Abstract 185: G-protein Coupled Receptor 55 Deficiency Promotes Atherosclerosis and Inflammation in Mice

Background: The endocannabinoid system plays a pathophysiological role in metabolic and cardiovascular disorders. G protein-coupled receptor (GPR) 55 is a novel cannabinoid receptor expressed by various lymphocyte subsets, in particular γδT cells, innate lymphoid cells and B1 cells. Its role in regulating immune functions and atherosclerosis is unknown.

Methods: We studied early and advanced atherosclerotic plaques and inflammatory parameters in apolipoprotein E deficient (ApoE-/-) and ApoE-/-GPR55-/- mice after 4 or 16 weeks Western Diet (WD), respectively (n=12-15 per group). GPR55 mRNA expression was assessed in human carotid artery plaques (n=29) and healthy control vessels (left internal thoracic arteries; n=28).

Results: ApoE-/-GPR55-/- mice had significantly 1.9 to 2.3-fold increased plaque sizes after 4 and 16 weeks WD compared to ApoE-/- controls with higher macrophage content at early stage, but less macrophage and more collagen content at advanced stage. This was accompanied by enhanced aortic pro-inflammatory cytokine mRNA expression (IL-6, TNFα, IL-1β, iNOS) as well as massively upregulated IgG1 plasma levels. Moreover, GPR55 deficiency was associated with increased circulating, splenic and aortic lymphocyte counts after 4 and 16 weeks WD. The most striking (2 to 4-fold) increase was found in γδT cells, with less pronounced increases in the total CD3+ T cell population and CD4+ and CD8+ subsets. This was paralleled by systemic increases in blood monocyte and neutrophil counts, likely due to enhanced myelopoiesis as suggested by enhanced bone marrow myeloid cell counts. At advanced atherosclerosis, ApoE-/-GPR55-/- had significantly higher NK cell numbers in blood and lymphoid organs, suggesting a possible regulation of cytotoxic lymphocyte responses. In view of a potential relevance for human pathophysiology, GPR55 mRNA levels were significantly higher in human plaque samples compared to non-atherosclerotic control vessels.

Conclusion: GPR55 deficiency promotes atherosclerosis associated with a more pro-inflammatory phenotype. We may speculate that GPR55 negatively regulates the proatherogenic activity of lymphocyte subsets such as γδT cells, which deserves further investigation.

The Ins and Outs of Myeloid Cells in Atherosclerosis

Atherosclerosis is a chronic inflammation of the arterial vessel wall that arises from an imbalanced lipid metabolism. A growing body of literature describes leukocyte recruitment as a critical step in the initiation and progression of lesion development. By contrast, the role of leukocytes during plaque regression has been described in less detail. Leukocyte egress might be an important step to resolving chronic inflammation and therefore it may be a promising target for limiting advanced lesion development. This review aims to summarize our current knowledge of leukocyte recruitment to the arterial vessel wall. We will discuss mechanisms of leukocyte egress from the lesion site, as well as potential therapeutic strategies to promote atherosclerotic regression.

Expression and Cellular Localization of CXCR4 and CXCL12 in Human Carotid Atherosclerotic Plaques

Background and Aims The CXCR4/CXCL12 complex has already been associated with progression of atherosclerosis; however, its exact role is yet unknown. The aim of this study was to analyse the expression and cellular localization of CXCL12 and its receptor CXCR4 in human carotid atherosclerotic plaques.

Methods Carotid plaques (n = 58; 31 stable, 27 unstable, based on histological characterization of plaque morphology) were obtained during carotid endarterectomy, and 10 healthy vessels were used as a control. Expression of cxcr4, cxcr7, cxcl12, ccl2/ccr2 and csf1/csf1r was analysed at mRNA, and level expression of CXCR4, CXCR7 and CXCL12 was analysed at protein level. Cellular localization was determined using consecutive and double immunohistochemical (IHC) staining and microdissection.

Results At mRNA level, cxcr4, cxcr7 and cxcl12 were significantly higher expressed in stable carotid plaques compared with controls (p = 0.011, p < 0.001 and p < 0.001). Cxcl12 mRNA expression was successively augmented toward unstable plaques (p < 0.001). At protein level, CXCR4, CXCR7 and CXCL12 expression was significantly increased in both stable (p = 0.001, p < 0.001 and p = 0.035, respectively) and unstable (p = 0.003, p < 0.001 and p = 0.045, respectively) plaques compared with controls. Using IHC, CXCR4 was particularly localized in macrophages and small neovessels. Microdissection confirmed strongest expression of cxcr4 in macrophages within atherosclerotic plaques. Leukocytes and smooth muscle cells showed cxcr4 expression as well. For cxcl12, only microdissected areas with macrophages were positive.

