{"gene":"SFTPA1","run_date":"2026-04-28T20:42:07","timeline":{"discoveries":[{"year":1989,"finding":"SP-A is assembled as large oligomers dependent on an intact collagen-like domain; the cysteines in the non-collagen domain form intrachain (intramolecular) disulfide bonds between residues 135-226 and 204-218; the collagen-like triple helix is confirmed by circular dichroism.","method":"Collagenase digestion, circular dichroism spectroscopy, recombinant expression in transfected fibroblasts","journal":"The American journal of physiology","confidence":"High","confidence_rationale":"Tier 1 — in vitro biochemical and structural characterization with mutagenesis/digestion in multiple SP-A forms","pmids":["2610270"],"is_preprint":false},{"year":1991,"finding":"SP-A aggregates phospholipid vesicles in a calcium-dependent manner requiring both the quaternary collagen-like triple helix and intermolecular disulfide bond at Cys-9; reduction of the intermolecular disulfide with DTT or collagenase digestion abolishes aggregation and phospholipid binding. Intramolecular bonds are Cys138-Cys229 and Cys207-Cys221.","method":"Light scattering aggregation assay, DTT reduction, collagenase digestion, HPLC tryptic peptide analysis, 14C-alkylation","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstituted in vitro assay with mutagenic/chemical dissection of specific structural requirements","pmids":["1988071"],"is_preprint":false},{"year":1991,"finding":"The C-terminal non-collagenous (globular) domain of SP-A is essential for correct folding and secretion; deletions in this domain reduce or abolish secretion, suggesting it acts as a nucleation center for collagen triple-helix folding in a zipper-like fashion from C- to N-terminus.","method":"Transient expression of deletion mutants in COS cells; secretion assay","journal":"European journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 — systematic deletion mutagenesis with functional secretion readout","pmids":["1712301"],"is_preprint":false},{"year":1992,"finding":"SP-A binds specifically and saturably to rat alveolar macrophages; binding is mediated through the collagen-like domain of SP-A (blocked by C1q and type V collagen but not albumin), consistent with a specific SP-A receptor on alveolar macrophages.","method":"125I-labeled SP-A binding assay at 4°C with competitive displacement by collagen-domain ligands","journal":"The American journal of physiology","confidence":"High","confidence_rationale":"Tier 2 — saturable binding with domain-specific competition, replicated conceptually by multiple labs","pmids":["1314502"],"is_preprint":false},{"year":1992,"finding":"SP-A enhances adsorption of lipid extract surfactant to the air-water interface in a calcium-dependent manner and induces surface sorting (enrichment of DPPC), reducing the need for compression to achieve low surface tensions.","method":"Captive bubble surfactometry with varying concentrations and SP-A supplementation","journal":"The American journal of physiology","confidence":"High","confidence_rationale":"Tier 1 — direct in vitro biophysical assay with quantitative SP-A concentration series","pmids":["1514646"],"is_preprint":false},{"year":1993,"finding":"Glucocorticoid inhibition of SP-A expression is receptor-mediated, involves induction of a labile protein that decreases gene transcription and transiently reduces SP-A mRNA stability; the inhibitory response requires new protein synthesis (blocked by cycloheximide).","method":"Nuclear elongation transcription assay, actinomycin D/label-chase mRNA stability assay, RU-486 receptor blockade, cycloheximide treatment in cultured human fetal lung explants","journal":"The American journal of physiology","confidence":"High","confidence_rationale":"Tier 1 — multiple orthogonal mechanistic assays in primary tissue","pmids":["8460712"],"is_preprint":false},{"year":1993,"finding":"SP-A is localized by immunogold EM to lamellar bodies, endoplasmic reticulum, and cytoplasmic membrane of type II cells, and to extracellular tubular myelin; SP-A is absent from tubular myelin in RDS lungs, supporting a required role for SP-A in the conversion of lamellar bodies to tubular myelin.","method":"Immunogold electron microscopy with affinity-purified anti-SP-A IgG on ultrathin sections of human lung","journal":"The American journal of pathology","confidence":"Medium","confidence_rationale":"Tier 2 — direct ultrastructural localization; mechanistic role inferred from absence in RDS; single study","pmids":["8494055"],"is_preprint":false},{"year":1994,"finding":"SP-A binds to influenza virus (strain A/X31) through its lectin (carbohydrate recognition) domain in a calcium-dependent, saturable manner and inhibits hemagglutination; the viral neuraminidase (68 kDa) was identified as the SP-A binding target.","method":"Saturable binding assay, ligand blot, neuraminidase isolation and inhibition of SP-A/MBP binding","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 — direct biochemical identification of viral binding partner with domain requirement established","pmids":["7998980"],"is_preprint":false},{"year":1994,"finding":"SP-A upregulates secretion of GM-CSF and IL-3-like colony-stimulating factors from alveolar type II cells and macrophages in a concentration-dependent manner (0.1–5 µg/ml), but not from control non-lung cells, indicating a cell-type-specific cytokine-regulatory role.","method":"In vitro CFU-C myeloid progenitor assay, antibody neutralization in cultured rat alveolar cells","journal":"The American journal of physiology","confidence":"Medium","confidence_rationale":"Tier 2 — functional in vitro assay with antibody validation; single study","pmids":["8141310"],"is_preprint":false},{"year":1994,"finding":"SP-A-mediated surfactant endocytosis by type II pneumocytes is inhibited by monensin (an endocytosis inhibitor), and SP-A accumulates with the lung after monensin treatment, indicating SP-A is cleared from alveolar space partly via an endocytic pathway in alveolar epithelial cells.","method":"125I-SP-A instillation in anesthetized rabbits with pharmacological endocytosis inhibitors (monensin, nocodazole)","journal":"The American journal of physiology","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo pharmacological dissection of SP-A clearance pathway","pmids":["8203547"],"is_preprint":false},{"year":1995,"finding":"SP-A binding to its receptor on alveolar macrophages is inversely regulated relative to the mannose receptor: agents that upregulate macrophage activation (LPS, IFN-γ, PMA) increase SP-A receptor binding while decreasing mannose receptor activity, and vice versa for dexamethasone, suggesting SP-A receptor acts as an inflammation-upregulated opsonin receptor.","method":"Competitive binding assays on rat marrow-derived macrophages and alveolar macrophages after pharmacological or in vivo treatment","journal":"The American journal of physiology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple conditions in vitro and in vivo; mechanistic inference from receptor co-regulation","pmids":["8572233"],"is_preprint":false},{"year":1995,"finding":"SP-A with DPPC shows partial miscibility and interaction in mixed monolayers; SP-A is squeezed out at ~30 mN/m but enhances respreading of DPPC films after collapse. SP-A mixes with DPPG only in the presence of calcium ions.","method":"Langmuir trough spread monolayer experiments with binary lipid-protein mixtures","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 1 — in vitro biophysical characterization; single study","pmids":["7640284"],"is_preprint":false},{"year":1996,"finding":"SP-A-mediated lipid uptake by rat type II pneumocytes is an energy- and temperature-dependent, receptor-mediated endocytic process involving the cell surface binding protein BP55; an auto-anti-idiotypic antibody against BP55 inhibits SP-A-mediated liposome uptake.","method":"Temperature/ATP-depletion uptake assay, antibody inhibition of BP55 in freshly isolated rat type II cells","journal":"The American journal of physiology","confidence":"Medium","confidence_rationale":"Tier 2 — functional receptor identification by antibody blockade; single study","pmids":["8843792"],"is_preprint":false},{"year":1997,"finding":"SP-A enhances phagocytosis of Klebsiella pneumoniae K21a (containing Manα1-Man capsular sequences) but not K2 by alveolar macrophages via two mechanisms: (1) opsonization by binding mannose-containing capsular polysaccharides through the CRD, and (2) activation of the macrophage mannose receptor; both activities are inhibited by mannan.","method":"Agglutination assay, binding of SP-A-coated particles to bacterial surface, macrophage phagocytosis and killing assay, mannan inhibition","journal":"The American journal of physiology","confidence":"High","confidence_rationale":"Tier 1 — multiple orthogonal in vitro assays with competitive inhibition establishing dual mechanism","pmids":["9124386"],"is_preprint":false},{"year":1998,"finding":"SP-A (-/-) mice have normal surfactant phospholipid composition and lung function under basal conditions but lack tubular myelin figures in the lung and show impaired clearance of Group B streptococci and Pseudomonas aeruginosa, demonstrating SP-A's role in tubular myelin formation and innate lung defense.","method":"Gene-targeted SP-A knockout mice; electron microscopy; bacterial clearance assays in vivo","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined structural and functional phenotypes; foundational study","pmids":["9813377"],"is_preprint":false},{"year":1998,"finding":"SP-A-deficient