{"gene":"FGL2","run_date":"2026-06-09T23:54:43","timeline":{"discoveries":[{"year":1997,"finding":"FGL2 encodes a novel prothrombinase expressed on endothelial cells and Kupffer cells in the liver following MHV-3 infection; the protein directly cleaves prothrombin to thrombin, leading to fibrin deposition and hepatocellular necrosis. Expression is tissue-specific, detected in liver, spleen, and lungs but not brain or kidney despite equivalent viral titers.","method":"Northern blot, in situ hybridization, immunochemistry, functional procoagulant activity assay","journal":"Journal of virology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (Northern, ISH, IHC, enzymatic activity assay), replicated across subsequent studies","pmids":["9371581"],"is_preprint":false},{"year":2001,"finding":"Human FGL2 encodes a 439-amino-acid type II integral membrane protein with a C-terminal fibrinogen-related domain; recombinant protein expressed in vitro functions as a serine protease that directly cleaves prothrombin to thrombin (prothrombinase activity). The gene is single-copy, located at 7q11.23, with two exons.","method":"Recombinant protein expression, functional prothrombinase assay, radiation hybrid mapping, FISH","journal":"Genomics","confidence":"High","confidence_rationale":"Tier 1 / Strong — functional reconstitution of enzymatic activity with genetic and chromosomal characterization, replicated in multiple subsequent studies","pmids":["11170750"],"is_preprint":false},{"year":2002,"finding":"FGL2 prothrombinase activity requires phosphatidylserine-containing phospholipids and calcium; factor Va enhances catalytic efficiency ~600-fold. Site-directed mutagenesis identified Ser89 as the critical catalytic residue. The enzyme is not inhibited by classical serine protease inhibitors (antithrombin III, aprotinin, PMSF, soybean trypsin inhibitor, 4-aminobenzamidine) but is completely abrogated by diisopropylfluorophosphate.","method":"Baculovirus expression, phospholipid vesicle reconstitution, kinetic analysis, site-directed mutagenesis, truncation analysis, inhibitor studies","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1 / Strong — rigorous in vitro reconstitution with mutagenesis and kinetic characterization in a single study","pmids":["11994472"],"is_preprint":false},{"year":1999,"finding":"The nucleocapsid (N) protein of virulent MHV-3 (but not non-pathogenic strains) induces transcription of the fgl2 gene; cotransfection of the N protein construct with an fgl2 promoter-luciferase reporter produced a 6-fold increase in activity. A region from -372 to -306 upstream of the ATG was defined as responsive to the N protein.","method":"Luciferase reporter assay, cotransfection, parental and recombinant MHV strain comparison","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — direct promoter mapping with functional reporter assay and multiple viral strain comparisons","pmids":["10187767"],"is_preprint":false},{"year":2003,"finding":"Viral N protein-induced fgl2 transcription requires the HNF4α transcription factor binding to a -331/-325 HNF4 cis-element in the fgl2 promoter. HNF4α is present in peritoneal macrophages (unprecedented finding) and binds the fgl2 promoter upon MHV-A59 infection as shown by EMSA. Specific amino acid mutations in domain 1 of the N protein (Gly-12, Pro-38, Asn-40, Gln-41, Asn-42) abrogated fgl2 transcription.","method":"EMSA, site-directed mutagenesis of N protein, promoter deletion analysis, cotransfection, Western blot","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — mutagenesis of viral protein combined with promoter EMSA and functional transcription assays","pmids":["12594208"],"is_preprint":false},{"year":1998,"finding":"MHV-3-induced fgl2 expression in macrophages is controlled by the p38 MAPK pathway; selective p38 inhibition (SB203580) abolished virally stimulated fgl2 mRNA, protein, and functional procoagulant activity. ERK activation also occurs and contributes to fgl2 functional activity but not to its mRNA/protein expression. p38 inhibition increased MHV-3-induced ERK activity, indicating crosstalk.","method":"Western blot, immunoprecipitation, in vitro kinase assay, selective MAPK inhibitors (SB203580, PD98059), mRNA analysis, procoagulant activity assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods with pharmacological dissection in both in vitro and in vivo settings","pmids":["9822700"],"is_preprint":false},{"year":2003,"finding":"Constitutive fgl2 transcription in endothelial cells is controlled by a 119 bp minimal promoter containing a positive regulatory domain (PRD, -87 to -49). Nucleoprotein complexes on this PRD contain Sp1, Sp3, Oct-1, and Ets-1 transcription factors; Ets-1 controls expression while both Sp1 and Sp3 are required. Viral-induced fgl2 expression also requires this PRD.","method":"EMSA, promoter deletion analysis, 5'-RACE, primer extension, heterologous expression in Drosophila Schneider cells","journal":"European journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — EMSA with heterologous expression validation, comprehensive promoter dissection","pmids":["12752447"],"is_preprint":false},{"year":2006,"finding":"IFN-γ induces fgl2 transcription in macrophages via a STAT1-dependent pathway involving composite cis elements Sp1/Sp3 and GAS/PU.1; PU.1 interacts with IFN-γ-activated STAT1 and Sp1/Sp3, and this interaction determines macrophage-specific fgl2 induction. TNF-α induces fgl2 in endothelial cells but not macrophages (and vice versa for IFN-γ). fgl2-dependent fibrin deposition mediates cytokine-induced hepatic apoptosis in vivo, as fgl2-/- mice are protected.","method":"Northern blot, EMSA, reporter assay, in vivo cytokine infusion, fgl2 knockout mouse, TUNEL/histopathology","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — mechanistic EMSA + reporter assay combined with in vivo KO phenotype, multiple cell types","pmids":["16709865"],"is_preprint":false},{"year":2003,"finding":"Fgl2/fibroleukin-deficient mice show markedly reduced procoagulant activity in peritoneal macrophages upon MHV-3 infection, reduced fibrin deposition and liver necrosis, and improved survival, directly establishing a non-redundant in vivo role for fgl2 prothrombinase in viral hepatitis pathogenesis.","method":"Fgl2 knockout mouse, MHV-3 infection model, procoagulant activity assay, histopathology, survival analysis","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO mouse with specific cellular phenotype, replicated across multiple subsequent studies","pmids":["12840059"],"is_preprint":false},{"year":2008,"finding":"FGL2 binds specifically to FcγRIIB and FcγRIII receptors on antigen-presenting cells (B cells, macrophages, dendritic cells), as shown by flow cytometry and surface plasmon resonance. FGL2 inhibits DC maturation only in FcγRIIB+/+ but not FcγRIIB-/- mice. FGL2 induces apoptosis in FcγRIIB+ A20 B cells but not in FcγRIIB-deficient A20IIA1.6 cells. Recombinant FGL2 prolonged allograft survival in FcγRIIB+/+ but not FcγRIIB-/- mice.","method":"Flow cytometry, surface plasmon resonance, FcγRIIB knockout mouse, B cell apoptosis assay, skin allograft survival","journal":"European journal of immunology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal binding and functional assays with receptor-deficient cell lines and KO mice","pmids":["18991288"],"is_preprint":false},{"year":2008,"finding":"FGL2 produced by CD4+CD25+ Treg cells is required for their suppressive activity; anti-FGL2 antibody completely inhibited Treg activity in vitro. FGL2 deficiency led to impaired Treg suppression, increased T cell proliferation, Th1 polarization, increased DC numbers with enhanced CD80/MHCII expression after LPS, and spontaneous autoimmune glomerulonephritis. FGL2 induces B cell apoptosis via FcγRIIB.","method":"Fgl2 knockout mouse, bone marrow reconstitution, T cell proliferation assay, DC maturation assay, B cell apoptosis assay, anti-FGL2 antibody blockade","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal functional assays in KO and reconstituted mice, replicated in subsequent studies","pmids":["18097026"],"is_preprint":false},{"year":2004,"finding":"Porcine fgl2 (pfgl2) expressed on vascular endothelial cells generates thrombin from human prothrombin. In pig-to-Lewis-rat cardiac xenograft model, fgl2+/+ and fgl2+/- hearts developed thrombosis associated with fgl2 induction in graft ECs, while fgl2-/- xenografts were completely devoid of thrombosis, directly demonstrating that endothelial fgl2 is the key procoagulant in acute vascular xenograft rejection.","method":"Gene cloning, recombinant protein expression, functional prothrombinase assay, fgl2-/- mouse heterotopic cardiac xenotransplantation model, immunohistochemistry","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — functional reconstitution plus definitive KO mouse xenograft model","pmids":["15100314"],"is_preprint":false},{"year":2011,"finding":"FGL2 binding to FcγRIIB on sinusoidal endothelial cells (SECs) induces apoptosis and initiates hepatic ischemia-reperfusion injury. In vitro, FGL2 induced apoptosis of SECs from WT but not FcγRIIB-/- mice. In vivo, deletion of either FGL2 or FcγRIIB markedly reduced SEC and hepatocyte apoptosis (caspase-3 and TUNEL staining) and dramatically improved survival after hepatic ischemia.","method":"Fgl2 KO and FcγRIIB KO mouse I/R model, caspase-3 immunostaining, TUNEL, AST/ALT measurement, in vitro SEC apoptosis assay with recombinant FGL2","journal":"Journal of hepatology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal KO experiments (both ligand and receptor) with orthogonal apoptosis readouts in vitro and in vivo","pmids":["21756857"],"is_preprint":false},{"year":2012,"finding":"Native FGL2 exists as an oligomer (~260 kDa tetramer of 65 kDa monomers). Cysteines at positions 94, 97, 184, and 187 in the coiled-coil domain are critical for oligomerization (site-directed mutagenesis). Monomeric FGL2 has lower binding affinity to APCs but greater immunosuppressive activity than oligomeric FGL2. Deglycosylation reduces FGL2 solubility. The functional immunosuppressive domain maps to the C-terminal globular domain.","method":"COS-7 recombinant expression, site-directed mutagenesis of cysteines, SDS-PAGE/reducing conditions, deglycosylation, peptide blockade assay, SWISS-MODEL structural analysis, APC binding assay","journal":"The international journal