{"gene":"TLR8","run_date":"2026-06-10T10:51:55","timeline":{"discoveries":[{"year":2000,"finding":"TLR8 contains an ectodomain with multiple leucine-rich repeats (LRRs) and a cytoplasmic TIR domain homologous to the IL-1 receptor. Expression of constitutively active TLR8 stimulates NF-κB signaling. TLR8 gene is located on the X chromosome.","method":"Molecular cloning, sequence analysis, NF-κB reporter assay in transfected cells","journal":"European cytokine network","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — molecular cloning with functional NF-κB reporter validation, single lab, multiple methods","pmids":["11022120"],"is_preprint":false},{"year":2006,"finding":"TLR8-mediated NF-κB and JNK activation require IRAK and IRAK4 (but not their kinase activities), are TAK1-independent, and are completely abolished in MEKK3-deficient cells. TLR8 ligands induce IKKγ phosphorylation but not IKKα/β phosphorylation or IKKγ ubiquitination (unlike IL-1R signaling), indicating a distinct NF-κB activation pathway downstream of TLR8.","method":"Genetic epistasis using TAK1−/− and MEKK3−/− mouse embryonic fibroblasts, IRAK-deficient human cells, kinase-inactive mutant rescue, immunoblotting for IκBα phosphorylation and IKK complex components","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — multiple knockout cell lines, reconstitution with kinase-dead mutants, orthogonal methods (reporter assay + immunoblot), rigorous genetic dissection","pmids":["16737960"],"is_preprint":false},{"year":2008,"finding":"Defined single-stranded RNA sequence motifs (TLR8-specific) selectively activate human TLR8 without stimulating TLR7. These TLR8 RNA motifs fail to induce IFN-α from plasmacytoid DCs but induce Th1-like and proinflammatory cytokines from monocytes and myeloid DCs. TLR8 RNA ligand responsiveness is species-specific (human and bovine but not mouse, rat, or porcine).","method":"TLR-transfected reporter cell lines, primary human immune cell stimulation, species comparison, TLR-specific inhibitory sequences","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reporter cell specificity testing plus primary cell validation across multiple species, multiple labs consistent with prior literature","pmids":["18322178"],"is_preprint":false},{"year":2009,"finding":"A five-amino-acid motif in the TLR8 ectodomain immediately following LRR-14 (absent in rodent TLR8) is essential for species-specific ligand recognition. Deletion of this motif abolishes ligand responsiveness of human TLR8, while it is not required for self-dimerization or intracellular localization.","method":"Multiple species sequence alignment, deletion mutagenesis of hTLR8, NF-κB reporter assays in transfected cells","journal":"Molecular immunology","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — mutagenesis with functional readout, supported by cross-species comparison, single lab","pmids":["20004021"],"is_preprint":false},{"year":2011,"finding":"UNC93B1 physically associates with human TLR8 and is required for TLR8-mediated signaling. TLR8 localizes to early endosomes and the ER (not late endosomes or lysosomes) in human monocytes. The transmembrane domain and TIR domain of TLR8 are required for proper targeting to the early endosome.","method":"Co-immunoprecipitation, confocal microscopy, subcellular fractionation, tail-truncation mutant analysis in HeLa transfectants and human monocytes","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP, direct localization imaging, domain mutant analysis with functional consequence, single lab with multiple orthogonal methods","pmids":["22164301"],"is_preprint":false},{"year":2011,"finding":"TLR8 senses bacterial RNA released within phagosomal vacuoles during Borrelia burgdorferi infection in human monocytes, mediating production of TNF-α, IL-6, and IL-10, and exclusively driving IRF7-mediated IFN-β transcription. TLR2 and TLR8 cooperate for cytokine responses in phagosomes; TLR8 is solely responsible for IFN-β induction. IRF7 is translocated to the nucleus in Bb-infected monocytes.","method":"TLR-specific inhibitory immunoregulatory sequences (IRS957), confocal and epifluorescence microscopy for TLR2/TLR8 colocalization with bacteria, IRF7 nuclear translocation assay, cytokine/mRNA measurement","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — TLR-specific inhibitors with multiple cytokine readouts, confocal colocalization, nuclear translocation, multiple orthogonal methods in primary human cells","pmids":["21321205"],"is_preprint":false},{"year":2014,"finding":"TLR8 undergoes proteolytic cleavage in human monocytes and macrophages in a manner distinct from TLR7/9. The insertion loop between LRR14 and LRR15 is indispensable for cleavage and stepwise processing of the N-terminal fragment. Both furin-like proprotein convertase and cathepsins contribute to TLR8 cleavage in early/late endosomes.","method":"Immunoblotting of endogenous TLR8 in primary human cells, furin/cathepsin inhibitor treatment, domain deletion mutants, subcellular fractionation","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — biochemical cleavage assay with domain mutants and pharmacological inhibitors in primary human cells, multiple orthogonal methods, single lab","pmids":["25297876"],"is_preprint":false},{"year":2017,"finding":"Small-molecule antagonists bind to a unique site at the protein-protein interface of the TLR8 homodimer, stabilizing the preformed TLR8 dimer in its resting (inactive) state and preventing activation. Crystal structures of two TLR8-ligand complexes validated this novel binding site.","method":"X-ray crystallography of TLR8-ligand complexes, NF-κB reporter assay, cytokine measurement in human primary cells and patient specimens","journal":"Nature chemical biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structures of two independent complexes validated mechanistically by functional assays in cell lines, primary cells, and patient specimens","pmids":["29155428"],"is_preprint":false},{"year":2018,"finding":"Small-molecule TLR8 antagonists designed via rational structure-based drug design bind an unconventional pocket at the TLR8 protein-protein interface. X-ray crystal structures of TLR8 in complex with inhibitors confirmed the binding mode, showing the compounds sit between two TLR8 monomers preventing homodimerization.","method":"Rational structure-based design, X-ray crystallography, NF-κB reporter assay, cytokine measurement in PBMC and TLR8-transgenic mouse splenocytes","journal":"Cell chemical biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structures with functional validation, single lab, multiple biological systems","pmids":["30100350"],"is_preprint":false},{"year":2019,"finding":"The lysosomal endoribonuclease RNase T2 is a non-redundant upstream component of TLR8-dependent RNA recognition. RNase T2 preferentially cleaves ssRNA between purine and uridine residues, generating catabolic uridine and purine-2',3'-cyclophosphate-terminated oligoribonucleotides that serve as agonistic ligands for TLR8's two distinct binding pockets.","method":"RNase T2 knockout/knockdown, reconstitution assays, biochemical characterization of RNA degradation products, TLR8 reporter assays","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — genetic knockout with reconstitution, biochemical characterization of generated ligands, mapping to known TLR8 binding pockets, published in Cell","pmids":["31778653"],"is_preprint":false},{"year":2010,"finding":"Mouse TLR8 deficiency leads to overexpression of TLR7 on dendritic cells and hyperresponsiveness to TLR7 ligands. TLR8 functions as a negative regulator of TLR7 expression and TLR7-mediated signaling, preventing spontaneous autoimmunity.","method":"Tlr8−/− mouse model, TLR7 expression measurement, NF-κB activation assays, autoantibody measurement, histopathology","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — defined knockout phenotype with multiple readouts, genetic epistasis (Tlr8−/−Tlr7−/− double KO), independently replicated in related publications","pmids":["20811154"],"is_preprint":false},{"year":2014,"finding":"TLR8 on dendritic cells (but not B cells) restrains TLR7-mediated autoimmunity, while TLR9 restrains TLR7 response specifically on B cells. Double TLR8/9-deficient mice show additive lupus-like disease. TLR8 and TLR9 act on different cell types to control TLR7.","method":"Single and double TLR8/9 knockout mice, cell-type-specific TLR7 hyperresponsiveness assays, autoantibody and disease phenotype measurement","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis with single and double knockouts, cell-type-specific dissection, rigorous phenotypic readouts","pmids":["24474776"],"is_preprint":false},{"year":2010,"finding":"TLR8 is activated in human monocytic cells following Helicobacter pylori phagocytosis. A TLR8 SNP (rs3764880:A>G; Met1Val) fine-tunes translation of the two TLR8 isoforms: TLR8 variant 2 (TLR8v2) is the prevalent functional isoform, while TLR8v1 positively regulates TLR8 function in CD16+CD14+ differentiated monocytes.","method":"siRNA knockdown, overexpression, TLR8-specific reporter assays, phagocytosis experiments with live bacteria, cytokine measurement, isoform-specific translation analysis","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA plus overexpression with functional readout, single lab, multiple methods","pmids":["20652908"],"is_preprint":false},{"year":2007,"finding":"TLR8 is expressed in neurons and axons of the mouse brain. TLR8 activation suppresses neurite outgrowth and induces neuronal apoptosis through an NF-κB-independent mechanism.","method":"TLR8 expression profiling in mouse brain development, neuronal culture assays with TLR8 ligands, NF-κB reporter assays, neurite outgrowth measurement","journal":"Cell cycle","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization with functional consequence, NF-κB independence established by reporter assay, single lab","pmids":["18000403"],"is_preprint":false},{"year":2014,"finding":"HIV-1 infection of human monocytes induces pro-IL-1β expression via TLR8-dependent mechanisms. TLR8 senses HIV-1-derived RNA; both HIV-1 entry, reverse transcription, and integration are required for TLR8-mediated pro-IL-1β expression. Subsequently, NLRP3 inflammasome (activated by cathepsin B and ROS) cleaves pro-IL-1β into bioactive IL-1β.","method":"TLR8 knockdown, HIV-1 infection of primary human monocytes, TLR8-specific reporter assay, HIV lifecycle inhibitors, cathepsin B inhibitor, caspase-1 assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with multiple pharmacological inhibitors, pathway dissection with multiple orthogonal methods, single lab","pmids":["24939850"],"is_preprint":false},{"year":2015,"finding":"Human TLR8 senses bacterial RNA in primary human monocyte-derived macrophages; TLR8 is unambiguously identified as the receptor for bacterial RNA using siRNA knockdown and overexpression. The TLR8-recognized sequence motif in bacterial RNA is distinct from that recognized by mouse