surfactant has lower buoyant density, decreased large-aggregate forms, increased conversion of large to small aggregates during cycling, increased sensitivity to plasma protein inhibition, and lacks tubular myelin, showing SP-A is required for normal surfactant aggregate structure.","method":"Buoyant density centrifugation, surface area cycling, biophysical inhibition assays, electron microscopy in SP-A KO mice","journal":"The American journal of physiology","confidence":"High","confidence_rationale":"Tier 2 — multiple biophysical assays in SP-A KO vs. WT with clean genetic model","pmids":["9700084"],"is_preprint":false},{"year":1998,"finding":"SP-A suppresses the respiratory burst (superoxide anion production) in bronchoalveolar lavage cells and peripheral neutrophils after PMA stimulation; this inhibitory effect is abolished by prior collagenase treatment of SP-A, implicating the collagen-like domain in this immunosuppressive function.","method":"Lucigenin-dependent chemiluminescence assay; collagenase pre-treatment of SP-A","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 — domain-specific ablation with functional readout; single study","pmids":["2171995"],"is_preprint":false},{"year":1999,"finding":"Glucocorticoid inhibition of the SP-A1 promoter is mediated by a region between -32/+63 relative to the transcription start; sequences within +18/+63 are necessary for dexamethasone responsiveness, and this region forms a sequence-specific DNA-protein complex with nuclear extract that is induced by dexamethasone.","method":"Deletional analysis of SP-A1 promoter with reporter gene in NCI-H441 cells; gel mobility shift (EMSA)","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 2 — promoter dissection with EMSA; single study in cell line","pmids":["10229660"],"is_preprint":false},{"year":1999,"finding":"SP-A enhances clearance of adenovirus from the lung and reduces adenoviral-induced lung inflammation (decreased TNF-α, IL-6, IL-1β, chemokines); SP-A-/- mice show decreased uptake of adenovirus by alveolar macrophages, restored by exogenous SP-A.","method":"Intratracheal infection of SP-A-/- vs. SP-A+/+ mice; BALF cytokine measurement; fluorescent adenovirus uptake assay; exogenous SP-A rescue","journal":"The American journal of physiology","confidence":"High","confidence_rationale":"Tier 2 — clean KO with multiple functional readouts and rescue experiment","pmids":["10484466"],"is_preprint":false},{"year":2000,"finding":"Amiodarone inhibits degradation of SP-A in alveolar macrophages and in vivo in rabbit lungs by disrupting the endocytic pathway after early endosomes and altering trafficking of lysosomal enzymes, without affecting DPPC degradation, indicating SP-A degradation follows a specific clathrin/endosomal route distinct from lipid degradation.","method":"In vitro macrophage exposure to amiodarone; SP-A degradation assay; lysosomal enzyme distribution; in vivo tracheal instillation in newborn rabbits","journal":"American journal of physiology. Lung cellular and molecular physiology","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological dissection with in vitro and in vivo concordance; single study","pmids":["11597911"],"is_preprint":false},{"year":2001,"finding":"After endocytosis by rat type II pneumocytes, SP-A and surfactant lipid are initially co-localized in EEA1-positive early endosomes via the coated-pit pathway, then SP-A is rapidly recycled to the cell surface via Rab4-positive vesicles, while lipid is directed to Rab7/CD63/lamellar body compartments; calmodulin inhibition blocks transport out of early endosomes.","method":"Immunofluorescence with endosomal markers (EEA1, Rab4, Rab7, CD63), pharmacological inhibitors (bafilomycin A1, calmodulin inhibitor) in isolated rat type II cells","journal":"American journal of physiology. Lung cellular and molecular physiology","confidence":"High","confidence_rationale":"Tier 2 — multiple organelle markers, pharmacological dissection, direct live-cell imaging equivalents; single study with multiple orthogonal methods","pmids":["11435209"],"is_preprint":false},{"year":2000,"finding":"SP-A degradation by alveolar macrophages requires clathrin-mediated internalization, an intact cytoskeleton, and an acidic lysosomal milieu; protein kinase C stimulation increases SP-A degradation; PI3K regulates both internalization speed and subsequent intracellular steps. DPPC degradation is unaffected by these treatments, establishing separate degradative pathways.","method":"Pharmacological inhibitors of clathrin, cytoskeleton, lysosomal acidification, PKC, and PI3K in rabbit alveolar macrophages; SP-A and DPPC degradation assays","journal":"American journal of physiology. Lung cellular and molecular physiology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple pharmacological dissections; single study","pmids":["10893207"],"is_preprint":false},{"year":2002,"finding":"Absence of SP-A in mice results in decreased influenza A virus clearance, impaired neutrophil myeloperoxidase activity, and skewed adaptive immunity toward increased Th1 responses; exogenous SP-A restores viral clearance and reduces inflammation.","method":"Intranasal influenza infection of SP-A-/- and SP-A+/+ mice; BAL myeloperoxidase; lymphocyte/cytokine analysis; exogenous SP-A rescue","journal":"American journal of physiology. Lung cellular and molecular physiology","confidence":"High","confidence_rationale":"Tier 2 — clean KO with multiple functional and immune readouts plus rescue","pmids":["11839553"],"is_preprint":false},{"year":2003,"finding":"SP-A is required for increased DPPC clearance in response to CO2-induced hyperventilation or secretagogue treatment; SP-A-/- mice show no increase in DPPC uptake under these stimuli and have increased lysosomal phospholipase A2 activity, suggesting SP-A normally channels surfactant lipid into a receptor-mediated uptake pathway suppressing lysosomal degradation.","method":"3H-DPPC liposome instillation in SP-A-/- vs. SP-A+/+ anesthetized mice; hyperventilation and secretagogue challenge; lysosomal PLA2 activity assay","journal":"American journal of physiology. Lung cellular and molecular physiology","confidence":"High","confidence_rationale":"Tier 2 — clean KO with multiple physiological challenges and biochemical readout","pmids":["12676766"],"is_preprint":false},{"year":2005,"finding":"SP-A permeabilizes Pseudomonas aeruginosa membranes; signature-tagged mutagenesis identified bacterial genes for salicylate biosynthesis (pch) and phosphoenolpyruvate-protein phosphotransferase (ptsP) that confer resistance to SP-A-mediated membrane permeabilization but not opsonization, establishing that SP-A's bactericidal and opsonization functions are mechanistically separable.","method":"Comparative signature-tagged mutagenesis in SP-A+/+ vs. SP-A-/- mice; in vitro membrane permeabilization assays","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 2 — large-scale genetic screen in vivo plus in vitro validation; two orthogonal mechanisms distinguished","pmids":["16322768"],"is_preprint":false},{"year":2008,"finding":"SP-A permeabilizes rough LPS membranes by forming large protein aggregates on the LPS surface (calcium-dependent) that extract LPS molecules from the membrane, reducing van der Waals interactions between acyl chains; coexistence of gel and fluid lipid phases within the LPS membrane is required for susceptibility.","method":"Epifluorescence microscopy of labeled SP-A on LPS films, LPS monolayer relaxation at constant pressure, differential scanning calorimetry, lipid vesicle leakage assay","journal":"Biophysical journal","confidence":"High","confidence_rationale":"Tier 1 — multiple orthogonal biophysical methods defining mechanism of membrane disruption","pmids":["18599636"],"is_preprint":false},{"year":2008,"finding":"SP-A suppresses T cell-mediated immune responses to Mycobacterium tuberculosis via its receptor SP-R210; antibodies cross-linking SP-R210 through the SP-A-binding (neck) domain markedly inhibit proliferation and IFN-γ while increasing IL-10 and TGF-β1; neutralization of IL-10 and TGF-β1 abrogates the inhibition.","method":"Antibody cross-linking of SP-R210 on PBMC; cell proliferation assay; cytokine ELISA; neutralizing antibody rescue experiment","journal":"Journal of leukocyte biology","confidence":"Medium","confidence_rationale":"Tier 2 — domain-specific receptor cross-linking with cytokine pathway dissection; single study","pmids":["18443188"],"is_preprint":false},{"year":2009,"finding":"P63/CKAP4 (a 63 kDa transmembrane protein) functions as an SP-A receptor on type II pneumocytes and mediates clathrin-dependent endocytosis of surfactant; SP-A-/- mice use an actin-dependent non-clathrin pathway, and addition of exogenous SP-A rescues the normal clathrin-mediated phenotype.","method":"Receptor identification, endocytosis pathway pharmacology, SP-A-/- rescue experiment; reviewed in synthesis paper with primary data","journal":"Cellular physiology and biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 — receptor identification with KO rescue; primary data reviewed in synthesis paper","pmids":["20054143"],"is_preprint":false},{"year":2010,"finding":"Tubular myelin formation in vivo requires both SP-A1 (SFTPA1) and SP-A2 (SFTPA2) gene products; humanized transgenic mice expressing only SP-A1 or only SP-A2 both lack tubular myelin, while mice expressing both have tubular myelin. Human BAL fluid with predominantly a single SP-A gene product also lacks tubular myelin, confirming functional divergence.","method":"Humanized transgenic mice (SP-A