A need for a 'whole-istic functional genomics' approach in complex human diseases: arthritis

Chemokines play an essential role in the progression of rheumatoid arthritis (RA). In the present study we examined the expression and regulatory mechanisms of IFN-γ inducible protein (IP)-10 in RA synovitis. RA synovial fluid contained greater amounts of IP-10 than did synovial fluid from patients with osteoarthritis. Immunolocalization analysis indicated that IP-10 was associated mainly with infiltrating macrophage-like cells, and fibroblast-like cells in the RA synovium. The interaction of activated leukocytes with fibroblast-like synoviocytes resulted in marked increases in IP-10 expression and secretion. Moreover, induction of IP-10 was mediated via specific adhesion molecules, as indicated by the finding that both anti-integrin (CD11b and CD18) and intercellular adhesion molecule-1 antibodies significantly inhibited IP-10 induction. These results suggest that IP-10 expression within inflamed joints appears to be regulated not only by inflammatory cytokines but also by the physical interaction of activated leukocytes with fibroblast-like synoviocytes, and that IP-10 may contribute to the recruitment of specific subpopulations of T cells (Th1 type) from the bloodstream into the synovial joints.     

CD147 overexpression on synoviocytes in rheumatoid arthritis enhances matrix metalloproteinase production and invasiveness of synoviocytes

Macrophage-like synoviocytes and fibroblast-like synoviocytes (FLS) are known as the most active cells of rheumatoid arthritis (RA) and are close to the articular cartilage in a position enabling them to invade the cartilage. Macrophage-like synoviocytes and FLS expression of matrix metalloproteinases (MMPs) and their interaction has aroused great interest. The present article studied the expression of CD147, also called extracellular matrix metalloproteinase inducer, on monocytes/macrophages and FLS from RA patients and its potential role in enhancing MMPs and the invasiveness of synoviocytes. Expression of CD147 on FLS derived from RA patients and from osteoarthritis patients, and expression of CD147 on monocytes/macrophages from rheumatic synovial fluid and healthy peripheral blood were analyzed by flow cytometry. The levels of CD147, MMP-2 and MMP-9 mRNA in FLS were detected by RT-PCR. The role of CD147 in MMP production and the cells' invasiveness in vitro were studied by the co-culture of FLS with the human THP-1 cell line or monocytes/macrophages, by gel zymography and by invasion assay. The results showed that the expression of CD147 was higher on RA FLS than on osteoarthritis FLS and was higher on monocytes/macrophages from rheumatic synovial fluid than on monocytes/macrophages from healthy peripheral blood. RT-PCR showed that the expressions of CD147, MMP-2 and MMP-9 mRNA was higher in RA FLS than in osteoarthritis FLS. A significantly elevated secretion and activation of MMP-2 and MMP-9 were observed in RA FLS co-cultured with differentiated THP-1 cells or RA synovial monocytes/macrophages, compared with those co-cultured with undifferentiated THP-1 cells or healthy control peripheral blood monocytes. Invasion assays showed an increased number of invading cells in the co-cultured RA FLS with differentiated THP-1 cells or RA synovial monocytes/macrophages. CD147 antagonistic peptide inhibited the MMP production and the invasive potential. Our studies demonstrated that the CD147 overexpression on monocytes/macrophages and FLS in RA patients may be responsible for the enhanced MMP secretion and activation and for the invasiveness of synoviocytes. These findings suggest that CD147 may be one of the important factors in progressive joint destruction of RA and that CD147 may be a potential therapeutic target in RA treatment.     

Fibroblast activation protein is expressed by rheumatoid myofibroblast-like synoviocytes

