{"gene":"CD14","run_date":"2026-04-28T17:28:52","timeline":{"discoveries":[{"year":1988,"finding":"CD14 is anchored to the monocyte plasma membrane via a glycosylphosphatidylinositol (GPI) linkage, as demonstrated by removal of surface CD14 with PI-phospholipase C and absence of CD14 on monocytes from a paroxysmal nocturnal hemoglobinuria patient lacking GPI-anchored proteins; a smaller soluble form lacking the GPI anchor is also secreted.","method":"PI-phospholipase C treatment, immunofluorescence of PNH patient monocytes, biosynthetic labeling, SDS-PAGE","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1 — direct biochemical cleavage assay with PNH genetic validation, independently replicated","pmids":["3385210","2462937"],"is_preprint":false},{"year":1988,"finding":"CD14 maps to chromosome 5q31 in a region encoding myeloid growth factors and receptors, and encodes a myelomonocytic differentiation antigen expressed on monocytes, macrophages, and activated granulocytes.","method":"cDNA cloning, genomic mapping, flow cytometry","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — cDNA cloning with chromosomal mapping, foundational paper","pmids":["2448876"],"is_preprint":false},{"year":1989,"finding":"CD14 cDNA encodes a protein lacking a transmembrane domain, confirmed to be GPI-anchored by PI-PLC release and absence on PNH monocytes; a single mRNA species is abundantly expressed in monocytes and is induced during myeloid differentiation.","method":"cDNA library expression cloning, RNA/DNA blot, PI-PLC treatment, PNH patient cells","journal":"Blood","confidence":"High","confidence_rationale":"Tier 1 — reconstitution-level biochemistry with genetic (PNH) validation","pmids":["2462937"],"is_preprint":false},{"year":1990,"finding":"CD14 functions as a receptor for complexes of LPS and LPS-binding protein (LBP): LPS-LBP complexes bind to CD14 on monocyte surfaces, and anti-CD14 monoclonal antibody blockade prevents LPS/LBP-induced TNF-α synthesis.","method":"Binding assays with LPS-LBP complexes, anti-CD14 mAb blocking, TNF-α measurement in whole blood","journal":"Science","confidence":"High","confidence_rationale":"Tier 1–2 — direct binding assay plus functional blockade, highly replicated foundational paper (>3000 citations)","pmids":["1698311"],"is_preprint":false},{"year":1993,"finding":"Transgenic mice expressing human CD14 on monocytes, neutrophils, and lymphocytes are hypersensitive to LPS-induced endotoxin shock, establishing CD14 as a primary mediator of LPS lethality in vivo.","method":"Transgenic mouse generation, LPS challenge survival assay, flow cytometry","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 2 — in vivo genetic gain-of-function with defined phenotypic readout","pmids":["7681594"],"is_preprint":false},{"year":1993,"finding":"CD14 on neutrophils in whole blood mediates LPS-induced upregulation of CR3 (CD11b/CD18); anti-CD14 antibodies inhibit this CR3 upregulation, indicating CD14 is the primary neutrophil sensor for LPS.","method":"Flow cytometry in whole blood, anti-CD14 mAb inhibition","journal":"Journal of leukocyte biology","confidence":"Medium","confidence_rationale":"Tier 2 — functional antibody blockade in physiological whole-blood system","pmids":["7684764"],"is_preprint":false},{"year":1994,"finding":"CD14 acts as a pattern recognition receptor for diverse bacterial envelope components from Gram-negative and Gram-positive bacteria and mycobacteria, initiating cell activation beyond just LPS.","method":"Cell activation assays with diverse bacterial ligands, anti-CD14 mAb blocking","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal ligand systems, foundational paper with >500 citations","pmids":["7534618"],"is_preprint":false},{"year":1995,"finding":"The N-terminal 65 amino acids of CD14, specifically four small regions (including AVEVE, DDED, PQPD, DPRQY), are critical for serum-dependent LPS binding and NF-κB activation; deletion mutants in this region largely abolish LPS receptor function.","method":"Deletion mutagenesis in CHO cells, LPS binding assays, NF-κB activation","journal":"Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1 — systematic mutagenesis with multiple functional readouts","pmids":["7529231"],"is_preprint":false},{"year":1995,"finding":"Soluble CD14 (recombinant, truncated to N-terminal 152 amino acids) enables LPS activation of CD14-deficient PNH monocytes and endothelial cells, demonstrating that soluble CD14 in serum can substitute for membrane CD14 in LPS signaling.","method":"Recombinant soluble CD14, tissue factor and TNF-α assays in CD14-deficient PNH cells and endothelial cells","journal":"Journal of laboratory and clinical medicine","confidence":"High","confidence_rationale":"Tier 1–2 — reconstitution with truncated protein in genetically defined CD14-deficient cells","pmids":["7537790"],"is_preprint":false},{"year":1996,"finding":"CD14 is a functional cell-activating receptor for bacterial peptidoglycan; the N-terminal 151 amino acids are sufficient for full responsiveness, and similar but not identical sequences within the N-terminal 65 amino acids are critical for responses to both peptidoglycan and LPS.","method":"CD14 transfection in 70Z/3 cells, NF-κB activation, IκB-α degradation, IgM expression, deletion mutagenesis","journal":"Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1 — transfection plus mutagenesis with multiple functional readouts","pmids":["8798531"],"is_preprint":false},{"year":1996,"finding":"CD14-deficient mice generated by gene targeting are highly resistant to endotoxin shock from live Gram-negative bacteria or LPS, and also show dramatically reduced bacteremia, revealing an unexpected role for CD14 in bacterial dissemination.","method":"Gene targeting in ES cells, LPS/bacterial challenge survival, bacteremia measurement","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 1 — knockout mouse with multiple in vivo phenotypic readouts, >580 citations","pmids":["8612135"],"is_preprint":false},{"year":1998,"finding":"CD14 mediates recognition and phagocytosis of apoptotic cells by human macrophages; this interaction depends on a region of CD14 that overlaps with the LPS-binding site, yet unlike LPS, apoptotic cells do not provoke pro-inflammatory cytokine release.","method":"Anti-CD14 blocking antibodies, phagocytosis assays, cytokine measurement","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — antibody blockade with functional phagocytosis readout, >500 citations","pmids":["9548256"],"is_preprint":false},{"year":1998,"finding":"CD14 internalizes via macropinocytosis (not clathrin-coated pits or caveolae): CD14 localizes to microfilament-enriched ruffles and large macropinosomes, LPS co-localizes with CD14 in endosomal compartments, and cytochalasin D blocks internalization but not LPS-dependent cell activation, dissociating endocytosis from signaling.","method":"Electron microscopy, sucrose density gradient fractionation, confocal microscopy, cytochalasin D inhibition, radiolabeled LPS tracking in GPI and transmembrane CD14 THP-1 transfectants","journal":"Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal imaging and biochemical methods with functional dissection","pmids":["9685378"],"is_preprint":false},{"year":1998,"finding":"Both GPI-anchored and transmembrane forms of CD14 support LPS-mediated NF-κB activation and cytokine production similarly, indicating GPI anchoring is not required for LPS signaling; however, only GPI-anchored CD14 mediates rapid calcium mobilization upon antibody cross-linking, implicating phospholipase C and protein tyrosine kinases.","method":"THP-1 cells stably expressing GPI or transmembrane CD14, NF-κB activation, cytokine ELISA, calcium mobilization assays, pharmacological inhibitors, Triton X-100 fractionation","journal":"Infection and immunity","confidence":"High","confidence_rationale":"Tier 1 — isogenic comparison of GPI vs. transmembrane CD14 with multiple readouts","pmids":["9488411"],"is_preprint":false},{"year":1999,"finding":"Distinct CD14 ligands LAM and LPS utilize different TLR proteins for intracellular signaling: CHO/CD14 cells acquire LAM responsiveness only when also engineered to express functional TLR2, while LPS signaling does not require TLR2, establishing a paradigm where a common binding receptor (CD14) pairs with distinct signal-transducing receptors.","method":"CHO transfection with CD14 and TLR2, cytokine activation assays, TLR2 overexpression in macrophages","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — epistasis by gain-of-function transfection, replicated in macrophages","pmids":["10586073"],"is_preprint":false},{"year":2000,"finding":"Membrane and soluble forms of CD14 have different structural determinants for LPS receptor function: deletions that abolish LPS binding in membrane CD14 may not affect binding in soluble CD14, yet all five tested deletions ablated soluble CD14 receptor function whereas only two completely destroyed membrane CD14 receptor function.","method":"Deletion mutants of CD14 expressed in CHO cells, LPS binding assays, soluble CD14-dependent cellular activation assays","journal":"Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1 — systematic mutagenesis comparing membrane and soluble forms","pmids":["10652298"],"is_preprint":false},{"year":2001,"finding":"LPS cross-links specifically to TLR4 and MD-2 only when CD14 is co-expressed, establishing that LPS is in close proximity to all three members of the tripartite receptor complex (CD14, TLR4, MD-2) and that CD14 is required for LPS transfer to TLR4/MD-2.","method":"Transient transfection in HEK293 cells, UV cross-linking with radio-iodinated ASD-LPS, immunoprecipitation","journal":"Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1 — photo-crosslinking with reconstituted components identifies direct molecular contacts","pmids":["11274165"],"is_preprint":false},{"year":2001,"finding":"Following LPS stimulation, CD14 forms an activation cluster with heat-shock proteins Hsp70 and Hsp90, chemokine receptor CXCR4, and GDF5, as identified by affinity chromatography and confirmed by FRET, suggesting these proteins serve as the transmembrane signaling components downstream of CD14.","method":"Affinity chromatography, peptide mass fingerprinting, fluorescence resonance energy transfer (FRET)","journal":"Nature immunology","confidence":"Medium","confidence_rationale":"Tier 2 — FRET confirms molecular proximity; single lab, orthogonal biochemical and biophysical methods","pmids":["11276205"],"is_preprint":false},{"year":2002,"finding":"LPS traffics rapidly to and from the Golgi apparatus with the TLR4-MD-2-CD14 complex; LPS follows CD14-dependent trafficking pathways in CD14-positive cells, but Golgi-associated TLR4 expression disrupted by brefeldin A does not prevent LPS signaling, indicating signaling is initiated at the plasma membrane.","method":"Fluorescent TLR4 expression, confocal microscopy of LPS trafficking, brefeldin A inhibition, MyD88 translocation assays, cross-linking signaling assays","journal":"Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 2 — live-cell imaging with functional dissection using pharmacological inhibitor","pmids":["12324469"],"is_preprint":false},{"year":2003,"finding":"Human CMV virions are recognized by TLR2 and CD14 to trigger NF-κB-dependent inflammatory cytokine production; both receptors are required for CMV-induced innate immune activation.","method":"TLR2/CD14 antibody blocking, dominant-negative TLR constructs, NF-κB reporter assays, cytokine measurement","journal":"Journal of virology","confidence":"High","confidence_rationale":"Tier 2 — multiple blocking approaches with NF-κB and cytokine readouts, >500 citations","pmids":["12663765"],"is_preprint":false},{"year":2003,"finding":"Lipoteichoic acid from S. pneumoniae and S. aureus activates immune cells via LBP, CD14, and TLR2, but not TLR4/MD-2; LBP catalytically transfers LTA to CD14, and TLR2 transfection in HEK293/CD14 and CHO cells confers LTA responsiveness.","method":"PhastGel native gel electrophoresis, HEK293/CHO transfection, cytokine induction assays, anti-CD14/anti-LBP blocking","journal":"Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1–2 — biochemical transfer assay plus epistasis by transfection, >470 citations","pmids":["12594207"],"is_preprint":false},{"year":2003,"finding":"CD14 interacts directly with Alzheimer's amyloid-β peptide (Aβ42) fibrils and mediates microglial activation; anti-CD14 antibodies and CD14 genetic deficiency significantly reduce amyloid-induced microglial activation and toxicity.","method":"FRET/FLIM, antibody neutralization, CD14-knockout cell experiments, flow cytometry, confocal microscopy","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 — direct molecular interaction confirmed by FRET, functional validation with KO and antibody blockade","pmids":["14597556"],"is_preprint":false},{"year":2004,"finding":"Soluble CD14 is produced by the liver as a type 2 acute-phase protein regulated by IL-6: IL-6 stimulates CD14 mRNA and protein production in HepG2 cells and primary hepatocytes, and CD14 mRNA induction during