KO background) expressing SP-A1 or SP-A2 individually or together; electron microscopy; in vivo rescue with exogenous combined SP-A; human BAL analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple transgenic lines, in vivo rescue, human BAL validation; replicated across models","pmids":["20048345"],"is_preprint":false},{"year":2010,"finding":"SFTPA1 3' UTR variants differentially regulate translation efficiency: the 6A3 and 6A4 variants exhibit higher translation efficiency than 6A2 in vitro and in cell transfection; an 11-nucleotide element in the 3' UTR alters predicted mRNA secondary structure and miRNA binding sites, accounting for differential translational regulation.","method":"In vitro transcription/translation with luciferase reporter; transient transfection of NCI-H441 cells; 11-nt deletion/insertion mutagenesis; RNA secondary structure prediction","journal":"American journal of physiology. Lung cellular and molecular physiology","confidence":"Medium","confidence_rationale":"Tier 2 — reporter assay with mutagenesis; single study","pmids":["20693318"],"is_preprint":false},{"year":2016,"finding":"A germline missense mutation in SFTPA1 (p.Trp211Arg) in the carbohydrate recognition domain impairs SP-A1 secretion while protein production is maintained; this causes familial IPF and lung adenocarcinoma, and SP-A1 and SP-A2 are shown to be non-redundant despite structural similarity.","method":"Whole-family genetic analysis, in vitro secretion assay of mutant protein, immunohistochemistry on patient alveolar epithelium","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 — functional secretion assay combined with patient tissue immunostaining; segregation in large family","pmids":["26792177"],"is_preprint":false},{"year":2016,"finding":"SP-A1 (encoded by SFTPA1) confers better biophysical surfactant film properties than SP-A2: surfactant containing SP-A1 reaches lower surface tension after post-expansion adsorption, reorganizes better under cycling compression, and provides greater resistance to serum inhibition; these functions are SP-A1-specific.","method":"Captive bubble surfactometry on BAL from humanized transgenic mice expressing SP-A1, SP-A2, or both; recombinant SP-A reconstitution with porcine surfactant","journal":"Biophysical journal","confidence":"High","confidence_rationale":"Tier 1 — in vitro biophysical reconstitution with humanized transgenic mouse models and recombinant protein; multiple functional endpoints","pmids":["27508436"],"is_preprint":false},{"year":2019,"finding":"A homozygous missense mutation in SFTPA1 causes IPF by impairing SFTPA1 protein secretion, leading to necroptosis of alveolar type II epithelial cells via phosphorylation of IRE1α, JNK-mediated upregulation of Ripk3; JNK inhibition ameliorates pulmonary fibrosis in knock-in mice, and Ripk3 overexpression rescues the fibrotic phenotype.","method":"Knock-in mouse model with patient mutation; immunoblotting for IRE1α/JNK/Ripk3 signaling; JNK inhibitor treatment; Ripk3 overexpression rescue; necroptosis assay","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 — knock-in model with pharmacological rescue and genetic overexpression dissection of pathway","pmids":["31601679"],"is_preprint":false},{"year":2020,"finding":"Pathogenic SFTPA1 (and SFTPA2) mutations preserve protein production but abolish secretion in cell models; 11 distinct mutations from 14 unrelated patients all share this secretion-null phenotype, with altered SP-A expression pattern in patient lung tissue.","method":"In vitro mutant protein expression and secretion assay; ex vivo SP-A immunostaining in patient lung biopsy","journal":"The European respiratory journal","confidence":"High","confidence_rationale":"Tier 2 — multiple independent mutations tested in parallel with orthogonal in vitro and ex vivo methods; large patient series","pmids":["32855221"],"is_preprint":false},{"year":2022,"finding":"SP-A deficiency (CRISPR/Cas9-mediated) exacerbates bleomycin-induced pulmonary fibrosis; in vitro, TGF-β1 decreases SP-A protein expression in lung epithelial cells, and exogenous SP-A inhibits TGF-β1-induced upregulation of fibrotic markers, establishing an antifibrotic function of SP-A.","method":"CRISPR/Cas9 SP-A KO mouse + bleomycin model; in vitro TGF-β1 treatment of LA-4 cells; exogenous SP-A rescue; Western blotting for fibrotic markers","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO with in vitro mechanistic rescue; single study","pmids":["35628104"],"is_preprint":false}],"current_model":"SFTPA1-encoded SP-A1 is a collagen-containing C-type lectin (collectin) that forms oligomers via collagen-like triple helices and intermolecular disulfide bonds; its C-terminal carbohydrate recognition domain (CRD) binds calcium-dependently to mannose-containing pathogen surfaces (bacteria, viruses) enabling opsonization and direct membrane permeabilization, while its collagen-like domain engages specific receptors (SP-R210/CKAP4, BP55) on alveolar macrophages and type II pneumocytes to mediate clathrin-dependent surfactant endocytosis and recycling, regulate lysosomal degradation, suppress pro-inflammatory cytokine production and the respiratory burst, and modulate adaptive immunity via IL-10/TGF-β1 upregulation; SP-A1 uniquely cooperates with SP-A2 for tubular myelin formation in vivo and provides superior surfactant film biophysical properties; pathogenic SFTPA1 missense mutations in the CRD abolish protein secretion, leading to ER stress, IRE1α phosphorylation, JNK-mediated RIPK3 upregulation, and necroptosis of alveolar type II cells, causing familial interstitial pneumonia and lung cancer."},"narrative":{"teleology":[{"year":1989,"claim":"Establishing how SP-A oligomerizes revealed that the collagen-like domain is essential for higher-order assembly and that CRD cysteines form intramolecular disulfide bonds stabilizing the globular head, defining the basic structural architecture of the protein.","evidence":"Collagenase digestion, circular dichroism, and recombinant expression/mutagenesis in transfected fibroblasts","pmids":["2610270"],"confidence":"High","gaps":["Three-dimensional atomic structure of SP-A1 oligomer not determined","Relative contributions of individual cysteines to folding versus function not dissected"]},{"year":1991,"claim":"Demonstrating that both the collagen triple helix and the intermolecular disulfide at Cys-9 are required for calcium-dependent phospholipid aggregation established the structural prerequisites for SP-A's surfactant organizing activity, while the C-terminal globular domain was shown to nucleate folding and be required for secretion.","evidence":"Light scattering aggregation assay with DTT reduction and collagenase treatment; deletion mutagenesis with secretion assay in COS cells","pmids":["1988071","1712301"],"confidence":"High","gaps":["Precise lipid-binding site on the CRD not mapped","Whether SP-A1 and SP-A2 differ in phospholipid aggregation not addressed"]},{"year":1992,"claim":"Identifying saturable, collagen-domain-mediated binding of SP-A to alveolar macrophages and demonstrating calcium-dependent enhancement of surfactant adsorption to the air-water interface established SP-A's dual role as an immune receptor ligand and biophysical surfactant organizer.","evidence":"125I-SP-A binding with domain-specific competitive displacement on macrophages; captive bubble surfactometry with SP-A supplementation","pmids":["1314502","1514646"],"confidence":"High","gaps":["Molecular identity of the macrophage SP-A receptor not yet known","Whether the biophysical and receptor-binding activities are coordinated in vivo unclear"]},{"year":1994,"claim":"Demonstrating that SP-A binds influenza neuraminidase via its lectin domain and modulates cytokine secretion (GM-CSF) from alveolar cells established SP-A as both a pattern-recognition receptor for viruses and a regulator of innate immune signaling.","evidence":"Saturable binding/ligand blot with influenza A/X31; CFU-C myeloid progenitor assay with antibody neutralization in rat alveolar cells","pmids":["7998980","8141310"],"confidence":"High","gaps":["Downstream signaling pathway from SP-A to cytokine secretion not identified","Whether binding to neuraminidase neutralizes viral infectivity in vivo not tested"]},{"year":1996,"claim":"Identification of BP55 as a type II pneumocyte receptor mediating SP-A-dependent lipid uptake, along with evidence for energy-dependent receptor-mediated endocytosis, defined the cellular machinery for SP-A-directed surfactant recycling.","evidence":"Temperature/ATP-depletion uptake assay and anti-BP55 antibody inhibition in freshly isolated rat type II cells","pmids":["8843792"],"confidence":"Medium","gaps":["Molecular cloning and full characterization of BP55 not completed","Relative contribution of BP55 versus other candidate receptors not established"]},{"year":1998,"claim":"SP-A knockout mice lacking tubular myelin and showing impaired bacterial clearance provided definitive genetic evidence that SP-A is essential for both surfactant ultrastructure and innate pulmonary defense, while suppression of the respiratory burst via the collagen domain revealed an anti-inflammatory function.","evidence":"SP-A−/− mice with EM, bacterial clearance assays, biophysical surfactant analysis; lucigenin chemiluminescence with collagenase-treated SP-A","pmids":["9813377","9700084","2171995"],"confidence":"High","gaps":["Relative roles of SP-A1 vs. SP-A2 not resolved in murine single-gene KO","Signaling pathway downstream of collagen-domain receptor engagement