Throwing light on DARC

The DARC Side of Inflamm-Aging: Duffy Antigen Receptor for Chemokines (DARC/ACKR1) as a Potential Biomarker of Aging, Immunosenescence, and Breast Oncogenesis among High-Risk Subpopulations

The proclivity of certain pre-malignant and pre-invasive breast lesions to progress while others do not continues to perplex clinicians. Clinicians remain at a crossroads with effectively managing the high-risk patient subpopulation owing to the paucity of biomarkers that can adequately risk-stratify and inform clinical decisions that circumvent unnecessary administration of cytotoxic and invasive treatments. The immune system mounts the most important line of defense against tumorigenesis and progression. Unfortunately, this defense declines or "ages" over time-a phenomenon known as immunosenescence. This results in "inflamm-aging" or the excessive infiltration of pro-inflammatory chemokines, which alters the leukocyte composition of the tissue microenvironment, and concomitant immunoediting of these leukocytes to diminish their antitumor immune functions. Collectively, these effects can foster the sequelae of neoplastic transformation and progression. The erythrocyte cell antigen, Duffy antigen receptor for chemokines(DARC/ACKR1), binds and internalizes chemokines to maintain homeostatic levels and modulate leukocyte trafficking. A negative DARC status is highly prevalent among subpopulations of West African genetic ancestry, who are at higher risk of developing breast cancer and disease progression at a younger age. However, the role of DARC in accelerated inflamm-aging and malignant transformation remains underexplored. Herein, we review compelling evidence suggesting that DARC may be protective against inflamm-aging and, therefore, reduce the risk of a high-risk lesion progressing to malignancy. We also discuss evidence supporting that immunotherapeutic intervention-based on DARC status-among high-risk subpopulations may evade malignant transformation and progression. A closer look into this unique role of DARC could glean deeper insight into the immune response profile of individual high-risk patients and their predisposition to progress as well as guide the administration of more "cyto-friendly" immunotherapeutic intervention to potentially "turn back the clock" on inflamm-aging-mediated oncogenesis and progression.

Mapping the human kidney using single-cell genomics

The field of single-cell genomics and spatial technologies is rapidly evolving and has already provided unprecedented insights into complex tissues. Major advances have been made in dissecting the cellular composition and spatiotemporal interactions that mediate developmental processes in the fetal kidney. Single-cell technologies have also provided detailed insights into the heterogeneity of cell types within the healthy adult and shed light on the complex cellular mechanisms that contribute to kidney disease. The in-depth characterization of specific cell types associated with acute kidney injury and glomerular diseases has potential for the development of prognostic biomarkers and new therapeutics. Analyses of pathway activity in clear-cell renal cell carcinoma can predict the sensitivity of tumour cells to specific inhibitors. The identification of the cell of origin of renal cell carcinoma and of new cell types within the tumour microenvironment also has implications for the development of targeted therapeutics. Similarly, single-cell sequencing has provided new insights into the mechanisms underlying kidney fibrosis, specifically our understanding of myofibroblast origins and the contribution of cell crosstalk within the fibrotic niche to disease progression. These and future studies will enable the creation of a map to aid our understanding of the cellular processes and interactions in the developing, healthy and diseased kidney.

Passing the Vascular Barrier: Endothelial Signaling Processes Controlling Extravasation

A central function of the vascular endothelium is to serve as a barrier between the blood and the surrounding tissue of the body. At the same time, solutes and cells have to pass the endothelium to leave or to enter the bloodstream to maintain homeostasis. Under pathological conditions, for example, inflammation, permeability for fluid and cells is largely increased in the affected area, thereby facilitating host defense. To appropriately function as a regulated permeability filter, the endothelium uses various mechanisms to allow solutes and cells to pass the endothelial layer. These include transcellular and paracellular pathways of which the latter requires remodeling of intercellular junctions for its regulation. This review provides an overview on endothelial barrier regulation and focuses on the endothelial signaling mechanisms controlling the opening and closing of paracellular pathways for solutes and cells such as leukocytes and metastasizing tumor cells.

The Duffy antigen receptor for chemokines, ACKR1,- 'Jeanne DARC' of benign neutropenia

Benign neutropenia, observed in different ethnic groups, is the most common form of neutropenia worldwide. A specific single nucleotide polymorphism, rs2814778, located at the promoter of the ACKR1 (previously termed DARC) gene, which disrupts a binding site for the GATA1 erythroid transcription factor, resulting in a ACKR1-null phenotype, was found to serve as a predictor of low white blood cell and neutrophil counts in African-Americans and Yemenite Jews. Individuals with benign neutropenia due to the ACKR1-null allele have been found to have an increased susceptibility to human immunodeficiency virus infection and, on the other hand, a protective effect against malaria. The associated protective effect may explain the spread of the ACKR1-null allele by natural selection. The reviewed relationships between ACKR1 polymorphism and various pathological states may have important clinical implications to individuals with and without benign neutropenia. Potential mechanisms for ACKR1 (previously termed DARC) modulation during neutrophil recruitment to inflammation, and chemokine bioavailability in the circulation and in local tissue are reviewed and discussed.

The "Aging Factor" Eotaxin-1 (CCL11) Is Detectable in Transfusion Blood Products and Increases with the Donor's Age

Background: High blood levels of the chemokine eotaxin-1 (CCL11) have recently been associated with aging and dementia, as well as impaired memory and learning in humans. Importantly, eotaxin-1 was shown to pass the blood-brain-barrier (BBB) and has been identified as crucial mediator of decreased neurogenesis and cognitive impairment in young mice after being surgically connected to the vessel system of old animals in a parabiosis model. It thus has to be assumed that differences in eotaxin-1 levels between blood donors and recipients might influence cognitive functions also in humans. However, it is unknown if eotaxin-1 is stable during processing and storage of transfusion blood components. This study assesses eotaxin-1 concentrations in fresh-frozen plasma (FFP), erythrocyte concentrate (EC), and platelet concentrate (PC) in dependence of storage time as well as the donor’s age and gender.

Methods: Eotaxin-1 was measured in FFP (n = 168), EC (n = 160) and PC (n = 8) ready-to-use for transfusion employing a Q-Plex immunoassay for eotaxin-1. Absolute quantification of eotaxin-1 was performed with Q-view software.

Results: Eotaxin-1 was consistently detected at a physiological level in FFP and EC but not PC. Eotaxin-1 levels were comparable in male and female donors but increased significantly with rising age of donors in both, FFP and EC. Furthermore, eotaxin-1 was not influenced by storage time of either blood component. Finally, eotaxin-1 is subject to only minor fluctuations within one donor over a longer period of time.

Conclusion: Eotaxin-1 is detectable and stable in FFP and EC and increases with donor’s age. Considering the presumed involvement in aging and cognitive malfunction, differences in donor- and recipient eotaxin-1 levels might affect mental factors after blood transfusion.

