{"gene":"CFHR1","run_date":"2026-06-09T22:57:18","timeline":{"discoveries":[{"year":2009,"finding":"CFHR1 (FHR-1) inhibits complement C5 convertase activity and blocks C5b surface deposition and MAC (membrane attack complex) formation. This activity is distinct from complement factor H (CFH), which regulates the C3 convertase. Both proteins bind to the same or similar sites at cellular surfaces, suggesting sequential and partially competitive roles in complement regulation.","method":"In vitro functional assays (C5 convertase activity assays, MAC deposition assays, cell surface binding experiments)","journal":"Blood","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct in vitro enzymatic/functional assays with defined readouts; single lab but multiple orthogonal functional methods","pmids":["19528535"],"is_preprint":false},{"year":2009,"finding":"A novel CFHR1 polymorphism (CFHR1*B), arising from gene conversion between CFH and CFHR1, associates with aHUS susceptibility. Patients with aHUS lacking CFHR1 (but not CFHR3) present anti-factor H autoantibodies, indicating CFHR1 deficiency specifically drives anti-FH autoantibody generation. The CFHR1*B allotype, with greater sequence similarity to FH, may compete with FH and reduce protection of cellular surfaces.","method":"Proteomics strategy (2D-PAGE/MS), sequencing of CFHR1 genomic DNA, functional inference from allotype characterization","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — proteomics plus sequencing in patient cohorts; mechanistic competition model is inferred rather than directly reconstituted","pmids":["19745068"],"is_preprint":false},{"year":2010,"finding":"CFHR1 binds to Group A streptococcal collagen-like protein Scl1 via its conserved C-terminal short consensus repeats SCR3-5. Binding of CFHR1 to Scl1 interferes with Factor H-mediated C3 convertase regulation (competitive inhibition), while maintaining terminal complement complex inhibition by CFHR1 at the C5 convertase level. This interaction enables streptococci to evade complement via two distinct surface protein classes.","method":"Binding assays (pulldown/ELISA), functional hemolysis/complement regulation assays, domain mutagenesis (ionic strength and heparin competition), bacterial surface binding experiments","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct binding assays with domain mapping, mutagenesis, and functional complement regulation readouts in a single rigorous study","pmids":["20855886"],"is_preprint":false},{"year":2012,"finding":"CFHR1 (FHR-1) is acquired on Leptospira surfaces via binding to leptospiral immunoglobulin-like (Lig) proteins, facilitating complement evasion. CFHR1 was shown to bind to Lig proteins from human serum alongside FH, FHL-1, and C4BP.","method":"Co-incubation binding assays, competition assays, serum-based complement evasion experiments","journal":"The Journal of Infectious Diseases","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — pulldown/binding assays with competition experiments, replicated across multiple complement regulators but single lab","pmids":["22291192"],"is_preprint":false},{"year":2013,"finding":"A C3 glomerulopathy-associated mutation in CFHR1 causes duplication of the N-terminal SCRs (conserved in FHR2 and FHR5), resulting in unusually large multimeric FHR complexes. Native FHR1, FHR2, and FHR5 circulate as homo- and hetero-oligomeric complexes mediated by the conserved N-terminal domain. Mutant FHR1 shows increased avidity for C3b, iC3b, and C3dg and enhanced competition with FH in SPR and hemolytic assays.","method":"Plasma protein characterization, surface plasmon resonance (SPR), hemolytic assays, size-exclusion chromatography/native PAGE, genomic sequencing","journal":"The Journal of Clinical Investigation","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal methods including SPR, functional hemolytic assays, and biochemical oligomerization studies; disease mutation provides natural mechanistic probe","pmids":["23728178"],"is_preprint":false},{"year":2016,"finding":"CFHR1 binds to complement components C3b and C3d via a single shared interface identical to that of the two C-terminal domains (SCR19-20) of CFH. CFHR1 dimerization is required for effective binding to C3b and C3d and for competition with CFH. CFHR1 also competes with complement factor H-like protein 1 (CFHL-1/FHL-1) for C3b binding, sterically blocking the N-terminal CFH interaction required for CFH-mediated regulation.","method":"Site-directed mutagenesis, ELISA-based binding assays, functional complement assays","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1 / Moderate — site-directed mutagenesis combined with ELISA-based binding and functional assays; multiple orthogonal approaches in one study","pmids":["27814381"],"is_preprint":false},{"year":2017,"finding":"FHR-1 binds strongly to monomeric CRP (but not native pentameric CRP) via its C-terminal domains. FHR-1/CRP interactions increased complement activation via both classical and alternative pathways on surfaces such as extracellular matrix and necrotic cells. FHR-1 did not inhibit FH-mediated regulation of solid-phase C3 convertase or terminal complement complex formation induced by zymosan; instead, by binding C3b, FHR-1 allowed C3 convertase formation and enhanced complement activation.","method":"ELISA-based binding assays, complement activation assays (classical and alternative pathway), C3 convertase formation assays, competition binding assays","journal":"Journal of Immunology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multiple functional assays with defined readouts; reconstitution of complement activation on defined surfaces; single lab with orthogonal methods","pmids":["28533443"],"is_preprint":false},{"year":2017,"finding":"FHR-1 circulates in human plasma as homodimers and as FHR-1/FHR-2 heterodimers. FHR-1, FHR-2, and FHR-5 homodimerize and FHR-1/FHR-2 heterodimers form, with monomer exchange occurring rapidly as shown by FRET. In individuals with homozygous CFHR1 deletions, FHR-1 homo- and heterodimers are absent.","method":"FRET, ELISA with specific antibodies, serum analysis from CFHR1-deletion individuals","journal":"Frontiers in Immunology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — FRET-based dimerization analysis, confirmed ex vivo in deletion individuals; multiple orthogonal methods in one study","pmids":["29093712"],"is_preprint":false},{"year":2018,"finding":"FHR-1 competes with Factor H for binding to Plasmodium falciparum surfaces (intraerythrocytic schizonts and free merozoites). In FHR-1-deficient human serum, FH binding to parasite surfaces is increased; addition of recombinant FHR-1 decreases FH binding, impairs C3b inactivation, and reduces parasite viability.","method":"FHR-1-deficient human serum experiments, recombinant FHR-1 add-back, parasite viability assays, binding competition assays","journal":"Journal of Immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal loss-of-function and add-back with defined functional readout; single lab","pmids":["30455399"],"is_preprint":false},{"year":2019,"finding":"FHR1 selectively binds to necrotic cells via its N-terminus. FHR1 (but not FH, FHR2, or FHR3) strongly induces NLRP3 inflammasome activation in blood-derived human monocytes, leading to secretion of IL-1β, TNFα, IL-18, and IL-6. This FHR1-mediated inflammasome activation occurs via the phospholipase C pathway through the G-protein coupled receptor EMR2, independent of complement. FHR1 also binds near necrotic glomerular sites in AAV patients and necrotic areas in atherosclerotic plaques.","method":"In vitro monocyte stimulation assays, NLRP3 inflammasome activation (IL-1β secretion), receptor identification (EMR2), signaling pathway inhibitor experiments, immunohistochemistry on patient tissue, in vitro necrotic cell binding assays","journal":"Nature Communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal methods including specific receptor identification, pathway inhibition, cell-based functional assays, and patient tissue validation","pmids":["31273197"],"is_preprint":false},{"year":2020,"finding":"FHR-1 