unknown"]},{"year":2001,"claim":"Tracing SP-A trafficking through EEA1→Rab4 recycling vesicles in type II cells, while lipid proceeded to Rab7/lamellar bodies, revealed that SP-A and surfactant lipid are sorted into distinct endosomal pathways after co-internalization, explaining how SP-A is recycled for repeated use.","evidence":"Immunofluorescence with endosomal markers and pharmacological inhibitors (bafilomycin A1, calmodulin inhibitor) in isolated rat type II cells; clathrin/PI3K/PKC inhibitor dissection in macrophages","pmids":["11435209","10893207"],"confidence":"High","gaps":["Sorting signal on SP-A that directs it to Rab4 vesicles not identified","Whether SP-A recycling differs between type II cells and macrophages not compared directly"]},{"year":2005,"claim":"Genetic separation of SP-A's bactericidal (membrane permeabilization) and opsonic activities using bacterial mutant screens established that SP-A kills bacteria through direct membrane disruption mechanistically distinct from phagocytosis enhancement.","evidence":"Signature-tagged mutagenesis of P. aeruginosa in SP-A+/+ vs. SP-A−/− mice with in vitro permeabilization assays","pmids":["16322768"],"confidence":"High","gaps":["Structural basis for SP-A insertion into bacterial membranes not resolved","Whether SP-A1 and SP-A2 differ in membrane permeabilization not tested"]},{"year":2008,"claim":"Biophysical visualization of SP-A forming calcium-dependent aggregates on LPS surfaces that extract LPS molecules defined the physical mechanism of membrane permeabilization, while identification of SP-R210-mediated adaptive immune suppression via IL-10/TGF-β1 extended SP-A's role to T cell regulation.","evidence":"Epifluorescence on LPS films, DSC, vesicle leakage; antibody cross-linking of SP-R210 on PBMC with cytokine ELISA and neutralization","pmids":["18599636","18443188"],"confidence":"High","gaps":["Whether SP-R210-mediated immunosuppression operates in vivo during infection not shown","Stoichiometry of SP-A aggregates on bacterial surfaces unknown"]},{"year":2010,"claim":"Humanized transgenic mice proved SP-A1 and SP-A2 are both required for tubular myelin formation and are functionally non-redundant, while SP-A1 was shown to confer superior biophysical surfactant properties including lower surface tension and inhibition resistance.","evidence":"Transgenic mice expressing SP-A1, SP-A2, or both on SP-A KO background; EM; captive bubble surfactometry; human BAL validation","pmids":["20048345","27508436"],"confidence":"High","gaps":["Structural basis for SP-A1 vs. SP-A2 functional divergence not determined at atomic level","Whether specific SP-A1 variants differ in biophysical activity not tested"]},{"year":2016,"claim":"Discovery that a CRD missense mutation (p.Trp211Arg) in SFTPA1 abolishes secretion while preserving production, causing familial IPF and lung adenocarcinoma, established SFTPA1 as a Mendelian disease gene and linked its pathogenesis to protein misfolding rather than loss of extracellular function alone.","evidence":"Whole-family genetic segregation analysis; in vitro mutant secretion assay; patient lung immunohistochemistry","pmids":["26792177"],"confidence":"High","gaps":["Whether retained mutant protein triggers ER stress not yet demonstrated","Mechanism linking SFTPA1 mutation to lung cancer not elucidated"]},{"year":2019,"claim":"Demonstration that secretion-defective SFTPA1 mutations cause ER stress → IRE1α phosphorylation → JNK activation → RIPK3-mediated necroptosis of type II cells, with JNK inhibition rescuing fibrosis in knock-in mice, defined the intracellular pathogenic cascade from misfolded SP-A1 to pulmonary fibrosis.","evidence":"Knock-in mouse with patient SFTPA1 mutation; immunoblotting for IRE1α/JNK/RIPK3; JNK inhibitor rescue; RIPK3 overexpression","pmids":["31601679"],"confidence":"High","gaps":["Whether all 11 known pathogenic mutations converge on the same IRE1α-JNK-RIPK3 axis not tested","Role of necroptosis versus apoptosis in human patient lungs not confirmed"]},{"year":2020,"claim":"Systematic testing of 11 distinct SFTPA1/SFTPA2 mutations from 14 families confirmed a unifying secretion-null phenotype across all pathogenic variants, consolidating the gain-of-toxic-function disease model.","evidence":"Parallel in vitro mutant expression/secretion assays; ex vivo immunostaining of patient lung biopsies","pmids":["32855221"],"confidence":"High","gaps":["Whether partial secretion rescue could be therapeutic not explored","Genotype-phenotype correlations across variants not fully resolved"]},{"year":null,"claim":"The atomic structure of SP-A1 oligomers, the precise sorting signals that direct SP-A1 recycling versus degradation, the mechanism by which SFTPA1 mutations promote lung adenocarcinoma, and whether therapeutic chaperones can rescue mutant SP-A1 secretion remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of full-length SP-A1 oligomer","Mechanism linking SFTPA1 mutations to lung cancer not defined","Whether pharmacological chaperones can restore mutant secretion not tested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[1,4,11]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,15,28]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[8,16,26,34]},{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[3,12,27]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[6,14,15]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[6,32]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[6,20]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[20,21]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[7,13,14,18,22,24,25,26]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[32]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[9,20,21,27]}],"complexes":["Tubular myelin (with SP-A2)"],"partners":["CKAP4","BP55","SP-A2","RIPK3"],"other_free_text":[]},"mechanistic_narrative":"SFTPA1 encodes surfactant protein A1 (SP-A1), a collagen-containing C-type lectin (collectin) that is central to pulmonary surfactant homeostasis and innate immune defense in the alveolar space. SP-A1 oligomerizes via its collagen-like domain and intermolecular disulfide bonds, binds calcium-dependently to mannose-containing pathogen surfaces through its carbohydrate recognition domain (CRD) to opsonize bacteria and viruses and directly permeabilize microbial membranes, while its collagen-like domain engages receptors (CKAP4/P63, BP55) on alveolar macrophages and type II pneumocytes to drive clathrin-mediated surfactant endocytosis, suppress the respiratory burst and pro-inflammatory cytokines, and modulate adaptive immunity via IL-10/TGF-β1 [PMID:2610270, PMID:1988071, PMID:9124386, PMID:18599636, PMID:20054143, PMID:18443188, PMID:2171995]. SP-A1 cooperates non-redundantly with SP-A2 for tubular myelin formation and provides superior biophysical surfactant film properties including lower minimum surface tension and resistance to serum inhibition [PMID:20048345, PMID:27508436]. Pathogenic missense mutations in the SFTPA1 CRD abolish protein secretion while preserving production, triggering ER stress, IRE1α–JNK–RIPK3-mediated necroptosis of alveolar type II cells, and causing familial interstitial pulmonary fibrosis and lung adenocarcinoma [PMID:26792177, PMID:31601679, PMID:32855221]."},"prefetch_data":{"uniprot":{"accession":"Q8IWL2","full_name":"Pulmonary surfactant-associated protein A1","aliases":["35 kDa pulmonary surfactant-associated protein","Alveolar proteinosis protein","Collectin-4"],"length_aa":248,"mass_kda":26.2,"function":"In presence of calcium ions, it binds to surfactant phospholipids and contributes to lower the surface tension at the air-liquid interface in the alveoli of the mammalian lung and is essential for normal respiration. Enhances the expression of MYO18A/SP-R210 on alveolar macrophages (By similarity) (Microbial infection) Recognition of M.tuberculosis by dendritic cells may occur partially via this molecule (PubMed:17158455, PubMed:21203928). Can recognize, bind, and opsonize pathogens to enhance their elimination by alveolar macrophages (PubMed:21123169) (Microbial infection) Binds M.pneumoniae CARDS toxin, serves as one receptor for this pathogen (PubMed:15845487, PubMed:25139904). When SFTPA1 is down-regulated by siRNA, less toxin binds to human cells and less vacuolization (a symptom of M.pneumoniae infection) is seen (PubMed:25139904)","subcellular_location":"Secreted; Secreted, extracellular space, extracellular matrix; Secreted, extracellular space, surface film","url":"https://www.uniprot.org/uniprotkb/Q8IWL2/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SFTPA1","classification":"Not Classified","n_dependent_lines":5,"n_total_lines":1165,"dependency_fraction":0.004291845493562232},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SFTPA1","total_profiled":1310},"omim":[{"mim_id":"619611","title":"INTERSTITIAL LUNG DISEASE 1; ILD1","url":"https://www.omim.org/entry/619611"},{"mim_id":"610913","title":"SURFACTANT METABOLISM DYSFUNCTION, PULMONARY, 2; SMDP2","url":"https://www.omim.org/entry/610913"},{"mim_id":"607948","title":"MYCOBACTERIUM TUBERCULOSIS, SUSCEPTIBILITY TO","url":"https://www.omim.org/entry/607948"},{"mim_id":"606531","title":"SECRETOGLOBIN, FAMILY 3A, MEMBER 2; SCGB3A2","url":"https://www.omim.org/entry/606531"},{"mim_id":"602039","title":"EUKARYOTIC TRANSLATION INITIATION FACTOR 3, SUBUNIT A; EIF3A","url":"https://www.omim.org/entry/602039"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"lung","ntpm":6679.7}],"url":"https://www.proteinatlas.org/search/SFTPA1"},"hgnc":{"alias_symbol":["SP-A","SP-A1","COLEC4"],"prev_symbol":["SFTP1"]},"alphafold":{"accession":"Q8IWL2","domains":[{"cath_id":"3.10.100.10","chopping":"133-246","consensus_level":"high","plddt":96.8712,"start":133,"end":246}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8IWL2","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8IWL2-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8IWL2-F1-predicted_aligned_error_v6.png","plddt_mean":81.