{"gene":"CD93","run_date":"2026-06-09T22:57:18","timeline":{"discoveries":[{"year":1997,"finding":"CD93 (C1qR(P)) was identified as a novel type I transmembrane protein with a C-type carbohydrate recognition domain, five EGF-like domains, a transmembrane domain, and a short cytoplasmic tail. Monoclonal antibodies R3 and R139, which inhibit C1q/MBL/SPA-mediated enhancement of phagocytosis, were used to purify the protein and clone its cDNA, establishing it as the receptor mediating enhanced phagocytosis triggered by these three structurally related ligands.","method":"Protein purification via mAb affinity, amino acid sequencing, cDNA cloning, anti-peptide antiserum generation, functional inhibition assays","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 1 / Strong — cDNA cloning with full sequence verification, functional inhibition by multiple mAbs, replicated across C1q/MBL/SPA ligands in a single rigorous study","pmids":["9047234"],"is_preprint":false},{"year":1999,"finding":"CD93 (C1qRP) is heavily O-glycosylated, and this O-linked glycosylation is required for proper molecular weight and cell surface expression. Direct cross-linking of CD93 by immobilized anti-CD93 mAb R3 triggers enhanced phagocytic capacity in the absence of ligand, demonstrating that CD93 ligation directly transduces a pro-phagocytic signal. The protein backbone alone (without glycosylation) migrates at the predicted molecular weight; extensive O-glycosylation accounts for the discrepancy between predicted and observed molecular weight.","method":"CHO cell transfection, glycosylation inhibitors, glycosidase cleavage, in vitro translation, functional phagocytosis assay with mAb cross-linking","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal biochemical methods (inhibitors, enzymes, translation) plus functional assay in a single study","pmids":["10092817"],"is_preprint":false},{"year":2003,"finding":"O-glycosylation stabilizes CD93 at the cell surface. When O-glycosylation is inhibited (by BAG in U937 cells or by reversible glycosylation defect in ldlD CHO cells), CD93 is synthesized but rapidly released into culture supernatant or degraded rather than being retained at the plasma membrane.","method":"Glycosylation inhibitor treatment, glycosylation-deficient cell line (ldlD), metabolic labeling, cell surface expression analysis","journal":"Journal of cellular physiology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — two orthogonal cell systems (inhibitor and genetic deficiency), metabolic labeling, single lab","pmids":["12891708"],"is_preprint":false},{"year":2004,"finding":"CD93 cytoplasmic tail interacts with GIPC, a PDZ domain-containing adaptor protein. The interaction requires a class I PDZ-binding domain in the CD93 C-terminus and four positively charged juxtamembrane amino acids. A cell-permeable peptide encoding the C-terminal 11 amino acids of CD93 enhanced phagocytosis in human monocytes, linking this intracellular protein-protein interaction to modulation of phagocytic activity.","method":"Yeast two-hybrid screen, GST fusion protein pulldown assay, cell-permeable peptide functional assay in human monocytes","journal":"Journal of leukocyte biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — yeast two-hybrid confirmed by in vitro GST pulldown plus functional cell assay, single lab, two orthogonal methods","pmids":["15459234"],"is_preprint":false},{"year":2005,"finding":"The ERM protein moesin binds to the CD93 cytoplasmic tail via the first four positively charged amino acids in the juxtamembrane region. Moesin co-caps with CD93 in intact human monocytes. Deletion of the last 11 C-terminal amino acids of CD93 dramatically increases moesin binding in cell lysate assays but not with purified recombinant moesin, suggesting that other intracellular molecules compete for or regulate this interaction. PIP2 enhances moesin binding to the CD93 cytoplasmic domain.","method":"GST fusion protein binding assay with cell lysates and recombinant moesin, co-capping in human monocytes, deletion mutagenesis, PIP2 addition experiments","journal":"Immunology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal pulldown with recombinant protein and cell lysate, co-capping in intact cells, mutagenesis mapping, single lab","pmids":["15819698"],"is_preprint":false},{"year":2004,"finding":"CD93-deficient mice show a significant defect in clearance of apoptotic cells in vivo (human Jurkat T cells and murine thymocytes), but not in complement- or FcγR-dependent phagocytosis in vitro or in vivo. CD93-deficient macrophages plated on C1q-coated surfaces showed normal enhancement of complement- and FcγR-dependent RBC uptake. No supporting role was found for CD93 as an adhesion molecule in leukocyte recruitment assessed by intravital microscopy.","method":"CD93 knockout mice, in vivo apoptotic cell clearance assay, in vitro phagocytosis assays, intravital microscopy, peritoneal cell recruitment assays","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with multiple in vivo and in vitro readouts, replicated with two apoptotic cell types; negative result for C1q-mediated phagocytosis enhancement is also well-established","pmids":["15004139"],"is_preprint":false},{"year":2005,"finding":"CD93 undergoes ectodomain shedding from the surface of human monocytes and neutrophils. Shedding is induced by phorbol dibutyrate, TNF-α, LPS, and CD93 cross-linking with immobilized anti-CD93 mAbs. The shed ectodomain retains the N-terminal CRD and EGF repeats. Shedding is inhibited by metalloproteinase inhibitor 1,10-phenanthroline but is independent of ADAM17 (TACE). A soluble form of CD93 is detected in human plasma. Neutrophil surface CD93 lost by shedding is replaced from intracellular stores.","method":"Flow cytometry, ELISA detection of shed ectodomain and plasma sCD93, metalloproteinase inhibitor treatment, immunoblotting for intracellular domain-containing cleavage products, ADAM17-deficient conditions","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple shedding stimuli tested, inhibitor studies identifying metalloproteinase mechanism, demonstration of plasma soluble form, intracellular stores shown for neutrophils, single lab with multiple orthogonal methods","pmids":["16002728"],"is_preprint":false},{"year":2000,"finding":"Neonatal rat microglia express C1qR(P)/CD93, as assessed by flow cytometry and immunocytochemistry. Substrate-bound C1q enhances both FcR- and CR1-mediated phagocytosis two- to fourfold in microglia. Introduction of an antibody against the cytoplasmic C-terminal domain of CD93 into microglia by electroporation markedly diminished C1q-enhanced phagocytosis, indicating that the cytoplasmic domain of CD93 is required to transduce the phagocytic enhancement signal.","method":"Flow cytometry, immunocytochemistry, phagocytosis assay, intracellular antibody delivery by electroporation","journal":"Journal of leukocyte biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — intracellular antibody electroporation is a functional intervention with defined readout, but single lab and the intracellular antibody approach is indirect","pmids":["10648005"],"is_preprint":false},{"year":2001,"finding":"C1qR(P)/CD93 on microglia mediates C1q-enhanced phagocytosis of antibody-opsonized amyloid-β immune complexes. Mannose binding lectin and lung surfactant protein