{"gene":"PTGDR2","run_date":"2026-04-28T19:45:45","timeline":{"discoveries":[{"year":2001,"finding":"CRTH2 (PTGDR2) is a seven-transmembrane G protein-coupled receptor that binds PGD2 and induces intracellular Ca2+ mobilization and chemotaxis in Th2 cells, eosinophils, and basophils in a Gαi-dependent manner.","method":"Radioligand binding, Ca2+ mobilization assay, chemotaxis assay, pertussis toxin inhibition in CRTH2-transfected cells and primary leukocytes","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 1 — multiple orthogonal functional assays (binding, Ca2+ flux, chemotaxis) with pertussis toxin controls, foundational paper with 878 citations","pmids":["11208866"],"is_preprint":false},{"year":2002,"finding":"Recombinant human CRTH2 binds PGD2 with high and low affinity sites (KD 2.5 nM and 109 nM) and couples to Gαi/o to decrease intracellular cAMP in a pertussis toxin-sensitive manner; the ligand selectivity rank order differs markedly from the DP receptor.","method":"Radioligand saturation binding, competition binding assays, cAMP functional assay, pertussis toxin inhibition in HEK293-EBNA cells expressing recombinant hCRTH2","journal":"British journal of pharmacology","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with recombinant receptor, multiple orthogonal assays (binding kinetics, signal transduction)","pmids":["12466225"],"is_preprint":false},{"year":2002,"finding":"Indomethacin acts as a CRTH2 (PTGDR2) agonist, inducing Gαi-dependent Ca2+ mobilization at submicromolar concentrations (~50 nM EC50) and chemotaxis in Th2 cells, eosinophils, and basophils; this effect is blocked by anti-CRTH2 mAb and is not shared by other NSAIDs.","method":"Ca2+ mobilization assay in CRTH2-transfected K562 cells, chemotaxis assay with primary human leukocytes, anti-CRTH2 mAb blocking, pertussis toxin inhibition","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1–2 — functional assays in transfected cells and primary leukocytes with receptor-specific blocking antibody","pmids":["11801628"],"is_preprint":false},{"year":2001,"finding":"CRTH2 mediates PGD2-induced eosinophil chemokinesis, morphology change, and degranulation, while the DP receptor (not CRTH2) mediates delay of eosinophil apoptosis; these two receptors have pharmacologically distinct and independent functions on eosinophils.","method":"Selective agonists (DK-PGD2 for CRTH2, BW245C for DP) and functional assays on primary human eosinophils (chemokinesis, degranulation, apoptosis)","journal":"The Journal of allergy and clinical immunology","confidence":"High","confidence_rationale":"Tier 2 — selective pharmacological dissection with receptor-specific agonists across multiple functional readouts","pmids":["11742277"],"is_preprint":false},{"year":2003,"finding":"11-dehydro-thromboxane B2 (11-dehydro-TXB2) is a full agonist of CRTH2, inducing Ca2+ flux from intracellular stores in eosinophils (desensitized by PGD2 pre-treatment), shape change in eosinophils and basophils (blocked by ramatroban but not TP antagonist SQ29548), and chemotaxis of CRTH2-transfected BaF/3 cells but not naïve BaF/3 cells; the response is inhibited by phospholipase C inhibitor U73122.","method":"Flow cytometric shape change assay, Ca2+ flux, chemotaxis assay with CRTH2-transfected cells, receptor desensitization, selective antagonists","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 — transfected cell line controls, receptor desensitization cross-experiment, PLC inhibitor mechanistic follow-up","pmids":["14668348"],"is_preprint":false},{"year":2005,"finding":"Site-directed mutagenesis of CRTH2 identified His-106 (TM III), Lys-209 (TM V), Glu-268 (TM VI), and Arg-178 (ECL2) as residues required for PGD2 binding and functional responses (cAMP inhibition, chemotaxis); Glu-268 also determines prostanoid selectivity, and Tyr-261 is critical for indomethacin binding but not PGD2 binding.","method":"Site-directed mutagenesis of mouse CRTH2, radioligand binding, cAMP assay, chemotaxis assay in HEK293 cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — active-site mutagenesis with multiple orthogonal functional assays defining the ligand-binding pocket","pmids":["16030019"],"is_preprint":false},{"year":2005,"finding":"9α,11β-PGF2 (a major in vivo metabolite of PGD2 after allergen challenge) and its stereoisomer PGF2α are CRTH2 agonists capable of inducing cell migration and activation through this receptor.","method":"Chemotaxis assay, receptor activation assay with primary eosinophils/basophils and CRTH2-expressing cells","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 — functional assays with primary leukocytes, single laboratory","pmids":["16378605"],"is_preprint":false},{"year":2006,"finding":"Ramatroban and structural analogs (TM30642, TM30643, TM30089) bind human CRTH2 at the orthosteric site with nanomolar affinity; insurmountable antagonism of TM30643/TM30089 is mechanistically linked to long-lasting CRTH2 inhibition via depression of ligand binding capacity (Bmax reduction), distinct from competitive surmountable antagonism of ramatroban.","method":"[3H]PGD2 saturation analysis, GTPγS binding, β-arrestin translocation assay, eosinophil shape change assay in CRTH2-expressing cells","journal":"Molecular pharmacology","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal assays distinguishing mechanism of insurmountability at the receptor level","pmids":["16418339"],"is_preprint":false},{"year":2004,"finding":"In vivo eosinophil trafficking into rat airways in response to PGD2 is mediated by CRTH2, not DP or TP receptors; three CRTH2-specific agonists replicate PGD2-induced BAL eosinophilia while DP and TP agonists do not, and the CRTH2/TP antagonist ramatroban (but not DP- or TP-selective antagonists alone) abolishes the effect.","method":"Intratracheal PGD2/agonist instillation in IL-5-primed rats, BAL cell counts, lung histology, selective receptor agonists/antagonists","journal":"The Journal of pharmacology and experimental therapeutics","confidence":"High","confidence_rationale":"Tier 2 — in vivo pharmacological dissection with receptor-selective tools, establishing CRTH2 as the mediating receptor for eosinophil trafficking","pmids":["15528449"],"is_preprint":false},{"year":2009,"finding":"CRTH2 activation by PGD2 inhibits cytokine deprivation-induced apoptosis of human Th2 cells via the phosphatidylinositol 3-kinase (PI3K)/Akt pathway, inducing Akt and BAD phosphorylation, preventing cytochrome c release, and suppressing caspase-3 cleavage; this anti-apoptotic effect is blocked by the PI3K inhibitor LY294002 and CRTH2 antagonists, but is not mediated by DP1 or TP receptors.","method":"Apoptosis assays (caspase-3, PARP cleavage, cytochrome c release), Akt/BAD phosphorylation western blot, PI3K inhibitor (LY294002), selective CRTH2 agonist (DK-PGD2) and antagonists (ramatroban, TM30089) in primary human Th2 cells","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1–2 — mechanistic pathway delineated by multiple signaling readouts plus pharmacological dissection of receptor and kinase involvement","pmids":["19494281"],"is_preprint":false},{"year":2008,"finding":"PGH2 (the PGD2 precursor) directly activates CRTH2 to induce eosinophil and basophil chemotaxis and Ca2+ flux; the response is subject to homologous desensitization with PGD2, blocked by CRTH2 antagonist (CAY10471) but not by hematopoietic PGD synthase inhibitor HQL79, and is reproduced in CRTH2-transfected HEK293 cells.","method":"Ca2+ flux assay, chemotaxis assay, eosinophil shape change, HEK293 transfection, receptor desensitization, selective antagonists","journal":"Journal of leukocyte biology","confidence":"High","confidence_rationale":"Tier 1–2 — transfected cell model confirms direct CRTH2 engagement; desensitization and enzymatic inhibitor controls rule out indirect mechanism","pmids":["18835884"],"is_preprint":false},{"year":2018,"finding":"Crystal structures of human CRTH2 with antagonists fevipiprant and CAY10471 reveal a semi-occluded ligand-binding pocket covered by a well-structured amino terminus; structural analysis identifies a ligand entry port and a charge-attraction-facilitated binding process for PGD2 distinct from that of lysophospholipids and endocannabinoids at other GPCRs.","method":"X-ray crystallography of human CRTH2 with two antagonists, computational docking, radioligand binding validation","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with functional validation by ligand-binding assays; mechanistic insight into GPCR lipid recognition","pmids":["30220562"],"is_preprint":false},{"year":2007,"finding":"Activated CRTH2+ CD4+ Th2 cells produce PGD2 in a COX-dependent manner, which acts in a paracrine fashion through CRTH2 to promote chemotaxis of naïve Th2 cells; additional non-COX CRTH2 agonist factors are also produced by activated Th2 cells, revealing a paracrine autocrine amplification loop.","method":"CRTH2+ Th2 cell activation, COX inhibitor (diclofenac), CRTH2/TP antagonist (ramatroban), TP-selective antagonist (SQ29548), supernatant transfer chemotaxis assays","journal":"Immunology","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological dissection of receptor and COX contributions in primary human T cells, single laboratory","pmids":["17437532"],"is_preprint":false},{"year":2012,"finding":"CRTH2 is a critical regulator of neutrophil migration in sepsis; genetic ablation of CRTH2 in mice improves neutrophil peritoneal accumulation during cecal ligation and puncture (CLP) by epigenetically upregulating CXCR2 via increased histone H3 acetylation at the CXCR2 promoter in neutrophils, reducing bacterial load and inflammatory cytokines (TNF-α, IL-6, CCL3) while increasing IL-10.","method":"CRTH2 knockout mice, CLP sepsis model, peritoneal neutrophil counts, CXCR2 flow cytometry, ChIP for histone H3 acetylation at CXCR2 promoter, neutrophil depletion, CXCR2 inhibition","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — genetic knockout with mechanistic chromatin-level follow-up plus pharmacological validation; multiple orthogonal methods","pmids":["22544936"],"is_preprint":false},{"year":2015,"finding":"CRTH2 on ILC2s mediates their accumulation in the lung in response to PGD2; CRTH2-deficient mice show reduced ILC2 pulmonary accumulation in helminth-induced inflammation, and adoptive transfer of CRTH2-sufficient (but not CRTH2-deficient) ILC2s restores pulmonary inflammation in CRTH2-deficient recipients.","method":"CRTH2 knockout mice, helminth infection model, ILC2 adoptive transfer, in vitro PGD2 migration assay, in vivo PGD2 administration","journal":"Mucosal immunology","confidence":"High","confidence_rationale":"Tier 2 — genetic knockout plus adoptive transfer epistasis establishing CRTH2 cell-autonomous role in ILC2 migration","pmids":["25850654"],"is_preprint":false},{"year":2014,"finding":"PGD2 acts through the Dp2 receptor in the foetal mouse testis to promote mitotic arrest in male germ cells by activating expression and nuclear localization of CDK inhibitor p21Cip1, repressing pluripotency markers, and upregulating the spermatogonial master gene Nanos2.","method":"In vitro and in vivo approaches in foetal mouse testis, Dp2 receptor pharmacology, immunostaining for p21Cip1 nuclear localization, gene expression analysis","journal":"Development (Cambridge, England)","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo and in vitro combined with specific receptor pharmacology in a defined biological context","pmids":["25142465"],"is_preprint":false},{"year":2014,"finding":"PGD2 via the GPR44/CRTH2 receptor inhibits wound-induced hair follicle neogenesis (WIHN); Gpr44-null mice show increased WIHN and are resistant to exogenous PGD2-induced inhibition of follicle neogenesis.","method":"Gpr44 knockout mice, wound-induced hair follicle neogenesis model, exogenous PGD2 application, histological quantification of neogenesis","journal":"The Journal of investigative dermatology","confidence":"High","confidence_rationale":"Tier 2 — genetic knockout with rescue/inhibition by exogenous ligand application, specific phenotypic readout","pmids":["23190891"],"is_preprint":false},{"year":2014,"finding":"The prostaglandin D2 synthase/GPR44 (CRTH2) signaling axis is required for PNS myelination; neuronal L-PGDS produces PGD2 that signals through glial Gpr44/CRTH2, activating the transcription factor Nfatc4 as a downstream effector; L-PGDS knockout mice are hypomyelinated, and glial Gpr44 knockdown impairs in vitro myelination.","method":"L-PGDS knockout mice, Gpr44 in vivo ablation and in vitro knockdown, myelination assays, L-PGDS inhibition, NRG1 intracellular domain signaling upstream analysis, Nfatc4 identification as downstream effector","journal":"Nature neuroscience","confidence":"High","confidence_rationale":"Tier 1–2 — genetic loss-of-function in vivo and in vitro, multiple orthogonal approaches identifying pathway from L-PGDS to CRTH2 to Nfatc4","pmids":["25362470"],"is_preprint":false},{"year":2013,"finding":"COX-1-dependent