and FHR-5 bind to both plasmid DNA and human genomic DNA, and inhibit FH-DNA interaction by competing with FH binding. The FHR-1 cofactor activity inhibition was due to reduced FH binding to DNA. Both FHRs cause increased complement activation on DNA. FHR-1 and FHR-5 bind to late apoptotic and necrotic cells and recruit monomeric CRP and pentraxin 3; FHR-pentraxin interactions promote enhanced activation of both classical and alternative complement pathways on dead cells.","method":"ELISA-based binding assays, cofactor activity assays, complement activation assays on DNA and dead cell surfaces, competition binding experiments","journal":"Frontiers in Immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal functional assays; single lab","pmids":["32765490"],"is_preprint":false},{"year":2020,"finding":"In a Cfhr1 knockout mouse model, murine FHR-1 homolog (FHR-E) deficiency enhanced LPS-induced alternative complement pathway (AP) activation both in vitro and in vivo, and knockout mice exhibited more severe sepsis and acute kidney injury. This establishes that FHR-E/FHR-1 regulates AP activation in vivo in the context of infection.","method":"Cfhr1 knockout mouse generation, LPS-induced sepsis model, complement activation measurements, in vitro complement assays","journal":"Frontiers in Immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — defined knockout mouse model with in vivo and in vitro complement activation readouts; single lab","pmids":["32636836"],"is_preprint":false},{"year":2021,"finding":"FHR-1 lacks the capacity to bind sialic acids (unlike FH), which prevents C3b-binding competition between FH and FHR-1 at host-cell surfaces under normal circumstances. aHUS-associated FHR-1 mutants are pathogenic because they acquire sialic acid-binding capacity, increasing FHR-1 avidity for surface-bound C3-activated fragments and enabling C3b-binding competition with FH. FHR-1 also binds to native C3 (in addition to C3b, iC3b, C3dg), and surface-bound FHR-1 promotes complement activation by attracting native C3 to the cell surface.","method":"Biochemical assays, NMR spectroscopy, computational/homology modeling, mutagenesis of FHR-1, sialic acid binding experiments, complement activation assays","journal":"Blood","confidence":"High","confidence_rationale":"Tier 1 / Strong — NMR structural validation combined with mutagenesis and biochemical functional assays; disease-associated mutants provide direct mechanistic insight","pmids":["33651882"],"is_preprint":false},{"year":2021,"finding":"FHR1 is deposited in atherosclerotic plaques and circulates on extracellular vesicles. Surface-bound FHR-1 induces expression of pro-inflammatory cytokines and tissue factor in monocytes and neutrophils.","method":"Isolation of FHR-1 from human plasma, immunohistochemistry of plaques, monocyte/neutrophil stimulation assays, cytokine measurement","journal":"Scientific Reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — purified protein stimulation of primary immune cells with cytokine readout; single lab, multiple cell types","pmids":["34795372"],"is_preprint":false},{"year":2022,"finding":"FHR1 binds to extracellular matrix (ECM) proteins laminin, fibromodulin, osteoadherin, and PRELP through its C-terminal CCP domains 4-5. FHR1 competitively inhibits FH binding to these ECM proteins in a dose-dependent manner, reduces FH cofactor activity, and enhances alternative complement pathway activation on immobilized ECM proteins when exposed to human serum.","method":"ELISA-based binding assays, domain-specific binding studies (CCP domain mapping), FH cofactor activity assays, complement activation assays on ECM surfaces","journal":"Frontiers in Immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — binding domain mapping plus functional complement activation assays; single lab","pmids":["35392081"],"is_preprint":false},{"year":2022,"finding":"The aHUS-associated FHR1 isoform FHR1*B (c.469T, c.475G, c.523C) displays higher capacity for binding C3b and necrotic cells compared to FHR1*A. FHR1*B more strongly inhibits FH-mediated cofactor function (resulting in fewer C3b cleavage products) and more powerfully de-regulates FH inhibition of C3bBb assembly. FHR1*B also triggers higher IL-1β and IL-6 secretion from monocytes than FHR1*A.","method":"Recombinant protein expression, homology modeling, C3b binding assays, cofactor activity assays, C3 convertase assays, monocyte stimulation assays","journal":"Frontiers in Immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — recombinant protein functional comparison with multiple orthogonal assays; single lab","pmids":["35126388"],"is_preprint":false},{"year":2014,"finding":"A novel hybrid CFHR1/CFH fusion protein (containing first four SCRs of FHR1 and terminal SCR20 of FH) acts as a competitive antagonist of FH in an FH-dependent hemolysis assay, causing sheep erythrocyte lysis. Sera from carriers of the hybrid gene induce more C5b-9 deposition on endothelial cells than control serum.","method":"Functional hemolysis assay, C5b-9 deposition assay on endothelial cells, genomic sequencing","journal":"Journal of the American Society of Nephrology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional hemolysis and cell deposition assays with defined fusion protein; single lab","pmids":["24904082"],"is_preprint":false},{"year":2025,"finding":"FHR1 accumulates below the retinal pigment epithelium (RPE) in AMD donor tissue and in AMD-relevant mouse models. The murine FHR1 receptor EMR2 (EGF-like module-containing mucin-like hormone receptor 1, also known as Emr1 in mice) is expressed on RPE and invading mononuclear phagocytes (MP). FHR1 triggers EMR2-dependent calcium signals and gene expression changes in both human RPE cells and in vivo. Deletion of muFHR1 in mice significantly reduced mononuclear phagocyte invasion and neoangiogenesis in laser-induced choroidal neovascularization.","method":"RNAseq, Ca2+ signaling assays in RPE cells, muFHR1 knockout mouse experiments, laser-induced choroidal neovascularization model, immunohistochemistry","journal":"Journal of Neuroinflammation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — receptor identification with functional signaling and in vivo knockout readouts; single lab, multiple methods","pmids":["40611130"],"is_preprint":false},{"year":2024,"finding":"Deletion of murine FHR1 (muFHR1, the mouse homolog of human FHR1) in ApoE-/- mice normalizes cholesterol levels, reduces inflammation, and decreases plaque formation. muFHR1 deletion enhanced lipid conversion in the liver (shown by RNAseq), and FHR1 directs uptake of oxidized LDL by macrophages, supporting foam cell formation and plaque development.","method":"muFHR1 knockout mouse generation, cross with ApoE-/- mice, RNAseq analysis of liver, lipid/cholesterol measurements, plaque quantification","journal":"International Journal of Medical Sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — defined knockout mouse with atherosclerosis model and transcriptomic readout; single lab","pmids":["41583528"],"is_preprint":false},{"year":2024,"finding":"Cfhr1 gene deletion in mice leads to excessive alternative complement pathway (AP) activation following Staphylococcus aureus infection, with significantly increased C3a formation in lung tissues, higher bacterial colony counts in lungs, and exacerbated sepsis and acute lung injury compared to wild-type mice.","method":"Cfhr1 knockout mouse model, S. aureus tail vein injection, complement factor measurements, bacterial colony counts, RNA-seq transcriptome analysis","journal":"Biochemical and Biophysical Research Communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — defined knockout with in vivo infection model and multi-parameter complement/bacterial readouts; single lab","pmids":["39128222"],"is_preprint":false}],"current_model":"CFHR1 (FHR-1) is a circulating complement protein that circulates as homodimers (and FHR-1/FHR-2 heterodimers) and acts primarily as a context-dependent modulator of complement activation: it inhibits the C5 convertase and MAC formation at cell surfaces, competes with complement factor H (CFH) for binding to surface-bound C3b/C3d and extracellular matrix ligands (thereby de-regulating CFH-mediated C3 convertase inhibition and enhancing complement activation), binds necrotic cells via its N-terminus and triggers NLRP3 inflammasome activation in monocytes through the G-protein coupled receptor EMR2/phospholipase C pathway independent of complement, binds monomeric CRP and pentraxins to further enhance complement activation on dead cells and ECM, and lacks sialic acid binding (unlike CFH), which normally prevents it from competing with CFH on host cells—a restriction overcome by aHUS-associated mutants that acquire sialic acid binding, explaining their pathogenicity."