Conclusion Expression of CXCR4 and CXCL12 was significantly increased in both stable and unstable carotid atherosclerotic plaques compared with healthy vessels, both at mRNA and protein level. CXCR4 and CXCL12 were localized particularly in macrophages.

Potential cell-specific functions of CXCR4 in atherosclerosis

Der Chemokinrezeptor CXCR4 and sein Ligand CXCL12 bilden eine wichtige Achse in der Regulation von Zellfunktionen bei normaler Homöostase und bei Erkrankungen. Zusätzlich kann der atypische CXCL12 Rezeptor CXCR7 die Verfügbarkeit und Funktion von CXCL12 modulieren. Neben ihrer Rolle in der Mobilisierung von Stamm- und Vorläuferzellen, können CXCR4 und CXCL12 auch die Entwicklung der Atherosklerose über verschiedene Zellfunktionen beeinflussen. Dieser kurze Übersichtsartikel fasst das gegenwärtige Wissen zu den zellspezifischen Funktionen von CXCL12 und den Rezeptoren CXCR4 und CXCR7 mit möglichen Implikationen für die Entstehung und Progression der Atherosklerose zusammen

Chemokine interactome mapping enables tailored intervention in acute and chronic inflammation

Chemokines orchestrate leukocyte trafficking and function in health and disease. Heterophilic interactions between chemokines in a given microenvironment may amplify, inhibit, or modulate their activity; however, a systematic evaluation of the chemokine interactome has not been performed. We used immunoligand blotting and surface plasmon resonance to obtain a comprehensive map of chemokine-chemokine interactions and to confirm their specificity. Structure-function analyses revealed that chemokine activity can be enhanced by CC-type heterodimers but inhibited by CXC-type heterodimers. Functional synergism was achieved through receptor heteromerization induced by CCL5-CCL17 or receptor retention at the cell surface via auxiliary proteoglycan binding of CCL5-CXCL4. In contrast, inhibitory activity relied on conformational changes (in CXCL12), affecting receptor signaling. Obligate CC-type heterodimers showed high efficacy and potency and drove acute lung injury and atherosclerosis, processes abrogated by specific CCL5-derived peptide inhibitors or knock-in of an interaction-deficient CXCL4 variant. Atheroprotective effects of CCL17 deficiency were phenocopied by a CCL5-derived peptide disrupting CCL5-CCL17 heterodimers, whereas a CCL5 α-helix peptide mimicked inhibitory effects on CXCL12-driven platelet aggregation. Thus, formation of specific chemokine heterodimers differentially dictates functional activity and can be exploited for therapeutic targeting.

Neutrophilic granulocytes – promiscuous accelerators of atherosclerosis

Neutrophils, as part of the innate immune system, are classically described to be main actors during the onset of inflammation enforcing rapid neutralisation and clearance of pathogens. Besides their wellstudied role in acute inflammatory processes, recent advances strongly indicate a so far underappreciated importance of neutrophils in initiation and development of atherosclerosis. This review focuses on current findings on the role of neutrophils in atherosclerosis. As pro-inflammatory mechanisms of neutrophils have primarily been studied in the microvascular environment; we here aim at translating these into the context of macrovascular inflammation in atherosclerosis. Since much of the pro-inflammatory activities of neutrophils stem from instructing neighbouring cell types, we highlight the promiscuous interplay between neutrophils and platelets, monocytes, T lymphocytes, and dendritic cells and its possible relevance to atherosclerosis.

Platelet-derived PF4 reduces neutrophil apoptosis following arterial occlusion

Note: The editorial process for this manuscript was fully handled by Gregory Y. H. Lip, Editor in Chief.

Presence of luminal neutrophil extracellular traps in atherosclerosis

Note: The editorial process for this article was fully handled by Prof. G. Y. H. Lip, Editor-in-Chief.