Duffy blood group system: New genotyping method and distribution in a Brazilian extra-Amazonian population

Duffy blood group system is of interest in several fields of science including transfusion medicine, immunology and malariology. Although some methods have been developed for Duffy polymorphism genotyping, not all of them have been sufficiently described and validated, and all present limitations. At the same time, the frequency of Duffy alleles and antigens in some densely populated regions of the world are still missing. In this study we present new tests for genotyping the major alleles of the Duffy blood system and describe Duffy alleles and antigens in blood donors and transfusion-dependent patients in Minas Gerais, Brazil. A simple and reproducible strategy was devised for Duffy genotyping based on real-time PCR that included SNPs rs12075 and rs2814778. No significant differences between the allele frequencies were observed comparing blood donors and patients. Among the blood donors, the phenotype Fy(a-b+) was the most common and the Fy(a-b-) phenotype, associated with populations of African descent, was remarkably less common among subjects who self-identified as black in comparison to other ethnoracial categories. However, the African ancestry estimated by molecular markers was significantly higher in individuals with the allele associated to the Duffy null phenotype. The genotyping method presented may be useful to study Duffy genotypes accurately in different contexts and populations. The results suggest a reduced risk of alloimmunization for Duffy antigens and increased susceptibility for malaria in Minas Gerais, considering the high frequency of Duffy-positive individuals.

Leukocidins: staphylococcal bi-component pore-forming toxins find their receptors

Staphylococcus aureus is a major bacterial pathogen that causes disease worldwide. The emergence of strains that are resistant to commonly used antibiotics and the failure of vaccine development have resulted in a renewed interest in the pathophysiology of this bacterium. Staphylococcal leukocidins are a family of bi-component pore-forming toxins that are important virulence factors. During the past five years, cellular receptors have been identified for all of the bi-component leukocidins. The identification of the leukocidin receptors explains the cellular tropism and species specificity that is exhibited by these toxins, which has important biological consequences. In this Review, we summarize the recent discoveries that have reignited interest in these toxins and provide an outlook for future research.

Reversible binding of hemoglobin to band 3 constitutes the molecular switch that mediates O2 regulation of erythrocyte properties

Functional studies have shown that the oxygenation state of the erythrocyte regulates many important pathways, including glucose metabolism, membrane mechanical stability, and cellular adenosine triphosphate (ATP) release. Deoxyhemoglobin (deoxyHb), but not oxyhemoglobin, binds avidly and reversibly to band 3, the major erythrocyte membrane protein. Because band 3 associates with multiple metabolic, solute transport, signal transduction, and structural proteins, the hypothesis naturally arises that the O₂-dependent regulation of erythrocyte properties might be mediated by the reversible association of deoxyHb with band 3. To explore whether the band 3-deoxyHb interaction constitutes a "molecular switch" for regulating erythrocyte biology, we have generated transgenic mice with mutations in the deoxyHb-binding domain of band 3. One strain of mouse contains a "humanized" band 3 in which the N-terminal 45 residues of mouse band 3 are replaced by the homologous sequence from human band 3, including the normal human band 3 deoxyHb-binding site. The second mouse contains the same substitution as the first, except the deoxyHb site on band 3 (residues 12-23) has been deleted. Comparison of these animals with wild-type mice demonstrates that the following erythrocyte properties are controlled by the O₂-dependent association of hemoglobin with band 3: (1) assembly of a glycolytic enzyme complex on the erythrocyte membrane which is associated with a shift in glucose metabolism between the pentose phosphate pathway and glycolysis, (2) interaction of ankyrin with band 3 and the concomitant regulation of erythrocyte membrane stability, and (3) release of ATP from the red cell which has been linked to vasodilation.

Association between Duffy antigen receptor expression and disease severity in sickle cell disease patients

OBJECTIVES

Sickle cell disease (SCD) is associated with a pro-inflammatory state, characterized by an elevated baseline leukocyte count and inflammatory cytokines. Inflammation, white blood cell (WBC) adhesion to vascular endothelium with subsequent endothelial injury, and repeated ischemia-reperfusion injury contribute to disease pathogenesis. Identification of genetic polymorphisms that may modulate disease severity in SCD is becoming a field of interest. The Duffy blood group antigen has been identified as a receptor for various chemokines involved in neutrophil activation and trafficking. This study aimed at investigating the effect of RBCs' Duffy antigen expression and its genetic polymorphisms on modulating disease severity and its complications among Egyptian sickle cell patients. Methods We analyzed the association of Duffy genotypes and phenotypes with clinical expression of SCD in 100 Egyptian patients. The Duffy phenotype expression was detected by indirect anti-globulin test while Duffy genotyping was conducted with polymerase chain reaction-restriction fragment length polymorphism-based assay. Results Total WBC count was strongly associated with Duffy genotype. WBCs were significantly higher in Duffy-positive patients (P = 0.002). No statistical significance was evident between individual measures of disease severity (pulmonary dysfunction, avascular necrosis, central nervous system dysfunction, kidney dysfunction, and leg ulcers) and Duffy genotype. Conclusion Our study suggests that RBC Duffy expression increases levels of WBCs in SCD patients and that Duffy genotype may not be a potential biomarker for end-organ damage in SCD.

Chemokine and chemokine receptors in autoimmunity: the case of primary biliary cholangitis

Chemokines represent a major mediator of innate immunity and play a key role in the selective recruitment of cells during localized inflammatory responses. Beyond critical extracellular mediators of leukocyte trafficking, chemokines and their cognate receptors are expressed by a variety of resident and infiltrating cells (monocytes, lymphocytes, NK cells, mast cells, and NKT cells). Chemokines represent ideal candidates for mechanistic studies (particularly in murine models) to better understand the pathogenesis of chronic inflammation and possibly become biomarkers of disease. Nonetheless, therapeutic approaches targeting chemokines have led to unsatisfactory results in rheumatoid arthritis, while biologics against pro-inflammatory cytokines are being used worldwide with success. In this comprehensive review we will discuss the evidence supporting the involvement of chemokines and their specific receptors in mediating the effector cell response, utilizing the autoimmune/primary biliary cholangitis setting as a paradigm.

Distinct Transcript Isoforms of the Atypical Chemokine Receptor 1 (ACKR1)/Duffy Antigen Receptor for Chemokines (DARC) Gene Are Expressed in Lymphoblasts and Altered Isoform Levels Are Associated with Genetic Ancestry and the Duffy-Null Allele

The Atypical ChemoKine Receptor 1 (ACKR1) gene, better known as Duffy Antigen Receptor for Chemokines (DARC or Duffy), is responsible for the Duffy Blood Group and plays a major role in regulating the circulating homeostatic levels of pro-inflammatory chemokines. Previous studies have shown that one common variant, the Duffy Null (Fy-) allele that is specific to African Ancestry groups, completely removes expression of the gene on erythrocytes; however, these individuals retain endothelial expression. Additional alleles are associated with a myriad of clinical outcomes related to immune responses and inflammation. In addition to allele variants, there are two distinct transcript isoforms of DARC which are expressed from separate promoters, and very little is known about the distinct transcriptional regulation or the distinct functionality of these protein isoforms. Our objective was to determine if the African specific Fy- allele alters the expression pattern of DARC isoforms and therefore could potentially result in a unique signature of the gene products, commonly referred to as antigens. Our work is the first to establish that there is expression of DARC on lymphoblasts. Our data indicates that people of African ancestry have distinct relative levels of DARC isoforms expressed in these cells. We conclude that the expression of both isoforms in combination with alternate alleles yields multiple Duffy antigens in ancestry groups, depending upon the haplotypes across the gene. Importantly, we hypothesize that DARC isoform expression patterns will translate into ancestry-specific inflammatory responses that are correlated with the axis of pro-inflammatory chemokine levels and distinct isoform-specific interactions with these chemokines. Ultimately, this work will increase knowledge of biological mechanisms underlying disparate clinical outcomes of inflammatory-related diseases among ethnic and geographic ancestry groups.