of biochemistry & cell biology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — mutagenesis + biochemical characterization + functional assays in single rigorous study","pmids":["23127799"],"is_preprint":false},{"year":2004,"finding":"FGL2 is the major secretory protein (HEP64) of hamster proximal cauda epididymidis principal cells; it specifically binds nonviable spermatozoa and assembles into a 'death cocoon' complex (~260 and 280 kDa disulfide-linked oligomers of 64 kDa monomers) coating defective sperm. The protein is absent from viable spermatozoa.","method":"cDNA library screening, Northern blot, in situ hybridization, immunohistochemistry, immunoelectron microscopy, SDS-PAGE, microsequencing","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods identifying protein identity, localization, and oligomeric structure","pmids":["15377663"],"is_preprint":false},{"year":2011,"finding":"mFGL2 prothrombinase is markedly up-regulated in joints of mice with collagen-induced arthritis and is associated with fibrin deposition in synovium. fgl2-/- mice injected with anti-collagen II antibody did not develop any clinical or histological manifestations of arthritis, whereas fgl2+/+ mice developed severe arthritis, directly establishing fgl2 as required for fibrin-mediated pathogenesis of experimental arthritis.","method":"fgl2-/- mouse model of collagen-induced arthritis, RT-PCR, immunohistochemistry, clinical arthritis scoring, histopathology","journal":"Scandinavian journal of rheumatology","confidence":"High","confidence_rationale":"Tier 2 / Strong — definitive KO mouse experiment with specific disease phenotype, multiple readouts","pmids":["21469939"],"is_preprint":false},{"year":2019,"finding":"FGL2 expressed in glioma stem cells inhibits GM-CSF-induced CD103+ DC differentiation by suppressing NF-κB, STAT1/5, and p38 activation. FGL2 KO in tumor cells had no effect on tumor growth in immunodeficient mice but completely impaired GBM progression in immune-competent mice; this impairment was reversed by DC deficiency, establishing a DC-dependent immune mechanism.","method":"FGL2 CRISPR/KO in tumor cells, syngeneic GBM mouse models (immunocompetent vs. immunodeficient), DC differentiation assay, NF-κB/STAT/p38 signaling analysis","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO in tumor with isogenic immune-competent/deficient comparison and epistasis via DC-deficient mice","pmids":["30683885"],"is_preprint":false},{"year":1998,"finding":"Ribavirin inhibits MHV-3-induced macrophage production of fgl2 prothrombinase (procoagulant activity) as well as TNF-α and IL-1β at the level of gene transcription (Northern analysis), without inhibiting LPS-stimulated macrophage TNF-α/IL-1β production, demonstrating virus-specific transcriptional regulation of fgl2.","method":"Procoagulant activity assay, ELISA, Northern blot, in vitro and in vivo MHV-3 infection with ribavirin treatment","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Northern blot + functional assay in single study, transcriptional mechanism established","pmids":["9531310"],"is_preprint":false},{"year":2013,"finding":"TNF-α and IFN-γ induce soluble FGL2 secretion from CD4+ T cells via the JNK MAPK pathway; JNK inhibition (not p38 or ERK) significantly reduced sFGL2 secretion in vitro, and sFGL2/TNF-α/IFN-γ were all elevated in peripheral blood of renal allograft recipients with acute rejection.","method":"CD4+ T cell isolation, cytokine stimulation, JNK/p38/ERK inhibitors, ELISA for sFGL2","journal":"The Journal of surgical research","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — pathway inhibitor pharmacology in primary human cells; single lab","pmids":["23664593"],"is_preprint":false},{"year":2014,"finding":"C5a/C5aR signaling promotes FGL2 expression in macrophages and LSECs via ERK1/2 and p38 pathways during viral fulminant hepatitis; C5aR-/- or Fgl2-/- mice had significantly reduced complement activation and coagulation, establishing a C5a→TNF-α→FGL2 regulatory axis in vascular endothelial cells.","method":"C5aR-/-, Fgl2-/-, Tnfα-/- mouse infection models, C5a administration in vitro, ERK/p38 inhibitors, immunofluorescence, qRT-PCR, ELISA","journal":"Journal of hepatology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple KO mouse models with epistasis plus in vitro pathway inhibition","pmids":["25200905"],"is_preprint":false},{"year":2021,"finding":"FGL2-producing glioma cells recruit macrophages into the tumor microenvironment and induce them to secrete CXCL7 via CD16/SyK/PI3K/HIF1α pathways; CXCL7 in turn enhances stem-like functionality of glioma cells. This FGL2-CXCL7 paracrine loop was blocked by a neutralizing anti-CXCL7 antibody.","method":"Mass cytometry, RNA sequencing, immunocompetent mouse GBM model, anti-CXCL7 neutralizing antibody, pathway inhibition","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo model with antibody blockade and pathway analysis, single lab","pmids":["33676940"],"is_preprint":false},{"year":2022,"finding":"FGL2 directly interacts with mucolipin 3 (MCOLN3) in neutrophils, regulating calcium influx and initiating autophagy, which leads to neutrophil extracellular trap (NET) formation. Neutrophil-specific FGL2 promotes NETs formation in fulminant viral hepatitis; adoptive transfer confirmed the neutrophil-intrinsic mechanism.","method":"Single-cell RNA sequencing, whole-transcriptome sequencing, adoptive transfer experiment, DNase 1 NET depletion, co-immunoprecipitation (FGL2-MCOLN3 interaction), mouse MHV-3 model","journal":"Cellular and molecular gastroenterology and hepatology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP for protein-protein interaction plus adoptive transfer for cell-intrinsic mechanism; single lab","pmids":["35926777"],"is_preprint":false},{"year":2022,"finding":"FGL2 expressed by T follicular helper (TFH) cells (not only Tregs) represses allergen-specific IgE production. Conditional deletion of Fgl2 specifically in TFH and T follicular regulatory (TFR) cells, but not TFR cells alone, increased antigen-specific IgE levels and IgE-mediated anaphylactic responses, establishing TFH-derived FGL2 as a suppressor of IgE+ germinal center B cell responses.","method":"Conditional Fgl2 deletion (TFH- and TFR-specific), food allergy mouse model, IgE ELISA, flow cytometry of GC B cells, anaphylaxis assay","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional cell-type-specific KO with specific functional readout, two genetic conditions tested","pmids":["35767958"],"is_preprint":false},{"year":2022,"finding":"A homozygous truncating mutation (c.614_617del:p.V205fs) in human FGL2, which preserves the N-terminal domain but eliminates the C-terminal immunoregulatory domain, causes immune dysregulation with impaired Treg suppressive function. Addition of full-length FGL2 (but not the truncated mutant) rescued the Treg suppressive defect in vitro, demonstrating that the C-terminal domain is required for immunosuppressive function.","method":"Whole-exome sequencing, immunoblotting of transfected HEK293 cells, flow cytometry, Treg suppression assay, rescue with recombinant full-length vs. truncated FGL2","journal":"The Journal of allergy and clinical immunology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — human genetic mutation with cellular functional rescue experiment using truncated vs. full-length protein","pmids":["36243222"],"is_preprint":false},{"year":2024,"finding":"CD8+ T cell-intrinsic FGL2 suppresses anti-tumor and anti-viral CD8+ T cell responses via cell-autonomous binding of secreted FGL2 to FcγRIIB expressed on the same CD8+ T cells, triggering caspase 3/7-mediated apoptosis. Conditional deletion of Fgl2 specifically in antigen-specific CD8+ T cells prolonged their persistence, reduced exhaustion signatures, and improved tumor control.","method":"Conditional CD8+ T cell-specific Fgl2 deletion, tumor and chronic viral infection mouse models, transcriptomics, caspase 3/7 apoptosis assay, FcγRIIB-/- CD8+ T cell adoptive transfer","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — cell-type-specific conditional KO with receptor-deficient controls and mechanistic apoptosis assays","pmids":["38902261"],"is_preprint":false},{"year":2019,"finding":"FGL2 prothrombinase participates in pulmonary hypertension pathogenesis; Fgl2 knockout reduced in situ thrombus formation, vascular remodeling, and endothelial apoptosis. FGL2 loss downregulated PAR1 (proteinase-activated receptor 1) expression and decreased platelet overactivation in hypoxia-induced PH, establishing a FGL2-thrombin-PAR1 signaling axis.","method":"Fgl2 knockout mouse, monocrotaline rat PH model, hypoxia mouse PH model, immunohistochemistry, PAR1 expression analysis, platelet activation assay","journal":"Journal of applied physiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO mouse with multiple PH models and pathway identification (PAR1)","pmids":["31580221"],"is_preprint":false},{"year":2012,"finding":"FGL2 knockdown in HCCLM6 hepatocellular carcinoma cells decreased tumor growth and angiogenesis in xenografts, and was associated with decreased ERK and JNK phosphorylation. Overexpression of FGL2 or addition of recombinant hFGL2 protein induced phosphorylation of p38-MAPK and ERK1/2 via protease-activated receptor (PAR) activation in vitro.","method":"MicroRNA-mediated knockdown, xenograft model in nude mice, cytometric bead array, recombinant FGL2 stimulation, MAPK phosphorylation assay","journal":"Liver international","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — in vitro and in vivo knockdown/OE with pathway analysis; single lab","pmids":["22925132"],"is_preprint":false},{"year":2016,"finding":"FGL2 oligomers in the hamster cauda epididymis are composed of two disulfide-linked subunits: 64 kDa FGL2 and 33 kDa FGL1. Both proteins are present in soluble epididymal fluid and in the sperm-associated death cocoon complex. Co-immunoprecipitation with anti-FGL2 antibody demonstrated that FGL1 and FGL2 associate in soluble form as well.","method":"Proteomics, PCR-based cloning, co-immunoprecipitation, immunocytochemistry, Northern blot, in situ hybridization","journal":"The international journal of biochemistry & cell biology","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — co-IP plus proteomic identification; single lab","pmids":["27732889"],"is_preprint":false},{"year":2013,"finding":"SNF2L (imitation switch ATPase) directly regulates Fgl2 expression in granulosa cells; Snf2l mutant mice fail to induce Fgl2 in response to hCG stimulation, while SNF2L overexpression drives Fgl2 expression. SNF2L interacts with the nuclear receptor co-activator flightless I (FLI-I) as shown by immunoprecipitation.","method":"Snf2l mutant mouse, hCG stimulation, granulosa cell overexpression, immunoprecipitation (SNF2L-FLI-I interaction), superovulation assay","journal":"Biology of reproduction","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — genetic mouse model with upstream regulator identification and Co-IP; single lab","pmids":["23616592"],"is_preprint":false},{"year":2022,"finding":"FGL2 interacts with Tyrobp in cutaneous squamous cell carcinoma cells, promoting ERK-dependent autophagy and cell proliferation. Co-immunoprecipitation and immunofluorescence colocalization confirmed the FGL2-Tyrobp interaction; knockdown of FGL2 reduced autophagy and proliferation while gain-of-function rescued Tyrobp-dependent effects.","method":"Co-immunoprecipitation, immunofluorescence colocalization, siRNA knockdown, overexpression, xenograft mouse model, ERK phosphorylation assay","journal":"International journal of medical sciences","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — Co-IP with functional gain/loss-of-function; single lab","pmids":["34975313"],"is_preprint":false},{"year":2024,"finding":"Macrophage-secreted FGL2 dampens CD8+ T cell responses through direct binding to FcγRIIB expressed on CD8+ T cells, inducing T cell apoptosis in a CD8+ T cell-autonomous manner (not via APC intermediary). Absence of FcγRIIB from CD8+ T cells rendered them insensitive to FGL2-mediated regulation; macrophages are the dominant FGL2-producing cell in the tumor microenvironment across 10 cancer types.","method":"Melanoma mouse model, macrophage-specific Fgl2 analysis, FcγRIIB-/- CD8+ T cell adoptive transfer, apoptosis assay, scRNA-seq of human cancer data","journal":"JCI insight","confidence":"High","confidence_rationale":"Tier 2 / Strong — receptor-deficient T cell adoptive transfer establishing cell-autonomous mechanism, multiple cancer types validated","pmids":["40125553"],"is_preprint":false},{"year":2026,"finding":"Tumor-derived exosomes deliver membrane-bound FGL2 (mFgl2) to MDSCs via FcγRIIB-mediated endocytosis, enhancing their immunosuppressive function (upregulated Arg-1 and iNOS, increased suppression of CD8+ T cells). Genetic ablation of FcγRIIB or antibody-mediated neutralization of FGL2 abolished exosome-mediated MDSC programming.","method":"Tumor-derived exosome isolation, FcγRIIB-/- MDSC functional assay, anti-Fgl2 neutralizing antibody, CD8+ T cell suppression assay, in vivo tumor model","journal":"Advanced science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — receptor KO and antibody blockade with functional MDSC readout; single lab, preprint-equivalent","pmids":["41875310"],"is_preprint":false},{"year":2024,"finding":"Arterial fluid shear stress (FSS) on venous endothelial cells increases FGL2 secretion via NF-κB signaling; secreted FGL2 promotes endothelial apoptosis via FcγRIIB. FcγRIIB blocking antibody reduced FGL2-induced caspase-3 activation in HUVECs exposed to arterial FSS.","method":"Tandem Mass Tagging proteomics of HUVEC secretome, Western blot, NF-κB inhibitor (BAY 11-7085), recombinant FGL2 treatment, FcγRIIB blocking antibody, caspase-3 immunocytochemistry","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — secretome proteomics + functional antibody blockade + recombinant protein; single lab","pmids":["39062880"],"is_preprint":false},{"year":2026,"finding":"FGL2 in MASLD regulates NETs formation through direct interaction with HDAC11, promoting histone H3 deacetylation and facilitating PAD4-mediated citrullination to drive NET release. Genetic disruption of FGL2 or NETs inhibition restores LSEC fenestration, improves microvascular hemodynamics, and attenuates fibrosis.","method":"FGL2 KO mouse MASLD model, FGL2-HDAC11 interaction (implied by mechanistic studies), PAD4 citrullination assay, LSEC fenestration imaging, DNase 1 NET depletion","journal":"Advanced science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO mouse with molecular mechanism (HDAC11 interaction and PAD4 pathway); single lab, recent publication","pmids":["42107082"],"is_preprint":false},{"year":2026,"finding":"FGL2 promotes PD-L1 expression in hepatocellular carcinoma cells by activating mTORC1 signaling, which phosphorylates and prevents nuclear translocation of TFEB, thereby inhibiting lysosome biosynthesis and lysosomal degradation of PD-L1. FGL2 KO in mice reduced tumor PD-L1 expression and synergized with anti-PD1 therapy.","method":"Fgl2 KO mouse HCC models, TFEB phosphorylation/nuclear translocation assay, mTORC1 signaling analysis, lysosome function assay, anti-PD1 combination treatment","journal":"Cell communication and signaling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO mouse with defined molecular pathway (mTOR-TFEB-PD-L1); single lab, very recent","pmids":["41629991"],"is_preprint":false},{"year":2025,"finding":"FGL2 stimulation of enteric neural crest cells (ENCCs) increases apoptosis by enhancing oxidative phosphorylation (OXPHOS) through activation of JAK2-STAT3 signaling, leading to ROS accumulation. FGL2 is upregulated in aganglionic colon tissues from Hirschsprung disease patients.","method":"Primary ENCC isolation, FGL2 stimulation in vitro, JAK2-STAT3 pathway analysis, OXPHOS/ROS measurement, apoptosis assay, patient tissue immunostaining","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — in vitro mechanistic assay with pathway inhibition; single lab, single study","pmids":["40978140"],"is_preprint":false},{"year":2025,"finding":"FGL2-KO in tumor cells suppresses CD47 expression through the Src and PKCα pathways; reconstitution of CD47 in Fgl2-KO tumor cells reversed immune protection. This Fgl2-CD47 circuit controls tumor immunogenicity and ability to induce brain-resident memory T cells.","method":"CRISPR/Cas9 Fgl2-KO in multiple tumor cell lines, CD47 reconstitution experiment, Src/PKCα inhibition, proteomic analysis, adoptive transfer of brain immune cells","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CRISPR KO with rescue experiment and pathway identification; single lab","pmids":["41380903"],"is_preprint":false},{"year":2009,"finding":"SARS-CoV nucleocapsid (N) protein does NOT modulate FGL2 promoter activity or FGL2 mRNA/protein expression in human cells (including SARS-CoV-infected cells), in contrast to MHV-3 N protein, despite SARS-CoV N protein being able to repress interferon-stimulated response elements.","method":"Transfection of SARS-CoV N protein into human cell lines, luciferase reporter assay with FGL2 promoter, Northern blot, SARS-CoV infection experiment","journal":"The Journal of general virology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — negative result established by direct promoter reporter assay and viral infection; single lab","pmids":["19423547"],"is_preprint":false}],"current_model":"FGL2/fibroleukin is a bifunctional protein existing in two forms: a membrane-associated type II transmembrane prothrombinase that directly cleaves prothrombin to thrombin (requiring phospholipids, calcium, and Ser89 as the catalytic residue, and enhanced by factor Va) via a coagulation-cascade-independent mechanism, and a secreted/soluble form that acts as an immunosuppressive cytokine by binding FcγRIIB and FcγRIII on antigen-presenting cells, B cells, and CD8+ T cells to suppress DC maturation, induce B cell apoptosis, mediate Treg effector function, and drive CD8+ T cell apoptosis through a cell-autonomous FcγRIIB-caspase3/7 axis; its transcription is induced by IFN-γ (via STAT1/Sp1/Sp3/PU.1 in macrophages) and TNF-α (via NF-κB/p38 in endothelial cells), and by viral nucleocapsid proteins via HNF4α and an Ets-1/Oct-1/Sp1/Sp3 promoter complex."},"narrative":{"mechanistic_narrative":"FGL2/fibroleukin is a bifunctional immune effector that links innate coagulation to adaptive immune suppression [PMID:9371581, PMID:18991288]. In its membrane-associated form it is a type II integral membrane protein with a C-terminal fibrinogen-related domain that functions as a prothrombinase, directly cleaving prothrombin to thrombin independently of the classical coagulation cascade [PMID:9371581, PMID:11170750]; this enzymatic activity requires phosphatidylserine-containing phospholipids and calcium, uses Ser89 as the catalytic residue, and is enhanced ~600-fold by factor Va [PMID:11994472]. This prothrombinase drives fibrin deposition and tissue injury across multiple disease models, including MHV-3 viral hepatitis [PMID:9371581, PMID:12840059], acute vascular xenograft rejection [PMID:15100314], collagen-induced arthritis [PMID:21469939], and pulmonary hypertension via a thrombin-PAR1 axis [PMID:31580221]. A secreted/oligomeric form acts as an immunosuppressive cytokine that binds FcγRIIB and FcγRIII on antigen-presenting cells, B cells, and T cells [PMID:18991288]; through FcγRIIB it suppresses dendritic cell maturation, induces B cell apoptosis, mediates the suppressive effector function of regulatory T cells [PMID:18991288, PMID:18097026], and triggers apoptosis of sinusoidal and venous endothelial cells [PMID:21756857, PMID:39062880]. FGL2 is required cell-intrinsically for CD8+ T cell control: secreted FGL2 binds FcγRIIB on the same CD8+ T cell to trigger caspase-3/7-mediated apoptosis, and macrophage-derived FGL2 dampens anti-tumor and anti-viral CD8+ responses by this cell-autonomous route [PMID:38902261, PMID:40125553]. Its immunoregulatory activity maps to the C-terminal globular domain, and a homozygous truncating mutation eliminating this domain causes human immune dysregulation with impaired Treg suppression, rescuable by full-length but not truncated protein [PMID:23127799, PMID:36243222]. FGL2 transcription is inducible by IFN-γ (via STAT1 with Sp1/Sp3 and GAS/PU.1 elements in macrophages), TNF-α and NF-κB in endothelial cells, and by virulent MHV-3 nucleocapsid protein acting through HNF4α and an Ets-1/Oct-1/Sp1/Sp3 promoter complex [PMID:16709865, PMID:12752447, PMID:12594208].","teleology":[{"year":1997,"claim":"Established FGL2 as a virally induced prothrombinase, answering how MHV-3 infection triggers fibrin-mediated hepatocellular necrosis through a host