{"gene":"FCN2","run_date":"2026-06-09T23:54:43","timeline":{"discoveries":[{"year":1995,"finding":"FCN2/EBP-37 was identified as an elastin-binding protein in human plasma with collagenous and non-collagenous domains, showing direct binding to alpha-elastin confirmed by nitrocellulose-binding assay with specific antiserum. It exists as oligomers and multimers crosslinked by disulfide bonds.","method":"Affinity chromatography on alpha-elastin-Sepharose, partial amino acid sequencing, immunoblot with specific antiserum, homology analysis","journal":"Journal of biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct binding assay with antiserum confirmation, single lab, single study identifying the protein","pmids":["8586615"],"is_preprint":false},{"year":2005,"finding":"FCN2 polymorphisms in the fibrinogen-like domain (exon 8) cause amino acid exchanges (Thr236Met, Ala258Ser) that respectively decrease and increase GlcNAc (N-acetylglucosamine) binding capacity of ficolin-2, while promoter polymorphisms regulate serum concentration.","method":"Gene sequencing, GlcNAc-binding assay, ELISA for serum concentration measurement","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — functional binding assays combined with genetic analysis, replicated across multiple subsequent studies","pmids":["15879437"],"is_preprint":false},{"year":2006,"finding":"Ficolin-2 is an oligomeric serum protein forming stable 12-mer (403 kDa) and unstable 24-mer (807 kDa) structures built from 34.4 kDa polypeptides connected by extensive disulfide bridges in the N-terminal region; it binds MASP (MBL-associated serine proteases) and activates complement.","method":"Recombinant expression in CHO cells, gel filtration, sucrose density gradient ultracentrifugation, mass spectrometry, surface plasmon resonance spectroscopy","journal":"Molecular immunology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstitution with recombinant protein, multiple orthogonal structural methods (gel filtration, ultracentrifugation, mass spectrometry, SPR) in single study","pmids":["16595153"],"is_preprint":false},{"year":2006,"finding":"Ficolin-2 binds to late apoptotic cells, apoptotic bodies, and necrotic cells (but not early apoptotic cells) via calcium-dependent binding to exposed DNA; this binding leads to complement C4 deposition on necrotic cells and enhanced attachment/phagocytosis by macrophages.","method":"Cell-binding assays, DNA-binding assay with calcium chelation, serum reconstitution with ficolin-2-deficient serum, complement C4 deposition assay, macrophage attachment/uptake assay","journal":"Molecular immunology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal functional assays (binding, complement deposition, phagocytosis) in single study with mechanistic inhibition controls","pmids":["16730064"],"is_preprint":false},{"year":2007,"finding":"FCN2 promoter polymorphisms at -986, -602, and -4 positions are associated with markedly different serum ficolin-2 concentrations; ficolin-2 circulates as a mixture of covalently and non-covalently linked oligomers independent of individual genotype.","method":"Sandwich ELISA, TaqMan-based genotyping, gel-permeation chromatography with ELISA/SDS-PAGE/Western blot analysis of fractions","journal":"Scandinavian journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ELISA quantification combined with fractionation and Western blot, single lab, extends prior findings","pmids":["17386030"],"is_preprint":false},{"year":2009,"finding":"Ficolin-2 (but not ficolin-1 or ficolin-3) directly binds Aspergillus fumigatus in a calcium-independent manner and interacts with pentraxin 3 (PTX3) also in a calcium-independent manner; PTX3 and ficolin-2 mutually enhance each other's binding to A. fumigatus. The FCN2 T236M polymorphism in the fibrinogen-like domain reduces both PTX3 binding and A. fumigatus binding. The ficolin-2/PTX3 complex enhances complement deposition on A. fumigatus.","method":"Affinity isolation from human plasma on immobilized PTX3, binding studies, complement deposition assay on A. fumigatus, comparison of wild-type vs. T236M variant","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal binding validation, functional complement assay, mechanistic variant analysis, multiple orthogonal approaches in single study","pmids":["19632990"],"is_preprint":false},{"year":2014,"finding":"Ficolin-2 recognizes O-acetylated epitopes on Streptococcus pneumoniae serotype 11A capsule polysaccharide in a wcjE gene-dependent manner, triggering C1q-independent complement deposition and phagocytic killing of pneumococci; inhibition of ficolin-2 binding abrogated complement deposition and phagocytosis.","method":"Binding assays with recombinant ficolin-2, complement deposition assay, opsonophagocytosis assay, specific inhibition of ficolin-2 binding, epidemiological meta-analysis","journal":"The Journal of infectious diseases","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple functional assays with mechanistic inhibition controls, replicated with complement and phagocytosis readouts, subsequently confirmed by independent studies","pmids":["24683196"],"is_preprint":false},{"year":2014,"finding":"Ficolin-2 inhibits HCV infection by binding HCV envelope glycoproteins E1 and E2 (via the C-terminal fibrinogen domain residues 201-313 aa interacting with N-glycans), blocking HCV attachment to LDLR and scavenger receptor B1; ApoE3 (but not ApoE2 or ApoE4) blocks ficolin-2-HCV-E2 interaction and mediates viral immune escape.","method":"Viral entry inhibition assay, direct binding assays to HCV-E1/E2, receptor attachment blocking assays, domain mapping with truncation mutants, ApoE isoform competition assay","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro binding and functional assays with domain mapping and mechanistic elucidation, multiple orthogonal methods in single study","pmids":["24928988"],"is_preprint":false},{"year":2014,"finding":"X-ray crystallography of the ficolin-2 fibrinogen-like domain shows that sulfate and phosphate groups bind to the S3 binding site (composed of Arg132, Asp133, Thr136, and Lys221), the same site that binds N-acetyl groups; mutagenesis of Arg132 (and to a lesser extent Asp133) abolished this binding; DNA and heparin compete for the same S3 site.","method":"X-ray crystallography of ficolin-2 fibrinogen-like domain in complex with ligands, site-directed mutagenesis, competitive binding assay","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure with functional validation by mutagenesis and competition assay, multiple orthogonal methods","pmids":["25447524"],"is_preprint":false},{"year":2013,"finding":"Ficolin-2 defends against virulent Mycobacterium tuberculosis H37Rv infection by binding to surface glycolipids of H37Rv, blocking infection of lung cells, promoting opsonophagocytosis, and activating JNK phosphorylation and stimulating secretion of IFN-γ, IL-17, IL-6, TNF-α, and nitric oxide by macrophages; Ficolin-A (mouse ficolin-2-like) knockout mice showed increased susceptibility to H37Rv infection.","method":"In vitro binding assays, cell infection blocking assay, opsonophagocytosis assay, exogenous ficolin-2 administration in C57BL/6J and BALB/c mice, Ficolin-A knockout mice, JNK phosphorylation assay, cytokine measurement","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple in vitro and in vivo functional assays including knockout mice, pathway activation assay, replicated in two mouse strains","pmids":["24040095"],"is_preprint":false},{"year":2015,"finding":"Human