 from these various species in in vitro functional assays. For in vivo studies we have engineered a chimeric antibody to contain the same human heavy and light chain variable genes along with mouse constant regions. Treatment with this antibody led to a reduction in the number of germinal centers in mice immunized with 4-Hydroxy-3-nitrophenylacetyl hapten conjugated to Keyhole Limpet Hemocyanin (NP-KLH) and, in adoptive transfer studies, interfered with the trafficking of B cells to the B cell areas of mouse spleen. Furthermore, this mouse anti-CXCL13 antibody demonstrated efficacy in a mouse model of Rheumatoid arthritis (Collagen-Induced Arthritis (CIA)) and Th17-mediated murine model of Multiple Sclerosis (passively-induced Experimental Autoimmune Encephalomyelitis (EAE)).

CONCLUSIONS

We developed a novel therapeutic antibody targeting CXCL13-mediated signaling pathway for the treatment of autoimmune disorders.

Synthesis of some CC chemokines and their receptors in the synovium in rheumatoid arthritis

We studied the expression of some CC chemokines and their receptors in the synovium of patients with rheumatoid arthritis, osteoarthrosis, and a history of joint injury. In patients with rheumatoid arthritis, the levels mRNA for some angiogenic and proinflammatory chemokines (CCL5/RANTES, CCL11/eotaxin, CCL24/eotaxin-2, and CCL26/eotaxin-3) and their receptors (CCR1, CCR2, CCR3, CCR4, and CCR5) was elevated. mRNA expression correlated with activity, stage, and serological status of rheumatoid arthritis. Obtained data confirm the importance of CC chemokines as mediators of angiogenesis and inflammation in the synovium in rheumatoid arthritis.

Orphan receptor GPR15/BOB is up-regulated in rheumatoid arthritis

Chemokine receptors on leukocytes mediate the recruitment and accumulation of these cells within affected joints in chronic inflammatory diseases such as rheumatoid arthritis (RA). Identification of involved receptors offers potential for development of therapeutic interventions. The objective of this study was to investigate the expression of orphan receptor GPR15/BOB in the synovium of RA and non-RA patients and in peripheral blood of RA patients and healthy donors. GPR15/BOB protein and messenger RNA expression were examined in RA and non-RA synovium by immunofluorescence and reverse-transcription polymerase chain reaction (RT-PCR) respectively. GPR15/BOB expression on peripheral blood leukocytes was analysed by flow cytometry and GPR15/BOB messenger RNA was examined in peripheral blood monocytes by RT-PCR. GPR15/BOB protein was observed in CD68+ and CD14+ macrophages in synovia, with greater expression in RA synovia. GPR15/BOB protein was expressed in all patient synovia whereas in non-RA synovia expression was low or absent. Similarly GPR15/BOB messenger RNA was detected in all RA and a minority of non-RA synovia. GPR15/BOB protein was expressed on peripheral blood leukocytes from RA and healthy individuals with increased expression by monocytes and neutrophils in RA. GPR15/BOB messenger RNA expression was confirmed in peripheral blood monocytes. In conclusion GPR15/BOB is expressed by macrophages in synovial tissue and on monocytes and neutrophils in peripheral blood, and expression is up-regulated in RA patients compared to non-RA controls. This orphan receptor on monocytes/macrophages and neutrophils may play a role in RA pathophysiology.

Lung disease, T-cells and inflammation in common variable immunodeficiency disorders

INTRODUCTION

Besides hypogammaglobulinemia and recurrent infections, abnormalities of T-cells might contribute to lung damage in common variable immunodeficiency disorders (CVID).

MATERIALS AND METHODS

In 16 adult patients, the majority of whom had pulmonary abnormalities, we studied T-cell subsets and markers of inflammation in bronchoalveolar lavage fluid (BALF) and blood and their relations with pulmonary function and high resolution computed tomography (HRCT).