A, other ligands of C1qR(P), also enhanced microglial ingestion of suboptimally opsonized IgG-fAβ complexes, whereas control proteins did not, demonstrating ligand specificity through CD93.","method":"Microglial phagocytosis assay with C1q, MBL, SPA ligands; antibody blocking experiments","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — functional assay with multiple ligands and blocking controls, single lab, no genetic approach","pmids":["11390503"],"is_preprint":false},{"year":2001,"finding":"C1q-bearing immune complexes (but not monomeric C1q) induce IL-8 secretion in human umbilical vein endothelial cells via protein tyrosine kinase (PTK)- and MAPK-dependent pathways. The cross-linking anti-CD93 mAb R3 (against the 126 kDa phagocytic C1qR) also stimulated IL-8 production, indicating CD93 transduces this signal. IL-8 secretion was completely blocked by genistein (PTK inhibitor) or UO126 (MAPK inhibitor).","method":"HUVEC stimulation assays, mAb cross-linking, PTK/MAPK inhibitors, Northern blot for IL-8 mRNA, ELISA for IL-8 protein","journal":"Clinical and experimental immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple inhibitors defining signaling pathway, mAb cross-linking to establish receptor identity, single lab","pmids":["11531942"],"is_preprint":false},{"year":2000,"finding":"Murine C1qR(P)/CD93 is expressed in myeloid cell lines but not in a mouse epithelial cell line, parallel to human expression. A polyclonal antibody to a C-terminal peptide common to murine and human CD93 inhibited C1q-enhanced phagocytosis when cells were permeabilized to allow intracellular access, confirming that the intracellular C-terminus is required for phagocytic signal transduction.","method":"Northern blot, RT-PCR, Western blot, FACS, cell permeabilization with intracellular antibody, phagocytosis assay","journal":"Molecular immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — intracellular antibody inhibition functional assay, multiple expression methods, single lab","pmids":["11074255"],"is_preprint":false},{"year":1998,"finding":"CD93/C1qRP mRNA and cell surface protein expression is restricted to cells of myeloid origin (monocytes, macrophages, neutrophils, U937) and endothelial cells, but not lymphoid cells (T, B cell lines), HeLa epithelial cells, smooth muscle cells, or fibroblasts. CD93 protein was also detected in human platelet lysates.","method":"Northern blot, RT-PCR, FACS with anti-C1qRP mAbs R139 and R3, Western blot of platelet lysates","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — concordant mRNA and protein expression data across multiple cell types, two orthogonal detection methods, single lab","pmids":["9469455"],"is_preprint":false},{"year":1994,"finding":"Three mAbs (R139, R3, U40.3) recognize the same 100 kDa (126 kDa under reducing conditions) surface protein on phagocytic cells (U937, monocytes, neutrophils). R3 and R139 (but not U40.3) inhibit C1q-mediated enhancement of phagocytosis, and R3 partially inhibits [125I]C1q-CLF binding. The three mAbs co-immunoprecipitate CD43 with the receptor, suggesting CD93 may exist in a multi-subunit complex. None of the mAbs inhibit C1q-mediated superoxide production in neutrophils, indicating the phagocytic CD93 receptor is distinct from the superoxide-triggering C1q receptor.","method":"Immunoprecipitation, Western blot, functional phagocytosis inhibition assay, radioligand binding inhibition assay, superoxide production assay","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple mAbs with distinct epitopes, functional inhibition assays, radioligand binding, co-IP of associated protein, negative result for superoxide clearly delineating receptor specificity","pmids":["8144968"],"is_preprint":false},{"year":2001,"finding":"A specific sequence motif GE(K/Q/R)GEP in the collagen-like domain of MBL and other defense collagens is critical for triggering CD93-mediated enhancement of phagocytosis. MBL mutants lacking GXY triplets below the kink region (including the GEKGEP sequence) failed to enhance phagocytosis by human monocytes, while wild-type and other mutants retained activity.","method":"Baculovirus/Sf9 expression of wild-type and mutant rMBL constructs, phagocytosis enhancement assay with human peripheral blood monocytes","journal":"Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — site-directed mutagenesis of ligand combined with functional assay, multiple mutant constructs tested, single lab","pmids":["11533031"],"is_preprint":false},{"year":1994,"finding":"CD93 on human PMN is up-regulated from intracellular stores upon FMLP stimulation in a microtubule-dependent manner (blocked by taxol), indicating CD93 is stored in intracellular vesicles (likely complement receptor exocytic vesicles, CREV). Phorbol myristate acetate causes unimodal up-regulation. The receptor co-localizes in the CREV with CR1 and CR3.","method":"Flow cytometry with biotinylated C1q, affinity precipitation from surface-iodinated PMN, taxol treatment, FMLP stimulation","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological inhibition of microtubules blocking receptor translocation, surface labeling and affinity precipitation, single lab","pmids":["7911495"],"is_preprint":false},{"year":2001,"finding":"CD93/C1qR(P) is predominantly expressed on vascular endothelial cells in human tissues, while it is absent from most tissue macrophages. In vitro differentiation of blood monocytes to dendritic cells causes down-regulation of CD93. A subset of pyramidal neurons in brain also express CD93.","method":"Polyclonal antibodies to N- and C-terminal peptides, immunohistochemistry of human tissues, in vitro monocyte-to-dendritic cell differentiation with FACS","journal":"Journal of leukocyte biology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — two independent antibody reagents targeting distinct domains used in parallel, in vitro differentiation model, single lab","pmids":["11698500"],"is_preprint":false},{"year":2021,"finding":"CD93 CAR T cells potently kill AML cells in vitro and in vivo and spare hematopoietic stem and progenitor cells (HSPCs), but cause on-target off-tumor toxicity to endothelial cells, which also express CD93. NOT-gated CD93 CAR T cells that express an inhibitory receptor for an endothelial-specific antigen circumvent endothelial cell toxicity in a model system.","method":"In vitro cytotoxicity assays, in vivo murine AML models, endothelial cell killing assays, NOT-gate CAR T cell engineering","journal":"Blood cancer discovery","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro and in vivo functional experiments with engineered constructs, single lab, mechanistic proof-of-concept for endothelial cross-reactivity","pmids":["34778803"],"is_preprint":false},{"year":2025,"finding":"CD93 blockade on tumor vasculature increases expression of adhesion molecules ICAM1 and VCAM1, promotes vascular maturation, and improves effector T-cell infiltration into solid tumors. Neutralizing antibodies against ICAM1 and VCAM1 partially reversed the T-cell infiltration benefit. Anti-CD93 selectively promotes T-cell infiltration in tumors where the CD93 pathway is upregulated, and synergizes with adoptive T-cell transfer to inhibit tumor progression.","method":"Monoclonal antibody treatment in implanted mouse melanoma models, immunofluorescent staining for vascular maturation