Duffy antigen receptor genetic variant and the association with Interleukin 8 levels

The aim of this study is to identify loci associated with circulating levels of Interleukin 8 (IL8). We investigated the associations of 121,445 single nucleotide polymorphisms (SNPs) from the Illumina 200K CardioMetabochip with IL8 levels in 1077 controls from the Stockholm Heart Epidemiology Program (SHEEP) study, using linear regression under an additive model of inheritance. Five SNPs (rs12075A/G, rs13179413C/T, rs6907989T/A, rs9352745A/C, rs1779553T/C) reached the pre-defined threshold of genome-wide significance (p<1.0×10(-5)) and were tested for in silico replication in three independent populations, derived from the PIVUS, MDC-CC and SCARF studies. IL8 was measured in serum (SHEEP, PIVUS) and plasma (MDC-CC, SCARF). The strongest association was found with the SNP rs12075 A/G, Asp42Gly (p=1.6×10(-6)), mapping to the Duffy antigen receptor for chemokines (DARC) gene on chromosome 1. The minor allele G was associated with 15.6% and 10.4% reduction in serum IL8 per copy of the allele in SHEEP and PIVUS studies respectively. No association was observed between rs12075 and plasma IL8.

CONCLUSION

rs12075 was associated with serum levels but not with plasma levels of IL8. It is likely that serum IL8 represents the combination of levels of circulating plasma IL8 and additional chemokine liberated from the erythrocyte DARC reservoir due to clotting. These findings highlight the importance of understanding IL8 as a biomarker in cardiometabolic diseases.

Chemokine receptor oligomerization and allostery

Oligomerization of chemokine receptors has been reported to influence many aspects of receptor function through allosteric communication between receptor protomers. Allosteric interactions within chemokine receptor hetero-oligomers have been shown to cause negative cooperativity in the binding of chemokines and to inhibit receptor activation in the case of some receptor pairs. Other receptor pairs can cause enhanced signaling and even activate entirely new, hetero-oligomer-specific signaling complexes and responses downstream of receptor activation. Many mechanisms contribute to these effects including direct allosteric coupling between the receptors, G protein-mediated allostery, G protein stealing, ligand sequestration, and recruitment of new intracellular proteins by exposing unique binding interfaces on the oligomerized receptors. These effects present both challenges as well as exciting opportunities for drug discovery. One of the most difficult challenges will involve determining if and when hetero-oligomers versus homomeric receptors are involved in specific disease states.

Chemokines and Their Receptors Are Key Players in the Orchestra That Regulates Wound Healing

SIGNIFICANCE

Normal wound healing progresses through a series of overlapping phases, all of which are coordinated and regulated by a variety of molecules, including chemokines. Because these regulatory molecules play roles during the various stages of healing, alterations in their presence or function can lead to dysregulation of the wound-healing process, potentially leading to the development of chronic, nonhealing wounds.

RECENT ADVANCES

A discovery that chemokines participate in a variety of disease conditions has propelled the study of these proteins to a level that potentially could lead to new avenues to treat disease. Their small size, exposed termini, and the fact that their only modifications are two disulfide bonds make them excellent targets for manipulation. In addition, because they bind to G-protein-coupled receptors (GPCRs), they are highly amenable to pharmacological modulation.

CRITICAL ISSUES

Chemokines are multifunctional, and in many situations, their functions are highly dependent on the microenvironment. Moreover, each specific chemokine can bind to several GPCRs to stimulate the function, and both can function as monomers, homodimers, heterodimers, and even oligomers. Activation of one receptor by any single chemokine can lead to desensitization of other chemokine receptors, or even other GPCRs in the same cell, with implications for how these proteins or their receptors could be used to manipulate function.

FUTURE DIRECTIONS

Investment in better understanding of the functions of chemokines and their receptors in a local context can reveal new ways for therapeutic intervention. Understanding how different chemokines can activate the same receptor and vice versa could identify new possibilities for drug development based on their heterotypic interactions.

Dissecting trafficking and signaling of atypical chemokine receptors

Atypical chemokine receptors are a distinct subset of chemokine receptors able to modulate immune responses by acting as chemokine decoy/scavengers or transporters. Intracellular trafficking properties sustained by Gαi-independent signaling have emerged as a major determinant of their biological properties, which support continuous uptake, transport, and/or concentration, of the ligands. Here, we are providing methods to study both trafficking and signaling of this class of chemokine receptors focusing on the atypical chemokine receptor D6 that degrades inflammatory CC chemokines.

The chemokine superfamily revisited

The chemokine superfamily consists of a large number of ligands and receptors. At first glance, this family appears redundant and their ligand-receptor relationships promiscuous, making its study challenging. However, analyzing this family from the evolutionary perspective greatly simplifies understanding both the organization and function of this apparently complex system. In particular, the functions of a subgroup of chemokines (designated homeostatic chemokines) have played pivotal roles in advancing our understanding of the organization and function of the cellular networks that shape the immune system. Here, we update the full scope of the human and mouse chemokine superfamilies and their relationships and summarize several important roles that homeostatic chemokines play in the immune system.

The biochemistry and biology of the atypical chemokine receptors

A subset of chemokine receptors, initially called "silent" on the basis of their apparent failure to activate conventional signalling events, has recently attracted growing interest due to their ability to internalize, degrade, or transport ligands and thus modify gradients and create functional chemokine patterns in tissues. These receptors recognize distinct and complementary sets of ligands with high affinity, are strategically expressed in different cellular contexts, and lack structural determinants supporting Gα(i) activation, a key signalling event in cell migration. This is in keeping with the hypothesis that they have evolved to fulfil fundamentally different functions to the classical signalling chemokine receptors. Based on these considerations, these receptors (D6, Duffy antigen receptor for chemokines (DARC), CCX-CKR1 and CXCR7) are now collectively considered as an emerging class of 'atypical' chemokine receptors. In this article, we review the biochemistry and biology of this emerging chemokine receptor subfamily.

Genome-wide association replicates the association of Duffy antigen receptor for chemokines (DARC) polymorphisms with serum monocyte chemoattractant protein-1 (MCP-1) levels in Hispanic children

Obesity is associated with a chronic low inflammatory state characterized by elevated levels of chemokines. Monocyte chemoattractant protein-1 (MCP-1) is a member of the cysteine-cysteine (CC) chemokine family and is increased in obesity. The purpose of this study was to identify loci regulating serum MCP-1 in obese Hispanic children from the Viva La Familia Study. A genome-wide association (GWA) analysis was performed in 815 children, ages 4-19 years, using genotypes assayed with the Illumina HumanOmni1-Quad v1.0 BeadChips. All analyses were performed in SOLAR using a linear regression-based test under an additive model of allelic effect, while accounting for the relatedness of family members via a kinship variance component. The strongest association for MCP-1 levels was found with a non-synonymous single nucleotide polymorphism (SNP), rs12075, resulting in an amino acid substitution (Asp42Gly) in the Duffy antigen receptor for chemokines (DARC) gene product (minor allele frequency=43.6%, p=1.3 × 10(-21)) on chromosome 1. Four other DARC SNPs were also significantly associated with MCP-1 levels (p<10(-16)-10(-6)). The Asp42Gly variant was associated with higher levels of MCP-1 and accounted for approximately 10% of its variability. In addition, MCP-1 levels were significantly associated with SNPs in chemokine receptor 3 (CCR3) and caspase recruitment domain family, member 9 (CARD9). In summary, the association of the DARC Asp42Gly variant with MCP-1 levels replicates previous GWA results substantiating a potential role for DARC in the regulation of pro-inflammatory cytokines.

