Chemokine blockade: a new era in the treatment of rheumatoid arthritis?

Essential role of the CCL2-CCR2 axis in Mayaro virus-induced disease

Mayaro virus (MAYV) is an emerging arbovirus member of the Togaviridae family and Alphavirus genus. MAYV infection causes an acute febrile illness accompanied by persistent polyarthralgia and myalgia. Understanding the mechanisms involved in arthritis caused by alphaviruses is necessary to develop specific therapies. In this work, we investigated the role of the CCL2/CCR2 axis in the pathogenesis of MAYV-induced disease. For this, wild-type (WT) C57BL/6J and CCR2-/- mice were infected with MAYV subcutaneously and evaluated for disease development. MAYV infection induced an acute inflammatory disease in WT mice. The immune response profile was characterized by an increase in the production of inflammatory mediators, such as IL-6, TNF, and CCL2. Higher levels of CCL2 at the local and systemic levels were followed by the significant recruitment of CCR2+ macrophages and a cellular response orchestrated by these cells. CCR2-/- mice showed an increase in CXCL-1 levels, followed by a replacement of the macrophage inflammatory infiltrate by neutrophils. Additionally, the absence of the CCR2 receptor protected mice from bone loss induced by MAYV. Accordingly, the silencing of CCL2 chemokine expression in vivo and the pharmacological blockade of CCR2 promoted a partial improvement in disease. Cell culture data support the mechanism underlying the bone pathology of MAYV, in which MAYV infection promotes a pro-osteoclastogenic microenvironment mediated by CCL2, IL-6, and TNF, which induces the migration and differentiation of osteoclast precursor cells. Overall, these data contribute to the understanding of the pathophysiology of MAYV infection and the identification future of specific therapeutic targets in MAYV-induced disease.IMPORTANCEThis work demonstrates the role of the CCL2/CCR2 axis in MAYV-induced disease. The infection of wild-type (WT) C57BL/6J and CCR2-/- mice was associated with high levels of CCL2, an important chemoattractant involved in the recruitment of macrophages, the main precursor of osteoclasts. In the absence of the CCR2 receptor, there is a mitigation of macrophage migration to the target organs of infection and protection of these mice against bone loss induced by MAYV infection. Much evidence has shown that host immune response factors contribute significantly to the tissue damage associated with alphavirus infections. Thus, this work highlights molecular and cellular targets involved in the pathogenesis of arthritis triggered by MAYV and identifies novel therapeutic possibilities directed to the host inflammatory response unleashed by MAYV.

Chitinase 3-like 1 is involved in the induction of IL-8 expression by double-stranded RNA in airway epithelial cells

Viral respiratory infection causes inflammatory lung disease. Chitinase 3-like 1 (CHI3L1) contributes to airway inflammation, but its role in human airway epithelial cells following viral infection is unclear. Thus, we investigated whether CHI3L1 regulates inflammatory responses caused by viral infections in airway epithelial cells. Human bronchial epithelial cells, BEAS-2B, were stimulated with a synthetic analog of viral double-stranded RNA, polyinosinic:polycytidylic acid (poly(I:C)). To confirm the specific role of CHI3L1, CHI3L1 was knocked down in BEAS-2B cells using shRNA lentivirus. The expression of CHI3L1 and proinflammatory cytokines such as IL-8 and phosphorylation of mitogen-activated protein kinase (MAPK) pathways were analyzed. In addition to poly(I:C), BEAS-2B cells were infected with the human respiratory syncytial virus (RSV) A2 strain, and CHI3L1 and IL-8 expression was analyzed. Stimulating the cells with poly(I:C) increased CHI3L1 and IL-8 expression, whereas IL-8 expression was abrogated in CHI3L1 knockdown BEAS-2B cells. Poly(I:C) stimulation of BEAS-2B cells resulted in phosphorylation of MAPK pathways, and inhibition of MAPK pathways significantly abolished IL-8 secretion. Phosphorylation of MAPK pathways was diminished in CHI3L1 knockdown BEAS-2B cells. Infection with RSV increased CHI3L1 and IL-8 expression. IL-8 expression induced by RSV infection was abrogated in CHI3L1 knockdown cells. In conclusion, CHI3L1 may be involved in IL-8 secretion by regulating MAPK pathways during respiratory viral infections in airway epithelial cells.