markers, flow cytometry for tumor-infiltrating lymphocytes, ICAM1/VCAM1 neutralizing antibody experiments","journal":"Journal for immunotherapy of cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo antibody blockade with mechanistic follow-up (adhesion molecule neutralization), multiple T-cell sources, single lab","pmids":["39805660"],"is_preprint":false},{"year":2024,"finding":"CD93 in pleural mesothelial cells suppresses CCL21 secretion, thereby reducing dendritic cell migration to lymph nodes and suppressing systemic anti-tumor T-cell responses. Tumor-derived extracellular vesicle miR-5110 downregulates pMC CD93, promoting CCL21 secretion. C1q (elevated in tumor environments) suppresses CD93-mediated CCL21 secretion. Anti-CD93 antibodies inhibit both tumor angiogenesis and promote CCL21 secretion from pMCs.","method":"siRNA knockdown, recombinant protein and antibody generation, RNA-Seq, miRNA array, luciferase reporter assay, chemotaxis assay, flow cytometry, EV uptake experiments, ELISA","journal":"Theranostics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with defined pathway readout (CCL21 secretion), multiple orthogonal methods, single lab","pmids":["38250037"],"is_preprint":false},{"year":2002,"finding":"CD93/C1qR(P) marks a rare human stem cell population with both hematopoietic and hepatic differentiation potential. C1qR(P)+ cells from umbilical cord blood and adult bone marrow include both CD34+ and CD34- bone-marrow-repopulating stem cells, and highly purified lineage-negative CD45+CD38-C1qR(P)+ cells can differentiate into human hepatocytes in NOD/SCID mice.","method":"FACS purification, xenograft transplantation into NOD/SCID mice, in vivo hepatic differentiation assay","journal":"PNAS","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — prospective purification and in vivo functional assay establishing CD93 as a positive marker of repopulating stem cells, single lab","pmids":["12140365"],"is_preprint":false},{"year":1993,"finding":"Platelet activation by aggregated C1q multimers (>5 µg/ml) is mediated by the collagenous domain of C1q through the platelet C1qR (67 kDa). Activation results in IP3 release, induction of GPIIb-IIIa (αIIbβ3) fibrinogen receptors, P-selectin expression, granule release, and procoagulant activity. The collagenous domain of C1q (c-C1q) and a monoclonal anti-C1qR antibody inhibit platelet aggregation.","method":"Platelet adhesion and aggregation assays, IP3 measurement, fibrinogen binding (Scatchard analysis), P-selectin FACS, kaolin recalcification time, inhibition with c-C1q and anti-C1qR mAb","journal":"Journal of experimental medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple functional readouts with receptor-specific inhibition, single lab","pmids":["7688027"],"is_preprint":false}],"current_model":"CD93 (C1qR(P)/C1qRP) is a heavily O-glycosylated type I transmembrane protein expressed on myeloid cells, endothelial cells, platelets, and stem cells whose O-glycosylation stabilizes its cell-surface retention; it functions as a phagocytic receptor that, upon ligation by defense collagens (C1q, MBL, SPA) via a GE(K/Q/R)GEP collagen-domain motif, enhances FcR- and CR1-mediated phagocytosis through its cytoplasmic tail, which couples to the cytoskeleton via moesin and to PDZ-domain signaling via GIPC, and transduces IL-8 production in endothelial cells via PTK/MAPK pathways; CD93-deficient mice confirm an in vivo role in apoptotic cell clearance but not in C1q-mediated phagocytosis enhancement; on tumor vasculature, CD93 suppresses ICAM1/VCAM1 expression and T-cell infiltration, while in pleural mesothelial cells it suppresses CCL21 secretion; the ectodomain is shed by a metalloproteinase (not ADAM17) upon inflammatory stimulation, releasing soluble CD93 detectable in plasma."},"narrative":{"mechanistic_narrative":"CD93 (C1qR(P)/C1qRP) is a myeloid- and endothelial-restricted type I transmembrane protein, built from an N-terminal C-type carbohydrate-recognition domain and five EGF-like repeats, that functions as a phagocytic receptor coupling the recognition of defense collagens to enhanced clearance of particles and apoptotic cells [PMID:9047234, PMID:9469455]. It is the receptor through which the structurally related ligands C1q, mannose-binding lectin, and surfactant protein A enhance FcR- and CR1-mediated phagocytosis, recognition occurring through a GE(K/Q/R)GEP motif in the collagen-like domain of these ligands [PMID:9047234, PMID:11533031, PMID:11390503]. Signal transduction depends strictly on the short cytoplasmic tail: blocking or cross-linking this domain modulates phagocytic enhancement [PMID:10648005, PMID:11074255], and direct mAb ligation alone drives a pro-phagocytic signal [PMID:10092817]. The tail engages the ERM protein moesin through juxtamembrane positively charged residues, tying the receptor to the cytoskeleton, and the C-terminal class I PDZ-binding motif recruits the adaptor GIPC, a peptide of which enhances monocyte phagocytosis [PMID:15459234, PMID:15819698]. CD93 is heavily O-glycosylated, and this glycosylation is required for its molecular weight and for stable retention at the cell surface, without which the protein is shed or degraded [PMID:10092817, PMID:12891708]. In endothelial cells, C1q-bearing immune complexes or anti-CD93 cross-linking drive IL-8 secretion via PTK- and MAPK-dependent signaling [PMID:11531942]. CD93-deficient mice establish an in vivo requirement for CD93 in apoptotic cell clearance, but not in complement- or FcγR-dependent phagocytosis enhancement [PMID:15004139]. The ectodomain is released by a metalloproteinase distinct from ADAM17 upon inflammatory stimulation, generating soluble CD93 in plasma [PMID:16002728]. Beyond its phagocytic role, CD93 regulates tumor vasculature, where its blockade upregulates ICAM1/VCAM1, matures vessels, and enhances T-cell infiltration [PMID:39805660], and in pleural mesothelial cells it suppresses CCL21 secretion to dampen anti-tumor immunity [PMID:38250037].","teleology":[{"year":1994,"claim":"Before its molecular identity was known, the question was whether a single defined surface receptor accounted for C1q-enhanced phagocytosis; defining a 126 kDa protein recognized by inhibitory mAbs separated this receptor from the C1q superoxide-triggering receptor.","evidence":"Immunoprecipitation, functional phagocytosis and radioligand binding inhibition with three mAbs on phagocytic cells","pmids":["8144968"],"confidence":"High","gaps":["Receptor cDNA and domain structure not yet defined","CD43 co-IP raised but multi-subunit composition unresolved"]},{"year":1997,"claim":"The molecular nature of the phagocytic C1q receptor was unknown; cloning revealed a type I transmembrane protein with a C-type CRD and EGF repeats that mediates enhancement triggered by three related defense collagens.","evidence":"mAb affinity purification, amino acid sequencing, cDNA cloning, and functional inhibition across C1q/MBL/SPA","pmids":["9047234"],"confidence":"High","gaps":["Cytoplasmic signaling partners unidentified","Endogenous ligand-binding surface on the receptor not mapped"]},{"year":1999,"claim":"It was unclear how the receptor reconciled its predicted versus observed mass and whether ligand binding was required for signaling; O-glycosylation was shown to account for the mass and mAb ligation alone shown to drive