acute-phase response is abolished in IL-6-knockout mice.","method":"ELISA, real-time PCR, HepG2 cell stimulation, IL-6 knockout mouse model with turpentine injection","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — in vitro and in vivo concordant data with genetic KO validation","pmids":["15034063"],"is_preprint":false},{"year":2005,"finding":"CD14 directly interacts with Aβ42 at nanometer range (confirmed by FRET/FLIM) and mediates phagocytosis of exogenous Aβ42 by primary microglia at sub-inflammatory concentrations in a CD14-dependent manner; CD14 knockout cells fail to internalize Aβ42.","method":"Flow cytometry, confocal microscopy, two-photon FLIM-FRET, CD14-deficient microglial cells, phagocytosis assay","journal":"Brain","confidence":"High","confidence_rationale":"Tier 1–2 — FRET-confirmed direct interaction with KO functional validation","pmids":["15857927"],"is_preprint":false},{"year":2005,"finding":"CD14 determines ligand specificity of the LPS receptor complex: CD14+/+ macrophages show exquisite sensitivity (up to 150,000-fold greater than CD14-/- cells) and structural discrimination between smooth LPS and partial structures, whereas CD14-/- macrophages cannot distinguish LPS structural variants.","method":"Comparison of CD14+/+ and CD14-/- macrophage responses to structurally diverse LPS variants, TNF production assays","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — genetic KO comparison with quantitative dose-response and multiple LPS structures","pmids":["16148141"],"is_preprint":false},{"year":2005,"finding":"Lipopeptide binding to CD14 is the first step in LP recognition; after Pam3CSK4 binding, CD14 and the lipopeptide associate with TLR2/TLR1, and TLR2 is recruited to a low-mobility signaling complex. CD14 enables lipopeptide binding while TLR2 is required for signaling.","method":"FRET and FRAP imaging, flow cytometry, confocal microscopy with FLAG-labeled lipopeptide","journal":"European journal of immunology","confidence":"High","confidence_rationale":"Tier 1–2 — FRET and FRAP confirm molecular proximity and complex formation in intact cells","pmids":["15714590"],"is_preprint":false},{"year":2005,"finding":"Ethanol disrupts LPS-induced lipid raft clustering by altering CD14 partition into lipid rafts; EtOH interferes with IRAK-1 activation and suppresses TLR4-mediated TNF-α production in a manner additive with chemical lipid raft disruptors.","method":"Cell fractionation, TNF-α ELISA, IRAK-1 activation assay, methyl-β-cyclodextrin/nystatin comparison","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 — fractionation with functional correlation; single lab, mechanistic follow-up limited","pmids":["15896296"],"is_preprint":false},{"year":2012,"finding":"LPS causes CD14 membrane expression and colocalization with TLR-4 in intestinal enterocytes, and this TLR-4-dependent CD14 upregulation mediates LPS-induced increase in intestinal tight junction permeability both in vitro and in vivo.","method":"Caco-2 monolayer transepithelial resistance, mouse intestinal perfusion, TLR-4 KO comparison, confocal colocalization","journal":"American Journal of Pathology","confidence":"High","confidence_rationale":"Tier 2 — in vitro and in vivo concordance with genetic (TLR-4 KO) validation","pmids":["23201091"],"is_preprint":false},{"year":2015,"finding":"Gαi1 and Gαi3 form complexes with CD14 and Gab1 in response to LPS, which are required for PI3K-Akt signaling activation; Gαi1/3 deficiency decreases TLR4 endocytosis, reduces IRF3 phosphorylation, causes an M2-like macrophage phenotype with suppressed pro-inflammatory cytokine production, and leads to LPS tolerance in vivo.","method":"Co-immunoprecipitation, Gαi1/3 siRNA knockdown in BMDMs, Gαi1/3 KO mice, cytokine ELISA, TLR4 endocytosis assay, IRF3 phosphorylation","journal":"PNAS","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP with multiple functional KO phenotypes in vitro and in vivo","pmids":["25825741"],"is_preprint":false},{"year":2016,"finding":"CD14 is required for TLR4 endocytosis and thereby for the TRAM-TRIF-dependent signaling pathway activated from early endosomes; without CD14, TLR4 cannot be internalized efficiently, abrogating IFN-β production downstream of TRIF while MyD88-dependent signaling at the plasma membrane is less affected.","method":"Review synthesizing CD14 KO, endocytosis assays, TLR4 trafficking studies","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 1–2 — mechanistic dissection of LPS transfer cascade by EM, single-molecule TIRF, and structural determinants","pmids":["27986454"],"is_preprint":false},{"year":2017,"finding":"A single LPS molecule bound to CD14 is transferred to TLR4-MD2 in a TLR4-dependent manner; LBP binds longitudinally to LPS micelles and catalyzes multi-round LPS transfer to CD14 via electrostatic interactions; CD14 then delivers single LPS molecules to TLR4-MD2 through a defined cascade involving LBP/LPS micelle → CD14/LBP/LPS ternary → CD14-LPS-TLR4-MD2 intermediates.","method":"Negative-stain electron microscopy, single-molecule TIRF fluorescence analysis, reconstituted in vitro LPS transfer cascade","journal":"BMB reports","confidence":"High","confidence_rationale":"Tier 1 — reconstituted in vitro cascade with single-molecule resolution and EM structural data","pmids":["28115037"],"is_preprint":false},{"year":2020,"finding":"P2X7 receptor activation induces release of CD14 from macrophages via extracellular vesicles, reducing plasma membrane CD14 and functionally attenuating LPS-induced (but not monophosphoryl lipid A-induced) pro-inflammatory cytokine production; P2X7 activity is required during murine sepsis to maintain elevated circulating CD14 levels and control bacterial load.","method":"Extracellular vesicle isolation, flow cytometry, P2X7 KO mice, cecal ligation/puncture sepsis model, cytokine measurement","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — KO mouse with multiple in vitro and in vivo phenotypic readouts, mechanistic vesicle analysis","pmids":["33135636"],"is_preprint":false},{"year":2020,"finding":"CD14 governs TLR4 endocytosis and thus the spatiotemporal control of LPS-induced signaling: CD14-driven internalization of TLR4 terminates TIRAP/MyD88-dependent signaling at the plasma membrane while activating the TRAM/TRIF-dependent pathway from early endosomes; subsequent endo-lysosomal trafficking of TLR4 determines the duration and magnitude of TRIF-dependent responses.","method":"Review synthesizing CD14 KO, TLR4 endocytosis, TRIF/MyD88 pathway activation assays from multiple studies","journal":"Cellular and molecular life sciences","confidence":"High","confidence_rationale":"Tier 2 — mechanistic synthesis supported by multiple independent KO/trafficking studies","pmids":["33057840"],"is_preprint":false},{"year":2022,"finding":"Externalized phosphatidylinositides (PIPs) on apoptotic cell surfaces are eat-me signals recognized by CD14; masking exofacial PIPs or CD14 knockout in phagocytes blocks phagocytosis of apoptotic cells, and CD14-deficient mice accumulate PIP+ apoptotic cells in tissues.","method":"Unbiased proteomics, anti-PI(3,4,5)P3 antibody/PH-domain probes, CD14 KO phagocytes, in vivo irradiation model, flow cytometry","journal":"Cell death and differentiation","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods in vitro and in vivo with CD14 KO genetic validation","pmids":["35017647"],"is_preprint":false},{"year":1999,"finding":"CD14 is expressed on Kupffer cells and is functional: LPS induces CD14-dependent intracellular calcium rises and TNF-α mRNA in collagenase-isolated Kupffer cells; Pronase treatment removes surface CD14 and abolishes LPS responses, while PI-PLC cleavage of CD14 blunts calcium signaling.","method":"Western blotting, RT-PCR, intracellular calcium measurement, TNF-α mRNA, Pronase vs. collagenase isolation comparison, PI-PLC treatment","journal":"American Journal of Physiology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple biochemical and functional approaches in primary Kupffer cells","pmids":["10070034"],"is_preprint":false},{"year":2009,"finding":"Chicken CD14, unlike its mammalian ortholog, is a transmembrane protein rather than GPI-anchored: it contains a 23-aa transmembrane segment and a cytoplasmic tail, and PI-PLC treatment does not remove chicken CD14 from the cell surface in transfected COS-7 cells.","method":"RT-PCR cloning, COS-7 transfection with FLAG-tagged constructs, PI-PLC treatment, flow cytometry","journal":"Developmental and comparative immunology","confidence":"High","confidence_rationale":"Tier 1 — direct biochemical comparison of chicken and human CD14 membrane anchorage","pmids":["18761368"],"is_preprint":false}],"current_model":"CD14 is a GPI-anchored (in mammals) pattern recognition co-receptor that binds bacterial LPS, peptidoglycan, lipoteichoic acid, lipopeptides, and apoptotic cell signals (externalized PIPs and phosphatidylserine); it acts as a ligand-delivery/transfer molecule that presents LPS to TLR4/MD-2 (via an LBP→CD14→TLR4-MD2 transfer cascade) and to TLR2/TLR1 or TLR2/TLR6 for other ligands, drives TLR4 endocytosis to activate the TRAM-TRIF signaling pathway from endosomes while terminating the MyD88-dependent pathway at the plasma membrane, forms a signaling complex with Gαi1/3 and Gab1 to activate PI3K-Akt, and can be shed via P2X7-driven extracellular vesicle release to modulate circulating LPS-sensing capacity; a soluble form produced by the liver as an IL-6-regulated acute-phase protein extends CD14-dependent LPS sensing to CD14-low cells such as endothelial cells."},"narrative":{"teleology":[{"year":1988,"claim":"Establishing the membrane topology of CD14 resolved how a differentiation antigen lacking a transmembrane domain is surface-expressed: via a GPI linkage, with a smaller soluble isoform also produced.","evidence":"PI-phospholipase C cleavage, PNH patient monocytes lacking GPI-anchored proteins, cDNA cloning and SDS-PAGE","pmids":["3385210","2462937","2448876"],"confidence":"High","gaps":["Three-dimensional structure of CD14 not yet determined","Mechanism of soluble CD14 generation (proteolytic vs. secretory) not resolved"]},{"year":1990,"claim":"Identifying CD14 as the receptor for LPS–LBP complexes established the molecular basis of monocyte endotoxin sensing, answering how picomolar LPS concentrations activate innate immunity.","evidence":"Direct LPS-LBP binding assays on monocytes, anti-CD14 mAb blockade of TNF-α production","pmids":["1698311"],"confidence":"High","gaps":["Signal transduction mechanism downstream of a GPI-anchored protein unknown","Identity of transmembrane signaling partner not yet identified"]},{"year":1994,"claim":"Demonstrating that CD14 recognizes diverse Gram-positive and mycobacterial envelope components beyond LPS expanded it from an LPS receptor to a broad pattern recognition receptor.","evidence":"Cell activation assays with peptidoglycan, LTA, mycobacterial products; anti-CD14 blocking","pmids":["7534618","8798531"],"confidence":"High","gaps":["Structural basis for multi-ligand binding not determined","Which downstream signaling receptors pair with CD14 for non-LPS ligands unknown"]},{"year":1995,"claim":"Mapping the LPS-binding determinants to four short motifs within the N-terminal 65 residues defined the functional domain architecture and showed that soluble CD14 fragments (152 aa) can reconstitute LPS signaling on CD14-deficient cells.","evidence":"Systematic deletion mutagenesis in CHO cells, NF-κB and LPS binding assays, reconstitution on PNH monocytes and endothelial cells","pmids":["7529231","7537790"],"confidence":"High","gaps":["Atomic-resolution structure of CD14 N-terminal domain–LPS interaction not available","Determinants distinguishing membrane vs. soluble CD14 function not fully resolved"]},{"year":1996,"claim":"CD14 knockout mice proved CD14 is required for lethal endotoxin shock in vivo and unexpectedly revealed a role in bacterial dissemination, validating CD14 as a central innate immune gatekeeper.","evidence":"Gene-targeted CD14−/− mice challenged with LPS and live Gram-negative bacteria","pmids":["8612135"],"confidence":"High","gaps":["How CD14 promotes bacterial dissemination mechanistically was not defined","Relative contributions of membrane vs. soluble CD14 in vivo not dissected"]},{"year":1998,"claim":"Discovering that CD14 mediates phagocytosis of apoptotic cells without provoking inflammation revealed a dual function — pathogen sensing and silent corpse clearance — through an overlapping but non-identical binding site.","evidence":"Anti-CD14 blocking antibodies, macrophage phagocytosis assays, cytokine measurement","pmids":["9548256"],"confidence":"High","gaps":["Specific apoptotic cell ligand recognized by CD14 not identified at this point","Structural basis for anti-inflammatory vs. pro-inflammatory outcome unknown"]},{"year":1999,"claim":"Showing that CD14-dependent LAM signaling requires TLR2 while LPS signaling does not established the paradigm of CD14 as a shared ligand-capture receptor that routes different PAMPs to distinct TLR signaling complexes.","evidence":"CHO/CD14 transfection with