gene rather than the classical cascade.","evidence":"Northern blot, in situ hybridization, immunochemistry, and procoagulant activity assay in MHV-3-infected liver","pmids":["9371581"],"confidence":"High","gaps":["Catalytic residue and cofactor requirements not yet defined","Human ortholog not yet characterized"]},{"year":1998,"claim":"Defined the signaling and pharmacological controls on viral fgl2 induction, showing transcription is p38 MAPK-dependent and selectively blockable by ribavirin.","evidence":"MAPK inhibitor pharmacology, kinase assays, and Northern blot in MHV-3-infected macrophages","pmids":["9822700","9531310"],"confidence":"High","gaps":["Transcription factors downstream of p38 not identified here","ribavirin (idx 17) is Medium-confidence single-study"]},{"year":1999,"claim":"Identified the viral trigger of fgl2 transcription, mapping induction to the virulent MHV-3 nucleocapsid protein acting on a defined promoter region.","evidence":"Luciferase reporter cotransfection with parental and recombinant MHV strain comparison","pmids":["10187767"],"confidence":"High","gaps":["Host transcription factor mediating the N-protein response not yet identified"]},{"year":2001,"claim":"Characterized human FGL2 as a single-copy gene encoding a type II membrane protein with a fibrinogen-related domain and reconstituted its prothrombinase activity, confirming the enzyme is conserved in humans.","evidence":"Recombinant expression, functional prothrombinase assay, radiation hybrid mapping, FISH","pmids":["11170750"],"confidence":"High","gaps":["Catalytic mechanism and cofactor dependence still undefined at this stage"]},{"year":2002,"claim":"Resolved the enzymatic mechanism, identifying Ser89 as catalytic residue and defining phospholipid, calcium, and factor Va requirements that distinguish FGL2 from canonical serine proteases.","evidence":"Baculovirus expression, phospholipid vesicle reconstitution, kinetics, site-directed mutagenesis, inhibitor panel","pmids":["11994472"],"confidence":"High","gaps":["Structural basis of substrate recognition not determined","regulation of membrane vs secreted forms unresolved"]},{"year":2003,"claim":"Mapped the cis/trans architecture of fgl2 transcription, defining HNF4α as the N-protein-responsive factor and a constitutive Ets-1/Sp1/Sp3/Oct-1 promoter complex in endothelium.","evidence":"EMSA, promoter deletion, viral protein mutagenesis, heterologous Drosophila expression","pmids":["12594208","12752447"],"confidence":"High","gaps":["How distinct cell types deploy different factor combinations not fully resolved"]},{"year":2003,"claim":"Provided definitive in vivo proof that fgl2 prothrombinase is non-redundant for viral hepatitis pathogenesis using a knockout mouse.","evidence":"Fgl2 knockout mouse in MHV-3 model with procoagulant, histopathology, and survival readouts","pmids":["12840059"],"confidence":"High","gaps":["Did not address any immunomodulatory function of FGL2"]},{"year":2004,"claim":"Extended FGL2's procoagulant pathology to transplant rejection and revealed a distinct reproductive role, identifying it as a secretory protein forming sperm-coating oligomeric complexes.","evidence":"fgl2-/- pig-to-rat cardiac xenograft model; cDNA cloning and immunoEM in hamster epididymis","pmids":["15100314","15377663"],"confidence":"High","gaps":["Function of the epididymal 'death cocoon' relative to prothrombinase activity unclear","partner subunits of the oligomer not yet defined"]},{"year":2006,"claim":"Defined cytokine-specific, cell-type-restricted transcriptional induction and linked fibrin deposition to cytokine-driven hepatic apoptosis in vivo.","evidence":"EMSA, reporter assays, in vivo cytokine infusion, fgl2 knockout, TUNEL","pmids":["16709865"],"confidence":"High","gaps":["Mechanism restricting IFN-γ response to macrophages and TNF-α to endothelium only partially explained"]},{"year":2008,"claim":"Established the second function of FGL2 as an immunosuppressive cytokine, identifying FcγRIIB/FcγRIII as receptors and showing FGL2 mediates Treg suppression and DC/B cell control.","evidence":"Surface plasmon resonance, flow cytometry, FcγRIIB-/- mice, Treg suppression and B cell apoptosis assays, allograft survival","pmids":["18991288","18097026"],"confidence":"High","gaps":["Downstream apoptotic signaling from FcγRIIB not yet defined","relationship between membrane prothrombinase and secreted cytokine forms unclear"]},{"year":2011,"claim":"Connected FGL2-FcγRIIB signaling to direct endothelial apoptosis in tissue injury and extended pathology to ischemia-reperfusion, using reciprocal ligand and receptor knockouts.","evidence":"Fgl2-/- and FcγRIIB-/- hepatic I/R models with caspase-3, TUNEL, in vitro SEC apoptosis; collagen arthritis KO model","pmids":["21756857","21469939"],"confidence":"High","gaps":["Apoptotic effector pathway downstream of FcγRIIB not fully mapped"]},{"year":2012,"claim":"Defined FGL2 quaternary structure and mapped its immunosuppressive activity to the C-terminal globular domain, while showing monomer-oligomer state tunes binding versus activity.","evidence":"Recombinant expression, cysteine mutagenesis, SDS-PAGE, deglycosylation, peptide blockade, APC binding","pmids":["23127799"],"confidence":"High","gaps":["High-resolution structure not determined","in vivo relevance of oligomeric state unclear"]},{"year":2013,"claim":"Identified upstream signaling and chromatin-level control of FGL2 secretion in distinct contexts, including JNK-dependent secretion from CD4+ T cells and SNF2L-driven expression in granulosa cells.","evidence":"MAPK inhibitor pharmacology and ELISA in primary CD4+ T cells; Snf2l mutant mouse and Co-IP","pmids":["23664593","23616592"],"confidence":"Medium","gaps":["Single-lab pathway studies without independent confirmation","SNF2L-FLI-I link to fgl2 chromatin remodeling indirect"]},{"year":2014,"claim":"Placed FGL2 within an upstream complement axis, establishing C5a/C5aR→TNF-α→FGL2 regulation in viral fulminant hepatitis.","evidence":"C5aR-/-, Fgl2-/-, Tnfα-/- mouse infection models with epistasis and in vitro pathway inhibition","pmids":["25200905"],"confidence":"High","gaps":["Direct biochemical link between C5aR signaling and fgl2 promoter not shown"]},{"year":2019,"claim":"Demonstrated FGL2's pro-tumor immunosuppression in glioma is DC-dependent and extended procoagulant pathology to pulmonary hypertension via a thrombin-PAR1 axis.","evidence":"Tumor CRISPR-KO with immunocompetent vs immunodeficient and DC-deficient mice; Fgl2-/- PH models with PAR1 analysis","pmids":["30683885","31580221"],"confidence":"High","gaps":["Whether glioma effect is prothrombinase- or cytokine-dependent not separated"]},{"year":2022,"claim":"Expanded FGL2's immunosuppressive sources and mechanisms, identifying TFH-derived FGL2 as an IgE suppressor, a human truncating mutation causing immune dysregulation, and novel interactors (MCOLN3, Tyrobp) driving autophagy/NETs.","evidence":"Conditional Fgl2 deletion (TFH/TFR), whole-exome sequencing with Treg rescue, Co-IP of FGL2-MCOLN3 and FGL2-Tyrobp, adoptive transfer","pmids":["35767958","36243222","35926777","34975313"],"confidence":"High","gaps":["MCOLN3 and Tyrobp interactions are single-lab Co-IPs without reciprocal validation","how secreted FGL2 reaches intracellular partners unresolved"]},{"year":2024,"claim":"Established the cell-autonomous immunosuppressive circuit, showing secreted FGL2 binds FcγRIIB on the same CD8+ T cell to trigger caspase-3/7 apoptosis, dampening anti-tumor immunity.","evidence":"CD8+ T cell-specific conditional Fgl2 deletion and macrophage-source analysis with FcγRIIB-/- adoptive transfer and apoptosis assays","pmids":["38902261","40125553"],"confidence":"High","gaps":["Intracellular caspase activation pathway downstream of FcγRIIB not fully detailed"]},{"year":2025,"claim":"Broadened FGL2 signaling into metabolic and developmental contexts, linking it to JAK2-STAT3-driven OXPHOS/ROS apoptosis in enteric neural crest cells and Src/PKCα-dependent CD47 control of tumor immunogenicity.","evidence":"Primary ENCC stimulation with pathway analysis; CRISPR Fgl2-KO with CD47 reconstitution and inhibitor studies","pmids":["40978140","41380903"],"confidence":"Medium","gaps":["Single-lab mechanistic studies","receptor mediating these effects not identified"]},{"year":2026,"claim":"Defined additional context-specific effector 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1997,\n      \"finding\": \"FGL2 encodes a novel prothrombinase expressed on endothelial cells and Kupffer cells in the liver following MHV-3 infection; the protein directly cleaves prothrombin to thrombin, leading to fibrin deposition and hepatocellular necrosis. Expression is tissue-specific, detected in liver, spleen, and lungs but not brain or kidney despite equivalent viral titers.\",\n      \"method\": \"Northern blot, in situ hybridization, immunochemistry, functional procoagulant activity assay\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (Northern, ISH, IHC, enzymatic activity assay), replicated across subsequent studies\",\n      \"pmids\": [\"9371581\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Human FGL2 encodes a 439-amino-acid type II integral membrane protein with a C-terminal fibrinogen-related domain; recombinant protein expressed in vitro functions as a serine protease that directly cleaves prothrombin to thrombin (prothrombinase activity). The gene is single-copy, located at 7q11.23, with two exons.\",\n      \"method\": \"Recombinant protein expression, functional prothrombinase assay, radiation hybrid mapping, FISH\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — functional reconstitution of enzymatic activity with genetic and chromosomal characterization, replicated in multiple subsequent studies\",\n      \"pmids\": [\"11170750\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"FGL2 prothrombinase activity requires phosphatidylserine-containing phospholipids and calcium; factor Va enhances catalytic efficiency ~600-fold. Site-directed mutagenesis identified Ser89 as the critical catalytic residue. The enzyme is not inhibited by classical serine protease inhibitors (antithrombin III, aprotinin, PMSF, soybean trypsin inhibitor, 4-aminobenzamidine) but is completely abrogated by diisopropylfluorophosphate.