Extracellular microRNAs induce dendritic cell-dependent joint inflammation and potentiate osteoclast differentiation via TLR7/8 engagement.

OBJECTIVES: Monocyte-derived dendritic cells (DCs) are key players in the induction of inflammation, autoreactive T cell activation and loss of tolerance in rheumatoid arthritis (RA), but the precise mechanisms underlying their activation remain elusive. Here, we hypothesized that extracellular microRNAs released in RA synovial fluids may represent a novel, physiological stimulus triggering unwanted immune response via TLR8-expressing DC stimulation. METHODS: Human monocyte-derived DCs were stimulated with a mixture of GU-rich miRNAs upregulated in RA tissues and released in synovial fluids (Ex-miRNAs). Activation of DCs was assessed in terms of NF-κB activation by Western blot, cytokine production by ELISA, T cell proliferation and polarization by allogeneic mixed lymphocyte reaction. DC differentiation into osteoclasts was evaluated in terms of tartrate-resistant acid phosphatase production and formation of resorption pits in dentine slices. Induction of joint inflammation in vivo was evaluated using a murine model of DC-induced arthritis. TLR7/8 involvement was assessed by specific inhibitors. RESULTS: Ex-miRNAs activate DCs to secrete TNFα, induce joint inflammation, start an early autoimmune response and potentiate the differentiation of DCs into aggressive osteoclasts. CONCLUSIONS: This work represents a proof of concept that the pool of extracellular miRNAs overexpressed in RA joints can act as a physiological activator of inflammation via the stimulation of TLR8 expressed by human DCs, which in turn exert arthritogenic functions. In this scenario, pharmacological inhibition of TLR8 might offer a new therapeutic option to reduce inflammation and osteoclast-mediated bone destruction in RA.

The PDE4 inhibitor tanimilast shows distinct immunomodulatory properties associated with a type 2 endotype and CD141 upregulation.

BACKGROUND: Tanimilast is a novel and selective inhaled inhibitor of phosphodiesterase-4 in advanced clinical development for chronic obstructive pulmonary disease (COPD). Tanimilast is known to exert prominent anti-inflammatory activity when tested in preclinical experimental models as well as in human clinical studies. Recently, we have demonstrated that it also finely tunes, rather than suppressing, the cytokine network secreted by activated dendritic cells (DCs). This study was designed to characterize the effects of tanimilast on T-cell polarizing properties of DCs and to investigate additional functional and phenotypical features induced by tanimilast. METHODS: DCs at day 6 of culture were stimulated with LPS in the presence or absence of tanimilast or the control drug budesonide. After 24 h, DCs were analyzed for the expression of surface markers of maturation and activation by flow cytometry and cocultured with T cells to investigate cell proliferation and activation/polarization. The regulation of type 2-skewing mediators was investigated by real-time PCR in DCs and compared to results obtained in vivo in a randomized placebo-controlled trial on COPD patients treated with tanimilast. RESULTS: Our results show that both tanimilast and budesonide reduced the production of the immunostimulatory cytokine IFN-γ by CD4+ T cells. However, the two drugs acted at different levels since budesonide mainly blocked T cell proliferation, while tanimilast skewed T cells towards a Th2 phenotype without affecting cell proliferation. In addition, only DCs matured in the presence of tanimilast displayed increased CD86/CD80 ratio and CD141 expression, which correlated with Th2 T cell induction and dead cell uptake respectively. These cells also upregulated cAMP-dependent immunosuppressive molecules such as IDO1, TSP1, VEGF-A and Amphiregulin. Notably, the translational value of these data was confirmed by the finding that these same genes were upregulated also in sputum cells of COPD patients treated with tanimilast as add-on to inhaled glucocorticoids and bronchodilators. CONCLUSION: Taken together, these findings demonstrate distinct immunomodulatory properties of tanimilast associated with a type 2 endotype and CD141 upregulation in DCs and provide a mechanistic rationale for the administration of tanimilast on top of inhaled corticosteroids.