TLR2, differential cytokine activation for LAM vs. LPS","pmids":["10586073"],"confidence":"High","gaps":["Molecular mechanism by which CD14 hands off ligands to specific TLRs not defined","Role of co-receptors MD-1/MD-2 in this routing not addressed"]},{"year":2001,"claim":"UV cross-linking of LPS to TLR4/MD-2 only in the presence of CD14 demonstrated that CD14 is required for physical LPS transfer to TLR4-MD2, defining the tripartite receptor complex.","evidence":"HEK293 reconstitution, radio-iodinated ASD-LPS UV cross-linking, immunoprecipitation","pmids":["11274165"],"confidence":"High","gaps":["Stoichiometry and kinetics of the transfer reaction not measured","Whether CD14 remains in the complex after LPS transfer or dissociates was unclear"]},{"year":2005,"claim":"Quantitative comparison of CD14+/+ and CD14−/− macrophages revealed that CD14 confers up to 150,000-fold sensitivity enhancement and structural discrimination among LPS variants, establishing CD14 as the specificity determinant of the LPS receptor.","evidence":"Dose-response TNF production with structurally diverse LPS variants in WT vs. CD14 KO macrophages","pmids":["16148141"],"confidence":"High","gaps":["Structural basis for CD14's discriminatory capacity unresolved","Whether soluble CD14 can restore full discrimination in CD14−/− cells not tested"]},{"year":2015,"claim":"Identification of Gαi1/3–CD14–Gab1 complexes revealed a G-protein-coupled signaling axis linking CD14 to PI3K-Akt activation, TLR4 endocytosis, and IRF3-dependent interferon production.","evidence":"Co-immunoprecipitation, Gαi1/3 siRNA knockdown and KO mice, TLR4 endocytosis and IRF3 phosphorylation assays","pmids":["25825741"],"confidence":"High","gaps":["Whether Gαi proteins bind CD14 directly or through an intermediary adapter not established","Structural basis of GPI-anchored CD14 coupling to heterotrimeric G proteins unknown"]},{"year":2017,"claim":"Reconstitution of the entire LBP→CD14→TLR4-MD2 LPS transfer cascade at single-molecule resolution defined the mechanism: LBP binds longitudinally to LPS micelles and catalytically loads single LPS monomers onto CD14, which then delivers them to TLR4-MD2.","evidence":"Negative-stain EM, single-molecule TIRF fluorescence, in vitro reconstituted cascade","pmids":["28115037"],"confidence":"High","gaps":["High-resolution cryo-EM structure of CD14–LPS intermediate not available","Whether CD14 undergoes conformational change upon LPS binding is unresolved"]},{"year":2020,"claim":"Two advances resolved how CD14 controls the spatiotemporal switch between TLR4 signaling pathways and how macrophages regulate their own CD14 levels: CD14 drives TLR4 endocytosis to activate TRAM-TRIF while terminating TIRAP-MyD88 signaling, and P2X7-driven vesicular shedding of CD14 attenuates LPS responsiveness during sepsis.","evidence":"CD14 KO with TLR4 trafficking assays; P2X7 KO mice in cecal ligation-puncture sepsis model; extracellular vesicle analysis","pmids":["33057840","33135636"],"confidence":"High","gaps":["Molecular trigger linking CD14 engagement to the endocytic machinery not identified","How P2X7-shed CD14-bearing vesicles function systemically — as decoys or as soluble CD14 equivalents — is not resolved"]},{"year":2022,"claim":"Identification of externalized phosphatidylinositides as the specific eat-me signal recognized by CD14 on apoptotic cells resolved a two-decade-old question about CD14's non-inflammatory ligand in efferocytosis.","evidence":"Unbiased proteomics, anti-PIP masking, CD14 KO phagocytes, in vivo irradiation model","pmids":["35017647"],"confidence":"High","gaps":["Binding affinity and structural basis of CD14–PIP interaction not defined","Whether CD14-dependent efferocytosis uses the same N-terminal domain as LPS binding is unresolved"]},{"year":null,"claim":"A high-resolution structure of CD14 bound to LPS or phosphatidylinositides, and the molecular mechanism by which GPI-anchored CD14 engages heterotrimeric G proteins and the endocytic machinery to drive TLR4 internalization, remain undefined.","evidence":"","pmids":[],"confidence":"High","gaps":["No atomic-resolution structure of CD14 in complex with any ligand","Mechanism coupling GPI-anchored CD14 to Gαi and endocytic machinery unresolved","Relative in vivo contributions of membrane-anchored vs. soluble vs. vesicular CD14 in sepsis and efferocytosis not quantified"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[3,7,9,20,24,25,30,33]},{"term_id":"GO:0038024","term_label":"cargo receptor activity","supporting_discovery_ids":[16,25,29,30]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[3,6,14,20]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[14,25,29]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,2,12,13,25,26,27]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,8,22,31]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[12,31]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[12,29,32]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[3,4,6,10,14,16,19,20,24,25,28,29,30,32]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[13,28,29,32]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[11,33]}],"complexes":["TLR4/MD-2/CD14","TLR2/CD14","LBP/CD14/LPS"],"partners":["TLR4","MD2","LBP","TLR2","GNAI1","GNAI3","GAB1","P2RX7"],"other_free_text":[]},"mechanistic_narrative":"CD14 is a GPI-anchored pattern recognition co-receptor on monocytes, macrophages, and neutrophils that serves as the primary sensor and transfer molecule for bacterial lipopolysaccharide (LPS), peptidoglycan, lipoteichoic acid, lipopeptides, and apoptotic cell-derived phosphatidylinositides, coupling ligand capture to activation of distinct Toll-like receptor signaling pathways [PMID:1698311, PMID:7534618, PMID:35017647]. The N-terminal leucine-rich region binds LPS–LBP complexes and transfers individual LPS molecules to TLR4/MD-2 via a defined LBP→CD14→TLR4-MD2 cascade, while presenting other microbial ligands to TLR2/TLR1 or TLR2/TLR6; CD14 additionally drives TLR4 endocytosis, thereby terminating MyD88-dependent signaling at the plasma membrane and initiating the TRAM-TRIF pathway from endosomes [PMID:28115037, PMID:27986454, PMID:10586073]. A soluble form produced by hepatocytes as an IL-6-regulated acute-phase protein extends LPS sensing to CD14-low cells such as endothelial cells, while P2X7-dependent shedding of CD14 on extracellular vesicles modulates macrophage LPS responsiveness during sepsis [PMID:15034063, PMID:33135636]. CD14 also mediates non-inflammatory phagocytosis of apoptotic cells by recognizing externalized phosphatidylinositides and phosphatidylserine, and participates in microglial recognition and phagocytosis of amyloid-β fibrils [PMID:9548256, PMID:35017647, PMID:15857927]."},"prefetch_data":{"uniprot":{"accession":"P08571","full_name":"Monocyte differentiation antigen CD14","aliases":["My23 antigen","Myeloid cell-specific leucine-rich glycoprotein"],"length_aa":375,"mass_kda":40.1,"function":"Coreceptor for bacterial lipopolysaccharide (PubMed:1698311, PubMed:23264655). In concert with LBP, binds to monomeric lipopolysaccharide and delivers it to the LY96/TLR4 complex, thereby mediating the innate immune response to bacterial lipopolysaccharide (LPS) (PubMed:20133493, PubMed:22265692, PubMed:23264655). Acts via MyD88, TIRAP and TRAF6, leading to NF-kappa-B activation, cytokine secretion and the inflammatory response (PubMed:8612135). 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replicated widely\",\n      \"pmids\": [\"2462937\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Transgenic mice expressing human CD14 are hypersensitive to LPS-induced endotoxin shock in vivo, demonstrating that CD14 is a primary mediator of LPS-induced septic lethality.\",\n      \"method\": \"Transgenic mouse model; endotoxin challenge; survival assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean gain-of-function transgenic with defined lethality phenotype; replicated concept in multiple subsequent studies\",\n      \"pmids\": [\"7681594\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"CD14 on neutrophils in whole blood mediates LPS-induced upregulation of CR3 (CD11b/CD18); anti-CD14 antibodies block LPS-induced CR3 increase, indicating CD14 links LPS recognition to integrin upregulation.\",\n      \"method\": \"Whole-blood flow cytometry; anti-CD14 antibody blocking\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean blocking experiment in whole blood, single lab\",\n      \"pmids\": [\"7684764\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"CD14 acts as a broad pattern recognition receptor that initiates cell activation by diverse bacterial envelope components from Gram-negative, Gram-positive, and mycobacterial pathogens, not only LPS.\",\n      \"method\": \"Cell activation assays with bacterial components; anti-CD14 antibody blocking; CD14-transfected cell lines\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple bacterial ligands tested, anti-CD14 blocking, replicated across many subsequent studies\",\n      \"pmids\": [\"7534618\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"The N-terminal 65 amino acids of CD14, particularly four short regions within them (AVEVE, DDED, PQPD, DPRQY), are critical for serum-dependent LPS binding and NF-κB activation; deletion of these regions selectively abrogates LPS receptor function.\",\n      \"method\": \"Site-directed deletion mutagenesis; stable transfection in CHO cells; LPS binding assays; NF-κB reporter assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis with structure-function readouts for binding and signaling\",\n      \"pmids\": [\"7529231\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Soluble CD14 (sCD14) can substitute for serum to enable LPS responses in CD14-deficient PNH monocytes and endothelial cells (which lack membrane CD14); a truncated sCD14 containing only the N-terminal 152 amino acids retains this receptor function.\",\n      \"method\": \"LPS stimulation assays on PNH monocytes and endothelial cells; recombinant soluble CD14 supplementation; tissue factor and TNF-α readouts\",\n      \"journal\": \"The Journal of laboratory and clinical medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean reconstitution experiment using CD14-deficient primary cells and recombinant protein fragments\",\n      \"pmids\": [\"7537790\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Anti-CD14 monoclonal antibodies protect primates from LPS-induced endotoxin shock, reducing hypotension, plasma cytokines (TNF-α, IL-1β, IL-6, IL-8), and lung permeability changes, demonstrating the CD14 pathway is essential in vivo in a primate model.\",\n      \"method\": \"Primate endotoxemia model; anti-CD14 mAb pretreatment; cytokine ELISA; hemodynamic monitoring\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — well-controlled in vivo loss-of-function with multiple mechanistic readouts; primate model\",\n      \"pmids\": [\"8833900\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"CD14 functions as a cell-activating receptor for bacterial peptidoglycan; the N-terminal 151 amino acids are sufficient for full responsiveness; specific small regions within the N-terminal 65 amino acids differentially control responses to peptidoglycan vs. LPS.\",\n      \"method\": \"CD14-transfected 70Z/3 cells; NF-κB activation; IκB-α degradation; surface IgM expression; anti-CD14 blocking\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — structure-function mutagenesis with multiple activation readouts; clean transfection system\",\n      \"pmids\": [\"8798531\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"CD14 on macrophages mediates recognition and phagocytosis of apoptotic cells; this interaction requires the same or closely associated region used for LPS binding, yet apoptotic cells, unlike LPS, do not provoke pro-inflammatory cytokine release.\",\n      \"method\": \"Anti-CD14 antibody blocking of apoptotic cell phagocytosis; competition with LPS binding region; cytokine assays\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — antibody blocking plus functional phagocytosis assay; landmark Nature paper replicated subsequently\",\n      \"pmids\": [\"9548256\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"CD14 internalizes LPS via a macropinocytic pathway; GPI-anchored and transmembrane forms of CD14 sort to different plasma membrane subdomains but both associate with microfilament-enriched ruffles; CD14-enriched ruffles fuse into large vacuoles that condense into phago-lysosomes; cytochalasin D blocks internalization but not LPS-dependent activation, dissociating the two processes.\",\n      \"method\": \"Sucrose density gradient fractionation; electron microscopy; confocal microscopy; radiolabeled LPS internalization; cytochalasin D treatment; THP-1 transfectants\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple imaging and biochemical methods; pharmacological dissection of internalization from signaling\",\n      \"pmids\": [\"9685378\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"GPI-anchored CD14 localizes to Triton X-100-insoluble (lipid raft) membrane domains, whereas transmembrane CD14 is fully Triton X-100-soluble; both forms support LPS-induced NF-κB activation and cytokine production similarly; GPI anchoring confers an additional antibody cross-linking-induced calcium signal involving phospholipase C and protein tyrosine kinases.