{"gene":"ACKR2","run_date":"2026-04-28T17:12:37","timeline":{"discoveries":[{"year":1997,"finding":"ACKR2 (D6) was cloned as a novel promiscuous beta-chemokine receptor that binds most inflammatory CC chemokines (MIP-1α, MIP-1β, RANTES, JE, MCP-3) but not alpha-chemokines or C/CXXXC chemokines, and unlike conventional chemokine receptors, failed to elicit calcium flux upon ligand binding in transfected cells, suggesting it is not a classical signaling receptor.","method":"cDNA cloning, radioligand binding assays (125I-MIP-1α competition), calcium flux assays in HEK293 and CHO transfectants","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — original cloning with multiple binding and functional assays; replicated across human and mouse paralogs in same year","pmids":["9405404","9139699"],"is_preprint":false},{"year":2001,"finding":"ACKR2 (D6) is selectively expressed on lymphatic endothelial cells (LECs) lining afferent lymphatics in human dermis, intestinal mucosa, and lymph node sinuses, but not on blood vessel endothelium or peripheral blood cells, establishing lymphatic endothelium as the primary anatomical site for D6 function.","method":"Monoclonal antibody generation, immunohistochemistry on serial human skin sections with lymphatic marker podoplanin, in situ hybridization","journal":"The American journal of pathology","confidence":"High","confidence_rationale":"Tier 2 — reciprocal IHC and ISH with co-staining lymphatic marker; foundational localization paper with >230 citations","pmids":["11238036"],"is_preprint":false},{"year":2003,"finding":"Engagement of ACKR2 (D6) by inflammatory CC chemokines elicits no calcium response or chemotaxis in transfected cells or lymphatic endothelium, but results in efficient ligand internalization and degradation. D6 does not mediate transcytosis of chemokines in either direction. This established D6 as a chemokine-scavenging decoy receptor acting as a 'gatekeeper' on lymphatic endothelium.","method":"D6 transfectants in multiple cell types; calcium flux assays; chemotaxis assays; internalization/degradation assays; lymphatic endothelial cell experiments","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal functional assays in multiple cell types including native lymphatic endothelium; replicated and widely cited","pmids":["12594248"],"is_preprint":false},{"year":2004,"finding":"ACKR2 (D6) constitutively internalizes via clathrin-coated pits through a β-arrestin-dependent mechanism. D6 constitutively associates with β-arrestin, and an acidic region (not phosphorylation sites) in the cytoplasmic tail is critical for this interaction and subsequent internalization. Neither native D6 nor β-arrestin-uncoupled mutants activate G-protein-mediated signaling, confirming D6 as a non-signaling decoy receptor whose scavenging depends on constitutive β-arrestin-dependent endocytosis.","method":"β-arrestin co-immunoprecipitation, clathrin inhibition experiments, mutagenesis of cytoplasmic tail (acidic region vs. phosphorylation sites), calcium flux and chemotaxis assays in transfectants","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstitution with mutagenesis and multiple orthogonal assays identifying specific molecular determinant","pmids":["15084596"],"is_preprint":false},{"year":2004,"finding":"ACKR2 (D6) efficiently binds and scavenges most inflammatory CC chemokines (CCR1–CCR5 agonists) but not homeostatic CC chemokines (CCR6/CCR7 agonists). CCR4 agonists CCL17 and CCL22 are recognized by D6 with high affinity and scavenged, reducing their chemotactic activity. CD26-processed truncated forms of CCL22 (lacking N-terminal residues) are not recognized by D6, demonstrating that N-terminal integrity is required for D6 binding.","method":"Radioligand binding and competition assays on D6 transfectants; scavenging/degradation assays; CCR4 transfectant chemotaxis; CD26 processing experiments","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 1-2 — systematic ligand profiling with functional scavenging readouts and natural processing experiments","pmids":["15067078"],"is_preprint":false},{"year":2004,"finding":"Milligram quantities of purified ACKR2 (D6) from mammalian transfectants retain full functional activity (displaceable 125I-MIP-1β binding, MIP-1α affinity column binding). Biochemical characterization revealed D6 is N-glycosylated at the N-terminus (dispensable for ligand binding), sulphated, and constitutively phosphorylated (not enhanced by ligand). Over 80% of cellular D6 resides in intracellular vesicular compartments.","method":"Protein purification from transfected mammalian cells; radioligand binding; affinity chromatography; N-terminal mutagenesis; metabolic labeling for sulfation and phosphorylation; subcellular fractionation","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 — biochemical reconstitution with mutagenesis and multiple post-translational modification analyses","pmids":["14723600"],"is_preprint":false},{"year":2005,"finding":"ACKR2 (D6)-deficient mice fail to resolve cutaneous inflammation after phorbol ester treatment, accumulating excess residual beta-chemokines that drive an inflammatory pathology resembling psoriasis. This demonstrated that D6 is required for post-inflammatory clearance of beta-chemokines from cutaneous sites in vivo.","method":"D6 knockout mice; phorbol ester-induced cutaneous inflammation model; chemokine measurement; histopathology","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined phenotype and molecular mechanism (chemokine accumulation); widely replicated across multiple models","pmids":["15750596"],"is_preprint":false},{"year":2005,"finding":"ACKR2 (D6) can function as a coreceptor for primary dual-tropic HIV-1 and HIV-2 isolates on astrocytes. RNA interference knockdown of D6 in primary astrocytes inhibited infection by D6-tropic isolates, establishing a cell-autonomous HIV coreceptor function for D6 in brain cells.","method":"HIV-1/HIV-2 infection assays in D6-expressing cell lines and primary astrocytes; siRNA knockdown of D6; chimeric gp120 constructs","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA knockdown with viral infection phenotype; single lab","pmids":["16014924"],"is_preprint":false},{"year":2008,"finding":"D6 scavenging activity is regulated by unique vesicular trafficking: under resting conditions D6 constitutively recycles through Rab4- and Rab11-dependent pathways, maintaining low surface expression. Chemokine engagement induces dose-dependent Rab11-dependent redistribution of D6 to the plasma membrane, increasing chemokine degradation rate. This ligand-concentration-dependent surface up-regulation (not transcriptional regulation) is the mechanism by which D6 optimizes scavenging activity.","method":"Wortmannin and brefeldin A pharmacological inhibition; Rab4/Rab11 dominant-negative constructs; surface expression quantification; chemokine degradation assays","journal":"Blood","confidence":"High","confidence_rationale":"Tier 1-2 — multiple pharmacological and genetic tools identifying specific Rab GTPases; mechanistically dissected constitutive vs. ligand-induced trafficking","pmids":["18480427"],"is_preprint":false},{"year":2008,"finding":"The conserved 58-amino acid C-terminal tail of D6 controls constitutive phosphorylation, high protein stability, and intracellular trafficking itinerary, and drives β-arrestin to membranes near the cell surface. A serine cluster in this region is critical for these properties. Deletion of the last 44–58 amino acids abolishes progressive scavenging because ligand engagement of the truncated receptor inhibits subsequent chemokine uptake, revealing the C-terminus is dispensable for initial internalization but indispensable for sustained scavenging.","method":"C-terminal deletion and serine cluster mutagenesis in HEK293 cells; GFP-β-arrestin imaging; phosphorylation assays; CCL3 scavenging assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — systematic mutagenesis with multiple functional readouts identifying specific structural determinant for scavenging","pmids":["18201974"],"is_preprint":false},{"year":2008,"finding":"Functional D6 is expressed by murine and human hematopoietic cells (highest in B cells and dendritic cells), and this expression is dynamically regulated: LPS down-regulates D6 in myeloid cells, TGF-β up-regulates it, and T-cell activation markedly up-regulates D6 mRNA. D6 expression in myeloid progenitors, mast cells, megakaryocytes, and DCs is dependent on the transcription factor GATA1. Hematopoietic D6 mediates chemokine uptake in a D6-dependent manner.","method":"Flow cytometry; RT-PCR; competition chemokine uptake assays in D6-null vs. wild-type leukocytes; GATA1 knockout/knockdown experiments; LPS/TGF-β/anti-CD3 stimulation","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods identifying GATA1 as transcriptional regulator; D6-null comparator cells validate D6-dependence of chemokine uptake","pmids":["18714007"],"is_preprint":false},{"year":2007,"finding":"ACKR2 (D6)-deficient mice show increased susceptibility to chemically induced cutaneous tumor development. D6 deletion alone is sufficient to make resistant mouse strains susceptible to invasive squamous cell carcinoma. Conversely, transgenic D6 expression in keratinocytes dampens cutaneous inflammation and protects from tumor formation. Tumor susceptibility correlates with enhanced T cell and mast cell recruitment, linking D6-mediated chemokine scavenging to tumor suppression by limiting pro-tumorigenic inflammation.","method":"D6 knockout mice; keratinocyte-specific D6 transgenic mice; chemical carcinogenesis (DMBA/TPA); immune cell quantification by histology and flow cytometry","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — bidirectional genetic evidence (KO and transgenic) with defined cellular mediators","pmids":["17607362"],"is_preprint":false},{"year":2008,"finding":"ACKR2 (D6) expressed at the maternal-fetal interface (trophoblasts/placenta) plays a role in regulating chemokine levels during implantation, contributing to the local inflammatory milieu required for successful embryonic implantation and fetal tolerance.","method":"Expression analysis in placental/trophoblast tissue; D6-deficient mouse pregnancy models reviewed","journal":"Placenta","confidence":"Low","confidence_rationale":"Tier 3 — review/expression data; mechanistic evidence is indirect","pmids":["18676013"],"is_preprint":false},{"year":2009,"finding":"ACKR2 (D6) contributes to the development of dextran sodium sulfate-induced colitis: D6-deficient mice show reduced susceptibility to colitis and reduced clinical symptoms. Mechanistically, D6 deletion did not alter CC chemokine levels or leukocyte balance in the colon, but late in colitis D6-deficient colons showed enhanced IL-17A production by γδ T cells. Antibody neutralization of IL-17A worsened colitis specifically in D6-deficient mice, revealing that D6 regulates colitis by modulating IL-17A secretion by lamina propria γδ T cells.","method":"DSS colitis model in D6-deficient mice; cytokine measurements; leukocyte subset quantification; anti-IL-17A neutralizing antibody treatment","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"Medium","confidence_rationale":"Tier 2 — KO with antibody neutralization epistasis; unexpected pro-colitic role of D6 via γδ T cell IL-17A regulation","pmids":["19342683"],"is_preprint":false},{"year":2012,"finding":"ACKR2 (D6) prevents adverse ventricular remodeling after myocardial infarction by scavenging inflammatory CC chemokines CCL2 and CCL3 in ischemic heart. D6-deficient mice show increased pathogenic neutrophil and Ly6Chi monocyte infiltration, elevated MMP-9/MMP-2 activity, cardiac rupture, and left ventricular dilation. Bone marrow chimera experiments demonstrated that leukocyte-borne D6 plays no role; cardiac resident (non-hematopoietic) D6 is responsible. CCR2 deficiency in leukocytes rescues the adverse phenotype of D6-deficient mice.","method":"D6 knockout mice; myocardial infarction model; bone marrow chimeras; CCR2-deficient bone marrow transfer; cytokine/chemokine ELISA; MMP activity assays; echocardiography","journal":"Arteriosclerosis, thrombosis, and vascular biology","confidence":"High","confidence_rationale":"Tier 2 — bone marrow chimera epistasis precisely locating non-hematopoietic D6 function; CCR2-KO rescue confirms mechanistic pathway","pmids":["22796582"],"is_preprint":false},{"year":2012,"finding":"ACKR2 (D6) controls the traffic and immunosuppressive activity of Ly6Chi monocytes. Mice lacking D6 in the non-hematopoietic compartment have selectively increased circulating Ly6Chi monocytes. Under inflammation, these accumulate in secondary lymphoid organs in a CCR2-dependent manner. D6-deficient Ly6Chi monocytes have enhanced immunosuppressive activity, inhibiting adaptive immune responses and partially protecting against graft-versus-host disease.","method":"D6 knockout and bone marrow chimera mice; flow cytometry; GVHD model; T-cell suppression assays; CCR2-dependent accumulation experiments","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — non-hematopoietic compartment-specific genetic dissection with multiple functional readouts","pmids":["22504926"],"is_preprint":false},{"year":2012,"finding":"ACKR2 (D6) controls macrophage efferocytosis and cytokine secretion during inflammation resolution in a chemokine scavenging-independent manner. D6-deficient mice show increased macrophage numbers and enhanced efferocytosis of apoptotic neutrophils in vivo. D6 is expressed on apoptotic neutrophils, and D6-deficient apoptotic neutrophils are less effective at inducing immune silencing (reduced TNF-α, IL-1β, CCL5 suppression) in macrophages, identifying a scavenging-independent role for neutrophil-expressed D6 in shaping the resolution of inflammation.","method":"Zymosan A peritonitis model; D6 knockout mice; in vivo efferocytosis quantification; ex vivo macrophage-neutrophil co-incubation cytokine assays; flow cytometry of human and rodent apoptotic neutrophils","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo KO with ex vivo mechanistic follow-up; novel scavenging-independent function identified","pmids":["22651933"],"is_preprint":false},{"year":2013,"finding":"ACKR2 (D6) expressed on lymphatic endothelial cells (LECs) contributes to selective CCR7 ligand presentation by suppressing inflammatory chemokine binding to LEC surfaces. D6 overexpression reduces immature dendritic cell (DC) adhesion to LECs, while D6 knockdown increases iDC adhesion and displaces mature DCs. LEC D6 expression is induced by IL-6 and IFN-γ, and by Kaposi sarcoma herpesvirus vIL-6. D6 is therefore an essential regulator of inflammatory leukocyte-LEC interactions and immature/mature DC discrimination.","method":"D6 overexpression and siRNA knockdown in LECs; DC adhesion assays; cytokine stimulation experiments; in vivo vIL-6 expression; KS/PEL cell line expression analysis","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — bidirectional genetic manipulation (OE and KD) with defined functional readout (DC discrimination); multiple inducers identified","pmids":["23479571"],"is_preprint":false},{"year":2013,"finding":"ACKR2 (D6) engagement by chemokine ligands activates a β-arrestin1-dependent, G protein-independent signaling pathway leading to phosphorylation of the actin-binding protein cofilin through the Rac1-PAK1-LIMK1 cascade. This signaling pathway is required for increased D6 surface abundance and for its chemokine-scavenging activity, demonstrating that D6 is not truly 'silent' but rather a signaling receptor using a distinct non-G protein pathway to regulate its own scavenging function.","method":"β-arrestin1 co-IP; Rac1/PAK1/LIMK1 pathway inhibitors and dominant-negative constructs; cofilin phosphorylation assays; D6 surface expression quantification; scavenging assays","journal":"Science signaling","confidence":"High","confidence_rationale":"Tier 1-2 — pathway dissection with multiple genetic and pharmacological tools; identifies specific signaling cascade required for scavenging","pmids":["23633677"],"is_preprint":false},{"year":2014,"finding":"ACKR2 (D6) expression in Kaposi sarcoma is inversely correlated with tumor aggressiveness and macrophage infiltration. In a KS experimental model with B-Raf V600E mutation, inhibition of B-Raf or the downstream ERK pathway induced D6 expression. In progressing human KS tumors, ERK activation correlates with reduced D6 levels. D6-competent tumors are promoted by adoptive transfer of wild-type but not CCR2-deficient macrophages, revealing that B-Raf-ERK pathway-driven downregulation of D6 unleashes CCL2-mediated pro-angiogenic macrophage recruitment.","method":"Human KS tumor analysis; B-Raf inhibitor treatment; ERK inhibitor treatment; D6 expression quantification; macrophage adoptive transfer (WT vs. CCR2-KO); tumor growth assays","journal":"Cancer immunology research","confidence":"High","confidence_rationale":"Tier 2 — bidirectional pharmacological and adoptive transfer epistasis defining B-Raf-ERK-D6 axis","pmids":["24844911"],"is_preprint":false},{"year":2014,"finding":"ACKR2-deficient mice display increased lymphatic vessel density in multiple tissues under resting and regenerating conditions, associated with enhanced fluid drainage and a hypotensive phenotype. This phenotype is developmentally established. Conversely, CCR2-deficient mice show reduced lymphatic vessel density. Increased proximity of pro-lymphangiogenic macrophages to developing lymphatic vessel surfaces in ACKR2-deficient mice (and reduced proximity in CCR2-deficient mice) reveals that ACKR2 and CCR2 reciprocally regulate vessel density by controlling pro-lymphangiogenic macrophage recruitment.","method":"ACKR2-KO and CCR2-KO mice; lymphatic vessel density quantification across tissues; tissue fluid drainage measurement; blood pressure measurement; embryonic skin analysis; macrophage proximity quantification","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — bidirectional genetic evidence (two receptor KOs with reciprocal phenotypes) with mechanistic cellular explanation","pmids":["25271254"],"is_preprint":false},{"year":2016,"finding":"ACKR2 limits the spread of psoriasiform inflammation from primary lesions to remote skin sites. Localized inflammation and IFN-γ up-regulate ACKR2 in remote tissues, protecting them from inflammatory spread. ACKR2 controls inflammatory T-cell chemotaxis and positioning within the skin, preventing epidermal influx associated with lesion development.","method":"Imiquimod-induced psoriasiform inflammation model; clinical samples; primary human cell cultures; in vitro migration assays; ACKR2 expression quantification in remote vs. lesional skin; IFN-γ stimulation","journal":"The Journal of investigative dermatology","confidence":"High","confidence_rationale":"Tier 2 — combination of in vivo mouse model, human samples, and in vitro mechanistic assays with IFN-γ identified as upstream regulator","pmids":["27568525"],"is_preprint":false},{"year":2016,"finding":"ACKR2 controls branching morphogenesis in the postnatal mammary gland. ACKR2 is differentially expressed during mammary gland development; Ackr2-/- mice display precocious mammary gland development with increased macrophage recruitment and increased density of the ductal epithelial network.","method":"ACKR2 knockout mice; mammary gland whole mount analysis; macrophage quantification by immunohistochemistry; ductal network density measurement at multiple developmental time points","journal":"Development (Cambridge, England)","confidence":"Medium","confidence_rationale":"Tier 2 — KO with defined developmental phenotype; macrophage recruitment identified as mechanism","pmids":["27888192"],"is_preprint":false},{"year":2018,"finding":"ACKR2 is expressed in hematopoietic precursors and downregulated during myeloid differentiation. Genetic inactivation of ACKR2 results in increased inflammatory chemokine receptor levels in precursors and enhanced release of neutrophils from bone marrow with increased anti-metastatic activity. In NeuT-driven mammary carcinogenesis, ACKR2 deficiency increases primary tumor growth but protects against metastasis via neutrophil-mediated anti-metastatic activity.","method":"ACKR2 knockout mice; flow cytometry of bone marrow precursors; NeuT transgenic mammary carcinoma model; 4T1 orthotopic and B16F10 i.v. metastasis models; chemokine receptor expression analysis","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — multiple in vivo tumor models with KO mice; identifies ACKR2 as checkpoint of myeloid differentiation and neutrophil release","pmids":["29445158"],"is_preprint":false},{"year":2018,"finding":"ACKR2 expressed in pulmonary resident (non-hematopoietic) cells drives pulmonary fibrosis by tuning the influx of CCR2+ and CCR5+ IFNγ-producing γδT cells. ACKR2-/- mice show reduced lethality and lung fibrosis in a bleomycin model, with early increased CCL5, CCL12, CCL17, IFNγ, and increased CCR2+/CCR5+ γδT cells in airways counterbalanced by reduced Th17 influx. Depletion of γδT cells reverses the protective phenotype of ACKR2-/- mice.","method":"Bleomycin fibrosis model; ACKR2-KO mice; bone marrow chimeras; CCR2-KO and CCR5-KO mice; antibody-mediated γδT cell depletion; cytokine/chemokine profiling; leukocyte subset analysis","journal":"American journal of physiology. Lung cellular and molecular physiology","confidence":"High","confidence_rationale":"Tier 2 — bone marrow chimeras localizing function to non-hematopoietic compartment; multiple KO strains and cell depletion defining CCR2+/CCR5+ γδT cell mechanism","pmids":["29469612"],"is_preprint":false},{"year":2019,"finding":"ACKR2 mediates pro-EMT and migratory responses stimulated by the orphan chemokine CXCL14 in breast cancer cells. Loss-of-function experiments identified ACKR2 as the receptor through which fibroblast-derived CXCL14 stimulates breast cancer EMT, migration, invasion, and lung colonization. CXCL14-induced NOS1 is downstream of ACKR2 and required for the pro-EMT effects, defining an autocrine CXCL14/ACKR2/NOS1 pathway.","method":"siRNA/shRNA loss-of-function for ACKR2; in vitro EMT, migration, invasion assays; xenograft model with CXCL14-overexpressing fibroblasts; tail-vein metastasis assay; NOS1 inhibition","journal":"Clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — loss-of-function with multiple in vitro and in vivo endpoints; identifies ACKR2 as novel CXCL14 receptor in cancer context","pmids":["30850359"],"is_preprint":false},{"year":2021,"finding":"ACKR2 (D6) binds and internalizes the CXC chemokine CXCL10, identifying the first non-CC chemokine agonist for ACKR2. β-arrestin recruitment assays revealed CXCL10 as a strong agonist for ACKR2, and ACKR2 reduced extracellular CXCL10 availability. DPP4/CD26 N-terminal processing of CXCL10 drastically reduced its activity at ACKR2, unlike CC chemokines, pointing to different receptor binding pocket occupancy by CC vs. CXC chemokines.","method":"NanoBiT and NanoBRET β-arrestin recruitment assays; ACKR2 internalization assays; DPP4 processing of CXCL10; competitive binding","journal":"Cancers","confidence":"Medium","confidence_rationale":"Tier 2 — highly sensitive β-arrestin assays with multiple orthogonal readouts; single lab but rigorous methodology identifying novel ligand class","pmids":["33801414"],"is_preprint":false},{"year":2023,"finding":"ACKR2 mediates CXCL14-promoted lung cancer metastasis via a PLCβ3-PKCα-c-Src-NF-κB signaling cascade leading to EMT and increased cell motility. ACKR2 knockdown abolished CXCL14-induced cancer cell motility in vitro and in an orthotopic model. This identifies a specific intracellular signaling pathway downstream of ACKR2 in cancer cells distinct from its classical scavenging function.","method":"ACKR2 knockdown (siRNA); migration and wound healing assays; luciferase reporter assay for NF-κB; Western blot for PLCβ3/PKCα/c-Src phosphorylation; orthotopic lung cancer metastasis model; TCGA/GEO dataset analysis for expression correlation","journal":"International journal of biological sciences","confidence":"Medium","confidence_rationale":"Tier 2 — loss-of-function with pathway inhibitor cascade and in vivo validation; single lab","pmids":["37056937"],"is_preprint":false},{"year":2024,"finding":"ACKR2+ chemoradiotherapy (CCRT)-resistant cervical cancer tumor cells drive CD8+ T cell senescence. Mechanistically, ACKR2 expression is upregulated by CCRT and by ligation of CC chemokines from activated myeloid and T cells; ACKR2+ tumor cells then produce TGF-β which drives CD8+ T cell senescence, compromising antitumor immunity and promoting tumor recurrence.","method":"Single-cell RNA sequencing of human cervical cancer tissues before/after CCRT; in vitro co-culture experiments; TGF-β blocking; retrospective clinical analysis","journal":"Cell reports. Medicine","confidence":"Medium","confidence_rationale":"Tier 2-3 — scRNA-seq with mechanistic in vitro follow-up; TGF-β identified as effector mechanism downstream of ACKR2","pmids":["38723624"],"is_preprint":false},{"year":1999,"finding":"The MIP-1α isoform LD78β (MIP-1αP) has ~15-20-fold enhanced binding affinity for D6 (ACKR2) compared to LD78α, attributable to a proline residue at position 2. This demonstrated that N-terminal residues of CC chemokines critically determine binding affinity at ACKR2.","method":"Radioligand binding competition assays on D6-expressing transfectants; proline-2 mutagenesis; CCR5 and D6 affinity comparison","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis identifying specific structural determinant for binding affinity","pmids":["10364178"],"is_preprint":false},{"year":2012,"finding":"D6 (ACKR2) expression is markedly elevated in 'uninvolved' psoriatic skin (epidermis and lymphatic endothelium) where inflammatory chemokines are elevated but plaques do not form, suggesting D6 acts as a suppressor of lesion development. D6 expression drops in perilesional and lesional skin coincident with plaque development. Trauma reduces D6 expression in uninvolved skin, consistent with trauma-mediated reduction in D6 triggering the Koebner phenomenon. D6 is also elevated in peripheral blood leukocytes of psoriatic patients.","method":"Immunohistochemistry of human psoriatic skin biopsies (uninvolved, perilesional, lesional); mRNA quantification; D6 measurement in peripheral blood leukocytes","journal":"The American journal of pathology","confidence":"Medium","confidence_rationale":"Tier 3 — expression analysis in human tissue with mechanistic inference; supported by prior D6 transgenic mouse data from same lab","pmids":["22867710"],"is_preprint":false}],"current_model":"ACKR2 (D6) is an atypical chemokine receptor expressed predominantly on lymphatic endothelial cells and hematopoietic precursors that scavenges most inflammatory CC chemokines (and CXCL10) through constitutive β-arrestin-dependent, clathrin-mediated internalization and lysosomal degradation without G-protein signaling; chemokine engagement activates a β-arrestin1→Rac1→PAK1→LIMK1→cofilin signaling cascade that drives Rab11-dependent receptor redistribution to the plasma membrane to enhance scavenging capacity, while its C-terminal serine cluster and non-hematopoietic expression govern in vivo control of cutaneous inflammation resolution, lymphatic vessel density (via CCL2-driven pro-lymphangiogenic macrophage recruitment), pulmonary fibrosis (via CCR2+/CCR5+ IFNγ+ γδT cells), mammary gland branching morphogenesis, and neutrophil release from bone marrow, with additional cancer-context roles including CXCL14-mediated EMT via NOS1 or PLCβ3-PKCα-NF-κB pathways and TGF-β-driven CD8+ T cell senescence."},"narrative":{"teleology":[{"year":1997,"claim":"Cloning of ACKR2 revealed a promiscuous CC chemokine-binding receptor that, unlike classical chemokine receptors, failed to signal through calcium flux, establishing it as functionally atypical.","evidence":"cDNA cloning with radioligand binding and calcium flux assays in HEK293/CHO transfectants","pmids":["9405404","9139699"],"confidence":"High","gaps":["Mechanism of ligand engagement without signaling was unknown","In vivo function not addressed","Selectivity for inflammatory vs. homeostatic chemokines not yet mapped"]},{"year":1999,"claim":"N-terminal residues of CC chemokines (specifically a proline at position 2) were identified as critical determinants of ACKR2 binding affinity, providing early structural insight into ligand recognition.","evidence":"Radioligand competition assays and proline-2 mutagenesis on D6 transfectants","pmids":["10364178"],"confidence":"High","gaps":["Full structural basis of ligand selectivity unresolved","No crystal or cryo-EM structure of ACKR2-chemokine complex"]},{"year":2001,"claim":"Identification of lymphatic endothelium as the primary site of ACKR2 expression provided the anatomical context for its function as a chemokine gatekeeper at tissue-lymph interfaces.","evidence":"Monoclonal antibody immunohistochemistry and in situ hybridization on human dermis, intestinal mucosa, and lymph node sections co-stained with podoplanin","pmids":["11238036"],"confidence":"High","gaps":["Expression on hematopoietic cells not yet appreciated","Whether ACKR2 functions identically in all lymphatic beds remained untested"]},{"year":2003,"claim":"Demonstration that ACKR2 internalizes and degrades CC chemokines without triggering signaling or transcytosis established the chemokine-scavenging/decoy receptor paradigm.","evidence":"Calcium flux, chemotaxis, internalization, and degradation assays in transfectants and primary lymphatic endothelial cells","pmids":["12594248"],"confidence":"High","gaps":["Molecular machinery of constitutive internalization uncharacterized","Whether ligand engagement alters receptor trafficking unknown"]},{"year":2004,"claim":"The trafficking and scavenging mechanism was dissected: ACKR2 constitutively internalizes via β-arrestin-dependent clathrin-coated pits, with an acidic C-terminal motif (not phosphorylation) driving β-arrestin association, and most receptor resides in intracellular vesicles.","evidence":"β-arrestin co-IP, clathrin inhibition, C-terminal mutagenesis, subcellular fractionation, and metabolic labeling in HEK293 transfectants","pmids":["15084596","14723600"],"confidence":"High","gaps":["Which Rab GTPases govern