{"gene":"FGL2","run_date":"2026-04-28T17:46:03","timeline":{"discoveries":[{"year":1997,"finding":"FGL2 is a novel prothrombinase expressed on the cell surface of endothelial cells and macrophages (Kupffer cells) in the liver following MHV-3 infection; it generates thrombin from prothrombin, leading to fibrin deposition and hepatic necrosis. Expression is tissue-specific and restricted to reticuloendothelial cells.","method":"Northern analysis, in situ hybridization, immunohistochemistry in MHV-3-infected mice","journal":"Journal of virology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (Northern, ISH, IHC), replicated across multiple papers in the same laboratory context","pmids":["9371581","9782336"],"is_preprint":false},{"year":2002,"finding":"FGL2 is a serine protease that directly cleaves prothrombin to thrombin; activity requires phosphatidylserine-containing membranes, calcium, and is greatly enhanced by factor Va. Serine residue Ser89 is critical for catalytic activity. The enzyme is not inhibited by classical serine protease inhibitors (antithrombin III, aprotinin, PMSF) but is abolished by diisopropylfluorophosphate.","method":"In vitro reconstitution of purified baculovirus-expressed FGL2 into phospholipid vesicles, kinetic analysis, site-directed mutagenesis of Ser89, truncation constructs","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 1 — rigorous in vitro reconstitution, mutagenesis, and kinetic analysis in a single study","pmids":["11994472"],"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; it functions as a prothrombinase (serine protease) that directly cleaves prothrombin to thrombin. The gene is single-copy, located at 7q11.23, with two exons.","method":"Cloning, heterologous expression, functional prothrombinase assay, radiation hybrid mapping, FISH","journal":"Genomics","confidence":"High","confidence_rationale":"Tier 1 — functional expression assay with multiple molecular characterization methods","pmids":["11170750"],"is_preprint":false},{"year":1999,"finding":"The nucleocapsid (N) protein of virulent MHV-3 (but not non-pathogenic strains) induces transcription of the fgl2 prothrombinase gene. A region from -372 to -306 upstream of the ATG start site in the fgl2 promoter is responsive to nucleocapsid protein.","method":"Co-transfection of nucleocapsid expression constructs with fgl2 promoter-luciferase reporter in CHO cells, use of parental and recombinant MHV strains","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — promoter-reporter assay with mutagenesis and strain comparison","pmids":["10187767"],"is_preprint":false},{"year":2003,"finding":"Induction of fgl2 by the MHV-3 nucleocapsid protein requires host hepatic nuclear factor-4 alpha (HNF4α) binding to a -331/-325 HNF4 cis-element in the fgl2 promoter. Specific residues (Gly-12, Pro-38, Asn-40, Gln-41, Asn-42) in domain 1 of the N protein are required for fgl2 transcription induction. HNF4α is unexpectedly present in peritoneal macrophages.","method":"Site-directed mutagenesis of N protein domains, EMSA, luciferase reporter assays, deletion mapping of fgl2 promoter","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — EMSA plus promoter mutagenesis with multiple mutant constructs","pmids":["12594208"],"is_preprint":false},{"year":2003,"finding":"Constitutive fgl2 transcription in vascular endothelial cells is controlled by a 119 bp minimal promoter region containing a complex positive regulatory domain (-87 to -49) bound by Sp1/Sp3, Oct-1, and Ets-1. Both Sp1 and Sp3 are required for constitutive expression, and viral-induced fgl2 expression also requires this PRD.","method":"5'-RACE, primer extension, EMSA, heterologous expression in Drosophila Schneider cells, promoter deletion/mutation analysis","journal":"European journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 — EMSA, heterologous expression system, and systematic promoter deletion analysis","pmids":["12752447"],"is_preprint":false},{"year":1998,"finding":"MHV-3-induced fgl2 expression in macrophages is mediated via p38 MAPK signaling; selective p38 inhibition (SB203580) abolishes fgl2 mRNA, protein, and procoagulant activity. ERK activation also contributes to fgl2 functional activity but not mRNA/protein levels. p38 and ERK form interconnected cascades in macrophage activation.","method":"Western blot, immunoprecipitation, in vitro kinase assay, selective kinase inhibitors (SB203580, PD98059) in vitro and in vivo","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro kinase assays plus pharmacological inhibition confirmed in vivo","pmids":["9822700"],"is_preprint":false},{"year":2006,"finding":"IFN-γ induces fgl2 expression in macrophages through a STAT1-dependent pathway involving composite cis-elements Sp1/Sp3 and GAS/PU.1; PU.1 interaction with the GAS/ETS site determines macrophage-specific fgl2 induction. TNF-α induces fgl2 in endothelial cells. Cytokine-induced hepatic apoptosis in vivo is dependent on fgl2 (absent in fgl2-/- mice).","method":"Promoter-reporter assays, EMSA, in vivo cytokine infusion in fgl2+/+ vs fgl2-/- mice, cell-type-specific induction experiments","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 1-2 — EMSA, reporter assay, and genetic knockout with clear phenotypic readout","pmids":["16709865"],"is_preprint":false},{"year":2003,"finding":"Fgl2/fibroleukin deficiency in mice completely abolishes macrophage procoagulant response to MHV-3 infection, markedly reduces fibrin deposition and liver necrosis, and improves survival. This establishes fgl2 as essential for immune-coagulation in viral hepatitis.","method":"Gene-targeted fgl2-/- mouse, peritoneal macrophage procoagulant assay, histopathology, survival analysis","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — clean genetic knockout with multiple functional readouts, replicated across laboratories","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 dendritic cell maturation and induces apoptosis in FcγRIIB+ B cells; these effects are abrogated in FcγRIIB-/- cells. In vivo, recombinant FGL2 prolongs allograft survival only in FcγRIIB+/+ mice.","method":"Flow cytometry, surface plasmon resonance (SPR), FcγRIIB-/- mice, A20 vs A20IIA1.6 cell lines, skin allograft model","journal":"European journal of immunology","confidence":"High","confidence_rationale":"Tier 1-2 — SPR for binding affinity plus receptor-deficient cells and in vivo confirmation","pmids":["18991288"],"is_preprint":false},{"year":2008,"finding":"FGL2 is produced by CD4+CD25+ Foxp3+ regulatory T cells (Tregs) and mediates their suppressive activity. Deficiency of FGL2 in Treg cells results in impaired Treg suppression, increased T cell proliferation, Th1 polarization, increased B cell antibody production, and spontaneous autoimmune glomerulonephritis. Anti-FGL2 antibody completely inhibits Treg activity in vitro. FGL2 induces B cell apoptosis via FcγRIIB.","method":"fgl2-/- mice and bone marrow reconstitution, in vitro Treg suppression assays, anti-FGL2 antibody blockade, flow cytometry, immunization experiments","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 2 — genetic knockout plus functional rescue experiments with multiple orthogonal readouts","pmids":["18097026"],"is_preprint":false},{"year":2012,"finding":"Native secreted FGL2 exists as a ~260 kDa oligomer composed of four ~65 kDa monomers linked by disulfide bonds. Cysteines at positions 94, 97, 184, and 187 in the coiled-coil domain are required for oligomerization. Monomeric FGL2 has lower APC-binding affinity but greater immunosuppressive activity than oligomeric FGL2. The functional immunosuppressive motifs map to the C-terminal globular domain.","method":"Site-directed mutagenesis of cysteine residues, SDS-PAGE under reducing/non-reducing conditions, deglycosylation, peptide blockade assay, SWISS-MODEL structural analysis","journal":"The international journal of biochemistry & cell biology","confidence":"High","confidence_rationale":"Tier 1-2 — mutagenesis combined with biochemical characterization and functional assays","pmids":["23127799"],"is_preprint":false},{"year":2004,"finding":"FGL2 is expressed on vascular endothelial cells of xenografts undergoing acute vascular rejection (AVR); porcine fgl2 generates thrombin from human prothrombin in vitro. Hearts from fgl2-/- mice transplanted into rats are devoid of intravascular thrombosis associated with AVR, whereas fgl2+/+ and fgl2+/- grafts develop thrombosis, directly establishing fgl2 as the endothelial procoagulant mediating AVR-associated thrombosis.","method":"Cloning of porcine fgl2, recombinant protein prothrombinase assay, fgl2-/- heterotopic heart xenograft model, histopathology","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro enzymatic assay plus genetic knockout with clear in vivo phenotype","pmids":["15100314"],"is_preprint":false},{"year":2011,"finding":"FGL2 binding to FcγRIIB on sinusoidal endothelial cells (SECs) induces apoptosis of SECs and hepatocytes during hepatic ischemia-reperfusion injury. FGL2-/- or FcγRIIB-/- mice are markedly protected from liver injury, with dramatically reduced caspase-3 and TUNEL staining and improved survival. In vitro, FGL2 induces apoptosis of SECs from WT but not FcγRIIB-/- mice.","method":"fgl2-/- and FcγRIIB-/- mouse ischemia-reperfusion model, caspase-3 staining, TUNEL, AST/ALT measurement, in vitro SEC apoptosis assay","journal":"Journal of hepatology","confidence":"High","confidence_rationale":"Tier 2 — dual genetic knockouts with multiple apoptosis readouts and in vitro confirmation","pmids":["21756857"],"is_preprint":false},{"year":2011,"finding":"mFGL2 prothrombinase is upregulated in the joints of mice with collagen-induced arthritis, associated with fibrin deposition in synovium. fgl2-/- mice fail to develop clinical or histological manifestations of arthritis after anti-collagen II antibody injection, directly demonstrating the necessity of mFGL2 prothrombinase activity for experimental arthritis.","method":"fgl2-/- mice in anti-CII arthritis