{"gene":"FCER2","run_date":"2026-04-28T17:46:03","timeline":{"discoveries":[{"year":1992,"finding":"CD23 (FcεRII) directly binds CD21 (complement receptor 2) on B cells and follicular dendritic cells; this CD23–CD21 interaction specifically increases IL-4-induced IgE production from blood mononuclear cells, establishing CD21 as a functional ligand of CD23 that participates in IgE regulation.","method":"Fluorescent liposome-binding assay with recombinant CD23, CD21-transfected cell lines, inhibition by anti-CD21/anti-CD23 monoclonal antibodies, Western blot, and functional IgE production assay","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1-2 — reconstitution with recombinant protein, transfected cell lines, multiple orthogonal methods, replicated functionally","pmids":["1386409"],"is_preprint":false},{"year":2005,"finding":"The NMR solution structure of the CD23 C-type lectin domain reveals that CD23 self-associates into a trimer, binds IgE and CD21 at distinct sites on the lectin head, and can bind both ligands simultaneously; none of these interactions require calcium despite the C-type lectin fold. IgE and CD23 can also form high-molecular-mass multimeric complexes.","method":"NMR spectroscopy, concentration-dependent chemical shift perturbation mapping, ligand-induced chemical shift analysis","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 1 — NMR structure with functional ligand-binding site mapping, multiple orthogonal NMR experiments","pmids":["16172256"],"is_preprint":false},{"year":2017,"finding":"Crystal structure of a CD23/IgE-Fc complex shows that two lectin-like head domains of CD23 bind IgE-Fc with affinities differing by more than an order of magnitude, with only one head domain bound to one of the two identical IgE heavy chains in the asymmetrically bent IgE-Fc, revealing asymmetric binding.","method":"X-ray crystallography, isothermal titration calorimetry","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1 — crystal structure plus ITC binding quantification","pmids":["28361904"],"is_preprint":false},{"year":2003,"finding":"ADAM8, ADAM15, and ADAM28 (MDC-L) catalyze ectodomain shedding of CD23; ADAM8-dependent sCD23 release requires proteolytically active ADAM8, which physically associates with membrane-bound CD23, and this release is inhibited by hydroxamic acid metalloprotease inhibitors.","method":"Synthetic peptide substrate library screening, in vitro ectodomain shedding assay, co-immunoprecipitation of ADAM8 with CD23, metalloprotease inhibitor treatment","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro enzymatic assay, physical association demonstrated, active-site mutant used, inhibitor confirmation","pmids":["12777399"],"is_preprint":false},{"year":2007,"finding":"ADAM10 is the primary metalloprotease responsible for cleaving CD23 at two distinct stalk sites to release soluble CD23 (sCD23); tissue inhibitors of metalloproteinases, a prodomain-based ADAM10 inhibitor, dominant-negative ADAM10, and siRNA knockdown of ADAM10 all partially inhibit sCD23 release and cause accumulation of membrane CD23.","method":"Peptide cleavage assays, ADAM10 dominant-negative construct expression, siRNA knockdown, ADAM10-specific inhibitor treatment, ELISA for sCD23","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — multiple complementary loss-of-function approaches (dominant-negative, siRNA, inhibitor) with direct substrate cleavage assays","pmids":["17389606"],"is_preprint":false},{"year":1998,"finding":"CD23 is cleaved from the cell surface by an integral membrane metalloprotease of ~63 kDa; this activity is inhibited by metalloprotease inhibitors (1,10-phenanthroline, imidazole, batimastat) but not by serine, cysteine, or acid protease inhibitors, and the same or similar activity is present in fibroblasts and monocytic cell lines not expressing CD23.","method":"Plasma membrane fractionation, gel-filtration chromatography, neo-epitope antibody cleavage assay, pharmacological inhibitor panel","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 — biochemical characterization with purified CD23 substrate and comprehensive inhibitor