Decreased Th17 and antigen-specific humoral responses in CX₃ CR1-deficient mice in the collagen-induced arthritis model

Assessment of mesenchymal stem/stromal cell-based therapy in K/BxN serum transfer-induced arthritis

Rheumatoid arthritis (RA) is an autoimmune disease characterized by synovial hyperplasia and cartilage/bone destruction with systemic comorbidities. Despite advances in understanding the aetiology of RA and novel biologic drugs, a substantial number of individuals with RA remain intolerant or resistant to these therapies. In this context, mesenchymal stem/stromal cell (MSC)-based therapy has emerged as an innovative therapeutic alternative to address unresolved treatment issues for patients with RA thanks to the immunomodulatory properties of these cells. The majority of preclinical studies in MSC-based therapy have been conducted using the well-known collagen-induced arthritis (CIA) mouse model however due to its low incidence, the mouse strain restriction and the prolonged induction phase of collagen-induced arthritis, alternative experimental models of RA have been developed such as K/BxN serum transfer-induced arthritis (STIA), which mimics many of human RA features. In this study, we evaluate whether the K/BxN STIA model could be used as an alternative model to study the immunomodulatory potential of MSC-based therapy. Unexpectedly, our data suggest that adipose-derived MSC-based therapy is unsuitable for modulating the progression of K/BxN serum-transfer arthritis in mice despite the various experimental parameters tested. Based on the differences in the immune status and monocytic/macrophage balance among the different arthritic models, these results could help to identify the cellular targets of the MSCs and, most importantly to predict the RA patients that will respond positively to MSC-based therapy.

Light-Triggered Drug Release from Red Blood Cells Suppresses Arthritic Inflammation

Arthritis is a leading cause of disability in adults, which can be intensely incapacitating. The location and intensity of the pain is both subjective and challenging to manage. Consequently, patient-directed delivery of anti-inflammatories is an essential component of future therapeutic strategies for the management of this disorder. We describe the design and application of a light responsive red blood cell (RBC) conveyed dexamethasone (Dex) construct that enables targeted drug delivery upon illumination of the inflamed site. The red wavelength (650 nm) responsive nature of the phototherapeutic was validated using tissue phantoms mimicking the light absorbing properties of various skin types. Furthermore, photoreleased Dex has the same impact on cellular responses as conventional Dex. Murine RBCs containing the photoactivatable therapeutic display comparable circulation properties as fluorescently labelled RBCs. In addition, a single dose of light-targeted Dex delivery is 5-fold more effective in suppressing inflammation than the parent drug, delivered serially over multiple days. These results are consistent with the notion that the circulatory system be used as an on-command drug depot, providing the means to therapeutically target diseased sites both efficiently and effectively.

Role of Fractalkine in promoting inflammation in sepsis-induced multiple organ dysfunction

OBJECTIVE

Fractalkine, CX3CL1, is involved in the directional movement of chemokine cells, immune response, inflammatory response, tissue repair, and other processes. However, its role in sepsis is not well known.

METHODS

We measured circulating Fractalkine in adult patients with sepsis. Effects of Fractalkine on the survival, inflammation, tissue injury, and bacterial clearance were assessed using the WT or CX3CL^-/- murine model of cecal ligation and puncture (CLP)-induced sepsis.

RESULTS

Serum Fractalkine concentrations were significantly elevated in adult patients with sepsis compared to healthy adults. Increased Fractalkine correlated positively with the number of blood leukocytes and the level of inflammatory cytokines, including IL-6, IL-1β, IL-17A, IFN-γ, and TNF-α, and correlated negatively with IL-10 in clinical sepsis. Recombinant Fractalkine impaired survival whereas Fractalkine gene knockout or anti-Fractalkine antibody improved survival in the murine model of CLP-induced sepsis. Fractalkine administration increased inflammatory response, evident by higher levels of cytokines (TNF-α, IL-1β, IL-17A, IFN-γ, and IL-6 but not IL-10), and tissue damage (lung, liver, and kidney) in CLP-induced sepsis. Fractalkine reduced bacterial clearance in CLP-induced polymicrobial sepsis by reducing macrophage or neutrophil phagocytosis and intracellular elimination of E. coli.

CONCLUSIONS

Fractalkine aggravates sepsis by increasing inflammation and decreasing bacterial clearance, and is a potential tool for anti-sepsis therapy.