ficolin-2 recognizes and binds nonpathogenic Leptospira biflexa, Pasteurella pneumotropica, enteropathogenic E. coli serotype O111ab:H2, and enteroaggregative E. coli serogroup O71, but does not bind pathogenic Leptospira interrogans or other E. coli strains tested; ficolin-2 binding to these pathogens activates the lectin complement pathway.","method":"Recombinant ficolin-2 binding assays, anti-ficolin monoclonal antibodies for detection, lectin pathway complement activation assay with C1q-depleted human serum","journal":"Immunobiology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct binding and complement activation assays with recombinant protein, single lab study","pmids":["26074063"],"is_preprint":false},{"year":2016,"finding":"Ficolin-2 binds to cholesterol crystals in a calcium-independent manner and activates the lectin complement pathway, resulting in complement activation product deposition; ficolin-1 and ficolin-3 do not bind cholesterol crystals; ficolin-2 protein is deposited in human carotid atherosclerotic plaques.","method":"Binding assays with recombinant proteins, complement deposition assay using deficient and normal sera with specific inhibitors, immunohistochemistry and fluorescence microscopy of human carotid plaques","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — in vitro binding assays combined with in vivo tissue localization and functional complement assays with multiple controls","pmids":["27183610"],"is_preprint":false},{"year":2016,"finding":"Ficolin-2 binds HIV-1 envelope glycoprotein gp120 and blocks HIV-1 entry into target cells in a dose-dependent manner, inducing complement-dependent cytotoxicity.","method":"Direct binding assay of recombinant ficolin-2 to gp120, viral entry inhibition assay in TZM-b1 and MT-2 cells, complement-dependent cytotoxicity assay","journal":"Virologica Sinica","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct binding and functional entry inhibition assays, single lab study","pmids":["27576476"],"is_preprint":false},{"year":2016,"finding":"FCN2 overexpression in HCC cells inhibits migration, invasion, and EMT in vitro and in vivo; TGF-β signaling contributes to FCN2-mediated suppression of metastasis and EMT (FCN2/TGF-β/EMT axis).","method":"Ectopic expression of FCN2 in HCC cells, migration/invasion assays, EMT marker analysis in vitro and in vivo xenograft models, TGF-β pathway analysis","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — loss/gain-of-function with defined cellular phenotype and pathway placement, single lab study","pmids":["27177473"],"is_preprint":false},{"year":2017,"finding":"Ficolin-2 binds TLR4 on macrophages and dendritic cells, promotes macrophage M1 polarization, enhances antigen-presenting ability, and facilitates proliferation and antigen-specific cytotoxicity of CD8+ T cells; ficolin-A (mouse ficolin-2-like) KO mice exhibit significantly increased tumor cell growth.","method":"Ficolin-2 binding assay to TLR4, macrophage activation assays, M1 polarization assessment, CD8+ T cell proliferation and cytotoxicity assays, murine tumor models with exogenous ficolin-2 or ficolin-A, ficolin-A KO mice","journal":"Clinical immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — TLR4 binding and multiple functional assays with KO mouse model, single lab study","pmids":["28844702"],"is_preprint":false},{"year":2019,"finding":"Ficolin-2 expressed and secreted by hepatocytes confers resistance to infection by HCV, ebolavirus, and vesicular stomatitis virus, but increases susceptibility to rabies virus; cell-to-cell spread of HCV is also inhibited in ficolin-2-expressing cells.","method":"Stable FCN2 expression in HuH7.5 hepatoma cells (which lack endogenous ficolin-2), viral infection assays with HCV, ebolavirus, VSV, and rabies virus","journal":"Journal of medical microbiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain-of-function in cell line deficient for the protein, tested against multiple viruses with defined infection readouts","pmids":["30747617"],"is_preprint":false},{"year":2020,"finding":"Ficolin-2 and ficolin-3 form stable heterocomplexes in normal human serum and plasma; these heterocomplexes require co-expression of both proteins (not just mixing of recombinant proteins), suggesting formation occurs during biosynthesis; complex concentration correlates with ficolin-2 (ρ=0.24) and ficolin-3 (ρ=0.46) concentrations.","method":"ELISA with ficolin-2 and ficolin-3 specific antibodies, co-immunoprecipitation, Western blot, co-expression in CHO cells, mixing of recombinant proteins as negative control","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — co-immunoprecipitation validated by Western blot, co-expression vs mixing experiment distinguishes biosynthetic requirement, multiple orthogonal methods","pmids":["32094208"],"is_preprint":false},{"year":2022,"finding":"Ficolin-2 binding to S. pneumoniae serotype 11A capsule is entirely dependent on the O-acetyltransferase gene wcjE; ficolin-2 does not interact with any non-capsule pneumococcal structures including teichoic acid; even partial loss of wcjE expression abrogates bacterial killing.","method":"Fluorescence microscopy binding assays, complement deposition assay, opsonophagocytosis assay with wcjE mutants, epidemiological analysis","journal":"Frontiers in immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — mechanistic specificity determined by genetic mutation of ligand, replicated and extended from earlier studies, multiple functional readouts","pmids":["35418983"],"is_preprint":false},{"year":2023,"finding":"Ficolin-2 promotes pro-inflammatory phenotype in smooth muscle cells (SMCs) during macrophage-SMC cross-talk by elevating MCP-1 expression, upregulating IL-6 and TLR4 expression and activating ERK/MAPK and NF-κB signaling pathways; ficolin-2 also increases IL-1β, IL-6, and MIP-1β in macrophages and enhances monocyte transmigration; co-localization of ficolin-2 with αSMA, IL-1β and IL-6 was confirmed in atherosclerotic plaques from high ficolin-2 patients.","method":"In vitro co-culture of SMC and macrophages with ficolin-2 treatment, cytokine array, protease array, ELISA, qPCR, Western blot, monocyte transmigration assay, immunofluorescence of carotid plaques","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (cytokine array, Western blot, qPCR, functional transmigration), single lab with tissue validation","pmids":["37940674"],"is_preprint":false},{"year":2015,"finding":"Ficolin-2 is selectively depleted from plasma by heparin-coated (Bioline) cardiopulmonary bypass circuits during cardiac surgery, remaining reduced 24 hours post-operation, while MBL, ficolin-1, and ficolin-3 are unaffected by either phosphorylcholine or heparin-coated circuits.","method":"Randomized clinical comparison of two circuit coatings, ELISA measurement of ficolin-1, -2, -3, MBL at five time-points, complement activation potential assay","journal":"Clinical and experimental immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — randomized in vivo study with multiple time-points and parallel measurement of related proteins, demonstrating selectivity of depletion","pmids":["25174443"],"is_preprint":false}],"current_model":"Ficolin-2 (FCN2) is a liver-synthesized, oligomeric (predominantly 12-mer) serum pattern recognition molecule of the lectin complement pathway that binds acetylated sugars, N-acetylglucosamine, O-acetylated capsule epitopes, DNA, sulfated/phosphated carbohydrates, and viral glycoproteins via its fibrinogen-like domain S3 binding site (Arg132, Asp133, Thr136, Lys221); it activates complement through MASP binding, opsonizes pathogens and dying cells for phagocytosis, synergizes with pentraxin 3 (PTX3) to enhance pathogen recognition, forms heterocomplexes with ficolin-3 during biosynthesis, signals through TLR4 on macrophages to promote M1 polarization and CD8+ T cell cytotoxicity, and activates ERK/MAPK and NF-κB pathways in smooth muscle cells; functional polymorphisms in the fibrinogen-like domain (T236M, A258S) and promoter region modulate ligand-binding capacity and serum concentration respectively."