},"narrative":{"mechanistic_narrative":"CFHR1 (FHR-1) is a circulating complement regulatory protein that acts as a context-dependent modulator of the alternative complement pathway, distinct in mechanism from its relative complement factor H (CFH) [PMID:19528535]. At the terminal complement level it inhibits the C5 convertase and blocks C5b surface deposition and membrane attack complex formation [PMID:19528535]. In contrast, at the C3 convertase level it antagonizes CFH: FHR-1 binds C3b and C3d through a C-terminal interface essentially identical to the two C-terminal domains of CFH (SCR19-20), and this binding—which requires FHR-1 dimerization—sterically displaces CFH and CFHL-1, de-regulating CFH-mediated C3 convertase control and enhancing complement activation [PMID:27814381, PMID:33651882]. FHR-1 circulates as homodimers and as FHR-1/FHR-2 heterodimers whose subunits exchange rapidly, oligomerization being mediated by its conserved N-terminal domains [PMID:29093712, PMID:23728178]. Its lack of sialic-acid binding (unlike CFH) normally restricts competition with CFH on host surfaces; aHUS-associated FHR-1 mutants acquire sialic-acid binding and increased C3-fragment avidity, explaining their pathogenicity, as do gene-conversion allotypes and CFHR1/CFH hybrid proteins that potentiate FH antagonism and endothelial complement deposition [PMID:33651882, PMID:35126388, PMID:24904082]. Beyond complement, FHR-1 binds necrotic cells via its N-terminus and triggers NLRP3 inflammasome activation and pro-inflammatory cytokine release in monocytes through the G-protein coupled receptor EMR2 and phospholipase C, independent of complement [PMID:31273197]. It engages monomeric CRP, pentraxin 3, DNA, and extracellular matrix proteins (laminin, fibromodulin, osteoadherin, PRELP) through its C-terminal domains to further amplify complement activation on dead cells and ECM [PMID:28533443, PMID:32765490, PMID:35392081]. FHR-1 is exploited by pathogens (Group A Streptococcus, Leptospira, Plasmodium falciparum) for complement evasion [PMID:20855886, PMID:22291192, PMID:30455399], and murine knockout studies establish its in vivo role in restraining alternative-pathway activation during bacterial infection and in promoting tissue inflammation in atherosclerosis and choroidal neovascularization [PMID:32636836, PMID:39128222, PMID:40611130, PMID:41583528]. CFHR1 polymorphisms and copy-number variation are linked to atypical hemolytic uremic syndrome and C3 glomerulopathy [PMID:19745068, PMID:23728178].","teleology":[{"year":2009,"claim":"Established that FHR-1 is not redundant with CFH but acts at a distinct step—the C5 convertase—blocking terminal complement assembly, defining its first molecular function.","evidence":"In vitro C5 convertase activity and MAC deposition assays with cell-surface binding","pmids":["19528535"],"confidence":"High","gaps":["Did not resolve the structural basis for C5 convertase inhibition","Did not address how FHR-1 and CFH share surface sites in vivo"]},{"year":2009,"claim":"Linked CFHR1 genetic variation and deficiency to aHUS, showing CFHR1 deficiency drives anti-factor-H autoantibody generation and that a gene-conversion allotype may antagonize FH.","evidence":"Proteomics, CFHR1 genomic sequencing and allotype characterization in patient cohorts","pmids":["19745068"],"confidence":"Medium","gaps":["FH-competition model was inferred, not directly reconstituted","Mechanism connecting CFHR1 deficiency to autoantibody production unresolved"]},{"year":2010,"claim":"Showed pathogens exploit FHR-1: binding to streptococcal Scl1 via SCR3-5 interferes with FH-mediated C3 convertase regulation while preserving FHR-1 C5-level inhibition, demonstrating dual surface-protein-mediated complement evasion.","evidence":"Binding/ELISA, domain mutagenesis, hemolysis and complement regulation assays on bacterial surfaces","pmids":["20855886"],"confidence":"High","gaps":["Did not establish in vivo relevance to streptococcal virulence"]},{"year":2012,"claim":"Extended pathogen complement-evasion role by showing FHR-1 is acquired on Leptospira surfaces via Lig proteins alongside other host regulators.","evidence":"Serum-based binding and competition assays on leptospiral proteins","pmids":["22291192"],"confidence":"Medium","gaps":["Functional consequence for Leptospira survival not directly measured","Single lab, no in vivo confirmation"]},{"year":2013,"claim":"Defined FHR oligomerization architecture: native FHR-1/2/5 circulate as homo- and hetero-oligomers via conserved N-terminal domains, and a C3G mutation duplicating these domains creates large multimers with enhanced C3b avidity and FH competition—linking oligomerization state to disease.","evidence":"Plasma protein characterization, SPR, hemolytic assays, native PAGE/SEC, genomic sequencing","pmids":["23728178"],"confidence":"High","gaps":["Did not resolve stoichiometry of mutant multimers at surfaces","Causal chain from multimerization to glomerular pathology incomplete"]},{"year":2016,"claim":"Mapped the molecular basis of FH antagonism: FHR-1 binds C3b/C3d through an interface identical to CFH SCR19-20 and requires dimerization to compete with both CFH and CFHL-1, defining the steric mechanism of de-regulation.","evidence":"Site-directed mutagenesis, ELISA binding and functional complement assays","pmids":["27814381"],"confidence":"High","gaps":["No co-crystal structure of FHR-1 with C3b","Did not quantify competition at native cell surfaces"]},{"year":2017,"claim":"Revealed a complement-enhancing role via pentraxins: FHR-1 binds monomeric (not pentameric) CRP through C-terminal domains and amplifies classical and alternative pathway activation on ECM and necrotic cells.","evidence":"ELISA binding, classical/alternative pathway and C3 convertase activation assays","pmids":["28533443"],"confidence":"High","gaps":["In vivo contribution of FHR-1/CRP axis to inflammation not established"]},{"year":2017,"claim":"Quantified FHR-1 dimer dynamics, showing homodimers and FHR-1/FHR-2 heterodimers with rapid monomer exchange, absent in homozygous CFHR1-deletion individuals—confirming the dimer as the functional plasma unit.","evidence":"FRET, ELISA with specific antibodies, serum from CFHR1-deletion individuals","pmids":["29093712"],"confidence":"High","gaps":["Functional difference between homo- and heterodimers not resolved"]},{"year":2018,"claim":"Demonstrated FHR-1 competes with FH on Plasmodium falciparum surfaces, where add-back of FHR-1 impairs C3b inactivation and reduces parasite viability, framing FHR-1 as a host-protective complement amplifier in malaria.","evidence":"FHR-1-deficient serum, recombinant add-back, binding competition and parasite viability assays","pmids":["30455399"],"confidence":"Medium","gaps":["Single lab, no in vivo malaria model","Effect size on parasite control in physiological serum uncertain"]},{"year":2019,"claim":"Uncovered a complement-independent inflammatory function: FHR-1 selectively binds necrotic cells and activates the NLRP3 inflammasome in monocytes via the GPCR EMR2 and phospholipase C, with in situ binding at necrotic glomerular and atherosclerotic sites.","evidence":"Monocyte stimulation, NLRP3/IL-1β readouts, EMR2 receptor identification, pathway inhibitors, patient tissue IHC","pmids":["31273197"],"confidence":"High","gaps":["Structural