Sex-Based Differences in Monocytic Lineage Cells Contribute to More Severe Collagen-Induced Arthritis in Female Rats Compared with Male Rats

Monocytes' plasticity has an important role in the development of rheumatoid arthritis (RA), an autoimmune disease exhibiting greater prevalence in women. Contribution of this phenomenon to sex bias in RA severity was investigated in rat collagen-induced arthritis (CIA) model of RA. The greater severity of CIA in females (exhibiting signs of bone resorption) was accompanied by the higher blood level of advanced oxidation protein products and a more pro-oxidant profile. Consistently, in females, the greater density of giant multinuclear cells (monocytes/macrophages and osteoclasts) in inflamed joint tissue was found. This correlated with the higher frequencies of CCR2- and CX3CR1- expressing cells (precursors of inflammatory monocytes/macrophages and osteoclasts) among CD11b+ splenocytes. This in conjunction with the enhanced migratory capacity of CD11b+ monocytic cells in females compared with males could be linked with the higher frequencies of CCR2+CX3CR1-CD43^lowCD11b+ and CCR2-CX3CR1+CD43^hiCD11b+ cells (corresponding to "classical" and "non-classical" monocytes, respectively) and the greater density of CD68+ cells (monocytes/macrophages and osteoclast precursors/osteoclasts) in blood and inflamed paws from female rats, respectively. Consistently, the higher levels of GM-CSF, TNF-α and IL-6, IL-1β (driving Th17 cell differentiation), and IL-17 followed by the lower level of IL-10 were measured in inflamed paw cultures from female compared with male rats. To the greater IL-17 production (associated with enhanced monocyte immigration and differentiation into osteoclasts) most likely contributed augmented Th17 cell generation in the lymph nodes draining arthritic joints from female compared with male rats. Overall, the study suggests the sex-specific contribution of monocytic lineage cells to CIA, and possibly RA development.

CCDC88B is required for mobility and inflammatory functions of dendritic cells

The Coiled Coil Domain Containing Protein 88B (CCDC88B) gene is associated with susceptibility to several inflammatory diseases in humans and its inactivation in mice protects against acute neuroinflammation and models of intestinal colitis. We report that mice lacking functional CCDC88B (Ccdc88b^Mut ) are defective in several dendritic cells (DCs)-dependent inflammatory and immune reactions in vivo. In these mice, an inflammatory stimulus (LPS) fails to induce the recruitment of DCs into the draining lymph nodes (LNs). In addition, OVA-pulsed Ccdc88b^Mut DCs injected in the footpad do not induce recruitment and activation of antigen-specific CD4⁺ and CD8⁺ T cells in their draining LN. Experiments in vitro indicate that this defect is independent of the ability of mutant DCs to capture and present peptide antigen to T cells. Rather, kinetic analyses in vivo of wild-type and Ccdc88b^Mut DCs indicate a reduced migration capacity in the absence of the CCDC88B protein expression. Moreover, using time-lapse light microscopy imaging, we show that Ccdc88b^Mut DCs have an intrinsic motility defect. Furthermore, in vivo studies reveal that these reduced migratory properties lead to dampened contact hypersensitivity reactions in Ccdc88b mutant mice. These findings establish a critical role of CCDC88B in regulating movement and migration of DCs. Thus, regulatory variants impacting Ccdc88b expression in myeloid cells may cause variable degrees of DC-dependent inflammatory response in situ, providing a rationale for the genetic association of CCDC88B with several inflammatory and autoimmune diseases in humans.

Dissecting the phenotypic and functional heterogeneity of mouse inflammatory osteoclasts by the expression of Cx3cr1

Bone destruction relies on interactions between bone and immune cells. Bone-resorbing osteoclasts (OCLs) were recently identified as innate immune cells activating T cells toward tolerance or inflammation. Thus, pathological bone destruction not only relies on increased osteoclast differentiation, but also on the presence of inflammatory OCLs (i-OCLs), part of which express Cx3cr1. Here, we investigated the contribution of mouse Cx3cr1⁺ and Cx3cr1^neg i-OCLs to bone loss. We showed that Cx3cr1⁺ and Cx3cr1^neg i-OCLs differ considerably in transcriptional and functional aspects. Cx3cr1^neg i-OCLs have a high ability to resorb bone and activate inflammatory CD4⁺ T cells. Although Cx3cr1⁺ i-OCLs are associated with inflammation, they resorb less and have in vitro an immune-suppressive effect on Cx3cr1^neg i-OCLs, mediated by PD-L1. Our results provide new insights into i-OCL heterogeneity. They also reveal that different i-OCL subsets may interact to regulate inflammation. This contributes to a better understanding and prevention of inflammatory bone destruction.

