Duffy Antigen Receptor For Chemokines Research Articles

Genetic variants related to disease susceptibility and immunotolerance in the Duffy antigen receptor for chemokines (DARC, Fy) gene in the black lion tamarin (Leontopithecus chrysopygus, primates)

The DARC (Duffy antigen receptor for chemokines) gene encodes the DARC protein, which serves multiple roles in the immune system, as a binding site for the malarial parasites Plasmodium vivax and Plasmodium knowlesi, a promiscuous chemokine receptor and a blood group antigen. Variation in DARC may play particularly significant roles in innate immunity, immunotolerance and pathogen entry in callitrichines, such as the black lion tamarin (Leontopithecus chrysopygus). We compared amino acid sequences of DARC in the black lion tamarin (BLT) to non-human Haplorhine primates and Homo sapiens. Consistent with prior studies in other Haplorhines, we observed that the chemokine receptor experiences two opposing selection forces: (1) positive selection on the Plasmodium binding site and (2) purifying selection. We observed also that D21N, F22L, and V25L differentiated BLT from humans at a critical site for P. vivax and P. knowlesi binding. One amino acid residue, F22L, was subject to both positive selection and fixation in New World monkeys, suggesting a beneficial role as an adaptive barrier to Plasmodium entry. Unlike in humans, we observed no variation in DARC among BLTs, suggesting that the protein does not play a role in immunotolerance. In addition, lion tamarins differed from humans at the blood compatibility Fya /Fyb antigen-binding site 44, as well as at the putative destabilizing residues A61, T68, A187, and L215, further supporting a difference in the functional role of DARC in these primates compared with humans. Further research is needed to determine whether changes in the Plasmodium and Fya /Fyb antigen-binding sites disrupt DARC function in callitrichines.

The Duffy binding protein (PkDBP\u03b1II) of Plasmodium knowlesi from Peninsular Malaysia and Malaysian Borneo show different binding activity level to human erythrocytes

BackgroundThe zoonotic Plasmodium knowlesi is a major cause of human malaria in Malaysia. This parasite uses the Duffy binding protein (PkDBPαII) to interact with the Duffy antigen receptor for chemokines (DARC) receptor on human and macaque erythrocytes to initiate invasion. Previous studies on P. knowlesi have reported distinct Peninsular Malaysia and Malaysian Borneo PkDBPαII haplotypes. In the present study, the differential binding activity of these haplotypes with human and macaque (Macaca fascicularis) erythrocytes was investigated.MethodsThe PkDBPαII of Peninsular Malaysia and Malaysian Borneo were expressed on the surface of COS-7 cells and tested with human and monkey erythrocytes, with and without anti-Fy6 (anti-Duffy) monoclonal antibody treatment. Binding activity level was determined by counting the number of rosettes formed between the transfected COS-7 cells and the erythrocytes.ResultsAnti-Fy6 treatment was shown to completely block the binding of human erythrocytes with the transfected COS-7 cells, thus verifying the specific binding of human DARC with PkDBPαII. Interestingly, the PkDBPαII of Peninsular Malaysia displayed a higher binding activity with human erythrocytes when compared with the Malaysian Borneo PkDBPαII haplotype (mean number of rosettes formed = 156.89 ± 6.62 and 46.00 ± 3.57, respectively; P < 0.0001). However, no difference in binding activity level was seen in the binding assay using M. fascicularis erythrocytes.ConclusionThis study is the first report of phenotypic difference between PkDBPαII haplotypes. The biological implication of this finding is yet to be determined. Therefore, further studies need to be carried out to determine whether this differential binding level can be associated with severity of knowlesi malaria in human.

The Duffy null genotype is associated with a lower level of CCL2, leukocytes and neutrophil count but not with the clinical outcome of HTLV-1 infection.

Purpose. Chemokines are important in the immune response against viral infections, and may play a role in human T-lymphotropic virus 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) pathogenesis. Polymorphisms in the Duffy antigen receptor for chemokines (DARC), such as rs12075 (A>G; FY*B>FY*A) and rs281477 (-46T>C; GATA-1 box) may influence circulating concentrations of proinflammatory chemokines. We investigate whether Duffy genotypes influence the HTLV-1 proviral load (PVL) level, HTLV-1 infection outcome and chemokine concentrations in HTLV-1 asymptomatic carriers (AC=162), HAM/TSP patients (HAM=135) and seronegative individuals (SN=71).Methodology. Quantification of plasmatic IL8, CCL2 and CCL5 were performed by flow cytometry and Duffy genotypes were investigated by real-time PCR. HTLV-1 PVL was quantified in peripheral blood. To control for spurious association, individual ancestry profiles in AC and HAM groups were investigated.Results/Key findings. PVL and IL8 level were significantly higher in the HAM group than in the AC group, but were not associated with Duffy genotypes. The highest CCL2 and CCL5 levels were seen in the SN group, and there was no difference when comparing the infected groups. The level of CCL5 was not associated with Duffy genotypes. The polymorphism -46 C/C that abrogates the DARC expression on the erythrocytes was significantly associated with lower levels of CCL2, neutrophil and white blood cell (WBC) counts in HTLV-1-infected individuals.Conclusion. We conclude that although the Duffy null genotype was associated with leukopenia, neutropenia and lower levels of CCL2, the data do not suggest the influence of Duffy genotypes on the neurologic outcome of HTLV-1 infection, but may be a confounding factor in comparison HTLV-1-infected populations with different ancestries, especially when defining inflammatory biomarkers.