\",\n      \"method\": \"Triton X-100 fractionation; NF-κB reporter; cytokine ELISA; calcium mobilization assay; pharmacological inhibitors; THP-1 transfectants\",\n      \"journal\": \"Infection and immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — biochemical fractionation plus functional signaling assays with pharmacological dissection\",\n      \"pmids\": [\"9488411\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"CD14 and CD11/CD18 integrins share a common LPS signaling pathway; LPS-binding protein can transfer LPS to CD11/CD18 as it does to CD14; the ligand discrimination between LPS agonists and antagonists is mediated by an associated signal transducer distinct from both CD14 and CD11/CD18.\",\n      \"method\": \"CHO cell transfectants expressing CD14 or CD11/CD18; cytoplasmic deletion mutants; LPS analog activation assays; LBP supplementation\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reconstitution in transfected cells with LPS analogs, single lab\",\n      \"pmids\": [\"9820516\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"CD14 ligands LPS and mycobacterial lipoarabinomannan (LAM) use different TLR co-receptors for signaling: LPS requires TLR4, while LAM requires functional TLR2; CD14 is common to both as a ligand-binding component, establishing a novel receptor paradigm where a shared binding chain delivers ligands to distinct signal-transducing chains.\",\n      \"method\": \"CHO/CD14 cells with TLR2 frame-shift mutation; TLR2 transfection rescue; macrophage TLR2 overexpression; cell activation assays\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis via TLR2 rescue in CD14-expressing cells; multiple cell types tested\",\n      \"pmids\": [\"10586073\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Kupffer cells possess functional CD14 (confirmed by RT-PCR and Western blot); CD14 mediates LPS-induced intracellular calcium increase and TNF-α mRNA induction in a serum-dependent manner; PI-PLC cleavage of CD14 from the membrane blunts LPS-induced calcium responses.\",\n      \"method\": \"RT-PCR; Western blot; PI-PLC treatment; intracellular calcium imaging; TNF-α mRNA Northern blot; collagenase vs. collagenase-Pronase isolation comparison\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods including enzymatic removal of CD14 with functional calcium and cytokine readouts\",\n      \"pmids\": [\"10070034\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Soluble and membrane-anchored forms of CD14 have different structural determinants for LPS receptor function; deletions in the N-terminal region that ablate LPS binding in membrane CD14 do not necessarily abolish LPS binding by soluble CD14, yet all five deletions tested eliminated soluble CD14's receptor (cell-activation) function.\",\n      \"method\": \"Deletion mutagenesis; LPS binding assays; cell activation assays with soluble vs. membrane CD14\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis comparing two forms of CD14 with binding and functional readouts\",\n      \"pmids\": [\"10652298\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"LPS stimulation forms a CD14-independent receptor cluster containing HSP70, HSP90, CXCR4, and GDF5, identified by affinity chromatography and peptide mass fingerprinting; FRET imaging confirms these proteins associate at the cell surface after LPS ligation.\",\n      \"method\": \"Affinity chromatography; peptide mass fingerprinting; FRET imaging\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mass spectrometry identification plus FRET validation, single lab\",\n      \"pmids\": [\"11276205\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"CD14 directly interacts with Alzheimer's amyloid-β(42) fibrils; neutralizing antibodies against CD14 and CD14 genetic deficiency significantly reduce amyloid-induced microglial activation and microglial toxicity.\",\n      \"method\": \"FRET/FLIM imaging of CD14–Aβ42 proximity in CD14-transfected CHO cells; CD14 knockout microglial cells; cytokine production assays\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct molecular interaction by FRET plus genetic KO functional readout\",\n      \"pmids\": [\"14597556\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Soluble CD14 is produced by the liver as a type 2 acute-phase protein regulated by IL-6; IL-6 induces CD14 mRNA and protein in HepG2 cells and primary hepatocytes in vitro; IL-6-knockout mice fail to upregulate liver CD14 mRNA during acute-phase response.\",\n      \"method\": \"ELISA; real-time PCR; IL-6-deficient mouse model of turpentine-induced acute-phase response; HepG2 and primary hepatocyte cultures\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vitro and in vivo genetic KO with mRNA and protein readouts; multiple cell types\",\n      \"pmids\": [\"15034063\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"CD14 directly binds Aβ42 at the nanometer scale and mediates phagocytosis of Aβ42 by primary microglia at sub-inflammatory concentrations; CD14-deficient microglia show markedly reduced Aβ42 internalization.\",\n      \"method\": \"FLIM-FRET; flow cytometry; confocal microscopy; CD14-knockout primary microglial cells; phagocytosis assay\",\n      \"journal\": \"Brain\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct molecular interaction by FRET plus KO functional phagocytosis assay\",\n      \"pmids\": [\"15857927\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Lipopeptide (Pam3CSK4) binding to cells is enabled by CD14; after binding, CD14 and the lipopeptide associate in physical proximity with TLR2 and TLR1, driving TLR2 into a low-mobility signaling complex; TLR2 is required for signaling but CD14 is required for binding.\",\n      \"method\": \"FLAG-labeled lipopeptide; flow cytometry; confocal microscopy; FRET; FRAP imaging\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — FRET and FRAP directly demonstrate proximity of CD14–lipopeptide–TLR2/TLR1 complex\",\n      \"pmids\": [\"15714590\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"CD14 confers exquisite ligand specificity on the LPS receptor complex: CD14(+/+) macrophages discriminate smooth LPS from its partial structures (up to 500-fold sensitivity difference) and between LPS from different bacteria, whereas CD14(-/-) macrophages cannot make these distinctions and are 150,000-fold less sensitive to smooth LPS.\",\n      \"method\": \"TNF induction assays comparing CD14+/+ vs. CD14-/- macrophages with diverse LPS partial structures and bacterial species LPS\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic comparison using genetic KO with multiple LPS ligands; strong evidence for CD14 as a specificity determinant\",\n      \"pmids\": [\"16148141\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Ethanol alters LPS-induced partitioning of CD14 into lipid rafts and interferes with IRAK-1 activation, suppressing TLR4-mediated TNF-α production; this effect is additive with lipid raft-disrupting drugs, suggesting ethanol suppresses TLR signaling partly by perturbing lipid raft clustering of CD14.\",\n      \"method\": \"Cell fractionation; IRAK-1 activation assay; TNF-α ELISA; pharmacological lipid raft disruption\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — biochemical fractionation plus signaling readout, single lab\",\n      \"pmids\": [\"15896296\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"In response to LPS, Gαi1 and Gαi3 form a complex with CD14 and Gab1 that is required for PI3K-Akt activation and TLR4 endocytosis; Gαi1/3 deficiency reduces IRF3 phosphorylation, shifts macrophages to an M2-like anti-inflammatory phenotype, and causes LPS tolerance in vivo.\",\n      \"method\": \"Co-immunoprecipitation; knockdown in BMDMs; PI3K-Akt and IRF3 phosphorylation assays; macrophage polarization cytokine assays; in vivo LPS tolerance model\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP demonstrating complex plus KD phenotype with multiple mechanistic readouts in vitro and in vivo\",\n      \"pmids\": [\"25825741\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CD14 catalyzes LPS transfer to the TLR4/MD2 complex in a dynamic multi-step cascade: LBP binds longitudinally to LPS micelle surfaces; CD14 repeatedly binds/unbinds single LBP/LPS micelles via key charged residues; a single LPS molecule bound to CD14 is then transferred to TLR4/MD2 in a TLR4-dependent manner.\",\n      \"method\": \"Negative-stain electron microscopy; single-molecule TIRF fluorescence analysis; reconstituted LPS transfer cascade\",\n      \"journal\": \"BMB reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in vitro transfer cascade visualized at single-molecule level with EM structural data\",\n      \"pmids\": [\"28115037\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"P2X7 receptor activation induces release of CD14 in extracellular vesicles, reducing macrophage plasma membrane CD14 and functionally attenuating LPS (but not monophosphoryl lipid A) pro-inflammatory cytokine production; P2X7 activity is required to maintain elevated circulating CD14 during murine sepsis, and its absence leads to higher bacterial load and organ damage.\",\n      \"method\": \"Extracellular vesicle isolation; flow cytometry; cytokine assays; P2X7-deficient murine sepsis model\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mechanism of CD14 shedding identified, combined with KO sepsis model with defined phenotype\",\n      \"pmids\": [\"33135636\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Externalized phosphatidylinositides (PIPs) on apoptotic cell surfaces are eat-me signals recognized by CD14 on phagocytes; masking exofacial PIPs or CD14 knockout in phagocytes blocks apoptotic cell phagocytosis; exofacial PIP+ apoptotic cells accumulate in tissues of Cd14-/- mice.\",\n      \"method\": \"Unbiased proteomics; anti-PIP antibody and PH-domain probes; CD14 knockout phagocytes; in vivo irradiation model; flow cytometry\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — proteomics discovery plus KO functional assay in vitro and in vivo; identifies specific molecular eat-me signals\",\n      \"pmids\": [\"35017647\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Surfactant protein SP-C interacts directly with CD14 in a dose-dependent manner and facilitates LPS binding to CD14-expressing cells similarly to LBP; LPS blocks SP-C binding to CD14, indicating SP-C and LPS share overlapping binding regions on CD14.\",\n      \"method\": \"Radiolabeled CD14 binding to SP-C-coated wells; LPS competition; fluorescent LPS binding assay on CD14-expressing cells\",\n      \"journal\": \"Infection and immunity\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct binding assay with competition, single lab\",\n      \"pmids\": [\"12496149\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"CD14 expression is induced in tubular epithelial cells (not from infiltrating mononuclear cells) during unilateral ureteral obstruction and ischemia/reperfusion kidney injury; this induction is regulated by TNF-α through TNFR1 (blunted in TNFR1-KO mice); CD14 may promote tubular cell apoptosis via a pathway absent in LPS-hyporesponsive C3H/HeJ mice.\",\n      \"method\": \"RT-PCR; immunocytochemistry; TNFR knockout mice; C3H/HeJ (TLR4-mutant) comparison; apoptosis measurement\",\n      \"journal\": \"Journal of the American Society of Nephrology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse models with defined phenotype; identifies TNFR1-regulated CD14 induction in non-immune cells\",\n      \"pmids\": [\"10966493\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Neutrophil recruitment into the liver sinusoids during endotoxemia is completely CD14-independent (equivalent in wild-type and CD14-KO mice regardless of hematopoietic or non-hematopoietic CD14 expression or soluble CD14), whereas CD14 is required for systemic inflammation (pulmonary neutrophil sequestration, leukopenia, serum cytokines).\",\n      \"method\": \"Dynamic in vivo liver imaging; bone marrow chimeras; CD14-knockout mice; systemic vs. local neutrophil recruitment assays\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — rigorous KO dissection using chimeras and in vivo imaging; clearly defines CD14-independent organ-specific pathway\",\n      \"pmids\": [\"21217012\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"CD14 supports TLR4 endocytosis and the TLR4-TRAM-TRIF signaling pathway upon LPS stimulation; CD14 also transduces a TLR4-independent signaling pathway leading to NFAT transcription factor activation in myeloid cells.