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SFTPA1","jax_strain_url":"https://www.jax.org/strain/search?query=SFTPA1"},"sequence":{"accession":"Q8IWL2","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8IWL2.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8IWL2/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8IWL2"}},"corpus_meta":[{"pmid":"16213021","id":"PMC_16213021","title":"Surfactant proteins SP-A and SP-D: structure, function and receptors.","date":"2005","source":"Molecular immunology","url":"https://pubmed.ncbi.nlm.nih.gov/16213021","citation_count":410,"is_preprint":false},{"pmid":"15589315","id":"PMC_15589315","title":"The lung collectins, SP-A and SP-D, modulate pulmonary innate immunity.","date":"2005","source":"Molecular immunology","url":"https://pubmed.ncbi.nlm.nih.gov/15589315","citation_count":154,"is_preprint":false},{"pmid":"15862582","id":"PMC_15862582","title":"Echinococcus shiquicus n. sp., a taeniid cestode from Tibetan fox and plateau pika in China.","date":"2005","source":"International journal for parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/15862582","citation_count":132,"is_preprint":false},{"pmid":"11839553","id":"PMC_11839553","title":"Absence of SP-A modulates innate and adaptive defense responses to pulmonary influenza infection.","date":"2002","source":"American journal of physiology. 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Intramolecular bonds are Cys138-Cys229 and Cys207-Cys221.\",\n      \"method\": \"Light scattering aggregation assay, DTT reduction, collagenase digestion, HPLC tryptic peptide analysis, 14C-alkylation\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in vitro assay with mutagenic/chemical dissection of specific structural requirements\",\n      \"pmids\": [\"1988071\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"The C-terminal non-collagenous (globular) domain of SP-A is essential for correct folding and secretion; deletions in this domain reduce or abolish secretion, suggesting it acts as a nucleation center for collagen triple-helix folding in a zipper-like fashion from C- to N-terminus.\",\n      \"method\": \"Transient expression of deletion mutants in COS cells; secretion assay\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic deletion mutagenesis with functional secretion readout\",\n      \"pmids\": [\"1712301\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"SP-A binds specifically and saturably to rat alveolar macrophages; binding is mediated through the collagen-like domain of SP-A (blocked by C1q and type V collagen but not albumin), consistent with a specific SP-A receptor on alveolar macrophages.\",\n      \"method\": \"125I-labeled SP-A binding assay at 4°C with competitive displacement by collagen-domain ligands\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — saturable binding with domain-specific competition, replicated conceptually by multiple labs\",\n      \"pmids\": [\"1314502\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"SP-A enhances adsorption of lipid extract surfactant to the air-water interface in a calcium-dependent manner and induces surface sorting (enrichment of DPPC), reducing the need for compression to achieve low surface tensions.\",\n      \"method\": \"Captive bubble surfactometry with varying concentrations and SP-A supplementation\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in vitro biophysical assay with quantitative SP-A concentration series\",\n      \"pmids\": [\"1514646\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Glucocorticoid inhibition of SP-A expression is receptor-mediated, involves induction of a labile protein that decreases gene transcription and transiently reduces SP-A mRNA stability; the inhibitory response requires new protein synthesis (blocked by cycloheximide).\",\n      \"method\": \"Nuclear elongation transcription assay, actinomycin D/label-chase mRNA stability assay, RU-486 receptor blockade, cycloheximide treatment in cultured human fetal lung explants\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal mechanistic assays in primary tissue\",\n      \"pmids\": [\"8460712\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"SP-A is localized by immunogold EM to lamellar bodies, endoplasmic reticulum, and cytoplasmic membrane of type II cells, and to extracellular tubular myelin; SP-A is absent from tubular myelin in RDS lungs, supporting a required role for SP-A in the conversion of lamellar bodies to tubular myelin.\",\n      \"method\": \"Immunogold electron microscopy with affinity-purified anti-SP-A IgG on ultrathin sections of human lung\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct ultrastructural localization; mechanistic role inferred from absence in RDS; single study\",\n      \"pmids\": [\"8494055\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"SP-A binds to influenza virus (strain A/X31) through its lectin (carbohydrate recognition) domain in a calcium-dependent, saturable manner and inhibits hemagglutination; the viral neuraminidase (68 kDa) was identified as the SP-A binding target.\",\n      \"method\": \"Saturable binding assay, ligand blot, neuraminidase isolation and inhibition of SP-A/MBP binding\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct biochemical identification of viral binding partner with domain requirement established\",\n      \"pmids\": [\"7998980\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"SP-A upregulates secretion of GM-CSF and IL-3-like colony-stimulating factors from alveolar type II cells and macrophages in a concentration-dependent manner (0.1–5 µg/ml), but not from control non-lung cells, indicating a cell-type-specific cytokine-regulatory role.\",\n      \"method\": \"In vitro CFU-C myeloid progenitor assay, antibody neutralization in cultured rat alveolar cells\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional in vitro assay with antibody validation; single study\",\n      \"pmids\": [\"8141310\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"SP-A-mediated surfactant endocytosis by type II pneumocytes is inhibited by monensin (an endocytosis inhibitor), and SP-A accumulates with the lung after monensin treatment, indicating SP-A is cleared from alveolar space partly via an endocytic pathway in alveolar epithelial cells.\",\n      \"method\": \"125I-SP-A instillation in anesthetized rabbits with pharmacological endocytosis inhibitors (monensin, nocodazole)\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo pharmacological dissection of SP-A clearance pathway\",\n      \"pmids\": [\"8203547\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"SP-A binding to its receptor on alveolar macrophages is inversely regulated relative to the mannose receptor: agents that upregulate macrophage activation (LPS, IFN-γ, PMA) increase SP-A receptor binding while decreasing mannose receptor activity, and vice versa for dexamethasone, suggesting SP-A receptor acts as an inflammation-upregulated opsonin receptor.\",\n      \"method\": \"Competitive binding assays on rat marrow-derived macrophages and alveolar macrophages after pharmacological or in vivo treatment\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple conditions in vitro and in vivo; mechanistic inference from receptor co-regulation\",\n      \"pmids\": [\"8572233\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"SP-A with DPPC shows partial miscibility and interaction in mixed monolayers; SP-A is squeezed out at ~30 mN/m but enhances respreading of DPPC films after collapse. SP-A mixes with DPPG only in the presence of calcium ions.\",\n      \"method\": \"Langmuir trough spread monolayer experiments with binary lipid-protein mixtures\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — in vitro biophysical characterization; single study\",\n      \"pmids\": [\"7640284\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"SP-A-mediated lipid uptake by rat type II pneumocytes is an energy- and temperature-dependent, receptor-mediated endocytic process involving the cell surface binding protein BP55; an auto-anti-idiotypic antibody against BP55 inhibits SP-A-mediated liposome uptake.\",\n      \"method\": \"Temperature/ATP-depletion uptake assay, antibody inhibition of BP55 in freshly isolated rat type II cells\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional receptor identification by antibody blockade; single study\",\n      \"pmids\": [\"8843792\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"SP-A enhances phagocytosis of Klebsiella pneumoniae K21a (containing Manα1-Man capsular sequences) but not K2 by alveolar macrophages via two mechanisms: (1) opsonization by binding mannose-containing capsular polysaccharides through the CRD, and (2) activation of the macrophage mannose receptor; both activities are inhibited by mannan.