Proinflammatory role of fractalkine (CX3CL1) in rheumatoid arthritis.

Fractalkine (CX3CL1) represents the sole member of the so-called CX3C chemokines. In rheumatoid arthritis (RA), functional studies suggest a role for this chemokine in monocyte chemotaxis and angiogenesis in the rheumatoid synovium. We analyzed the expression of fractalkine within different T cell subsets of the peripheral blood and expression of its receptor CX3CR1 within the rheumatoid synovium to further characterize its pathogenic role in RA. Peripheral blood mononuclear cells (PBMC) were isolated from 17 patients with RA and analyzed by flow cytometry in comparison to healthy blood donors. To identify the T helper cell cytokine profile of fractalkine-expressing cells, flow cytometric analysis of PBMC was performed after stimulation with PMA and ionomycin. Expression of fractalkine and its receptor was characterized in RA synovium by immunohistochemistry and laser capture microdissection microscopy. Flow cytometric analysis of fractalkine-expressing T cell subsets revealed a low proportion of fractalkine-expressing CD4+ and CD8+ T cells in both RA patients and controls. In addition, fractalkine was predominantly expressed in CD4+ T cells with a Th1-type cytokine expression profile. In RA synovium, fractalkine was detected in synovial macrophages, dendritic cells, endothelial cells, and a small proportion of T cells. The fractalkine receptor CX3CR1 was found in synovial macrophages, dendritic cells, and T cells as well as in synovial fibroblasts. Fractalkine stimulation of cultured synovial fibroblasts resulted in a marked upregulation of matrix metalloproteinase-2 (MMP-2) production. The results suggest that fractalkine may represent a Th1-type chemokine. Upregulation of MMP-2 production in synovial fibroblasts upon fractalkine stimulation in vitro supports the hypothesis of a proinflammatory role of this chemokine in RA.

Blaschke S ，Koziolek M ，Schwarz A ，Benöhr P ，Middel P ，Schwarz G ，Hummel KM ，Müller GA ... -  《JOURNAL OF RHEUMATOLOGY》

Fractalkine, a novel chemokine in rheumatoid arthritis and in rat adjuvant-induced arthritis.

To examine the expression of the novel CX3C chemokine fractalkine (Fkn) and its receptor (CX3CR1) in rheumatoid arthritis (RA) and rat adjuvant-induced arthritis (AIA), a model of RA. Immunohistochemistry, flow cytometry, enzyme-linked immunosorbent assay (ELISA), reverse transcriptase-polymerase chain reaction (RT-PCR), and chemotaxis assays were used. In rat AIA, synovial tissue (ST) macrophages, fibroblasts, endothelial cells, and dendritic cells were Fkn immunopositive, whereas lymphocytes did not significantly express Fkn. Significant staining for CX3CR1 was found in ST macrophages, fibroblasts, and dendritic cells, whereas only a small percentage of endothelial cells stained for CX3CR1 in rat AIA. We immunolocalized Fkn to RA ST macrophages, fibroblasts, endothelial cells, and dendritic cells. We also found intense ST macrophage and dendritic cell staining for CX3CR1 in RA ST. Flow cytometry analysis of RA synovial fluid (SF) and peripheral blood revealed a greater percentage of monocytes expressing Fkn and CX3CR1 compared with T cells. By ELISA, we found significantly elevated soluble Fkn (sFkn) levels in RA SF compared with SF from patients with osteoarthritis or other forms of arthritis. By RT-PCR, we found enhanced expression of Fkn and CX3CR1 mRNA on day 18 in rat AIA, a time of pronounced inflammation in the rat joint. Soluble Fkn-depleted RA SF showed significantly decreased chemotactic activity for monocytes compared with sham-depleted RA SF. These results indicate that Fkn and its receptor are both expressed in RA and in rat AIA, and that sFkn is up-regulated in RA SF. Furthermore, our data suggest a new role for Fkn in monocyte chemotaxis in the inflamed RA joint.

Ruth JH ，Volin MV ，Haines GK 3rd ，Woodruff DC ，Katschke KJ Jr ，Woods JM ，Park CC ，Morel JC ，Koch AE ... -  《ARTHRITIS AND RHEUMATISM》

Migration of CX3CR1-positive T cells producing type 1 cytokines and cytotoxic molecules into the synovium of patients with rheumatoid arthritis.