\",\n      \"method\": \"Genetic and pharmacological dissection of TLR4 endocytosis; TRIF pathway activation; NFAT reporter assays (reviewed from primary mechanistic studies)\",\n      \"journal\": \"Frontiers in cellular and infection microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — review summarizing mechanistic studies from multiple labs; NFAT pathway described as molecularly defined finding\",\n      \"pmids\": [\"23898465\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"CD14 is part of a receptor complex mediating microglial responses to PrP82-146 (prion), Aβ42 (Alzheimer), and α-synuclein (Parkinson); glimepiride activates GPI-phospholipase C to shed CD14 from macrophages/microglia, reducing TLR4 translocation into membrane rafts and cytokine secretion in response to all these ligands; CD14-KO microglia confirm CD14 dependence.\",\n      \"method\": \"Glimepiride and PI-PLC treatment; ELISA for TNF, IL-1, IL-6; TLR4 raft fractionation; CD14-KO microglial cells; immunoblot\",\n      \"journal\": \"Journal of neuroinflammation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — enzymatic shedding, pharmacological dissection, and KO cells; multiple ligands and readouts\",\n      \"pmids\": [\"24952384\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"CAP18 and CAP11 cathelicidin peptides inhibit LPS binding to CD14+ cells by two mechanisms: binding directly to LPS (competing with LBP-mediated LPS transfer to CD14) and binding directly to cell-surface CD14, thereby blocking FITC-LPS binding and suppressing TNF-α expression.\",\n      \"method\": \"Flow cytometry (FITC-LPS binding); Northern and Western blot for TNF-α; LPS-binding assays; in vivo endotoxin shock model\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct binding competition assays plus in vivo confirmation\",\n      \"pmids\": [\"11544322\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CD14 is a GPI-anchored (in mammals) pattern recognition co-receptor that binds diverse bacterial ligands (LPS, lipopeptides, peptidoglycan, LAM) and endogenous signals (apoptotic cell phosphatidylinositides, amyloid-β, α-synuclein), concentrates these ligands in lipid rafts, catalyzes their transfer to TLR4/MD2 (and differentially to TLR2/TLR1 for lipopeptides), facilitates TLR4 endocytosis and TRAM-TRIF signaling, forms complexes with Gαi1/3 and Gab1 to activate PI3K-Akt, mediates phagocytosis of apoptotic cells and Aβ via distinct ligand-binding regions, and is shed from the membrane in extracellular vesicles via P2X7 receptor activation, with soluble CD14 additionally enabling LPS responses in CD14-deficient or non-myeloid cells.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1988,\n      \"finding\": \"CD14 is anchored to the monocyte plasma membrane via a glycosylphosphatidylinositol (GPI) linkage, as demonstrated by removal of surface CD14 with PI-phospholipase C and absence of CD14 on monocytes from a paroxysmal nocturnal hemoglobinuria patient lacking GPI-anchored proteins; a smaller soluble form lacking the GPI anchor is also secreted.\",\n      \"method\": \"PI-phospholipase C treatment, immunofluorescence of PNH patient monocytes, biosynthetic labeling, SDS-PAGE\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct biochemical cleavage assay with PNH genetic validation, independently replicated\",\n      \"pmids\": [\"3385210\", \"2462937\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1988,\n      \"finding\": \"CD14 maps to chromosome 5q31 in a region encoding myeloid growth factors and receptors, and encodes a myelomonocytic differentiation antigen expressed on monocytes, macrophages, and activated granulocytes.\",\n      \"method\": \"cDNA cloning, genomic mapping, flow cytometry\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cDNA cloning with chromosomal mapping, foundational paper\",\n      \"pmids\": [\"2448876\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1989,\n      \"finding\": \"CD14 cDNA encodes a protein lacking a transmembrane domain, confirmed to be GPI-anchored by PI-PLC release and absence on PNH monocytes; a single mRNA species is abundantly expressed in monocytes and is induced during myeloid differentiation.\",\n      \"method\": \"cDNA library expression cloning, RNA/DNA blot, PI-PLC treatment, PNH patient cells\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution-level biochemistry with genetic (PNH) validation\",\n      \"pmids\": [\"2462937\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"CD14 functions as a receptor for complexes of LPS and LPS-binding protein (LBP): LPS-LBP complexes bind to CD14 on monocyte surfaces, and anti-CD14 monoclonal antibody blockade prevents LPS/LBP-induced TNF-α synthesis.\",\n      \"method\": \"Binding assays with LPS-LBP complexes, anti-CD14 mAb blocking, TNF-α measurement in whole blood\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct binding assay plus functional blockade, highly replicated foundational paper (>3000 citations)\",\n      \"pmids\": [\"1698311\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Transgenic mice expressing human CD14 on monocytes, neutrophils, and lymphocytes are hypersensitive to LPS-induced endotoxin shock, establishing CD14 as a primary mediator of LPS lethality in vivo.\",\n      \"method\": \"Transgenic mouse generation, LPS challenge survival assay, flow cytometry\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo genetic gain-of-function with defined phenotypic readout\",\n      \"pmids\": [\"7681594\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"CD14 on neutrophils in whole blood mediates LPS-induced upregulation of CR3 (CD11b/CD18); anti-CD14 antibodies inhibit this CR3 upregulation, indicating CD14 is the primary neutrophil sensor for LPS.\",\n      \"method\": \"Flow cytometry in whole blood, anti-CD14 mAb inhibition\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional antibody blockade in physiological whole-blood system\",\n      \"pmids\": [\"7684764\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"CD14 acts as a pattern recognition receptor for diverse bacterial envelope components from Gram-negative and Gram-positive bacteria and mycobacteria, initiating cell activation beyond just LPS.\",\n      \"method\": \"Cell activation assays with diverse bacterial ligands, anti-CD14 mAb blocking\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal ligand systems, foundational paper with >500 citations\",\n      \"pmids\": [\"7534618\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"The N-terminal 65 amino acids of CD14, specifically four small regions (including AVEVE, DDED, PQPD, DPRQY), are critical for serum-dependent LPS binding and NF-κB activation; deletion mutants in this region largely abolish LPS receptor function.\",\n      \"method\": \"Deletion mutagenesis in CHO cells, LPS binding assays, NF-κB activation\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis with multiple functional readouts\",\n      \"pmids\": [\"7529231\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Soluble CD14 (recombinant, truncated to N-terminal 152 amino acids) enables LPS activation of CD14-deficient PNH monocytes and endothelial cells, demonstrating that soluble CD14 in serum can substitute for membrane CD14 in LPS signaling.\",\n      \"method\": \"Recombinant soluble CD14, tissue factor and TNF-α assays in CD14-deficient PNH cells and endothelial cells\",\n      \"journal\": \"Journal of laboratory and clinical medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — reconstitution with truncated protein in genetically defined CD14-deficient cells\",\n      \"pmids\": [\"7537790\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"CD14 is a functional cell-activating receptor for bacterial peptidoglycan; the N-terminal 151 amino acids are sufficient for full responsiveness, and similar but not identical sequences within the N-terminal 65 amino acids are critical for responses to both peptidoglycan and LPS.\",\n      \"method\": \"CD14 transfection in 70Z/3 cells, NF-κB activation, IκB-α degradation, IgM expression, deletion mutagenesis\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — transfection plus mutagenesis with multiple functional readouts\",\n      \"pmids\": [\"8798531\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"CD14-deficient mice generated by gene targeting are highly resistant to endotoxin shock from live Gram-negative bacteria or LPS, and also show dramatically reduced bacteremia, revealing an unexpected role for CD14 in bacterial dissemination.\",\n      \"method\": \"Gene targeting in ES cells, LPS/bacterial challenge survival, bacteremia measurement\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — knockout mouse with multiple in vivo phenotypic readouts, >580 citations\",\n      \"pmids\": [\"8612135\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"CD14 mediates recognition and phagocytosis of apoptotic cells by human macrophages; this interaction depends on a region of CD14 that overlaps with the LPS-binding site, yet unlike LPS, apoptotic cells do not provoke pro-inflammatory cytokine release.\",\n      \"method\": \"Anti-CD14 blocking antibodies, phagocytosis assays, cytokine measurement\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — antibody blockade with functional phagocytosis readout, >500 citations\",\n      \"pmids\": [\"9548256\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"CD14 internalizes via macropinocytosis (not clathrin-coated pits or caveolae): CD14 localizes to microfilament-enriched ruffles and large macropinosomes, LPS co-localizes with CD14 in endosomal compartments, and cytochalasin D blocks internalization but not LPS-dependent cell activation, dissociating endocytosis from signaling.\",\n      \"method\": \"Electron microscopy, sucrose density gradient fractionation, confocal microscopy, cytochalasin D inhibition, radiolabeled LPS tracking in GPI and transmembrane CD14 THP-1 transfectants\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal imaging and biochemical methods with functional dissection\",\n      \"pmids\": [\"9685378\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Both GPI-anchored and transmembrane forms of CD14 support LPS-mediated NF-κB activation and cytokine production similarly, indicating GPI anchoring is not required for LPS signaling; however, only GPI-anchored CD14 mediates rapid calcium mobilization upon antibody cross-linking, implicating phospholipase C and protein tyrosine kinases.\",\n      \"method\": \"THP-1 cells stably expressing GPI or transmembrane CD14, NF-κB activation, cytokine ELISA, calcium mobilization assays, pharmacological inhibitors, Triton X-100 fractionation\",\n      \"journal\": \"Infection and immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — isogenic comparison of GPI vs. transmembrane CD14 with multiple readouts\",\n      \"pmids\": [\"9488411\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Distinct CD14 ligands LAM and LPS utilize different TLR proteins for intracellular signaling: CHO/CD14 cells acquire LAM responsiveness only when also engineered to express functional TLR2, while LPS signaling does not require TLR2, establishing a paradigm where a common binding receptor (CD14) pairs with distinct signal-transducing receptors.\",\n      \"method\": \"CHO transfection with CD14 and TLR2, cytokine activation assays, TLR2 overexpression in macrophages\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — epistasis by gain-of-function transfection, replicated in macrophages\",\n      \"pmids\": [\"10586073\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Membrane and soluble forms of CD14 have different structural determinants for LPS receptor function: deletions that abolish LPS binding in membrane CD14 may not affect binding in soluble CD14, yet all five tested deletions ablated soluble CD14 receptor function whereas only two completely destroyed membrane CD14 receptor function.\",\n      \"method\": \"Deletion mutants of CD14 expressed in CHO cells, LPS binding assays, soluble CD14-dependent cellular activation assays\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis comparing membrane and soluble forms\",\n      \"pmids\": [\"10652298\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"LPS cross-links specifically to TLR4 and MD-2 only when CD14 is co-expressed, establishing that LPS is in close proximity to all three members of the tripartite receptor complex (CD14, TLR4, MD-2) and that CD14 is required for LPS transfer to TLR4/MD-2.\",\n      \"method\": \"Transient transfection in HEK293 cells, UV cross-linking with radio-iodinated ASD-LPS, immunoprecipitation\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — photo-crosslinking with reconstituted components identifies direct molecular contacts\",\n      \"pmids\": [\"11274165\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Following LPS stimulation, CD14 forms an activation cluster with heat-shock proteins Hsp70 and Hsp90, chemokine receptor CXCR4, and GDF5, as identified by affinity chromatography and confirmed by FRET, suggesting these proteins serve as the transmembrane signaling components downstream of CD14.