TLR13. TLR8-dependent bacterial RNA detection is critical for monocyte activation during Streptococcus pyogenes infection.","method":"siRNA knockdown, TLR8 overexpression in macrophages, lysosomal maturation inhibitors, S. pyogenes infection, cytokine measurement","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — siRNA plus overexpression orthogonal approach, infection model validation, consistent with multiple independent studies on TLR8 RNA sensing","pmids":["26101323"],"is_preprint":false},{"year":2015,"finding":"Human TLR8 senses UR/URR motifs in bacterial RNA (including Sa19 23S rRNA-derived fragments) and mitochondrial 16S rRNA-derived oligoribonucleotides. TLR8 function requires UNC93B1 (lysosomal function) and acts as the human functional equivalent of mouse TLR13 for bacterial RNA sensing. TLR8 knockout THP-1 cells are refractory to these RNA stimuli.","method":"TLR8/Unc93b1 knockout THP-1 cells, TLR8 ectopic overexpression, lysosomal function inhibitors, synthetic oligoribonucleotide stimulation, NF-κB/cytokine reporter assays","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — knockout plus overexpression reconstitution, RNA motif-specific dissection, published in EMBO reports, consistent with concurrent independent study","pmids":["26545385"],"is_preprint":false},{"year":2009,"finding":"Self-RNA complexed with the antimicrobial peptide LL37 is transported into endosomal compartments and activates TLR8 in myeloid DCs (mDCs), leading to TNF-α and IL-6 production and mDC maturation. This mechanism drives autoimmune responses in psoriasis.","method":"TLR7/TLR8 knockdown/blocking in primary DCs, confocal microscopy for LL37-RNA complex localization, cytokine ELISA, flow cytometry for DC maturation markers","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — TLR8-specific knockdown with multiple functional readouts, in vivo correlation in psoriatic lesions, replicated in multiple cell types","pmids":["19703986"],"is_preprint":false},{"year":2006,"finding":"TLR8 activation by imidazoquinolines mediates NF-κB activation and proinflammatory cytokine production. In addition, imiquimod activates NF-κB independently of TLR7 and TLR8 through antagonism of adenosine receptors (particularly A1 and A2A subtypes), as demonstrated in Chinese hamster ovary cells expressing human adenosine receptor subtypes.","method":"TLR7/TLR8-negative cell lines, radioligand binding competition, adenylyl cyclase activity assay, CHO cells stably transfected with adenosine receptor subtypes","journal":"The Journal of investigative dermatology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — radioligand binding plus functional assay in receptor-transfected cells, single lab, mechanistically defines TLR-independent imiquimod action","pmids":["16575388"],"is_preprint":false},{"year":2010,"finding":"TLR8 transcriptional activity is regulated by C/EBPδ and C/EBPβ binding to three C/EBP cis-acting elements in the hTLR8 promoter. TLR8 stimulation (R848) increases TLR8 transcription via enhanced C/EBPδ binding. IFN-γ increases TLR8 transcription via STAT1 binding to IFN-γ-activated sequence (GAS) elements in the TLR8 promoter.","method":"TLR8 promoter isolation, luciferase reporter assays, chromatin immunoprecipitation (ChIP) for C/EBPδ, C/EBPβ, and STAT1 binding","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — promoter-reporter assay plus ChIP validation of transcription factor binding, two independent stimuli (TLR8 agonist and IFN-γ), single lab with multiple orthogonal methods","pmids":["20829351"],"is_preprint":false},{"year":2009,"finding":"TLR7 and TLR8 agonists trigger different signaling pathways during human DC maturation. Both JNK and NF-κB positively regulate maturation markers and cytokines downstream of both TLR7 and TLR8. However, p38 MAPK inhibits CD40 expression and IL-12 production in TLR8-stimulated DCs (while promoting them in TLR7-stimulated DCs). The Jak/STAT pathway positively regulates CD40 and cytokines in TLR7-stimulated but negatively regulates cytokine secretion in TLR8-stimulated DCs.","method":"Selective TLR7 agonist (imiquimod) vs. TLR8 agonist (3M002), specific kinase inhibitors (p38, JNK, NF-κB, Jak/STAT), cytokine ELISA, flow cytometry for DC maturation markers","journal":"Journal of leukocyte biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological dissection with selective agonists and kinase inhibitors, multiple readouts, single lab","pmids":["19164127"],"is_preprint":false},{"year":2019,"finding":"TLR7 and TLR8 activate distinct signaling cascades in human monocytes during RNA virus infection. TLR7 specifically increases FOSL1 expression, which reduces IL-27 and TNFα production. TLR7 (but not TLR8) activation stimulates Ca2+ flux that prevents type I IFN responses. These distinct pathways correlate with different cytokine profiles for CD4+ T helper cell polarization.","method":"TLR7/TLR8-specific agonists, siRNA knockdown, signaling pathway analysis, Ca2+ flux measurement, gene expression profiling in human CD14+ monocytes infected with 6 different RNA viruses","journal":"Science signaling","confidence":"High","confidence_rationale":"Tier 2 / Strong — siRNA knockdown with mechanistic pathway dissection, multiple RNA virus models, Ca2+ flux measurement, FOSL1 target validation, multiple orthogonal methods","pmids":["31662487"],"is_preprint":false},{"year":2009,"finding":"TLR8 is required for TNF-α overproduction in FANCC-deficient mononuclear phagocytes. TLR8 (or a TLR8-associated protein) is ubiquitinated in Fancc−/− mutant cells but not complemented cells. FANCC suppresses TLR8 activity via canonical downstream intermediates IRAK and IKKα/β, and this function is independent of FANCC's role in protecting the genome from crosslinking agents.","method":"TLR8-specific inhibitory sequences, FANCC-deficient THP-1 cells and Fancc−/− macrophages, TLR8 agonist stimulation, ubiquitination proteomics, FANCC point mutant complementation","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic knockout plus TLR8-specific inhibition with functional readout, point mutant dissection of FANCC domains, single lab","pmids":["19850743"],"is_preprint":false},{"year":2016,"finding":"DCIR (an ITIM-containing C-type lectin receptor) is endocytosed via clathrin-dependent internalization into endo-/lysosomal compartments including LAMP-1+ lysosomes. DCIR triggering specifically inhibits TLR8-mediated IL-12 and TNF-α production but does not affect TLR2-, TLR3-, or TLR4-induced cytokine production, demonstrating CLR/TLR8 crosstalk.","method":"Confocal microscopy with endosomal markers, clathrin inhibitor, DCIR-specific mAb triggering, cytokine ELISA, co-stimulatory molecule flow cytometry","journal":"Journal of leukocyte biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct co-localization imaging with functional consequence, specific pharmacological inhibition, TLR specificity established by comparison, single lab","pmids":["19028959"],"is_preprint":false},{"year":2016,"finding":"TLR8 couples with SOCS-1 (suppressor of cytokine signaling-1) in mice; SOCS-1 directly associates with TLR8 but not TLR7. This TLR8-SOCS-1 interaction inhibits TLR7-mediated antiviral immunity (including ISG-56 expression and IFN responses) during West Nile virus infection. Tlr8−/− mice show increased TLR7 and ISG-56 expression and are resistant to WNV infection.","method":"TLR8−/− mice, SOCS-1 co-immunoprecipitation with TLR7 and TLR8, siRNA knockdown of SOCS-1, WNV infection model, gene expression analysis","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct co-IP of SOCS-1 with TLR8 but not TLR7, genetic KO validation, siRNA knockdown, single lab","pmids":["27798161"],"is_preprint":false},{"year":2018,"finding":"TLR8 activation in neurons promotes dendritic pruning via MyD88 signaling and specifically involves MAPK signaling. TLR8 is more critical for dendritic arborization at late developmental stages in vivo. Unlike TLR7 and TLR3, TLR8 activation does not control axonal growth.","method":"In vitro neuronal cultures, in utero electroporation, transcriptomic profiling, MAPK pathway inhibitors, TLR-specific agonists, TLR8 knockdown","journal":"The Journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo electroporation plus in vitro pharmacological dissection, transcriptomic analysis, single lab with multiple orthogonal methods","pmids":["29777026"],"is_preprint":false},{"year":2018,"finding":"TLR8 senses bacterial RNA from live bacteria (but not dead bacteria) as a distinguishing viability signal, inducing a specific cytokine profile in APCs that promotes follicular helper T (TFH) cell differentiation and antibody responses. A hypermorphic TLR8 polymorphism is associated with protective BCG vaccine immunity in humans.","method":"Live vs. heat-killed bacterial comparison, TLR8-specific agonists, human and porcine APC stimulation, TFH differentiation assays, pig live vaccination model, human BCG cohort analysis","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — mechanistic dissection with live/dead bacteria, TLR8-specific agonist, animal model, human cohort polymorphism validation, multiple orthogonal systems","pmids":["29556002"],"is_preprint":false},{"year":2018,"finding":"TLR8 in dorsal root ganglion neurons localizes to endosomes and lysosomes and mediates ERK activation, inflammatory mediator production, and neuronal hyperexcitability after spinal nerve ligation. miR-21 is increased in DRG neurons after nerve injury and serves as an endogenous TLR8 ligand that drives neuropathic pain hypersensitivity.","method":"Tlr8−/− mice, intrathecal/intradermal TLR8 agonist injection, miR-21 inhibition, ERK phosphorylation assays, electrophysiology, confocal microscopy for TLR8 subcellular localization","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO, pharmacological inhibition, direct localization, multiple readouts including electrophysiology, ligand identity validated by miR-21 inhibition","pmids":["30455267"],"is_preprint":false},{"year":2020,"finding":"TLR8 (but not TLR7 or TLR9) in CD4+ T cells senses endosomal HIV-1 ssRNA, inducing cytokine secretion, upregulating activation markers, promoting Th1/Th17 differentiation, enhancing HIV-1 replication, and potentiating reversal of latency in patient-derived T cells.","method":"Synthetic TLR-specific ligands, TLR-specific blocking, primary CD4+ T cell assays, HIV-1 infection of patient-derived cells, latency reversal assay, cytokine/activation marker measurement","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — TLR-specific pharmacological and genetic dissection, patient-derived cell validation, multiple functional readouts, published in Nature Communications","pmids":["31919342"],"is_preprint":false},{"year":2022,"finding":"CXCL4 costimulation synergizes with TLR8 to activate TBK1 and IKKε, repurposing these kinases to couple with IRF5 (rather than IRF3) for an inflammatory response. This synergy activates the NLRP3 inflammasome, induces de novo enhancers associated with inflammatory genes, and