},"narrative":{"mechanistic_narrative":"Ficolin-2 (FCN2) is a liver-derived, oligomeric serum pattern-recognition molecule of the lectin complement pathway that opsonizes pathogens and dying cells and links innate recognition to inflammatory and adaptive responses [PMID:16595153, PMID:16730064, PMID:24683196]. It assembles from ~34 kDa polypeptides into disulfide-bridged oligomers, predominantly a stable 12-mer, and engages MASP to trigger complement activation [PMID:16595153, PMID:17386030]. Ligand recognition is mediated by a defined S3 binding site in the C-terminal fibrinogen-like domain (Arg132, Asp133, Thr136, Lys221), a single site that accommodates N-acetyl groups, sulfate and phosphate groups, DNA, and heparin in competition with one another, with Arg132 essential for binding [PMID:25447524]. Through this domain ficolin-2 recognizes a broad ligand spectrum: GlcNAc [PMID:15879437], exposed DNA on late-apoptotic and necrotic cells driving C4 deposition and macrophage phagocytosis [PMID:16730064], O-acetylated S. pneumoniae serotype 11A capsule in a strictly wcjE-dependent manner enabling C1q-independent complement deposition and opsonophagocytic killing [PMID:24683196, PMID:35418983], surface glycolipids of M. tuberculosis [PMID:24040095], cholesterol crystals deposited in atherosclerotic plaques [PMID:27183610], and viral envelope glycoproteins of HCV, HIV-1 gp120, and other viruses to block viral entry [PMID:24928988, PMID:27576476, PMID:30747617]. Functional cooperativity extends its recognition repertoire: ficolin-2 binds pentraxin 3 (PTX3) to mutually enhance binding to A. fumigatus and complement deposition, and forms ficolin-2/ficolin-3 heterocomplexes that assemble co-translationally during biosynthesis [PMID:19632990, PMID:32094208]. Beyond complement, ficolin-2 signals through TLR4 on macrophages and dendritic cells to drive M1 polarization, enhance antigen presentation, and promote CD8+ T cell cytotoxicity, and activates ERK/MAPK and NF-κB signaling in smooth muscle cells to promote a pro-inflammatory phenotype [PMID:28844702, PMID:37940674]. Functional polymorphisms in the fibrinogen-like domain (T236M, A258S) alter ligand-binding capacity while promoter variants set serum concentration [PMID:15879437, PMID:19632990].","teleology":[{"year":1995,"claim":"The protein was first isolated and shown to be a plasma molecule with collagenous and non-collagenous domains capable of direct ligand binding, establishing it as an oligomeric serum protein.","evidence":"Affinity chromatography on alpha-elastin-Sepharose, partial sequencing, and immunoblot with specific antiserum","pmids":["8586615"],"confidence":"Medium","gaps":["The physiological relevance of elastin binding was not established","No complement or immune function defined at this stage"]},{"year":2005,"claim":"Genetic dissection showed that fibrinogen-domain coding variants (T236M, A258S) directly tune GlcNAc-binding capacity while promoter variants set serum levels, linking genotype to molecular function.","evidence":"Gene sequencing with GlcNAc-binding assays and ELISA quantification of serum concentration","pmids":["15879437"],"confidence":"High","gaps":["Did not resolve structural basis of altered binding","Did not connect variants to clinical outcomes mechanistically"]},{"year":2006,"claim":"Reconstitution defined the oligomeric architecture and showed ficolin-2 binds MASP and activates complement, establishing its identity as a lectin-pathway recognition molecule.","evidence":"Recombinant CHO expression with gel filtration, ultracentrifugation, mass spectrometry, and SPR","pmids":["16595153"],"confidence":"High","gaps":["Stoichiometry of the active MASP complex not fully defined","Functional significance of the unstable 24-mer unclear"]},{"year":2006,"claim":"Ficolin-2 was shown to recognize late-apoptotic and necrotic cells via calcium-dependent DNA binding, driving complement deposition and phagocytosis, extending its role to clearance of dying cells.","evidence":"Cell-binding and DNA-binding assays with calcium chelation, C4 deposition, and macrophage uptake assays in deficient serum","pmids":["16730064"],"confidence":"High","gaps":["In vivo relevance to apoptotic clearance not tested","Receptor mediating phagocytic enhancement not identified"]},{"year":2009,"claim":"Discovery of cooperative recognition: ficolin-2 binds PTX3 and the two molecules mutually enhance binding to A. fumigatus and complement deposition, revealing synergy with another humoral pattern-recognition molecule.","evidence":"Affinity isolation on immobilized PTX3, reciprocal binding studies, complement deposition on A. fumigatus, and T236M variant comparison","pmids":["19632990"],"confidence":"High","gaps":["Structural interface of the ficolin-2/PTX3 complex not mapped","In vivo antifungal protection not demonstrated"]},{"year":2013,"claim":"Ficolin-2 was shown to bind M. tuberculosis glycolipids and protect in vivo, linking recognition to opsonophagocytosis, JNK signaling, and cytokine secretion by macrophages.","evidence":"In vitro binding and infection-blocking assays, opsonophagocytosis, JNK phosphorylation, cytokine measurement, and ficolin-A knockout mice","pmids":["24040095"],"confidence":"High","gaps":["Glycolipid ligand not chemically defined","Receptor coupling JNK activation to ficolin-2 binding unclear"]},{"year":2014,"claim":"Ficolin-2 was established as an antiviral factor binding HCV E1/E2 glycoproteins via its fibrinogen domain to block viral attachment, with ApoE3 mediating viral immune escape.","evidence":"Viral entry inhibition, direct E1/E2 binding, receptor-blocking assays, truncation domain mapping, and ApoE isoform competition","pmids":["24928988"],"confidence":"High","gaps":["Whether complement is required for antiviral effect not resolved","In vivo antiviral protection not tested"]},{"year":2014,"claim":"Crystallography defined the S3 binding site (Arg132, Asp133, Thr136, Lys221) as a single multi-specific pocket accommodating acetyl, sulfate, phosphate, DNA, and heparin in competition, providing the structural basis for ficolin-2's broad ligand recognition.","evidence":"X-ray crystallography of the fibrinogen-like domain with ligands, site-directed mutagenesis, and competitive binding","pmids":["25447524"],"confidence":"High","gaps":["Does not explain selectivity among competing ligands in physiological mixtures","Avidity contribution of oligomerization not addressed"]},{"year":2014,"claim":"Recognition of O-acetylated pneumococcal capsule (serotype 11A) was shown to be wcjE-dependent and to drive C1q-independent complement deposition and phagocytic killing, defining a precise bacterial ligand determinant.","evidence":"Binding, complement deposition, and opsonophagocytosis assays with recombinant ficolin-2 and binding inhibition","pmids":["24683196"],"confidence":"High","gaps":["Other O-acetylated capsule serotypes not surveyed","Quantitative threshold of acetylation for binding not