Proportion of the CD19-Positive and CD19-Negative Lymphocytes and Monocytes within the Peripheral Blood Mononuclear Cell Set is Characteristic for Rheumatoid Arthritis

Background and objectives: Composition of the peripheral blood (PB) cell populations and their activation state reflect the immune status of a patient. Rheumatoid arthritis (RA) is characterized by abnormal B- and T-cell functions. The objective of this study was to assess the profiles of the PB mononuclear cell (PBMC) populations in patients with rheumatoid and osteoarthritis (OA) in comparison with healthy control (HC) subjects in order to evaluate the PBMC profiles as a potential diagnostic characteristic in RA. The second aim was to assess the CCR1 and CCR2 expression on PB lymphocytes and correlate it with the plasma levels of matrix metallopeptidase 9 (MMP-9), IL-17F, TNF-α, IL-6, and IL-10. Materials and Methods: The frequency and phenotype, including CCR1 and CCR2, of the PBMC populations (monocytes, CD19⁺B cells, and T/NK lymphocytes) in RA (n = 15) and OA (n = 10) patients and HC (n = 12) were analyzed by five-color flow cytometry. DNA of the viruses, HHV-6, HHV-7, and B19, in the whole blood and cell-free plasma, were assessed by nested-polymerase chain reaction (PCR). Results: Active persistent or acute infections, caused by HHV-6, HHV-7, or B19, were not detected in patients of this study. Both CCR1 and CCR2 were determined on the PB B and T/NK lymphocytes in several RA and OA patients and HCs. However, in patients, the frequency of the CCR1-positive T/NK lymphocytes showed a weak negative correlation with the IL-10 level, while the frequency of the CCR2-positive B cells correlated positively with the level of IL-6. Statistically significant differences in the proportions of the CD19-positive and CD19-negative lymphocyte and monocyte subsets within the PBMC set were determined between RA and OA patients and HC adults. Conclusions: We have shown in our pilot study with rather small cohorts of patients that the PBMC-population profiles were very consistent, and statistically significantly differed between RA and OA patients and HC subjects.

Neutrophils: Beneficial and Harmful Cells in Septic Arthritis

Septic arthritis is an inflammatory joint disease that is induced by pathogens such as Staphylococcus aureus. Infection of the joint triggers an acute inflammatory response directed by inflammatory mediators including microbial danger signals and cytokines and is accompanied by an influx of leukocytes. The recruitment of these inflammatory cells depends on gradients of chemoattractants including formylated peptides from the infectious agent or dying cells, host-derived leukotrienes, complement proteins and chemokines. Neutrophils are of major importance and play a dual role in the pathogenesis of septic arthritis. On the one hand, these leukocytes are indispensable in the first-line defense to kill invading pathogens in the early stage of disease. However, on the other hand, neutrophils act as mediators of tissue destruction. Since the elimination of inflammatory neutrophils from the site of inflammation is a prerequisite for resolution of the acute inflammatory response, the prolonged stay of these leukocytes at the inflammatory site can lead to irreversible damage to the infected joint, which is known as an important complication in septic arthritis patients. Thus, timely reduction of the recruitment of inflammatory neutrophils to infected joints may be an efficient therapy to reduce tissue damage in septic arthritis.

CXCR2 is critical for bacterial control and development of joint damage and pain in Staphylococcus aureus-induced septic arthritis in mouse

Staphylococcus aureus is the main pathogen associated with septic arthritis. Upon infection, neutrophils are quickly recruited to the joint by different chemoattractants, especially CXCR1/2 binding chemokines. Although their excessive accumulation is associated with intense pain and permanent articular damage, neutrophils have an important function in controlling bacterial burden. This work aimed to study the role of CXCR2 in the control of infection, hypernociception and tissue damage in S. aureus-induced septic arthritis in mice. The kinetics of neutrophil recruitment correlated with the bacterial load recovered from inflamed joint after intra-articular injection of S. aureus. Treatment of mice from the start of infection with the non-competitive antagonist of CXCR1/2, DF2156A, reduced neutrophil accumulation, cytokine production in the tissue, joint hypernociception and articular damage. However, early DF2156A treatment increased the bacterial load locally. CXCR2 was important for neutrophil activation and clearance of bacteria in vitro and in vivo. Start of treatment with DF2156A 3 days after infection prevented increase in bacterial load and reduced the hypernociception in the following days, but did not improve tissue damage. In conclusion, treatment with DF2156A seems be effective in controlling tissue inflammation and dysfunction but its effects are highly dependent on the timing of the treatment start.