Inhibition of Class I Histone Deacetylase Activity Blocks the Induction of TNFAIP3 Both Directly and Indirectly via the Suppression of Endogenous TNF-α.

Histone deacetylase inhibitors (HDIs) are promising drugs for the treatment of inflammatory diseases. However, their therapeutical exploitation is slowed down by severe adverse manifestations that can hardly be foreseen, mainly due to incomplete knowledge of how HDIs impact the delicate balance of inflammatory mediators. In this work, we characterized the effects of the HDI trichostatin A (TSA) on the expression of TNFAIP3, which is a crucial inhibitor of the classical NF-kB pathway and an LPS-induced negative feedback regulator. The accumulation of TNFAIP3 mRNA after LPS stimulation showed biphasic behavior, with one wave within the first hour of stimulation and a second wave several hours later, which were both reduced by TSA. By using inhibition and knockdown approaches, we identified two temporally and mechanistically distinct modes of action. The first wave of TNAIP3 accumulation was directly blunted by the histone deacetylase (HDAC) blockade. By contrast, the second wave was decreased mainly because of the lack of endogenous TNF-α induction, which, in turn, depended on the intact HDAC activity. In both cases, class I HDACs appeared to play a nonredundant role, with HDAC3 required, but not sufficient, for TNF-α and TNFAIP3 induction. In addition to TNFAIP3, TNF-α is known to induce many response genes that orchestrate the inflammatory cascade. Thus, suppression of TNF-α may represent a general mechanism through which HDIs regulate a selected set of target genes.

The PDE4 Inhibitor Tanimilast Restrains the Tissue-Damaging Properties of Human Neutrophils.

Neutrophils, the most abundant subset of leukocytes in the blood, play a pivotal role in host response against invading pathogens. However, in respiratory diseases, excessive infiltration and activation of neutrophils can lead to tissue damage. Tanimilast-international non-proprietary name of CHF6001-is a novel inhaled phosphodiesterase 4 (PDE4) inhibitor in advanced clinical development for the treatment of chronic obstructive pulmonary disease (COPD), a chronic inflammatory lung disease where neutrophilic inflammation plays a key pathological role. Human neutrophils from healthy donors were exposed to pro-inflammatory stimuli in the presence or absence of tanimilast and budesonide-a typical inhaled corticosteroid drug-to investigate the modulation of effector functions including adherence to endothelial cells, granule protein exocytosis, release of extracellular DNA traps, cytokine secretion, and cell survival. Tanimilast significantly decreased neutrophil-endothelium adhesion, degranulation, extracellular DNA traps casting, and cytokine secretion. In contrast, it promoted neutrophil survival by decreasing both spontaneous apoptosis and cell death in the presence of pro-survival factors. The present work suggests that tanimilast can alleviate the severe tissue damage caused by massive recruitment and activation of neutrophils in inflammatory diseases such as COPD.

Functional Role of Dendritic Cell Subsets in Cancer Progression and Clinical Implications.

Dendritic cells (DCs) constitute a complex network of cell subsets with common functions but also with many divergent aspects. All dendritic cell subsets share the ability to prime T cell response and to undergo a complex trafficking program related to their stage of maturation and function. For these reasons, dendritic cells are implicated in a large variety of both protective and detrimental immune responses, including a crucial role in promoting anti-tumor responses. Although cDC1s are the most potent subset in tumor antigen cross-presentation, they are not sufficient to induce full-strength anti-tumor cytotoxic T cell response and need close interaction and cooperativity with the other dendritic cell subsets, namely cDC2s and pDCs. This review will take into consideration different aspects of DC biology, including the functional role of dendritic cell subsets in both fostering and suppressing tumor growth, the mechanisms underlying their recruitment into the tumor microenvironment, as well as the prognostic value and the potentiality of dendritic cell therapeutic targeting. Understanding the specificity of dendritic cell subsets will allow to gain insights on role of these cells in pathological conditions and to design new selective promising therapeutic approaches.

