{"gene":"MBL2","run_date":"2026-04-28T18:30:28","timeline":{"discoveries":[{"year":1983,"finding":"MBL2 protein (mannan-binding protein) was isolated from human serum as a glycine-rich lectin of ~600 kDa composed of ~31 kDa subunits, with calcium-dependent, saturable, and reversible binding to mannan distinct from CRP and SAP.","method":"Affinity chromatography on Sepharose-mannan, Scatchard plot binding analysis, immunoassay","journal":"Journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 — direct biochemical isolation and binding characterization with quantitative analysis","pmids":["6643429"],"is_preprint":false},{"year":1988,"finding":"MBL2 encodes a human serum lectin with three structural domains: an N-terminal cysteine-rich region (interchain disulfide bonds), a collagen-like region (19 Gly-X-Y repeats), and a C-terminal carbohydrate recognition domain; the protein is an acute-phase reactant secreted by the liver and homologous to C-type lectins.","method":"cDNA cloning from human liver library, sequence analysis, comparison with rat MBP and other lectins","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 1 — full cDNA cloning and domain structure determination, foundational study","pmids":["2450948"],"is_preprint":false},{"year":1989,"finding":"The MBL2 gene is located on chromosome 10q11.2-q21, comprises four exons each encoding a distinct protein domain, and evolved by recombination of an ancestral non-fibrillar collagen gene with a carbohydrate-recognition gene, similar to surfactant SP-A.","method":"Genomic cloning, exon structure analysis, chromosomal localization by in situ hybridization","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 1 — direct genomic structural determination and chromosomal mapping","pmids":["2477486"],"is_preprint":false},{"year":1989,"finding":"Low serum MBL levels are directly linked to a common opsonic defect; purified MBL corrects the defect in a dose-dependent manner by promoting C3b deposition on mannan-coated surfaces, establishing MBL as a functional opsonin.","method":"In vitro opsonization assay measuring complement C3b deposition on mannan-coated surfaces, immunoassay of serum MBL levels","journal":"Lancet","confidence":"High","confidence_rationale":"Tier 1 — reconstitution experiment showing dose-dependent restoration of opsonic function by purified MBL","pmids":["2573758"],"is_preprint":false},{"year":1991,"finding":"A point mutation at codon 54 of MBL2 exon 1 (GGC→GAC, Gly→Asp) disrupts the fifth Gly-X-Y repeat of the collagen-like domain, prevents normal triple helix formation, and causes low serum MBL with autosomal dominant co-inheritance of the opsonic defect.","method":"DNA sequencing of MBL2 exon 1, family segregation analysis, serum MBL immunoassay","journal":"Lancet","confidence":"High","confidence_rationale":"Tier 1 — direct identification of causal mutation with structural rationale and genetic co-segregation","pmids":["1675710"],"is_preprint":false},{"year":1992,"finding":"Two independent point mutations in MBL2 exon 1 — codon 54 (GGC→GAC) prevalent in non-Africans and codon 57 (GGA→GAA) prevalent in West Africans — each substitute carboxylic acids for axial glycines, disrupting the collagen-like triple helix and profoundly reducing serum MBL and complement activation capacity.","method":"PCR, sequence analysis, restriction analysis of population samples, complement activation assay","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 1 — structural mutations identified with functional complement assay validation across multiple populations","pmids":["1304173"],"is_preprint":false},{"year":1994,"finding":"A third MBL2 exon 1 point mutation at codon 52 was identified, completing the structural polymorphism; together codons 52, 54, and 57 account for all cases of MBL deficiency across ethnic groups in Hardy-Weinberg equilibrium.","method":"PCR-based genotyping, population genetic analysis (Hardy-Weinberg testing) across Eskimo, Caucasian, and African populations","journal":"Immunogenetics","confidence":"High","confidence_rationale":"Tier 2 — comprehensive population-based genetic characterization replicated across multiple ethnic groups","pmids":["8206524"],"is_preprint":false},{"year":1994,"finding":"The carbohydrate recognition domain (CRD) and 'neck' region of MBL2 form a trimeric structure in solution and crystals; the neck region forms a triple α-helical coiled-coil, and each α-helix contacts a neighboring CRD, defining the spatial arrangement of CRDs for branched oligosaccharide recognition on microorganisms.","method":"X-ray crystallography of recombinant neck+CRD peptide in two crystal forms","journal":"Nature structural biology","confidence":"High","confidence_rationale":"Tier 1 — crystal structure determination in two crystal forms providing atomic-level structural insight","pmids":["7634089"],"is_preprint":false},{"year":1994,"finding":"MBL2 binds to influenza virus through its lectin domain in a calcium-dependent, saturable, concentration-dependent manner; ligand blot analysis identified the 68 kDa viral neuraminidase as the specific MBL-binding species, and bound MBL inhibits hemagglutinating activity.","method":"Saturable binding assay, ligand blot, purification of the 68 kDa MBL-binding viral protein and identification as neuraminidase, hemagglutination inhibition assay","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 — direct identification of viral binding partner by ligand blot and purification, with functional inhibition assay","pmids":["7998980"],"is_preprint":false},{"year":1997,"finding":"A second MBL-associated serine protease, MASP-2, was identified; MASP-2 associates with MBL oligomers and activates complement via C4 and C2 cleavage, demonstrating that the MBL pathway, like the classical pathway, involves two serine proteases (MASP-1 and MASP-2).","method":"Protein purification, cDNA cloning, sequence homology analysis, complement C4 and C2 cleavage assays","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — protein isolation, cloning, and enzymatic characterization; landmark discovery replicated extensively","pmids":["9087411"],"is_preprint":false},{"year":1998,"finding":"Low MBL serum concentrations in African and South American populations are caused by distinct molecular mechanisms: high frequency of the codon 57 (C) variant in Africans versus extremely high frequency of the codon 54 (B) variant in South American natives, with promoter haplotypes further modulating levels.","method":"MBL2 genotyping, serum MBL concentration measurement, population allele frequency analysis","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — systematic genotype-phenotype correlation across geographically diverse populations with functional MBL measurement","pmids":["9743385"],"is_preprint":false},{"year":1998,"finding":"Chicken MBL is a single-form serum collectin with structural homology to mammalian MBL; phylogenetic analysis indicates that the gene duplication producing two MBL forms in mammals (MBL1 and MBL2) occurred after the bird-reptile split, supporting the evolutionary origin of the MBL2 locus.","method":"RT-PCR, cDNA library screening, sequencing, phylogenetic analysis of deduced amino acid sequences","journal":"Immunology","confidence":"Medium","confidence_rationale":"Tier 2 — cloning and phylogenetic analysis; single study establishing avian MBL evolutionary relationship","pmids":["9640255"],"is_preprint":false},{"year":2000,"finding":"MBL binds to a broad range of clinically relevant pathogens (Candida spp., Aspergillus fumigatus, S. aureus, beta-hemolytic group A streptococci) and bound MBL promotes C4 deposition in a concentration-dependent manner, directly linking pathogen surface recognition to complement activation.","method":"Flow cytometry binding assay with purified MBL on pathogen isolates, C4 deposition assay","journal":"Infection and immunity","confidence":"High","confidence_rationale":"Tier 1-2 — direct binding assay combined with functional complement activation measurement across diverse pathogens","pmids":["10639434"],"is_preprint":false},{"year":2000,"finding":"MBL-MASP complex activity is controlled by C1 inhibitor (which inhibits both classical and MBL pathways) but not by α2-macroglobulin; C1 inhibitor and α2-macroglobulin both associate with the MBL complex, and MASP-1, MASP-2, and MAp19 dissociate from MBL at 37°C in physiological buffer but not at high ionic strength (1M NaCl), indicating the MBL-MASP interaction is distinct from the C1 complex.","method":"Complement activation assay specific for MBL pathway, co-purification/association analysis, inhibitor profiling","journal":"Molecular immunology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods including functional assays and association analysis with rigorous inhibitor controls","pmids":["11257302"],"is_preprint":false},{"year":2001,"finding":"MBL2 binds to apoptotic cells and, via ligation of calreticulin (cC1qR) on phagocytes which in turn binds CD91 (α2-macroglobulin receptor), stimulates macropinocytic engulfment of apoptotic cells, identifying a novel receptor-ligand mechanism for MBL-mediated apoptotic cell clearance.","method":"Co-IP, calreticulin/CD91 blocking antibodies, macropinocytosis assay, apoptotic cell uptake quantification","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 1-2 — receptor identification by blocking antibodies and co-IP, mechanistic pathway established with functional phagocytosis readout","pmids":["11560994"],"is_preprint":false},{"year":2001,"finding":"MASP-3, generated by alternative splicing of the MASP-1/3 gene, associates preferentially with larger MBL oligomers together with MASP-2, and downregulates the C4 and C2 cleaving activity of MASP-2; smaller MBL oligomers preferentially associate with MASP-1, MAp19, and direct C3-cleaving activity, demonstrating that distinct MBL oligomers form functionally different complexes.","method":"Protein purification, cDNA cloning, alternative splicing analysis, functional C4/C2/C3 cleavage assays, oligomer fractionation","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 1 — protein isolation, cloning, and biochemical characterization with functional complement activity assays","pmids":["11485744"],"is_preprint":false},{"year":2002,"finding":"MASP-1, despite initial suggestions, does not efficiently cleave C3 directly at biologically relevant rates; instead, MASP-1 cleaves fibrinogen (releasing fibrinopeptide B) and activates plasma transglutaminase (Factor XIII), indicating MASPs have biologically significant substrates beyond complement components.","method":"In vitro cleavage assays with recombinant and purified native MASP-1, fibrinogen cleavage, Factor XIII activation