A homeostatic function of CXCR2 signalling in articular cartilage

OBJECTIVE

ELR+ CXC chemokines are heparin-binding cytokines signalling through the CXCR1 and CXCR2 receptors. ELR+ CXC chemokines have been associated with inflammatory arthritis due to their capacity to attract inflammatory cells. Here, we describe an unsuspected physiological function of these molecules in articular cartilage homeostasis.

METHODS

Chemokine receptors and ligands were detected by immunohistochemistry, western blotting and RT-PCR. Osteoarthritis was induced in wild-type and CXCR2(-/-) mice by destabilisation of the medial meniscus (DMM). CXCR1/2 signalling was inhibited in vitro using blocking antibodies or siRNA. Chondrocyte phenotype was analysed using Alcian blue staining, RT-PCR and western blotting. AKT phosphorylation and SOX9 expression were upregulated using constitutively active AKT or SOX9 plasmids. Apoptosis was detected by terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assay.

RESULTS

CXCL6 was expressed in healthy cartilage and was retained through binding to heparan sulfate proteoglycans. CXCR2(-/-) mice developed more severe osteoarthritis than wild types following DMM, with increased chondrocyte apoptosis. Disruption of CXCR1/2 in human and CXCR2 signalling in mouse chondrocytes led to a decrease in extracellular matrix production, reduced expression of chondrocyte differentiation markers and increased chondrocyte apoptosis. CXCR2-dependent chondrocyte homeostasis was mediated by AKT signalling since forced expression of constitutively active AKT rescued the expression of phenotypic markers and the apoptosis induced by CXCR2 blockade.

CONCLUSIONS

Our study demonstrates an important physiological role for CXCR1/2 signalling in maintaining cartilage homeostasis and suggests that the loss of ELR+ CXC chemokines during cartilage breakdown in osteoarthritis contributes to the characteristic loss of chondrocyte phenotypic stability.

Effect of phenolic glycolipids from Mycobacterium kansasii on proinflammatory cytokine release. A structure-activity relationship study

The cell wall of pathogenic mycobacteria is abundant with virulence factors, among which phenolic glycolipids (PGLs) are prominent examples. Mycobacterium kansasii, an important opportunistic pathogen, produces seven PGLs and their effect on the release of important proinflammatory cytokines that mediate disease progression has not been investigated. We previously showed that proinflammatory cytokines are modulated by PGLs from M. tuberculosis, M. leprae and M. bovis. In this paper we describe the synthesis of a series of 17 analogs of M. kansasii PGLs containing a truncated aglycone. Subsequently, the effect of these compounds on the release of proinflammatory cytokines (TNF-α, IL-6, IL-1β, MCP-1) and nitric oxide (NO) was evaluated. These compounds exerted an immunoinhibitory effect on the release of the tested cytokines. The concentration-dependent inhibitory profile of the tested molecules was also found to be dependent on the methylation pattern of the molecule and was mediated via toll-like receptor (TLR)-2. This study led to the discovery of a glycolipid (18) that shows promising potent anti-inflammatory properties making it a potential candidate for further optimization of its anti-inflammatory profile.

TGF-β type II receptor/MCP-5 axis: at the crossroad between joint and growth plate development

Despite its clinical significance, the mechanisms of joint morphogenesis are elusive. By combining laser-capture microdissection for RNA sampling with microarrays, we show that the setting in which joint-forming interzone cells develop is distinct from adjacent growth plate chondrocytes and is characterized by downregulation of chemokines, such as monocyte-chemoattractant protein-5 (MCP-5). Using in vivo, ex vivo, and in vitro approaches, we show that low levels of interzone-MCP-5 are essential for joint formation and contribute to proper growth plate organization. Mice lacking the TGF-β-type-II-receptor (TβRII) in their limbs (Tgfbr2(Prx1KO)), which lack joint development and fail chondrocyte hypertrophy, show upregulation of interzone-MCP-5. In vivo and ex vivo blockade of the sole MCP-5 receptor, CCR2, led to the rescue of joint formation and growth plate maturation in Tgfbr2(Prx1KO) but an acceleration of growth plate mineralization in control mice. Our study characterized the TβRII/MCP-5 axis as an essential crossroad for joint development and endochondral growth.