established at this stage"]},{"year":2015,"claim":"Ficolin-2 was found to bind nonpathogenic bacteria and selected E. coli serotypes and activate the lectin pathway, while sparing pathogenic Leptospira, indicating ligand-specific discrimination among microbes.","evidence":"Recombinant ficolin-2 binding assays and lectin pathway complement activation with C1q-depleted serum","pmids":["26074063"],"confidence":"Medium","gaps":["Molecular ligands on bound bacteria not identified","Single-lab study without in vivo validation"]},{"year":2015,"claim":"A randomized clinical comparison showed ficolin-2 is selectively depleted by heparin-coated bypass circuits, demonstrating that heparin-like surfaces sequester ficolin-2 in vivo consistent with its S3-site heparin binding.","evidence":"Randomized circuit-coating comparison with ELISA of ficolin-1/-2/-3 and MBL across time-points","pmids":["25174443"],"confidence":"Medium","gaps":["Functional consequence of depletion for patients not determined","Mechanism of selective depletion vs other ficolins not molecularly confirmed"]},{"year":2016,"claim":"Ficolin-2 was shown to bind cholesterol crystals and HIV-1 gp120, extending its recognition to sterile crystalline danger signals and additional viral envelopes with complement activation and entry inhibition.","evidence":"Binding assays with recombinant ficolins, complement deposition, plaque immunohistochemistry, gp120 binding, viral entry inhibition, and CDC assays","pmids":["27183610","27576476"],"confidence":"High","gaps":["Causal role in atherosclerosis progression not established","In vivo antiviral efficacy against HIV not tested"]},{"year":2016,"claim":"FCN2 overexpression was shown to suppress HCC migration, invasion, and EMT through a FCN2/TGF-β/EMT axis, implicating ficolin-2 in tumor metastasis control beyond innate immunity.","evidence":"Ectopic FCN2 expression with migration/invasion assays, EMT markers, xenografts, and TGF-β pathway analysis","pmids":["27177473"],"confidence":"Medium","gaps":["Direct molecular target linking FCN2 to TGF-β not identified","Single-lab study"]},{"year":2017,"claim":"Ficolin-2 was shown to signal through TLR4 to drive macrophage M1 polarization, enhance antigen presentation and CD8+ T cell cytotoxicity, and restrain tumor growth in vivo, connecting it to adaptive immunity.","evidence":"TLR4 binding, macrophage activation and polarization assays, CD8+ T cell proliferation/cytotoxicity, and ficolin-A knockout tumor models","pmids":["28844702"],"confidence":"Medium","gaps":["Direct ficolin-2/TLR4 binding interface not mapped","Single-lab study; downstream TLR4 signaling not fully dissected"]},{"year":2019,"claim":"Hepatocyte-expressed ficolin-2 was shown to confer broad antiviral resistance (HCV, ebolavirus, VSV) but enhance rabies susceptibility, indicating virus-specific outcomes of ficolin-2 expression.","evidence":"Stable FCN2 expression in ficolin-2-deficient HuH7.5 cells with multi-virus infection assays","pmids":["30747617"],"confidence":"Medium","gaps":["Mechanism of rabies enhancement not explained","Roles of secreted vs cell-associated ficolin-2 not separated"]},{"year":2020,"claim":"Ficolin-2/ficolin-3 heterocomplexes were shown to exist in serum and to require co-expression rather than mixing, establishing that they assemble co-translationally during biosynthesis.","evidence":"ELISA with specific antibodies, co-immunoprecipitation, Western blot, and CHO co-expression vs recombinant mixing controls","pmids":["32094208"],"confidence":"High","gaps":["Functional consequence of heterocomplex formation for complement activity unknown","Stoichiometry and structure of heterocomplexes not resolved"]},{"year":2023,"claim":"Ficolin-2 was shown to drive a pro-inflammatory smooth muscle cell phenotype in macrophage-SMC cross-talk via MCP-1, IL-6, TLR4 upregulation and ERK/MAPK and NF-κB activation, with plaque co-localization, linking ficolin-2 to vascular inflammation.","evidence":"SMC-macrophage co-culture with cytokine/protease arrays, qPCR, Western blot, transmigration assays, and plaque immunofluorescence","pmids":["37940674"],"confidence":"Medium","gaps":["Receptor coupling ficolin-2 to ERK/NF-κB in SMCs not definitively identified","Causal role in human atherogenesis not established"]},{"year":null,"claim":"How ficolin-2's single multi-specific S3 site, oligomeric avidity, MASP coupling, and TLR4 signaling are coordinated to achieve ligand-selective and context-dependent outcomes in vivo remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified structural model linking S3 ligand selectivity to oligomer geometry","Receptor(s) mediating ficolin-2 signaling in SMCs not defined","Functional role of ficolin-2/ficolin-3 heterocomplexes in complement activation unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[3,8]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[2,3,6]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[14,18]},{"term_id":"GO:0001618","term_label":"virus receptor activity","supporting_discovery_ids":[7,12,15]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,2,4]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[2,3,6,9,14]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[14,18]}],"complexes":["ficolin-2/ficolin-3 heterocomplex","ficolin-2/MASP complex","ficolin-2/PTX3 complex"],"partners":["MASP","PTX3","FCN3","TLR4"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q15485","full_name":"Ficolin-2","aliases":["37 kDa elastin-binding protein","EBP-37","Collagen/fibrinogen domain-containing protein 2","Ficolin-B","Ficolin-beta","Hucolin","L-ficolin","Serum lectin p35"],"length_aa":313,"mass_kda":34.0,"function":"Calcium-dependent lectin, which acts as a pattern recognition receptor that initiates the lectin pathway of the complement system, a cascade of proteins that leads to phagocytosis and breakdown of pathogens and signaling that strengthens the adaptive immune system (PubMed:10679061, PubMed:14707097, PubMed:15804047, PubMed:17215869, PubMed:25344472, PubMed:8576206). Specifically recognizes and binds carbohydrates on the pathogen surface, activating the MASP1 serine protease and initiating the proteolytic cascade of the lectin complement pathway (PubMed:14707097). Specifically binds N-Acetylglucosamine (GlcNAc), as well as phosphocholine and lipoteichoic acid moieties on the surface of pathogens (PubMed:14707097, PubMed:17215869, PubMed:25344472, PubMed:8576206). Enhances phagocytosis of S.typhimurium by neutrophils, suggesting an opsonic effect (PubMed:8576206)","subcellular_location":"Secreted; Cell surface","url":"https://www.uniprot.org/uniprotkb/Q15485/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/FCN2","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/FCN2","total_profiled":1310},"omim":[{"mim_id":"613860","title":"FICOLIN 3 DEFICIENCY","url":"https://www.omim.org/entry/613860"},{"mim_id":"613357","title":"FIBRINOGEN C DOMAIN-CONTAINING PROTEIN 1; FIBCD1","url":"https://www.omim.org/entry/613357"},{"mim_id":"605102","title":"MANNAN-BINDING LECTIN SERINE PROTEASE 2; 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A link between the complement system and angiogenic imbalance inpreeclampsia: ficolin-2 deficiency.","date":"2012","source":"Pregnancy hypertension","url":"https://pubmed.ncbi.nlm.nih.gov/26105219","citation_count":1,"is_preprint":false},{"pmid":"36833169","id":"PMC_36833169","title":"Selected SNPs of FCN2 Associated with Chronic Tonsillitis in the Polish Adult Population.","date":"2023","source":"Genes","url":"https://pubmed.ncbi.nlm.nih.gov/36833169","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":43767,"output_tokens":5228,"usd":0.10486,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":13586,"output_tokens":5534,"usd":0.10314,"stage2_stop_reason":"end_turn"},"total_usd":0.208,"stage1_batch_id":"msgbatch_01AsR7g8dGTEiEw9U83bJeWn","stage2_batch_id":"msgbatch_01YV5ZyxtFNUZEjxRcpd9jzb","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1995,\n      \"finding\": \"FCN2/EBP-37 was identified as an elastin-binding protein in human plasma with collagenous and non-collagenous domains, showing direct binding to alpha-elastin confirmed by nitrocellulose-binding assay with specific antiserum. It exists as oligomers and multimers crosslinked by disulfide bonds.