Neutrophil Extracellular Traps in Atherosclerosis and Atherothrombosis

Neutrophil extracellular traps expelled from suicidal neutrophils comprise a complex structure of nuclear chromatin and proteins of nuclear, granular, and cytosolic origin. These net-like structures have also been detected in atherosclerotic lesions and arterial thrombi in humans and mice. Functionally, neutrophil extracellular traps have been shown to induce activation of endothelial cells, antigen-presenting cells, and platelets, resulting in a proinflammatory immune response. Overall, this suggests that they are not only present in plaques and thrombi but also they may play a causative role in triggering atherosclerotic plaque formation and arterial thrombosis. This review will focus on current findings of the involvement of neutrophil extracellular traps in atherogenesis and atherothrombosis.

Targeting mannose receptor expression on macrophages in atherosclerotic plaques of apolipoprotein E-knockout mice using 111In-tilmanocept

Background

Atherosclerotic plaque phenotypes are classified based on the extent of macrophage infiltration into the lesions, and the presence of certain macrophage subsets might be a sign for plaque vulnerability. The mannose receptor (MR) is over-expressed in activated macrophages. Tilmanocept is a tracer that targets MR and is approved in Europe and the USA for the detection of sentinel lymph nodes. In this study, our aim was to evaluate the potential of ¹¹¹In-labelled tilmanocept for the detection of MR-positive macrophages in atherosclerotic plaques of apolipoprotein E-knockout (ApoE-KO) mouse model.

Methods

Tilmanocept was labelled with ¹¹¹In. The labelling stability and biodistribution of the tracer was first evaluated in control mice (n = 10) 1 h post injection (p.i.). For in vivo imaging studies, ¹¹¹In-tilmanocept was injected into ApoE-KO (n = 8) and control (n = 8) mice intravenously (i.v.). The mice were scanned 90 min p.i. using a dedicated animal SPECT/CT. For testing the specificity of ¹¹¹In-tilmanocept uptake in plaques, a group of ApoE-KO mice was co-injected with excess amount of non-labelled tilmanocept. For ex vivo imaging studies, the whole aortas (n = 9 from ApoE-KO and n = 4 from control mice) were harvested free from adventitial tissue for Sudan IV staining and autoradiography. Cryosections were prepared for immunohistochemistry (IHC).

Results

¹¹¹In radiolabelling of tilmanocept provided a yield of greater than 99%. After i.v. injection, ¹¹¹In-tilmanocept accumulated in vivo in MR-expressing organs (i.e. liver and spleen) and showed only low residual blood signal 1 h p.i. MR-binding specificity in receptor-positive organs was demonstrated by a 1.5- to 3-fold reduced uptake of ¹¹¹In-tilmanocept after co-injection of a blocking dose of non-labelled tilmanocept. Focal signal was detected in atherosclerotic plaques of ApoE-KO mice, whereas no signal was detected in the aortas of control mice. ¹¹¹In-tilmanocept uptake was detected in atherosclerotic plaques on autoradiography correlating well with Sudan IV-positive areas and associating with subendothelial accumulations of MR-positive macrophages as demonstrated by IHC.

Conclusions

After i.v. injection, ¹¹¹In-tilmanocept accumulated in MR-expressing organs and was associated with only low residual blood signal. In addition, ¹¹¹In-tilmanocept uptake was detected in atherosclerotic plaques of mice containing MR-expressing macrophages suggesting that tilmanocept represents a promising tracer for the non-invasive detection of macrophages in atherosclerotic plaques.

Vascular CXCR4 Limits Atherosclerosis by Maintaining Arterial Integrity: Evidence From Mouse and Human Studies

BACKGROUND

The CXCL12/CXCR4 chemokine ligand/receptor axis controls (progenitor) cell homeostasis and trafficking. So far, an atheroprotective role of CXCL12/CXCR4 has only been implied through pharmacological intervention, in particular, because the somatic deletion of the CXCR4 gene in mice is embryonically lethal. Moreover, cell-specific effects of CXCR4 in the arterial wall and underlying mechanisms remain elusive, prompting us to investigate the relevance of CXCR4 in vascular cell types for atheroprotection.

METHODS

We examined the role of vascular CXCR4 in atherosclerosis and plaque composition by inducing an endothelial cell (BmxCreER^T2-driven)-specific or smooth muscle cell (SMC, SmmhcCreER^T2- or TaglnCre-driven)-specific deficiency of CXCR4 in an apolipoprotein E-deficient mouse model. To identify underlying mechanisms for effects of CXCR4, we studied endothelial permeability, intravital leukocyte adhesion, involvement of the Akt/WNT/β-catenin signaling pathway and relevant phosphatases in VE-cadherin expression and function, vascular tone in aortic rings, cholesterol efflux from macrophages, and expression of SMC phenotypic markers. Finally, we analyzed associations of common genetic variants at the CXCR4 locus with the risk for coronary heart disease, along with CXCR4 transcript expression in human atherosclerotic plaques.