The atypical receptor CCRL2 is required for CXCR2-dependent neutrophil recruitment and tissue damage.

CCRL2 is a 7-transmembrane domain receptor that shares structural and functional similarities with the family of atypical chemokine receptors (ACKRs). CCRL2 is upregulated by inflammatory signals and, unlike other ACKRs, it is not a chemoattractant-scavenging receptor, does not activate ß-arrestins, and is widely expressed by many leukocyte subsets. Therefore, the biological role of CCRL2 in immunity is still unclear. We report that CCRL2-deficient mice have a defect in neutrophil recruitment and are protected in 2 models of inflammatory arthritis. In vitro, CCRL2 was found to constitutively form homodimers and heterodimers with CXCR2, a main neutrophil chemotactic receptor. By heterodimerization, CCRL2 could regulate membrane expression and promote CXCR2 functions, including the activation of ß2-integrins. Therefore, upregulation of CCRL2 observed under inflammatory conditions is functional to finely tune CXCR2-mediated neutrophil recruitment at sites of inflammation.

Dendritic cell recruitment and activation in autoimmunity.

Dendritic cells (DCs) are professional antigen presenting cells displaying the unique capability to activate naïve T cells. DCs react to pathogen encounter also by the production of mediators of inflammation, including pro-inflammatory cytokines. Because of this complex role, any imbalance in DC function reflects into defective or exaggerated immune response and tissue damage. DCs comprise two main subsets, namely conventional or classical DCs (cDCs), that are dedicated antigen presenting cells, and plasmacytoid DCs (pDCs), that respond to nucleic acids by releasing high amounts of type I interferons (IFNs). Since the formal demonstration that DC can prime autoreactive naïve T cells, a full body of evidence has implicated DCs in virtually all manifestations of autoimmunity, although their exact pathogenic role often remains poorly characterized. The recent availability of progressively more refined strategies of constitutive and inducible DC ablation is contributing in defining the precise role of DCs at least in some autoimmune disease models. This review aims at critically summarizing the current literature concerning selected aspects of DC biology that, when altered, facilitate autoimmunity. These aspects include: i) mechanisms of tissue entry and accumulation, ii) mechanisms of activation and iii) orchestration of the immune balance by cytokine production. A special focus will be on inappropriate DC activation by signals released by damaged tissues via innate immune receptors, such as Toll-like receptors. These signals are responsible, in pDCs, for exaggerated type I IFN production, the hallmark of a set of apparently distant autoimmune conditions such as systemic lupus erythematosus and type 1 diabetes; whereas in cDCs, they trigger DC rapid maturation and Th1/Th17 cytokine secretion. Tissue-derived molecules also contribute to further promote tissue damage and autoantigen spreading, possibly through pDC-derived Granzyme B secretion. Finally, the therapeutic possibilities based on DC targeting in human autoimmune diseases will be briefly summarized.

Mesenchymal stromal cell-secreted chemerin is a novel immunomodulatory molecule driving the migration of ChemR23-expressing cells.