\",\n      \"method\": \"Baculovirus expression, phospholipid vesicle reconstitution, kinetic analysis, site-directed mutagenesis, truncation analysis, inhibitor studies\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — rigorous in vitro reconstitution with mutagenesis and kinetic characterization in a single study\",\n      \"pmids\": [\"11994472\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The nucleocapsid (N) protein of virulent MHV-3 (but not non-pathogenic strains) induces transcription of the fgl2 gene; cotransfection of the N protein construct with an fgl2 promoter-luciferase reporter produced a 6-fold increase in activity. A region from -372 to -306 upstream of the ATG was defined as responsive to the N protein.\",\n      \"method\": \"Luciferase reporter assay, cotransfection, parental and recombinant MHV strain comparison\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — direct promoter mapping with functional reporter assay and multiple viral strain comparisons\",\n      \"pmids\": [\"10187767\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Viral N protein-induced fgl2 transcription requires the HNF4α transcription factor binding to a -331/-325 HNF4 cis-element in the fgl2 promoter. HNF4α is present in peritoneal macrophages (unprecedented finding) and binds the fgl2 promoter upon MHV-A59 infection as shown by EMSA. Specific amino acid mutations in domain 1 of the N protein (Gly-12, Pro-38, Asn-40, Gln-41, Asn-42) abrogated fgl2 transcription.\",\n      \"method\": \"EMSA, site-directed mutagenesis of N protein, promoter deletion analysis, cotransfection, Western blot\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — mutagenesis of viral protein combined with promoter EMSA and functional transcription assays\",\n      \"pmids\": [\"12594208\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"MHV-3-induced fgl2 expression in macrophages is controlled by the p38 MAPK pathway; selective p38 inhibition (SB203580) abolished virally stimulated fgl2 mRNA, protein, and functional procoagulant activity. ERK activation also occurs and contributes to fgl2 functional activity but not to its mRNA/protein expression. p38 inhibition increased MHV-3-induced ERK activity, indicating crosstalk.\",\n      \"method\": \"Western blot, immunoprecipitation, in vitro kinase assay, selective MAPK inhibitors (SB203580, PD98059), mRNA analysis, procoagulant activity assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods with pharmacological dissection in both in vitro and in vivo settings\",\n      \"pmids\": [\"9822700\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Constitutive fgl2 transcription in endothelial cells is controlled by a 119 bp minimal promoter containing a positive regulatory domain (PRD, -87 to -49). Nucleoprotein complexes on this PRD contain Sp1, Sp3, Oct-1, and Ets-1 transcription factors; Ets-1 controls expression while both Sp1 and Sp3 are required. Viral-induced fgl2 expression also requires this PRD.\",\n      \"method\": \"EMSA, promoter deletion analysis, 5'-RACE, primer extension, heterologous expression in Drosophila Schneider cells\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — EMSA with heterologous expression validation, comprehensive promoter dissection\",\n      \"pmids\": [\"12752447\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"IFN-γ induces fgl2 transcription in macrophages via a STAT1-dependent pathway involving composite cis elements Sp1/Sp3 and GAS/PU.1; PU.1 interacts with IFN-γ-activated STAT1 and Sp1/Sp3, and this interaction determines macrophage-specific fgl2 induction. TNF-α induces fgl2 in endothelial cells but not macrophages (and vice versa for IFN-γ). fgl2-dependent fibrin deposition mediates cytokine-induced hepatic apoptosis in vivo, as fgl2-/- mice are protected.\",\n      \"method\": \"Northern blot, EMSA, reporter assay, in vivo cytokine infusion, fgl2 knockout mouse, TUNEL/histopathology\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — mechanistic EMSA + reporter assay combined with in vivo KO phenotype, multiple cell types\",\n      \"pmids\": [\"16709865\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Fgl2/fibroleukin-deficient mice show markedly reduced procoagulant activity in peritoneal macrophages upon MHV-3 infection, reduced fibrin deposition and liver necrosis, and improved survival, directly establishing a non-redundant in vivo role for fgl2 prothrombinase in viral hepatitis pathogenesis.\",\n      \"method\": \"Fgl2 knockout mouse, MHV-3 infection model, procoagulant activity assay, histopathology, survival analysis\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO mouse with specific cellular phenotype, replicated across multiple subsequent studies\",\n      \"pmids\": [\"12840059\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"FGL2 binds specifically to FcγRIIB and FcγRIII receptors on antigen-presenting cells (B cells, macrophages, dendritic cells), as shown by flow cytometry and surface plasmon resonance. FGL2 inhibits DC maturation only in FcγRIIB+/+ but not FcγRIIB-/- mice. FGL2 induces apoptosis in FcγRIIB+ A20 B cells but not in FcγRIIB-deficient A20IIA1.6 cells. Recombinant FGL2 prolonged allograft survival in FcγRIIB+/+ but not FcγRIIB-/- mice.\",\n      \"method\": \"Flow cytometry, surface plasmon resonance, FcγRIIB knockout mouse, B cell apoptosis assay, skin allograft survival\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal binding and functional assays with receptor-deficient cell lines and KO mice\",\n      \"pmids\": [\"18991288\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"FGL2 produced by CD4+CD25+ Treg cells is required for their suppressive activity; anti-FGL2 antibody completely inhibited Treg activity in vitro. FGL2 deficiency led to impaired Treg suppression, increased T cell proliferation, Th1 polarization, increased DC numbers with enhanced CD80/MHCII expression after LPS, and spontaneous autoimmune glomerulonephritis. FGL2 induces B cell apoptosis via FcγRIIB.\",\n      \"method\": \"Fgl2 knockout mouse, bone marrow reconstitution, T cell proliferation assay, DC maturation assay, B cell apoptosis assay, anti-FGL2 antibody blockade\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal functional assays in KO and reconstituted mice, replicated in subsequent studies\",\n      \"pmids\": [\"18097026\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Porcine fgl2 (pfgl2) expressed on vascular endothelial cells generates thrombin from human prothrombin. In pig-to-Lewis-rat cardiac xenograft model, fgl2+/+ and fgl2+/- hearts developed thrombosis associated with fgl2 induction in graft ECs, while fgl2-/- xenografts were completely devoid of thrombosis, directly demonstrating that endothelial fgl2 is the key procoagulant in acute vascular xenograft rejection.\",\n      \"method\": \"Gene cloning, recombinant protein expression, functional prothrombinase assay, fgl2-/- mouse heterotopic cardiac xenotransplantation model, immunohistochemistry\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — functional reconstitution plus definitive KO mouse xenograft model\",\n      \"pmids\": [\"15100314\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"FGL2 binding to FcγRIIB on sinusoidal endothelial cells (SECs) induces apoptosis and initiates hepatic ischemia-reperfusion injury. In vitro, FGL2 induced apoptosis of SECs from WT but not FcγRIIB-/- mice. In vivo, deletion of either FGL2 or FcγRIIB markedly reduced SEC and hepatocyte apoptosis (caspase-3 and TUNEL staining) and dramatically improved survival after hepatic ischemia.\",\n      \"method\": \"Fgl2 KO and FcγRIIB KO mouse I/R model, caspase-3 immunostaining, TUNEL, AST/ALT measurement, in vitro SEC apoptosis assay with recombinant FGL2\",\n      \"journal\": \"Journal of hepatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal KO experiments (both ligand and receptor) with orthogonal apoptosis readouts in vitro and in vivo\",\n      \"pmids\": [\"21756857\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Native FGL2 exists as an oligomer (~260 kDa tetramer of 65 kDa monomers). Cysteines at positions 94, 97, 184, and 187 in the coiled-coil domain are critical for oligomerization (site-directed mutagenesis). Monomeric FGL2 has lower binding affinity to APCs but greater immunosuppressive activity than oligomeric FGL2. Deglycosylation reduces FGL2 solubility. The functional immunosuppressive domain maps to the C-terminal globular domain.\",\n      \"method\": \"COS-7 recombinant expression, site-directed mutagenesis of cysteines, SDS-PAGE/reducing conditions, deglycosylation, peptide blockade assay, SWISS-MODEL structural analysis, APC binding assay\",\n      \"journal\": \"The international journal of biochemistry & cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — mutagenesis + biochemical characterization + functional assays in single rigorous study\",\n      \"pmids\": [\"23127799\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"FGL2 is the major secretory protein (HEP64) of hamster proximal cauda epididymidis principal cells; it specifically binds nonviable spermatozoa and assembles into a 'death cocoon' complex (~260 and 280 kDa disulfide-linked oligomers of 64 kDa monomers) coating defective sperm. The protein is absent from viable spermatozoa.\",\n      \"method\": \"cDNA library screening, Northern blot, in situ hybridization, immunohistochemistry, immunoelectron microscopy, SDS-PAGE, microsequencing\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods identifying protein identity, localization, and oligomeric structure\",\n      \"pmids\": [\"15377663\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"mFGL2 prothrombinase is markedly up-regulated in joints of mice with collagen-induced arthritis and is associated with fibrin deposition in synovium. fgl2-/- mice injected with anti-collagen II antibody did not develop any clinical or histological manifestations of arthritis, whereas fgl2+/+ mice developed severe arthritis, directly establishing fgl2 as required for fibrin-mediated pathogenesis of experimental arthritis.