Abstract 1283: Mutations in the Duffy Antigen Receptor for Chemokines (DARC/ACKR1) gene result in population-private variants

Abstract By studying the breast cancer microenvironment, we can specifically address novel aspects of cancer development and progression at the molecular level. Chemokines are small signaling molecules that are an important component of this microenvironment, as they shape cellular composition of this space through recruitment of immune cells, among other functions. DARC, the Duffy Antigen Receptor for Chemokines, is an atypical chemokine receptor (ACKR1) that can bind different classes of chemokines. It is a non-signaling receptor that mainly acts as a regulator of chemokine homeostasis by removing them from circulation to recruit appropriate immune cell types. The purpose of this study is to determine how population-private variants of the DARC/ACKR1 gene across global population render distinct function and define aspects of human diversity in immune responses. A well-studied example of this would be the Duffy-null allele. This allele carries a mutation that is population-specific to recent decedents of Sub-Saharan Africans, and removes expression of DARC on red blood cells. Loss of expression on red blood cells presumably causes these “Duffy-Null” individuals to lose the ability to sequester chemokines, therefore losing homeostatic balance of these molecules in circulation. To identify additional mutations, we completed in silico analysis of minor allele frequencies across the gene in the 1000 Genomes Project data, and identified several other putative functional mutations that likely result in additional gene variants, specific to geographic ancestry groups and likely under similar selection as the Duffy null allele. We have prioritized our initial functional study to include mutations in the regulatory regions of the gene, as these mutations can change how and where the gene is expressed. Future work is focused on investigating these functional variants in situ, using human tissue and human breast cell lines, by isolating and re-engineering ancestry-specific variants in these cell lines. By identifying and determining functional outcomes of these population-specific mutation, we can observe differences in immune responses across these global populations, further defining the role that DARC/ACKR1 plays in the breast tumor microenvironment. Citation Format: Rachel Martini, Brittany Jenkins, Melissa Davis. Mutations in the Duffy Antigen Receptor for Chemokines (DARC/ACKR1) gene result in population-private variants [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1283. doi:10.1158/1538-7445.AM2017-1283

Human vaccination against Plasmodium vivax Duffy-binding protein induces strain-transcending antibodies.

BACKGROUND. Plasmodium vivax is the most widespread human malaria geographically; however, no effective vaccine exists. Red blood cell invasion by the P. vivax merozoite depends on an interaction between the Duffy antigen receptor for chemokines (DARC) and region II of the parasite’s Duffy-binding protein (PvDBP_RII). Naturally acquired binding-inhibitory antibodies against this interaction associate with clinical immunity, but it is unknown whether these responses can be induced by human vaccination.METHODS. Safety and immunogenicity of replication-deficient chimpanzee adenovirus serotype 63 (ChAd63) and modified vaccinia virus Ankara (MVA) viral vectored vaccines targeting PvDBP_RII (Salvador I strain) were assessed in an open-label dose-escalation phase Ia study in 24 healthy UK adults. Vaccines were delivered by the intramuscular route in a ChAd63-MVA heterologous prime-boost regimen using an 8-week interval.RESULTS. Both vaccines were well tolerated and demonstrated a favorable safety profile in malaria-naive adults. PvDBP_RII–specific ex-vivo IFN-γ T cell, antibody-secreting cell, memory B cell, and serum IgG responses were observed after the MVA boost immunization. Vaccine-induced antibodies inhibited the binding of vaccine homologous and heterologous variants of recombinant PvDBP_RII to the DARC receptor, with median 50% binding-inhibition titers greater than 1:100.CONCLUSION. We have demonstrated for the first time to our knowledge that strain-transcending antibodies can be induced against the PvDBP_RII antigen by vaccination in humans. These vaccine candidates warrant further clinical evaluation of efficacy against the blood-stage P. vivax parasite.TRIAL REGISTRATION. Clinicaltrials.gov NCT01816113.FUNDING. Support was provided by the UK Medical Research Council, UK National Institute of Health Research Oxford Biomedical Research Centre, and the Wellcome Trust.

The Duffy antigen receptor for chemokines regulates asthma pathophysiology.