Duffy antigen receptor for chemokines and its involvement in patterning and control of inflammatory chemokines

Leukocyte functions are linked to their migratory responses, which, in turn, are largely determined by the expression profile of classical chemokine receptors. Upon binding their cognate chemokines, these G-protein-coupled receptors (GPCRs) initiate signaling cascades and downstream molecular and cellular responses, including integrin activation and cell locomotion. Chemokines also bind to an alternative subset of chemokine receptors, which have serpentine structure characteristic for GPCRs but lack DRYLAIV consensus motive required for coupling to G-proteins. Duffy antigen receptor for chemokines (DARC) is a member of this atypical receptor subfamily. DARC binds a broad range of inflammatory CXC and CC chemokines and is expressed by erythrocytes, venular endothelial cells, and cerebellar neurons. Erythrocyte DARC serves as blood reservoir of cognate chemokines but also as a chemokine sink, buffering potential surges in plasma chemokine levels. Endothelial cell DARC internalizes chemokines on the basolateral cell surface resulting in subsequent transcytosis of chemokines and their immobilization on the tips of apical microvilli. These DARC-mediated endothelial cell interactions allow chemokines produced in the extravascular tissues to optimally function as arrest chemokines on the luminal endothelial cell surface.

Structural Diversity in Conserved Regions Like the DRY-Motif among Viral 7TM Receptors-A Consequence of Evolutionary Pressure?

Several herpes- and poxviruses have captured chemokine receptors from their hosts and modified these to their own benefit. The human and viral chemokine receptors belong to class A 7 transmembrane (TM) receptors which are characterized by several structural motifs like the DRY-motif in TM3 and the C-terminal tail. In the DRY-motif, the arginine residue serves important purposes by being directly involved in G protein coupling. Interestingly, among the viral receptors there is a greater diversity in the DRY-motif compared to their endogenous receptor homologous. The C-terminal receptor tail constitutes another regulatory region that through a number of phosphorylation sites is involved in signaling, desensitization, and internalization. Also this region is more variable among virus-encoded 7TM receptors compared to human class A receptors. In this review we will focus on these two structural motifs and discuss their role in viral 7TM receptor signaling compared to their endogenous counterparts.

Genetic variants associated with the white blood cell count in 13,923 subjects in the eMERGE Network

White blood cell count (WBC) is unique among identified inflammatory predictors of chronic disease in that it is routinely measured in asymptomatic patients in the course of routine patient care. We led a genome-wide association analysis to identify variants associated with WBC levels in 13,923 subjects in the electronic Medical Records and Genomics (eMERGE) Network. We identified two regions of interest that were each unique to subjects of genetically determined ancestry to the African continent (AA) or to the European continent (EA). WBC varies among different ancestry groups. Despite being ancestry specific, these regions were identifiable in the combined analysis. In AA subjects, the region surrounding the Duffy antigen/chemokine receptor gene (DARC) on 1q21 exhibited significant association (p value = 6.71e-55). These results validate the previously reported association between WBC and of the regulatory variant rs2814778 in the promoter region, which causes the Duffy negative phenotype (Fy-/-). A second missense variant (rs12075) is responsible for the two principal antigens, Fya and Fyb of the Duffy blood group system. The two variants, consisting of four alleles, act in concert to produce five antigens and subsequent phenotypes. We were able to identify the marginal and novel interaction effects of these two variants on WBC. In the EA subjects, we identified significantly associated SNPs tagging three separate genes in the 17q21 region: (1) GSDMA, (2) MED24, and (3) PSMD3. Variants in this region have been reported to be associated with WBC, neutrophil count, and inflammatory diseases including asthma and Crohn's disease.

Erythrocyte Duffy antigen receptor for chemokines (DARC): diagnostic and therapeutic implications in atherosclerotic cardiovascular disease

Atherosclerosis is an inflammatory disease. The last three decades efforts have been made to elucidate the biochemical pathways that are implicated in the process of atherogenesis and plaque development. Chemokines are crucial mediators in every step of this process. Additionally, cellular components of the peripheral blood have been proved important mediators in the formation and progression of atherosclerotic lesions. However, until recently data were mostly focusing on leukocytes and platelets. Erythrocytes were considered unreceptive bystanders and limited data supported their importance in the progression and destabilization of the atherosclerotic plaque. Recently erythrocytes, through their Duffy antigen receptor for chemokines (DARC), have been proposed as appealing regulators of chemokine-induced pathways. Dissimilar to every other chemokine receptor DARC possesses high affinity for several ligands from both CC and CXC chemokine sub-families. Moreover, DARC is not coupled to a G-protein or any other intracellular signalling system; thus it is incapable of generating second messages. The exact biochemical role of erythrocyte DARC remains to be determined. It is however challenging the fact that DARC is a regulator of almost every CC and CXC chemokine ligand and therefore DARC antagonism could effectively block the complex pre-inflammatory chemokine network. In the present review we intent to provide recent evidence supporting the role of erythrocytes in atherosclerosis focusing on the erythrocyte-chemokine interaction through the Duffy antigen system.

Atypical chemokine receptors

Atypical chemokine receptors (ACRs) are cell surface receptors with seven transmembrane domains structurally homologous to chemokine G-protein coupled receptors (GPCRs). However, upon ligation by cognate chemokines, ACRs fail to induce classical signaling and downstream cellular responses characteristic for GPCRs. Despite this, by affecting chemokine availability and function, ACRs impact on a multitude of pathophysiological events and have emerged as important molecular players in health and disease. This review discusses individual characteristics of the currently known ACRs, highlights their similarities and differences and attempts to establish their group identity. It summarizes the progress made in mapping ACR expression, understanding their diverse in vitro and in vivo functions of ACRs and uncovering their contributions to disease pathogeneses.