model, qRT-PCR, immunohistochemistry, clinical scoring","journal":"Scandinavian journal of rheumatology","confidence":"Medium","confidence_rationale":"Tier 2 — genetic knockout with clear phenotype, single laboratory","pmids":["21469939"],"is_preprint":false},{"year":2019,"finding":"FGL2 expressed by glioblastoma stem cells suppresses NF-κB, STAT1/5, and p38 signaling in dendritic cells, thereby inhibiting GM-CSF-induced CD103+ DC differentiation in the brain and tumor-draining lymph nodes. This impairs antitumor immunity and promotes GBM progression in immune-competent but not immunodeficient mice.","method":"FGL2-knockout glioma cells in immune-competent vs immunodeficient mice, DC-deficient mice, signaling pathway analysis","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — genetic knockout with multiple mouse models and mechanistic pathway validation","pmids":["30683885"],"is_preprint":false},{"year":2021,"finding":"FGL2-producing glioma cells recruit macrophages into the tumor microenvironment and induce macrophages to secrete CXCL7 via CD16/SyK/PI3K/HIF1α pathway. CXCL7 in turn enhances the stem-like functionality of glioma cells, forming a FGL2-CXCL7 paracrine loop that promotes tumor progression.","method":"Mass cytometry, RNA sequencing, neutralizing antibody blockade, pathway inhibition in immunocompetent mice","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 — multiple omics methods plus functional blockade, single laboratory","pmids":["33676940"],"is_preprint":false},{"year":2004,"finding":"fgl2 is required for physiological early embryonic development; fgl2-/- embryos show hemorrhage at the anti-mesometrial pole and selective occult loss before gestation day 11.5. LPS-induced abortion in mice requires fgl2 (abortions do not occur in fgl2-/- matings), placing fgl2 in the pathway linking inflammatory cytokines/LPS to pregnancy loss via coagulation.","method":"fgl2-/- knockout mouse, timed matings, PCR genotyping of embryos, LPS injection model, immunostaining","journal":"Molecular human reproduction","confidence":"Medium","confidence_rationale":"Tier 2 — genetic knockout with clear developmental phenotype, single laboratory","pmids":["14742694"],"is_preprint":false},{"year":2001,"finding":"Th1 cytokines (TNF-α, IFN-γ) upregulate fgl2 mRNA in fetal trophoblast and secondary decidua, leading to fibrin deposition and abortion. OX-2 glycoprotein is co-expressed at the same sites and is reduced by Th1 cytokines; anti-OX-2 raises the abortion rate while recombinant OX-2 reduces it, indicating OX-2 can counteract fgl2-mediated coagulation/abortion.","method":"In situ hybridization for fgl2 and OX-2, anti-OX-2 antibody treatment, recombinant OX-2 administration, fibrin staining in CBA/J mouse pregnancy models","journal":"Molecular human reproduction","confidence":"Medium","confidence_rationale":"Tier 2 — ISH with functional antibody and recombinant protein experiments, single laboratory","pmids":["11160845"],"is_preprint":false},{"year":2013,"finding":"Soluble FGL2 (sFGL2) secretion by CD4+ T cells is induced by TNF-α and IFN-γ via MAPK signaling, specifically through c-Jun N-terminal kinase (JNK) phosphorylation; JNK inhibition significantly reduces sFGL2 secretion. Neither p38 MAPK nor ERK1/2 show significant changes.","method":"In vitro stimulation of human CD4+ T cells with TNF-α or IFN-γ, JNK inhibitor treatment, ELISA for sFGL2, Western blot for MAPK phosphorylation","journal":"The Journal of surgical research","confidence":"Medium","confidence_rationale":"Tier 2-3 — pharmacological inhibition with functional readout, single laboratory","pmids":["23664593"],"is_preprint":false},{"year":2014,"finding":"C5a/C5aR pathway promotes FGL2 expression in liver sinusoidal endothelial cells and macrophages through ERK1/2 and p38 MAPK signaling during viral fulminant hepatitis. C5aR-/- mice show reduced FGL2 expression and coagulation. In vitro C5a stimulates TNF-α production in CD11b+ cells, which then promotes FGL2 expression in endothelial cells.","method":"C5aR-/-, Fgl2-/-, Tnfα-/- mice, in vitro C5a stimulation, ERK1/2 and p38 inhibitors, sorted liver cell populations","journal":"Journal of hepatology","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic knockout models plus in vitro mechanistic validation","pmids":["25200905"],"is_preprint":false},{"year":2022,"finding":"FGL2 directly interacts with mucolipin 3 (MCOLN3) in neutrophils, which regulates calcium influx and initiates autophagy, leading to neutrophil extracellular trap (NET) formation. Neutrophil-specific FGL2 promotes NETs, which exacerbate liver injury in fulminant viral hepatitis via fibrin deposition and inflammation.","method":"Single-cell RNA sequencing, adoptive transfer of FGL2-expressing neutrophils, DNase 1 NET depletion, interaction studies between FGL2 and MCOLN3","journal":"Cellular and molecular gastroenterology and hepatology","confidence":"Medium","confidence_rationale":"Tier 2-3 — adoptive transfer plus mechanistic interaction studies, single laboratory","pmids":["35926777"],"is_preprint":false},{"year":2024,"finding":"CD8+ T cell-derived FGL2 mediates cell-autonomous immunosuppression by binding to FcγRIIB expressed on the same CD8+ T cells, triggering caspase 3/7-mediated apoptosis. Conditional deletion of Fgl2 specifically in CD8+ T cells prolongs their persistence, reduces T cell exhaustion phenotype, and improves antitumor control. FcγRIIB-deficient CD8+ T cells are insensitive to Fgl2 regulation.","method":"Conditional Fgl2 knockout in antigen-specific CD8+ T cells, transcriptomic analysis, caspase 3/7 apoptosis assay, tumor models, chronic LCMV infection","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — conditional genetic knockout with mechanistic apoptosis assays and receptor-deficient controls","pmids":["38902261"],"is_preprint":false},{"year":2025,"finding":"Macrophage-secreted FGL2 dampens CD8+ T cell responses by binding FcγRIIB on CD8+ T cells and inducing their apoptosis in a cell-autonomous (non-APC-intermediary) manner. FcγRIIB-/- CD8+ T cells are insensitive to Fgl2 regulation. Macrophages are identified as the major tumor-microenvironment source of Fgl2 in melanoma and multiple cancer types.","method":"Fgl2-/- mice, Fcgr2b conditional knockout in CD8+ T cells, melanoma tumor models, scRNA-seq of human tumors","journal":"JCI insight","confidence":"High","confidence_rationale":"Tier 2 — cell-type-specific knockouts with mechanistic apoptosis and functional readouts, replicated across tumor models","pmids":["40125553"],"is_preprint":false},{"year":2019,"finding":"FGL2 prothrombinase in pulmonary vascular endothelium contributes to in situ thrombosis and vascular remodeling in pulmonary hypertension (PH). FGL2 knockout attenuates PH development, reduces PAR1 (proteinase-activated receptor 1) expression, and decreases platelet overactivation in hypoxia-induced PH models.","method":"Fgl2-/- mice in monocrotaline-rat and hypoxia-mouse PH models, PAR1 expression analysis, platelet activation assays, immunohistochemistry","journal":"Journal of applied physiology","confidence":"Medium","confidence_rationale":"Tier 2 — genetic knockout with multiple disease models and pathway analysis, single laboratory","pmids":["31580221"],"is_preprint":false},{"year":2019,"finding":"FGL2 regulates IKK/NF-κB signaling in intestinal epithelial cells and lamina propria dendritic cells. FGL2-/- mice show stronger NF-κB activation and more severe DSS-induced colitis. Recombinant FGL2 inhibits proinflammatory cytokine production and NF-κB signaling in HT-29 cells and rescues the FGL2-/- colitis phenotype.","method":"FGL2-/- mice in DSS colitis model, recombinant FGL2 rescue, NF-κB signaling analysis in IECs and LPDCs, flow cytometry of DC maturation markers","journal":"Molecular immunology","confidence":"Medium","confidence_rationale":"Tier 2 — genetic knockout plus recombinant protein rescue with pathway analysis, single laboratory","pmids":["31743856"],"is_preprint":false},{"year":2022,"finding":"FGL2 expressed by T follicular helper (TFH) cells represses IgE responses. Conditional deletion of Fgl2 in TFH (and TFR) cells, but not TFR cells alone, increases antigen-specific IgE levels and IgE-mediated anaphylaxis in a food-allergy model. Fgl2 and CD39 are downregulated in TFH cells under optimal IgE sensitization conditions.","method":"Conditional Fgl2 deletion in TFH/TFR cells, food-allergy model with timed Ag sensitizations, flow cytometry of IgE+ GC B cells, anaphylaxis assay","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 — conditional knockout with clear mechanistic cell-type assignment, single laboratory","pmids":["35767958"],"is_preprint":false},{"year":2022,"finding":"A human homozygous truncating mutation in FGL2 (c.614_617del:p.V205fs) retains the N-terminal domain but lacks the C-terminal immunoregulatory domain. The truncated protein fails to suppress T cell proliferation. Full-length recombinant FGL2 rescues the impaired Treg suppressive function, establishing the C-terminal domain as essential for FGL2's immunosuppressive activity.","method":"Whole-exome sequencing, HEK293 transfection/immunoblotting, flow cytometry of Treg function, in vitro Treg suppression assay with full-length vs truncated FGL2","journal":"The Journal of allergy and clinical immunology","confidence":"High","confidence_rationale":"Tier 1-2 — human loss-of-function mutation with protein structure-function validation and functional rescue","pmids":["36243222"],"is_preprint":false},{"year":2004,"finding":"In the hamster epididymis, FGL2 (HEP64) is secreted by principal cells of the proximal cauda epididymidis and specifically coats nonviable spermatozoa as part of a 'death cocoon' complex composed of FGL2 monomers (64 kDa) assembled into disulfide-linked oligomers of 260 and 280 kDa. FGL2 does not bind to viable spermatozoa.","method":"Expression screening of cDNA library, Northern blot, in situ hybridization, immunohistochemistry, immunoelectron microscopy, SDS-PAGE, microsequencing of isolated death