Why CCR2 and CCR5 blockade failed and why CCR1 blockade might still be effective in the treatment of rheumatoid arthritis

Background

The aim of this study was to provide more insight into the question as to why blockade of CCR1, CCR2, and CCR5 may have failed in clinical trials in rheumatoid arthritis (RA) patients, using an in vitro monocyte migration system model.

Methodology/Principal Findings

Monocytes from healthy donors (HD; n = 8) or from RA patients (for CCR2 and CCR5 antibody n = 8; for CCR1 blockade n = 13) were isolated from peripheral blood and pre-incubated with different concentrations of either anti-CCR1, anti-CCR2, or anti-CCR5 blocking antibodies (or medium or isotype controls). In addition, a small molecule CCR1 antagonist (BX471) was tested. Chemotaxis was induced by CCL2/MCP-1 (CCR2 ligand), CCL5/RANTES (CCR1 and CCR5 ligand), or by a mix of 5 RA synovial fluids (SFs), and cellular responses compared to chemotaxis in the presence of medium alone. Anti-CCR2 antibody treatment blocked CCL2/MCP-1-induced chemotaxis of both HD and RA monocytes compared to isotype control. Similarly, anti-CCR5 antibody treatment blocked CCL5/RANTES-induced chemotaxis of RA monocytes. While neither CCR2 nor CCR5 blocking antibodies were able to inhibit SF-induced monocyte chemotaxis, even when both receptors were blocked simultaneously, both anti-CCR1 antibodies and the CCR1 antagonist were able to inhibit SF-induced monocyte chemotaxis.

Conclusions/Significance

The RA synovial compartment contains several ligands for CCR1, CCR2, and CCR5 as well as other chemokines and receptors involved in monocyte recruitment to the site of inflammation. The results suggest that CCR2 and CCR5 are not critical for the migration of monocytes towards the synovial compartment in RA. In contrast, blockade of CCR1 may be effective. Conceivably, CCR1 blockade failed in clinical trials, not because CCR1 is not a good target, but because very high levels of receptor occupancy at all times may be needed to inhibit monocyte migration in vivo.

Genome-wide haplotype association analysis and gene prioritization identify CCL3 as a risk locus for rheumatoid arthritis

Rheumatoid arthritis (RA) is a common autoimmune disease caused by a complex interaction of multiple genetic variants and environmental factors. The association between RA and genetic susceptibility loci has been observed in many different populations, and most studies have focused on univariate analyses of single nucleotide polymorphisms. We performed a genome-wide haplotype association study and prioritized RA-related genes within 100 kb in either direction of significant haplotypes (P < 0.0001), based on their similarity to known RA susceptibility genes. The results showed that the chemokine CCL3 was associated with susceptibility to RA. A haplotype that located CCL3 on chromosome 17q12 had significant correlation with RA (P = 7.56E-05), and the global similarity score of CCL3 was ranked in the top of all RA-related genes, excluding known susceptibility genes (P = 8.42E-07). Our findings provide further evidence for the potential importance of the chemokine CCL3 in RA, and will facilitate the further understanding of its role in immunological regulation and the pathogenesis of RA.

Visualizing CD4 T-cell migration into inflamed skin and its inhibition by CCR4/CCR10 blockades using in vivo imaging model

BACKGROUND

Chemokines are critical mediators of T-cell homing into inflamed skin. The complex nature of this multicellular response makes it difficult to analyse mechanisms mediating the early responses in vivo.

OBJECTIVES

To visualize directly T-cell homing into inflamed skin and its inhibition by blockades using a unique noninvasive confocal microscopy.

