{"gene":"CCRL2","run_date":"2026-04-28T17:28:52","timeline":{"discoveries":[{"year":1998,"finding":"CCRL2 (originally named HCR) was cloned as a novel seven-transmembrane chemokine receptor from a human neutrophil cDNA library, predicted to encode a 345 amino acid protein with homology to CCR1 (MIP-1α receptor, 43% identity), and mapped to chromosome 3p21. Expression was found in spleen, fetal liver, lymph node, bone marrow, lung, and heart.","method":"cDNA library screening, Northern blot, chromosome mapping","journal":"Biochemical and Biophysical Research Communications","confidence":"Medium","confidence_rationale":"Tier 2 — original cloning with expression characterization; single study","pmids":["9473515"],"is_preprint":false},{"year":2002,"finding":"CCRL2 (designated HCR) is expressed on CD4+ and CD8+ T lymphocytes, monocytes, macrophages, monocyte-derived dendritic cells, neutrophils, and CD34+ hematopoietic precursors in peripheral blood and bone marrow. Expression is upregulated on T cells by OKT3/IL-2, and on dendritic cells by LPS, poly(I:C), IFN-γ, or CD40L stimulation.","method":"Monoclonal antibody generation, flow cytometry, real-time PCR","journal":"European Journal of Immunology","confidence":"Medium","confidence_rationale":"Tier 2 — monoclonal antibodies with direct cell surface staining confirmed by PCR; single lab","pmids":["11828366"],"is_preprint":false},{"year":2004,"finding":"CCRL2 is expressed on synovial neutrophils and some macrophages in rheumatoid arthritis patients. CCRL2 mRNA is rapidly upregulated in primary neutrophils by LPS or TNF stimulation. HEK293 cells expressing either splice variant CCRL2A or CCRL2B migrated in response to fractions of RA synovial fluid, demonstrating functional receptor activity.","method":"Immunocytochemistry, Northern blot, Western blot, RT-PCR, retroviral expression, 48-well chemotaxis chamber","journal":"Arthritis and Rheumatism","confidence":"Medium","confidence_rationale":"Tier 2-3 — functional migration assay with two splice variants; single lab","pmids":["15188357"],"is_preprint":false},{"year":2008,"finding":"Chemerin is identified as a natural nonsignaling protein ligand for both human and mouse CCRL2. Unlike other atypical chemokine receptors (DARC, D6), chemerin binding to CCRL2 does not trigger ligand internalization. Instead, CCRL2 binds chemerin and increases local concentrations of bioactive chemerin, thereby presenting it to the signaling chemerin receptor CMKLR1 on nearby cells, linking CCRL2 expression to inflammation.","method":"Binding assays, chemerin internalization assays, IgE-mediated passive cutaneous anaphylaxis mouse model, CCRL2-deficient mice","journal":"The Journal of Experimental Medicine","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods, replicated in human and mouse, mechanistic model supported by in vivo genetics","pmids":["18794339"],"is_preprint":false},{"year":2008,"finding":"CCRL2 (CRAM-A/B) is expressed on human B lymphocytes in a maturation-stage-dependent manner and is specifically upregulated by CCL5 exposure. CCL5 stimulation through CRAM induces ERK1/2 phosphorylation in pre-B cell lines lacking other known CCL5 receptors, but does not cause calcium mobilization or migration. This ERK1/2 phosphorylation is not inhibitable by pertussis toxin, indicating CCRL2 does not couple to Gi proteins.","method":"Flow cytometry, Western blot (ERK1/2 phosphorylation), calcium flux assay, migration assay, pertussis toxin inhibition","journal":"Immunology","confidence":"Medium","confidence_rationale":"Tier 2-3 — direct signaling assays with pharmacological controls; single lab","pmids":["18397265"],"is_preprint":false},{"year":2009,"finding":"CCL19 is identified as a specific ligand for CCRL2 (CRAM-B). CCL19 binds CCRL2-expressing cells with nanomolar affinity similar to CCR7. Unlike the CCL19/CCR7 pair, CCL19 stimulation of CCRL2 does not induce calcium mobilization or cell migration. CCRL2 constitutively recycles via clathrin-coated pits and internalizes CCL19 as well as anti-CCRL2 antibodies, classifying it as an atypical non-classical chemokine receptor.","method":"Radioactive ligand binding, calcium mobilization assay, migration assay, internalization assay, clathrin-coated pit analysis","journal":"Immunology","confidence":"Medium","confidence_rationale":"Tier 2-3 — multiple functional assays; single lab","pmids":["20002784"],"is_preprint":false},{"year":2010,"finding":"CCRL2 mRNA is rapidly (within 30 minutes) and transiently (2-4 hours) upregulated during dendritic cell maturation, with protein expression paralleling RNA regulation. CCRL2-deficient mice show normal DC recruitment to the lung but defective trafficking of antigen-loaded lung DCs to mediastinal lymph nodes, resulting in reduced T helper cell 2 priming. Adoptive transfer of CCRL2-deficient antigen-loaded DCs into wild-type mice recapitulates this phenotype.","method":"CCRL2 knockout mice, adoptive DC transfer, lung inflammation model (OVA), flow cytometry, BAL analysis","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with adoptive transfer rescue, multiple orthogonal in vivo readouts","pmids":["20606167"],"is_preprint":false},{"year":2012,"finding":"CCRL2 is upregulated on vascular endothelial cells by proinflammatory stimuli via NF-κB and JAK/STAT signaling pathways. Endothelial CCRL2 expression enables chemerin binding and triggers robust adhesion of CMKLR1+ lymphoid cells through an α4β1 integrin/VCAM-1-dependent mechanism. In CCRL2-deficient mice, plasma chemerin levels are elevated and CMKLR1+ NK cell recruitment to the airways during acute LPS-induced pulmonary inflammation is significantly impaired.","method":"CCRL2 KO mice, NF-κB/JAK/STAT pathway inhibitors, integrin blocking antibodies, lymphocyte adhesion assay, in vivo LPS lung inflammation model, flow cytometry","journal":"Journal of Immunology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (genetic KO, pharmacological inhibition, blocking antibodies) with in vitro and in vivo validation","pmids":["22696441"],"is_preprint":false},{"year":2012,"finding":"CCRL2 overexpression significantly enhances migration rate and invasiveness of glioblastoma cells (U87, U373) without affecting proliferation, as determined by gain-of-function and loss-of-function studies.","method":"Overexpression and siRNA knockdown, migration and invasion assays (transwell), proliferation assay","journal":"Biochemical and Biophysical Research Communications","confidence":"Low","confidence_rationale":"Tier 3 — single lab, phenotypic readout without pathway mechanism","pmids":["23142225"],"is_preprint":false},{"year":2016,"finding":"CCRL2 binds chemerin with low nanomolar affinity, but unlike CMKLR1, chemerin binding to CCRL2 does not activate any of the three Gαi subtypes, two Gαo isoforms, or recruit β-arrestin1 or β-arrestin2. CCRL2 also does not promote receptor internalization or ERK1/2 phosphorylation upon chemerin binding, establishing it as a non-signaling receptor that is functionally distinct from CMKLR1 and GPR1.","method":"BRET-based biosensors for G protein activation, β-arrestin recruitment assays, receptor internalization assays, ERK1/2 phosphorylation assay","journal":"PloS One","confidence":"High","confidence_rationale":"Tier 1-2 — multiple BRET-based signaling readouts systematically compared across all three chemerin receptors; rigorous controls","pmids":["27716822"],"is_preprint":false},{"year":2016,"finding":"CCRL2-deficient mice develop exacerbated, non-resolving experimental autoimmune encephalitis (EAE) with protracted inflammation and increased demyelination. This is associated with higher microglia/macrophage activation markers and imbalanced M1/M2 polarization, indicating CCRL2 promotes M2 polarization during the recovery phase to downregulate CNS inflammation.","method":"CCRL2 KO mice, EAE model, histological analysis, flow cytometry for M1/M2 markers","journal":"Journal of Leukocyte Biology","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO with defined inflammatory phenotype; single lab","pmids":["26744451"],"is_preprint":false},{"year":2017,"finding":"CCRL2 constitutively forms homodimers and heterodimers with CXCR2 as demonstrated by co-immunoprecipitation. By heterodimerization with CXCR2, CCRL2 regulates membrane CXCR2 expression and promotes CXCR2-mediated functions including activation of β2-integrins. CCRL2-deficient mice have a specific defect in neutrophil recruitment and are protected in two models of inflammatory arthritis.","method":"Co-immunoprecipitation (homodimer/heterodimer detection), CCRL2 KO mice, inflammatory arthritis models, β2-integrin activation assay, neutrophil migration assay","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP for dimerization plus in vivo KO models with specific mechanistic follow-up; single lab with multiple orthogonal methods","pmids":["28743719"],"is_preprint":false},{"year":2017,"finding":"CCRL2 undergoes weak constitutive ligand-independent internalization and recycling, slower than ACKR3 or other chemotactic receptors. Intracellularly, CCRL2 colocalizes with EEA1- and Rab5-positive early endosomes and Rab11-positive recycling compartments. Critically, CCRL2-transfected cells and activated endothelial cells endogenously expressing CCRL2 cannot scavenge chemerin, confirming CCRL2 is not a decoy/scavenging receptor.","method":"Cell membrane internalization assays, immunofluorescence colocalization with endosomal markers (EEA1, Rab5, Rab11), chemerin scavenging assay in transfected and primary endothelial cells","journal":"Frontiers in Immunology","confidence":"High","confidence_rationale":"Tier 1-2 — direct subcellular localization with multiple endosomal markers, functional scavenging assay in both transfected and primary cells","pmids":["29056935"],"is_preprint":false},{"year":2017,"finding":"CCRL2 absence in mice leads to exaggerated local and systemic inflammatory responses in zymosan- and thioglycollate-induced acute inflammation, characterized by increased myeloid cell recruitment associated with elevated chemerin and CXCL1 levels. Antibody neutralization of chemerin in CCRL2-deficient mice abrogates the amplified inflammatory response, demonstrating that CCRL2 regulates local chemerin concentration as its primary in vivo mechanism.","method":"CCRL2 KO mice, zymosan/thioglycollate peritonitis models, chemerin neutralizing antibody, cytokine/chemokine quantification, flow cytometry","journal":"Frontiers in Immunology","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with antibody neutralization rescue across two independent in vivo inflammation models","pmids":["29209334"],"is_preprint":false},{"year":2019,"finding":"CCRL2 expression by the non-hematopoietic (endothelial) cell compartment, as shown by bone marrow chimeras, is responsible for suppressing lung tumor formation. CCRL2 is expressed by a fraction of CD31+ lung endothelial cells where it controls NK cell infiltration into lung tumors. Genetic deletion of Ccrl2 promotes tumor progression in urethane-induced and Kras-mutant/p53-flox lung cancer models with impaired NK cell recruitment.","method":"CCRL2 KO mice, bone marrow chimeras, urethane lung cancer model, Kras/p53 genetic lung tumor model, flow cytometry for NK cells","journal":"Cancer Immunology Research","confidence":"High","confidence_rationale":"Tier 2 — bone marrow chimeras definitively assign CCRL2 function to non-hematopoietic compartment; multiple tumor models","pmids":["31484658"],"is_preprint":false},{"year":2020,"finding":"MTB heat-shock protein Hsp16.3 induces macrophage M2 polarization through direct interaction with chemokine receptors CCRL2 and CX3CR1. Overexpression or silencing of CCRL2 modulates Hsp16.3-induced M2 polarization, and downstream signaling involves the AKT/ERK/p38-MAPK pathway.","method":"Overexpression and siRNA silencing, M2 marker quantification (Arg-1, IL-10, TGF-β, CD206), Western blot for AKT/ERK/p38-MAPK phosphorylation","journal":"Inflammation","confidence":"Low","confidence_rationale":"Tier 3 — gain/loss-of-function with pathway readout; single lab, no direct binding validation for Hsp16.3/CCRL2","pmids":["31748849"],"is_preprint":false},{"year":2021,"finding":"CCRL2 interacts with TLR4 on the macrophage cell surface to retain membrane TLR4 expression and enhance TLR4 downstream Myd88-NF-κB inflammatory signaling. CCRL2-deficient mice exhibit accelerated melanoma growth with reduced immunostimulatory macrophages and T-cell responses. Depletion of CD8+ T cells or macrophages eliminates the tumor growth difference between WT and CCRL2-deficient mice.","method":"Co-immunoprecipitation (CCRL2-TLR4 interaction), flow cytometry for membrane TLR4, NF-κB signaling assay, CCRL2 KO mice, melanoma tumor model, CD8+ T cell and macrophage depletion","journal":"PNAS","confidence":"High","confidence_rationale":"Tier 2 — co-IP for direct interaction, functional signaling validation, in vivo genetic model with depletion rescue; multiple orthogonal methods","pmids":["33846258"],"is_preprint":false},{"year":2021,"finding":"CCRL2 expression by tumor cells concentrates bioactive chemerin and reduces