The Duffy antigen receptor for chemokines (DARC) is an atypical receptor that regulates pro-inflammatory cytokines. However, the role of DARC in asthma pathophysiology is unknown. To determine the role of DARC in allergic airways disease in mice, and the association between DARC single nucleotide polymorphisms (SNPs) and clinical outcomes in patients with asthma. Mice with targeted disruption of the Darc gene (Darc∆E2 ) or WT mice were challenged over 3 weeks with house dust mite (HDM) antigen. Allergic airways disease was assessed 24 hours and 7 days following the final challenge. Additionally, associations between DARC SNPs and clinical outcomes were analysed in a cohort of poorly controlled asthmatics. Total airway inflammation following HDM did not differ between Darc∆E2 and WT mice. At 24 hours, Darc∆E2 mice had increased airway hyperresponsiveness; however, at 7 days airway hyperresponsiveness had completely resolved in Darc∆E2 but persisted in WT mice. In poorly controlled asthmatics, DARC SNPs were associated with worse asthma control at randomization and subsequent increased risk of healthcare utilization (odds ratio 3.13(1.37-7.27), P=.0062). Our animal model and human patient data suggest a novel role for DARC in the temporal regulation in asthma pathophysiology and symptoms.

Differential DARC/ACKR1 expression distinguishes venular from non-venular endothelial cells in murine tissues

BackgroundIntravascular leukocyte recruitment in most vertebrate tissues is restricted to postcapillary and collecting venules, whereas capillaries and arterioles usually support little or no leukocyte adhesion. This segmental restriction is thought to be mediated by endothelial, rather than hemodynamic, differences. The underlying mechanisms are largely unknown, in part because effective tools to distinguish, isolate, and analyze venular endothelial cells (V-ECs) and non-venular endothelial cells (NV-ECs) have been unavailable. We hypothesized that the atypical chemokine receptor DARC (Duffy Antigen Receptor for Chemokines, a.k.a. ACKR1 or CD234) may distinguish V-ECs versus NV-ECs in mice.MethodsWe generated a rat-anti-mouse monoclonal antibody (MAb) that specifically recognizes the erythroid and endothelial forms of native, surface-expressed DARC. Using this reagent, we characterized DARC expression and distribution in the microvasculature of murine tissues. ResultsDARC was exquisitely restricted to post-capillary and small collecting venules and completely absent from arteries, arterioles, capillaries, veins, and most lymphatics in every tissue analyzed. Accordingly, intravital microscopy showed that adhesive leukocyte-endothelial interactions were restricted to DARC+ venules. DARC was detectable over the entire circumference of V-ECs, but was more concentrated at cell-cell junctions. Analysis of single-cell suspensions suggested that the frequency of V-ECs among the total microvascular EC pool varies considerably between different tissues.ConclusionsImmunostaining of endothelial DARC allows the identification and isolation of intact V-ECs from multiple murine tissues. This strategy may be useful to dissect the mechanisms underlying segmental microvascular specialization in healthy and diseased tissues and to characterize the role of EC subsets in tissue-homeostasis, immune surveillance, infection, inflammation, and malignancies.

The expression of Duffy antigen receptor for chemokines by epithelial ovarian cancer decreases growth potential.

Epithelial ovarian cancer (EOC) is one of the main causes of cancer-associated mortality in females with gynecological malignancies. Duffy antigen receptor for chemokines (DARC) has previously been reported to be involved in tumor growth and the inhibition of tumor metastasis. However, the association between DARC and EOC remains unknown. The aim of the present study was to investigate the expression of DARC in the SKOV3 human epithelial ovarian cancer cell line with the establishment of a subcutaneous model in nude mice. To investigate the effects of DARC on the tumorigenesis of human epithelial ovarian cancer cells, GV287-DARC-L.V lentiviral vectors containing a DARC overexpression construct were transfected into SKOV3 cells. The present study revealed that transfection with DARC reduced the viability of SKOV3 cells in vitro by performing an MTT assay. SKOV3-DARC and SKOV3-negative control (NC) cells cultured in vitro were injected into nude mice to establish a subcutaneous model. The ovarian tumor volumes and the tumor weights were observed. Immunohistochemistry to detect CD31 expression was used to determine the microvessel density (MVD) in SKOV3-DARC and SKOV3-NC tumors. The results of the present study revealed that DARC-induced inhibition of tumor growth was associated with MVD in xenograft tumors. This suggested that DARC was a negative regulator of tumor growth in EOC, primarily via the inhibition of tumor angiogenesis.

Population genetic analysis of the DARC locus (Duffy) reveals adaptation from standing variation associated with malaria resistance in humans.

The human DARC (Duffy antigen receptor for chemokines) gene encodes a membrane-bound chemokine receptor crucial for the infection of red blood cells by Plasmodium vivax, a major causative agent of malaria. Of the three major allelic classes segregating in human populations, the FY*O allele has been shown to protect against P. vivax infection and is at near fixation in sub-Saharan Africa, while FY*B and FY*A are common in Europe and Asia, respectively. Due to the combination of strong geographic differentiation and association with malaria resistance, DARC is considered a canonical example of positive selection in humans. Despite this, details of the timing and mode of selection at DARC remain poorly understood. Here, we use sequencing data from over 1,000 individuals in twenty-one human populations, as well as ancient human genomes, to perform a fine-scale investigation of the evolutionary history of DARC. We estimate the time to most recent common ancestor (TMRCA) of the most common FY*O haplotype to be 42 kya (95% CI: 34–49 kya). We infer the FY*O null mutation swept to fixation in Africa from standing variation with very low initial frequency (0.1%) and a selection coefficient of 0.043 (95% CI:0.011–0.18), which is among the strongest estimated in the human genome. We estimate the TMRCA of the FY*A mutation in non-Africans to be 57 kya (95% CI: 48–65 kya) and infer that, prior to the sweep of FY*O, all three alleles were segregating in Africa, as highly diverged populations from Asia and ≠Khomani San hunter-gatherers share the same FY*A haplotypes. We test multiple models of admixture that may account for this observation and reject recent Asian or European admixture as the cause.