RESULTS

The cell-specific deletion of CXCR4 in arterial endothelial cells (n=12-15) or SMCs (n=13-24) markedly increased atherosclerotic lesion formation in hyperlipidemic mice. Endothelial barrier function was promoted by CXCL12/CXCR4, which triggered Akt/WNT/β-catenin signaling to drive VE-cadherin expression and stabilized junctional VE-cadherin complexes through associated phosphatases. Conversely, endothelial CXCR4 deficiency caused arterial leakage and inflammatory leukocyte recruitment during atherogenesis. In arterial SMCs, CXCR4 sustained normal vascular reactivity and contractile responses, whereas CXCR4 deficiency favored a synthetic phenotype, the occurrence of macrophage-like SMCs in the lesions, and impaired cholesterol efflux. Regression analyses in humans (n=259 796) identified the C-allele at rs2322864 within the CXCR4 locus to be associated with increased risk for coronary heart disease. In line, C/C risk genotype carriers showed reduced CXCR4 expression in carotid artery plaques (n=188), which was furthermore associated with symptomatic disease.

CONCLUSIONS

Our data clearly establish that vascular CXCR4 limits atherosclerosis by maintaining arterial integrity, preserving endothelial barrier function, and a normal contractile SMC phenotype. Enhancing these beneficial functions of arterial CXCR4 by selective modulators might open novel therapeutic options in atherosclerosis.

Human Neutrophil Peptide 1 Limits Hypercholesterolemia-induced Atherosclerosis by Increasing Hepatic LDL Clearance

Increases in plasma LDL-cholesterol have unequivocally been established as a causal risk factor for atherosclerosis. Hence, strategies for lowering of LDL-cholesterol may have immediate therapeutic relevance. Here we study the role of human neutrophil peptide 1 (HNP1) in a mouse model of atherosclerosis and identify its potent atheroprotective effect both upon transgenic overexpression and therapeutic delivery. The effect was found to be due to a reduction of plasma LDL-cholesterol. Mechanistically, HNP1 binds to apolipoproteins enriched in LDL. This interaction facilitates clearance of LDL particles in the liver via LDL receptor. Thus, we here identify a non-redundant mechanism by which HNP1 allows for reduction of LDL-cholesterol, a process that may be therapeutically instructed to lower cardiovascular risk.

•

Mice with transgenic expression of human neutrophil peptide 1 (HNP1) exhibit lower plasma VLDL/LDL levels and smaller atherosclerotic lesion sizes.

•

Repetitive HNP1 delivery is atheroprotective by reducing hypercholesterolemia.

•

HNP1 binds to apolipoproteins in LDL and facilitates LDL clearance in the liver involving LDL receptor.

Increased plasma lipid levels (i.e. hypercholesterolemia) are a primary risk factor for atherosclerosis, the pathology underlying myocardial infarction and stroke. Here we show that human neutrophil peptide 1 (HNP1, also known as α-defensin), an antimicrobial protein typically released from activated neutrophils, binds to apolipoproteins within plasma lipoproteins and facilitates the clearance of plasma lipids in the liver. As a consequence, repeated injection of hypercholesterolemic mice with HNP1 reduces atherosclerotic lesion formation. Thus, this study provides an innovative strategy to reduce hypercholesterolemia and hence a way to potentially reduce cardiovascular risk.

Functional ex-vivo Imaging of Arterial Cellular Recruitment and Lipid Extravasation

The main purpose of this sophisticated and highly versatile method is to visualize and quantify structural vessel wall properties, cellular recruitment, and lipid/dextran extravasation under physiological conditions in living arteries. This will be of interest for a broad range of researchers within the field of inflammation, hypertension, atherosclerosis, and even the pharmaceutical industry. Currently, many researchers are using in vitro techniques to evaluate cellular recruitment, like transwell or flow chamber systems with cultured cells, with unclear physiological comparability. The here introduced method describes in detail the use of a sophisticated and flexible method to study arterial wall properties and leukocyte recruitment in fresh and viable murine carotid arteries ex vivo under arterial flow conditions. This model mimics the in vivo situation and allows the use of cells and arteries isolated from two different donors (for example, wildtype vs. specific knockouts) to be combined into one experiments, thereby providing information on both leukocyte and/or endothelial cell properties of both donors. As such, this model can be considered an alternative for the complicated and invasive in vivo studies, such as parabiotic experiments.