neoangiogenesis in tumor grafts, mimicking the phenotype of chemerin-expressing tumors. Loss of Ccrl2 accelerates papilloma development in a DMBA/TPA skin carcinogenesis model. These phenotypes are abrogated by knockout of chemerin or Cmklr1, demonstrating that CCRL2 acts through the chemerin/CMKLR1 axis.","method":"CCRL2 KO mice, DMBA/TPA skin carcinogenesis model, B16/LLC tumor grafts with CCRL2 overexpression or knockout, chemerin and Cmklr1 KO epistasis, angiogenesis quantification","journal":"Cancers","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis (chemerin/CMKLR1 KO rescues CCRL2 phenotype) across multiple tumor models","pmids":["34638484"],"is_preprint":false},{"year":2022,"finding":"CCRL2 knockdown suppresses MDS92 and MDS-L cell growth and clonogenicity in vitro and in vivo, and decreases JAK2/STAT3/STAT5 phosphorylation. CCRL2 co-precipitates with JAK2 and potentiates JAK2-STAT interaction. Erythroleukemia cells with constitutively active JAK2V617F show less dependence on CCRL2, and JAK2 inhibitor fedratinib potentiates CCRL2 knockdown effects.","method":"siRNA knockdown, co-immunoprecipitation (CCRL2-JAK2), Western blot (JAK2/STAT3/STAT5 phosphorylation), xenograft mouse model, pharmacological JAK2 inhibition","journal":"Science Advances","confidence":"High","confidence_rationale":"Tier 2 — co-IP for direct interaction, phosphorylation readout, in vivo xenograft, and pharmacological epistasis; multiple orthogonal methods","pmids":["35179961"],"is_preprint":false},{"year":2022,"finding":"Accelerated molecular dynamics simulation of CCRL2 with chemerin docking identified putative hot-spot residues in the CCRL2 transmembrane domain and extracellular loops most frequently involved in chemerin binding, providing a structural model for the CCRL2-chemerin interaction.","method":"Protein-protein docking, accelerated molecular dynamics, principal component analysis, kernel density estimation","journal":"Proteins","confidence":"Low","confidence_rationale":"Tier 4 — computational prediction only, no experimental validation","pmids":["35437825"],"is_preprint":false},{"year":2023,"finding":"CCRL2 is expressed specifically by general alveolar lung capillary endothelial cells (identified by scRNA-seq as a hallmark marker). Conditional or constitutive endothelial CCRL2 ablation promotes lung tumor progression by reducing recruitment of CD27-CD11b+ mature NK cells. CCRL2 expression in lung endothelium is epigenetically regulated, and in vivo administration of the demethylating agent 5-aza-2'-deoxycytidine (5-Aza) upregulates CCRL2, increases NK cell recruitment, and reduces lung tumor growth.","method":"scRNA-seq, conditional/constitutive CCRL2 endothelial KO, Kras/p53 lung tumor model, 5-Aza treatment, flow cytometry for NK cell subsets, epigenetic regulation analysis","journal":"Cancer Immunology Research","confidence":"High","confidence_rationale":"Tier 2 — scRNA-seq identification, conditional KO with multiple tumor models, pharmacological upregulation with functional rescue; multiple orthogonal methods","pmids":["37343073"],"is_preprint":false},{"year":2023,"finding":"Endothelial CCRL2 induced by disturbed flow recruits chemerin, which activates β2 integrin on monocytes via a protein disulfide isomerase-like enzymatic activity of chemerin (rather than through monocytic CMKLR1), enhancing ERK1/2 phosphorylation and monocyte adhesion. CCRL2-deficient ApoE-/- mice are protected against atherosclerotic plaque formation in disturbed-flow areas.","method":"CCRL2-/-ApoE-/- mice, high-fat diet atherosclerosis model, scRNA-seq, Di-E-GSSG assay (PDI-like activity), proximity ligation assay (chemerin-β2 integrin interaction), ERK1/2 phosphorylation, monocyte adhesion assay","journal":"Cardiovascular Research","confidence":"High","confidence_rationale":"Tier 2 — genetic KO in vivo, proximity ligation assay for direct interaction, enzymatic activity assay; multiple orthogonal methods","pmids":["37279540"],"is_preprint":false},{"year":2023,"finding":"CCRL2 neutralizing antibodies confirm that chemerin (but not previously reported CC chemokines) directly binds CCRL2 by flow cytometry and Surface Plasmon Resonance microscopy. However, antibody-mediated neutralization of CCRL2 ligand-binding does not attenuate CXCL8-induced neutrophil degranulation or CXCL8-induced murine neutrophil peritoneal recruitment, suggesting CCRL2's ligand-binding function is dispensable for CXCR2-mediated CXCL8 signaling in neutrophils.","method":"Flow cytometry binding assay, Surface Plasmon Resonance microscopy, CCRL2 neutralizing antibodies, neutrophil degranulation assay, in vivo peritoneal neutrophil recruitment","journal":"PloS One","confidence":"Medium","confidence_rationale":"Tier 2 — SPRm binding confirmation plus functional antibody neutralization; challenges mechanism from PMID:28743719","pmids":["36662882"],"is_preprint":false},{"year":2023,"finding":"CCRL2 knockdown in MDS/sAML cell lines downregulates DNA methylation and PRC2 activity pathways, increases DNMT suppression by azacitidine, and sensitizes these cells to azacitidine both in vitro and in an MDS-L xenograft model. CCRL2 overexpression conversely decreases azacitidine sensitivity, demonstrating CCRL2 modulates epigenetic regulatory pathways.","method":"siRNA knockdown, CCRL2 overexpression, azacitidine sensitivity assays, xenograft model, gene expression profiling (PRC2/DNMT pathways)","journal":"Haematologica","confidence":"Medium","confidence_rationale":"Tier 2 — bidirectional gain/loss-of-function with in vivo xenograft; single lab","pmids":["36519323"],"is_preprint":false},{"year":2024,"finding":"CCRL2 binds SFRP1 on the surface of LepR+/CAR stromal cells, amplifying SFRP1's suppressive effect on Wnt signaling under inflammatory conditions. This CCRL2-SFRP1 interaction inhibits osteogenic differentiation of LepR+/CAR cells, resulting in impaired bone healing in periodontitis. CCRL2-knockout mice show significant improvements in extraction socket bone healing.","method":"CCRL2 KO mice, co-immunoprecipitation (CCRL2-SFRP1 interaction), Wnt signaling reporter assay, osteogenic differentiation assay, bone healing quantification by micro-CT","journal":"Journal of Bone and Mineral Research","confidence":"Medium","confidence_rationale":"Tier 2-3 — co-IP for novel interaction, functional readout in KO mice; single lab","pmids":["38477792"],"is_preprint":false},{"year":2021,"finding":"CCRL2 functions as a coreceptor for primary HIV-2 isolates (and to a lesser extent HIV-1) in NP-2/CD4/CCRL2 cells. HIV-2MIR infection was demonstrated by immunofluorescence, proviral DNA detection, reverse transcriptase activity measurement, and multinucleated giant cell formation, making CCRL2 a newly identified HIV-2 entry coreceptor.","method":"NP-2 cell transduction with CD4 and CCRL2, HIV infection assay, immunofluorescence, PCR for proviral DNA, reverse transcriptase activity assay, Giemsa staining for syncytia","journal":"Briefings in Bioinformatics","confidence":"Low","confidence_rationale":"Tier 3 — cell-based infection assay; single lab, in vivo relevance unverified","pmids":["33253374"],"is_preprint":false},{"year":2025,"finding":"Optogenetic vagal nerve stimulation decreases the proportion of CCRL2+ macrophages, which are monocyte-derived and exhibit a TNF-α-responsive, pro-hypertrophic, profibrotic signature. Elimination of CCRL2+ macrophages prevents cardiac remodeling and heart failure. α7nAChR activation inhibits CCRL2+ macrophage TNF-α responsiveness through increased NRF2 expression. CCRL2+-macrophage-specific overexpression or global loss of α7nAChR eliminates VNS-mediated cardioprotection.","method":"Optogenetic VNS, CCRL2+ macrophage depletion, macrophage-specific α7nAChR overexpression/KO, NRF2 expression assay, cardiac remodeling quantification, scRNA-seq","journal":"Immunity","confidence":"Medium","confidence_rationale":"Tier 2 — macrophage-specific genetic manipulation with functional cardiac readout; single study","pmids":["40580954"],"is_preprint":false}],"current_model":"CCRL2 is a non-signaling seven-transmembrane atypical chemokine receptor that binds chemerin with high affinity but does not activate G proteins, β-arrestins, or trigger ligand scavenging/internalization; instead, it acts as a chemerin-presenting molecule on endothelial and barrier cells to amplify local chemerin concentrations and facilitate CMKLR1-dependent leukocyte recruitment, while also forming constitutive homodimers and heterodimers with CXCR2 to regulate neutrophil β2-integrin activation, interacting with TLR4 to potentiate Myd88-NF-κB macrophage activation, co-precipitating with JAK2 to potentiate JAK2-STAT signaling in myeloid malignancies, and binding SFRP1 to suppress Wnt signaling in stromal cells, thereby functioning as a context-dependent positive or negative regulator of innate immunity, tumor surveillance, and tissue homeostasis."},"narrative":{"teleology":[{"year":1998,"claim":"Identification of CCRL2 as a novel orphan seven-transmembrane receptor with chemokine receptor homology established it as a candidate immune regulator expressed in hematopoietic tissues.","evidence":"cDNA library screening from human neutrophils, Northern blot, chromosomal mapping to 3p21","pmids":["9473515"],"confidence":"Medium","gaps":["No ligand identified","No functional activity demonstrated","Expression restricted to mRNA level"]},{"year":2002,"claim":"Demonstration that CCRL2 protein is expressed on multiple leukocyte subsets and upregulated by inflammatory stimuli positioned it as an inflammation-responsive receptor on both innate and adaptive immune cells.","evidence":"Monoclonal antibody-based flow cytometry and real-time PCR on primary human blood cells and dendritic cells","pmids":["11828366"],"confidence":"Medium","gaps":["Ligand still unidentified","No functional consequence of upregulation shown","No knockout data"]},{"year":2008,"claim":"Identification of chemerin as a non-signaling ligand that is presented rather than internalized by CCRL2 resolved the receptor's functional identity as a ligand-concentrating molecule rather than a classical signaling or scavenging receptor.","evidence":"Binding assays, internalization assays, CCRL2-deficient mice in IgE-mediated passive cutaneous anaphylaxis model","pmids":["18794339"],"confidence":"High","gaps":["Structural basis of chemerin binding unknown","Relative contribution of CCRL2 versus CMKLR1 in different tissues not resolved","Whether other ligands exist remained unclear"]},{"year":2008,"claim":"The finding that CCRL2 induces pertussis toxin-insensitive ERK1/2 phosphorylation upon CCL5 exposure in pre-B cells without calcium flux or migration demonstrated non-canonical signaling capacity independent of Gαi coupling.","evidence":"Western blot for ERK1/2 phosphorylation, calcium flux assay, pertussis toxin inhibition in pre-B cell lines","pmids":["18397265"],"confidence":"Medium","gaps":["Mechanism of Gi-independent ERK activation unresolved","Physiological relevance of CCL5/CCRL2 interaction debated","Later studies with neutralizing antibodies questioned CC chemokine binding"]},{"year":2010,"claim":"Demonstration that CCRL2 deficiency impairs antigen-loaded dendritic cell migration to draining lymph nodes revealed a cell-intrinsic role for CCRL2 in DC trafficking and subsequent T helper priming.","evidence":"CCRL2 knockout mice, adoptive DC transfer, OVA-induced lung inflammation model","pmids":["20606167"],"confidence":"High","gaps":["Whether DC trafficking function is chemerin-dependent not tested","Mechanism of CCRL2-mediated DC migration unknown","Relevance to Th1 or Th17 immunity not explored"]},{"year":2012,"claim":"Establishing that endothelial CCRL2 upregulated by NF-κB/JAK-STAT signaling binds chemerin and triggers α4β1 integrin/VCAM-1-dependent adhesion of CMKLR1+ cells demonstrated the in vivo mechanism by which CCRL2 converts circulating chemerin into a tissue-homing cue for NK cells.","evidence":"CCRL2 KO mice, pathway inhibitors, integrin-blocking antibodies, LPS lung inflammation model","pmids":["22696441"],"confidence":"High","gaps":["Whether endothelial CCRL2 interacts with chemerin in trans or cis with CMKLR1 not determined","Role in non-pulmonary vascular beds unexplored"]},{"year":2016,"claim":"Systematic BRET-based comparison across all Gαi subtypes, Gαo isoforms, and β-arrestins definitively classified CCRL2 as non-signaling upon chemerin binding, distinguishing it from CMKLR1 and GPR1.","evidence":"BRET biosensors for G protein activation and β-arrestin recruitment compared across three chemerin receptors","pmids":["27716822"],"confidence":"High","gaps":["Signaling through non-canonical pathways (e.g., JAK2) not tested in this system","No structural explanation for silent coupling"]},{"year":2017,"claim":"Discovery that CCRL2 constitutively homodimerizes and heterodimerizes with CXCR2 to regulate β2-integrin activation and neutrophil recruitment revealed a chemerin-independent mechanism by which CCRL2 tunes innate immune responses.","evidence":"Reciprocal co-immunoprecipitation, CCRL2 KO mice, inflammatory arthritis models, β2-integrin activation