\",\n      \"method\": \"Affinity chromatography, peptide mass fingerprinting, fluorescence resonance energy transfer (FRET)\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — FRET confirms molecular proximity; single lab, orthogonal biochemical and biophysical methods\",\n      \"pmids\": [\"11276205\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"LPS traffics rapidly to and from the Golgi apparatus with the TLR4-MD-2-CD14 complex; LPS follows CD14-dependent trafficking pathways in CD14-positive cells, but Golgi-associated TLR4 expression disrupted by brefeldin A does not prevent LPS signaling, indicating signaling is initiated at the plasma membrane.\",\n      \"method\": \"Fluorescent TLR4 expression, confocal microscopy of LPS trafficking, brefeldin A inhibition, MyD88 translocation assays, cross-linking signaling assays\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — live-cell imaging with functional dissection using pharmacological inhibitor\",\n      \"pmids\": [\"12324469\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Human CMV virions are recognized by TLR2 and CD14 to trigger NF-κB-dependent inflammatory cytokine production; both receptors are required for CMV-induced innate immune activation.\",\n      \"method\": \"TLR2/CD14 antibody blocking, dominant-negative TLR constructs, NF-κB reporter assays, cytokine measurement\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple blocking approaches with NF-κB and cytokine readouts, >500 citations\",\n      \"pmids\": [\"12663765\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Lipoteichoic acid from S. pneumoniae and S. aureus activates immune cells via LBP, CD14, and TLR2, but not TLR4/MD-2; LBP catalytically transfers LTA to CD14, and TLR2 transfection in HEK293/CD14 and CHO cells confers LTA responsiveness.\",\n      \"method\": \"PhastGel native gel electrophoresis, HEK293/CHO transfection, cytokine induction assays, anti-CD14/anti-LBP blocking\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — biochemical transfer assay plus epistasis by transfection, >470 citations\",\n      \"pmids\": [\"12594207\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"CD14 interacts directly with Alzheimer's amyloid-β peptide (Aβ42) fibrils and mediates microglial activation; anti-CD14 antibodies and CD14 genetic deficiency significantly reduce amyloid-induced microglial activation and toxicity.\",\n      \"method\": \"FRET/FLIM, antibody neutralization, CD14-knockout cell experiments, flow cytometry, confocal microscopy\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct molecular interaction confirmed by FRET, functional validation with KO and antibody blockade\",\n      \"pmids\": [\"14597556\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Soluble CD14 is produced by the liver as a type 2 acute-phase protein regulated by IL-6: IL-6 stimulates CD14 mRNA and protein production in HepG2 cells and primary hepatocytes, and CD14 mRNA induction during acute-phase response is abolished in IL-6-knockout mice.\",\n      \"method\": \"ELISA, real-time PCR, HepG2 cell stimulation, IL-6 knockout mouse model with turpentine injection\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vitro and in vivo concordant data with genetic KO validation\",\n      \"pmids\": [\"15034063\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"CD14 directly interacts with Aβ42 at nanometer range (confirmed by FRET/FLIM) and mediates phagocytosis of exogenous Aβ42 by primary microglia at sub-inflammatory concentrations in a CD14-dependent manner; CD14 knockout cells fail to internalize Aβ42.\",\n      \"method\": \"Flow cytometry, confocal microscopy, two-photon FLIM-FRET, CD14-deficient microglial cells, phagocytosis assay\",\n      \"journal\": \"Brain\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — FRET-confirmed direct interaction with KO functional validation\",\n      \"pmids\": [\"15857927\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"CD14 determines ligand specificity of the LPS receptor complex: CD14+/+ macrophages show exquisite sensitivity (up to 150,000-fold greater than CD14-/- cells) and structural discrimination between smooth LPS and partial structures, whereas CD14-/- macrophages cannot distinguish LPS structural variants.\",\n      \"method\": \"Comparison of CD14+/+ and CD14-/- macrophage responses to structurally diverse LPS variants, TNF production assays\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO comparison with quantitative dose-response and multiple LPS structures\",\n      \"pmids\": [\"16148141\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Lipopeptide binding to CD14 is the first step in LP recognition; after Pam3CSK4 binding, CD14 and the lipopeptide associate with TLR2/TLR1, and TLR2 is recruited to a low-mobility signaling complex. CD14 enables lipopeptide binding while TLR2 is required for signaling.\",\n      \"method\": \"FRET and FRAP imaging, flow cytometry, confocal microscopy with FLAG-labeled lipopeptide\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — FRET and FRAP confirm molecular proximity and complex formation in intact cells\",\n      \"pmids\": [\"15714590\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Ethanol disrupts LPS-induced lipid raft clustering by altering CD14 partition into lipid rafts; EtOH interferes with IRAK-1 activation and suppresses TLR4-mediated TNF-α production in a manner additive with chemical lipid raft disruptors.\",\n      \"method\": \"Cell fractionation, TNF-α ELISA, IRAK-1 activation assay, methyl-β-cyclodextrin/nystatin comparison\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — fractionation with functional correlation; single lab, mechanistic follow-up limited\",\n      \"pmids\": [\"15896296\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"LPS causes CD14 membrane expression and colocalization with TLR-4 in intestinal enterocytes, and this TLR-4-dependent CD14 upregulation mediates LPS-induced increase in intestinal tight junction permeability both in vitro and in vivo.\",\n      \"method\": \"Caco-2 monolayer transepithelial resistance, mouse intestinal perfusion, TLR-4 KO comparison, confocal colocalization\",\n      \"journal\": \"American Journal of Pathology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vitro and in vivo concordance with genetic (TLR-4 KO) validation\",\n      \"pmids\": [\"23201091\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Gαi1 and Gαi3 form complexes with CD14 and Gab1 in response to LPS, which are required for PI3K-Akt signaling activation; Gαi1/3 deficiency decreases TLR4 endocytosis, reduces IRF3 phosphorylation, causes an M2-like macrophage phenotype with suppressed pro-inflammatory cytokine production, and leads to LPS tolerance in vivo.\",\n      \"method\": \"Co-immunoprecipitation, Gαi1/3 siRNA knockdown in BMDMs, Gαi1/3 KO mice, cytokine ELISA, TLR4 endocytosis assay, IRF3 phosphorylation\",\n      \"journal\": \"PNAS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP with multiple functional KO phenotypes in vitro and in vivo\",\n      \"pmids\": [\"25825741\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CD14 is required for TLR4 endocytosis and thereby for the TRAM-TRIF-dependent signaling pathway activated from early endosomes; without CD14, TLR4 cannot be internalized efficiently, abrogating IFN-β production downstream of TRIF while MyD88-dependent signaling at the plasma membrane is less affected.\",\n      \"method\": \"Review synthesizing CD14 KO, endocytosis assays, TLR4 trafficking studies\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mechanistic dissection of LPS transfer cascade by EM, single-molecule TIRF, and structural determinants\",\n      \"pmids\": [\"27986454\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"A single LPS molecule bound to CD14 is transferred to TLR4-MD2 in a TLR4-dependent manner; LBP binds longitudinally to LPS micelles and catalyzes multi-round LPS transfer to CD14 via electrostatic interactions; CD14 then delivers single LPS molecules to TLR4-MD2 through a defined cascade involving LBP/LPS micelle → CD14/LBP/LPS ternary → CD14-LPS-TLR4-MD2 intermediates.\",\n      \"method\": \"Negative-stain electron microscopy, single-molecule TIRF fluorescence analysis, reconstituted in vitro LPS transfer cascade\",\n      \"journal\": \"BMB reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in vitro cascade with single-molecule resolution and EM structural data\",\n      \"pmids\": [\"28115037\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"P2X7 receptor activation induces release of CD14 from macrophages via extracellular vesicles, reducing plasma membrane CD14 and functionally attenuating LPS-induced (but not monophosphoryl lipid A-induced) pro-inflammatory cytokine production; P2X7 activity is required during murine sepsis to maintain elevated circulating CD14 levels and control bacterial load.\",\n      \"method\": \"Extracellular vesicle isolation, flow cytometry, P2X7 KO mice, cecal ligation/puncture sepsis model, cytokine measurement\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse with multiple in vitro and in vivo phenotypic readouts, mechanistic vesicle analysis\",\n      \"pmids\": [\"33135636\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CD14 governs TLR4 endocytosis and thus the spatiotemporal control of LPS-induced signaling: CD14-driven internalization of TLR4 terminates TIRAP/MyD88-dependent signaling at the plasma membrane while activating the TRAM/TRIF-dependent pathway from early endosomes; subsequent endo-lysosomal trafficking of TLR4 determines the duration and magnitude of TRIF-dependent responses.\",\n      \"method\": \"Review synthesizing CD14 KO, TLR4 endocytosis, TRIF/MyD88 pathway activation assays from multiple studies\",\n      \"journal\": \"Cellular and molecular life sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic synthesis supported by multiple independent KO/trafficking studies\",\n      \"pmids\": [\"33057840\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Externalized phosphatidylinositides (PIPs) on apoptotic cell surfaces are eat-me signals recognized by CD14; masking exofacial PIPs or CD14 knockout in phagocytes blocks phagocytosis of apoptotic cells, and CD14-deficient mice accumulate PIP+ apoptotic cells in tissues.\",\n      \"method\": \"Unbiased proteomics, anti-PI(3,4,5)P3 antibody/PH-domain probes, CD14 KO phagocytes, in vivo irradiation model, flow cytometry\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods in vitro and in vivo with CD14 KO genetic validation\",\n      \"pmids\": [\"35017647\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"CD14 is expressed on Kupffer cells and is functional: LPS induces CD14-dependent intracellular calcium rises and TNF-α mRNA in collagenase-isolated Kupffer cells; Pronase treatment removes surface CD14 and abolishes LPS responses, while PI-PLC cleavage of CD14 blunts calcium signaling.\",\n      \"method\": \"Western blotting, RT-PCR, intracellular calcium measurement, TNF-α mRNA, Pronase vs. collagenase isolation comparison, PI-PLC treatment\",\n      \"journal\": \"American Journal of Physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple biochemical and functional approaches in primary Kupffer cells\",\n      \"pmids\": [\"10070034\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Chicken CD14, unlike its mammalian ortholog, is a transmembrane protein rather than GPI-anchored: it contains a 23-aa transmembrane segment and a cytoplasmic tail, and PI-PLC treatment does not remove chicken CD14 from the cell surface in transfected COS-7 cells.\",\n      \"method\": \"RT-PCR cloning, COS-7 transfection with FLAG-tagged constructs, PI-PLC treatment, flow cytometry\",\n      \"journal\": \"Developmental and comparative immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct biochemical comparison of chicken and human CD14 membrane anchorage\",\n      \"pmids\": [\"18761368\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CD14 is a GPI-anchored (in mammals) pattern recognition co-receptor that binds bacterial LPS, peptidoglycan, lipoteichoic acid, lipopeptides, and apoptotic cell signals (externalized PIPs and phosphatidylserine); it acts as a ligand-delivery/transfer molecule that presents LPS to TLR4/MD-2 (via an LBP→CD14→TLR4-MD2 transfer cascade) and to TLR2/TLR1 or TLR2/TLR6 for other ligands, drives TLR4 endocytosis to activate the TRAM-TRIF signaling pathway from endosomes while terminating the MyD88-dependent pathway at the plasma membrane, forms a signaling complex with Gαi1/3 and Gab1 to activate PI3K-Akt, and can be shed via P2X7-driven extracellular vesicle release to modulate circulating LPS-sensing capacity; a soluble form produced by the liver as an IL-6-regulated acute-phase protein extends CD14-dependent LPS sensing to CD14-low cells such as endothelial cells.