MATERIALS AND METHODS

A mouse model of allergic contact dermatitis was used. T cells from oxazolone-sensitized and -challenged Balb/c mice were first analysed phenotypically in vitro. CD4 T cells were then labelled with a tracker dye and transferred into Balb/c-SCID mice. The recipient mice were challenged with oxazolone and CD4 T-cell homing into inflamed skin was visualized.

RESULTS

T cells with the skin homing receptors CCR4 and CCR10 were increased in the affected skin and draining lymph nodes, and effectively attracted by their specific chemokines CCL17, CCL22 and CCL27 in vitro. Using in vivo imaging, T-cell migration into the inflamed skin was observed at 2 h after application, peaking at 12 h and continuing for 48 h. Simultaneous systemic administration of neutralizing antibodies against CCR4 ligands (CCL17 and CCL22) and CCR10 ligand (CCL27) led to a significant suppression of T-cell migration and skin inflammation.

CONCLUSIONS

Our data indicate that these tissue-selective adhesion molecules and chemokine/receptor pathways act in concert to attract specialized T-cell populations to mediate cutaneous inflammation. The in vivo imaging technique can be applicable to other models of cutaneous diseases to help with better understanding of the pathogenesis and monitoring the therapeutic effects.

The role of chemokines in rheumatoid arthritis and osteoarthritis

The directed movement of immune cells is highly dependent on the chemokine network. Chemokines are key molecules early in the embryogenesis of lymph nodes and throughout adult life, where they regulate immune responses against pathogens. Although immune cells are best known for expressing chemokine receptors, through which they can respond to matching chemokines, endothelial cells also express chemokine receptors. The directed movement of endothelial cells facilitates angiogenesis. In chronic inflammatory conditions, such as rheumatoid arthritis (RA), chemokines are abundantly present at the site of inflammation and form a group of potential therapeutic targets. Some agents that block chemokine-chemokine receptor interaction are already under clinical investigation. The expression of chemokine receptors has also been found in cell types other than immune cells and endothelial cells. Chondrocytes, for instance, express several chemokine receptors. Elucidating their function may provide new insights into joint degradation in RA as well as in other conditions, including osteoarthritis (OA).

Cannabinoid CB(2)-selective inverse agonist protects against antigen-induced bone loss

Work to improve the therapeutic properties of cannabinoid CB(2) receptor-selective inverse agonists has led to the development of Sch.036, an aryl substituted triaryl bis-sulfone with improved oral pharmacokinetic parameters. In this report, we show that this compound blocks in vivo trafficking of various leukocyte populations, a property consistent with other members of this chemical series. This CB(2)-selective compound also shows efficacy in leukocyte recruitment models when added in concert with suboptimal doses of selected anti-inflammatory agents, consistent with its unique function and indicative of its potential therapeutic utility. Finally, studies with Sch.036 show that this cannabinoid CB(2)-specific inverse agonist can ameliorate bone damage in a rat model of relapsing-remitting arthritis. This result suggests that a cannabinoid CB(2)-selective inverse agonist may help ameliorate a particularly harmful property of this inflammatory joint disease.

Cytokines in the pathogenesis of rheumatoid arthritis

Cytokines regulate a broad range of inflammatory processes that are implicated in the pathogenesis of rheumatoid arthritis. In rheumatoid joints, it is well known that an imbalance between pro- and anti-inflammatory cytokine activities favours the induction of autoimmunity, chronic inflammation and thereby joint damage. However, it remains less clear how cytokines are organized within a hierarchical regulatory network, and therefore which cytokines may be the best targets for clinical intervention a priori. Here, we discuss the crucial effector function of cytokines in the immunological processes that are central to the pathogenesis of rheumatoid arthritis.

Chemokine inhibition in inflammatory arthritis

Synovial inflammation in rheumatoid arthritis (RA) and other arthritides is, in part, dependent on migration of inflammatory cells as well as retention of these cells at the site of inflammation. Chemokines play a critical role in these processes and represent an attractive target for therapeutic intervention. Animal models of RA have shown that it is possible to induce clinical improvement by specifically targeting chemokines or their receptors. Although at present only very limited data exist, initial data suggest that it may be possible to reduce synovial inflammation in patients with RA by specific chemokine blockade. Innovative trial design may help to screen for potentially interesting chemokine antagonists in an early stage of development.