cocoon fraction","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods identifying a novel biological role, single laboratory","pmids":["15377663"],"is_preprint":false},{"year":2022,"finding":"FGL2 interacts with Tyrobp (DAP12) in cutaneous squamous cell carcinoma cells, as shown by co-immunoprecipitation and immunofluorescence colocalization. This interaction promotes ERK-dependent autophagy, resulting in increased CSCC cell proliferation. Knockdown of FGL2 reduces ERK phosphorylation, autophagy, and proliferation.","method":"Co-immunoprecipitation, immunofluorescence, FGL2 knockdown/overexpression, autophagy assays, ERK signaling analysis, in vitro and xenograft models","journal":"International journal of medical sciences","confidence":"Medium","confidence_rationale":"Tier 2-3 — Co-IP with functional validation, single laboratory","pmids":["34975313"],"is_preprint":false},{"year":2023,"finding":"FGL2 deficiency alleviates maternal inflammation-induced blood-brain barrier (BBB) disruption by inhibiting PI3K/NF-κB-mediated oxidative stress in brain microvascular endothelial cells. PI3K overexpression in FGL2-deleted BMECs re-induces NOX2, iNOS, and NF-κB activation, placing FGL2 upstream of PI3K in this pathway.","method":"FGL2-/- mice with LPS-induced maternal inflammation, PI3K inhibitor (LY294002), PI3K lentivirus overexpression in FGL2-deleted BMECs, ROS/NO measurement, tight junction protein expression","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 2 — genetic knockout plus epistasis established via PI3K rescue experiments","pmids":["37051251"],"is_preprint":false},{"year":2013,"finding":"Snf2l (ISWI ATPase chromatin remodeling protein) 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 also directly interacts with the nuclear receptor co-activator flightless I (FLI-I) by immunoprecipitation.","method":"Snf2l exon 6 deletion mouse, hCG stimulation, immunoprecipitation of SNF2L-FLI-I, SNF2L overexpression in granulosa cells","journal":"Biology of reproduction","confidence":"Medium","confidence_rationale":"Tier 2-3 — genetic model plus co-IP and overexpression, single laboratory","pmids":["23616592"],"is_preprint":false},{"year":2026,"finding":"FGL2 in hepatocellular carcinoma cells regulates PD-L1 expression by activating mTORC1 signaling, which phosphorylates and retains TFEB in the cytoplasm, thereby inhibiting lysosome biosynthesis and PD-L1 lysosomal degradation. FGL2 knockout in hepatoma cells reduces PD-L1 expression and synergizes with anti-PD1 therapy.","method":"FGL2 knockout in Hepa1-6 cells, mTORC1 signaling analysis, TFEB phosphorylation/nuclear translocation assays, tumor models in Fgl2-/- mice, anti-PD1 combination","journal":"Cell communication and signaling : CCS","confidence":"Medium","confidence_rationale":"Tier 2 — genetic knockout with mechanistic pathway dissection, single laboratory","pmids":["41629991"],"is_preprint":false},{"year":2025,"finding":"FGL2 KO in tumor cells impairs CD47 expression through Src and PKCα pathways. Loss of FGL2 in tumor cells induces long-duration brain-resident memory T (TRM) cells that prevent brain tumor recurrence. Reconstitution of CD47 in FGL2-KO tumor cells reverses the anti-tumor protection.","method":"CRISPR/Cas9 FGL2 knockout, proteomic analysis of Src/PKCα pathway, CD47 reconstitution, brain immune cell transplant, TRM cell depletion, murine intracranial tumor challenge models","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 — epistasis established via CD47 reconstitution plus multiple mechanistic approaches, single laboratory","pmids":["41380903"],"is_preprint":false},{"year":2013,"finding":"FGL2 deficiency leads to increased LCMV WE viral titers early post-infection but enhanced DC maturation (CD80, MHC II), increased virus-specific CD8+ and CD4+ T cell IFN-γ production, and higher anti-LCMV antibody titers, demonstrating that FGL2 suppresses adaptive anti-viral immunity by binding to FcγRIIB on APCs.","method":"fgl2-/- mice infected with LCMV WE, DC maturation marker flow cytometry, tetramer staining, IFN-γ ELISpot, neutralizing antibody titers","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — genetic knockout with multiple functional immunological readouts, single laboratory","pmids":["24146739"],"is_preprint":false}],"current_model":"FGL2/fibroleukin is a multifunctional protein existing in two forms: a membrane-associated type II transmembrane serine protease (mFGL2) that directly cleaves prothrombin to thrombin via a Ser89 catalytic site in a phospholipid-, calcium-, and factor Va-dependent manner (bypassing classical coagulation cascades), and a secreted form (sFGL2) that functions as an immunosuppressive effector of regulatory T cells by binding to FcγRIIB and FcγRIII receptors on antigen-presenting cells and CD8+ T cells, inducing apoptosis and inhibiting DC maturation, T cell proliferation, and adaptive immunity; transcription of the FGL2 gene is induced by viral nucleocapsid protein (via HNF4α), IFN-γ (via STAT1/Sp1/PU.1), and TNF-α (via NF-κB/p38 MAPK) in a cell-type-specific manner, while its oligomeric structure (tetramers linked by Cys94/97/184/187) and C-terminal globular domain are essential for immunosuppressive function."},"narrative":{"teleology":[{"year":1997,"claim":"Identification of FGL2 as a novel cell-surface prothrombinase on reticuloendothelial cells resolved the long-standing question of how MHV-3 infection triggers fibrin deposition and hepatic necrosis independent of classical coagulation cascades.","evidence":"Northern blot, in situ hybridization, and immunohistochemistry in MHV-3-infected mouse livers","pmids":["9371581","9782336"],"confidence":"High","gaps":["Catalytic mechanism and active-site residues not yet identified","No purified protein reconstitution to confirm direct prothrombinase activity"]},{"year":1999,"claim":"Demonstration that the MHV-3 nucleocapsid protein induces fgl2 transcription via a specific promoter element (-372 to -306) established the first transcriptional mechanism linking viral pathogenicity to FGL2-mediated coagulation, subsequently refined to show HNF4α binding at a -331/-325 cis-element.","evidence":"Promoter-reporter assays with deletion mapping in CHO cells (1999); EMSA and site-directed mutagenesis of N protein domains (2003)","pmids":["10187767","12594208"],"confidence":"High","gaps":["How nucleocapsid protein activates HNF4α remains unclear","Relevance to human hepatitis viruses not established"]},{"year":2001,"claim":"Cloning of human FGL2 and identification of its domain architecture (type II transmembrane protein with C-terminal fibrinogen-related domain) provided the structural framework for understanding both prothrombinase and later-discovered immunoregulatory functions.","evidence":"Cloning, heterologous expression, functional prothrombinase assay, FISH mapping to 7q11.23","pmids":["11170750"],"confidence":"High","gaps":["No crystal structure available","Function of the C-terminal fibrinogen-related domain beyond prothrombinase not yet explored"]},{"year":2002,"claim":"Biochemical reconstitution of purified FGL2 into phospholipid vesicles proved it is a bona fide serine protease that cleaves prothrombin directly, with Ser89 as the catalytic residue and requirements for phosphatidylserine, calcium, and factor Va — establishing FGL2 as a non-classical prothrombinase.","evidence":"In vitro reconstitution of baculovirus-expressed FGL2 with kinetic analysis and Ser89 mutagenesis","pmids":["11994472"],"confidence":"High","gaps":["Structural basis for resistance to classical serine protease inhibitors unexplained","Whether FGL2 has substrates beyond prothrombin is unknown"]},{"year":2003,"claim":"The fgl2 knockout mouse demonstrated that FGL2 is essential for macrophage procoagulant activity and fibrin-mediated liver necrosis during MHV-3 infection, providing definitive genetic proof of its in vivo prothrombinase function and establishing its non-redundancy with classical coagulation factors.","evidence":"Gene-targeted fgl2−/− mouse with peritoneal macrophage procoagulant assay, histopathology, and survival analysis","pmids":["12840059"],"confidence":"High","gaps":["Whether sFGL2 immunosuppressive function also contributes to the infection phenotype was not dissected","Compensatory mechanisms in fgl2−/− mice not characterized"]},{"year":2003,"claim":"Mapping of constitutive and cytokine-induced fgl2 transcription revealed cell-type-specific promoter architecture: Sp1/Sp3 and Oct-1/Ets-1 drive basal expression in endothelial cells, while IFN-γ signals through STAT1/Sp1/PU.1 in macrophages and p38 MAPK mediates virus-induced expression.","evidence":"EMSA, heterologous Drosophila Schneider cell expression, promoter deletion analysis (2003); p38 and ERK inhibitor studies in macrophages (1998); IFN-γ/STAT1/PU.1 pathway in knockout mice (2006)","pmids":["12752447","9822700","16709865"],"confidence":"High","gaps":["Chromatin-level regulation of the FGL2 locus not characterized","Integration of multiple simultaneous cytokine signals not modeled"]},{"year":2004,"claim":"FGL2 was established as the endothelial prothrombinase mediating acute vascular rejection thrombosis in xenotransplantation — fgl2−/− donor hearts were devoid of intravascular thrombosis — and was also shown to be required for LPS-induced pregnancy loss and normal early embryonic vascular development.","evidence":"Porcine FGL2 prothrombinase assay and fgl2−/− heterotopic heart xenograft model (2004); fgl2−/− timed matings and LPS abortion model (2004)","pmids":["15100314","14742694"],"confidence":"High","gaps":["Whether sFGL2 immunoregulatory function contributes to graft rejection alongside prothrombinase activity","Mechanism of selective embryonic hemorrhage in fgl2−/− mice unclear"]},{"year":2008,"claim":"Discovery that FGL2 binds FcγRIIB and FcγRIII on APCs and induces B cell apoptosis, and that Treg-derived FGL2 is a critical effector of Treg suppressive activity, revealed a second, immunoregulatory function entirely distinct from the prothrombinase