{"gene":"SFTPA2","run_date":"2026-06-10T07:46:31","timeline":{"discoveries":[{"year":2004,"finding":"SP-A2 variants (1A0, 1A) enhance association of Pseudomonas aeruginosa with rat alveolar macrophages significantly more than SP-A1 variants (6A2, 6A4), with SP-A1 phagocytic index approximately 52-95% of SP-A2 activity; coexpressed SP-A1/SP-A2 at certain concentrations were more active than single gene products.","method":"Light microscopy-based phagocytic index assay using insect cell-expressed human SP-A variants with rat alveolar macrophages","journal":"American journal of physiology. Lung cellular and molecular physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean in vitro functional assay with multiple variants, single lab, but insect-cell expressed protein lacks mammalian PTMs","pmids":["15377498"],"is_preprint":false},{"year":2007,"finding":"CHO cell-expressed SP-A2 variants stimulate phagocytosis (cell association and internalization) of P. aeruginosa by rat and human alveolar macrophages more than SP-A1 variants, with activity order 1A1>1A0>6A2>6A4; CHO-expressed SP-A was considerably more active than insect cell-expressed variants, implicating mammalian post-translational modifications in SP-A phagocytic activity.","method":"Light microscopy (cell association) and FACS (internalization) using CHO cell-expressed SP-A variants with rat and human alveolar macrophages","journal":"Infection and immunity","confidence":"High","confidence_rationale":"Tier 2 / Strong — two orthogonal methods (microscopy + FACS), multiple variants, two macrophage types, replicates earlier finding with improved expression system","pmids":["17220308"],"is_preprint":false},{"year":2004,"finding":"SP-A2 variant (1A0) and coexpressed SP-A1/SP-A2 (1A0/6A2) inhibit ATP-stimulated phosphatidylcholine secretion from alveolar type II cells to a greater extent than SP-A1 (6A2); this biological activity is susceptible to ozone-induced oxidation. SP-A1 forms higher-order multimers than SP-A2 under various conditions, and ozone oxidation involves cysteine, methionine, and tryptophan residues.","method":"In vitro PC secretion assay with alveolar type II cells; oligomerization analysis; ozone exposure with amino acid oxidation characterization","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional assay with defined cellular readout plus biochemical characterization, single lab, multiple orthogonal approaches","pmids":["15065867"],"is_preprint":false},{"year":2002,"finding":"Recombinant SP-A2 binds carbohydrates with higher affinity and to a wider variety of sugars than SP-A1 at 1 or 5 mM Ca2+; all SP-A proteins bind fucose with greatest affinity; SP-A2 is only expressed in submucosal glands of conducting airways whereas both SP-A1 and SP-A2 are in alveoli.","method":"Carbohydrate-binding assays with recombinant human SP-A1 and SP-A2 proteins under defined calcium concentrations","journal":"American journal of physiology. Lung cellular and molecular physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding assay with recombinant proteins, multiple calcium conditions and sugar types, single lab","pmids":["12505869"],"is_preprint":false},{"year":2007,"finding":"SP-A2 (1A0) forms higher-order supratrimeric oligomers than SP-A1; greater supratrimeric assembly correlates with lower Kd for binding to bacterial Re-LPS, greater self-association in the presence of calcium, and greater capability to aggregate Re-LPS and phospholipids; SP-A1 is more resistant to trypsin degradation than SP-A2; coexpressed SP-A1/SP-A2 has greater thermal stability and combines properties of each.","method":"Analytical ultracentrifugation, differential scanning calorimetry, fluorescence spectroscopy, LPS binding and aggregation assays, proteolysis resistance assay using recombinant baculovirus-derived proteins","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal biophysical and functional methods in a single rigorous study establishing structure-function relationship","pmids":["17542781"],"is_preprint":false},{"year":2010,"finding":"Formation of tubular myelin in vivo requires both SP-A1 and SP-A2 gene products; humanized transgenic mice expressing only SP-A1(6A4) or only SP-A2(1A3) lacked tubular myelin, while mice carrying both had tubular myelin; tubular myelin was observed in human bronchoalveolar lavage only when both SP-A1 and SP-A2 were present; in vivo rescue confirmed tubular myelin restored only by exogenous SP-A containing both SP-A1 and SP-A2.","method":"Electron microscopy in humanized transgenic mice on SP-A knockout background; human BAL analysis; in vivo rescue with exogenous SP-A administration","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo transgenic model with KO background, electron microscopy, human BAL validation, and rescue experiment across multiple orthogonal approaches","pmids":["20048345"],"is_preprint":false},{"year":2007,"finding":"SP-A1 (6A2) and SP-A2 (1A0) variants have differential effects on the organization of phospholipid monolayers containing SP-B; lipid films with SP-B and SP-A2 (1A0) showed surface features similar to those with native human SP-A, including fluorescent probe-excluding clusters coexisting with liquid-expanded and liquid-condensed phases, whereas SP-A1 (6A2) showed different protein distribution.","method":"Fluorescence microscopy of phospholipid monolayers at the air-water interface containing SP-B and SP-A variants","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct biophysical assay with recombinant proteins and comparison to native SP-A, single lab","pmids":["17678872"],"is_preprint":false},{"year":1994,"finding":"SP-A2 gene is more highly regulated by cAMP and during fetal development than SP-A1; in adult lung, 65% of SP-A mRNA is from SP-A2, while in 28-week neonate only SP-A1 transcripts were detected; cAMP and glucocorticoids (dexamethasone) differentially regulate SP-A1 and SP-A2 transcription.","method":"Primer extension analysis of human adult and fetal lung tissues; organ culture of fetal lung with DBcAMP and dexamethasone; Northern analysis","journal":"The American journal of physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct measurement in human tissue and fetal lung culture with defined hormonal treatments, single lab","pmids":["8179013"],"is_preprint":false},{"year":1994,"finding":"SP-A2 mRNA transcripts are always comprised of sequences within six exons (with an extra exon II encoding additional 5'-UTR sequences absent in SP-A1); most SP-A1 transcripts use five exons; both genes produce alternatively spliced transcripts from alternate exons; SP-A1 majority transcripts initiate 5 bp downstream of the SP-A2 transcription initiation site.","method":"Primer extension, RACE (rapid amplification of cDNA ends), sequencing of 47 full-length primer-extended cDNAs from human fetal lung explants","journal":"The American journal of physiology","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct sequence analysis of 47 clones with multiple methods establishing exon-intron structure","pmids":["8179012"],"is_preprint":false},{"year":1996,"finding":"A CRE-like element (CRESP-A2: TGACCTTA) at -242 bp in the SP-A2 promoter is essential for basal and cAMP-inducible expression in alveolar type II cells; nuclear proteins from fetal lung bind specifically to CRESP-A2, with proteins of ~50, 36, and 30 kDa identified by UV cross-linking; upon DBcAMP-induced differentiation, the ~30 kDa protein binding is lost; mutation of CRESP-A2 markedly reduces both basal and cAMP-stimulated expression; CRESP-A2 binds different proteins than the canonical CRE.","method":"Transfection of SP-A2 5'-flanking DNA-hGH fusion genes into primary human type II cells; competitive EMSA; UV cross-linking with nuclear extracts; site-directed mutagenesis of CRESP-A2","journal":"The American journal of physiology","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis confirming functional necessity, UV cross-linking for protein identification, EMSA with nuclear extracts, multiple complementary methods in one study","pmids":["8770068"],"is_preprint":false},{"year":1998,"finding":"In baboon SP-A2 and