Blood and synovial fluid cytokine signatures in patients with juvenile idiopathic arthritis: a cross-sectional study

BACKGROUND

Juvenile idiopathic arthritis (JIA) consists of a heterogeneous group of disorders with, for the most part, an unknown immunopathogenesis. Although onset and disease course differ, the subtypes of JIA share the occurrence of chronic inflammation of the joints, with infiltrations of immunocompetent cells that secrete inflammatory mediators.

OBJECTIVE

To identify a panel of cytokines specifically related to the inflammatory process in JIA.

METHODS

Using a new technology, the multiplex immunoassay, 30 cytokines were measured in plasma of 65 patients with JIA, of which 34 were paired with synovial fluid. These data were compared with plasma of 20 healthy controls and 9 patients with type I diabetes, a chronic inflammatory disease.

RESULTS

Patients with JIA had, irrespective of their subclassification, significantly higher levels of tumour necrosis factor alpha, macrophage inhibitory factor (MIF), CCL2, CCL3, CCL11, CCL22 and CXCL9 in plasma than controls. In paired plasma and synovial fluid samples of patients with JIA, significantly higher levels of interleukin (IL)6, IL15, CCL2, CCL3, CXCL8, CXCL9 and CXCL10 were present in synovial fluid. Cluster analysis in all patients with JIA revealed a predominant pro-inflammatory cytokine cluster during active disease and a regulatory/anti-inflammatory-related cytokine cluster during remission. Whether a discrimination profile of various cytokines could help in the determination of disease classification was tested.

CONCLUSION

It is suggested that several cytokines (IL18, MIF, CCL2, CCL3, CCL11, CXCL9 and CXCL10) may correspond to the activation status during inflammation in JIA and could be instrumental in monitoring disease activity and outcomes of (new) immunotherapies.

Targeting the CB2 receptor for immune modulation

Early work on the biology of the components of Cannabis sativa showed evidence for a potential influence on immune regulation. With the discovery of a peripheral cannabinoid receptor associated with immune cells, many laboratories have sought to link the immunoregulatory activities of cannabinoid compounds with this receptor, hoping that such compounds would lack the psychoactive effects of marijuana and other nonspecific cannabinoid agonists. In this report, the authors investigate the role of the cannabinoid CB2 receptor in immune regulation, with particular emphasis on compounds shown to regulate immune cell recruitment. The authors conclude by using the immune cell recruitment model to rationalise cannabinoid CB2 receptor-specific effects in modulating immune disease, particularly the increasing evidence for its role in experimental autoimmune encephalomyelitis and in influencing bone density.

Osteoclast precursors: cytokine-stimulated immunomodulators of inflammatory bone disease

PURPOSE OF REVIEW

Proinflammatory cytokines produced in inflamed joints promote the generation and release from the bone marrow of osteoclast precursors (OCPs). These OCPs are recruited to inflamed joints where, in response to proinflammatory cytokines, they differentiate into osteoclasts and behave as immunomodulatory cells. We review the regulation of OCP formation and differentiation, and propose that they are not only sources of bone-resorbing osteoclasts, but also of immune cells that influence the progression of inflammatory bone diseases.

RECENT FINDINGS

OCP numbers are increased in the blood of humans and animals with tumor necrosis factor (TNF)-mediated arthritis and they correlate with serum TNF levels, which can be lowered by anti-TNF therapy. TNF stimulates bone marrow OCP generation in part by increasing their expression of c-Fms. These precursors then leave the bone marrow and circulate in the blood stream. Receptor activator NF-kappaB ligand (RANKL) and TNF, which are elevated in inflamed joints, mediate OCP differentiation into osteoclasts and other cell types, including dendritic cells. They also stimulate OCPs to produce proinflammatory cytokines and chemokines. RANKL inhibition prevents joint inflammation in TNF-mediated arthritis.

SUMMARY

OCPs are effector immunomodulatory cells in inflammatory bone diseases. They respond to and secrete cytokines, and are therefore targets for anti-inflammatory therapy.