\",\n      \"method\": \"fgl2-/- mouse model of collagen-induced arthritis, RT-PCR, immunohistochemistry, clinical arthritis scoring, histopathology\",\n      \"journal\": \"Scandinavian journal of rheumatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — definitive KO mouse experiment with specific disease phenotype, multiple readouts\",\n      \"pmids\": [\"21469939\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"FGL2 expressed in glioma stem cells inhibits GM-CSF-induced CD103+ DC differentiation by suppressing NF-κB, STAT1/5, and p38 activation. FGL2 KO in tumor cells had no effect on tumor growth in immunodeficient mice but completely impaired GBM progression in immune-competent mice; this impairment was reversed by DC deficiency, establishing a DC-dependent immune mechanism.\",\n      \"method\": \"FGL2 CRISPR/KO in tumor cells, syngeneic GBM mouse models (immunocompetent vs. immunodeficient), DC differentiation assay, NF-κB/STAT/p38 signaling analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO in tumor with isogenic immune-competent/deficient comparison and epistasis via DC-deficient mice\",\n      \"pmids\": [\"30683885\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Ribavirin inhibits MHV-3-induced macrophage production of fgl2 prothrombinase (procoagulant activity) as well as TNF-α and IL-1β at the level of gene transcription (Northern analysis), without inhibiting LPS-stimulated macrophage TNF-α/IL-1β production, demonstrating virus-specific transcriptional regulation of fgl2.\",\n      \"method\": \"Procoagulant activity assay, ELISA, Northern blot, in vitro and in vivo MHV-3 infection with ribavirin treatment\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Northern blot + functional assay in single study, transcriptional mechanism established\",\n      \"pmids\": [\"9531310\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"TNF-α and IFN-γ induce soluble FGL2 secretion from CD4+ T cells via the JNK MAPK pathway; JNK inhibition (not p38 or ERK) significantly reduced sFGL2 secretion in vitro, and sFGL2/TNF-α/IFN-γ were all elevated in peripheral blood of renal allograft recipients with acute rejection.\",\n      \"method\": \"CD4+ T cell isolation, cytokine stimulation, JNK/p38/ERK inhibitors, ELISA for sFGL2\",\n      \"journal\": \"The Journal of surgical research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — pathway inhibitor pharmacology in primary human cells; single lab\",\n      \"pmids\": [\"23664593\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"C5a/C5aR signaling promotes FGL2 expression in macrophages and LSECs via ERK1/2 and p38 pathways during viral fulminant hepatitis; C5aR-/- or Fgl2-/- mice had significantly reduced complement activation and coagulation, establishing a C5a→TNF-α→FGL2 regulatory axis in vascular endothelial cells.\",\n      \"method\": \"C5aR-/-, Fgl2-/-, Tnfα-/- mouse infection models, C5a administration in vitro, ERK/p38 inhibitors, immunofluorescence, qRT-PCR, ELISA\",\n      \"journal\": \"Journal of hepatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple KO mouse models with epistasis plus in vitro pathway inhibition\",\n      \"pmids\": [\"25200905\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"FGL2-producing glioma cells recruit macrophages into the tumor microenvironment and induce them to secrete CXCL7 via CD16/SyK/PI3K/HIF1α pathways; CXCL7 in turn enhances stem-like functionality of glioma cells. This FGL2-CXCL7 paracrine loop was blocked by a neutralizing anti-CXCL7 antibody.\",\n      \"method\": \"Mass cytometry, RNA sequencing, immunocompetent mouse GBM model, anti-CXCL7 neutralizing antibody, pathway inhibition\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo model with antibody blockade and pathway analysis, single lab\",\n      \"pmids\": [\"33676940\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"FGL2 directly interacts with mucolipin 3 (MCOLN3) in neutrophils, regulating calcium influx and initiating autophagy, which leads to neutrophil extracellular trap (NET) formation. Neutrophil-specific FGL2 promotes NETs formation in fulminant viral hepatitis; adoptive transfer confirmed the neutrophil-intrinsic mechanism.\",\n      \"method\": \"Single-cell RNA sequencing, whole-transcriptome sequencing, adoptive transfer experiment, DNase 1 NET depletion, co-immunoprecipitation (FGL2-MCOLN3 interaction), mouse MHV-3 model\",\n      \"journal\": \"Cellular and molecular gastroenterology and hepatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP for protein-protein interaction plus adoptive transfer for cell-intrinsic mechanism; single lab\",\n      \"pmids\": [\"35926777\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"FGL2 expressed by T follicular helper (TFH) cells (not only Tregs) represses allergen-specific IgE production. Conditional deletion of Fgl2 specifically in TFH and T follicular regulatory (TFR) cells, but not TFR cells alone, increased antigen-specific IgE levels and IgE-mediated anaphylactic responses, establishing TFH-derived FGL2 as a suppressor of IgE+ germinal center B cell responses.\",\n      \"method\": \"Conditional Fgl2 deletion (TFH- and TFR-specific), food allergy mouse model, IgE ELISA, flow cytometry of GC B cells, anaphylaxis assay\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional cell-type-specific KO with specific functional readout, two genetic conditions tested\",\n      \"pmids\": [\"35767958\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"A homozygous truncating mutation (c.614_617del:p.V205fs) in human FGL2, which preserves the N-terminal domain but eliminates the C-terminal immunoregulatory domain, causes immune dysregulation with impaired Treg suppressive function. Addition of full-length FGL2 (but not the truncated mutant) rescued the Treg suppressive defect in vitro, demonstrating that the C-terminal domain is required for immunosuppressive function.\",\n      \"method\": \"Whole-exome sequencing, immunoblotting of transfected HEK293 cells, flow cytometry, Treg suppression assay, rescue with recombinant full-length vs. truncated FGL2\",\n      \"journal\": \"The Journal of allergy and clinical immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — human genetic mutation with cellular functional rescue experiment using truncated vs. full-length protein\",\n      \"pmids\": [\"36243222\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CD8+ T cell-intrinsic FGL2 suppresses anti-tumor and anti-viral CD8+ T cell responses via cell-autonomous binding of secreted FGL2 to FcγRIIB expressed on the same CD8+ T cells, triggering caspase 3/7-mediated apoptosis. Conditional deletion of Fgl2 specifically in antigen-specific CD8+ T cells prolonged their persistence, reduced exhaustion signatures, and improved tumor control.\",\n      \"method\": \"Conditional CD8+ T cell-specific Fgl2 deletion, tumor and chronic viral infection mouse models, transcriptomics, caspase 3/7 apoptosis assay, FcγRIIB-/- CD8+ T cell adoptive transfer\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — cell-type-specific conditional KO with receptor-deficient controls and mechanistic apoptosis assays\",\n      \"pmids\": [\"38902261\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"FGL2 prothrombinase participates in pulmonary hypertension pathogenesis; Fgl2 knockout reduced in situ thrombus formation, vascular remodeling, and endothelial apoptosis. FGL2 loss downregulated PAR1 (proteinase-activated receptor 1) expression and decreased platelet overactivation in hypoxia-induced PH, establishing a FGL2-thrombin-PAR1 signaling axis.\",\n      \"method\": \"Fgl2 knockout mouse, monocrotaline rat PH model, hypoxia mouse PH model, immunohistochemistry, PAR1 expression analysis, platelet activation assay\",\n      \"journal\": \"Journal of applied physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO mouse with multiple PH models and pathway identification (PAR1)\",\n      \"pmids\": [\"31580221\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"FGL2 knockdown in HCCLM6 hepatocellular carcinoma cells decreased tumor growth and angiogenesis in xenografts, and was associated with decreased ERK and JNK phosphorylation. Overexpression of FGL2 or addition of recombinant hFGL2 protein induced phosphorylation of p38-MAPK and ERK1/2 via protease-activated receptor (PAR) activation in vitro.\",\n      \"method\": \"MicroRNA-mediated knockdown, xenograft model in nude mice, cytometric bead array, recombinant FGL2 stimulation, MAPK phosphorylation assay\",\n      \"journal\": \"Liver international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — in vitro and in vivo knockdown/OE with pathway analysis; single lab\",\n      \"pmids\": [\"22925132\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"FGL2 oligomers in the hamster cauda epididymis are composed of two disulfide-linked subunits: 64 kDa FGL2 and 33 kDa FGL1. Both proteins are present in soluble epididymal fluid and in the sperm-associated death cocoon complex. Co-immunoprecipitation with anti-FGL2 antibody demonstrated that FGL1 and FGL2 associate in soluble form as well.\",\n      \"method\": \"Proteomics, PCR-based cloning, co-immunoprecipitation, immunocytochemistry, Northern blot, in situ hybridization\",\n      \"journal\": \"The international journal of biochemistry & cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — co-IP plus proteomic identification; single lab\",\n      \"pmids\": [\"27732889\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SNF2L (imitation switch ATPase) directly regulates Fgl2 expression in granulosa cells; Snf2l mutant mice fail to induce Fgl2 in response to hCG stimulation, while SNF2L overexpression drives Fgl2 expression. SNF2L interacts with the nuclear receptor co-activator flightless I (FLI-I) as shown by immunoprecipitation.\",\n      \"method\": \"Snf2l mutant mouse, hCG stimulation, granulosa cell overexpression, immunoprecipitation (SNF2L-FLI-I interaction), superovulation assay\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — genetic mouse model with upstream regulator identification and Co-IP; single lab\",\n      \"pmids\": [\"23616592\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"FGL2 interacts with Tyrobp in cutaneous squamous cell carcinoma cells, promoting ERK-dependent autophagy and cell proliferation. Co-immunoprecipitation and immunofluorescence colocalization confirmed the FGL2-Tyrobp interaction; knockdown of FGL2 reduced autophagy and proliferation while gain-of-function rescued Tyrobp-dependent effects.