In vitro model for the assessment of human immune responses to subunit RSV vaccines

Respiratory syncytial virus (RSV) is the single most important cause of serious lower respiratory tract disease in infants and young children worldwide and a high priority for vaccine development. Despite over 50 years of research, however, no vaccine is yet available. One block to vaccine development is an incomplete understanding of the aberrant memory response to the formalin-inactivated RSV vaccine (FI-RSV) given to children in the 1960s. This vaccine caused enhanced respiratory disease (ERD) with later natural RSV infection. Concern that any non-live virus vaccine may also cause ERD has blocked development of subunit vaccines for young children. A number of animal FI-RSV studies suggest various immune mechanisms behind ERD. However, other than limited data from the original FI-RSV trial, there is no information on the human ERD-associated responses. An in vitro model with human blood specimens may shed light on the immune memory responses likely responsible for ERD. Memory T cell responses to an antigen are guided by the innate responses, particularly dendritic cells that present an antigen in conjunction with co-stimulatory molecules and cytokine signaling. Our in vitro model involves human monocyte derived dendritic cells (moDC) and allogenic T cell cultures to assess innate responses that direct T cell responses. Using this model, we evaluated human responses to live RSV, FI-RSV, and subunit RSV G vaccines (G-containing virus-like particles, G-VLP). Similar to findings in animal studies, FI-RSV induced prominent Th2/Th17-biased responses with deficient type-1 responses compared to live virus. Responses to G-VLPs were similar to live virus, i.e. biased towards a Th1 and not a Th2/Th17. Also mutating CX3C motif in G gave a more pronounced moDC responses associated with type-1 T cell responses. This in vitro model identifies human immune responses likely associated with ERD and provides another pre-clinical tool to assess the safety of RSV vaccines.

Deletion of tumour necrosis factor α receptor 1 elicits an increased TH17 immune response in the chronically inflamed liver

Tumour necrosis factor α receptor 1 (TNFR1) activation is known to induce cell death, inflammation, and fibrosis but also hepatocyte survival and regeneration. The multidrug resistance protein 2 knockout (Mdr2-/) mice are a model for chronic hepatitis and inflammation-associated hepatocellular carcinoma (HCC) development. This study analysed how the absence of TNFR1 mediated signalling shapes cytokine and chemokine production, immune cell recruitment and ultimately influences liver injury and fibrotic tissue remodelling in the Mdr2-/- mouse model. We show that Tnfr1-/-/Mdr2-/- mice displayed increased plasma levels of ALT, ALP, and bilirubin as well as a significantly higher collagen content, and markers of fibrosis than Mdr2-/- mice. The expression profile of inflammatory cytokines (Il1b, Il23, Tgfb1, Il17a), chemokines (Ccl2, Cxcl1, Cx3cl1) and chemokine receptors (Ccr6, Cxcr6, Cx3cr1) in livers of Tnfr1-/-/Mdr2-/- mice indicated TH17 cell infiltration. Flow cytometric analysis confirmed that the aggravated tissue injury in Tnfr1-/-/Mdr2-/- mice strongly correlated with increased hepatic recruitment of TH17 cells and enhanced IL-17 production in the injured liver. Moreover, we observed increased hepatic activation of RIPK3 in Tnfr1-/-/Mdr2-/- mice, which was not related to necroptotic cell death. Rather, frequencies of infiltrating CX3CR1+ monocytes increased over time in livers of Tnfr1-/-/Mdr2-/- mice, which expressed significantly higher levels of Ripk3 than those of Mdr2-/- mice. Overall, we conclude that the absence of TNFR1-mediated signalling did not improve the pathological phenotype of Mdr2-/- mice. It instead caused enhanced infiltration of TH17 cells and CX3CR1+ monocytes into the injured tissue, which was accompanied by increased RIPK3 activation and IL-17 production.

Chemerin-activated functions of CMKLR1 are regulated by G protein-coupled receptor kinase 6 (GRK6) and β-arrestin 2 in inflammatory macrophages

Chemerin receptor (CMKLR1) is a G protein-coupled receptor (GPCR) implicated in macrophage-mediated inflammation and in several forms of human arthritis. Analogous to other GPCR, CMKLR1 is likely regulated by G protein-coupled receptor kinase (GRK) phosphorylation of intracellular domains in an activation-dependent manner, which leads to recruitment and termination of intracellular signaling via desensitization and internalization of the receptor. The ubiquitously expressed GRK family members include GRK2, GRK3, GRK5, and GRK6, but it is unknown which GRK regulates CMKLR1 cellular and signaling functions. Our data show that activation of CMKLR1 by chemerin in primary macrophages leads to signaling and functional outcomes that are regulated by GRK6 and β-arrestin 2. We show that arrestin recruitment to CMKLR1 following chemerin stimulation is enhanced with co-expression of GRK6. Further, internalization of endogenous CMKLR1, following the addition of chemerin, is decreased in inflammatory macrophages from GRK6- and β-arrestin 2-deficient mice. These GRK6- and β-arrestin 2-deficient macrophages display increased migration toward chemerin and altered AKT and Extracellular-signal Related Kinase (ERK) signaling. Our findings show that chemerin-activated CMKLR1 regulation in inflammatory macrophages is largely GRK6 and β-arrestin mediated, which may impact innate immunity and have therapeutic implications in rheumatic disease.

