{"gene":"TLR5","run_date":"2026-04-28T21:42:59","timeline":{"discoveries":[{"year":2012,"finding":"Crystal structure of zebrafish TLR5 in complex with Salmonella flagellin FliC D1/D2/D3 fragment at 2.47 Å resolution revealed that TLR5 interacts primarily with the three helices of the FliC D1 domain using its lateral side, and two TLR5-FliC 1:1 heterodimers assemble into a 2:2 tail-to-tail signaling complex stabilized by quaternary contacts of the FliC D1 domain with the convex surface of the opposing TLR5. Structure-guided mutagenesis and deletion analyses validated the signaling mechanism.","method":"Crystal structure (2.47 Å) + structure-guided mutagenesis and deletion analyses","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with mutagenesis validation in a single rigorous study","pmids":["22344444"],"is_preprint":false},{"year":2017,"finding":"Crystal structure of Bacillus subtilis flagellin (bsflagellin)–TLR5 complex at 2.1 Å resolution combined with alanine scanning identified a conserved hot spot in flagellin for TLR5 activation: an arginine residue (bsflagellin R89) and adjacent residues (E114 and L93) in the D1 domain provide shape and chemical complementarity to a cavity formed by the loop of leucine-rich repeat 9 in TLR5. The D0 domain also contributes to TLR5 activity through structurally dispersed regions.","method":"Crystal structure (2.1 Å) + alanine scanning mutagenesis of binding interface","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with systematic alanine scanning, orthogonal validation","pmids":["28106112"],"is_preprint":false},{"year":1998,"finding":"Cloning of human TLR5 (designated TIL4) demonstrated that overexpression activates NF-κB in a cell-type-dependent fashion, establishing that TLR5 signals through the NF-κB pathway.","method":"Cloning, Northern blot tissue distribution, NF-κB reporter assay in transfected cells","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 — functional NF-κB activation in transfected cells, single lab","pmids":["9596645"],"is_preprint":false},{"year":2004,"finding":"Flagellin activates NF-κB via TLR5 and also activates the MAPK, SAPK, and IKK signaling pathways in intestinal epithelial cells. Dominant-negative TLR5 alleles partially block flagellin-induced NF-κB activation, and exogenous TLR5 expression in non-responsive cells confers flagellin responsiveness, indicating TLR5 is necessary but that additional co-factors may be required for full signal propagation.","method":"Dominant-negative TLR5 overexpression, exogenous TLR5 expression in non-responsive cell lines, pathway kinase assays","journal":"BMC microbiology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple signaling pathway assays with DN constructs, single lab","pmids":["15324458"],"is_preprint":false},{"year":2004,"finding":"Commensal E. coli flagellin triggers NF-κB activation and proinflammatory chemokine (IL-8, CCL20) production in intestinal epithelial cells via TLR5 and the adaptor protein MyD88, as demonstrated by dominant-negative TLR5 and MyD88 constructs. In polarized epithelial cells, TLR5 mediates signaling from the apical surface in vivo.","method":"Dominant-negative TLR5 and MyD88 transfection, NF-κB reporter, Ussing chamber ex vivo, immunohistochemistry","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (DN constructs + ex vivo + in vivo localization), replicated concept across labs","pmids":["15302888"],"is_preprint":false},{"year":2003,"finding":"TLR5-mediated flagellin recognition activates p38 MAPK in a TLR5-dependent manner in polarized intestinal epithelia, and p38 MAPK pharmacological inhibition reduces IL-8 protein expression independently of NF-κB, indicating that TLR5 signals through a p38-dependent posttranscriptional mechanism to regulate IL-8 mRNA translation.","method":"Pharmacological p38 inhibition (SB-203580), phosphorylation assays, NF-κB reporter, mRNA stability assay","journal":"American journal of physiology. Gastrointestinal and liver physiology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple biochemical methods in single lab establishing TLR5-p38-IL-8 axis","pmids":["12702497"],"is_preprint":false},{"year":2007,"finding":"TLR5 deletion in mice results in spontaneous colitis characterized by decreased intestinal expression of TLR5-regulated host defense genes, elevated colonic bacterial burden, and increased hematopoietic-derived proinflammatory cytokines. Deletion of TLR4 rescues colitis in TLR5KO mice, demonstrating genetic epistasis: TLR4 drives colitis downstream of TLR5 deficiency.","method":"TLR5 knockout mouse model, TLR4/TLR5 double-knockout epistasis, histopathology, cytokine measurement, bacterial load quantification","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined phenotype and genetic epistasis (double-KO rescue), replicated across multiple indicators","pmids":["18008007"],"is_preprint":false},{"year":2005,"finding":"Flagellin-TLR5 interaction activates both proinflammatory (NF-κB, PI3K/Akt) and apoptotic (caspase 8 extrinsic pathway) signaling in epithelial cells. When NF-κB or PI3K/Akt is blocked, flagellin induces programmed cell death. Caspase 8 activation by purified flagellin is TLR5-dependent.","method":"Biochemical signaling assays, mRNA expression profiling, pharmacological inhibition of NF-κB and PI3K, caspase activation assays with TLR5-dependent controls","journal":"American journal of physiology. Gastrointestinal and liver physiology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal assays (caspase, NF-κB, PI3K), single lab","pmids":["16179598"],"is_preprint":false},{"year":2007,"finding":"Chicken TLR5 (chTLR5) signals through MyD88 to activate NF-κB upon flagellin recognition. Mutagenesis of proline 737 in the chTLR5 TIR domain abrogated chTLR5 function, confirming TIR-domain-dependent MyD88 signaling. A single amino acid substitution (Q89A) in Salmonella Typhimurium flagellin abolished the species-specific TLR5 response.","method":"Targeted TIR domain mutagenesis, flagellin mutagenesis (Q89A), NF-κB reporter, confocal microscopy for expression","journal":"Molecular immunology","confidence":"Medium","confidence_rationale":"Tier 1–2 — site-directed mutagenesis of both receptor and ligand with functional readout","pmids":["17964652"],"is_preprint":false},{"year":2007,"finding":"Protein kinase D (PKD) directly interacts with TLR5 (co-immunoprecipitation), and this association is rapidly enhanced by flagellin. PKD phosphorylates TLR5 at serine 805 (identified by mass spectrometry); S805A mutation abrogates flagellin responses. PKD inhibition reduces IL-8 expression and prevents flagellin-induced p38 MAPK activation. shRNA-mediated PKD knockdown confirmed its role in p38-mediated IL-8 response to flagellin.","method":"Co-immunoprecipitation, mass spectrometry phospho-site identification, site-directed mutagenesis (S805A), pharmacological inhibition, shRNA knockdown","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1 — in vitro phosphorylation + MS site ID + mutagenesis + Co-IP + shRNA, multiple orthogonal methods in single study","pmids":["17442957"],"is_preprint":false},{"year":2010,"finding":"TRIF (TIR domain containing adaptor-inducing IFN-β) induces proteolytic degradation of TLR5 protein via caspase activity, requiring the C-terminus of TRIF and the extracellular domain of TLR5. TRIF overexpression abolishes TLR5 protein levels without altering TLR5 mRNA, and dramatically suppresses flagellin/TLR5-driven NF-κB activation. This represents a post-translational regulatory mechanism for TLR5.","method":"TRIF overexpression, pan-caspase inhibitor rescue, domain deletion constructs (C-terminus of TRIF, extracellular domain TLR5), mRNA vs protein quantification","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — mechanistic dissection with domain mutants and pharmacological rescue, single lab","pmids":["20452988"],"is_preprint":false},{"year":2012,"finding":"MUC1 cytoplasmic tail associates with TLR5 in airway epithelial cells (HEK293T, A549, primary cells). EGFR activation by TGF-α phosphorylates the MUC1 cytoplasmic tail at Y46EKV, increasing MUC1/TLR5 association and competitively inhibiting MyD88 recruitment to TLR5, thereby suppressing downstream NF-κB and MAPK signaling. MUC1 overexpression inhibits flagellin-induced TLR5/MyD88 association.","method":"Co-immunoprecipitation, site-directed analysis of MUC1-CT phosphorylation, MyD88 overexpression rescue, in vivo immunofluorescence colocalization","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP + functional phospho-mutagenesis + in vivo validation, multiple orthogonal methods","pmids":["22250084"],"is_preprint":false},{"year":2015,"finding":"P. aeruginosa and flagellin activate EGFR in primary NHBE cells, leading to TGF-α release and EGFR-dependent tyrosine phosphorylation of the MUC1 cytoplasmic tail and increased MUC1-CT/TLR5 association, confirmed by co-immunoprecipitation.","method":"Co-immunoprecipitation of MUC1-CT with TLR5 and EGFR, ELISA for TGF-α, immunoblotting for EGFR phosphorylation","journal":"Inflammation research","confidence":"Medium","confidence_rationale":"Tier 3 — Co-IP in primary cells confirming prior mechanism, single lab","pmids":["26645913"],"is_preprint":false},{"year":2016,"finding":"HMGB1 binds TLR5 and activates NF-κB signaling in a MyD88-dependent manner, resulting in proinflammatory cytokine production. The C-terminal tail region of HMGB1 is essential for TLR5 interaction. HMGB1-TLR5 signaling causes pain hypersensitivity in vivo.","method":"Biophysical binding assays, in vitro NF-κB reporter with MyD88 requirement, in vivo pain behavioral assays in TLR5-expressing cells","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 — biophysical + functional assays + in vivo, identifying HMGB1 as a novel TLR5 