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CD14 is a GPI-anchored pattern recognition co-receptor that binds a broad spectrum of microbial ligands—including LPS, peptidoglycan, lipoarabinomannan, and lipopeptides—as well as endogenous danger signals such as amyloid-β, α-synuclein, and phosphatidylinositides on apoptotic cells, and catalyzes their transfer to distinct TLR signaling complexes [PMID:7534618, PMID:28115037, PMID:14597556, PMID:35017647]. The N-terminal leucine-rich repeat region (particularly the first 65 residues) constitutes the principal ligand-binding domain, with overlapping but non-identical determinants for LPS, peptidoglycan, and apoptotic cell recognition; CD14 concentrates in lipid rafts and delivers ligands differentially to TLR4/MD-2 for LPS or TLR2/TLR1 for lipopeptides, while also promoting TLR4 endocytosis and TRAM-TRIF-dependent interferon signaling through a Gαi1/3–Gab1–PI3K–Akt complex [PMID:7529231, PMID:8798531, PMID:10586073, PMID:15714590, PMID:25825741, PMID:23898465]. A soluble form of CD14, released from the membrane by GPI-specific phospholipases or shed in extracellular vesicles via P2X7 receptor activation, confers LPS responsiveness on cells lacking membrane CD14 and modulates systemic inflammation during sepsis; hepatic production of soluble CD14 is upregulated as a type 2 acute-phase protein by IL-6 [PMID:7537790, PMID:33135636, PMID:15034063]. CD14 additionally mediates phagocytic clearance of apoptotic cells by recognizing externalized phosphatidylinositides as eat-me signals and of amyloid-β fibrils by microglia, linking innate immune pattern recognition to both inflammatory activation and non-inflammatory efferocytosis [PMID:9548256, PMID:35017647, PMID:15857927].\",\n  \"teleology\": [\n    {\n      \"year\": 1989,\n      \"claim\": \"Establishing how CD14 is anchored to the membrane resolved the paradox of a signaling receptor lacking a cytoplasmic domain and predicted the need for transmembrane co-receptors.\",\n      \"evidence\": \"cDNA cloning, PI-PLC release from transfected COS cells, absence from PNH monocytes\",\n      \"pmids\": [\"2462937\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the transmembrane signaling partner was unknown\", \"How a GPI-anchored protein could transduce signal remained unresolved\"]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Gain-of-function transgenic and antibody-blocking experiments in vivo established CD14 as the rate-limiting receptor for LPS-induced septic shock, not merely an in vitro binding factor.\",\n      \"evidence\": \"Human CD14 transgenic mice with lethal endotoxin hypersensitivity; anti-CD14 blocking in whole blood neutrophils\",\n      \"pmids\": [\"7681594\", \"7684764\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream signaling cascade was unidentified\", \"Relative contribution of membrane vs. soluble CD14 in vivo was unclear\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Demonstrating CD14 activation by Gram-positive and mycobacterial components, not just LPS, redefined it from an LPS receptor to a broad pattern recognition receptor.\",\n      \"evidence\": \"Cell activation assays with diverse bacterial envelope components; anti-CD14 blocking; CD14-transfected cell lines\",\n      \"pmids\": [\"7534618\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis for multi-ligand recognition was unknown\", \"How one receptor could distinguish multiple ligands was unclear\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Mapping the LPS-binding domain to the N-terminal 65 residues and identifying four critical short motifs provided the first structure-function model for CD14 ligand recognition and explained how soluble CD14 fragments retain activity.\",\n      \"evidence\": \"Site-directed deletion mutagenesis in CHO cells; LPS binding and NF-κB reporter assays; recombinant sCD14 reconstitution on PNH monocytes and endothelial cells\",\n      \"pmids\": [\"7529231\", \"7537790\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Three-dimensional structure was unavailable\", \"Whether the same residues contacted all ligands was unresolved\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Demonstrating that peptidoglycan uses the same N-terminal region but with differential dependence on specific sub-regions established that CD14 discriminates between ligands through overlapping but distinct binding determinants.\",\n      \"evidence\": \"CD14 N-terminal deletion mutants in 70Z/3 cells; NF-κB activation and IκBα degradation comparing PGN vs. LPS\",\n      \"pmids\": [\"8798531\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Biophysical binding constants for different ligands were not determined\", \"No crystal structure of CD14–ligand complexes\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Anti-CD14 antibody protection of primates from endotoxin shock validated CD14 as a therapeutic target and confirmed its non-redundant role in a primate innate immune system.\",\n      \"evidence\": \"Primate endotoxemia model with anti-CD14 mAb pretreatment; cytokine and hemodynamic readouts\",\n      \"pmids\": [\"8833900\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether anti-CD14 would protect from polymicrobial sepsis was untested\", \"Contribution of soluble CD14 to residual signaling was not addressed\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Discovery that CD14 mediates phagocytosis of apoptotic cells without pro-inflammatory cytokine release revealed a dual function: pathogen detection (inflammatory) and efferocytosis (non-inflammatory), using overlapping binding sites.\",\n      \"evidence\": \"Anti-CD14 antibody blocking of apoptotic cell phagocytosis; competition with LPS binding region; cytokine assays on macrophages\",\n      \"pmids\": [\"9548256\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The specific eat-me signal on apoptotic cells was unidentified\", \"How CD14 distinguishes inflammatory from non-inflammatory ligands mechanistically was unknown\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Localization of GPI-anchored CD14 to lipid rafts and demonstration that it internalizes LPS via macropinocytosis—dissociable from NF-κB signaling—established that CD14 has both a signaling and a clearance function.\",\n      \"evidence\": \"Triton X-100 fractionation; EM and confocal imaging of LPS internalization; cytochalasin D pharmacological dissociation of uptake from signaling\",\n      \"pmids\": [\"9685378\", \"9488411\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The endocytic adaptor linking GPI-anchored CD14 to internalization machinery was unidentified\", \"Fate of internalized CD14–LPS complex was not traced\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Showing that CD14 delivers LPS to TLR4 but LAM to TLR2 established the paradigm of CD14 as a shared ligand-binding subunit that sorts microbial products to distinct TLR signaling chains.\",\n      \"evidence\": \"CHO/CD14 cells with TLR2 frameshift mutation; TLR2 transfection rescue; macrophage TLR2 overexpression\",\n      \"pmids\": [\"10586073\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for differential TLR routing was unknown\", \"Whether CD14 contacts TLRs directly or via intermediates was unresolved\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Systematic comparison of membrane and soluble CD14 mutants showed that the two forms use structurally distinct mechanisms for LPS binding and cell activation, explaining why sCD14 can independently confer LPS responses on CD14-negative cells.\",\n      \"evidence\": \"Deletion mutagenesis comparing membrane vs. soluble CD14 for LPS binding and cell activation\",\n      \"pmids\": [\"10652298\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The cell-surface receptor engaged by sCD14–LPS complex on non-myeloid cells was not identified\", \"Conformational differences between membrane and soluble CD14 were not resolved\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Direct binding of CD14 to amyloid-β fibrils expanded CD14's role from microbial recognition to neurodegeneration-associated innate immune activation.\",\n      \"evidence\": \"FRET/FLIM in CD14-transfected CHO cells; CD14-KO microglia; cytokine assays\",\n      \"pmids\": [\"14597556\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Binding site on CD14 for Aβ was unmapped\", \"Whether CD14–Aβ interaction occurs in human brain in vivo was not shown\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Identification of the liver as the source of acute-phase soluble CD14 under IL-6 regulation connected CD14 biology to systemic innate immune amplification beyond myeloid cells.\",\n      \"evidence\": \"IL-6-deficient mouse acute-phase model; HepG2 and primary hepatocyte cultures; ELISA and real-time PCR\",\n      \"pmids\": [\"15034063\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether hepatocyte-derived sCD14 reaches threshold concentrations sufficient to activate distant cells in vivo was not quantified\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"CD14 was shown to confer exquisite ligand specificity—discriminating smooth LPS structures with up to 500-fold sensitivity—and to physically deliver lipopeptides to TLR2/TLR1 complexes, establishing it as the specificity determinant of the TLR system rather than a passive binding protein.\",\n      \"evidence\": \"CD14 KO vs. WT macrophage dose-response with diverse LPS partial structures; FRET and FRAP imaging of CD14–lipopeptide–TLR2/TLR1 complexes\",\n      \"pmids\": [\"16148141\", \"15714590\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How CD14 achieves such fine discrimination at the structural level was unresolved\", \"Whether CD14-dependent specificity extends to all TLR ligands was untested\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"CD14 was found to mediate phagocytic uptake of Aβ42 by microglia at sub-inflammatory concentrations, separating its clearance function from its inflammatory signaling function for amyloid.\",\n      \"evidence\": \"FLIM-FRET; CD14-KO primary microglia; phagocytosis assay with sub-inflammatory Aβ doses\",\n      \"pmids\": [\"15857927\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CD14-mediated Aβ clearance is neuroprotective or neurotoxic in vivo was undetermined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Demonstration that CD14 mediates microglial responses to prion, Aβ, and α-synuclein—and that GPI-phospholipase-mediated shedding of CD14 blocks TLR4 raft translocation—unified the neurodegenerative ligand story and identified a pharmacological intervention point.\",\n      \"evidence\": \"Glimepiride and PI-PLC treatment; TLR4 raft fractionation; CD14-KO microglia; cytokine ELISAs for multiple neurotoxic ligands\",\n      \"pmids\": [\"24952384\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo efficacy of CD14 shedding agents in neurodegenerative disease models was not tested\", \"Relative contribution of CD14 vs. other co-receptors for α-synuclein was unquantified\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Discovery that Gαi1/3 form a complex with CD14 and Gab1 to activate PI3K-Akt and drive TLR4 endocytosis revealed the long-sought mechanism by which a GPI-anchored receptor couples to intracellular signaling and endocytic trafficking.\",\n      \"evidence\": \"Co-immunoprecipitation; Gαi1/3 knockdown in BMDMs; PI3K-Akt, IRF3 phosphorylation; macrophage polarization assays; in vivo LPS tolerance model\",\n      \"pmids\": [\"25825741\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How a GPI-anchored protein physically recruits Gαi on the cytoplasmic face was not structurally resolved\", \"Whether the Gαi–CD14 complex also forms with non-LPS ligands was untested\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Single-molecule reconstitution of the LBP→CD14→TLR4/MD-2 LPS transfer cascade defined CD14 as a catalytic shuttle that repeatedly extracts single LPS molecules from micelles, establishing the biophysical basis of signal amplification.\",\n      \"evidence\": \"Negative-stain EM; single-molecule TIRF; reconstituted in vitro LPS transfer cascade\",\n      \"pmids\": [\"28115037\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinetic rate constants for each transfer step in cellular membranes were not measured\", \"Whether CD14 catalytic cycling is regulated post-translationally was unknown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"P2X7 receptor-driven shedding of CD14 in extracellular vesicles was identified as a feedback mechanism that attenuates macrophage LPS responses and modulates sepsis severity, explaining how circulating CD14 levels are dynamically regulated.\",\n      \"evidence\": \"Extracellular vesicle isolation; P2X7-deficient murine sepsis model; cytokine assays\",\n      \"pmids\": [\"33135636\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism linking P2X7 ion channel opening to CD14-containing vesicle budding was uncharacterized\", \"Whether this mechanism operates for non-LPS CD14 ligands was untested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identification of externalized phosphatidylinositides as the specific eat-me signals recognized by CD14 on apoptotic cells resolved a 24-year-old question about the molecular identity of the apoptotic cell ligand.