RESULTS

We demonstrated that some of the lymphocyte abnormalities previously demonstrated in peripheral blood from CVID patients, such as low CD4/CD8 T-cell ratio, were also present in BALF. Moreover, low BALF CD4/CD8 ratio (≤ 1), found in seven patients, was significantly associated with higher blood CD8⁺ cell count and to lower values of the lung function variables; forced expiratory volume (FVC), total lung capacity (TLC), vital capacity (VC) and residual volume (RV) in % of predicted. The expression of the inflammatory markers HLA-DR and CCR5 on T-cells was significantly higher, and the expression of CCR7 significantly lower, in BALF compared to blood, possibly reflecting an inflammatory/cytotoxic T-cell phenotype within pulmonary tissue in CVID. Furthermore, patients with bronchiectasis had higher concentrations of the pro-inflammatory cytokine TNFα in plasma, compared to those without.

CONCLUSION

Our findings suggest that inflammation and T-cell activation may be involved in the immunopathogenesis of pulmonary complications in CVID.

BAFF and TACI gene expression are increased in patients with untreated very early rheumatoid arthritis

OBJECTIVE

B cells play important roles in rheumatoid arthritis (RA). Given the beneficial effect of B cell depletion therapy in RA as well as the observed alterations in B cell subpopulations in this disease, we evaluated whether changes in the expression of genes related to B cell survival and activation were already present in patients with untreated very early RA (VERA; < 6 weeks of disease duration).

METHODS

The expression of a group of B cell-related activation and survival genes was quantified in peripheral blood mononuclear cells from patients with VERA by real-time PCR and compared with untreated early RA (< 1 year), established treated RA, and other untreated early arthritis conditions. Serum B cell-activating factor belonging to the tumor necrosis factor family (BAFF) was quantified by ELISA.

RESULTS

BAFF gene expression and serum levels were highest in patients with VERA. The expression of BAFF receptor (BAFF-R) increased with disease progression, while transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI) was elevated since the first weeks of RA onset. Paired box 5 gene expression was also increased at all RA stages. Chemokine (C-X-C motif) receptor 5 was elevated only in established RA. No differences were observed in B cell maturation antigen, activation-induced cytidine deaminase, B lymphocyte-induced maturation protein, and B cell lymphoma 2 expression.

CONCLUSION

Disturbances in the expression of B cell-related activation and survival genes, particularly BAFF and TACI, occur from the onset of RA and precede changes in BAFF-R. These alterations can lead to the development of autoreactive B cells from the first weeks of RA onset.

Effects of CXCL13 inhibition on lymphoid follicles in models of autoimmune disease

The chemokine CXCL13 has a key role in secondary lymphoid tissue orchestration and lymphoid neogenesis. Transgenic mice deficient in CXCL13 or its receptor CXCR5 have severely impaired lymph node development, lack peritoneal B-lymphocytes and are deficient in circulating antibodies to common bacterial antigens. However, total circulating numbers of B-lymphocytes are slightly elevated and humoral responses to T-dependent or blood-borne antigens are relatively normal. Lymphoid neogenesis is an aberrant process that occurs in chronically inflamed tissue and provides a microenvironment supportive of pathogenic B-cell survival and activation. Here, we describe the impact of therapeutic dosing of a CXCL13 antibody in a mouse model of arthritis, and detail the contribution CXCL13 makes to lymphoid follicle microenvironment, without affecting humoral immune responses.

Lack of chemokine signaling through CXCR5 causes increased mortality, ventricular dilatation and deranged matrix during cardiac pressure overload

RATIONALE

Inflammatory mechanisms have been suggested to play a role in the development of heart failure (HF), but a role for chemokines is largely unknown. Based on their role in inflammation and matrix remodeling in other tissues, we hypothesized that CXCL13 and CXCR5 could be involved in cardiac remodeling during HF.

OBJECTIVE

We sought to analyze the role of the chemokine CXCL13 and its receptor CXCR5 in cardiac pathophysiology leading to HF.