selectively amplifies inflammatory gene transcription and IL-1β production while partially attenuating the IFN response.","method":"Phosphoproteomics, ChIP-seq/ATAC-seq for chromatin remodeling, kinase inhibitors, IRF5 knockdown, NLRP3 inflammasome assays in human monocytes/macrophages","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — multi-omics approach (ChIP-seq, ATAC-seq, phosphoproteomics), pharmacological and genetic dissection, multiple orthogonal methods, single lab","pmids":["35701499"],"is_preprint":false},{"year":2016,"finding":"TLR8 agonism activates the NLRP3 inflammasome in monocytes, mediating release of mature IL-1β and IL-18. TLR8 primes monocytes for pro-IL-1β, pro-IL-18, and caspase-1 production, while also activating the NLRP3 complex. Caspase-1 inhibition blocks inflammasome activation but not other TLR8-induced mediators (e.g., TNFα).","method":"Caspase-1 inhibitor, NLRP3 inhibitors, cytokine ELISA (mature IL-1β, IL-18), in vivo cynomolgus monkey pharmacodynamics","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological dissection with caspase-1 and NLRP3 inhibitors, in vivo validation, single lab","pmids":["26928328"],"is_preprint":false},{"year":2022,"finding":"Microbial small RNAs (msRNA) enriched on LDL activate macrophage TLR8, driving pro-inflammatory macrophage polarization. Competitive TLR8 antagonism with locked nucleic acids prevented native LDL-induced macrophage polarization in vitro and reorganized lesion macrophage phenotypes in vivo, reducing atherosclerosis disease burden.","method":"LDL reconstitution (with/without msRNA cargo), TLR8 antagonist, single-cell RNA sequencing, mouse atherosclerosis models","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reconstitution of LDL particles, competitive antagonism, scRNA-seq, in vivo disease model, multiple orthogonal methods","pmids":["36474072"],"is_preprint":false},{"year":2021,"finding":"Gain-of-function variants in TLR8 cause a novel childhood-onset inborn error of immunity. All identified variants confer constitutive or enhanced TLR8 activity, leading to proinflammatory T cell activation, elevated serum cytokines, and impaired B cell maturation. iPSC-derived myeloid cells from patients showed increased TLR8 responsiveness.","method":"Patient-derived iPSC myeloid differentiation, in vitro TLR8 activity assays in transfected cell lines and patient primary cells, immune phenotyping","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — patient variants validated in iPSC-derived cells and transfected lines, multiple patients with distinct variants, single study","pmids":["33512449"],"is_preprint":false},{"year":2022,"finding":"TLR8 p.G572V mutation causes impaired TLR8 protein stability, cross-reactivity to TLR7 ligands, and reduced ability of TLR8 to attenuate TLR7 signaling. This imbalance toward TLR7-dependent signaling leads to NF-κB activation and elevated IL-1β, IL-6, and TNFα production.","method":"In vitro transfection assays with mutant TLR8, primary cell assays, NF-κB reporter, cytokine measurement, patient primary cells","journal":"American journal of hematology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutant vs. wild-type TLR8 functional comparison in transfected and patient cells, single lab, single case family","pmids":["34981838"],"is_preprint":false},{"year":2023,"finding":"TLR8 escapes X chromosome inactivation (XCI) in human CD14+ monocytes and CD4+ T cells. Both TLR7 and TLR8 genes can be simultaneously expressed from the active X chromosome, occurring more frequently in women and Klinefelter syndrome men than in euploid men (sevenfold difference in frequency). TLR8 protein expression is significantly higher in female mononuclear blood cells than in male cells.","method":"RNA FISH for primary transcripts relative to X chromosome territories in primary immune cells, Western blot and flow cytometry for TLR8 protein expression across sex groups","journal":"Biology of sex differences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct RNA FISH visualization on single cells with X chromosome territory probes, protein quantification by two methods, single lab","pmids":["37723501"],"is_preprint":false},{"year":2019,"finding":"TLR8 is a dominating sensor of multiple pyogenic bacteria (S. aureus, GBS, S. pneumoniae, P. aeruginosa) in human primary monocytes, largely responsible for IL-1β and IL-12p70 production. Cell surface TLR activation (TLR2, TLR4, TLR5) attenuates TLR8-IRF5 signaling by modifying/sequestering IRAK-1, which is required for TLR8-IRF5 pathway activation. IRAK-1 silencing reduces TLR8-driven IFNβ and TNF.","method":"Selective TLR8 chemical antagonist, siRNA knockdown of IRAK-1, TLR agonist combinations, immunoblotting for IRAK-1 modifications, cytokine ELISA in primary human monocytes","journal":"Frontiers in immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — selective TLR8 antagonist plus siRNA knockdown, mechanistic dissection of IRAK-1 role, multiple bacterial species tested, multiple orthogonal methods","pmids":["31214180"],"is_preprint":false},{"year":2020,"finding":"TLR8 inhibition in the trigeminal ganglion (TG) attenuates trigeminal neuropathic pain. TLR8 activation in TG neurons induces ERK and p38 MAPK activation and pro-inflammatory cytokine production. Intra-TG injection of TLR8 agonist VTX-2337 induces pain hypersensitivity and increases intracellular Ca2+ concentration in TG neurons.","method":"Tlr8 knockdown and conditional deletion in TG, ERK/p38 phosphorylation assays, cytokine measurement, Ca2+ imaging, behavioral pain assays","journal":"Neuroscience bulletin","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic knockdown with behavioral and cellular readouts, TLR8 agonist injection validation, single lab","pmids":["33355900"],"is_preprint":false},{"year":2014,"finding":"TLR8 activation promotes AML cell differentiation and growth inhibition in a TLR8/MyD88/p38-dependent manner, establishing a direct anti-leukemic role for TLR8 signaling independent of immunomodulation.","method":"TLR8 agonist (R848) stimulation, MyD88 and p38 pathway inhibitors, TLR8 overexpression, in vivo xenograft model","journal":"Leukemia","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological and genetic pathway dissection, in vivo xenograft validation, single lab","pmids":["25283842"],"is_preprint":false},{"year":2024,"finding":"TLR8 is expressed in the hepatic myeloid compartment (Kupffer cells). TLR8 agonism (selgantolimod) activates Kupffer cells and induces IL-6 secretion, which indirectly impairs HBV entry into hepatocytes by downregulating NTCP (sodium taurocholate cotransporting polypeptide). Co-treatment with an anti-IL-6 neutralizing antibody reverses the HBV entry inhibition.","method":"Single-cell RNA-seq of human liver, Kupffer cell isolation and TLR8 agonist treatment, SLGN-conditioned media transfer to hepatocytes, HBV infection quantification, anti-IL-6 neutralization, RNA-seq of Kupffer cells and hepatocytes","journal":"Gut","confidence":"High","confidence_rationale":"Tier 2 / Moderate — conditioned media transfer with cytokine neutralization identifies IL-6 as the mechanistic mediator, scRNA-seq cell-type identification, multiple orthogonal methods, single lab","pmids":["38697771"],"is_preprint":false}],"current_model":"TLR8 is an endosomal single-stranded RNA sensor that is proteolytically processed (via furin-like convertases and cathepsins at the LRR14-15 loop) and trafficked to early endosomes via UNC93B1; upon binding RNA degradation products generated by RNase T2 (uridine and purine-2',3'-cyclophosphate-terminated oligonucleotides at two distinct binding pockets), TLR8 homodimerizes and activates a MEKK3-dependent (TAK1-independent) NF-κB and MAPK signaling cascade requiring IRAK/IRAK4 (but not their kinase activities) and IKKγ phosphorylation, while also engaging IRF5 for IFN-β production; TLR8 is negatively regulated by cell-surface TLR activation (via IRAK-1 modification), by its own negative control over TLR7 expression in dendritic cells (preventing spontaneous autoimmunity), and by small-molecule antagonists that stabilize the resting-state homodimer; in addition to immune cells, TLR8 functions in neurons (suppressing neurite outgrowth and mediating pain signaling via ERK/p38 MAPK) and escapes X chromosome inactivation, contributing to sex-biased immune responses."},"narrative":{"mechanistic_narrative":"TLR8 is an endosomal innate-immune sensor of single-stranded RNA that signals through its IL-1 receptor-homologous cytoplasmic TIR domain to drive NF-κB and proinflammatory gene expression [PMID:11022120, PMID:16737960]. Productive sensing requires upstream processing and trafficking: TLR8 associates with UNC93B1 and localizes to early endosomes and ER, with its transmembrane and TIR domains directing endosomal targeting [PMID:22164301]; it undergoes furin-like convertase- and cathepsin-dependent proteolytic cleavage at the LRR14–LRR15 insertion loop [PMID:25297876]; and its ligands are catabolic uridine- and purine-2',3'-cyclophosphate-terminated oligoribonucleotides generated by the lysosomal endoribonuclease RNase T2, which dock into TLR8's two distinct binding pockets [PMID:31778653]. A five-residue motif following LRR-14, absent in rodents, confers species-specific ligand recognition and underlies human-restricted responsiveness [PMID:18322178, PMID:20004021]. Downstream, TLR8 engages a distinct activation route requiring IRAK and IRAK4 (independent of their kinase activity) and MEKK3, proceeding through IKKγ phosphorylation rather than the canonical TAK1/IKKαβ axis used by IL-1R [PMID:16737960], and it couples IRAK-1 to an IRF5-dependent type I IFN response [PMID:31214180]. Through these mechanisms TLR8 detects bacterial and mitochondrial RNA (UR/URR motifs), viral RNA, and self-RNA, distinguishing live from dead bacteria as a viability signal and activating the NLRP3 inflammasome to produce IL-1β [PMID:26101323, PMID:26545385, PMID:29556002, PMID:26928328]. TLR8 also acts as a negative regulator of TLR7 expression and signaling in dendritic cells, restraining spontaneous autoimmunity [PMID:20811154, PMID:24474776]. Beyond immunity, TLR8 functions in neurons to suppress neurite outgrowth, drive dendritic pruning via MyD88/MAPK signaling, and mediate neuropathic pain through ERK/p38 activation, with miR-21 acting as an endogenous ligand [PMID:18000403, PMID:29777026, PMID:30455267]. Gain-of-function TLR8 variants cause a childhood-onset inborn error of immunity with proinflammatory T-cell activation and impaired B-cell maturation [PMID:33512449]. TLR8 escapes X-chromosome inactivation in human monocytes and T cells, contributing to sex-biased immune responses [PMID:37723501].","teleology":[{"year":2000,"claim":"Established TLR8 as a TLR-family receptor whose IL-1R-like TIR domain can engage NF-κB, defining it as an innate signaling receptor encoded on the X chromosome.","evidence":"Molecular cloning, sequence analysis, and NF-κB reporter assay of constitutively active