activity — transforming FGL2 from a coagulation factor into a dual-function immune-coagulation mediator.","evidence":"SPR binding assays, FcγRIIB−/− cell lines and mice, skin allograft model (2008); fgl2−/− Treg suppression assays, anti-FGL2 antibody blockade, bone marrow reconstitution (2008)","pmids":["18991288","18097026"],"confidence":"High","gaps":["Precise binding epitope on FcγRIIB not mapped","Whether FGL2 signals through FcγRIII with distinct downstream consequences unknown"]},{"year":2011,"claim":"Extension of FGL2–FcγRIIB signaling to hepatic ischemia-reperfusion injury and to experimental arthritis broadened the pathophysiological scope, showing FGL2 induces sinusoidal endothelial cell apoptosis via FcγRIIB and that membrane FGL2 prothrombinase is required for fibrin-driven joint inflammation.","evidence":"Dual fgl2−/− and FcγRIIB−/− mouse I/R models with caspase-3/TUNEL readouts (2011); fgl2−/− anti-CII arthritis model (2011)","pmids":["21756857","21469939"],"confidence":"High","gaps":["Whether apoptotic and prothrombinase functions operate simultaneously in the same tissue","Role of sFGL2 vs mFGL2 in arthritis not dissected"]},{"year":2012,"claim":"Structural characterization revealed that secreted FGL2 is a disulfide-linked tetramer (Cys94/97/184/187), with the C-terminal globular domain containing the immunosuppressive motifs; unexpectedly, monomeric FGL2 showed greater immunosuppressive potency than the oligomer, indicating oligomerization modulates rather than enables function.","evidence":"Cysteine-to-alanine mutagenesis, non-reducing SDS-PAGE, peptide blockade, deglycosylation","pmids":["23127799"],"confidence":"High","gaps":["High-resolution structure not available","Physiological regulation of oligomeric state unknown"]},{"year":2019,"claim":"FGL2 was identified as a tumor immune-evasion molecule: glioblastoma stem cell-derived FGL2 suppresses GM-CSF-induced CD103+ DC differentiation by inhibiting NF-κB, STAT1/5, and p38 signaling, and FGL2 prothrombinase in pulmonary endothelium drives in situ thrombosis in pulmonary hypertension.","evidence":"FGL2-KO glioma cells in immunocompetent vs immunodeficient mice (2019); fgl2−/− mice in hypoxia-induced PH models (2019)","pmids":["30683885","31580221"],"confidence":"High","gaps":["Whether FGL2 suppresses DCs through FcγRIIB or an independent receptor in the brain microenvironment","Therapeutic window for anti-FGL2 in tumors not defined"]},{"year":2022,"claim":"A human homozygous truncating FGL2 mutation (p.V205fs) lacking the C-terminal domain failed to suppress T cell proliferation and was rescued by full-length recombinant FGL2, providing the first human genetic validation that the fibrinogen-related domain is essential for immunosuppressive function.","evidence":"Whole-exome sequencing, HEK293 expression of truncated vs full-length protein, Treg suppression assay with rescue","pmids":["36243222"],"confidence":"High","gaps":["Clinical phenotype associated with this mutation not fully delineated in the timeline","Whether prothrombinase activity is also affected by this truncation not tested"]},{"year":2022,"claim":"FGL2 was shown to regulate IgE class-switching: TFH cell-derived FGL2 represses antigen-specific IgE responses, and FGL2 in neutrophils interacts with mucolipin 3 (MCOLN3) to regulate calcium-dependent autophagy and NET formation, revealing additional cell-type-specific functions.","evidence":"Conditional Fgl2 deletion in TFH/TFR cells with food-allergy model (2022); scRNA-seq and FGL2-MCOLN3 interaction studies in neutrophils (2022)","pmids":["35767958","35926777"],"confidence":"Medium","gaps":["FGL2–MCOLN3 interaction not confirmed by reciprocal IP or structural studies","Whether FGL2 regulates IgE through FcγRIIB on B cells or another mechanism not resolved"]},{"year":2024,"claim":"Conditional deletion of Fgl2 in CD8+ T cells demonstrated cell-autonomous immunosuppression: CD8+ T cell-derived FGL2 binds FcγRIIB on the same cells to trigger caspase 3/7-mediated apoptosis and T cell exhaustion, and macrophage-secreted FGL2 acts on CD8+ T cells via the same receptor, establishing a paracrine and autocrine FGL2–FcγRIIB axis that limits antitumor and antiviral CD8+ T cell responses.","evidence":"Conditional Fgl2 KO in CD8+ T cells, FcγRIIB conditional KO, caspase assays, chronic LCMV and tumor models (2024); Fgl2−/− mice plus Fcgr2b conditional KO in CD8+ T cells across melanoma models (2025)","pmids":["38902261","40125553"],"confidence":"High","gaps":["Signaling intermediates downstream of FcγRIIB in CD8+ T cells not fully mapped","Whether autocrine vs paracrine FGL2 has differential potency in vivo remains unclear"]},{"year":2025,"claim":"FGL2 was linked to regulation of immune checkpoint molecules: tumor cell FGL2 sustains PD-L1 expression via mTORC1-mediated TFEB phosphorylation that blocks lysosomal PD-L1 degradation, and FGL2 promotes CD47 expression through Src/PKCα, identifying FGL2 as an upstream regulator of multiple immune checkpoint pathways.","evidence":"FGL2-KO hepatoma cells with mTORC1/TFEB pathway analysis (2026 pub); CRISPR FGL2 KO with Src/PKCα proteomics and CD47 reconstitution in brain tumor models (2025)","pmids":["41629991","41380903"],"confidence":"Medium","gaps":["Direct physical interaction between FGL2 and mTORC1 or Src not demonstrated","Whether these checkpoint regulatory mechanisms operate through the same FcγRIIB axis or independently is unknown","Single-laboratory findings await independent replication"]},{"year":null,"claim":"Key unresolved questions include: the structural basis for FGL2's dual prothrombinase and immunosuppressive activities; how the switch between membrane-bound and secreted forms is regulated; the precise signaling cascade downstream of FcγRIIB engagement by FGL2; and whether anti-FGL2 therapeutic strategies can selectively target immunosuppressive versus coagulant functions.","evidence":"","pmids":[],"confidence":"High","gaps":["No crystal or cryo-EM structure of FGL2","Mechanism of membrane-to-secreted form switching unknown","Full downstream signaling pathway from FcγRIIB upon FGL2 engagement not mapped","No clinical trials targeting FGL2 reported in the timeline"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,2,8,12]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[9,10,15,22,23,34]},{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[9,10,13,22,23]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,1,2,12,24]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[10,11,23,28]}],"pathway":[{"term_id":"R-HSA-109582","term_label":"Hemostasis","supporting_discovery_ids":[0,1,2,8,12,24]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[9,10,15,22,23,34]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[9,13,22,23]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[6,7,20,25]}],"complexes":[],"partners":["FCGR2B","FCGR3","MCOLN3","TYROBP","HNF4A","STAT1"],"other_free_text":[]},"mechanistic_narrative":"FGL2/fibroleukin is a dual-function protein operating at the intersection of coagulation and immune regulation. As a membrane-associated type II transmembrane protein, FGL2 acts as a serine prothrombinase that directly cleaves prothrombin to thrombin via a catalytic Ser89 residue in a phospholipid-, calcium-, and factor Va-dependent manner, driving fibrin deposition in viral hepatitis, xenograft rejection, and vascular thrombosis [PMID:11994472, PMID:12840059, PMID:15100314]. As a secreted oligomeric effector produced by regulatory T cells and other immune cells, FGL2 binds FcγRIIB and FcγRIII on antigen-presenting cells and CD8+ T cells, inducing apoptosis via caspase 3/7, inhibiting dendritic cell maturation and T cell proliferation, and suppressing adaptive immunity in infection, transplantation, and tumor microenvironments [PMID:18991288, PMID:18097026, PMID:38902261, PMID:30683885]. Transcription of FGL2 is induced by viral nucleocapsid protein through HNF4α, by IFN-γ through STAT1/Sp1/PU.1, and by TNF-α through NF-κB and p38 MAPK pathways in a cell-type-specific manner, while its immunosuppressive function requires the C-terminal fibrinogen-related globular domain and is modulated by disulfide-linked tetramerization [PMID:10187767, PMID:12594208, PMID:16709865, PMID:23127799, PMID:36243222]."},"prefetch_data":{"uniprot":{"accession":"Q14314","full_name":"Fibroleukin","aliases":["Fibrinogen-like protein 2","pT49"],"length_aa":439,"mass_kda":50.2,"function":"May play a role in physiologic lymphocyte functions at mucosal sites","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/Q14314/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/FGL2","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/FGL2","total_profiled":1310},"omim":[{"mim_id":"605776","title":"FIBRINOGEN-LIKE 1; FGL1","url":"https://www.omim.org/entry/605776"},{"mim_id":"605351","title":"FIBRINOGEN-LIKE 2; FGL2","url":"https://www.omim.org/entry/605351"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"blood vessel","ntpm":153.8},{"tissue":"lymphoid tissue","ntpm":153.1}],"url":"https://www.proteinatlas.org/search/FGL2"},"hgnc":{"alias_symbol":["pT49","T49"],"prev_symbol":[]},"alphafold":{"accession":"Q14314","domains":[{"cath_id":"3.90.215.10","chopping":"212-433","consensus_level":"medium","plddt":94.3803,"start":212,"end":433},{"cath_id":"1.20.5","chopping":"151-178","consensus_level":"medium","plddt":74.4832,"start":151,"end":178}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q14314","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q14314-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q14314-F1-predicted_aligned_error_v6.png","plddt_mean":78.69},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=FGL2","jax_strain_url":"https://www.jax.org/strain/search?query=FGL2"},"sequence":{"accession":"Q14314","fasta_url":"https://rest.uniprot.org/uniprotkb/Q14314.