Tissue-specific Role of CX3CR1 Expressing Immune Cells and Their Relationships with Human Disease

Chemokine (C-X3-C motif) ligand 1 (CX₃CL1, also known as fractalkine) and its receptor chemokine (C-X3-C motif) receptor 1 (CX₃CR1) are widely expressed in immune cells and non-immune cells throughout organisms. However, their expression is mostly cell type-specific in each tissue. CX₃CR1 expression can be found in monocytes, macrophages, dendritic cells, T cells, and natural killer (NK) cells. Interaction between CX₃CL1 and CX₃CR1 can mediate chemotaxis of immune cells according to concentration gradient of ligands. CX₃CR1 expressing immune cells have a main role in either pro-inflammatory or anti-inflammatory response depending on environmental condition. In a given tissue such as bone marrow, brain, lung, liver, gut, and cancer, CX₃CR1 expressing cells can maintain tissue homeostasis. Under pathologic conditions, however, CX₃CR1 expressing cells can play a critical role in disease pathogenesis. Here, we discuss recent progresses of CX₃CL1/CX₃CR1 in major tissues and their relationships with human diseases.

Dendritic cell migration in health and disease

Dendritic cells (DCs) are potent and versatile antigen-presenting cells, and their ability to migrate is key for the initiation of protective pro-inflammatory as well as tolerogenic immune responses. Recent comprehensive studies have highlighted the importance of DC migration in the maintenance of immune surveillance and tissue homeostasis, and also in the pathogenesis of a range of diseases. In this Review, we summarize the anatomical, cellular and molecular factors that regulate the migration of different DC subsets in health and disease. In particular, we focus on new insights concerning the role of migratory DCs in the pathogenesis of diseases of the skin, intestine, lung, and brain, as well as in autoimmunity and atherosclerosis.

Inflammatory Osteoclasts Prime TNFα-Producing CD4+ T Cells and Express CX3 CR1

Bone destruction is a hallmark of chronic rheumatic diseases. Although the role of osteoclasts in bone loss is clearly established, their implication in the inflammatory response has not been investigated despite their monocytic origin. Moreover, specific markers are lacking to characterize osteoclasts generated in inflammatory conditions. Here, we have explored the phenotype of inflammatory osteoclasts and their effect on CD4⁺ T cell responses in the context of bone destruction associated with inflammatory bowel disease. We used the well-characterized model of colitis induced by transfer of naive CD4⁺ T cells into Rag1^-/- mice, which is associated with severe bone destruction. We set up a novel procedure to sort pure osteoclasts generated in vitro to analyze their phenotype and specific immune responses by FACS and qPCR. We demonstrated that osteoclasts generated from colitic mice induced the emergence of TNFα-producing CD4⁺ T cells, whereas those generated from healthy mice induced CD4⁺ FoxP3⁺ regulatory T cells, in an antigen-dependent manner. This difference is related to the osteoclast origin from monocytes or dendritic cells, to their cytokine expression pattern, and their environment. We identified CX₃ CR1 as a marker of inflammatory osteoclasts and we demonstrated that the differentiation of CX₃ CR1⁺ osteoclasts is controlled by IL-17 in vitro. This work is the first demonstration that, in addition to participating to bone destruction, osteoclasts also induce immunogenic CD4⁺ T cell responses upon inflammation. They highlight CX₃ CR1 as a novel dual target for antiresorptive and anti-inflammatory treatment in inflammatory chronic diseases. © 2016 American Society for Bone and Mineral Research.

T Cell CX3CR1 Mediates Excess Atherosclerotic Inflammation in Renal Impairment

Reduced kidney function increases the risk for atherosclerosis and cardiovascular death. Leukocytes in the arterial wall contribute to atherosclerotic plaque formation. We investigated the role of fractalkine receptor CX3CR1 in atherosclerotic inflammation in renal impairment. Apoe(-/-) (apolipoprotein E) CX3CR1(-/-) mice with renal impairment were protected from increased aortic atherosclerotic lesion size and macrophage accumulation. Deficiency of CX3CR1 in bone marrow, only, attenuated atherosclerosis in renal impairment in an independent atherosclerosis model of LDL receptor-deficient (LDLr(-/-)) mice as well. Analysis of inflammatory leukocytes in atherosclerotic mixed bone-marrow chimeric mice (50% wild-type/50% CX3CR1(-/-) bone marrow into LDLr(-/-) mice) showed that CX3CR1 cell intrinsically promoted aortic T cell accumulation much more than CD11b(+)CD11c(+) myeloid cell accumulation and increased IL-17-producing T cell counts. In vitro, fewer TH17 cells were obtained from CX3CR1(-/-) splenocytes than from wild-type splenocytes after polarization with IL-6, IL-23, and TGFβ Polarization of TH17 or TREG cells, or stimulation of splenocytes with TGFβ alone, increased T cell CX3CR1 reporter gene expression. Furthermore, TGFβ induced CX3CR1 mRNA expression in wild-type cells in a dose- and time-dependent manner. In atherosclerotic LDLr(-/-) mice, CX3CR1(+/-) T cells upregulated CX3CR1 and IL-17A production in renal impairment, whereas CX3CR1(-/-) T cells did not. Transfer of CX3CR1(+/-) but not Il17a(-/-) T cells into LDLr(-/-)CX3CR1(-/-) mice increased aortic lesion size and aortic CD11b(+)CD11c(+) myeloid cell accumulation in renal impairment. In summary, T cell CX3CR1 expression can be induced by TGFβ and is instrumental in enhanced atherosclerosis in renal impairment.