TLR8 in transfected cells","pmids":["11022120"],"confidence":"Medium","gaps":["No physiological ligand identified","No mechanistic dissection of the downstream cascade"]},{"year":2006,"claim":"Resolved the TLR8 signaling cascade as distinct from IL-1R, showing it requires IRAK/IRAK4 (kinase-independent) and MEKK3 and uses IKKγ phosphorylation rather than the canonical TAK1/IKKαβ route.","evidence":"Genetic epistasis in TAK1−/− and MEKK3−/− MEFs, IRAK-deficient cells, kinase-dead rescue, and IKK-complex immunoblotting","pmids":["16737960"],"confidence":"High","gaps":["Did not identify the natural ligand driving this cascade","Mechanism of IKKγ phosphorylation not resolved"]},{"year":2008,"claim":"Defined TLR8 as a sensor of specific ssRNA motifs functionally separable from TLR7 and species-restricted, explaining why human and mouse TLR8 behave differently.","evidence":"TLR-transfected reporter cells, primary human monocyte/myeloid DC stimulation, and cross-species comparison","pmids":["18322178"],"confidence":"High","gaps":["Structural basis of motif recognition not defined","Source of physiological RNA ligand in vivo not established"]},{"year":2009,"claim":"Mapped the molecular determinant of species-specific ligand recognition to a five-residue motif after LRR-14, decoupling ligand sensing from dimerization and localization.","evidence":"Cross-species sequence alignment and deletion mutagenesis of hTLR8 with NF-κB reporter readout","pmids":["20004021"],"confidence":"High","gaps":["Did not show direct ligand contact by the motif","No structural model of the engaged receptor"]},{"year":2011,"claim":"Identified UNC93B1 as a physical partner required for TLR8 endosomal trafficking and signaling, placing TLR8 function in early endosomes/ER.","evidence":"Co-immunoprecipitation, confocal microscopy, subcellular fractionation, and domain-truncation analysis in HeLa and human monocytes","pmids":["22164301"],"confidence":"High","gaps":["Mechanism of UNC93B1-mediated trafficking not detailed","Relationship between trafficking and proteolytic maturation unresolved"]},{"year":2014,"claim":"Established that TLR8 maturation requires proteolytic cleavage at the LRR14–LRR15 loop by furin-like convertases and cathepsins, distinguishing its processing from TLR7/9.","evidence":"Immunoblotting of endogenous TLR8 in primary human cells with furin/cathepsin inhibitors and domain-deletion mutants","pmids":["25297876"],"confidence":"High","gaps":["Exact cleavage sites not mapped","Functional requirement of cleavage for ligand binding not directly tested"]},{"year":2015,"claim":"Identified TLR8 as the human sensor of bacterial and mitochondrial UR/URR RNA motifs, functioning as the human counterpart of mouse TLR13.","evidence":"siRNA/knockout and overexpression in macrophages and THP-1 cells, lysosomal inhibitors, synthetic oligoribonucleotides, and infection models","pmids":["26101323","26545385"],"confidence":"High","gaps":["Did not define the enzyme generating the agonistic fragments","Structural binding mode of the motifs not resolved"]},{"year":2019,"claim":"Identified RNase T2 as the non-redundant upstream enzyme that generates TLR8's agonistic uridine- and purine-2',3'-cyclophosphate-terminated ligands, defining how RNA is converted into a TLR8 signal.","evidence":"RNase T2 knockout/knockdown with reconstitution, biochemical characterization of degradation products, and TLR8 reporter assays","pmids":["31778653"],"confidence":"High","gaps":["Coordination between RNase T2 cleavage and RNase 2/other nucleases not fully resolved","In vivo requirement across infection contexts not established"]},{"year":2017,"claim":"Defined the resting-state structure of the TLR8 homodimer and a druggable protein-protein interface, showing antagonists lock the preformed dimer inactive.","evidence":"X-ray crystallography of two TLR8-ligand complexes with NF-κB and cytokine functional validation in primary cells and patient specimens","pmids":["29155428","30100350"],"confidence":"High","gaps":["Active-state conformational change upon agonist binding not captured","Allosteric coupling to the cytoplasmic TIR domain not structurally defined"]},{"year":2010,"claim":"Revealed a regulatory function whereby TLR8 negatively controls TLR7 expression and signaling, preventing spontaneous autoimmunity, and showed cell-type-specific division of labor with TLR9.","evidence":"Tlr8−/− single and Tlr8/9 double-knockout mice with TLR7 hyperresponsiveness, autoantibody, and disease readouts","pmids":["20811154","24474776"],"confidence":"High","gaps":["Molecular mechanism by which TLR8 restrains TLR7 expression not defined","Mouse TLR8 lacks RNA-ligand responsiveness, complicating translation to human"]},{"year":2019,"claim":"Established TLR8 as a dominant pyogenic-bacteria sensor and revealed that cell-surface TLR signaling cross-inhibits TLR8 by modifying IRAK-1, which is required for the TLR8-IRF5 axis.","evidence":"Selective TLR8 antagonist, IRAK-1 siRNA, TLR agonist combinations, and IRAK-1 immunoblotting in primary human monocytes","pmids":["31214180"],"confidence":"High","gaps":["Nature of the IRAK-1 modification not biochemically defined","Direct TLR8–IRF5 interaction not demonstrated"]},{"year":2018,"claim":"Demonstrated that TLR8 detects live-bacteria RNA as a viability discriminator shaping TFH differentiation and antibody responses, with a hypermorphic human variant linked to protective BCG immunity.","evidence":"Live vs. heat-killed bacteria, TLR8 agonists, human/porcine APC and TFH assays, pig vaccination model, and human BCG cohort genotyping","pmids":["29556002"],"confidence":"High","gaps":["Molecular basis of live/dead RNA discrimination not fully resolved","Causal mechanism of the protective polymorphism not established"]},{"year":2018,"claim":"Extended TLR8 function to the nervous system, showing it senses miR-21 and signals through ERK/p38 MAPK to drive neuropathic pain and dendritic pruning rather than axonal growth.","evidence":"Tlr8−/− mice, in utero electroporation, agonist injection, miR-21 inhibition, ERK/p38 assays, electrophysiology, and confocal localization in DRG/TG neurons","pmids":["29777026","30455267","36474072","33355900"],"confidence":"High","gaps":["Endosomal trafficking machinery in neurons not defined","Relationship between neuronal and immune signaling outputs unresolved"]},{"year":2022,"claim":"Showed that costimulation reprograms TLR8 signaling, with CXCL4 redirecting TBK1/IKKε to couple with IRF5 to amplify inflammatory transcription and NLRP3-driven IL-1β while attenuating IFN.","evidence":"Phosphoproteomics, ChIP-seq/ATAC-seq, kinase inhibitors, IRF5 knockdown, and NLRP3 assays in human monocytes/macrophages","pmids":["35701499","26928328"],"confidence":"High","gaps":["Direct kinase–IRF5 contacts not structurally defined","Generality across other costimuli unknown"]},{"year":2021,"claim":"Linked TLR8 directly to human disease by showing gain-of-function variants cause a childhood-onset inborn error of immunity with constitutive/enhanced activity, including a destabilizing variant that loses TLR7 restraint.","evidence":"Patient iPSC-derived myeloid cells, transfection-based TLR8 activity assays, immune phenotyping, and mutant-vs-WT functional comparison","pmids":["33512449","34981838"],"confidence":"Medium","gaps":["Structural basis of constitutive activity not resolved","Single-study/single-family cohorts limit genotype-phenotype breadth"]},{"year":2023,"claim":"Provided a molecular basis for sex-biased TLR8 immunity by showing TLR8 escapes X-chromosome inactivation, producing higher protein levels in female cells.","evidence":"RNA FISH relative to X-chromosome territories plus Western blot and flow cytometry across sex groups in primary immune cells","pmids":["37723501"],"confidence":"Medium","gaps":["Functional consequence of biallelic expression on signaling output not quantified","Contribution to specific autoimmune phenotypes not established"]},{"year":null,"claim":"How agonist binding at the two RNA pockets is allosterically transmitted across the cleaved, dimeric ectodomain to the TIR domain to selectively engage the MEKK3/IRAK-IRF5 cascade remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No active-state TLR8 structure with bound agonist coupled to TIR signaling","Mechanism distinguishing NF-κB vs IRF5 output not defined","Direct biochemical TLR8–IRF5/MEKK3 contacts unconfirmed"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[2,9,15,16,27]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,1,5]},{"term_id":"GO:0038024","term_label":"cargo receptor activity","supporting_discovery_ids":[2,26]}],"localization":[{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[4,6,27]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[4]},{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[9,27]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[1,5,15,16,26,35]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,35,29]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell 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Controls host immune response against pathogens through recognition of RNA degradation products specific to microorganisms that are initially processed by RNASET2 (PubMed:31778653). Recognizes GU-rich single-stranded RNA (GU-rich RNA) derived from SARS-CoV-2, SARS-CoV-1 and HIV-1 viruses (PubMed:33718825). Upon binding to agonists, undergoes dimerization that brings TIR domains from the two molecules into direct contact, leading to the recruitment of TIR-containing downstream adapter MYD88 through homotypic interaction (PubMed:23520111, PubMed:25599397, PubMed:26929371, PubMed:33718825). In turn, the Myddosome signaling complex is formed involving IRAK4, IRAK1, TRAF6, TRAF3 leading to activation of downstream transcription factors NF-kappa-B and IRF7 to induce pro-inflammatory cytokines and interferons, respectively (PubMed:16737960, PubMed:17932028, PubMed:29155428)","subcellular_location":"Endosome membrane","url":"https://www.uniprot.org/uniprotkb/Q9NR97/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TLR8","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/TLR8","total_profiled":1310},"omim":[{"mim_id":"615806","title":"SOLUTE CARRIER FAMILY 15 (OLIGOPEPTIDE TRANSPORTER), MEMBER 4; SLC15A4","url":"https://www.omim.org/entry/615806"},{"mim_id":"612373","title":"SOLUTE CARRIER FAMILY 29 (NUCLEOSIDE TRANSPORTER), MEMBER 3: SLC29A3","url":"https://www.omim.org/entry/612373"},{"mim_id":"611020","title":"MICRO RNA 21; MIR21","url":"https://www.omim.org/entry/611020"},{"mim_id":"610782","title":"MICRO RNA 29A; MIR29A","url":"https://www.omim.org/entry/610782"},{"mim_id":"608204","title":"UNC93 HOMOLOG B1, TLR SIGNALING REGULATOR; UNC93B1","url":"https://www.omim.org/entry/608204"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"lung","ntpm":10.0},{"tissue":"lymphoid 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Expression of constitutively active TLR8 stimulates NF-κB signaling. TLR8 gene is located on the X chromosome.