Fractalkine in vascular biology: from basic research to clinical disease

Microinflammation in the pathogenesis of diabetic nephropathy

Diabetic nephropathy is the leading cause of end‐stage renal failure in developed countries. Furthermore, diabetic nephropathy is related to the risk of cardiovascular diseases and an increase in mortality of diabetic patients. Several factors are involved in the development of nephropathy, including glomerular hyperfiltration, oxidative stress, accumulation of advanced glycation end‐products, activation of protein kinase C, acceleration of the polyol pathway and over‐expression of transforming growth factor‐β. Recently, accumulated data have emphasized the critical roles of chronic low‐grade inflammation, ‘microinflammation’, in the pathogenesis of diabetic nephropathy, suggesting that microinflammation is a common mechanism in the development of diabetic vascular complications. Expression of cell adhesion molecules, chemokines and pro‐inflammatory cytokines are increased in the renal tissues of diabetic patients and animals. Deficiency of pro‐inflammatory molecules results in amelioration of renal injuries after induction of diabetes in mice. Plasma and urinary levels of cytokines, chemokines and cell adhesion molecules, are elevated and correlated with albuminuria. Several kinds of drugs that have anti‐inflammatory actions as their pleiotropic effects showed renoprotective effects on diabetic animals. Modulation of the inflammatory process prevents renal insufficiency in diabetic animal models, suggesting that microinflammation is one of the promising therapeutic targets for diabetic nephropathy, as well as for cardiovascular diseases.

The chemokine fractalkine can activate integrins without CX3CR1 through direct binding to a ligand-binding site distinct from the classical RGD-binding site

The chemokine domain of fractalkine (FKN-CD) binds to the classical RGD-binding site of αvβ3 and that the resulting ternary complex formation (integrin-FKN-CX3CR1) is critical for CX3CR1 signaling and FKN-induced integrin activation. However, only certain cell types express CX3CR1. Here we studied if FKN-CD can activate integrins in the absence of CX3CR1. We describe that WT FKN-CD activated recombinant soluble αvβ3 in cell-free conditions, but the integrin-binding defective mutant of FKN-CD (K36E/R37E) did not. This suggests that FKN-CD can activate αvβ3 in the absence of CX3CR1 through the direct binding of FKN-CD to αvβ3. WT FKN-CD activated αvβ3 on CX3CR1-negative cells (K562 and CHO) but K36E/R37E did not, suggesting that FKN-CD can activate integrin at the cellular levels in a manner similar to that in cell-free conditions. We hypothesized that FKN-CD enhances ligand binding to the classical RGD-binding site (site 1) through binding to a second binding site (site 2) that is distinct from site 1 in αvβ3. To identify the possible second FKN-CD binding site we performed docking simulation of αvβ3-FKN-CD interaction using αvβ3 with a closed inactive conformation as a target. The simulation predicted a potential FKN-CD-binding site in inactive αvβ3 (site 2), which is located at a crevice between αv and β3 on the opposite side of site 1 in the αvβ3 headpiece. We studied if FKN-CD really binds to site 2 using a peptide that is predicted to interact with FKN-CD in site 2. Notably the peptide specifically bound to FKN-CD and effectively suppressed integrin activation by FKN-CD. This suggests that FKN-CD actually binds to site 2, and this leads to integrin activation. We obtained very similar results in α4β1 and α5β1. The FKN binding to site 2 and resulting integrin activation may be a novel mechanism of integrin activation and of FKN signaling.

Metalloprotease dependent release of placenta derived fractalkine

The chemokine fractalkine is considered as unique since it exists both as membrane-bound adhesion molecule and as shed soluble chemoattractant. Here the hypothesis was tested whether placental fractalkine can be shed and released into the maternal circulation. Immunohistochemical staining of human first trimester and term placenta sections localized fractalkine at the apical microvillous plasma membrane of the syncytiotrophoblast. Gene expression analysis revealed abundant upregulation in placental fractalkine at term, compared to first trimester. Fractalkine expression and release were detected in the trophoblast cell line BeWo, in primary term trophoblasts and placental explants. Incubation of BeWo cells and placental explants with metalloprotease inhibitor Batimastat inhibited the release of soluble fractalkine and at the same time increased the membrane-bound form. These results demonstrate that human placenta is a source for fractalkine, which is expressed in the syncytiotrophoblast and can be released into the maternal circulation by constitutive metalloprotease dependent shedding. Increased expression and release of placental fractalkine may contribute to low grade systemic inflammatory responses in third trimester of normal pregnancy. Aberrant placental metalloprotease activity may not only affect the release of placenta derived fractalkine but may at the same time affect the abundance of the membrane-bound form of the chemokine.

CXCR5+CD4+ follicular helper T cells accumulate in resting human lymph nodes and have superior B cell helper activity

Although many relevant immune reactions are initiated in the lymph nodes, this compartment has not been systematically studied in humans. Analyses have been performed on immune cells derived from tonsils, but as this tissue is most often inflamed, generalization of these data is difficult. Here, we analyzed the phenotype and function of the human CD4(+) T-cell subsets and lineages in paired resting lymph node and peripheral blood samples. Naive, central memory cells and effector memory cells as well as Th1, Th2, Th17 and Treg cells were equally represented in both compartments. On the other hand, cytotoxic CD4(+) T cells were strikingly absent in the lymph nodes. CXCR5(+)CD4(+) T cells, representing putative follicular Th (Tfh) cells were over-represented in lymph nodes and expressed higher levels of Tfh markers than their peripheral blood counterparts. Compared with the circulating pool, lymph-node-derived CXCR5(+)CD4(+) T cells were superior in providing help to B cells. Thus, functionally competent Tfh cells accumulate in resting human lymph nodes, providing a swift induction of naive and memory antibody responses upon antigenic challenge.

CX3CL1 (fractalkine) and TNFα production by perfused human placental lobules under normoxic and hypoxic conditions in vitro: the importance of CX3CR1 signaling

Objective

Inflammation and hypoxia activate the fractalkine (CX3CL1) receptor (CX3CR1)-related signaling pathway. Tumor necrosis factor alpha (TNFα) induces CX3CL1, influencing a mechanism of CX3CL1 autoregulation by CX3CR1 expression. We compared spontaneous and lipopolysaccharide (LPS)-induced CX3CL1 and TNFα production by human placenta under normoxic vs. hypoxic conditions, with respect to CX3CR1 expression and its functional status.

Methods

Placental lobules of term placentae (N = 24) were perfused extracorporeally. CX3CL1 and TNFα concentrations were measured in the perfusion fluid by ELISA. LPS, anti-CX3CR1 antibodies and pirfenidone were used in respective subgroups. After perfusion, CX3CR1 expression was estimated in placental tissue using quantitative immunohistochemistry, and the final results were adjusted for the mean microvascular density.

Results

The highest increase in CX3CL1 concentration in response to LPS was observed in hypoxia (p < 0.05). Unlike in normoxia, anti-CX3CR1 administration in hypoxia significantly reduced the LPS-evoked response. CX3CR1 expression was augmented by hypoxia and reached 260.9 ± 41 (% ±SEM) of the reference value in normoxia. Positive immunostaining for CX3CR1 corresponded to the vascular endothelium. Pirfenidone inhibited hypoxia + LPS-related increase in TNFα production and prevented the up-regulation of CX3CR1.

Conclusion

The modulatory influence of TNFα on CX3CR1 expression in hypoxia and CX3CL1/CX3CR1 interaction may serve as a compensatory mechanism to preserve or augment the pro-inflammatory course of intercellular interactions in placental endothelium.

Plasma granzyme B in ST elevation myocardial infarction versus non-ST elevation acute coronary syndrome: comparisons with IL-18 and fractalkine

OBJECTIVE

The proapoptotic protein, granzyme B (GZB), was identified as a contributor to the atherosclerotic plaque instability and recently as inflammatory activator. We studied the release kinetics of GZB and other markers of inflammation such as high sensitivity C reactive protein (hsCRP), interleukin 18 (IL-18), and fractalkine (FKN) in the early phase after acute cardiac events in different ACS subgroups.