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q14314/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q14314"}},"corpus_meta":[{"pmid":"9531310","id":"PMC_9531310","title":"Ribavirin 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novel prothrombinase expressed on the cell surface of endothelial cells and macrophages (Kupffer cells) in the liver following MHV-3 infection; it generates thrombin from prothrombin, leading to fibrin deposition and hepatic necrosis. Expression is tissue-specific and restricted to reticuloendothelial cells.\",\n      \"method\": \"Northern analysis, in situ hybridization, immunohistochemistry in MHV-3-infected mice\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (Northern, ISH, IHC), replicated across multiple papers in the same laboratory context\",\n      \"pmids\": [\"9371581\", \"9782336\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"FGL2 is a serine protease that directly cleaves prothrombin to thrombin; activity requires phosphatidylserine-containing membranes, calcium, and is greatly enhanced by factor Va. Serine residue Ser89 is critical for catalytic activity. The enzyme is not inhibited by classical serine protease inhibitors (antithrombin III, aprotinin, PMSF) but is abolished by diisopropylfluorophosphate.\",\n      \"method\": \"In vitro reconstitution of purified baculovirus-expressed FGL2 into phospholipid vesicles, kinetic analysis, site-directed mutagenesis of Ser89, truncation constructs\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — rigorous in vitro reconstitution, mutagenesis, and kinetic analysis in a single study\",\n      \"pmids\": [\"11994472\"],\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; it functions as a prothrombinase (serine protease) that directly cleaves prothrombin to thrombin. The gene is single-copy, located at 7q11.23, with two exons.\",\n      \"method\": \"Cloning, heterologous expression, functional prothrombinase assay, radiation hybrid mapping, FISH\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — functional expression assay with multiple molecular characterization methods\",\n      \"pmids\": [\"11170750\"],\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 prothrombinase gene. A region from -372 to -306 upstream of the ATG start site in the fgl2 promoter is responsive to nucleocapsid protein.\",\n      \"method\": \"Co-transfection of nucleocapsid expression constructs with fgl2 promoter-luciferase reporter in CHO cells, use of parental and recombinant MHV strains\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — promoter-reporter assay with mutagenesis and strain comparison\",\n      \"pmids\": [\"10187767\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Induction of fgl2 by the MHV-3 nucleocapsid protein requires host hepatic nuclear factor-4 alpha (HNF4α) binding to a -331/-325 HNF4 cis-element in the fgl2 promoter. Specific residues (Gly-12, Pro-38, Asn-40, Gln-41, Asn-42) in domain 1 of the N protein are required for fgl2 transcription induction. HNF4α is unexpectedly present in peritoneal macrophages.\",\n      \"method\": \"Site-directed mutagenesis of N protein domains, EMSA, luciferase reporter assays, deletion mapping of fgl2 promoter\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — EMSA plus promoter mutagenesis with multiple mutant constructs\",\n      \"pmids\": [\"12594208\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Constitutive fgl2 transcription in vascular endothelial cells is controlled by a 119 bp minimal promoter region containing a complex positive regulatory domain (-87 to -49) bound by Sp1/Sp3, Oct-1, and Ets-1. Both Sp1 and Sp3 are required for constitutive expression, and viral-induced fgl2 expression also requires this PRD.\",\n      \"method\": \"5'-RACE, primer extension, EMSA, heterologous expression in Drosophila Schneider cells, promoter deletion/mutation analysis\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — EMSA, heterologous expression system, and systematic promoter deletion analysis\",\n      \"pmids\": [\"12752447\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"MHV-3-induced fgl2 expression in macrophages is mediated via p38 MAPK signaling; selective p38 inhibition (SB203580) abolishes fgl2 mRNA, protein, and procoagulant activity. ERK activation also contributes to fgl2 functional activity but not mRNA/protein levels. p38 and ERK form interconnected cascades in macrophage activation.\",\n      \"method\": \"Western blot, immunoprecipitation, in vitro kinase assay, selective kinase inhibitors (SB203580, PD98059) in vitro and in vivo\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro kinase assays plus pharmacological inhibition confirmed in vivo\",\n      \"pmids\": [\"9822700\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"IFN-γ induces fgl2 expression in macrophages through a STAT1-dependent pathway involving composite cis-elements Sp1/Sp3 and GAS/PU.1; PU.1 interaction with the GAS/ETS site determines macrophage-specific fgl2 induction. TNF-α induces fgl2 in endothelial cells. Cytokine-induced hepatic apoptosis in vivo is dependent on fgl2 (absent in fgl2-/- mice).\",\n      \"method\": \"Promoter-reporter assays, EMSA, in vivo cytokine infusion in fgl2+/+ vs fgl2-/- mice, cell-type-specific induction experiments\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — EMSA, reporter assay, and genetic knockout with clear phenotypic readout\",\n      \"pmids\": [\"16709865\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Fgl2/fibroleukin deficiency in mice completely abolishes macrophage procoagulant response to MHV-3 infection, markedly reduces fibrin deposition and liver necrosis, and improves survival. This establishes fgl2 as essential for immune-coagulation in viral hepatitis.\",\n      \"method\": \"Gene-targeted fgl2-/- mouse, peritoneal macrophage procoagulant assay, histopathology, survival analysis\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic knockout with multiple functional readouts, replicated across laboratories\",\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 dendritic cell maturation and induces apoptosis in FcγRIIB+ B cells; these effects are abrogated in FcγRIIB-/- cells. In vivo, recombinant FGL2 prolongs allograft survival only in FcγRIIB+/+ mice.\",\n      \"method\": \"Flow cytometry, surface plasmon resonance (SPR), FcγRIIB-/- mice, A20 vs A20IIA1.6 cell lines, skin allograft model\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — SPR for binding affinity plus receptor-deficient cells and in vivo confirmation\",\n      \"pmids\": [\"18991288\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"FGL2 is produced by CD4+CD25+ Foxp3+ regulatory T cells (Tregs) and mediates their suppressive activity. Deficiency of FGL2 in Treg cells results in impaired Treg suppression, increased T cell proliferation, Th1 polarization, increased B cell antibody production, and spontaneous autoimmune glomerulonephritis. Anti-FGL2 antibody completely inhibits Treg activity in vitro. FGL2 induces B cell apoptosis via FcγRIIB.\",\n      \"method\": \"fgl2-/- mice and bone marrow reconstitution, in vitro Treg suppression assays, anti-FGL2 antibody blockade, flow cytometry, immunization experiments\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout plus functional rescue experiments with multiple orthogonal readouts\",\n      \"pmids\": [\"18097026\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Native secreted FGL2 exists as a ~260 kDa oligomer composed of four ~65 kDa monomers linked by disulfide bonds. Cysteines at positions 94, 97, 184, and 187 in the coiled-coil domain are required for oligomerization. Monomeric FGL2 has lower APC-binding affinity but greater immunosuppressive activity than oligomeric FGL2. The functional immunosuppressive motifs map to the C-terminal globular domain.\",\n      \"method\": \"Site-directed mutagenesis of cysteine residues, SDS-PAGE under reducing/non-reducing conditions, deglycosylation, peptide blockade assay, SWISS-MODEL structural analysis\",\n      \"journal\": \"The international journal of biochemistry & cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mutagenesis combined with biochemical characterization and functional assays\",\n      \"pmids\": [\"23127799\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"FGL2 is expressed on vascular endothelial cells of xenografts undergoing acute vascular rejection (AVR); porcine fgl2 generates thrombin from human prothrombin in vitro. Hearts from fgl2-/- mice transplanted into rats are devoid of intravascular thrombosis associated with AVR, whereas fgl2+/+ and fgl2+/- grafts develop thrombosis, directly establishing fgl2 as the endothelial procoagulant mediating AVR-associated thrombosis.\",\n      \"method\": \"Cloning of porcine fgl2, recombinant protein prothrombinase assay, fgl2-/- heterotopic heart xenograft model, histopathology\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro enzymatic assay plus genetic knockout with clear in vivo phenotype\",\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 of SECs and hepatocytes during hepatic ischemia-reperfusion injury. FGL2-/- or FcγRIIB-/- mice are markedly protected from liver injury, with dramatically reduced caspase-3 and TUNEL staining and improved survival. In vitro, FGL2 induces apoptosis of SECs from WT but not FcγRIIB-/- mice.\",\n      \"method\": \"fgl2-/- and FcγRIIB-/- mouse ischemia-reperfusion model, caspase-3 staining, TUNEL, AST/ALT measurement, in vitro SEC apoptosis assay\",\n      \"journal\": \"Journal of hepatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — dual genetic knockouts with multiple apoptosis readouts and in vitro confirmation\",\n      \"pmids\": [\"21756857\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"mFGL2 prothrombinase is upregulated in the joints of mice with collagen-induced arthritis, associated with fibrin deposition in synovium. fgl2-/- mice fail to develop clinical or histological manifestations of arthritis after anti-collagen II antibody injection, directly demonstrating the necessity of mFGL2 prothrombinase activity for experimental arthritis.