Knockdown of ADAM10 inhibits migration and invasion of fibroblast-like synoviocytes in rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disease with high rates of morbidity and mortality. Previous studies proposed that the A disintegrin and metalloprotease (ADAM) family is involved in the regulation of inflammation and arthritis. Thus, the present study investigated whether ADAM10 is involved in the progression of RA. The effects of ADAM10 small interfering (si)RNA on the expression levels of tumor necrosis factor (TNF)‑α, interleukin (IL)‑6, IL‑8 and chemokine (C-X-C motif) ligand 16 (CXCL16) were determined in fibroblast‑like synoviocytes (FLS). In addition, the effects of ADAM10 siRNA on cell proliferation, invasion and migration in human RA‑FLS were assessed in vitro. The therapeutic efficacy and side‑effects of ADAM10 siRNA were examined in a mouse model of collagen‑induced arthritis (CIA). In vitro, ADAM10 silencing suppressed the expression of TNF‑α, IL‑6, IL‑8 and CXCL16 in lipopolysaccharide (LPS)‑stimulated human RA‑FLS. LPS‑induced RA‑FLS proliferation, migration and invasion were significantly attenuated by ADAM10 knockdown. ADAM10 silencing inhibited the secretion of vascular endothelial growth factor A (VEGF‑A) and matrix metalloproteinase (MMP)‑3 and ‑9 from LPS‑stimulated human RA‑FLS, in addition to inhibiting the phosphoinositide 3‑kinase/AKT activation in LPS‑stimulated human RA‑FLS. In vivo, treatment with siRNA against ADAM10 for three weeks reduced the arthritis score. Serum levels of VEGF‑A, MMP‑3 and MMP‑9 were also reduced in CIA mice. These observations indicate that the inhibition of ADAM10 may be a viable therapeutic target in the amelioration of disease progression in RA by attenuating FLS proliferation, migration and invasion.

CX3CR1 is dispensable for control of mucosal Candida albicans infections in mice and humans

Candida albicans is part of the normal commensal microbiota of mucosal surfaces in a large percentage of the human population. However, perturbations of the host's immune response or bacterial microbiota have been shown to predispose individuals to the development of opportunistic Candida infections. It was recently discovered that a defect in the chemokine receptor CX3CR1 increases susceptibility of mice and humans to systemic candidiasis. However, whether CX3CR1 confers protection against mucosal C. albicans infection has not been investigated. Using two different mouse models, we found that Cx3cr1 is dispensable for the induction of interleukin 17A (IL-17A), IL-22, and IL-23 in the tongue after infection, as well as for the clearance of mucosal candidiasis from the tongue or lower gastrointestinal (GI) tract colonization. Furthermore, the dysfunctional human CX3CR1 allele CX3CR1-M280 was not associated with development of recurrent vulvovaginal candidiasis (RVVC) in women. Taken together, these data indicate that CX3CR1 is not essential for protection of the host against mucosal candidiasis, underscoring the dependence on different mammalian immune factors for control of mucosal versus systemic Candida infections.

Chemokine receptors expression on peripheral CD4-lymphocytes in rheumatoid arthritis: Coexpression of CCR7 and CD95 is associated with disease activity