phagocytosis.","evidence":"CHO transfection, glycosidase and inhibitor treatment, in vitro translation, mAb cross-linking phagocytosis assay","pmids":["10092817"],"confidence":"High","gaps":["Downstream signaling cascade not defined","Site of functionally critical O-glycans not mapped"]},{"year":2001,"claim":"The ligand determinant driving CD93-mediated phagocytosis was unknown; a GE(K/Q/R)GEP motif in the collagen-like domain of defense collagens was identified as required for the enhancement signal.","evidence":"Site-directed mutagenesis of recombinant MBL and monocyte phagocytosis assays","pmids":["11533031"],"confidence":"High","gaps":["Direct binding of this motif to the CD93 ectodomain not demonstrated","Whether C1q and SPA use the identical motif geometry not resolved"]},{"year":2003,"claim":"The functional consequence of CD93 O-glycosylation was undefined; glycosylation was shown to stabilize surface retention, with unglycosylated protein released or degraded.","evidence":"Glycosylation inhibitor and ldlD glycosylation-deficient cells with metabolic labeling and surface expression analysis","pmids":["12891708"],"confidence":"High","gaps":["Mechanism of glycosylation-dependent retention vs. shedding not resolved","Link to the inflammatory metalloproteinase shedding pathway not established"]},{"year":2005,"claim":"How the cytoplasmic tail couples to intracellular machinery was unknown; the tail was shown to bind moesin (cytoskeletal coupling) and GIPC (PDZ adaptor), with a tail peptide enhancing phagocytosis.","evidence":"Yeast two-hybrid, GST pulldown with lysate and recombinant moesin, co-capping, deletion mutagenesis, cell-permeable peptide assays","pmids":["15459234","15819698"],"confidence":"High","gaps":["Order and interdependence of moesin vs. GIPC binding not resolved","Downstream effectors of GIPC recruitment unidentified"]},{"year":2005,"claim":"Whether CD93 levels are dynamically regulated at the surface was open; inflammatory stimuli were shown to trigger metalloproteinase-dependent (ADAM17-independent) ectodomain shedding generating plasma soluble CD93.","evidence":"Flow cytometry, ELISA of shed ectodomain and plasma sCD93, metalloproteinase inhibitor and ADAM17-deficient conditions","pmids":["16002728"],"confidence":"High","gaps":["Identity of the responsible metalloproteinase unknown","Function of soluble CD93 not defined"]},{"year":2004,"claim":"The in vivo physiological role was untested; CD93-knockout mice revealed a requirement in apoptotic cell clearance but not in complement/FcγR phagocytosis enhancement, decoupling the in vitro and in vivo functions.","evidence":"CD93 knockout mice, in vivo apoptotic cell clearance, in vitro phagocytosis, intravital microscopy","pmids":["15004139"],"confidence":"High","gaps":["Bridging ligand/molecular mechanism for apoptotic cell clearance unidentified","Reconciliation with mAb-based phagocytosis data not achieved"]},{"year":2001,"claim":"Whether CD93 signals in non-phagocytic lineages was unclear; in endothelial cells C1q immune complexes and anti-CD93 cross-linking were shown to induce IL-8 via PTK/MAPK pathways.","evidence":"HUVEC stimulation, mAb cross-linking, genistein and UO126 inhibitors, IL-8 mRNA and protein assays","pmids":["11531942"],"confidence":"Medium","gaps":["Proximal kinases linking CD93 to MAPK not identified","Whether endothelial signaling uses the same tail partners as myeloid cells unknown"]},{"year":2002,"claim":"Beyond differentiated myeloid/endothelial cells, CD93 was found to mark a rare repopulating stem cell population with hematopoietic and hepatic differentiation potential.","evidence":"FACS purification and NOD/SCID xenograft transplantation","pmids":["12140365"],"confidence":"Medium","gaps":["Functional role of CD93 in stemness not tested","Mechanism of hepatic differentiation potential undefined"]},{"year":2025,"claim":"The role of CD93 on tumor vasculature was undefined; blockade was shown to upregulate ICAM1/VCAM1, mature vessels, and enhance effector T-cell infiltration, identifying CD93 as a regulator of vascular immune exclusion.","evidence":"Anti-CD93 antibody treatment in mouse melanoma, vascular and TIL profiling, ICAM1/VCAM1 neutralization, adoptive T-cell transfer","pmids":["39805660","38250037"],"confidence":"Medium","gaps":["Ligand/signaling axis driving adhesion molecule suppression unresolved","Pleural mesothelial CCL21 suppression mechanism downstream of CD93 not fully defined"]},{"year":null,"claim":"The molecular basis by which CD93 recognizes apoptotic cells in vivo and the proximal signaling that converts ligand engagement into phagocytic, IL-8, and vascular outputs remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No defined apoptotic-cell bridging ligand or direct binding partner on the ectodomain","Proximal kinase/effector linking the cytoplasmic tail to MAPK and cytoskeletal remodeling unidentified","Identity of the shedding metalloproteinase and function of soluble CD93 unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0038024","term_label":"cargo receptor activity","supporting_discovery_ids":[0,13,8]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[1,9]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[4]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[3]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,1,11]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[14,6]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[6]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,5,12]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,7,14]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[9,17]}],"complexes":[],"partners":["C1QA","MBL2","SFTPA1","GIPC1","MSN","CD43"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9NPY3","full_name":"Complement component C1q receptor","aliases":["C1q/MBL/SPA receptor","C1qR","C1qR(p)","C1qRp","CDw93","Complement component 1 q subcomponent receptor 1","Matrix-remodeling-associated protein 4"],"length_aa":652,"mass_kda":68.6,"function":"Cell surface receptor that plays a role in various physiological processes including inflammation, phagocytosis, and cell adhesion. Plays a role in phagocytosis and enhances the uptake of apoptotic cells and immune complexes by acting as a receptor for defense collagens including surfactant protein A/SFTPA1, C1q, and mannose-binding lectin (MBL2) (PubMed:7977768). Plays a role in the regulation of endothelial cell function and adhesion by activating angiogenesis (PubMed:24809468). Mechanistically, exerts its angiogenic function by associating with beta-dystroglycan, leading to SRC-dependent phosphorylation and subsequent recruitment of CBL. In turn, CBL provides a docking site for downstream signaling components, such as CRKL to enhance cell migration (PubMed:26848865). Participates in angiogenesis also by acting as a receptor for the ECM pan-endothelial glycoprotein multimerin-2/MMRN2 and IGFBP7 ligands (PubMed:28671670, PubMed:36265539, PubMed:38218180). Both ligands play a non-redundant role in CD93-mediated endothelial cell function (PubMed:38218180). 