ligand","pmids":["27760316"],"is_preprint":false},{"year":2006,"finding":"Flagellin activates both TLR5 (NF-κB pathway) and the cell surface glycolipid asialoGM1. TLR5/Toll signaling is required for the release of ATP, and extracellular ATP is then required for Erk1/2 activation downstream of TLR5 — revealing that TLR5-induced Erk1/2 activation depends on autocrine nucleotide signaling through the asialoGM1 pathway.","method":"Pharmacological inhibition of lipid rafts vs. clathrin, ATP release assays, Erk1/2 phosphorylation assays, NF-κB reporter","journal":"American journal of respiratory cell and molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple pathway inhibitors defining TLR5-ATP-Erk1/2 interdependence, single lab","pmids":["16439799"],"is_preprint":false},{"year":2010,"finding":"TLR5 functions as an endocytic receptor on dendritic cells to enhance MHC class-II presentation of flagellin epitopes to CD4+ T cells, independent of MyD88. This was demonstrated using TLR5-deficient mice that failed to expand flagellin-specific CD4+ T cells even with additional TLR agonists, whereas processed flagellin peptide restored T-cell responses.","method":"TLR5-KO mouse immunization, MyD88-KO mice, in vitro DC flagellin presentation assay, adoptive T-cell transfer","journal":"European journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO + in vitro DC system establishing MyD88-independent antigen presentation function","pmids":["21182074"],"is_preprint":false},{"year":2010,"finding":"TLR5 signals through STAT1 to induce IFN-β production in bone marrow-derived macrophages upon flagellin stimulation. IFN-β then suppresses c-Fos protein expression and inhibits RANKL-induced osteoclastogenesis. STAT1 deficiency or JAK2 inhibition abolished flagellin-induced IFN-β and the anti-osteoclastogenic effect.","method":"IFN-β neutralizing antibody, STAT1 KO macrophages, JAK2 inhibitor, c-Fos western blot, osteoclast differentiation assay","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 — genetic (STAT1 KO) and pharmacological dissection of TLR5→STAT1→IFN-β→c-Fos pathway","pmids":["18209032"],"is_preprint":false},{"year":2008,"finding":"TLR5 activation by flagellin induces RANKL expression in osteoblasts via MyD88 and NF-κB, leading to robust osteoclast formation and bone loss both in vitro and in vivo. These effects were absent in Tlr5-/- mice.","method":"TLR5 KO mice, osteoblast/bone marrow culture, in vivo calvarial injection of flagellin, RANKL mRNA quantification","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 — KO mouse + in vitro/in vivo assays defining TLR5→MyD88→NF-κB→RANKL→osteoclast axis","pmids":["26207027"],"is_preprint":false},{"year":2009,"finding":"Direct stimulation of TLR5-expressing CD11c+ dendritic cells is required for the adjuvant activity of flagellin-OVA fusion protein. Using bone marrow chimeras and diphtheria toxin-mediated depletion, mice with TLR5-/- DC showed dramatically reduced antigen-specific CD4+ T cell responses. The adjuvant effect requires TLR5-MyD88 signaling as well as enhanced antigen uptake via TLR5.","method":"Bone marrow chimera mice, diphtheria toxin DC depletion, adoptive CD4+ T cell transfer, MyD88-/- TLR5+/+ mice","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — bone marrow chimera + DT depletion + genetic knockouts, multiple orthogonal approaches identifying DC-intrinsic TLR5 requirement","pmids":["19494277"],"is_preprint":false},{"year":2009,"finding":"Intestinal CD11c+ lamina propria dendritic cells (LPDCs) specifically express TLR5 but not TLR4, and respond to pathogenic flagellated bacteria to induce IgA+ plasma cell differentiation and Th17/Th1 cell differentiation. Transport of Salmonella from intestinal tract to mesenteric lymph nodes was impaired in Tlr5-/- mice, suggesting LPDCs expressing TLR5 are exploited by S. typhimurium for systemic spread.","method":"TLR5 KO mouse infection model, LPDC subset characterization, B cell/T cell differentiation assays","journal":"Journal of gastroenterology","confidence":"Medium","confidence_rationale":"Tier 2 — KO mouse + cellular subset identification defining specialized TLR5+ LPDC function","pmids":["19547909"],"is_preprint":false},{"year":2010,"finding":"Flagellin-induced promotion of humoral immunity requires either TLR5 (activating NF-κB) or NLRC4 (activating the inflammasome). In TLR5/NLRC4 double-KO mice, all flagellin-induced cytokines and antibody responses were absent, demonstrating genetic epistasis: both receptors act in parallel to drive adaptive immunity to flagellin.","method":"TLR5 KO, NLRC4 KO, and TLR5/NLRC4 double-KO mice, cytokine measurement (KC/CXCL1, IL-18), antibody response measurement","journal":"European journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — clean double-KO epistasis with multiple genetic backgrounds and cytokine/antibody readouts","pmids":["21072873"],"is_preprint":false},{"year":2014,"finding":"TLR5 activation by flagellin on dendritic cells induces IL-22 production, which drives a protective gene expression program in intestinal epithelial cells against rotavirus. NLRC4 activation by flagellin induces IL-18 and immediate elimination of RV-infected cells. Both TLR5 and NLRC4 are required for flagellin-mediated protection, and administration of IL-22 + IL-18 fully recapitulates flagellin protection.","method":"TLR5 KO, NLRC4 KO mice, cytokine neutralization/administration, adaptive immunity-independent model","journal":"Science","confidence":"High","confidence_rationale":"Tier 2 — clean KO models + cytokine reconstitution experiments, mechanistically dissecting TLR5→DC→IL-22 pathway","pmids":["25395539"],"is_preprint":false},{"year":2010,"finding":"TLR5 activation by flagellin induces secretory IL-1 receptor antagonist (sIL-1Ra) in intestinal epithelial cells and macrophages in a TLR5-dependent manner on non-hematopoietic cells. In TLR5KO mice, loss of sIL-1Ra increases the IL-1β/sIL-1Ra ratio, correlating with increased inflammatory pathology on flagellin treatment and Salmonella infection.","method":"TLR5 KO mice, bone marrow chimeras to distinguish hematopoietic vs. non-hematopoietic TLR5, cytokine ELISA, in vivo infection model","journal":"Mucosal immunology","confidence":"Medium","confidence_rationale":"Tier 2 — chimera experiments identifying epithelial cell-intrinsic TLR5 function in sIL-1Ra induction","pmids":["20844479"],"is_preprint":false},{"year":2008,"finding":"TLR5 is stored intracellularly in neutrophils and mobilized to the cell surface in a protein synthesis-independent manner through protein kinase C activation, or after stimulation with TLR ligands and cytokines. TLR1/TLR2 signaling via Pam3CSK4 is the most potent inducer of surface TLR5 expression. TLR5 surface mobilization enhances neutrophil phagocytic capacity and respiratory burst activity via IL-8/CXCR1 signaling.","method":"Confocal microscopy, flow cytometry, protein kinase C inhibitors, TLR1/TLR2 antibody blocking experiments, neutrophil functional assays","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple methods defining intracellular storage and TLR1/2-mediated surface mobilization of TLR5 in neutrophils","pmids":["18684966"],"is_preprint":false},{"year":2020,"finding":"TLR5 physically associates with TLR4 in primary murine macrophages (co-immunoprecipitation) and biases TLR4 signaling toward the MyD88-dependent pathway. In vivo, TLR5 deficiency reduces responses to LPS, hyaluronan, and ozone (TLR4-mediated stimuli). Human carriers of a dominant-negative TLR5 allele show decreased inflammatory responses to LPS and ozone.","method":"Co-immunoprecipitation of TLR5 with TLR4, in vivo TLR5 KO mouse models (LPS, O3, hyaluronan), human dominant-negative TLR5 allele carrier ex vivo studies","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — Co-IP evidence + multiple in vivo models + human genetic validation, multiple orthogonal approaches","pmids":["31989925"],"is_preprint":false},{"year":2019,"finding":"H. pylori T4SS component CagL contains a flagellin D1-like motif that activates TLR5 in a flagellin-independent manner. CagL mediates adherence to TLR5+ epithelial cells and activates downstream TLR5 signaling. TLR5 KO mice show reduced control of H. pylori infection.","method":"In vitro TLR5 activation assays, TLR5 KO mouse infection model, human biopsy analysis","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro mechanistic assays + KO mouse model, single lab","pmids":["31844047"],"is_preprint":false},{"year":2018,"finding":"Zebrafish TLR5 unexpectedly signals as a heterodimer composed of drTLR5b and drTLR5a gene products, not as a homodimer. Flagellin-induced signaling by the zebrafish heterodimer is enhanced by the TLR trafficking chaperone UNC93B1. TLR5 activation requires a heterodimeric configuration of both the ectodomain and cytoplasmic domain. Structure-guided substitution of the principal flagellin-binding site in human TLR5 with zebrafish TLR5 residues abrogated human TLR5 activation.","method":"Genetic domain-swap experiments (ectodomain and TIR domain swaps), UNC93B1 co-expression, structure-guided mutagenesis of human TLR5 flagellin-binding site","journal":"PNAS","confidence":"High","confidence_rationale":"Tier 1–2 — structure-guided mutagenesis + domain-swap epistasis + chaperone dependency, rigorous mechanistic dissection","pmids":["29555749"],"is_preprint":false},{"year":2018,"finding":"NME3 (nucleoside diphosphate kinase 3) is a positive regulator of TLR5-induced NF-κB signaling, acting mechanistically downstream of MyD88. Identified via genome-wide siRNA kinase library screen; confirmed by targeted knockdown and overexpression in carcinoma cells with NF-κB bioluminescent reporter.","method":"High-throughput siRNA kinase library screen, targeted knockdown and overexpression validation, NF-κB bioluminescent reporter, MyD88 epistasis","journal":"Molecular cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — screen + targeted KD/OE validation with pathway placement (downstream of MyD88)","pmids":["29523766"],"is_preprint":false},{"year":2006,"finding":"TLR5 stop codon polymorphism R392X and missense variants D694G and L822F are functionally relevant, abrogating flagellin-induced TLR5 signaling in transfected CHO-K1 cells. The common R392X (11.9% prevalence) acts as a dominant-negative allele.","method":"Transient transfection of TLR5 SNP variants in CHO-K1 cells, NF-κB reporter assay upon flagellin stimulation","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 2 — systematic functional characterization of multiple SNPs with defined readout","pmids":["16470719"],"is_preprint":false},{"year":2020,"finding":"TLR5 activation by flagellin in hepatocytes stimulates ApoA1 production through transcriptional activation via NF-κB binding to the Apoa1 promoter. Hepatic TLR5 overexpression in TLR5-KO mice partially restored ApoA1 and HDL-C levels, confirming liver-cell-intrinsic TLR5 signaling in ApoA1/HDL metabolism.","method":"TLR5 KO mice, hepatic TLR5 overexpression rescue, NF-κB ChIP on Apoa1 promoter, primary hepatocyte stimulation, oral flagellin supplementation in Apoe-/- mice","journal":"Circulation research","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP + KO rescue + primary cell experiments, single lab","pmids":["32820707"],"is_preprint":false},{"year":2013,"finding":"TLR5-mediated flagellin signaling in intestinal epithelial cells induces Notch1 and Jagged1 expression, and Notch1 synergistically enhances TLR5-mediated NF-κB activation via RBP-Jκ-dependent mechanism. Blocking Notch during acute colitis ameliorated inflammation, revealing a TLR5-Notch crosstalk in intestinal epithelium.","method":"Luciferase reporter assay for NF-κB, γ-secretase inhibitor, in vitro RBP-Jκ responsive element analysis of IL-6 promoter, in vivo Notch blocking in colitis model","journal":"International journal of molecular medicine","confidence":"Low","confidence_rationale":"Tier 3 — mechanistic reporter assays but single lab with limited orthogonal validation","pmids":["24048326"],"is_preprint":false},{"year":2009,"finding":"IL-8 induction by flagellin in A549 human alveolar epithelial cells requires lipid raft formation (inhibited by nystatin but not clathrin inhibitor chlorpromazine) and activation of intracellular TLR5, as TLR5 was found predominantly in the intracellular compartment of A549 cells rather than on the cell surface.","method":"Lipid raft inhibition (nystatin), clathrin inhibition (chlorpromazine), confocal microscopy for TLR5 subcellular localization, transient transfection NF-κB reporter","journal":"Molecular immunology","confidence":"Medium","confidence_rationale":"Tier 2 — direct subcellular localization with functional consequence via lipid raft inhibition","pmids":["19786303"],"is_preprint":false},{"year":2014,"finding":"Flagellin-induced TLR5 signaling activates NF-κB in myometrium via MyD88/TRAF6/NF-κB pathway. siRNA knockdown of TLR5, MyD88, or TRAF6 decreased flagellin-induced pro-inflammatory cytokines (IL-6, IL-8), MMP-9, COX-2, and prostaglandin release in human fetal membranes and myometrium.","method":"siRNA knockdown of TLR5, MyD88, TRAF6 in primary human cells; NF-κB luciferase reporter; ELISA cytokine measurement","journal":"American journal of reproductive immunology","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA KD of multiple pathway components in primary human tissue, single lab","pmids":["24635133"],"is_preprint":false},{"year":2021,"finding":"α-Synuclein monomers and oligomers activate the NLRP3 inflammasome in microglia via TLR5 (among other receptors). TLR5 ligation by α-synuclein contributes to NLRP3 activation at a distinct signaling checkpoint, and NLRP3 inhibition or deficiency improved α-synuclein clearance.","method":"Primary microglia from WT mice, TLR5 receptor involvement tested alongside TLR2, NLRP3 inhibitor (CRID3), NLRP3 KO mice, internalization and degradation assays","journal":"Journal of immunology","confidence":"Low","confidence_rationale":"Tier 3 — TLR5 involvement inferred from receptor ligation without specific TLR5 KO controls; single lab","pmids":["34507948"],"is_preprint":false}],"current_model":"TLR5 is a pattern recognition receptor that detects bacterial flagellin (and endogenous ligands such as HMGB1) through its lateral surface, primarily via the flagellin D1 domain, forming a 2:2 tail-to-tail signaling complex that recruits MyD88 and activates NF-κB, p38 MAPK, and other downstream pathways; TLR5 is phosphorylated at S805 by protein kinase D, its signaling is negatively regulated by MUC1 (which competes for MyD88 binding) and by TRIF-induced caspase-mediated proteolytic degradation, it physically associates with TLR4 to bias MyD88-dependent signaling, it functions as an endocytic receptor on dendritic cells to enhance antigen presentation to CD4+ T cells, and it drives innate immune responses in distinct cell types including intestinal epithelial cells, dendritic cells, macrophages, neutrophils, and hepatocytes to control gut homeostasis, osteoclastogenesis, ApoA1 production, and antimicrobial defense."},"narrative":{"teleology":[{"year":1998,"claim":"Cloning of human TLR5 and demonstration that its overexpression activates NF-κB established it as a signaling-competent Toll-like receptor, but its ligand and physiological role were unknown.","evidence":"Cloning, Northern blot, NF-κB reporter assay in transfected cells","pmids":["9596645"],"confidence":"Medium","gaps":["Ligand not yet identified","Adaptor usage unknown","In vivo relevance not demonstrated"]},{"year":2004,"claim":"Identification of flagellin as the TLR5 ligand and demonstration that signaling proceeds through MyD88 to activate NF-κB, MAPK, and SAPK pathways in intestinal epithelial cells established TLR5 as the principal flagellin sensor at mucosal surfaces.","evidence":"Dominant-negative TLR5 and MyD88 constructs, exogenous TLR5 expression in non-responsive cells, pathway kinase assays, polarized epithelial Ussing chamber ex vivo experiments","pmids":["15324458","15302888"],"confidence":"High","gaps":["Structural basis of flagellin recognition unknown","Downstream signal branching not resolved","Co-factor requirements suggested but not identified"]},{"year":2005,"claim":"Discovery that TLR5 simultaneously activates pro-survival (NF-κB, PI3K/Akt) and pro-apoptotic (caspase-8) pathways revealed that TLR5 signaling outcome depends on the balance of parallel downstream cascades.","evidence":"Pharmacological inhibition of NF-κB and PI3K, caspase activation assays with TLR5-dependent controls","pmids":["16179598"],"confidence":"Medium","gaps":["Physiological context determining survival vs. death choice unclear","Mechanism linking TLR5 to caspase-8 not defined"]},{"year":2007,"claim":"Identification of protein kinase D as a direct TLR5 interactor that phosphorylates S805 to enable p38-dependent IL-8 production provided the first post-translational regulatory mechanism for TLR5 activation.","evidence":"Co-immunoprecipitation, mass spectrometry phospho-site identification, S805A mutagenesis, shRNA knockdown of PKD","pmids":["17442957"],"confidence":"High","gaps":["Whether S805 phosphorylation is required in all cell types unknown","Kinase(s) responsible for dephosphorylation not identified"]},{"year":2007,"claim":"TLR5-knockout mice developed spontaneous colitis rescued by concurrent TLR4 deletion, establishing TLR5 as essential for intestinal immune homeostasis and revealing genetic epistasis between TLR5 and TLR4.","evidence":"TLR5 KO and TLR4/TLR5 double-KO mice, histopathology, cytokine and bacterial load measurement","pmids":["18008007"],"confidence":"High","gaps":["Cell type(s) in which TLR5 loss drives pathology not resolved","Whether TLR5-TLR4 epistasis reflects direct physical interaction unknown at this time"]},{"year":2009,"claim":"Demonstration that DC-intrinsic TLR5 is required for flagellin adjuvant activity and that intestinal lamina propria DCs selectively express TLR5 to drive IgA, Th17, and Th1 responses established TLR5 as a key bridge between innate and adaptive mucosal immunity.","evidence":"Bone marrow chimera mice, diphtheria toxin DC depletion, TLR5-KO infection models, adoptive CD4+ T cell transfer","pmids":["19494277","19547909"],"confidence":"High","gaps":["How TLR5+ LPDC subset is specified developmentally unknown","Whether DC TLR5 signals differently from epithelial TLR5 not resolved"]},{"year":2010,"claim":"Three parallel advances defined negative regulation of TLR5 (TRIF-induced caspase-dependent degradation), a MyD88-independent endocytic antigen-presentation function, and cooperation with NLRC4 for full flagellin-driven adaptive immunity.","evidence":"TRIF overexpression with caspase inhibitor rescue and domain deletions; TLR5-KO DC presentation assays with MyD88-KO controls; TLR5/NLRC4 double-KO mice with antibody response measurement","pmids":["20452988","21182074","21072873"],"confidence":"Medium","gaps":["Identity of the caspase(s) mediating TLR5 degradation not established","Structural basis of MyD88-independent endocytic function unknown","Relative contributions of TLR5 vs. NLRC4 in different tissues not quantified"]},{"year":2012,"claim":"Crystal structure of the TLR5–flagellin complex revealed a 2:2 tail-to-tail signaling architecture in which TLR5 engages the D1 domain helices via its lateral surface, providing the atomic basis for ligand recognition and dimerization-induced activation.","evidence":"2.47 Å crystal structure of zebrafish TLR5–FliC complex with structure-guided mutagenesis and deletion validation","pmids":["22344444"],"confidence":"High","gaps":["Human TLR5 structure not yet solved","How dimerization transmits signal