PGD2 produced by spinal microglia after peripheral nerve injury signals through DP2 (CRTH2) receptors on spinal neurons to contribute to mechanical allodynia in neuropathic pain; intrathecal COX-1 inhibitor and DP2 antagonist both attenuate allodynia.","method":"Spared nerve injury model, COX-1 inhibitor intrathecal injection, DP2 receptor antagonist, in situ hybridization and mRNA expression in spinal cord","journal":"Glia","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo pharmacological loss-of-function with two independent inhibitors in a defined pain model","pmids":["23505121"],"is_preprint":false},{"year":2018,"finding":"PGD2/PTGDR2 signaling inhibits STAT3 phosphorylation at Thr705 and nuclear expression in gastric cancer stem-like cells, restricting their self-renewal; PTGDR2 knockdown enhances CSC markers, and mutation of the STAT3 Thr705 phosphorylation site abolishes the inhibitory effect of PGD2 on CSC marker expression.","method":"PTGDR2 knockdown, PGD2 stimulation, L-PTGDS overexpression, STAT3 phosphorylation western blot, STAT3 phosphorylation-site mutagenesis, in vitro sphere formation, in vivo xenograft and peritoneal metastasis models","journal":"Stem cells (Dayton, Ohio)","confidence":"High","confidence_rationale":"Tier 1–2 — mechanistic mutagenesis of STAT3 site plus multiple in vitro and in vivo readouts linking PTGDR2 to STAT3 suppression","pmids":["29604141"],"is_preprint":false},{"year":2018,"finding":"PGD2/DP2 (CRTH2) signaling suppresses interferon-λ (IFN-λ/IL-28) production during RSV infection, promoting severe bronchiolitis; DP2 antagonism increases IFN-λ expression via the DP1 pathway, accelerating viral clearance, while dual DP1/DP2 antagonism abolishes this protection, revealing a DP2-DP1 counter-regulatory axis controlling antiviral IFN-λ responses.","method":"Neonatal mouse bronchiolitis model, DP2 antagonism, dual DP1/DP2 antagonism, DP1 agonism, IL-28A neutralization, RSV-infected primary airway epithelial cell cultures, IFN-stimulated gene expression measurement","journal":"Science translational medicine","confidence":"High","confidence_rationale":"Tier 2 — in vivo and in vitro with multiple receptor-specific pharmacological tools and cytokine neutralization establishing DP2→IFN-λ suppression axis","pmids":["29743346"],"is_preprint":false},{"year":2018,"finding":"CRTH2-mediated Th2 activation drives pulmonary arterial hypertension; CRTH2 activation in Th2 cells promotes pulmonary arterial smooth muscle cell proliferation through STAT6 activation, and both CRTH2-sufficient bone marrow reconstitution and CD4+ T cell adoptive transfer restore PAH in CRTH2-deficient mice, an effect reversed by dual IL-4/IL-13 neutralization.","method":"CRTH2 knockout mice, PAH mouse models, bone marrow reconstitution, adoptive transfer, STAT6 pathway analysis in co-culture, IL-4/IL-13 dual neutralization","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 — genetic, adoptive transfer, and cytokine neutralization epistasis experiments in vivo, mechanistic in vitro STAT6 link","pmids":["29970474"],"is_preprint":false},{"year":2021,"finding":"CRTH2 is trafficked to the endoplasmic reticulum (ER) membrane in fibroblasts in a caveolin-1-dependent manner, where it binds La ribonucleoprotein domain family member 6 (LARP6) at the collagen mRNA recognition motif and promotes degradation of collagen mRNA, thereby suppressing collagen biosynthesis; CRTH2 deficiency increases collagen production and exacerbates organ fibrosis in mice rescued by LARP6 depletion.","method":"Subcellular fractionation, Co-immunoprecipitation of CRTH2 with LARP6, caveolin-1 dependency experiments, collagen mRNA stability assay, CRTH2-null mouse fibrosis models (bleomycin, UUO), LARP6 depletion rescue, CRTH2 N-terminal peptide administration","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1–2 — direct protein-protein interaction (Co-IP), subcellular localization with functional consequence, in vivo genetic rescue epistasis, peptide intervention","pmids":["34223653"],"is_preprint":false},{"year":2021,"finding":"The PGD2-CRTH2 pathway in intestinal epithelial cells (stem, goblet, and tuft cells) negatively regulates IL-13Rα1 expression and counteracts Type 2 cytokine-driven goblet cell hyperplasia and epithelial proliferation suppression during helminth infection; CRTH2-deficient small intestinal organoids show enhanced budding and terminal differentiation to the goblet cell lineage.","method":"CRTH2 knockout mice (whole body and non-hematopoietic conditional), helminth infection model (N. brasiliensis), intestinal organoid culture, goblet cell quantification, IL-13Rα1 expression analysis","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 — conditional and global knockout with organoid mechanistic follow-up establishing epithelial-autonomous CRTH2 function","pmids":["34283207"],"is_preprint":false},{"year":2017,"finding":"PGD2 suppresses lipolysis in adipocytes via Gi-coupled DP2 (CRTH2) receptors by repressing the cAMP-PKA-hormone-sensitive lipase (HSL) axis; DP2 knockout mouse embryonic fibroblasts show enhanced lipolysis, and the DP2 agonist 15R-15-methyl PGD2 increases adipogenic/lipogenic gene expression and decreases glycerol release.","method":"DP2 receptor agonist/antagonist pharmacology, PKA activity assay, HSL phosphorylation western blot, glycerol release lipolysis assay, DP2 gene-knockout MEF adipocyte differentiation","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — genetic knockout plus receptor-specific pharmacology with molecular signaling readouts, single laboratory","pmids":["28623133"],"is_preprint":false},{"year":2014,"finding":"15-deoxy-Δ12,14-PGJ2 induces cardiomyocyte apoptosis via DP2 (CRTH2) receptor-mediated ROS production and p38/p42/44 MAPK phosphorylation, leading to TNFα upregulation and activation of both extrinsic (caspase-8) and intrinsic (Bax, caspase-9) apoptotic pathways; the electrophilic cyclopentenone moiety of 15d-PGJ2 is required, and TNFα silencing attenuates the apoptotic cascade.","method":"DP2-specific agonists/antagonists in HL-1 cardiomyocyte cell line and primary murine cardiomyocytes, ROS measurement, MAPK phosphorylation, TNFα siRNA knockdown, caspase activation assays, 9,10-dihydro-15d-PGJ2 structural control","journal":"International journal of cardiology","confidence":"Medium","confidence_rationale":"Tier 2 — receptor pharmacology and siRNA epistasis in primary and cell line models, single laboratory","pmids":["24698234"],"is_preprint":false},{"year":2012,"finding":"The PGD2-CRTH2 pathway promotes tubulointerstitial renal fibrosis via CRTH2-mediated activation of Th2 lymphocytes and their production of IL-4 and IL-13; both L-PGDS and CRTH2 knockout mice show reduced fibrosis, reduced Th2 infiltration, and decreased IL-4/IL-13; ablation of IL-4/IL-13 also ameliorates fibrosis, placing them downstream of CRTH2.","method":"L-PGDS and CRTH2 knockout mice, unilateral ureteral obstruction model, oral CRTH2 antagonist administration, IL-4/IL-13 neutralization, renal histology and cytokine measurement","journal":"Journal of the American Society of Nephrology","confidence":"High","confidence_rationale":"Tier 2 — double genetic knockout plus pharmacological inhibition plus cytokine neutralization epistasis, establishing CRTH2→IL-4/IL-13→fibrosis pathway","pmids":["22997255"],"is_preprint":false},{"year":2015,"finding":"Central CRTH2 mediates depression-related emotional behaviors in mice; CRTH2-deficient mice show antidepressant-like phenotypes and are protected from LPS- and tumor-induced social and exploratory behavioral impairment; chronic corticosterone increases COX-2 and L-PGDS mRNA in brain; CRTH2 deficiency increases hippocampal noradrenergic system activity.","method":"CRTH2 knockout mice, chronic corticosterone model, LPS and tumor sickness models, forced swim test, social interaction/novel exploratory behavior assays, CRTH2 antagonist (ramatroban), monoamine system analysis","journal":"Behavioural brain research","confidence":"Medium","confidence_rationale":"Tier 2 — genetic and pharmacological loss-of-function with specific behavioral readouts and neurochemical mechanistic follow-up","pmids":["25698598"],"is_preprint":false},{"year":2018,"finding":"PGD2 stimulates androgen receptor (AR) expression and AKT signaling through DP2 (CRTH2) in human dermal papilla cells; DP2 knockdown or antagonism (TM30089) and AKT inhibition (LY294002) both decrease AR expression and AKT pathway activation, establishing a DP2→AKT→AR axis.","method":"PGD2 stimulation, siRNA-mediated DP2 knockdown, DP2 antagonist (TM30089), AKT inhibitor (LY294002), qRT-PCR, western blot, immunocytochemistry in human dermal papilla cells","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA knockdown plus pharmacological inhibitor convergence on same readout, single laboratory","pmids":["29439547"],"is_preprint":false},{"year":2004,"finding":"CRTH2/DP2 is the primary mediator of pro-inflammatory PGD2 effects on human basophils (Ca2+ influx, CD11b upregulation, migration, degranulation), while DP receptor activation exerts opposing inhibitory effects on basophil migration and IgE-mediated degranulation; CRTH2 transcript levels are approximately 100-fold higher than DP in basophils.","method":"Selective agonists (DK-PGD2 for CRTH2; BW245C for DP), antagonists (ramatroban for CRTH2; BWA868C for DP), Ca2+ mobilization, migration, degranulation, CD11b expression, survival assays on primary human basophils, real-time PCR","journal":"Clinical and experimental allergy","confidence":"High","confidence_rationale":"Tier 2 — comprehensive pharmacological dissection with receptor-selective tools across multiple functional readouts in primary human basophils","pmids":["15298571"],"is_preprint":false}],"current_model":"CRTH2 (PTGDR2) is a Gαi-coupled seven-transmembrane GPCR that binds PGD2 and related prostanoid metabolites (including 11-dehydro-TXB2, 9α,11β-PGF2, PGH2, and indomethacin) to drive Ca2+ mobilization, cAMP inhibition, chemotaxis, degranulation, Th2 cytokine production, and PI3K/Akt-mediated survival in Th2 cells, eosinophils, basophils, and ILC2s; at the structural level, a semi-occluded pocket covered by the receptor N-terminus accommodates antagonists such as fevipiprant; additional non-canonical functions include ER-membrane localization (caveolin-1-dependent) in fibroblasts where it binds LARP6 to degrade collagen mRNA, suppression of STAT3 in cancer stem cells, promotion of myelination via Nfatc4, negative regulation of intestinal epithelial IL-13Rα1/goblet cell differentiation, and modulation of lipolysis via the cAMP-PKA-HSL axis in adipocytes."},"narrative":{"teleology":[{"year":2001,"claim":"Establishing that CRTH2 is the PGD2 receptor mediating Th2/eosinophil/basophil chemotaxis resolved the longstanding question of how PGD2 recruits type 2 effector cells independently of the DP1 receptor.","evidence":"Radioligand binding, Ca²⁺ mobilization, chemotaxis, and pertussis toxin inhibition in CRTH2-transfected cells and primary leukocytes; pharmacological dissection with DP-selective vs CRTH2-selective agonists on eosinophils","pmids":["11208866","11742277"],"confidence":"High","gaps":["Downstream intracellular signaling cascades beyond Gαi not yet mapped","In vivo relevance of CRTH2-mediated eosinophil trafficking not yet demonstrated"]},{"year":2002,"claim":"Defining dual-affinity PGD2 binding kinetics and cAMP inhibition established the quantitative pharmacology of CRTH2 as a Gαi/o-coupled receptor, while identification of indomethacin as a non-prostanoid agonist broadened the receptor's ligand repertoire beyond classical eicosanoids.","evidence":"Radioligand saturation/competition binding and cAMP assays in recombinant HEK293 cells; indomethacin agonism confirmed by Ca²⁺ flux, chemotaxis, and anti-CRTH2 mAb blocking","pmids":["12466225","11801628"],"confidence":"High","gaps":["Structural basis of ligand selectivity unknown","Physiological significance of indomethacin agonism unclear"]},{"year":2004,"claim":"In vivo pharmacological dissection proved that CRTH2 — not DP or TP — mediates PGD2-induced eosinophil airway trafficking, validating CRTH2 as a drug target for allergic airway inflammation and confirming it as the dominant pro-inflammatory PGD2 receptor on basophils.","evidence":"Intratracheal agonist instillation in IL-5-primed rats with selective receptor antagonists; comprehensive pharmacological profiling of primary human basophils with selective agonists/antagonists","pmids":["15528449","15298571"],"confidence":"High","gaps":["Genetic (knockout) confirmation of airway eosinophilia role not yet available","Relative contribution to human asthma not established"]},{"year":2005,"claim":"Site-directed mutagenesis of CRTH2 identified the critical ligand-binding residues (His-106, Lys-209, Glu-268, Arg-178) and showed that Tyr-261 discriminates between PGD2 and indomethacin binding, providing the first