basis of FHR-1–EMR2 engagement undefined","Selectivity over FHR-2/FHR-3 mechanistically unexplained"]},{"year":2020,"claim":"Broadened FHR-1 ligand repertoire to DNA and dead-cell surfaces, where it inhibits FH-DNA binding and recruits CRP and pentraxin 3 to amplify complement on apoptotic/necrotic material.","evidence":"ELISA binding, cofactor activity and complement activation assays on DNA and dead cells","pmids":["32765490"],"confidence":"Medium","gaps":["Single lab","Physiological relevance of DNA binding in vivo unclear"]},{"year":2020,"claim":"Provided in vivo genetic proof that FHR-1 restrains alternative-pathway activation, as Cfhr1-knockout mice showed enhanced LPS-induced AP activation and more severe sepsis and acute kidney injury.","evidence":"Cfhr1 knockout mouse, LPS sepsis model, complement measurements","pmids":["32636836"],"confidence":"Medium","gaps":["Murine FHR-E may differ functionally from human FHR-1","Single lab"]},{"year":2021,"claim":"Explained aHUS mutant pathogenicity at atomic resolution: wild-type FHR-1 lacks sialic-acid binding (preventing host-surface competition with FH), while aHUS mutants acquire it, raising avidity for surface C3 fragments; FHR-1 also binds native C3 to attract it to surfaces and promote activation.","evidence":"NMR, homology modeling, mutagenesis, sialic-acid binding and complement activation assays","pmids":["33651882"],"confidence":"High","gaps":["Full-length FHR-1 surface structure not solved","Quantitative threshold of avidity gain for disease unknown"]},{"year":2021,"claim":"Connected FHR-1 to vascular inflammation, showing it deposits in atherosclerotic plaques, circulates on extracellular vesicles, and induces pro-inflammatory cytokines and tissue factor in monocytes and neutrophils.","evidence":"FHR-1 plasma isolation, plaque IHC, immune-cell stimulation and cytokine assays","pmids":["34795372"],"confidence":"Medium","gaps":["Receptor/pathway for tissue factor induction not defined here","Single lab"]},{"year":2022,"claim":"Identified ECM proteins (laminin, fibromodulin, osteoadherin, PRELP) as FHR-1 ligands bound via CCP4-5, where FHR-1 competitively displaces FH and enhances alternative-pathway activation on matrix surfaces.","evidence":"ELISA binding, CCP domain mapping, FH cofactor and complement activation assays on ECM","pmids":["35392081"],"confidence":"Medium","gaps":["In vivo ECM complement dysregulation not tested","Single lab"]},{"year":2022,"claim":"Functionally distinguished aHUS-risk allotype FHR1*B from FHR1*A, showing FHR1*B has higher C3b and necrotic-cell binding, more strongly de-regulates FH, and elicits greater monocyte cytokine secretion—linking sequence variation to both complement and inflammatory gain of function.","evidence":"Recombinant protein expression, homology modeling, C3b/cofactor/convertase and monocyte assays","pmids":["35126388"],"confidence":"Medium","gaps":["Structural cause of the FHR1*B avidity gain not resolved","Single lab"]},{"year":2014,"claim":"Showed a CFHR1/CFH hybrid protein (FHR1 SCR1-4 plus FH SCR20) acts as a competitive FH antagonist causing hemolysis and increased C5b-9 deposition on endothelial cells, linking gene rearrangements to complement dysregulation.","evidence":"FH-dependent hemolysis assay, endothelial C5b-9 deposition, genomic sequencing","pmids":["24904082"],"confidence":"Medium","gaps":["Single carrier-derived material","Mechanism of the hybrid's surface targeting incomplete"]},{"year":2024,"claim":"Provided in vivo evidence that FHR-1 limits AP activation during S. aureus infection, as Cfhr1-knockout mice showed excessive C3a, higher bacterial burden, and exacerbated sepsis and lung injury.","evidence":"Cfhr1 knockout mouse, S. aureus infection, complement and bacterial readouts, RNA-seq","pmids":["39128222"],"confidence":"Medium","gaps":["Murine-to-human FHR-1 functional correspondence assumed","Single lab"]},{"year":2024,"claim":"Implicated FHR-1 in lipid metabolism and atherosclerosis, as muFHR1 deletion in ApoE-/- mice normalized cholesterol, reduced inflammation and plaque, and FHR-1 was shown to direct macrophage oxidized-LDL uptake driving foam cell formation.","evidence":"muFHR1 knockout crossed to ApoE-/-, liver RNAseq, lipid measurements, plaque quantification","pmids":["41583528"],"confidence":"Medium","gaps":["Molecular mechanism of FHR-1-directed oxLDL uptake not defined","Reliance on murine homolog"]},{"year":2025,"claim":"Extended the FHR-1/EMR2 inflammatory axis to retinal disease, showing FHR-1 accumulates beneath the RPE in AMD, triggers EMR2-dependent calcium signaling and transcriptional changes, and that muFHR1 deletion reduces mononuclear phagocyte invasion and neoangiogenesis.","evidence":"RNAseq, Ca2+ signaling in RPE cells, muFHR1 knockout, laser-induced choroidal neovascularization, IHC","pmids":["40611130"],"confidence":"Medium","gaps":["Direct human genetic link to AMD via this axis not established","Single lab"]},{"year":null,"claim":"It remains unresolved how the competing complement-regulatory (C5-inhibitory) and complement-enhancing (FH-antagonist) activities of FHR-1 are balanced at specific surfaces in vivo, and whether the dimer/multimer state, allotype, and EMR2-mediated inflammatory signaling are coordinately controlled.","evidence":"No single study integrates surface-context selectivity with oligomer state and receptor signaling","pmids":[],"confidence":"Low","gaps":["No integrated structural model of FHR-1 functions at a defined surface","Selectivity determinants for inflammasome activation versus complement modulation unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,5,6,14]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[9,17]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[10]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[7,13]},{"term_id":"GO:0031012","term_label":"extracellular matrix","supporting_discovery_ids":[14,6]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,5,9,11]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[9,17]}],"complexes":["FHR-1 homodimer","FHR-1/FHR-2 heterodimer"],"partners":["CFH","C3B","CRP","EMR2","PTX3","CFHL-1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q03591","full_name":"Complement factor H-related protein 1","aliases":["H factor-like protein 1","FHL-1","H-factor-like 1","H36"],"length_aa":330,"mass_kda":37.7,"function":"Involved in complement regulation. The dimerized forms have avidity for tissue-bound complement fragments and efficiently compete with the physiological complement inhibitor CFH. 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through complement alternative pathway hyperactivation.","date":"2024","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/39128222","citation_count":0,"is_preprint":false},{"pmid":"41583528","id":"PMC_41583528","title":"Deletion of the Mouse Homolog of Human FHR1 (muFHR1) Alleviates Atherosclerosis in ApoE-/- mice.","date":"2026","source":"International journal of medical sciences","url":"https://pubmed.ncbi.nlm.nih.gov/41583528","citation_count":0,"is_preprint":false},{"pmid":"42113272","id":"PMC_42113272","title":"Dual pathogenic variants in ADAMTS13 and CFHR1/CFHR3 deletion: divergent thrombotic microangiopathy phenotypes in siblings.","date":"2026","source":"Pediatric nephrology (Berlin, Germany)","url":"https://pubmed.ncbi.nlm.nih.gov/42113272","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2024.11.13.24317290","title":"Rare predicted loss-of-function and damaging missense variants in<i>CFHR5</i>associate with protection from age-related macular degeneration","date":"2024-11-15","source":"bioRxiv","url":"https://doi.org/10.1101/2024.11.13.24317290","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":40315,"output_tokens":5439,"usd":0.101265,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":13827,"output_tokens":6105,"usd":0.11088,"stage2_stop_reason":"end_turn"},"total_usd":0.212145,"stage1_batch_id":"msgbatch_01ACAxJQabDsht39JXeWG22d","stage2_batch_id":"msgbatch_01QEU22A9U5sbPTgsMzTmvSf","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2009,\n      \"finding\": \"CFHR1 (FHR-1) inhibits complement C5 convertase activity and blocks C5b surface deposition and MAC (membrane attack complex) formation. This activity is distinct from complement factor H (CFH), which regulates the C3 convertase. Both proteins bind to the same or similar sites at cellular surfaces, suggesting sequential and partially competitive roles in complement regulation.