Fibroblast activation protein (FAP), as described so far, is a type II cell surface serine protease expressed by fibroblastic cells in areas of active tissue remodelling such as tumour stroma or healing wounds. We investigated the expression of FAP by fibroblast-like synoviocytes (FLSs) and compared the synovial expression pattern in rheumatoid arthritis (RA) and osteoarthritis (OA) patients. Synovial tissue from diseased joints of 20 patients, 10 patients with refractory RA and 10 patients with end-stage OA, was collected during routine surgery. As a result, FLSs from intensively inflamed synovial tissues of refractory RA expressed FAP at high density. Moreover, FAP expression was co-localised with matrix metalloproteinases (MMP-1 and MMP-13) and CD44 splice variants v3 and v7/8 known to play a major role in the concert of extracellular matrix degradation. The pattern of signals appeared to constitute a characteristic feature of FLSs involved in rheumatoid arthritic joint-destructive processes. These FAP-expressing FLSs with a phenotype of smooth muscle actin-positive myofibroblasts were located in the lining layer of the synovium and differ distinctly from Thy-1-expressing and non-proliferating fibroblasts of the articular matrix. The intensity of FAP-specific staining in synovial tissue from patients with RA was found to be different when compared with end-stage OA. Because expression of FAP by RA FLSs has not been described before, the findings of this study highlight a novel element in cartilage and bone destruction of arthritic joints. Moreover, the specific expression pattern qualifies FAP as a therapeutic target for inhibiting the destructive potential of fibroblast-like synovial cells.     

IL-27-producing CD14(+) cells infiltrate inflamed joints of rheumatoid arthritis and regulate inflammation and chemotactic migration

Interleukin (IL)-27, a heterodimeric cytokine, has been reported to be involved in the pathogenesis of autoimmune diseases through mediating differentiation of Th1 or Th17 cells and immune cell activity or survival. However, the origin and effects of IL-27 in joints of rheumatoid arthritis (RA) remain unclear. In this study, we investigated the distribution and anti-inflammatory roles of IL-27 in RA synovium. The IL-27 levels in plasma of RA patients, osteoarthritis (OA) patients, or healthy volunteers (n=15 per group) were equivalent and were at most 1 ng/ml, but the IL-27 level in synovial fluid of RA patients (n=15, mean 0.13 ng/ml; range 0.017-0.37 ng/ml) was significantly higher than that in synovial fluid of OA patients (n=15, mean 0.003 ng/ml; range 0-0.033 ng/ml) and potentially lower than in plasma. We analyzed the protein level of IL-27 produced by RA fibroblast-like synoviocytes (FLSs) or mononuclear cells (MNCs) from RA or OA synovial fluid or peripheral blood and showed that IL-27 in RA joints was derived from MNCs but not from FLSs. We also found by flow cytometry that IL-27-producing MNCs were CD14(+), and that these CD14(+)IL-27(+) cells were clearly detected in RA synovium but rarely in OA synovium by immunohistochemistry. Furthermore, we demonstrated that a relatively physiological concentration of IL-27 below 10 ng/ml suppressed the production of IL-6 and CCL20 from RA FLSs induced by proinflammatory cytokines through the IL-27/IL-27R axis. In the synovial fluid of RA, the IL-27 level interestingly had positive correlation with the IFN-γ level (r=0.56, p=0.03), but weak negative correlation with the IL-17A level (r=-0.30, p=0.27), implying that IL-27 in inflammatory joints of RA induces Th1 differentiation and suppresses the development or the migration of Th17 cells. These findings indicate that circulating IL-27-producing CD14(+) cells significantly infiltrate into inflamed regions such as RA synovium and have anti-inflammatory effects in several ways: both directly through the reduction of IL-6 production, and possibly through the induction of Th1 development and the suppression of Th17 development; and indirectly by regulation of recruitment of CCR6(+) cells, such as Th17 cells, through the suppression of CCL20 production. Our results suggest that such a serial negative feedback system could be applied to RA therapy.     

Molecular aspects of rheumatoid arthritis: chemokines in the joints of patients

Rheumatoid arthritis (RA) is a chronic symmetric polyarticular joint disease that primarily affects the small joints of the hands and feet. The inflammatory process is characterized by infiltration of inflammatory cells into the joints, leading to proliferation of synoviocytes and destruction of cartilage and bone. In RA synovial tissue, the infiltrating cells such as macrophages, T cells, B cells and dendritic cells play important role in the pathogenesis of RA. Migration of leukocytes into the synovium is a regulated multi-step process, involving interactions between leukocytes and endothelial cells, cellular adhesion molecules, as well as chemokines and chemokine receptors. Chemokines are small, chemoattractant cytokines which play key roles in the accumulation of inflammatory cells at the site of inflammation. It is known that synovial tissue and synovial fluid from RA patients contain increased concentrations of several chemokines, such as monocyte chemoattractant protein-4 (MCP-4)/CCL13, pulmonary and activation-regulated chemokine (PARC)/CCL18, monokine induced by interferon-gamma (Mig)/CXCL9, stromal cell-derived factor 1 (SDF-1)/CXCL12, monocyte chemotactic protein 1 (MCP-1)/CCL2, macrophage inflammatory protein 1alpha (MIP-1alpha)/CCL3, and Fractalkine/CXC3CL1. Therefore, chemokines and chemokine-receptors are considered to be important molecules in RA pathology.     