G-CSF-mediated thrombopoietin release triggers neutrophil motility and mobilization from bone marrow via induction of Cxcr2 ligands

Emergency mobilization of neutrophil granulocytes (neutrophils) from the bone marrow (BM) is a key event of early cellular immunity. The hematopoietic cytokine granulocyte-colony stimulating factor (G-CSF) stimulates this process, but it is unknown how individual neutrophils respond in situ. We show by intravital 2-photon microscopy that a systemic dose of human clinical-grade G-CSF rapidly induces the motility and entry of neutrophils into blood vessels within the tibial BM of mice. Simultaneously, the neutrophil-attracting chemokine KC (Cxcl1) spikes in the blood. In mice lacking the KC receptor Cxcr2, G-CSF fails to mobilize neutrophils and antibody blockade of Cxcr2 inhibits the mobilization and induction of neutrophil motility in the BM. KC is expressed by megakaryocytes and endothelial cells in situ and is released in vitro by megakaryocytes isolated directly from BM. This production of KC is strongly increased by thrombopoietin (TPO). Systemic G-CSF rapidly induces the increased production of TPO in BM. Accordingly, a single injection of TPO mobilizes neutrophils with kinetics similar to G-CSF, and mice lacking the TPO receptor show impaired neutrophil mobilization after short-term G-CSF administration. Thus, a network of signaling molecules, chemokines, and cells controls neutrophil release from the BM, and their mobilization involves rapidly induced Cxcr2-mediated motility controlled by TPO as a pacemaker.

Genetic polymorphisms of Rh, Kell, Duffy and Kidd systems in a population from the State of Paraná, southern Brazil

BACKGROUND

Red blood group genes are highly polymorphic and the distribution of alleles varies among different populations and ethnic groups.

AIM

To evaluate allele polymorphisms of the Rh, Kell, Duffy and Kidd blood group systems in a population of the State of Paraná

METHODS

Rh, Kell, Duffy and Kidd blood group polymorphisms were evaluated in 400 unrelated blood or bone marrow donors from the northwestern region of Paraná State between September 2008 and October 2009. The following techniques were used: multiplex-polymerase chain reaction genotyping for the identification of the RHD gene and RHCE*C/c genotype; allele-specific polymerase chain reaction for the RHDψ and restriction fragment length polymorphism polymerase chain reaction for the RHCE*E/e, KEL, FY-GATA and JK alleles.

RESULTS

These techniques enabled the evaluation of the frequencies of Rh, Kell, Duffy and Kidd polymorphisms in the population studied, which were compared to frequencies in two populations from the eastern region of São Paulo State.

CONCLUSION

The RHCE*c/c, FY*A/FY*B, GATA-33 T/T, JK*B/JK*B genotypes were more prevalent in the population from Paraná, while RHCE*C/c, FY*B/FY*B, GATA-33 C/C, JK*A/JK*B genotypes were more common in the populations from São Paulo.

Host chemokines bind to Staphylococcus aureus and stimulate protein A release

There are few examples of host signals that are beneficial to bacteria during infection. Here we found that 31 out of 42 host immunoregulatory chemokines were able to induce release of the virulence factor protein A (SPA) from a strain of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA). Detailed study of chemokine CXCL9 revealed that SPA release occurred through a post-translational mechanism and was inversely proportional to bacterial density. CXCL9 bound specifically to the cell membrane of CA-MRSA, and the related SPA-releasing chemokine CXCL10 bound to both cell wall and cell membrane. Clinical samples from patients infected with S. aureus and samples from a mouse model of CA-MRSA skin abscess all contained extracellular SPA. Further, SPA-releasing chemokines were present in mouse skin lesions infected with CA-MRSA. Our data identify a potential new mode of immune evasion, in which the pathogen exploits a host defense factor to release a virulence factor; moreover, chemokine binding may serve a scavenging function in immune evasion by S. aureus.

A recombinant dromedary antibody fragment (VHH or nanobody) directed against human Duffy antigen receptor for chemokines

Fy blood group antigens are carried by the Duffy antigen receptor for chemokines (DARC), a red cells receptor for Plasmodium vivax broadly implicated in human health and diseases. Recombinant VHHs, or nanobodies, the smallest intact antigen binding fragment derivative from the heavy chain-only antibodies present in camelids, were prepared from a dromedary immunized against DARC N-terminal extracellular domain and selected for DARC binding. A described VHH, CA52, does recognize native DARC on cells. It inhibits P. vivax invasion of erythrocytes and displaces interleukin-8 bound to DARC. The targeted epitope overlaps the well-defined DARC Fy6 epitope. K (D) of CA52-DARC equilibrium is sub-nanomolar, hence ideal to develop diagnostic or therapeutic compounds. Immunocapture by immobilized CA52 yielded highly purified DARC from engineered K562 cells. This first report on a VHH with specificity for a red blood cell protein exemplifies VHHs' potentialities to target, to purify, and to modulate the function of cellular markers.

Expression of chemokine decoy receptors and their ligands at the porcine maternal-fetal interface

Successful pregnancy requires coordinated maternal-fetal cross-talk to establish vascular connections that support conceptus growth. In pigs, two waves of spontaneous fetal loss occur and 30-40% of conceptuses are lost before parturition. Previous studies associated these losses with decreased angiogenic and increased inflammatory cytokines. Chemokines, a sub-category of cytokines, and decoy receptors control leukocyte trafficking, angiogenesis and development. The availability of chemokines is regulated by three non-signalling decoy receptors: chemokine decoy receptor (D6), Duffy antigen receptor for chemokines (DARC) and Chemocentryx decoy receptor (CCX CKR). We hypothesized that the expression of these receptors and their chemokine ligands regulate the porcine pregnancy success or failure. Here, we describe for the first time the transcription and translation of all three decoy receptors and several chemokine ligands in endometrium and trophoblast associated with healthy and arresting conceptuses at gestation day (gd) 20 and gd50. Among decoy receptors, transcripts for DARC were significantly reduced in endometrium, whereas that for CCX CKR were significantly increased in endometrium and trophoblast at gd50 arresting compared with healthy sites. However, western blot analysis revealed no differences in decoy receptor expression between healthy and arresting tissues. Transcripts for decoy receptor ligands CCL2, CCL3, CCL4, CCL5, CCL11, CCL19, CCL21, CXCL2 and CXCL8 were stable between healthy and arresting littermates. Quantification by SearchLight chemiluminescent protein array confirmed ligand expression at the protein level. These data indicate that decoy receptors and ligands are expressed at the porcine maternal-fetal interface and dysregulation of decoy receptor (DARC and CCX CKR) transcripts occurs at sites of fetal arrest.

Multiple interests in structural models of DARC transmembrane protein

Duffy Antigen Receptor for Chemokines (DARC) is an unusual transmembrane chemokine receptor which (i) binds the two main chemokine families and (ii) does not transduct any signal as it lacks the DRY consensus sequence. It is considered as silent chemokine receptor, a tank useful for chemiotactism. DARC had been particularly studied as a major actor of malaria infection by Plasmodium vivax. It is also implicated in multiple chemokine inflammation, inflammatory diseases, in cancer and might play a role in HIV infection and AIDS. In this review, we focus on the interest to build structural model of DARC to understand more precisely its abilities to bind its physiological ligand CXCL8 and its malaria ligand. We also present innovative development on VHHs able to bind DARC protein. We underline difficulties and limitations of such bioinformatics approaches and highlight the crucial importance of biological data to conduct these kinds of researches.