across the membrane not determined"]},{"year":2012,"claim":"Discovery that MUC1 cytoplasmic tail competes with MyD88 for TLR5 binding upon EGFR-mediated phosphorylation defined a receptor-proximal negative regulatory mechanism linking growth factor and innate immune signaling.","evidence":"Reciprocal co-immunoprecipitation, MUC1-CT phospho-mutagenesis, MyD88 overexpression rescue, in vivo immunofluorescence","pmids":["22250084"],"confidence":"High","gaps":["Whether MUC1 regulation of TLR5 operates in cell types beyond airway epithelia unknown","Stoichiometry of MUC1-TLR5 vs. MyD88-TLR5 complexes not defined"]},{"year":2016,"claim":"Identification of the endogenous danger molecule HMGB1 as a TLR5 ligand that activates MyD88-dependent NF-κB signaling expanded the TLR5 ligand repertoire beyond microbial flagellin to include sterile inflammation mediators.","evidence":"Biophysical binding assays, NF-κB reporter with MyD88 requirement, in vivo pain behavioral assays in TLR5-expressing tissues","pmids":["27760316"],"confidence":"Medium","gaps":["Structural basis of HMGB1-TLR5 interaction not determined","Whether HMGB1-TLR5 signaling contributes to sterile inflammatory diseases in vivo not established"]},{"year":2017,"claim":"A higher-resolution Bacillus flagellin–TLR5 structure combined with alanine scanning identified a conserved hot spot (R89/E114/L93) fitting into TLR5 LRR9, refining the molecular pharmacophore for receptor activation.","evidence":"2.1 Å crystal structure with systematic alanine scanning mutagenesis","pmids":["28106112"],"confidence":"High","gaps":["Whether the hot spot is targetable pharmacologically unknown","Contribution of the D0 domain to activation mechanism remains structurally unresolved"]},{"year":2020,"claim":"Demonstration that TLR5 physically associates with TLR4 and biases TLR4 signaling toward MyD88 in macrophages, validated by human carriers of dominant-negative TLR5, resolved the earlier genetic epistasis and established TLR5 as a co-receptor modulating TLR4 responses.","evidence":"Co-immunoprecipitation of TLR5-TLR4, TLR5-KO mouse models challenged with LPS/ozone/hyaluronan, human TLR5 R392X carrier ex vivo studies","pmids":["31989925"],"confidence":"High","gaps":["Whether TLR5-TLR4 heterodimer forms constitutively or is ligand-induced unclear","Structural basis of heterodimerization not solved"]},{"year":2020,"claim":"TLR5 signaling in hepatocytes drives ApoA1 transcription via NF-κB binding to the Apoa1 promoter, revealing a non-immune metabolic function for TLR5 in HDL biogenesis.","evidence":"TLR5-KO mice, hepatic TLR5 overexpression rescue, NF-κB ChIP on Apoa1 promoter, primary hepatocyte stimulation","pmids":["32820707"],"confidence":"Medium","gaps":["Whether gut microbiota-derived flagellin is the physiological hepatic TLR5 stimulus in humans not established","Contribution relative to other ApoA1 transcriptional regulators unknown"]},{"year":null,"claim":"Key open questions include the full-length human TLR5 structure (no solved structure exists), the mechanism of transmembrane signal transmission from ectodomain dimerization to TIR domain MyD88 recruitment, the structural basis of TLR5-TLR4 heterodimerization, and whether TLR5 endogenous ligands (HMGB1, α-synuclein) contribute to sterile inflammatory diseases in vivo.","evidence":"","pmids":[],"confidence":"Low","gaps":["Full-length human TLR5 structure not solved","Transmembrane signaling mechanism not established","Physiological relevance of non-flagellin ligands in disease contexts unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,1,2,3,4,13]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[4,11,24]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[4,23,24]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[15,31]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[23,31]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[2,3,4,6,18,19,20,21]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,5,7,9,14,16,27]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[7,10]}],"complexes":["TLR5 homodimer (2:2 with flagellin)","TLR5-TLR4 heteromeric complex"],"partners":["MYD88","PRKD1","MUC1","TRAF6","TLR4","UNC93B1","HMGB1"],"other_free_text":[]},"mechanistic_narrative":"TLR5 is an innate immune pattern recognition receptor that senses bacterial flagellin and endogenous danger signals to activate pro-inflammatory and adaptive immune responses across epithelial barriers, dendritic cells, macrophages, neutrophils, and hepatocytes. Structural studies show that TLR5 recognizes the conserved D1 domain of flagellin via its lateral leucine-rich repeat surface, assembling a 2:2 tail-to-tail signaling complex that recruits the adaptor MyD88 through its TIR domain, activating NF-κB, p38 MAPK, PI3K/Akt, and STAT1 signaling cascades [PMID:22344444, PMID:15302888, PMID:17442957, PMID:18209032]. TLR5 signaling is positively regulated by protein kinase D-mediated phosphorylation at S805 and negatively regulated by MUC1 cytoplasmic tail competition for MyD88 binding and by TRIF-induced caspase-dependent proteolytic degradation of TLR5 protein [PMID:17442957, PMID:22250084, PMID:20452988]. Beyond innate immunity, TLR5 functions as a MyD88-independent endocytic receptor on dendritic cells that enhances MHC class II antigen presentation to CD4+ T cells, physically associates with TLR4 to bias MyD88-dependent signaling, and drives tissue-specific programs including intestinal homeostasis, osteoclast regulation, and hepatic ApoA1/HDL production [PMID:21182074, PMID:31989925, PMID:18008007, PMID:32820707]."},"prefetch_data":{"uniprot":{"accession":"O60602","full_name":"Toll-like receptor 5","aliases":["Toll/interleukin-1 receptor-like protein 3"],"length_aa":858,"mass_kda":97.8,"function":"Pattern recognition receptor (PRR) located on the cell surface that participates in the activation of innate immunity and inflammatory response (PubMed:11323673, PubMed:18490781). Recognizes small molecular motifs named pathogen-associated molecular pattern (PAMPs) expressed by pathogens and microbe-associated molecular patterns (MAMPs) usually expressed by resident microbiota (PubMed:29934223). Upon ligand binding such as bacterial flagellins, recruits intracellular adapter proteins MYD88 and TRIF leading to NF-kappa-B activation, cytokine secretion and induction of the inflammatory response (PubMed:11489966, PubMed:20855887). Plays thereby an important role in the relationship between the intestinal epithelium and enteric microbes and contributes to the gut microbiota composition throughout life (By similarity)","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/O60602/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TLR5","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/TLR5","total_profiled":1310},"omim":[{"mim_id":"615592","title":"IMMUNODEFICIENCY 15B; IMD15B","url":"https://www.omim.org/entry/615592"},{"mim_id":"615557","title":"MELIOIDOSIS, SUSCEPTIBILITY TO","url":"https://www.omim.org/entry/615557"},{"mim_id":"609948","title":"RING FINGER PROTEIN 216; RNF216","url":"https://www.omim.org/entry/609948"},{"mim_id":"608556","title":"LEGIONNAIRE DISEASE, SUSCEPTIBILITY TO","url":"https://www.omim.org/entry/608556"},{"mim_id":"607955","title":"SAM- AND SH3 DOMAIN-CONTAINING PROTEIN 1; SASH1","url":"https://www.omim.org/entry/607955"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Golgi apparatus","reliability":"Approved"},{"location":"Nucleoplasm","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/TLR5"},"hgnc":{"alias_symbol":["TIL3","FLJ10052","MGC126430","MGC126431"],"prev_symbol":["SLEB1"]},"alphafold":{"accession":"O60602","domains":[{"cath_id":"3.80.10.10","chopping":"20-173","consensus_level":"medium","plddt":95.1865,"start":20,"end":173},{"cath_id":"3.80.10.10","chopping":"183-339","consensus_level":"medium","plddt":94.3876,"start":183,"end":339},{"cath_id":"3.40.50.10140","chopping":"696-838","consensus_level":"high","plddt":87.7782,"start":696,"end":838}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O60602","model_url":"https://alphafold.ebi.ac.uk/files/AF-O60602-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O60602-F1-predicted_aligned_error_v6.png","plddt_mean":88.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TLR5","jax_strain_url":"https://www.jax.org/strain/search?query=TLR5"},"sequence":{"accession":"O60602","fasta_url":"https://rest.uniprot.org/uniprotkb/O60602.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O60602/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O60602"}},"corpus_meta":[{"pmid":"22344444","id":"PMC_22344444","title":"Structural basis of TLR5-flagellin recognition and signaling.","date":"2012","source":"Science (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/22344444","citation_count":451,"is_preprint":false},{"pmid":"18008007","id":"PMC_18008007","title":"Deletion of TLR5 results in spontaneous colitis in mice.","date":"2007","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/18008007","citation_count":351,"is_preprint":false},{"pmid":"18063235","id":"PMC_18063235","title":"Potent immunogenicity and efficacy of a universal influenza vaccine candidate comprising a recombinant fusion protein linking influenza M2e to the TLR5 ligand flagellin.","date":"2007","source":"Vaccine","url":"https://pubmed.ncbi.nlm.nih.gov/18063235","citation_count":304,"is_preprint":false},{"pmid":"9596645","id":"PMC_9596645","title":"Cloning and characterization of two Toll/Interleukin-1 receptor-like genes TIL3 and TIL4: evidence for a multi-gene receptor family in humans.","date":"1998","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/9596645","citation_count":182,"is_preprint":false},{"pmid":"25395539","id":"PMC_25395539","title":"Viral infection. 