\",\n      \"method\": \"fgl2-/- mice in anti-CII arthritis model, qRT-PCR, immunohistochemistry, clinical scoring\",\n      \"journal\": \"Scandinavian journal of rheumatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout with clear phenotype, single laboratory\",\n      \"pmids\": [\"21469939\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"FGL2 expressed by glioblastoma stem cells suppresses NF-κB, STAT1/5, and p38 signaling in dendritic cells, thereby inhibiting GM-CSF-induced CD103+ DC differentiation in the brain and tumor-draining lymph nodes. This impairs antitumor immunity and promotes GBM progression in immune-competent but not immunodeficient mice.\",\n      \"method\": \"FGL2-knockout glioma cells in immune-competent vs immunodeficient mice, DC-deficient mice, signaling pathway analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout with multiple mouse models and mechanistic pathway validation\",\n      \"pmids\": [\"30683885\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"FGL2-producing glioma cells recruit macrophages into the tumor microenvironment and induce macrophages to secrete CXCL7 via CD16/SyK/PI3K/HIF1α pathway. CXCL7 in turn enhances the stem-like functionality of glioma cells, forming a FGL2-CXCL7 paracrine loop that promotes tumor progression.\",\n      \"method\": \"Mass cytometry, RNA sequencing, neutralizing antibody blockade, pathway inhibition in immunocompetent mice\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple omics methods plus functional blockade, single laboratory\",\n      \"pmids\": [\"33676940\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"fgl2 is required for physiological early embryonic development; fgl2-/- embryos show hemorrhage at the anti-mesometrial pole and selective occult loss before gestation day 11.5. LPS-induced abortion in mice requires fgl2 (abortions do not occur in fgl2-/- matings), placing fgl2 in the pathway linking inflammatory cytokines/LPS to pregnancy loss via coagulation.\",\n      \"method\": \"fgl2-/- knockout mouse, timed matings, PCR genotyping of embryos, LPS injection model, immunostaining\",\n      \"journal\": \"Molecular human reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout with clear developmental phenotype, single laboratory\",\n      \"pmids\": [\"14742694\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Th1 cytokines (TNF-α, IFN-γ) upregulate fgl2 mRNA in fetal trophoblast and secondary decidua, leading to fibrin deposition and abortion. OX-2 glycoprotein is co-expressed at the same sites and is reduced by Th1 cytokines; anti-OX-2 raises the abortion rate while recombinant OX-2 reduces it, indicating OX-2 can counteract fgl2-mediated coagulation/abortion.\",\n      \"method\": \"In situ hybridization for fgl2 and OX-2, anti-OX-2 antibody treatment, recombinant OX-2 administration, fibrin staining in CBA/J mouse pregnancy models\",\n      \"journal\": \"Molecular human reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ISH with functional antibody and recombinant protein experiments, single laboratory\",\n      \"pmids\": [\"11160845\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Soluble FGL2 (sFGL2) secretion by CD4+ T cells is induced by TNF-α and IFN-γ via MAPK signaling, specifically through c-Jun N-terminal kinase (JNK) phosphorylation; JNK inhibition significantly reduces sFGL2 secretion. Neither p38 MAPK nor ERK1/2 show significant changes.\",\n      \"method\": \"In vitro stimulation of human CD4+ T cells with TNF-α or IFN-γ, JNK inhibitor treatment, ELISA for sFGL2, Western blot for MAPK phosphorylation\",\n      \"journal\": \"The Journal of surgical research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — pharmacological inhibition with functional readout, single laboratory\",\n      \"pmids\": [\"23664593\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"C5a/C5aR pathway promotes FGL2 expression in liver sinusoidal endothelial cells and macrophages through ERK1/2 and p38 MAPK signaling during viral fulminant hepatitis. C5aR-/- mice show reduced FGL2 expression and coagulation. In vitro C5a stimulates TNF-α production in CD11b+ cells, which then promotes FGL2 expression in endothelial cells.\",\n      \"method\": \"C5aR-/-, Fgl2-/-, Tnfα-/- mice, in vitro C5a stimulation, ERK1/2 and p38 inhibitors, sorted liver cell populations\",\n      \"journal\": \"Journal of hepatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic knockout models plus in vitro mechanistic validation\",\n      \"pmids\": [\"25200905\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"FGL2 directly interacts with mucolipin 3 (MCOLN3) in neutrophils, which regulates calcium influx and initiates autophagy, leading to neutrophil extracellular trap (NET) formation. Neutrophil-specific FGL2 promotes NETs, which exacerbate liver injury in fulminant viral hepatitis via fibrin deposition and inflammation.\",\n      \"method\": \"Single-cell RNA sequencing, adoptive transfer of FGL2-expressing neutrophils, DNase 1 NET depletion, interaction studies between FGL2 and MCOLN3\",\n      \"journal\": \"Cellular and molecular gastroenterology and hepatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — adoptive transfer plus mechanistic interaction studies, single laboratory\",\n      \"pmids\": [\"35926777\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CD8+ T cell-derived FGL2 mediates cell-autonomous immunosuppression by binding to FcγRIIB expressed on the same CD8+ T cells, triggering caspase 3/7-mediated apoptosis. Conditional deletion of Fgl2 specifically in CD8+ T cells prolongs their persistence, reduces T cell exhaustion phenotype, and improves antitumor control. FcγRIIB-deficient CD8+ T cells are insensitive to Fgl2 regulation.\",\n      \"method\": \"Conditional Fgl2 knockout in antigen-specific CD8+ T cells, transcriptomic analysis, caspase 3/7 apoptosis assay, tumor models, chronic LCMV infection\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional genetic knockout with mechanistic apoptosis assays and receptor-deficient controls\",\n      \"pmids\": [\"38902261\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Macrophage-secreted FGL2 dampens CD8+ T cell responses by binding FcγRIIB on CD8+ T cells and inducing their apoptosis in a cell-autonomous (non-APC-intermediary) manner. FcγRIIB-/- CD8+ T cells are insensitive to Fgl2 regulation. Macrophages are identified as the major tumor-microenvironment source of Fgl2 in melanoma and multiple cancer types.\",\n      \"method\": \"Fgl2-/- mice, Fcgr2b conditional knockout in CD8+ T cells, melanoma tumor models, scRNA-seq of human tumors\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cell-type-specific knockouts with mechanistic apoptosis and functional readouts, replicated across tumor models\",\n      \"pmids\": [\"40125553\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"FGL2 prothrombinase in pulmonary vascular endothelium contributes to in situ thrombosis and vascular remodeling in pulmonary hypertension (PH). FGL2 knockout attenuates PH development, reduces PAR1 (proteinase-activated receptor 1) expression, and decreases platelet overactivation in hypoxia-induced PH models.\",\n      \"method\": \"Fgl2-/- mice in monocrotaline-rat and hypoxia-mouse PH models, PAR1 expression analysis, platelet activation assays, immunohistochemistry\",\n      \"journal\": \"Journal of applied physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout with multiple disease models and pathway analysis, single laboratory\",\n      \"pmids\": [\"31580221\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"FGL2 regulates IKK/NF-κB signaling in intestinal epithelial cells and lamina propria dendritic cells. FGL2-/- mice show stronger NF-κB activation and more severe DSS-induced colitis. Recombinant FGL2 inhibits proinflammatory cytokine production and NF-κB signaling in HT-29 cells and rescues the FGL2-/- colitis phenotype.\",\n      \"method\": \"FGL2-/- mice in DSS colitis model, recombinant FGL2 rescue, NF-κB signaling analysis in IECs and LPDCs, flow cytometry of DC maturation markers\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout plus recombinant protein rescue with pathway analysis, single laboratory\",\n      \"pmids\": [\"31743856\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"FGL2 expressed by T follicular helper (TFH) cells represses IgE responses. Conditional deletion of Fgl2 in TFH (and TFR) cells, but not TFR cells alone, increases antigen-specific IgE levels and IgE-mediated anaphylaxis in a food-allergy model. Fgl2 and CD39 are downregulated in TFH cells under optimal IgE sensitization conditions.\",\n      \"method\": \"Conditional Fgl2 deletion in TFH/TFR cells, food-allergy model with timed Ag sensitizations, flow cytometry of IgE+ GC B cells, anaphylaxis assay\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — conditional knockout with clear mechanistic cell-type assignment, single laboratory\",\n      \"pmids\": [\"35767958\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"A human homozygous truncating mutation in FGL2 (c.614_617del:p.V205fs) retains the N-terminal domain but lacks the C-terminal immunoregulatory domain. The truncated protein fails to suppress T cell proliferation. Full-length recombinant FGL2 rescues the impaired Treg suppressive function, establishing the C-terminal domain as essential for FGL2's immunosuppressive activity.\",\n      \"method\": \"Whole-exome sequencing, HEK293 transfection/immunoblotting, flow cytometry of Treg function, in vitro Treg suppression assay with full-length vs truncated FGL2\",\n      \"journal\": \"The Journal of allergy and clinical immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — human loss-of-function mutation with protein structure-function validation and functional rescue\",\n      \"pmids\": [\"36243222\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"In the hamster epididymis, FGL2 (HEP64) is secreted by principal cells of the proximal cauda epididymidis and specifically coats nonviable spermatozoa as part of a 'death cocoon' complex composed of FGL2 monomers (64 kDa) assembled into disulfide-linked oligomers of 260 and 280 kDa. FGL2 does not bind to viable spermatozoa.