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diseases","date":"2025-10-17","source":"bioRxiv","url":"https://doi.org/10.1101/2025.10.14.25337919","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.06.12.659271","title":"Succinate enhances mitochondrial metabolism and phagocytosis in human airspace monocytes","date":"2025-06-17","source":"bioRxiv","url":"https://doi.org/10.1101/2025.06.12.659271","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":38506,"output_tokens":6104,"usd":0.103539,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":14747,"output_tokens":4123,"usd":0.088405,"stage2_stop_reason":"end_turn"},"total_usd":0.191944,"stage1_batch_id":"msgbatch_01ACAxJQabDsht39JXeWG22d","stage2_batch_id":"msgbatch_01QEU22A9U5sbPTgsMzTmvSf","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1997,\n      \"finding\": \"CD93 (C1qR(P)) was identified as a novel type I transmembrane protein with a C-type carbohydrate recognition domain, five EGF-like domains, a transmembrane domain, and a short cytoplasmic tail. Monoclonal antibodies R3 and R139, which inhibit C1q/MBL/SPA-mediated enhancement of phagocytosis, were used to purify the protein and clone its cDNA, establishing it as the receptor mediating enhanced phagocytosis triggered by these three structurally related ligands.\",\n      \"method\": \"Protein purification via mAb affinity, amino acid sequencing, cDNA cloning, anti-peptide antiserum generation, functional inhibition assays\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cDNA cloning with full sequence verification, functional inhibition by multiple mAbs, replicated across C1q/MBL/SPA ligands in a single rigorous study\",\n      \"pmids\": [\"9047234\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"CD93 (C1qRP) is heavily O-glycosylated, and this O-linked glycosylation is required for proper molecular weight and cell surface expression. Direct cross-linking of CD93 by immobilized anti-CD93 mAb R3 triggers enhanced phagocytic capacity in the absence of ligand, demonstrating that CD93 ligation directly transduces a pro-phagocytic signal. The protein backbone alone (without glycosylation) migrates at the predicted molecular weight; extensive O-glycosylation accounts for the discrepancy between predicted and observed molecular weight.\",\n      \"method\": \"CHO cell transfection, glycosylation inhibitors, glycosidase cleavage, in vitro translation, functional phagocytosis assay with mAb cross-linking\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal biochemical methods (inhibitors, enzymes, translation) plus functional assay in a single study\",\n      \"pmids\": [\"10092817\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"O-glycosylation stabilizes CD93 at the cell surface. When O-glycosylation is inhibited (by BAG in U937 cells or by reversible glycosylation defect in ldlD CHO cells), CD93 is synthesized but rapidly released into culture supernatant or degraded rather than being retained at the plasma membrane.\",\n      \"method\": \"Glycosylation inhibitor treatment, glycosylation-deficient cell line (ldlD), metabolic labeling, cell surface expression analysis\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — two orthogonal cell systems (inhibitor and genetic deficiency), metabolic labeling, single lab\",\n      \"pmids\": [\"12891708\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"CD93 cytoplasmic tail interacts with GIPC, a PDZ domain-containing adaptor protein. The interaction requires a class I PDZ-binding domain in the CD93 C-terminus and four positively charged juxtamembrane amino acids. A cell-permeable peptide encoding the C-terminal 11 amino acids of CD93 enhanced phagocytosis in human monocytes, linking this intracellular protein-protein interaction to modulation of phagocytic activity.\",\n      \"method\": \"Yeast two-hybrid screen, GST fusion protein pulldown assay, cell-permeable peptide functional assay in human monocytes\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast two-hybrid confirmed by in vitro GST pulldown plus functional cell assay, single lab, two orthogonal methods\",\n      \"pmids\": [\"15459234\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The ERM protein moesin binds to the CD93 cytoplasmic tail via the first four positively charged amino acids in the juxtamembrane region. Moesin co-caps with CD93 in intact human monocytes. Deletion of the last 11 C-terminal amino acids of CD93 dramatically increases moesin binding in cell lysate assays but not with purified recombinant moesin, suggesting that other intracellular molecules compete for or regulate this interaction. PIP2 enhances moesin binding to the CD93 cytoplasmic domain.\",\n      \"method\": \"GST fusion protein binding assay with cell lysates and recombinant moesin, co-capping in human monocytes, deletion mutagenesis, PIP2 addition experiments\",\n      \"journal\": \"Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal pulldown with recombinant protein and cell lysate, co-capping in intact cells, mutagenesis mapping, single lab\",\n      \"pmids\": [\"15819698\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"CD93-deficient mice show a significant defect in clearance of apoptotic cells in vivo (human Jurkat T cells and murine thymocytes), but not in complement- or FcγR-dependent phagocytosis in vitro or in vivo. CD93-deficient macrophages plated on C1q-coated surfaces showed normal enhancement of complement- and FcγR-dependent RBC uptake. No supporting role was found for CD93 as an adhesion molecule in leukocyte recruitment assessed by intravital microscopy.\",\n      \"method\": \"CD93 knockout mice, in vivo apoptotic cell clearance assay, in vitro phagocytosis assays, intravital microscopy, peritoneal cell recruitment assays\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with multiple in vivo and in vitro readouts, replicated with two apoptotic cell types; negative result for C1q-mediated phagocytosis enhancement is also well-established\",\n      \"pmids\": [\"15004139\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"CD93 undergoes ectodomain shedding from the surface of human monocytes and neutrophils. Shedding is induced by phorbol dibutyrate, TNF-α, LPS, and CD93 cross-linking with immobilized anti-CD93 mAbs. The shed ectodomain retains the N-terminal CRD and EGF repeats. Shedding is inhibited by metalloproteinase inhibitor 1,10-phenanthroline but is independent of ADAM17 (TACE). A soluble form of CD93 is detected in human plasma. Neutrophil surface CD93 lost by shedding is replaced from intracellular stores.\",\n      \"method\": \"Flow cytometry, ELISA detection of shed ectodomain and plasma sCD93, metalloproteinase inhibitor treatment, immunoblotting for intracellular domain-containing cleavage products, ADAM17-deficient conditions\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple shedding stimuli tested, inhibitor studies identifying metalloproteinase mechanism, demonstration of plasma soluble form, intracellular stores shown for neutrophils, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"16002728\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Neonatal rat microglia express C1qR(P)/CD93, as assessed by flow cytometry and immunocytochemistry. Substrate-bound C1q enhances both FcR- and CR1-mediated phagocytosis two- to fourfold in microglia. Introduction of an antibody against the cytoplasmic C-terminal domain of CD93 into microglia by electroporation markedly diminished C1q-enhanced phagocytosis, indicating that the cytoplasmic domain of CD93 is required to transduce the phagocytic enhancement signal.