assays","pmids":["28743719"],"confidence":"High","gaps":["CCRL2 neutralizing antibody studies later found no effect on CXCL8-driven neutrophil responses, raising questions about context-dependence of the CXCR2 interaction","Stoichiometry and structural basis of heterodimer unknown"]},{"year":2017,"claim":"Confirmation that CCRL2 undergoes slow constitutive recycling through early and recycling endosomes without scavenging chemerin solidified the model that CCRL2 is a surface-presenting rather than internalizing receptor.","evidence":"Internalization assays, colocalization with EEA1/Rab5/Rab11 endosomal markers in transfected and primary endothelial cells","pmids":["29056935"],"confidence":"High","gaps":["What regulates the balance of surface versus endosomal CCRL2 is unknown","Whether post-translational modifications control recycling not tested"]},{"year":2019,"claim":"Bone marrow chimera experiments assigning anti-tumor function to non-hematopoietic (endothelial) CCRL2 in lung cancer established that endothelial chemerin presentation drives NK cell-dependent tumor immunosurveillance.","evidence":"Bone marrow chimeras, urethane-induced and Kras/p53 genetic lung tumor models, NK cell flow cytometry","pmids":["31484658"],"confidence":"High","gaps":["Whether CCRL2 also regulates T-cell recruitment to lung tumors not resolved","Human relevance of endothelial CCRL2 in lung cancer not confirmed"]},{"year":2021,"claim":"Identification of a CCRL2–TLR4 interaction that retains surface TLR4 and potentiates MyD88–NF-κB signaling in macrophages revealed a second chemerin-independent mechanism linking CCRL2 to anti-tumor immunity via macrophage–CD8+ T cell crosstalk.","evidence":"Co-immunoprecipitation, surface TLR4 quantification, NF-κB signaling assay, CCRL2 KO mice, melanoma model with macrophage/CD8 depletion","pmids":["33846258"],"confidence":"High","gaps":["Whether TLR4 interaction is direct or adaptor-mediated not resolved","Generalizability beyond melanoma not tested"]},{"year":2022,"claim":"Co-precipitation of CCRL2 with JAK2 and demonstration that CCRL2 knockdown reduces JAK2–STAT3/STAT5 phosphorylation in MDS cells uncovered a cell-intrinsic oncogenic function distinct from its chemerin-presenting role, establishing CCRL2 as a context-dependent positive regulator of myeloid malignancy.","evidence":"Co-immunoprecipitation, Western blot for phospho-JAK2/STAT, siRNA knockdown, xenograft model, fedratinib epistasis","pmids":["35179961"],"confidence":"High","gaps":["How a seven-transmembrane receptor potentiates JAK2 signaling mechanistically is unknown","Whether the JAK2 interaction is relevant outside MDS/AML not tested"]},{"year":2023,"claim":"Identification of CCRL2 as a hallmark marker of general alveolar capillary endothelial cells by scRNA-seq, combined with evidence that its epigenetic silencing is reversible by 5-Aza treatment to restore NK recruitment and suppress lung tumors, provided a translational framework for re-activating CCRL2-dependent immunosurveillance.","evidence":"scRNA-seq, conditional endothelial CCRL2 KO, Kras/p53 lung model, 5-Aza pharmacological treatment, NK subset analysis","pmids":["37343073"],"confidence":"High","gaps":["Whether 5-Aza effects are specific to CCRL2 re-expression versus global demethylation not fully dissected","Optimal therapeutic window for CCRL2 re-expression undefined"]},{"year":2023,"claim":"Demonstration that endothelial CCRL2-presented chemerin activates monocyte β2-integrins via a protein disulfide isomerase-like enzymatic activity—independent of CMKLR1—revealed a novel pro-atherogenic mechanism of CCRL2-mediated monocyte adhesion at disturbed-flow sites.","evidence":"CCRL2−/−ApoE−/− mice on high-fat diet, proximity ligation assay for chemerin–β2-integrin interaction, Di-E-GSSG PDI activity assay, ERK1/2 phosphorylation","pmids":["37279540"],"confidence":"High","gaps":["Whether the PDI-like activity of chemerin is relevant in other vascular beds unknown","How disturbed flow specifically induces CCRL2 transcription not fully defined"]},{"year":2024,"claim":"Discovery that CCRL2 binds SFRP1 on LepR+/CAR stromal cells to amplify Wnt suppression and inhibit osteogenic differentiation identified a novel non-chemerin ligand and a role for CCRL2 in bone homeostasis under inflammatory conditions.","evidence":"Co-immunoprecipitation of CCRL2-SFRP1, Wnt reporter assay, osteogenic differentiation assay, CCRL2 KO mice, micro-CT bone healing quantification","pmids":["38477792"],"confidence":"Medium","gaps":["Whether SFRP1 binding uses the same site as chemerin not tested","Relevance beyond periodontitis-associated bone loss unknown","Single study requiring independent replication"]},{"year":2025,"claim":"Identification of CCRL2+ monocyte-derived macrophages as pro-hypertrophic, profibrotic effectors in heart failure whose TNF-α responsiveness is suppressed by vagal α7nAChR–NRF2 signaling positioned CCRL2 as a functional marker linking neuroimmunomodulation to cardiac remodeling.","evidence":"Optogenetic vagal nerve stimulation, CCRL2+ macrophage depletion, macrophage-specific α7nAChR manipulation, scRNA-seq, cardiac remodeling quantification","pmids":["40580954"],"confidence":"Medium","gaps":["Whether CCRL2 is mechanistically required or merely a marker of these macrophages not fully resolved","Single study requiring independent replication"]},{"year":null,"claim":"Key unresolved questions include the structural basis of CCRL2's multi-ligand binding (chemerin, SFRP1, and receptor partners), how a non-signaling receptor potentiates JAK2–STAT signaling, the relative contributions of chemerin-dependent versus chemerin-independent mechanisms across tissues, and whether pharmacological modulation of CCRL2 surface expression can be exploited therapeutically.","evidence":"","pmids":[],"confidence":"High","gaps":["No crystal or cryo-EM structure of CCRL2 or CCRL2–chemerin complex","Mechanism of JAK2 potentiation by a seven-transmembrane receptor unexplained","Relative weight of CXCR2 heterodimerization versus TLR4 interaction versus chemerin presentation in different cell types not systematically compared"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[3,7,11,16,24]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[11,16,18]},{"term_id":"GO:0038024","term_label":"cargo receptor activity","supporting_discovery_ids":[3,7,12,14,21]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,1,3,7,9,11,12,16,22]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[12]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[12]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[3,6,7,10,11,13,14,16,17,20,21]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[7,11,16,18,24]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[18,23]}],"complexes":[],"partners":["RARRES2","CXCR2","TLR4","JAK2","SFRP1","CMKLR1"],"other_free_text":[]},"mechanistic_narrative":"CCRL2 is a non-signaling atypical seven-transmembrane chemokine receptor that orchestrates innate immune cell recruitment, tumor surveillance, and tissue homeostasis by concentrating bioactive ligands at cell surfaces and modulating signaling through heterotypic receptor interactions. CCRL2 binds chemerin with nanomolar affinity without activating G proteins, β-arrestins, or triggering ligand scavenging; instead, it presents chemerin to the signaling receptor CMKLR1 on nearby cells, thereby controlling NK cell and leukocyte recruitment to sites of inflammation and tumors [PMID:18794339, PMID:27716822, PMID:31484658]. Beyond chemerin presentation, CCRL2 forms constitutive heterodimers with CXCR2 to regulate β2-integrin activation and neutrophil recruitment [PMID:28743719], interacts with TLR4 to sustain membrane TLR4 expression and potentiate MyD88–NF-κB signaling in macrophages [PMID:33846258], co-precipitates with JAK2 to amplify JAK2–STAT3/STAT5 signaling in myeloid malignancies [PMID:35179961], and binds SFRP1 on stromal cells to suppress Wnt-dependent osteogenic differentiation [PMID:38477792]. Endothelial CCRL2, particularly on lung alveolar capillary endothelium, is a critical determinant of anti-tumor NK cell infiltration, and its epigenetic silencing promotes lung tumor progression in Kras-driven cancer models [PMID:37343073, PMID:31484658]."},"prefetch_data":{"uniprot":{"accession":"O00421","full_name":"C-C chemokine receptor-like 2","aliases":["Chemokine receptor CCR11","Chemokine receptor X","Putative MCP-1 chemokine receptor"],"length_aa":344,"mass_kda":39.5,"function":"Receptor for CCL19 and chemerin/RARRES2. Does not appear to be a signaling receptor, but may have a role in modulating chemokine-triggered immune responses by capturing and internalizing CCL19 or by presenting RARRES2 ligand to CMKLR1, a functional signaling receptors. Plays a critical role for the development of Th2 responses","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/O00421/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CCRL2","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/CCRL2","total_profiled":1310},"omim":[{"mim_id":"612007","title":"CELIAC DISEASE, SUSCEPTIBILITY TO, 9; CELIAC9","url":"https://www.omim.org/entry/612007"},{"mim_id":"608379","title":"CHEMOKINE, CC MOTIF, RECEPTOR-LIKE PROTEIN 2; CCRL2","url":"https://www.omim.org/entry/608379"},{"mim_id":"602227","title":"CHEMOKINE, CC MOTIF, LIGAND 19; CCL19","url":"https://www.omim.org/entry/602227"},{"mim_id":"601973","title":"RETINOIC ACID RECEPTOR RESPONDER 2; RARRES2","url":"https://www.omim.org/entry/601973"},{"mim_id":"187011","title":"CHEMOKINE, CC MOTIF, LIGAND 5; CCL5","url":"https://www.omim.org/entry/187011"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Plasma membrane","reliability":"Supported"},{"location":"Primary cilium","reliability":"Additional"},{"location":"Primary cilium tip","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/CCRL2"},"hgnc":{"alias_symbol":["HCR","CRAM-B","CKRX","CRAM-A","ACKR5"],"prev_symbol":[]},"alphafold":{"accession":"O00421","domains":[{"cath_id":"1.20.1070.10","chopping":"40-314","consensus_level":"medium","plddt":85.2898,"start":40,"end":314}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O00421","model_url":"https://alphafold.ebi.ac.uk/files/AF-O00421-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O00421-F1-predicted_aligned_error_v6.png","plddt_mean":77.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CCRL2","jax_strain_url":"https://www.jax.org/strain/search?query=CCRL2"},"sequence":{"accession":"O00421","fasta_url":"https://rest.uniprot.org/uniprotkb/O00421.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O00421/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O00421"}},"corpus_meta":[{"pmid":"17179747","id":"PMC_17179747","title":"miR-122, 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studies\",\n      \"pmids\": [\"18794339\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Chemerin binds CCRL2 with low nanomolar affinity but CCRL2 does not activate any G protein subtypes (Gαi1, Gαi2, Gαi3, Gαoa, Gαob) and does not recruit β-arrestin1 or β-arrestin2, confirming CCRL2 as a non-signaling receptor for chemerin; the C-terminus of chemerin contributes differently to binding across the three chemerin receptors (CMKLR1, GPR1, CCRL2).\",\n      \"method\": \"BRET-based biosensors for G-protein activation and β-arrestin recruitment; radioligand binding assays\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal BRET biosensor assays with rigorous controls demonstrating absence of G protein and β-arrestin coupling\",\n      \"pmids\": [\"27716822\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CCRL2 on vascular endothelial cells binds chemerin and, through a presenting mechanism, promotes adhesion of CMKLR1+ lymphoid cells via an α4β1 integrin/VCAM-1-dependent mechanism; endothelial CCRL2 regulates circulating chemerin levels and CMKLR1+ NK cell recruitment to inflamed airways in vivo.\",\n      \"method\": \"In vitro chemerin binding assay on EC, CCRL2-/- mouse model with LPS-induced pulmonary inflammation, adhesion assays with blocking antibodies\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse model combined with in vitro mechanistic assays using integrin/VCAM-1 blocking\",\n      \"pmids\": [\"22696441\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CCRL2 constitutively forms homodimers and heterodimers with CXCR2; by heterodimerization, CCRL2 regulates membrane expression of CXCR2 and promotes CXCR2-dependent functions including β2-integrin activation and neutrophil chemotaxis; CCRL2-deficient mice show defective neutrophil recruitment and are protected in inflammatory arthritis models.\",\n      \"method\": \"Co-immunoprecipitation, BRET/FRET dimerization assays, CCRL2-/- mouse models of inflammatory arthritis, β2-integrin activation assays\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP and dimerization assays combined with KO mouse phenotyping with defined cellular readout\",\n      \"pmids\": [\"28743719\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"CCRL2 is required for antigen-loaded lung dendritic cell trafficking to mediastinal lymph nodes; CCRL2-/- mice show defective DC migration and reduced T helper cell 2 priming, and adoptive transfer of CCRL2-/- DCs into wild-type mice recapitulates the KO phenotype.