molecular map of the orthosteric pocket.","evidence":"Mutagenesis of mouse CRTH2 with radioligand binding, cAMP, and chemotaxis assays in HEK293 cells","pmids":["16030019"],"confidence":"High","gaps":["No three-dimensional structure available","Mechanism of ligand entry and binding dynamics unknown"]},{"year":2006,"claim":"Characterization of insurmountable antagonism by ramatroban analogs revealed that long-lasting CRTH2 blockade involves reduction of ligand binding capacity (Bmax) rather than simple competitive displacement, informing antagonist design.","evidence":"[³H]PGD2 saturation analysis, GTPγS binding, β-arrestin translocation, and eosinophil shape change assays","pmids":["16418339"],"confidence":"High","gaps":["Structural mechanism of insurmountable antagonism not resolved","In vivo pharmacokinetic relevance not demonstrated"]},{"year":2008,"claim":"Demonstration that the upstream prostaglandin PGH2 directly activates CRTH2 expanded the physiological ligand repertoire to include the PGD2 precursor, establishing that CRTH2 can be activated even without PGD synthase activity.","evidence":"Ca²⁺ flux, chemotaxis, homologous desensitization with PGD2, CRTH2-transfected HEK293 confirmation, PGDS inhibitor control","pmids":["18835884"],"confidence":"High","gaps":["Quantitative contribution of PGH2 vs PGD2 signaling in vivo unknown"]},{"year":2009,"claim":"Identification of the PI3K/Akt/BAD anti-apoptotic pathway downstream of CRTH2 in Th2 cells explained how PGD2 promotes Th2 cell survival beyond chemotaxis, linking CRTH2 to immune persistence in allergic inflammation.","evidence":"Akt/BAD phosphorylation, cytochrome c release, caspase-3 cleavage assays with PI3K inhibitor and CRTH2 antagonist epistasis in primary human Th2 cells","pmids":["19494281"],"confidence":"High","gaps":["Whether PI3K activation is direct or via Gβγ subunits not resolved","Relevance to Th2 survival in vivo not tested"]},{"year":2012,"claim":"Genetic ablation of CRTH2 revealed two unexpected in vivo roles: epigenetic regulation of neutrophil CXCR2 expression in sepsis and promotion of tubulointerstitial renal fibrosis through Th2-derived IL-4/IL-13, extending CRTH2 function beyond classical type 2 immunity.","evidence":"CRTH2 knockout mice in CLP sepsis model with ChIP for H3 acetylation at CXCR2 promoter; CRTH2 and L-PGDS knockout mice in UUO fibrosis model with IL-4/IL-13 neutralization","pmids":["22544936","22997255"],"confidence":"High","gaps":["Molecular mechanism linking CRTH2 to histone acetylation at CXCR2 promoter unknown","Whether fibrosis role is exclusively Th2-mediated or involves non-immune cell CRTH2 not fully resolved"]},{"year":2014,"claim":"Discovery of CRTH2 roles in gonadal development (promoting male germ cell mitotic arrest via p21Cip1/Nanos2), hair follicle neogenesis inhibition, and PNS myelination (via Nfatc4 in Schwann cells) revealed tissue-specific developmental functions far removed from immune regulation.","evidence":"Dp2 pharmacology in fetal mouse testis; Gpr44 knockout mice in WIHN model; L-PGDS knockout and Gpr44 knockdown with myelination assays identifying Nfatc4","pmids":["25142465","23190891","25362470"],"confidence":"High","gaps":["Whether Nfatc4 is a direct CRTH2 signaling target or requires intermediate kinases unknown","CRTH2 signaling pathway in germ cells not fully delineated"]},{"year":2015,"claim":"Demonstrating that CRTH2 is required for ILC2 pulmonary accumulation via adoptive transfer epistasis established CRTH2 as cell-autonomous on ILC2s and positioned it as a key driver of innate type 2 immunity in helminth infection.","evidence":"CRTH2 knockout mice, helminth infection, adoptive transfer of CRTH2-sufficient vs CRTH2-deficient ILC2s","pmids":["25850654"],"confidence":"High","gaps":["Downstream ILC2 effector programs activated by CRTH2 not characterized","Relative contribution of ILC2 vs Th2 CRTH2 signaling in helminth clearance unclear"]},{"year":2018,"claim":"Crystal structures of CRTH2 with fevipiprant and CAY10471 resolved the semi-occluded binding pocket architecture with an N-terminal lid, explaining how lipid ligands access the orthosteric site through a lateral entry port — a mechanism distinct from other lipid GPCRs.","evidence":"X-ray crystallography of human CRTH2 bound to two antagonists, computational docking, radioligand binding validation","pmids":["30220562"],"confidence":"High","gaps":["No agonist-bound or active-state structure available","Mechanism of receptor activation and G protein coupling at structural level unresolved"]},{"year":2018,"claim":"Multiple 2018 studies expanded CRTH2's pathological roles: suppressing IFN-λ during RSV bronchiolitis (revealing a DP2-DP1 counter-regulatory axis), driving pulmonary arterial hypertension through Th2/STAT6/IL-4/IL-13, and inhibiting STAT3 in gastric cancer stem cells.","evidence":"DP2 antagonism in neonatal mouse RSV model with IFN-λ neutralization; CRTH2 KO with bone marrow reconstitution and IL-4/IL-13 neutralization in PAH models; PTGDR2 knockdown with STAT3 phospho-site mutagenesis in gastric cancer spheroids and xenografts","pmids":["29743346","29970474","29604141"],"confidence":"High","gaps":["Whether STAT3 inhibition is direct or through an intermediate signaling step unknown","Clinical relevance of DP2 antagonism in RSV bronchiolitis not demonstrated","CRTH2 expression and function in human PAH tissue not confirmed"]},{"year":2021,"claim":"Discovery that CRTH2 localizes to the ER membrane via caveolin-1 and binds LARP6 to degrade collagen mRNA revealed a ligand-independent, non-canonical anti-fibrotic function distinct from its GPCR signaling activity; simultaneously, epithelial CRTH2 was shown to restrain IL-13Rα1-driven goblet cell differentiation.","evidence":"Co-IP of CRTH2-LARP6, subcellular fractionation, caveolin-1 dependency, collagen mRNA stability, CRTH2-null mouse fibrosis models with LARP6 rescue; conditional and global CRTH2 KO mice in helminth infection with intestinal organoid culture","pmids":["34223653","34283207"],"confidence":"High","gaps":["Whether ER-localized CRTH2 retains any signaling capacity unknown","Structural basis of CRTH2-LARP6 interaction not determined","Signaling pathway by which epithelial CRTH2 suppresses IL-13Rα1 not identified"]},{"year":null,"claim":"Key unresolved questions include the active-state structure and G protein coupling mechanism, how CRTH2 toggles between canonical GPCR signaling and non-canonical ER/LARP6 functions, and whether its diverse tissue-specific roles (myelination, germ cell arrest, cancer stem cell suppression) share common downstream effectors.","evidence":"","pmids":[],"confidence":"Low","gaps":["No active-state or agonist-bound CRTH2 structure exists","Molecular switch between canonical signaling and ER-localized mRNA regulatory function unknown","Integration of PI3K/Akt, STAT3, STAT6, and Nfatc4 pathways into a unified CRTH2 signaling model not achieved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,1,5,11]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[0,1,4,10,11]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[22,19]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,1,11]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[22]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,5,9,11,24]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[3,8,14,21,23,26,29]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[9,25]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[15,17]}],"complexes":[],"partners":["LARP6","CAV1","NFATC4","STAT3","STAT6"],"other_free_text":[]},"mechanistic_narrative":"CRTH2 (PTGDR2) is a Gαi-coupled prostaglandin D2 receptor that orchestrates type 2 immune cell activation, chemotaxis, and survival, while also serving non-canonical roles in fibrosis, myelination, and epithelial differentiation. The receptor binds PGD2 and related prostanoids (PGH2, 11-dehydro-TXB2, 9α,11β-PGF2, 15d-PGJ2, and indomethacin) at a semi-occluded pocket defined by key residues His-106, Lys-209, Glu-268, and Arg-178, coupling through Gαi to inhibit cAMP, mobilize intracellular Ca²⁺ via PLC, and activate PI3K/Akt-dependent anti-apoptotic signaling in Th2 cells, eosinophils, basophils, and ILC2s [PMID:11208866, PMID:12466225, PMID:16030019, PMID:30220562, PMID:19494281, PMID:25850654]. Beyond canonical immune functions, CRTH2 localizes to the endoplasmic reticulum in fibroblasts in a caveolin-1-dependent manner, where it binds LARP6 to promote collagen mRNA degradation and suppress fibrosis [PMID:34223653]; in Schwann cells it drives PNS myelination through Nfatc4 [PMID:25362470]; and in intestinal epithelium it negatively regulates IL-13Rα1 expression and goblet cell hyperplasia [PMID:34283207]. CRTH2-mediated Th2 activation also drives pathological remodeling in pulmonary arterial hypertension via STAT6 and IL-4/IL-13 signaling, and in tubulointerstitial renal fibrosis [PMID:29970474, PMID:22997255]."},"prefetch_data":{"uniprot":{"accession":"Q9Y5Y4","full_name":"Prostaglandin D2 receptor 2","aliases":["Chemoattractant receptor-homologous molecule expressed on Th2 cells","G-protein coupled receptor 44"],"length_aa":395,"mass_kda":43.3,"function":"Receptor for prostaglandin D2 (PGD2). Coupled to the G(i)-protein. Receptor activation may result in pertussis toxin-sensitive decreases in cAMP levels and Ca(2+) mobilization. PI3K signaling is also implicated in mediating PTGDR2 effects. PGD2 induced receptor internalization. CRTH2 internalization can be regulated by diverse kinases such as, PKC, PKA, GRK2, GPRK5/GRK5 and GRK6. Receptor activation is responsible, at least in part, in immune regulation and allergic/inflammation responses","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q9Y5Y4/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PTGDR2","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/PTGDR2","total_profiled":1310},"omim":[{"mim_id":"604837","title":"PROSTAGLANDIN D2 RECEPTOR 2; PTGDR2","url":"https://www.omim.org/entry/604837"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"heart muscle","ntpm":6.7},{"tissue":"intestine","ntpm":8.0},{"tissue":"skeletal muscle","ntpm":6.8},{"tissue":"stomach 1","ntpm":8.8}],"url":"https://www.proteinatlas.org/search/PTGDR2"},"hgnc":{"alias_symbol":["CRTH2","CD294","DP2"],"prev_symbol":["GPR44"]},"alphafold":{"accession":"Q9Y5Y4","domains":[{"cath_id":"1.20.1070.10","chopping":"13-321","consensus_level":"high","plddt":90.0497,"start":13,"end":321}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y5Y4","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y5Y4-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y5Y4-F1-predicted_aligned_error_v6.png","plddt_mean":81.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PTGDR2","jax_strain_url":"https://www.jax.org/strain/search?query=PTGDR2"},"sequence":{"accession":"Q9Y5Y4","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9Y5Y4.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9Y5Y4/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y5Y4"}},"corpus_meta":[{"pmid":"11208866","id":"PMC_11208866","title":"Prostaglandin D2 selectively induces chemotaxis in T helper type 2 cells, eosinophils, and basophils via seven-transmembrane receptor CRTH2.","date":"2001","source":"The Journal of experimental medicine","url":"https://pubmed.ncbi.nlm.nih.gov/11208866","citation_count":878,"is_preprint":false},{"pmid":"11069080","id":"PMC_11069080","title":"CRTH2 is the most reliable marker for the detection of circulating human type 2 Th and type 2 T cytotoxic cells in health and disease.","date":"2000","source":"European journal of immunology","url":"https://pubmed.ncbi.nlm.nih.gov/11069080","citation_count":249,"is_preprint":false},{"pmid":"11742277","id":"PMC_11742277","title":"Selective modulation of chemokinesis, degranulation, and apoptosis in eosinophils through the PGD2 receptors CRTH2 and DP.","date":"2001","source":"The Journal of allergy and clinical immunology","url":"https://pubmed.ncbi.nlm.nih.gov/11742277","citation_count":200,"is_preprint":false},{"pmid":"25850654","id":"PMC_25850654","title":"The prostaglandin D₂ receptor CRTH2 regulates accumulation of group 2 innate lymphoid cells in the inflamed lung.","date":"2015","source":"Mucosal immunology","url":"https://pubmed.ncbi.nlm.nih.gov/25850654","citation_count":191,"is_preprint":false},{"pmid":"15749909","id":"PMC_15749909","title":"Activation of the prostaglandin D2 receptor DP2/CRTH2 increases allergic inflammation in mouse.","date":"2005","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/15749909","citation_count":174,"is_preprint":false},{"pmid":"23379537","id":"PMC_23379537","title":"Anti-eosinophil activity and clinical efficacy of the CRTH2 antagonist OC000459 in eosinophilic esophagitis.","date":"2013","source":"Allergy","url":"https://pubmed.ncbi.nlm.nih.gov/23379537","citation_count":173,"is_preprint":false},{"pmid":"16545607","id":"PMC_16545607","title":"Emerging roles of DP and CRTH2 in allergic