assay","journal":"Immunobiology","confidence":"High","confidence_rationale":"Tier 1 — in vitro enzymatic assays with recombinant and native protein; multiple non-complement substrates identified","pmids":["12396008"],"is_preprint":false},{"year":2002,"finding":"MBL2 genotypes (promoter and structural SNPs at codons 52, 54, 57 and promoter positions -550, -221) show significant correlation with plasma MBL antigen levels and functional MBL activity as measured by both mannan-binding and C4-deposition assays, validating comprehensive genotype-phenotype relationships.","method":"PCR-SSP genotyping, double-antibody ELISA for MBL antigen, mannan-binding assay, C4-deposition assay in 236 blood donors","journal":"Scandinavian journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — three independent functional assays correlated with genotype in a large cohort","pmids":["12472676"],"is_preprint":false},{"year":2003,"finding":"Recombinant MBL produced in a transfected human cell line shows identical biological activity and MS profile to plasma-derived MBL, demonstrating that the oligomeric structure and function can be reconstituted recombinantly, enabling therapeutic application.","method":"Recombinant protein production in human cell line, mass spectrometry, functional activity comparison with plasma-derived MBL","journal":"Biochemical Society transactions","confidence":"Medium","confidence_rationale":"Tier 2 — functional and structural equivalence demonstrated by MS and bioactivity assay in single study","pmids":["12887299"],"is_preprint":false},{"year":2004,"finding":"MBL-null mice (lacking both MBL-A and MBL-C) show 100% mortality within 48h of intravenous S. aureus infection compared to 45% mortality in wild-type mice, directly demonstrating that MBL is essential for in vivo host defense against S. aureus; neutrophils and MBL cooperate to limit intraperitoneal infection.","method":"MBL-A and MBL-C double gene knockout mice, intravenous and intraperitoneal S. aureus infection models, survival analysis, neutrophil depletion experiments","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 — clean double-KO with specific lethal phenotype and defined cellular cooperation (neutrophils + MBL)","pmids":["15148336"],"is_preprint":false},{"year":2005,"finding":"MBL binds to HIV-1 gp120 through high-mannose glycans on the envelope protein in a calcium-dependent, strain-independent manner; MBL can directly neutralize HIV produced in T-cell lines, activate complement on gp120, opsonize HIV, and block HIV interaction with DC-SIGN.","method":"Binding assays (ELISA, flow cytometry), neutralization assays, complement C4 deposition on gp120, DC-SIGN blocking assay","journal":"Molecular immunology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal binding and functional assays; replicated across labs","pmids":["15488604"],"is_preprint":false},{"year":2005,"finding":"MBL serum levels vary widely due to MBL2 polymorphisms, and genetically determined differences in complement activation via MBL may play a role in diabetic micro- and macrovascular complications, with complement activation following ischemia-reperfusion as a proposed mechanism.","method":"Review of functional MBL complement activation data and clinical association studies","journal":"Hormone and metabolic research","confidence":"Low","confidence_rationale":"Tier 4 — mechanistic proposal based on existing functional data; no direct experimental validation in this paper","pmids":["15918118"],"is_preprint":false},{"year":2005,"finding":"MBL binds to SARS-CoV in a dose-dependent, calcium-dependent, and mannan-inhibitable manner (confirming binding through the CRDs), enhances complement C4 deposition on SARS-CoV, and inhibits viral infectivity in FRhK-4 cells; lower MBL levels/haplotypes associated with SARS acquisition.","method":"In vitro binding assay, mannan competition, C4 deposition on SARS-CoV, infectivity inhibition assay in cell culture, case-control genotyping","journal":"The Journal of infectious diseases","confidence":"High","confidence_rationale":"Tier 1-2 — direct virus binding with mechanistic controls (calcium-dependence, mannan inhibition), complement activation, and infectivity assay","pmids":["15838797"],"is_preprint":false},{"year":2006,"finding":"C1r/C1s and MASP-1/MASP-2 associate through a common mechanism involving their N-terminal CUB1-EGF region, but the C1s-C1r-C1r-C1s tetramer and (MASP)₂ dimers have evolved distinct strategies to associate with their recognition proteins (C1q vs. MBL/ficolins), establishing the structural basis for MBL-MASP complex assembly.","method":"Structural analysis (crystallography), functional domain mapping, comparison of C1 and MBL-MASP complexes","journal":"Immunobiology","confidence":"Medium","confidence_rationale":"Tier 1 — structural data from crystallography but review/comparison article; structural basis described","pmids":["17544813"],"is_preprint":false},{"year":2009,"finding":"MASP-2 polymorphisms D120G and CHNHdup abolish binding to MBL (preventing complement C4 cleavage), while R439H binds MBL normally but cannot autoactivate or cleave C4, identifying distinct molecular defects in MASP-2 function; the R439H variant is common in Sub-Saharan Africans (10% gene frequency).","method":"Recombinant MASP-2 production for each naturally occurring variant, MBL-binding assay, C4 cleavage assay, autoactivation assay","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1 — recombinant protein biochemistry with multiple orthogonal assays distinguishing binding vs. catalytic defects","pmids":["19234189"],"is_preprint":false},{"year":2010,"finding":"In MBL-KO mice, MBL deficiency is protective (not detrimental) in experimental systemic aspergillosis: KO mice were less susceptible to lethal infection than wild-type at certain inocula, suggesting MBL plays a deleterious role in systemic aspergillosis, possibly through excessive complement-mediated inflammation.","method":"MBL-A and MBL-C double gene knockout mice, intravenous Aspergillus fumigatus infection model, dose-response survival analysis","journal":"Immunology letters","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO with specific survival phenotype, single study without mechanistic pathway placement","pmids":["20064561"],"is_preprint":false},{"year":2014,"finding":"Among MBL-MASP complexes, only MASP-1 (not MASP-2, MASP-3, or non-enzymatic MASP domains) activates endothelial cells (Ca²⁺ signaling in HUVECs) when present in the serum MBL-MASP complex; this activation requires MASP-1's proteolytic activity (zymogen mutant is inactive) and occurs via cleavage of protease-activated receptor 4 (PAR-4).","method":"Ca²⁺ signaling assay in HUVECs, recombinant MASP catalytic fragments, stable zymogen MASP-1 mutant, serum-derived MBL-MASP complexes","journal":"Molecular immunology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple recombinant fragments, zymogen mutant control, specific receptor (PAR-4) identified previously; mechanistic assignment to MASP-1 proteolytic activity","pmids":["24472859"],"is_preprint":false},{"year":2015,"finding":"MBL-MASP complexes are heterogeneous in serum; MASP-1 activity per unit MBL is inversely correlated with MASP-2 activity per unit MBL across individuals, consistent with separate populations of MBL-MASP-1 and MBL-MASP-2 complexes rather than fixed stoichiometric MBL-(MASP-1)-(MASP-2) trimolecular complexes.","method":"Mannan-plate capture of MBL from 152 individual sera, ELISA for MBL, amidolytic assay for MASP-1, C4-fixation assay for MASP-2; correlation analysis","journal":"Molecular immunology","confidence":"Medium","confidence_rationale":"Tier 2 — large population-level functional assay revealing complex heterogeneity; indirect inference of complex composition","pmids":["16102832"],"is_preprint":false},{"year":2015,"finding":"Fasciola hepatica newly excysted juveniles (NEJ) resist MBL-mediated complement killing by two mechanisms: (1) MBL does not bind to the NEJ surface despite mannosylated surface proteins, and (2) secreted NEJ serpins (rFhSrp1, rFhSrp2) directly inhibit MASP-1 and MASP-2, preventing C3b and C4b deposition.","method":"In vitro MBL binding assay on live NEJ, recombinant serpin production, MASP-1 and MASP-2 inhibition assays, immunofluorescence for MBL/C3b/C4b/MAC deposition on NEJ in human serum","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 1-2 — recombinant inhibitors tested against purified native and recombinant MASPs, combined with immunofluorescence validation","pmids":["35007288"],"is_preprint":false},{"year":2019,"finding":"Fungi (especially Malassezia spp.) that migrate into pancreatic ductal adenocarcinoma (PDA) tumors activate MBL2 through binding to fungal wall glycans, triggering complement cascade activation (C3); deletion of MBL2 or C3, or knockdown of C3aR in tumor cells, protects against tumor growth, and reprogramming the mycobiome does not alter PDA progression in Mbl2-deficient mice, establishing MBL2-mediated complement as required for fungus-driven oncogenesis.","method":"MBL2 and C3 knockout mice, C3aR knockdown in tumor cells, mycobiome ablation/repopulation experiments, tumor growth assays in slow-progressive and invasive PDA mouse models","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic deletion models with specific tumor growth phenotype; epistasis (Mbl2-KO blocks effect of mycobiome repopulation) establishes pathway position","pmids":["31578522"],"is_preprint":false}],"current_model":"MBL2 encodes mannose-binding lectin (MBL), a liver-secreted, calcium-dependent C-type lectin that assembles as oligomers of trimeric subunits (neck coiled-coil + CRD) via a collagen-like domain; it recognizes high-mannose and other carbohydrate arrays on microorganisms, apoptotic cells, and tumor-associated fungi, then activates the lectin complement pathway through associated serine proteases MASP-1 and MASP-2 (which form distinct, heterogeneous complexes with MBL oligomers), leading to C4/C2/C3 cleavage and MAC formation, while MASP-1's proteolytic activity also directly activates endothelial cells via PAR-4 cleavage and cleaves fibrinogen/Factor XIII; MBL also promotes phagocytosis by binding calreticulin/CD91 on phagocytes, and common exon-1 mutations at codons 52, 54, and 57 disrupt the collagen-like triple helix, reducing oligomer formation and serum MBL levels with consequent susceptibility to bacterial, viral, and fungal infections."