SP-A1 genes, three TTF-1 (thyroid transcription factor-1) binding elements are present within 255 bp of 5'-flanking sequence of each gene but differ in position and spacing; 255 bp of 5'-flanking DNA from either bSP-A1 or bSP-A2 is sufficient to mediate high basal and cAMP-inducible expression in type II cells.","method":"DNase I footprinting, EMSA with bacterially expressed TTF-1 and type II cell nuclear extracts, transfection of 5'-flanking DNA-hGH fusion genes into primary type II cells","journal":"The American journal of physiology","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — footprinting and EMSA establish TTF-1 binding; functional validation by transfection; ortholog study (baboon), single lab","pmids":["9843844"],"is_preprint":false},{"year":2000,"finding":"Phorbol ester (TPA) represses SP-A2 promoter activity (~55-65% reduction); a region in SP-A2 intron 1 (+309/+329) forms TPA-induced sequence-specific DNA-protein complexes; the consensus AP-1-like sequence (TCACTGA in SP-A2) is required for complex formation; TPA-induced complex contains Jun family proteins (not Fos); mutation of this AP-1-like site prevents TPA-induced complex formation.","method":"Deletional analysis of SP-A promoter by transfection in NCI-H441 cells; EMSA with NCI-H441 nuclear proteins; antibody supershift for Jun/Fos family proteins; site-directed mutagenesis of AP-1-like site","journal":"Experimental lung research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — EMSA plus antibody supershift plus mutagenesis, single lab, multiple complementary methods","pmids":["10914330"],"is_preprint":false},{"year":2005,"finding":"SP-A 5'-UTR splice variants differentially regulate SP-A production through mRNA stability and translational efficiency; the ABD variant has the lowest rate of mRNA decay; ABD and AB'D' 5'-UTR variants have higher translational efficiency than control; A'D' and A'CD' have lower translational efficiency than control; all four variants studied increased luciferase mRNA stability.","method":"In vitro transient expression of hSP-A 5'-UTR constructs with luciferase reporter; quantitative real-time PCR for mRNA levels; mRNA decay assays","journal":"American journal of physiology. Lung cellular and molecular physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reporter gene assays plus quantitative PCR in two orthogonal readouts (activity and mRNA), single lab","pmids":["15894557"],"is_preprint":false},{"year":2015,"finding":"Allelic differences in SP-A2 at position Gln223Lys affect binding to Mycoplasma pneumoniae membrane fractions (MMF); humanized SP-A2 transgenic mice with 223K allele exhibit reduced neutrophil influx and mucin production when challenged with MMF compared to SP-A-/- mice; mice expressing 223Q have increased neutrophil influx and mucin production similar to SP-A-/- mice; SP-A interaction with EGFR signaling pathway limits MMF-stimulated mucin production in an allele-specific manner; EGFR phosphorylation is increased in MMF-challenged SP-A-/- lungs and pharmacologic EGFR inhibition reduces mucin production.","method":"Humanized SP-A2 transgenic mouse model with MMF challenge; measurement of neutrophil recruitment and mucin production; pharmacologic EGFR inhibition; Western blot for EGFR phosphorylation; tracheal epithelial cell cultures","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo transgenic model with allele-specific comparison, pharmacologic epistasis experiment, multiple readouts (neutrophil, mucin, EGFR phosphorylation), mechanistic pathway identified","pmids":["25957169"],"is_preprint":false},{"year":2020,"finding":"A 20-mer peptide derived from the lectin/carbohydrate recognition domain of SP-A2 containing the 223Q variant significantly decreases TNF-α mRNA and protein levels during M. pneumoniae infection; the 223Q-20mer peptide reduces NF-κB p65 phosphorylation in both SP-A KO mice and RAW 264.7 cells; neither 20-mer (223Q or 223K) affected p38 phosphorylation.","method":"SP-A knockout mouse model challenged with live M. pneumoniae; RAW 264.7 macrophage cell line; qPCR for TNF-α mRNA; ELISA for TNF-α protein; Western blot for NF-κB p65 and p38 phosphorylation","journal":"Infection and immunity","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two model systems (in vivo and in vitro), multiple endpoints, negative result for p38 informative, single lab","pmids":["32513852"],"is_preprint":false},{"year":2018,"finding":"Pathogenic mutations in SFTPA2 (including G231V and F198S) cause preserved protein production but abolished secretion; mutant SP-A2 forms aggregates intracellularly; chemical chaperone 4-PBA enhances secretion and decreases aggregation of mutant SP-A2; GRP78 (BiP) overexpression reduces mutant SP-A2 aggregation while GRP78 knockdown enhances it; 4-PBA upregulates GRP78 expression, partially accounting for its aggregate-alleviating effect.","method":"In vitro expression of mutant SP-A2 in CHO-K1 cells; secretion and aggregation assays; MG-132 proteasome inhibition; chymotrypsin degradation assay; GRP78 overexpression and shRNA knockdown; Western blot","journal":"Biochimica et biophysica acta. Molecular basis of disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple cellular perturbations (overexpression, knockdown, chemical chaperone, proteasome inhibition) in single lab establishing GRP78 as regulator of SP-A2 aggregation","pmids":["30293573"],"is_preprint":false},{"year":2020,"finding":"Pathogenic SFTPA2 mutations preserve protein production but abolish SP-A secretion in cell models; ex vivo lung tissue from mutation carriers showed altered SP-A expression patterns; secretion defect confirmed in 11 different SFTPA1/SFTPA2 mutations.","method":"In vitro expression of mutant proteins with secretion/production assays; ex vivo immunostaining of lung tissue from mutation carriers","journal":"The European respiratory journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro functional assay plus ex vivo tissue validation across 11 mutations in 14 independent patients, multiple labs/centers","pmids":["32855221"],"is_preprint":false},{"year":2007,"finding":"SP-A1 and SP-A2 CHO-expressed variants both display α(2,3)-linked sialic acids and have similar activity against influenza A virus PR-8 strain (which preferentially binds α(2,3)-linked sialic acids), suggesting no difference between SP-A1 and SP-A2 in inhibiting hemagglutination of avian-like IAV strains.","method":"Hemagglutination inhibition assay with CHO-expressed SP-A variants; sialic acid linkage analysis","journal":"Medical microbiology and immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct functional assay with characterized proteins; negative finding (no difference for α2,3-sialic acid-preferring strains) explicitly reported","pmids":["17520282"],"is_preprint":false},{"year":2022,"finding":"Full-length recombinant SP-A2 223Q is more effective than SP-A2 223K at reducing IL-13-induced MUC5AC gene expression in primary bronchial epithelial cells from asthmatic participants; 10- and 20-mer peptides spanning position 223Q of SP-A2 reduce eosinophilic inflammation, mucin production and airway hyperresponsiveness in a house dust mite mouse model and protect from lung function decline during IL-13 challenge.","method":"Recombinant protein treatment of primary human bronchial epithelial cells; humanized SP-A2 transgenic mouse models; house dust mite and IL-13 challenge models; measurement of mucin (MUC5AC), eosinophils, and airway hyperresponsiveness","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple mouse models and human primary cells, allele-specific comparison, multiple functional readouts, single lab","pmids":["35874703"],"is_preprint":false},{"year":2018,"finding":"SP-A2 (1A3) transgenic male mice show increased total and central airway resistance after methacholine challenge following K. pneumoniae infection; allele-specific differences exist with SP-A2 (1A3) exhibiting significantly higher lung resistance than SP-A2 (1A0); sex-specific differences in airway responses are observed with SP-A2 variants.","method":"Humanized transgenic mouse model; flexiVent forced