inflammation.","date":"2006","source":"Trends in molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/16545607","citation_count":169,"is_preprint":false},{"pmid":"12466225","id":"PMC_12466225","title":"Molecular pharmacology of the human prostaglandin D2 receptor, CRTH2.","date":"2002","source":"British journal of pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/12466225","citation_count":169,"is_preprint":false},{"pmid":"17965752","id":"PMC_17965752","title":"The roles of the prostaglandin D(2) receptors DP(1) and CRTH2 in promoting allergic responses.","date":"2007","source":"British journal of pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/17965752","citation_count":133,"is_preprint":false},{"pmid":"11801628","id":"PMC_11801628","title":"Cutting edge: agonistic effect of indomethacin on a prostaglandin D2 receptor, CRTH2.","date":"2002","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/11801628","citation_count":124,"is_preprint":false},{"pmid":"12895600","id":"PMC_12895600","title":"The second PGD(2) receptor CRTH2: structure, properties, and functions in leukocytes.","date":"2003","source":"Prostaglandins, leukotrienes, and essential fatty acids","url":"https://pubmed.ncbi.nlm.nih.gov/12895600","citation_count":118,"is_preprint":false},{"pmid":"17328802","id":"PMC_17328802","title":"Antagonism of the prostaglandin D2 receptor CRTH2 attenuates asthma pathology in mouse eosinophilic airway inflammation.","date":"2007","source":"Respiratory research","url":"https://pubmed.ncbi.nlm.nih.gov/17328802","citation_count":106,"is_preprint":false},{"pmid":"31201208","id":"PMC_31201208","title":"KLRG1 and NKp46 discriminate subpopulations of human CD117+CRTH2- ILCs biased toward ILC2 or ILC3.","date":"2019","source":"The Journal of experimental medicine","url":"https://pubmed.ncbi.nlm.nih.gov/31201208","citation_count":104,"is_preprint":false},{"pmid":"20356827","id":"PMC_20356827","title":"Crystal structure of HLA-DP2 and implications for chronic beryllium disease.","date":"2010","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/20356827","citation_count":95,"is_preprint":false},{"pmid":"20559016","id":"PMC_20559016","title":"CRTH2 and D-type prostanoid receptor antagonists as novel therapeutic agents for inflammatory diseases.","date":"2010","source":"Pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/20559016","citation_count":95,"is_preprint":false},{"pmid":"15528449","id":"PMC_15528449","title":"Prostaglandin D2-induced eosinophilic airway inflammation is mediated by CRTH2 receptor.","date":"2004","source":"The Journal of pharmacology and experimental therapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/15528449","citation_count":93,"is_preprint":false},{"pmid":"27354118","id":"PMC_27354118","title":"The oral CRTh2 antagonist QAW039 (fevipiprant): A phase II study in uncontrolled allergic asthma.","date":"2016","source":"Pulmonary pharmacology & therapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/27354118","citation_count":86,"is_preprint":false},{"pmid":"7784053","id":"PMC_7784053","title":"Cloning and characterization of human DP2, a novel dimerization partner of E2F.","date":"1995","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/7784053","citation_count":85,"is_preprint":false},{"pmid":"14668348","id":"PMC_14668348","title":"11-Dehydro-thromboxane B2, a stable thromboxane metabolite, is a full agonist of chemoattractant receptor-homologous molecule expressed on TH2 cells (CRTH2) in human eosinophils and basophils.","date":"2003","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/14668348","citation_count":84,"is_preprint":false},{"pmid":"28838980","id":"PMC_28838980","title":"Fevipiprant, an oral prostaglandin DP2 receptor (CRTh2) antagonist, in allergic asthma uncontrolled on low-dose inhaled corticosteroids.","date":"2017","source":"The European respiratory journal","url":"https://pubmed.ncbi.nlm.nih.gov/28838980","citation_count":84,"is_preprint":false},{"pmid":"29604141","id":"PMC_29604141","title":"PGD2/PTGDR2 Signaling Restricts the Self-Renewal and Tumorigenesis of Gastric Cancer.","date":"2018","source":"Stem cells (Dayton, Ohio)","url":"https://pubmed.ncbi.nlm.nih.gov/29604141","citation_count":75,"is_preprint":false},{"pmid":"24964348","id":"PMC_24964348","title":"Setipiprant, a selective CRTH2 antagonist, reduces allergen-induced airway responses in allergic asthmatics.","date":"2014","source":"Clinical and experimental allergy : journal of the British Society for Allergy and Clinical Immunology","url":"https://pubmed.ncbi.nlm.nih.gov/24964348","citation_count":75,"is_preprint":false},{"pmid":"15298571","id":"PMC_15298571","title":"Differential modulation of human basophil functions through prostaglandin D2 receptors DP and chemoattractant receptor-homologous molecule expressed on Th2 cells/DP2.","date":"2004","source":"Clinical and experimental allergy : journal of the British Society for Allergy and Clinical Immunology","url":"https://pubmed.ncbi.nlm.nih.gov/15298571","citation_count":72,"is_preprint":false},{"pmid":"23190891","id":"PMC_23190891","title":"Prostaglandin D2 inhibits wound-induced hair follicle neogenesis through the receptor, Gpr44.","date":"2012","source":"The Journal of investigative dermatology","url":"https://pubmed.ncbi.nlm.nih.gov/23190891","citation_count":71,"is_preprint":false},{"pmid":"18097056","id":"PMC_18097056","title":"Cyclooxygenase-2/prostaglandin D2/CRTH2 pathway mediates double-stranded RNA-induced enhancement of allergic airway inflammation.","date":"2008","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/18097056","citation_count":70,"is_preprint":false},{"pmid":"25362470","id":"PMC_25362470","title":"Prostaglandin D2 synthase/GPR44: a signaling axis in PNS myelination.","date":"2014","source":"Nature neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/25362470","citation_count":64,"is_preprint":false},{"pmid":"30220562","id":"PMC_30220562","title":"Structures of the Human PGD2 Receptor CRTH2 Reveal Novel Mechanisms for Ligand Recognition.","date":"2018","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/30220562","citation_count":63,"is_preprint":false},{"pmid":"19494281","id":"PMC_19494281","title":"Novel function of CRTH2 in preventing apoptosis of human Th2 cells through activation of the phosphatidylinositol 3-kinase pathway.","date":"2009","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/19494281","citation_count":63,"is_preprint":false},{"pmid":"225516","id":"PMC_225516","title":"Characterization of a fused protein specified by the adenovirus type 2-simian virus 40 hybrid Ad2+ND1 dp2.","date":"1979","source":"Journal of virology","url":"https://pubmed.ncbi.nlm.nih.gov/225516","citation_count":60,"is_preprint":false},{"pmid":"30760581","id":"PMC_30760581","title":"DP2 antagonism reduces airway smooth muscle mass in asthma by decreasing eosinophilia and myofibroblast recruitment.","date":"2019","source":"Science translational medicine","url":"https://pubmed.ncbi.nlm.nih.gov/30760581","citation_count":59,"is_preprint":false},{"pmid":"29970474","id":"PMC_29970474","title":"Inhibition of CRTH2-mediated Th2 activation attenuates pulmonary hypertension in mice.","date":"2018","source":"The Journal of experimental medicine","url":"https://pubmed.ncbi.nlm.nih.gov/29970474","citation_count":56,"is_preprint":false},{"pmid":"15715457","id":"PMC_15715457","title":"Minor structural modifications convert the dual TP/CRTH2 antagonist ramatroban into a highly selective and potent CRTH2 antagonist.","date":"2005","source":"Journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/15715457","citation_count":55,"is_preprint":false},{"pmid":"18757520","id":"PMC_18757520","title":"CRTH2 antagonism significantly ameliorates airway hyperreactivity and downregulates inflammation-induced genes in a mouse model of airway inflammation.","date":"2008","source":"American journal of physiology. Lung cellular and molecular physiology","url":"https://pubmed.ncbi.nlm.nih.gov/18757520","citation_count":55,"is_preprint":false},{"pmid":"22997255","id":"PMC_22997255","title":"PGD2-CRTH2 pathway promotes tubulointerstitial fibrosis.","date":"2012","source":"Journal of the American Society of Nephrology : JASN","url":"https://pubmed.ncbi.nlm.nih.gov/22997255","citation_count":54,"is_preprint":false},{"pmid":"27621597","id":"PMC_27621597","title":"Two Phase II randomized trials on the CRTh2 antagonist AZD1981 in adults with asthma.","date":"2016","source":"Drug design, development and therapy","url":"https://pubmed.ncbi.nlm.nih.gov/27621597","citation_count":54,"is_preprint":false},{"pmid":"29743346","id":"PMC_29743346","title":"PGD2/DP2 receptor activation promotes severe viral bronchiolitis by suppressing IFN-λ production.","date":"2018","source":"Science translational medicine","url":"https://pubmed.ncbi.nlm.nih.gov/29743346","citation_count":53,"is_preprint":false},{"pmid":"29276415","id":"PMC_29276415","title":"CRTH2 antagonists in asthma: current perspectives.","date":"2017","source":"Clinical pharmacology : advances and applications","url":"https://pubmed.ncbi.nlm.nih.gov/29276415","citation_count":52,"is_preprint":false},{"pmid":"19066314","id":"PMC_19066314","title":"A small molecule CRTH2 antagonist inhibits FITC-induced allergic cutaneous inflammation.","date":"2008","source":"International immunology","url":"https://pubmed.ncbi.nlm.nih.gov/19066314","citation_count":48,"is_preprint":false},{"pmid":"26916831","id":"PMC_26916831","title":"Fevipiprant (QAW039), a Slowly Dissociating CRTh2 Antagonist with the Potential for Improved Clinical Efficacy.","date":"2016","source":"Molecular pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/26916831","citation_count":48,"is_preprint":false},{"pmid":"21752305","id":"PMC_21752305","title":"Peptide binding prediction for the human class II MHC allele HLA-DP2: a molecular docking approach.","date":"2011","source":"BMC structural biology","url":"https://pubmed.ncbi.nlm.nih.gov/21752305","citation_count":48,"is_preprint":false},{"pmid":"25323233","id":"PMC_25323233","title":"Prostaglandin D2 and the role of the DP1, DP2 and TP receptors in the control of airway reflex events.","date":"2014","source":"The European respiratory journal","url":"https://pubmed.ncbi.nlm.nih.gov/25323233","citation_count":47,"is_preprint":false},{"pmid":"34283207","id":"PMC_34283207","title":"PGD2 and CRTH2 counteract Type 2 cytokine-elicited intestinal epithelial responses during helminth infection.","date":"2021","source":"The Journal of experimental medicine","url":"https://pubmed.ncbi.nlm.nih.gov/34283207","citation_count":47,"is_preprint":false},{"pmid":"32032632","id":"PMC_32032632","title":"Optimal identification of human conventional and nonconventional (CRTH2-IL7Rα-) ILC2s using additional surface markers.","date":"2020","source":"The Journal of allergy and clinical immunology","url":"https://pubmed.ncbi.nlm.nih.gov/32032632","citation_count":46,"is_preprint":false},{"pmid":"25268140","id":"PMC_25268140","title":"Expression of DP2 (CRTh2), a prostaglandin D₂ receptor, in human mast cells.","date":"2014","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/25268140","citation_count":46,"is_preprint":false},{"pmid":"16418339","id":"PMC_16418339","title":"On the mechanism of interaction of potent surmountable and insurmountable antagonists with the prostaglandin D2 receptor CRTH2.","date":"2006","source":"Molecular pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/16418339","citation_count":45,"is_preprint":false},{"pmid":"20943773","id":"PMC_20943773","title":"Pharmacological characterization of MK-7246, a potent and selective CRTH2 (chemoattractant receptor-homologous molecule expressed on T-helper type 2 cells) antagonist.","date":"2010","source":"Molecular pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/20943773","citation_count":45,"is_preprint":false},{"pmid":"31900341","id":"PMC_31900341","title":"The Prostaglandin D2 Receptor CRTH2 Promotes IL-33-Induced ILC2 Accumulation in the Lung.","date":"2020","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/31900341","citation_count":43,"is_preprint":false},{"pmid":"20447387","id":"PMC_20447387","title":"Therapeutic efficacy of AM156, a novel prostanoid DP2 receptor antagonist, in murine models of allergic rhinitis and house dust mite-induced pulmonary inflammation.","date":"2010","source":"European journal of pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/20447387","citation_count":41,"is_preprint":false},{"pmid":"16378605","id":"PMC_16378605","title":"9alpha,11beta-PGF2 and its stereoisomer PGF2alpha are novel agonists of the chemoattractant receptor, CRTH2.","date":"2005","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/16378605","citation_count":41,"is_preprint":false},{"pmid":"20713302","id":"PMC_20713302","title":"The prostaglandin D₂ receptor CRTH2 is important for allergic skin inflammation after epicutaneous antigen challenge.","date":"2010","source":"The Journal of