},"narrative":{"teleology":[{"year":1983,"claim":"Identification of MBL as a discrete serum lectin resolved the molecular identity of the mannan-binding opsonic activity in human plasma, establishing its calcium-dependent carbohydrate-binding specificity and oligomeric architecture.","evidence":"Affinity chromatography on mannan-Sepharose with Scatchard binding analysis of human serum","pmids":["6643429"],"confidence":"High","gaps":["Subunit stoichiometry and quaternary structure not determined","Gene encoding the protein not yet cloned"]},{"year":1988,"claim":"cDNA cloning revealed that MBL2 encodes a three-domain protein (N-terminal cysteine-rich, collagen-like, C-terminal CRD) homologous to C-type lectins and expressed as a liver acute-phase reactant, providing the structural framework for understanding oligomer assembly and ligand recognition.","evidence":"cDNA cloning from human liver library with full sequence analysis","pmids":["2450948"],"confidence":"High","gaps":["Genomic structure and chromosomal location unknown","Mechanism of complement activation not yet linked to MBL"]},{"year":1989,"claim":"Two advances established MBL as a functional opsonin and mapped the gene: the MBL2 locus was placed at 10q11.2-q21 with a four-exon structure, and purified MBL was shown to correct a common opsonic defect by promoting C3b deposition in a dose-dependent manner.","evidence":"Genomic cloning with in situ hybridization; in vitro opsonization and C3b deposition reconstitution assay","pmids":["2477486","2573758"],"confidence":"High","gaps":["Genetic basis of the opsonic defect not yet identified","Mechanism linking MBL to complement activation (serine protease partners) unknown"]},{"year":1992,"claim":"Discovery of exon 1 point mutations at codons 54 and 57 (and subsequently codon 52 in 1994) explained MBL deficiency: each substitutes a carboxylic acid for an axial glycine in the collagen-like domain, disrupting triple-helix assembly and lowering serum MBL, with distinct mutations predominating in different ethnic groups.","evidence":"DNA sequencing, family segregation, restriction analysis across Eskimo/Caucasian/African populations, complement activation assays","pmids":["1675710","1304173","8206524"],"confidence":"High","gaps":["Precise structural consequence of each mutation on oligomer assembly not visualized","Promoter contributions to MBL levels only partially characterized"]},{"year":1994,"claim":"Crystal structure of the CRD-neck trimer revealed the coiled-coil neck organizing three CRDs into a fixed spatial array, explaining how MBL achieves avidity for clustered carbohydrate epitopes on microbial surfaces.","evidence":"X-ray crystallography of recombinant neck+CRD fragment in two crystal forms","pmids":["7634089"],"confidence":"High","gaps":["Full-length oligomer structure not determined","Atomic details of carbohydrate-bound CRD not resolved in this study"]},{"year":1997,"claim":"Discovery of MASP-2 as the second MBL-associated serine protease, capable of cleaving C4 and C2, established that the lectin pathway parallels the classical pathway architecture with two distinct proteases, and defined the enzymatic mechanism by which MBL triggers complement.","evidence":"Protein purification and cDNA cloning of MASP-2 with C4/C2 cleavage assays","pmids":["9087411"],"confidence":"High","gaps":["Relative contributions of MASP-1 vs MASP-2 to complement activation in vivo unclear","Stoichiometry and heterogeneity of MBL-MASP complexes not resolved"]},{"year":2001,"claim":"Two findings expanded MBL function beyond complement: MBL was shown to promote macropinocytic engulfment of apoptotic cells via calreticulin/CD91 on phagocytes, and MASP-3 was identified as a preferential partner of larger MBL oligomers that downregulates MASP-2-mediated complement activation, revealing oligomer-specific complex heterogeneity.","evidence":"Co-IP and blocking antibody experiments for calreticulin/CD91 with phagocytosis assays; MASP-3 cloning with oligomer fractionation and C4/C2/C3 cleavage assays","pmids":["11560994","11485744"],"confidence":"High","gaps":["In vivo contribution of calreticulin/CD91 pathway to apoptotic clearance not tested","Regulatory interplay among MASP-1, MASP-2, and MASP-3 in vivo not quantified"]},{"year":2005,"claim":"Demonstration that MBL binds enveloped viruses—HIV-1 gp120 and SARS-CoV—through high-mannose glycans, directly neutralizing infectivity and activating complement, broadened MBL's recognized pathogen spectrum to include viruses and linked MBL2 genotype to susceptibility to emerging infections.","evidence":"Calcium-dependent binding assays, mannan competition, C4 deposition on virions, neutralization assays, DC-SIGN blocking, and case-control genotyping","pmids":["15488604","15838797"],"confidence":"High","gaps":["Whether MBL-mediated viral neutralization is significant in vivo at physiological MBL concentrations remains untested in animal models","Relative contribution of direct neutralization versus complement opsonization not dissected"]},{"year":2004,"claim":"MBL double-knockout mice demonstrated that MBL is essential for in vivo defense against S. aureus (100% lethality in KO vs 45% in WT), directly proving the non-redundant protective role inferred from human deficiency studies.","evidence":"MBL-A/MBL-C double-KO mice with IV and IP S. aureus infection, survival analysis, neutrophil depletion","pmids":["15148336"],"confidence":"High","gaps":["Murine system has two MBL genes; direct extrapolation to single-gene human MBL2 deficiency requires caution","Whether the lethal phenotype reflects complement activation, opsonophagocytosis, or both not fully resolved"]},{"year":2014,"claim":"Identification of MASP-1 as the MBL-MASP complex component that activates endothelial cells via PAR-4 cleavage, combined with its fibrinogen/Factor XIII substrates, established that the MBL pathway intersects coagulation and vascular inflammation beyond canonical complement.","evidence":"Ca²⁺ signaling in HUVECs with recombinant MASP catalytic fragments and stable zymogen mutant; prior enzymatic assays showing fibrinogen and Factor XIII cleavage by MASP-1","pmids":["24472859","12396008"],"confidence":"High","gaps":["In vivo significance of MASP-1-PAR-4 endothelial activation not demonstrated","Whether MBL oligomer composition determines MASP-1 vs MASP-2 signaling outputs in vascular contexts is unknown"]},{"year":2019,"claim":"A non-canonical role for MBL2 in cancer was established: tumor-infiltrating fungi activate MBL, which triggers complement (C3/C3aR) to promote pancreatic ductal adenocarcinoma growth; Mbl2 deletion blocks this tumor-promoting pathway, demonstrating that MBL-mediated complement can be co-opted for oncogenesis.","evidence":"MBL2-KO and C3-KO mice, C3aR knockdown in tumor cells, mycobiome manipulation in slow-progressive and invasive PDA models","pmids":["31578522"],"confidence":"High","gaps":["Whether this mechanism extends to other fungal-colonized tumors is untested","The specific fungal glycan(s) recognized by MBL in the tumor microenvironment are not characterized","Therapeutic targeting of MBL in PDA not explored"]},{"year":null,"claim":"Major unresolved questions include the full-length oligomeric structure of MBL-MASP complexes at atomic resolution, the in vivo balance between protective antimicrobial and deleterious inflammatory/pro-tumorigenic roles of MBL-mediated complement activation, and whether therapeutic MBL replacement can safely correct immunodeficiency without exacerbating complement-driven pathology.","evidence":"Open question from synthesis of timeline","pmids":[],"confidence":"Low","gaps":["No full-length MBL oligomer atomic structure available","No clinical trial data on recombinant MBL replacement in the timeline","Context-dependent switching between protective and pathological MBL functions is mechanistically undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[0,3,14]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[0,7,8,12]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,1,3]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[3,9,12,15,22,29]},{"term_id":"R-HSA-109582","term_label":"Hemostasis","supporting_discovery_ids":[16,26]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[29]}],"complexes":["MBL-MASP-1 complex","MBL-MASP-2 complex","MBL-MASP-3 complex"],"partners":["MASP1","MASP2","SERPING1","CALR","LRP1"],"other_free_text":[]},"mechanistic_narrative":"MBL2 encodes mannose-binding lectin (MBL), a liver-secreted, calcium-dependent C-type lectin that functions as a central pattern-recognition molecule of innate immunity and the initiating component of the lectin complement pathway. The mature protein assembles from ~31 kDa subunits into trimers stabilized by a collagen-like domain and a coiled-coil neck region, which further oligomerize via N-terminal disulfide bonds into ~600 kDa higher-order structures that bind mannosylated glycans on bacteria, fungi, and enveloped viruses (including influenza, HIV-1, and SARS-CoV), triggering complement activation through associated serine proteases MASP-1 and MASP-2 that cleave C4, C2, and downstream components [PMID:6643429, PMID:9087411, PMID:15838797, PMID:10639434]. MBL also promotes phagocytic clearance of apoptotic cells by engaging calreticulin/CD91 on macrophages [PMID:11560994], and MBL-dependent complement activation by tumor-associated fungi drives pancreatic ductal adenocarcinoma progression via C3a/C3aR signaling [PMID:31578522]. Common point mutations at codons 52, 54, and 57 of exon 1 disrupt collagen-like triple-helix formation, reduce serum MBL and complement-activating capacity, and cause an opsonic defect associated with susceptibility to recurrent infections [PMID:1675710, PMID:1304173, PMID:8206524]."},"prefetch_data":{"uniprot":{"accession":"P11226","full_name":"Mannose-binding protein C","aliases":["Collectin-1","MBP1","Mannan-binding protein","Mannose-binding lectin"],"length_aa":248,"mass_kda":26.1,"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:14515269, PubMed:22966085, PubMed:7634089, PubMed:9087411). Specifically recognizes and binds the mannose moiety of carbohydrates on the pathogen surface, activating the MASP1 serine protease and initiating the proteolytic cascade of the lectin complement pathway (PubMed:22966085, PubMed:2573758, PubMed:6643429, PubMed:8082295, PubMed:9087411). Upon SARS coronavirus-2/SARS-CoV-2 infection, activates the complement lectin pathway which leads to the inhibition SARS-CoV-2 infection and a reduction of the induced inflammatory response (PubMed:35102342). May bind DNA (PubMed:15145932)","subcellular_location":"Secreted; Cell surface","url":"https://www.uniprot.org/uniprotkb/P11226/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MBL2","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/MBL2","total_profiled":1310},"omim":[{"mim_id":"614372","title":"MANNOSE-BINDING LECTIN DEFICIENCY; MBLD","url":"https://www.omim.org/entry/614372"},{"mim_id":"613860","title":"FICOLIN 3 DEFICIENCY","url":"https://www.omim.org/entry/613860"},{"mim_id":"613791","title":"MASP2 DEFICIENCY","url":"https://www.omim.org/entry/613791"},{"mim_id":"610424","title":"HEPATITIS B VIRUS, SUSCEPTIBILITY 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MASP-1 and MASP-2 dissociate from MBL upon incubation at 37°C in physiological buffer.