METHODS

Thirty-six nondiabetic patients with ACS were compared to 12 control subjects. According to ACS diagnosis, the patients were classified into 22 patients with ST elevation myocardial infarction (STEMI) and 14 patients with non-ST elevation myocardial infarction or unstable angina (NSTEMI/UA). Blood samples were taken on day 1 (day of onset) and day 3 to measure hsCRP, IL-18, FKN, and GZB by ELISA.

RESULTS

Patients with ACS showed significantly higher GZB, IL-18, and FKN levels than the controls. STEMI group showed significantly higher GZB levels than NSTEMI/UA group. On day 3, FKN levels displayed a significant decrease, while GZB levels were significantly increased. IL-18 levels were more or less constant. GZB levels were positively correlated with IL-18 (r = 0.416, P < 0.01) and FKN (r = 0.58, P < 0.001).

CONCLUSIONS

Unlike IL-18 and FKN, plasma GZB may be a marker of ACS disease severity.

Fractalkine (CX3CL1) and its receptor CX3CR1 may contribute to increased angiogenesis in diabetic placenta

Chemokine CX3CL1 is unique, possessing the ability to act as a dual agent: chemoattractant and adhesive compound. Acting via its sole receptor CX3CR1, CX3CL1 participates in many processes in human placental tissue, including inflammation and angiogenesis. Strongly upregulated by hypoxia and/or inflammation-induced inflammatory cytokines secretion, CX3CL1 may act locally as a key angiogenic factor. Both clinical observations and histopathological studies of the diabetic placenta have confirmed an increased incidence of hypoxia and inflammatory reactions with defective angiogenesis. In this study we examined comparatively (diabetes class C complicated versus normal pregnancy) the correlation between CX3CL1 content in placental tissue, the mean CX3CR1 expression, and density of the network of placental microvessels. A sandwich enzyme immunoassay was applied for CX3CL1 measurement in placental tissue homogenates, whereas quantitative immunohistochemical techniques were used for the assessment of CX3CR1 expression and the microvascular density. Significant differences have been observed for all analyzed parameters between the groups. The mean concentration of CX3CL1 in diabetes was increased and accompanied by augmented placental microvessel density as well as a higher expression of CX3CR1. In conclusion, we suggest involvement of CX3CL1/CX3CR1 signaling pathway in the pathomechanism of placental microvasculature remodeling in diabetes class C.

In situ tissue regeneration: chemoattractants for endogenous stem cell recruitment

Tissue engineering uses cells, signaling molecules, and/or biomaterials to regenerate injured or diseased tissues. Ex vivo expanded mesenchymal stem cells (MSC) have long been a cornerstone of regeneration therapies; however, drawbacks that include altered signaling responses and reduced homing capacity have prompted investigation of regeneration based on endogenous MSC recruitment. Recent successful proof-of-concept studies have further motivated endogenous MSC recruitment-based approaches. Stem cell migration is required for morphogenesis and organogenesis during development and for tissue maintenance and injury repair in adults. A biomimetic approach to in situ tissue regeneration by endogenous MSC requires the orchestration of three main stages: MSC recruitment, MSC differentiation, and neotissue maturation. The first stage must result in recruitment of a sufficient number of MSC, capable of effecting regeneration, to the injured or diseased tissue. One of the challenges for engineering endogenous MSC recruitment is the selection of effective chemoattractant(s). The objective of this review is to synthesize and evaluate evidence of recruitment efficacy by reported chemoattractants, including growth factors, chemokines, and other more recently appreciated MSC chemoattractants. The influence of MSC tissue sources, cell culture methods, and the in vitro and in vivo environments is discussed. This growing body of knowledge will serve as a basis for the rational design of regenerative therapies based on endogenous MSC recruitment. Successful endogenous MSC recruitment is the first step of successful tissue regeneration.

Fractalkine and its receptor mediate extracellular matrix accumulation in diabetic nephropathy in mice

AIMS/HYPOTHESIS

Fractalkine (FKN) is a unique chemokine that works as a chemoattractant and an adhesion molecule. Previous studies have demonstrated that FKN plays a role in ischaemic and protein-overload renal injury via its cognate receptor chemokine (C-X3-C motif) receptor 1 (CX3CR1). However, involvement of the FKN/CX3CR1 system in diabetic nephropathy remains unclear. We examined the role of FKN/CX3CR1 in diabetic mice and mouse mesangial cells (MMCs).

METHODS

Streptozotocin (50 mg kg(-1) day(-1)) was intraperitoneally administered for 5 days to male Cx3cr1-knockout (KO) mice and wild-type (WT) mice. MMCs transfected with Fkn (also known as Cx3cl1) or Cx3cr1 siRNA, respectively, were used to elucidate the role of FKN/CX3CR1 in extracellular matrix (ECM) synthesis.

RESULTS

At 12 weeks, diabetic Cx3cr1 KO mice showed no significant changes in plasma glucose, but markers of renal inflammation, fibrosis and ECM, such as the fractional mesangial area, fibronectin and collagen, were significantly lower in diabetic Cx3cr1 KO mice compared with diabetic WT mice. High glucose, oleic acid and TGF-β1 stimulated FKN and CX3CR1 expression, together with the expression of ECM proteins in MMCs, but the effects were significantly attenuated by Fkn or Cx3cr1 siRNA. More importantly, FKN itself increased mesangial ECM through CX3CR1 and subsequent activation of reactive oxygen species and mitogen-activated protein kinases. A neutralising TGF-β antibody inhibited FKN/CX3CR1 in MMCs treated with diabetic stimuli and decreased FKN-induced ECM accumulation.

CONCLUSIONS/INTERPRETATION

These results demonstrate that FKN/CX3CR1 may play an important role in diabetic renal injury through upregulation of ECM synthesis and could therefore be a therapeutic target for preventing diabetic nephropathy.

A specific immune transcriptomic profile discriminates chronic kidney disease patients in predialysis from hemodialyzed patients

BACKGROUND

Chronic kidney disease (CKD) patients present a complex interaction between the innate and adaptive immune systems, in which immune activation (hypercytokinemia and acute-phase response) and immune suppression (impairment of response to infections and poor development of adaptive immunity) coexist. In this setting, circulating uremic toxins and microinflammation play a critical role. This condition, already present in the last stages of renal damage, seems to be enhanced by the contact of blood with bioincompatible extracorporeal hemodialysis (HD) devices. However, although largely described, the cellular machinery associated to the CKD- and HD-related immune-dysfunction is still poorly defined. Understanding the mechanisms behind this important complication may generate a perspective for improving patients outcome.

METHODS

To better recognize the biological bases of the CKD-related immune dysfunction and to identify differences between CKD patients in conservative (CKD) from those in HD treatment, we used an high-throughput strategy (microarray) combined with classical bio-molecular approaches.

RESULTS

Immune transcriptomic screening of peripheral blood mononuclear cells (1030 gene probe sets selected by Gene-Ontology) showed that 275 gene probe sets (corresponding to 213 genes) discriminated 9 CKD patients stage III-IV (mean±SD of eGFR: 32.27+/-14.7 ml/min) from 17 HD patients (p<0.0001, FDR=5%). Seventy-one genes were up- and 142 down-regulated in HD patients. Functional analysis revealed, then, close biological links among the selected genes with a pivotal role of PTX3, IL-15 (up-regulated in HD) and HLA-G (down-regulated in HD). ELISA, performed on an independent testing-group [11 CKD stage III-IV (mean±SD of eGFR: 30.26±14.89 ml/min) and 13 HD] confirmed that HLA-G, a protein with inhibition effects on several immunological cell lines including natural killers (NK), was down-expressed in HD (p=0.04). Additionally, in the testing-group, protein levels of CX3CR1, an highly selective chemokine receptor and surface marker for cytotoxic effector lymphocytes, resulted higher expressed in HD compared to CKD (p<0.01).