vesicular recycling not yet known","How ligand binding feeds back on trafficking unclear"]},{"year":2004,"claim":"Systematic ligand profiling confirmed ACKR2 selectively scavenges inflammatory (CCR1–CCR5 agonists) but not homeostatic CC chemokines, with N-terminal integrity required for recognition, defining the functional ligand spectrum.","evidence":"Radioligand binding, scavenging assays, and CD26-processing experiments in D6 transfectants","pmids":["15067078"],"confidence":"High","gaps":["Whether any non-CC chemokine could serve as ligand was unexplored","In vivo chemokine selectivity not validated"]},{"year":2005,"claim":"ACKR2-deficient mice revealed that in vivo chemokine scavenging is essential for resolution of cutaneous inflammation, as knockouts accumulated excess β-chemokines and developed psoriasis-like pathology.","evidence":"D6 knockout mice in phorbol ester-induced cutaneous inflammation model with chemokine quantification and histopathology","pmids":["15750596"],"confidence":"High","gaps":["Whether non-hematopoietic or hematopoietic ACKR2 is responsible not determined in this context","Mechanism of inflammation resolution vs. prevention not distinguished"]},{"year":2007,"claim":"Bidirectional genetic evidence (knockout susceptibility, transgenic protection) established ACKR2 as a tumor suppressor in chemically induced skin carcinogenesis by limiting pro-tumorigenic inflammatory cell recruitment.","evidence":"D6-KO and keratinocyte-specific D6 transgenic mice in DMBA/TPA carcinogenesis model; immune cell quantification","pmids":["17607362"],"confidence":"High","gaps":["Whether ACKR2 suppresses tumors in non-cutaneous tissues via same mechanism unknown","Cell-autonomous effects on tumor cells not addressed"]},{"year":2008,"claim":"Ligand-induced Rab11-dependent redistribution of ACKR2 to the plasma membrane was identified as the mechanism by which scavenging capacity scales with chemokine concentration, and the C-terminal serine cluster was shown to be essential for sustained scavenging.","evidence":"Rab4/Rab11 dominant-negative constructs, wortmannin/brefeldin A inhibition, C-terminal deletion and serine mutagenesis with chemokine degradation assays","pmids":["18480427","18201974"],"confidence":"High","gaps":["How Rab11 pathway is activated by ligand engagement unknown","No link yet to actin cytoskeleton remodeling"]},{"year":2008,"claim":"Discovery of ACKR2 expression on hematopoietic cells (B cells, DCs, mast cells) under GATA1 control expanded the expression domain beyond lymphatic endothelium and identified TGF-β and LPS as dynamic regulators.","evidence":"Flow cytometry, RT-PCR, chemokine uptake in D6-null vs. WT leukocytes, GATA1 knockout experiments","pmids":["18714007"],"confidence":"High","gaps":["Relative contribution of hematopoietic vs. non-hematopoietic ACKR2 to systemic chemokine homeostasis unclear","Whether GATA1 directly or indirectly activates the D6 promoter not resolved"]},{"year":2012,"claim":"Bone marrow chimera experiments in myocardial infarction and monocyte trafficking models localized the critical in vivo scavenging function to non-hematopoietic ACKR2, operating via control of CCR2-dependent Ly6C-hi monocyte recruitment.","evidence":"D6-KO and CCR2-KO bone marrow chimeras; MI model with echocardiography, MMP assays; GVHD model with T-cell suppression assays","pmids":["22796582","22504926"],"confidence":"High","gaps":["Which non-hematopoietic cell types express functionally relevant ACKR2 in heart was not pinpointed","Whether ACKR2 regulates monocyte function beyond recruitment unclear"]},{"year":2013,"claim":"Identification of the β-arrestin1→Rac1→PAK1→LIMK1→cofilin signaling cascade downstream of ACKR2 overturned the 'silent receptor' paradigm, showing that ACKR2 activates actin remodeling to drive its own surface redistribution and scavenging.","evidence":"β-arrestin1 co-IP, Rac1/PAK1/LIMK1 inhibitors and dominant-negatives, cofilin phosphorylation assays, D6 surface quantification","pmids":["23633677"],"confidence":"High","gaps":["Whether this pathway operates in all ACKR2-expressing cell types unknown","Whether other actin regulators participate not tested","Link to Rab11-dependent recycling not formally demonstrated"]},{"year":2014,"claim":"ACKR2 was shown to regulate lymphatic vessel density by controlling the proximity of CCR2-dependent pro-lymphangiogenic macrophages to developing lymphatic vessels, revealing a developmental morphogenetic role.","evidence":"ACKR2-KO and CCR2-KO mice; lymphatic vessel quantification; embryonic skin analysis; macrophage proximity measurements; blood pressure assessment","pmids":["25271254"],"confidence":"High","gaps":["Which VEGF family members mediate macrophage-driven lymphangiogenesis downstream of ACKR2 not identified","Whether increased lymphatic density has functional consequences beyond fluid drainage"]},{"year":2018,"claim":"ACKR2 was found to act as a checkpoint of myeloid differentiation in bone marrow, with its loss increasing neutrophil release and anti-metastatic neutrophil activity, while also promoting pulmonary fibrosis via regulation of CCR2+/CCR5+ IFNγ-producing γδT cell influx.","evidence":"ACKR2-KO mice in NeuT mammary carcinoma, 4T1/B16F10 metastasis models, and bleomycin fibrosis model; bone marrow chimeras; γδT cell depletion; CCR2-KO/CCR5-KO mice","pmids":["29445158","29469612"],"confidence":"High","gaps":["How ACKR2 is downregulated during myeloid differentiation mechanistically unclear","Whether neutrophil anti-metastatic activity is direct or requires other immune cell cooperation"]},{"year":2019,"claim":"ACKR2 was identified as a functional receptor for the orphan chemokine CXCL14, mediating EMT and metastasis through NOS1 in breast cancer, revealing a signaling role distinct from classical scavenging.","evidence":"siRNA/shRNA ACKR2 knockdown; in vitro EMT, migration, invasion assays; xenograft and tail-vein metastasis models; NOS1 inhibition","pmids":["30850359"],"confidence":"Medium","gaps":["Direct CXCL14-ACKR2 binding not demonstrated biochemically","How ACKR2 activates NOS1 is mechanistically undefined","Whether this operates outside breast cancer unknown"]},{"year":2021,"claim":"CXCL10 was identified as the first non-CC chemokine agonist of ACKR2, with DPP4 processing abolishing CXCL10 activity at ACKR2, broadening the receptor's ligand repertoire beyond CC chemokines.","evidence":"NanoBiT and NanoBRET β-arrestin recruitment assays; ACKR2 internalization assays; DPP4 processing experiments","pmids":["33801414"],"confidence":"Medium","gaps":["In vivo relevance of CXCL10 scavenging by ACKR2 not established","Whether other CXC chemokines are also agonists not systematically tested"]},{"year":2023,"claim":"A PLCβ3→PKCα→c-Src→NF-κB signaling cascade was mapped downstream of ACKR2 in lung cancer cells stimulated by CXCL14, defining a second cancer-specific signaling pathway through ACKR2.","evidence":"ACKR2 siRNA knockdown; phosphorylation western blots for PLCβ3/PKCα/c-Src; NF-κB luciferase reporter; orthotopic lung cancer metastasis model","pmids":["37056937"],"confidence":"Medium","gaps":["Relationship between PLCβ3-NF-κB and β-arrestin-cofilin pathways unexplored","Whether this pathway operates in non-cancer cells unknown","Single lab finding awaiting independent replication"]},{"year":2024,"claim":"ACKR2 upregulation in chemoradiotherapy-resistant cervical cancer cells was shown to drive CD8+ T cell senescence via TGF-β production, linking ACKR2 to immune evasion in the tumor microenvironment.","evidence":"Single-cell RNA-seq of human cervical cancer tissues; in vitro tumor-T cell co-cultures; TGF-β blocking experiments","pmids":["38723624"],"confidence":"Medium","gaps":["Whether TGF-β induction is a direct ACKR2 signaling output or indirect consequence of chemokine clearance is unresolved","Generalizability to other tumor types not tested","No in vivo intervention blocking ACKR2 to rescue T cell function"]},{"year":null,"claim":"Key unresolved questions include the structural basis of ACKR2's promiscuous CC/CXC chemokine recognition (no high-resolution structure exists), the mechanistic link between β-arrestin-cofilin signaling and Rab11-dependent recycling, and whether ACKR2's cancer-context signaling functions (CXCL14/NOS1, PLCβ3-NF-κB, TGF-β) are physiologically relevant outside tumors.","evidence":"","pmids":[],"confidence":"High","gaps":["No structural model of ACKR2 alone or in complex with any ligand","Connection between actin remodeling and vesicular recycling pathways not formally demonstrated","Cancer-associated signaling pathways not validated in non-malignant contexts"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0038024","term_label":"cargo receptor activity","supporting_discovery_ids":[0,2,4,26]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,18,27]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[6,14,20]},{"term_id":"GO:0120274","term_label":"virus coreceptor activity","supporting_discovery_ids":[7]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,5,8,9]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[5,8]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[8]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[5]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,2,4,6,14,15,21,24]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,18,27]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[3,8,9]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[20,22]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[11,25,28]}],"complexes":[],"partners":["ARRB1","RAC1","PAK1","LIMK1","CFL1","RAB11A","CXCL14","CXCL10"],"other_free_text":[]},"mechanistic_narrative":"ACKR2 is an atypical chemokine receptor that scavenges inflammatory CC chemokines (and CXCL10) through constitutive β-arrestin-dependent, clathrin-mediated internalization and lysosomal degradation, without activating G-protein signaling or calcium flux [PMID:9405404, PMID:12594248, PMID:15084596]. Expressed predominantly on lymphatic endothelial cells and hematopoietic precursors, ACKR2 constitutively recycles via Rab4/Rab11 pathways and upregulates its surface abundance in response to chemokine engagement through a β-arrestin1→Rac1→PAK1→LIMK1→cofilin signaling cascade that optimizes scavenging capacity [PMID:18480427, PMID:23633677]. In vivo, ACKR2-mediated chemokine clearance by non-hematopoietic cells is essential for resolution of cutaneous inflammation, prevention of adverse cardiac remodeling after myocardial infarction, regulation of lymphatic vessel density via control of pro-lymphangiogenic macrophage positioning, and modulation of neutrophil release from bone marrow [PMID:15750596, PMID:22796582, PMID:25271254, PMID:29445158]. In cancer contexts, ACKR2 can also serve as a receptor for CXCL14, activating NOS1- or PLCβ3-PKCα-NF-κB-dependent signaling that promotes epithelial-mesenchymal transition and metastasis [PMID:30850359, PMID:37056937]."},"prefetch_data":{"uniprot":{"accession":"O00590","full_name":"Atypical chemokine receptor 2","aliases":["C-C chemokine receptor D6","Chemokine receptor CCR-10","Chemokine receptor CCR-9","Chemokine-binding protein 2","Chemokine-binding protein D6"],"length_aa":384,"mass_kda":43.4,"function":"Atypical chemokine receptor that controls chemokine levels and localization via high-affinity chemokine binding that is uncoupled from classic ligand-driven signal transduction cascades, resulting instead in chemokine sequestration, degradation, or transcytosis (PubMed:18201974, PubMed:20373092, PubMed:23479571). Also known as interceptor (internalizing receptor) or chemokine-scavenging receptor or chemokine decoy receptor (PubMed:18201974, PubMed:20373092, PubMed:23479571). Acts as a receptor for chemokines including CCL2, CCL3, CCL3L1, CCL4, CCL5, CCL7, CCL8, CCL11, CCL13, CCL17, CCL22, CCL23, CCL24, SCYA2/MCP-1, SCY3/MIP-1-alpha, SCYA5/RANTES and SCYA7/MCP-3 (PubMed:18201974, PubMed:20373092, PubMed:23479571). Upon active ligand stimulation, activates a beta-arrestin 1 (ARRB1)-dependent, G protein-independent signaling pathway that results in the phosphorylation of the actin-binding protein cofilin (CFL1) through a RAC1-PAK1-LIMK1 signaling pathway (PubMed:23633677). Activation of this pathway results in up-regulation of ACKR2 from endosomal compartment to cell membrane, increasing its efficiency in chemokine uptake and degradation (PubMed:23633677). By scavenging chemokines in tissues, on the surfaces of lymphatic vessels, and in placenta, plays an essential role in the resolution (termination) of the inflammatory response and in the regulation of adaptive immune responses (PubMed:23479571). Plays a major role in the immune silencing of macrophages during the resolution of inflammation (By similarity). Acts as a regulator of inflammatory leukocyte interactions with lymphatic endothelial cells (LECs) and is required for immature/mature dendritic cells discrimination by LECs (PubMed:23479571)","subcellular_location":"Early endosome; Recycling endosome; Cell membrane","url":"https://www.uniprot.org/uniprotkb/O00590/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ACKR2","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/ACKR2","total_profiled":1310},"omim":[{"mim_id":"602648","title":"ATYPICAL CHEMOKINE RECEPTOR 2; ACKR2","url":"https://www.omim.org/entry/602648"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Vesicles","reliability":"Supported"},{"location":"Cytosol","reliability":"Supported"},{"location":"Nucleoplasm","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"liver","ntpm":8.8},{"tissue":"placenta","ntpm":15.0}],"url":"https://www.proteinatlas.org/search/ACKR2"},"hgnc":{"alias_symbol":["CCR10","D6","CCR9"],"prev_symbol":["CMKBR9","CCBP2"]},"alphafold":{"accession":"O00590","domains":[{"cath_id":"1.20.1070.10","chopping":"58-331","consensus_level":"high","plddt":89.2259,"start":58,"end":331}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O00590","model_url":"https://alphafold.ebi.ac.uk/files/AF-O00590-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O00590-F1-predicted_aligned_error_v6.png","plddt_mean":80.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ACKR2","jax_strain_url":"https://www.jax.org/strain/search?query=ACKR2"},"sequence":{"accession":"O00590","fasta_url":"https://rest.uniprot.org/uniprotkb/O00590.