IL-26 Is Overexpressed in Rheumatoid Arthritis and Induces Proinflammatory Cytokine Production and Th17 Cell Generation

Interleukin-26 (IL-26), a member of the IL-10 cytokine family, induces the production of proinflammatory cytokines by epithelial cells. IL-26 has been also reported overexpressed in Crohn''s disease, suggesting that it may be involved in the physiopathology of chronic inflammatory disorders. Here, we have analyzed the expression and role of IL-26 in rheumatoid arthritis (RA), a chronic inflammatory disorder characterized by joint synovial inflammation. We report that the concentrations of IL-26 are higher in the serums of RA patients than of healthy subjects and dramatically elevated in RA synovial fluids compared to RA serums. Immunohistochemistry reveals that synoviolin⁺ fibroblast-like synoviocytes and CD68⁺ macrophage-like synoviocytes are the main IL-26-producing cells in RA joints. Fibroblast-like synoviocytes from RA patients constitutively produce IL-26 and this production is upregulated by IL-1-beta and IL-17A. We have therefore investigated the role of IL-26 in the inflammatory process. Results show that IL-26 induces the production of the proinflammatory cytokines IL-1-beta, IL-6, and tumor necrosis factor (TNF)-alpha by human monocytes and also upregulates the expression of numerous chemokines (mainly CCL20). Interestingly, IL-26-stimulated monocytes selectively promote the generation of RORgamma t⁺ Th17 cells, through IL-1-beta secretion by monocytes. More precisely, IL-26-stimulated monocytes switch non-Th17 committed (IL-23R⁻ or CCR6⁻ CD161⁻) CD4⁺ memory T cells into Th17 cells. Finally, synovial fluids from RA patients also induce Th17 cell generation and this effect is reduced after IL-26 depletion. These findings show that IL-26 is constitutively produced by RA synoviocytes, induces proinflammatory cytokine secretion by myeloid cells, and favors Th17 cell generation. IL-26 thereby appears as a novel proinflammatory cytokine, located upstream of the proinflammatory cascade, that may constitute a promising target to treat RA and chronic inflammatory disorders.     

Characterization and functional consequences of underexpression of clusterin in rheumatoid arthritis

We previously compared by microarray analysis gene expression in rheumatoid arthritis (RA) and osteoarthritis (OA) tissues. Among the set of genes identified as a molecular signature of RA, clusterin (clu) was one of the most differentially expressed. In the present study we sought to assess the expression and the role of CLU (mRNA and protein) in the affected joints and in cultured fibroblast-like synoviocytes (FLS) and to determine its functional role. Quantitative RT-PCR, Northern blot, in situ hybridization, immunohistochemistry, and Western blot were used to specify and quantify the expression of CLU in ex vivo synovial tissue. In synovial tissue, the protein was predominantly expressed by synoviocytes and it was detected in synovial fluids. Both full-length and spliced isoform CLU mRNA levels of expression were lower in RA tissues compared with OA and healthy synovium. In synovium and in cultured FLS, the overexpression of CLU concerned all protein isoforms in OA whereas in RA, the intracellular forms of the protein were barely detectable. Transgenic overexpression of CLU in RA FLS promoted apoptosis within 24 h. We observed that CLU knockdown with small interfering RNA promoted IL-6 and IL-8 production. CLU interacted with phosphorylated IkappaBalpha. Differential expression of CLU by OA and RA FLS appeared to be an intrinsic property of the cells. Expression of intracellular isoforms of CLU is differentially regulated between OA and RA. We propose that in RA joints, high levels of extracellular CLU and low expression of intracellular CLU may enhance NF-kappaB activation and survival of the synoviocytes.     