CONCLUSION

Taken together our results show, for the first time, that HD patients present a different immune-pattern compared to the un-dialyzed CKD patients. Among the selected genes, some of them encode for important biological elements involved in proliferation/activation of cytotoxic effector lymphocytes and in the immune-inflammatory cellular machinery. Additionally, this study reveals new potential diagnostic bio-markers and therapeutic targets.

A possible role for CCR5 in the progression of atherosclerosis in HIV-infected patients: a cross-sectional study

Background

Chemokines can block viral entry by interfering with HIV co-receptors and are recognised mediators of atherosclerosis development. A number of experimental drugs that inhibit HIV entry arrest the development of atherosclerosis in animal models. We hypothesised that the expression of chemokine receptors in circulating leukocytes is associated with the rate of atherosclerosis progression in HIV-infected patients.

Methods

The increase in intima-media thickness during a 2-year follow-up was used to classify HIV-infected patients (n = 178) as progressors (n = 142) or non-progressors (n = 36) with respect to atherosclerosis. Logistic regression was used to assess variables associated with atherosclerosis progression. Mutations in the CCR5Δ32, CCR2 64I, and CX3CR1 (T280M and V249I) co-receptors as well as the levels of CCR5, CXCR4, CX3CR1, and CCR2 mRNA expression in circulating leukocytes were analysed as independent variables.

Results

Among the baseline variables, only genetic variants explained the dichotomous outcome. The expression of CCR2 and CXCR4 did not discriminate between progressors and non-progressors. Conversely, CCR5 and CX3CR1 expression was higher in not only progressors but also patients with detectable viral load. The logistic regression, however, demonstrated a significant role for CCR5 expression as a predictor of atherosclerosis progression (B = 2.1, OR = 8.1, p = 0.04) and a negligible effect for CXC3R1 and CCR2 expression.

Conclusions

Available CCR5 antagonists should be investigated for their potential to delay the course of atherosclerosis in HIV-infected patients.

Interaction between CX3CL1 and CX3CR1 regulates vasculitis induced by immune complex deposition

A type III hypersensitivity reaction induced by an immune complex, such as leukocytoclastic vasculitis, is mediated by inflammatory cell infiltration that is highly regulated by multiple adhesion molecules. CX3CL1, a ligand for CX3C chemokine receptor 1 (CX3CR1), has recently been identified as a key mediator of leukocyte adhesion that functions without the recruitment of integrins or selectin-mediated rolling. To elucidate the role of CX3CL1 and CX3CR1 in the development of leukocytoclastic vasculitis, the cutaneous and peritoneal reverse Arthus reactions, classic experimental models for immune complex-mediated tissue injury, were examined in mice lacking CX3CR1. CX3CL1 expression in sera and lesional skin of patients with polyarteritis nodosa (PN) and healthy controls was also examined. Edema and hemorrhage were significantly reduced in CX3CR1(-/-) mice compared with wild-type mice. Infiltration of neutrophils and mast cells and expression of IL-6 and tumor necrosis factor-α were also decreased in CX3CR1(-/-) mice. CX3CL1 was expressed in endothelial cells during the cutaneous reverse Arthus reactions. Furthermore, serum CX3CL1 levels were significantly higher in patients with PN than in healthy controls. Endothelial cells in lesional skin of patients with PN strongly expressed CX3CL1. These results suggest that interactions between CX3CL1 and CX3CR1 may contribute to the development of leukocytoclastic vasculitis by regulating neutrophil and mast cell recruitment and cytokine expression.

Inflammation in atherosclerosis: a cause or a result of vascular disorders?

Sound data support the concept that in atherosclerosis, inflammation and dyslipidemia intersect each other and that irrespective of the initiator, both participate from the early stages to the ultimate fate of the atheromatous plaque. The two partakers manoeuvre a vicious circle in atheroma formation: dyslipidaemia triggers an inflammatory process and inflammation elicits dyslipidaemia. Independent of the initial cause, the atherosclerotic lesions occur focally, in particular arterial-susceptible sites, by a process that, although continuous, can be arbitrarily divided into a sequence of consecutive stages that lead from fatty streak to the fibro-lipid plaque and ultimately to plaque rupture and thrombosis. In the process, the initial event is a change in endothelial cells (EC) constitutive properties. Then, the molecular alarm signals send by dysfunctional EC are decoded by specific blood immune cells (monocytes, T lymphocytes, neutrophils, mast cells) and by the resident vascular cells, that respond by initiating a robust inflammatory process, in which the cells and the factors they secrete hasten the atheroma development. Direct and indirect crosstalk between the cells housed within the nascent plaque, complemented by the increase in risk factors of atherosclerosis lead to atheroma development and outcome. The initial inflammatory response can be regarded as a defense/protective reaction mechanism, but its further amplification, speeds up atherosclerosis. In this review, we provide an overview on the role of inflammation and dyslipidaemia and their intersection in atherogenesis. The data may add to the foundation of a novel attitude in the diagnosis and treatment of atherosclerosis.

Innate immunity modulation by the IL-33/ST2 system in intestinal mucosa

Innate immunity prevents pathogens from entering and spreading within the body. This function is especially important in the gastrointestinal tract and skin, as these organs have a large surface contact area with the outside environment. In the intestine, luminal commensal bacteria are necessary for adequate food digestion and play a crucial role in tolerance to benign antigens. Immune system damage can create an intestinal inflammatory response, leading to chronic disease including inflammatory bowel diseases (IBD). Ulcerative colitis (UC) is an IBD of unknown etiology with increasing worldwide prevalence. In the intestinal mucosa of UC patients, there is an imbalance in the IL-33/ST2 axis, an important modulator of the innate immune response. This paper reviews the role of the IL-33/ST2 system in innate immunity of the intestinal mucosa and its importance in inflammatory bowel diseases, especially ulcerative colitis.

Targeting chemokines in proteinuria-induced renal disease

INTRODUCTION

Proteinuria is a common finding in glomerular diseases that contributes to the progression of chronic kidney injury. Tubular cells reabsorb the excess of albumin and other plasma proteins from the tubular lumen, triggering several pathophysiologic responses, such as overexpression of fibrogenic mediators and inflammatory chemokines. Chemokines are implicated both in the recruitment of inflammatory infiltrate and in a number of physiological and pathological processes related to protein overload.

AREAS COVERED

In recent years, the specific chemokines and their receptors and the intracellular signaling pathways involved in proteinuria-induced renal damage have been identified. This review provides an overview of the role of chemokines and their receptors in proteinuria-related renal disease and summarizes novel therapeutic approaches to restrain the progression of renal damage.

EXPERT OPINION

Inhibition of chemokine-induced biological activities is a promising therapeutic strategy in proteinuric disorders. Neutralizing antibodies and small organic molecules targeting chemokines and chemokine receptors have been proven to prevent inflammation and renal damage in experimental models of protein overload. Some of these compounds are currently being tested in human clinical trials.

Integrins αvβ3 and α4β1 act as coreceptors for fractalkine, and the integrin-binding defective mutant of fractalkine is an antagonist of CX3CR1

The membrane-bound chemokine fractalkine (FKN, CX3CL1) on endothelial cells plays a role in leukocyte trafficking. The chemokine domain (FKN-CD) is sufficient for inducing FKN signaling (e.g., integrin activation), and FKN-CD binds to its receptor CX3CR1 on leukocytes. Whereas previous studies suggest that FKN-CD does not directly bind to integrins, our docking simulation studies predicted that FKN-CD directly interacts with integrin α(v)β(3). Consistent with this prediction, we demonstrated that FKN-CD directly bound to α(v)β(3) and α(4)β(1) at a very high affinity (K(D) of 3.0 × 10(-10) M to α(v)β(3) in 1 mM Mn(2+)). Also, membrane-bound FKN bound to integrins α(v)β(3) and α(4)β(1), suggesting that the FKN-CD/integrin interaction is biologically relevant. The binding site for FKN-CD in α(v)β(3) was similar to those for other known α(v)β(3) ligands. Wild-type FKN-CD induced coprecipitation of integrins and CX3CR1 in U937 cells, suggesting that FKN-CD induces ternary complex formation (CX3CR1, FKN-CD, and integrin). Based on the docking model, we generated an integrin-binding defective FKN-CD mutant (the K36E/R37E mutant). K36E/R37E was defective in ternary complex formation and integrin activation, whereas K36E/R37E still bound to CX3CR1. These results suggest that FKN-CD binding to CX3CR1 is not sufficient for FKN signaling, and that FKN-CD binding to integrins as coreceptors and the resulting ternary complex formation are required for FKN signaling. Notably, excess K36E/R37E suppressed integrin activation induced by wild-type FKN-CD and effectively suppressed leukocyte infiltration in thioglycollate-induced peritonitis. These findings suggest that K36E/R37E acts as a dominant-negative CX3CR1 antagonist and that FKN-CD/integrin interaction is a novel therapeutic target in inflammatory diseases.