oscillation technique measurements after K. pneumoniae infection and methacholine challenge","journal":"Respiratory research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo lung function measurements with multiple SP-A variant transgenic lines and KO controls, single lab","pmids":["29394894"],"is_preprint":false},{"year":2018,"finding":"SP-A1 and SP-A2 variants differentially affect survival after K. pneumoniae infection in a gene-, variant-, and sex-specific manner with order co-ex = SP-A2 > SP-A1 > KO; SP-A1 and SP-A2 differentially bind to phagocytic (but not non-phagocytic) cells; alveolar macrophages from SP-A1 and SP-A2 transgenic mice exhibit differential expression of cell surface proteins; treatment of KO mice with exogenous SP-A1 or SP-A2 significantly improves survival.","method":"Humanized transgenic mouse survival study with intratracheal K. pneumoniae infection; flow cytometry for cell surface protein expression on AMs; SP-A binding assays with phagocytic and non-phagocytic cells; exogenous SP-A rescue treatment","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo survival plus binding assay plus rescue experiment, multiple SP-A variant lines, single lab","pmids":["30459763"],"is_preprint":false},{"year":2017,"finding":"SP-A2 in male transgenic mice influences miRNA-mediated sex-specific differences in response to ozone-induced oxidative stress; 11 miRNAs were differentially expressed under oxidative stress with targets including BCL2, CAT, FOXO1, IL-6, NF-κB, SOD2, and STAT3; SP-A2 promotes anti-apoptotic BCL2 mRNA increase and pro-inflammatory IL-6 elevation after oxidative stress; SOD2 protein increased while CAT was unchanged; sex hormones contribute to miRNome changes (confirmed by gonadectomy).","method":"Humanized SP-A2 transgenic and KO mice with ozone exposure; miRNA microarray; qPCR for target mRNAs; ELISA for cytokines and proteins; gonadectomy experiment","journal":"Biology of sex differences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — transgenic vs KO comparison, multiple molecular readouts, gonadectomy as mechanistic intervention, single lab","pmids":["29202868"],"is_preprint":false},{"year":2024,"finding":"Human SP-A2 variant 1A0 transgenic mice infected with SARS-CoV-2 show more severe acute lung injury and higher mortality, similar to SP-A KO mice; SP-A-expressing mice have reduced viral titers relative to KO; 1A0 mice show upregulation of MyD88, Stat3, IL-18, and Jak2; Mapk1 is significantly downregulated in 6A2 versus 1A0 mice; NOD1/2 and Trem1 signaling pathways are involved; IL-6, G-CSF, and IL-1β levels are higher in KO and 1A0 mice.","method":"Humanized double-transgenic mice (hACE2 + individual SP-A variants) with intranasal SARS-CoV-2 challenge; survival monitoring; lung histology; viral titer measurement; transcriptomic analysis; cytokine/chemokine multiplex assay","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — in vivo transgenic model with multiple readouts but preprint without peer review, single lab","pmids":["bio_10.1101_2024.09.11.612497"],"is_preprint":true}],"current_model":"SFTPA2 encodes SP-A2, a C-type lectin collectin that forms supratrimeric oligomers and functions in pulmonary innate immunity and surfactant biology; SP-A2 variants are generally more biologically active than SP-A1 variants in enhancing phagocytosis of bacteria (P. aeruginosa, K. pneumoniae, M. pneumoniae) by alveolar macrophages, bind carbohydrates with higher affinity and broader specificity, interact with pathogen-derived molecules in an allele-specific manner (e.g., Gln223Lys affecting MMF binding and EGFR-mediated mucin regulation), require co-expression with SP-A1 for tubular myelin formation in vivo, and are regulated at the transcriptional level by a CRE-like element (CRESP-A2) bound by fetal lung nuclear proteins, by TTF-1 binding elements, by AP-1/Jun in response to phorbol esters, and by differential effects of cAMP, glucocorticoids, and IFN-γ; pathogenic SFTPA2 mutations cause preserved protein production but abolished secretion with intracellular aggregation, the latter regulated by GRP78/BiP."},"narrative":{"mechanistic_narrative":"SFTPA2 encodes SP-A2, a calcium-dependent carbohydrate-binding collectin of pulmonary surfactant that contributes to innate host defense and surfactant structural organization in the lung [PMID:12505869, PMID:17542781]. SP-A2 assembles into higher-order supratrimeric oligomers, and this degree of oligomeric assembly correlates with tighter binding to bacterial Re-LPS, calcium-dependent self-association, and the capacity to aggregate LPS and phospholipids [PMID:17542781]; through its lectin/carbohydrate-recognition domain SP-A2 binds a wide range of sugars with higher affinity than the SP-A1 gene product [PMID:12505869]. Functionally, SP-A2 variants enhance the association and internalization of bacteria such as Pseudomonas aeruginosa by alveolar macrophages more potently than SP-A1, an activity dependent on mammalian post-translational modification [PMID:15377498, PMID:17220308], and modulate surfactant phospholipid handling by inhibiting type II cell phosphatidylcholine secretion and organizing SP-B-containing lipid monolayers [PMID:15065867, PMID:17678872]. SP-A1 and SP-A2 gene products are functionally non-redundant: both are required together for tubular myelin formation in vivo [PMID:20048345]. SP-A2 shapes host responses to infection and injury in an allele-specific manner, with the Gln223Lys polymorphism governing binding to Mycoplasma pneumoniae membrane fractions, EGFR-dependent limitation of mucin production and neutrophil influx, NF-κB-dependent TNF-α induction, and IL-13/MUC5AC-driven airway responses, where the 223Q allele and 223Q-spanning peptides are protective [PMID:25957169, PMID:32513852, PMID:35874703]. SFTPA2 expression is controlled transcriptionally through a CRE-like element (CRESP-A2) bound by fetal lung nuclear proteins for basal and cAMP-inducible activity [PMID:8770068], TTF-1 binding elements [PMID:9843844], and an intronic AP-1/Jun element mediating phorbol ester repression [PMID:10914330], with additional regulation by 5'-UTR splice variants affecting mRNA stability and translation [PMID:15894557]. Pathogenic SFTPA2 mutations (including G231V and F198S) preserve protein production but abolish secretion, causing intracellular aggregation that is alleviated by the chaperone GRP78/BiP and the chemical chaperone 4-PBA [PMID:30293573, PMID:32855221].","teleology":[{"year":1994,"claim":"Establishing the SFTPA2 gene/transcript architecture and its distinct developmental and hormonal regulation defined SP-A2 as a separately controlled gene rather than a redundant duplicate of SP-A1.","evidence":"Primer extension, RACE and sequencing of fetal lung cDNAs plus organ culture with cAMP/dexamethasone","pmids":["8179012","8179013"],"confidence":"High","gaps":["Did not address functional consequences of the SP-A1/SP-A2 sequence differences","Promoter elements responsible for differential regulation not yet mapped"]},{"year":1996,"claim":"Identifying the CRESP-A2 CRE-like element answered how SP-A2 achieves basal and cAMP-inducible transcription in type II cells, distinguishing its regulation from a canonical CRE.","evidence":"Reporter transfection, competitive EMSA, UV cross-linking and mutagenesis in primary human type II cells","pmids":["8770068"],"confidence":"High","gaps":["Identities of the ~50/36/30 kDa CRESP-A2-binding proteins not determined","Relationship between the ~30 kDa protein loss and differentiation not mechanistically resolved"]},{"year":1998,"claim":"Mapping TTF-1 binding elements in the proximal promoter identified a lineage-specific transcription factor input governing SP-A2 expression in alveolar epithelium.","evidence":"DNase I footprinting, EMSA with recombinant TTF-1, and reporter transfection (baboon ortholog)","pmids":["9843844"],"confidence":"Medium","gaps":["Performed on baboon genes; human element positioning not directly tested here","Combinatorial logic with CRESP-A2 not resolved"]},{"year":2000,"claim":"An intronic AP-1/Jun element explained phorbol-ester repression of