Stimulatory role of lysophosphatidic acid in cyclooxygenase-2 induction by synovial fluid of patients with rheumatoid arthritis in fibroblast-like synovial cells

While inflammatory cytokines are well-recognized critical factors for the induction of cyclooxygenase-2 (COX-2) in activated fibroblast-like synovial cells, the roles of biologically active components other than inflammatory cytokines in synovial fluid remain unknown. Herein, we assessed the role of lysophosphatidic acid (LPA), a pleiotropic lipid mediator, in COX-2 induction using synovial fluid of patients with rheumatoid arthritis (RA) in fibroblast-like RA synovial cells. Synovial fluid from RA patients stimulated COX-2 induction, which was associated with prostaglandin E(2) production, in RA synovial cells. The synovial fluid-induced actions were inhibited by G(i/o) protein inhibitor pertussis toxin and LPA receptor antagonist 3-(4-[4-([1-(2-chlorophenyl)ethoxy]carbonyl amino)-3-methyl-5-isoxazolyl] benzylsulfanyl) propanoic acid (Ki16425). In fact, LPA alone significantly induced COX-2 expression and enhanced IL-1alpha- or IL-1beta-induced enzyme expression in a manner sensitive to pertussis toxin and Ki16425. RA synovial cells abundantly expressed LPA(1) receptor compared with other LPA receptor subtypes. Moreover, synovial fluid contains a significant amount of LPA, an LPA-synthesizing enzyme autotaxin, and its substrate lysophosphatidylcholine. In conclusion, LPA existing in synovial fluid plays a critical role in COX-2 induction in collaboration with inflammatory cytokines in RA synovial cells. Ki16425-sensitive LPA receptors may be therapeutic targets for RA.     

Sphingosine 1-phosphate (S1P)/S1P receptor 1 signaling regulates receptor activator of NF-κB ligand (RANKL) expression in rheumatoid arthritis

Sphingosine 1-phosphate (S1P)/S1P receptor 1 (S1P1) signaling plays an important role in synovial cell proliferation and inflammatory gene expression by rheumatoid arthritis (RA) synoviocytes. The purpose of this study is to clarify the role of S1P/S1P1 signaling in the expression of receptor activator of NF-κB ligand (RANKL) in RA synoviocytes and CD4(+) T cells. We demonstrated MH7A cells, a human RA synovial cell line, and CD4(+) T cells expressed S1P1 and RANKL. Surprisingly, S1P increased RANKL expression in MH7A cells and CD4(+) T cells in a dose-dependent manner. Moreover, S1P enhanced RANKL expression induced by stimulation with TNF-α in MH7A cells and CD4(+) T cells. These effects of S1P in MH7A cells were inhibited by pretreatment with PTX, a specific Gi/Go inhibitor. These findings suggest that S1P/S1P1 signaling may play an important role in RANKL expression by MH7A cells and CD4(+) T cells. S1P/S1P1 signaling of RA synoviocytes is closely connected with synovial hyperplasia, inflammation, and RANKL-induced osteoclastogenesis in RA. Thus, regulation of S1P/S1P1 signaling may become a novel therapeutic target for RA.     

Persistent induction of the chemokine receptor CXCR4 by TGF-beta 1 on synovial T cells contributes to their accumulation within the rheumatoid synovium

Chemokines and their receptors determine the distribution of leukocytes within tissues in health and disease. We have studied the role of the constitutive chemokine receptor CXCR4 and its ligand, stromal-derived factor-1 (SDF-1) in the perivascular accumulation of T cells in rheumatoid arthritis. We show that synovial T cells, which are primed CD45RO+CD45RBdull cells and consequently not expected to express constitutive chemokine receptors, have high levels of the chemokine receptor CXCR4. Sustained expression of CXCR4 was maintained on synovial T cells by specific factors present within the synovial microenvironment. Extensive screening revealed that TGF-beta isoforms induce the expression of CXCR4 on CD4 T cells in vitro. Depletion studies using synovial fluid confirmed an important role for TGF-beta1 in the induction of CXCR4 expression in vivo. The only known ligand for CXCR4 is SDF-1. We found SDF-1 on synovial endothelial cells and showed that SDF-1 was able to induce strong integrin-mediated adhesion of synovial fluid T cells to fibronectin and ICAM-1, confirming that CXCR4 expressed on synovial T cells was functional. These results suggest that the persistent induction of CXCR4 on synovial T cells by TGF-beta1 leads to their active, SDF-1-mediated retention in a perivascular distribution within the rheumatoid synovium.     