NF-κB-mediated inverse regulation of fractalkine and CX3CR1 during CLP-induced sepsis

Fractalkine is a unique member of the CX3C chemokine family by unfolding its potential through the chemokine (C-X3-C motif) receptor 1 (CX3CR1) with dual function acting both as an adhesion molecule and a soluble chemokine. The regulation of this chemokine is still not clear. Therefore, we were interested in the regulation of fractalkine and of CX3CR1 in experimental sepsis. In addition, we investigated the role of NF-κB for the regulation of fractalkine and of CX3CR1. Using a mouse model of cecal ligation and puncture (CLP)-induced sepsis, we found elevated fractalkine mRNA levels in the heart, lung, kidney, and liver, as well as increased plasma levels 24 and 48h after CLP, respectively. In parallel, CLP resulted in a significant downregulation of CX3CR1 mRNA receptor expression in all investigated murine tissues. Septic mice that were pretreated with the selective NF-κB inhibitor pyrrolidine dithiocarbamate (PDTC) were found to have a decreased liberation of proinflammtory cytokines such as TNF-α, IL-1β, IL-6, or IFN-γ. Further PDTC pretreatment attenuated CLP-induced downregulation of CX3CR1 mRNA as well as CLP-induced upregulation of fractalkine mRNA expression in the heart, lung, kidney, liver, and the increase in fractalkine plasma levels of septic mice. In addition, CLP-induced downregulation of renal CX3CR1 protein expression was inhibited by PDTC-pretreatment. Taken together, our data indicate a CLP-induced inverse regulation of the expression between the relating ligand and the receptor with an upregulation of fractalkine and downregulation of CX3CR1, which seems to be mediated by the transcripting factor NF-κB likely via reduced liberation of proinflammtory cytokines in the whole murine organism.

Fractalkine upregulates inflammation through CX3CR1 and the Jak-Stat pathway in severe acute pancreatitis rat model

Based on the function of chemokine fractalkine (FKN), acting as both adhesion and chemoattractant, FKN plays a role in acute inflammatory response. In this study, we investigated the mechanism of FKN mediated upregulation inflammation in severe acute pancreatitis (SAP) rat models. Western blot, reverse transcriptase-polymerase chain reaction, and immunofluorescence demonstrated that FKN and its receptor CX3CR1 were overexpressed in cerulein-stimulated AR42J cells. AG490 and FKN-siRNA inhibited activation of Janus kinase/signal transducers and activators of transcription (Jak/Stat) in cerulein-stimulated AR42J cells. Following exposure AG490 and FKN-siRNA inhibited tumor necrosis factor-alpha expression by enzyme-linked immunosorbent assay and immunohistochemistry in vivo the SAP rat models. These results showed FKN and CX3CR1 were involved inflammatory response in cerulein-stimulated AR42J cells. FKN upregulates inflammation through CX3CR1 and the Jak/Stat pathway in SAP rat models.

Fractalkine increases mesangial cell proliferation through reactive oxygen species and mitogen-activated protein kinases

Mesangial cell proliferation is one of the main features of chronic renal allograft rejection. One unique feature of fractalkine (CX3CL1) is its existence as both a membrane-tethered and a soluble form. Fractalkine expression is increased in acute and chronic allograft rejection. However, its role in mesangial cell proliferation has not yet been clearly explored. Thus, the present study examined whether fractalkine induced mesangial cell proliferation through production of reactive oxygen species (ROS) and activation of mitogen-activated protein kinase (MAPK), two known mediators of mesangial cell proliferation. Growth-arrested and synchronized mouse mesangial cells were stimulated with fractalkine in the presence versus absence of inhibitors against ROS, extracellular signal-regulated protein kinase (ERK), and p38 MAPK. Cell proliferation was assessed by methylthiazoletetrazolium assay, dichlorofluorescein (DCF)-sensitive cellular ROS production by a fluorometer, and MAPK activation by Western blot analysis. Fractalkine (10-50 ng/mL) significantly increased mesangial cell proliferation at 24 hours in a dose-dependent manner, an effect that was abrogated by the ROS and MAPK inhibitors. Fractalkine (50 ng/mL) also induced cellular ROS production and activation of ERK1/2 and p38 MAPK in mesangial cells. These results demonstrated that fractalkine can induce mesangial cell proliferation through production of cellular ROS and activation of MAPK.

Lipopolysaccharide increases monocyte binding to mesangial cells through fractalkine and its receptor

Fractalkine (CX3CL1) is a unique chemokine that functions not only as a chemokine but also as an adhesion molecule. Fractalkine plays an important role in the recruitment of macrophages into the kidneys by binding to its specific receptor CX3CR1, and renal fractalkine expression was shown to be increased in chronic renal allograft rejection. Considering that microcapillary inflammation is a key feature of chronic renal allograft rejection, the present study examined whether monocytes bind to mesangial cells cultured in the presence of lipopolysaccharide (LPS) through fractalkine/CX3CR1 in order to understand their regulation with respect to inflammation-induced renal allograft dysfunction. Mouse mesangial cells were stimulated with LPS in the presence or absence of fractalkine or CX3CR1 siRNA. Calcein-AM-labeled monocytes were used to evaluate monocyte binding. Fractalkine and CX3CR1 mRNA and protein expression were measured by real-time quantitative polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. LPS at 100 ng/mL significantly increased monocyte binding to mesangial cells. Each siRNA against fractalkine or CX3CR1 effectively inhibited LPS-induced monocyte-mesangial cell binding. Fractalkine and CX3CR1 mRNA expression were enhanced in mesangial cells stimulated with LPS. Fractalkine protein synthesis in media and lysate of mesangial cells were also induced by LPS. These results demonstrated that LPS induces monocyte-mesangial cell binding through the fractalkine/CX3CR1 system and suggested that fractalkine/CX3CR1 system may contribute to renal inflammation leading to chronic renal allograft rejection.

Prevalence of circulating CD4+CD28null T cells is associated with early atherosclerotic damage in patients with end-stage renal disease undergoing hemodialysis

CD4(+) T-cell subsets lacking surface CD28 in peripheral blood have been suggested to predispose people to atherosclerosis. To determine if CD4(+)CD28(null) T cells are involved in the immunopathological process of atherosclerotic damage in end-stage renal disease (ESRD) patients undergoing hemodialysis (HD), we characterized peripheral-blood CD4(+)CD28(null) T cells from HD patients and investigated the association between these cells and early atherosclerotic damage. Four color flow cytometric analyses showed that HD patients had significantly higher percentages of CD4(+)CD28(null) T cells in circulating blood than healthy subjects (HS). Most HD patient-derived CD4(+)CD28(null) T cells expressed higher levels of CX3CR1 and produced more intracellular IFN-γ, perforin and granzyme B than their counterparts. Regression analyses demonstrated that the increased levels of CD4(+)CD28(null) T cells were positively correlated to serum levels of C-reactive protein, suggesting systemic inflammation and atherosclerosis. Furthermore, phenotypic and functional studies of CD4(+)CD28(null) T cells showed that these cells were closely correlated with impaired flow-mediated vasodilation and increased intima-media thickness in the carotid artery, which are markers of early atherosclerosis. These data suggested that CD4(+)CD28(null) T cells are important effector cells in HD patients, and that these cells may have a critical role in mediating early atherosclerotic damage.