Expression of the inflammatory chemokines CCL5, CCL3 and CXCL10 in juvenile idiopathic arthritis, and demonstration of CCL5 production by an atypical subset of CD8+ T cells

This study focuses upon three chemokines, namely CCL5, CXCL10 and CCL3, which are potential novel therapeutic targets in arthritis. The aim of the study was to analyse the expression and production of these three chemokines within the joints of children with juvenile idiopathic arthritis (JIA) of the oligoarticular and polyarticular subtypes. All three of these chemokines are highly expressed at the level of mRNA, with the most significant increase in mRNA levels being demonstrated for CCL5 when compared with matched peripheral blood samples and controls. We show that high levels of all three chemokines are present in synovial fluid of children with JIA. We investigate the major source of CCL5 from inflammatory synovial cells, which we show to be CD8+ T cells. This CD8+ synovial T cell population has an unexpected phenotype that has not been described previously, being CCR7- yet predominantly CD28+ and CD45RA-. These cells contain high levels of stored intracellular CCL5, and rapid release of CCL5 takes place on T cell stimulation, without requiring new protein synthesis. In addition, we demonstrate that CCL5 is present in synovial biopsies from these patients, in particular on the endothelium of small and medium sized vessels. We believe this to be the first in depth analysis of these mediators of inflammation in JIA.

Osteoclast precursors, RANKL/RANK, and immunology

Rapid progress has been made in recent years in our understanding of the mechanisms regulating the formation, activation, and survival of osteoclasts, which are derived from precursor cells in the myeloid lineage. In contrast, study of the regulation of osteoclast precursors (OCPs) has been relatively slow, in part because it has been hard to accurately identify them. However, following the discovery of cell-surface markers that facilitated purification of OCPs, recent studies have demonstrated that peripheral blood OCP numbers are increased in tumor necrosis factor (TNF)-mediated arthritis, both in animals and humans, and these numbers correlate with serum TNF levels. The increase can be reversed by anti-TNF therapy. Furthermore, the precursor cells that give rise to osteoclasts can also differentiate into other cell types, including dendritic cells. Receptor activator nuclear factor-kappaB ligand (RANKL) stimulates OCPs to produce pro-inflammatory cytokines and chemokines, and RANKL blockade prevents joint inflammation in a murine model of inflammatory arthritis. These findings suggest that OCPs may serve as a source for both osteoclasts and other effector cells and participate actively in the pathogenesis of diseases. Here, we review our current understanding of the regulation of OCP formation and differentiation and provide a model of a vicious cycle in which pro-inflammatory cytokines produced in inflamed joints feedback on the bone marrow to promote the generation and release of OCPs. The OCPs then home to the inflamed joints to differentiate into mature osteoclasts or to produce more inflammatory factors in the presence of RANKL. Disruption of this cycle could provide a new strategy for the development of drugs to treat inflammatory arthritis and other disorders associated with elevated OCP/myeloid progenitors.

CD97 neutralisation increases resistance to collagen-induced arthritis in mice

Synovial tissue of rheumatoid arthritis (RA) patients is characterised by an influx and retention of CD97-positive inflammatory cells. The ligands of CD97, CD55, chondroitin sulfate B, and alpha5beta1 (very late antigen [VLA]-5) are expressed abundantly in the synovial tissue predominantly on fibroblast-like synoviocytes, endothelium, and extracellular matrix. Based upon this expression pattern, we hypothesise CD97 expression to result in accumulation of inflammatory cells in the synovial tissue of RA patients. To determine the therapeutic effect of blocking CD97 in an animal model of RA, collagen-induced arthritis was induced in a total of 124 DBA/J1 mice. Treatment was started on day 21 (early disease) or on day 35 (longstanding disease) with the blocking hamster anti-mouse CD97 monoclonal antibody (mAb) 1B2, control hamster immunoglobulin, or NaCl, applied intraperitoneally three times a week. The paws were evaluated for clinical signs of arthritis and, in addition, examined by radiological and histological analysis. Mice receiving 0.5 mg CD97 mAb starting from day 21 had significantly less arthritis activity and hind paw swelling. Furthermore, joint damage and inflammation were reduced and granulocyte infiltration was decreased. When treatment was started on day 35, CD97 mAb treatment had similar effects, albeit less pronounced. The results support the notion that CD97 contributes to synovial inflammation and joint destruction in arthritis.