Soluble Fas ligand inhibits angiogenesis in rheumatoid arthritis

The characteristics of rheumatoid arthritis (RA) pathology include the infiltration of inflammatory leukocytes, the proliferation of synovial cells, and the presence of extensive angiogenesis, referred to as rheumatoid pannus. Fas ligand is critical to the homeostatic regulation of the immune response, but its role in the angiogenic process of RA remains to be defined. In this study, we investigated whether soluble Fas ligand (sFasL) induces synoviocyte apoptosis and regulates angiogenesis of endothelial cells in RA. The levels of sFasL were elevated in the synovial fluids of RA patients when compared to those of osteoarthritis (OA) patients, and they correlated inversely with vascular endothelial growth factor₁₆₅ (VEGF₁₆₅) concentrations. sFasL, ranging from 10 to 100 ng/ml, induced the apoptosis of RA fibroblast-like synoviocytes (FLS) in vitro, and thereby decreased VEGF₁₆₅ production. In addition, sFasL inhibited VEGF₁₆₅-induced migration and chemotaxis of endothelial cells to basal levels in a manner independent of the Fas-mediated cell death. sFasL dose-dependently suppressed the VEGF₁₆₅-stimulated increase in pAkt expression in endothelial cells, which might be associated with its anti-migratory effect on endothelial cells. Moreover, sFasL strongly inhibited neovascularization in the Matrigel plug in vivo. Our data suggest that sFasL shows anti-angiogenic activity within RA joints not only by inducing apoptosis of VEGF₁₆₅-producing cells but also by blocking VEGF₁₆₅-induced migration of endothelial cells, independent of Fas-mediated apoptosis.     

A novel role for interleukin-18 in adhesion molecule induction through NF kappa B and phosphatidylinositol (PI) 3-kinase-dependent signal transduction pathways

Interleukin-18 (IL-18) is a novel proinflammatory cytokine found in serum and joints of patients with rheumatoid arthritis (RA). We studied a novel role for IL-18 in mediating cell adhesion, a vital component of the inflammation found in RA and other inflammatory diseases. We examined the expression of cellular cell adhesion molecules E-selectin, vascular cell adhesion molecule-1 (VCAM-1), and intercellular adhesion molecule-1 (ICAM-1) on endothelial cells and RA synovial fibroblasts using flow cytometry. Adhesion of the monocyte-like cell line HL-60 to endothelial cells was determined by immunofluorescence. IL-18 significantly enhanced ICAM-1 and VCAM-1 expression on endothelial cells and RA synovial fibroblasts. In addition, IL-18 induced E-selectin expression on endothelial cells and promoted the adhesion of HL-60 cells to IL-18-stimulated endothelial cells. Neutralizing anti-VCAM-1 and anti-E-selectin could completely inhibit HL-60 adherence to endothelial cells. IL-18-induced adhesion molecule expression appears to be mediated through nuclear factor kappa B (NF kappa B) and phosphatidyl-inositol 3 kinase (PI 3-kinase) since addition of inhibitors to either NF kappa B (pyrrolidine dithiocarbamate and N-acetyl-l-cysteine) or PI 3-kinase (LY294002) inhibited RA synovial fibroblast VCAM-1 expression by 50 to 60%. Addition of both inhibitors resulted in inhibition of VCAM-1 expression by 85%. In conclusion, the ability of IL-18 to induce adhesion molecule expression on endothelial cells and RA synovial fibroblasts indicates that IL-18 may contribute to RA joint inflammation by enhancing the recruitment of leukocytes into the joint. IL-18 requires NF kappa B as well as PI 3-kinase to induce VCAM-1 on RA synovial fibroblasts, suggesting that there may be two distinct pathways in IL-18-induced adhesion molecule expression.     

Th1-Induced CD106 Expression Mediates Leukocytes Adhesion on Synovial Fibroblasts from Juvenile Idiopathic Arthritis Patients