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O00590/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O00590"}},"corpus_meta":[{"pmid":"11821900","id":"PMC_11821900","title":"CCL27-CCR10 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missense mutations for developmental disorders.","date":"2018","source":"Nature genetics","url":"https://pubmed.ncbi.nlm.nih.gov/29892012","citation_count":61,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"18201974","id":"PMC_18201974","title":"Multiple roles for the C-terminal tail of the chemokine scavenger D6.","date":"2008","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/18201974","citation_count":58,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"10725696","id":"PMC_10725696","title":"Cutting edge: identification of the orphan receptor G-protein-coupled receptor 2 as CCR10, a specific receptor for the chemokine ESkine.","date":"2000","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/10725696","citation_count":56,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"16814608","id":"PMC_16814608","title":"Chemokine scavenging by D6: a movable feast?","date":"2006","source":"Trends in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/16814608","citation_count":52,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"23314186","id":"PMC_23314186","title":"Genetic variation associated with circulating monocyte count in the eMERGE Network.","date":"2013","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/23314186","citation_count":51,"is_preprint":false,"source_track":"gene2pubmed"}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":47665,"output_tokens":5343,"usd":0.11157},"stage2":{"model":"claude-opus-4-6","input_tokens":9005,"output_tokens":4247,"usd":0.2268},"total_usd":0.774694,"stage1_batch_id":"msgbatch_01TqNM6p6FsoMBT2jzQTwKBr","stage2_batch_id":"msgbatch_01Ya473eco8sTHbvRymQaU8o","note":"batch pricing = 50% of standard","round2_stage1":{"model":"claude-sonnet-4-6","input_tokens":61478,"output_tokens":9283,"usd":0.161839},"round2_rules_fired":"R2","round2_stage2":{"model":"claude-opus-4-6","input_tokens":13208,"output_tokens":4678,"usd":0.274485}},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1997,\n      \"finding\": \"ACKR2 (D6) is a promiscuous beta-chemokine receptor that binds the majority of beta-chemokine family members but does not flux calcium following ligand binding, indicating it lacks conventional signaling capacity, and is not able to function as a HIV-1 co-receptor.\",\n      \"method\": \"Cloning, radioligand binding assays, calcium flux assays, HIV co-receptor assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — original cloning paper with multiple functional assays establishing ligand binding and lack of signaling\",\n      \"pmids\": [\"9405404\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"ACKR2 (D6) is selectively expressed on lymphatic endothelial cells of afferent lymphatics in human dermis, as well as in mucosal tissues, and not on blood vessel endothelium or peripheral blood cells, positioning it to regulate chemokine-driven leukocyte recirculation through lymphatics.\",\n      \"method\": \"Monoclonal antibody generation, immunohistochemistry, in situ hybridization with lymphatic marker co-staining\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal localization with orthogonal methods (IHC, ISH, co-staining with podoplanin)\",\n      \"pmids\": [\"11238036\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Purified ACKR2 (D6) protein retains full functional ligand binding activity, is N-terminally glycosylated (dispensable for ligand binding), and is constitutively phosphorylated in a ligand-independent manner; >80% of total cellular D6 resides in intracellular vesicular structures.\",\n      \"method\": \"Protein purification from mammalian transfectants, 125I-ligand binding, affinity chromatography, mutational analysis of glycosylation, metabolic labeling for phosphorylation/sulfation, subcellular fractionation\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — biochemical reconstitution with purified protein and mutagenesis\",\n      \"pmids\": [\"14723600\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"ACKR2 (D6) is required for post-inflammatory clearance of beta-chemokines from cutaneous sites; D6-deficient mice develop excess residual chemokines and psoriasis-like inflammatory pathology after phorbol ester-induced inflammation.\",\n      \"method\": \"D6 knockout mouse, phorbol ester-induced skin inflammation model, chemokine measurement, histopathology\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout with defined inflammatory phenotype and chemokine accumulation, replicated in vivo\",\n      \"pmids\": [\"15750596\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"ACKR2 (D6) acts as a decoy and scavenger receptor for inflammatory (but not homeostatic) CC chemokines, constitutively cycling between plasma membrane and endocytic compartments where chemokines are targeted for degradation, in the absence of G-protein signaling.\",\n      \"method\": \"In vitro internalization assays, endocytic pathway analysis, gene-targeted mice, chemokine degradation assays\",\n      \"journal\": \"Cytokine & growth factor reviews\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods including in vitro assays and KO mice establishing scavenging mechanism\",\n      \"pmids\": [\"15996892\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"ACKR2 (D6) suppresses cutaneous tumor development by scavenging proinflammatory CC chemokines; D6-deficient mice show increased susceptibility to chemical carcinogenesis and invasive squamous cell carcinoma, while transgenic D6 expression in keratinocytes confers protection, associated with reduced T cell and mast cell recruitment.\",\n      \"method\": \"D6 knockout mice, D6 transgenic mice, chemical carcinogenesis (DMBA/TPA) protocol, histopathology, flow cytometry\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal KO and transgenic models with mechanistic pathway placement\",\n      \"pmids\": [\"17607362\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"ACKR2 (D6) scavenging activity is regulated by ligand-dependent Rab11-mediated redistribution to the cell membrane: under resting conditions D6 constitutively recycles via Rab4 and Rab11 pathways; ligand engagement triggers dose-dependent, BFA-sensitive and Rab11-dependent D6 upregulation to the plasma membrane, increasing chemokine degradation rate.\",\n      \"method\": \"Fluorescence microscopy, pharmacological inhibitors (wortmannin, brefeldin A), Rab11 dominant-negative constructs, chemokine degradation assays\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mechanistic dissection of receptor trafficking with multiple inhibitors and dominant-negative mutants\",\n      \"pmids\": [\"18480427\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"ACKR2 (D6) on lymphatic endothelial cells contributes to selective presentation of CCR7 ligands by suppressing inflammatory chemokine binding to LEC surfaces and specifically regulates LEC discrimination between mature and immature dendritic cells; LEC D6 expression is induced by IL-6, IFN-γ, and viral IL-6 (KSHV).\",\n      \"method\": \"D6 knockdown and overexpression in LECs, DC adhesion assays, cytokine treatment, in vitro and in vivo D6 upregulation by viral IL-6\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple functional assays (adhesion, knockdown, overexpression) with mechanistic readout\",\n      \"pmids\": [\"23479571\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"ACKR2 (D6) in the non-hematopoietic compartment controls traffic of Ly6C-high monocytes via scavenging CCR2 ligands; D6-deficient mice lacking D6 in non-hematopoietic cells show selective increase in Ly6C-high monocytes with enhanced immunosuppressive activity in a CCR2-dependent manner.\",\n      \"method\": \"Bone marrow chimeras, D6 KO mice, flow cytometry, GVHD model\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — bone marrow chimeras dissect compartment-specific function with epistasis to CCR2\",\n      \"pmids\": [\"22504926\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"ACKR2 (D6) prevents excessive inflammation and adverse ventricular remodeling after myocardial infarction by scavenging CCL2 and CCL3 in the ischemic heart; bone marrow chimeras show the protective effect is mediated by non-hematopoietic D6, and CCR2 deficiency in leukocytes rescues the adverse phenotype of D6-deficient mice.\",\n      \"method\": \"D6 KO mice, myocardial infarction model, bone marrow chimeras, ELISA, MMP activity assays, echocardiography\",\n      \"journal\": \"Arteriosclerosis, thrombosis, and vascular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — bone marrow chimeras with epistasis to CCR2 and multiple mechanistic readouts\",\n      \"pmids\": [\"22796582\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"ACKR2 (D6) controls macrophage efferocytosis and cytokine secretion during resolution of inflammation independently of chemokine scavenging; D6 is expressed on apoptotic neutrophils and D6-deficient apoptotic PMN cells fail to induce immune silencing in macrophages.\",\n      \"method\": \"D6 KO mice, peritonitis resolution model, efferocytosis assays, cytokine measurements, flow cytometry\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO mice with defined cellular phenotype, novel non-scavenging mechanism proposed but single lab\",\n      \"pmids\": [\"22651933\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"ACKR2 (D6) expressed by neutrophils functions cell-autonomously as a migratory rheostat: D6 expressed on neutrophils limits their migrational response to CCR1 ligands (e.g. CCL3) and controls spatial positioning of neutrophils at inflamed sites.\",\n      \"method\": \"D6 KO mice, neutrophil-specific D6 expression, chemotaxis assays, psoriasis and other inflammation models, cell transfer experiments\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cell-autonomous function demonstrated by adoptive transfer and reconstitution experiments\",\n      \"pmids\": [\"23670187\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"ACKR2 and CCR2 reciprocally regulate lymphatic vessel density: ACKR2 scavenges CCL2, limiting pro-lymphangiogenic macrophage proximity to developing lymphatic vessels; ACKR2-deficient mice show increased lymphatic vessel density developmentally established in embryonic skin, while CCR2-deficient mice show reciprocally reduced density.\",\n      \"method\": \"ACKR2 KO and CCR2 KO mice, lymphatic vessel imaging, macrophage depletion, embryonic skin analysis, fluid drainage assays, blood pressure measurement\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal genetic models with mechanistic pathway placement and multiple readouts\",\n      \"pmids\": [\"25271254\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"ERK pathway activation during Kaposi sarcoma progression downregulates ACKR2 (D6) expression, unleashing CC chemokine-mediated macrophage (CCR2+) recruitment with M2-like polarization that supports angiogenesis and tumor growth.\",\n      \"method\": \"KS tumor samples, experimental KS model, B-Raf/ERK inhibitors, CCR2 KO macrophage adoptive transfer, D6-competent tumor model\",\n      \"journal\": \"Cancer immunology research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic link between ERK pathway and D6 established by inhibitors plus adoptive transfer with defined macrophage phenotype\",\n      \"pmids\": [\"24844911\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"ACKR2 controls inflammatory T-cell chemotaxis and positioning within the skin, preventing epidermal influx associated with psoriatic lesion development; localized inflammation and IFN-γ upregulate ACKR2 in remote tissues to restrict spread of psoriasiform inflammation.\",\n      \"method\": \"Imiquimod-induced psoriasiform inflammation model, ACKR2 KO mice, primary human cell cultures, in vitro migration assays, clinical sample analysis\",\n      \"journal\": \"The Journal of investigative dermatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KO mice, human primary cells and clinical samples with mechanistic pathway placement\",\n      \"pmids\": [\"27568525\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"ACKR2 is expressed in the developing mammary gland and regulates branching morphogenesis by scavenging inflammatory CC-chemokines that control pro-lymphangiogenic macrophage dynamics; Ackr2-/- mice display precocious mammary gland development with increased macrophage recruitment and ductal epithelial network density.\",\n      \"method\": \"ACKR2 KO mice, mammary gland wholemount analysis, macrophage quantification, developmental time-course\",\n      \"journal\": \"Development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KO mice with defined developmental phenotype and macrophage recruitment mechanism\",\n      \"pmids\": [\"27888192\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"ACKR2 is expressed in hematopoietic precursors and is downregulated during myeloid differentiation; genetic inactivation of ACKR2 results in increased inflammatory chemokine receptor levels on neutrophils, their release from bone marrow, and enhanced anti-metastatic neutrophil activity.\",\n      \"method\": \"ACKR2 KO mice, NeuT-driven mammary carcinoma model, 4T1 orthotopic transplant, B16F10 IV injection, bone marrow analysis, flow cytometry\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple in vivo tumor models with mechanistic dissection of myeloid differentiation checkpoint\",\n      \"pmids\": [\"29445158\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"ACKR2 expressed in pulmonary resident (non-hematopoietic) cells drives pulmonary fibrosis by controlling CC chemokine levels that regulate influx of CCR2+ and CCR5+ IFNγ-producing γδT cells; ACKR2-/- mice show reduced fibrosis with early increased CCL5/CCL12/CCL17/IFNγ and more IFNγ-producing γδT cells that provide protection.\",\n      \"method\": \"ACKR2 KO mice, bleomycin model, bone marrow chimeras, CCR2 KO, CCR5 KO, γδT cell depletion, chemokine profiling\",\n      \"journal\": \"American journal of physiology. Lung cellular and molecular physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — bone marrow chimeras dissect cellular compartment, multiple KO models with epistasis\",\n      \"pmids\": [\"29469612\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"ACKR2 mediates CXCL14-stimulated epithelial-to-mesenchymal transition (EMT), migration, and invasion in breast cancer cells via induction of NOS1; loss-of-function of ACKR2 attenuates CXCL14-induced pro-EMT and migratory capacity, identifying ACKR2 as a receptor for CXCL14.\",\n      \"method\": \"ACKR2 loss-of-function (siRNA/shRNA), CXCL14 fibroblast co-culture, EMT marker analysis, invasion assays, xenograft model, NOS1 inhibition\",\n      \"journal\": \"Clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — loss-of-function with molecular endpoints identifying novel ligand, single lab\",\n      \"pmids\": [\"30850359\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ACKR2 binds the CXC chemokine CXCL10 as a new strong agonist ligand, internalizes it and reduces its extracellular availability; DPP4/CD26 N-terminal processing of CXCL10 drastically reduces its activity at ACKR2, indicating a different receptor binding pocket occupancy compared to CC chemokines.\",\n      \"method\": \"NanoBiT and NanoBRET β-arrestin recruitment assays, CXCL10 internalization assays, DPP4 processing experiments\",\n      \"journal\": \"Cancers\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — sensitive functional assays with biochemical dissection of ligand processing, multiple orthogonal methods\",\n      \"pmids\": [\"33801414\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"ACKR2 mediates CXCL14-induced lung cancer cell motility and metastasis via activation of PLCβ3, PKCα, and c-Src signaling pathway leading to NF-κB transcription and EMT; ACKR2 knockdown abolishes CXCL14-induced cancer cell motility.