355 - Mutation of duffy antigen receptor for chemokines (DARC) as an indicator of prostate cancer severity in Afro-Caribbean men

355 - Mutation of duffy antigen receptor for chemokines (DARC) as an indicator of prostate cancer severity in Afro-Caribbean men

Duffy antigen receptor for chemokines (DARC) expressing in cancer cells inhibits tumor progression by suppressing CXCR2 signaling in human pancreatic ductal adenocarcinoma

BackgroundPancreatic ductal adenocarcinoma (PDAC) has a dismal prognosis. Chemokines play important roles in the progression of many malignancies; however, the role of chemokine receptor expression in clinical cases of PDAC is unclear. Moreover, little is known about DARC, a decoy receptor of CXC chemokines, in the regulation of tumor progression. MethodsFunctions of chemokine receptors were evaluated using surgical specimens collected from PDAC patients, and PDAC cell lines. ResultsCXCR2 expression had no impacts on predicting prognosis, but low DARC expression in cancer cells was an independent risk factor for poor prognosis. In PDAC with low DARC expression, tumor sizes were larger and vascular invasion was increased. High CXCR2 expression was a significant predictor for poor prognosis, only in PDAC patients with low DARC expression. CXCR2 signaling induced STAT3 activation in PDAC, resulting in promoting cell cycle progression, inhibiting apoptosis, inducing angiogenesis, and enhancing invasiveness. DARC inhibited STAT3 activation by down-regulating CXCR2 signaling. These effects were confirmed by EMSA in vitro. DARC knockdown significantly increased cell proliferation in CFPAC-1 cells with high DARC expression, by activating STAT3. In contrast, CXCR2 knockdown inhibited the proliferative effects of IL-8 in MIA PaCa-2 cells with low DARC expression. Moreover, the inhibitory effect of CXCR2 antagonist on PDAC cell proliferation was more powerful in MIA PaCa-2 cells than CFPAC-1 cells. ConclusionsDARC expressing in cancer cells inhibits PDAC progression by suppressing STAT3 activation through the inhibition of CXCR2 signaling. Therefore, DARC is a novel prognostic predictor and a potential therapeutic target for PDAC.

The Presence, Persistence and Functional Properties of Plasmodium vivax Duffy Binding Protein II Antibodies Are Influenced by HLA Class II Allelic Variants.

BackgroundThe human malaria parasite Plasmodium vivax infects red blood cells through a key pathway that requires interaction between Duffy binding protein II (DBPII) and its receptor on reticulocytes, the Duffy antigen/receptor for chemokines (DARC). A high proportion of P. vivax-exposed individuals fail to develop antibodies that inhibit DBPII-DARC interaction, and genetic factors that modulate this humoral immune response are poorly characterized. Here, we investigate if DBPII responsiveness could be HLA class II-linked.Methodology/Principal FindingsA community-based open cohort study was carried out in an agricultural settlement of the Brazilian Amazon, in which 336 unrelated volunteers were genotyped for HLA class II (DRB1, DQA1 and DQB1 loci), and their DBPII immune responses were monitored over time (baseline, 6 and 12 months) by conventional serology (DBPII IgG ELISA-detected) and functional assays (inhibition of DBPII–erythrocyte binding). The results demonstrated an increased susceptibility of the DRB1*13:01 carriers to develop and sustain an anti-DBPII IgG response, while individuals with the haplotype DRB1*14:02-DQA1*05:03-DQB1*03:01 were persistent non-responders. HLA class II gene polymorphisms also influenced the functional properties of DBPII antibodies (BIAbs, binding inhibitory antibodies), with three alleles (DRB1*07:01, DQA1*02:01 and DQB1*02:02) comprising a single haplotype linked with the presence and persistence of the BIAbs response. Modelling the structural effects of the HLA-DRB1 variants revealed a number of differences in the peptide-binding groove, which is likely to lead to altered antigen binding and presentation profiles, and hence may explain the differences in subject responses.Conclusions/SignificanceThe current study confirms the heritability of the DBPII antibody response, with genetic variation in HLA class II genes influencing both the development and persistence of IgG antibody responses. Cellular studies to increase knowledge of the binding affinities of DBPII peptides for class II molecules linked with good or poor antibody responses might lead to the development of strategies for controlling the type of helper T cells activated in response to DBPII.