\",\n      \"method\": \"Functional complement activation assay, inhibitor studies, complex dissociation experiments\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (functional assay + complex characterization) in single study\",\n      \"pmids\": [\"11257302\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"MASP-1 cleaves fibrinogen (releasing fibrinopeptide B) and activates plasma transglutaminase (Factor XIII), demonstrating that MBL-associated serine proteases have substrates beyond complement proteins. MASP-2 cleaves complement factors C4 and C2.\",\n      \"method\": \"In vitro enzyme activity assays with recombinant and purified native MASP-1 and MASP-2\",\n      \"journal\": \"Immunobiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with purified recombinant proteins\",\n      \"pmids\": [\"12396008\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"MBL (mannose-binding protein/MBP) binds to influenza virus neuraminidase (a 68 kDa viral species) through its lectin domain in a calcium-dependent, saturable, and concentration-dependent manner, inhibiting hemagglutinating activity of the virus.\",\n      \"method\": \"Ligand-blot analysis, binding saturation assays, inhibition of hemagglutination, purification of the 68 kDa species\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct binding assay with protein purification and functional inhibition\",\n      \"pmids\": [\"7998980\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"MBL binds to the high-mannose glycans on HIV-1 gp120, blocking the interaction between HIV and DC-SIGN and mediating complement activation on gp120; neutralization of HIV by MBL is enhanced by drugs that alter carbohydrate processing.\",\n      \"method\": \"Binding assays, neutralization assays, complement activation assays\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — multiple functional assays but synthesis of findings across multiple studies\",\n      \"pmids\": [\"15488604\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"MASP-2 polymorphisms D120G and the CHNHdup insertion prevent association with MBL, abolishing C4 activation; R439H variant binds MBL normally but cannot cleave C4 or autoactivate in the presence of MBL and mannan, indicating its catalytic domain is defective.\",\n      \"method\": \"Recombinant protein production, binding assays (MASP-2 to MBL), C4 cleavage functional assay, autoactivation assay\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in vitro with recombinant variants, multiple functional readouts\",\n      \"pmids\": [\"19234189\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"C1q, MBL, and ficolins share a common mechanism for associating with their respective serine proteases through the N-terminal CUB1-EGF region of the MASPs; however, the C1s-C1r tetramer and the (MASP)2 dimers evolved distinct strategies for association with their partner recognition proteins.\",\n      \"method\": \"Structural and functional analysis, 3D structural data\",\n      \"journal\": \"Immunobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 — structural and functional data but review-level synthesis\",\n      \"pmids\": [\"17544813\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Within native MBL-MASP complexes in serum, MASP-1 activity and MASP-2 activity are inversely correlated when normalized to MBL concentration, indicating that MBL-MASP complexes do not have a fixed MBL-(MASP-1)-(MASP-2) stoichiometry but rather exist as separate MBL-MASP-1 and MBL-MASP-2 populations.\",\n      \"method\": \"Mannan-binding assay for MBL, amidolytic assay for MASP-1 activity, C4 fixation assay for MASP-2 activity in 152 healthy individuals' sera\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional enzyme assays on native complexes with large sample size\",\n      \"pmids\": [\"16102832\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Among MBL-MASP complex components, only MASP-1 activates endothelial cells (HUVECs) via Ca2+ signaling by cleaving protease-activated receptor 4; MASP-2 and MASP-3 catalytic fragments cannot activate HUVECs; non-enzymatic MASP-1 domains and zymogen MASP-1 mutant are also ineffective, demonstrating that proteolytic activity of MASP-1 within MBL-containing complexes is required.\",\n      \"method\": \"Ca2+ signaling assay in HUVECs, recombinant fragment studies, stable zymogen mutant testing\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstitution with recombinant components plus mutagenesis and multiple controls\",\n      \"pmids\": [\"24472859\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Recombinant MBL produced in transfected human cell lines shows the same biological activity (complement activation and opsonization) and essentially identical mass spectrometry profile as plasma-derived MBL, confirming the functional assembly requirements of the oligomeric structure.\",\n      \"method\": \"Recombinant protein production, functional complement activation assay, mass spectrometry\",\n      \"journal\": \"Biochemical Society transactions\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional validation of recombinant protein with MS confirmation\",\n      \"pmids\": [\"12887299\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"MBL gene knockout (MBL A and C double KO) mice are not more susceptible to systemic aspergillosis than wild-type mice; at certain inocula KO mice showed less susceptibility, suggesting MBL may play a detrimental role in systemic aspergillosis.\",\n      \"method\": \"MBL gene knockout mouse model, survival analysis after intravenous Aspergillus fumigatus infection\",\n      \"journal\": \"Immunology letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic KO with defined survival phenotype\",\n      \"pmids\": [\"20064561\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"MBL binds to the inner core heptose region of Yersinia enterocolitica LPS but not to outer core hexasaccharide structures; LPS structures with both O-specific polysaccharide and enterobacterial common antigen prevent MBL binding, demonstrating carbohydrate specificity of MBL for pathogen recognition.\",\n      \"method\": \"Binding assays with defined LPS mutants, sequential truncation analysis\",\n      \"journal\": \"International journal of medical microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic binding assays with defined LPS mutants\",\n      \"pmids\": [\"26188838\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The newly excysted juvenile (NEJ) stage of Fasciola hepatica prevents MBL binding to its surface despite expressing mannosylated proteins; secreted serine protease inhibitors (rFhSrp1 and rFhSrp2) from NEJ inhibit native and recombinant MASPs, blocking C3b and C4b deposition and MAC assembly via the lectin pathway.\",\n      \"method\": \"Immunofluorescence, recombinant protein inhibition assays with native/recombinant MASPs, serum complement deposition assays\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods with recombinant proteins and functional complement assays\",\n      \"pmids\": [\"35007288\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Comprehensive genotyping of MBL2 structural (codon 52, 54, 57) and promoter (-550, -221) polymorphisms shows significant associations with both MBL antigenic levels and functional activity (mannan-binding and C4-deposition assays), and all three functional assays are significantly correlated.\",\n      \"method\": \"PCR-SSP genotyping, double-antibody ELISA, mannan-binding assay, C4-deposition assay in 236 blood donors\",\n      \"journal\": \"Scandinavian journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — three orthogonal functional assays correlated with genotype, large sample\",\n      \"pmids\": [\"12472676\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"MBL2 and ficolin genes (FCN1, FCN2, FCN3) contain common variant alleles in both promoter and structural regions that influence serum protein concentration and stability; these molecules bind sugar structures on microorganisms and dying host cells to initiate lectin complement pathway activation via MASP-1 and MASP-2.\",\n      \"method\": \"Molecular genetics and population studies of MBL2 polymorphisms, complement activation assays\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — review-level synthesis of genetic and functional data\",\n      \"pmids\": [\"19501910\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"MBL polypeptide chains associate in trimers (subunits with collagen-like helix and three clustered lectin domains) that then associate into larger oligomers (typically 12-18 polypeptides); mutations in the collagen-like region decrease MBL assembly and stability. MBL is the only collectin that activates complement; MASP-2 cleaves C4 and C2 upon MBL surface binding.\",\n      \"method\": \"Protein biochemistry, structural analysis, functional complement assays\",\n      \"journal\": \"Biochemical Society transactions\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — well-established structural and biochemical mechanism replicated across multiple labs\",\n      \"pmids\": [\"12887296\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MBL2 encodes mannose-binding lectin (MBL), an oligomeric collectin that binds calcium-dependently to carbohydrate arrays on microbial and apoptotic cell surfaces, recruits MASP-1 and MASP-2 in distinct, non-fixed-stoichiometry complexes, and initiates the lectin complement pathway by MASP-2-mediated cleavage of C4 and C2; additionally, MASP-1 within these complexes cleaves fibrinogen, activates Factor XIII, and directly activates endothelial cells via PAR4 proteolysis, while common MBL2 structural and promoter polymorphisms alter protein oligomerization, stability, and serum concentration to modulate innate immune function.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll classify each paper and extract discoveries only from papers about the canonical MBL2 protein (mannose-binding lectin 2).\n\n**Classification summary:**\n- KEEP: Papers about human/vertebrate mannose-binding lectin (MBL2) and its complement pathway function\n- EXCLUDE: Papers about MBP (myelin basic protein), MBL (monoclonal B-cell lymphocytosis), MBP1 (c-myc promoter binding protein/alpha-enolase), Mbp1 (yeast transcription factor), MBP (maltose-binding protein), monobutyl phthalate (MBP), eosinophil MBP, bleomycin resistance protein, and other alias collisions\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1983,\n      \"finding\": \"MBL2 protein (mannan-binding protein) was isolated from human serum as a glycine-rich lectin of ~600 kDa composed of ~31 kDa subunits, with calcium-dependent, saturable, and reversible binding to mannan distinct from CRP and SAP.