BACKGROUND: Mesenchymal stromal cells (MSCs) are multipotent cells characterized by broad immunomodulatory properties exploited for the treatment of inflammatory disorders. However, the efficacy of MSC-based therapy is highly variable and tightly linked to MSC culture conditions and treatment schedule. Thus, the identification of novel key molecules regulating MSC immunomodulatory activities in vivo might constitute a crucial step toward the optimization of currently available clinical protocols. In this regard, herein, we sought to determine whether the newly identified chemotactic protein, chemerin, plays a role in MSC-mediated regulation of inflammation. METHODS: Chemerin production by human MSCs was investigated under different culture conditions using enzyme-linked immunosorbent assay (ELISA). After purification, MSC-secreted chemerin was identified using mass spectrometry analysis and the biological activity of secreted isoforms was evaluated using migration assay. RESULTS: Bone marrow-derived MSCs secrete chemerin and express its receptors ChemR23 and CCRL2. Chemerin production is dependent on culture conditions and increases upon stimulation with inflammatory cytokines. In particular, platelet lysate (PL)-MSCs produce higher levels of chemerin compared with fetal bovine serum (FBS)-MSCs. Furthermore, chemerin is secreted by MSCs as an inactive precursor, which can be converted into its active form by exogenous chemerin-activating serine and cysteine proteases. DISCUSSION: Our data indicate that, in response to various inflammatory stimuli, MSCs secrete high amounts of inactive chemerin, which can then be activated by inflammation-induced tissue proteases. In light of these initial findings, we propose that further analysis of chemerin functions in vivo might constitute a crucial step toward optimizing MSC-based therapy for inflammatory diseases.

Chemokines as relay signals in human dendritic cell migration: serum amyloid A kicks off chemotaxis.

Cell migration is a response highly conserved in evolution. Chemotactic factors secreted in injured and inflamed tissues generate a concentration-based, chemotactic gradient that directs leukocytes from the blood compartment into tissue. In this issue of the European Journal of Immunology, Gouwy et al. [Eur. J. Immunol. 2015. 45: 101-112] show that the SAA1α isoform of serum amyloid A (SAA), which is an acute phase protein upregulated in inflammation and shown to chemoattract some leukocyte subsets, is also able to chemoattract monocyte-derived immature dendritic cells (DCs). The authors also show that the chemotactic activity of SAA1α for monocytes and DCs is indirectly mediated by rapid chemokine induction, providing evidence that proposes a new level of regulation of leukocyte migration.

Endothelial cell-derived chemerin promotes dendritic cell transmigration.

ChemR23 is a chemotactic receptor expressed by APCs, such as dendritic cells, macrophages, and NK cells. Chemerin, the ChemR23 ligand, was detected by immunohistochemistry, to be associated with inflamed endothelial cells in autoimmune diseases, such as lupus erythematosus, psoriasis, and rheumatoid arthritis. This study reports that blood and lymphatic murine endothelial cells produce chemerin following retinoic acid stimulation. Conversely, proinflammatory cytokines, such as TNF-α, IFN-γ, and LPS, or calcitriol, are not effective. Retinoic acid-stimulated endothelial cells promoted dendritic cell adhesion under shear stress conditions and transmigration in a ChemR23-dependent manner. Activated endothelial cells upregulated the expression of the atypical chemotactic receptor CCRL2/ACKR5, a nonsignaling receptor able to bind and present chemerin to ChemR23(+) dendritic cells. Accordingly, activated endothelial cells expressed chemerin on the plasma membrane and promoted in a more efficient manner chemerin-dependent transmigration of dendritic cells. Finally, chemerin stimulation of myeloid dendritic cells induced the high-affinity binding of VCAM-1/CD106 Fc chimeric protein and promoted VCAM-1-dependent arrest to immobilized ligands under shear stress conditions. In conclusion, this study reports that retinoic acid-activated endothelial cells can promote myeloid and plasmacytoid dendritic cell transmigration across endothelial cell monolayers through the endogenous production of chemerin, the upregulation of CCRL2, and the activation of dendritic cell ß1 integrin affinity.

CCRL2, a fringe member of the atypical chemoattractant receptor family.

The term atypical chemoattractant receptors is generally used to refer to a subset of G-protein-coupled receptors devoid of chemotactic activity and characterized by the ability to scavenge chemotactic factors from the inflammatory milieu. However, emerging evidence suggests that this class of receptors is heterogeneous in function. In this Viewpoint, we discuss the properties of CCRL2, a molecule devoid of ligand scavenging functions and suggested to regulate leukocyte recruitment by alternative mechanisms.