METHODS AND RESULTS

Mice harboring a systemic knockout of the CXCR5 (CXCR5(-/-)) displayed increased mortality during a follow-up of 80 days after aortic banding (AB). Following three weeks of AB, CXCR5(-/-) developed significant left ventricular (LV) dilatation compared to wild type (WT) mice. Microarray analysis revealed altered expression of several small leucine-rich proteoglycans (SLRPs) that bind to collagen and modulate fibril assembly. Protein levels of fibromodulin, decorin and lumican (all SLRPs) were significantly reduced in AB CXCR5(-/-) compared to AB WT mice. Electron microscopy revealed loosely packed extracellular matrix with individual collagen fibers and small networks of proteoglycans in AB CXCR5(-/-) mice. Addition of CXCL13 to cultured cardiac fibroblasts enhanced the expression of SLRPs. In patients with HF, we observed increased myocardial levels of CXCR5 and SLRPs, which was reversed following LV assist device treatment.

CONCLUSIONS

Lack of CXCR5 leads to LV dilatation and increased mortality during pressure overload, possibly via lack of an increase in SLRPs. This study demonstrates a critical role of the chemokine CXCL13 and CXCR5 in survival and maintaining of cardiac structure upon pressure overload, by regulating proteoglycans essential for correct collagen assembly.

Monocytes/macrophages express chemokine receptor CCR9 in rheumatoid arthritis and CCL25 stimulates their differentiation

INTRODUCTION

Monocytes/macrophages accumulate in the rheumatoid (RA) synovium where they play a central role in inflammation and joint destruction. Identification of molecules involved in their accumulation and differentiation is important to inform therapeutic strategies. This study investigated the expression and function of chemokine receptor CCR9 in the peripheral blood (PB) and synovium of RA, non-RA patients and healthy volunteers.

METHODS

CCR9 expression on PB monocytes/macrophages was analysed by flow cytometry and in synovium by immunofluorescence. Chemokine receptor CCR9 mRNA expression was examined in RA and non-RA synovium, monocytes/macrophages from PB and synovial fluid (SF) of RA patients and PB of healthy donors using the reverse transcription polymerase chain reaction (RT-PCR). Monocyte differentiation and chemotaxis to chemokine ligand 25 (CCL25)/TECK were used to study CCR9 function.

RESULTS

CCR9 was expressed by PB monocytes/macrophages in RA and healthy donors, and increased in RA. In RA and non-RA synovia, CCR9 co-localised with cluster of differentiation 14+ (CD14+) and cluster of differentiation 68+ (CD68+) macrophages, and was more abundant in RA synovium. CCR9 mRNA was detected in the synovia of all RA patients and in some non-RA controls, and monocytes/macrophages from PB and SF of RA and healthy controls. CCL25 was detected in RA and non-RA synovia where it co-localised with CD14+ and CD68+ cells. Tumour necrosis factor alpha (TNFα) increased CCR9 expression on human acute monocytic leukemia cell line THP-1 monocytic cells. CCL25 induced a stronger monocyte differentiation in RA compared to healthy donors. CCL25 induced significant chemotaxis of PB monocytes but not consistently among individuals.

CONCLUSIONS

CCR9 expression by monocytes is increased in RA. CCL25 may be involved in the differentiation of monocytes to macrophages particularly in RA.

Gene expression profiles of systemic lupus erythematosus and rheumatoid arthritis

Gene expression profiling using microarray technology is being employed to define specific molecular mediators and pathways involved in immunobiology, to understand the intricate interplay of genes participating in the pathogenesis, and to develop biomarkers of disease activity in both systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). This review summarizes the latest information on the pathogenesis of SLE and RA and describes the utilization of microarray technology in these systemic autoimmune diseases.