\",\n      \"method\": \"Affinity chromatography on alpha-elastin-Sepharose, partial amino acid sequencing, immunoblot with specific antiserum, homology analysis\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct binding assay with antiserum confirmation, single lab, single study identifying the protein\",\n      \"pmids\": [\"8586615\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"FCN2 polymorphisms in the fibrinogen-like domain (exon 8) cause amino acid exchanges (Thr236Met, Ala258Ser) that respectively decrease and increase GlcNAc (N-acetylglucosamine) binding capacity of ficolin-2, while promoter polymorphisms regulate serum concentration.\",\n      \"method\": \"Gene sequencing, GlcNAc-binding assay, ELISA for serum concentration measurement\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — functional binding assays combined with genetic analysis, replicated across multiple subsequent studies\",\n      \"pmids\": [\"15879437\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Ficolin-2 is an oligomeric serum protein forming stable 12-mer (403 kDa) and unstable 24-mer (807 kDa) structures built from 34.4 kDa polypeptides connected by extensive disulfide bridges in the N-terminal region; it binds MASP (MBL-associated serine proteases) and activates complement.\",\n      \"method\": \"Recombinant expression in CHO cells, gel filtration, sucrose density gradient ultracentrifugation, mass spectrometry, surface plasmon resonance spectroscopy\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstitution with recombinant protein, multiple orthogonal structural methods (gel filtration, ultracentrifugation, mass spectrometry, SPR) in single study\",\n      \"pmids\": [\"16595153\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Ficolin-2 binds to late apoptotic cells, apoptotic bodies, and necrotic cells (but not early apoptotic cells) via calcium-dependent binding to exposed DNA; this binding leads to complement C4 deposition on necrotic cells and enhanced attachment/phagocytosis by macrophages.\",\n      \"method\": \"Cell-binding assays, DNA-binding assay with calcium chelation, serum reconstitution with ficolin-2-deficient serum, complement C4 deposition assay, macrophage attachment/uptake assay\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal functional assays (binding, complement deposition, phagocytosis) in single study with mechanistic inhibition controls\",\n      \"pmids\": [\"16730064\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"FCN2 promoter polymorphisms at -986, -602, and -4 positions are associated with markedly different serum ficolin-2 concentrations; ficolin-2 circulates as a mixture of covalently and non-covalently linked oligomers independent of individual genotype.\",\n      \"method\": \"Sandwich ELISA, TaqMan-based genotyping, gel-permeation chromatography with ELISA/SDS-PAGE/Western blot analysis of fractions\",\n      \"journal\": \"Scandinavian journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ELISA quantification combined with fractionation and Western blot, single lab, extends prior findings\",\n      \"pmids\": [\"17386030\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Ficolin-2 (but not ficolin-1 or ficolin-3) directly binds Aspergillus fumigatus in a calcium-independent manner and interacts with pentraxin 3 (PTX3) also in a calcium-independent manner; PTX3 and ficolin-2 mutually enhance each other's binding to A. fumigatus. The FCN2 T236M polymorphism in the fibrinogen-like domain reduces both PTX3 binding and A. fumigatus binding. The ficolin-2/PTX3 complex enhances complement deposition on A. fumigatus.\",\n      \"method\": \"Affinity isolation from human plasma on immobilized PTX3, binding studies, complement deposition assay on A. fumigatus, comparison of wild-type vs. T236M variant\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal binding validation, functional complement assay, mechanistic variant analysis, multiple orthogonal approaches in single study\",\n      \"pmids\": [\"19632990\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Ficolin-2 recognizes O-acetylated epitopes on Streptococcus pneumoniae serotype 11A capsule polysaccharide in a wcjE gene-dependent manner, triggering C1q-independent complement deposition and phagocytic killing of pneumococci; inhibition of ficolin-2 binding abrogated complement deposition and phagocytosis.\",\n      \"method\": \"Binding assays with recombinant ficolin-2, complement deposition assay, opsonophagocytosis assay, specific inhibition of ficolin-2 binding, epidemiological meta-analysis\",\n      \"journal\": \"The Journal of infectious diseases\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple functional assays with mechanistic inhibition controls, replicated with complement and phagocytosis readouts, subsequently confirmed by independent studies\",\n      \"pmids\": [\"24683196\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Ficolin-2 inhibits HCV infection by binding HCV envelope glycoproteins E1 and E2 (via the C-terminal fibrinogen domain residues 201-313 aa interacting with N-glycans), blocking HCV attachment to LDLR and scavenger receptor B1; ApoE3 (but not ApoE2 or ApoE4) blocks ficolin-2-HCV-E2 interaction and mediates viral immune escape.\",\n      \"method\": \"Viral entry inhibition assay, direct binding assays to HCV-E1/E2, receptor attachment blocking assays, domain mapping with truncation mutants, ApoE isoform competition assay\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro binding and functional assays with domain mapping and mechanistic elucidation, multiple orthogonal methods in single study\",\n      \"pmids\": [\"24928988\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"X-ray crystallography of the ficolin-2 fibrinogen-like domain shows that sulfate and phosphate groups bind to the S3 binding site (composed of Arg132, Asp133, Thr136, and Lys221), the same site that binds N-acetyl groups; mutagenesis of Arg132 (and to a lesser extent Asp133) abolished this binding; DNA and heparin compete for the same S3 site.\",\n      \"method\": \"X-ray crystallography of ficolin-2 fibrinogen-like domain in complex with ligands, site-directed mutagenesis, competitive binding assay\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure with functional validation by mutagenesis and competition assay, multiple orthogonal methods\",\n      \"pmids\": [\"25447524\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Ficolin-2 defends against virulent Mycobacterium tuberculosis H37Rv infection by binding to surface glycolipids of H37Rv, blocking infection of lung cells, promoting opsonophagocytosis, and activating JNK phosphorylation and stimulating secretion of IFN-γ, IL-17, IL-6, TNF-α, and nitric oxide by macrophages; Ficolin-A (mouse ficolin-2-like) knockout mice showed increased susceptibility to H37Rv infection.