Adipokines as potential biomarkers in rheumatoid arthritis.

Rheumatoid arthritis (RA) is a chronic systemic inflammatory autoimmune disease characterized by severe joint injury. Recently, research has been focusing on the possible identification of predictor markers of disease onset and/or progression, of joint damage, and of therapeutic response. Recent findings have uncovered the role of white adipose tissue as a pleiotropic organ not only specialized in endocrine functions but also able to control multiple physiopathological processes, including inflammation. Adipokines are a family of soluble mediators secreted by white adipose tissue endowed with a wide spectrum of actions. This review will focus on the recent advances on the role of the adipokine network in the pathogenesis of RA. A particular attention will be devoted to the action of these proteins on RA effector cells, and on the possibility to use circulating levels of adipokines as potential biomarkers of disease activity and therapeutic response.

Inhibitory receptors of plasmacytoid dendritic cells as possible targets for checkpoint blockade in cancer.

Plasmacytoid dendritic cells (pDCs) are the major producers of type I interferons (IFNs), which are essential to mount antiviral and antitumoral immune responses. To avoid exaggerated levels of type I IFNs, which pave the way to immune dysregulation and autoimmunity, pDC activation is strictly regulated by a variety of inhibitory receptors (IRs). In tumors, pDCs display an exhausted phenotype and correlate with an unfavorable prognosis, which largely depends on the accumulation of immunosuppressive cytokines and oncometabolites. This review explores the hypothesis that tumor microenvironment may reduce the release of type I IFNs also by a more pDC-specific mechanism, namely the engagement of IRs. Literature shows that many cancer types express de novo, or overexpress, IR ligands (such as BST2, PCNA, CAECAM-1 and modified surface carbohydrates) which often represent a strong predictor of poor outcome and metastasis. In line with this, tumor cells expressing ligands engaging IRs such as BDCA-2, ILT7, TIM3 and CD44 block pDC activation, while this blocking is prevented when IR engagement or signaling is inhibited. Based on this evidence, we propose that the regulation of IFN secretion by IRs may be regarded as an "innate checkpoint", reminiscent of the function of "classical" adaptive immune checkpoints, like PD1 expressed in CD8+ T cells, which restrain autoimmunity and immunopathology but favor chronic infections and tumors. However, we also point out that further work is needed to fully unravel the biology of tumor-associated pDCs, the neat contribution of pDC exhaustion in tumor growth following the engagement of IRs, especially those expressed also by other leukocytes, and their therapeutic potential as targets of combined immune checkpoint blockade in cancer immunotherapy.

Trafficking properties of plasmacytoid dendritic cells in health and disease.

Plasmacytoid dendritic cells (PDCs) represent a subset of circulating leukocytes characterized by the ability to release high levels of type I interferon (IFN). Under homeostatic conditions PDCs are confined to primary and secondary lymphoid organs. This is consistent with the restricted profile of functional chemotactic receptors expressed by circulating PDCs (i.e. CXCR4 and ChemR23). Accumulation of PDCs in non-lymphoid tissue is, however, observed in certain autoimmune diseases, allergic reactions and tumors. Indeed, PDCs are now considered to be involved in the pathogenesis of diseases characterized by a type I IFN-signature and are considered as a promising target for new intervention strategies. Here, current knowledge of the molecular mechanisms involved in the recruitment of PDCs under homeostatic and pathological conditions are summarized.

Dendritic cell subsets in cancer immunity and tumor antigen sensing.

Dendritic cells (DCs) exhibit a specialized antigen-presenting function and play crucial roles in both innate and adaptive immune responses. Due to their ability to cross-present tumor cell-associated antigens to naïve T cells, DCs are instrumental in the generation of specific T-cell-mediated antitumor effector responses in the control of tumor growth and tumor cell dissemination. Within an immunosuppressive tumor microenvironment, DC antitumor functions can, however, be severely impaired. In this review, we focus on the mechanisms of DC capture and activation by tumor cell antigens and the role of the tumor microenvironment in shaping DC functions, taking advantage of recent studies showing the phenotype acquisition, transcriptional state and functional programs revealed by scRNA-seq analysis. The therapeutic potential of DC-mediated tumor antigen sensing in priming antitumor immunity is also discussed.