allergy and clinical immunology","url":"https://pubmed.ncbi.nlm.nih.gov/20713302","citation_count":39,"is_preprint":false},{"pmid":"25142465","id":"PMC_25142465","title":"Prostaglandin D2 acts through the Dp2 receptor to influence male germ cell differentiation in the foetal mouse testis.","date":"2014","source":"Development (Cambridge, England)","url":"https://pubmed.ncbi.nlm.nih.gov/25142465","citation_count":38,"is_preprint":false},{"pmid":"16918458","id":"PMC_16918458","title":"Targeting the prostaglandin D2 receptors DP and CRTH2 for treatment of inflammation.","date":"2006","source":"Current topics in medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16918458","citation_count":38,"is_preprint":false},{"pmid":"22544936","id":"PMC_22544936","title":"CRTH2 is a critical regulator of neutrophil migration and resistance to polymicrobial sepsis.","date":"2012","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/22544936","citation_count":38,"is_preprint":false},{"pmid":"28818625","id":"PMC_28818625","title":"The therapeutic potential of CRTH2/DP2 beyond allergy and asthma.","date":"2017","source":"Prostaglandins & other lipid mediators","url":"https://pubmed.ncbi.nlm.nih.gov/28818625","citation_count":37,"is_preprint":false},{"pmid":"20615077","id":"PMC_20615077","title":"DP(2) receptor antagonists in development.","date":"2010","source":"Expert opinion on investigational drugs","url":"https://pubmed.ncbi.nlm.nih.gov/20615077","citation_count":37,"is_preprint":false},{"pmid":"17234745","id":"PMC_17234745","title":"GATA3 up-regulation associated with surface expression of CD294/CRTH2: a unique feature of human Th cells.","date":"2007","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/17234745","citation_count":36,"is_preprint":false},{"pmid":"19796209","id":"PMC_19796209","title":"Genetic variability in CRTH2 polymorphism increases eotaxin-2 levels in patients with aspirin exacerbated respiratory disease.","date":"2009","source":"Allergy","url":"https://pubmed.ncbi.nlm.nih.gov/19796209","citation_count":36,"is_preprint":false},{"pmid":"24900359","id":"PMC_24900359","title":"Optimization of the Central Core of Indolinone-Acetic Acid-Based CRTH2 (DP2) Receptor Antagonists.","date":"2011","source":"ACS medicinal chemistry letters","url":"https://pubmed.ncbi.nlm.nih.gov/24900359","citation_count":35,"is_preprint":false},{"pmid":"27079298","id":"PMC_27079298","title":"Elevated levels of circulating CD4(+) CRTh2(+) T cells characterize severe asthma.","date":"2016","source":"Clinical and experimental allergy : journal of the British Society for Allergy and Clinical Immunology","url":"https://pubmed.ncbi.nlm.nih.gov/27079298","citation_count":35,"is_preprint":false},{"pmid":"29208633","id":"PMC_29208633","title":"In Vivo Visualization of β-Cells by Targeting of GPR44.","date":"2017","source":"Diabetes","url":"https://pubmed.ncbi.nlm.nih.gov/29208633","citation_count":34,"is_preprint":false},{"pmid":"24073896","id":"PMC_24073896","title":"Update on the status of DP2 receptor antagonists; from proof of concept through clinical failures to promising new drugs.","date":"2013","source":"Expert opinion on investigational drugs","url":"https://pubmed.ncbi.nlm.nih.gov/24073896","citation_count":34,"is_preprint":false},{"pmid":"24512187","id":"PMC_24512187","title":"Discovery of isoquinolinone indole acetic acids as antagonists of chemoattractant receptor homologous molecule expressed on Th2 cells (CRTH2) for the treatment of allergic inflammatory diseases.","date":"2014","source":"Journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/24512187","citation_count":34,"is_preprint":false},{"pmid":"18836589","id":"PMC_18836589","title":"Antagonists of the prostaglandin D2 receptor CRTH2.","date":"2008","source":"Drug news & perspectives","url":"https://pubmed.ncbi.nlm.nih.gov/18836589","citation_count":33,"is_preprint":false},{"pmid":"20457519","id":"PMC_20457519","title":"3-Indolyl sultams as selective CRTh2 antagonists.","date":"2010","source":"Bioorganic & medicinal chemistry letters","url":"https://pubmed.ncbi.nlm.nih.gov/20457519","citation_count":33,"is_preprint":false},{"pmid":"16951350","id":"PMC_16951350","title":"Recombinant HLA-DP2 binds beryllium and tolerizes beryllium-specific pathogenic CD4+ T cells.","date":"2006","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/16951350","citation_count":32,"is_preprint":false},{"pmid":"23505121","id":"PMC_23505121","title":"COX-1-dependent prostaglandin D2 in microglia contributes to neuropathic pain via DP2 receptor in spinal neurons.","date":"2013","source":"Glia","url":"https://pubmed.ncbi.nlm.nih.gov/23505121","citation_count":32,"is_preprint":false},{"pmid":"30879003","id":"PMC_30879003","title":"Effects of an Oral CRTh2 Antagonist (AZD1981) on Eosinophil Activity and Symptoms in Chronic Spontaneous Urticaria.","date":"2019","source":"International archives of allergy and immunology","url":"https://pubmed.ncbi.nlm.nih.gov/30879003","citation_count":32,"is_preprint":false},{"pmid":"26928963","id":"PMC_26928963","title":"Eosinophils Contribute to Intestinal Inflammation via Chemoattractant Receptor-homologous Molecule Expressed on Th2 Cells, CRTH2, in Experimental Crohn's Disease.","date":"2016","source":"Journal of Crohn's & colitis","url":"https://pubmed.ncbi.nlm.nih.gov/26928963","citation_count":31,"is_preprint":false},{"pmid":"24698234","id":"PMC_24698234","title":"15-deoxy-Δ¹²,¹⁴-PGJ₂ promotes inflammation and apoptosis in cardiomyocytes via the DP2/MAPK/TNFα axis.","date":"2014","source":"International journal of cardiology","url":"https://pubmed.ncbi.nlm.nih.gov/24698234","citation_count":31,"is_preprint":false},{"pmid":"21232644","id":"PMC_21232644","title":"An alkali-thermotolerant extracellular protease from a newly isolated Streptomyces sp. DP2.","date":"2011","source":"New biotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/21232644","citation_count":31,"is_preprint":false},{"pmid":"23721423","id":"PMC_23721423","title":"Identification of 2-(2-(1-naphthoyl)-8-fluoro-3,4-dihydro-1H-pyrido[4,3-b]indol-5(2H)-yl)acetic acid (setipiprant/ACT-129968), a potent, selective, and orally bioavailable chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2) antagonist.","date":"2013","source":"Journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/23721423","citation_count":30,"is_preprint":false},{"pmid":"15755909","id":"PMC_15755909","title":"Identification of a potent and selective synthetic agonist at the CRTH2 receptor.","date":"2005","source":"Molecular pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/15755909","citation_count":30,"is_preprint":false},{"pmid":"26467464","id":"PMC_26467464","title":"GPR44 is a pancreatic protein restricted to the human beta cell.","date":"2015","source":"Acta diabetologica","url":"https://pubmed.ncbi.nlm.nih.gov/26467464","citation_count":29,"is_preprint":false},{"pmid":"34223653","id":"PMC_34223653","title":"ER-anchored CRTH2 antagonizes collagen biosynthesis and organ fibrosis via binding LARP6.","date":"2021","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/34223653","citation_count":28,"is_preprint":false},{"pmid":"19230460","id":"PMC_19230460","title":"Accumulation of CRTH2-positive leukocytes in human allergic nasal mucosa.","date":"2009","source":"Annals of allergy, asthma & immunology : official publication of the American College of Allergy, Asthma, & Immunology","url":"https://pubmed.ncbi.nlm.nih.gov/19230460","citation_count":28,"is_preprint":false},{"pmid":"16753296","id":"PMC_16753296","title":"Discovery of potent CRTh2 (DP2) receptor antagonists.","date":"2006","source":"Bioorganic & medicinal chemistry letters","url":"https://pubmed.ncbi.nlm.nih.gov/16753296","citation_count":27,"is_preprint":false},{"pmid":"16030019","id":"PMC_16030019","title":"Identification of determinants of ligand binding affinity and selectivity in the prostaglandin D2 receptor CRTH2.","date":"2005","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16030019","citation_count":27,"is_preprint":false},{"pmid":"30306748","id":"PMC_30306748","title":"Decreased CRTH2 Expression and Response to Allergen Re-stimulation on Innate Lymphoid Cells in Patients With Allergen-Specific Immunotherapy.","date":"2018","source":"Allergy, asthma & immunology research","url":"https://pubmed.ncbi.nlm.nih.gov/30306748","citation_count":27,"is_preprint":false},{"pmid":"27699264","id":"PMC_27699264","title":"Depletion of major pathogenic cells in asthma by targeting CRTh2.","date":"2016","source":"JCI insight","url":"https://pubmed.ncbi.nlm.nih.gov/27699264","citation_count":27,"is_preprint":false},{"pmid":"19592244","id":"PMC_19592244","title":"7-Azaindole-3-acetic acid derivatives: potent and selective CRTh2 receptor antagonists.","date":"2009","source":"Bioorganic & medicinal chemistry letters","url":"https://pubmed.ncbi.nlm.nih.gov/19592244","citation_count":27,"is_preprint":false},{"pmid":"21703412","id":"PMC_21703412","title":"Dual functions of prostaglandin D2 in murine contact hypersensitivity via DP and CRTH2.","date":"2011","source":"The American journal of pathology","url":"https://pubmed.ncbi.nlm.nih.gov/21703412","citation_count":26,"is_preprint":false},{"pmid":"31077596","id":"PMC_31077596","title":"Modulation of CRTh2 expression on allergen-specific T cells following peptide immunotherapy.","date":"2019","source":"Allergy","url":"https://pubmed.ncbi.nlm.nih.gov/31077596","citation_count":25,"is_preprint":false},{"pmid":"16022566","id":"PMC_16022566","title":"Small-molecule CRTH2 antagonists for the treatment of allergic inflammation: an overview.","date":"2005","source":"Expert opinion on investigational drugs","url":"https://pubmed.ncbi.nlm.nih.gov/16022566","citation_count":25,"is_preprint":false},{"pmid":"23827726","id":"PMC_23827726","title":"Efficacy and safety of AZD1981, a CRTH2 receptor antagonist, in patients with moderate to severe COPD.","date":"2013","source":"Respiratory medicine","url":"https://pubmed.ncbi.nlm.nih.gov/23827726","citation_count":25,"is_preprint":false},{"pmid":"24900313","id":"PMC_24900313","title":"Discovery of AMG 853, a CRTH2 and DP Dual Antagonist.","date":"2011","source":"ACS medicinal chemistry letters","url":"https://pubmed.ncbi.nlm.nih.gov/24900313","citation_count":25,"is_preprint":false},{"pmid":"19896843","id":"PMC_19896843","title":"Tetrahydroquinoline derivatives as CRTH2 antagonists.","date":"2009","source":"Bioorganic & medicinal chemistry letters","url":"https://pubmed.ncbi.nlm.nih.gov/19896843","citation_count":25,"is_preprint":false},{"pmid":"25698598","id":"PMC_25698598","title":"CRTH2, a prostaglandin D2 receptor, mediates depression-related behavior in mice.","date":"2015","source":"Behavioural brain research","url":"https://pubmed.ncbi.nlm.nih.gov/25698598","citation_count":24,"is_preprint":false},{"pmid":"17437532","id":"PMC_17437532","title":"A paracrine role for chemoattractant receptor-homologous molecule expressed on T helper type 2 cells (CRTH2) in mediating chemotactic activation of CRTH2+ CD4+ T helper type 2 lymphocytes.","date":"2007","source":"Immunology","url":"https://pubmed.ncbi.nlm.nih.gov/17437532","citation_count":24,"is_preprint":false},{"pmid":"28523115","id":"PMC_28523115","title":"Discovery of Fevipiprant (NVP-QAW039), a Potent and Selective DP2 Receptor Antagonist for Treatment of Asthma.","date":"2017","source":"ACS medicinal chemistry letters","url":"https://pubmed.ncbi.nlm.nih.gov/28523115","citation_count":23,"is_preprint":false},{"pmid":"18691063","id":"PMC_18691063","title":"Prostaglandin D2 receptors DP and CRTH2 in the pathogenesis of asthma.","date":"2008","source":"Current molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/18691063","citation_count":23,"is_preprint":false},{"pmid":"19066315","id":"PMC_19066315","title":"Antagonism of CRTH2 ameliorates chronic epicutaneous sensitization-induced inflammation by multiple mechanisms.","date":"2008","source":"International immunology","url":"https://pubmed.ncbi.nlm.nih.gov/19066315","citation_count":23,"is_preprint":false},{"pmid":"12911667","id":"PMC_12911667","title":"Differential expression of CCR5 and CRTH2 on infiltrated cells in colonic mucosa of patients with ulcerative colitis.","date":"2003","source":"Journal of gastroenterology and hepatology","url":"https://pubmed.ncbi.nlm.nih.gov/12911667","citation_count":23,"is_preprint":false},{"pmid":"23146091","id":"PMC_23146091","title":"Biochemical and pharmacological characterization of AZD1981, an orally available selective DP2 antagonist in clinical development for asthma.","date":"2013","source":"British journal of pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/23146091","citation_count":22,"is_preprint":false},{"pmid":"15507393","id":"PMC_15507393","title":"The Th2 response as monitored by CRTH2 or CCR3 expression is severely decreased during septic shock.","date":"2004","source":"Clinical immunology (Orlando, Fla.)","url":"https://pubmed.ncbi.nlm.nih.gov/15507393","citation_count":22,"is_preprint":false},{"pmid":"24523542","id":"PMC_24523542","title":"Central CRTH2, a second prostaglandin D2 receptor, mediates emotional impairment in the lipopolysaccharide and tumor-induced sickness behavior model.","date":"2014","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/24523542","citation_count":21,"is_preprint":false},{"pmid":"29765200","id":"PMC_29765200","title":"Efficacy and safety of the CRTh2 antagonist AZD1981 as add-on therapy to inhaled corticosteroids and long-acting β2-agonists in patients with atopic asthma.","date":"2018","source":"Drug design, development and therapy","url":"https://pubmed.ncbi.nlm.nih.gov/29765200","citation_count":21,"is_preprint":false},{"pmid":"18835884","id":"PMC_18835884","title":"Prostaglandin H2 induces the migration of human eosinophils through the chemoattractant receptor homologous molecule of Th2 cells, CRTH2.","date":"2008","source":"Journal of leukocyte biology","url":"https://pubmed.ncbi.nlm.nih.gov/18835884","citation_count":21,"is_preprint":false},{"pmid":"28623133","id":"PMC_28623133","title":"Prostaglandin D2 enhances lipid accumulation through suppression of lipolysis via DP2 (CRTH2) receptors in adipocytes.","date":"2017","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/28623133","citation_count":20,"is_preprint":false},{"pmid":"29439547","id":"PMC_29439547","title":"Prostaglandin D2-Mediated DP2 and AKT Signal Regulate the Activation of Androgen Receptors in Human Dermal Papilla Cells.","date":"2018","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/29439547","citation_count":20,"is_preprint":false},{"pmid":"16940740","id":"PMC_16940740","title":"Prostaglandin D2 induces IL-8 and GM-CSF by bronchial epithelial cells in a CRTH2-independent pathway.","date":"2006","source":"International archives of allergy and immunology","url":"https://pubmed.ncbi.nlm.nih.gov/16940740","citation_count":20,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":51214,"output_tokens":8299,"usd":0.139064},"stage2":{"model":"claude-opus-4-6","input_tokens":12080,"output_tokens":3999,"usd":0.240563},"total_usd":0.379627,"stage1_batch_id":"msgbatch_01SUR8NDzVrNmyszWyJeCct7","stage2_batch_id":"msgbatch_01G7Yfutko3cDWzejrwH5AMx","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2001,\n      \"finding\": \"CRTH2 (PTGDR2) is a seven-transmembrane G protein-coupled receptor that binds PGD2 and induces intracellular Ca2+ mobilization and chemotaxis in Th2 cells, eosinophils, and basophils in a Gαi-dependent manner.\",\n      \"method\": \"Radioligand binding, Ca2+ mobilization assay, chemotaxis assay, pertussis toxin inhibition in CRTH2-transfected cells and primary leukocytes\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal functional assays (binding, Ca2+ flux, chemotaxis) with pertussis toxin controls, foundational paper with 878 citations\",\n      \"pmids\": [\"11208866\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Recombinant human CRTH2 binds PGD2 with high and low affinity sites (KD 2.5 nM and 109 nM) and couples to Gαi/o to decrease intracellular cAMP in a pertussis toxin-sensitive manner; the ligand selectivity rank order differs markedly from the DP receptor.\",\n      \"method\": \"Radioligand saturation binding, competition binding assays, cAMP functional assay, pertussis toxin inhibition in HEK293-EBNA cells expressing recombinant hCRTH2\",\n      \"journal\": \"British journal of pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with recombinant receptor, multiple orthogonal assays (binding kinetics, signal transduction)\",\n      \"pmids\": [\"12466225\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Indomethacin acts as a CRTH2 (PTGDR2) agonist, inducing Gαi-dependent Ca2+ mobilization at submicromolar concentrations (~50 nM EC50) and chemotaxis in Th2 cells, eosinophils, and basophils; this effect is blocked by anti-CRTH2 mAb and is not shared by other NSAIDs.\",\n      \"method\": \"Ca2+ mobilization assay in CRTH2-transfected K562 cells, chemotaxis assay with primary human leukocytes, anti-CRTH2 mAb blocking, pertussis toxin inhibition\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — functional assays in transfected cells and primary leukocytes with receptor-specific blocking antibody\",\n      \"pmids\": [\"11801628\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"CRTH2 mediates PGD2-induced eosinophil chemokinesis, morphology change, and degranulation, while the DP receptor (not CRTH2) mediates delay of eosinophil apoptosis; these two receptors have pharmacologically distinct and independent functions on eosinophils.\",\n      \"method\": \"Selective agonists (DK-PGD2 for CRTH2, BW245C for DP) and functional assays on primary human eosinophils (chemokinesis, degranulation, apoptosis)\",\n      \"journal\": \"The Journal of allergy and clinical immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — selective pharmacological dissection with receptor-specific agonists across multiple functional readouts\",\n      \"pmids\": [\"11742277\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"11-dehydro-thromboxane B2 (11-dehydro-TXB2) is a full agonist of CRTH2, inducing Ca2+ flux from intracellular stores in eosinophils (desensitized by PGD2 pre-treatment), shape change in eosinophils and basophils (blocked by ramatroban but not TP antagonist SQ29548), and chemotaxis of CRTH2-transfected BaF/3 cells but not naïve BaF/3 cells; the response is inhibited by phospholipase C inhibitor U73122.\",\n      \"method\": \"Flow cytometric shape change assay, Ca2+ flux, chemotaxis assay with CRTH2-transfected cells, receptor desensitization, selective antagonists\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — transfected cell line controls, receptor desensitization cross-experiment, PLC inhibitor mechanistic follow-up\",\n      \"pmids\": [\"14668348\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Site-directed mutagenesis of CRTH2 identified His-106 (TM III), Lys-209 (TM V), Glu-268 (TM VI), and Arg-178 (ECL2) as residues required for PGD2 binding and functional responses (cAMP inhibition, chemotaxis); Glu-268 also determines prostanoid selectivity, and Tyr-261 is critical for indomethacin binding but not PGD2 binding.\",\n      \"method\": \"Site-directed mutagenesis of mouse CRTH2, radioligand binding, cAMP assay, chemotaxis assay in HEK293 cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — active-site mutagenesis with multiple orthogonal functional assays defining the ligand-binding pocket\",\n      \"pmids\": [\"16030019\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"9α,11β-PGF2 (a major in vivo metabolite of PGD2 after allergen challenge) and its stereoisomer PGF2α are CRTH2 agonists capable of inducing cell migration and activation through this receptor.\",\n      \"method\": \"Chemotaxis assay, receptor activation assay with primary eosinophils/basophils and CRTH2-expressing cells\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional assays with primary leukocytes, single laboratory\",\n      \"pmids\": [\"16378605\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Ramatroban and structural analogs (TM30642, TM30643, TM30089) bind human CRTH2 at the orthosteric site with nanomolar affinity; insurmountable antagonism of TM30643/TM30089 is mechanistically linked to long-lasting CRTH2 inhibition via depression of ligand binding capacity (Bmax reduction), distinct from competitive surmountable antagonism of ramatroban.\",\n      \"method\": \"[3H]PGD2 saturation analysis, GTPγS binding, β-arrestin translocation assay, eosinophil shape change assay in CRTH2-expressing cells\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal assays distinguishing mechanism of insurmountability at the receptor level\",\n      \"pmids\": [\"16418339\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"In vivo eosinophil trafficking into rat airways in response to PGD2 is mediated by CRTH2, not DP or TP receptors; three CRTH2-specific agonists replicate PGD2-induced BAL eosinophilia while DP and TP agonists do not, and the CRTH2/TP antagonist ramatroban (but not DP- or TP-selective antagonists alone) abolishes the effect.\",\n      \"method\": \"Intratracheal PGD2/agonist instillation in IL-5-primed rats, BAL cell counts, lung histology, selective receptor agonists/antagonists\",\n      \"journal\": \"The Journal of pharmacology and experimental therapeutics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo pharmacological dissection with receptor-selective tools, establishing CRTH2 as the mediating receptor for eosinophil trafficking\",\n      \"pmids\": [\"15528449\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"CRTH2 activation by PGD2 inhibits cytokine deprivation-induced apoptosis of human Th2 cells via the phosphatidylinositol 3-kinase (PI3K)/Akt pathway, inducing Akt and BAD phosphorylation, preventing cytochrome c release, and suppressing caspase-3 cleavage; this anti-apoptotic effect is blocked by the PI3K inhibitor LY294002 and CRTH2 antagonists, but is not mediated by DP1 or TP receptors.\",\n      \"method\": \"Apoptosis assays (caspase-3, PARP cleavage, cytochrome c release), Akt/BAD phosphorylation western blot, PI3K inhibitor (LY294002), selective CRTH2 agonist (DK-PGD2) and antagonists (ramatroban, TM30089) in primary human Th2 cells\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mechanistic pathway delineated by multiple signaling readouts plus pharmacological dissection of receptor and kinase involvement\",\n      \"pmids\": [\"19494281\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PGH2 (the PGD2 precursor) directly activates CRTH2 to induce eosinophil and basophil chemotaxis and Ca2+ flux; the response is subject to homologous desensitization with PGD2, blocked by CRTH2 antagonist (CAY10471) but not by hematopoietic PGD synthase inhibitor HQL79, and is reproduced in CRTH2-transfected HEK293 cells.\",\n      \"method\": \"Ca2+ flux assay, chemotaxis assay, eosinophil shape change, HEK293 transfection, receptor desensitization, selective antagonists\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — transfected cell model confirms direct CRTH2 engagement; desensitization and enzymatic inhibitor controls rule out indirect mechanism\",\n      \"pmids\": [\"18835884\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Crystal structures of human CRTH2 with antagonists fevipiprant and CAY10471 reveal a semi-occluded ligand-binding pocket covered by a well-structured amino terminus; structural analysis identifies a ligand entry port and a charge-attraction-facilitated binding process for PGD2 distinct from that of lysophospholipids and endocannabinoids at other GPCRs.\",\n      \"method\": \"X-ray crystallography of human CRTH2 with two antagonists, computational docking, radioligand binding validation\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with functional validation by ligand-binding assays; mechanistic insight into GPCR lipid recognition\",\n      \"pmids\": [\"30220562\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Activated CRTH2+ CD4+ Th2 cells produce PGD2 in a COX-dependent manner, which acts in a paracrine fashion through CRTH2 to promote chemotaxis of naïve Th2 cells; additional non-COX CRTH2 agonist factors are also produced by activated Th2 cells, revealing a paracrine autocrine amplification loop.\",\n      \"method\": \"CRTH2+ Th2 cell activation, COX inhibitor (diclofenac), CRTH2/TP antagonist (ramatroban), TP-selective antagonist (SQ29548), supernatant transfer chemotaxis assays\",\n      \"journal\": \"Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological dissection of receptor and COX contributions in primary human T cells, single laboratory\",\n      \"pmids\": [\"17437532\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CRTH2 is a critical regulator of neutrophil migration in sepsis; genetic ablation of CRTH2 in mice improves neutrophil peritoneal accumulation during cecal ligation and puncture (CLP) by epigenetically upregulating CXCR2 via increased histone H3 acetylation at the CXCR2 promoter in neutrophils, reducing bacterial load and inflammatory cytokines (TNF-α, IL-6, CCL3) while increasing IL-10.\",\n      \"method\": \"CRTH2 knockout mice, CLP sepsis model, peritoneal neutrophil counts, CXCR2 flow cytometry, ChIP for histone H3 acetylation at CXCR2 promoter, neutrophil depletion, CXCR2 inhibition\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout with mechanistic chromatin-level follow-up plus pharmacological validation; multiple orthogonal methods\",\n      \"pmids\": [\"22544936\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"CRTH2 on ILC2s mediates their accumulation in the lung in response to PGD2; CRTH2-deficient mice show reduced ILC2 pulmonary accumulation in helminth-induced inflammation, and adoptive transfer of CRTH2-sufficient (but not CRTH2-deficient) ILC2s restores pulmonary inflammation in CRTH2-deficient recipients.