Fractalkine and its receptor (CX3CR1) in patients with stable coronary artery disease and diabetes mellitus

BACKGROUND

Fractalkine and its receptor CX3CR1 are associated with atherosclerosis. In vitro studies have shown increased expression of fractalkine in endothelial and vascular smooth muscle cells when stimulated with a high concentration of glucose. Increased serum levels of fractalkine have been shown in patients with type 2 diabetes mellitus (T2DM) and also in unstable coronary artery disease (CAD) patients. We investigated whether CAD patients with T2DM or metabolic syndrome have increased circulating and gene expression levels of fractalkine compared to CAD patients without these conditions.

METHODS

Serum levels of fractalkine were analyzed by the enzyme-linked immunosorbent assay (ELISA) method in 1001 patients with angiographically verified CAD, of which 200 had T2DM and 244 had metabolic syndrome. All patients were taking aspirin as an antithrombotic treatment. Gene expression of fractalkine and CX3CR1 in circulating leukocytes was explored in a subset of patients (n=168).

RESULTS

We found no significant difference in circulating levels of fractalkine in patients with T2DM [653 (556, 775) pg/mL] compared to patients without T2DM [646 (553, 761) pg/mL], p=0.50. There was also no difference between patients with and without metabolic syndrome (p=0.60). Fractalkine was not expressed in circulating leukocytes, and CX3CR1 was not expressed differently between any of the groups (p=0.13 and p=0.32, respectively). Smokers had lower fractalkine levels (p<0.001), and patients on angiotensin II receptor blockers had higher levels (p=0.047) compared to nonaffected patients.

CONCLUSIONS

In the present CAD population, no differences in circulating levels of fractalkine or expression levels of CX3CR1 were observed between patients with and without T2DM, or with and without metabolic syndrome, which may be related to their underlying disease.

siRNA-based targeting of fractalkine overexpression suppresses inflammation development in a severe acute pancreatitis rat model

Fractalkine (FKN), a chemokine that acts as both an adhesion molecule and a chemoattractant, is expressed in many inflammatory diseases. Chemokines play a crucial role in severe acute pancreatitis (SAP). This study used adenovirus-mediated siRNA to target FKN overexpression and assessed its ability to suppress inflammation development in a SAP rat model. Adenovirus-mediated FKN siRNA was transfected into cerulein-stimulated AR42J cells. The growth of cerulein-stimulated AR42J cells was determined by colony formation and MTT assays. The inhibitory effect of the FKN siRNA was studied in a SAP rat model in vivo and detected by ELISA, RT-PCR, western blot analysis and immunohistochemistry. FKN, IL-8 and TNF-α were found to be overexpressed in cerulein-stimulated AR42J cells by ELISA and western blot analysis (P<0.05). The animal experiments confirmed that FKN siRNA could inhibit inflammation development in SAP. The values of serum FKN, TNF-α and IL-8 levels were decreased after FKN siRNA treatment (P<0.05). Furthermore, western blotting and RT-PCR analysis showed that FKN protein and mRNA levels were decreased after injection with FKN siRNA (P<0.05). Immunohistochemistry also showed that inflammation was decreased after injection with FKN-siRNA in the SAP rat model. Treatment with siRNA can inhibit FKN overexpression and also suppresses inflammation development in a SAP rat model. More importantly, this study indicated that FKN, which is overexpressed in the SAP rat model, may serve as a novel and effective therapeutic target for SAP.

The immunologic outcome of enhanced function of mouse liver lymphocytes and Kupffer cells by high-fat and high-cholesterol diet

Dietary lipids/cholesterol may modulate liver immune function. We have recently found that mouse F4/80 Kupffer cells are classified into phagocytic CD68 Kupffer cells and cytokine-producing CD11b Kupffer cells. We here investigate how a high-fat and/or high-cholesterol diet affects innate immune liver mononuclear cells. For 4 weeks, C57BL/6 mice were fed a high-fat and high-cholesterol diet (HFCD), a high-cholesterol diet (HCD), a high-fat diet (HFD), or a control diet (CD). High-fat and high-cholesterol diet and HCD increased liver cholesterol levels; serum cholesterol levels increased in HFCD and HFD mice but not in HCD mice. The increased proportion of natural killer (NK) cells, downregulated NK1.1 expression of natural killer T cells, and enhanced CD69 and IL-12 receptor β mRNA expression of liver lymphocytes indicate the activation of them by HFCD. IL-12 production from Kupffer cells and interferon γ production from NK/natural killer T cells activated by LPS and/or IL-12 both increased. IL-12 pretreatment more effectively improved the survival of HFCD mice relative to the survival of CD mice upon injections of liver metastatic EL-4 cells. In contrast, HFCD mouse survival decreased after LPS injection and generalized Shwartzman reaction. Consistently in HFCD mice, Toll-like receptor 4 mRNA expression of whole Kupffer cells was upregulated, and CD11b Kupffer cells proportionally increased. Although the proportion of CD68 Kupffer cells decreased in HFCD mice, phagocytic activity of them was enhanced. Mice fed with HCD rather than those fed with HFD showed features closer to HFCD mice. Thus, enhanced function of mouse liver mononuclear cells is likely dependent on the liver cholesterol level, rather than the liver triglyceride level.

Activated innate immunity and the involvement of CX3CR1-fractalkine in promoting hematuria in patients with IgA nephropathy

A hallmark of immunoglobulin A nephropathy (IgAN) is episodes of gross hematuria coinciding with mucosal infections that can represent the disease-triggering event. Here we performed a whole genomic screen of IgAN patients during gross hematuria to clarify the link between mucosal antigens and glomerular hematuria. Modulated genes showed a clear involvement of the intracellular interferon signaling, antigen-presenting pathway, and the immunoproteasome. The mRNA and protein level of the chemokine receptor characterizing cytotoxic effector lymphocytes, CX3CR1, was upregulated. In vitro antigenic stimulation of peripheral blood mononuclear cells from IgAN patients, healthy blood donors, and other nephropathies with microscopic hematuria showed that only in IgAN patients was CX3CR1 enhanced in a dose-dependent manner. A significantly higher amount of glomerular and urinary fractalkine, the only ligand of CX3CR1, was also found in IgAN patients with recurrent episodes of gross hematuria compared with other patients with microscopic or no hematuria. This suggests a predisposition for cytotoxic cell extravasation only in patients with recurrent gross hematuria. Thus, we found a defect in antigen handling in peripheral blood mononuclear cells of IgAN patients with a specific increase of CX3CR1. This constitutive upregulation of glomerular and urinary fractalkine suggests an involvement of the CX3CR1-fractalkine axis in the exacerbation of gross hematuria.

Increased expression of fractalkine and its receptor CX3CR1 in canine inflammatory bowel disease and their possible role in recruitment of intraepithelial lymphocytes

The interaction between fractalkine/CX(3)CL1 and its receptor CX(3)CR1 has been reported to play an important role in various human inflammatory diseases, including inflammatory bowel disease (IBD) mediated by lymphocyte chemoattraction. The objective of this study was to investigate the role of fractalkine and CX(3)CR1 in lymphocyte migration in canine IBD. IBD was diagnosed in 34 dogs, and 19 healthy beagles were used as normal controls. We quantified intestinal mRNA and protein expression of fractalkine and CX(3)CR1 by real-time RT-PCR and ELISA, respectively, and examined the localization of fractalkine in canine intestine by immunohistochemistry. The expression of CX(3)CR1 and surface antigens on peripheral blood mononuclear cells (PBMCs) and intraepithelial lymphocytes (IELs) was analyzed by flow cytometry. Intestinal fractalkine and CX(3)CR1 mRNA was significantly up-regulated in IBD dogs compared with the healthy control dogs. In addition, fractalkine expression on intestinal epithelial cells was significantly increased in the intestinal mucosa of IBD dogs compared with the healthy dogs. CX(3)CR1(+) PBMCs were significantly elevated in IBD dogs and positively correlated with the histopathological severity of IELs infiltration. These CX(3)CR1(+) PBMCs predominantly expressed markers for cytotoxic T cells. Almost all IELs expressed CD3, and the majority of cells expressed CD8 rather than CD4, which was analogous to the CX(3)CR1(+) PBMCs. These results suggest that the fractalkine-CX(3)CR1 interaction may contribute to the pathogenesis of canine IBD through migration of IELs.