The chemerin/CMKLR1 axis regulates intestinal graft-versus-host disease.

Gastrointestinal graft-versus-host disease (GvHD) is a major cause of mortality and morbidity following allogeneic bone marrow transplantation (allo-BMT). Chemerin is a chemotactic protein that recruits leukocytes to inflamed tissues by interacting with ChemR23/CMKLR1, a chemotactic receptor expressed by leukocytes, including macrophages. During acute GvHD, chemerin plasma levels were strongly increased in allo-BM-transplanted mice. The role of the chemerin/CMKLR1 axis in GvHD was investigated using Cmklr1-KO mice. WT mice transplanted with an allogeneic graft from Cmklr1-KO donors (t-KO) had worse survival and more severe GvHD. Histological analysis demonstrated that the gastrointestinal tract was the organ mostly affected by GvHD in t-KO mice. The severe colitis of t-KO mice was characterized by massive neutrophil infiltration and tissue damage associated with bacterial translocation and exacerbated inflammation. Similarly, Cmklr1-KO recipient mice showed increased intestinal pathology in both allogeneic transplant and dextran sulfate sodium-induced colitis. Notably, the adoptive transfer of WT monocytes into t-KO mice mitigated GvHD manifestations by decreasing gut inflammation and T cell activation. In patients, higher chemerin serum levels were predictive of GvHD development. Overall, these results suggest that CMKLR1/chemerin may be a protective pathway for the control of intestinal inflammation and tissue damage in GvHD.

CCRL2 Expression by Specialized Lung Capillary Endothelial Cells Controls NK-cell Homing in Lung Cancer.

Patterns of receptors for chemotactic factors regulate the homing of leukocytes to tissues. Here we report that the CCRL2/chemerin/CMKLR1 axis represents a selective pathway for the homing of natural killer (NK) cells to the lung. C-C motif chemokine receptor-like 2 (CCRL2) is a nonsignaling seven-transmembrane domain receptor able to control lung tumor growth. CCRL2 constitutive or conditional endothelial cell targeted ablation, or deletion of its ligand chemerin, were found to promote tumor progression in a Kras/p53Flox lung cancer cell model. This phenotype was dependent on the reduced recruitment of CD27- CD11b+ mature NK cells. Other chemotactic receptors identified in lung-infiltrating NK cells by single-cell RNA sequencing (scRNA-seq), such as Cxcr3, Cx3cr1, and S1pr5, were found to be dispensable in the regulation of NK-cell infiltration of the lung and lung tumor growth. scRNA-seq identified CCRL2 as the hallmark of general alveolar lung capillary endothelial cells. CCRL2 expression was epigenetically regulated in lung endothelium and it was upregulated by the demethylating agent 5-aza-2'-deoxycytidine (5-Aza). In vivo administration of low doses of 5-Aza induced CCRL2 upregulation, increased recruitment of NK cells, and reduced lung tumor growth. These results identify CCRL2 as an NK-cell lung homing molecule that has the potential to be exploited to promote NK cell-mediated lung immune surveillance.

Nonredundant role of CCRL2 in lung dendritic cell trafficking.