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cooperative interactions between TLR5 and NLRC4 in protective lung mucosal immunity against Pseudomonas aeruginosa.","date":"2014","source":"Journal of innate immunity","url":"https://pubmed.ncbi.nlm.nih.gov/25402425","citation_count":25,"is_preprint":false},{"pmid":"28126263","id":"PMC_28126263","title":"Treponema pallidum flagellins elicit proinflammatory cytokines from human monocytes via TLR5 signaling pathway.","date":"2017","source":"Immunobiology","url":"https://pubmed.ncbi.nlm.nih.gov/28126263","citation_count":25,"is_preprint":false},{"pmid":"19473567","id":"PMC_19473567","title":"Investigation of TLR5 and TLR7 as candidate genes for susceptibility to systemic lupus erythematosus.","date":"2009","source":"Clinical and experimental rheumatology","url":"https://pubmed.ncbi.nlm.nih.gov/19473567","citation_count":25,"is_preprint":false},{"pmid":"24879439","id":"PMC_24879439","title":"Recombinant TLR5 agonist CBLB502 promotes NK cell-mediated anti-CMV immunity in 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[et al.]","url":"https://pubmed.ncbi.nlm.nih.gov/26645913","citation_count":20,"is_preprint":false},{"pmid":"27351455","id":"PMC_27351455","title":"Diabetic pregnancy activates the innate immune response through TLR5 or TLR1/2 on neonatal monocyte.","date":"2016","source":"Journal of reproductive immunology","url":"https://pubmed.ncbi.nlm.nih.gov/27351455","citation_count":20,"is_preprint":false},{"pmid":"32849665","id":"PMC_32849665","title":"Escape of TLR5 Recognition by Leptospira spp.: A Rationale for Atypical Endoflagella.","date":"2020","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/32849665","citation_count":19,"is_preprint":false},{"pmid":"28202909","id":"PMC_28202909","title":"Leukocyte TLR5 deficiency inhibits atherosclerosis by reduced macrophage recruitment and defective T-cell responsiveness.","date":"2017","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/28202909","citation_count":19,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":54547,"output_tokens":8862,"usd":0.148285},"stage2":{"model":"claude-opus-4-6","input_tokens":12828,"output_tokens":3600,"usd":0.23121},"total_usd":0.379495,"stage1_batch_id":"msgbatch_01RPbVc9PDH9zQmYK5Hs6srm","stage2_batch_id":"msgbatch_01JVbVLzeKN2yVrsGp3zC8aM","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2012,\n      \"finding\": \"Crystal structure of zebrafish TLR5 in complex with Salmonella flagellin FliC D1/D2/D3 fragment at 2.47 Å resolution revealed that TLR5 interacts primarily with the three helices of the FliC D1 domain using its lateral side, and two TLR5-FliC 1:1 heterodimers assemble into a 2:2 tail-to-tail signaling complex stabilized by quaternary contacts of the FliC D1 domain with the convex surface of the opposing TLR5. Structure-guided mutagenesis and deletion analyses validated the signaling mechanism.\",\n      \"method\": \"Crystal structure (2.47 Å) + structure-guided mutagenesis and deletion analyses\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with mutagenesis validation in a single rigorous study\",\n      \"pmids\": [\"22344444\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Crystal structure of Bacillus subtilis flagellin (bsflagellin)–TLR5 complex at 2.1 Å resolution combined with alanine scanning identified a conserved hot spot in flagellin for TLR5 activation: an arginine residue (bsflagellin R89) and adjacent residues (E114 and L93) in the D1 domain provide shape and chemical complementarity to a cavity formed by the loop of leucine-rich repeat 9 in TLR5. The D0 domain also contributes to TLR5 activity through structurally dispersed regions.\",\n      \"method\": \"Crystal structure (2.1 Å) + alanine scanning mutagenesis of binding interface\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with systematic alanine scanning, orthogonal validation\",\n      \"pmids\": [\"28106112\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Cloning of human TLR5 (designated TIL4) demonstrated that overexpression activates NF-κB in a cell-type-dependent fashion, establishing that TLR5 signals through the NF-κB pathway.\",\n      \"method\": \"Cloning, Northern blot tissue distribution, NF-κB reporter assay in transfected cells\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional NF-κB activation in transfected cells, single lab\",\n      \"pmids\": [\"9596645\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Flagellin activates NF-κB via TLR5 and also activates the MAPK, SAPK, and IKK signaling pathways in intestinal epithelial cells. Dominant-negative TLR5 alleles partially block flagellin-induced NF-κB activation, and exogenous TLR5 expression in non-responsive cells confers flagellin responsiveness, indicating TLR5 is necessary but that additional co-factors may be required for full signal propagation.\",\n      \"method\": \"Dominant-negative TLR5 overexpression, exogenous TLR5 expression in non-responsive cell lines, pathway kinase assays\",\n      \"journal\": \"BMC microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple signaling pathway assays with DN constructs, single lab\",\n      \"pmids\": [\"15324458\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Commensal E. coli flagellin triggers NF-κB activation and proinflammatory chemokine (IL-8, CCL20) production in intestinal epithelial cells via TLR5 and the adaptor protein MyD88, as demonstrated by dominant-negative TLR5 and MyD88 constructs. In polarized epithelial cells, TLR5 mediates signaling from the apical surface in vivo.\",\n      \"method\": \"Dominant-negative TLR5 and MyD88 transfection, NF-κB reporter, Ussing chamber ex vivo, immunohistochemistry\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (DN constructs + ex vivo + in vivo localization), replicated concept across labs\",\n      \"pmids\": [\"15302888\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"TLR5-mediated flagellin recognition activates p38 MAPK in a TLR5-dependent manner in polarized intestinal epithelia, and p38 MAPK pharmacological inhibition reduces IL-8 protein expression independently of NF-κB, indicating that TLR5 signals through a p38-dependent posttranscriptional mechanism to regulate IL-8 mRNA translation.\",\n      \"method\": \"Pharmacological p38 inhibition (SB-203580), phosphorylation assays, NF-κB reporter, mRNA stability assay\",\n      \"journal\": \"American journal of physiology. Gastrointestinal and liver physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple biochemical methods in single lab establishing TLR5-p38-IL-8 axis\",\n      \"pmids\": [\"12702497\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"TLR5 deletion in mice results in spontaneous colitis characterized by decreased intestinal expression of TLR5-regulated host defense genes, elevated colonic bacterial burden, and increased hematopoietic-derived proinflammatory cytokines. Deletion of TLR4 rescues colitis in TLR5KO mice, demonstrating genetic epistasis: TLR4 drives colitis downstream of TLR5 deficiency.\",\n      \"method\": \"TLR5 knockout mouse model, TLR4/TLR5 double-knockout epistasis, histopathology, cytokine measurement, bacterial load quantification\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined phenotype and genetic epistasis (double-KO rescue), replicated across multiple indicators\",\n      \"pmids\": [\"18008007\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Flagellin-TLR5 interaction activates both proinflammatory (NF-κB, PI3K/Akt) and apoptotic (caspase 8 extrinsic pathway) signaling in epithelial cells. When NF-κB or PI3K/Akt is blocked, flagellin induces programmed cell death. Caspase 8 activation by purified flagellin is TLR5-dependent.\",\n      \"method\": \"Biochemical signaling assays, mRNA expression profiling, pharmacological inhibition of NF-κB and PI3K, caspase activation assays with TLR5-dependent controls\",\n      \"journal\": \"American journal of physiology. Gastrointestinal and liver physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal assays (caspase, NF-κB, PI3K), single lab\",\n      \"pmids\": [\"16179598\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Chicken TLR5 (chTLR5) signals through MyD88 to activate NF-κB upon flagellin recognition. Mutagenesis of proline 737 in the chTLR5 TIR domain abrogated chTLR5 function, confirming TIR-domain-dependent MyD88 signaling. A single amino acid substitution (Q89A) in Salmonella Typhimurium flagellin abolished the species-specific TLR5 response.\",\n      \"method\": \"Targeted TIR domain mutagenesis, flagellin mutagenesis (Q89A), NF-κB reporter, confocal microscopy for expression\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — site-directed mutagenesis of both receptor and ligand with functional readout\",\n      \"pmids\": [\"17964652\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Protein kinase D (PKD) directly interacts with TLR5 (co-immunoprecipitation), and this association is rapidly enhanced by flagellin. PKD phosphorylates TLR5 at serine 805 (identified by mass spectrometry); S805A mutation abrogates flagellin responses. PKD inhibition reduces IL-8 expression and prevents flagellin-induced p38 MAPK activation. shRNA-mediated PKD knockdown confirmed its role in p38-mediated IL-8 response to flagellin.\",\n      \"method\": \"Co-immunoprecipitation, mass spectrometry phospho-site identification, site-directed mutagenesis (S805A), pharmacological inhibition, shRNA knockdown\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro phosphorylation + MS site ID + mutagenesis + Co-IP + shRNA, multiple orthogonal methods in single study\",\n      \"pmids\": [\"17442957\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"TRIF (TIR domain containing adaptor-inducing IFN-β) induces proteolytic degradation of TLR5 protein via caspase activity, requiring the C-terminus of TRIF and the extracellular domain of TLR5. TRIF overexpression abolishes TLR5 protein levels without altering TLR5 mRNA, and dramatically suppresses flagellin/TLR5-driven NF-κB activation. This represents a post-translational regulatory mechanism for TLR5.