\",\n      \"method\": \"CCRL2-/- mouse model, in vivo DC trafficking assays, adoptive transfer experiments, ovalbumin-induced airway inflammation model\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse model with adoptive transfer establishing cell-autonomous DC role\",\n      \"pmids\": [\"20606167\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CCRL2 expression by non-hematopoietic (endothelial) cells controls NK cell recruitment to the lung and suppresses lung tumor progression; bone marrow chimera experiments established that CCRL2 on the non-hematopoietic compartment, not hematopoietic cells, is responsible for NK-cell-dependent lung cancer immune surveillance.\",\n      \"method\": \"CCRL2-/- mouse models (urethane-induced and KrasG12D/p53Flox), bone marrow chimeras, flow cytometric leukocyte analysis\",\n      \"journal\": \"Cancer immunology research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — bone marrow chimera epistasis combined with two independent tumor models\",\n      \"pmids\": [\"31484658\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CCRL2 interacts with TLR4 on the macrophage cell surface to retain membrane TLR4 expression and enhance downstream MyD88-NF-κB inflammatory signaling, thereby amplifying immunostimulatory macrophage activation and antitumor T-cell responses.\",\n      \"method\": \"Co-immunoprecipitation of CCRL2 with TLR4, CCRL2-/- mouse melanoma model, macrophage depletion, CD8+ T-cell depletion, NF-κB reporter assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP demonstrating direct interaction plus multiple KO/depletion experiments with defined signaling readout\",\n      \"pmids\": [\"33846258\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CCRL2 does not scavenge chemerin: CCRL2-transfected cells and activated endothelial cells expressing endogenous CCRL2 show only weak constitutive ligand-independent internalization and recycling (slower than ACKR3 or CMKLR1), and do not reduce extracellular chemerin levels; intracellularly, CCRL2 co-localizes with EEA1/Rab5 early endosomes and Rab11 recycling compartments.\",\n      \"method\": \"Internalization and scavenging assays in CCRL2-transfected cells and activated mouse endothelial cells, confocal co-localization with endosomal markers\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal cell biology methods in both transfected and endogenously expressing cells\",\n      \"pmids\": [\"29056935\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CCRL2 deficiency in mice leads to exacerbated, non-resolving experimental autoimmune encephalitis with increased M1/M2 macrophage imbalance and protracted inflammatory response, identifying CCRL2 as a regulator of macrophage polarization during CNS inflammation resolution.\",\n      \"method\": \"CCRL2-/- EAE mouse model, macrophage activation marker analysis, M1/M2 polarization profiling\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse with defined phenotype; single lab\",\n      \"pmids\": [\"26744451\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"CCL19 is a specific ligand for the CCRL2 splice variant CRAM-B; CCRL2/CRAM constitutively recycles via clathrin-coated pits and internalizes CCL19 without triggering calcium mobilization, migration, or classical chemokine receptor signaling.\",\n      \"method\": \"Radioactive labeling binding assays, calcium flux assays, migration assays, internalization/recycling assays in CRAM-expressing cells\",\n      \"journal\": \"Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — binding and functional assays with multiple readouts; single lab\",\n      \"pmids\": [\"20002784\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Absence of CCRL2 results in elevated local and systemic chemerin levels in vivo; antibody neutralization of chemerin in CCRL2-/- mice abrogates the amplified inflammatory response (increased myeloid cell recruitment and CXCL1 levels), establishing that CCRL2 restrains inflammation by limiting bioavailable chemerin.\",\n      \"method\": \"CCRL2-/- mouse models of zymosan- and thioglycollate-induced acute inflammation, chemerin ELISA, anti-chemerin antibody neutralization\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse model with antibody rescue epistasis definitively linking CCRL2 to chemerin regulation\",\n      \"pmids\": [\"29209334\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CCRL2 coprecipitates with JAK2 and potentiates JAK2-STAT3/STAT5 interaction; CCRL2 knockdown in MDS/sAML cell lines decreases JAK2/STAT3/STAT5 phosphorylation and suppresses cell growth in vitro and in vivo, placing CCRL2 upstream of JAK-STAT signaling in myeloid malignancy.\",\n      \"method\": \"Co-immunoprecipitation of CCRL2 with JAK2, shRNA knockdown in MDS cell lines, xenograft mouse model, phospho-flow cytometry for STAT3/STAT5\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP plus KD with defined signaling and in vivo phenotype; single lab\",\n      \"pmids\": [\"35179961\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CCRL2 on lung alveolar capillary endothelial cells (identified as the hallmark gene of this subset by scRNA-seq) controls homing of CD27-CD11b+ mature NK cells to the lung; conditional endothelial CCRL2 ablation or chemerin deletion promotes lung tumor progression; epigenetic upregulation of endothelial CCRL2 by 5-aza-2'-deoxycytidine increases NK cell recruitment and reduces tumor growth.\",\n      \"method\": \"Conditional endothelial CCRL2 KO, scRNA-seq, in vivo KrasG12D/p53Flox lung tumor model, 5-aza pharmacological treatment, NK cell depletion\",\n      \"journal\": \"Cancer immunology research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with scRNA-seq validation and pharmacological rescue; multiple independent genetic approaches\",\n      \"pmids\": [\"37343073\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Endothelial CCRL2, induced by disturbed flow, recruits chemerin which activates β2-integrin on monocytes via a protein disulfide isomerase-like enzymatic activity of chemerin, enhancing ERK1/2 phosphorylation and monocyte adhesion; CCRL2-/-ApoE-/- mice are protected from atherosclerotic plaque formation at disturbed-flow sites.\",\n      \"method\": \"CCRL2-/-ApoE-/- mouse model, Di-E-GSSG PDI activity assay, proximity ligation assay for chemerin-β2 integrin interaction, ERK1/2 phosphorylation assays, scRNA-seq\",\n      \"journal\": \"Cardiovascular research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — enzymatic activity assay plus in vivo KO mouse model with multiple orthogonal methods\",\n      \"pmids\": [\"37279540\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"MTB Hsp16.3-induced macrophage M2 polarization depends on CCRL2 and CX3CR1; overexpression or silencing of CCRL2 modulates Hsp16.3-driven M2 markers (Arg-1, IL-10, TGF-β, CD206) and downstream AKT/ERK/p38-MAPK signaling.\",\n      \"method\": \"Overexpression and siRNA knockdown of CCRL2 in macrophages, western blotting for AKT/ERK/p38 phosphorylation, cytokine ELISA\",\n      \"journal\": \"Inflammation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — gain/loss of function with signaling readout; single lab, no direct binding demonstrated\",\n      \"pmids\": [\"31748849\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"CCL5 upregulates CCRL2 (CRAM) surface expression on pre-B cell lines; CCL5 stimulation of CRAM-expressing cells phosphorylates ERK1/2 in a pertussis-toxin-insensitive manner (not Gi-coupled), without calcium mobilization or cell migration, indicating a non-classical signaling mode.\",\n      \"method\": \"Flow cytometry for surface CCRL2 upregulation, ERK1/2 phosphorylation assays, calcium flux assays, pertussis toxin inhibition, migration assays in B-cell lines\",\n      \"journal\": \"Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple signaling readouts in endogenously expressing cells; single lab\",\n      \"pmids\": [\"18397265\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"CCRL2 overexpression in breast cancer cells attenuates CCL2-stimulated chemotaxis and invasion by inhibiting p38 MAPK phosphorylation and upregulating E-cadherin expression; the anti-invasive effect is abolished by p38 MAPK inhibitor.\",\n      \"method\": \"Stable CCRL2 overexpression in MDA-MB-231 and BT-549 cells, Transwell migration/invasion assays, western blotting for p38 phosphorylation and E-cadherin, xenograft tumor model\",\n      \"journal\": \"Medical oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gain-of-function with defined signaling pathway and inhibitor rescue; single lab\",\n      \"pmids\": [\"26487662\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CCRL2 binds SFRP1 on the surface of LepR+/CAR stromal cells in the periodontitis microenvironment, amplifying SFRP1's suppressive effect on Wnt signaling and thereby inhibiting osteogenic differentiation; CCRL2-KO mice show improved alveolar bone healing in extraction sockets with periodontitis.\",\n      \"method\": \"CCRL2-KO mouse model with periodontitis, Co-immunoprecipitation/binding of CCRL2 with SFRP1, Wnt signaling reporter assays, osteogenesis differentiation assays\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse combined with CCRL2-SFRP1 binding and defined Wnt signaling readout; single lab\",\n      \"pmids\": [\"38477792\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Vagal nerve stimulation reduces the proportion of CCRL2+ macrophages derived from myeloid monocytes; these CCRL2+ macrophages exhibit a TNF-α-responsive, pro-hypertrophic, and profibrotic signature; α7nAChR activation on CCRL2+ macrophages suppresses their TNF-α responsiveness via increased NRF2 expression, mediating cardioprotection.\",\n      \"method\": \"Optogenetic VNS in pressure-overload HF mouse model, single-cell transcriptomics, cell-type-specific α7nAChR manipulation, CCRL2+ macrophage depletion and genetic models\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — single lab but multiple orthogonal approaches including scRNA-seq and cell-specific genetic models\",\n      \"pmids\": [\"40580954\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Computational accelerated molecular dynamics and protein-protein docking identified putative hot-spot residues on CCRL2 involved in chemerin binding, with principal component analysis revealing receptor regions most frequently engaged in ligand contacts.\",\n      \"method\": \"Protein-protein docking followed by accelerated molecular dynamics simulation; PCA and kernel density estimation of trajectories\",\n      \"journal\": \"Proteins\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 — computational prediction only, no experimental validation\",\n      \"pmids\": [\"35437825\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CCRL2 is a non-signaling seven-transmembrane receptor that binds chemerin with low-nanomolar affinity without activating G proteins or β-arrestins; when expressed on barrier cells (especially lung endothelium), it presents chemerin to the signaling receptor CMKLR1 on leukocytes to concentrate chemotactic gradients and recruit NK cells and dendritic cells; it also forms heterodimers with CXCR2 to potentiate CXCR2-dependent β2-integrin activation in neutrophils, interacts with TLR4 to enhance MyD88-NF-κB macrophage activation, coprecipitates with JAK2 to potentiate JAK-STAT signaling in myeloid cells, and binds SFRP1 to amplify Wnt inhibition in stromal cells, thereby acting as a context-dependent regulator of inflammation, leukocyte trafficking, and immune surveillance rather than a classical chemokine-scavenging decoy receptor.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll systematically classify papers before extracting discoveries.