CXCL5 regulates chemokine scavenging and pulmonary host defense to bacterial infection

The chemokine sink hypothesis pertaining to erythrocyte Duffy Antigen Receptor for Chemokines (DARC) during inflammation has received considerable attention, but lacks direct in vivo evidence. Here we demonstrate, using mice with a targeted deletion in CXCL5, that CXCL5 bound erythrocyte DARC and impaired its chemokine scavenging in blood. CXCL5 increased the plasma concentrations of CXCL1 and CXCL2 in part through inhibiting chemokine scavenging, impairing chemokine gradients and desensitizing CXCR2, which led to decreased neutrophil influx to the lung, increased lung bacterial burden and mortality in an Escherichia coli pneumonia model. In contrast, CXCL5 exerted a predominant role in mediating neutrophil influx to the lung during inflammation after LPS inhalation. Platelets and lung resident cells were the sources of homeostatic CXCL5 in blood and inflammatory CXCL5 in the lung respectively. This study presents a paradigm whereby platelets and red cells alter chemokine scavenging and neutrophil-chemokine interaction during inflammation.

Erythrocyte binding ligands in malaria parasites: intracellular trafficking and parasite virulence

The intracellular trafficking of an Erythrocyte Binding Like (EBL) ligand has recently been shown to dramatically affect the multiplication rate and virulence of the rodent malaria parasite Plasmodium yoelii yoelii. In this review, we describe the current understanding of the role of EBL and other erythrocyte binding ligands in erythrocyte invasion, and discuss the mechanisms by which they may control multiplication rates and virulence in malaria parasites.

Gene expression profiling in autoantibody-positive patients with arthralgia predicts development of arthritis

OBJECTIVE

To identify molecular features associated with the development of rheumatoid arthritis (RA), to understand the pathophysiology of preclinical development of RA, and to assign predictive biomarkers.

METHODS

The study group comprised 109 anti-citrullinated protein antibody (ACPA)- and/or rheumatoid factor-positive patients with arthralgia who did not have arthritis but were at risk of RA, and 25 patients with RA. The gene expression profiles of blood samples obtained from these patients were determined by DNA microarray analysis and quantitative polymerase chain reaction.

RESULTS

In 20 of the 109 patients with arthralgia who were at risk of RA, arthritis developed after a median of 7 months. Gene expression profiling of blood cells revealed heterogeneity among the at-risk patients, based on differential expression of immune-related genes. This report is the first to describe gene signatures relevant to the development of arthritis. Signatures significantly associated with arthritis development were involved in interferon (IFN)-mediated immunity, hematopoiesis, and chemokine/cytokine activity. Logistic regression analysis revealed that the odds ratio (OR) for developing arthritis within 12 months was 21.0 (95% confidence interval [95% CI] 2.8-156.1 [P = 0.003]) for the subgroup characterized by increased expression of genes involved in IFN-mediated immunity and/or cytokine/chemokine-activity. Genes involved in B cell immunology were associated with protection against progression to arthritis (OR 0.38, 95% CI 0.21-0.70 [P = 0.002]). These processes were reminiscent of those in patients with RA, implying that the preclinical phase of disease is associated with features of established disease.

CONCLUSION

The results of this study indicate that IFN-mediated immunity, hematopoiesis, and cell trafficking specify processes relevant to the progression of arthritis independent of ACPA positivity. These findings strongly suggest that certain gene signatures have value for predicting the progression to arthritis, which will pave the way to preventive medicine.

Effect of interleukin-8 and RANTES on the Gardos channel activity in sickle human red blood cells: role of the Duffy antigen receptor for chemokines

We investigated the effects of the chemokines IL-8 and RANTES on the activity of the Gardos channel (GC) of sickle red blood cells (SSRBCs). SSRBCs expressing the Duffy antigen receptor for chemokines (DARC) incubated under oxygenated conditions exhibit GC activation. The deoxygenation-stimulated K(+) loss via the GC is activated by the chemokines in the Duffy-positive SSRBCs. The percentage of cells with high density is 17 times higher in the Duffy-positive group. These findings are consistent with a greater susceptibility of Duffy-positive SSRBCs to inflammatory chemokines leading to GC activation and cellular dehydration and suggest a coupling, promoted by the sickling process, between DARC and the GC.

Chemokine decoy receptors: structure-function and biological properties

Chemokines induce cell migration through the activation of a distinct family of structurally related heterotrimeric G protein-coupled receptors (GPCR). Over the last few years, several receptors in this family that recognize chemokines but do not induce cell migration have been identified. These "atypical" chemokine receptors are unable to activate transduction events that lead directly to cell migration, but appear nonetheless to play a nonredundant role in the control of leukocyte recruitment at inflammatory sites and in tumors by shaping the chemoattractant gradient, either by removing, transporting, or concentrating their cognate ligands.

The C5a receptor (C5aR) C5L2 is a modulator of C5aR-mediated signal transduction

The complement anaphylatoxin C5a is a proinflammatory component of host defense that functions through two identified receptors, C5a receptor (C5aR) and C5L2. C5aR is a classical G protein-coupled receptor, whereas C5L2 is structurally homologous but deficient in G protein coupling. In human neutrophils, we show C5L2 is predominantly intracellular, whereas C5aR is expressed on the plasma membrane. Confocal analysis shows internalized C5aR following ligand binding is co-localized with both C5L2 and beta-arrestin. Antibody blockade of C5L2 results in a dramatic increase in C5a-mediated chemotaxis and ERK1/2 phosphorylation but does not alter C5a-mediated calcium mobilization, supporting its role in modulation of the beta-arrestin pathway. Association of C5L2 with beta-arrestin is confirmed by cellular co-immunoprecipitation assays. C5L2 blockade also has no effect on ligand uptake or C5aR endocytosis in human polymorphonuclear leukocytes, distinguishing its role from that of a rapid recycling or scavenging receptor in this cell type. This is thus the first example of a naturally occurring seven-transmembrane segment receptor that is both obligately uncoupled from G proteins and a negative modulator of signal transduction through the beta-arrestin pathway. Physiologically, these properties provide the possibility for additional fine-tuning of host defense.

Duffy antigen receptor for chemokines (Darc) polymorphism regulates circulating concentrations of monocyte chemoattractant protein-1 and other inflammatory mediators

To identify the genetic basis of circulating concentrations of monocyte chemoattractant protein-1 (MCP-1), we conducted genome-wide association analyses for MCP-1 in 3 independent cohorts (n = 9598). The strongest association was for serum MCP-1 with a nonsynonymous polymorphism, rs12075 (Asp42Gly) in DARC, the gene for Duffy antigen receptor for chemokines, a known vascular reservoir of proinflammatory cytokines (minor allele frequency, 45.6%; P < 1.0 * 10(-323)). This association was supported by family-based genetic linkage at a locus encompassing the DARC gene (genome-wide P = 8.0 * 10(-13)). Asp42Gly accounted for approximately 20% of the variability in serum MCP-1 concentrations and also was associated with serum concentrations of interleukin-8 and RANTES. While exploring a lack of association between this polymorphism and EDTA plasma MCP-1 concentrations (P = .82), we determined that both clotting and exogenous heparan sulfate (unfractionated heparin) released substantial amounts of MCP-1 from Darc. Quantitative immunoflow cytometry failed to identify meaningful Asp42Gly-associated differences in Darc expression, suggesting that a functional change is responsible for the differential cytokine binding. We conclude that Asp42Gly is a major regulator of erythrocyte Darc-mediated cytokine binding and thereby the circulating concentrations of several proinflammatory cytokines. We have also identified for the first time 2 mechanisms for the release of reservoir chemokines with possible clinical implications.