Fractalkine as a marker for assessment of severe acute pancreatitis

OBJECTIVE

The aim of this study was to study the role of fractalkine (FKN) in the development of severe acute pancreatitis (SAP) in animal model.

METHODS

Serum FKN levels in rat model (control, SAP6 h, 16 h, 24 h and 48 h) were determined by enzyme-linked immunosorbent assay. FKN mRNA and protein levels in the pancreas tissue were measured by reverse transcription polymerase chain reaction (RT-PCR), Western blot and immunohistochemistry.

RESULTS

Serum FKN level in the SAP rat increased significantly (P < 0.05 compared with the control group). FKN mRNA and protein levels in pancreas and lung increased significantly and reached the peak at 16 h after the induction of SAP, while those in kidney reached the peak at 48 h. Immunohistochemistry showed the overexpression of FKN in pancreas, lung and kidney tissue.

CONCLUSION

FKN involves in the progression of SAP and might be a valuable marker for the assessment of SAP.

The association of V249I and T280M fractalkine receptor haplotypes with disease course of multiple sclerosis

We investigated the association of CX3CR1 genotypes/haplotypes with MS and performed the prediction analysis of protein sequence variants' effects on CX3CL1/CX3CR1 interaction. We found no association of CX3CR1 with MS susceptibility. Frequency of I(249)T(280) haplotype was significantly lower in SP compared to RR patients (RR>10 years, OR=0.30, 95%CI=0.11-0.79, p=0.01; OR=0.53, 95%CI=0.18-1.56, p=0.2, in SP<10 years vs. RR>10 years). Prediction analysis showed that I249 T280 protein variant would significantly affect CX3CL1/CX3CR1 interaction. Our results suggest that CX3CR1 I₂₄₉T₂₈₀ haplotype could have protective effect for switch to SP MS. Further research is warranted to validate and replicate currently observed results.

Pathological role of fractalkine/CX3CL1 in rheumatic diseases: a unique chemokine with multiple functions

Understanding rheumatic diseases from the perspective of chemokine biology has shaped and will continue to shape our approach for targeted drug design. Among different kinds of chemokines, fractalkine/CX3CL1 has been found to play an important role in inflammation, portraying unique functional, and structural characteristics. This review summarizes the emerging role of fractalkine/CX3CL1 from a functional and clinical perspective and provides evidence to validate it as a potential therapeutic target in rheumatic diseases such as rheumatoid arthritis, Sjögren's syndrome, systemic lupus erythematosus, scleroderma, as well as diseases related to vascular inflammation. From this, recent studies investigating potential therapeutic agents against fractalkine/CX3CL1's role in pathology have shown promise.

Human virus-specific effector-type T cells accumulate in blood but not in lymph nodes

It is believed that the size of the CD8(+) T-cell pool is fixed and that with every new viral challenge, the size of the pre-existing memory-cell population shrinks to make way for the new virus-specific cells. CMV-seropositive individuals have high numbers of CMV-specific resting-effector type CD8(+) T cells in their peripheral blood (PB). This prompted us to investigate whether CMV infection limits immunologic space at sites where immune reactions are initiated, such as in the lymph nodes (LNs). LN and paired PB samples were analyzed for CMV-, EBV-, and influenza-specific CD8(+) T cells. In marked contrast to blood, LNs contained significantly lower numbers of CX3CR1-expressing effector-type CD8(+) T cells, whereas the CMV-specific cells that were found in the LNs resembled polyfunctional memory-type cells. In contrast, EBV- and influenza-specific CD8(+) T cells were highly similar between PB and LNs both in number and function. Therefore, it is unlikely that CMV-specific CD8(+) T cells in the LNs restrain the immunologic space of other virus-specific cells.

Tolerance and lymphoid organ structure and function

This issue of Frontiers in Immunologic Tolerance explores barriers to tolerance from a variety of views of cells, molecules, and processes of the immune system. Our laboratory has spent over a decade focused on the migration of the cells of the immune system, and dissecting the signals that determine how and where effector and suppressive regulatory T cells traffic from one site to another in order to reject or protect allografts. These studies have led us to a greater appreciation of the anatomic structure of the immune system, and the realization that the path taken by lymphocytes during the course of the immune response to implanted organs determines the final outcome. In particular, the structures, microanatomic domains, and the cells and molecules that lymphocytes encounter during their transit through blood, tissues, lymphatics, and secondary lymphoid organs are powerful determinants for whether tolerance is achieved. Thus, the understanding of complex cellular and molecular processes of tolerance will not come from “96-well plate immunology,” but from an integrated understanding of the temporal and spatial changes that occur during the response to the allograft. The study of the precise positioning and movement of cells in lymphoid organs has been difficult since it is hard to visualize cells within their three-dimensional setting; instead techniques have tended to be dominated by two-dimensional renderings, although advanced confocal and two-photon systems are changing this view. It is difficult to precisely modify key molecules and events in lymphoid organs, so that existing knockouts, transgenics, inhibitors, and activators have global and pleiotropic effects, rather than precise anatomically restricted influences. Lastly, there are no well-defined postal codes or tracking systems for leukocytes, so that while we can usually track cells from point A to point B, it is exponentially more difficult or even impossible to track them to point C and beyond. We believe this represents one of the fundamental barriers to understanding the immune system and devising therapeutic approaches that take into account anatomy and structure as major controlling principles of tolerance.

Fractalkine expression induces endothelial progenitor cell lysis by natural killer cells

Background

Circulating CD34⁺ cells, a population that includes endothelial progenitors, participate in the maintenance of endothelial integrity. Better understanding of the mechanisms that regulate their survival is crucial to improve their regenerative activity in cardiovascular and renal diseases. Chemokine-receptor cross talk is critical in regulating cell homeostasis. We hypothesized that cell surface expression of the chemokine fractalkine (FKN) could target progenitor cell injury by Natural Killer (NK) cells, thereby limiting their availability for vascular repair.

Methodology/Principal Findings

We show that CD34⁺-derived Endothelial Colony Forming Cells (ECFC) can express FKN in response to TNF-α and IFN-γ inflammatory cytokines and that FKN expression by ECFC stimulates NK cell adhesion, NK cell-mediated ECFC lysis and microparticles release in vitro. The specific involvement of membrane FKN in these processes was demonstrated using FKN-transfected ECFC and anti-FKN blocking antibody. FKN expression was also evidenced on circulating CD34⁺ progenitor cells and was detected at higher frequency in kidney transplant recipients, when compared to healthy controls. The proportion of CD34⁺ cells expressing FKN was identified as an independent variable inversely correlated to CD34⁺ progenitor cell count. We further showed that treatment of CD34⁺ circulating cells isolated from adult blood donors with transplant serum or TNF-α/IFN-γ can induce FKN expression.

Conclusions

Our data highlights a novel mechanism by which FKN expression on CD34⁺ progenitor cells may target their NK cell mediated killing and participate to their immune depletion in transplant recipients. Considering the numerous diseased contexts shown to promote FKN expression, our data identify FKN as a hallmark of altered progenitor cell homeostasis with potential implications in better evaluation of vascular repair in patients.