\n\n**Classification:**\n\nKEEP (about canonical CCRL2 protein):\n- [2] PMID:18794339 - CCRL2 binds chemerin, mast cells\n- [3] PMID:27716822 - Signaling properties of chemerin receptors including CCRL2\n- [4] PMID:21056554 - CMKLR1 and CCRL2 review\n- [5] PMID:22696441 - CCRL2 on endothelial cells\n- [9] PMID:28743719 - CCRL2 homodimers/heterodimers with CXCR2\n- [11] PMID:20606167 - CCRL2 in lung DC trafficking\n- [14] PMID:33846258 - CCRL2 interacts with TLR4, macrophage activation\n- [15] PMID:15188357 - CCRL2 in RA, splice variants\n- [17] PMID:33363177 - Molecular basis review\n- [18] PMID:20002784 - CCL19 binds CRAM-B/CCRL2\n- [22] PMID:11828366 - HCR = human chemokine receptor = CCRL2 (this is the original cloning paper for CCRL2 in leukocytes - KEEP)\n- [26] PMID:23580473 - CCRL2 fringe member review\n- [30] PMID:31484658 - CCRL2 in lung cancer immune surveillance\n- [31] PMID:26744451 - CCRL2 in EAE, M1/M2 polarization\n- [34] PMID:26383527 - CCR1 and CCRL2 in CRC\n- [40] PMID:29056935 - CCRL2 not a decoy receptor, localization\n- [47] PMID:31748849 - CCRL2/CX3CR1 and Hsp16.3, macrophage M2\n- [48] PMID:37279540 - CCRL2 in atherosclerosis, chemerin-β2 integrin\n- [49] PMID:18397265 - CRAM-A/B on B cells, CCL5\n- [55] PMID:23142225 - CCRL2 in glioblastoma migration\n- [60] PMID:29209334 - CCRL2 absence exacerbates inflammation\n- [61] PMID:22046140 - CCRL2 F167Y variant, AIDS\n- [63] PMID:32398173 - CCRL2 expression in porcine uterus\n- [64] PMID:35179961 - CCRL2 in MDS, JAK2/STAT signaling\n- [65] PMID:36519323 - CCRL2 in MDS, azacitidine sensitivity\n- [66] PMID:26563945 - CRAM-A in breast cancer\n- [69] PMID:26487662 - CCRL2 suppresses CCL2-induced p38 MAPK\n- [77] PMID:35224158 - CCRL2 in obesity/insulin resistance\n- [78] PMID:34638484 - CCRL2 concentrates chemerin, inhibits angiogenesis\n- [79] PMID:29497024 - CCRL2 in prostate cancer\n- [87] PMID:37343073 - CCRL2 in lung capillary endothelial cells, NK homing\n- [91] PMID:40580954 - CCRL2+ macrophages in heart failure\n- [94] PMID:35437825 - Molecular dynamics of CCRL2-chemerin binding\n- [96] PMID:38477792 - CCRL2 binds SFRP1, inhibits Wnt signaling\n- [14-curated] PMID:14530373 - Chemerin/ChemR23 (CMKLR1) - relevant context\n- [23-curated] PMID:33253374 - CCRL2 as HIV-2 coreceptor\n- [14-curated-fan] PMID:9473515 - Original cloning of HCR/CCRL2\n- [22-curated] PMID:36662882 - CCRL2 ligand binding, CXCL8/CXCR2\n- [22-curated-GPR1] PMID:39466725 - GPR1/chemerin structure (context for CCRL2)\n\nEXCLUDE (alias collisions or off-target):\n- [1] miR-122/hcr - woodchuck hcr locus, not CCRL2\n- [6],[7],[19],[32],[39],[44],[82] - HCR = alpha-helix coiled-coil rod homolog (psoriasis gene CCHCR1), not CCRL2\n- [8] - HCR.1/HCR.2 = hepatic control regions for apolipoprotein genes\n- [10] - CRAM = CRMP3-associated molecule (neural protein), not CCRL2\n- [12] - Hcr = hybrid cluster protein reductase in E. coli\n- [13] - HCR-FlowFISH = hybridization chain reaction technique\n- [16],[20],[21],[23-28],[29],[33],[36],[37],[38],[41],[45],[50],[52],[53],[54],[57],[58],[70],[71],[72],[73],[74],[75],[76],[80],[81],[84],[85],[86],[90],[92],[93],[95],[97],[99],[100] - HCR = hybridization chain reaction (biosensor/imaging technology)\n- [35],[46] - hcr = woodchuck hepatocyte locus rearranged with c-myc\n- [42] - HCR-20 = Historical Clinical Risk assessment tool (psychiatry)\n- [43] - Hcr = hepatocarcinogen resistance loci in mice\n- [51] - HCR-1 = hepatic control region for apoC-II gene\n- [56] - HCR = HWP1 control region in Candida albicans\n- [59],[98] - Hcr+ = E. coli UV repair strain designation\n- [62] - HCR = alpha-helix coiled-coil rod homolog interacting with RPB3 (psoriasis)\n- [83] - 4-HCR = 4-hydroperoxycyclophosphamide-resistant cell line\n- [88],[89] - hcp-hcr operon in E. coli\n- Curated [1],[2],[3],[4],[5],[7],[8],[9],[10],[11],[12],[13],[15],[16],[17] - interactome/GWAS/genomics papers without CCRL2-specific mechanistic findings\n- Curated [18] - CCRL2 expression in NASH (expression correlation, no mechanism)\n- Curated [19],[20] - SNP associations\n\nNow extracting discoveries from KEPT papers:\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1998,\n      \"finding\": \"CCRL2 (originally named HCR) was cloned as a novel seven-transmembrane chemokine receptor from a human neutrophil cDNA library, predicted to encode a 345 amino acid protein with homology to CCR1 (MIP-1α receptor, 43% identity), and mapped to chromosome 3p21. Expression was found in spleen, fetal liver, lymph node, bone marrow, lung, and heart.\",\n      \"method\": \"cDNA library screening, Northern blot, chromosome mapping\",\n      \"journal\": \"Biochemical and Biophysical Research Communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — original cloning with expression characterization; single study\",\n      \"pmids\": [\"9473515\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"CCRL2 (designated HCR) is expressed on CD4+ and CD8+ T lymphocytes, monocytes, macrophages, monocyte-derived dendritic cells, neutrophils, and CD34+ hematopoietic precursors in peripheral blood and bone marrow. Expression is upregulated on T cells by OKT3/IL-2, and on dendritic cells by LPS, poly(I:C), IFN-γ, or CD40L stimulation.\",\n      \"method\": \"Monoclonal antibody generation, flow cytometry, real-time PCR\",\n      \"journal\": \"European Journal of Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — monoclonal antibodies with direct cell surface staining confirmed by PCR; single lab\",\n      \"pmids\": [\"11828366\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"CCRL2 is expressed on synovial neutrophils and some macrophages in rheumatoid arthritis patients. CCRL2 mRNA is rapidly upregulated in primary neutrophils by LPS or TNF stimulation. HEK293 cells expressing either splice variant CCRL2A or CCRL2B migrated in response to fractions of RA synovial fluid, demonstrating functional receptor activity.\",\n      \"method\": \"Immunocytochemistry, Northern blot, Western blot, RT-PCR, retroviral expression, 48-well chemotaxis chamber\",\n      \"journal\": \"Arthritis and Rheumatism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — functional migration assay with two splice variants; single lab\",\n      \"pmids\": [\"15188357\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Chemerin is identified as a natural nonsignaling protein ligand for both human and mouse CCRL2. Unlike other atypical chemokine receptors (DARC, D6), chemerin binding to CCRL2 does not trigger ligand internalization. Instead, CCRL2 binds chemerin and increases local concentrations of bioactive chemerin, thereby presenting it to the signaling chemerin receptor CMKLR1 on nearby cells, linking CCRL2 expression to inflammation.\",\n      \"method\": \"Binding assays, chemerin internalization assays, IgE-mediated passive cutaneous anaphylaxis mouse model, CCRL2-deficient mice\",\n      \"journal\": \"The Journal of Experimental Medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods, replicated in human and mouse, mechanistic model supported by in vivo genetics\",\n      \"pmids\": [\"18794339\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"CCRL2 (CRAM-A/B) is expressed on human B lymphocytes in a maturation-stage-dependent manner and is specifically upregulated by CCL5 exposure. CCL5 stimulation through CRAM induces ERK1/2 phosphorylation in pre-B cell lines lacking other known CCL5 receptors, but does not cause calcium mobilization or migration. This ERK1/2 phosphorylation is not inhibitable by pertussis toxin, indicating CCRL2 does not couple to Gi proteins.\",\n      \"method\": \"Flow cytometry, Western blot (ERK1/2 phosphorylation), calcium flux assay, migration assay, pertussis toxin inhibition\",\n      \"journal\": \"Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — direct signaling assays with pharmacological controls; single lab\",\n      \"pmids\": [\"18397265\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"CCL19 is identified as a specific ligand for CCRL2 (CRAM-B). CCL19 binds CCRL2-expressing cells with nanomolar affinity similar to CCR7. Unlike the CCL19/CCR7 pair, CCL19 stimulation of CCRL2 does not induce calcium mobilization or cell migration. CCRL2 constitutively recycles via clathrin-coated pits and internalizes CCL19 as well as anti-CCRL2 antibodies, classifying it as an atypical non-classical chemokine receptor.\",\n      \"method\": \"Radioactive ligand binding, calcium mobilization assay, migration assay, internalization assay, clathrin-coated pit analysis\",\n      \"journal\": \"Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — multiple functional assays; single lab\",\n      \"pmids\": [\"20002784\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"CCRL2 mRNA is rapidly (within 30 minutes) and transiently (2-4 hours) upregulated during dendritic cell maturation, with protein expression paralleling RNA regulation. CCRL2-deficient mice show normal DC recruitment to the lung but defective trafficking of antigen-loaded lung DCs to mediastinal lymph nodes, resulting in reduced T helper cell 2 priming. Adoptive transfer of CCRL2-deficient antigen-loaded DCs into wild-type mice recapitulates this phenotype.\",\n      \"method\": \"CCRL2 knockout mice, adoptive DC transfer, lung inflammation model (OVA), flow cytometry, BAL analysis\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with adoptive transfer rescue, multiple orthogonal in vivo readouts\",\n      \"pmids\": [\"20606167\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CCRL2 is upregulated on vascular endothelial cells by proinflammatory stimuli via NF-κB and JAK/STAT signaling pathways. Endothelial CCRL2 expression enables chemerin binding and triggers robust adhesion of CMKLR1+ lymphoid cells through an α4β1 integrin/VCAM-1-dependent mechanism. In CCRL2-deficient mice, plasma chemerin levels are elevated and CMKLR1+ NK cell recruitment to the airways during acute LPS-induced pulmonary inflammation is significantly impaired.\",\n      \"method\": \"CCRL2 KO mice, NF-κB/JAK/STAT pathway inhibitors, integrin blocking antibodies, lymphocyte adhesion assay, in vivo LPS lung inflammation model, flow cytometry\",\n      \"journal\": \"Journal of Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (genetic KO, pharmacological inhibition, blocking antibodies) with in vitro and in vivo validation\",\n      \"pmids\": [\"22696441\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CCRL2 overexpression significantly enhances migration rate and invasiveness of glioblastoma cells (U87, U373) without affecting proliferation, as determined by gain-of-function and loss-of-function studies.\",\n      \"method\": \"Overexpression and siRNA knockdown, migration and invasion assays (transwell), proliferation assay\",\n      \"journal\": \"Biochemical and Biophysical Research Communications\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, phenotypic readout without pathway mechanism\",\n      \"pmids\": [\"23142225\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CCRL2 binds chemerin with low nanomolar affinity, but unlike CMKLR1, chemerin binding to CCRL2 does not activate any of the three Gαi subtypes, two Gαo isoforms, or recruit β-arrestin1 or β-arrestin2. CCRL2 also does not promote receptor internalization or ERK1/2 phosphorylation upon chemerin binding, establishing it as a non-signaling receptor that is functionally distinct from CMKLR1 and GPR1.\",\n      \"method\": \"BRET-based biosensors for G protein activation, β-arrestin recruitment assays, receptor internalization assays, ERK1/2 phosphorylation assay\",\n      \"journal\": \"PloS One\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple BRET-based signaling readouts systematically compared across all three chemerin receptors; rigorous controls\",\n      \"pmids\": [\"27716822\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CCRL2-deficient mice develop exacerbated, non-resolving experimental autoimmune encephalitis (EAE) with protracted inflammation and increased demyelination. This is associated with higher microglia/macrophage activation markers and imbalanced M1/M2 polarization, indicating CCRL2 promotes M2 polarization during the recovery phase to downregulate CNS inflammation.\",\n      \"method\": \"CCRL2 KO mice, EAE model, histological analysis, flow cytometry for M1/M2 markers\",\n      \"journal\": \"Journal of Leukocyte Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with defined inflammatory phenotype; single lab\",\n      \"pmids\": [\"26744451\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CCRL2 constitutively forms homodimers and heterodimers with CXCR2 as demonstrated by co-immunoprecipitation. By heterodimerization with CXCR2, CCRL2 regulates membrane CXCR2 expression and promotes CXCR2-mediated functions including activation of β2-integrins. CCRL2-deficient mice have a specific defect in neutrophil recruitment and are protected in two models of inflammatory arthritis.\",\n      \"method\": \"Co-immunoprecipitation (homodimer/heterodimer detection), CCRL2 KO mice, inflammatory arthritis models, β2-integrin activation assay, neutrophil migration assay\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP for dimerization plus in vivo KO models with specific mechanistic follow-up; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"28743719\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CCRL2 undergoes weak constitutive ligand-independent internalization and recycling, slower than ACKR3 or other chemotactic receptors. Intracellularly, CCRL2 colocalizes with EEA1- and Rab5-positive early endosomes and Rab11-positive recycling compartments. Critically, CCRL2-transfected cells and activated endothelial cells endogenously expressing CCRL2 cannot scavenge chemerin, confirming CCRL2 is not a decoy/scavenging receptor.\",\n      \"method\": \"Cell membrane internalization assays, immunofluorescence colocalization with endosomal markers (EEA1, Rab5, Rab11), chemerin scavenging assay in transfected and primary endothelial cells\",\n      \"journal\": \"Frontiers in Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct subcellular localization with multiple endosomal markers, functional scavenging assay in both transfected and primary cells\",\n      \"pmids\": [\"29056935\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CCRL2 absence in mice leads to exaggerated local and systemic inflammatory responses in zymosan- and thioglycollate-induced acute inflammation, characterized by increased myeloid cell recruitment associated with elevated chemerin and CXCL1 levels. Antibody neutralization of chemerin in CCRL2-deficient mice abrogates the amplified inflammatory response, demonstrating that CCRL2 regulates local chemerin concentration as its primary in vivo mechanism.