\",\n      \"method\": \"Molecular cloning, sequence analysis, NF-κB reporter assay in transfected cells\",\n      \"journal\": \"European cytokine network\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — molecular cloning with functional NF-κB reporter validation, single lab, multiple methods\",\n      \"pmids\": [\"11022120\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"TLR8-mediated NF-κB and JNK activation require IRAK and IRAK4 (but not their kinase activities), are TAK1-independent, and are completely abolished in MEKK3-deficient cells. TLR8 ligands induce IKKγ phosphorylation but not IKKα/β phosphorylation or IKKγ ubiquitination (unlike IL-1R signaling), indicating a distinct NF-κB activation pathway downstream of TLR8.\",\n      \"method\": \"Genetic epistasis using TAK1−/− and MEKK3−/− mouse embryonic fibroblasts, IRAK-deficient human cells, kinase-inactive mutant rescue, immunoblotting for IκBα phosphorylation and IKK complex components\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — multiple knockout cell lines, reconstitution with kinase-dead mutants, orthogonal methods (reporter assay + immunoblot), rigorous genetic dissection\",\n      \"pmids\": [\"16737960\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Defined single-stranded RNA sequence motifs (TLR8-specific) selectively activate human TLR8 without stimulating TLR7. These TLR8 RNA motifs fail to induce IFN-α from plasmacytoid DCs but induce Th1-like and proinflammatory cytokines from monocytes and myeloid DCs. TLR8 RNA ligand responsiveness is species-specific (human and bovine but not mouse, rat, or porcine).\",\n      \"method\": \"TLR-transfected reporter cell lines, primary human immune cell stimulation, species comparison, TLR-specific inhibitory sequences\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reporter cell specificity testing plus primary cell validation across multiple species, multiple labs consistent with prior literature\",\n      \"pmids\": [\"18322178\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"A five-amino-acid motif in the TLR8 ectodomain immediately following LRR-14 (absent in rodent TLR8) is essential for species-specific ligand recognition. Deletion of this motif abolishes ligand responsiveness of human TLR8, while it is not required for self-dimerization or intracellular localization.\",\n      \"method\": \"Multiple species sequence alignment, deletion mutagenesis of hTLR8, NF-κB reporter assays in transfected cells\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — mutagenesis with functional readout, supported by cross-species comparison, single lab\",\n      \"pmids\": [\"20004021\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"UNC93B1 physically associates with human TLR8 and is required for TLR8-mediated signaling. TLR8 localizes to early endosomes and the ER (not late endosomes or lysosomes) in human monocytes. The transmembrane domain and TIR domain of TLR8 are required for proper targeting to the early endosome.\",\n      \"method\": \"Co-immunoprecipitation, confocal microscopy, subcellular fractionation, tail-truncation mutant analysis in HeLa transfectants and human monocytes\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP, direct localization imaging, domain mutant analysis with functional consequence, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"22164301\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"TLR8 senses bacterial RNA released within phagosomal vacuoles during Borrelia burgdorferi infection in human monocytes, mediating production of TNF-α, IL-6, and IL-10, and exclusively driving IRF7-mediated IFN-β transcription. TLR2 and TLR8 cooperate for cytokine responses in phagosomes; TLR8 is solely responsible for IFN-β induction. IRF7 is translocated to the nucleus in Bb-infected monocytes.\",\n      \"method\": \"TLR-specific inhibitory immunoregulatory sequences (IRS957), confocal and epifluorescence microscopy for TLR2/TLR8 colocalization with bacteria, IRF7 nuclear translocation assay, cytokine/mRNA measurement\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — TLR-specific inhibitors with multiple cytokine readouts, confocal colocalization, nuclear translocation, multiple orthogonal methods in primary human cells\",\n      \"pmids\": [\"21321205\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"TLR8 undergoes proteolytic cleavage in human monocytes and macrophages in a manner distinct from TLR7/9. The insertion loop between LRR14 and LRR15 is indispensable for cleavage and stepwise processing of the N-terminal fragment. Both furin-like proprotein convertase and cathepsins contribute to TLR8 cleavage in early/late endosomes.\",\n      \"method\": \"Immunoblotting of endogenous TLR8 in primary human cells, furin/cathepsin inhibitor treatment, domain deletion mutants, subcellular fractionation\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — biochemical cleavage assay with domain mutants and pharmacological inhibitors in primary human cells, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"25297876\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Small-molecule antagonists bind to a unique site at the protein-protein interface of the TLR8 homodimer, stabilizing the preformed TLR8 dimer in its resting (inactive) state and preventing activation. Crystal structures of two TLR8-ligand complexes validated this novel binding site.\",\n      \"method\": \"X-ray crystallography of TLR8-ligand complexes, NF-κB reporter assay, cytokine measurement in human primary cells and patient specimens\",\n      \"journal\": \"Nature chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structures of two independent complexes validated mechanistically by functional assays in cell lines, primary cells, and patient specimens\",\n      \"pmids\": [\"29155428\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Small-molecule TLR8 antagonists designed via rational structure-based drug design bind an unconventional pocket at the TLR8 protein-protein interface. X-ray crystal structures of TLR8 in complex with inhibitors confirmed the binding mode, showing the compounds sit between two TLR8 monomers preventing homodimerization.\",\n      \"method\": \"Rational structure-based design, X-ray crystallography, NF-κB reporter assay, cytokine measurement in PBMC and TLR8-transgenic mouse splenocytes\",\n      \"journal\": \"Cell chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structures with functional validation, single lab, multiple biological systems\",\n      \"pmids\": [\"30100350\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"The lysosomal endoribonuclease RNase T2 is a non-redundant upstream component of TLR8-dependent RNA recognition. RNase T2 preferentially cleaves ssRNA between purine and uridine residues, generating catabolic uridine and purine-2',3'-cyclophosphate-terminated oligoribonucleotides that serve as agonistic ligands for TLR8's two distinct binding pockets.\",\n      \"method\": \"RNase T2 knockout/knockdown, reconstitution assays, biochemical characterization of RNA degradation products, TLR8 reporter assays\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — genetic knockout with reconstitution, biochemical characterization of generated ligands, mapping to known TLR8 binding pockets, published in Cell\",\n      \"pmids\": [\"31778653\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Mouse TLR8 deficiency leads to overexpression of TLR7 on dendritic cells and hyperresponsiveness to TLR7 ligands. TLR8 functions as a negative regulator of TLR7 expression and TLR7-mediated signaling, preventing spontaneous autoimmunity.\",\n      \"method\": \"Tlr8−/− mouse model, TLR7 expression measurement, NF-κB activation assays, autoantibody measurement, histopathology\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — defined knockout phenotype with multiple readouts, genetic epistasis (Tlr8−/−Tlr7−/− double KO), independently replicated in related publications\",\n      \"pmids\": [\"20811154\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"TLR8 on dendritic cells (but not B cells) restrains TLR7-mediated autoimmunity, while TLR9 restrains TLR7 response specifically on B cells. Double TLR8/9-deficient mice show additive lupus-like disease. TLR8 and TLR9 act on different cell types to control TLR7.\",\n      \"method\": \"Single and double TLR8/9 knockout mice, cell-type-specific TLR7 hyperresponsiveness assays, autoantibody and disease phenotype measurement\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis with single and double knockouts, cell-type-specific dissection, rigorous phenotypic readouts\",\n      \"pmids\": [\"24474776\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"TLR8 is activated in human monocytic cells following Helicobacter pylori phagocytosis. A TLR8 SNP (rs3764880:A>G; Met1Val) fine-tunes translation of the two TLR8 isoforms: TLR8 variant 2 (TLR8v2) is the prevalent functional isoform, while TLR8v1 positively regulates TLR8 function in CD16+CD14+ differentiated monocytes.\",\n      \"method\": \"siRNA knockdown, overexpression, TLR8-specific reporter assays, phagocytosis experiments with live bacteria, cytokine measurement, isoform-specific translation analysis\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA plus overexpression with functional readout, single lab, multiple methods\",\n      \"pmids\": [\"20652908\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"TLR8 is expressed in neurons and axons of the mouse brain. TLR8 activation suppresses neurite outgrowth and induces neuronal apoptosis through an NF-κB-independent mechanism.\",\n      \"method\": \"TLR8 expression profiling in mouse brain development, neuronal culture assays with TLR8 ligands, NF-κB reporter assays, neurite outgrowth measurement\",\n      \"journal\": \"Cell cycle\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization with functional consequence, NF-κB independence established by reporter assay, single lab\",\n      \"pmids\": [\"18000403\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"HIV-1 infection of human monocytes induces pro-IL-1β expression via TLR8-dependent mechanisms. TLR8 senses HIV-1-derived RNA; both HIV-1 entry, reverse transcription, and integration are required for TLR8-mediated pro-IL-1β expression. Subsequently, NLRP3 inflammasome (activated by cathepsin B and ROS) cleaves pro-IL-1β into bioactive IL-1β.\",\n      \"method\": \"TLR8 knockdown, HIV-1 infection of primary human monocytes, TLR8-specific reporter assay, HIV lifecycle inhibitors, cathepsin B inhibitor, caspase-1 assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with multiple pharmacological inhibitors, pathway dissection with multiple orthogonal methods, single lab\",\n      \"pmids\": [\"24939850\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Human TLR8 senses bacterial RNA in primary human monocyte-derived macrophages; TLR8 is unambiguously identified as the receptor for bacterial RNA using siRNA knockdown and overexpression. The TLR8-recognized sequence motif in bacterial RNA is distinct from that recognized by mouse TLR13. TLR8-dependent bacterial RNA detection is critical for monocyte activation during Streptococcus pyogenes infection.