\",\n      \"method\": \"ACKR2 knockdown (siRNA), migration/wound-healing assays, luciferase reporter for NF-κB, orthotopic lung cancer model, Western blot for signaling intermediates\",\n      \"journal\": \"International journal of biological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — KD with signaling pathway dissection, single lab, mechanistic pathway defined\",\n      \"pmids\": [\"37056937\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ACKR2 expression is upregulated in CCRT-resistant tumor cells in response to chemoradiotherapy and CC chemokines; ACKR2+ tumor cells produce TGF-β that drives CD8+ T cell senescence, compromising antitumor immunity and contributing to cervical cancer recurrence.\",\n      \"method\": \"Single-cell RNA sequencing, mechanistic in vitro/in vivo validation, TGF-β pathway analysis, retrospective clinical analysis\",\n      \"journal\": \"Cell reports. Medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — scRNA-seq plus mechanistic follow-up showing TGF-β as effector, single study\",\n      \"pmids\": [\"38723624\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"ACKR2 (D6) contributes to the development of colitis by regulating IL-17A secretion by γδ T cells in the inflamed colon; D6-deficient mice show reduced susceptibility to DSS colitis with enhanced IL-17A-secreting γδ T cells in the lamina propria, and IL-17A neutralization worsens colitis only in D6-deficient mice.\",\n      \"method\": \"D6 KO mice, DSS colitis model, cytokine profiling, flow cytometry, colon explant cultures\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO mice with mechanistic epistasis to IL-17A and γδ T cells, unexpected (pro-inflammatory) role for D6\",\n      \"pmids\": [\"19342683\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ACKR2 (D6) is an atypical chemokine receptor that lacks conventional G-protein signaling but constitutively cycles through Rab4/Rab11 endocytic compartments to scavenge and degrade inflammatory CC chemokines (and also CXCL10); it is expressed predominantly on lymphatic endothelial cells, hematopoietic precursors, and apoptotic neutrophils, where it regulates inflammatory resolution, lymphatic vessel density, macrophage and neutrophil trafficking, dendritic cell–LEC discrimination, mammary gland branching morphogenesis, and pulmonary fibrosis by controlling the availability of inflammatory CC chemokines, and additionally mediates CXCL14-driven EMT and metastasis via NOS1 and PLCβ3/PKCα/NF-κB signaling in cancer cells.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll systematically classify each paper, then extract mechanistic discoveries only from KEPT papers about ACKR2 (also known as D6/CCBP2).\n\n**Classification Summary:**\n- Papers about ACKR2/D6: KEEP (papers [4], [7], [11], [15], [20], [24], [27], [29], [33], [35], [37], [39], [45], [52], [57], [59], [60], [61], [65], [67], [69], [72], [74], [75], [77], [80], [85], [88], [89], [90], [94], and curated [10], [12], [15], [16], [17], [20], [24], [25], [27], [29])\n- Papers about CCR9, CCR10, or other receptors: EXCLUDE (alias collision)\n- Arabidopsis D6PK, PP2C.D6: EXCLUDE (symbol collision, plant genes)\n- NMR solvent paper [43]: EXCLUDE (unrelated)\n- Generic genomics/interactome papers with no ACKR2 mechanistic content: EXCLUDE\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1997,\n      \"finding\": \"ACKR2 (D6) was cloned as a novel promiscuous beta-chemokine receptor that binds most inflammatory CC chemokines (MIP-1α, MIP-1β, RANTES, JE, MCP-3) but not alpha-chemokines or C/CXXXC chemokines, and unlike conventional chemokine receptors, failed to elicit calcium flux upon ligand binding in transfected cells, suggesting it is not a classical signaling receptor.\",\n      \"method\": \"cDNA cloning, radioligand binding assays (125I-MIP-1α competition), calcium flux assays in HEK293 and CHO transfectants\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — original cloning with multiple binding and functional assays; replicated across human and mouse paralogs in same year\",\n      \"pmids\": [\"9405404\", \"9139699\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"ACKR2 (D6) is selectively expressed on lymphatic endothelial cells (LECs) lining afferent lymphatics in human dermis, intestinal mucosa, and lymph node sinuses, but not on blood vessel endothelium or peripheral blood cells, establishing lymphatic endothelium as the primary anatomical site for D6 function.\",\n      \"method\": \"Monoclonal antibody generation, immunohistochemistry on serial human skin sections with lymphatic marker podoplanin, in situ hybridization\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal IHC and ISH with co-staining lymphatic marker; foundational localization paper with >230 citations\",\n      \"pmids\": [\"11238036\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Engagement of ACKR2 (D6) by inflammatory CC chemokines elicits no calcium response or chemotaxis in transfected cells or lymphatic endothelium, but results in efficient ligand internalization and degradation. D6 does not mediate transcytosis of chemokines in either direction. This established D6 as a chemokine-scavenging decoy receptor acting as a 'gatekeeper' on lymphatic endothelium.\",\n      \"method\": \"D6 transfectants in multiple cell types; calcium flux assays; chemotaxis assays; internalization/degradation assays; lymphatic endothelial cell experiments\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal functional assays in multiple cell types including native lymphatic endothelium; replicated and widely cited\",\n      \"pmids\": [\"12594248\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"ACKR2 (D6) constitutively internalizes via clathrin-coated pits through a β-arrestin-dependent mechanism. D6 constitutively associates with β-arrestin, and an acidic region (not phosphorylation sites) in the cytoplasmic tail is critical for this interaction and subsequent internalization. Neither native D6 nor β-arrestin-uncoupled mutants activate G-protein-mediated signaling, confirming D6 as a non-signaling decoy receptor whose scavenging depends on constitutive β-arrestin-dependent endocytosis.\",\n      \"method\": \"β-arrestin co-immunoprecipitation, clathrin inhibition experiments, mutagenesis of cytoplasmic tail (acidic region vs. phosphorylation sites), calcium flux and chemotaxis assays in transfectants\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with mutagenesis and multiple orthogonal assays identifying specific molecular determinant\",\n      \"pmids\": [\"15084596\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"ACKR2 (D6) efficiently binds and scavenges most inflammatory CC chemokines (CCR1–CCR5 agonists) but not homeostatic CC chemokines (CCR6/CCR7 agonists). CCR4 agonists CCL17 and CCL22 are recognized by D6 with high affinity and scavenged, reducing their chemotactic activity. CD26-processed truncated forms of CCL22 (lacking N-terminal residues) are not recognized by D6, demonstrating that N-terminal integrity is required for D6 binding.\",\n      \"method\": \"Radioligand binding and competition assays on D6 transfectants; scavenging/degradation assays; CCR4 transfectant chemotaxis; CD26 processing experiments\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — systematic ligand profiling with functional scavenging readouts and natural processing experiments\",\n      \"pmids\": [\"15067078\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Milligram quantities of purified ACKR2 (D6) from mammalian transfectants retain full functional activity (displaceable 125I-MIP-1β binding, MIP-1α affinity column binding). Biochemical characterization revealed D6 is N-glycosylated at the N-terminus (dispensable for ligand binding), sulphated, and constitutively phosphorylated (not enhanced by ligand). Over 80% of cellular D6 resides in intracellular vesicular compartments.\",\n      \"method\": \"Protein purification from transfected mammalian cells; radioligand binding; affinity chromatography; N-terminal mutagenesis; metabolic labeling for sulfation and phosphorylation; subcellular fractionation\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — biochemical reconstitution with mutagenesis and multiple post-translational modification analyses\",\n      \"pmids\": [\"14723600\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"ACKR2 (D6)-deficient mice fail to resolve cutaneous inflammation after phorbol ester treatment, accumulating excess residual beta-chemokines that drive an inflammatory pathology resembling psoriasis. This demonstrated that D6 is required for post-inflammatory clearance of beta-chemokines from cutaneous sites in vivo.\",\n      \"method\": \"D6 knockout mice; phorbol ester-induced cutaneous inflammation model; chemokine measurement; histopathology\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined phenotype and molecular mechanism (chemokine accumulation); widely replicated across multiple models\",\n      \"pmids\": [\"15750596\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"ACKR2 (D6) can function as a coreceptor for primary dual-tropic HIV-1 and HIV-2 isolates on astrocytes. RNA interference knockdown of D6 in primary astrocytes inhibited infection by D6-tropic isolates, establishing a cell-autonomous HIV coreceptor function for D6 in brain cells.\",\n      \"method\": \"HIV-1/HIV-2 infection assays in D6-expressing cell lines and primary astrocytes; siRNA knockdown of D6; chimeric gp120 constructs\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA knockdown with viral infection phenotype; single lab\",\n      \"pmids\": [\"16014924\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"D6 scavenging activity is regulated by unique vesicular trafficking: under resting conditions D6 constitutively recycles through Rab4- and Rab11-dependent pathways, maintaining low surface expression. Chemokine engagement induces dose-dependent Rab11-dependent redistribution of D6 to the plasma membrane, increasing chemokine degradation rate. This ligand-concentration-dependent surface up-regulation (not transcriptional regulation) is the mechanism by which D6 optimizes scavenging activity.\",\n      \"method\": \"Wortmannin and brefeldin A pharmacological inhibition; Rab4/Rab11 dominant-negative constructs; surface expression quantification; chemokine degradation assays\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple pharmacological and genetic tools identifying specific Rab GTPases; mechanistically dissected constitutive vs. ligand-induced trafficking\",\n      \"pmids\": [\"18480427\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The conserved 58-amino acid C-terminal tail of D6 controls constitutive phosphorylation, high protein stability, and intracellular trafficking itinerary, and drives β-arrestin to membranes near the cell surface. A serine cluster in this region is critical for these properties. Deletion of the last 44–58 amino acids abolishes progressive scavenging because ligand engagement of the truncated receptor inhibits subsequent chemokine uptake, revealing the C-terminus is dispensable for initial internalization but indispensable for sustained scavenging.\",\n      \"method\": \"C-terminal deletion and serine cluster mutagenesis in HEK293 cells; GFP-β-arrestin imaging; phosphorylation assays; CCL3 scavenging assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis with multiple functional readouts identifying specific structural determinant for scavenging\",\n      \"pmids\": [\"18201974\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Functional D6 is expressed by murine and human hematopoietic cells (highest in B cells and dendritic cells), and this expression is dynamically regulated: LPS down-regulates D6 in myeloid cells, TGF-β up-regulates it, and T-cell activation markedly up-regulates D6 mRNA. D6 expression in myeloid progenitors, mast cells, megakaryocytes, and DCs is dependent on the transcription factor GATA1. Hematopoietic D6 mediates chemokine uptake in a D6-dependent manner.\",\n      \"method\": \"Flow cytometry; RT-PCR; competition chemokine uptake assays in D6-null vs. wild-type leukocytes; GATA1 knockout/knockdown experiments; LPS/TGF-β/anti-CD3 stimulation\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods identifying GATA1 as transcriptional regulator; D6-null comparator cells validate D6-dependence of chemokine uptake\",\n      \"pmids\": [\"18714007\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"ACKR2 (D6)-deficient mice show increased susceptibility to chemically induced cutaneous tumor development. D6 deletion alone is sufficient to make resistant mouse strains susceptible to invasive squamous cell carcinoma. Conversely, transgenic D6 expression in keratinocytes dampens cutaneous inflammation and protects from tumor formation. Tumor susceptibility correlates with enhanced T cell and mast cell recruitment, linking D6-mediated chemokine scavenging to tumor suppression by limiting pro-tumorigenic inflammation.\",\n      \"method\": \"D6 knockout mice; keratinocyte-specific D6 transgenic mice; chemical carcinogenesis (DMBA/TPA); immune cell quantification by histology and flow cytometry\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — bidirectional genetic evidence (KO and transgenic) with defined cellular mediators\",\n      \"pmids\": [\"17607362\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"ACKR2 (D6) expressed at the maternal-fetal interface (trophoblasts/placenta) plays a role in regulating chemokine levels during implantation, contributing to the local inflammatory milieu required for successful embryonic implantation and fetal tolerance.\",\n      \"method\": \"Expression analysis in placental/trophoblast tissue; D6-deficient mouse pregnancy models reviewed\",\n      \"journal\": \"Placenta\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — review/expression data; mechanistic evidence is indirect\",\n      \"pmids\": [\"18676013\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"ACKR2 (D6) contributes to the development of dextran sodium sulfate-induced colitis: D6-deficient mice show reduced susceptibility to colitis and reduced clinical symptoms. Mechanistically, D6 deletion did not alter CC chemokine levels or leukocyte balance in the colon, but late in colitis D6-deficient colons showed enhanced IL-17A production by γδ T cells. Antibody neutralization of IL-17A worsened colitis specifically in D6-deficient mice, revealing that D6 regulates colitis by modulating IL-17A secretion by lamina propria γδ T cells.\",\n      \"method\": \"DSS colitis model in D6-deficient mice; cytokine measurements; leukocyte subset quantification; anti-IL-17A neutralizing antibody treatment\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO with antibody neutralization epistasis; unexpected pro-colitic role of D6 via γδ T cell IL-17A regulation\",\n      \"pmids\": [\"19342683\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"ACKR2 (D6) prevents adverse ventricular remodeling after myocardial infarction by scavenging inflammatory CC chemokines CCL2 and CCL3 in ischemic heart. D6-deficient mice show increased pathogenic neutrophil and Ly6Chi monocyte infiltration, elevated MMP-9/MMP-2 activity, cardiac rupture, and left ventricular dilation. Bone marrow chimera experiments demonstrated that leukocyte-borne D6 plays no role; cardiac resident (non-hematopoietic) D6 is responsible. CCR2 deficiency in leukocytes rescues the adverse phenotype of D6-deficient mice.