Peripheral immune contributions to the maintenance of central glial activation underlying neuropathic pain

Recent evidence implicates an adaptive immune response in the central nervous system (CNS) mechanisms of neuropathic pain. This review identifies how neuropathic pain alters CNS immune privilege to facilitate T cell infiltration. Once in the CNS, T cells may interact with the local antigen presenting cells, microglia, via the major histocompatibility complex and the costimulatory molecules CD40 and B7. In this way, T cells may contribute to the maintenance of neuropathic pain through pro-inflammatory interactions with microglia and by facilitating the activation of astrocytes in the spinal dorsal horn. Based on the evidence presented in this review, we suggest that this bidirectional, pro-inflammatory system of neurons, glia and T cells in neuropathic pain should be renamed the pentapartite synapse, and identifies the latest member as a potential disease-modifying therapeutic target.

Deficiency of CX3CR1 delays burn wound healing and is associated with reduced myeloid cell recruitment and decreased sub-dermal angiogenesis

The development of a good blood supply is a key step in burn wound healing and appears to be regulated in part by myeloid cells. CX3CR1 positive cells have recently been identified as myeloid cells with a potential role in angiogenesis. The role of functional CX3CR1 system in burn wound healing is not previously investigated. A 2% contact burn was induced in CX3CR1(+/gfp) and CX3CR1(gfp/gfp) mice. These transgenic mice facilitate the tracking of CX3CR1 cells (CX3CR1(+/gfp)) and allow evaluation of the consequence of CX3CR1 functional knockout (CX3CR1(gfp/gfp)) on burn wound healing. The progression of wound healing was monitored before tissue was harvested and analyzed at day 6 and day 12 for migration of CX3CR1 cells into burn wound. Deficiency of a functional CX3CR1 system resulted in decreased recruitment of CX3CR1 positive cells into the burn wound associated with decreased myeloid cell recruitment (p<0.001) and reduced maintenance of new vessels (p<0.001). Burn wound healing was prolonged (p<0.05). Our study is the first to establish a role for CX3CR1 in burn wound healing which is associated with sub-dermal angiogenesis. This chemokine receptor pathway may be attractive for therapeutic manipulation as it could increase sub dermal angiogenesis and thereby improve time to healing.

Perforin-mediated cytotoxicity in non-ST elevation myocardial infarction

The aim of this investigation was to examine the role of perforin (P)-mediated cytotoxicity in the dynamics of tissue damage in patients with non-ST-segment elevation myocardial infarction (NSTEMI) treated with anti-ischaemic drugs. We enrolled 48 patients with NSTEMI in this study [age, 71.5 years; 61.5/76 (median, 25th/75th percentiles)]. The percentage of total peripheral blood P(+) lymphocytes was elevated owing to the increased frequency of P(+) cells within natural killer (NK) subsets, T and NKT cells in patients on day 1 after NSTEMI when compared with healthy controls. Positive correlations were found between cardiac troponin I plasma concentrations and the frequency of P(+) cells, P(+) T cells, P(+) NK cells and their CD56(+dim) and CD56(+bright) subsets during the first week after the NSTEMI. The expression of P in NK cells was accompanied by P-mediated cytotoxicity against K-562 targets at all days examined, except day 21, when an anti-perforin monoclonal antibody did not completely abolish the killing. The percentage of P(+) T cells, P(+) NKT cells and P(+) NK subsets was the highest on the day 1 after NSTEMI and decreased in the post-infarction period. CD56(+) lymphocytes were found in damaged myocardium, suggesting their tissue recruitment. In conclusion, patients with NSTEMI have a strong and prolonged P-mediated systemic inflammatory reaction, which may sustain autoaggressive reactions towards myocardial tissue during the development of myocardial infarction.

Association of circulating fractalkine (CX3CL1) and CX3CR1(+)CD4(+) T cells with common carotid artery intima-media thickness in patients with chronic kidney disease

AIM

Fractalkine (CX3CL1), a chemokine, and its receptor CX3CR1 (expressed on T lymphocytes), have been shown to be abnormal in atherosclerosis. We investigated whether CX3CL1 levels and CX3CR1 expression were altered in patients with chronic kidney disease (CKD) and their association with common carotid artery intima-media thickness (CCA-IMT).

METHODS

CX3CR1 expression on CD4(+) T cells was analyzed by flow cytometry in 62 healthy controls (HC) and 128 Stage III-V CKD subjects. Fractalkine and highly sensitive C-reactive protein (hsCRP) were analyzed by ELISA. CCA-IMT was measured by ultrasound.

RESULTS

Compared to HC, CKD patients exhibited a 2.5-fold increase in the CD4(+)CX3CR1(+) T cell population (14.8±0.6 vs 5.9±0.34%, p < 0.0001). The expression of CX3CR1 was largely restricted to those CD4(+) cells that lacked CD28 co-stimulatory molecule. Fractalkine (pg/mL) and hsCRP (µg/mL) levels were increased in CKD subjects (510.6±61.6 vs. 239.7±9.67, p =0.003, and 93.8± 5.3 vs. 48.4±6.8, p < 0.0001), as was the CCA-IMT (0.71±0.01 vs. 0.56±0.01 mm, p < 0.0001). There was a significant relationship between CD4(+)CX3CR1(+) T cells and fractalkine levels (r = 0.2, p =0.01). CCA-IMT correlated positively with CX3CR1(+) T cells (r =0.34, p < 0.0001), CD4(+) CX3CR1(+) T cells (r =0.39, p < 0.0001), CD4(+)CD28(null)CX3CR1(+) T cells (r =0.23, p =0.02), fractalkine (r =0.3, p =0.001), age (r =0.33, p < 0.0001) and diabetes (p =0.01). On multiple regression, only CD4(+)CX3CR1(+) T cells and the presence of diabetes continued to show an association with IMT (p < 0.0001 and 0.0029 respectively).

CONCLUSIONS

CKD subjects showed an increase in CD4(+)CX3CR1(+) T cell population, plasma fractalkine and IMT; the association of CD4(+)CX3CR1(+) T cells and plasma fractalkine with CCA-IMT indicates that the fractalkine-CX3CR1 pathway may be important in the development and/or progression of atherosclerosis in CKD.

Immunohistochemical staining for transcription factor MafB in alveolar macrophages is correlated with spirometric measures of airflow limitation in smokers

BACKGROUND AND OBJECTIVE

Alveolar macrophages (AM) play an important role in the pathogenesis of COPD, and their numbers are significantly increased in patients with COPD. We previously demonstrated that expression of the transcription factor, MafB, was upregulated in AM of mice exposed to cigarette smoke. The aim of this study was to investigate whether the expression of MafB is associated with the degree of airflow limitation (AFL) in smokers.

METHODS

Lung tissue specimens were obtained from male patients undergoing resection of small peripheral lung tumours. The patients were classified into three groups according to smoking index and FEV1 /FVC: (i) non-smokers or non-heavy ex-smokers without AFL (FEV1 /FVC ≥ 0.7, smoking index ≤ 400) (n=8); (ii) heavy current smokers without AFL (FEV1 /FVC ≥ 0.7, smoking index ≥ 800) (n=8); and (iii) heavy current smokers with AFL (FEV1 /FVC < 0.6, smoking index ≥ 800) (n=8). The intensity of immunostaining for MafB in AM was quantified by image analysis.

RESULTS

Immunostaining for MafB was significantly enhanced in AM of smokers with AFL compared with AM of subjects without AFL. Smoking index, FEV1/FVC and FEF(25-75%) (% predicted) were significantly correlated with the intensity of MafB immunostaining. Multiple linear regression analysis revealed that FEV1 % was also an independent negative predictor of the intensity of MafB immunostaining.

CONCLUSIONS

The degree of immunostaining for MafB in AM was correlated with the degree of AFL in smokers. MafB may be involved in the pathophysiology of COPD.