\",\n      \"method\": \"In vitro binding assays, cell infection blocking assay, opsonophagocytosis assay, exogenous ficolin-2 administration in C57BL/6J and BALB/c mice, Ficolin-A knockout mice, JNK phosphorylation assay, cytokine measurement\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple in vitro and in vivo functional assays including knockout mice, pathway activation assay, replicated in two mouse strains\",\n      \"pmids\": [\"24040095\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Human ficolin-2 recognizes and binds nonpathogenic Leptospira biflexa, Pasteurella pneumotropica, enteropathogenic E. coli serotype O111ab:H2, and enteroaggregative E. coli serogroup O71, but does not bind pathogenic Leptospira interrogans or other E. coli strains tested; ficolin-2 binding to these pathogens activates the lectin complement pathway.\",\n      \"method\": \"Recombinant ficolin-2 binding assays, anti-ficolin monoclonal antibodies for detection, lectin pathway complement activation assay with C1q-depleted human serum\",\n      \"journal\": \"Immunobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct binding and complement activation assays with recombinant protein, single lab study\",\n      \"pmids\": [\"26074063\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Ficolin-2 binds to cholesterol crystals in a calcium-independent manner and activates the lectin complement pathway, resulting in complement activation product deposition; ficolin-1 and ficolin-3 do not bind cholesterol crystals; ficolin-2 protein is deposited in human carotid atherosclerotic plaques.\",\n      \"method\": \"Binding assays with recombinant proteins, complement deposition assay using deficient and normal sera with specific inhibitors, immunohistochemistry and fluorescence microscopy of human carotid plaques\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro binding assays combined with in vivo tissue localization and functional complement assays with multiple controls\",\n      \"pmids\": [\"27183610\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Ficolin-2 binds HIV-1 envelope glycoprotein gp120 and blocks HIV-1 entry into target cells in a dose-dependent manner, inducing complement-dependent cytotoxicity.\",\n      \"method\": \"Direct binding assay of recombinant ficolin-2 to gp120, viral entry inhibition assay in TZM-b1 and MT-2 cells, complement-dependent cytotoxicity assay\",\n      \"journal\": \"Virologica Sinica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct binding and functional entry inhibition assays, single lab study\",\n      \"pmids\": [\"27576476\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"FCN2 overexpression in HCC cells inhibits migration, invasion, and EMT in vitro and in vivo; TGF-β signaling contributes to FCN2-mediated suppression of metastasis and EMT (FCN2/TGF-β/EMT axis).\",\n      \"method\": \"Ectopic expression of FCN2 in HCC cells, migration/invasion assays, EMT marker analysis in vitro and in vivo xenograft models, TGF-β pathway analysis\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — loss/gain-of-function with defined cellular phenotype and pathway placement, single lab study\",\n      \"pmids\": [\"27177473\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Ficolin-2 binds TLR4 on macrophages and dendritic cells, promotes macrophage M1 polarization, enhances antigen-presenting ability, and facilitates proliferation and antigen-specific cytotoxicity of CD8+ T cells; ficolin-A (mouse ficolin-2-like) KO mice exhibit significantly increased tumor cell growth.\",\n      \"method\": \"Ficolin-2 binding assay to TLR4, macrophage activation assays, M1 polarization assessment, CD8+ T cell proliferation and cytotoxicity assays, murine tumor models with exogenous ficolin-2 or ficolin-A, ficolin-A KO mice\",\n      \"journal\": \"Clinical immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — TLR4 binding and multiple functional assays with KO mouse model, single lab study\",\n      \"pmids\": [\"28844702\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Ficolin-2 expressed and secreted by hepatocytes confers resistance to infection by HCV, ebolavirus, and vesicular stomatitis virus, but increases susceptibility to rabies virus; cell-to-cell spread of HCV is also inhibited in ficolin-2-expressing cells.\",\n      \"method\": \"Stable FCN2 expression in HuH7.5 hepatoma cells (which lack endogenous ficolin-2), viral infection assays with HCV, ebolavirus, VSV, and rabies virus\",\n      \"journal\": \"Journal of medical microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain-of-function in cell line deficient for the protein, tested against multiple viruses with defined infection readouts\",\n      \"pmids\": [\"30747617\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Ficolin-2 and ficolin-3 form stable heterocomplexes in normal human serum and plasma; these heterocomplexes require co-expression of both proteins (not just mixing of recombinant proteins), suggesting formation occurs during biosynthesis; complex concentration correlates with ficolin-2 (ρ=0.24) and ficolin-3 (ρ=0.46) concentrations.\",\n      \"method\": \"ELISA with ficolin-2 and ficolin-3 specific antibodies, co-immunoprecipitation, Western blot, co-expression in CHO cells, mixing of recombinant proteins as negative control\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-immunoprecipitation validated by Western blot, co-expression vs mixing experiment distinguishes biosynthetic requirement, multiple orthogonal methods\",\n      \"pmids\": [\"32094208\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Ficolin-2 binding to S. pneumoniae serotype 11A capsule is entirely dependent on the O-acetyltransferase gene wcjE; ficolin-2 does not interact with any non-capsule pneumococcal structures including teichoic acid; even partial loss of wcjE expression abrogates bacterial killing.\",\n      \"method\": \"Fluorescence microscopy binding assays, complement deposition assay, opsonophagocytosis assay with wcjE mutants, epidemiological analysis\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — mechanistic specificity determined by genetic mutation of ligand, replicated and extended from earlier studies, multiple functional readouts\",\n      \"pmids\": [\"35418983\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Ficolin-2 promotes pro-inflammatory phenotype in smooth muscle cells (SMCs) during macrophage-SMC cross-talk by elevating MCP-1 expression, upregulating IL-6 and TLR4 expression and activating ERK/MAPK and NF-κB signaling pathways; ficolin-2 also increases IL-1β, IL-6, and MIP-1β in macrophages and enhances monocyte transmigration; co-localization of ficolin-2 with αSMA, IL-1β and IL-6 was confirmed in atherosclerotic plaques from high ficolin-2 patients.\",\n      \"method\": \"In vitro co-culture of SMC and macrophages with ficolin-2 treatment, cytokine array, protease array, ELISA, qPCR, Western blot, monocyte transmigration assay, immunofluorescence of carotid plaques\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (cytokine array, Western blot, qPCR, functional transmigration), single lab with tissue validation\",\n      \"pmids\": [\"37940674\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Ficolin-2 is selectively depleted from plasma by heparin-coated (Bioline) cardiopulmonary bypass circuits during cardiac surgery, remaining reduced 24 hours post-operation, while MBL, ficolin-1, and ficolin-3 are unaffected by either phosphorylcholine or heparin-coated circuits.