\",\n      \"method\": \"D6 knockout mice; myocardial infarction model; bone marrow chimeras; CCR2-deficient bone marrow transfer; cytokine/chemokine ELISA; MMP activity assays; echocardiography\",\n      \"journal\": \"Arteriosclerosis, thrombosis, and vascular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — bone marrow chimera epistasis precisely locating non-hematopoietic D6 function; CCR2-KO rescue confirms mechanistic pathway\",\n      \"pmids\": [\"22796582\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"ACKR2 (D6) controls the traffic and immunosuppressive activity of Ly6Chi monocytes. Mice lacking D6 in the non-hematopoietic compartment have selectively increased circulating Ly6Chi monocytes. Under inflammation, these accumulate in secondary lymphoid organs in a CCR2-dependent manner. D6-deficient Ly6Chi monocytes have enhanced immunosuppressive activity, inhibiting adaptive immune responses and partially protecting against graft-versus-host disease.\",\n      \"method\": \"D6 knockout and bone marrow chimera mice; flow cytometry; GVHD model; T-cell suppression assays; CCR2-dependent accumulation experiments\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — non-hematopoietic compartment-specific genetic dissection with multiple functional readouts\",\n      \"pmids\": [\"22504926\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"ACKR2 (D6) controls macrophage efferocytosis and cytokine secretion during inflammation resolution in a chemokine scavenging-independent manner. D6-deficient mice show increased macrophage numbers and enhanced efferocytosis of apoptotic neutrophils in vivo. D6 is expressed on apoptotic neutrophils, and D6-deficient apoptotic neutrophils are less effective at inducing immune silencing (reduced TNF-α, IL-1β, CCL5 suppression) in macrophages, identifying a scavenging-independent role for neutrophil-expressed D6 in shaping the resolution of inflammation.\",\n      \"method\": \"Zymosan A peritonitis model; D6 knockout mice; in vivo efferocytosis quantification; ex vivo macrophage-neutrophil co-incubation cytokine assays; flow cytometry of human and rodent apoptotic neutrophils\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo KO with ex vivo mechanistic follow-up; novel scavenging-independent function identified\",\n      \"pmids\": [\"22651933\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"ACKR2 (D6) expressed on lymphatic endothelial cells (LECs) contributes to selective CCR7 ligand presentation by suppressing inflammatory chemokine binding to LEC surfaces. D6 overexpression reduces immature dendritic cell (DC) adhesion to LECs, while D6 knockdown increases iDC adhesion and displaces mature DCs. LEC D6 expression is induced by IL-6 and IFN-γ, and by Kaposi sarcoma herpesvirus vIL-6. D6 is therefore an essential regulator of inflammatory leukocyte-LEC interactions and immature/mature DC discrimination.\",\n      \"method\": \"D6 overexpression and siRNA knockdown in LECs; DC adhesion assays; cytokine stimulation experiments; in vivo vIL-6 expression; KS/PEL cell line expression analysis\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — bidirectional genetic manipulation (OE and KD) with defined functional readout (DC discrimination); multiple inducers identified\",\n      \"pmids\": [\"23479571\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"ACKR2 (D6) engagement by chemokine ligands activates a β-arrestin1-dependent, G protein-independent signaling pathway leading to phosphorylation of the actin-binding protein cofilin through the Rac1-PAK1-LIMK1 cascade. This signaling pathway is required for increased D6 surface abundance and for its chemokine-scavenging activity, demonstrating that D6 is not truly 'silent' but rather a signaling receptor using a distinct non-G protein pathway to regulate its own scavenging function.\",\n      \"method\": \"β-arrestin1 co-IP; Rac1/PAK1/LIMK1 pathway inhibitors and dominant-negative constructs; cofilin phosphorylation assays; D6 surface expression quantification; scavenging assays\",\n      \"journal\": \"Science signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — pathway dissection with multiple genetic and pharmacological tools; identifies specific signaling cascade required for scavenging\",\n      \"pmids\": [\"23633677\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"ACKR2 (D6) expression in Kaposi sarcoma is inversely correlated with tumor aggressiveness and macrophage infiltration. In a KS experimental model with B-Raf V600E mutation, inhibition of B-Raf or the downstream ERK pathway induced D6 expression. In progressing human KS tumors, ERK activation correlates with reduced D6 levels. D6-competent tumors are promoted by adoptive transfer of wild-type but not CCR2-deficient macrophages, revealing that B-Raf-ERK pathway-driven downregulation of D6 unleashes CCL2-mediated pro-angiogenic macrophage recruitment.\",\n      \"method\": \"Human KS tumor analysis; B-Raf inhibitor treatment; ERK inhibitor treatment; D6 expression quantification; macrophage adoptive transfer (WT vs. CCR2-KO); tumor growth assays\",\n      \"journal\": \"Cancer immunology research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — bidirectional pharmacological and adoptive transfer epistasis defining B-Raf-ERK-D6 axis\",\n      \"pmids\": [\"24844911\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"ACKR2-deficient mice display increased lymphatic vessel density in multiple tissues under resting and regenerating conditions, associated with enhanced fluid drainage and a hypotensive phenotype. This phenotype is developmentally established. Conversely, CCR2-deficient mice show reduced lymphatic vessel density. Increased proximity of pro-lymphangiogenic macrophages to developing lymphatic vessel surfaces in ACKR2-deficient mice (and reduced proximity in CCR2-deficient mice) reveals that ACKR2 and CCR2 reciprocally regulate vessel density by controlling pro-lymphangiogenic macrophage recruitment.\",\n      \"method\": \"ACKR2-KO and CCR2-KO mice; lymphatic vessel density quantification across tissues; tissue fluid drainage measurement; blood pressure measurement; embryonic skin analysis; macrophage proximity quantification\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — bidirectional genetic evidence (two receptor KOs with reciprocal phenotypes) with mechanistic cellular explanation\",\n      \"pmids\": [\"25271254\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"ACKR2 limits the spread of psoriasiform inflammation from primary lesions to remote skin sites. Localized inflammation and IFN-γ up-regulate ACKR2 in remote tissues, protecting them from inflammatory spread. ACKR2 controls inflammatory T-cell chemotaxis and positioning within the skin, preventing epidermal influx associated with lesion development.\",\n      \"method\": \"Imiquimod-induced psoriasiform inflammation model; clinical samples; primary human cell cultures; in vitro migration assays; ACKR2 expression quantification in remote vs. lesional skin; IFN-γ stimulation\",\n      \"journal\": \"The Journal of investigative dermatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — combination of in vivo mouse model, human samples, and in vitro mechanistic assays with IFN-γ identified as upstream regulator\",\n      \"pmids\": [\"27568525\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"ACKR2 controls branching morphogenesis in the postnatal mammary gland. ACKR2 is differentially expressed during mammary gland development; Ackr2-/- mice display precocious mammary gland development with increased macrophage recruitment and increased density of the ductal epithelial network.\",\n      \"method\": \"ACKR2 knockout mice; mammary gland whole mount analysis; macrophage quantification by immunohistochemistry; ductal network density measurement at multiple developmental time points\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO with defined developmental phenotype; macrophage recruitment identified as mechanism\",\n      \"pmids\": [\"27888192\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"ACKR2 is expressed in hematopoietic precursors and downregulated during myeloid differentiation. Genetic inactivation of ACKR2 results in increased inflammatory chemokine receptor levels in precursors and enhanced release of neutrophils from bone marrow with increased anti-metastatic activity. In NeuT-driven mammary carcinogenesis, ACKR2 deficiency increases primary tumor growth but protects against metastasis via neutrophil-mediated anti-metastatic activity.\",\n      \"method\": \"ACKR2 knockout mice; flow cytometry of bone marrow precursors; NeuT transgenic mammary carcinoma model; 4T1 orthotopic and B16F10 i.v. metastasis models; chemokine receptor expression analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple in vivo tumor models with KO mice; identifies ACKR2 as checkpoint of myeloid differentiation and neutrophil release\",\n      \"pmids\": [\"29445158\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"ACKR2 expressed in pulmonary resident (non-hematopoietic) cells drives pulmonary fibrosis by tuning the influx of CCR2+ and CCR5+ IFNγ-producing γδT cells. ACKR2-/- mice show reduced lethality and lung fibrosis in a bleomycin model, with early increased CCL5, CCL12, CCL17, IFNγ, and increased CCR2+/CCR5+ γδT cells in airways counterbalanced by reduced Th17 influx. Depletion of γδT cells reverses the protective phenotype of ACKR2-/- mice.\",\n      \"method\": \"Bleomycin fibrosis model; ACKR2-KO mice; bone marrow chimeras; CCR2-KO and CCR5-KO mice; antibody-mediated γδT cell depletion; cytokine/chemokine profiling; leukocyte subset analysis\",\n      \"journal\": \"American journal of physiology. Lung cellular and molecular physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — bone marrow chimeras localizing function to non-hematopoietic compartment; multiple KO strains and cell depletion defining CCR2+/CCR5+ γδT cell mechanism\",\n      \"pmids\": [\"29469612\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"ACKR2 mediates pro-EMT and migratory responses stimulated by the orphan chemokine CXCL14 in breast cancer cells. Loss-of-function experiments identified ACKR2 as the receptor through which fibroblast-derived CXCL14 stimulates breast cancer EMT, migration, invasion, and lung colonization. CXCL14-induced NOS1 is downstream of ACKR2 and required for the pro-EMT effects, defining an autocrine CXCL14/ACKR2/NOS1 pathway.\",\n      \"method\": \"siRNA/shRNA loss-of-function for ACKR2; in vitro EMT, migration, invasion assays; xenograft model with CXCL14-overexpressing fibroblasts; tail-vein metastasis assay; NOS1 inhibition\",\n      \"journal\": \"Clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function with multiple in vitro and in vivo endpoints; identifies ACKR2 as novel CXCL14 receptor in cancer context\",\n      \"pmids\": [\"30850359\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ACKR2 (D6) binds and internalizes the CXC chemokine CXCL10, identifying the first non-CC chemokine agonist for ACKR2. β-arrestin recruitment assays revealed CXCL10 as a strong agonist for ACKR2, and ACKR2 reduced extracellular CXCL10 availability. DPP4/CD26 N-terminal processing of CXCL10 drastically reduced its activity at ACKR2, unlike CC chemokines, pointing to different receptor binding pocket occupancy by CC vs. CXC chemokines.\",\n      \"method\": \"NanoBiT and NanoBRET β-arrestin recruitment assays; ACKR2 internalization assays; DPP4 processing of CXCL10; competitive binding\",\n      \"journal\": \"Cancers\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — highly sensitive β-arrestin assays with multiple orthogonal readouts; single lab but rigorous methodology identifying novel ligand class\",\n      \"pmids\": [\"33801414\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"ACKR2 mediates CXCL14-promoted lung cancer metastasis via a PLCβ3-PKCα-c-Src-NF-κB signaling cascade leading to EMT and increased cell motility. ACKR2 knockdown abolished CXCL14-induced cancer cell motility in vitro and in an orthotopic model. This identifies a specific intracellular signaling pathway downstream of ACKR2 in cancer cells distinct from its classical scavenging function.\",\n      \"method\": \"ACKR2 knockdown (siRNA); migration and wound healing assays; luciferase reporter assay for NF-κB; Western blot for PLCβ3/PKCα/c-Src phosphorylation; orthotopic lung cancer metastasis model; TCGA/GEO dataset analysis for expression correlation\",\n      \"journal\": \"International journal of biological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function with pathway inhibitor cascade and in vivo validation; single lab\",\n      \"pmids\": [\"37056937\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ACKR2+ chemoradiotherapy (CCRT)-resistant cervical cancer tumor cells drive CD8+ T cell senescence. Mechanistically, ACKR2 expression is upregulated by CCRT and by ligation of CC chemokines from activated myeloid and T cells; ACKR2+ tumor cells then produce TGF-β which drives CD8+ T cell senescence, compromising antitumor immunity and promoting tumor recurrence.\",\n      \"method\": \"Single-cell RNA sequencing of human cervical cancer tissues before/after CCRT; in vitro co-culture experiments; TGF-β blocking; retrospective clinical analysis\",\n      \"journal\": \"Cell reports. Medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — scRNA-seq with mechanistic in vitro follow-up; TGF-β identified as effector mechanism downstream of ACKR2\",\n      \"pmids\": [\"38723624\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The MIP-1α isoform LD78β (MIP-1αP) has ~15-20-fold enhanced binding affinity for D6 (ACKR2) compared to LD78α, attributable to a proline residue at position 2. This demonstrated that N-terminal residues of CC chemokines critically determine binding affinity at ACKR2.\",\n      \"method\": \"Radioligand binding competition assays on D6-expressing transfectants; proline-2 mutagenesis; CCR5 and D6 affinity comparison\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis identifying specific structural determinant for binding affinity\",\n      \"pmids\": [\"10364178\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"D6 (ACKR2) expression is markedly elevated in 'uninvolved' psoriatic skin (epidermis and lymphatic endothelium) where inflammatory chemokines are elevated but plaques do not form, suggesting D6 acts as a suppressor of lesion development. D6 expression drops in perilesional and lesional skin coincident with plaque development. Trauma reduces D6 expression in uninvolved skin, consistent with trauma-mediated reduction in D6 triggering the Koebner phenomenon. D6 is also elevated in peripheral blood leukocytes of psoriatic patients.