Independent Origin and Global Distribution of Distinct Plasmodium vivax Duffy Binding Protein Gene Duplications.

BackgroundPlasmodium vivax causes the majority of malaria episodes outside Africa, but remains a relatively understudied pathogen. The pathology of P. vivax infection depends critically on the parasite’s ability to recognize and invade human erythrocytes. This invasion process involves an interaction between P. vivax Duffy Binding Protein (PvDBP) in merozoites and the Duffy antigen receptor for chemokines (DARC) on the erythrocyte surface. Whole-genome sequencing of clinical isolates recently established that some P. vivax genomes contain two copies of the PvDBP gene. The frequency of this duplication is particularly high in Madagascar, where there is also evidence for P. vivax infection in DARC-negative individuals. The functional significance and global prevalence of this duplication, and whether there are other copy number variations at the PvDBP locus, is unknown.Methodology/Principal FindingsUsing whole-genome sequencing and PCR to study the PvDBP locus in P. vivax clinical isolates, we found that PvDBP duplication is widespread in Cambodia. The boundaries of the Cambodian PvDBP duplication differ from those previously identified in Madagascar, meaning that current molecular assays were unable to detect it. The Cambodian PvDBP duplication did not associate with parasite density or DARC genotype, and ranged in prevalence from 20% to 38% over four annual transmission seasons in Cambodia. This duplication was also present in P. vivax isolates from Brazil and Ethiopia, but not India.Conclusions/SignificancePvDBP duplications are much more widespread and complex than previously thought, and at least two distinct duplications are circulating globally. The same duplication boundaries were identified in parasites from three continents, and were found at high prevalence in human populations where DARC-negativity is essentially absent. It is therefore unlikely that PvDBP duplication is associated with infection of DARC-negative individuals, but functional tests will be required to confirm this hypothesis.

A Novel Erythrocyte Binding Protein of Plasmodium vivax Suggests an Alternate Invasion Pathway into Duffy-Positive Reticulocytes.

ABSTRACTErythrocyte invasion by malaria parasites is essential for blood-stage development and an important determinant of host range. In Plasmodium vivax, the interaction between the Duffy binding protein (DBP) and its cognate receptor, the Duffy antigen receptor for chemokines (DARC), on human erythrocytes is central to blood-stage infection. Contrary to this established pathway of invasion, there is growing evidence of P. vivax infections occurring in Duffy blood group-negative individuals, suggesting that the parasite might have gained an alternative pathway to infect this group of individuals. Supporting this concept, a second distinct erythrocyte binding protein (EBP2), representing a new member of the DBP family, was discovered in P. vivax and may be the ligand in an alternate invasion pathway. Our study characterizes this novel ligand and determines its potential role in reticulocyte invasion by P. vivax merozoites. EBP2 binds preferentially to young (CD71high) Duffy-positive (Fy+) reticulocytes and has minimal binding capacity for Duffy-negative reticulocytes. Importantly, EBP2 is antigenically distinct from DBP and cannot be functionally inhibited by anti-DBP antibodies. Consequently, our results do not support EBP2 as a ligand for invasion of Duffy-negative blood cells, but instead, EBP2 may represent a novel ligand for an alternate invasion pathway of Duffy-positive reticulocytes.

Sequence diversity and positive selection at the Duffy-binding protein genes of Plasmodium knowlesi and P. cynomolgi: Analysis of the complete coding sequences of Thai isolates

Plasmodium knowlesi and P. cynomolgi are simian malaria parasites capable of causing symptomatic human infections. The interaction between the Duffy binding protein alpha on P. knowlesi merozoite and the Duffy-antigen receptor for chemokine (DARC) on human and macaque erythrocyte membrane is prerequisite for establishment of blood stage infection whereas DARC is not required for erythrocyte invasion by P. cynomolgi. To gain insights into the evolution of the PkDBP gene family comprising PkDBPα, PkDBPβ and PkDBPγ, and a member of the DBP gene family of P. cynomolgi (PcyDBP1), the complete coding sequences of these genes were analyzed from Thai field isolates and compared with the publicly available DBP sequences of P. vivax (PvDBP). The complete coding sequences of PkDBPα (n=11), PkDBPβ (n=11), PkDBPγ (n=10) and PcyDBP1 (n=11) were obtained from direct sequencing of the PCR products. Nucleotide diversity of DBP is highly variable across malaria species. PcyDBP1 displayed the greatest level of nucleotide diversity while all PkDBP gene members exhibited comparable levels of diversity. Positive selection occurred in domains I, II and IV of PvDBP and in domain V of PcyDBP1. Although deviation from neutrality was not detected in domain II of PkDBPα, a signature of positive selection was identified in the putative DARC binding site in this domain. The DBP gene families seem to have arisen following the model of concerted evolution because paralogs rather than orthologs are clustered in the phylogenetic tree. The presence of identical or closely related repeats exclusive for the PkDBP gene family suggests that duplication of gene members postdated their divergence from the ancestral PcyDBP and PvDBP lineages. Intragenic recombination was detected in all DBP genes of these malaria species. Despite the limited number of isolates, P. knowlesi from Thailand shared phylogenetically related domain II sequences of both PkDBPα and PkDBPγ with those from Peninsular Malaysia, consistent with their geographic proximity.