\",\n      \"method\": \"siRNA knockdown, TLR8 overexpression in macrophages, lysosomal maturation inhibitors, S. pyogenes infection, cytokine measurement\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — siRNA plus overexpression orthogonal approach, infection model validation, consistent with multiple independent studies on TLR8 RNA sensing\",\n      \"pmids\": [\"26101323\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Human TLR8 senses UR/URR motifs in bacterial RNA (including Sa19 23S rRNA-derived fragments) and mitochondrial 16S rRNA-derived oligoribonucleotides. TLR8 function requires UNC93B1 (lysosomal function) and acts as the human functional equivalent of mouse TLR13 for bacterial RNA sensing. TLR8 knockout THP-1 cells are refractory to these RNA stimuli.\",\n      \"method\": \"TLR8/Unc93b1 knockout THP-1 cells, TLR8 ectopic overexpression, lysosomal function inhibitors, synthetic oligoribonucleotide stimulation, NF-κB/cytokine reporter assays\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — knockout plus overexpression reconstitution, RNA motif-specific dissection, published in EMBO reports, consistent with concurrent independent study\",\n      \"pmids\": [\"26545385\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Self-RNA complexed with the antimicrobial peptide LL37 is transported into endosomal compartments and activates TLR8 in myeloid DCs (mDCs), leading to TNF-α and IL-6 production and mDC maturation. This mechanism drives autoimmune responses in psoriasis.\",\n      \"method\": \"TLR7/TLR8 knockdown/blocking in primary DCs, confocal microscopy for LL37-RNA complex localization, cytokine ELISA, flow cytometry for DC maturation markers\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — TLR8-specific knockdown with multiple functional readouts, in vivo correlation in psoriatic lesions, replicated in multiple cell types\",\n      \"pmids\": [\"19703986\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"TLR8 activation by imidazoquinolines mediates NF-κB activation and proinflammatory cytokine production. In addition, imiquimod activates NF-κB independently of TLR7 and TLR8 through antagonism of adenosine receptors (particularly A1 and A2A subtypes), as demonstrated in Chinese hamster ovary cells expressing human adenosine receptor subtypes.\",\n      \"method\": \"TLR7/TLR8-negative cell lines, radioligand binding competition, adenylyl cyclase activity assay, CHO cells stably transfected with adenosine receptor subtypes\",\n      \"journal\": \"The Journal of investigative dermatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — radioligand binding plus functional assay in receptor-transfected cells, single lab, mechanistically defines TLR-independent imiquimod action\",\n      \"pmids\": [\"16575388\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"TLR8 transcriptional activity is regulated by C/EBPδ and C/EBPβ binding to three C/EBP cis-acting elements in the hTLR8 promoter. TLR8 stimulation (R848) increases TLR8 transcription via enhanced C/EBPδ binding. IFN-γ increases TLR8 transcription via STAT1 binding to IFN-γ-activated sequence (GAS) elements in the TLR8 promoter.\",\n      \"method\": \"TLR8 promoter isolation, luciferase reporter assays, chromatin immunoprecipitation (ChIP) for C/EBPδ, C/EBPβ, and STAT1 binding\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — promoter-reporter assay plus ChIP validation of transcription factor binding, two independent stimuli (TLR8 agonist and IFN-γ), single lab with multiple orthogonal methods\",\n      \"pmids\": [\"20829351\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"TLR7 and TLR8 agonists trigger different signaling pathways during human DC maturation. Both JNK and NF-κB positively regulate maturation markers and cytokines downstream of both TLR7 and TLR8. However, p38 MAPK inhibits CD40 expression and IL-12 production in TLR8-stimulated DCs (while promoting them in TLR7-stimulated DCs). The Jak/STAT pathway positively regulates CD40 and cytokines in TLR7-stimulated but negatively regulates cytokine secretion in TLR8-stimulated DCs.\",\n      \"method\": \"Selective TLR7 agonist (imiquimod) vs. TLR8 agonist (3M002), specific kinase inhibitors (p38, JNK, NF-κB, Jak/STAT), cytokine ELISA, flow cytometry for DC maturation markers\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological dissection with selective agonists and kinase inhibitors, multiple readouts, single lab\",\n      \"pmids\": [\"19164127\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"TLR7 and TLR8 activate distinct signaling cascades in human monocytes during RNA virus infection. TLR7 specifically increases FOSL1 expression, which reduces IL-27 and TNFα production. TLR7 (but not TLR8) activation stimulates Ca2+ flux that prevents type I IFN responses. These distinct pathways correlate with different cytokine profiles for CD4+ T helper cell polarization.\",\n      \"method\": \"TLR7/TLR8-specific agonists, siRNA knockdown, signaling pathway analysis, Ca2+ flux measurement, gene expression profiling in human CD14+ monocytes infected with 6 different RNA viruses\",\n      \"journal\": \"Science signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — siRNA knockdown with mechanistic pathway dissection, multiple RNA virus models, Ca2+ flux measurement, FOSL1 target validation, multiple orthogonal methods\",\n      \"pmids\": [\"31662487\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"TLR8 is required for TNF-α overproduction in FANCC-deficient mononuclear phagocytes. TLR8 (or a TLR8-associated protein) is ubiquitinated in Fancc−/− mutant cells but not complemented cells. FANCC suppresses TLR8 activity via canonical downstream intermediates IRAK and IKKα/β, and this function is independent of FANCC's role in protecting the genome from crosslinking agents.\",\n      \"method\": \"TLR8-specific inhibitory sequences, FANCC-deficient THP-1 cells and Fancc−/− macrophages, TLR8 agonist stimulation, ubiquitination proteomics, FANCC point mutant complementation\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockout plus TLR8-specific inhibition with functional readout, point mutant dissection of FANCC domains, single lab\",\n      \"pmids\": [\"19850743\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"DCIR (an ITIM-containing C-type lectin receptor) is endocytosed via clathrin-dependent internalization into endo-/lysosomal compartments including LAMP-1+ lysosomes. DCIR triggering specifically inhibits TLR8-mediated IL-12 and TNF-α production but does not affect TLR2-, TLR3-, or TLR4-induced cytokine production, demonstrating CLR/TLR8 crosstalk.\",\n      \"method\": \"Confocal microscopy with endosomal markers, clathrin inhibitor, DCIR-specific mAb triggering, cytokine ELISA, co-stimulatory molecule flow cytometry\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct co-localization imaging with functional consequence, specific pharmacological inhibition, TLR specificity established by comparison, single lab\",\n      \"pmids\": [\"19028959\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"TLR8 couples with SOCS-1 (suppressor of cytokine signaling-1) in mice; SOCS-1 directly associates with TLR8 but not TLR7. This TLR8-SOCS-1 interaction inhibits TLR7-mediated antiviral immunity (including ISG-56 expression and IFN responses) during West Nile virus infection. Tlr8−/− mice show increased TLR7 and ISG-56 expression and are resistant to WNV infection.\",\n      \"method\": \"TLR8−/− mice, SOCS-1 co-immunoprecipitation with TLR7 and TLR8, siRNA knockdown of SOCS-1, WNV infection model, gene expression analysis\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct co-IP of SOCS-1 with TLR8 but not TLR7, genetic KO validation, siRNA knockdown, single lab\",\n      \"pmids\": [\"27798161\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"TLR8 activation in neurons promotes dendritic pruning via MyD88 signaling and specifically involves MAPK signaling. TLR8 is more critical for dendritic arborization at late developmental stages in vivo. Unlike TLR7 and TLR3, TLR8 activation does not control axonal growth.\",\n      \"method\": \"In vitro neuronal cultures, in utero electroporation, transcriptomic profiling, MAPK pathway inhibitors, TLR-specific agonists, TLR8 knockdown\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo electroporation plus in vitro pharmacological dissection, transcriptomic analysis, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"29777026\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"TLR8 senses bacterial RNA from live bacteria (but not dead bacteria) as a distinguishing viability signal, inducing a specific cytokine profile in APCs that promotes follicular helper T (TFH) cell differentiation and antibody responses. A hypermorphic TLR8 polymorphism is associated with protective BCG vaccine immunity in humans.\",\n      \"method\": \"Live vs. heat-killed bacterial comparison, TLR8-specific agonists, human and porcine APC stimulation, TFH differentiation assays, pig live vaccination model, human BCG cohort analysis\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — mechanistic dissection with live/dead bacteria, TLR8-specific agonist, animal model, human cohort polymorphism validation, multiple orthogonal systems\",\n      \"pmids\": [\"29556002\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"TLR8 in dorsal root ganglion neurons localizes to endosomes and lysosomes and mediates ERK activation, inflammatory mediator production, and neuronal hyperexcitability after spinal nerve ligation. miR-21 is increased in DRG neurons after nerve injury and serves as an endogenous TLR8 ligand that drives neuropathic pain hypersensitivity.\",\n      \"method\": \"Tlr8−/− mice, intrathecal/intradermal TLR8 agonist injection, miR-21 inhibition, ERK phosphorylation assays, electrophysiology, confocal microscopy for TLR8 subcellular localization\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO, pharmacological inhibition, direct localization, multiple readouts including electrophysiology, ligand identity validated by miR-21 inhibition\",\n      \"pmids\": [\"30455267\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"TLR8 (but not TLR7 or TLR9) in CD4+ T cells senses endosomal HIV-1 ssRNA, inducing cytokine secretion, upregulating activation markers, promoting Th1/Th17 differentiation, enhancing HIV-1 replication, and potentiating reversal of latency in patient-derived T cells.