This study tested the hypothesis that subsets of human T helper cells can orchestrate leukocyte adhesion to synovial fibroblasts (SFbs), thus regulating the retention of leukocytes in the joints of juvenile idiopathic arthritis (JIA) patients. Several cell types, such as monocytes/macrophages, granulocytes, T and B lymphocytes, SFbs and osteoclasts participate in joint tissue damage JIA. Among T cells, an enrichment of classic and non-classic Th1 subsets, has been found in JIA synovial fluid (SF), compared to peripheral blood (PB). Moreover, it has been shown that IL-12 in the SF of inflamed joints mediates the shift of Th17 lymphocytes towards the non-classic Th1 subset. Culture supernatants of Th17, classic and non-classic Th1 clones, have been tested for their ability to stimulate proliferation, and to induce expression of adhesion molecules on SFbs, obtained from healthy donors. Culture supernatants of both classic and non-classic Th1, but not of Th17, clones, were able to induce CD106 (VCAM-1) up-regulation on SFbs. This effect, mediated by tumor necrosis factor (TNF)-α, was crucial for the adhesion of circulating leukocytes on SFbs. Finally, we found that SFbs derived from SF of JIA patients expressed higher levels of CD106 than those from healthy donors, resembling the phenotype of SFbs activated in vitro with Th1-clones supernatants. On the basis of these findings, we conclude that classic and non-classic Th1 cells induce CD106 expression on SFbs through TNF-α, an effect that could play a role in leukocytes retention in inflamed joints.     

Expression of MDC/CCL22 and its receptor CCR4 in rheumatoid arthritis,psoriatic arthritis and osteoarthritis

The pathogenesis of rheumatoid arthritis (RA) and psoriatic arthritis (PsA) involves an abnormal chemokine regulation. The chemokine receptor CCR4 is necessary for T cell migration to the skin. We, therefore, studied if CCR4 and its ligand macrophage-derived chemokine (MDC/CCL22) could participate in spreading the disease between skin and joints by examining RA, PsA and osteoarthritis (OA) patients. In synovial fluid from RA and PsA patients we observed a significantly higher MDC/CCL22 level compared to OA patients. Additionally, the MDC/CCL22 protein was found to be elevated in RA and PsA plasma compared to OA and healthy volunteers. Flow cytometry revealed that most CD4⁺CCR4⁺ lymphocytes also co-expressed CD45RO. Neither the MDC/CCL22 level nor the expression of CCR4 correlated to CRP. Immunohistochemistry of the RA and OA synovial membrane demonstrated CCR4 to be expressed by mononuclear cells and endothelial cells. Our results show that MDC/CCL22 is present within the synovial membrane of RA and OA patients and in high amount in the synovial fluid of patients with RA and PsA. This will enable migration of CCR4 expressing memory cells supporting that MDC/CCR4 could play a role in attracting skin specific memory T cells to the joints.     

FMS-related tyrosine kinase 3 ligand (Flt3L)/CD135 axis in rheumatoid arthritis

Introduction

The FMS-related tyrosine kinase 3 ligand (Flt3L)/CD135 axis plays a fundamental role in proliferation and differentiation of dendritic cells (DCs). As DCs play an important role in rheumatoid arthritis (RA) immunopathology we studied in detail the Flt3L/CD135 axis in RA patients.

Methods

The levels of Flt3L in (paired) serum and synovial fluid (SF) were quantified by enzyme-link immunosorbent assay (ELISA). Expression of Flt3L and CD135 in paired peripheral blood mononuclear cells (PBMCs) and synovial fluid mononuclear cells (SFMCs) was quantified by fluorescence-activated cell sorting (FACS). The expression of Flt3L, CD135 and TNF-Converting Enzyme (TACE) in synovial tissues (STs) and in vitro polarized macrophages and monocyte-derived DCs (Mo-DCs) was assessed by quantitative PCR (qPCR). CD135 ST expression was evaluated by immunohistochemistry and TACE ST expression was assessed by immunofluorescence. Flt3L serum levels were assessed in RA patients treated with oral prednisolone or adalimumab.

Results

Flt3L levels in RA serum, SF and ST were significantly elevated compared to gout patients and healthy individuals (HI). RA SF monocytes, natural killer cells and DCs expressed high levels of Flt3L and CD135 compared to HI. RA ST CD68⁺ and CD163⁺ macrophages, CD55⁺ fibroblast-like synoviocytes (FLS), CD31⁺ endothelial cells or infiltrating monocytes and CD19⁺ B cells co-expressed TACE. IFN-γ-differentiated macrophages expressed higher levels of Flt3L compared to other polarized macrophages. Importantly, Flt3L serum levels were reduced by effective therapy.

Conclusions

The Flt3L/CD135 axis is active in RA patients and is responsive to both prednisolone and adalimumab treatment. Conceivably, this ligand receptor pair represents a novel therapeutic target.     

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 α5β1 (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.