\",\n      \"method\": \"Affinity chromatography on Sepharose-mannan, Scatchard plot binding analysis, immunoassay\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct biochemical isolation and binding characterization with quantitative analysis\",\n      \"pmids\": [\"6643429\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1988,\n      \"finding\": \"MBL2 encodes a human serum lectin with three structural domains: an N-terminal cysteine-rich region (interchain disulfide bonds), a collagen-like region (19 Gly-X-Y repeats), and a C-terminal carbohydrate recognition domain; the protein is an acute-phase reactant secreted by the liver and homologous to C-type lectins.\",\n      \"method\": \"cDNA cloning from human liver library, sequence analysis, comparison with rat MBP and other lectins\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — full cDNA cloning and domain structure determination, foundational study\",\n      \"pmids\": [\"2450948\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1989,\n      \"finding\": \"The MBL2 gene is located on chromosome 10q11.2-q21, comprises four exons each encoding a distinct protein domain, and evolved by recombination of an ancestral non-fibrillar collagen gene with a carbohydrate-recognition gene, similar to surfactant SP-A.\",\n      \"method\": \"Genomic cloning, exon structure analysis, chromosomal localization by in situ hybridization\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct genomic structural determination and chromosomal mapping\",\n      \"pmids\": [\"2477486\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1989,\n      \"finding\": \"Low serum MBL levels are directly linked to a common opsonic defect; purified MBL corrects the defect in a dose-dependent manner by promoting C3b deposition on mannan-coated surfaces, establishing MBL as a functional opsonin.\",\n      \"method\": \"In vitro opsonization assay measuring complement C3b deposition on mannan-coated surfaces, immunoassay of serum MBL levels\",\n      \"journal\": \"Lancet\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution experiment showing dose-dependent restoration of opsonic function by purified MBL\",\n      \"pmids\": [\"2573758\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"A point mutation at codon 54 of MBL2 exon 1 (GGC→GAC, Gly→Asp) disrupts the fifth Gly-X-Y repeat of the collagen-like domain, prevents normal triple helix formation, and causes low serum MBL with autosomal dominant co-inheritance of the opsonic defect.\",\n      \"method\": \"DNA sequencing of MBL2 exon 1, family segregation analysis, serum MBL immunoassay\",\n      \"journal\": \"Lancet\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct identification of causal mutation with structural rationale and genetic co-segregation\",\n      \"pmids\": [\"1675710\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"Two independent point mutations in MBL2 exon 1 — codon 54 (GGC→GAC) prevalent in non-Africans and codon 57 (GGA→GAA) prevalent in West Africans — each substitute carboxylic acids for axial glycines, disrupting the collagen-like triple helix and profoundly reducing serum MBL and complement activation capacity.\",\n      \"method\": \"PCR, sequence analysis, restriction analysis of population samples, complement activation assay\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — structural mutations identified with functional complement assay validation across multiple populations\",\n      \"pmids\": [\"1304173\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"A third MBL2 exon 1 point mutation at codon 52 was identified, completing the structural polymorphism; together codons 52, 54, and 57 account for all cases of MBL deficiency across ethnic groups in Hardy-Weinberg equilibrium.\",\n      \"method\": \"PCR-based genotyping, population genetic analysis (Hardy-Weinberg testing) across Eskimo, Caucasian, and African populations\",\n      \"journal\": \"Immunogenetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — comprehensive population-based genetic characterization replicated across multiple ethnic groups\",\n      \"pmids\": [\"8206524\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"The carbohydrate recognition domain (CRD) and 'neck' region of MBL2 form a trimeric structure in solution and crystals; the neck region forms a triple α-helical coiled-coil, and each α-helix contacts a neighboring CRD, defining the spatial arrangement of CRDs for branched oligosaccharide recognition on microorganisms.\",\n      \"method\": \"X-ray crystallography of recombinant neck+CRD peptide in two crystal forms\",\n      \"journal\": \"Nature structural biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure determination in two crystal forms providing atomic-level structural insight\",\n      \"pmids\": [\"7634089\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"MBL2 binds to influenza virus through its lectin domain in a calcium-dependent, saturable, concentration-dependent manner; ligand blot analysis identified the 68 kDa viral neuraminidase as the specific MBL-binding species, and bound MBL inhibits hemagglutinating activity.\",\n      \"method\": \"Saturable binding assay, ligand blot, purification of the 68 kDa MBL-binding viral protein and identification as neuraminidase, hemagglutination inhibition assay\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct identification of viral binding partner by ligand blot and purification, with functional inhibition assay\",\n      \"pmids\": [\"7998980\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"A second MBL-associated serine protease, MASP-2, was identified; MASP-2 associates with MBL oligomers and activates complement via C4 and C2 cleavage, demonstrating that the MBL pathway, like the classical pathway, involves two serine proteases (MASP-1 and MASP-2).\",\n      \"method\": \"Protein purification, cDNA cloning, sequence homology analysis, complement C4 and C2 cleavage assays\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — protein isolation, cloning, and enzymatic characterization; landmark discovery replicated extensively\",\n      \"pmids\": [\"9087411\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Low MBL serum concentrations in African and South American populations are caused by distinct molecular mechanisms: high frequency of the codon 57 (C) variant in Africans versus extremely high frequency of the codon 54 (B) variant in South American natives, with promoter haplotypes further modulating levels.\",\n      \"method\": \"MBL2 genotyping, serum MBL concentration measurement, population allele frequency analysis\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic genotype-phenotype correlation across geographically diverse populations with functional MBL measurement\",\n      \"pmids\": [\"9743385\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Chicken MBL is a single-form serum collectin with structural homology to mammalian MBL; phylogenetic analysis indicates that the gene duplication producing two MBL forms in mammals (MBL1 and MBL2) occurred after the bird-reptile split, supporting the evolutionary origin of the MBL2 locus.\",\n      \"method\": \"RT-PCR, cDNA library screening, sequencing, phylogenetic analysis of deduced amino acid sequences\",\n      \"journal\": \"Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — cloning and phylogenetic analysis; single study establishing avian MBL evolutionary relationship\",\n      \"pmids\": [\"9640255\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"MBL binds to a broad range of clinically relevant pathogens (Candida spp., Aspergillus fumigatus, S. aureus, beta-hemolytic group A streptococci) and bound MBL promotes C4 deposition in a concentration-dependent manner, directly linking pathogen surface recognition to complement activation.\",\n      \"method\": \"Flow cytometry binding assay with purified MBL on pathogen isolates, C4 deposition assay\",\n      \"journal\": \"Infection and immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct binding assay combined with functional complement activation measurement across diverse pathogens\",\n      \"pmids\": [\"10639434\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"MBL-MASP complex activity is controlled by C1 inhibitor (which inhibits both classical and MBL pathways) but not by α2-macroglobulin; C1 inhibitor and α2-macroglobulin both associate with the MBL complex, and MASP-1, MASP-2, and MAp19 dissociate from MBL at 37°C in physiological buffer but not at high ionic strength (1M NaCl), indicating the MBL-MASP interaction is distinct from the C1 complex.\",\n      \"method\": \"Complement activation assay specific for MBL pathway, co-purification/association analysis, inhibitor profiling\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods including functional assays and association analysis with rigorous inhibitor controls\",\n      \"pmids\": [\"11257302\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"MBL2 binds to apoptotic cells and, via ligation of calreticulin (cC1qR) on phagocytes which in turn binds CD91 (α2-macroglobulin receptor), stimulates macropinocytic engulfment of apoptotic cells, identifying a novel receptor-ligand mechanism for MBL-mediated apoptotic cell clearance.\",\n      \"method\": \"Co-IP, calreticulin/CD91 blocking antibodies, macropinocytosis assay, apoptotic cell uptake quantification\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — receptor identification by blocking antibodies and co-IP, mechanistic pathway established with functional phagocytosis readout\",\n      \"pmids\": [\"11560994\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"MASP-3, generated by alternative splicing of the MASP-1/3 gene, associates preferentially with larger MBL oligomers together with MASP-2, and downregulates the C4 and C2 cleaving activity of MASP-2; smaller MBL oligomers preferentially associate with MASP-1, MAp19, and direct C3-cleaving activity, demonstrating that distinct MBL oligomers form functionally different complexes.\",\n      \"method\": \"Protein purification, cDNA cloning, alternative splicing analysis, functional C4/C2/C3 cleavage assays, oligomer fractionation\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — protein isolation, cloning, and biochemical characterization with functional complement activity assays\",\n      \"pmids\": [\"11485744\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"MASP-1, despite initial suggestions, does not efficiently cleave C3 directly at biologically relevant rates; instead, MASP-1 cleaves fibrinogen (releasing fibrinopeptide B) and activates plasma transglutaminase (Factor XIII), indicating MASPs have biologically significant substrates beyond complement components.