\",\n      \"method\": \"CRTH2 knockout mice, helminth infection model, ILC2 adoptive transfer, in vitro PGD2 migration assay, in vivo PGD2 administration\",\n      \"journal\": \"Mucosal immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout plus adoptive transfer epistasis establishing CRTH2 cell-autonomous role in ILC2 migration\",\n      \"pmids\": [\"25850654\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PGD2 acts through the Dp2 receptor in the foetal mouse testis to promote mitotic arrest in male germ cells by activating expression and nuclear localization of CDK inhibitor p21Cip1, repressing pluripotency markers, and upregulating the spermatogonial master gene Nanos2.\",\n      \"method\": \"In vitro and in vivo approaches in foetal mouse testis, Dp2 receptor pharmacology, immunostaining for p21Cip1 nuclear localization, gene expression analysis\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo and in vitro combined with specific receptor pharmacology in a defined biological context\",\n      \"pmids\": [\"25142465\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PGD2 via the GPR44/CRTH2 receptor inhibits wound-induced hair follicle neogenesis (WIHN); Gpr44-null mice show increased WIHN and are resistant to exogenous PGD2-induced inhibition of follicle neogenesis.\",\n      \"method\": \"Gpr44 knockout mice, wound-induced hair follicle neogenesis model, exogenous PGD2 application, histological quantification of neogenesis\",\n      \"journal\": \"The Journal of investigative dermatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout with rescue/inhibition by exogenous ligand application, specific phenotypic readout\",\n      \"pmids\": [\"23190891\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The prostaglandin D2 synthase/GPR44 (CRTH2) signaling axis is required for PNS myelination; neuronal L-PGDS produces PGD2 that signals through glial Gpr44/CRTH2, activating the transcription factor Nfatc4 as a downstream effector; L-PGDS knockout mice are hypomyelinated, and glial Gpr44 knockdown impairs in vitro myelination.\",\n      \"method\": \"L-PGDS knockout mice, Gpr44 in vivo ablation and in vitro knockdown, myelination assays, L-PGDS inhibition, NRG1 intracellular domain signaling upstream analysis, Nfatc4 identification as downstream effector\",\n      \"journal\": \"Nature neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — genetic loss-of-function in vivo and in vitro, multiple orthogonal approaches identifying pathway from L-PGDS to CRTH2 to Nfatc4\",\n      \"pmids\": [\"25362470\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"COX-1-dependent PGD2 produced by spinal microglia after peripheral nerve injury signals through DP2 (CRTH2) receptors on spinal neurons to contribute to mechanical allodynia in neuropathic pain; intrathecal COX-1 inhibitor and DP2 antagonist both attenuate allodynia.\",\n      \"method\": \"Spared nerve injury model, COX-1 inhibitor intrathecal injection, DP2 receptor antagonist, in situ hybridization and mRNA expression in spinal cord\",\n      \"journal\": \"Glia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo pharmacological loss-of-function with two independent inhibitors in a defined pain model\",\n      \"pmids\": [\"23505121\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PGD2/PTGDR2 signaling inhibits STAT3 phosphorylation at Thr705 and nuclear expression in gastric cancer stem-like cells, restricting their self-renewal; PTGDR2 knockdown enhances CSC markers, and mutation of the STAT3 Thr705 phosphorylation site abolishes the inhibitory effect of PGD2 on CSC marker expression.\",\n      \"method\": \"PTGDR2 knockdown, PGD2 stimulation, L-PTGDS overexpression, STAT3 phosphorylation western blot, STAT3 phosphorylation-site mutagenesis, in vitro sphere formation, in vivo xenograft and peritoneal metastasis models\",\n      \"journal\": \"Stem cells (Dayton, Ohio)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mechanistic mutagenesis of STAT3 site plus multiple in vitro and in vivo readouts linking PTGDR2 to STAT3 suppression\",\n      \"pmids\": [\"29604141\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PGD2/DP2 (CRTH2) signaling suppresses interferon-λ (IFN-λ/IL-28) production during RSV infection, promoting severe bronchiolitis; DP2 antagonism increases IFN-λ expression via the DP1 pathway, accelerating viral clearance, while dual DP1/DP2 antagonism abolishes this protection, revealing a DP2-DP1 counter-regulatory axis controlling antiviral IFN-λ responses.\",\n      \"method\": \"Neonatal mouse bronchiolitis model, DP2 antagonism, dual DP1/DP2 antagonism, DP1 agonism, IL-28A neutralization, RSV-infected primary airway epithelial cell cultures, IFN-stimulated gene expression measurement\",\n      \"journal\": \"Science translational medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo and in vitro with multiple receptor-specific pharmacological tools and cytokine neutralization establishing DP2→IFN-λ suppression axis\",\n      \"pmids\": [\"29743346\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CRTH2-mediated Th2 activation drives pulmonary arterial hypertension; CRTH2 activation in Th2 cells promotes pulmonary arterial smooth muscle cell proliferation through STAT6 activation, and both CRTH2-sufficient bone marrow reconstitution and CD4+ T cell adoptive transfer restore PAH in CRTH2-deficient mice, an effect reversed by dual IL-4/IL-13 neutralization.\",\n      \"method\": \"CRTH2 knockout mice, PAH mouse models, bone marrow reconstitution, adoptive transfer, STAT6 pathway analysis in co-culture, IL-4/IL-13 dual neutralization\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic, adoptive transfer, and cytokine neutralization epistasis experiments in vivo, mechanistic in vitro STAT6 link\",\n      \"pmids\": [\"29970474\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CRTH2 is trafficked to the endoplasmic reticulum (ER) membrane in fibroblasts in a caveolin-1-dependent manner, where it binds La ribonucleoprotein domain family member 6 (LARP6) at the collagen mRNA recognition motif and promotes degradation of collagen mRNA, thereby suppressing collagen biosynthesis; CRTH2 deficiency increases collagen production and exacerbates organ fibrosis in mice rescued by LARP6 depletion.\",\n      \"method\": \"Subcellular fractionation, Co-immunoprecipitation of CRTH2 with LARP6, caveolin-1 dependency experiments, collagen mRNA stability assay, CRTH2-null mouse fibrosis models (bleomycin, UUO), LARP6 depletion rescue, CRTH2 N-terminal peptide administration\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct protein-protein interaction (Co-IP), subcellular localization with functional consequence, in vivo genetic rescue epistasis, peptide intervention\",\n      \"pmids\": [\"34223653\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The PGD2-CRTH2 pathway in intestinal epithelial cells (stem, goblet, and tuft cells) negatively regulates IL-13Rα1 expression and counteracts Type 2 cytokine-driven goblet cell hyperplasia and epithelial proliferation suppression during helminth infection; CRTH2-deficient small intestinal organoids show enhanced budding and terminal differentiation to the goblet cell lineage.\",\n      \"method\": \"CRTH2 knockout mice (whole body and non-hematopoietic conditional), helminth infection model (N. brasiliensis), intestinal organoid culture, goblet cell quantification, IL-13Rα1 expression analysis\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional and global knockout with organoid mechanistic follow-up establishing epithelial-autonomous CRTH2 function\",\n      \"pmids\": [\"34283207\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PGD2 suppresses lipolysis in adipocytes via Gi-coupled DP2 (CRTH2) receptors by repressing the cAMP-PKA-hormone-sensitive lipase (HSL) axis; DP2 knockout mouse embryonic fibroblasts show enhanced lipolysis, and the DP2 agonist 15R-15-methyl PGD2 increases adipogenic/lipogenic gene expression and decreases glycerol release.\",\n      \"method\": \"DP2 receptor agonist/antagonist pharmacology, PKA activity assay, HSL phosphorylation western blot, glycerol release lipolysis assay, DP2 gene-knockout MEF adipocyte differentiation\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout plus receptor-specific pharmacology with molecular signaling readouts, single laboratory\",\n      \"pmids\": [\"28623133\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"15-deoxy-Δ12,14-PGJ2 induces cardiomyocyte apoptosis via DP2 (CRTH2) receptor-mediated ROS production and p38/p42/44 MAPK phosphorylation, leading to TNFα upregulation and activation of both extrinsic (caspase-8) and intrinsic (Bax, caspase-9) apoptotic pathways; the electrophilic cyclopentenone moiety of 15d-PGJ2 is required, and TNFα silencing attenuates the apoptotic cascade.\",\n      \"method\": \"DP2-specific agonists/antagonists in HL-1 cardiomyocyte cell line and primary murine cardiomyocytes, ROS measurement, MAPK phosphorylation, TNFα siRNA knockdown, caspase activation assays, 9,10-dihydro-15d-PGJ2 structural control\",\n      \"journal\": \"International journal of cardiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — receptor pharmacology and siRNA epistasis in primary and cell line models, single laboratory\",\n      \"pmids\": [\"24698234\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The PGD2-CRTH2 pathway promotes tubulointerstitial renal fibrosis via CRTH2-mediated activation of Th2 lymphocytes and their production of IL-4 and IL-13; both L-PGDS and CRTH2 knockout mice show reduced fibrosis, reduced Th2 infiltration, and decreased IL-4/IL-13; ablation of IL-4/IL-13 also ameliorates fibrosis, placing them downstream of CRTH2.\",\n      \"method\": \"L-PGDS and CRTH2 knockout mice, unilateral ureteral obstruction model, oral CRTH2 antagonist administration, IL-4/IL-13 neutralization, renal histology and cytokine measurement\",\n      \"journal\": \"Journal of the American Society of Nephrology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — double genetic knockout plus pharmacological inhibition plus cytokine neutralization epistasis, establishing CRTH2→IL-4/IL-13→fibrosis pathway\",\n      \"pmids\": [\"22997255\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Central CRTH2 mediates depression-related emotional behaviors in mice; CRTH2-deficient mice show antidepressant-like phenotypes and are protected from LPS- and tumor-induced social and exploratory behavioral impairment; chronic corticosterone increases COX-2 and L-PGDS mRNA in brain; CRTH2 deficiency increases hippocampal noradrenergic system activity.\",\n      \"method\": \"CRTH2 knockout mice, chronic corticosterone model, LPS and tumor sickness models, forced swim test, social interaction/novel exploratory behavior assays, CRTH2 antagonist (ramatroban), monoamine system analysis\",\n      \"journal\": \"Behavioural brain research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic and pharmacological loss-of-function with specific behavioral readouts and neurochemical mechanistic follow-up\",\n      \"pmids\": [\"25698598\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PGD2 stimulates androgen receptor (AR) expression and AKT signaling through DP2 (CRTH2) in human dermal papilla cells; DP2 knockdown or antagonism (TM30089) and AKT inhibition (LY294002) both decrease AR expression and AKT pathway activation, establishing a DP2→AKT→AR axis.\",\n      \"method\": \"PGD2 stimulation, siRNA-mediated DP2 knockdown, DP2 antagonist (TM30089), AKT inhibitor (LY294002), qRT-PCR, western blot, immunocytochemistry in human dermal papilla cells\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA knockdown plus pharmacological inhibitor convergence on same readout, single laboratory\",\n      \"pmids\": [\"29439547\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"CRTH2/DP2 is the primary mediator of pro-inflammatory PGD2 effects on human basophils (Ca2+ influx, CD11b upregulation, migration, degranulation), while DP receptor activation exerts opposing inhibitory effects on basophil migration and IgE-mediated degranulation; CRTH2 transcript levels are approximately 100-fold higher than DP in basophils.\",\n      \"method\": \"Selective agonists (DK-PGD2 for CRTH2; BW245C for DP), antagonists (ramatroban for CRTH2; BWA868C for DP), Ca2+ mobilization, migration, degranulation, CD11b expression, survival assays on primary human basophils, real-time PCR\",\n      \"journal\": \"Clinical and experimental allergy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — comprehensive pharmacological dissection with receptor-selective tools across multiple functional readouts in primary human basophils\",\n      \"pmids\": [\"15298571\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CRTH2 (PTGDR2) is a Gαi-coupled seven-transmembrane GPCR that binds PGD2 and related prostanoid metabolites (including 11-dehydro-TXB2, 9α,11β-PGF2, PGH2, and indomethacin) to drive Ca2+ mobilization, cAMP inhibition, chemotaxis, degranulation, Th2 cytokine production, and PI3K/Akt-mediated survival in Th2 cells, eosinophils, basophils, and ILC2s; at the structural level, a semi-occluded pocket covered by the receptor N-terminus accommodates antagonists such as fevipiprant; additional non-canonical functions include ER-membrane localization (caveolin-1-dependent) in fibroblasts where it binds LARP6 to degrade collagen mRNA, suppression of STAT3 in cancer stem cells, promotion of myelination via Nfatc4, negative regulation of intestinal epithelial IL-13Rα1/goblet cell differentiation, and modulation of lipolysis via the cAMP-PKA-HSL axis in adipocytes.