profiling","pmids":["9677315"],"is_preprint":false},{"year":2012,"finding":"Soluble CD23 monomers (derCD23 and exCD23) inhibit IgE synthesis in human B cells, whereas trimeric/oligomeric soluble CD23 (lzCD23) stimulates IgE synthesis; trimeric sCD23 binds cells co-expressing mIgE and mCD21 and caps these proteins on the B cell membrane, indicating that oligomerization state determines the functional outcome of sCD23 on IgE regulation.","method":"Recombinant protein production, human B cell IL-4/anti-CD40 IgE synthesis assay, ADAM10 inhibitor (GI254023X) to uncouple cleavage from sCD23 effects, siRNA knockdown, cell-surface capping assay","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 1-2 — reconstituted recombinant fragments with defined oligomeric states, multiple orthogonal approaches including siRNA and pharmacological inhibition","pmids":["22393152"],"is_preprint":false},{"year":2007,"finding":"Soluble CD23 monomers inhibit and oligomers stimulate IgE synthesis in human B cells after heavy-chain class switching; three defined fragments (monomeric derCD23, monomeric exCD23, oligomeric lzCD23) were characterized biochemically to establish this structure–activity relationship.","method":"Recombinant fragment preparation, B cell IgE synthesis assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstituted defined recombinant fragments tested in functional assay","pmids":["17576766"],"is_preprint":false},{"year":1991,"finding":"CD23/FcεRII is physically associated with the Src-family tyrosine kinase p59Fyn (but not p56Lck); cross-linking of CD23 in CD23-transfected YT cells activates IL-2 receptor (p55/Tac) expression, indicating that CD23 delivers activation signals via Fyn kinase.","method":"cDNA transfection of YT cells, anti-FcεRII crosslinking, co-immunoprecipitation with anti-Fyn antibody, IL-2 receptor induction assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP of endogenous kinase with receptor, functional crosslinking assay, single lab","pmids":["1717997"],"is_preprint":false},{"year":1999,"finding":"Cross-linking of CD23 in monocytic U937 cells activates IKKβ, which phosphorylates IκBα at Ser32/Ser36, leading to IκBα degradation and NF-κB activation; this pathway requires upstream tyrosine kinase activity. A dominant-negative IκBα(S32A/S36A) or dominant-negative IKKβ completely blocks CD23-induced NF-κB activation and gene transcription.","method":"Dominant-negative IκBα and IKKβ overexpression, co-transfection assays, IKK activity assays, NF-κB EMSA, phosphospecific IκBα immunoblotting","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 1-2 — dominant-negative constructs, biochemical kinase assays, multiple orthogonal readouts in single study","pmids":["10490984"],"is_preprint":false},{"year":2000,"finding":"CD23 expressed on intestinal epithelial cells mediates IgE-dependent transcytosis of antigen (HRP) across enterocytes in sensitized rats; anti-CD23 antibody applied luminally inhibits both antigen transport and the hypersensitivity reaction, and sensitization induces CD23 expression on enterocytes.","method":"Active sensitization rat model, immunohistochemistry for CD23, immunogold EM co-localization of CD23 and antigen in endosomes, serum transfer, anti-CD23 blocking antibody in Ussing chamber","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal in vivo and ex vivo methods, including serum transfer, EM co-localization, and receptor blocking","pmids":["11018076"],"is_preprint":false},{"year":2006,"finding":"CD23a isoform (but not CD23b) is constitutively expressed by primary human intestinal epithelial cells and acts as a bidirectional transporter of IgE; CD23a diverts allergen-IgE complexes away from lysosomal degradation and delivers them transcellularly, enabling degranulation of mast cells below the epithelial barrier.","method":"RT-PCR of primary IECs, retroviral transfection of polarized T84 cells with CD23a or CD23b, transcytosis assay, RBL degranulation assay","journal":"Gastroenterology","confidence":"High","confidence_rationale":"Tier 2 — isoform-specific gain-of-function in polarized epithelial cells with multiple functional readouts","pmids":["16831589"],"is_preprint":false},{"year":2003,"finding":"Mouse