\",\n      \"method\": \"Expression screening of cDNA library, Northern blot, in situ hybridization, immunohistochemistry, immunoelectron microscopy, SDS-PAGE, microsequencing of isolated death cocoon fraction\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods identifying a novel biological role, single laboratory\",\n      \"pmids\": [\"15377663\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"FGL2 interacts with Tyrobp (DAP12) in cutaneous squamous cell carcinoma cells, as shown by co-immunoprecipitation and immunofluorescence colocalization. This interaction promotes ERK-dependent autophagy, resulting in increased CSCC cell proliferation. Knockdown of FGL2 reduces ERK phosphorylation, autophagy, and proliferation.\",\n      \"method\": \"Co-immunoprecipitation, immunofluorescence, FGL2 knockdown/overexpression, autophagy assays, ERK signaling analysis, in vitro and xenograft models\",\n      \"journal\": \"International journal of medical sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — Co-IP with functional validation, single laboratory\",\n      \"pmids\": [\"34975313\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"FGL2 deficiency alleviates maternal inflammation-induced blood-brain barrier (BBB) disruption by inhibiting PI3K/NF-κB-mediated oxidative stress in brain microvascular endothelial cells. PI3K overexpression in FGL2-deleted BMECs re-induces NOX2, iNOS, and NF-κB activation, placing FGL2 upstream of PI3K in this pathway.\",\n      \"method\": \"FGL2-/- mice with LPS-induced maternal inflammation, PI3K inhibitor (LY294002), PI3K lentivirus overexpression in FGL2-deleted BMECs, ROS/NO measurement, tight junction protein expression\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout plus epistasis established via PI3K rescue experiments\",\n      \"pmids\": [\"37051251\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Snf2l (ISWI ATPase chromatin remodeling protein) 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 also directly interacts with the nuclear receptor co-activator flightless I (FLI-I) by immunoprecipitation.\",\n      \"method\": \"Snf2l exon 6 deletion mouse, hCG stimulation, immunoprecipitation of SNF2L-FLI-I, SNF2L overexpression in granulosa cells\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — genetic model plus co-IP and overexpression, single laboratory\",\n      \"pmids\": [\"23616592\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"FGL2 in hepatocellular carcinoma cells regulates PD-L1 expression by activating mTORC1 signaling, which phosphorylates and retains TFEB in the cytoplasm, thereby inhibiting lysosome biosynthesis and PD-L1 lysosomal degradation. FGL2 knockout in hepatoma cells reduces PD-L1 expression and synergizes with anti-PD1 therapy.\",\n      \"method\": \"FGL2 knockout in Hepa1-6 cells, mTORC1 signaling analysis, TFEB phosphorylation/nuclear translocation assays, tumor models in Fgl2-/- mice, anti-PD1 combination\",\n      \"journal\": \"Cell communication and signaling : CCS\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout with mechanistic pathway dissection, single laboratory\",\n      \"pmids\": [\"41629991\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FGL2 KO in tumor cells impairs CD47 expression through Src and PKCα pathways. Loss of FGL2 in tumor cells induces long-duration brain-resident memory T (TRM) cells that prevent brain tumor recurrence. Reconstitution of CD47 in FGL2-KO tumor cells reverses the anti-tumor protection.\",\n      \"method\": \"CRISPR/Cas9 FGL2 knockout, proteomic analysis of Src/PKCα pathway, CD47 reconstitution, brain immune cell transplant, TRM cell depletion, murine intracranial tumor challenge models\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — epistasis established via CD47 reconstitution plus multiple mechanistic approaches, single laboratory\",\n      \"pmids\": [\"41380903\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"FGL2 deficiency leads to increased LCMV WE viral titers early post-infection but enhanced DC maturation (CD80, MHC II), increased virus-specific CD8+ and CD4+ T cell IFN-γ production, and higher anti-LCMV antibody titers, demonstrating that FGL2 suppresses adaptive anti-viral immunity by binding to FcγRIIB on APCs.\",\n      \"method\": \"fgl2-/- mice infected with LCMV WE, DC maturation marker flow cytometry, tetramer staining, IFN-γ ELISpot, neutralizing antibody titers\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout with multiple functional immunological readouts, single laboratory\",\n      \"pmids\": [\"24146739\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FGL2/fibroleukin is a multifunctional protein existing in two forms: a membrane-associated type II transmembrane serine protease (mFGL2) that directly cleaves prothrombin to thrombin via a Ser89 catalytic site in a phospholipid-, calcium-, and factor Va-dependent manner (bypassing classical coagulation cascades), and a secreted form (sFGL2) that functions as an immunosuppressive effector of regulatory T cells by binding to FcγRIIB and FcγRIII receptors on antigen-presenting cells and CD8+ T cells, inducing apoptosis and inhibiting DC maturation, T cell proliferation, and adaptive immunity; transcription of the FGL2 gene is induced by viral nucleocapsid protein (via HNF4α), IFN-γ (via STAT1/Sp1/PU.1), and TNF-α (via NF-κB/p38 MAPK) in a cell-type-specific manner, while its oligomeric structure (tetramers linked by Cys94/97/184/187) and C-terminal globular domain are essential for immunosuppressive function.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"FGL2/fibroleukin is a dual-function protein operating at the intersection of coagulation and immune regulation. As a membrane-associated type II transmembrane protein, FGL2 acts as a serine prothrombinase that directly cleaves prothrombin to thrombin via a catalytic Ser89 residue in a phospholipid-, calcium-, and factor Va-dependent manner, driving fibrin deposition in viral hepatitis, xenograft rejection, and vascular thrombosis [PMID:11994472, PMID:12840059, PMID:15100314]. As a secreted oligomeric effector produced by regulatory T cells and other immune cells, FGL2 binds FcγRIIB and FcγRIII on antigen-presenting cells and CD8+ T cells, inducing apoptosis via caspase 3/7, inhibiting dendritic cell maturation and T cell proliferation, and suppressing adaptive immunity in infection, transplantation, and tumor microenvironments [PMID:18991288, PMID:18097026, PMID:38902261, PMID:30683885]. Transcription of FGL2 is induced by viral nucleocapsid protein through HNF4α, by IFN-γ through STAT1/Sp1/PU.1, and by TNF-α through NF-κB and p38 MAPK pathways in a cell-type-specific manner, while its immunosuppressive function requires the C-terminal fibrinogen-related globular domain and is modulated by disulfide-linked tetramerization [PMID:10187767, PMID:12594208, PMID:16709865, PMID:23127799, PMID:36243222].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Identification of FGL2 as a novel cell-surface prothrombinase on reticuloendothelial cells resolved the long-standing question of how MHV-3 infection triggers fibrin deposition and hepatic necrosis independent of classical coagulation cascades.\",\n      \"evidence\": \"Northern blot, in situ hybridization, and immunohistochemistry in MHV-3-infected mouse livers\",\n      \"pmids\": [\"9371581\", \"9782336\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Catalytic mechanism and active-site residues not yet identified\", \"No purified protein reconstitution to confirm direct prothrombinase activity\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Demonstration that the MHV-3 nucleocapsid protein induces fgl2 transcription via a specific promoter element (-372 to -306) established the first transcriptional mechanism linking viral pathogenicity to FGL2-mediated coagulation, subsequently refined to show HNF4α binding at a -331/-325 cis-element.\",\n      \"evidence\": \"Promoter-reporter assays with deletion mapping in CHO cells (1999); EMSA and site-directed mutagenesis of N protein domains (2003)\",\n      \"pmids\": [\"10187767\", \"12594208\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How nucleocapsid protein activates HNF4α remains unclear\", \"Relevance to human hepatitis viruses not established\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Cloning of human FGL2 and identification of its domain architecture (type II transmembrane protein with C-terminal fibrinogen-related domain) provided the structural framework for understanding both prothrombinase and later-discovered immunoregulatory functions.\",\n      \"evidence\": \"Cloning, heterologous expression, functional prothrombinase assay, FISH mapping to 7q11.23\",\n      \"pmids\": [\"11170750\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal structure available\", \"Function of the C-terminal fibrinogen-related domain beyond prothrombinase not yet explored\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Biochemical reconstitution of purified FGL2 into phospholipid vesicles proved it is a bona fide serine protease that cleaves prothrombin directly, with Ser89 as the catalytic residue and requirements for phosphatidylserine, calcium, and factor Va — establishing FGL2 as a non-classical prothrombinase.\",\n      \"evidence\": \"In vitro reconstitution of baculovirus-expressed FGL2 with kinetic analysis and Ser89 mutagenesis\",\n      \"pmids\": [\"11994472\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for resistance to classical serine protease inhibitors unexplained\", \"Whether FGL2 has substrates beyond prothrombin is unknown\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"The fgl2 knockout mouse demonstrated that FGL2 is essential for macrophage procoagulant activity and fibrin-mediated liver necrosis during MHV-3 infection, providing definitive genetic proof of its in vivo prothrombinase function and establishing its non-redundancy with classical coagulation factors.