\",\n      \"method\": \"Agglutination assay, binding of SP-A-coated particles to bacterial surface, macrophage phagocytosis and killing assay, mannan inhibition\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal in vitro assays with competitive inhibition establishing dual mechanism\",\n      \"pmids\": [\"9124386\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"SP-A (-/-) mice have normal surfactant phospholipid composition and lung function under basal conditions but lack tubular myelin figures in the lung and show impaired clearance of Group B streptococci and Pseudomonas aeruginosa, demonstrating SP-A's role in tubular myelin formation and innate lung defense.\",\n      \"method\": \"Gene-targeted SP-A knockout mice; electron microscopy; bacterial clearance assays in vivo\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined structural and functional phenotypes; foundational study\",\n      \"pmids\": [\"9813377\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"SP-A-deficient surfactant has lower buoyant density, decreased large-aggregate forms, increased conversion of large to small aggregates during cycling, increased sensitivity to plasma protein inhibition, and lacks tubular myelin, showing SP-A is required for normal surfactant aggregate structure.\",\n      \"method\": \"Buoyant density centrifugation, surface area cycling, biophysical inhibition assays, electron microscopy in SP-A KO mice\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple biophysical assays in SP-A KO vs. WT with clean genetic model\",\n      \"pmids\": [\"9700084\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"SP-A suppresses the respiratory burst (superoxide anion production) in bronchoalveolar lavage cells and peripheral neutrophils after PMA stimulation; this inhibitory effect is abolished by prior collagenase treatment of SP-A, implicating the collagen-like domain in this immunosuppressive function.\",\n      \"method\": \"Lucigenin-dependent chemiluminescence assay; collagenase pre-treatment of SP-A\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — domain-specific ablation with functional readout; single study\",\n      \"pmids\": [\"2171995\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Glucocorticoid inhibition of the SP-A1 promoter is mediated by a region between -32/+63 relative to the transcription start; sequences within +18/+63 are necessary for dexamethasone responsiveness, and this region forms a sequence-specific DNA-protein complex with nuclear extract that is induced by dexamethasone.\",\n      \"method\": \"Deletional analysis of SP-A1 promoter with reporter gene in NCI-H441 cells; gel mobility shift (EMSA)\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — promoter dissection with EMSA; single study in cell line\",\n      \"pmids\": [\"10229660\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"SP-A enhances clearance of adenovirus from the lung and reduces adenoviral-induced lung inflammation (decreased TNF-α, IL-6, IL-1β, chemokines); SP-A-/- mice show decreased uptake of adenovirus by alveolar macrophages, restored by exogenous SP-A.\",\n      \"method\": \"Intratracheal infection of SP-A-/- vs. SP-A+/+ mice; BALF cytokine measurement; fluorescent adenovirus uptake assay; exogenous SP-A rescue\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with multiple functional readouts and rescue experiment\",\n      \"pmids\": [\"10484466\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Amiodarone inhibits degradation of SP-A in alveolar macrophages and in vivo in rabbit lungs by disrupting the endocytic pathway after early endosomes and altering trafficking of lysosomal enzymes, without affecting DPPC degradation, indicating SP-A degradation follows a specific clathrin/endosomal route distinct from lipid degradation.\",\n      \"method\": \"In vitro macrophage exposure to amiodarone; SP-A degradation assay; lysosomal enzyme distribution; in vivo tracheal instillation in newborn rabbits\",\n      \"journal\": \"American journal of physiology. Lung cellular and molecular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological dissection with in vitro and in vivo concordance; single study\",\n      \"pmids\": [\"11597911\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"After endocytosis by rat type II pneumocytes, SP-A and surfactant lipid are initially co-localized in EEA1-positive early endosomes via the coated-pit pathway, then SP-A is rapidly recycled to the cell surface via Rab4-positive vesicles, while lipid is directed to Rab7/CD63/lamellar body compartments; calmodulin inhibition blocks transport out of early endosomes.\",\n      \"method\": \"Immunofluorescence with endosomal markers (EEA1, Rab4, Rab7, CD63), pharmacological inhibitors (bafilomycin A1, calmodulin inhibitor) in isolated rat type II cells\",\n      \"journal\": \"American journal of physiology. Lung cellular and molecular physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple organelle markers, pharmacological dissection, direct live-cell imaging equivalents; single study with multiple orthogonal methods\",\n      \"pmids\": [\"11435209\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"SP-A degradation by alveolar macrophages requires clathrin-mediated internalization, an intact cytoskeleton, and an acidic lysosomal milieu; protein kinase C stimulation increases SP-A degradation; PI3K regulates both internalization speed and subsequent intracellular steps. DPPC degradation is unaffected by these treatments, establishing separate degradative pathways.\",\n      \"method\": \"Pharmacological inhibitors of clathrin, cytoskeleton, lysosomal acidification, PKC, and PI3K in rabbit alveolar macrophages; SP-A and DPPC degradation assays\",\n      \"journal\": \"American journal of physiology. Lung cellular and molecular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple pharmacological dissections; single study\",\n      \"pmids\": [\"10893207\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Absence of SP-A in mice results in decreased influenza A virus clearance, impaired neutrophil myeloperoxidase activity, and skewed adaptive immunity toward increased Th1 responses; exogenous SP-A restores viral clearance and reduces inflammation.\",\n      \"method\": \"Intranasal influenza infection of SP-A-/- and SP-A+/+ mice; BAL myeloperoxidase; lymphocyte/cytokine analysis; exogenous SP-A rescue\",\n      \"journal\": \"American journal of physiology. Lung cellular and molecular physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with multiple functional and immune readouts plus rescue\",\n      \"pmids\": [\"11839553\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"SP-A is required for increased DPPC clearance in response to CO2-induced hyperventilation or secretagogue treatment; SP-A-/- mice show no increase in DPPC uptake under these stimuli and have increased lysosomal phospholipase A2 activity, suggesting SP-A normally channels surfactant lipid into a receptor-mediated uptake pathway suppressing lysosomal degradation.\",\n      \"method\": \"3H-DPPC liposome instillation in SP-A-/- vs. SP-A+/+ anesthetized mice; hyperventilation and secretagogue challenge; lysosomal PLA2 activity assay\",\n      \"journal\": \"American journal of physiology. Lung cellular and molecular physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with multiple physiological challenges and biochemical readout\",\n      \"pmids\": [\"12676766\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"SP-A permeabilizes Pseudomonas aeruginosa membranes; signature-tagged mutagenesis identified bacterial genes for salicylate biosynthesis (pch) and phosphoenolpyruvate-protein phosphotransferase (ptsP) that confer resistance to SP-A-mediated membrane permeabilization but not opsonization, establishing that SP-A's bactericidal and opsonization functions are mechanistically separable.\",\n      \"method\": \"Comparative signature-tagged mutagenesis in SP-A+/+ vs. SP-A-/- mice; in vitro membrane permeabilization assays\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — large-scale genetic screen in vivo plus in vitro validation; two orthogonal mechanisms distinguished\",\n      \"pmids\": [\"16322768\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"SP-A permeabilizes rough LPS membranes by forming large protein aggregates on the LPS surface (calcium-dependent) that extract LPS molecules from the membrane, reducing van der Waals interactions between acyl chains; coexistence of gel and fluid lipid phases within the LPS membrane is required for susceptibility.\",\n      \"method\": \"Epifluorescence microscopy of labeled SP-A on LPS films, LPS monolayer relaxation at constant pressure, differential scanning calorimetry, lipid vesicle leakage assay\",\n      \"journal\": \"Biophysical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal biophysical methods defining mechanism of membrane disruption\",\n      \"pmids\": [\"18599636\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"SP-A suppresses T cell-mediated immune responses to Mycobacterium tuberculosis via its receptor SP-R210; antibodies cross-linking SP-R210 through the SP-A-binding (neck) domain markedly inhibit proliferation and IFN-γ while increasing IL-10 and TGF-β1; neutralization of IL-10 and TGF-β1 abrogates the inhibition.\",\n      \"method\": \"Antibody cross-linking of SP-R210 on PBMC; cell proliferation assay; cytokine ELISA; neutralizing antibody rescue experiment\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — domain-specific receptor cross-linking with cytokine pathway dissection; single study\",\n      \"pmids\": [\"18443188\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"P63/CKAP4 (a 63 kDa transmembrane protein) functions as an SP-A receptor on type II pneumocytes and mediates clathrin-dependent endocytosis of surfactant; SP-A-/- mice use an actin-dependent non-clathrin pathway, and addition of exogenous SP-A rescues the normal clathrin-mediated phenotype.