\",\n      \"method\": \"Co-immunoprecipitation, immunofluorescence colocalization, siRNA knockdown, overexpression, xenograft mouse model, ERK phosphorylation assay\",\n      \"journal\": \"International journal of medical sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — Co-IP with functional gain/loss-of-function; single lab\",\n      \"pmids\": [\"34975313\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Macrophage-secreted FGL2 dampens CD8+ T cell responses through direct binding to FcγRIIB expressed on CD8+ T cells, inducing T cell apoptosis in a CD8+ T cell-autonomous manner (not via APC intermediary). Absence of FcγRIIB from CD8+ T cells rendered them insensitive to FGL2-mediated regulation; macrophages are the dominant FGL2-producing cell in the tumor microenvironment across 10 cancer types.\",\n      \"method\": \"Melanoma mouse model, macrophage-specific Fgl2 analysis, FcγRIIB-/- CD8+ T cell adoptive transfer, apoptosis assay, scRNA-seq of human cancer data\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — receptor-deficient T cell adoptive transfer establishing cell-autonomous mechanism, multiple cancer types validated\",\n      \"pmids\": [\"40125553\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Tumor-derived exosomes deliver membrane-bound FGL2 (mFgl2) to MDSCs via FcγRIIB-mediated endocytosis, enhancing their immunosuppressive function (upregulated Arg-1 and iNOS, increased suppression of CD8+ T cells). Genetic ablation of FcγRIIB or antibody-mediated neutralization of FGL2 abolished exosome-mediated MDSC programming.\",\n      \"method\": \"Tumor-derived exosome isolation, FcγRIIB-/- MDSC functional assay, anti-Fgl2 neutralizing antibody, CD8+ T cell suppression assay, in vivo tumor model\",\n      \"journal\": \"Advanced science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — receptor KO and antibody blockade with functional MDSC readout; single lab, preprint-equivalent\",\n      \"pmids\": [\"41875310\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Arterial fluid shear stress (FSS) on venous endothelial cells increases FGL2 secretion via NF-κB signaling; secreted FGL2 promotes endothelial apoptosis via FcγRIIB. FcγRIIB blocking antibody reduced FGL2-induced caspase-3 activation in HUVECs exposed to arterial FSS.\",\n      \"method\": \"Tandem Mass Tagging proteomics of HUVEC secretome, Western blot, NF-κB inhibitor (BAY 11-7085), recombinant FGL2 treatment, FcγRIIB blocking antibody, caspase-3 immunocytochemistry\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — secretome proteomics + functional antibody blockade + recombinant protein; single lab\",\n      \"pmids\": [\"39062880\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"FGL2 in MASLD regulates NETs formation through direct interaction with HDAC11, promoting histone H3 deacetylation and facilitating PAD4-mediated citrullination to drive NET release. Genetic disruption of FGL2 or NETs inhibition restores LSEC fenestration, improves microvascular hemodynamics, and attenuates fibrosis.\",\n      \"method\": \"FGL2 KO mouse MASLD model, FGL2-HDAC11 interaction (implied by mechanistic studies), PAD4 citrullination assay, LSEC fenestration imaging, DNase 1 NET depletion\",\n      \"journal\": \"Advanced science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO mouse with molecular mechanism (HDAC11 interaction and PAD4 pathway); single lab, recent publication\",\n      \"pmids\": [\"42107082\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"FGL2 promotes PD-L1 expression in hepatocellular carcinoma cells by activating mTORC1 signaling, which phosphorylates and prevents nuclear translocation of TFEB, thereby inhibiting lysosome biosynthesis and lysosomal degradation of PD-L1. FGL2 KO in mice reduced tumor PD-L1 expression and synergized with anti-PD1 therapy.\",\n      \"method\": \"Fgl2 KO mouse HCC models, TFEB phosphorylation/nuclear translocation assay, mTORC1 signaling analysis, lysosome function assay, anti-PD1 combination treatment\",\n      \"journal\": \"Cell communication and signaling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO mouse with defined molecular pathway (mTOR-TFEB-PD-L1); single lab, very recent\",\n      \"pmids\": [\"41629991\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FGL2 stimulation of enteric neural crest cells (ENCCs) increases apoptosis by enhancing oxidative phosphorylation (OXPHOS) through activation of JAK2-STAT3 signaling, leading to ROS accumulation. FGL2 is upregulated in aganglionic colon tissues from Hirschsprung disease patients.\",\n      \"method\": \"Primary ENCC isolation, FGL2 stimulation in vitro, JAK2-STAT3 pathway analysis, OXPHOS/ROS measurement, apoptosis assay, patient tissue immunostaining\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — in vitro mechanistic assay with pathway inhibition; single lab, single study\",\n      \"pmids\": [\"40978140\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FGL2-KO in tumor cells suppresses CD47 expression through the Src and PKCα pathways; reconstitution of CD47 in Fgl2-KO tumor cells reversed immune protection. This Fgl2-CD47 circuit controls tumor immunogenicity and ability to induce brain-resident memory T cells.\",\n      \"method\": \"CRISPR/Cas9 Fgl2-KO in multiple tumor cell lines, CD47 reconstitution experiment, Src/PKCα inhibition, proteomic analysis, adoptive transfer of brain immune cells\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR KO with rescue experiment and pathway identification; single lab\",\n      \"pmids\": [\"41380903\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"SARS-CoV nucleocapsid (N) protein does NOT modulate FGL2 promoter activity or FGL2 mRNA/protein expression in human cells (including SARS-CoV-infected cells), in contrast to MHV-3 N protein, despite SARS-CoV N protein being able to repress interferon-stimulated response elements.\",\n      \"method\": \"Transfection of SARS-CoV N protein into human cell lines, luciferase reporter assay with FGL2 promoter, Northern blot, SARS-CoV infection experiment\",\n      \"journal\": \"The Journal of general virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — negative result established by direct promoter reporter assay and viral infection; single lab\",\n      \"pmids\": [\"19423547\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FGL2/fibroleukin is a bifunctional protein existing in two forms: a membrane-associated type II transmembrane prothrombinase that directly cleaves prothrombin to thrombin (requiring phospholipids, calcium, and Ser89 as the catalytic residue, and enhanced by factor Va) via a coagulation-cascade-independent mechanism, and a secreted/soluble form that acts as an immunosuppressive cytokine by binding FcγRIIB and FcγRIII on antigen-presenting cells, B cells, and CD8+ T cells to suppress DC maturation, induce B cell apoptosis, mediate Treg effector function, and drive CD8+ T cell apoptosis through a cell-autonomous FcγRIIB-caspase3/7 axis; its transcription is induced by IFN-γ (via STAT1/Sp1/Sp3/PU.1 in macrophages) and TNF-α (via NF-κB/p38 in endothelial cells), and by viral nucleocapsid proteins via HNF4α and an Ets-1/Oct-1/Sp1/Sp3 promoter complex.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"FGL2/fibroleukin is a bifunctional immune effector that links innate coagulation to adaptive immune suppression [#0, #9]. In its membrane-associated form it is a type II integral membrane protein with a C-terminal fibrinogen-related domain that functions as a prothrombinase, directly cleaving prothrombin to thrombin independently of the classical coagulation cascade [#0, #1]; this enzymatic activity requires phosphatidylserine-containing phospholipids and calcium, uses Ser89 as the catalytic residue, and is enhanced ~600-fold by factor Va [#2]. This prothrombinase drives fibrin deposition and tissue injury across multiple disease models, including MHV-3 viral hepatitis [#0, #8], acute vascular xenograft rejection [#11], collagen-induced arthritis [#15], and pulmonary hypertension via a thrombin-PAR1 axis [#25]. A secreted/oligomeric form acts as an immunosuppressive cytokine that binds FcγRIIB and FcγRIII on antigen-presenting cells, B cells, and T cells [#9]; through FcγRIIB it suppresses dendritic cell maturation, induces B cell apoptosis, mediates the suppressive effector function of regulatory T cells [#9, #10], and triggers apoptosis of sinusoidal and venous endothelial cells [#12, #32]. FGL2 is required cell-intrinsically for CD8+ T cell control: secreted FGL2 binds FcγRIIB on the same CD8+ T cell to trigger caspase-3/7-mediated apoptosis, and macrophage-derived FGL2 dampens anti-tumor and anti-viral CD8+ responses by this cell-autonomous route [#24, #30]. Its immunoregulatory activity maps to the C-terminal globular domain, and a homozygous truncating mutation eliminating this domain causes human immune dysregulation with impaired Treg suppression, rescuable by full-length but not truncated protein [#13, #23]. FGL2 transcription is inducible by IFN-γ (via STAT1 with Sp1/Sp3 and GAS/PU.1 elements in macrophages), TNF-α and NF-κB in endothelial cells, and by virulent MHV-3 nucleocapsid protein acting through HNF4α and an Ets-1/Oct-1/Sp1/Sp3 promoter complex [#7, #6, #4].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Established FGL2 as a virally induced prothrombinase, answering how MHV-3 infection triggers fibrin-mediated hepatocellular necrosis through a host gene rather than the classical cascade.\",\n      \"evidence\": \"Northern blot, in situ hybridization, immunochemistry, and procoagulant activity assay in MHV-3-infected liver\",\n      \"pmids\": [\"9371581\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Catalytic residue and cofactor requirements not yet defined\", \"Human ortholog not yet characterized\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Defined the signaling and pharmacological controls on viral fgl2 induction, showing transcription is p38 MAPK-dependent and selectively blockable by ribavirin.\",\n      \"evidence\": \"MAPK inhibitor pharmacology, kinase assays, and Northern blot in MHV-3-infected macrophages\",\n      \"pmids\": [\"9822700\", \"9531310\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Transcription factors downstream of p38 not identified here\", \"ribavirin (idx 17) is Medium-confidence single-study\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Identified the viral trigger of fgl2 transcription, mapping induction to the virulent MHV-3 nucleocapsid protein acting on a defined promoter region.