SP-A2, linking PKC signaling to negative transcriptional control.","evidence":"Deletional reporter analysis, EMSA, antibody supershift and mutagenesis in NCI-H441 cells","pmids":["10914330"],"confidence":"Medium","gaps":["Physiological stimulus driving Jun recruitment in vivo not identified","Specific Jun family member not pinpointed"]},{"year":2002,"claim":"Direct carbohydrate-binding comparison established that SP-A2 binds sugars with higher affinity and broader specificity than SP-A1, providing a biochemical basis for differential lectin function.","evidence":"Carbohydrate-binding assays with recombinant SP-A1 and SP-A2 at defined calcium concentrations","pmids":["12505869"],"confidence":"Medium","gaps":["Structural basis of the affinity difference not defined","In vivo relevance of submucosal-gland-restricted SP-A2 expression not tested"]},{"year":2004,"claim":"Functional assays showed SP-A2 variants are more active than SP-A1 in promoting bacterial phagocytosis and in suppressing type II cell PC secretion, beginning the case for SP-A2 as the more biologically active gene product.","evidence":"Phagocytic index assay and PC secretion assay using insect-cell-expressed variants plus ozone-oxidation analysis","pmids":["15377498","15065867"],"confidence":"Medium","gaps":["Insect-cell proteins lack mammalian PTMs","Mechanism linking oxidation of specific residues to activity loss not resolved"]},{"year":2005,"claim":"5'-UTR splice variants were shown to tune SP-A output post-transcriptionally via mRNA stability and translational efficiency, adding a layer of expression control beyond promoter activity.","evidence":"Luciferase reporter constructs with qPCR and mRNA decay assays","pmids":["15894557"],"confidence":"Medium","gaps":["Trans-acting factors recognizing the 5'-UTRs not identified","Reporter context may not reflect native SP-A mRNA"]},{"year":2007,"claim":"Biophysical and improved expression studies linked SP-A2 supratrimeric oligomerization to LPS binding/aggregation and confirmed PTM-dependent phagocytic potency, connecting quaternary structure to innate-immune function.","evidence":"Analytical ultracentrifugation, DSC, fluorescence spectroscopy and binding assays; CHO-expressed variants in macrophage assays; lipid monolayer microscopy; hemagglutination inhibition","pmids":["17542781","17220308","17678872","17520282"],"confidence":"High","gaps":["No atomic structure of the oligomer","SP-A1 vs SP-A2 equivalence against avian-like IAV indicates the activity difference is pathogen-specific, mechanism unresolved"]},{"year":2010,"claim":"Humanized transgenic and rescue experiments demonstrated that tubular myelin formation requires both SP-A1 and SP-A2, defining a non-redundant structural cooperation between the two gene products in vivo.","evidence":"Electron microscopy in humanized transgenic mice on SP-A-null background, human BAL analysis, and exogenous SP-A rescue","pmids":["20048345"],"confidence":"High","gaps":["Molecular interface mediating SP-A1/SP-A2 cooperation unknown","Functional consequence of tubular myelin loss for surfactant function not quantified here"]},{"year":2015,"claim":"The Gln223Lys polymorphism was shown to control SP-A2 binding to M. pneumoniae and allele-specific limitation of mucin production through EGFR signaling, defining a genotype-dependent host-defense mechanism.","evidence":"Humanized SP-A2 transgenic mice with MMF challenge, pharmacologic EGFR inhibition, and EGFR phosphorylation Westerns","pmids":["25957169"],"confidence":"High","gaps":["Direct biochemical interaction of SP-A2 with EGFR not demonstrated","How allelic binding difference translates to EGFR modulation not resolved"]},{"year":2018,"claim":"In vivo infection, lung-function and stress studies extended the allele- and gene-specific functional hierarchy of SP-A2 to survival, airway resistance, miRNA-mediated stress responses, and revealed pathogenic mutations as secretion-deficient.","evidence":"Humanized transgenic mouse K. pneumoniae survival and methacholine challenge, ozone-stress miRNA profiling, and CHO-cell secretion/aggregation assays of mutant SP-A2","pmids":["29394894","30459763","29202868","30293573"],"confidence":"Medium","gaps":["Molecular basis of sex-specific SP-A2 effects not fully defined","Cell-surface receptors mediating differential phagocytic-cell binding not identified"]},{"year":2020,"claim":"Studies on disease mutations and 223Q-derived peptides clarified that pathogenic SFTPA2 mutations cause GRP78-regulated intracellular aggregation, and that the 223Q lectin-domain region dampens NF-κB-driven inflammation.","evidence":"GRP78 overexpression/knockdown and 4-PBA in CHO cells with ex vivo carrier tissue; SP-A KO mouse and RAW 264.7 cells with 20-mer peptides and NF-κB/p38 Westerns","pmids":["32513852","32855221","30293573"],"confidence":"Medium","gaps":["Structural nature of the aggregates and the exact GRP78 interaction interface unknown","Whether peptide effects translate beyond rodent/cell models untested"]},{"year":2022,"claim":"Allele-specific protection in asthma models established SP-A2 223Q (full-length and peptides) as a suppressor of IL-13/MUC5AC-driven mucin and airway hyperresponsiveness, generalizing the 223 polymorphism's role to allergic airway disease.","evidence":"Recombinant protein treatment of asthmatic primary bronchial epithelial cells and humanized SP-A2 mice in house dust mite and IL-13 challenge models","pmids":["35874703"],"confidence":"Medium","gaps":["Receptor/target through which 223Q peptides act on epithelium not defined","Durability and human applicability of peptide protection not established"]},{"year":2024,"claim":"A SARS-CoV-2 model probed SP-A2 variant effects on viral lung injury, indicating SP-A reduces viral titers while the 1A0 variant associates with severe injury and altered innate signaling.","evidence":"Humanized hACE2 + SP-A variant double-transgenic mice with SARS-CoV-2 challenge, transcriptomics and cytokine multiplex (preprint)","pmids":["bio_10.1101_2024.09.11.612497"],"confidence":"Medium","gaps":["Preprint not peer-reviewed","Mechanistic link between variant and the implicated signaling pathways not established"]},{"year":null,"claim":"How SP-A2 oligomers engage specific alveolar macrophage and epithelial receptors to drive phagocytosis, EGFR/NF-κB modulation, and surfactant organization remains structurally and mechanistically undefined.","evidence":"","pmids":[],"confidence":"Low","gaps":["No atomic structure of SP-A2 oligomers or its receptor complexes","Direct SP-A2 receptor(s) on phagocytic cells not molecularly identified","Mechanism connecting carbohydrate binding to downstream EGFR and NF-κB signaling unresolved"]}],"mechanism_profile":{"molecular_activity":[],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[5,16]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[15]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,1,13,20]}],"complexes":["tubular myelin (SP-A1/SP-A2)"],"partners":["SFTPA1","SFTPB","GRP78/HSPA5","EGFR"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8IWL1","full_name":"Pulmonary surfactant-associated protein A2","aliases":["35 kDa pulmonary surfactant-associated protein","Alveolar proteinosis protein","Collectin-5"],"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","subcellular_location":"Secreted; Secreted, extracellular space, extracellular matrix; Secreted, extracellular space, surface film","url":"https://www.uniprot.org/uniprotkb/Q8IWL1/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SFTPA2","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SFTPA2","total_profiled":1310},"omim":[{"mim_id":"619611","title":"INTERSTITIAL LUNG DISEASE 1; ILD1","url":"https://www.omim.org/entry/619611"},{"mim_id":"607948","title":"MYCOBACTERIUM TUBERCULOSIS, SUSCEPTIBILITY TO","url":"https://www.omim.org/entry/607948"},{"mim_id":"267450","title":"RESPIRATORY DISTRESS SYNDROME IN PREMATURE INFANTS","url":"https://www.omim.org/entry/267450"},{"mim_id":"211980","title":"LUNG CANCER","url":"https://www.omim.org/entry/211980"},{"mim_id":"178642","title":"SURFACTANT, PULMONARY-ASSOCIATED PROTEIN A2; 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Lung cellular and molecular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean in vitro functional assay with multiple variants, single lab, but insect-cell expressed protein lacks mammalian PTMs\",\n      \"pmids\": [\"15377498\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"CHO cell-expressed SP-A2 variants stimulate phagocytosis (cell association and internalization) of P. aeruginosa by rat and human alveolar macrophages more than SP-A1 variants, with activity order 1A1>1A0>6A2>6A4; CHO-expressed SP-A was considerably more active than insect cell-expressed variants, implicating mammalian post-translational modifications in SP-A phagocytic activity.