\",\n      \"method\": \"In vitro functional assays (C5 convertase activity assays, MAC deposition assays, cell surface binding experiments)\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct in vitro enzymatic/functional assays with defined readouts; single lab but multiple orthogonal functional methods\",\n      \"pmids\": [\"19528535\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"A novel CFHR1 polymorphism (CFHR1*B), arising from gene conversion between CFH and CFHR1, associates with aHUS susceptibility. Patients with aHUS lacking CFHR1 (but not CFHR3) present anti-factor H autoantibodies, indicating CFHR1 deficiency specifically drives anti-FH autoantibody generation. The CFHR1*B allotype, with greater sequence similarity to FH, may compete with FH and reduce protection of cellular surfaces.\",\n      \"method\": \"Proteomics strategy (2D-PAGE/MS), sequencing of CFHR1 genomic DNA, functional inference from allotype characterization\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — proteomics plus sequencing in patient cohorts; mechanistic competition model is inferred rather than directly reconstituted\",\n      \"pmids\": [\"19745068\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"CFHR1 binds to Group A streptococcal collagen-like protein Scl1 via its conserved C-terminal short consensus repeats SCR3-5. Binding of CFHR1 to Scl1 interferes with Factor H-mediated C3 convertase regulation (competitive inhibition), while maintaining terminal complement complex inhibition by CFHR1 at the C5 convertase level. This interaction enables streptococci to evade complement via two distinct surface protein classes.\",\n      \"method\": \"Binding assays (pulldown/ELISA), functional hemolysis/complement regulation assays, domain mutagenesis (ionic strength and heparin competition), bacterial surface binding experiments\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct binding assays with domain mapping, mutagenesis, and functional complement regulation readouts in a single rigorous study\",\n      \"pmids\": [\"20855886\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CFHR1 (FHR-1) is acquired on Leptospira surfaces via binding to leptospiral immunoglobulin-like (Lig) proteins, facilitating complement evasion. CFHR1 was shown to bind to Lig proteins from human serum alongside FH, FHL-1, and C4BP.\",\n      \"method\": \"Co-incubation binding assays, competition assays, serum-based complement evasion experiments\",\n      \"journal\": \"The Journal of Infectious Diseases\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — pulldown/binding assays with competition experiments, replicated across multiple complement regulators but single lab\",\n      \"pmids\": [\"22291192\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"A C3 glomerulopathy-associated mutation in CFHR1 causes duplication of the N-terminal SCRs (conserved in FHR2 and FHR5), resulting in unusually large multimeric FHR complexes. Native FHR1, FHR2, and FHR5 circulate as homo- and hetero-oligomeric complexes mediated by the conserved N-terminal domain. Mutant FHR1 shows increased avidity for C3b, iC3b, and C3dg and enhanced competition with FH in SPR and hemolytic assays.\",\n      \"method\": \"Plasma protein characterization, surface plasmon resonance (SPR), hemolytic assays, size-exclusion chromatography/native PAGE, genomic sequencing\",\n      \"journal\": \"The Journal of Clinical Investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal methods including SPR, functional hemolytic assays, and biochemical oligomerization studies; disease mutation provides natural mechanistic probe\",\n      \"pmids\": [\"23728178\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CFHR1 binds to complement components C3b and C3d via a single shared interface identical to that of the two C-terminal domains (SCR19-20) of CFH. CFHR1 dimerization is required for effective binding to C3b and C3d and for competition with CFH. CFHR1 also competes with complement factor H-like protein 1 (CFHL-1/FHL-1) for C3b binding, sterically blocking the N-terminal CFH interaction required for CFH-mediated regulation.\",\n      \"method\": \"Site-directed mutagenesis, ELISA-based binding assays, functional complement assays\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — site-directed mutagenesis combined with ELISA-based binding and functional assays; multiple orthogonal approaches in one study\",\n      \"pmids\": [\"27814381\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"FHR-1 binds strongly to monomeric CRP (but not native pentameric CRP) via its C-terminal domains. FHR-1/CRP interactions increased complement activation via both classical and alternative pathways on surfaces such as extracellular matrix and necrotic cells. FHR-1 did not inhibit FH-mediated regulation of solid-phase C3 convertase or terminal complement complex formation induced by zymosan; instead, by binding C3b, FHR-1 allowed C3 convertase formation and enhanced complement activation.\",\n      \"method\": \"ELISA-based binding assays, complement activation assays (classical and alternative pathway), C3 convertase formation assays, competition binding assays\",\n      \"journal\": \"Journal of Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple functional assays with defined readouts; reconstitution of complement activation on defined surfaces; single lab with orthogonal methods\",\n      \"pmids\": [\"28533443\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"FHR-1 circulates in human plasma as homodimers and as FHR-1/FHR-2 heterodimers. FHR-1, FHR-2, and FHR-5 homodimerize and FHR-1/FHR-2 heterodimers form, with monomer exchange occurring rapidly as shown by FRET. In individuals with homozygous CFHR1 deletions, FHR-1 homo- and heterodimers are absent.\",\n      \"method\": \"FRET, ELISA with specific antibodies, serum analysis from CFHR1-deletion individuals\",\n      \"journal\": \"Frontiers in Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — FRET-based dimerization analysis, confirmed ex vivo in deletion individuals; multiple orthogonal methods in one study\",\n      \"pmids\": [\"29093712\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"FHR-1 competes with Factor H for binding to Plasmodium falciparum surfaces (intraerythrocytic schizonts and free merozoites). In FHR-1-deficient human serum, FH binding to parasite surfaces is increased; addition of recombinant FHR-1 decreases FH binding, impairs C3b inactivation, and reduces parasite viability.\",\n      \"method\": \"FHR-1-deficient human serum experiments, recombinant FHR-1 add-back, parasite viability assays, binding competition assays\",\n      \"journal\": \"Journal of Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal loss-of-function and add-back with defined functional readout; single lab\",\n      \"pmids\": [\"30455399\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"FHR1 selectively binds to necrotic cells via its N-terminus. FHR1 (but not FH, FHR2, or FHR3) strongly induces NLRP3 inflammasome activation in blood-derived human monocytes, leading to secretion of IL-1β, TNFα, IL-18, and IL-6. This FHR1-mediated inflammasome activation occurs via the phospholipase C pathway through the G-protein coupled receptor EMR2, independent of complement. FHR1 also binds near necrotic glomerular sites in AAV patients and necrotic areas in atherosclerotic plaques.