Imaging the Cytokine Receptor CXCR4 in Atherosclerotic Plaques with the Radiotracer 68Ga-Pentixafor for PET

⁶⁸Ga-pentixafor is a radiotracer for PET that binds with nanomolar affinity to CXCR4. The CXCR4 receptor is expressed at the surface of inflammatory cells. The objective of the study was to analyze the ability of radiolabeled pentixafor to detect CXCR4 expression on inflammatory cells present in atherosclerotic plaques of an experimental rabbit model. Methods: Atherosclerotic plaques were induced by endothelial abrasion of the right carotid artery and abdominal aorta of 7 rabbits fed an atherogenic diet. Five noninjured rabbits fed a chow diet were used as controls. Rabbits were imaged on a PET/MR system after injection of ⁶⁸Ga-pentixafor (15 MBq/kg). Vascular signal was quantified as tissue-to-background ratio (TBR). Biodistribution and autoradiographic studies were performed 1 h after injection of ¹²⁵I-pentixafor (7.5 MBq/kg). In addition, blocking studies were performed in 2 atherosclerotic rabbits with preinjection of the CXCR4 inhibitor AMD3100. Tracer uptake was quantified on arterial cryosections using autoradiography and compared with CXCR4 and RAM-11 (macrophage) expression on adjacent histologic sections. Results: One hour after injection of ⁶⁸Ga-pentixafor, strong signals were detected in vivo with PET/MR imaging in atherosclerotic plaques of the abdominal aorta and right carotid artery as compared with normal control arteries (mean TBR = 1.95 ± 0.51 vs. 1.22 ± 0.25 and mean TBR = 1.24 ± 0.38 vs. 0.96 ± 0.37, respectively; P < 0.05 for both). Blocking studies with preinjection of a CXCR4 inhibitor reduced ¹²⁵I-pentixafor uptake in atherosclerotic plaques by approximately 40%. ¹²⁵I-pentixafor uptake in the vessel wall on autoradiographies was located in macrophage-rich regions of atherosclerotic plaques and correlated with the intensity of CXCR4 expression on corresponding cryosections (r² = 0.61; P < 0.05). Conclusion:⁶⁸Ga-pentixafor allows for the noninvasive detection of CXCR4 expression in the vessel wall with PET and emerges as a potential alternative to ¹⁸F-FDG for the assessment of macrophage infiltration in atherosclerotic plaques.

Cathepsin G Controls Arterial But Not Venular Myeloid Cell Recruitment

BACKGROUND

Therapeutic targeting of arterial leukocyte recruitment in the context of atherosclerosis has been disappointing in clinical studies. Reasons for such failures include the lack of knowledge of arterial-specific recruitment patterns. Here we establish the importance of the cathepsin G (CatG) in the context of arterial myeloid cell recruitment.

METHODS

Intravital microscopy of the carotid artery, the jugular vein, and cremasteric arterioles and venules in Apoe^-/-and CatG-deficient mice (Apoe^-/-Ctsg^-/-) was used to study site-specific myeloid cell behavior after high-fat diet feeding or tumor necrosis factor stimulation. Atherosclerosis development was assessed in aortic root sections after 4 weeks of high-fat diet, whereas lung inflammation was assessed after inhalation of lipopolysaccharide. Endothelial deposition of CatG and CCL5 was quantified in whole-mount preparations using 2-photon and confocal microscopy.

RESULTS

Our observations elucidated a crucial role for CatG during arterial leukocyte adhesion, an effect not found during venular adhesion. Consequently, CatG deficiency attenuates atherosclerosis but not acute lung inflammation. Mechanistically, CatG is immobilized on arterial endothelium where it activates leukocytes to firmly adhere engaging integrin clustering, a process of crucial importance to achieve effective adherence under high-shear flow. Therapeutic neutralization of CatG specifically abrogated arterial leukocyte adhesion without affecting myeloid cell adhesion in the microcirculation. Repetitive application of CatG-neutralizing antibodies permitted inhibition of atherogenesis in mice.

CONCLUSIONS

Taken together, these findings present evidence of an arterial-specific recruitment pattern centered on CatG-instructed adhesion strengthening. The inhibition of this process could provide a novel strategy for treatment of arterial inflammation with limited side effects.