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by synovial inflammation triggered by infiltrating CD4 lymphocytes. The positioning and activation of lymphocyte in inflamed synovial tissues are dependent on a number of factors including their chemokine receptor expression profile. We aimed to investigate which chemokine receptors pattern correlate with serum cytokine levels and with disease activity. Forty patients with RA (34 female and 6 male) with age range from 21 to 68 years were included. Twenty healthy volunteers (16 female and 4 male) with matched age (range 21-48 years) were served as healthy controls (HCs). Expression of chemokine receptors (CCR5, CX3CR1 and CCR7) together with the apoptosis-related marker (CD95) was analyzed using three-color flow cytometry analysis after gating on CD4(+) peripheral blood lymphocytes. Plasma levels of IL-6, IL-10, IL-12 and TNF-α cytokines were measured in all participants using ELISA. Disease activity score (DAS28-CRP) system was assessed and active disease was defined as DAS28 ⩾3.2. Twenty-five (62.4%) patients were classified as active RA (ARA) and 15 (37.5%) patients with inactive RA (IRA). Percentages of CD4(+) lymphocytes expressing CD95 with either of CCR7 or CCR5 were significantly higher in ARA compared to IRA and HCs groups, while the expression of CX3CR1 on T-cells was found significantly lower in both CD95(-) and CD95(+) T-cells in RA groups than HC. Percentages of CD4(+)CD95(+)CCR7(+) cells correlated positively with IL-6 (r = 0.390). Whereas CD4(+)CD95(+)CX3CR1(+) were negatively correlated with TNF-α (r = -0.261). Correlation of CD4(+)CD95(+)CCR7(+) T cell subset with disease activity and inflammatory cytokines suggests a role for this cell subset in the pathogenesis of RA. Further investigation will be required to fully characterize this cell subset and its role in disease progression.

A disintegrin and metallproteinase 15 knockout decreases migration of fibroblast-like synoviocytes and inflammation in rheumatoid arthritis

The aim of the present study was to determine whether the expression of A disintegrin and metallproteinase 15 (ADAM15) affected the inflammatory conditions and cell migration in human fibroblast‑like synoviocytes (FLSs) in a rat model of rheumatoid arthritis (RA). The expression of ADAM15 in FLSs stimulated with lipopolysaccharide (LPS) was confirmed by reverse transcription‑quantitative polymerase chain reaction and western blot analysis. The effects of small interfering RNA targeting ADAM15 (siADAM5) on pro‑inflammatory cytokines and chemokines were assessed using an enzyme‑linked immunosorbent assay. The effects of siADAM15 on cell invasion and migration in FLS were also assessed in vitro. The therapeutic effects and side effects of ADAM15 in a rat model of collagen‑induced arthritis (CIA) were examined in vivo. The present results revealed that ADAM15 expression was significantly elevated at the mRNA and protein level in FLSs stimulated with LPS and that silencing ADAM15 suppressed the expression of pro‑inflammatory cytokines and chemokines, preventing FLS cell migration and invasion via inhibiting vascular endothelial growth factor‑A, matrix metalloproteinase (MMP)1 and MMP‑3 expression. In addition, treatment of CIA rats using siADAM15 significantly reduced the arthritis score and extent of joint damage in the rats. These findings indicated that silencing ADAM15 had anti‑inflammatory effects in FLSs and efficiently inhibited the development of CIA. Therefore, ADAM15 may be a potential target molecule for RA therapies.

Tumor necrosis factor receptor-associated factor 6 promotes migration of rheumatoid arthritis fibroblast-like synoviocytes

Fibroblast‑like synoviocytes (FLSs) have a pivotal role in the destruction of joints in rheumatoid arthritis (RA). Tumor necrosis factor receptor‑associated factor 6 (TRAF6) is a critical mediator in the inflammatory pathway and of the activity of osteoclasts. The aim of the present study was to investigate whether TRAF6 is involved in the progression of RA in mouse collagen‑induced arthritis (CIA) and human RA FLSs in vitro. In vivo mouse models were transfected with TRAF6 small interfering (si)RNA (siTRAF6) and TRAF6 inhibition was achieved in FLSs using an anti‑TRAF6 monoclonal antibody in vitro in order to assess the effects of TRAF6 inhibition on the migration and invasion of FLSs. Inhibition of TRAF6 using mouse specific siTRAF6 reduced the severity of arthritis and joint inflammation. Serum anti‑collagen II antibodies, matrix metalloproteinase (MMP)‑1, MMP‑3 and MMP‑9 were also inhibited in CIA mice by siTRAF6. The levels of MMPs produced by IL‑1β‑stimulated human RA‑FLSs were reduced by anti‑TRAF6 monoclonal antibody. TRAF6 blockade significantly suppressed the IL‑1β‑stimulated migration and invasion of human RA‑FLSs. These results support a role for TRAF6 in the pathogenesis of RA, and suggest that the TRAF6 blockade may be a potential strategy in the management of RA.