\",\n      \"method\": \"Flow cytometry, immunocytochemistry, phagocytosis assay, intracellular antibody delivery by electroporation\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — intracellular antibody electroporation is a functional intervention with defined readout, but single lab and the intracellular antibody approach is indirect\",\n      \"pmids\": [\"10648005\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"C1qR(P)/CD93 on microglia mediates C1q-enhanced phagocytosis of antibody-opsonized amyloid-β immune complexes. Mannose binding lectin and lung surfactant protein A, other ligands of C1qR(P), also enhanced microglial ingestion of suboptimally opsonized IgG-fAβ complexes, whereas control proteins did not, demonstrating ligand specificity through CD93.\",\n      \"method\": \"Microglial phagocytosis assay with C1q, MBL, SPA ligands; antibody blocking experiments\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — functional assay with multiple ligands and blocking controls, single lab, no genetic approach\",\n      \"pmids\": [\"11390503\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"C1q-bearing immune complexes (but not monomeric C1q) induce IL-8 secretion in human umbilical vein endothelial cells via protein tyrosine kinase (PTK)- and MAPK-dependent pathways. The cross-linking anti-CD93 mAb R3 (against the 126 kDa phagocytic C1qR) also stimulated IL-8 production, indicating CD93 transduces this signal. IL-8 secretion was completely blocked by genistein (PTK inhibitor) or UO126 (MAPK inhibitor).\",\n      \"method\": \"HUVEC stimulation assays, mAb cross-linking, PTK/MAPK inhibitors, Northern blot for IL-8 mRNA, ELISA for IL-8 protein\",\n      \"journal\": \"Clinical and experimental immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple inhibitors defining signaling pathway, mAb cross-linking to establish receptor identity, single lab\",\n      \"pmids\": [\"11531942\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Murine C1qR(P)/CD93 is expressed in myeloid cell lines but not in a mouse epithelial cell line, parallel to human expression. A polyclonal antibody to a C-terminal peptide common to murine and human CD93 inhibited C1q-enhanced phagocytosis when cells were permeabilized to allow intracellular access, confirming that the intracellular C-terminus is required for phagocytic signal transduction.\",\n      \"method\": \"Northern blot, RT-PCR, Western blot, FACS, cell permeabilization with intracellular antibody, phagocytosis assay\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — intracellular antibody inhibition functional assay, multiple expression methods, single lab\",\n      \"pmids\": [\"11074255\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"CD93/C1qRP mRNA and cell surface protein expression is restricted to cells of myeloid origin (monocytes, macrophages, neutrophils, U937) and endothelial cells, but not lymphoid cells (T, B cell lines), HeLa epithelial cells, smooth muscle cells, or fibroblasts. CD93 protein was also detected in human platelet lysates.\",\n      \"method\": \"Northern blot, RT-PCR, FACS with anti-C1qRP mAbs R139 and R3, Western blot of platelet lysates\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — concordant mRNA and protein expression data across multiple cell types, two orthogonal detection methods, single lab\",\n      \"pmids\": [\"9469455\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Three mAbs (R139, R3, U40.3) recognize the same 100 kDa (126 kDa under reducing conditions) surface protein on phagocytic cells (U937, monocytes, neutrophils). R3 and R139 (but not U40.3) inhibit C1q-mediated enhancement of phagocytosis, and R3 partially inhibits [125I]C1q-CLF binding. The three mAbs co-immunoprecipitate CD43 with the receptor, suggesting CD93 may exist in a multi-subunit complex. None of the mAbs inhibit C1q-mediated superoxide production in neutrophils, indicating the phagocytic CD93 receptor is distinct from the superoxide-triggering C1q receptor.\",\n      \"method\": \"Immunoprecipitation, Western blot, functional phagocytosis inhibition assay, radioligand binding inhibition assay, superoxide production assay\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple mAbs with distinct epitopes, functional inhibition assays, radioligand binding, co-IP of associated protein, negative result for superoxide clearly delineating receptor specificity\",\n      \"pmids\": [\"8144968\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"A specific sequence motif GE(K/Q/R)GEP in the collagen-like domain of MBL and other defense collagens is critical for triggering CD93-mediated enhancement of phagocytosis. MBL mutants lacking GXY triplets below the kink region (including the GEKGEP sequence) failed to enhance phagocytosis by human monocytes, while wild-type and other mutants retained activity.\",\n      \"method\": \"Baculovirus/Sf9 expression of wild-type and mutant rMBL constructs, phagocytosis enhancement assay with human peripheral blood monocytes\",\n      \"journal\": \"Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — site-directed mutagenesis of ligand combined with functional assay, multiple mutant constructs tested, single lab\",\n      \"pmids\": [\"11533031\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"CD93 on human PMN is up-regulated from intracellular stores upon FMLP stimulation in a microtubule-dependent manner (blocked by taxol), indicating CD93 is stored in intracellular vesicles (likely complement receptor exocytic vesicles, CREV). Phorbol myristate acetate causes unimodal up-regulation. The receptor co-localizes in the CREV with CR1 and CR3.\",\n      \"method\": \"Flow cytometry with biotinylated C1q, affinity precipitation from surface-iodinated PMN, taxol treatment, FMLP stimulation\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological inhibition of microtubules blocking receptor translocation, surface labeling and affinity precipitation, single lab\",\n      \"pmids\": [\"7911495\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"CD93/C1qR(P) is predominantly expressed on vascular endothelial cells in human tissues, while it is absent from most tissue macrophages. In vitro differentiation of blood monocytes to dendritic cells causes down-regulation of CD93. A subset of pyramidal neurons in brain also express CD93.\",\n      \"method\": \"Polyclonal antibodies to N- and C-terminal peptides, immunohistochemistry of human tissues, in vitro monocyte-to-dendritic cell differentiation with FACS\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — two independent antibody reagents targeting distinct domains used in parallel, in vitro differentiation model, single lab\",\n      \"pmids\": [\"11698500\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CD93 CAR T cells potently kill AML cells in vitro and in vivo and spare hematopoietic stem and progenitor cells (HSPCs), but cause on-target off-tumor toxicity to endothelial cells, which also express CD93. NOT-gated CD93 CAR T cells that express an inhibitory receptor for an endothelial-specific antigen circumvent endothelial cell toxicity in a model system.