Aspirin, but Not Tirofiban Displays Protective Effects in Endotoxin Induced Lung Injury

Background

Treatment of acute lung injury (ALI) remains an unsolved problem in intensive care medicine. Recruitment of neutrophils into the lungs, regarded as a key mechanism in progression of ALI, depends on signaling between neutrophils and platelets. Consequently we explored the effect of platelet-targeted aspirin and tirofiban treatment in endotoxin induced acute lung injury

Methods

C57Bl/6 mice were exposed to aerosolized LPS (500μg/ml) for 30min and treated with Aspirin (100μg/g bodyweight via intraperitoneal injection, 30 min before or 1 hour after LPS inhalation) or Tirofiban (0.5μg/ g bodyweight via tail vein injection 30 min before or 1 hour after LPS inhalation). The count of alveolar, interstitial, and intravascular neutrophils was assessed 4h later by flow cytometry. Lung permeability changes were assessed by FITC-dextran clearance and protein content in the BAL fluid.

Results

Aspirin both before and after LPS inhalation reduced neutrophil influx into the lung and lung permeability indicating the protective role of Aspirin in ALI. Tirofiban, however, did not alter neutrophil recruitment after LPS inhalation. Release of platelet-derived chemokines CCL5 and PF4 and neutrophil extracellular traps was reduced by Aspirin but not by Tirofiban.

Conclusion

Aspirin, but not Tirofiban reduces neutrophil recruitment and displays protective effects during endotoxin induced lung injury.

Resolving Lipid Mediators Maresin 1 and Resolvin D2 Prevent Atheroprogression in Mice

RATIONALE

Atheroprogression is a consequence of nonresolved inflammation, and currently a comprehensive overview of the mechanisms preventing resolution is missing. However, in acute inflammation, resolution is known to be orchestrated by a switch from inflammatory to resolving lipid mediators. Therefore, we hypothesized that lesional lipid mediator imbalance favors atheroprogression.

OBJECTIVE

To understand the lipid mediator balance during atheroprogression and to establish an interventional strategy based on the delivery of resolving lipid mediators.

METHODS AND RESULTS

Aortic lipid mediator profiling of aortas from Apoe^-/- mice fed a high-fat diet for 4 weeks, 8 weeks, or 4 months revealed an expansion of inflammatory lipid mediators, Leukotriene B4 and Prostaglandin E2, and a concomitant decrease of resolving lipid mediators, Resolvin D2 (RvD2) and Maresin 1 (MaR1), during advanced atherosclerosis. Functionally, aortic Leukotriene B4 and Prostaglandin E2 levels correlated with traits of plaque instability, whereas RvD2 and MaR1 levels correlated with the signs of plaque stability. In a therapeutic context, repetitive RvD2 and MaR1 delivery prevented atheroprogression as characterized by halted expansion of the necrotic core and accumulation of macrophages along with increased fibrous cap thickness and smooth muscle cell numbers. Mechanistically, RvD2 and MaR1 induced a shift in macrophage profile toward a reparative phenotype, which secondarily stimulated collagen synthesis in smooth muscle cells.

CONCLUSIONS

We present evidence for the imbalance between inflammatory and resolving lipid mediators during atheroprogression. Delivery of RvD2 and MaR1 successfully prevented atheroprogression, suggesting that resolving lipid mediators potentially represent an innovative strategy to resolve arterial inflammation.

Chemokines and their receptors in Atherosclerosis

Atherosclerosis, a chronic inflammatory disease of the medium- and large-sized arteries, is the main underlying cause of cardiovascular diseases (CVDs) most often leading to a myocardial infarction or stroke. However, atherosclerosis can also develop without this clinical manifestation. The pathophysiology of atherosclerosis is very complex and consists of many cells and molecules interacting with each other. Over the last years, chemokines (small 8-12 kDa cytokines with chemotactic properties) have been identified as key players in atherogenesis. However, this remains a very active and dynamic field of research. Here, we will give an overview of the current knowledge about the involvement of chemokines in all phases of atherosclerotic lesion development. Furthermore, we will focus on two chemokines that recently have been associated with atherogenesis, CXCL12, and macrophage migration inhibitory factor (MIF). Both chemokines play a crucial role in leukocyte recruitment and arrest, a critical step in atherosclerosis development. MIF has shown to be a more pro-inflammatory and thus pro-atherogenic chemokine, instead CXCL12 seems to have a more protective function. However, results about this protective role are still quite debatable. Future research will further elucidate the precise role of these chemokines in atherosclerosis and determine the potential of chemokine-based therapies.