\",\n      \"method\": \"Randomized clinical comparison of two circuit coatings, ELISA measurement of ficolin-1, -2, -3, MBL at five time-points, complement activation potential assay\",\n      \"journal\": \"Clinical and experimental immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — randomized in vivo study with multiple time-points and parallel measurement of related proteins, demonstrating selectivity of depletion\",\n      \"pmids\": [\"25174443\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"Ficolin-2 (FCN2) is a liver-synthesized, oligomeric (predominantly 12-mer) serum pattern recognition molecule of the lectin complement pathway that binds acetylated sugars, N-acetylglucosamine, O-acetylated capsule epitopes, DNA, sulfated/phosphated carbohydrates, and viral glycoproteins via its fibrinogen-like domain S3 binding site (Arg132, Asp133, Thr136, Lys221); it activates complement through MASP binding, opsonizes pathogens and dying cells for phagocytosis, synergizes with pentraxin 3 (PTX3) to enhance pathogen recognition, forms heterocomplexes with ficolin-3 during biosynthesis, signals through TLR4 on macrophages to promote M1 polarization and CD8+ T cell cytotoxicity, and activates ERK/MAPK and NF-κB pathways in smooth muscle cells; functional polymorphisms in the fibrinogen-like domain (T236M, A258S) and promoter region modulate ligand-binding capacity and serum concentration respectively.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"Ficolin-2 (FCN2) is a liver-derived, oligomeric serum pattern-recognition molecule of the lectin complement pathway that opsonizes pathogens and dying cells and links innate recognition to inflammatory and adaptive responses [#2, #3, #6]. It assembles from ~34 kDa polypeptides into disulfide-bridged oligomers, predominantly a stable 12-mer, and engages MASP to trigger complement activation [#2, #4]. Ligand recognition is mediated by a defined S3 binding site in the C-terminal fibrinogen-like domain (Arg132, Asp133, Thr136, Lys221), a single site that accommodates N-acetyl groups, sulfate and phosphate groups, DNA, and heparin in competition with one another, with Arg132 essential for binding [#8]. Through this domain ficolin-2 recognizes a broad ligand spectrum: GlcNAc [#1], exposed DNA on late-apoptotic and necrotic cells driving C4 deposition and macrophage phagocytosis [#3], O-acetylated S. pneumoniae serotype 11A capsule in a strictly wcjE-dependent manner enabling C1q-independent complement deposition and opsonophagocytic killing [#6, #17], surface glycolipids of M. tuberculosis [#9], cholesterol crystals deposited in atherosclerotic plaques [#11], and viral envelope glycoproteins of HCV, HIV-1 gp120, and other viruses to block viral entry [#7, #12, #15]. Functional cooperativity extends its recognition repertoire: ficolin-2 binds pentraxin 3 (PTX3) to mutually enhance binding to A. fumigatus and complement deposition, and forms ficolin-2/ficolin-3 heterocomplexes that assemble co-translationally during biosynthesis [#5, #16]. Beyond complement, ficolin-2 signals through TLR4 on macrophages and dendritic cells to drive M1 polarization, enhance antigen presentation, and promote CD8+ T cell cytotoxicity, and activates ERK/MAPK and NF-\\u03baB signaling in smooth muscle cells to promote a pro-inflammatory phenotype [#14, #18]. Functional polymorphisms in the fibrinogen-like domain (T236M, A258S) alter ligand-binding capacity while promoter variants set serum concentration [#1, #5].\",\n  \"teleology\": [\n    {\n      \"year\": 1995,\n      \"claim\": \"The protein was first isolated and shown to be a plasma molecule with collagenous and non-collagenous domains capable of direct ligand binding, establishing it as an oligomeric serum protein.\",\n      \"evidence\": \"Affinity chromatography on alpha-elastin-Sepharose, partial sequencing, and immunoblot with specific antiserum\",\n      \"pmids\": [\"8586615\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"The physiological relevance of elastin binding was not established\", \"No complement or immune function defined at this stage\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Genetic dissection showed that fibrinogen-domain coding variants (T236M, A258S) directly tune GlcNAc-binding capacity while promoter variants set serum levels, linking genotype to molecular function.\",\n      \"evidence\": \"Gene sequencing with GlcNAc-binding assays and ELISA quantification of serum concentration\",\n      \"pmids\": [\"15879437\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve structural basis of altered binding\", \"Did not connect variants to clinical outcomes mechanistically\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Reconstitution defined the oligomeric architecture and showed ficolin-2 binds MASP and activates complement, establishing its identity as a lectin-pathway recognition molecule.\",\n      \"evidence\": \"Recombinant CHO expression with gel filtration, ultracentrifugation, mass spectrometry, and SPR\",\n      \"pmids\": [\"16595153\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry of the active MASP complex not fully defined\", \"Functional significance of the unstable 24-mer unclear\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Ficolin-2 was shown to recognize late-apoptotic and necrotic cells via calcium-dependent DNA binding, driving complement deposition and phagocytosis, extending its role to clearance of dying cells.\",\n      \"evidence\": \"Cell-binding and DNA-binding assays with calcium chelation, C4 deposition, and macrophage uptake assays in deficient serum\",\n      \"pmids\": [\"16730064\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo relevance to apoptotic clearance not tested\", \"Receptor mediating phagocytic enhancement not identified\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Discovery of cooperative recognition: ficolin-2 binds PTX3 and the two molecules mutually enhance binding to A. fumigatus and complement deposition, revealing synergy with another humoral pattern-recognition molecule.\",\n      \"evidence\": \"Affinity isolation on immobilized PTX3, reciprocal binding studies, complement deposition on A. fumigatus, and T236M variant comparison\",\n      \"pmids\": [\"19632990\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural interface of the ficolin-2/PTX3 complex not mapped\", \"In vivo antifungal protection not demonstrated\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Ficolin-2 was shown to bind M. tuberculosis glycolipids and protect in vivo, linking recognition to opsonophagocytosis, JNK signaling, and cytokine secretion by macrophages.\",\n      \"evidence\": \"In vitro binding and infection-blocking assays, opsonophagocytosis, JNK phosphorylation, cytokine measurement, and ficolin-A knockout mice\",\n      \"pmids\": [\"24040095\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Glycolipid ligand not chemically defined\", \"Receptor coupling JNK activation to ficolin-2 binding unclear\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Ficolin-2 was established as an antiviral factor binding HCV E1/E2 glycoproteins via its fibrinogen domain to block viral attachment, with ApoE3 mediating viral immune escape.