Perturbation of chemokine networks by gene deletion alters the reinforcing actions of ethanol

Microarray analysis of human alcoholic brain and cultured cells exposed to ethanol showed significant changes in expression of genes related to immune or inflammatory responses, including chemokines and chemokine receptors. To test the hypothesis that chemokines exhibit previously undiscovered pleiotropic effects important for the behavioral actions of ethanol, we studied mutant mice with deletion of the Ccr2, Ccr5, Ccl2 or Ccl3 genes. Deletion of Ccr2, Ccl2 (females) or Ccl3 in mice resulted in lower preference for alcohol and consumption of lower amounts of alcohol in a two-bottle choice test as compared with wild-type mice. Ethanol treatment (2.5 g/kg, i.p.) induced stronger conditioned taste aversion in Ccr2, Ccl2 or Ccl3 null mutant mice than in controls. Ccr2 and Ccr5 null mutant mice did not differ from wild-type mice in ethanol-induced loss of righting reflex (LORR), but mice lacking Ccl2 or Ccl3 showed longer LORR than wild-type mice. There were no differences between mutant strains and wild-type mice in severity of ethanol-induced withdrawal. Genetic mapping of chromosome 11 for the Ccl2 and Ccl3 genes (46.5 and 47.6 cM, respectively) revealed that an alcohol-induced LORR QTL region was contained within the introgressed region derived from 129/SvJ, which may cause some behavioral phenotypes observed in the null mice. On the contrary, known QTLs on Chr 9 are outside of 129/SvJ region in Ccr2 and Ccr5 (71.9 and 72.0 cM, respectively) null mutant mice. These data show that disruption of the chemokine network interferes with motivational effects of alcohol.

Chemokine and chemokine receptor expression in paired peripheral blood mononuclear cells and synovial tissue of patients with rheumatoid arthritis, osteoarthritis, and reactive arthritis

BACKGROUND

Chemokine receptors and chemokines have a crucial role in leucocyte recruitment into inflamed tissue.

OBJECTIVE

To examine the expression of an extensive number of chemokines and receptors in a unique bank of paired samples of synovial tissue (ST) and peripheral blood (PB) from patients with different forms of arthritis to assist in identifying suitable targets for therapeutic intervention.

METHODS

Synovial biopsy specimens were obtained from 23 patients with rheumatoid arthritis (RA), 16 with osteoarthritis, and 8 with reactive arthritis. ST chemokine (CCL2/MCP-1, CCL5/RANTES, CCL7/MCP-3, CCL8/MCP-2, CCL14/HCC-1, CCL15/HCC-2, CCL16/HCC-4), chemokine receptor (CCR1, CCR2b, CCR5, CXCR4), and CD13 expression was analysed by immunohistochemistry and two colour immunofluorescence. Chemokine receptor expression (CCR1, CCR3, CCR5, CCR6, CCR7) on PB cells was studied by flow cytometry. Non-parametric tests were used for statistical analysis.

RESULTS

Abundant expression of CCR1, CXCR4, and CCR5 was found in all forms of arthritis, with a specific increase of CCL5 and CCL15 in RA. CCL7, CCL8, CCL14, CCL15, and CCL16 were detected for the first time in ST. The results for PB analysis were comparable among different arthritides. Interestingly, compared with healthy controls, significantly lower expression of CCR1 (p<0.005) and CCR5 (p<0.05) by PB monocytes in the patient groups was seen.

DISCUSSION

A variety of chemokines and receptors might have an important role in several inflammatory joint disorders. Although other receptors are involved as well, migration of CCR1(+) and CCR5(+) cells towards the synovial compartment may play a part in the effector phase of various forms of arthritis.

Targeting cellular adhesion molecules, chemokines and chemokine receptors in rheumatoid arthritis

The development of specific targeted therapies, such as anti-TNF-alpha treatment, for chronic inflammatory disorders such as rheumatoid arthritis, has significantly improved treatment, although not all patients respond. Targeting cellular adhesion molecules and chemokines/chemokine receptors as regulators of the extravasation and migration of leukocytes may provide a novel approach for the treatment of these diseases. Moreover, the possibility of developing small-molecule antagonists offers an excellent method for the oral delivery of compounds with a short half-life.