\",\n      \"method\": \"Light microscopy (cell association) and FACS (internalization) using CHO cell-expressed SP-A variants with rat and human alveolar macrophages\",\n      \"journal\": \"Infection and immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — two orthogonal methods (microscopy + FACS), multiple variants, two macrophage types, replicates earlier finding with improved expression system\",\n      \"pmids\": [\"17220308\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"SP-A2 variant (1A0) and coexpressed SP-A1/SP-A2 (1A0/6A2) inhibit ATP-stimulated phosphatidylcholine secretion from alveolar type II cells to a greater extent than SP-A1 (6A2); this biological activity is susceptible to ozone-induced oxidation. SP-A1 forms higher-order multimers than SP-A2 under various conditions, and ozone oxidation involves cysteine, methionine, and tryptophan residues.\",\n      \"method\": \"In vitro PC secretion assay with alveolar type II cells; oligomerization analysis; ozone exposure with amino acid oxidation characterization\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional assay with defined cellular readout plus biochemical characterization, single lab, multiple orthogonal approaches\",\n      \"pmids\": [\"15065867\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Recombinant SP-A2 binds carbohydrates with higher affinity and to a wider variety of sugars than SP-A1 at 1 or 5 mM Ca2+; all SP-A proteins bind fucose with greatest affinity; SP-A2 is only expressed in submucosal glands of conducting airways whereas both SP-A1 and SP-A2 are in alveoli.\",\n      \"method\": \"Carbohydrate-binding assays with recombinant human SP-A1 and SP-A2 proteins under defined calcium concentrations\",\n      \"journal\": \"American journal of physiology. Lung cellular and molecular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding assay with recombinant proteins, multiple calcium conditions and sugar types, single lab\",\n      \"pmids\": [\"12505869\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"SP-A2 (1A0) forms higher-order supratrimeric oligomers than SP-A1; greater supratrimeric assembly correlates with lower Kd for binding to bacterial Re-LPS, greater self-association in the presence of calcium, and greater capability to aggregate Re-LPS and phospholipids; SP-A1 is more resistant to trypsin degradation than SP-A2; coexpressed SP-A1/SP-A2 has greater thermal stability and combines properties of each.\",\n      \"method\": \"Analytical ultracentrifugation, differential scanning calorimetry, fluorescence spectroscopy, LPS binding and aggregation assays, proteolysis resistance assay using recombinant baculovirus-derived proteins\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal biophysical and functional methods in a single rigorous study establishing structure-function relationship\",\n      \"pmids\": [\"17542781\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Formation of tubular myelin in vivo requires both SP-A1 and SP-A2 gene products; humanized transgenic mice expressing only SP-A1(6A4) or only SP-A2(1A3) lacked tubular myelin, while mice carrying both had tubular myelin; tubular myelin was observed in human bronchoalveolar lavage only when both SP-A1 and SP-A2 were present; in vivo rescue confirmed tubular myelin restored only by exogenous SP-A containing both SP-A1 and SP-A2.\",\n      \"method\": \"Electron microscopy in humanized transgenic mice on SP-A knockout background; human BAL analysis; in vivo rescue with exogenous SP-A administration\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo transgenic model with KO background, electron microscopy, human BAL validation, and rescue experiment across multiple orthogonal approaches\",\n      \"pmids\": [\"20048345\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"SP-A1 (6A2) and SP-A2 (1A0) variants have differential effects on the organization of phospholipid monolayers containing SP-B; lipid films with SP-B and SP-A2 (1A0) showed surface features similar to those with native human SP-A, including fluorescent probe-excluding clusters coexisting with liquid-expanded and liquid-condensed phases, whereas SP-A1 (6A2) showed different protein distribution.\",\n      \"method\": \"Fluorescence microscopy of phospholipid monolayers at the air-water interface containing SP-B and SP-A variants\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct biophysical assay with recombinant proteins and comparison to native SP-A, single lab\",\n      \"pmids\": [\"17678872\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"SP-A2 gene is more highly regulated by cAMP and during fetal development than SP-A1; in adult lung, 65% of SP-A mRNA is from SP-A2, while in 28-week neonate only SP-A1 transcripts were detected; cAMP and glucocorticoids (dexamethasone) differentially regulate SP-A1 and SP-A2 transcription.\",\n      \"method\": \"Primer extension analysis of human adult and fetal lung tissues; organ culture of fetal lung with DBcAMP and dexamethasone; Northern analysis\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct measurement in human tissue and fetal lung culture with defined hormonal treatments, single lab\",\n      \"pmids\": [\"8179013\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"SP-A2 mRNA transcripts are always comprised of sequences within six exons (with an extra exon II encoding additional 5'-UTR sequences absent in SP-A1); most SP-A1 transcripts use five exons; both genes produce alternatively spliced transcripts from alternate exons; SP-A1 majority transcripts initiate 5 bp downstream of the SP-A2 transcription initiation site.\",\n      \"method\": \"Primer extension, RACE (rapid amplification of cDNA ends), sequencing of 47 full-length primer-extended cDNAs from human fetal lung explants\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct sequence analysis of 47 clones with multiple methods establishing exon-intron structure\",\n      \"pmids\": [\"8179012\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"A CRE-like element (CRESP-A2: TGACCTTA) at -242 bp in the SP-A2 promoter is essential for basal and cAMP-inducible expression in alveolar type II cells; nuclear proteins from fetal lung bind specifically to CRESP-A2, with proteins of ~50, 36, and 30 kDa identified by UV cross-linking; upon DBcAMP-induced differentiation, the ~30 kDa protein binding is lost; mutation of CRESP-A2 markedly reduces both basal and cAMP-stimulated expression; CRESP-A2 binds different proteins than the canonical CRE.\",\n      \"method\": \"Transfection of SP-A2 5'-flanking DNA-hGH fusion genes into primary human type II cells; competitive EMSA; UV cross-linking with nuclear extracts; site-directed mutagenesis of CRESP-A2\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis confirming functional necessity, UV cross-linking for protein identification, EMSA with nuclear extracts, multiple complementary methods in one study\",\n      \"pmids\": [\"8770068\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"In baboon SP-A2 and SP-A1 genes, three TTF-1 (thyroid transcription factor-1) binding elements are present within 255 bp of 5'-flanking sequence of each gene but differ in position and spacing; 255 bp of 5'-flanking DNA from either bSP-A1 or bSP-A2 is sufficient to mediate high basal and cAMP-inducible expression in type II cells.