Fibroblast-like synoviocytes: key effector cells in rheumatoid arthritis

Rheumatoid arthritis (RA) remains a significant unmet medical need despite significant therapeutic advances. The pathogenesis of RA is complex and includes many cell types, including T cells, B cells, and macrophages. Fibroblast-like synoviocytes (FLS) in the synovial intimal lining also play a key role by producing cytokines that perpetuate inflammation and proteases that contribute to cartilage destruction. Rheumatoid FLS develop a unique aggressive phenotype that increases invasiveness into the extracellular matrix and further exacerbates joint damage. Recent advances in understanding the biology of FLS, including their regulation regulate innate immune responses and activation of intracellular signaling mechanisms that control their behavior, provide novel insights into disease mechanisms. New agents that target FLS could potentially complement the current therapies without major deleterious effect on adaptive immune responses.

Chemokines and chemokine receptors in arthritis

Chemokines are involved in leukocyte recruitment to inflammatory sites, such as the synovial tissue in rheumatoid arthritis (RA). There is a structural and a functional classification of chemokines. The former includes four groups: CXC, CC, C and CX3C chemokines. Chemokines may also be either inflammatory or homeostatic, however, these functions often overlap. Anti-chemokine and anti-chemokine receptor targeting may be therapeutically used in the future biological therapy of arthritis. Most data in this field have been obtained from animal models of arthritis as only very few human RA trials have been completed. However, it is very likely that various specific chemokine and chemokine receptor antagonists will be developed and administered to RA patients.

Alterations in peripheral blood memory B cells in patients with active rheumatoid arthritis are dependent on the action of tumour necrosis factor

INTRODUCTION

Disturbances in peripheral blood memory B cell subpopulations have been observed in various autoimmune diseases, but have not been fully delineated in rheumatoid arthritis (RA). Additionally, the possible role of tumour necrosis factor (TNF) in regulating changes in specific peripheral blood memory B cell subsets in RA is still unclear.

METHODS

The frequency and distribution of B cell subsets in the peripheral blood and synovial membrane of active RA patients with long-standing disease have been analysed. Additionally, the possible role of TNF in causing disturbances in memory B cell subsets in RA patients was assessed in a clinical trial with the specific TNF-neutralising antibody, infliximab.

RESULTS

RA patients, independent of disease duration, have a significantly lower frequency of peripheral blood pre-switch IgD+CD27+ memory B cells than healthy individuals, whereas post-switch IgD-CD27+ accumulate with increased disease duration. Notably, both pre-switch IgD+CD27+ and post-switch IgD-CD27+ memory B cells accumulate in the synovial membrane of RA patients. Finally, anti-TNF therapy increased the frequency of pre-switch IgD+CD27 memory B cells in the peripheral blood.

CONCLUSIONS

The data suggest that decreases in peripheral blood IgD+CD27+ pre-switch memory B cells in RA reflect their accumulation in the synovial tissue. Moreover, the significant increase in the peripheral blood pre-switch memory B cells in patients who underwent specific TNF-blockade with infliximab indicates that trafficking of memory B cells into inflamed tissue in RA patients is regulated by TNF and can be corrected by neutralising TNF.

CXCR5- and CCR7-dependent lymphoid neogenesis in a murine model of chronic antigen-induced arthritis

OBJECTIVE

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease with unknown etiology and only partially defined pathogenesis. The aim of this study was to establish a murine model of chronic arthritis in which the development of tertiary lymphoid tissue, a hallmark of human RA, is locally induced, and to characterize the roles of the homeostatic chemokine receptors CXCR5 and CCR7 in this process.

METHODS

We developed a modified model of chronic antigen-induced arthritis (AIA) in mice with a strong bias toward inflammation. Disease pathology was assessed up to 9 months in wild-type, CXCR5-deficient, and CCR7-deficient mice by determination of knee joint swelling and cellular and humoral immune responses, as well as by histologic analysis of arthritic knee joints.