Involvement of the CX3CL1 (fractalkine)/CX3CR1 pathway in the pathogenesis of acute graft-versus-host disease

This study investigated the role of cytokines and chemokines in aGVHD incidence and severity in 109 patients who underwent reduced-intensity conditioning allogeneic stem cell transplantation (HSCT). Among the 42 cytokines tested at d 0 HSCT, only CX3CL1 levels at d 0 HSCT were significantly associated with Grades II-IV aGVHD development (P = 0.04). Increased levels of CX3CL1 at d 20-30 and 50 post-HSCT were also significantly associated with aGVHD (P = 0.02 and P = 0.03, respectively). No such association was found before the conditioning regimen or at d 100-120 post-HSCT. As the receptor for CX3CL1 is CX3CR1, the number of CX3CR1(+) cells was determined by flow cytometry. The CX3CR1(+)CD8(+) T cell proportion was significantly higher in patients with aGVHD than those without aGVHD (P = 0.01). To investigate the distribution of the CX3CL1/CX3CR1 axis in the anatomic sites of aGVHD, CX3CL1 and CX3CR1 levels were studied by use of an in situ immunohistochemical analysis on GI biopsies of patients with intestinal aGVHD. CX3CL1 expression was increased significantly in the epithelial cells and mononuclear cells of the lamina propria. CX3CR1(+) mononuclear cells were identified in close contact with epithelial cells. These findings strongly suggest the implication of the CX3CL1/CX3CR1 axis in the pathogenesis of aGVHD.

Role of fractalkine in the pathogenesis of primary Sjögren syndrome: increased serum levels of fractalkine, its expression in labial salivary glands, and the association with clinical manifestations

OBJECTIVE

To investigate the expression of fractalkine and identify the clinical effects of fractalkine and its receptor (CX3CR1) in patients with primary Sjögren syndrome (pSS).

METHODS

Serum fractalkine levels were determined by ELISA. Immunohistochemical staining was done to compare the expression of fractalkine and CX3CR1 between salivary glands (SG) of patients with SS and controls. The cells to be merged with fractalkine were evaluated by confocal microscopy. Type of CX3CR1-expressing cells among infiltrating lymphocytes in SG was analyzed by confocal microscopy. Further, associations among fractalkine, proinflammatory cytokines, and clinical profiles were investigated.

RESULTS

Serum fractalkine levels in patients with pSS were higher than those in the control group (p = 0.026). SG expression of fractalkine and its receptor was upregulated in patients with pSS compared to that in the controls by immunohistochemistry. Higher histological grade was associated with more fractalkine-positive cells per total epithelial cells. Epithelial cells were the main fractalkine-expressing cell type in the SG. Serum fractalkine levels were significantly correlated with proinflammatory cytokines levels (interleukin 17: r = 0.685, p = 0.029; tumor necrosis factor-α: r = 0.444, p = 0.003), antinuclear antibody (r = 0.349, p = 0.022), and immunoglobulin G levels (r = 0.325, p = 0.044). Serum fractalkine levels in patients with extraglandular manifestations of pSS were significantly higher than in those without extraglandular manifestations (p = 0.026).

CONCLUSION

Fractalkine and CX3CR1 may play a role in the pathogenesis of pSS, including extraglandular manifestations.

Up-regulation of interleukin-23 induces persistent allodynia via CX3CL1 and interleukin-18 signaling in the rat spinal cord after tetanic sciatic stimulation

Tetanic stimulation of the sciatic nerve (TSS) induces sciatic nerve injury and long-lasting pain hypersensitivity in rats, and spinal glial activation and proinflammatory cytokines releases are involved. In the present study, we showed that spinal interleukin (IL)-23 and its receptor, IL-23R, are crucial for the development of mechanical allodynia after TSS. In the spinal dorsal horn, both IL-23 and IL-23R are expressed in astrocytes, and this expression is substantially increased after TSS. Inhibition of IL-23 signaling attenuated TSS-induced allodynia and decreased the induction of glial fibrillary acidic protein (GFAP, an astrocytic marker). Conversely, intrathecally delivered IL-23 induced a persistent allodynia. Similar to IL-23 signaling, an increase in IL-18 and its receptor, IL-18R, as well as CX3CL1 and its receptor, CX3CR1, was simultaneously observed in the spinal dorsal horn after TSS. Interestingly, IL-18 and CX3CR1 were exclusively expressed in microglia, while IL-18R was mainly localized in astrocytes. In contrast, CX3CL1 was predominately expressed in neurons and secondarily in astrocytes. The functional inhibition of CX3CL1 and IL-18 signaling attenuated TSS-induced allodynia and suppressed IL-23 and IL-23R upregulation. Activation of CX3CR1 and IL-18R induced similar behavioral and biochemical changes to those observed after TSS. These results indicate that the interaction among CX3CL1, IL-18 and IL-23 signaling in the spinal cord plays a critical role in the development of allodynia. Thus, interrupting this chemokine-cytokine network might provide a novel therapeutic strategy for neuropathic pain.