\",\n      \"method\": \"DNase I footprinting, EMSA with bacterially expressed TTF-1 and type II cell nuclear extracts, transfection of 5'-flanking DNA-hGH fusion genes into primary type II cells\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — footprinting and EMSA establish TTF-1 binding; functional validation by transfection; ortholog study (baboon), single lab\",\n      \"pmids\": [\"9843844\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Phorbol ester (TPA) represses SP-A2 promoter activity (~55-65% reduction); a region in SP-A2 intron 1 (+309/+329) forms TPA-induced sequence-specific DNA-protein complexes; the consensus AP-1-like sequence (TCACTGA in SP-A2) is required for complex formation; TPA-induced complex contains Jun family proteins (not Fos); mutation of this AP-1-like site prevents TPA-induced complex formation.\",\n      \"method\": \"Deletional analysis of SP-A promoter by transfection in NCI-H441 cells; EMSA with NCI-H441 nuclear proteins; antibody supershift for Jun/Fos family proteins; site-directed mutagenesis of AP-1-like site\",\n      \"journal\": \"Experimental lung research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — EMSA plus antibody supershift plus mutagenesis, single lab, multiple complementary methods\",\n      \"pmids\": [\"10914330\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"SP-A 5'-UTR splice variants differentially regulate SP-A production through mRNA stability and translational efficiency; the ABD variant has the lowest rate of mRNA decay; ABD and AB'D' 5'-UTR variants have higher translational efficiency than control; A'D' and A'CD' have lower translational efficiency than control; all four variants studied increased luciferase mRNA stability.\",\n      \"method\": \"In vitro transient expression of hSP-A 5'-UTR constructs with luciferase reporter; quantitative real-time PCR for mRNA levels; mRNA decay assays\",\n      \"journal\": \"American journal of physiology. Lung cellular and molecular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reporter gene assays plus quantitative PCR in two orthogonal readouts (activity and mRNA), single lab\",\n      \"pmids\": [\"15894557\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Allelic differences in SP-A2 at position Gln223Lys affect binding to Mycoplasma pneumoniae membrane fractions (MMF); humanized SP-A2 transgenic mice with 223K allele exhibit reduced neutrophil influx and mucin production when challenged with MMF compared to SP-A-/- mice; mice expressing 223Q have increased neutrophil influx and mucin production similar to SP-A-/- mice; SP-A interaction with EGFR signaling pathway limits MMF-stimulated mucin production in an allele-specific manner; EGFR phosphorylation is increased in MMF-challenged SP-A-/- lungs and pharmacologic EGFR inhibition reduces mucin production.\",\n      \"method\": \"Humanized SP-A2 transgenic mouse model with MMF challenge; measurement of neutrophil recruitment and mucin production; pharmacologic EGFR inhibition; Western blot for EGFR phosphorylation; tracheal epithelial cell cultures\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo transgenic model with allele-specific comparison, pharmacologic epistasis experiment, multiple readouts (neutrophil, mucin, EGFR phosphorylation), mechanistic pathway identified\",\n      \"pmids\": [\"25957169\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"A 20-mer peptide derived from the lectin/carbohydrate recognition domain of SP-A2 containing the 223Q variant significantly decreases TNF-α mRNA and protein levels during M. pneumoniae infection; the 223Q-20mer peptide reduces NF-κB p65 phosphorylation in both SP-A KO mice and RAW 264.7 cells; neither 20-mer (223Q or 223K) affected p38 phosphorylation.\",\n      \"method\": \"SP-A knockout mouse model challenged with live M. pneumoniae; RAW 264.7 macrophage cell line; qPCR for TNF-α mRNA; ELISA for TNF-α protein; Western blot for NF-κB p65 and p38 phosphorylation\",\n      \"journal\": \"Infection and immunity\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two model systems (in vivo and in vitro), multiple endpoints, negative result for p38 informative, single lab\",\n      \"pmids\": [\"32513852\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Pathogenic mutations in SFTPA2 (including G231V and F198S) cause preserved protein production but abolished secretion; mutant SP-A2 forms aggregates intracellularly; chemical chaperone 4-PBA enhances secretion and decreases aggregation of mutant SP-A2; GRP78 (BiP) overexpression reduces mutant SP-A2 aggregation while GRP78 knockdown enhances it; 4-PBA upregulates GRP78 expression, partially accounting for its aggregate-alleviating effect.\",\n      \"method\": \"In vitro expression of mutant SP-A2 in CHO-K1 cells; secretion and aggregation assays; MG-132 proteasome inhibition; chymotrypsin degradation assay; GRP78 overexpression and shRNA knockdown; Western blot\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular basis of disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple cellular perturbations (overexpression, knockdown, chemical chaperone, proteasome inhibition) in single lab establishing GRP78 as regulator of SP-A2 aggregation\",\n      \"pmids\": [\"30293573\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Pathogenic SFTPA2 mutations preserve protein production but abolish SP-A secretion in cell models; ex vivo lung tissue from mutation carriers showed altered SP-A expression patterns; secretion defect confirmed in 11 different SFTPA1/SFTPA2 mutations.\",\n      \"method\": \"In vitro expression of mutant proteins with secretion/production assays; ex vivo immunostaining of lung tissue from mutation carriers\",\n      \"journal\": \"The European respiratory journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro functional assay plus ex vivo tissue validation across 11 mutations in 14 independent patients, multiple labs/centers\",\n      \"pmids\": [\"32855221\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"SP-A1 and SP-A2 CHO-expressed variants both display α(2,3)-linked sialic acids and have similar activity against influenza A virus PR-8 strain (which preferentially binds α(2,3)-linked sialic acids), suggesting no difference between SP-A1 and SP-A2 in inhibiting hemagglutination of avian-like IAV strains.\",\n      \"method\": \"Hemagglutination inhibition assay with CHO-expressed SP-A variants; sialic acid linkage analysis\",\n      \"journal\": \"Medical microbiology and immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct functional assay with characterized proteins; negative finding (no difference for α2,3-sialic acid-preferring strains) explicitly reported\",\n      \"pmids\": [\"17520282\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Full-length recombinant SP-A2 223Q is more effective than SP-A2 223K at reducing IL-13-induced MUC5AC gene expression in primary bronchial epithelial cells from asthmatic participants; 10- and 20-mer peptides spanning position 223Q of SP-A2 reduce eosinophilic inflammation, mucin production and airway hyperresponsiveness in a house dust mite mouse model and protect from lung function decline during IL-13 challenge.\",\n      \"method\": \"Recombinant protein treatment of primary human bronchial epithelial cells; humanized SP-A2 transgenic mouse models; house dust mite and IL-13 challenge models; measurement of mucin (MUC5AC), eosinophils, and airway hyperresponsiveness\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple mouse models and human primary cells, allele-specific comparison, multiple functional readouts, single lab\",\n      \"pmids\": [\"35874703\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SP-A2 (1A3) transgenic male mice show increased total and central airway resistance after methacholine challenge following K. pneumoniae infection; allele-specific differences exist with SP-A2 (1A3) exhibiting significantly higher lung resistance than SP-A2 (1A0); sex-specific differences in airway responses are observed with SP-A2 variants.