Modulation of syndecan-1 shedding after hemorrhagic shock and resuscitation

The early use of fresh frozen plasma as a resuscitative agent after hemorrhagic shock has been associated with improved survival, but the mechanism of protection is unknown. Hemorrhagic shock causes endothelial cell dysfunction and we hypothesized that fresh frozen plasma would restore endothelial integrity and reduce syndecan-1 shedding after hemorrhagic shock. A prospective, observational study in severely injured patients in hemorrhagic shock demonstrated significantly elevated levels of syndecan-1 (554±93 ng/ml) after injury, which decreased with resuscitation (187±36 ng/ml) but was elevated compared to normal donors (27±1 ng/ml). Three pro-inflammatory cytokines, interferon-γ, fractalkine, and interleukin-1β, negatively correlated while one anti-inflammatory cytokine, IL-10, positively correlated with shed syndecan-1. These cytokines all play an important role in maintaining endothelial integrity. An in vitro model of endothelial injury then specifically examined endothelial permeability after treatment with fresh frozen plasma orlactated Ringers. Shock or endothelial injury disrupted junctional integrity and increased permeability, which was improved with fresh frozen plasma, but not lactated Ringers. Changes in endothelial cell permeability correlated with syndecan-1 shedding. These data suggest that plasma based resuscitation preserved endothelial syndecan-1 and maintained endothelial integrity, and may help to explain the protective effects of fresh frozen plasma after hemorrhagic shock.

Stem cells decreased neuronal cell death after hypoxic stress in primary fetal rat neurons in vitro

To explore stem cell-mediated neuronal protection through extracellular signaling pathways by transplanted stem cells, we sought to identify potential candidate molecules responsible for neuronal protection using an in vitro coculture system. Primary fetal rat hippocampal neurons underwent hypoxia (≤1% oxygen) for 96 h nad then were returned to a normoxic condition. The study group then received rat umbilical cord matrix-derived stem cells, while the control group received fresh media only. The experimental group showed decreased neuronal apoptosis compared to the control group [44.5 ± 1.6% vs. 71.0 ± 4.2% (mean ± SD, p = 0.0005) on day 5] and higher neuronal survival (4.9 ± 1.2 cells/100× field vs. 2.2 ± 0.3, p = 0.02 on day 5). Among 90 proteins evaluated using a protein array, stem cell coculture media showed increased protein secretion of TIMP-1 (5.61-fold), TIMP-2 (4.88), CNTF-Rα (3.42), activin A (2.20), fractalkine (2.04), CCR4 (2.02), and decreased secretion in MIP-2 (0.30-fold), AMPK α1 (0.43), TROY (0.48), and TIMP-3 (0.50). This study demonstrated that coculturing stem cells with primary neurons in vitro decreased neuronal cell death after hypoxia with significantly altered protein secretion. The results suggest that stem cells may offer neuronal protection through extracellular signaling.

Mesenchymal cell proliferation and programmed cell death: key players in fibrogenesis and new targets for therapeutic intervention

An exquisite equilibrium between cell proliferation and programmed cell death is required to maintain physiological homeostasis. In inflammatory bowel disease, and especially in Crohn's disease, enhanced proliferation along with defective apoptosis of immune cells are considered key elements of pathogenesis. Despite the relatively limited attention that has been given to research efforts devoted to intestinal fibrosis to date, there is evidence suggesting that enhanced proliferation along with defective programmed cell death of mesenchymal cells can significantly contribute to the development of excessive fibrogenesis in many different tissues. Moreover, some therapies have demonstrated potential antifibrogenic efficacy through the regulation of mesenchymal cell proliferation and programmed cell death. Further understanding of the pathways involved in the regulation of mesenchymal cell proliferation and apoptosis is, however, required.

Fractalkine is a novel human adipochemokine associated with type 2 diabetes

OBJECTIVE

Leukocyte infiltration of adipose is a critical determinant of obesity-related metabolic diseases. Fractalkine (CX3CL1) and its receptor (CX3CR1) comprise a chemokine system involved in leukocyte recruitment and adhesion in atherosclerosis, but its role in adipose inflammation and type 2 diabetes is unknown.

RESEARCH DESIGN AND METHODS

CX3CL1 mRNA and protein were quantified in subcutaneous adipose and blood during experimental human endotoxemia and in lean and obese human adipose. CX3CL1 cellular source was probed in human adipocytes, monocytes, and macrophages, and CX3CL1-blocking antibodies were used to assess its role in monocyte-adipocyte adhesion. The association of genetic variation in CX3CR1 with metabolic traits was determined in a community-based sample. Finally, plasma CX3CL1 levels were measured in a case-control study of type 2 diabetes.

RESULTS

Endotoxemia induced adipose CX3CL1 mRNA (32.7-fold, P < 1 × 10(-5)) and protein (43-fold, P = 0.006). Obese subjects had higher CX3CL1 levels in subcutaneous adipose compared with lean (0.420 ± 0.387 vs. 0.228 ± 0.187 ng/mL, P = 0.04). CX3CL1 was expressed and secreted by human adipocytes and stromal vascular cells. Inflammatory cytokine induction of CX3CL1 in human adipocytes (27.5-fold mRNA and threefold protein) was completely attenuated by pretreatment with a peroxisome proliferator-activated receptor-γ agonist. A putative functional nonsynonymous single nucleotide polymorphism (rs3732378) in CX3CR1 was associated with adipose and metabolic traits, and plasma CX3CL1 levels were increased in patients with type 2 diabetes vs. nondiabetics (0.506 ± 0.262 vs. 0.422 ± 0.210 ng/mL, P < 0.0001).

CONCLUSIONS

CX3CL1-CX3CR1 is a novel inflammatory adipose chemokine system that modulates monocyte adhesion to adipocytes and is associated with obesity, insulin resistance, and type 2 diabetes. These data provide support for CX3CL1 as a diagnostic and therapeutic target in cardiometabolic disease.

Delta chemokine (fractalkine)--a novel mediator of pulmonary arterial hypertension in children undergoing cardiac surgery

BACKGROUND

Fractalkine (FKN), a unique chemokine associated with pulmonary hypertension, may be involved in the acute stress response that regulates inflammation after cardiopulmonary bypass (CPB) surgery. We characterized FKN levels and correlated them with clinical parameters in children undergoing cardiac surgery involving CPB.

METHODS

Twenty-seven consecutive patients, aged 30 days to 11.5 years, who underwent surgery for correction of congenital heart defects, were prospectively studied. Serial blood samples were collected preoperatively, upon termination of CPB, and at six points postoperatively. Plasma was recovered immediately, aliquoted, and frozen at -70° C until assayed. Clinical and laboratory data were collected.

RESULTS

Baseline FKN levels were skewed between patients. Patients with low FKN levels showed significantly higher levels of oxygen saturation in room air compared to patients with high FKN levels (p<0.05). Moreover, there was a positive correlation between preoperative pulmonary arterial hypertension and FKN levels (p<0.05). Surprisingly, FKN elevation from preoperative to postoperative levels displayed no discernible pattern.

CONCLUSIONS

FKN levels significantly correlate with preoperative hypoxemia and PAH, suggesting that FKN may be up-regulated during hypoxemia. CPB is not associated with acute changes in circulating FKN levels. The role of FKN in the postoperative course should be further investigated.

Syk regulates multiple signaling pathways leading to CX3CL1 chemotaxis in macrophages

Several studies have clearly established the importance of the interaction between macrophages and CX3CL1 in the progression of disease. A previous study demonstrated that Syk was required for CX3CL1-mediated actin polymerization and chemotaxis. Here, we delineated the signaling cascade of Syk-mediated cell migration in response to CX3CL1. Inhibition of Syk in bone marrow-derived macrophages or reduction of Syk expression using siRNA in RAW/LR5 cells indicated that Syk was required for the activation of PI3K, Cdc42, and Rac1. Also, reduction in WASP or WAVE2 levels, common downstream effectors of Cdc42 or Rac1, resulted in impaired cell migration to CX3CL1. Syk indirectly regulated WASP tyrosine phosphorylation through Cdc42 activation. Altogether, our data identify that Syk mediated chemotaxis toward CX3CL1 by regulating both Rac1/WAVE2 and Cdc42/WASP pathways, whereas Src family kinases were required for proper WASP tyrosine phosphorylation.