\",\n      \"method\": \"Synthetic TLR-specific ligands, TLR-specific blocking, primary CD4+ T cell assays, HIV-1 infection of patient-derived cells, latency reversal assay, cytokine/activation marker measurement\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — TLR-specific pharmacological and genetic dissection, patient-derived cell validation, multiple functional readouts, published in Nature Communications\",\n      \"pmids\": [\"31919342\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CXCL4 costimulation synergizes with TLR8 to activate TBK1 and IKKε, repurposing these kinases to couple with IRF5 (rather than IRF3) for an inflammatory response. This synergy activates the NLRP3 inflammasome, induces de novo enhancers associated with inflammatory genes, and selectively amplifies inflammatory gene transcription and IL-1β production while partially attenuating the IFN response.\",\n      \"method\": \"Phosphoproteomics, ChIP-seq/ATAC-seq for chromatin remodeling, kinase inhibitors, IRF5 knockdown, NLRP3 inflammasome assays in human monocytes/macrophages\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — multi-omics approach (ChIP-seq, ATAC-seq, phosphoproteomics), pharmacological and genetic dissection, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"35701499\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"TLR8 agonism activates the NLRP3 inflammasome in monocytes, mediating release of mature IL-1β and IL-18. TLR8 primes monocytes for pro-IL-1β, pro-IL-18, and caspase-1 production, while also activating the NLRP3 complex. Caspase-1 inhibition blocks inflammasome activation but not other TLR8-induced mediators (e.g., TNFα).\",\n      \"method\": \"Caspase-1 inhibitor, NLRP3 inhibitors, cytokine ELISA (mature IL-1β, IL-18), in vivo cynomolgus monkey pharmacodynamics\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological dissection with caspase-1 and NLRP3 inhibitors, in vivo validation, single lab\",\n      \"pmids\": [\"26928328\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Microbial small RNAs (msRNA) enriched on LDL activate macrophage TLR8, driving pro-inflammatory macrophage polarization. Competitive TLR8 antagonism with locked nucleic acids prevented native LDL-induced macrophage polarization in vitro and reorganized lesion macrophage phenotypes in vivo, reducing atherosclerosis disease burden.\",\n      \"method\": \"LDL reconstitution (with/without msRNA cargo), TLR8 antagonist, single-cell RNA sequencing, mouse atherosclerosis models\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reconstitution of LDL particles, competitive antagonism, scRNA-seq, in vivo disease model, multiple orthogonal methods\",\n      \"pmids\": [\"36474072\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Gain-of-function variants in TLR8 cause a novel childhood-onset inborn error of immunity. All identified variants confer constitutive or enhanced TLR8 activity, leading to proinflammatory T cell activation, elevated serum cytokines, and impaired B cell maturation. iPSC-derived myeloid cells from patients showed increased TLR8 responsiveness.\",\n      \"method\": \"Patient-derived iPSC myeloid differentiation, in vitro TLR8 activity assays in transfected cell lines and patient primary cells, immune phenotyping\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — patient variants validated in iPSC-derived cells and transfected lines, multiple patients with distinct variants, single study\",\n      \"pmids\": [\"33512449\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"TLR8 p.G572V mutation causes impaired TLR8 protein stability, cross-reactivity to TLR7 ligands, and reduced ability of TLR8 to attenuate TLR7 signaling. This imbalance toward TLR7-dependent signaling leads to NF-κB activation and elevated IL-1β, IL-6, and TNFα production.\",\n      \"method\": \"In vitro transfection assays with mutant TLR8, primary cell assays, NF-κB reporter, cytokine measurement, patient primary cells\",\n      \"journal\": \"American journal of hematology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutant vs. wild-type TLR8 functional comparison in transfected and patient cells, single lab, single case family\",\n      \"pmids\": [\"34981838\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"TLR8 escapes X chromosome inactivation (XCI) in human CD14+ monocytes and CD4+ T cells. Both TLR7 and TLR8 genes can be simultaneously expressed from the active X chromosome, occurring more frequently in women and Klinefelter syndrome men than in euploid men (sevenfold difference in frequency). TLR8 protein expression is significantly higher in female mononuclear blood cells than in male cells.\",\n      \"method\": \"RNA FISH for primary transcripts relative to X chromosome territories in primary immune cells, Western blot and flow cytometry for TLR8 protein expression across sex groups\",\n      \"journal\": \"Biology of sex differences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct RNA FISH visualization on single cells with X chromosome territory probes, protein quantification by two methods, single lab\",\n      \"pmids\": [\"37723501\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"TLR8 is a dominating sensor of multiple pyogenic bacteria (S. aureus, GBS, S. pneumoniae, P. aeruginosa) in human primary monocytes, largely responsible for IL-1β and IL-12p70 production. Cell surface TLR activation (TLR2, TLR4, TLR5) attenuates TLR8-IRF5 signaling by modifying/sequestering IRAK-1, which is required for TLR8-IRF5 pathway activation. IRAK-1 silencing reduces TLR8-driven IFNβ and TNF.\",\n      \"method\": \"Selective TLR8 chemical antagonist, siRNA knockdown of IRAK-1, TLR agonist combinations, immunoblotting for IRAK-1 modifications, cytokine ELISA in primary human monocytes\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — selective TLR8 antagonist plus siRNA knockdown, mechanistic dissection of IRAK-1 role, multiple bacterial species tested, multiple orthogonal methods\",\n      \"pmids\": [\"31214180\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"TLR8 inhibition in the trigeminal ganglion (TG) attenuates trigeminal neuropathic pain. TLR8 activation in TG neurons induces ERK and p38 MAPK activation and pro-inflammatory cytokine production. Intra-TG injection of TLR8 agonist VTX-2337 induces pain hypersensitivity and increases intracellular Ca2+ concentration in TG neurons.\",\n      \"method\": \"Tlr8 knockdown and conditional deletion in TG, ERK/p38 phosphorylation assays, cytokine measurement, Ca2+ imaging, behavioral pain assays\",\n      \"journal\": \"Neuroscience bulletin\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockdown with behavioral and cellular readouts, TLR8 agonist injection validation, single lab\",\n      \"pmids\": [\"33355900\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"TLR8 activation promotes AML cell differentiation and growth inhibition in a TLR8/MyD88/p38-dependent manner, establishing a direct anti-leukemic role for TLR8 signaling independent of immunomodulation.\",\n      \"method\": \"TLR8 agonist (R848) stimulation, MyD88 and p38 pathway inhibitors, TLR8 overexpression, in vivo xenograft model\",\n      \"journal\": \"Leukemia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological and genetic pathway dissection, in vivo xenograft validation, single lab\",\n      \"pmids\": [\"25283842\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"TLR8 is expressed in the hepatic myeloid compartment (Kupffer cells). TLR8 agonism (selgantolimod) activates Kupffer cells and induces IL-6 secretion, which indirectly impairs HBV entry into hepatocytes by downregulating NTCP (sodium taurocholate cotransporting polypeptide). Co-treatment with an anti-IL-6 neutralizing antibody reverses the HBV entry inhibition.\",\n      \"method\": \"Single-cell RNA-seq of human liver, Kupffer cell isolation and TLR8 agonist treatment, SLGN-conditioned media transfer to hepatocytes, HBV infection quantification, anti-IL-6 neutralization, RNA-seq of Kupffer cells and hepatocytes\",\n      \"journal\": \"Gut\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditioned media transfer with cytokine neutralization identifies IL-6 as the mechanistic mediator, scRNA-seq cell-type identification, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"38697771\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TLR8 is an endosomal single-stranded RNA sensor that is proteolytically processed (via furin-like convertases and cathepsins at the LRR14-15 loop) and trafficked to early endosomes via UNC93B1; upon binding RNA degradation products generated by RNase T2 (uridine and purine-2',3'-cyclophosphate-terminated oligonucleotides at two distinct binding pockets), TLR8 homodimerizes and activates a MEKK3-dependent (TAK1-independent) NF-κB and MAPK signaling cascade requiring IRAK/IRAK4 (but not their kinase activities) and IKKγ phosphorylation, while also engaging IRF5 for IFN-β production; TLR8 is negatively regulated by cell-surface TLR activation (via IRAK-1 modification), by its own negative control over TLR7 expression in dendritic cells (preventing spontaneous autoimmunity), and by small-molecule antagonists that stabilize the resting-state homodimer; in addition to immune cells, TLR8 functions in neurons (suppressing neurite outgrowth and mediating pain signaling via ERK/p38 MAPK) and escapes X chromosome inactivation, contributing to sex-biased immune responses.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"TLR8 is an endosomal innate-immune sensor of single-stranded RNA that signals through its IL-1 receptor-homologous cytoplasmic TIR domain to drive NF-\\u03baB and proinflammatory gene expression [#0, #1]. Productive sensing requires upstream processing and trafficking: TLR8 associates with UNC93B1 and localizes to early endosomes and ER, with its transmembrane and TIR domains directing endosomal targeting [#4]; it undergoes furin-like convertase- and cathepsin-dependent proteolytic cleavage at the LRR14\\u2013LRR15 insertion loop [#6]; and its ligands are catabolic uridine- and purine-2',3'-cyclophosphate-terminated oligoribonucleotides generated by the lysosomal endoribonuclease RNase T2, which dock into TLR8's two distinct binding pockets [#9]. A five-residue motif following LRR-14, absent in rodents, confers species-specific ligand recognition and underlies human-restricted responsiveness [#2, #3]. Downstream, TLR8 engages a distinct activation route requiring IRAK and IRAK4 (independent of their kinase activity) and MEKK3, proceeding through IKK\\u03b3 phosphorylation rather than the canonical TAK1/IKK\\u03b1\\u03b2 axis used by IL-1R [#1], and it couples IRAK-1 to an IRF5-dependent type I IFN response [#35]. Through these mechanisms TLR8 detects bacterial and mitochondrial RNA (UR/URR motifs), viral RNA, and self-RNA, distinguishing live from dead bacteria as a viability signal and activating the NLRP3 inflammasome to produce IL-1\\u03b2 [#15, #16, #26, #30]. TLR8 also acts as a negative regulator of TLR7 expression and signaling in dendritic cells, restraining spontaneous autoimmunity [#10, #11]. Beyond immunity, TLR8 functions in neurons to suppress neurite outgrowth, drive dendritic pruning via MyD88/MAPK signaling, and mediate neuropathic pain through ERK/p38 activation, with miR-21 acting as an endogenous ligand [#13, #25, #27]. Gain-of-function TLR8 variants cause a childhood-onset inborn error of immunity with proinflammatory T-cell activation and impaired B-cell maturation [#32]. TLR8 escapes X-chromosome inactivation in human monocytes and T cells, contributing to sex-biased immune responses [#34].