\",\n      \"evidence\": \"Unbiased proteomics; anti-PIP antibodies and PH-domain probes; CD14-KO phagocytes; in vivo irradiation model\",\n      \"pmids\": [\"35017647\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which PIP species (PI(4,5)P2, PI(3,4,5)P3, etc.) is the dominant eat-me signal was not fully resolved\", \"Structural basis of CD14–PIP interaction is unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A high-resolution structure of CD14 in complex with its diverse ligands (LPS, PIPs, Aβ) and with TLR4/MD-2 remains unavailable, leaving the molecular basis of multi-ligand recognition and differential TLR routing unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No atomic-resolution co-crystal or cryo-EM structure of CD14–ligand or CD14–TLR complexes\", \"Mechanism by which CD14 routes ligands to TLR4 vs. TLR2 is inferred but not structurally defined\", \"Whether CD14-dependent NFAT activation proceeds through an identified signaling intermediate remains open\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [4, 7, 14, 20, 23, 25]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [3, 12, 19]},\n      {\"term_id\": \"GO:0038024\", \"supporting_discovery_ids\": [23, 19]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 10, 21]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [24]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [5, 17, 24]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [1, 3, 6, 12, 20, 22, 29]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [10, 22, 29]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [8, 25]}\n    ],\n    \"complexes\": [\n      \"TLR4/MD-2/CD14\",\n      \"Gαi1/3–CD14–Gab1\"\n    ],\n    \"partners\": [\n      \"TLR4\",\n      \"TLR2\",\n      \"TLR1\",\n      \"GNAI1\",\n      \"GNAI3\",\n      \"GAB1\",\n      \"LBP\",\n      \"P2RX7\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"CD14 is a GPI-anchored pattern recognition co-receptor on monocytes, macrophages, and neutrophils that serves as the primary sensor and transfer molecule for bacterial lipopolysaccharide (LPS), peptidoglycan, lipoteichoic acid, lipopeptides, and apoptotic cell-derived phosphatidylinositides, coupling ligand capture to activation of distinct Toll-like receptor signaling pathways [PMID:1698311, PMID:7534618, PMID:35017647]. The N-terminal leucine-rich region binds LPS–LBP complexes and transfers individual LPS molecules to TLR4/MD-2 via a defined LBP→CD14→TLR4-MD2 cascade, while presenting other microbial ligands to TLR2/TLR1 or TLR2/TLR6; CD14 additionally drives TLR4 endocytosis, thereby terminating MyD88-dependent signaling at the plasma membrane and initiating the TRAM-TRIF pathway from endosomes [PMID:28115037, PMID:27986454, PMID:10586073]. A soluble form produced by hepatocytes as an IL-6-regulated acute-phase protein extends LPS sensing to CD14-low cells such as endothelial cells, while P2X7-dependent shedding of CD14 on extracellular vesicles modulates macrophage LPS responsiveness during sepsis [PMID:15034063, PMID:33135636]. CD14 also mediates non-inflammatory phagocytosis of apoptotic cells by recognizing externalized phosphatidylinositides and phosphatidylserine, and participates in microglial recognition and phagocytosis of amyloid-β fibrils [PMID:9548256, PMID:35017647, PMID:15857927].\",\n  \"teleology\": [\n    {\n      \"year\": 1988,\n      \"claim\": \"Establishing the membrane topology of CD14 resolved how a differentiation antigen lacking a transmembrane domain is surface-expressed: via a GPI linkage, with a smaller soluble isoform also produced.\",\n      \"evidence\": \"PI-phospholipase C cleavage, PNH patient monocytes lacking GPI-anchored proteins, cDNA cloning and SDS-PAGE\",\n      \"pmids\": [\"3385210\", \"2462937\", \"2448876\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Three-dimensional structure of CD14 not yet determined\", \"Mechanism of soluble CD14 generation (proteolytic vs. secretory) not resolved\"]\n    },\n    {\n      \"year\": 1990,\n      \"claim\": \"Identifying CD14 as the receptor for LPS–LBP complexes established the molecular basis of monocyte endotoxin sensing, answering how picomolar LPS concentrations activate innate immunity.\",\n      \"evidence\": \"Direct LPS-LBP binding assays on monocytes, anti-CD14 mAb blockade of TNF-α production\",\n      \"pmids\": [\"1698311\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signal transduction mechanism downstream of a GPI-anchored protein unknown\", \"Identity of transmembrane signaling partner not yet identified\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Demonstrating that CD14 recognizes diverse Gram-positive and mycobacterial envelope components beyond LPS expanded it from an LPS receptor to a broad pattern recognition receptor.\",\n      \"evidence\": \"Cell activation assays with peptidoglycan, LTA, mycobacterial products; anti-CD14 blocking\",\n      \"pmids\": [\"7534618\", \"8798531\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for multi-ligand binding not determined\", \"Which downstream signaling receptors pair with CD14 for non-LPS ligands unknown\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Mapping the LPS-binding determinants to four short motifs within the N-terminal 65 residues defined the functional domain architecture and showed that soluble CD14 fragments (152 aa) can reconstitute LPS signaling on CD14-deficient cells.\",\n      \"evidence\": \"Systematic deletion mutagenesis in CHO cells, NF-κB and LPS binding assays, reconstitution on PNH monocytes and endothelial cells\",\n      \"pmids\": [\"7529231\", \"7537790\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-resolution structure of CD14 N-terminal domain–LPS interaction not available\", \"Determinants distinguishing membrane vs. soluble CD14 function not fully resolved\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"CD14 knockout mice proved CD14 is required for lethal endotoxin shock in vivo and unexpectedly revealed a role in bacterial dissemination, validating CD14 as a central innate immune gatekeeper.\",\n      \"evidence\": \"Gene-targeted CD14−/− mice challenged with LPS and live Gram-negative bacteria\",\n      \"pmids\": [\"8612135\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How CD14 promotes bacterial dissemination mechanistically was not defined\", \"Relative contributions of membrane vs. soluble CD14 in vivo not dissected\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Discovering that CD14 mediates phagocytosis of apoptotic cells without provoking inflammation revealed a dual function — pathogen sensing and silent corpse clearance — through an overlapping but non-identical binding site.\",\n      \"evidence\": \"Anti-CD14 blocking antibodies, macrophage phagocytosis assays, cytokine measurement\",\n      \"pmids\": [\"9548256\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific apoptotic cell ligand recognized by CD14 not identified at this point\", \"Structural basis for anti-inflammatory vs. pro-inflammatory outcome unknown\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Showing that CD14-dependent LAM signaling requires TLR2 while LPS signaling does not established the paradigm of CD14 as a shared ligand-capture receptor that routes different PAMPs to distinct TLR signaling complexes.\",\n      \"evidence\": \"CHO/CD14 transfection with TLR2, differential cytokine activation for LAM vs. LPS\",\n      \"pmids\": [\"10586073\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism by which CD14 hands off ligands to specific TLRs not defined\", \"Role of co-receptors MD-1/MD-2 in this routing not addressed\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"UV cross-linking of LPS to TLR4/MD-2 only in the presence of CD14 demonstrated that CD14 is required for physical LPS transfer to TLR4-MD2, defining the tripartite receptor complex.\",\n      \"evidence\": \"HEK293 reconstitution, radio-iodinated ASD-LPS UV cross-linking, immunoprecipitation\",\n      \"pmids\": [\"11274165\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and kinetics of the transfer reaction not measured\", \"Whether CD14 remains in the complex after LPS transfer or dissociates was unclear\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Quantitative comparison of CD14+/+ and CD14−/− macrophages revealed that CD14 confers up to 150,000-fold sensitivity enhancement and structural discrimination among LPS variants, establishing CD14 as the specificity determinant of the LPS receptor.\",\n      \"evidence\": \"Dose-response TNF production with structurally diverse LPS variants in WT vs. CD14 KO macrophages\",\n      \"pmids\": [\"16148141\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for CD14's discriminatory capacity unresolved\", \"Whether soluble CD14 can restore full discrimination in CD14−/− cells not tested\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identification of Gαi1/3–CD14–Gab1 complexes revealed a G-protein-coupled signaling axis linking CD14 to PI3K-Akt activation, TLR4 endocytosis, and IRF3-dependent interferon production.\",\n      \"evidence\": \"Co-immunoprecipitation, Gαi1/3 siRNA knockdown and KO mice, TLR4 endocytosis and IRF3 phosphorylation assays\",\n      \"pmids\": [\"25825741\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Gαi proteins bind CD14 directly or through an intermediary adapter not established\", \"Structural basis of GPI-anchored CD14 coupling to heterotrimeric G proteins unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Reconstitution of the entire LBP→CD14→TLR4-MD2 LPS transfer cascade at single-molecule resolution defined the mechanism: LBP binds longitudinally to LPS micelles and catalytically loads single LPS monomers onto CD14, which then delivers them to TLR4-MD2.\",\n      \"evidence\": \"Negative-stain EM, single-molecule TIRF fluorescence, in vitro reconstituted cascade\",\n      \"pmids\": [\"28115037\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"High-resolution cryo-EM structure of CD14–LPS intermediate not available\", \"Whether CD14 undergoes conformational change upon LPS binding is unresolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Two advances resolved how CD14 controls the spatiotemporal switch between TLR4 signaling pathways and how macrophages regulate their own CD14 levels: CD14 drives TLR4 endocytosis to activate TRAM-TRIF while terminating TIRAP-MyD88 signaling, and P2X7-driven vesicular shedding of CD14 attenuates LPS responsiveness during sepsis.\",\n      \"evidence\": \"CD14 KO with TLR4 trafficking assays; P2X7 KO mice in cecal ligation-puncture sepsis model; extracellular vesicle analysis\",\n      \"pmids\": [\"33057840\", \"33135636\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular trigger linking CD14 engagement to the endocytic machinery not identified\", \"How P2X7-shed CD14-bearing vesicles function systemically — as decoys or as soluble CD14 equivalents — is not resolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identification of externalized phosphatidylinositides as the specific eat-me signal recognized by CD14 on apoptotic cells resolved a two-decade-old question about CD14's non-inflammatory ligand in efferocytosis.\",\n      \"evidence\": \"Unbiased proteomics, anti-PIP masking, CD14 KO phagocytes, in vivo irradiation model\",\n      \"pmids\": [\"35017647\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Binding affinity and structural basis of CD14–PIP interaction not defined\", \"Whether CD14-dependent efferocytosis uses the same N-terminal domain as LPS binding is unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A high-resolution structure of CD14 bound to LPS or phosphatidylinositides, and the molecular mechanism by which GPI-anchored CD14 engages heterotrimeric G proteins and the endocytic machinery to drive TLR4 internalization, remain undefined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No atomic-resolution structure of CD14 in complex with any ligand\", \"Mechanism coupling GPI-anchored CD14 to Gαi and endocytic machinery unresolved\", \"Relative in vivo contributions of membrane-anchored vs. soluble vs. vesicular CD14 in sepsis and efferocytosis not quantified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [3, 7, 9, 20, 24, 25, 30, 33]},\n      {\"term_id\": \"GO:0038024\", \"supporting_discovery_ids\": [16, 25, 29, 30]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [3, 6, 14, 20]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [14, 25, 29]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 2, 12, 13, 25, 26, 27]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 8, 22, 31]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [12, 31]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [12, 29, 32]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [3, 4, 6, 10, 14, 16, 19, 20, 24, 25, 28, 29, 30, 32]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [13, 28, 29, 32]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [11, 33]}\n    ],\n    \"complexes\": [\n      \"TLR4/MD-2/CD14\",\n      \"TLR2/CD14\",\n      \"LBP/CD14/LPS\"\n    ],\n    \"partners\": [\n      \"TLR4\",\n      \"MD2\",\n      \"LBP\",\n      \"TLR2\",\n      \"GNAI1\",\n      \"GNAI3\",\n      \"GAB1\",\n      \"P2RX7\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}