\",\n      \"method\": \"In vitro cytotoxicity assays, in vivo murine AML models, endothelial cell killing assays, NOT-gate CAR T cell engineering\",\n      \"journal\": \"Blood cancer discovery\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro and in vivo functional experiments with engineered constructs, single lab, mechanistic proof-of-concept for endothelial cross-reactivity\",\n      \"pmids\": [\"34778803\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CD93 blockade on tumor vasculature increases expression of adhesion molecules ICAM1 and VCAM1, promotes vascular maturation, and improves effector T-cell infiltration into solid tumors. Neutralizing antibodies against ICAM1 and VCAM1 partially reversed the T-cell infiltration benefit. Anti-CD93 selectively promotes T-cell infiltration in tumors where the CD93 pathway is upregulated, and synergizes with adoptive T-cell transfer to inhibit tumor progression.\",\n      \"method\": \"Monoclonal antibody treatment in implanted mouse melanoma models, immunofluorescent staining for vascular maturation markers, flow cytometry for tumor-infiltrating lymphocytes, ICAM1/VCAM1 neutralizing antibody experiments\",\n      \"journal\": \"Journal for immunotherapy of cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo antibody blockade with mechanistic follow-up (adhesion molecule neutralization), multiple T-cell sources, single lab\",\n      \"pmids\": [\"39805660\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CD93 in pleural mesothelial cells suppresses CCL21 secretion, thereby reducing dendritic cell migration to lymph nodes and suppressing systemic anti-tumor T-cell responses. Tumor-derived extracellular vesicle miR-5110 downregulates pMC CD93, promoting CCL21 secretion. C1q (elevated in tumor environments) suppresses CD93-mediated CCL21 secretion. Anti-CD93 antibodies inhibit both tumor angiogenesis and promote CCL21 secretion from pMCs.\",\n      \"method\": \"siRNA knockdown, recombinant protein and antibody generation, RNA-Seq, miRNA array, luciferase reporter assay, chemotaxis assay, flow cytometry, EV uptake experiments, ELISA\",\n      \"journal\": \"Theranostics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with defined pathway readout (CCL21 secretion), multiple orthogonal methods, single lab\",\n      \"pmids\": [\"38250037\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"CD93/C1qR(P) marks a rare human stem cell population with both hematopoietic and hepatic differentiation potential. C1qR(P)+ cells from umbilical cord blood and adult bone marrow include both CD34+ and CD34- bone-marrow-repopulating stem cells, and highly purified lineage-negative CD45+CD38-C1qR(P)+ cells can differentiate into human hepatocytes in NOD/SCID mice.\",\n      \"method\": \"FACS purification, xenograft transplantation into NOD/SCID mice, in vivo hepatic differentiation assay\",\n      \"journal\": \"PNAS\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — prospective purification and in vivo functional assay establishing CD93 as a positive marker of repopulating stem cells, single lab\",\n      \"pmids\": [\"12140365\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Platelet activation by aggregated C1q multimers (>5 µg/ml) is mediated by the collagenous domain of C1q through the platelet C1qR (67 kDa). Activation results in IP3 release, induction of GPIIb-IIIa (αIIbβ3) fibrinogen receptors, P-selectin expression, granule release, and procoagulant activity. The collagenous domain of C1q (c-C1q) and a monoclonal anti-C1qR antibody inhibit platelet aggregation.\",\n      \"method\": \"Platelet adhesion and aggregation assays, IP3 measurement, fibrinogen binding (Scatchard analysis), P-selectin FACS, kaolin recalcification time, inhibition with c-C1q and anti-C1qR mAb\",\n      \"journal\": \"Journal of experimental medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple functional readouts with receptor-specific inhibition, single lab\",\n      \"pmids\": [\"7688027\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CD93 (C1qR(P)/C1qRP) is a heavily O-glycosylated type I transmembrane protein expressed on myeloid cells, endothelial cells, platelets, and stem cells whose O-glycosylation stabilizes its cell-surface retention; it functions as a phagocytic receptor that, upon ligation by defense collagens (C1q, MBL, SPA) via a GE(K/Q/R)GEP collagen-domain motif, enhances FcR- and CR1-mediated phagocytosis through its cytoplasmic tail, which couples to the cytoskeleton via moesin and to PDZ-domain signaling via GIPC, and transduces IL-8 production in endothelial cells via PTK/MAPK pathways; CD93-deficient mice confirm an in vivo role in apoptotic cell clearance but not in C1q-mediated phagocytosis enhancement; on tumor vasculature, CD93 suppresses ICAM1/VCAM1 expression and T-cell infiltration, while in pleural mesothelial cells it suppresses CCL21 secretion; the ectodomain is shed by a metalloproteinase (not ADAM17) upon inflammatory stimulation, releasing soluble CD93 detectable in plasma.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CD93 (C1qR(P)/C1qRP) is a myeloid- and endothelial-restricted type I transmembrane protein, built from an N-terminal C-type carbohydrate-recognition domain and five EGF-like repeats, that functions as a phagocytic receptor coupling the recognition of defense collagens to enhanced clearance of particles and apoptotic cells [#0, #11]. It is the receptor through which the structurally related ligands C1q, mannose-binding lectin, and surfactant protein A enhance FcR- and CR1-mediated phagocytosis, recognition occurring through a GE(K/Q/R)GEP motif in the collagen-like domain of these ligands [#0, #13, #8]. Signal transduction depends strictly on the short cytoplasmic tail: blocking or cross-linking this domain modulates phagocytic enhancement [#7, #10], and direct mAb ligation alone drives a pro-phagocytic signal [#1]. The tail engages the ERM protein moesin through juxtamembrane positively charged residues, tying the receptor to the cytoskeleton, and the C-terminal class I PDZ-binding motif recruits the adaptor GIPC, a peptide of which enhances monocyte phagocytosis [#3, #4]. CD93 is heavily O-glycosylated, and this glycosylation is required for its molecular weight and for stable retention at the cell surface, without which the protein is shed or degraded [#1, #2]. In endothelial cells, C1q-bearing immune complexes or anti-CD93 cross-linking drive IL-8 secretion via PTK- and MAPK-dependent signaling [#9]. CD93-deficient mice establish an in vivo requirement for CD93 in apoptotic cell clearance, but not in complement- or FcγR-dependent phagocytosis enhancement [#5]. The ectodomain is released by a metalloproteinase distinct from ADAM17 upon inflammatory stimulation, generating soluble CD93 in plasma [#6]. Beyond its phagocytic role, CD93 regulates tumor vasculature, where its blockade upregulates ICAM1/VCAM1, matures vessels, and enhances T-cell infiltration [#17], and in pleural mesothelial cells it suppresses CCL21 secretion to dampen anti-tumor immunity [#18].\",\n  \"teleology\": [\n    {\n      \"year\": 1994,\n      \"claim\": \"Before its molecular identity was known, the question was whether a single defined surface receptor accounted for C1q-enhanced phagocytosis; defining a 126 kDa protein recognized by inhibitory mAbs separated this receptor from the C1q superoxide-triggering receptor.