\",\n      \"method\": \"In vitro cleavage assays with recombinant and purified native MASP-1, fibrinogen cleavage, Factor XIII activation assay\",\n      \"journal\": \"Immunobiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro enzymatic assays with recombinant and native protein; multiple non-complement substrates identified\",\n      \"pmids\": [\"12396008\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"MBL2 genotypes (promoter and structural SNPs at codons 52, 54, 57 and promoter positions -550, -221) show significant correlation with plasma MBL antigen levels and functional MBL activity as measured by both mannan-binding and C4-deposition assays, validating comprehensive genotype-phenotype relationships.\",\n      \"method\": \"PCR-SSP genotyping, double-antibody ELISA for MBL antigen, mannan-binding assay, C4-deposition assay in 236 blood donors\",\n      \"journal\": \"Scandinavian journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — three independent functional assays correlated with genotype in a large cohort\",\n      \"pmids\": [\"12472676\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Recombinant MBL produced in a transfected human cell line shows identical biological activity and MS profile to plasma-derived MBL, demonstrating that the oligomeric structure and function can be reconstituted recombinantly, enabling therapeutic application.\",\n      \"method\": \"Recombinant protein production in human cell line, mass spectrometry, functional activity comparison with plasma-derived MBL\",\n      \"journal\": \"Biochemical Society transactions\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional and structural equivalence demonstrated by MS and bioactivity assay in single study\",\n      \"pmids\": [\"12887299\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"MBL-null mice (lacking both MBL-A and MBL-C) show 100% mortality within 48h of intravenous S. aureus infection compared to 45% mortality in wild-type mice, directly demonstrating that MBL is essential for in vivo host defense against S. aureus; neutrophils and MBL cooperate to limit intraperitoneal infection.\",\n      \"method\": \"MBL-A and MBL-C double gene knockout mice, intravenous and intraperitoneal S. aureus infection models, survival analysis, neutrophil depletion experiments\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean double-KO with specific lethal phenotype and defined cellular cooperation (neutrophils + MBL)\",\n      \"pmids\": [\"15148336\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"MBL binds to HIV-1 gp120 through high-mannose glycans on the envelope protein in a calcium-dependent, strain-independent manner; MBL can directly neutralize HIV produced in T-cell lines, activate complement on gp120, opsonize HIV, and block HIV interaction with DC-SIGN.\",\n      \"method\": \"Binding assays (ELISA, flow cytometry), neutralization assays, complement C4 deposition on gp120, DC-SIGN blocking assay\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal binding and functional assays; replicated across labs\",\n      \"pmids\": [\"15488604\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"MBL serum levels vary widely due to MBL2 polymorphisms, and genetically determined differences in complement activation via MBL may play a role in diabetic micro- and macrovascular complications, with complement activation following ischemia-reperfusion as a proposed mechanism.\",\n      \"method\": \"Review of functional MBL complement activation data and clinical association studies\",\n      \"journal\": \"Hormone and metabolic research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 — mechanistic proposal based on existing functional data; no direct experimental validation in this paper\",\n      \"pmids\": [\"15918118\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"MBL binds to SARS-CoV in a dose-dependent, calcium-dependent, and mannan-inhibitable manner (confirming binding through the CRDs), enhances complement C4 deposition on SARS-CoV, and inhibits viral infectivity in FRhK-4 cells; lower MBL levels/haplotypes associated with SARS acquisition.\",\n      \"method\": \"In vitro binding assay, mannan competition, C4 deposition on SARS-CoV, infectivity inhibition assay in cell culture, case-control genotyping\",\n      \"journal\": \"The Journal of infectious diseases\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct virus binding with mechanistic controls (calcium-dependence, mannan inhibition), complement activation, and infectivity assay\",\n      \"pmids\": [\"15838797\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"C1r/C1s and MASP-1/MASP-2 associate through a common mechanism involving their N-terminal CUB1-EGF region, but the C1s-C1r-C1r-C1s tetramer and (MASP)₂ dimers have evolved distinct strategies to associate with their recognition proteins (C1q vs. MBL/ficolins), establishing the structural basis for MBL-MASP complex assembly.\",\n      \"method\": \"Structural analysis (crystallography), functional domain mapping, comparison of C1 and MBL-MASP complexes\",\n      \"journal\": \"Immunobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — structural data from crystallography but review/comparison article; structural basis described\",\n      \"pmids\": [\"17544813\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"MASP-2 polymorphisms D120G and CHNHdup abolish binding to MBL (preventing complement C4 cleavage), while R439H binds MBL normally but cannot autoactivate or cleave C4, identifying distinct molecular defects in MASP-2 function; the R439H variant is common in Sub-Saharan Africans (10% gene frequency).\",\n      \"method\": \"Recombinant MASP-2 production for each naturally occurring variant, MBL-binding assay, C4 cleavage assay, autoactivation assay\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — recombinant protein biochemistry with multiple orthogonal assays distinguishing binding vs. catalytic defects\",\n      \"pmids\": [\"19234189\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"In MBL-KO mice, MBL deficiency is protective (not detrimental) in experimental systemic aspergillosis: KO mice were less susceptible to lethal infection than wild-type at certain inocula, suggesting MBL plays a deleterious role in systemic aspergillosis, possibly through excessive complement-mediated inflammation.\",\n      \"method\": \"MBL-A and MBL-C double gene knockout mice, intravenous Aspergillus fumigatus infection model, dose-response survival analysis\",\n      \"journal\": \"Immunology letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with specific survival phenotype, single study without mechanistic pathway placement\",\n      \"pmids\": [\"20064561\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Among MBL-MASP complexes, only MASP-1 (not MASP-2, MASP-3, or non-enzymatic MASP domains) activates endothelial cells (Ca²⁺ signaling in HUVECs) when present in the serum MBL-MASP complex; this activation requires MASP-1's proteolytic activity (zymogen mutant is inactive) and occurs via cleavage of protease-activated receptor 4 (PAR-4).\",\n      \"method\": \"Ca²⁺ signaling assay in HUVECs, recombinant MASP catalytic fragments, stable zymogen MASP-1 mutant, serum-derived MBL-MASP complexes\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple recombinant fragments, zymogen mutant control, specific receptor (PAR-4) identified previously; mechanistic assignment to MASP-1 proteolytic activity\",\n      \"pmids\": [\"24472859\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"MBL-MASP complexes are heterogeneous in serum; MASP-1 activity per unit MBL is inversely correlated with MASP-2 activity per unit MBL across individuals, consistent with separate populations of MBL-MASP-1 and MBL-MASP-2 complexes rather than fixed stoichiometric MBL-(MASP-1)-(MASP-2) trimolecular complexes.\",\n      \"method\": \"Mannan-plate capture of MBL from 152 individual sera, ELISA for MBL, amidolytic assay for MASP-1, C4-fixation assay for MASP-2; correlation analysis\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — large population-level functional assay revealing complex heterogeneity; indirect inference of complex composition\",\n      \"pmids\": [\"16102832\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Fasciola hepatica newly excysted juveniles (NEJ) resist MBL-mediated complement killing by two mechanisms: (1) MBL does not bind to the NEJ surface despite mannosylated surface proteins, and (2) secreted NEJ serpins (rFhSrp1, rFhSrp2) directly inhibit MASP-1 and MASP-2, preventing C3b and C4b deposition.\",\n      \"method\": \"In vitro MBL binding assay on live NEJ, recombinant serpin production, MASP-1 and MASP-2 inhibition assays, immunofluorescence for MBL/C3b/C4b/MAC deposition on NEJ in human serum\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — recombinant inhibitors tested against purified native and recombinant MASPs, combined with immunofluorescence validation\",\n      \"pmids\": [\"35007288\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Fungi (especially Malassezia spp.) that migrate into pancreatic ductal adenocarcinoma (PDA) tumors activate MBL2 through binding to fungal wall glycans, triggering complement cascade activation (C3); deletion of MBL2 or C3, or knockdown of C3aR in tumor cells, protects against tumor growth, and reprogramming the mycobiome does not alter PDA progression in Mbl2-deficient mice, establishing MBL2-mediated complement as required for fungus-driven oncogenesis.\",\n      \"method\": \"MBL2 and C3 knockout mice, C3aR knockdown in tumor cells, mycobiome ablation/repopulation experiments, tumor growth assays in slow-progressive and invasive PDA mouse models\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic deletion models with specific tumor growth phenotype; epistasis (Mbl2-KO blocks effect of mycobiome repopulation) establishes pathway position\",\n      \"pmids\": [\"31578522\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MBL2 encodes mannose-binding lectin (MBL), a liver-secreted, calcium-dependent C-type lectin that assembles as oligomers of trimeric subunits (neck coiled-coil + CRD) via a collagen-like domain; it recognizes high-mannose and other carbohydrate arrays on microorganisms, apoptotic cells, and tumor-associated fungi, then activates the lectin complement pathway through associated serine proteases MASP-1 and MASP-2 (which form distinct, heterogeneous complexes with MBL oligomers), leading to C4/C2/C3 cleavage and MAC formation, while MASP-1's proteolytic activity also directly activates endothelial cells via PAR-4 cleavage and cleaves fibrinogen/Factor XIII; MBL also promotes phagocytosis by binding calreticulin/CD91 on phagocytes, and common exon-1 mutations at codons 52, 54, and 57 disrupt the collagen-like triple helix, reducing oligomer formation and serum MBL levels with consequent susceptibility to bacterial, viral, and fungal infections.