Effects of PARP-1 deficiency on airway inflammatory cell recruitment in response to LPS or TNF: differential effects on CXCR2 ligands and Duffy Antigen Receptor for Chemokines

We reported that PARP-1 exhibits differential roles in expression of inflammatory factors. Here, we show that PARP-1 deletion was associated with a significant reduction in inflammatory cell recruitment to mouse airways upon intratracheal administration of LPS. However, PARP-1 deletion exerted little effect in response to TNF exposure. LPS induced massive neutrophilia and moderate recruitment of macrophages, and TNF induced recruitment of primarily macrophages with smaller numbers of neutrophils in the lungs. Following either exposure, macrophage recruitment was blocked severely in PARP-1(-/-) mice, and this was associated with a marked reduction in MCP-1 and MIP-1alpha. This association was corroborated partly by macrophage recruitment in response to intratracheal administration of MCP-1 in PARP-1(-/-) mice. Surprisingly, although neutrophil recruitment was reduced significantly in LPS-treated PARP-1(-/-) mice, neutrophil numbers increased in TNF-treated mice, suggesting that PARP-1 deletion may promote a macrophagic-to-neutrophilic shift in the inflammatory response upon TNF exposure. Neutrophil-specific chemokines mKC and MIP-2 were reduced significantly in lungs of LPS-treated but only partially reduced in TNF-treated PARP-1(-/-) mice. Furthermore, the MIP-2 antagonist abrogated the shift to a neutrophilic response in TNF-exposed PARP-1(-/-) mice. Although CXCR2 expression increased in response to either stimulus in PARP-1(+/+) mice, the DARC increased only in lungs of TNF-treated PARP-1(+/+) mice; both receptors were reduced to basal levels in treated PARP-1(-/-) mice. Our results show that the balance of pro-neutrophilic or pro-macrophagic stimulatory factors and the differential influence of PARP-1 on these factors are critical determinants for the nature of the airway inflammatory response.

The molecular genetics of blood group polymorphism

Over 300 blood group specificities on red cells have been identified, many of which are polymorphic. The molecular mechanisms responsible for these polymorphisms are diverse, though many simply represent single nucleotide polymorphisms (SNPs). Other mechanisms include the following: gene deletion; single nucleotide deletion and sequence duplication, which introduce reading-frame shifts; nonsense mutation; intergenic recombination between closely linked genes, giving rise to hybrid genes and hybrid proteins; and a SNP in the promoter region of a blood group gene. Examples of these various genetic mechanisms are taken from the ABO, Rh, Kell, and Duffy blood group systems. Null phenotypes, in which no antigens of a blood group system are expressed, are not generally polymorphic, but provide good examples of the effect of inactivating mutations on blood group expression. As natural human 'knock-outs', null phenotypes provide useful clues to the functions of blood group antigens. Knowledge of the molecular backgrounds of blood group polymorphisms provides a means to predict blood group phenotypes from genomic DNA. This has two main applications in transfusion medicine: determination of foetal blood groups to assess whether the foetus is at risk from haemolytic disease and ascertainment of blood group phenotypes in multiply transfused, transfusion-dependent patients, where serological tests are precluded by the presence of donor red cells. Other applications are being developed for the future.

CCR5 signalling, but not DARC or D6 regulatory, chemokine receptors are targeted by herpesvirus U83A chemokine which delays receptor internalisation via diversion to a caveolin-linked pathway

Background

Herpesviruses have evolved chemokines and chemokine receptors, which modulate the recruitment of human leukocytes during the inflammatory response to infection. Early post-infection, human herpesvirus 6A (HHV-6A) infected cells express the chemokine receptor U51A and chemokine U83A which have complementary effects in subverting the CC-chemokine family thereby controlling anti-viral leukocyte recruitment. Here we show that, to potentiate this activity, the viral chemokine can also avoid clearance by scavenger chemokine receptors, DARC and D6, which normally regulate an inflammatory response. Conversely, U83A delays internalisation of its signalling target receptor CCR5 with diversion to caveolin rich membrane domains. This mechanism can redirect displaced human chemokines to DARC and D6 for clearance of the anti-viral inflammatory response, leaving the viral chemokine unchecked.

Methods

Cell models for competitive binding assays were established using radiolabeled human chemokines and cold U83A on CCR5, DARC or D6 expressing cells. Flow cytometry was used to assess specific chemotaxis of CCR5 bearing cells to U83A, and internalisation of CCR5 specific chemokine CCL4 after stimulation with U83A. Internalisation analyses were supported by confocal microscopy of internalisation and co-localisation of CCR5 with caveosome marker caveolin-1, after virus or human chemokine stimulation.

Results

U83A displaced efficiently human chemokines from CCR5, with a high affinity of 0.01nM, but not from DARC or D6. Signalling via CCR5 resulted in specific chemoattraction of primary human leukocytes bearing CCR5. However, U83A effective binding and signalling to CCR5 resulted in delayed internalisation and recycling up to 2 hours in the absence of continual re-stimulation. This resulted in diversion to a delayed caveolin-linked pathway rather than the rapid clathrin mediated endocytosis previously shown with human chemokines CCL3 or CCL4.

Conclusion

U83A diverts human chemokines from signalling, but not regulatory or scavenger, receptors facilitating their clearance, while occupying signalling receptors at the cell surface. This can enhance virus specific inflammation, facilitating dissemination to replication sensitive leukocytes while evading clearance; this has implications for linked neuro-inflammatory pathologies.

Efficient renal recruitment of macrophages and T cells in mice lacking the duffy antigen/receptor for chemokines

The Duffy antigen/receptor for chemokines (DARC) is a chemokine-binding protein that is expressed on erythrocytes and renal endothelial cells. DARC-mediated endothelial transcytosis of chemokines may facilitate the renal recruitment of macrophages and T cells, as has been suggested for neutrophils. We studied the role of Darc in two mouse models of prolonged renal inflammation, one that primarily involves the tubulointerstitium (unilateral ureteral obstruction), and one that requires an adaptive immune response that leads to glomerulonephritis (accelerated nephrotoxic nephritis). Renal expression of Darc and its ligands was increased in both models. Leukocytes effectively infiltrated obstructed kidneys in Darc-deficient mice with pronounced T-cell infiltration at early time points. Development of interstitial fibrosis was comparable in both genotypes. Nephrotoxic nephritis was inducible in Darc-deficient mice, with both an increased humoral immune response and functional impairment during the early phase of disease. Leukocytes efficiently infiltrated kidneys of Darc-deficient mice, with increased cell numbers at early but not late time points. Taken together, renal inflammation developed more rapidly in DARC-deficient mice, without affecting the extent of renal injury at later time points. Thus, genetic elimination of Darc in mice does not prevent the development of renal infiltrates and may even enhance such development during the early phases of interstitial and glomerular diseases in mouse models of prolonged renal inflammation.