RESULTS

In this novel model of AIA, mice developed organized ectopic lymphoid follicles with topologically segregated B cell and T cell areas, high endothelial venules, and germinal center formation within the chronically inflamed synovial tissue. Analysis of the initiation and progression of AIA in wild-type, CXCR5-/-, and CCR7-/- mice revealed a reduction of acute inflammatory parameters in both knockout strains as well as significantly reduced joint destruction in CXCR5-/- mice. Most importantly, the development and organization of tertiary lymphoid tissue were significantly impaired in CXCR5-deficient and CCR7-deficient mice.

CONCLUSION

Our results suggest that an inflammatory microenvironment efficiently triggers lymphoid neogenesis in autoimmune diseases such as RA. Moreover, the generation of autoreactive tertiary lymphoid tissues, which is entirely dependent on homeostatic chemokines, may in turn maintain local aberrant chronic immune responses.

Gene signatures reflect the marked heterogeneity of tissue-resident macrophages

Tissue-resident macrophages play an important role in defense against pathogens and perform key functions in organ homeostasis, innate and adaptive immunity. Tissue macrophages originate from blood monocytes that infiltrate virtually every organ in the body. Macrophages in different tissues share many characteristics, including their ability to migrate, phagocytose particles, metabolize lipids and present antigens. Morphologically they are quite heterogeneous, and some distinct functions have been reported. The gene expression profile of macrophages is reflective of both their shared and distinct biological functions. Here, we show that macrophages from murine spleen, liver and peritoneum display dramatically different expression profiles. Clusters of genes were found to represent unique biological functions related to adhesion, antigen presentation, phagocytosis, lipid metabolism and signal transduction. Some gene families, such as integrins, are differentially expressed among the macrophages resident in different tissues, suggesting that the tissue of residence influences their biological function.

Cathepsin G: the significance in rheumatoid arthritis as a monocyte chemoattractant

Human cathepsin G (EC 3.4.21.20) has been reported to have the in vitro chemotactic activity for human monocytes. In this study, we examined the role of cathepsin G in monocyte involvement in joint inflammation of rheumatoid arthritis (RA) as a monocyte chemoattractant. Eighteen patients with RA and four patients with osteoarthritis (OA) were used in this study. Thiobenzylester substrate, Succ-Phe-Leu-Phe-S-Bzl, was used to measure the activity of cathepsin G in synovial fluids. Monocyte migration induced by cathepsin G and synovial fluids was assessed by a 48-well microchemotaxis chamber technique. Immunohistochemical staining was performed to determine the cellular origin of cathepsin G in RA synovial tissue. A very low activity of cathepsin G was detected in synovial fluids from patients with OA. On the other hand, significantly increased activity of cathepsin G was detected in patients with RA when compared with the value of OA patients. A considerable monocyte chemotactic activity was detected in the synovial fluid of RA patients, and the activity was partially decreased by the treatment with inhibitors for cathepsin G, alpha1-antichymotrypsin and phenylmethylsulfonyl fluoride. The activity of cathepsin G was significantly correlated with the neutrophil counts in synovial fluids and the concentration of interleukin-6. Immunohistochemical studies showed that cathepsin G was strongly expressed by synovial lining cells, and weakly expressed by macrophages and neutrophils in synovial tissues. This study indicates that the monocyte chemotactic activity of cathepsin G may have a role in the pathogenesis of RA synovial inflammation.

Variability in synovial inflammation in rheumatoid arthritis investigated by microarray technology