\",\n      \"method\": \"CCRL2 KO mice, zymosan/thioglycollate peritonitis models, chemerin neutralizing antibody, cytokine/chemokine quantification, flow cytometry\",\n      \"journal\": \"Frontiers in Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with antibody neutralization rescue across two independent in vivo inflammation models\",\n      \"pmids\": [\"29209334\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CCRL2 expression by the non-hematopoietic (endothelial) cell compartment, as shown by bone marrow chimeras, is responsible for suppressing lung tumor formation. CCRL2 is expressed by a fraction of CD31+ lung endothelial cells where it controls NK cell infiltration into lung tumors. Genetic deletion of Ccrl2 promotes tumor progression in urethane-induced and Kras-mutant/p53-flox lung cancer models with impaired NK cell recruitment.\",\n      \"method\": \"CCRL2 KO mice, bone marrow chimeras, urethane lung cancer model, Kras/p53 genetic lung tumor model, flow cytometry for NK cells\",\n      \"journal\": \"Cancer Immunology Research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — bone marrow chimeras definitively assign CCRL2 function to non-hematopoietic compartment; multiple tumor models\",\n      \"pmids\": [\"31484658\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"MTB heat-shock protein Hsp16.3 induces macrophage M2 polarization through direct interaction with chemokine receptors CCRL2 and CX3CR1. Overexpression or silencing of CCRL2 modulates Hsp16.3-induced M2 polarization, and downstream signaling involves the AKT/ERK/p38-MAPK pathway.\",\n      \"method\": \"Overexpression and siRNA silencing, M2 marker quantification (Arg-1, IL-10, TGF-β, CD206), Western blot for AKT/ERK/p38-MAPK phosphorylation\",\n      \"journal\": \"Inflammation\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — gain/loss-of-function with pathway readout; single lab, no direct binding validation for Hsp16.3/CCRL2\",\n      \"pmids\": [\"31748849\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CCRL2 interacts with TLR4 on the macrophage cell surface to retain membrane TLR4 expression and enhance TLR4 downstream Myd88-NF-κB inflammatory signaling. CCRL2-deficient mice exhibit accelerated melanoma growth with reduced immunostimulatory macrophages and T-cell responses. Depletion of CD8+ T cells or macrophages eliminates the tumor growth difference between WT and CCRL2-deficient mice.\",\n      \"method\": \"Co-immunoprecipitation (CCRL2-TLR4 interaction), flow cytometry for membrane TLR4, NF-κB signaling assay, CCRL2 KO mice, melanoma tumor model, CD8+ T cell and macrophage depletion\",\n      \"journal\": \"PNAS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — co-IP for direct interaction, functional signaling validation, in vivo genetic model with depletion rescue; multiple orthogonal methods\",\n      \"pmids\": [\"33846258\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CCRL2 expression by tumor cells concentrates bioactive chemerin and reduces neoangiogenesis in tumor grafts, mimicking the phenotype of chemerin-expressing tumors. Loss of Ccrl2 accelerates papilloma development in a DMBA/TPA skin carcinogenesis model. These phenotypes are abrogated by knockout of chemerin or Cmklr1, demonstrating that CCRL2 acts through the chemerin/CMKLR1 axis.\",\n      \"method\": \"CCRL2 KO mice, DMBA/TPA skin carcinogenesis model, B16/LLC tumor grafts with CCRL2 overexpression or knockout, chemerin and Cmklr1 KO epistasis, angiogenesis quantification\",\n      \"journal\": \"Cancers\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis (chemerin/CMKLR1 KO rescues CCRL2 phenotype) across multiple tumor models\",\n      \"pmids\": [\"34638484\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CCRL2 knockdown suppresses MDS92 and MDS-L cell growth and clonogenicity in vitro and in vivo, and decreases JAK2/STAT3/STAT5 phosphorylation. CCRL2 co-precipitates with JAK2 and potentiates JAK2-STAT interaction. Erythroleukemia cells with constitutively active JAK2V617F show less dependence on CCRL2, and JAK2 inhibitor fedratinib potentiates CCRL2 knockdown effects.\",\n      \"method\": \"siRNA knockdown, co-immunoprecipitation (CCRL2-JAK2), Western blot (JAK2/STAT3/STAT5 phosphorylation), xenograft mouse model, pharmacological JAK2 inhibition\",\n      \"journal\": \"Science Advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — co-IP for direct interaction, phosphorylation readout, in vivo xenograft, and pharmacological epistasis; multiple orthogonal methods\",\n      \"pmids\": [\"35179961\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Accelerated molecular dynamics simulation of CCRL2 with chemerin docking identified putative hot-spot residues in the CCRL2 transmembrane domain and extracellular loops most frequently involved in chemerin binding, providing a structural model for the CCRL2-chemerin interaction.\",\n      \"method\": \"Protein-protein docking, accelerated molecular dynamics, principal component analysis, kernel density estimation\",\n      \"journal\": \"Proteins\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 — computational prediction only, no experimental validation\",\n      \"pmids\": [\"35437825\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CCRL2 is expressed specifically by general alveolar lung capillary endothelial cells (identified by scRNA-seq as a hallmark marker). Conditional or constitutive endothelial CCRL2 ablation promotes lung tumor progression by reducing recruitment of CD27-CD11b+ mature NK cells. CCRL2 expression in lung endothelium is epigenetically regulated, and in vivo administration of the demethylating agent 5-aza-2'-deoxycytidine (5-Aza) upregulates CCRL2, increases NK cell recruitment, and reduces lung tumor growth.\",\n      \"method\": \"scRNA-seq, conditional/constitutive CCRL2 endothelial KO, Kras/p53 lung tumor model, 5-Aza treatment, flow cytometry for NK cell subsets, epigenetic regulation analysis\",\n      \"journal\": \"Cancer Immunology Research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — scRNA-seq identification, conditional KO with multiple tumor models, pharmacological upregulation with functional rescue; multiple orthogonal methods\",\n      \"pmids\": [\"37343073\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Endothelial CCRL2 induced by disturbed flow recruits chemerin, which activates β2 integrin on monocytes via a protein disulfide isomerase-like enzymatic activity of chemerin (rather than through monocytic CMKLR1), enhancing ERK1/2 phosphorylation and monocyte adhesion. CCRL2-deficient ApoE-/- mice are protected against atherosclerotic plaque formation in disturbed-flow areas.\",\n      \"method\": \"CCRL2-/-ApoE-/- mice, high-fat diet atherosclerosis model, scRNA-seq, Di-E-GSSG assay (PDI-like activity), proximity ligation assay (chemerin-β2 integrin interaction), ERK1/2 phosphorylation, monocyte adhesion assay\",\n      \"journal\": \"Cardiovascular Research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO in vivo, proximity ligation assay for direct interaction, enzymatic activity assay; multiple orthogonal methods\",\n      \"pmids\": [\"37279540\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CCRL2 neutralizing antibodies confirm that chemerin (but not previously reported CC chemokines) directly binds CCRL2 by flow cytometry and Surface Plasmon Resonance microscopy. However, antibody-mediated neutralization of CCRL2 ligand-binding does not attenuate CXCL8-induced neutrophil degranulation or CXCL8-induced murine neutrophil peritoneal recruitment, suggesting CCRL2's ligand-binding function is dispensable for CXCR2-mediated CXCL8 signaling in neutrophils.\",\n      \"method\": \"Flow cytometry binding assay, Surface Plasmon Resonance microscopy, CCRL2 neutralizing antibodies, neutrophil degranulation assay, in vivo peritoneal neutrophil recruitment\",\n      \"journal\": \"PloS One\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — SPRm binding confirmation plus functional antibody neutralization; challenges mechanism from PMID:28743719\",\n      \"pmids\": [\"36662882\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CCRL2 knockdown in MDS/sAML cell lines downregulates DNA methylation and PRC2 activity pathways, increases DNMT suppression by azacitidine, and sensitizes these cells to azacitidine both in vitro and in an MDS-L xenograft model. CCRL2 overexpression conversely decreases azacitidine sensitivity, demonstrating CCRL2 modulates epigenetic regulatory pathways.\",\n      \"method\": \"siRNA knockdown, CCRL2 overexpression, azacitidine sensitivity assays, xenograft model, gene expression profiling (PRC2/DNMT pathways)\",\n      \"journal\": \"Haematologica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — bidirectional gain/loss-of-function with in vivo xenograft; single lab\",\n      \"pmids\": [\"36519323\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CCRL2 binds SFRP1 on the surface of LepR+/CAR stromal cells, amplifying SFRP1's suppressive effect on Wnt signaling under inflammatory conditions. This CCRL2-SFRP1 interaction inhibits osteogenic differentiation of LepR+/CAR cells, resulting in impaired bone healing in periodontitis. CCRL2-knockout mice show significant improvements in extraction socket bone healing.\",\n      \"method\": \"CCRL2 KO mice, co-immunoprecipitation (CCRL2-SFRP1 interaction), Wnt signaling reporter assay, osteogenic differentiation assay, bone healing quantification by micro-CT\",\n      \"journal\": \"Journal of Bone and Mineral Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — co-IP for novel interaction, functional readout in KO mice; single lab\",\n      \"pmids\": [\"38477792\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CCRL2 functions as a coreceptor for primary HIV-2 isolates (and to a lesser extent HIV-1) in NP-2/CD4/CCRL2 cells. HIV-2MIR infection was demonstrated by immunofluorescence, proviral DNA detection, reverse transcriptase activity measurement, and multinucleated giant cell formation, making CCRL2 a newly identified HIV-2 entry coreceptor.\",\n      \"method\": \"NP-2 cell transduction with CD4 and CCRL2, HIV infection assay, immunofluorescence, PCR for proviral DNA, reverse transcriptase activity assay, Giemsa staining for syncytia\",\n      \"journal\": \"Briefings in Bioinformatics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — cell-based infection assay; single lab, in vivo relevance unverified\",\n      \"pmids\": [\"33253374\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Optogenetic vagal nerve stimulation decreases the proportion of CCRL2+ macrophages, which are monocyte-derived and exhibit a TNF-α-responsive, pro-hypertrophic, profibrotic signature. Elimination of CCRL2+ macrophages prevents cardiac remodeling and heart failure. α7nAChR activation inhibits CCRL2+ macrophage TNF-α responsiveness through increased NRF2 expression. CCRL2+-macrophage-specific overexpression or global loss of α7nAChR eliminates VNS-mediated cardioprotection.\",\n      \"method\": \"Optogenetic VNS, CCRL2+ macrophage depletion, macrophage-specific α7nAChR overexpression/KO, NRF2 expression assay, cardiac remodeling quantification, scRNA-seq\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — macrophage-specific genetic manipulation with functional cardiac readout; single study\",\n      \"pmids\": [\"40580954\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CCRL2 is a non-signaling seven-transmembrane atypical chemokine receptor that binds chemerin with high affinity but does not activate G proteins, β-arrestins, or trigger ligand scavenging/internalization; instead, it acts as a chemerin-presenting molecule on endothelial and barrier cells to amplify local chemerin concentrations and facilitate CMKLR1-dependent leukocyte recruitment, while also forming constitutive homodimers and heterodimers with CXCR2 to regulate neutrophil β2-integrin activation, interacting with TLR4 to potentiate Myd88-NF-κB macrophage activation, co-precipitating with JAK2 to potentiate JAK2-STAT signaling in myeloid malignancies, and binding SFRP1 to suppress Wnt signaling in stromal cells, thereby functioning as a context-dependent positive or negative regulator of innate immunity, tumor surveillance, and tissue homeostasis.