Potential Role of DARC-Chemokine Interaction in the Recruitment of Osteoclast Precursors in Response to Bacterial Lipopolysaccharide Challenge.

Duffy antigen receptor for chemokines (DARC) binds to a number of pro-inflammatory chemokines, and since chemokines are known to regulate trafficking of osteoclast (OC) precursors, we predicted that DARC would regulate OC recruitment to sites of inflammation by modulating chemokine activity. To test this hypothesis, we evaluated the mRNA expression of Darc and the chemokines known to bind to DARC, in endothelial cells treated with bacterial lipopolysaccharide (LPS). The mRNA expression of Mcp-1, Rantes, Darc and Ccr5 was significantly increased in endothelial cells in response to LPS treatment. Blocking the function of DARC with neutralizing antibody partially abrogated the effect of LPS on the mRNA expression of Mcp-1 and Rantes. In vivo, mice with targeted disruption of Darc gene (Darc-KO) and control wild-type (WT) mice were used to assess the role of DARC in response to single LPS application on the top of parietal bones. Five hours post-LPS injection, local expression of Cd14 mRNA (a marker of inflammatory monocytes) was significantly increased in both lines of mice. However, the magnitude of increase was greater in WT mice compared with Darc-KO mice suggesting a role for DARC in mediating the recruitment of monocytes in response to LPS. Histological staining for tartrate-resistant acid phosphatase (TRAP) in calvaria sections taken from the injection sites revealed a significant reduction in TRAP-labeled surface per bone surface in response to LPS in Darc-KO mice compared with WT mice. Based on these findings, we concluded that DARC regulates recruitment of OC precursors at the inflammation site, probably through regulation of chemokines transcytosis across endothelial cell barrier.

The Role of the Duffy Antigen Receptor for Chemokines in Metabolic Disease

Inflammation in adipose tissues contributes to obesity‐related insulin resistance and metabolic disease, a problem with greater prevalence in African, Asian, and Hispanic populations. The Duffy Antigen Receptor for Chemokines (DARC) is a promiscuous non‐signaling receptor expressed primarily on erythrocytes and classically thought to modulate inflammation by binding chemokines such as MCP‐1 to buffer tissue inflammation and act as a chemokine reservoir. DARC allele variants protect against malaria and are prevalent in African, Asian, and Hispanic populations. We hypothesized that genetic deletion of DARC would augment adipose tissue inflammation and glucose intolerance in the setting of diet‐induced obesity.Eight week‐old male Wild Type (WT) and DARC−/− mice (C57BL/6 background) were maintained either on chow diet or switched to high fat diet (HFD, 60% calories from fat) for up to 24 weeks. Thereafter, metabolic phenotyping was performed, mice were subsequently euthanized, and tissues and blood were collected for analysis. Bone marrow (BM) transplants were performed by irradiating eight week old WT mice and injecting BM harvested from either DARC−/− (to eliminate BM‐derived DARC) or WT mice (control).Food intake, energy expenditure and locomotion were similar between WT and DARC−/− mice, leading to equivalent body‐weight gain and adipose tissue mass. Compared to WT mice, HFD‐fed DARC−/− mice exhibited lower plasma levels of the DARC‐bound cytokines MCP‐1, CCL11 and CXCL5, but higher adipose tissue MCP‐1 mRNA expression, more adipose tissue macrophages, and significantly larger adipocytes in the visceral adipose depots, implying enhanced adipose tissue inflammation. In addition, glucose tolerance and insulin sensitivity were significantly impaired in DARC−/− mice compared to WT mice on HFD. CD DARC−/− mice did not display increased adipose inflammation; however, they were less sensitive to insulin, exhibited larger subcutaneous adipocytes, and had higher levels of leptin mRNA and AKT phosphorylation (SER473) upon insulin stimulation when compared to WT mice. Mice reconstituted with DARC −/− BM and fed a HFD did not exhibit glucose intolerance or insulin resistance compared to mice with WT BM. Notably, we detected high levels of DARC mRNA in subcutaneous and visceral (but not brown) fat depots, and DARC protein immunoreactivity was detected in subcutaneous fat from WT but not DARC −/− mice.We conclude that loss of DARC enhances HFD‐induced adipose tissue inflammation and metabolic disease. However, the mechanism appears to be independent of its expression on erythrocytes and its classic role as a chemokine buffer‐sink. We report for the first time that DARC is expressed on adipocytes, where it may regulate insulin signaling.

The role of the human Duffy antigen receptor for chemokines in malaria susceptibility: current opinions and future treatment prospects.