Rheumatoid arthritis (RA) is characterized by chronic inflammation of multiple joints. Large numbers of T cells, which produce type 1 cytokines, infiltrate into RA synovium. Chemokines and chemokine receptors are considered to contribute to the T cell infiltration. In this study, we examined the role of CX3CL1/fractalkine and its receptor CX3C chemokine receptor 1 (CX3CR1) in the T cell migration into RA synovium. Using flow cytometry, immunohistochemistry, and reverse transcription-polymerase chain reaction, we analyzed CX3CR1 expression by peripheral blood and synovial T cells, and CX3CL1 expression in synovium from patients with RA. Cytokine and cytotoxic molecule expression by CX3CR1-positive T cells was analyzed by flow cytometry. CX3CR1 expression by peripheral CD4+ and CD8+ T cells was up-regulated in RA patients. The peripheral CD4+ and CD8+ T cells expressing CX3CR1 predominantly produced interferon-gamma and tumor necrosis factor alpha, and expressed cytotoxic molecules such as granzyme A and perforin. Furthermore, CX3CR1+,CD3+ T cells infiltrated into RA synovium. CX3CL1, the unique ligand of CX3CR1, was expressed by endothelial cells and synoviocytes in RA synovium, but not in osteoarthritis synovium. Our findings suggest that the interactions of CX3CL1 and CX3CR1 might contribute to the accumulation of CX3CR1+ T cells expressing type 1 cytokines and possessing cytotoxic granules in RA synovium.

Nanki T ，Imai T ，Nagasaka K ，Urasaki Y ，Nonomura Y ，Taniguchi K ，Hayashida K ，Hasegawa J ，Yoshie O ，Miyasaka N ... -  《ARTHRITIS AND RHEUMATISM》

Anti-inflammatory effects of atorvastatin on peripheral blood mononuclear cells and synovial fibroblasts in rheumatoid arthritis.

Statins, such as atorvastatin (ATV), are 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors known to exert lipid-lowering but also anti-inflammatory, effects. In this study, we analysed the in vitro effects of ATV on peripheral blood mononuclear cells (PBMCs) and fibroblast-like synoviocytes (FLS) in rheumatoid arthritis (RA), a chronic inflammatory joint disease. PBMCs isolated from 25 RA patients and 20 healthy blood donors were stimulated in vitro with 0.1 microM ATV for 24 h. PBMC cultures were analysed for cell surface markers to characterize T-cell subtypes (CD4, CD8, CD69, HLA-DR) by flow cytometry and for T helper cell type 1 (Th1) and type 2 (Th2) cytokines [interferon-gamma (IFN-gamma), interleukin-4 (IL-4), IL-10] in culture supernatants by enzyme-linked immunosorbent assay (ELISA). Furthermore, RNA isolated from ATV-stimulated RA-FLS pre- and post-ATV stimulation was analysed by microarray and quantitative reverse transcription polymerase chain reaction (RT-PCR). Flow cytometric analysis of T-cell subsets revealed no significant differences for CD4, CD8, CD69, and HLA-DR surface marker expression of PBMCs in RA patients and healthy controls after ATV stimulation. However, the proportion of IFN-gamma expressing CD4+ T cells and the IFN-gamma cytokine concentrations in culture supernatants were significantly reduced in T-cell cultures from RA patients. In ATV-stimulated FLS a significant downregulation of proinflammatory cytokine (IL-6) and chemokine (IL-8) expression was detected (p<0.001). Our study demonstrates a marked in vitro anti-inflammatory activity of ATV in RA including a systemic effect on a pathogenic CD4+ T-cell population (Th1) and a local effect on FLS. These findings may provide a scientific rationale for statins as add-on therapy in RA.

Blaschke S ，Viereck V ，Schwarz G ，Klinger HM ，Guerluek S ，Müller GA ... -  《-》

Increased expression of fractalkine (CX3CL1) and its receptor, CX3CR1, in Wegener's granulomatosis--possible role in vascular inflammation.

Based on the function of fractalkine (CX3CL1), the unique member of the CX3C chemokine subfamily, in endothelial-related inflammation, we hypothesized a role for CX3CL1 and its receptor (CX3CR) in Wegener's granulomatosis (WG). In the present study, this hypothesis was tested by different experimental approaches. We examined plasma levels of CX3CL1 (enzyme immunoassay) and CX3CR1 expression in peripheral blood mononuclear cells (PBMCs) (real-time quantitative RT-PCR and flow cytometry) in 18 WG patients and 15 healthy controls. In eight of these individuals, we also examined CX3CR1-mediated chemotaxis and adhesion in T cells and monocytes as well as the effects of CX3CL1 on monocyte chemoattractant protein (MCP) 1 levels in PBMC supernatants. Our main findings were: (i) WG patients had markedly increased plasma levels of CX3CL1, with particularly high levels in those with active disease, (ii) These increased CX3CL1 levels were accompanied by enhanced expression of its corresponding receptor, CX3XR1, in PBMC, primarily reflecting an increased proportion of CX3CR1(+)CD3(+)CD4(+) T cells and (iii) The up-regulation of CX3CR1 in PBMC from WG patients affected their functional potential as shown by CX3CL1-induced enhancement of chemotaxis, adhesion, responses as well as MCP-1 stimulation. Based on the ability of CX3CL1 to promote leucocyte infiltration into the vessel wall of inflammatory levels, it is tempting to hypothesize that increased CX3CL1/CX3CR1 interaction could be involved in the pathogenesis of the granulomatous vasculitis characterizing WG.

Bjerkeli V ，Damås JK ，Fevang B ，Holter JC ，Aukrust P ，Frøland SS ... -  《RHEUMATOLOGY》