\",\n      \"method\": \"In vitro monocyte stimulation assays, NLRP3 inflammasome activation (IL-1β secretion), receptor identification (EMR2), signaling pathway inhibitor experiments, immunohistochemistry on patient tissue, in vitro necrotic cell binding assays\",\n      \"journal\": \"Nature Communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal methods including specific receptor identification, pathway inhibition, cell-based functional assays, and patient tissue validation\",\n      \"pmids\": [\"31273197\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"FHR-1 and FHR-5 bind to both plasmid DNA and human genomic DNA, and inhibit FH-DNA interaction by competing with FH binding. The FHR-1 cofactor activity inhibition was due to reduced FH binding to DNA. Both FHRs cause increased complement activation on DNA. FHR-1 and FHR-5 bind to late apoptotic and necrotic cells and recruit monomeric CRP and pentraxin 3; FHR-pentraxin interactions promote enhanced activation of both classical and alternative complement pathways on dead cells.\",\n      \"method\": \"ELISA-based binding assays, cofactor activity assays, complement activation assays on DNA and dead cell surfaces, competition binding experiments\",\n      \"journal\": \"Frontiers in Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal functional assays; single lab\",\n      \"pmids\": [\"32765490\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"In a Cfhr1 knockout mouse model, murine FHR-1 homolog (FHR-E) deficiency enhanced LPS-induced alternative complement pathway (AP) activation both in vitro and in vivo, and knockout mice exhibited more severe sepsis and acute kidney injury. This establishes that FHR-E/FHR-1 regulates AP activation in vivo in the context of infection.\",\n      \"method\": \"Cfhr1 knockout mouse generation, LPS-induced sepsis model, complement activation measurements, in vitro complement assays\",\n      \"journal\": \"Frontiers in Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined knockout mouse model with in vivo and in vitro complement activation readouts; single lab\",\n      \"pmids\": [\"32636836\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"FHR-1 lacks the capacity to bind sialic acids (unlike FH), which prevents C3b-binding competition between FH and FHR-1 at host-cell surfaces under normal circumstances. aHUS-associated FHR-1 mutants are pathogenic because they acquire sialic acid-binding capacity, increasing FHR-1 avidity for surface-bound C3-activated fragments and enabling C3b-binding competition with FH. FHR-1 also binds to native C3 (in addition to C3b, iC3b, C3dg), and surface-bound FHR-1 promotes complement activation by attracting native C3 to the cell surface.\",\n      \"method\": \"Biochemical assays, NMR spectroscopy, computational/homology modeling, mutagenesis of FHR-1, sialic acid binding experiments, complement activation assays\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — NMR structural validation combined with mutagenesis and biochemical functional assays; disease-associated mutants provide direct mechanistic insight\",\n      \"pmids\": [\"33651882\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"FHR1 is deposited in atherosclerotic plaques and circulates on extracellular vesicles. Surface-bound FHR-1 induces expression of pro-inflammatory cytokines and tissue factor in monocytes and neutrophils.\",\n      \"method\": \"Isolation of FHR-1 from human plasma, immunohistochemistry of plaques, monocyte/neutrophil stimulation assays, cytokine measurement\",\n      \"journal\": \"Scientific Reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — purified protein stimulation of primary immune cells with cytokine readout; single lab, multiple cell types\",\n      \"pmids\": [\"34795372\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"FHR1 binds to extracellular matrix (ECM) proteins laminin, fibromodulin, osteoadherin, and PRELP through its C-terminal CCP domains 4-5. FHR1 competitively inhibits FH binding to these ECM proteins in a dose-dependent manner, reduces FH cofactor activity, and enhances alternative complement pathway activation on immobilized ECM proteins when exposed to human serum.\",\n      \"method\": \"ELISA-based binding assays, domain-specific binding studies (CCP domain mapping), FH cofactor activity assays, complement activation assays on ECM surfaces\",\n      \"journal\": \"Frontiers in Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — binding domain mapping plus functional complement activation assays; single lab\",\n      \"pmids\": [\"35392081\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The aHUS-associated FHR1 isoform FHR1*B (c.469T, c.475G, c.523C) displays higher capacity for binding C3b and necrotic cells compared to FHR1*A. FHR1*B more strongly inhibits FH-mediated cofactor function (resulting in fewer C3b cleavage products) and more powerfully de-regulates FH inhibition of C3bBb assembly. FHR1*B also triggers higher IL-1β and IL-6 secretion from monocytes than FHR1*A.\",\n      \"method\": \"Recombinant protein expression, homology modeling, C3b binding assays, cofactor activity assays, C3 convertase assays, monocyte stimulation assays\",\n      \"journal\": \"Frontiers in Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — recombinant protein functional comparison with multiple orthogonal assays; single lab\",\n      \"pmids\": [\"35126388\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"A novel hybrid CFHR1/CFH fusion protein (containing first four SCRs of FHR1 and terminal SCR20 of FH) acts as a competitive antagonist of FH in an FH-dependent hemolysis assay, causing sheep erythrocyte lysis. Sera from carriers of the hybrid gene induce more C5b-9 deposition on endothelial cells than control serum.\",\n      \"method\": \"Functional hemolysis assay, C5b-9 deposition assay on endothelial cells, genomic sequencing\",\n      \"journal\": \"Journal of the American Society of Nephrology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional hemolysis and cell deposition assays with defined fusion protein; single lab\",\n      \"pmids\": [\"24904082\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FHR1 accumulates below the retinal pigment epithelium (RPE) in AMD donor tissue and in AMD-relevant mouse models. The murine FHR1 receptor EMR2 (EGF-like module-containing mucin-like hormone receptor 1, also known as Emr1 in mice) is expressed on RPE and invading mononuclear phagocytes (MP). FHR1 triggers EMR2-dependent calcium signals and gene expression changes in both human RPE cells and in vivo. Deletion of muFHR1 in mice significantly reduced mononuclear phagocyte invasion and neoangiogenesis in laser-induced choroidal neovascularization.\",\n      \"method\": \"RNAseq, Ca2+ signaling assays in RPE cells, muFHR1 knockout mouse experiments, laser-induced choroidal neovascularization model, immunohistochemistry\",\n      \"journal\": \"Journal of Neuroinflammation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — receptor identification with functional signaling and in vivo knockout readouts; single lab, multiple methods\",\n      \"pmids\": [\"40611130\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Deletion of murine FHR1 (muFHR1, the mouse homolog of human FHR1) in ApoE-/- mice normalizes cholesterol levels, reduces inflammation, and decreases plaque formation. muFHR1 deletion enhanced lipid conversion in the liver (shown by RNAseq), and FHR1 directs uptake of oxidized LDL by macrophages, supporting foam cell formation and plaque development.\",\n      \"method\": \"muFHR1 knockout mouse generation, cross with ApoE-/- mice, RNAseq analysis of liver, lipid/cholesterol measurements, plaque quantification\",\n      \"journal\": \"International Journal of Medical Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined knockout mouse with atherosclerosis model and transcriptomic readout; single lab\",\n      \"pmids\": [\"41583528\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Cfhr1 gene deletion in mice leads to excessive alternative complement pathway (AP) activation following Staphylococcus aureus infection, with significantly increased C3a formation in lung tissues, higher bacterial colony counts in lungs, and exacerbated sepsis and acute lung injury compared to wild-type mice.