In recent years microarray technology has been used increasingly to acquire knowledge about the pathogenic processes involved in rheumatoid arthritis. The present study investigated variations in gene expression in synovial tissues within and between patients with rheumatoid arthritis. This was done by applying microarray technology on multiple synovial biopsies obtained from the same knee joints. In this way the relative levels of intra-patient and inter-patient variation could be assessed. The biopsies were obtained from 13 different patients: 7 by orthopedic surgery and 6 by rheumatic arthroscopy. The data show that levels of heterogeneity varied substantially between the biopsies, because the number of genes found to be differentially expressed between pairs of biopsies from the same knee ranged from 6 to 2,133. Both arthroscopic and orthopedic biopsies were examined, allowing us to compare the two sampling methods. We found that the average number of differentially expressed genes between biopsies from the same patient was about three times larger in orthopedic than in arthroscopic biopsies. Using a parallel analysis of the tissues by immunohistochemistry, we also identified orthopedic biopsies that were unsuitable for gene expression analysis of synovial inflammation due to sampling of non-inflamed parts of the tissue. Removing these biopsies reduced the average number of differentially expressed genes between the orthopedic biopsies from 455 to 171, in comparison with 143 for the arthroscopic biopsies. Hierarchical clustering analysis showed that the remaining orthopedic and arthroscopic biopsies had gene expression signatures that were unique for each patient, apparently reflecting patient variation rather than tissue heterogeneity. Subsets of genes found to vary between biopsies were investigated for overrepresentation of biological processes by using gene ontology. This revealed representative 'themes' likely to vary between synovial biopsies affected by inflammatory disease.

Mechanisms of Disease: the molecular and cellular basis of joint destruction in rheumatoid arthritis

Rheumatoid arthritis is a complex systemic disease that ultimately leads to the progressive destruction of articular and periarticular structures. Novel data indicate that the innate immune system (through activation of Toll-like receptors) is involved in articular pathophysiology, including the recruitment of inflammatory cells, and that periarticular factors such as adipocytokines contribute to the perpetuation of joint inflammation. The deleterious process of joint destruction is mediated by intracellular signaling pathways involving transcription factors, such as nuclear factor kappaB, cytokines, chemokines, growth factors, cellular ligands, and adhesion molecules. Advances in molecular biology techniques have identified T-cell-independent and B-cell-independent pathways that operate at different stages of the disease. Cytokine-independent pathways appear to be responsible for maintaining basic disease activity that is not affected by currently available therapies. Using this knowledge in combination with gene-transfer and gene-silencing approaches, bench-to-bedside strategies will be developed, thus enabling the creation of novel treatments for rheumatoid arthritis.

Chemokine receptor expression in rat adjuvant-induced arthritis

OBJECTIVE

Chemokine receptors mediate leukocyte migration into inflamed rheumatoid arthritis (RA) synovial tissue (ST). Knowledge of their distribution is crucial for understanding the evolution of the inflammatory process. In this study, we used rat adjuvant-induced arthritis (AIA), a model for RA, to define the temporospatial expression of chemokine receptors.

METHODS

ST from rats with AIA was immunostained, the percentage of cells expressing each receptor was determined, and findings were correlated with levels of inflammation. Chemokine receptor expression was evaluated on rat macrophages in vitro.

RESULTS

CCR1, a receptor for macrophage inflammatory protein 1alpha (MIP-1alpha)/CCL3 and RANTES/CCL5, exhibited high constitutive expression on macrophages in AIA. CCR5, binding MIP-1alpha/CCL3 and RANTES/CCL5, was up-regulated on ST macrophages during the course of AIA, correlating with macrophage expression of CCR2, a receptor for monocyte chemoattractant protein 1/CCL2. Endothelial cell (EC) CCR2 was down-regulated as arthritis progressed, inversely correlating with inflammation. CCR3, another RANTES/CCL5 receptor, was constitutively high on macrophages in vivo and in vitro, with down-regulation during AIA. CXCR4, a receptor for stromal cell-derived factor 1/CXCL12), was prominently up-regulated on ECs, preceding the peak of inflammation.

CONCLUSION

These findings show that 1) constitutive expression of CCR1 on macrophages remains high during AIA; 2) CCR2 and CCR3 may play a role in initial recruitment of leukocytes to ST in AIA; 3) macrophage expression of CCR2 and CCR5 may be important for sustaining inflammatory changes; and 4) EC CXCR4 may be a harbinger of inflammatory changes. Our results may help guide chemokine receptor blockade-targeting treatment strategies in inflammatory arthritis.