intestinal enterocytes express only the CD23b isoform; a novel alternative splice variant CD23b-Δ5 (lacking exon 5) mediates constitutive internalization and uptake of free IgE or anti-CD23, whereas classic CD23b is less efficiently internalized but transports IgE/allergen complexes; CD23-deficient mice lack enhanced transepithelial antigen transport.","method":"RT-PCR and sequencing of enterocyte RNA, CD23-/- mouse intestinal transport assay, exon-specific functional comparison","journal":"American journal of physiology. Gastrointestinal and liver physiology","confidence":"High","confidence_rationale":"Tier 2 — knockout mouse functional assay plus isoform-specific molecular characterization","pmids":["12637252"],"is_preprint":false},{"year":2005,"finding":"CD23a undergoes constitutive clathrin-dependent endocytosis directed by an internalization signal in its CD23a-specific intracytoplasmic exon, which also serves as a basolateral targeting signal in polarized epithelial cells; CD23b is stable at the plasma membrane due to a negative regulatory signal in its CD23b-specific intracellular exon.","method":"Mutagenesis of intracellular exons, transfection into MDCK polarized cells, endocytosis/recycling assays in multiple cell lines","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 1-2 — exon-swap mutagenesis, polarized cell trafficking assays, multiple CD23 splice forms compared","pmids":["15843555"],"is_preprint":false},{"year":2001,"finding":"CD23 forms a non-covalent complex with HLA-DR (MHC class II) on the surface of human B cells; following endocytosis triggered by an IgE-antigen complex or anti-HLA-DR antibody, the HLA-DR–CD23 complex recycles to the cell surface via compartments resembling peptide-loading compartments, on a time scale consistent with antigen presentation.","method":"Surface labeling and intracellular trafficking of RPMI 8866 B cells, co-immunoprecipitation of CD23 with HLA-DR, confocal microscopy of endosomal routing","journal":"Immunology","confidence":"Medium","confidence_rationale":"Tier 2-3 — co-IP plus live-cell trafficking assay, single lab","pmids":["11454061"],"is_preprint":false},{"year":1999,"finding":"Soluble CD23 binds directly to the αv integrin subunit and the vitronectin receptor (αvβ3); co-expression of CD47 augments sCD23 binding; the vitronectin receptor/CD47 complex mediates sCD23-induced proinflammatory TNF-α, IL-12, and IFN-γ release from monocytes.","method":"Binding assays on αv+β3+ cell lines with/without CD47, purified αv protein binding, CHO single-chain transfectant binding, cytokine release inhibition by anti-CD47, anti-β3, and anti-αv monoclonal antibodies","journal":"The Journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple transfected cell lines, purified protein binding, functional cytokine assays, single lab","pmids":["10037797"],"is_preprint":false},{"year":2009,"finding":"TLR4 ligation by LPS induces transcriptional upregulation of CD23 and generation of soluble CD23 from B cells; this shedding requires matrix metalloprotease 9 (MMP9), as MMP9-deficient B cells fail to release sCD23 in response to LPS. Type 1 transitional B cells uniquely produce MMP9 upon LPS stimulation.","method":"MMP9 knockout mice, quantitative RT-PCR, flow cytometry, ELISA for sCD23, in vitro and in vivo LPS treatment of murine and human B cells","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 2 — MMP9 KO mice with in vitro and in vivo confirmation, human B cell validation","pmids":["19635918"],"is_preprint":false},{"year":2014,"finding":"P2X7 receptor activation by extracellular ATP induces rapid shedding of CD23 from primary human and murine B cells via ADAM10; this process is blocked by the P2X7 antagonist AZ10606120, is absent in P2X7 knockout mouse B cells, and is inhibited by the ADAM10 antagonist GI254023X and the broad metalloprotease inhibitor BB-94.","method":"P2X7 knockout mice, P2X7-specific antagonist, ADAM10-specific inhibitor, broad metalloprotease inhibitor, flow cytometry, ELISA","journal":"Immunology and cell biology","confidence":"High","confidence_rationale":"Tier 2 — genetic KO plus pharmacological