\",\n      \"method\": \"Receptor identification, endocytosis pathway pharmacology, SP-A-/- rescue experiment; reviewed in synthesis paper with primary data\",\n      \"journal\": \"Cellular physiology and biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — receptor identification with KO rescue; primary data reviewed in synthesis paper\",\n      \"pmids\": [\"20054143\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Tubular myelin formation in vivo requires both SP-A1 (SFTPA1) and SP-A2 (SFTPA2) gene products; humanized transgenic mice expressing only SP-A1 or only SP-A2 both lack tubular myelin, while mice expressing both have tubular myelin. Human BAL fluid with predominantly a single SP-A gene product also lacks tubular myelin, confirming functional divergence.\",\n      \"method\": \"Humanized transgenic mice (SP-A KO background) expressing SP-A1 or SP-A2 individually or together; electron microscopy; in vivo rescue with exogenous combined SP-A; human BAL analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple transgenic lines, in vivo rescue, human BAL validation; replicated across models\",\n      \"pmids\": [\"20048345\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"SFTPA1 3' UTR variants differentially regulate translation efficiency: the 6A3 and 6A4 variants exhibit higher translation efficiency than 6A2 in vitro and in cell transfection; an 11-nucleotide element in the 3' UTR alters predicted mRNA secondary structure and miRNA binding sites, accounting for differential translational regulation.\",\n      \"method\": \"In vitro transcription/translation with luciferase reporter; transient transfection of NCI-H441 cells; 11-nt deletion/insertion mutagenesis; RNA secondary structure prediction\",\n      \"journal\": \"American journal of physiology. Lung cellular and molecular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reporter assay with mutagenesis; single study\",\n      \"pmids\": [\"20693318\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"A germline missense mutation in SFTPA1 (p.Trp211Arg) in the carbohydrate recognition domain impairs SP-A1 secretion while protein production is maintained; this causes familial IPF and lung adenocarcinoma, and SP-A1 and SP-A2 are shown to be non-redundant despite structural similarity.\",\n      \"method\": \"Whole-family genetic analysis, in vitro secretion assay of mutant protein, immunohistochemistry on patient alveolar epithelium\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional secretion assay combined with patient tissue immunostaining; segregation in large family\",\n      \"pmids\": [\"26792177\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SP-A1 (encoded by SFTPA1) confers better biophysical surfactant film properties than SP-A2: surfactant containing SP-A1 reaches lower surface tension after post-expansion adsorption, reorganizes better under cycling compression, and provides greater resistance to serum inhibition; these functions are SP-A1-specific.\",\n      \"method\": \"Captive bubble surfactometry on BAL from humanized transgenic mice expressing SP-A1, SP-A2, or both; recombinant SP-A reconstitution with porcine surfactant\",\n      \"journal\": \"Biophysical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro biophysical reconstitution with humanized transgenic mouse models and recombinant protein; multiple functional endpoints\",\n      \"pmids\": [\"27508436\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"A homozygous missense mutation in SFTPA1 causes IPF by impairing SFTPA1 protein secretion, leading to necroptosis of alveolar type II epithelial cells via phosphorylation of IRE1α, JNK-mediated upregulation of Ripk3; JNK inhibition ameliorates pulmonary fibrosis in knock-in mice, and Ripk3 overexpression rescues the fibrotic phenotype.\",\n      \"method\": \"Knock-in mouse model with patient mutation; immunoblotting for IRE1α/JNK/Ripk3 signaling; JNK inhibitor treatment; Ripk3 overexpression rescue; necroptosis assay\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — knock-in model with pharmacological rescue and genetic overexpression dissection of pathway\",\n      \"pmids\": [\"31601679\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Pathogenic SFTPA1 (and SFTPA2) mutations preserve protein production but abolish secretion in cell models; 11 distinct mutations from 14 unrelated patients all share this secretion-null phenotype, with altered SP-A expression pattern in patient lung tissue.\",\n      \"method\": \"In vitro mutant protein expression and secretion assay; ex vivo SP-A immunostaining in patient lung biopsy\",\n      \"journal\": \"The European respiratory journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple independent mutations tested in parallel with orthogonal in vitro and ex vivo methods; large patient series\",\n      \"pmids\": [\"32855221\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SP-A deficiency (CRISPR/Cas9-mediated) exacerbates bleomycin-induced pulmonary fibrosis; in vitro, TGF-β1 decreases SP-A protein expression in lung epithelial cells, and exogenous SP-A inhibits TGF-β1-induced upregulation of fibrotic markers, establishing an antifibrotic function of SP-A.\",\n      \"method\": \"CRISPR/Cas9 SP-A KO mouse + bleomycin model; in vitro TGF-β1 treatment of LA-4 cells; exogenous SP-A rescue; Western blotting for fibrotic markers\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with in vitro mechanistic rescue; single study\",\n      \"pmids\": [\"35628104\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SFTPA1-encoded SP-A1 is a collagen-containing C-type lectin (collectin) that forms oligomers via collagen-like triple helices and intermolecular disulfide bonds; its C-terminal carbohydrate recognition domain (CRD) binds calcium-dependently to mannose-containing pathogen surfaces (bacteria, viruses) enabling opsonization and direct membrane permeabilization, while its collagen-like domain engages specific receptors (SP-R210/CKAP4, BP55) on alveolar macrophages and type II pneumocytes to mediate clathrin-dependent surfactant endocytosis and recycling, regulate lysosomal degradation, suppress pro-inflammatory cytokine production and the respiratory burst, and modulate adaptive immunity via IL-10/TGF-β1 upregulation; SP-A1 uniquely cooperates with SP-A2 for tubular myelin formation in vivo and provides superior surfactant film biophysical properties; pathogenic SFTPA1 missense mutations in the CRD abolish protein secretion, leading to ER stress, IRE1α phosphorylation, JNK-mediated RIPK3 upregulation, and necroptosis of alveolar type II cells, causing familial interstitial pneumonia and lung cancer.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SFTPA1 encodes surfactant protein A1 (SP-A1), a collagen-containing C-type lectin (collectin) that is central to pulmonary surfactant homeostasis and innate immune defense in the alveolar space. SP-A1 oligomerizes via its collagen-like domain and intermolecular disulfide bonds, binds calcium-dependently to mannose-containing pathogen surfaces through its carbohydrate recognition domain (CRD) to opsonize bacteria and viruses and directly permeabilize microbial membranes, while its collagen-like domain engages receptors (CKAP4/P63, BP55) on alveolar macrophages and type II pneumocytes to drive clathrin-mediated surfactant endocytosis, suppress the respiratory burst and pro-inflammatory cytokines, and modulate adaptive immunity via IL-10/TGF-β1 [PMID:2610270, PMID:1988071, PMID:9124386, PMID:18599636, PMID:20054143, PMID:18443188, PMID:2171995]. SP-A1 cooperates non-redundantly with SP-A2 for tubular myelin formation and provides superior biophysical surfactant film properties including lower minimum surface tension and resistance to serum inhibition [PMID:20048345, PMID:27508436]. Pathogenic missense mutations in the SFTPA1 CRD abolish protein secretion while preserving production, triggering ER stress, IRE1α–JNK–RIPK3-mediated necroptosis of alveolar type II cells, and causing familial interstitial pulmonary fibrosis and lung adenocarcinoma [PMID:26792177, PMID:31601679, PMID:32855221].\",\n  \"teleology\": [\n    {\n      \"year\": 1989,\n      \"claim\": \"Establishing how SP-A oligomerizes revealed that the collagen-like domain is essential for higher-order assembly and that CRD cysteines form intramolecular disulfide bonds stabilizing the globular head, defining the basic structural architecture of the protein.\",\n      \"evidence\": \"Collagenase digestion, circular dichroism, and recombinant expression/mutagenesis in transfected fibroblasts\",\n      \"pmids\": [\"2610270\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Three-dimensional atomic structure of SP-A1 oligomer not determined\", \"Relative contributions of individual cysteines to folding versus function not dissected\"]\n    },\n    {\n      \"year\": 1991,\n      \"claim\": \"Demonstrating that both the collagen triple helix and the intermolecular disulfide at Cys-9 are required for calcium-dependent phospholipid aggregation established the structural prerequisites for SP-A's surfactant organizing activity, while the C-terminal globular domain was shown to nucleate folding and be required for secretion.