\",\n      \"method\": \"Cfhr1 knockout mouse model, S. aureus tail vein injection, complement factor measurements, bacterial colony counts, RNA-seq transcriptome analysis\",\n      \"journal\": \"Biochemical and Biophysical Research Communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined knockout with in vivo infection model and multi-parameter complement/bacterial readouts; single lab\",\n      \"pmids\": [\"39128222\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CFHR1 (FHR-1) is a circulating complement protein that circulates as homodimers (and FHR-1/FHR-2 heterodimers) and acts primarily as a context-dependent modulator of complement activation: it inhibits the C5 convertase and MAC formation at cell surfaces, competes with complement factor H (CFH) for binding to surface-bound C3b/C3d and extracellular matrix ligands (thereby de-regulating CFH-mediated C3 convertase inhibition and enhancing complement activation), binds necrotic cells via its N-terminus and triggers NLRP3 inflammasome activation in monocytes through the G-protein coupled receptor EMR2/phospholipase C pathway independent of complement, binds monomeric CRP and pentraxins to further enhance complement activation on dead cells and ECM, and lacks sialic acid binding (unlike CFH), which normally prevents it from competing with CFH on host cells—a restriction overcome by aHUS-associated mutants that acquire sialic acid binding, explaining their pathogenicity.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CFHR1 (FHR-1) is a circulating complement regulatory protein that acts as a context-dependent modulator of the alternative complement pathway, distinct in mechanism from its relative complement factor H (CFH) [#0]. At the terminal complement level it inhibits the C5 convertase and blocks C5b surface deposition and membrane attack complex formation [#0]. In contrast, at the C3 convertase level it antagonizes CFH: FHR-1 binds C3b and C3d through a C-terminal interface essentially identical to the two C-terminal domains of CFH (SCR19-20), and this binding\\u2014which requires FHR-1 dimerization\\u2014sterically displaces CFH and CFHL-1, de-regulating CFH-mediated C3 convertase control and enhancing complement activation [#5, #12]. FHR-1 circulates as homodimers and as FHR-1/FHR-2 heterodimers whose subunits exchange rapidly, oligomerization being mediated by its conserved N-terminal domains [#7, #4]. Its lack of sialic-acid binding (unlike CFH) normally restricts competition with CFH on host surfaces; aHUS-associated FHR-1 mutants acquire sialic-acid binding and increased C3-fragment avidity, explaining their pathogenicity, as do gene-conversion allotypes and CFHR1/CFH hybrid proteins that potentiate FH antagonism and endothelial complement deposition [#12, #15, #16]. Beyond complement, FHR-1 binds necrotic cells via its N-terminus and triggers NLRP3 inflammasome activation and pro-inflammatory cytokine release in monocytes through the G-protein coupled receptor EMR2 and phospholipase C, independent of complement [#9]. It engages monomeric CRP, pentraxin 3, DNA, and extracellular matrix proteins (laminin, fibromodulin, osteoadherin, PRELP) through its C-terminal domains to further amplify complement activation on dead cells and ECM [#6, #10, #14]. FHR-1 is exploited by pathogens (Group A Streptococcus, Leptospira, Plasmodium falciparum) for complement evasion [#2, #3, #8], and murine knockout studies establish its in vivo role in restraining alternative-pathway activation during bacterial infection and in promoting tissue inflammation in atherosclerosis and choroidal neovascularization [#11, #19, #17, #18]. CFHR1 polymorphisms and copy-number variation are linked to atypical hemolytic uremic syndrome and C3 glomerulopathy [#1, #4].\",\n  \"teleology\": [\n    {\n      \"year\": 2009,\n      \"claim\": \"Established that FHR-1 is not redundant with CFH but acts at a distinct step\\u2014the C5 convertase\\u2014blocking terminal complement assembly, defining its first molecular function.\",\n      \"evidence\": \"In vitro C5 convertase activity and MAC deposition assays with cell-surface binding\",\n      \"pmids\": [\"19528535\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve the structural basis for C5 convertase inhibition\", \"Did not address how FHR-1 and CFH share surface sites in vivo\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Linked CFHR1 genetic variation and deficiency to aHUS, showing CFHR1 deficiency drives anti-factor-H autoantibody generation and that a gene-conversion allotype may antagonize FH.\",\n      \"evidence\": \"Proteomics, CFHR1 genomic sequencing and allotype characterization in patient cohorts\",\n      \"pmids\": [\"19745068\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"FH-competition model was inferred, not directly reconstituted\", \"Mechanism connecting CFHR1 deficiency to autoantibody production unresolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Showed pathogens exploit FHR-1: binding to streptococcal Scl1 via SCR3-5 interferes with FH-mediated C3 convertase regulation while preserving FHR-1 C5-level inhibition, demonstrating dual surface-protein-mediated complement evasion.\",\n      \"evidence\": \"Binding/ELISA, domain mutagenesis, hemolysis and complement regulation assays on bacterial surfaces\",\n      \"pmids\": [\"20855886\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish in vivo relevance to streptococcal virulence\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Extended pathogen complement-evasion role by showing FHR-1 is acquired on Leptospira surfaces via Lig proteins alongside other host regulators.\",\n      \"evidence\": \"Serum-based binding and competition assays on leptospiral proteins\",\n      \"pmids\": [\"22291192\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence for Leptospira survival not directly measured\", \"Single lab, no in vivo confirmation\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Defined FHR oligomerization architecture: native FHR-1/2/5 circulate as homo- and hetero-oligomers via conserved N-terminal domains, and a C3G mutation duplicating these domains creates large multimers with enhanced C3b avidity and FH competition\\u2014linking oligomerization state to disease.\",\n      \"evidence\": \"Plasma protein characterization, SPR, hemolytic assays, native PAGE/SEC, genomic sequencing\",\n      \"pmids\": [\"23728178\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve stoichiometry of mutant multimers at surfaces\", \"Causal chain from multimerization to glomerular pathology incomplete\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Mapped the molecular basis of FH antagonism: FHR-1 binds C3b/C3d through an interface identical to CFH SCR19-20 and requires dimerization to compete with both CFH and CFHL-1, defining the steric mechanism of de-regulation.\",\n      \"evidence\": \"Site-directed mutagenesis, ELISA binding and functional complement assays\",\n      \"pmids\": [\"27814381\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No co-crystal structure of FHR-1 with C3b\", \"Did not quantify competition at native cell surfaces\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Revealed a complement-enhancing role via pentraxins: FHR-1 binds monomeric (not pentameric) CRP through C-terminal domains and amplifies classical and alternative pathway activation on ECM and necrotic cells.\",\n      \"evidence\": \"ELISA binding, classical/alternative pathway and C3 convertase activation assays\",\n      \"pmids\": [\"28533443\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo contribution of FHR-1/CRP axis to inflammation not established\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Quantified FHR-1 dimer dynamics, showing homodimers and FHR-1/FHR-2 heterodimers with rapid monomer exchange, absent in homozygous CFHR1-deletion individuals\\u2014confirming the dimer as the functional plasma unit.