validation with pathway-specific inhibitors, orthogonal assays","pmids":["25155463"],"is_preprint":false},{"year":2016,"finding":"CD23 negatively regulates B-cell receptor (BCR) signaling: CD23 knockout B cells show increased cell spreading area, BCR clustering, phosphotyrosine levels, Btk phosphorylation, F-actin accumulation, and phospho-WASp in the contact zone upon stimulation with membrane-associated antigen.","method":"CD23 knockout mice, membrane antigen presentation assay, flow cytometry, confocal microscopy, phospho-Western blotting","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 — KO mouse with multiple defined molecular readouts (Btk, WASp, actin), mechanistically linked to actin-mediated BCR clustering","pmids":["27181049"],"is_preprint":false},{"year":2016,"finding":"The stalk region of CD23 contains a previously unrecognized IgE-binding site; non-N-glycosylated monomeric CD23 shows superior IgE binding compared with glycosylated CD23; the therapeutic anti-IgE antibody omalizumab blocks IgE binding to both FcεRI and CD23.","method":"Expression of four CD23 variants (full extracellular, N-glycosylation site mutant, complete head, truncated head), gel filtration, circular dichroism, binding and inhibition assays, negative-stain electron microscopy","journal":"The Journal of allergy and clinical immunology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple defined structural variants with glycosylation mutagenesis, EM, and inhibition assays","pmids":["27343203"],"is_preprint":false},{"year":2015,"finding":"Epithelial CD23 on airway epithelial cells transcytoses IgE and OVA-IgE immune complexes across the airway epithelial barrier in vivo; CD23 knockout mice or chimeric mice lacking CD23 on radioresistant airway structural/epithelial cells have significantly reduced allergic airway inflammation, eosinophilia, collagen deposition, and airway hyperreactivity after OVA challenge.","method":"CD23 knockout mice, bone-marrow chimera experiments, in vivo OVA sensitization/challenge, airway hyperreactivity measurement, histology, CD23-blocking antibody inhalation","journal":"Mucosal immunology","confidence":"High","confidence_rationale":"Tier 2 — genetic KO, bone marrow chimeras delineating cell compartment, in vivo functional readouts, antibody blocking validation","pmids":["25783969"],"is_preprint":false},{"year":2011,"finding":"CD23-dependent transcytosis of IgE and IgE-immune complexes occurs across polarized human airway epithelial (Calu-3) cells and primary human airway epithelial monolayers; IL-4 upregulates CD23 expression and enhances transcytosis; anti-CD23 antibody or soluble CD23 competitively reduces transcytosis efficiency; transcytosed IgE-antigen complexes retain biological activity to induce mast cell degranulation.","method":"Transcytosis assay in polarized Calu-3 monolayers, primary human airway epithelial cells, IL-4 stimulation, CD23-blocking antibody/soluble CD23, human mast cell degranulation assay","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 2 — multiple cell models, receptor-specific blocking, functional downstream readout, primary human cells","pmids":["21307287"],"is_preprint":false},{"year":2007,"finding":"CD23 cross-linking on human intestinal epithelial Caco-2 cells by IgE-allergen complexes activates ERK and JNK MAP kinases and AP-1, triggering upregulation and release of CCL20 and IL-8; silencing CD23 expression with shRNA abrogates this response; secreted CCL20 induces dendritic cell migration.","method":"IgE-antigen complex stimulation of Caco-2, RT-PCR and ELISA for CCL20/IL-8, phospho-Western blotting (ERK, JNK, p38, NF-κB), stable CD23 shRNA knockdown, dendritic cell migration assay","journal":"Gastroenterology","confidence":"High","confidence_rationale":"Tier 2 — shRNA knockdown with multiple signaling readouts and functional downstream assay","pmids":["18054562"],"is_preprint":false},{"year":2012,"finding":"CD23 is identified as a functional receptor for the proinflammatory cytokine AIMP1/p43; AIMP1 binds CD23 with high affinity (identified in a screen of 499 soluble receptors), CD23 knockdown attenuates AIMP1-induced TNF-α secretion from