The Duffy antigen receptor for chemokine (DARC) is a nonspecific receptor for several proinflammatory cytokines. It is homologous to the G-protein chemokine receptor superfamily, which is suggested to function as a scavenger in many inflammatory-and proinflammatory-related diseases. G-protein chemokine receptors are also known to play a critical role in infectious diseases; they are commonly used as entry vehicles by infectious agents. A typical example is the chemokine receptor CCR5 or CXCR4 used by HIV for infecting target cells. In malaria, DARC is considered an essential receptor that mediates the entry of the human and zoonotic malaria parasites Plasmodium vivax and Plasmodium knowlesi into human reticulocytes and erythrocytes, respectively. This process is mediated through interaction with the parasite ligand known as the Duffy binding protein (DBP). Most therapeutic strategies have been focused on blocking the interaction between DBP and DARC by targeting the parasite ligand, while strategies targeting the receptor, DARC, have not been intensively investigated. The rapid increase in drug resistance and the lack of new effective drugs or a vaccine for malaria constitute a major threat and a need for novel therapeutics to combat disease. This review explores strategies that can be used to target the receptor. Inhibitors of DARC, which block DBP–DARC interaction, can potentially provide an effective strategy for preventing malaria caused by P. vivax.

Staphylococcus Aureus Targets the Duffy Antigen Receptor for Chemokines (DARC) to Lyse Erythrocytes

Introduction: Staphylococcus aureus is a major human pathogen. Infections by this bacterium range from minor skin and soft tissue infections, to more invasive and life threating infections like sepsis, osteomyelitis, and pneumonia. In order to successfully infect the mammalian host, S. aureus has to overcome iron scarcity within the host. As such, S. aureus is thought to produce toxins that lyse erythrocytes, releasing hemoglobin, a critical iron source for S. aureus in mammals. The bi-component β-barrel pore-forming leukocidins kill human neutrophils and were mostly considered as virulence factors fighting the host innate immune system. We show here thatHlgAB and LukED are two potent hemolytic leukocidins against human erythrocytes. Furthermore, we describe the identification of the Duffy antigen receptor for chemokines (DARC) as the red blood cell receptor for both LukED and HlgAB leukocidins.Results: We took advantage of erythrocyte samples from different Duffy (Fy) genotyped individuals from the French National Blood Transfusion Institute. We evaluated the receptor expression on the surface of erythrocytes (Figure 1). DARC-negative erythrocytes (phenotype Fya-/b-) were fully resistant to HlgAB and LukED. Compared to individuals expressing normal levels of DARC (phenotypes Fya+/b+, Fya+/b+weak, Fya+/a+, and Fyb+/b+), individuals expressing intermediate (phenotype Fyb+weak/b+weak) or very low levels of DARC (phenotype Fyb-/b+weak) showed intermediate susceptibility to both HlgAB and LukED (Figure 1). These data demonstrate that the hemolytic activity of HlgAB and LukED is dependent on the expression of DARC at the red blood cell surface. To better understand the interaction of HlgAB and LukED with DARC, we screened HEK293T cells transfected with plasmids encoding DARC mutants (Tournamille et al, 2003). We demonstrate that while both HlgAB and LukED bind to DARC with nanomolar affinities, they do so by recognizing different domains of the receptor. To directly evaluate whether LukED and HlgAB can promote bacterial replication as a result of erythrocyte lysis, S. aureus was grown in iron-starved medium supplemented with cell-free extracts of erythrocytes treated with LukED or HlgAB. We observed that HlgAB and LukED were each capable of promoting S. aureus growth in a DARC and hemoglobin scavenging system (IsdBH)-dependent manner. These in vitro studies were supported by a murine bacteremia model.Discussion: By combining human studies of DARC polymorphisms with gain and loss of function experiments and biochemical analyses, we demonstrate that DARC is necessary and sufficient to render host cells susceptible to LukED and HlgAB. By targeting DARC, HlgAB and LukED support S. aureus growth in a hemoglobin-acquisition dependent-manner. Thus, these findings provide the missing link of how S. aureus targets and lyses erythrocytes to release one of the scarcest nutrient within the mammalian host. Human epidemiological studies comparing the severity of S. aureus infection in patients with DARC positive or DARC negative erythrocytes are now required to evaluate the contribution of DARC-mediated hemolysis in human staphylococcal diseases. Given the resistance of DARC negative erythrocytes to the parasites Plasmodium vivax and P. knowlesi, and now to the hemolytic activity of the bacterium S. aureus, our findings suggest the possibility of a positive selection event in response to these important human pathogens.(A) Susceptibility of human erythrocytes to S. aureus β-barrel pore forming toxins. The dashed line indicates 50% hemolysis. n = 6.(B) Levels of DARC and CD55 on erythrocytes of donors with different Fy phenotypes. The dashed line indicates the detection threshold. n = 2-7 ± SEM.(C,E) Susceptibility of human erythrocytes with different Fy phenotypes to HlgAB (C) and LukED (E). The dashed line indicates 50% hemolysis. n = 2-7 ± SEM.(D, F) Correlation of half-maximal effective concentrations (EC50) of HlgAB (D) and LukED (F) with the total number of receptors expressed on the erythrocyte surface.For Fyb+weak/Fyb- donors, LukED EC50 could not be calculated. n = 2-7 ± SEM. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Effects of Genetic Polymorphisms on Leukocyte and Neutrophil Counts and Maximum Tolerated Dose of Hydroxyurea in Children with Sickle Cell Anemia