Chemokine CC motif receptor-like 2 (CCRL2) is a heptahelic transmembrane receptor that shows the highest degree of homology with CCR1, an inflammatory chemokine receptor. CCRL2 mRNA was rapidly (30 minutes) and transiently (2-4 hours) regulated during dendritic cell (DC) maturation. Protein expression paralleled RNA regulation. In vivo, CCRL2 was expressed by activated DC and macrophages, but not by eosinophils and T cells. CCRL2(-/-) mice showed normal recruitment of circulating DC into the lung, but a defective trafficking of antigen-loaded lung DC to mediastinal lymph nodes. This defect was associated to a reduction in lymph node cellularity and reduced priming of T helper cell 2 response. CCRL2(-/-) mice were protected in a model of ovalbumin-induced airway inflammation, with reduced leukocyte recruitment in the BAL (eosinophils and mononuclear cells) and reduced production of the T helper cell 2 cytokines, interleukin-4 and -5, and chemokines CCL11 and CCL17. The central role of CCRL2 deficiency in DC was supported by the fact that adoptive transfer of CCRL2(-/-) antigen-loaded DC in wild-type animals recapitulated the phenotype observed in knockout mice. These data show a nonredundant role of CCRL2 in lung DC trafficking and propose a role for this receptor in the control of excessive airway inflammatory responses.

NCX1 is a novel target gene for hypoxia-inducible factor-1 in ischemic brain preconditioning.

BACKGROUND AND PURPOSE: The sodium-calcium exchanger-1 (NCX1) represents a key mediator for maintaining [Na(+)](i) and [Ca(2+)](i) homeostasis. Although changes in NCX1 protein and transcript expression have been detected during stroke, its transcriptional regulation is still unknown. Thus far, however, there is evidence that hypoxia-inducible factor-1 (HIF-1) is a nuclear factor required for transcriptional activation of several genes implicated in stroke. The main objective of this study was to investigate whether NCX1 gene might be a novel target of HIF-1 in the brain. METHODS: Here we report that: (1) in neuronal cells, NCX1 increased expression after oxygen and glucose deprivation or cobalt-induced HIF-1 activation was prevented by silencing HIF-1; (2) the brain NCX1 promoter cloned upstream of the firefly-luciferase gene contained 2 regions of HIF-1 target genes called hypoxia-responsive elements that are sensitive to oxygen and glucose deprivation or cobalt chloride; (3) HIF-1 specifically bound hypoxia-responsive elements on brain NCX1, as demonstrated by band-shift and chromatin immunoprecipitation assays; (4) HIF-1α silencing prevented NCX1 upregulation and neuroprotection induced by ischemic preconditioning; and (5) NCX1 silencing partially reverted the preconditioning-induced neuroprotection in rats. CONCLUSIONS: NCX1 gene is a novel HIF-1 target, and HIF-1 exerts its prosurvival role through NCX1 upregulation during brain preconditioning.

The possible role of ChemR23/Chemerin axis in the recruitment of dendritic cells in lupus nephritis.

Dendritic cells (DCs) have a pivotal role in the autoimmune response of systemic lupus erythematosus. Plasmacytoid DCs infiltrate the kidney of patients with lupus nephritis, but factors regulating their recruitment to the kidney are unknown. Chemerin is the recently identified natural ligand of ChemR23, a receptor highly expressed by plasmacytoid DCs. We performed immunohistochemical and immunofluorescence analysis to study the ChemR23/Chemerin axis in renal biopsies from patients with lupus nephritis. We found ChemR23-positive DCs had infiltrated the kidney tubulointerstitium in patients with severe lupus nephritis. Chemerin association with tubular epithelial cells and renal lymphatic endothelial cells was found in patients with lupus nephritis but not in normal kidneys. Proximal tubular epithelial cells produced Chemerin in vitro, which was significantly down-modulated by added tumor necrosis factor (TNF)-α and interferon-γ as measured by quantitative PCR and enzyme-linked immunosorbent assay. Interestingly, TNF-α was capable of inducing a functionally active form of renal Chemerin, resulting in an efficient transendothelial migration of plasmacytoid DCs measured in transwell systems. Thus, the ChemR23/Chemerin axis may have a role in the recruitment of DCs within the kidney in patients affected by lupus nephritis.