\",\n      \"method\": \"Humanized transgenic mouse model; flexiVent forced oscillation technique measurements after K. pneumoniae infection and methacholine challenge\",\n      \"journal\": \"Respiratory research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo lung function measurements with multiple SP-A variant transgenic lines and KO controls, single lab\",\n      \"pmids\": [\"29394894\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SP-A1 and SP-A2 variants differentially affect survival after K. pneumoniae infection in a gene-, variant-, and sex-specific manner with order co-ex = SP-A2 > SP-A1 > KO; SP-A1 and SP-A2 differentially bind to phagocytic (but not non-phagocytic) cells; alveolar macrophages from SP-A1 and SP-A2 transgenic mice exhibit differential expression of cell surface proteins; treatment of KO mice with exogenous SP-A1 or SP-A2 significantly improves survival.\",\n      \"method\": \"Humanized transgenic mouse survival study with intratracheal K. pneumoniae infection; flow cytometry for cell surface protein expression on AMs; SP-A binding assays with phagocytic and non-phagocytic cells; exogenous SP-A rescue treatment\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo survival plus binding assay plus rescue experiment, multiple SP-A variant lines, single lab\",\n      \"pmids\": [\"30459763\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SP-A2 in male transgenic mice influences miRNA-mediated sex-specific differences in response to ozone-induced oxidative stress; 11 miRNAs were differentially expressed under oxidative stress with targets including BCL2, CAT, FOXO1, IL-6, NF-κB, SOD2, and STAT3; SP-A2 promotes anti-apoptotic BCL2 mRNA increase and pro-inflammatory IL-6 elevation after oxidative stress; SOD2 protein increased while CAT was unchanged; sex hormones contribute to miRNome changes (confirmed by gonadectomy).\",\n      \"method\": \"Humanized SP-A2 transgenic and KO mice with ozone exposure; miRNA microarray; qPCR for target mRNAs; ELISA for cytokines and proteins; gonadectomy experiment\",\n      \"journal\": \"Biology of sex differences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — transgenic vs KO comparison, multiple molecular readouts, gonadectomy as mechanistic intervention, single lab\",\n      \"pmids\": [\"29202868\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Human SP-A2 variant 1A0 transgenic mice infected with SARS-CoV-2 show more severe acute lung injury and higher mortality, similar to SP-A KO mice; SP-A-expressing mice have reduced viral titers relative to KO; 1A0 mice show upregulation of MyD88, Stat3, IL-18, and Jak2; Mapk1 is significantly downregulated in 6A2 versus 1A0 mice; NOD1/2 and Trem1 signaling pathways are involved; IL-6, G-CSF, and IL-1β levels are higher in KO and 1A0 mice.\",\n      \"method\": \"Humanized double-transgenic mice (hACE2 + individual SP-A variants) with intranasal SARS-CoV-2 challenge; survival monitoring; lung histology; viral titer measurement; transcriptomic analysis; cytokine/chemokine multiplex assay\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — in vivo transgenic model with multiple readouts but preprint without peer review, single lab\",\n      \"pmids\": [\"bio_10.1101_2024.09.11.612497\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"SFTPA2 encodes SP-A2, a C-type lectin collectin that forms supratrimeric oligomers and functions in pulmonary innate immunity and surfactant biology; SP-A2 variants are generally more biologically active than SP-A1 variants in enhancing phagocytosis of bacteria (P. aeruginosa, K. pneumoniae, M. pneumoniae) by alveolar macrophages, bind carbohydrates with higher affinity and broader specificity, interact with pathogen-derived molecules in an allele-specific manner (e.g., Gln223Lys affecting MMF binding and EGFR-mediated mucin regulation), require co-expression with SP-A1 for tubular myelin formation in vivo, and are regulated at the transcriptional level by a CRE-like element (CRESP-A2) bound by fetal lung nuclear proteins, by TTF-1 binding elements, by AP-1/Jun in response to phorbol esters, and by differential effects of cAMP, glucocorticoids, and IFN-γ; pathogenic SFTPA2 mutations cause preserved protein production but abolished secretion with intracellular aggregation, the latter regulated by GRP78/BiP.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SFTPA2 encodes SP-A2, a calcium-dependent carbohydrate-binding collectin of pulmonary surfactant that contributes to innate host defense and surfactant structural organization in the lung [#3, #4]. SP-A2 assembles into higher-order supratrimeric oligomers, and this degree of oligomeric assembly correlates with tighter binding to bacterial Re-LPS, calcium-dependent self-association, and the capacity to aggregate LPS and phospholipids [#4]; through its lectin/carbohydrate-recognition domain SP-A2 binds a wide range of sugars with higher affinity than the SP-A1 gene product [#3]. Functionally, SP-A2 variants enhance the association and internalization of bacteria such as Pseudomonas aeruginosa by alveolar macrophages more potently than SP-A1, an activity dependent on mammalian post-translational modification [#0, #1], and modulate surfactant phospholipid handling by inhibiting type II cell phosphatidylcholine secretion and organizing SP-B-containing lipid monolayers [#2, #6]. SP-A1 and SP-A2 gene products are functionally non-redundant: both are required together for tubular myelin formation in vivo [#5]. SP-A2 shapes host responses to infection and injury in an allele-specific manner, with the Gln223Lys polymorphism governing binding to Mycoplasma pneumoniae membrane fractions, EGFR-dependent limitation of mucin production and neutrophil influx, NF-\\u03baB-dependent TNF-\\u03b1 induction, and IL-13/MUC5AC-driven airway responses, where the 223Q allele and 223Q-spanning peptides are protective [#13, #14, #18]. SFTPA2 expression is controlled transcriptionally through a CRE-like element (CRESP-A2) bound by fetal lung nuclear proteins for basal and cAMP-inducible activity [#9], TTF-1 binding elements [#10], and an intronic AP-1/Jun element mediating phorbol ester repression [#11], with additional regulation by 5'-UTR splice variants affecting mRNA stability and translation [#12]. Pathogenic SFTPA2 mutations (including G231V and F198S) preserve protein production but abolish secretion, causing intracellular aggregation that is alleviated by the chaperone GRP78/BiP and the chemical chaperone 4-PBA [#15, #16].\",\n  \"teleology\": [\n    {\n      \"year\": 1994,\n      \"claim\": \"Establishing the SFTPA2 gene/transcript architecture and its distinct developmental and hormonal regulation defined SP-A2 as a separately controlled gene rather than a redundant duplicate of SP-A1.\",\n      \"evidence\": \"Primer extension, RACE and sequencing of fetal lung cDNAs plus organ culture with cAMP/dexamethasone\",\n      \"pmids\": [\"8179012\", \"8179013\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address functional consequences of the SP-A1/SP-A2 sequence differences\", \"Promoter elements responsible for differential regulation not yet mapped\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Identifying the CRESP-A2 CRE-like element answered how SP-A2 achieves basal and cAMP-inducible transcription in type II cells, distinguishing its regulation from a canonical CRE.\",\n      \"evidence\": \"Reporter transfection, competitive EMSA, UV cross-linking and mutagenesis in primary human type II cells\",\n      \"pmids\": [\"8770068\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identities of the ~50/36/30 kDa CRESP-A2-binding proteins not determined\", \"Relationship between the ~30 kDa protein loss and differentiation not mechanistically resolved\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Mapping TTF-1 binding elements in the proximal promoter identified a lineage-specific transcription factor input governing SP-A2 expression in alveolar epithelium.\",\n      \"evidence\": \"DNase I footprinting, EMSA with recombinant TTF-1, and reporter transfection (baboon ortholog)\",\n      \"pmids\": [\"9843844\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Performed on baboon genes; human element positioning not directly tested here\", \"Combinatorial logic with CRESP-A2 not resolved\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"An intronic AP-1/Jun element explained phorbol-ester repression of SP-A2, linking PKC signaling to negative transcriptional control.