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CCRL2 is a non-signaling seven-transmembrane receptor that serves as a context-dependent regulator of inflammation, leukocyte trafficking, and immune surveillance by concentrating chemotactic ligands and modulating partner receptor signaling at the cell surface. CCRL2 binds chemerin with low-nanomolar affinity without activating G proteins or recruiting β-arrestins, and presents bioactive chemerin to the signaling receptor CMKLR1 on nearby leukocytes, thereby promoting integrin-dependent adhesion and recruitment of NK cells and dendritic cells, particularly at lung endothelial barriers where it controls antitumor immune surveillance [PMID:18794339, PMID:27716822, PMID:22696441, PMID:31484658, PMID:37343073]. Beyond chemerin presentation, CCRL2 heterodimerizes with CXCR2 to potentiate β2-integrin activation and neutrophil chemotaxis, interacts with TLR4 to enhance MyD88-NF-κB signaling in macrophages, coprecipitates with JAK2 to augment JAK-STAT3/STAT5 phosphorylation in myeloid cells, and binds SFRP1 on stromal cells to amplify Wnt pathway inhibition [PMID:28743719, PMID:33846258, PMID:35179961, PMID:38477792]. CCRL2 deficiency in mice results in elevated bioavailable chemerin, dysregulated myeloid cell recruitment, exacerbated inflammatory disease, and impaired antitumor immunity, establishing CCRL2 as a non-redundant tuner of inflammatory and immune responses [PMID:29209334, PMID:26744451, PMID:31484658].\",\n  \"teleology\": [\n    {\n      \"year\": 2008,\n      \"claim\": \"The identity of CCRL2's natural ligand was unknown; the demonstration that CCRL2 binds chemerin without triggering internalization or classical signaling established it as a non-scavenging presentation receptor, fundamentally distinguishing it from other atypical chemokine receptors.\",\n      \"evidence\": \"Radioligand binding, flow cytometry, and CCRL2-KO mouse passive cutaneous anaphylaxis model\",\n      \"pmids\": [\"18794339\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of chemerin–CCRL2 interaction unknown\", \"Mechanism by which presented chemerin activates CMKLR1 on adjacent cells not resolved\", \"Relative contribution of CCRL2 versus CMKLR1 to chemerin clearance in vivo unclear\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Whether CCRL2 splice variants interact with classical chemokines was unclear; the finding that the CRAM-B splice variant binds and internalizes CCL19 without triggering calcium or migration revealed an additional ligand specificity and constitutive recycling behavior.\",\n      \"evidence\": \"Radioligand binding, calcium flux, migration, and internalization/recycling assays in CRAM-expressing cells\",\n      \"pmids\": [\"20002784\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"CCL19–CCRL2 interaction not confirmed by independent labs\", \"Physiological relevance of CRAM-B splice variant in vivo not established\", \"Relationship between CCL19 and chemerin binding at full-length CCRL2 not clarified\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Whether CCRL2 has cell-autonomous immune functions beyond chemerin presentation was unknown; demonstrating that CCRL2-deficient dendritic cells fail to migrate to draining lymph nodes established a DC-intrinsic role in adaptive immune priming.\",\n      \"evidence\": \"CCRL2-KO mouse, in vivo DC trafficking assays, adoptive transfer of CCRL2-KO DCs into wild-type recipients, OVA airway inflammation model\",\n      \"pmids\": [\"20606167\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether DC migration defect is chemerin-dependent or chemerin-independent not resolved\", \"Molecular mechanism by which CCRL2 promotes DC trafficking not identified\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"The cellular compartment responsible for chemerin presentation was undefined; showing that vascular endothelial CCRL2 concentrates chemerin to drive α4β1-integrin/VCAM-1-dependent adhesion of CMKLR1+ NK cells identified the endothelium as the critical barrier for chemerin-mediated leukocyte recruitment.\",\n      \"evidence\": \"CCRL2-KO mouse with LPS-induced pulmonary inflammation, endothelial chemerin binding assays, integrin/VCAM-1 blocking antibodies\",\n      \"pmids\": [\"22696441\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether other endothelial chemerin receptors contribute in vivo not excluded\", \"Kinetics of chemerin hand-off from CCRL2 to CMKLR1 unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Rigorous exclusion of CCRL2 signaling capacity was needed; BRET biosensors demonstrated that chemerin binding fails to activate any Gα subtype or recruit β-arrestin1/2, confirming CCRL2 as a bona fide non-signaling receptor and ruling out low-level coupling.\",\n      \"evidence\": \"BRET-based G-protein activation and β-arrestin recruitment biosensors with radioligand binding\",\n      \"pmids\": [\"27716822\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Non-canonical signaling modes independent of G proteins and β-arrestins not fully excluded\", \"Whether CCRL2 undergoes conformational changes upon chemerin binding remains uncharacterized structurally\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Whether CCRL2 functions through receptor–receptor interactions was unknown; the discovery that CCRL2 constitutively heterodimerizes with CXCR2 to regulate its membrane expression and potentiate β2-integrin activation in neutrophils revealed a chemerin-independent mechanism for controlling leukocyte recruitment in inflammatory arthritis.\",\n      \"evidence\": \"Co-IP, BRET/FRET dimerization assays, CCRL2-KO mouse arthritis models, β2-integrin activation assays\",\n      \"pmids\": [\"28743719\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CCRL2 heterodimerizes with other chemokine receptors beyond CXCR2 not tested\", \"Stoichiometry and structural basis of the CCRL2–CXCR2 heterodimer unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Whether CCRL2 restrains inflammation by scavenging chemerin (like classical ACKRs) needed resolution; demonstration that CCRL2 does not reduce extracellular chemerin but that CCRL2 deficiency elevates systemic chemerin levels—reversible by anti-chemerin antibodies—established a chemerin-concentrating rather than chemerin-depleting role.\",\n      \"evidence\": \"Internalization/scavenging assays in transfected and endothelial cells; CCRL2-KO mouse zymosan/thioglycollate inflammation with anti-chemerin antibody neutralization\",\n      \"pmids\": [\"29056935\", \"29209334\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which CCRL2 limits bioavailable chemerin in vivo (sequestration vs. localized presentation) not fully dissected\", \"Tissue-specific contributions to systemic chemerin regulation not mapped\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Whether endothelial versus hematopoietic CCRL2 is critical for antitumor immunity was ambiguous; bone marrow chimeras proved that non-hematopoietic (endothelial) CCRL2 drives NK cell recruitment and suppresses lung tumor growth, defining the barrier cell as the functional unit.\",\n      \"evidence\": \"CCRL2-KO mice in urethane and KrasG12D/p53Flox lung tumor models, bone marrow chimeras, flow cytometry\",\n      \"pmids\": [\"31484658\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether pharmacological upregulation of endothelial CCRL2 is therapeutically exploitable not yet demonstrated in this study\", \"Contribution of other non-hematopoietic cell types (fibroblasts, epithelial) not excluded\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"How CCRL2 influences innate immune activation beyond chemerin presentation was unclear; demonstrating that CCRL2 physically interacts with TLR4 to stabilize its surface expression and enhance MyD88-NF-κB signaling in macrophages uncovered a new receptor-level mechanism for amplifying antitumor immunity.\",\n      \"evidence\": \"Co-IP of CCRL2 with TLR4, CCRL2-KO melanoma model, macrophage and CD8+ T-cell depletion, NF-κB reporter assays\",\n      \"pmids\": [\"33846258\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct binding interface between CCRL2 and TLR4 not mapped\", \"Whether TLR4 interaction is chemerin-dependent or independent not determined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Whether CCRL2 influences intracellular kinase signaling beyond surface receptor interactions was unknown; the coprecipitation of CCRL2 with JAK2 and the dependence of JAK2-STAT3/STAT5 phosphorylation on CCRL2 expression in myeloid malignancy cells placed CCRL2 upstream of JAK-STAT oncogenic signaling.\",\n      \"evidence\": \"Co-IP of CCRL2 with JAK2, shRNA knockdown in MDS/sAML cell lines, xenograft mouse model, phospho-flow cytometry\",\n      \"pmids\": [\"35179961\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether CCRL2–JAK2 interaction is direct or bridged by an intermediary not established\", \"Generalizability beyond MDS/sAML to other myeloid contexts not shown\", \"Mechanism by which a seven-transmembrane receptor engages a cytoplasmic kinase not resolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Cell-type specificity of endothelial CCRL2 required refinement; conditional endothelial knockout and scRNA-seq identified CCRL2 as a hallmark gene of lung alveolar capillary endothelial cells and showed that its epigenetic upregulation by 5-aza-2'-deoxycytidine increases NK cell recruitment and reduces tumor burden, providing a therapeutic angle.\",\n      \"evidence\": \"Conditional endothelial CCRL2 KO, scRNA-seq, KrasG12D/p53Flox model, 5-aza pharmacological treatment, NK cell depletion\",\n      \"pmids\": [\"37343073\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Epigenetic regulators controlling CCRL2 promoter methylation in human tumors not identified\", \"Whether 5-aza effects are CCRL2-specific or pleiotropic not fully controlled\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Whether endothelial CCRL2 drives cardiovascular inflammation was untested; demonstration that disturbed-flow-induced CCRL2 recruits chemerin which activates β2-integrin on monocytes through a protein disulfide isomerase-like enzymatic activity, promoting atherosclerosis, extended the chemerin presentation paradigm to vascular disease.\",\n      \"evidence\": \"CCRL2-/-ApoE-/- mouse model, PDI activity assay, proximity ligation assay, ERK1/2 phosphorylation, scRNA-seq\",\n      \"pmids\": [\"37279540\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the PDI-like catalytic residues in chemerin not confirmed by mutagenesis\", \"Relative importance of chemerin's enzymatic versus chemotactic activities in plaque formation not dissected\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Whether CCRL2 engages non-chemokine ligands on stromal cells was unknown; the discovery that CCRL2 binds SFRP1 on LepR+ stromal cells to amplify Wnt signaling inhibition and suppress osteogenesis revealed a novel ligand-receptor pairing outside the chemerin axis.\",\n      \"evidence\": \"CCRL2-KO mouse with periodontitis, Co-IP of CCRL2 with SFRP1, Wnt reporter assays, osteogenesis differentiation assays\",\n      \"pmids\": [\"38477792\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Binding interface and affinity of CCRL2–SFRP1 interaction not characterized\", \"Whether SFRP1 binding competes with chemerin at CCRL2 not tested\", \"Generalizability to other bone remodeling contexts unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A high-resolution structure of CCRL2 — alone and in complex with chemerin, CXCR2, TLR4, or SFRP1 — is lacking, leaving unresolved how a single seven-transmembrane receptor engages such diverse partners; the relative physiological importance of its multiple interaction modes across tissues and disease contexts remains to be integrated into a unified signaling model.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal or cryo-EM structure of CCRL2 available\", \"How CCRL2 simultaneously or selectively engages chemerin, CXCR2, TLR4, JAK2, and SFRP1 is mechanistically unresolved\", \"Therapeutic targeting strategies for CCRL2 not validated in human studies\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 2, 5, 12, 13]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [3, 6, 11, 17]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 2, 3, 6, 7, 13]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [7]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": []},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 2, 4, 5, 6, 10]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 6, 11, 17]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [5, 12, 13]}\n    ],\n    \"complexes\": [\n      \"CCRL2–CXCR2 heterodimer\",\n      \"CCRL2–TLR4 complex\"\n    ],\n    \"partners\": [\n      \"CMKLR1\",\n      \"CXCR2\",\n      \"TLR4\",\n      \"JAK2\",\n      \"SFRP1\",\n      \"RARRES2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"CCRL2 is a non-signaling atypical seven-transmembrane chemokine receptor that orchestrates innate immune cell recruitment, tumor surveillance, and tissue homeostasis by concentrating bioactive ligands at cell surfaces and modulating signaling through heterotypic receptor interactions. CCRL2 binds chemerin with nanomolar affinity without activating G proteins, β-arrestins, or triggering ligand scavenging; instead, it presents chemerin to the signaling receptor CMKLR1 on nearby cells, thereby controlling NK cell and leukocyte recruitment to sites of inflammation and tumors [PMID:18794339, PMID:27716822, PMID:31484658]. Beyond chemerin presentation, CCRL2 forms constitutive heterodimers with CXCR2 to regulate β2-integrin activation and neutrophil recruitment [PMID:28743719], interacts with TLR4 to sustain membrane TLR4 expression and potentiate MyD88–NF-κB signaling in macrophages [PMID:33846258], co-precipitates with JAK2 to amplify JAK2–STAT3/STAT5 signaling in myeloid malignancies [PMID:35179961], and binds SFRP1 on stromal cells to suppress Wnt-dependent osteogenic differentiation [PMID:38477792]. Endothelial CCRL2, particularly on lung alveolar capillary endothelium, is a critical determinant of anti-tumor NK cell infiltration, and its epigenetic silencing promotes lung tumor progression in Kras-driven cancer models [PMID:37343073, PMID:31484658].