\",\n      \"method\": \"Immunohistochemistry of human psoriatic skin biopsies (uninvolved, perilesional, lesional); mRNA quantification; D6 measurement in peripheral blood leukocytes\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — expression analysis in human tissue with mechanistic inference; supported by prior D6 transgenic mouse data from same lab\",\n      \"pmids\": [\"22867710\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ACKR2 (D6) is an atypical chemokine receptor expressed predominantly on lymphatic endothelial cells and hematopoietic precursors that scavenges most inflammatory CC chemokines (and CXCL10) through constitutive β-arrestin-dependent, clathrin-mediated internalization and lysosomal degradation without G-protein signaling; chemokine engagement activates a β-arrestin1→Rac1→PAK1→LIMK1→cofilin signaling cascade that drives Rab11-dependent receptor redistribution to the plasma membrane to enhance scavenging capacity, while its C-terminal serine cluster and non-hematopoietic expression govern in vivo control of cutaneous inflammation resolution, lymphatic vessel density (via CCL2-driven pro-lymphangiogenic macrophage recruitment), pulmonary fibrosis (via CCR2+/CCR5+ IFNγ+ γδT cells), mammary gland branching morphogenesis, and neutrophil release from bone marrow, with additional cancer-context roles including CXCL14-mediated EMT via NOS1 or PLCβ3-PKCα-NF-κB pathways and TGF-β-driven CD8+ T cell senescence.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"ACKR2 (D6) is an atypical chemokine receptor that functions as a constitutive scavenger of inflammatory CC chemokines, thereby controlling leukocyte trafficking, inflammatory resolution, lymphatic vessel density, and tissue morphogenesis. ACKR2 binds most inflammatory CC chemokines (and CXCL10) without eliciting G-protein signaling or calcium flux; instead, it constitutively cycles between intracellular Rab4/Rab11 endocytic compartments and the plasma membrane, internalizing and targeting chemokines for degradation, with ligand engagement further driving Rab11-dependent surface upregulation to increase scavenging capacity [PMID:9405404, PMID:18480427, PMID:33801414]. Expressed predominantly on lymphatic endothelial cells, hematopoietic precursors, and apoptotic neutrophils, ACKR2 limits CC chemokine availability at tissue sites to restrain monocyte/macrophage and T-cell infiltration, thereby protecting against psoriasiform skin inflammation, chemical carcinogenesis, adverse cardiac remodeling after myocardial infarction, and pulmonary fibrosis, while also regulating developmental lymphatic vessel density and mammary gland branching morphogenesis [PMID:15750596, PMID:17607362, PMID:22796582, PMID:29469612, PMID:25271254, PMID:27888192]. In cancer cells, ACKR2 also serves as a receptor for CXCL14, transducing signals through NOS1 and PLCβ3/PKCα/NF-κB to promote epithelial-to-mesenchymal transition and metastasis [PMID:30850359, PMID:37056937].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"The initial cloning of ACKR2 (D6) established that it is a promiscuous CC chemokine-binding receptor that lacks conventional G-protein signaling, distinguishing it from classical chemokine receptors and raising the question of its biological function.\",\n      \"evidence\": \"Cloning with radioligand binding and calcium flux assays in transfected cells\",\n      \"pmids\": [\"9405404\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No biological function or in vivo role demonstrated\", \"Mechanism of ligand engagement without signaling unknown\", \"Endogenous expression pattern not defined\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Localization of ACKR2 to lymphatic endothelial cells of afferent lymphatics (but not blood vessels) provided the first anatomical context for a chemokine-scavenging function at the lymphatic interface.\",\n      \"evidence\": \"Monoclonal antibody-based immunohistochemistry and in situ hybridization with lymphatic marker co-staining in human dermis and mucosal tissues\",\n      \"pmids\": [\"11238036\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Expression in non-endothelial cell types not yet surveyed\", \"Functional consequence of LEC expression not tested\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Biochemical characterization revealed that ACKR2 is constitutively phosphorylated and predominantly intracellular (>80% in vesicles), indicating a pre-activated trafficking state consistent with a scavenging receptor rather than a classical signaling receptor.\",\n      \"evidence\": \"Purified protein radioligand binding, metabolic labeling for phosphorylation, subcellular fractionation\",\n      \"pmids\": [\"14723600\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of kinases responsible for constitutive phosphorylation unknown\", \"Endocytic pathway not yet defined\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Knockout mouse studies established that ACKR2 is required for in vivo clearance of inflammatory CC chemokines from tissues, with D6-deficient mice developing psoriasis-like pathology due to chemokine accumulation — the first genetic proof of its scavenging function.\",\n      \"evidence\": \"D6 knockout mice, phorbol ester-induced skin inflammation, chemokine ELISA, histopathology\",\n      \"pmids\": [\"15750596\", \"15996892\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cell type-specific contributions not dissected\", \"Molecular pathway for chemokine degradation after internalization not defined\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Reciprocal KO and transgenic models demonstrated that ACKR2 suppresses inflammation-driven cutaneous tumorigenesis by limiting T cell and mast cell recruitment, extending its role from inflammatory resolution to cancer protection.\",\n      \"evidence\": \"D6 KO and D6-transgenic mice in DMBA/TPA chemical carcinogenesis, histopathology and flow cytometry\",\n      \"pmids\": [\"17607362\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct scavenging versus indirect tumor-suppressive mechanisms not separated\", \"Applicability to non-skin cancers not tested\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Mechanistic dissection of ACKR2 trafficking revealed that constitutive recycling occurs via Rab4/Rab11 endocytic compartments, and that ligand engagement triggers Rab11-dependent mobilization of intracellular receptor pools to the surface, amplifying scavenging capacity — resolving how the receptor sustains chemokine clearance.\",\n      \"evidence\": \"Fluorescence microscopy, brefeldin A and wortmannin inhibitors, Rab11 dominant-negative mutants, chemokine degradation assays\",\n      \"pmids\": [\"18480427\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"β-arrestin versus other adaptor involvement in internalization not fully resolved\", \"Post-endocytic degradation pathway (lysosomal versus proteasomal) not specified\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"The unexpected finding that D6-deficient mice are protected from colitis — linked to enhanced γδ T cell IL-17A production — revealed that ACKR2's scavenging can be context-dependently pro-inflammatory, challenging the simple anti-inflammatory paradigm.\",\n      \"evidence\": \"D6 KO mice, DSS colitis model, cytokine profiling, IL-17A neutralization\",\n      \"pmids\": [\"19342683\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether the pro-inflammatory role is unique to the gut or generalizable is unclear\", \"Direct molecular link between ACKR2 and γδ T cell IL-17A secretion not defined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Bone marrow chimera studies across multiple disease models (myocardial infarction, GVHD, peritonitis resolution) established that ACKR2 in non-hematopoietic compartments controls monocyte trafficking via CCR2-ligand scavenging, while ACKR2 on apoptotic neutrophils separately regulates macrophage efferocytosis — revealing compartment-specific and scavenging-independent functions.\",\n      \"evidence\": \"Bone marrow chimeras with D6 KO and CCR2 KO epistasis, efferocytosis assays, MI model, GVHD model, peritonitis resolution\",\n      \"pmids\": [\"22504926\", \"22796582\", \"22651933\", \"23479571\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of scavenging-independent efferocytosis function unknown\", \"Whether ACKR2 on apoptotic neutrophils engages a distinct ligand is untested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Demonstration that neutrophil-expressed ACKR2 cell-autonomously limits CCR1-mediated chemotaxis established ACKR2 as a migratory rheostat on leukocytes themselves, not only on stromal barrier cells.\",\n      \"evidence\": \"D6 KO mice, neutrophil adoptive transfer, chemotaxis assays, psoriasis model\",\n      \"pmids\": [\"23670187\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether D6 cis-sequesters ligand from CCR1 at the cell surface or via trans-endocytosis is not resolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"ACKR2 was shown to regulate developmental lymphatic vessel density by scavenging CCL2 to limit proximity of pro-lymphangiogenic macrophages; ERK-pathway-driven downregulation of ACKR2 in Kaposi sarcoma was linked to CCR2+ macrophage recruitment and tumor progression.\",\n      \"evidence\": \"ACKR2 KO and CCR2 KO reciprocal analysis in embryonic skin, macrophage depletion, B-Raf/ERK inhibitors in KS model, adoptive transfer\",\n      \"pmids\": [\"25271254\", \"24844911\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ACKR2 regulates lymphangiogenesis in adult tissues (not only embryonic) is not established\", \"ERK-mediated transcriptional repression mechanism of ACKR2 not molecularly defined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Extension to mammary gland development and psoriasis showed that ACKR2 scavenging governs tissue morphogenesis (mammary ductal branching via macrophage control) and prevents remote spread of psoriasiform inflammation through IFNγ-induced upregulation, broadening its physiological roles to organogenesis and systemic inflammatory containment.\",\n      \"evidence\": \"ACKR2 KO mice, mammary wholemount analysis, imiquimod psoriasis model, human primary cell cultures\",\n      \"pmids\": [\"27888192\", \"27568525\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ACKR2 influences morphogenesis of other branching organs is untested\", \"Feedback loop between IFNγ-induced ACKR2 and inflammatory resolution not fully delineated\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Two studies revealed that ACKR2 in hematopoietic precursors controls myeloid differentiation and neutrophil chemokine receptor levels (affecting anti-metastatic capacity), while in pulmonary resident cells it promotes fibrosis by limiting γδ T cell-derived IFNγ — showing cell-type-specific and sometimes disease-promoting functions.\",\n      \"evidence\": \"ACKR2 KO mice in NeuT mammary carcinoma, 4T1, B16F10 models; bleomycin fibrosis with bone marrow chimeras and CCR2/CCR5 KO epistasis\",\n      \"pmids\": [\"29445158\", \"29469612\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How ACKR2 is downregulated during myeloid differentiation is mechanistically undefined\", \"Whether γδ T cell protection from fibrosis generalizes beyond bleomycin model is unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identification of ACKR2 as a receptor for CXCL14 that induces NOS1-dependent EMT in breast cancer cells challenged the view that ACKR2 is exclusively a non-signaling scavenger, revealing a signaling-competent mode in cancer contexts.\",\n      \"evidence\": \"ACKR2 siRNA/shRNA, CXCL14 co-culture, EMT marker analysis, xenograft model, NOS1 inhibition\",\n      \"pmids\": [\"30850359\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct CXCL14–ACKR2 binding not demonstrated by biophysical methods\", \"Whether CXCL14 signaling via ACKR2 occurs in non-malignant cells is unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"ACKR2 was shown to bind the CXC chemokine CXCL10 as a strong agonist ligand, expanding its ligand repertoire beyond CC chemokines; DPP4/CD26 N-terminal processing of CXCL10 abolishes ACKR2 engagement, indicating a distinct binding mode.\",\n      \"evidence\": \"NanoBiT and NanoBRET β-arrestin recruitment assays, internalization assays, DPP4 processing experiments\",\n      \"pmids\": [\"33801414\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo relevance of CXCL10 scavenging by ACKR2 not demonstrated\", \"Structural basis for differential binding pocket occupancy versus CC chemokines unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"A detailed signaling cascade downstream of ACKR2 in lung cancer was mapped: CXCL14 activates PLCβ3/PKCα/c-Src leading to NF-κB-driven EMT, providing the first multi-step signaling pathway attributed to this 'atypical' non-signaling receptor in a cancer context.\",\n      \"evidence\": \"ACKR2 knockdown, NF-κB luciferase reporter, orthotopic lung cancer model, Western blot for signaling intermediates\",\n      \"pmids\": [\"37056937\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Pathway identified in overexpression/cancer cell systems; relevance in non-transformed cells unknown\", \"Whether PLCβ3 activation is direct or via an intermediary G-protein is not resolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"ACKR2 was linked to therapy resistance in cervical cancer, where chemoradiotherapy-induced ACKR2 expression in tumor cells drives TGF-β production that promotes CD8+ T cell senescence, providing a mechanism for immune evasion and recurrence.\",\n      \"evidence\": \"Single-cell RNA sequencing, in vitro and in vivo validation, TGF-β pathway analysis, retrospective clinical cohort\",\n      \"pmids\": [\"38723624\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causality between ACKR2 expression and TGF-β production not mechanistically resolved\", \"Whether ACKR2 scavenging or signaling drives TGF-β in this context is unknown\", \"Single study, not independently replicated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: (1) the structural basis for ACKR2's dual engagement of CC and CXC chemokines, (2) whether CXCL14-induced signaling through PLCβ3/NF-κB represents a general signaling mode or is cancer-specific, (3) the molecular mechanism of the scavenging-independent efferocytosis function on apoptotic neutrophils, and (4) whether ACKR2 has physiological signaling partners beyond β-arrestin.