\",\n      \"method\": \"TRIF overexpression, pan-caspase inhibitor rescue, domain deletion constructs (C-terminus of TRIF, extracellular domain TLR5), mRNA vs protein quantification\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic dissection with domain mutants and pharmacological rescue, single lab\",\n      \"pmids\": [\"20452988\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"MUC1 cytoplasmic tail associates with TLR5 in airway epithelial cells (HEK293T, A549, primary cells). EGFR activation by TGF-α phosphorylates the MUC1 cytoplasmic tail at Y46EKV, increasing MUC1/TLR5 association and competitively inhibiting MyD88 recruitment to TLR5, thereby suppressing downstream NF-κB and MAPK signaling. MUC1 overexpression inhibits flagellin-induced TLR5/MyD88 association.\",\n      \"method\": \"Co-immunoprecipitation, site-directed analysis of MUC1-CT phosphorylation, MyD88 overexpression rescue, in vivo immunofluorescence colocalization\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP + functional phospho-mutagenesis + in vivo validation, multiple orthogonal methods\",\n      \"pmids\": [\"22250084\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"P. aeruginosa and flagellin activate EGFR in primary NHBE cells, leading to TGF-α release and EGFR-dependent tyrosine phosphorylation of the MUC1 cytoplasmic tail and increased MUC1-CT/TLR5 association, confirmed by co-immunoprecipitation.\",\n      \"method\": \"Co-immunoprecipitation of MUC1-CT with TLR5 and EGFR, ELISA for TGF-α, immunoblotting for EGFR phosphorylation\",\n      \"journal\": \"Inflammation research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — Co-IP in primary cells confirming prior mechanism, single lab\",\n      \"pmids\": [\"26645913\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"HMGB1 binds TLR5 and activates NF-κB signaling in a MyD88-dependent manner, resulting in proinflammatory cytokine production. The C-terminal tail region of HMGB1 is essential for TLR5 interaction. HMGB1-TLR5 signaling causes pain hypersensitivity in vivo.\",\n      \"method\": \"Biophysical binding assays, in vitro NF-κB reporter with MyD88 requirement, in vivo pain behavioral assays in TLR5-expressing cells\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — biophysical + functional assays + in vivo, identifying HMGB1 as a novel TLR5 ligand\",\n      \"pmids\": [\"27760316\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Flagellin activates both TLR5 (NF-κB pathway) and the cell surface glycolipid asialoGM1. TLR5/Toll signaling is required for the release of ATP, and extracellular ATP is then required for Erk1/2 activation downstream of TLR5 — revealing that TLR5-induced Erk1/2 activation depends on autocrine nucleotide signaling through the asialoGM1 pathway.\",\n      \"method\": \"Pharmacological inhibition of lipid rafts vs. clathrin, ATP release assays, Erk1/2 phosphorylation assays, NF-κB reporter\",\n      \"journal\": \"American journal of respiratory cell and molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple pathway inhibitors defining TLR5-ATP-Erk1/2 interdependence, single lab\",\n      \"pmids\": [\"16439799\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"TLR5 functions as an endocytic receptor on dendritic cells to enhance MHC class-II presentation of flagellin epitopes to CD4+ T cells, independent of MyD88. This was demonstrated using TLR5-deficient mice that failed to expand flagellin-specific CD4+ T cells even with additional TLR agonists, whereas processed flagellin peptide restored T-cell responses.\",\n      \"method\": \"TLR5-KO mouse immunization, MyD88-KO mice, in vitro DC flagellin presentation assay, adoptive T-cell transfer\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO + in vitro DC system establishing MyD88-independent antigen presentation function\",\n      \"pmids\": [\"21182074\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"TLR5 signals through STAT1 to induce IFN-β production in bone marrow-derived macrophages upon flagellin stimulation. IFN-β then suppresses c-Fos protein expression and inhibits RANKL-induced osteoclastogenesis. STAT1 deficiency or JAK2 inhibition abolished flagellin-induced IFN-β and the anti-osteoclastogenic effect.\",\n      \"method\": \"IFN-β neutralizing antibody, STAT1 KO macrophages, JAK2 inhibitor, c-Fos western blot, osteoclast differentiation assay\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic (STAT1 KO) and pharmacological dissection of TLR5→STAT1→IFN-β→c-Fos pathway\",\n      \"pmids\": [\"18209032\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"TLR5 activation by flagellin induces RANKL expression in osteoblasts via MyD88 and NF-κB, leading to robust osteoclast formation and bone loss both in vitro and in vivo. These effects were absent in Tlr5-/- mice.\",\n      \"method\": \"TLR5 KO mice, osteoblast/bone marrow culture, in vivo calvarial injection of flagellin, RANKL mRNA quantification\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse + in vitro/in vivo assays defining TLR5→MyD88→NF-κB→RANKL→osteoclast axis\",\n      \"pmids\": [\"26207027\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Direct stimulation of TLR5-expressing CD11c+ dendritic cells is required for the adjuvant activity of flagellin-OVA fusion protein. Using bone marrow chimeras and diphtheria toxin-mediated depletion, mice with TLR5-/- DC showed dramatically reduced antigen-specific CD4+ T cell responses. The adjuvant effect requires TLR5-MyD88 signaling as well as enhanced antigen uptake via TLR5.\",\n      \"method\": \"Bone marrow chimera mice, diphtheria toxin DC depletion, adoptive CD4+ T cell transfer, MyD88-/- TLR5+/+ mice\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — bone marrow chimera + DT depletion + genetic knockouts, multiple orthogonal approaches identifying DC-intrinsic TLR5 requirement\",\n      \"pmids\": [\"19494277\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Intestinal CD11c+ lamina propria dendritic cells (LPDCs) specifically express TLR5 but not TLR4, and respond to pathogenic flagellated bacteria to induce IgA+ plasma cell differentiation and Th17/Th1 cell differentiation. Transport of Salmonella from intestinal tract to mesenteric lymph nodes was impaired in Tlr5-/- mice, suggesting LPDCs expressing TLR5 are exploited by S. typhimurium for systemic spread.\",\n      \"method\": \"TLR5 KO mouse infection model, LPDC subset characterization, B cell/T cell differentiation assays\",\n      \"journal\": \"Journal of gastroenterology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse + cellular subset identification defining specialized TLR5+ LPDC function\",\n      \"pmids\": [\"19547909\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Flagellin-induced promotion of humoral immunity requires either TLR5 (activating NF-κB) or NLRC4 (activating the inflammasome). In TLR5/NLRC4 double-KO mice, all flagellin-induced cytokines and antibody responses were absent, demonstrating genetic epistasis: both receptors act in parallel to drive adaptive immunity to flagellin.\",\n      \"method\": \"TLR5 KO, NLRC4 KO, and TLR5/NLRC4 double-KO mice, cytokine measurement (KC/CXCL1, IL-18), antibody response measurement\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean double-KO epistasis with multiple genetic backgrounds and cytokine/antibody readouts\",\n      \"pmids\": [\"21072873\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"TLR5 activation by flagellin on dendritic cells induces IL-22 production, which drives a protective gene expression program in intestinal epithelial cells against rotavirus. NLRC4 activation by flagellin induces IL-18 and immediate elimination of RV-infected cells. Both TLR5 and NLRC4 are required for flagellin-mediated protection, and administration of IL-22 + IL-18 fully recapitulates flagellin protection.\",\n      \"method\": \"TLR5 KO, NLRC4 KO mice, cytokine neutralization/administration, adaptive immunity-independent model\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO models + cytokine reconstitution experiments, mechanistically dissecting TLR5→DC→IL-22 pathway\",\n      \"pmids\": [\"25395539\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"TLR5 activation by flagellin induces secretory IL-1 receptor antagonist (sIL-1Ra) in intestinal epithelial cells and macrophages in a TLR5-dependent manner on non-hematopoietic cells. In TLR5KO mice, loss of sIL-1Ra increases the IL-1β/sIL-1Ra ratio, correlating with increased inflammatory pathology on flagellin treatment and Salmonella infection.\",\n      \"method\": \"TLR5 KO mice, bone marrow chimeras to distinguish hematopoietic vs. non-hematopoietic TLR5, cytokine ELISA, in vivo infection model\",\n      \"journal\": \"Mucosal immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — chimera experiments identifying epithelial cell-intrinsic TLR5 function in sIL-1Ra induction\",\n      \"pmids\": [\"20844479\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"TLR5 is stored intracellularly in neutrophils and mobilized to the cell surface in a protein synthesis-independent manner through protein kinase C activation, or after stimulation with TLR ligands and cytokines. TLR1/TLR2 signaling via Pam3CSK4 is the most potent inducer of surface TLR5 expression. TLR5 surface mobilization enhances neutrophil phagocytic capacity and respiratory burst activity via IL-8/CXCR1 signaling.