\",\n      \"evidence\": \"FRET, ELISA with specific antibodies, serum from CFHR1-deletion individuals\",\n      \"pmids\": [\"29093712\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional difference between homo- and heterodimers not resolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrated FHR-1 competes with FH on Plasmodium falciparum surfaces, where add-back of FHR-1 impairs C3b inactivation and reduces parasite viability, framing FHR-1 as a host-protective complement amplifier in malaria.\",\n      \"evidence\": \"FHR-1-deficient serum, recombinant add-back, binding competition and parasite viability assays\",\n      \"pmids\": [\"30455399\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab, no in vivo malaria model\", \"Effect size on parasite control in physiological serum uncertain\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Uncovered a complement-independent inflammatory function: FHR-1 selectively binds necrotic cells and activates the NLRP3 inflammasome in monocytes via the GPCR EMR2 and phospholipase C, with in situ binding at necrotic glomerular and atherosclerotic sites.\",\n      \"evidence\": \"Monocyte stimulation, NLRP3/IL-1\\u03b2 readouts, EMR2 receptor identification, pathway inhibitors, patient tissue IHC\",\n      \"pmids\": [\"31273197\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of FHR-1\\u2013EMR2 engagement undefined\", \"Selectivity over FHR-2/FHR-3 mechanistically unexplained\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Broadened FHR-1 ligand repertoire to DNA and dead-cell surfaces, where it inhibits FH-DNA binding and recruits CRP and pentraxin 3 to amplify complement on apoptotic/necrotic material.\",\n      \"evidence\": \"ELISA binding, cofactor activity and complement activation assays on DNA and dead cells\",\n      \"pmids\": [\"32765490\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Physiological relevance of DNA binding in vivo unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Provided in vivo genetic proof that FHR-1 restrains alternative-pathway activation, as Cfhr1-knockout mice showed enhanced LPS-induced AP activation and more severe sepsis and acute kidney injury.\",\n      \"evidence\": \"Cfhr1 knockout mouse, LPS sepsis model, complement measurements\",\n      \"pmids\": [\"32636836\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Murine FHR-E may differ functionally from human FHR-1\", \"Single lab\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Explained aHUS mutant pathogenicity at atomic resolution: wild-type FHR-1 lacks sialic-acid binding (preventing host-surface competition with FH), while aHUS mutants acquire it, raising avidity for surface C3 fragments; FHR-1 also binds native C3 to attract it to surfaces and promote activation.\",\n      \"evidence\": \"NMR, homology modeling, mutagenesis, sialic-acid binding and complement activation assays\",\n      \"pmids\": [\"33651882\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length FHR-1 surface structure not solved\", \"Quantitative threshold of avidity gain for disease unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Connected FHR-1 to vascular inflammation, showing it deposits in atherosclerotic plaques, circulates on extracellular vesicles, and induces pro-inflammatory cytokines and tissue factor in monocytes and neutrophils.\",\n      \"evidence\": \"FHR-1 plasma isolation, plaque IHC, immune-cell stimulation and cytokine assays\",\n      \"pmids\": [\"34795372\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor/pathway for tissue factor induction not defined here\", \"Single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified ECM proteins (laminin, fibromodulin, osteoadherin, PRELP) as FHR-1 ligands bound via CCP4-5, where FHR-1 competitively displaces FH and enhances alternative-pathway activation on matrix surfaces.\",\n      \"evidence\": \"ELISA binding, CCP domain mapping, FH cofactor and complement activation assays on ECM\",\n      \"pmids\": [\"35392081\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo ECM complement dysregulation not tested\", \"Single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Functionally distinguished aHUS-risk allotype FHR1*B from FHR1*A, showing FHR1*B has higher C3b and necrotic-cell binding, more strongly de-regulates FH, and elicits greater monocyte cytokine secretion\\u2014linking sequence variation to both complement and inflammatory gain of function.\",\n      \"evidence\": \"Recombinant protein expression, homology modeling, C3b/cofactor/convertase and monocyte assays\",\n      \"pmids\": [\"35126388\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural cause of the FHR1*B avidity gain not resolved\", \"Single lab\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Showed a CFHR1/CFH hybrid protein (FHR1 SCR1-4 plus FH SCR20) acts as a competitive FH antagonist causing hemolysis and increased C5b-9 deposition on endothelial cells, linking gene rearrangements to complement dysregulation.\",\n      \"evidence\": \"FH-dependent hemolysis assay, endothelial C5b-9 deposition, genomic sequencing\",\n      \"pmids\": [\"24904082\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single carrier-derived material\", \"Mechanism of the hybrid's surface targeting incomplete\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Provided in vivo evidence that FHR-1 limits AP activation during S. aureus infection, as Cfhr1-knockout mice showed excessive C3a, higher bacterial burden, and exacerbated sepsis and lung injury.\",\n      \"evidence\": \"Cfhr1 knockout mouse, S. aureus infection, complement and bacterial readouts, RNA-seq\",\n      \"pmids\": [\"39128222\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Murine-to-human FHR-1 functional correspondence assumed\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Implicated FHR-1 in lipid metabolism and atherosclerosis, as muFHR1 deletion in ApoE-/- mice normalized cholesterol, reduced inflammation and plaque, and FHR-1 was shown to direct macrophage oxidized-LDL uptake driving foam cell formation.\",\n      \"evidence\": \"muFHR1 knockout crossed to ApoE-/-, liver RNAseq, lipid measurements, plaque quantification\",\n      \"pmids\": [\"41583528\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular mechanism of FHR-1-directed oxLDL uptake not defined\", \"Reliance on murine homolog\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Extended the FHR-1/EMR2 inflammatory axis to retinal disease, showing FHR-1 accumulates beneath the RPE in AMD, triggers EMR2-dependent calcium signaling and transcriptional changes, and that muFHR1 deletion reduces mononuclear phagocyte invasion and neoangiogenesis.\",\n      \"evidence\": \"RNAseq, Ca2+ signaling in RPE cells, muFHR1 knockout, laser-induced choroidal neovascularization, IHC\",\n      \"pmids\": [\"40611130\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct human genetic link to AMD via this axis not established\", \"Single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how the competing complement-regulatory (C5-inhibitory) and complement-enhancing (FH-antagonist) activities of FHR-1 are balanced at specific surfaces in vivo, and whether the dimer/multimer state, allotype, and EMR2-mediated inflammatory signaling are coordinately controlled.\",\n      \"evidence\": \"No single study integrates surface-context selectivity with oligomer state and receptor signaling\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No integrated structural model of FHR-1 functions at a defined surface\", \"Selectivity determinants for inflammasome activation versus complement modulation unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 5, 6, 14]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [9, 17]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [10]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [7, 13]},\n      {\"term_id\": \"GO:0031012\", \"supporting_discovery_ids\": [14, 6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 5, 9, 11]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [9, 17]}\n    ],\n    \"complexes\": [\"FHR-1 homodimer\", \"FHR-1/FHR-2 heterodimer\"],\n    \"partners\": [\"CFH\", \"C3b\", \"CRP\", \"EMR2\", \"PTX3\", \"CFHL-1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":9,"faith_total":9,"faith_pct":100.0}}