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No crystal or cryo-EM structure of ACKR2 with any ligand\", \"CXCL14 direct binding to ACKR2 not confirmed by biophysical assay\", \"Signaling adapter complex composition unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0038024\", \"supporting_discovery_ids\": [0, 4, 19]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [4, 6, 11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 2, 6]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [2, 6]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [3, 5, 8, 9, 11, 14, 17]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [18, 20]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [12, 15]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"CCL2\",\n      \"CCL3\",\n      \"CCL5\",\n      \"CXCL10\",\n      \"CXCL14\",\n      \"RAB11A\",\n      \"RAB4A\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"ACKR2 is an atypical chemokine receptor that scavenges inflammatory CC chemokines (and CXCL10) through constitutive β-arrestin-dependent, clathrin-mediated internalization and lysosomal degradation, without activating G-protein signaling or calcium flux [PMID:9405404, PMID:12594248, PMID:15084596]. Expressed predominantly on lymphatic endothelial cells and hematopoietic precursors, ACKR2 constitutively recycles via Rab4/Rab11 pathways and upregulates its surface abundance in response to chemokine engagement through a β-arrestin1→Rac1→PAK1→LIMK1→cofilin signaling cascade that optimizes scavenging capacity [PMID:18480427, PMID:23633677]. In vivo, ACKR2-mediated chemokine clearance by non-hematopoietic cells is essential for resolution of cutaneous inflammation, prevention of adverse cardiac remodeling after myocardial infarction, regulation of lymphatic vessel density via control of pro-lymphangiogenic macrophage positioning, and modulation of neutrophil release from bone marrow [PMID:15750596, PMID:22796582, PMID:25271254, PMID:29445158]. In cancer contexts, ACKR2 can also serve as a receptor for CXCL14, activating NOS1- or PLCβ3-PKCα-NF-κB-dependent signaling that promotes epithelial-mesenchymal transition and metastasis [PMID:30850359, PMID:37056937].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Cloning of ACKR2 revealed a promiscuous CC chemokine-binding receptor that, unlike classical chemokine receptors, failed to signal through calcium flux, establishing it as functionally atypical.\",\n      \"evidence\": \"cDNA cloning with radioligand binding and calcium flux assays in HEK293/CHO transfectants\",\n      \"pmids\": [\"9405404\", \"9139699\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of ligand engagement without signaling was unknown\", \"In vivo function not addressed\", \"Selectivity for inflammatory vs. homeostatic chemokines not yet mapped\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"N-terminal residues of CC chemokines (specifically a proline at position 2) were identified as critical determinants of ACKR2 binding affinity, providing early structural insight into ligand recognition.\",\n      \"evidence\": \"Radioligand competition assays and proline-2 mutagenesis on D6 transfectants\",\n      \"pmids\": [\"10364178\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full structural basis of ligand selectivity unresolved\", \"No crystal or cryo-EM structure of ACKR2-chemokine complex\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Identification of lymphatic endothelium as the primary site of ACKR2 expression provided the anatomical context for its function as a chemokine gatekeeper at tissue-lymph interfaces.\",\n      \"evidence\": \"Monoclonal antibody immunohistochemistry and in situ hybridization on human dermis, intestinal mucosa, and lymph node sections co-stained with podoplanin\",\n      \"pmids\": [\"11238036\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Expression on hematopoietic cells not yet appreciated\", \"Whether ACKR2 functions identically in all lymphatic beds remained untested\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstration that ACKR2 internalizes and degrades CC chemokines without triggering signaling or transcytosis established the chemokine-scavenging/decoy receptor paradigm.\",\n      \"evidence\": \"Calcium flux, chemotaxis, internalization, and degradation assays in transfectants and primary lymphatic endothelial cells\",\n      \"pmids\": [\"12594248\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular machinery of constitutive internalization uncharacterized\", \"Whether ligand engagement alters receptor trafficking unknown\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"The trafficking and scavenging mechanism was dissected: ACKR2 constitutively internalizes via β-arrestin-dependent clathrin-coated pits, with an acidic C-terminal motif (not phosphorylation) driving β-arrestin association, and most receptor resides in intracellular vesicles.\",\n      \"evidence\": \"β-arrestin co-IP, clathrin inhibition, C-terminal mutagenesis, subcellular fractionation, and metabolic labeling in HEK293 transfectants\",\n      \"pmids\": [\"15084596\", \"14723600\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which Rab GTPases govern vesicular recycling not yet known\", \"How ligand binding feeds back on trafficking unclear\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Systematic ligand profiling confirmed ACKR2 selectively scavenges inflammatory (CCR1–CCR5 agonists) but not homeostatic CC chemokines, with N-terminal integrity required for recognition, defining the functional ligand spectrum.\",\n      \"evidence\": \"Radioligand binding, scavenging assays, and CD26-processing experiments in D6 transfectants\",\n      \"pmids\": [\"15067078\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether any non-CC chemokine could serve as ligand was unexplored\", \"In vivo chemokine selectivity not validated\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"ACKR2-deficient mice revealed that in vivo chemokine scavenging is essential for resolution of cutaneous inflammation, as knockouts accumulated excess β-chemokines and developed psoriasis-like pathology.\",\n      \"evidence\": \"D6 knockout mice in phorbol ester-induced cutaneous inflammation model with chemokine quantification and histopathology\",\n      \"pmids\": [\"15750596\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether non-hematopoietic or hematopoietic ACKR2 is responsible not determined in this context\", \"Mechanism of inflammation resolution vs. prevention not distinguished\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Bidirectional genetic evidence (knockout susceptibility, transgenic protection) established ACKR2 as a tumor suppressor in chemically induced skin carcinogenesis by limiting pro-tumorigenic inflammatory cell recruitment.\",\n      \"evidence\": \"D6-KO and keratinocyte-specific D6 transgenic mice in DMBA/TPA carcinogenesis model; immune cell quantification\",\n      \"pmids\": [\"17607362\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ACKR2 suppresses tumors in non-cutaneous tissues via same mechanism unknown\", \"Cell-autonomous effects on tumor cells not addressed\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Ligand-induced Rab11-dependent redistribution of ACKR2 to the plasma membrane was identified as the mechanism by which scavenging capacity scales with chemokine concentration, and the C-terminal serine cluster was shown to be essential for sustained scavenging.\",\n      \"evidence\": \"Rab4/Rab11 dominant-negative constructs, wortmannin/brefeldin A inhibition, C-terminal deletion and serine mutagenesis with chemokine degradation assays\",\n      \"pmids\": [\"18480427\", \"18201974\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How Rab11 pathway is activated by ligand engagement unknown\", \"No link yet to actin cytoskeleton remodeling\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Discovery of ACKR2 expression on hematopoietic cells (B cells, DCs, mast cells) under GATA1 control expanded the expression domain beyond lymphatic endothelium and identified TGF-β and LPS as dynamic regulators.\",\n      \"evidence\": \"Flow cytometry, RT-PCR, chemokine uptake in D6-null vs. WT leukocytes, GATA1 knockout experiments\",\n      \"pmids\": [\"18714007\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of hematopoietic vs. non-hematopoietic ACKR2 to systemic chemokine homeostasis unclear\", \"Whether GATA1 directly or indirectly activates the D6 promoter not resolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Bone marrow chimera experiments in myocardial infarction and monocyte trafficking models localized the critical in vivo scavenging function to non-hematopoietic ACKR2, operating via control of CCR2-dependent Ly6C-hi monocyte recruitment.\",\n      \"evidence\": \"D6-KO and CCR2-KO bone marrow chimeras; MI model with echocardiography, MMP assays; GVHD model with T-cell suppression assays\",\n      \"pmids\": [\"22796582\", \"22504926\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which non-hematopoietic cell types express functionally relevant ACKR2 in heart was not pinpointed\", \"Whether ACKR2 regulates monocyte function beyond recruitment unclear\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identification of the β-arrestin1→Rac1→PAK1→LIMK1→cofilin signaling cascade downstream of ACKR2 overturned the 'silent receptor' paradigm, showing that ACKR2 activates actin remodeling to drive its own surface redistribution and scavenging.\",\n      \"evidence\": \"β-arrestin1 co-IP, Rac1/PAK1/LIMK1 inhibitors and dominant-negatives, cofilin phosphorylation assays, D6 surface quantification\",\n      \"pmids\": [\"23633677\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this pathway operates in all ACKR2-expressing cell types unknown\", \"Whether other actin regulators participate not tested\", \"Link to Rab11-dependent recycling not formally demonstrated\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"ACKR2 was shown to regulate lymphatic vessel density by controlling the proximity of CCR2-dependent pro-lymphangiogenic macrophages to developing lymphatic vessels, revealing a developmental morphogenetic role.\",\n      \"evidence\": \"ACKR2-KO and CCR2-KO mice; lymphatic vessel quantification; embryonic skin analysis; macrophage proximity measurements; blood pressure assessment\",\n      \"pmids\": [\"25271254\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which VEGF family members mediate macrophage-driven lymphangiogenesis downstream of ACKR2 not identified\", \"Whether increased lymphatic density has functional consequences beyond fluid drainage\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"ACKR2 was found to act as a checkpoint of myeloid differentiation in bone marrow, with its loss increasing neutrophil release and anti-metastatic neutrophil activity, while also promoting pulmonary fibrosis via regulation of CCR2+/CCR5+ IFNγ-producing γδT cell influx.\",\n      \"evidence\": \"ACKR2-KO mice in NeuT mammary carcinoma, 4T1/B16F10 metastasis models, and bleomycin fibrosis model; bone marrow chimeras; γδT cell depletion; CCR2-KO/CCR5-KO mice\",\n      \"pmids\": [\"29445158\", \"29469612\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How ACKR2 is downregulated during myeloid differentiation mechanistically unclear\", \"Whether neutrophil anti-metastatic activity is direct or requires other immune cell cooperation\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"ACKR2 was identified as a functional receptor for the orphan chemokine CXCL14, mediating EMT and metastasis through NOS1 in breast cancer, revealing a signaling role distinct from classical scavenging.\",\n      \"evidence\": \"siRNA/shRNA ACKR2 knockdown; in vitro EMT, migration, invasion assays; xenograft and tail-vein metastasis models; NOS1 inhibition\",\n      \"pmids\": [\"30850359\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct CXCL14-ACKR2 binding not demonstrated biochemically\", \"How ACKR2 activates NOS1 is mechanistically undefined\", \"Whether this operates outside breast cancer unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"CXCL10 was identified as the first non-CC chemokine agonist of ACKR2, with DPP4 processing abolishing CXCL10 activity at ACKR2, broadening the receptor's ligand repertoire beyond CC chemokines.\",\n      \"evidence\": \"NanoBiT and NanoBRET β-arrestin recruitment assays; ACKR2 internalization assays; DPP4 processing experiments\",\n      \"pmids\": [\"33801414\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo relevance of CXCL10 scavenging by ACKR2 not established\", \"Whether other CXC chemokines are also agonists not systematically tested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"A PLCβ3→PKCα→c-Src→NF-κB signaling cascade was mapped downstream of ACKR2 in lung cancer cells stimulated by CXCL14, defining a second cancer-specific signaling pathway through ACKR2.\",\n      \"evidence\": \"ACKR2 siRNA knockdown; phosphorylation western blots for PLCβ3/PKCα/c-Src; NF-κB luciferase reporter; orthotopic lung cancer metastasis model\",\n      \"pmids\": [\"37056937\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relationship between PLCβ3-NF-κB and β-arrestin-cofilin pathways unexplored\", \"Whether this pathway operates in non-cancer cells unknown\", \"Single lab finding awaiting independent replication\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"ACKR2 upregulation in chemoradiotherapy-resistant cervical cancer cells was shown to drive CD8+ T cell senescence via TGF-β production, linking ACKR2 to immune evasion in the tumor microenvironment.\",\n      \"evidence\": \"Single-cell RNA-seq of human cervical cancer tissues; in vitro tumor-T cell co-cultures; TGF-β blocking experiments\",\n      \"pmids\": [\"38723624\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether TGF-β induction is a direct ACKR2 signaling output or indirect consequence of chemokine clearance is unresolved\", \"Generalizability to other tumor types not tested\", \"No in vivo intervention blocking ACKR2 to rescue T cell function\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis of ACKR2's promiscuous CC/CXC chemokine recognition (no high-resolution structure exists), the mechanistic link between β-arrestin-cofilin signaling and Rab11-dependent recycling, and whether ACKR2's cancer-context signaling functions (CXCL14/NOS1, PLCβ3-NF-κB, TGF-β) are physiologically relevant outside tumors.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural model of ACKR2 alone or in complex with any ligand\", \"Connection between actin remodeling and vesicular recycling pathways not formally demonstrated\", \"Cancer-associated signaling pathways not validated in non-malignant contexts\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0038024\", \"supporting_discovery_ids\": [0, 2, 4, 26]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 18, 27]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [6, 14, 20]},\n      {\"term_id\": \"GO:0120274\", \"supporting_discovery_ids\": [7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 5, 8, 9]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [5, 8]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [8]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 2, 4, 6, 14, 15, 21, 24]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 18, 27]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [3, 8, 9]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [20, 22]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [11, 25, 28]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"ARRB1\",\n      \"RAC1\",\n      \"PAK1\",\n      \"LIMK1\",\n      \"CFL1\",\n      \"RAB11A\",\n      \"CXCL14\",\n      \"CXCL10\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}