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"MBL2 encodes mannose-binding lectin (MBL), a soluble oligomeric collectin of the innate immune system that recognizes carbohydrate arrays on microbial surfaces and dying host cells to initiate the lectin complement pathway. MBL binds calcium-dependently to mannose and related sugars on pathogens — including influenza neuraminidase, HIV-1 gp120, and bacterial LPS inner core heptose — and recruits MBL-associated serine proteases (MASP-1 and MASP-2) as distinct, non-fixed-stoichiometry complexes; MASP-2 cleaves C4 and C2 to propagate complement activation, while MASP-1 cleaves fibrinogen, activates Factor XIII, and activates endothelial cells via PAR4 proteolysis [PMID:9777416, PMID:12396008, PMID:24472859, PMID:16102832]. MBL polypeptide chains assemble into collagen-like trimers that further oligomerize into higher-order structures (typically 12–18 chains), and common MBL2 structural variants (codons 52, 54, 57) and promoter polymorphisms (−550, −221) disrupt oligomerization, reduce protein stability, and lower serum concentration, thereby modulating complement function [PMID:12887296, PMID:12472676]. Pathogens exploit this pathway: Fasciola hepatica secretes serine protease inhibitors that block MASP activity and prevent lectin pathway-mediated complement deposition [PMID:35007288].\",\n  \"teleology\": [\n    {\n      \"year\": 1994,\n      \"claim\": \"Establishing that MBL directly engages viral surface glycoproteins resolved how a soluble lectin could neutralize enveloped viruses, showing calcium-dependent, saturable binding to influenza neuraminidase that inhibits hemagglutination.\",\n      \"evidence\": \"Ligand-blot and binding saturation assays with purified influenza neuraminidase\",\n      \"pmids\": [\"7998980\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Binding affinity for other viral glycoproteins not determined\", \"Downstream complement activation on viral surfaces not tested\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Defining the core biochemistry of the lectin complement pathway established that MBL activates complement by recruiting MASP-1 and MASP-2, which cleave C4 and C2, providing a mechanistic framework parallel to but distinct from the classical pathway.\",\n      \"evidence\": \"Biochemical complement activation assays with purified MBL-MASP complexes\",\n      \"pmids\": [\"9777416\", \"12887296\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contributions of MASP-1 versus MASP-2 to pathway initiation not yet dissected\", \"Structural basis of MBL-MASP interaction not resolved\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Identifying C1 inhibitor as a regulator of the MBL complex and showing MASP dissociation at 37°C revealed that lectin pathway activation is actively controlled, distinguishing it from unregulated pattern recognition.\",\n      \"evidence\": \"Functional complement activation assays with purified inhibitors and temperature-dependent dissociation experiments\",\n      \"pmids\": [\"11257302\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo kinetics of MBL-MASP dissociation unknown\", \"Other physiological regulators not systematically surveyed\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Demonstrating that MASP-1 cleaves fibrinogen and activates Factor XIII expanded the functional scope of MBL complexes beyond complement, linking innate pattern recognition to coagulation and cross-linking pathways.\",\n      \"evidence\": \"In vitro enzyme activity assays with purified recombinant MASP-1 and MASP-2\",\n      \"pmids\": [\"12396008\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological relevance of MASP-1 coagulation activity in vivo not demonstrated\", \"Substrate specificity of MASP-1 beyond fibrinogen and FXIII not mapped\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Systematic genotype–phenotype correlation of MBL2 structural and promoter polymorphisms quantified how common variants control serum MBL concentration and functional activity, establishing the genetic basis of MBL deficiency.\",\n      \"evidence\": \"PCR-SSP genotyping correlated with ELISA, mannan-binding, and C4-deposition assays in 236 donors\",\n      \"pmids\": [\"12472676\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism by which collagen-region mutations impair oligomerization not structurally resolved\", \"Effect of compound heterozygosity on complex assembly not characterized\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Showing that MBL-MASP-1 and MBL-MASP-2 exist as separate populations with inversely correlated activities resolved the question of complex stoichiometry, indicating that individual MBL oligomers preferentially carry one MASP type.\",\n      \"evidence\": \"Amidolytic and C4-fixation assays on native serum complexes from 152 healthy individuals\",\n      \"pmids\": [\"16102832\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether MBL-MASP-1 and MBL-MASP-2 complexes have distinct biological functions in vivo remains unclear\", \"Structural determinants of preferential MASP binding not identified\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"MBL binding to high-mannose glycans on HIV-1 gp120, blocking DC-SIGN interaction and activating complement, demonstrated a direct antiviral effector mechanism and suggested therapeutic potential of carbohydrate-processing drugs.\",\n      \"evidence\": \"Binding, neutralization, and complement activation assays with HIV-1 gp120\",\n      \"pmids\": [\"15488604\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo relevance to HIV infection susceptibility not established by this study\", \"Whether MBL-mediated neutralization is strain-dependent not fully explored\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Structural analysis revealing that MBL, C1q, and ficolins share a common CUB1-EGF-based MASP association mechanism established a unifying model for lectin and classical pathway initiation, while highlighting divergent tetramer/dimer architectures.\",\n      \"evidence\": \"3D structural and functional analysis of MASP N-terminal domains\",\n      \"pmids\": [\"17544813\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Full atomic-resolution structure of intact MBL-MASP complex not available\", \"How oligomeric state of MBL influences MASP dimer binding geometry unknown\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Functional characterization of MASP-2 variants (D120G, CHNHdup, R439H) showed that both MASP-2 binding to MBL and catalytic competence are independently required for lectin pathway activation, dissecting the molecular requirements for pathway function.\",\n      \"evidence\": \"Recombinant MASP-2 variants tested for MBL binding, C4 cleavage, and autoactivation\",\n      \"pmids\": [\"19234189\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Prevalence and clinical impact of these MASP-2 variants in MBL-deficient populations not determined\", \"Whether MASP-1 can partially compensate for MASP-2 loss not tested\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identifying MASP-1 as the sole MBL-complex component that activates endothelial cells via PAR4 cleavage established a complement-independent pro-inflammatory effector function for MBL-MASP complexes.\",\n      \"evidence\": \"Ca2+ signaling assays in HUVECs with recombinant MASP catalytic fragments, zymogen mutants, and non-enzymatic domains\",\n      \"pmids\": [\"24472859\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream signaling consequences of PAR4 activation by MASP-1 in endothelial cells not fully mapped\", \"In vivo relevance of MBL-MASP-1-mediated endothelial activation not demonstrated\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defining that MBL binds specifically to inner core heptose of Yersinia LPS, while O-antigen and enterobacterial common antigen shield this epitope, revealed the structural logic of pathogen immune evasion of lectin pathway recognition.\",\n      \"evidence\": \"Binding assays with sequential LPS truncation mutants of Yersinia enterocolitica\",\n      \"pmids\": [\"26188838\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether this shielding mechanism is generalizable across Gram-negative species not tested\", \"Affinity measurements for individual LPS structures not reported\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstrating that Fasciola hepatica NEJ secretes serine protease inhibitors that block MASPs and prevent lectin pathway complement deposition revealed a parasite immune evasion strategy targeting the MBL-MASP axis.\",\n      \"evidence\": \"Recombinant FhSrp1/Srp2 inhibition assays with native and recombinant MASPs, serum complement deposition assays, immunofluorescence\",\n      \"pmids\": [\"35007288\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether similar MASP-targeting evasion is used by other helminths unknown\", \"Structural basis of Srp-MASP inhibition not resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A high-resolution structure of the intact MBL-MASP complex and in vivo dissection of MASP-1's complement-independent roles (coagulation, endothelial activation) remain outstanding questions for understanding the full physiological impact of MBL2.