Background: Elevated total white blood cell (WBC) count is associated with increased morbidity and mortality in sickle cell anemia (SCA), and is a biomarker for disease severity. In addition, a higher WBC and absolute neutrophil count (ANC) have been associated with a higher maximum tolerated dose (MTD) for hydroxyurea in treated patients. Several single nucleotide polymorphisms (SNPs), especially variants in the Duffy Antigen Receptor for Chemokine (DARC) gene, influence WBC and ANC in the general population; however, their effects on children with SCA have not been reported.Objectives: To determine the effects of candidate SNPs on the baseline WBC and ANC in children with SCA; to identify novel genetic variants affecting WBC and ANC; and to investigate their effects on hydroxyurea MTD.Design/Method: Genomic DNA was analyzed from children with SCA enrolled in prospective trials involving hydroxyurea treatment, including: (1) Hydroxyurea Study of Long-Term Effects (HUSTLE, NCT 00305175); (2) Stroke With Transfusions Changing to Hydroxyurea (SWiTCH, NCT 00122980); and (3) Transcranial Doppler With Transfusions Changing to Hydroxyurea (TWiTCH, NCT 01425307). DNA samples were genotyped for 6 candidate SNPs that were previously reported to have a significant effect on the WBC and ANC in the general population, using a combination of PCR-based allelic discrimination and Sanger sequencing (Table). WBC and ANC phenotypes (n=429) were obtained at study enrollment, as well as hydroxyurea MTD values (n=224) for children receiving the drug. An additive model and correlation trend test was used to perform statistical testing. Whole exome sequencing (WES) analysis was performed after randomizing the entire cohort into a discovery (n=256) and validation group (n=127), to identify novel associations with WBC and ANC.Results: The average age (mean ± SD) of the entire cohort was 10.7 ± 4.1 years, with WBC = 13.8 ± 4.4 x 109/L and ANC = 7.6 ± 3.2 x 109/L. The DARC SNP rs2814778 regulating Duffy antigen expression had a minor allele frequency (MAF) of 15.1%, similar to published reports in African-American populations. After adjusting for age, children either homozygous or heterozygous for the A allele had significantly higher WBC and ANC, compared to G homozygotes known as "Duffy null" (14.6 vs. 13.5 x 109/L and 8.5 vs. 7.2 x 109/L, p=0.015 and p=0.001, respectively). For DARC rs12075, which distinguishes the major Duffy alleles, the G allele that results in Fya expression was associated with higher ANC than Fyb, 8.8 vs. 7.4 x 109/L, p=0.017. The hydroxyurea MTD was 25.6 ± 4.5 mg/kg/day for the treated cohort, which was associated with pre-treated WBC (p=0.009) and ANC (0.002), but with none of the DARC polymorphisms. An unbiased search using WES identified a total of 45,228 non-synonymous variants with allele frequency >1%, including 2,238 variants associated with WBC and ANC in the discovery group (p<.05). Following replication testing in the validation group, 64 variants maintained association (p<0.05). Of these, 11 were located near the DARC gene and likely are in linkage with this known potent modifier. Five additional variants in the ZFHX4, RAB11FIP1, MAN2B1, RP1L1, and CD109 genes had overall p-values <.005 and represent polymorphisms that may affect WBC and ANC.Table 1GeneSNPLocationMAFWBCANCBeta valuep valueBeta valuep valueDARCrs28147781q23.1511.020.0151.010.001DARCrs120751q23.0590.800.2031.090.017IFI16rs46576161q23.0691.240.0410.790.077PSMD3-CSFrs406532117q21.1.3860.390.2190.320.442CDK6rs4457q21.2.188-0.220.586-0.230.577CXCL2rs91314q13.3.202-0.260.506-0.160.172Candidate genes associated with WBC count. Beta value represents the average change in levels with each allele copy.Conclusions: Common genetic variants affecting WBC and ANC in the general population also modify the phenotype of children with SCA, and can explain some of the observed WBC variability. This analysis confirms that children with SCA with Duffy alleles have significantly higher WBC and ANC compared to Duffy null individuals. Notably, the effect of Duffy null phenotype on lower WBC and ANC persists despite the highly inflammatory state and leukocytosis commonly observed in SCA. Hydroxyurea MTD was positively correlated with baseline WBC and ANC, but was not influenced by DARC. WES results suggest additional novel gene variants that may influence the WBC and ANC in children with SCA. DisclosuresOff Label Use: Hydroxyurea is FDA approved for the treatment of sickle cell anemia in adults, but has not yet been approved in children.. Nottage:Janssen Pharmaceuticals: Employment. Ware:Bayer Pharmaceuticals: Consultancy; Eli Lilly: Other: DSMB membership; Biomedomics: Research Funding; Bristol Myers Squibb: Research Funding.