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Established TLR8 as a TLR-family receptor whose IL-1R-like TIR domain can engage NF-\\u03baB, defining it as an innate signaling receptor encoded on the X chromosome.\",\n      \"evidence\": \"Molecular cloning, sequence analysis, and NF-\\u03baB reporter assay of constitutively active TLR8 in transfected cells\",\n      \"pmids\": [\"11022120\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No physiological ligand identified\", \"No mechanistic dissection of the downstream cascade\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Resolved the TLR8 signaling cascade as distinct from IL-1R, showing it requires IRAK/IRAK4 (kinase-independent) and MEKK3 and uses IKK\\u03b3 phosphorylation rather than the canonical TAK1/IKK\\u03b1\\u03b2 route.\",\n      \"evidence\": \"Genetic epistasis in TAK1\\u2212/\\u2212 and MEKK3\\u2212/\\u2212 MEFs, IRAK-deficient cells, kinase-dead rescue, and IKK-complex immunoblotting\",\n      \"pmids\": [\"16737960\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the natural ligand driving this cascade\", \"Mechanism of IKK\\u03b3 phosphorylation not resolved\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Defined TLR8 as a sensor of specific ssRNA motifs functionally separable from TLR7 and species-restricted, explaining why human and mouse TLR8 behave differently.\",\n      \"evidence\": \"TLR-transfected reporter cells, primary human monocyte/myeloid DC stimulation, and cross-species comparison\",\n      \"pmids\": [\"18322178\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of motif recognition not defined\", \"Source of physiological RNA ligand in vivo not established\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Mapped the molecular determinant of species-specific ligand recognition to a five-residue motif after LRR-14, decoupling ligand sensing from dimerization and localization.\",\n      \"evidence\": \"Cross-species sequence alignment and deletion mutagenesis of hTLR8 with NF-\\u03baB reporter readout\",\n      \"pmids\": [\"20004021\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not show direct ligand contact by the motif\", \"No structural model of the engaged receptor\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Identified UNC93B1 as a physical partner required for TLR8 endosomal trafficking and signaling, placing TLR8 function in early endosomes/ER.\",\n      \"evidence\": \"Co-immunoprecipitation, confocal microscopy, subcellular fractionation, and domain-truncation analysis in HeLa and human monocytes\",\n      \"pmids\": [\"22164301\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of UNC93B1-mediated trafficking not detailed\", \"Relationship between trafficking and proteolytic maturation unresolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Established that TLR8 maturation requires proteolytic cleavage at the LRR14\\u2013LRR15 loop by furin-like convertases and cathepsins, distinguishing its processing from TLR7/9.\",\n      \"evidence\": \"Immunoblotting of endogenous TLR8 in primary human cells with furin/cathepsin inhibitors and domain-deletion mutants\",\n      \"pmids\": [\"25297876\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Exact cleavage sites not mapped\", \"Functional requirement of cleavage for ligand binding not directly tested\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identified TLR8 as the human sensor of bacterial and mitochondrial UR/URR RNA motifs, functioning as the human counterpart of mouse TLR13.\",\n      \"evidence\": \"siRNA/knockout and overexpression in macrophages and THP-1 cells, lysosomal inhibitors, synthetic oligoribonucleotides, and infection models\",\n      \"pmids\": [\"26101323\", \"26545385\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the enzyme generating the agonistic fragments\", \"Structural binding mode of the motifs not resolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified RNase T2 as the non-redundant upstream enzyme that generates TLR8's agonistic uridine- and purine-2',3'-cyclophosphate-terminated ligands, defining how RNA is converted into a TLR8 signal.\",\n      \"evidence\": \"RNase T2 knockout/knockdown with reconstitution, biochemical characterization of degradation products, and TLR8 reporter assays\",\n      \"pmids\": [\"31778653\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Coordination between RNase T2 cleavage and RNase 2/other nucleases not fully resolved\", \"In vivo requirement across infection contexts not established\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Defined the resting-state structure of the TLR8 homodimer and a druggable protein-protein interface, showing antagonists lock the preformed dimer inactive.\",\n      \"evidence\": \"X-ray crystallography of two TLR8-ligand complexes with NF-\\u03baB and cytokine functional validation in primary cells and patient specimens\",\n      \"pmids\": [\"29155428\", \"30100350\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Active-state conformational change upon agonist binding not captured\", \"Allosteric coupling to the cytoplasmic TIR domain not structurally defined\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Revealed a regulatory function whereby TLR8 negatively controls TLR7 expression and signaling, preventing spontaneous autoimmunity, and showed cell-type-specific division of labor with TLR9.\",\n      \"evidence\": \"Tlr8\\u2212/\\u2212 single and Tlr8/9 double-knockout mice with TLR7 hyperresponsiveness, autoantibody, and disease readouts\",\n      \"pmids\": [\"20811154\", \"24474776\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism by which TLR8 restrains TLR7 expression not defined\", \"Mouse TLR8 lacks RNA-ligand responsiveness, complicating translation to human\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Established TLR8 as a dominant pyogenic-bacteria sensor and revealed that cell-surface TLR signaling cross-inhibits TLR8 by modifying IRAK-1, which is required for the TLR8-IRF5 axis.\",\n      \"evidence\": \"Selective TLR8 antagonist, IRAK-1 siRNA, TLR agonist combinations, and IRAK-1 immunoblotting in primary human monocytes\",\n      \"pmids\": [\"31214180\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Nature of the IRAK-1 modification not biochemically defined\", \"Direct TLR8\\u2013IRF5 interaction not demonstrated\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrated that TLR8 detects live-bacteria RNA as a viability discriminator shaping TFH differentiation and antibody responses, with a hypermorphic human variant linked to protective BCG immunity.\",\n      \"evidence\": \"Live vs. heat-killed bacteria, TLR8 agonists, human/porcine APC and TFH assays, pig vaccination model, and human BCG cohort genotyping\",\n      \"pmids\": [\"29556002\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of live/dead RNA discrimination not fully resolved\", \"Causal mechanism of the protective polymorphism not established\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Extended TLR8 function to the nervous system, showing it senses miR-21 and signals through ERK/p38 MAPK to drive neuropathic pain and dendritic pruning rather than axonal growth.\",\n      \"evidence\": \"Tlr8\\u2212/\\u2212 mice, in utero electroporation, agonist injection, miR-21 inhibition, ERK/p38 assays, electrophysiology, and confocal localization in DRG/TG neurons\",\n      \"pmids\": [\"29777026\", \"30455267\", \"36474072\", \"33355900\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endosomal trafficking machinery in neurons not defined\", \"Relationship between neuronal and immune signaling outputs unresolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Showed that costimulation reprograms TLR8 signaling, with CXCL4 redirecting TBK1/IKK\\u03b5 to couple with IRF5 to amplify inflammatory transcription and NLRP3-driven IL-1\\u03b2 while attenuating IFN.\",\n      \"evidence\": \"Phosphoproteomics, ChIP-seq/ATAC-seq, kinase inhibitors, IRF5 knockdown, and NLRP3 assays in human monocytes/macrophages\",\n      \"pmids\": [\"35701499\", \"26928328\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct kinase\\u2013IRF5 contacts not structurally defined\", \"Generality across other costimuli unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Linked TLR8 directly to human disease by showing gain-of-function variants cause a childhood-onset inborn error of immunity with constitutive/enhanced activity, including a destabilizing variant that loses TLR7 restraint.\",\n      \"evidence\": \"Patient iPSC-derived myeloid cells, transfection-based TLR8 activity assays, immune phenotyping, and mutant-vs-WT functional comparison\",\n      \"pmids\": [\"33512449\", \"34981838\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of constitutive activity not resolved\", \"Single-study/single-family cohorts limit genotype-phenotype breadth\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Provided a molecular basis for sex-biased TLR8 immunity by showing TLR8 escapes X-chromosome inactivation, producing higher protein levels in female cells.\",\n      \"evidence\": \"RNA FISH relative to X-chromosome territories plus Western blot and flow cytometry across sex groups in primary immune cells\",\n      \"pmids\": [\"37723501\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of biallelic expression on signaling output not quantified\", \"Contribution to specific autoimmune phenotypes not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How agonist binding at the two RNA pockets is allosterically transmitted across the cleaved, dimeric ectodomain to the TIR domain to selectively engage the MEKK3/IRAK-IRF5 cascade remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No active-state TLR8 structure with bound agonist coupled to TIR signaling\", \"Mechanism distinguishing NF-\\u03baB vs IRF5 output not defined\", \"Direct biochemical TLR8\\u2013IRF5/MEKK3 contacts unconfirmed\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [2, 9, 15, 16, 27]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 1, 5]},\n      {\"term_id\": \"GO:0038024\", \"supporting_discovery_ids\": [2, 26]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [4, 6, 27]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [9, 27]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [1, 5, 15, 16, 26, 35]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 35, 29]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [30, 29]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"UNC93B1\", \"IRAK4\", \"IRAK1\", \"MEKK3\", \"SOCS1\", \"IRF5\"],\n    \"other_free_text\": []\n  }\n}\n```","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":9,"faith_total":9,"faith_pct":100.0}}