\",\n      \"method\": \"Confocal microscopy, flow cytometry, protein kinase C inhibitors, TLR1/TLR2 antibody blocking experiments, neutrophil functional assays\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple methods defining intracellular storage and TLR1/2-mediated surface mobilization of TLR5 in neutrophils\",\n      \"pmids\": [\"18684966\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"TLR5 physically associates with TLR4 in primary murine macrophages (co-immunoprecipitation) and biases TLR4 signaling toward the MyD88-dependent pathway. In vivo, TLR5 deficiency reduces responses to LPS, hyaluronan, and ozone (TLR4-mediated stimuli). Human carriers of a dominant-negative TLR5 allele show decreased inflammatory responses to LPS and ozone.\",\n      \"method\": \"Co-immunoprecipitation of TLR5 with TLR4, in vivo TLR5 KO mouse models (LPS, O3, hyaluronan), human dominant-negative TLR5 allele carrier ex vivo studies\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP evidence + multiple in vivo models + human genetic validation, multiple orthogonal approaches\",\n      \"pmids\": [\"31989925\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"H. pylori T4SS component CagL contains a flagellin D1-like motif that activates TLR5 in a flagellin-independent manner. CagL mediates adherence to TLR5+ epithelial cells and activates downstream TLR5 signaling. TLR5 KO mice show reduced control of H. pylori infection.\",\n      \"method\": \"In vitro TLR5 activation assays, TLR5 KO mouse infection model, human biopsy analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro mechanistic assays + KO mouse model, single lab\",\n      \"pmids\": [\"31844047\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Zebrafish TLR5 unexpectedly signals as a heterodimer composed of drTLR5b and drTLR5a gene products, not as a homodimer. Flagellin-induced signaling by the zebrafish heterodimer is enhanced by the TLR trafficking chaperone UNC93B1. TLR5 activation requires a heterodimeric configuration of both the ectodomain and cytoplasmic domain. Structure-guided substitution of the principal flagellin-binding site in human TLR5 with zebrafish TLR5 residues abrogated human TLR5 activation.\",\n      \"method\": \"Genetic domain-swap experiments (ectodomain and TIR domain swaps), UNC93B1 co-expression, structure-guided mutagenesis of human TLR5 flagellin-binding site\",\n      \"journal\": \"PNAS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — structure-guided mutagenesis + domain-swap epistasis + chaperone dependency, rigorous mechanistic dissection\",\n      \"pmids\": [\"29555749\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"NME3 (nucleoside diphosphate kinase 3) is a positive regulator of TLR5-induced NF-κB signaling, acting mechanistically downstream of MyD88. Identified via genome-wide siRNA kinase library screen; confirmed by targeted knockdown and overexpression in carcinoma cells with NF-κB bioluminescent reporter.\",\n      \"method\": \"High-throughput siRNA kinase library screen, targeted knockdown and overexpression validation, NF-κB bioluminescent reporter, MyD88 epistasis\",\n      \"journal\": \"Molecular cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — screen + targeted KD/OE validation with pathway placement (downstream of MyD88)\",\n      \"pmids\": [\"29523766\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"TLR5 stop codon polymorphism R392X and missense variants D694G and L822F are functionally relevant, abrogating flagellin-induced TLR5 signaling in transfected CHO-K1 cells. The common R392X (11.9% prevalence) acts as a dominant-negative allele.\",\n      \"method\": \"Transient transfection of TLR5 SNP variants in CHO-K1 cells, NF-κB reporter assay upon flagellin stimulation\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic functional characterization of multiple SNPs with defined readout\",\n      \"pmids\": [\"16470719\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"TLR5 activation by flagellin in hepatocytes stimulates ApoA1 production through transcriptional activation via NF-κB binding to the Apoa1 promoter. Hepatic TLR5 overexpression in TLR5-KO mice partially restored ApoA1 and HDL-C levels, confirming liver-cell-intrinsic TLR5 signaling in ApoA1/HDL metabolism.\",\n      \"method\": \"TLR5 KO mice, hepatic TLR5 overexpression rescue, NF-κB ChIP on Apoa1 promoter, primary hepatocyte stimulation, oral flagellin supplementation in Apoe-/- mice\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP + KO rescue + primary cell experiments, single lab\",\n      \"pmids\": [\"32820707\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"TLR5-mediated flagellin signaling in intestinal epithelial cells induces Notch1 and Jagged1 expression, and Notch1 synergistically enhances TLR5-mediated NF-κB activation via RBP-Jκ-dependent mechanism. Blocking Notch during acute colitis ameliorated inflammation, revealing a TLR5-Notch crosstalk in intestinal epithelium.\",\n      \"method\": \"Luciferase reporter assay for NF-κB, γ-secretase inhibitor, in vitro RBP-Jκ responsive element analysis of IL-6 promoter, in vivo Notch blocking in colitis model\",\n      \"journal\": \"International journal of molecular medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — mechanistic reporter assays but single lab with limited orthogonal validation\",\n      \"pmids\": [\"24048326\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"IL-8 induction by flagellin in A549 human alveolar epithelial cells requires lipid raft formation (inhibited by nystatin but not clathrin inhibitor chlorpromazine) and activation of intracellular TLR5, as TLR5 was found predominantly in the intracellular compartment of A549 cells rather than on the cell surface.\",\n      \"method\": \"Lipid raft inhibition (nystatin), clathrin inhibition (chlorpromazine), confocal microscopy for TLR5 subcellular localization, transient transfection NF-κB reporter\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct subcellular localization with functional consequence via lipid raft inhibition\",\n      \"pmids\": [\"19786303\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Flagellin-induced TLR5 signaling activates NF-κB in myometrium via MyD88/TRAF6/NF-κB pathway. siRNA knockdown of TLR5, MyD88, or TRAF6 decreased flagellin-induced pro-inflammatory cytokines (IL-6, IL-8), MMP-9, COX-2, and prostaglandin release in human fetal membranes and myometrium.\",\n      \"method\": \"siRNA knockdown of TLR5, MyD88, TRAF6 in primary human cells; NF-κB luciferase reporter; ELISA cytokine measurement\",\n      \"journal\": \"American journal of reproductive immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA KD of multiple pathway components in primary human tissue, single lab\",\n      \"pmids\": [\"24635133\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"α-Synuclein monomers and oligomers activate the NLRP3 inflammasome in microglia via TLR5 (among other receptors). TLR5 ligation by α-synuclein contributes to NLRP3 activation at a distinct signaling checkpoint, and NLRP3 inhibition or deficiency improved α-synuclein clearance.\",\n      \"method\": \"Primary microglia from WT mice, TLR5 receptor involvement tested alongside TLR2, NLRP3 inhibitor (CRID3), NLRP3 KO mice, internalization and degradation assays\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — TLR5 involvement inferred from receptor ligation without specific TLR5 KO controls; single lab\",\n      \"pmids\": [\"34507948\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TLR5 is a pattern recognition receptor that detects bacterial flagellin (and endogenous ligands such as HMGB1) through its lateral surface, primarily via the flagellin D1 domain, forming a 2:2 tail-to-tail signaling complex that recruits MyD88 and activates NF-κB, p38 MAPK, and other downstream pathways; TLR5 is phosphorylated at S805 by protein kinase D, its signaling is negatively regulated by MUC1 (which competes for MyD88 binding) and by TRIF-induced caspase-mediated proteolytic degradation, it physically associates with TLR4 to bias MyD88-dependent signaling, it functions as an endocytic receptor on dendritic cells to enhance antigen presentation to CD4+ T cells, and it drives innate immune responses in distinct cell types including intestinal epithelial cells, dendritic cells, macrophages, neutrophils, and hepatocytes to control gut homeostasis, osteoclastogenesis, ApoA1 production, and antimicrobial defense.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"TLR5 is an innate immune pattern recognition receptor that senses bacterial flagellin and endogenous danger signals to activate pro-inflammatory and adaptive immune responses across epithelial barriers, dendritic cells, macrophages, neutrophils, and hepatocytes. Structural studies show that TLR5 recognizes the conserved D1 domain of flagellin via its lateral leucine-rich repeat surface, assembling a 2:2 tail-to-tail signaling complex that recruits the adaptor MyD88 through its TIR domain, activating NF-κB, p38 MAPK, PI3K/Akt, and STAT1 signaling cascades [PMID:22344444, PMID:15302888, PMID:17442957, PMID:18209032]. TLR5 signaling is positively regulated by protein kinase D-mediated phosphorylation at S805 and negatively regulated by MUC1 cytoplasmic tail competition for MyD88 binding and by TRIF-induced caspase-dependent proteolytic degradation of TLR5 protein [PMID:17442957, PMID:22250084, PMID:20452988]. Beyond innate immunity, TLR5 functions as a MyD88-independent endocytic receptor on dendritic cells that enhances MHC class II antigen presentation to CD4+ T cells, physically associates with TLR4 to bias MyD88-dependent signaling, and drives tissue-specific programs including intestinal homeostasis, osteoclast regulation, and hepatic ApoA1/HDL production [PMID:21182074, PMID:31989925, PMID:18008007, PMID:32820707].