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Identification of CCRL2 as a novel orphan seven-transmembrane receptor with chemokine receptor homology established it as a candidate immune regulator expressed in hematopoietic tissues.\",\n      \"evidence\": \"cDNA library screening from human neutrophils, Northern blot, chromosomal mapping to 3p21\",\n      \"pmids\": [\"9473515\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No ligand identified\", \"No functional activity demonstrated\", \"Expression restricted to mRNA level\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Demonstration that CCRL2 protein is expressed on multiple leukocyte subsets and upregulated by inflammatory stimuli positioned it as an inflammation-responsive receptor on both innate and adaptive immune cells.\",\n      \"evidence\": \"Monoclonal antibody-based flow cytometry and real-time PCR on primary human blood cells and dendritic cells\",\n      \"pmids\": [\"11828366\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ligand still unidentified\", \"No functional consequence of upregulation shown\", \"No knockout data\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identification of chemerin as a non-signaling ligand that is presented rather than internalized by CCRL2 resolved the receptor's functional identity as a ligand-concentrating molecule rather than a classical signaling or scavenging receptor.\",\n      \"evidence\": \"Binding assays, internalization assays, CCRL2-deficient mice in IgE-mediated passive cutaneous anaphylaxis model\",\n      \"pmids\": [\"18794339\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of chemerin binding unknown\", \"Relative contribution of CCRL2 versus CMKLR1 in different tissues not resolved\", \"Whether other ligands exist remained unclear\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"The finding that CCRL2 induces pertussis toxin-insensitive ERK1/2 phosphorylation upon CCL5 exposure in pre-B cells without calcium flux or migration demonstrated non-canonical signaling capacity independent of Gαi coupling.\",\n      \"evidence\": \"Western blot for ERK1/2 phosphorylation, calcium flux assay, pertussis toxin inhibition in pre-B cell lines\",\n      \"pmids\": [\"18397265\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of Gi-independent ERK activation unresolved\", \"Physiological relevance of CCL5/CCRL2 interaction debated\", \"Later studies with neutralizing antibodies questioned CC chemokine binding\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstration that CCRL2 deficiency impairs antigen-loaded dendritic cell migration to draining lymph nodes revealed a cell-intrinsic role for CCRL2 in DC trafficking and subsequent T helper priming.\",\n      \"evidence\": \"CCRL2 knockout mice, adoptive DC transfer, OVA-induced lung inflammation model\",\n      \"pmids\": [\"20606167\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether DC trafficking function is chemerin-dependent not tested\", \"Mechanism of CCRL2-mediated DC migration unknown\", \"Relevance to Th1 or Th17 immunity not explored\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Establishing that endothelial CCRL2 upregulated by NF-κB/JAK-STAT signaling binds chemerin and triggers α4β1 integrin/VCAM-1-dependent adhesion of CMKLR1+ cells demonstrated the in vivo mechanism by which CCRL2 converts circulating chemerin into a tissue-homing cue for NK cells.\",\n      \"evidence\": \"CCRL2 KO mice, pathway inhibitors, integrin-blocking antibodies, LPS lung inflammation model\",\n      \"pmids\": [\"22696441\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether endothelial CCRL2 interacts with chemerin in trans or cis with CMKLR1 not determined\", \"Role in non-pulmonary vascular beds unexplored\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Systematic BRET-based comparison across all Gαi subtypes, Gαo isoforms, and β-arrestins definitively classified CCRL2 as non-signaling upon chemerin binding, distinguishing it from CMKLR1 and GPR1.\",\n      \"evidence\": \"BRET biosensors for G protein activation and β-arrestin recruitment compared across three chemerin receptors\",\n      \"pmids\": [\"27716822\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signaling through non-canonical pathways (e.g., JAK2) not tested in this system\", \"No structural explanation for silent coupling\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Discovery that CCRL2 constitutively homodimerizes and heterodimerizes with CXCR2 to regulate β2-integrin activation and neutrophil recruitment revealed a chemerin-independent mechanism by which CCRL2 tunes innate immune responses.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation, CCRL2 KO mice, inflammatory arthritis models, β2-integrin activation assays\",\n      \"pmids\": [\"28743719\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"CCRL2 neutralizing antibody studies later found no effect on CXCL8-driven neutrophil responses, raising questions about context-dependence of the CXCR2 interaction\", \"Stoichiometry and structural basis of heterodimer unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Confirmation that CCRL2 undergoes slow constitutive recycling through early and recycling endosomes without scavenging chemerin solidified the model that CCRL2 is a surface-presenting rather than internalizing receptor.\",\n      \"evidence\": \"Internalization assays, colocalization with EEA1/Rab5/Rab11 endosomal markers in transfected and primary endothelial cells\",\n      \"pmids\": [\"29056935\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"What regulates the balance of surface versus endosomal CCRL2 is unknown\", \"Whether post-translational modifications control recycling not tested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Bone marrow chimera experiments assigning anti-tumor function to non-hematopoietic (endothelial) CCRL2 in lung cancer established that endothelial chemerin presentation drives NK cell-dependent tumor immunosurveillance.\",\n      \"evidence\": \"Bone marrow chimeras, urethane-induced and Kras/p53 genetic lung tumor models, NK cell flow cytometry\",\n      \"pmids\": [\"31484658\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CCRL2 also regulates T-cell recruitment to lung tumors not resolved\", \"Human relevance of endothelial CCRL2 in lung cancer not confirmed\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identification of a CCRL2–TLR4 interaction that retains surface TLR4 and potentiates MyD88–NF-κB signaling in macrophages revealed a second chemerin-independent mechanism linking CCRL2 to anti-tumor immunity via macrophage–CD8+ T cell crosstalk.\",\n      \"evidence\": \"Co-immunoprecipitation, surface TLR4 quantification, NF-κB signaling assay, CCRL2 KO mice, melanoma model with macrophage/CD8 depletion\",\n      \"pmids\": [\"33846258\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether TLR4 interaction is direct or adaptor-mediated not resolved\", \"Generalizability beyond melanoma not tested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Co-precipitation of CCRL2 with JAK2 and demonstration that CCRL2 knockdown reduces JAK2–STAT3/STAT5 phosphorylation in MDS cells uncovered a cell-intrinsic oncogenic function distinct from its chemerin-presenting role, establishing CCRL2 as a context-dependent positive regulator of myeloid malignancy.\",\n      \"evidence\": \"Co-immunoprecipitation, Western blot for phospho-JAK2/STAT, siRNA knockdown, xenograft model, fedratinib epistasis\",\n      \"pmids\": [\"35179961\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How a seven-transmembrane receptor potentiates JAK2 signaling mechanistically is unknown\", \"Whether the JAK2 interaction is relevant outside MDS/AML not tested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identification of CCRL2 as a hallmark marker of general alveolar capillary endothelial cells by scRNA-seq, combined with evidence that its epigenetic silencing is reversible by 5-Aza treatment to restore NK recruitment and suppress lung tumors, provided a translational framework for re-activating CCRL2-dependent immunosurveillance.\",\n      \"evidence\": \"scRNA-seq, conditional endothelial CCRL2 KO, Kras/p53 lung model, 5-Aza pharmacological treatment, NK subset analysis\",\n      \"pmids\": [\"37343073\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether 5-Aza effects are specific to CCRL2 re-expression versus global demethylation not fully dissected\", \"Optimal therapeutic window for CCRL2 re-expression undefined\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Demonstration that endothelial CCRL2-presented chemerin activates monocyte β2-integrins via a protein disulfide isomerase-like enzymatic activity—independent of CMKLR1—revealed a novel pro-atherogenic mechanism of CCRL2-mediated monocyte adhesion at disturbed-flow sites.\",\n      \"evidence\": \"CCRL2−/−ApoE−/− mice on high-fat diet, proximity ligation assay for chemerin–β2-integrin interaction, Di-E-GSSG PDI activity assay, ERK1/2 phosphorylation\",\n      \"pmids\": [\"37279540\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the PDI-like activity of chemerin is relevant in other vascular beds unknown\", \"How disturbed flow specifically induces CCRL2 transcription not fully defined\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Discovery that CCRL2 binds SFRP1 on LepR+/CAR stromal cells to amplify Wnt suppression and inhibit osteogenic differentiation identified a novel non-chemerin ligand and a role for CCRL2 in bone homeostasis under inflammatory conditions.\",\n      \"evidence\": \"Co-immunoprecipitation of CCRL2-SFRP1, Wnt reporter assay, osteogenic differentiation assay, CCRL2 KO mice, micro-CT bone healing quantification\",\n      \"pmids\": [\"38477792\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether SFRP1 binding uses the same site as chemerin not tested\", \"Relevance beyond periodontitis-associated bone loss unknown\", \"Single study requiring independent replication\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identification of CCRL2+ monocyte-derived macrophages as pro-hypertrophic, profibrotic effectors in heart failure whose TNF-α responsiveness is suppressed by vagal α7nAChR–NRF2 signaling positioned CCRL2 as a functional marker linking neuroimmunomodulation to cardiac remodeling.\",\n      \"evidence\": \"Optogenetic vagal nerve stimulation, CCRL2+ macrophage depletion, macrophage-specific α7nAChR manipulation, scRNA-seq, cardiac remodeling quantification\",\n      \"pmids\": [\"40580954\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether CCRL2 is mechanistically required or merely a marker of these macrophages not fully resolved\", \"Single study requiring independent replication\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis of CCRL2's multi-ligand binding (chemerin, SFRP1, and receptor partners), how a non-signaling receptor potentiates JAK2–STAT signaling, the relative contributions of chemerin-dependent versus chemerin-independent mechanisms across tissues, and whether pharmacological modulation of CCRL2 surface expression can be exploited therapeutically.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal or cryo-EM structure of CCRL2 or CCRL2–chemerin complex\", \"Mechanism of JAK2 potentiation by a seven-transmembrane receptor unexplained\", \"Relative weight of CXCR2 heterodimerization versus TLR4 interaction versus chemerin presentation in different cell types not systematically compared\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [3, 7, 11, 16, 24]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [11, 16, 18]},\n      {\"term_id\": \"GO:0038024\", \"supporting_discovery_ids\": [3, 7, 12, 14, 21]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 3, 7, 9, 11, 12, 16, 22]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [12]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [12]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [3, 6, 7, 10, 11, 13, 14, 16, 17, 20, 21]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [7, 11, 16, 18, 24]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [18, 23]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"RARRES2\",\n      \"CXCR2\",\n      \"TLR4\",\n      \"JAK2\",\n      \"SFRP1\",\n      \"CMKLR1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}