\",\n      \"evidence\": \"Light scattering aggregation assay with DTT reduction and collagenase treatment; deletion mutagenesis with secretion assay in COS cells\",\n      \"pmids\": [\"1988071\", \"1712301\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise lipid-binding site on the CRD not mapped\", \"Whether SP-A1 and SP-A2 differ in phospholipid aggregation not addressed\"]\n    },\n    {\n      \"year\": 1992,\n      \"claim\": \"Identifying saturable, collagen-domain-mediated binding of SP-A to alveolar macrophages and demonstrating calcium-dependent enhancement of surfactant adsorption to the air-water interface established SP-A's dual role as an immune receptor ligand and biophysical surfactant organizer.\",\n      \"evidence\": \"125I-SP-A binding with domain-specific competitive displacement on macrophages; captive bubble surfactometry with SP-A supplementation\",\n      \"pmids\": [\"1314502\", \"1514646\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular identity of the macrophage SP-A receptor not yet known\", \"Whether the biophysical and receptor-binding activities are coordinated in vivo unclear\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Demonstrating that SP-A binds influenza neuraminidase via its lectin domain and modulates cytokine secretion (GM-CSF) from alveolar cells established SP-A as both a pattern-recognition receptor for viruses and a regulator of innate immune signaling.\",\n      \"evidence\": \"Saturable binding/ligand blot with influenza A/X31; CFU-C myeloid progenitor assay with antibody neutralization in rat alveolar cells\",\n      \"pmids\": [\"7998980\", \"8141310\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream signaling pathway from SP-A to cytokine secretion not identified\", \"Whether binding to neuraminidase neutralizes viral infectivity in vivo not tested\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Identification of BP55 as a type II pneumocyte receptor mediating SP-A-dependent lipid uptake, along with evidence for energy-dependent receptor-mediated endocytosis, defined the cellular machinery for SP-A-directed surfactant recycling.\",\n      \"evidence\": \"Temperature/ATP-depletion uptake assay and anti-BP55 antibody inhibition in freshly isolated rat type II cells\",\n      \"pmids\": [\"8843792\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular cloning and full characterization of BP55 not completed\", \"Relative contribution of BP55 versus other candidate receptors not established\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"SP-A knockout mice lacking tubular myelin and showing impaired bacterial clearance provided definitive genetic evidence that SP-A is essential for both surfactant ultrastructure and innate pulmonary defense, while suppression of the respiratory burst via the collagen domain revealed an anti-inflammatory function.\",\n      \"evidence\": \"SP-A−/− mice with EM, bacterial clearance assays, biophysical surfactant analysis; lucigenin chemiluminescence with collagenase-treated SP-A\",\n      \"pmids\": [\"9813377\", \"9700084\", \"2171995\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative roles of SP-A1 vs. SP-A2 not resolved in murine single-gene KO\", \"Signaling pathway downstream of collagen-domain receptor engagement unknown\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Tracing SP-A trafficking through EEA1→Rab4 recycling vesicles in type II cells, while lipid proceeded to Rab7/lamellar bodies, revealed that SP-A and surfactant lipid are sorted into distinct endosomal pathways after co-internalization, explaining how SP-A is recycled for repeated use.\",\n      \"evidence\": \"Immunofluorescence with endosomal markers and pharmacological inhibitors (bafilomycin A1, calmodulin inhibitor) in isolated rat type II cells; clathrin/PI3K/PKC inhibitor dissection in macrophages\",\n      \"pmids\": [\"11435209\", \"10893207\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Sorting signal on SP-A that directs it to Rab4 vesicles not identified\", \"Whether SP-A recycling differs between type II cells and macrophages not compared directly\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Genetic separation of SP-A's bactericidal (membrane permeabilization) and opsonic activities using bacterial mutant screens established that SP-A kills bacteria through direct membrane disruption mechanistically distinct from phagocytosis enhancement.\",\n      \"evidence\": \"Signature-tagged mutagenesis of P. aeruginosa in SP-A+/+ vs. SP-A−/− mice with in vitro permeabilization assays\",\n      \"pmids\": [\"16322768\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for SP-A insertion into bacterial membranes not resolved\", \"Whether SP-A1 and SP-A2 differ in membrane permeabilization not tested\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Biophysical visualization of SP-A forming calcium-dependent aggregates on LPS surfaces that extract LPS molecules defined the physical mechanism of membrane permeabilization, while identification of SP-R210-mediated adaptive immune suppression via IL-10/TGF-β1 extended SP-A's role to T cell regulation.\",\n      \"evidence\": \"Epifluorescence on LPS films, DSC, vesicle leakage; antibody cross-linking of SP-R210 on PBMC with cytokine ELISA and neutralization\",\n      \"pmids\": [\"18599636\", \"18443188\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SP-R210-mediated immunosuppression operates in vivo during infection not shown\", \"Stoichiometry of SP-A aggregates on bacterial surfaces unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Humanized transgenic mice proved SP-A1 and SP-A2 are both required for tubular myelin formation and are functionally non-redundant, while SP-A1 was shown to confer superior biophysical surfactant properties including lower surface tension and inhibition resistance.\",\n      \"evidence\": \"Transgenic mice expressing SP-A1, SP-A2, or both on SP-A KO background; EM; captive bubble surfactometry; human BAL validation\",\n      \"pmids\": [\"20048345\", \"27508436\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for SP-A1 vs. SP-A2 functional divergence not determined at atomic level\", \"Whether specific SP-A1 variants differ in biophysical activity not tested\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Discovery that a CRD missense mutation (p.Trp211Arg) in SFTPA1 abolishes secretion while preserving production, causing familial IPF and lung adenocarcinoma, established SFTPA1 as a Mendelian disease gene and linked its pathogenesis to protein misfolding rather than loss of extracellular function alone.\",\n      \"evidence\": \"Whole-family genetic segregation analysis; in vitro mutant secretion assay; patient lung immunohistochemistry\",\n      \"pmids\": [\"26792177\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether retained mutant protein triggers ER stress not yet demonstrated\", \"Mechanism linking SFTPA1 mutation to lung cancer not elucidated\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Demonstration that secretion-defective SFTPA1 mutations cause ER stress → IRE1α phosphorylation → JNK activation → RIPK3-mediated necroptosis of type II cells, with JNK inhibition rescuing fibrosis in knock-in mice, defined the intracellular pathogenic cascade from misfolded SP-A1 to pulmonary fibrosis.\",\n      \"evidence\": \"Knock-in mouse with patient SFTPA1 mutation; immunoblotting for IRE1α/JNK/RIPK3; JNK inhibitor rescue; RIPK3 overexpression\",\n      \"pmids\": [\"31601679\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether all 11 known pathogenic mutations converge on the same IRE1α-JNK-RIPK3 axis not tested\", \"Role of necroptosis versus apoptosis in human patient lungs not confirmed\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Systematic testing of 11 distinct SFTPA1/SFTPA2 mutations from 14 families confirmed a unifying secretion-null phenotype across all pathogenic variants, consolidating the gain-of-toxic-function disease model.\",\n      \"evidence\": \"Parallel in vitro mutant expression/secretion assays; ex vivo immunostaining of patient lung biopsies\",\n      \"pmids\": [\"32855221\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether partial secretion rescue could be therapeutic not explored\", \"Genotype-phenotype correlations across variants not fully resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The atomic structure of SP-A1 oligomers, the precise sorting signals that direct SP-A1 recycling versus degradation, the mechanism by which SFTPA1 mutations promote lung adenocarcinoma, and whether therapeutic chaperones can rescue mutant SP-A1 secretion remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution structure of full-length SP-A1 oligomer\", \"Mechanism linking SFTPA1 mutations to lung cancer not defined\", \"Whether pharmacological chaperones can restore mutant secretion not tested\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [1, 4, 11]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 15, 28]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [8, 16, 26, 34]},\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [3, 12, 27]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [6, 14, 15]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [6, 32]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [6, 20]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [20, 21]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [7, 13, 14, 18, 22, 24, 25, 26]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [32]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [9, 20, 21, 27]}\n    ],\n    \"complexes\": [\"Tubular myelin (with SP-A2)\"],\n    \"partners\": [\"CKAP4\", \"BP55\", \"SP-A2\", \"RIPK3\"],\n    \"other_free_text\": []\n  }\n}\n```"}