\",\n      \"evidence\": \"Deletional reporter analysis, EMSA, antibody supershift and mutagenesis in NCI-H441 cells\",\n      \"pmids\": [\"10914330\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological stimulus driving Jun recruitment in vivo not identified\", \"Specific Jun family member not pinpointed\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Direct carbohydrate-binding comparison established that SP-A2 binds sugars with higher affinity and broader specificity than SP-A1, providing a biochemical basis for differential lectin function.\",\n      \"evidence\": \"Carbohydrate-binding assays with recombinant SP-A1 and SP-A2 at defined calcium concentrations\",\n      \"pmids\": [\"12505869\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of the affinity difference not defined\", \"In vivo relevance of submucosal-gland-restricted SP-A2 expression not tested\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Functional assays showed SP-A2 variants are more active than SP-A1 in promoting bacterial phagocytosis and in suppressing type II cell PC secretion, beginning the case for SP-A2 as the more biologically active gene product.\",\n      \"evidence\": \"Phagocytic index assay and PC secretion assay using insect-cell-expressed variants plus ozone-oxidation analysis\",\n      \"pmids\": [\"15377498\", \"15065867\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Insect-cell proteins lack mammalian PTMs\", \"Mechanism linking oxidation of specific residues to activity loss not resolved\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"5'-UTR splice variants were shown to tune SP-A output post-transcriptionally via mRNA stability and translational efficiency, adding a layer of expression control beyond promoter activity.\",\n      \"evidence\": \"Luciferase reporter constructs with qPCR and mRNA decay assays\",\n      \"pmids\": [\"15894557\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Trans-acting factors recognizing the 5'-UTRs not identified\", \"Reporter context may not reflect native SP-A mRNA\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Biophysical and improved expression studies linked SP-A2 supratrimeric oligomerization to LPS binding/aggregation and confirmed PTM-dependent phagocytic potency, connecting quaternary structure to innate-immune function.\",\n      \"evidence\": \"Analytical ultracentrifugation, DSC, fluorescence spectroscopy and binding assays; CHO-expressed variants in macrophage assays; lipid monolayer microscopy; hemagglutination inhibition\",\n      \"pmids\": [\"17542781\", \"17220308\", \"17678872\", \"17520282\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No atomic structure of the oligomer\", \"SP-A1 vs SP-A2 equivalence against avian-like IAV indicates the activity difference is pathogen-specific, mechanism unresolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Humanized transgenic and rescue experiments demonstrated that tubular myelin formation requires both SP-A1 and SP-A2, defining a non-redundant structural cooperation between the two gene products in vivo.\",\n      \"evidence\": \"Electron microscopy in humanized transgenic mice on SP-A-null background, human BAL analysis, and exogenous SP-A rescue\",\n      \"pmids\": [\"20048345\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular interface mediating SP-A1/SP-A2 cooperation unknown\", \"Functional consequence of tubular myelin loss for surfactant function not quantified here\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"The Gln223Lys polymorphism was shown to control SP-A2 binding to M. pneumoniae and allele-specific limitation of mucin production through EGFR signaling, defining a genotype-dependent host-defense mechanism.\",\n      \"evidence\": \"Humanized SP-A2 transgenic mice with MMF challenge, pharmacologic EGFR inhibition, and EGFR phosphorylation Westerns\",\n      \"pmids\": [\"25957169\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct biochemical interaction of SP-A2 with EGFR not demonstrated\", \"How allelic binding difference translates to EGFR modulation not resolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"In vivo infection, lung-function and stress studies extended the allele- and gene-specific functional hierarchy of SP-A2 to survival, airway resistance, miRNA-mediated stress responses, and revealed pathogenic mutations as secretion-deficient.\",\n      \"evidence\": \"Humanized transgenic mouse K. pneumoniae survival and methacholine challenge, ozone-stress miRNA profiling, and CHO-cell secretion/aggregation assays of mutant SP-A2\",\n      \"pmids\": [\"29394894\", \"30459763\", \"29202868\", \"30293573\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of sex-specific SP-A2 effects not fully defined\", \"Cell-surface receptors mediating differential phagocytic-cell binding not identified\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Studies on disease mutations and 223Q-derived peptides clarified that pathogenic SFTPA2 mutations cause GRP78-regulated intracellular aggregation, and that the 223Q lectin-domain region dampens NF-\\u03baB-driven inflammation.\",\n      \"evidence\": \"GRP78 overexpression/knockdown and 4-PBA in CHO cells with ex vivo carrier tissue; SP-A KO mouse and RAW 264.7 cells with 20-mer peptides and NF-\\u03baB/p38 Westerns\",\n      \"pmids\": [\"32513852\", \"32855221\", \"30293573\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural nature of the aggregates and the exact GRP78 interaction interface unknown\", \"Whether peptide effects translate beyond rodent/cell models untested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Allele-specific protection in asthma models established SP-A2 223Q (full-length and peptides) as a suppressor of IL-13/MUC5AC-driven mucin and airway hyperresponsiveness, generalizing the 223 polymorphism's role to allergic airway disease.\",\n      \"evidence\": \"Recombinant protein treatment of asthmatic primary bronchial epithelial cells and humanized SP-A2 mice in house dust mite and IL-13 challenge models\",\n      \"pmids\": [\"35874703\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor/target through which 223Q peptides act on epithelium not defined\", \"Durability and human applicability of peptide protection not established\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"A SARS-CoV-2 model probed SP-A2 variant effects on viral lung injury, indicating SP-A reduces viral titers while the 1A0 variant associates with severe injury and altered innate signaling.\",\n      \"evidence\": \"Humanized hACE2 + SP-A variant double-transgenic mice with SARS-CoV-2 challenge, transcriptomics and cytokine multiplex (preprint)\",\n      \"pmids\": [\"bio_10.1101_2024.09.11.612497\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint not peer-reviewed\", \"Mechanistic link between variant and the implicated signaling pathways not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How SP-A2 oligomers engage specific alveolar macrophage and epithelial receptors to drive phagocytosis, EGFR/NF-\\u03baB modulation, and surfactant organization remains structurally and mechanistically undefined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No atomic structure of SP-A2 oligomers or its receptor complexes\", \"Direct SP-A2 receptor(s) on phagocytic cells not molecularly identified\", \"Mechanism connecting carbohydrate binding to downstream EGFR and NF-\\u03baB signaling unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0030246\", \"supporting_discovery_ids\": [3, 4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [5, 16]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 1, 13, 20]}\n    ],\n    \"complexes\": [\"tubular myelin (SP-A1/SP-A2)\"],\n    \"partners\": [\"SFTPA1\", \"SFTPB\", \"GRP78/HSPA5\", \"EGFR\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":7,"faith_total":7,"faith_pct":100.0}}