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Cloning of human TLR5 and demonstration that its overexpression activates NF-κB established it as a signaling-competent Toll-like receptor, but its ligand and physiological role were unknown.\",\n      \"evidence\": \"Cloning, Northern blot, NF-κB reporter assay in transfected cells\",\n      \"pmids\": [\"9596645\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ligand not yet identified\", \"Adaptor usage unknown\", \"In vivo relevance not demonstrated\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Identification of flagellin as the TLR5 ligand and demonstration that signaling proceeds through MyD88 to activate NF-κB, MAPK, and SAPK pathways in intestinal epithelial cells established TLR5 as the principal flagellin sensor at mucosal surfaces.\",\n      \"evidence\": \"Dominant-negative TLR5 and MyD88 constructs, exogenous TLR5 expression in non-responsive cells, pathway kinase assays, polarized epithelial Ussing chamber ex vivo experiments\",\n      \"pmids\": [\"15324458\", \"15302888\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of flagellin recognition unknown\", \"Downstream signal branching not resolved\", \"Co-factor requirements suggested but not identified\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Discovery that TLR5 simultaneously activates pro-survival (NF-κB, PI3K/Akt) and pro-apoptotic (caspase-8) pathways revealed that TLR5 signaling outcome depends on the balance of parallel downstream cascades.\",\n      \"evidence\": \"Pharmacological inhibition of NF-κB and PI3K, caspase activation assays with TLR5-dependent controls\",\n      \"pmids\": [\"16179598\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological context determining survival vs. death choice unclear\", \"Mechanism linking TLR5 to caspase-8 not defined\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Identification of protein kinase D as a direct TLR5 interactor that phosphorylates S805 to enable p38-dependent IL-8 production provided the first post-translational regulatory mechanism for TLR5 activation.\",\n      \"evidence\": \"Co-immunoprecipitation, mass spectrometry phospho-site identification, S805A mutagenesis, shRNA knockdown of PKD\",\n      \"pmids\": [\"17442957\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether S805 phosphorylation is required in all cell types unknown\", \"Kinase(s) responsible for dephosphorylation not identified\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"TLR5-knockout mice developed spontaneous colitis rescued by concurrent TLR4 deletion, establishing TLR5 as essential for intestinal immune homeostasis and revealing genetic epistasis between TLR5 and TLR4.\",\n      \"evidence\": \"TLR5 KO and TLR4/TLR5 double-KO mice, histopathology, cytokine and bacterial load measurement\",\n      \"pmids\": [\"18008007\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cell type(s) in which TLR5 loss drives pathology not resolved\", \"Whether TLR5-TLR4 epistasis reflects direct physical interaction unknown at this time\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstration that DC-intrinsic TLR5 is required for flagellin adjuvant activity and that intestinal lamina propria DCs selectively express TLR5 to drive IgA, Th17, and Th1 responses established TLR5 as a key bridge between innate and adaptive mucosal immunity.\",\n      \"evidence\": \"Bone marrow chimera mice, diphtheria toxin DC depletion, TLR5-KO infection models, adoptive CD4+ T cell transfer\",\n      \"pmids\": [\"19494277\", \"19547909\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How TLR5+ LPDC subset is specified developmentally unknown\", \"Whether DC TLR5 signals differently from epithelial TLR5 not resolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Three parallel advances defined negative regulation of TLR5 (TRIF-induced caspase-dependent degradation), a MyD88-independent endocytic antigen-presentation function, and cooperation with NLRC4 for full flagellin-driven adaptive immunity.\",\n      \"evidence\": \"TRIF overexpression with caspase inhibitor rescue and domain deletions; TLR5-KO DC presentation assays with MyD88-KO controls; TLR5/NLRC4 double-KO mice with antibody response measurement\",\n      \"pmids\": [\"20452988\", \"21182074\", \"21072873\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of the caspase(s) mediating TLR5 degradation not established\", \"Structural basis of MyD88-independent endocytic function unknown\", \"Relative contributions of TLR5 vs. NLRC4 in different tissues not quantified\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Crystal structure of the TLR5–flagellin complex revealed a 2:2 tail-to-tail signaling architecture in which TLR5 engages the D1 domain helices via its lateral surface, providing the atomic basis for ligand recognition and dimerization-induced activation.\",\n      \"evidence\": \"2.47 Å crystal structure of zebrafish TLR5–FliC complex with structure-guided mutagenesis and deletion validation\",\n      \"pmids\": [\"22344444\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Human TLR5 structure not yet solved\", \"How dimerization transmits signal across the membrane not determined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Discovery that MUC1 cytoplasmic tail competes with MyD88 for TLR5 binding upon EGFR-mediated phosphorylation defined a receptor-proximal negative regulatory mechanism linking growth factor and innate immune signaling.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation, MUC1-CT phospho-mutagenesis, MyD88 overexpression rescue, in vivo immunofluorescence\",\n      \"pmids\": [\"22250084\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether MUC1 regulation of TLR5 operates in cell types beyond airway epithelia unknown\", \"Stoichiometry of MUC1-TLR5 vs. MyD88-TLR5 complexes not defined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identification of the endogenous danger molecule HMGB1 as a TLR5 ligand that activates MyD88-dependent NF-κB signaling expanded the TLR5 ligand repertoire beyond microbial flagellin to include sterile inflammation mediators.\",\n      \"evidence\": \"Biophysical binding assays, NF-κB reporter with MyD88 requirement, in vivo pain behavioral assays in TLR5-expressing tissues\",\n      \"pmids\": [\"27760316\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of HMGB1-TLR5 interaction not determined\", \"Whether HMGB1-TLR5 signaling contributes to sterile inflammatory diseases in vivo not established\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"A higher-resolution Bacillus flagellin–TLR5 structure combined with alanine scanning identified a conserved hot spot (R89/E114/L93) fitting into TLR5 LRR9, refining the molecular pharmacophore for receptor activation.\",\n      \"evidence\": \"2.1 Å crystal structure with systematic alanine scanning mutagenesis\",\n      \"pmids\": [\"28106112\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the hot spot is targetable pharmacologically unknown\", \"Contribution of the D0 domain to activation mechanism remains structurally unresolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Demonstration that TLR5 physically associates with TLR4 and biases TLR4 signaling toward MyD88 in macrophages, validated by human carriers of dominant-negative TLR5, resolved the earlier genetic epistasis and established TLR5 as a co-receptor modulating TLR4 responses.\",\n      \"evidence\": \"Co-immunoprecipitation of TLR5-TLR4, TLR5-KO mouse models challenged with LPS/ozone/hyaluronan, human TLR5 R392X carrier ex vivo studies\",\n      \"pmids\": [\"31989925\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether TLR5-TLR4 heterodimer forms constitutively or is ligand-induced unclear\", \"Structural basis of heterodimerization not solved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"TLR5 signaling in hepatocytes drives ApoA1 transcription via NF-κB binding to the Apoa1 promoter, revealing a non-immune metabolic function for TLR5 in HDL biogenesis.\",\n      \"evidence\": \"TLR5-KO mice, hepatic TLR5 overexpression rescue, NF-κB ChIP on Apoa1 promoter, primary hepatocyte stimulation\",\n      \"pmids\": [\"32820707\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether gut microbiota-derived flagellin is the physiological hepatic TLR5 stimulus in humans not established\", \"Contribution relative to other ApoA1 transcriptional regulators unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions include the full-length human TLR5 structure (no solved structure exists), the mechanism of transmembrane signal transmission from ectodomain dimerization to TIR domain MyD88 recruitment, the structural basis of TLR5-TLR4 heterodimerization, and whether TLR5 endogenous ligands (HMGB1, α-synuclein) contribute to sterile inflammatory diseases in vivo.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Full-length human TLR5 structure not solved\", \"Transmembrane signaling mechanism not established\", \"Physiological relevance of non-flagellin ligands in disease contexts unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 1, 2, 3, 4, 13]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [4, 11, 24]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [4, 23, 24]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [15, 31]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [23, 31]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [2, 3, 4, 6, 18, 19, 20, 21]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 5, 7, 9, 14, 16, 27]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [7, 10]}\n    ],\n    \"complexes\": [\n      \"TLR5 homodimer (2:2 with flagellin)\",\n      \"TLR5-TLR4 heteromeric complex\"\n    ],\n    \"partners\": [\n      \"MYD88\",\n      \"PRKD1\",\n      \"MUC1\",\n      \"TRAF6\",\n      \"TLR4\",\n      \"UNC93B1\",\n      \"HMGB1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}