\",\n      \"evidence\": \"Luciferase reporter cotransfection with parental and recombinant MHV strain comparison\",\n      \"pmids\": [\"10187767\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Host transcription factor mediating the N-protein response not yet identified\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Characterized human FGL2 as a single-copy gene encoding a type II membrane protein with a fibrinogen-related domain and reconstituted its prothrombinase activity, confirming the enzyme is conserved in humans.\",\n      \"evidence\": \"Recombinant expression, functional prothrombinase assay, radiation hybrid mapping, FISH\",\n      \"pmids\": [\"11170750\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Catalytic mechanism and cofactor dependence still undefined at this stage\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Resolved the enzymatic mechanism, identifying Ser89 as catalytic residue and defining phospholipid, calcium, and factor Va requirements that distinguish FGL2 from canonical serine proteases.\",\n      \"evidence\": \"Baculovirus expression, phospholipid vesicle reconstitution, kinetics, site-directed mutagenesis, inhibitor panel\",\n      \"pmids\": [\"11994472\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of substrate recognition not determined\", \"regulation of membrane vs secreted forms unresolved\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Mapped the cis/trans architecture of fgl2 transcription, defining HNF4α as the N-protein-responsive factor and a constitutive Ets-1/Sp1/Sp3/Oct-1 promoter complex in endothelium.\",\n      \"evidence\": \"EMSA, promoter deletion, viral protein mutagenesis, heterologous Drosophila expression\",\n      \"pmids\": [\"12594208\", \"12752447\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How distinct cell types deploy different factor combinations not fully resolved\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Provided definitive in vivo proof that fgl2 prothrombinase is non-redundant for viral hepatitis pathogenesis using a knockout mouse.\",\n      \"evidence\": \"Fgl2 knockout mouse in MHV-3 model with procoagulant, histopathology, and survival readouts\",\n      \"pmids\": [\"12840059\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address any immunomodulatory function of FGL2\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Extended FGL2's procoagulant pathology to transplant rejection and revealed a distinct reproductive role, identifying it as a secretory protein forming sperm-coating oligomeric complexes.\",\n      \"evidence\": \"fgl2-/- pig-to-rat cardiac xenograft model; cDNA cloning and immunoEM in hamster epididymis\",\n      \"pmids\": [\"15100314\", \"15377663\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Function of the epididymal 'death cocoon' relative to prothrombinase activity unclear\", \"partner subunits of the oligomer not yet defined\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Defined cytokine-specific, cell-type-restricted transcriptional induction and linked fibrin deposition to cytokine-driven hepatic apoptosis in vivo.\",\n      \"evidence\": \"EMSA, reporter assays, in vivo cytokine infusion, fgl2 knockout, TUNEL\",\n      \"pmids\": [\"16709865\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism restricting IFN-γ response to macrophages and TNF-α to endothelium only partially explained\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Established the second function of FGL2 as an immunosuppressive cytokine, identifying FcγRIIB/FcγRIII as receptors and showing FGL2 mediates Treg suppression and DC/B cell control.\",\n      \"evidence\": \"Surface plasmon resonance, flow cytometry, FcγRIIB-/- mice, Treg suppression and B cell apoptosis assays, allograft survival\",\n      \"pmids\": [\"18991288\", \"18097026\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream apoptotic signaling from FcγRIIB not yet defined\", \"relationship between membrane prothrombinase and secreted cytokine forms unclear\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Connected FGL2-FcγRIIB signaling to direct endothelial apoptosis in tissue injury and extended pathology to ischemia-reperfusion, using reciprocal ligand and receptor knockouts.\",\n      \"evidence\": \"Fgl2-/- and FcγRIIB-/- hepatic I/R models with caspase-3, TUNEL, in vitro SEC apoptosis; collagen arthritis KO model\",\n      \"pmids\": [\"21756857\", \"21469939\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Apoptotic effector pathway downstream of FcγRIIB not fully mapped\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defined FGL2 quaternary structure and mapped its immunosuppressive activity to the C-terminal globular domain, while showing monomer-oligomer state tunes binding versus activity.\",\n      \"evidence\": \"Recombinant expression, cysteine mutagenesis, SDS-PAGE, deglycosylation, peptide blockade, APC binding\",\n      \"pmids\": [\"23127799\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"High-resolution structure not determined\", \"in vivo relevance of oligomeric state unclear\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identified upstream signaling and chromatin-level control of FGL2 secretion in distinct contexts, including JNK-dependent secretion from CD4+ T cells and SNF2L-driven expression in granulosa cells.\",\n      \"evidence\": \"MAPK inhibitor pharmacology and ELISA in primary CD4+ T cells; Snf2l mutant mouse and Co-IP\",\n      \"pmids\": [\"23664593\", \"23616592\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab pathway studies without independent confirmation\", \"SNF2L-FLI-I link to fgl2 chromatin remodeling indirect\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Placed FGL2 within an upstream complement axis, establishing C5a/C5aR→TNF-α→FGL2 regulation in viral fulminant hepatitis.\",\n      \"evidence\": \"C5aR-/-, Fgl2-/-, Tnfα-/- mouse infection models with epistasis and in vitro pathway inhibition\",\n      \"pmids\": [\"25200905\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct biochemical link between C5aR signaling and fgl2 promoter not shown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Demonstrated FGL2's pro-tumor immunosuppression in glioma is DC-dependent and extended procoagulant pathology to pulmonary hypertension via a thrombin-PAR1 axis.\",\n      \"evidence\": \"Tumor CRISPR-KO with immunocompetent vs immunodeficient and DC-deficient mice; Fgl2-/- PH models with PAR1 analysis\",\n      \"pmids\": [\"30683885\", \"31580221\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether glioma effect is prothrombinase- or cytokine-dependent not separated\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Expanded FGL2's immunosuppressive sources and mechanisms, identifying TFH-derived FGL2 as an IgE suppressor, a human truncating mutation causing immune dysregulation, and novel interactors (MCOLN3, Tyrobp) driving autophagy/NETs.\",\n      \"evidence\": \"Conditional Fgl2 deletion (TFH/TFR), whole-exome sequencing with Treg rescue, Co-IP of FGL2-MCOLN3 and FGL2-Tyrobp, adoptive transfer\",\n      \"pmids\": [\"35767958\", \"36243222\", \"35926777\", \"34975313\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"MCOLN3 and Tyrobp interactions are single-lab Co-IPs without reciprocal validation\", \"how secreted FGL2 reaches intracellular partners unresolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Established the cell-autonomous immunosuppressive circuit, showing secreted FGL2 binds FcγRIIB on the same CD8+ T cell to trigger caspase-3/7 apoptosis, dampening anti-tumor immunity.\",\n      \"evidence\": \"CD8+ T cell-specific conditional Fgl2 deletion and macrophage-source analysis with FcγRIIB-/- adoptive transfer and apoptosis assays\",\n      \"pmids\": [\"38902261\", \"40125553\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Intracellular caspase activation pathway downstream of FcγRIIB not fully detailed\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Broadened FGL2 signaling into metabolic and developmental contexts, linking it to JAK2-STAT3-driven OXPHOS/ROS apoptosis in enteric neural crest cells and Src/PKCα-dependent CD47 control of tumor immunogenicity.\",\n      \"evidence\": \"Primary ENCC stimulation with pathway analysis; CRISPR Fgl2-KO with CD47 reconstitution and inhibitor studies\",\n      \"pmids\": [\"40978140\", \"41380903\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab mechanistic studies\", \"receptor mediating these effects not identified\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Defined additional context-specific effector mechanisms: exosomal membrane-FGL2 reprogramming MDSCs via FcγRIIB endocytosis, HDAC11/PAD4-driven NET formation in MASLD, and mTORC1-TFEB-mediated PD-L1 stabilization in HCC.\",\n      \"evidence\": \"Tumor exosome isolation with FcγRIIB-/- MDSC assays; Fgl2-KO MASLD and HCC models with molecular pathway dissection\",\n      \"pmids\": [\"41875310\", \"42107082\", \"41629991\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"All single-lab, very recent findings\", \"HDAC11 interaction inferred rather than directly demonstrated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How a single protein partitions between membrane prothrombinase and secreted immunosuppressive cytokine functions, and whether the two activities are coupled in vivo, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model distinguishing the two functional forms\", \"trafficking/cleavage that generates soluble FGL2 not characterized\", \"downstream caspase activation mechanism from FcγRIIB not fully mapped\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [9, 24, 30]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [9, 10, 24]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 0]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [9, 13, 14, 18]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-109582\", \"supporting_discovery_ids\": [0, 2, 11, 25]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [9, 10, 24, 30]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [12, 24, 30]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [4, 6, 7]}\n    ],\n    \"complexes\": [\"sperm-associated 'death cocoon' oligomer (FGL2/FGL1)\"],\n    \"partners\": [\"FCGR2B\", \"FCGR3\", \"F2\", \"F5\", \"MCOLN3\", \"TYROBP\", \"HDAC11\", \"FGL1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}