G protein-coupled receptor kinase-3-deficient mice exhibit WHIM syndrome features and attenuated inflammatory responses

Chemokine receptor interactions coordinate leukocyte migration in inflammation. Chemokine receptors are GPCRs that when activated, are phosphorylated by GRKs to turn off G protein-mediated signaling yet recruit additional signaling machinery. Recently, GRK3 was identified as a negative regulator of CXCL12/CXCR4 signaling that is defective in human WHIM syndrome. Here, we report that GRK3-/- mice exhibit numerous features of human WHIM, such as impaired CXCL12-mediated desensitization, enhanced CXCR4 signaling to ERK activation, altered granulocyte migration, and a mild myelokathexis. Moreover, GRK3-/- protects mice from two acute models of inflammatory arthritis (K/BxN serum transfer and CAIA). In these granulocyte-dependent disease models, protection of GRK3-/- mice is mediated by retention of cells in the marrow, fewer circulating granulocytes in the peripheral blood, and reduced granulocytes in the joints during active inflammation. In contrast to WHIM, GRK3-/- mice have minimal hypogammaglobulinemia and a peripheral leukocytosis with increased lymphocytes and absent neutropenia. Thus, we conclude that the loss of GRK3-mediated regulation of CXCL12/CXCR4 signaling contributes to some, but not all, of the complete WHIM phenotype and that GRK3 inhibition may be beneficial in the treatment of inflammatory arthritis.

Genetic and cellular evidence of decreased inflammation associated with reduced incidence of posttraumatic arthritis in MRL/MpJ mice

OBJECTIVE

To examine the relationship between inflammation and posttraumatic arthritis (PTA) in a murine intraarticular fracture model.

METHODS

Male C57BL/6 and MRL/MpJ "superhealer" mice received tibial plateau fractures using a previously established method. Mice were killed on day 0 (within 4 hours of fracture) and days 1, 3, 5, 7, 28, and 56 after fracture. Synovial tissue samples, obtained prior to fracture and on days 0, 1, 3, 5, and 7 after fracture, were examined by reverse transcription-polymerase chain reaction for gene expression of proinflammatory cytokines and chemokines. Synovial fluid and serum samples were collected to measure cytokine concentrations, using enzyme-linked immunosorbent assay. Whole joints were examined histologically for the extent of synovitis and cartilage degradation, and joint tissue samples from all time points were analyzed immunohistochemically to evaluate the distribution of interleukin-1 (IL-1).

RESULTS

Compared to C57BL/6 mice, MRL/MpJ mice had less severe intraarticular and systemic inflammation following joint injury, as evidenced by lower gene expression of tumor necrosis factor α and IL-1β in the synovial tissue and lower protein levels of IL-1α and IL-1β in the synovial fluid, serum, and joint tissues. Furthermore, after joint injury, MRL/MpJ mice had lower gene expression of macrophage inflammatory proteins and macrophage-derived chemokine (CCL22) in the synovial tissue, and also had reduced acute and late-stage infiltration of synovial macrophages.

CONCLUSION

C57BL/6 mice exhibited higher levels of inflammation than MRL/MpJ mice, indicating that MRL/MpJ mice are protected from PTA in this model. These data thus suggest an association between joint tissue inflammation and the development and progression of PTA in mice.

G-protein signaling modulator-3, a gene linked to autoimmune diseases, regulates monocyte function and its deficiency protects from inflammatory arthritis

Polymorphism at the GPSM3 gene locus is inversely associated with four systemic autoimmune diseases, including rheumatoid arthritis and ankylosing spondylitis. G-protein signaling modulator-3 (GPSM3) expression is most pronounced in myeloid cells, in which it targets heterotrimeric G-protein Gαi subunits of chemokine receptors, critical to immune function. To begin to explore the regulatory role of GPSM3 in monocytes, human THP-1 and primary mouse myeloid cells were cultured under stimulus conditions; GPSM3 was found by immunoblotting to be expressed at highest levels in the mature monocyte. To evaluate the effects of GPSM3 deficiency on a myeloid-dependent autoimmune disease, collagen antibody-induced arthritis (CAIA) was induced in Gpsm3-/- and control mice, which were then analyzed for clinical score, paw swelling, intra-articular proinflammatory markers, and histopathology. Mice lacking GPSM3 were protected from CAIA, and expression of monocyte-representative pro-inflammatory chemokine receptors and cytokines in paws of Gpsm3-/- mice were decreased. Flow cytometry, apoptosis, and transwell chemotaxis experiments were conducted to further characterize the effect of GPSM3 deficiency on survival and chemokine responsiveness of monocytes. GPSM3-deficient myeloid cells had reduced migration ex vivo to CCL2, CX3CL1, and chemerin and enhanced apoptosis in vitro. Our results suggest that GPSM3 is an important regulator of monocyte function involving mechanisms of differentiation, survival, and chemotaxis, and deficiency in GPSM3 expression is protective in acute inflammatory arthritis.