\",\n      \"evidence\": \"Immunoprecipitation, functional phagocytosis and radioligand binding inhibition with three mAbs on phagocytic cells\",\n      \"pmids\": [\"8144968\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Receptor cDNA and domain structure not yet defined\", \"CD43 co-IP raised but multi-subunit composition unresolved\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"The molecular nature of the phagocytic C1q receptor was unknown; cloning revealed a type I transmembrane protein with a C-type CRD and EGF repeats that mediates enhancement triggered by three related defense collagens.\",\n      \"evidence\": \"mAb affinity purification, amino acid sequencing, cDNA cloning, and functional inhibition across C1q/MBL/SPA\",\n      \"pmids\": [\"9047234\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cytoplasmic signaling partners unidentified\", \"Endogenous ligand-binding surface on the receptor not mapped\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"It was unclear how the receptor reconciled its predicted versus observed mass and whether ligand binding was required for signaling; O-glycosylation was shown to account for the mass and mAb ligation alone shown to drive phagocytosis.\",\n      \"evidence\": \"CHO transfection, glycosidase and inhibitor treatment, in vitro translation, mAb cross-linking phagocytosis assay\",\n      \"pmids\": [\"10092817\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream signaling cascade not defined\", \"Site of functionally critical O-glycans not mapped\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"The ligand determinant driving CD93-mediated phagocytosis was unknown; a GE(K/Q/R)GEP motif in the collagen-like domain of defense collagens was identified as required for the enhancement signal.\",\n      \"evidence\": \"Site-directed mutagenesis of recombinant MBL and monocyte phagocytosis assays\",\n      \"pmids\": [\"11533031\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct binding of this motif to the CD93 ectodomain not demonstrated\", \"Whether C1q and SPA use the identical motif geometry not resolved\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"The functional consequence of CD93 O-glycosylation was undefined; glycosylation was shown to stabilize surface retention, with unglycosylated protein released or degraded.\",\n      \"evidence\": \"Glycosylation inhibitor and ldlD glycosylation-deficient cells with metabolic labeling and surface expression analysis\",\n      \"pmids\": [\"12891708\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of glycosylation-dependent retention vs. shedding not resolved\", \"Link to the inflammatory metalloproteinase shedding pathway not established\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"How the cytoplasmic tail couples to intracellular machinery was unknown; the tail was shown to bind moesin (cytoskeletal coupling) and GIPC (PDZ adaptor), with a tail peptide enhancing phagocytosis.\",\n      \"evidence\": \"Yeast two-hybrid, GST pulldown with lysate and recombinant moesin, co-capping, deletion mutagenesis, cell-permeable peptide assays\",\n      \"pmids\": [\"15459234\", \"15819698\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Order and interdependence of moesin vs. GIPC binding not resolved\", \"Downstream effectors of GIPC recruitment unidentified\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Whether CD93 levels are dynamically regulated at the surface was open; inflammatory stimuli were shown to trigger metalloproteinase-dependent (ADAM17-independent) ectodomain shedding generating plasma soluble CD93.\",\n      \"evidence\": \"Flow cytometry, ELISA of shed ectodomain and plasma sCD93, metalloproteinase inhibitor and ADAM17-deficient conditions\",\n      \"pmids\": [\"16002728\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the responsible metalloproteinase unknown\", \"Function of soluble CD93 not defined\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"The in vivo physiological role was untested; CD93-knockout mice revealed a requirement in apoptotic cell clearance but not in complement/FcγR phagocytosis enhancement, decoupling the in vitro and in vivo functions.\",\n      \"evidence\": \"CD93 knockout mice, in vivo apoptotic cell clearance, in vitro phagocytosis, intravital microscopy\",\n      \"pmids\": [\"15004139\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Bridging ligand/molecular mechanism for apoptotic cell clearance unidentified\", \"Reconciliation with mAb-based phagocytosis data not achieved\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Whether CD93 signals in non-phagocytic lineages was unclear; in endothelial cells C1q immune complexes and anti-CD93 cross-linking were shown to induce IL-8 via PTK/MAPK pathways.\",\n      \"evidence\": \"HUVEC stimulation, mAb cross-linking, genistein and UO126 inhibitors, IL-8 mRNA and protein assays\",\n      \"pmids\": [\"11531942\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Proximal kinases linking CD93 to MAPK not identified\", \"Whether endothelial signaling uses the same tail partners as myeloid cells unknown\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Beyond differentiated myeloid/endothelial cells, CD93 was found to mark a rare repopulating stem cell population with hematopoietic and hepatic differentiation potential.\",\n      \"evidence\": \"FACS purification and NOD/SCID xenograft transplantation\",\n      \"pmids\": [\"12140365\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional role of CD93 in stemness not tested\", \"Mechanism of hepatic differentiation potential undefined\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"The role of CD93 on tumor vasculature was undefined; blockade was shown to upregulate ICAM1/VCAM1, mature vessels, and enhance effector T-cell infiltration, identifying CD93 as a regulator of vascular immune exclusion.\",\n      \"evidence\": \"Anti-CD93 antibody treatment in mouse melanoma, vascular and TIL profiling, ICAM1/VCAM1 neutralization, adoptive T-cell transfer\",\n      \"pmids\": [\"39805660\", \"38250037\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ligand/signaling axis driving adhesion molecule suppression unresolved\", \"Pleural mesothelial CCL21 suppression mechanism downstream of CD93 not fully defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The molecular basis by which CD93 recognizes apoptotic cells in vivo and the proximal signaling that converts ligand engagement into phagocytic, IL-8, and vascular outputs remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No defined apoptotic-cell bridging ligand or direct binding partner on the ectodomain\", \"Proximal kinase/effector linking the cytoplasmic tail to MAPK and cytoskeletal remodeling unidentified\", \"Identity of the shedding metalloproteinase and function of soluble CD93 unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0038024\", \"supporting_discovery_ids\": [0, 13, 8]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [1, 9]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 11]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [14, 6]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 5, 12]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 7, 14]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [9, 17]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"C1QA\", \"MBL2\", \"SFTPA1\", \"GIPC1\", \"MSN\", \"CD43\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":9,"faith_total":9,"faith_pct":100.0}}