THP-1 and PBMCs, and AIMP1-induced TNF-α release via CD23 involves ERK1/2 activation.","method":"Screen of 499 soluble receptors, AIMP1 binding to CD23 confirmed by pull-down, CD23 siRNA knockdown, ERK1/2 phosphorylation assay, cytokine ELISA","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2-3 — receptor screen validated by knockdown and signaling assay, single lab","pmids":["22767513"],"is_preprint":false},{"year":2013,"finding":"β2-adrenergic receptor engagement on IL-4/CD40L-primed murine B cells increases CD23 and ADAM10 protein expression and promotes their co-localization on exosomes in a PKA- and p38 MAPK-dependent manner; transfer of these exosomes to recipient primed B cells increases IgE production per cell.","method":"β2AR agonist treatment, ADAM10/CD23 Western blot, flow cytometry of exosomes, electron microscopy, PKA and p38 MAPK inhibitors, ELISPOT for IgE, β2AR-deficient B cells as controls","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"Medium","confidence_rationale":"Tier 2-3 — multiple biochemical methods, genetic (β2AR-KO) and pharmacological controls, exosome transfer functional assay, single lab","pmids":["24140643"],"is_preprint":false},{"year":2002,"finding":"Notch2 intracellular domain (NotchIC) is a component of a transcription factor complex (C1) that binds CBF1-recognition sites in the CD23a core promoter; EBV infection and activated Notch2 drive CD23a transcription; transfection of activated Notch2 into REH pre-B cells induces endogenous CD23a expression, identifying CD23a as a Notch2/CBF1 target gene.","method":"EMSA with CBF1-site probes, supershift assays with Notch2 antibody, transient transfection of activated Notch2, RT-PCR for endogenous CD23a, EBV-infected B cells as model","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — EMSA, supershift, and gain-of-function transfection with endogenous gene induction, multiple complementary approaches","pmids":["11986231"],"is_preprint":false},{"year":1991,"finding":"EBNA-2 transactivates CD23a transcription through a 186-bp cis-acting element located at positions -275/-89 relative to the type a CD23 mRNA start site; this element confers EBNA-2 responsiveness to a heterologous promoter in either orientation and at variable distances, and type 1 EBNA-2 is more potent than type 2 EBNA-2 at activating this element.","method":"Transfection of CD23 promoter-reporter constructs with deletional analysis into EBV-negative B-lymphoma cells, heterologous promoter (HSV-TK) assays, Northern blot for mRNA","journal":"Journal of virology","confidence":"High","confidence_rationale":"Tier 1-2 — systematic deletion mapping of cis-element, orientation-independence test, heterologous promoter assay, mRNA quantification","pmids":["1649318"],"is_preprint":false},{"year":1997,"finding":"Egr-1 transcription factor overexpression in murine B cells (K46 line) and human Ramos B cells down-regulates CD23 and CD95 (Fas) expression, establishing CD23 as a transcriptional target repressed by Egr-1 following BCR activation.","method":"Egr-1 cDNA transfection into B cell lines, flow cytometry for CD23 and CD95, functional apoptosis assay with anti-CD95","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"Medium","confidence_rationale":"Tier 2-3 — gain-of-function transfection with functional readout, replicated in two cell lines, single lab","pmids":["9300687"],"is_preprint":false},{"year":1998,"finding":"In vivo, IgE directly regulates CD23 expression on murine B cells: IgE-deficient mice have ~3-fold less surface CD23 despite normal B cell numbers; intravenous infusion of IgE into IgE-/- mice restores CD23 expression to wild-type levels, demonstrating a positive feedback loop whereby IgE ligand stabilizes/upregulates its own low-affinity receptor.","method":"IgE-deficient mouse model, flow cytometry for CD23, in vivo IgE infusion rescue experiment, in vitro IL-4/CD40L stimulation controls","journal":"International immunology","confidence":"High","confidence_rationale":"Tier 2 — genetic KO mouse with in vivo rescue by IgE infusion, mechanistically defined positive feedback","pmids":["9786437"],"is_preprint":false},{"year":2001,"finding":"Suppression