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No full atomic structure of oligomeric MBL bound to MASP dimers\", \"In vivo significance of MASP-1 coagulation and endothelial activation functions not established\", \"Whether MBL deficiency is protective or detrimental in specific infectious contexts remains context-dependent\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0, 3, 4, 11]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 3, 11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 1, 7, 9, 15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 1, 5, 12, 13, 15]},\n      {\"term_id\": \"R-HSA-109582\", \"supporting_discovery_ids\": [2, 8]}\n    ],\n    \"complexes\": [\n      \"MBL-MASP-1 complex\",\n      \"MBL-MASP-2 complex\",\n      \"MBL-MASP-MAp19 complex\"\n    ],\n    \"partners\": [\n      \"MASP1\",\n      \"MASP2\",\n      \"MAp19\",\n      \"C4\",\n      \"SERPING1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"MBL2 encodes mannose-binding lectin (MBL), a liver-secreted, calcium-dependent C-type lectin that functions as a central pattern-recognition molecule of innate immunity and the initiating component of the lectin complement pathway. The mature protein assembles from ~31 kDa subunits into trimers stabilized by a collagen-like domain and a coiled-coil neck region, which further oligomerize via N-terminal disulfide bonds into ~600 kDa higher-order structures that bind mannosylated glycans on bacteria, fungi, and enveloped viruses (including influenza, HIV-1, and SARS-CoV), triggering complement activation through associated serine proteases MASP-1 and MASP-2 that cleave C4, C2, and downstream components [PMID:6643429, PMID:9087411, PMID:15838797, PMID:10639434]. MBL also promotes phagocytic clearance of apoptotic cells by engaging calreticulin/CD91 on macrophages [PMID:11560994], and MBL-dependent complement activation by tumor-associated fungi drives pancreatic ductal adenocarcinoma progression via C3a/C3aR signaling [PMID:31578522]. Common point mutations at codons 52, 54, and 57 of exon 1 disrupt collagen-like triple-helix formation, reduce serum MBL and complement-activating capacity, and cause an opsonic defect associated with susceptibility to recurrent infections [PMID:1675710, PMID:1304173, PMID:8206524].\",\n  \"teleology\": [\n    {\n      \"year\": 1983,\n      \"claim\": \"Identification of MBL as a discrete serum lectin resolved the molecular identity of the mannan-binding opsonic activity in human plasma, establishing its calcium-dependent carbohydrate-binding specificity and oligomeric architecture.\",\n      \"evidence\": \"Affinity chromatography on mannan-Sepharose with Scatchard binding analysis of human serum\",\n      \"pmids\": [\"6643429\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Subunit stoichiometry and quaternary structure not determined\", \"Gene encoding the protein not yet cloned\"]\n    },\n    {\n      \"year\": 1988,\n      \"claim\": \"cDNA cloning revealed that MBL2 encodes a three-domain protein (N-terminal cysteine-rich, collagen-like, C-terminal CRD) homologous to C-type lectins and expressed as a liver acute-phase reactant, providing the structural framework for understanding oligomer assembly and ligand recognition.\",\n      \"evidence\": \"cDNA cloning from human liver library with full sequence analysis\",\n      \"pmids\": [\"2450948\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Genomic structure and chromosomal location unknown\", \"Mechanism of complement activation not yet linked to MBL\"]\n    },\n    {\n      \"year\": 1989,\n      \"claim\": \"Two advances established MBL as a functional opsonin and mapped the gene: the MBL2 locus was placed at 10q11.2-q21 with a four-exon structure, and purified MBL was shown to correct a common opsonic defect by promoting C3b deposition in a dose-dependent manner.\",\n      \"evidence\": \"Genomic cloning with in situ hybridization; in vitro opsonization and C3b deposition reconstitution assay\",\n      \"pmids\": [\"2477486\", \"2573758\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Genetic basis of the opsonic defect not yet identified\", \"Mechanism linking MBL to complement activation (serine protease partners) unknown\"]\n    },\n    {\n      \"year\": 1992,\n      \"claim\": \"Discovery of exon 1 point mutations at codons 54 and 57 (and subsequently codon 52 in 1994) explained MBL deficiency: each substitutes a carboxylic acid for an axial glycine in the collagen-like domain, disrupting triple-helix assembly and lowering serum MBL, with distinct mutations predominating in different ethnic groups.\",\n      \"evidence\": \"DNA sequencing, family segregation, restriction analysis across Eskimo/Caucasian/African populations, complement activation assays\",\n      \"pmids\": [\"1675710\", \"1304173\", \"8206524\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise structural consequence of each mutation on oligomer assembly not visualized\", \"Promoter contributions to MBL levels only partially characterized\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Crystal structure of the CRD-neck trimer revealed the coiled-coil neck organizing three CRDs into a fixed spatial array, explaining how MBL achieves avidity for clustered carbohydrate epitopes on microbial surfaces.\",\n      \"evidence\": \"X-ray crystallography of recombinant neck+CRD fragment in two crystal forms\",\n      \"pmids\": [\"7634089\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length oligomer structure not determined\", \"Atomic details of carbohydrate-bound CRD not resolved in this study\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Discovery of MASP-2 as the second MBL-associated serine protease, capable of cleaving C4 and C2, established that the lectin pathway parallels the classical pathway architecture with two distinct proteases, and defined the enzymatic mechanism by which MBL triggers complement.\",\n      \"evidence\": \"Protein purification and cDNA cloning of MASP-2 with C4/C2 cleavage assays\",\n      \"pmids\": [\"9087411\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contributions of MASP-1 vs MASP-2 to complement activation in vivo unclear\", \"Stoichiometry and heterogeneity of MBL-MASP complexes not resolved\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Two findings expanded MBL function beyond complement: MBL was shown to promote macropinocytic engulfment of apoptotic cells via calreticulin/CD91 on phagocytes, and MASP-3 was identified as a preferential partner of larger MBL oligomers that downregulates MASP-2-mediated complement activation, revealing oligomer-specific complex heterogeneity.\",\n      \"evidence\": \"Co-IP and blocking antibody experiments for calreticulin/CD91 with phagocytosis assays; MASP-3 cloning with oligomer fractionation and C4/C2/C3 cleavage assays\",\n      \"pmids\": [\"11560994\", \"11485744\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo contribution of calreticulin/CD91 pathway to apoptotic clearance not tested\", \"Regulatory interplay among MASP-1, MASP-2, and MASP-3 in vivo not quantified\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Demonstration that MBL binds enveloped viruses—HIV-1 gp120 and SARS-CoV—through high-mannose glycans, directly neutralizing infectivity and activating complement, broadened MBL's recognized pathogen spectrum to include viruses and linked MBL2 genotype to susceptibility to emerging infections.\",\n      \"evidence\": \"Calcium-dependent binding assays, mannan competition, C4 deposition on virions, neutralization assays, DC-SIGN blocking, and case-control genotyping\",\n      \"pmids\": [\"15488604\", \"15838797\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether MBL-mediated viral neutralization is significant in vivo at physiological MBL concentrations remains untested in animal models\", \"Relative contribution of direct neutralization versus complement opsonization not dissected\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"MBL double-knockout mice demonstrated that MBL is essential for in vivo defense against S. aureus (100% lethality in KO vs 45% in WT), directly proving the non-redundant protective role inferred from human deficiency studies.\",\n      \"evidence\": \"MBL-A/MBL-C double-KO mice with IV and IP S. aureus infection, survival analysis, neutrophil depletion\",\n      \"pmids\": [\"15148336\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Murine system has two MBL genes; direct extrapolation to single-gene human MBL2 deficiency requires caution\", \"Whether the lethal phenotype reflects complement activation, opsonophagocytosis, or both not fully resolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identification of MASP-1 as the MBL-MASP complex component that activates endothelial cells via PAR-4 cleavage, combined with its fibrinogen/Factor XIII substrates, established that the MBL pathway intersects coagulation and vascular inflammation beyond canonical complement.\",\n      \"evidence\": \"Ca²⁺ signaling in HUVECs with recombinant MASP catalytic fragments and stable zymogen mutant; prior enzymatic assays showing fibrinogen and Factor XIII cleavage by MASP-1\",\n      \"pmids\": [\"24472859\", \"12396008\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo significance of MASP-1-PAR-4 endothelial activation not demonstrated\", \"Whether MBL oligomer composition determines MASP-1 vs MASP-2 signaling outputs in vascular contexts is unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"A non-canonical role for MBL2 in cancer was established: tumor-infiltrating fungi activate MBL, which triggers complement (C3/C3aR) to promote pancreatic ductal adenocarcinoma growth; Mbl2 deletion blocks this tumor-promoting pathway, demonstrating that MBL-mediated complement can be co-opted for oncogenesis.\",\n      \"evidence\": \"MBL2-KO and C3-KO mice, C3aR knockdown in tumor cells, mycobiome manipulation in slow-progressive and invasive PDA models\",\n      \"pmids\": [\"31578522\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this mechanism extends to other fungal-colonized tumors is untested\", \"The specific fungal glycan(s) recognized by MBL in the tumor microenvironment are not characterized\", \"Therapeutic targeting of MBL in PDA not explored\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major unresolved questions include the full-length oligomeric structure of MBL-MASP complexes at atomic resolution, the in vivo balance between protective antimicrobial and deleterious inflammatory/pro-tumorigenic roles of MBL-mediated complement activation, and whether therapeutic MBL replacement can safely correct immunodeficiency without exacerbating complement-driven pathology.\",\n      \"evidence\": \"Open question from synthesis of timeline\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No full-length MBL oligomer atomic structure available\", \"No clinical trial data on recombinant MBL replacement in the timeline\", \"Context-dependent switching between protective and pathological MBL functions is mechanistically undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 3, 14]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0, 7, 8, 12]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 1, 3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [3, 9, 12, 15, 22, 29]},\n      {\"term_id\": \"R-HSA-109582\", \"supporting_discovery_ids\": [16, 26]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [29]}\n    ],\n    \"complexes\": [\n      \"MBL-MASP-1 complex\",\n      \"MBL-MASP-2 complex\",\n      \"MBL-MASP-3 complex\"\n    ],\n    \"partners\": [\n      \"MASP1\",\n      \"MASP2\",\n      \"SERPING1\",\n      \"CALR\",\n      \"LRP1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}