\",\n      \"evidence\": \"Viral entry inhibition, direct E1/E2 binding, receptor-blocking assays, truncation domain mapping, and ApoE isoform competition\",\n      \"pmids\": [\"24928988\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether complement is required for antiviral effect not resolved\", \"In vivo antiviral protection not tested\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Crystallography defined the S3 binding site (Arg132, Asp133, Thr136, Lys221) as a single multi-specific pocket accommodating acetyl, sulfate, phosphate, DNA, and heparin in competition, providing the structural basis for ficolin-2's broad ligand recognition.\",\n      \"evidence\": \"X-ray crystallography of the fibrinogen-like domain with ligands, site-directed mutagenesis, and competitive binding\",\n      \"pmids\": [\"25447524\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not explain selectivity among competing ligands in physiological mixtures\", \"Avidity contribution of oligomerization not addressed\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Recognition of O-acetylated pneumococcal capsule (serotype 11A) was shown to be wcjE-dependent and to drive C1q-independent complement deposition and phagocytic killing, defining a precise bacterial ligand determinant.\",\n      \"evidence\": \"Binding, complement deposition, and opsonophagocytosis assays with recombinant ficolin-2 and binding inhibition\",\n      \"pmids\": [\"24683196\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Other O-acetylated capsule serotypes not surveyed\", \"Quantitative threshold of acetylation for binding not established at this stage\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Ficolin-2 was found to bind nonpathogenic bacteria and selected E. coli serotypes and activate the lectin pathway, while sparing pathogenic Leptospira, indicating ligand-specific discrimination among microbes.\",\n      \"evidence\": \"Recombinant ficolin-2 binding assays and lectin pathway complement activation with C1q-depleted serum\",\n      \"pmids\": [\"26074063\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular ligands on bound bacteria not identified\", \"Single-lab study without in vivo validation\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"A randomized clinical comparison showed ficolin-2 is selectively depleted by heparin-coated bypass circuits, demonstrating that heparin-like surfaces sequester ficolin-2 in vivo consistent with its S3-site heparin binding.\",\n      \"evidence\": \"Randomized circuit-coating comparison with ELISA of ficolin-1/-2/-3 and MBL across time-points\",\n      \"pmids\": [\"25174443\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of depletion for patients not determined\", \"Mechanism of selective depletion vs other ficolins not molecularly confirmed\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Ficolin-2 was shown to bind cholesterol crystals and HIV-1 gp120, extending its recognition to sterile crystalline danger signals and additional viral envelopes with complement activation and entry inhibition.\",\n      \"evidence\": \"Binding assays with recombinant ficolins, complement deposition, plaque immunohistochemistry, gp120 binding, viral entry inhibition, and CDC assays\",\n      \"pmids\": [\"27183610\", \"27576476\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Causal role in atherosclerosis progression not established\", \"In vivo antiviral efficacy against HIV not tested\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"FCN2 overexpression was shown to suppress HCC migration, invasion, and EMT through a FCN2/TGF-\\u03b2/EMT axis, implicating ficolin-2 in tumor metastasis control beyond innate immunity.\",\n      \"evidence\": \"Ectopic FCN2 expression with migration/invasion assays, EMT markers, xenografts, and TGF-\\u03b2 pathway analysis\",\n      \"pmids\": [\"27177473\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct molecular target linking FCN2 to TGF-\\u03b2 not identified\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Ficolin-2 was shown to signal through TLR4 to drive macrophage M1 polarization, enhance antigen presentation and CD8+ T cell cytotoxicity, and restrain tumor growth in vivo, connecting it to adaptive immunity.\",\n      \"evidence\": \"TLR4 binding, macrophage activation and polarization assays, CD8+ T cell proliferation/cytotoxicity, and ficolin-A knockout tumor models\",\n      \"pmids\": [\"28844702\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct ficolin-2/TLR4 binding interface not mapped\", \"Single-lab study; downstream TLR4 signaling not fully dissected\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Hepatocyte-expressed ficolin-2 was shown to confer broad antiviral resistance (HCV, ebolavirus, VSV) but enhance rabies susceptibility, indicating virus-specific outcomes of ficolin-2 expression.\",\n      \"evidence\": \"Stable FCN2 expression in ficolin-2-deficient HuH7.5 cells with multi-virus infection assays\",\n      \"pmids\": [\"30747617\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of rabies enhancement not explained\", \"Roles of secreted vs cell-associated ficolin-2 not separated\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Ficolin-2/ficolin-3 heterocomplexes were shown to exist in serum and to require co-expression rather than mixing, establishing that they assemble co-translationally during biosynthesis.\",\n      \"evidence\": \"ELISA with specific antibodies, co-immunoprecipitation, Western blot, and CHO co-expression vs recombinant mixing controls\",\n      \"pmids\": [\"32094208\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of heterocomplex formation for complement activity unknown\", \"Stoichiometry and structure of heterocomplexes not resolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Ficolin-2 was shown to drive a pro-inflammatory smooth muscle cell phenotype in macrophage-SMC cross-talk via MCP-1, IL-6, TLR4 upregulation and ERK/MAPK and NF-\\u03baB activation, with plaque co-localization, linking ficolin-2 to vascular inflammation.\",\n      \"evidence\": \"SMC-macrophage co-culture with cytokine/protease arrays, qPCR, Western blot, transmigration assays, and plaque immunofluorescence\",\n      \"pmids\": [\"37940674\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor coupling ficolin-2 to ERK/NF-\\u03baB in SMCs not definitively identified\", \"Causal role in human atherogenesis not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How ficolin-2's single multi-specific S3 site, oligomeric avidity, MASP coupling, and TLR4 signaling are coordinated to achieve ligand-selective and context-dependent outcomes in vivo remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified structural model linking S3 ligand selectivity to oligomer geometry\", \"Receptor(s) mediating ficolin-2 signaling in SMCs not defined\", \"Functional role of ficolin-2/ficolin-3 heterocomplexes in complement activation unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": []},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [3, 8]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [2, 3, 6]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [14, 18]},\n      {\"term_id\": \"GO:0001618\", \"supporting_discovery_ids\": [7, 12, 15]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 2, 4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [2, 3, 6, 9, 14]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [14, 18]}\n    ],\n    \"complexes\": [\n      \"ficolin-2/ficolin-3 heterocomplex\",\n      \"ficolin-2/MASP complex\",\n      \"ficolin-2/PTX3 complex\"\n    ],\n    \"partners\": [\n      \"MASP\",\n      \"PTX3\",\n      \"FCN3\",\n      \"TLR4\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}