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CRTH2 (PTGDR2) is a Gαi-coupled prostaglandin D2 receptor that orchestrates type 2 immune cell activation, chemotaxis, and survival, while also serving non-canonical roles in fibrosis, myelination, and epithelial differentiation. The receptor binds PGD2 and related prostanoids (PGH2, 11-dehydro-TXB2, 9α,11β-PGF2, 15d-PGJ2, and indomethacin) at a semi-occluded pocket defined by key residues His-106, Lys-209, Glu-268, and Arg-178, coupling through Gαi to inhibit cAMP, mobilize intracellular Ca²⁺ via PLC, and activate PI3K/Akt-dependent anti-apoptotic signaling in Th2 cells, eosinophils, basophils, and ILC2s [PMID:11208866, PMID:12466225, PMID:16030019, PMID:30220562, PMID:19494281, PMID:25850654]. Beyond canonical immune functions, CRTH2 localizes to the endoplasmic reticulum in fibroblasts in a caveolin-1-dependent manner, where it binds LARP6 to promote collagen mRNA degradation and suppress fibrosis [PMID:34223653]; in Schwann cells it drives PNS myelination through Nfatc4 [PMID:25362470]; and in intestinal epithelium it negatively regulates IL-13Rα1 expression and goblet cell hyperplasia [PMID:34283207]. CRTH2-mediated Th2 activation also drives pathological remodeling in pulmonary arterial hypertension via STAT6 and IL-4/IL-13 signaling, and in tubulointerstitial renal fibrosis [PMID:29970474, PMID:22997255].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Establishing that CRTH2 is the PGD2 receptor mediating Th2/eosinophil/basophil chemotaxis resolved the longstanding question of how PGD2 recruits type 2 effector cells independently of the DP1 receptor.\",\n      \"evidence\": \"Radioligand binding, Ca²⁺ mobilization, chemotaxis, and pertussis toxin inhibition in CRTH2-transfected cells and primary leukocytes; pharmacological dissection with DP-selective vs CRTH2-selective agonists on eosinophils\",\n      \"pmids\": [\"11208866\", \"11742277\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream intracellular signaling cascades beyond Gαi not yet mapped\", \"In vivo relevance of CRTH2-mediated eosinophil trafficking not yet demonstrated\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Defining dual-affinity PGD2 binding kinetics and cAMP inhibition established the quantitative pharmacology of CRTH2 as a Gαi/o-coupled receptor, while identification of indomethacin as a non-prostanoid agonist broadened the receptor's ligand repertoire beyond classical eicosanoids.\",\n      \"evidence\": \"Radioligand saturation/competition binding and cAMP assays in recombinant HEK293 cells; indomethacin agonism confirmed by Ca²⁺ flux, chemotaxis, and anti-CRTH2 mAb blocking\",\n      \"pmids\": [\"12466225\", \"11801628\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of ligand selectivity unknown\", \"Physiological significance of indomethacin agonism unclear\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"In vivo pharmacological dissection proved that CRTH2 — not DP or TP — mediates PGD2-induced eosinophil airway trafficking, validating CRTH2 as a drug target for allergic airway inflammation and confirming it as the dominant pro-inflammatory PGD2 receptor on basophils.\",\n      \"evidence\": \"Intratracheal agonist instillation in IL-5-primed rats with selective receptor antagonists; comprehensive pharmacological profiling of primary human basophils with selective agonists/antagonists\",\n      \"pmids\": [\"15528449\", \"15298571\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Genetic (knockout) confirmation of airway eosinophilia role not yet available\", \"Relative contribution to human asthma not established\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Site-directed mutagenesis of CRTH2 identified the critical ligand-binding residues (His-106, Lys-209, Glu-268, Arg-178) and showed that Tyr-261 discriminates between PGD2 and indomethacin binding, providing the first molecular map of the orthosteric pocket.\",\n      \"evidence\": \"Mutagenesis of mouse CRTH2 with radioligand binding, cAMP, and chemotaxis assays in HEK293 cells\",\n      \"pmids\": [\"16030019\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No three-dimensional structure available\", \"Mechanism of ligand entry and binding dynamics unknown\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Characterization of insurmountable antagonism by ramatroban analogs revealed that long-lasting CRTH2 blockade involves reduction of ligand binding capacity (Bmax) rather than simple competitive displacement, informing antagonist design.\",\n      \"evidence\": \"[³H]PGD2 saturation analysis, GTPγS binding, β-arrestin translocation, and eosinophil shape change assays\",\n      \"pmids\": [\"16418339\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural mechanism of insurmountable antagonism not resolved\", \"In vivo pharmacokinetic relevance not demonstrated\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Demonstration that the upstream prostaglandin PGH2 directly activates CRTH2 expanded the physiological ligand repertoire to include the PGD2 precursor, establishing that CRTH2 can be activated even without PGD synthase activity.\",\n      \"evidence\": \"Ca²⁺ flux, chemotaxis, homologous desensitization with PGD2, CRTH2-transfected HEK293 confirmation, PGDS inhibitor control\",\n      \"pmids\": [\"18835884\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Quantitative contribution of PGH2 vs PGD2 signaling in vivo unknown\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Identification of the PI3K/Akt/BAD anti-apoptotic pathway downstream of CRTH2 in Th2 cells explained how PGD2 promotes Th2 cell survival beyond chemotaxis, linking CRTH2 to immune persistence in allergic inflammation.\",\n      \"evidence\": \"Akt/BAD phosphorylation, cytochrome c release, caspase-3 cleavage assays with PI3K inhibitor and CRTH2 antagonist epistasis in primary human Th2 cells\",\n      \"pmids\": [\"19494281\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PI3K activation is direct or via Gβγ subunits not resolved\", \"Relevance to Th2 survival in vivo not tested\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Genetic ablation of CRTH2 revealed two unexpected in vivo roles: epigenetic regulation of neutrophil CXCR2 expression in sepsis and promotion of tubulointerstitial renal fibrosis through Th2-derived IL-4/IL-13, extending CRTH2 function beyond classical type 2 immunity.\",\n      \"evidence\": \"CRTH2 knockout mice in CLP sepsis model with ChIP for H3 acetylation at CXCR2 promoter; CRTH2 and L-PGDS knockout mice in UUO fibrosis model with IL-4/IL-13 neutralization\",\n      \"pmids\": [\"22544936\", \"22997255\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism linking CRTH2 to histone acetylation at CXCR2 promoter unknown\", \"Whether fibrosis role is exclusively Th2-mediated or involves non-immune cell CRTH2 not fully resolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Discovery of CRTH2 roles in gonadal development (promoting male germ cell mitotic arrest via p21Cip1/Nanos2), hair follicle neogenesis inhibition, and PNS myelination (via Nfatc4 in Schwann cells) revealed tissue-specific developmental functions far removed from immune regulation.\",\n      \"evidence\": \"Dp2 pharmacology in fetal mouse testis; Gpr44 knockout mice in WIHN model; L-PGDS knockout and Gpr44 knockdown with myelination assays identifying Nfatc4\",\n      \"pmids\": [\"25142465\", \"23190891\", \"25362470\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Nfatc4 is a direct CRTH2 signaling target or requires intermediate kinases unknown\", \"CRTH2 signaling pathway in germ cells not fully delineated\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Demonstrating that CRTH2 is required for ILC2 pulmonary accumulation via adoptive transfer epistasis established CRTH2 as cell-autonomous on ILC2s and positioned it as a key driver of innate type 2 immunity in helminth infection.\",\n      \"evidence\": \"CRTH2 knockout mice, helminth infection, adoptive transfer of CRTH2-sufficient vs CRTH2-deficient ILC2s\",\n      \"pmids\": [\"25850654\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream ILC2 effector programs activated by CRTH2 not characterized\", \"Relative contribution of ILC2 vs Th2 CRTH2 signaling in helminth clearance unclear\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Crystal structures of CRTH2 with fevipiprant and CAY10471 resolved the semi-occluded binding pocket architecture with an N-terminal lid, explaining how lipid ligands access the orthosteric site through a lateral entry port — a mechanism distinct from other lipid GPCRs.\",\n      \"evidence\": \"X-ray crystallography of human CRTH2 bound to two antagonists, computational docking, radioligand binding validation\",\n      \"pmids\": [\"30220562\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No agonist-bound or active-state structure available\", \"Mechanism of receptor activation and G protein coupling at structural level unresolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Multiple 2018 studies expanded CRTH2's pathological roles: suppressing IFN-λ during RSV bronchiolitis (revealing a DP2-DP1 counter-regulatory axis), driving pulmonary arterial hypertension through Th2/STAT6/IL-4/IL-13, and inhibiting STAT3 in gastric cancer stem cells.\",\n      \"evidence\": \"DP2 antagonism in neonatal mouse RSV model with IFN-λ neutralization; CRTH2 KO with bone marrow reconstitution and IL-4/IL-13 neutralization in PAH models; PTGDR2 knockdown with STAT3 phospho-site mutagenesis in gastric cancer spheroids and xenografts\",\n      \"pmids\": [\"29743346\", \"29970474\", \"29604141\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether STAT3 inhibition is direct or through an intermediate signaling step unknown\", \"Clinical relevance of DP2 antagonism in RSV bronchiolitis not demonstrated\", \"CRTH2 expression and function in human PAH tissue not confirmed\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Discovery that CRTH2 localizes to the ER membrane via caveolin-1 and binds LARP6 to degrade collagen mRNA revealed a ligand-independent, non-canonical anti-fibrotic function distinct from its GPCR signaling activity; simultaneously, epithelial CRTH2 was shown to restrain IL-13Rα1-driven goblet cell differentiation.\",\n      \"evidence\": \"Co-IP of CRTH2-LARP6, subcellular fractionation, caveolin-1 dependency, collagen mRNA stability, CRTH2-null mouse fibrosis models with LARP6 rescue; conditional and global CRTH2 KO mice in helminth infection with intestinal organoid culture\",\n      \"pmids\": [\"34223653\", \"34283207\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ER-localized CRTH2 retains any signaling capacity unknown\", \"Structural basis of CRTH2-LARP6 interaction not determined\", \"Signaling pathway by which epithelial CRTH2 suppresses IL-13Rα1 not identified\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the active-state structure and G protein coupling mechanism, how CRTH2 toggles between canonical GPCR signaling and non-canonical ER/LARP6 functions, and whether its diverse tissue-specific roles (myelination, germ cell arrest, cancer stem cell suppression) share common downstream effectors.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No active-state or agonist-bound CRTH2 structure exists\", \"Molecular switch between canonical signaling and ER-localized mRNA regulatory function unknown\", \"Integration of PI3K/Akt, STAT3, STAT6, and Nfatc4 pathways into a unified CRTH2 signaling model not achieved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 1, 5, 11]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0, 1, 4, 10, 11]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [22, 19]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 11]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [22]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 5, 9, 11, 24]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [3, 8, 14, 21, 23, 26, 29]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [9, 25]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [15, 17]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"LARP6\",\n      \"CAV1\",\n      \"NFATC4\",\n      \"STAT3\",\n      \"STAT6\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}