DARC on RBC limits lung injury by balancing compartmental distribution of CXC chemokines

The Duffy antigen receptor for chemokines (DARC) has a high affinity for CC and CXC chemokines. However, it lacks the ability to induce cell responses that are typical for classical chemokine receptors. The role of DARC in inflammatory conditions remains to be elucidated. We studied the role of DARC in a murine model of acute lung injury. We found that in Darc-gene-deficient (Darc(-/-)) mice, LPS-induced PMN migration into the alveolar space was elevated more than twofold. In contrast, PMN adhesion to endothelial cells and within the interstitial space was reduced in Darc(-/-) mice. Darc(-/-) mice also exhibited increased microvascular permeability. Elevated PMN migration in Darc(-/-) mice was associated with increased concentrations of two essential CXCR2 ligands, CXCL1 and CXCL2/3 in the alveolar space. In the blood, CXCL1 was mostly associated with RBC in WT mice and with plasma in Darc(-/-) mice. We found that DARC on RBC prevented excessive PMN migration into the alveolar space. In contrast, DARC on non-hematopoietic cells appeared to have only minor effects on leukocyte trafficking in this model. These findings show how DARC regulates lung inflammation by controlling the distribution and presentation of chemokines that bind CXCR2.

Monocyte-endothelial cell interactions in the development of atherosclerosis

The activation of endothelial cells at atherosclerotic lesion-prone sites in the arterial tree results in the up-regulation of cell adhesion molecules and chemokines, which mediate the recruitment of circulating monocytes. Accumulation of monocytes and monocyte-derived phagocytes in the wall of large arteries leads to chronic inflammation and the development and progression of atherosclerosis. This review discusses the nature of these molecules and the mechanisms involved in the early steps of monocyte recruitment into atherosclerotic lesion sites within the vessel wall.

In vivo imaging and quantitative analysis of leukocyte directional migration and polarization in inflamed tissue

Directional migration of transmigrated leukocytes to the site of injury is a central event in the inflammatory response. Here, we present an in vivo chemotaxis assay enabling the visualization and quantitative analysis of subtype-specific directional motility and polarization of leukocytes in their natural 3D microenvironment. Our technique comprises the combination of i) semi-automated in situ microinjection of chemoattractants or bacteria as local chemotactic stimulus, ii) in vivo near-infrared reflected-light oblique transillumination (RLOT) microscopy for the visualization of leukocyte motility and morphology, and iii) in vivo fluorescence microscopy for the visualization of different leukocyte subpopulations or fluorescence-labeled bacteria. Leukocyte motility parameters are quantified off-line in digitized video sequences using computer-assisted single cell tracking. Here, we show that perivenular microinjection of chemoattractants [macrophage inflammatory protein-1alpha (MIP-1alpha/Ccl3), platelet-activating factor (PAF)] or E. coli into the murine cremaster muscle induces target-oriented intravascular adhesion and transmigration as well as polarization and directional interstitial migration of leukocytes towards the locally administered stimuli. Moreover, we describe a crucial role of Rho kinase for the regulation of directional motility and polarization of transmigrated leukocytes in vivo. Finally, combining in vivo RLOT and fluorescence microscopy in Cx3CR1(gfp/gfp) mice (mice exhibiting green fluorescent protein-labeled monocytes), we are able to demonstrate differences in the migratory behavior of monocytes and neutrophils.Taken together, we propose a novel approach for investigating the mechanisms and spatiotemporal dynamics of subtype-specific motility and polarization of leukocytes during their directional interstitial migration in vivo.

Reduced neutrophil count in people of African descent is due to a regulatory variant in the Duffy antigen receptor for chemokines gene

Persistently low white blood cell count (WBC) and neutrophil count is a well-described phenomenon in persons of African ancestry, whose etiology remains unknown. We recently used admixture mapping to identify an approximately 1-megabase region on chromosome 1, where ancestry status (African or European) almost entirely accounted for the difference in WBC between African Americans and European Americans. To identify the specific genetic change responsible for this association, we analyzed genotype and phenotype data from 6,005 African Americans from the Jackson Heart Study (JHS), the Health, Aging and Body Composition (Health ABC) Study, and the Atherosclerosis Risk in Communities (ARIC) Study. We demonstrate that the causal variant must be at least 91% different in frequency between West Africans and European Americans. An excellent candidate is the Duffy Null polymorphism (SNP rs2814778 at chromosome 1q23.2), which is the only polymorphism in the region known to be so differentiated in frequency and is already known to protect against Plasmodium vivax malaria. We confirm that rs2814778 is predictive of WBC and neutrophil count in African Americans above beyond the previously described admixture association (P = 3.8 x 10(-5)), establishing a novel phenotype for this genetic variant.

The Duffy antigen receptor for chemokines transports chemokines and supports their promigratory activity

The Duffy antigen receptor for chemokines (DARC) belongs to a family of 'silent' heptahelical chemokine receptors that do not couple to G proteins and fail to transmit measurable intracellular signals. DARC binds most inflammatory chemokines and is prominently expressed on venular endothelial cells, where its function has remained contentious. Here we show that DARC, like other silent receptors, internalized chemokines but did not effectively scavenge them. Instead, DARC mediated chemokine transcytosis, which led to apical retention of intact chemokines and more leukocyte migration across monolayers expressing DARC. Mice overexpressing DARC on blood vessel endothelium had enhanced chemokine-induced leukocyte extravasation and contact-hypersensitivity reactions. Thus, interactions of chemokines with DARC support their activity on apposing leukocytes in vitro and in vivo.

Gene encoding Duffy antigen/receptor for chemokines is associated with asthma and IgE in three populations

RATIONALE

Asthma prevalence and severity are high among underserved minorities, including those of African descent. The Duffy antigen/receptor for chemokines is the receptor for Plasmodium vivax on erythrocytes and functions as a chemokine-clearing receptor. Unlike European populations, decreased expression of the receptor on erythrocytes is common among populations of African descent, and results from a functional T-46C polymorphism (rs2814778) in the promoter. This variant provides an evolutionary advantage in malaria-endemic regions, because Duffy antigen/receptor for chemokines-negative erythrocytes are more resistant to infection by P. vivax.

OBJECTIVES

To determine the role of the rs2814778 polymorphism in asthma and atopy as measured by total serum IgE levels among four populations of African descent (African Caribbean, African American, Brazilian, and Colombian) and a European American population.

METHODS

Family-based association tests were performed in each of the five populations to test for association between the rs2814778 polymorphism and asthma or total IgE concentration.

MEASUREMENTS AND MAIN RESULTS

Asthma was significantly associated with the rs2814778 polymorphism in the African Caribbean, Colombian, and Brazilian families (P < 0.05). High total IgE levels were associated with this variant in African Caribbean and Colombian families (P < 0.05). The variant allele was not polymorphic among European Americans.

CONCLUSIONS

Susceptibility to asthma and atopy among certain populations of African descent is influenced by a functional polymorphism in the gene encoding Duffy antigen/receptor for chemokines. This genetic variant, which confers resistance to malarial parasitic infection, may also partially explain ethnic differences in morbidity of asthma.

How chemokines invite leukocytes to dance

A prominent activity of the chemokine system is the regulation of leukocyte trafficking. Here we summarize recent findings on the initial steps in chemokine receptor-induced signal transduction in leukocytes. In particular, we discuss the potential influences of the formation of oligomers of ligand and receptor and of coupling between chemokine signals and regulators of the cytoskeleton, such as small GTPases.