\",\n      \"evidence\": \"Gene-targeted fgl2−/− mouse with peritoneal macrophage procoagulant assay, histopathology, and survival analysis\",\n      \"pmids\": [\"12840059\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether sFGL2 immunosuppressive function also contributes to the infection phenotype was not dissected\", \"Compensatory mechanisms in fgl2−/− mice not characterized\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Mapping of constitutive and cytokine-induced fgl2 transcription revealed cell-type-specific promoter architecture: Sp1/Sp3 and Oct-1/Ets-1 drive basal expression in endothelial cells, while IFN-γ signals through STAT1/Sp1/PU.1 in macrophages and p38 MAPK mediates virus-induced expression.\",\n      \"evidence\": \"EMSA, heterologous Drosophila Schneider cell expression, promoter deletion analysis (2003); p38 and ERK inhibitor studies in macrophages (1998); IFN-γ/STAT1/PU.1 pathway in knockout mice (2006)\",\n      \"pmids\": [\"12752447\", \"9822700\", \"16709865\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Chromatin-level regulation of the FGL2 locus not characterized\", \"Integration of multiple simultaneous cytokine signals not modeled\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"FGL2 was established as the endothelial prothrombinase mediating acute vascular rejection thrombosis in xenotransplantation — fgl2−/− donor hearts were devoid of intravascular thrombosis — and was also shown to be required for LPS-induced pregnancy loss and normal early embryonic vascular development.\",\n      \"evidence\": \"Porcine FGL2 prothrombinase assay and fgl2−/− heterotopic heart xenograft model (2004); fgl2−/− timed matings and LPS abortion model (2004)\",\n      \"pmids\": [\"15100314\", \"14742694\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether sFGL2 immunoregulatory function contributes to graft rejection alongside prothrombinase activity\", \"Mechanism of selective embryonic hemorrhage in fgl2−/− mice unclear\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Discovery that FGL2 binds FcγRIIB and FcγRIII on APCs and induces B cell apoptosis, and that Treg-derived FGL2 is a critical effector of Treg suppressive activity, revealed a second, immunoregulatory function entirely distinct from the prothrombinase activity — transforming FGL2 from a coagulation factor into a dual-function immune-coagulation mediator.\",\n      \"evidence\": \"SPR binding assays, FcγRIIB−/− cell lines and mice, skin allograft model (2008); fgl2−/− Treg suppression assays, anti-FGL2 antibody blockade, bone marrow reconstitution (2008)\",\n      \"pmids\": [\"18991288\", \"18097026\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise binding epitope on FcγRIIB not mapped\", \"Whether FGL2 signals through FcγRIII with distinct downstream consequences unknown\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Extension of FGL2–FcγRIIB signaling to hepatic ischemia-reperfusion injury and to experimental arthritis broadened the pathophysiological scope, showing FGL2 induces sinusoidal endothelial cell apoptosis via FcγRIIB and that membrane FGL2 prothrombinase is required for fibrin-driven joint inflammation.\",\n      \"evidence\": \"Dual fgl2−/− and FcγRIIB−/− mouse I/R models with caspase-3/TUNEL readouts (2011); fgl2−/− anti-CII arthritis model (2011)\",\n      \"pmids\": [\"21756857\", \"21469939\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether apoptotic and prothrombinase functions operate simultaneously in the same tissue\", \"Role of sFGL2 vs mFGL2 in arthritis not dissected\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Structural characterization revealed that secreted FGL2 is a disulfide-linked tetramer (Cys94/97/184/187), with the C-terminal globular domain containing the immunosuppressive motifs; unexpectedly, monomeric FGL2 showed greater immunosuppressive potency than the oligomer, indicating oligomerization modulates rather than enables function.\",\n      \"evidence\": \"Cysteine-to-alanine mutagenesis, non-reducing SDS-PAGE, peptide blockade, deglycosylation\",\n      \"pmids\": [\"23127799\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"High-resolution structure not available\", \"Physiological regulation of oligomeric state unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"FGL2 was identified as a tumor immune-evasion molecule: glioblastoma stem cell-derived FGL2 suppresses GM-CSF-induced CD103+ DC differentiation by inhibiting NF-κB, STAT1/5, and p38 signaling, and FGL2 prothrombinase in pulmonary endothelium drives in situ thrombosis in pulmonary hypertension.\",\n      \"evidence\": \"FGL2-KO glioma cells in immunocompetent vs immunodeficient mice (2019); fgl2−/− mice in hypoxia-induced PH models (2019)\",\n      \"pmids\": [\"30683885\", \"31580221\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether FGL2 suppresses DCs through FcγRIIB or an independent receptor in the brain microenvironment\", \"Therapeutic window for anti-FGL2 in tumors not defined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"A human homozygous truncating FGL2 mutation (p.V205fs) lacking the C-terminal domain failed to suppress T cell proliferation and was rescued by full-length recombinant FGL2, providing the first human genetic validation that the fibrinogen-related domain is essential for immunosuppressive function.\",\n      \"evidence\": \"Whole-exome sequencing, HEK293 expression of truncated vs full-length protein, Treg suppression assay with rescue\",\n      \"pmids\": [\"36243222\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Clinical phenotype associated with this mutation not fully delineated in the timeline\", \"Whether prothrombinase activity is also affected by this truncation not tested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"FGL2 was shown to regulate IgE class-switching: TFH cell-derived FGL2 represses antigen-specific IgE responses, and FGL2 in neutrophils interacts with mucolipin 3 (MCOLN3) to regulate calcium-dependent autophagy and NET formation, revealing additional cell-type-specific functions.\",\n      \"evidence\": \"Conditional Fgl2 deletion in TFH/TFR cells with food-allergy model (2022); scRNA-seq and FGL2-MCOLN3 interaction studies in neutrophils (2022)\",\n      \"pmids\": [\"35767958\", \"35926777\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"FGL2–MCOLN3 interaction not confirmed by reciprocal IP or structural studies\", \"Whether FGL2 regulates IgE through FcγRIIB on B cells or another mechanism not resolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Conditional deletion of Fgl2 in CD8+ T cells demonstrated cell-autonomous immunosuppression: CD8+ T cell-derived FGL2 binds FcγRIIB on the same cells to trigger caspase 3/7-mediated apoptosis and T cell exhaustion, and macrophage-secreted FGL2 acts on CD8+ T cells via the same receptor, establishing a paracrine and autocrine FGL2–FcγRIIB axis that limits antitumor and antiviral CD8+ T cell responses.\",\n      \"evidence\": \"Conditional Fgl2 KO in CD8+ T cells, FcγRIIB conditional KO, caspase assays, chronic LCMV and tumor models (2024); Fgl2−/− mice plus Fcgr2b conditional KO in CD8+ T cells across melanoma models (2025)\",\n      \"pmids\": [\"38902261\", \"40125553\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signaling intermediates downstream of FcγRIIB in CD8+ T cells not fully mapped\", \"Whether autocrine vs paracrine FGL2 has differential potency in vivo remains unclear\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"FGL2 was linked to regulation of immune checkpoint molecules: tumor cell FGL2 sustains PD-L1 expression via mTORC1-mediated TFEB phosphorylation that blocks lysosomal PD-L1 degradation, and FGL2 promotes CD47 expression through Src/PKCα, identifying FGL2 as an upstream regulator of multiple immune checkpoint pathways.\",\n      \"evidence\": \"FGL2-KO hepatoma cells with mTORC1/TFEB pathway analysis (2026 pub); CRISPR FGL2 KO with Src/PKCα proteomics and CD47 reconstitution in brain tumor models (2025)\",\n      \"pmids\": [\"41629991\", \"41380903\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct physical interaction between FGL2 and mTORC1 or Src not demonstrated\", \"Whether these checkpoint regulatory mechanisms operate through the same FcγRIIB axis or independently is unknown\", \"Single-laboratory findings await independent replication\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: the structural basis for FGL2's dual prothrombinase and immunosuppressive activities; how the switch between membrane-bound and secreted forms is regulated; the precise signaling cascade downstream of FcγRIIB engagement by FGL2; and whether anti-FGL2 therapeutic strategies can selectively target immunosuppressive versus coagulant functions.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal or cryo-EM structure of FGL2\", \"Mechanism of membrane-to-secreted form switching unknown\", \"Full downstream signaling pathway from FcγRIIB upon FGL2 engagement not mapped\", \"No clinical trials targeting FGL2 reported in the timeline\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 2, 8, 12]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [9, 10, 15, 22, 23, 34]},\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [9, 10, 13, 22, 23]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 2, 12, 24]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [10, 11, 23, 28]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-109582\", \"supporting_discovery_ids\": [0, 1, 2, 8, 12, 24]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [9, 10, 15, 22, 23, 34]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [9, 13, 22, 23]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [6, 7, 20, 25]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"FCGR2B\",\n      \"FCGR3\",\n      \"MCOLN3\",\n      \"TYROBP\",\n      \"HNF4A\",\n      \"STAT1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}