of IgE responses in CD23-transgenic mice is mediated by radioresistant non-lymphoid cells, not by transgenic B or T cells: adoptive transfer of normal lymphocytes into transgenic mice still shows IgE suppression, whereas transgenic lymphocytes in normal hosts give normal IgE responses; follicular dendritic cells (FDC) expressing high CD23 are identified as candidate suppressors, as CD23-Tg FDCs inhibit IgE production by normal B cells in vitro.","method":"Adoptive transfer experiments (normal ↔ CD23-Tg bone marrow), B cell proliferation and IgE synthesis assays in vitro, germinal center histology, co-culture of Tg FDCs with normal B cells","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 2 — reciprocal bone marrow transfers plus in vitro co-culture, mechanistically distinguishes cell compartments","pmids":["11290762"],"is_preprint":false},{"year":2005,"finding":"IgE-mediated enhancement of antibody and T-cell responses in vivo requires CD23+ B cells: transfer of CD23+ B cells into CD23-deficient mice rescues the ability to respond to IgE-antigen; B cells can take up antigen via CD23 and present it to activate naïve T cells in vivo, leading to T-cell expansion and enhanced antibody responses.","method":"Adoptive transfer of CD23+ B cells into CD23-deficient mice, TCR-transgenic CD4+ T cell transfer, in vivo immunization with IgE-antigen, flow cytometry, splenic immunohistochemistry","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 2 — genetic rescue by cell transfer, in vivo antigen presentation assay, multiple readouts","pmids":["16034084"],"is_preprint":false},{"year":2017,"finding":"JNK1 suppresses CD23 expression through negative regulation of NFATc1-mediated transcription at the CD23 gene promoter; JNK1-deficient mice upregulate CD23 and show enhanced antifungal immunity dependent on CD23-mediated nitric oxide production; pharmacological JNK inhibition recapitulates this antifungal effect in mouse and human cells.","method":"JNK1-deficient mice, C. albicans infection model, CD23 promoter reporter assays, NFATc1 transcription factor analysis, CD23 blockade experiment, NO production assay, JNK inhibitor treatment of mouse and human cells","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 2 — genetic KO, promoter mechanistic studies, pathway epistasis via CD23 blockade, human cell validation","pmids":["28112734"],"is_preprint":false},{"year":1988,"finding":"A monoclonal antibody recognizing amino acids 367–376 (CH3 domain) of IgE inhibits IgE binding to CD23 (FcεRII), mapping the CD23-binding site on IgE to a 10-amino acid stretch near N-glycosylation site Asn-371 in the Cε3 domain; the antibody does not recognize a carbohydrate epitope as it binds E. coli-derived IgE peptides.","method":"Anti-IgE monoclonal antibody binding to recombinant overlapping peptides, heat-denatured IgE, competition binding assay with CD23","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"Medium","confidence_rationale":"Tier 2 — epitope mapping by peptide binding plus functional inhibition of CD23 interaction","pmids":["2459242"],"is_preprint":false}],"current_model":"CD23 (FcεRII) is a type II transmembrane C-type lectin that functions as the low-affinity IgE receptor on B cells and epithelial cells, binding IgE at a site spanning the lectin head and stalk region (without requiring calcium), associating with CD21 and HLA-DR as co-receptors, transducing signals through Fyn kinase and the IKKβ–NF-κB pathway, being shed as soluble fragments by ADAM10 (and ADAM8/MMP9 in specific contexts), with soluble monomers inhibiting and trimeric sCD23 stimulating IgE synthesis; epithelial CD23a mediates transcytosis of IgE and IgE-allergen complexes to initiate allergic inflammation, while membrane CD23 negatively regulates BCR signaling by limiting actin-mediated BCR clustering, and its transcription is positively controlled by EBNA-2/CBF1, Notch2, IL-4, and IgE itself, and negatively by Egr-1."},"narrative":{"teleology":[{"year":1988,"claim":"Mapping the CD23-binding epitope on IgE to a 10-amino-acid stretch in the Cε3 domain (CH3, residues 367–376) provided the first molecular definition of the IgE–CD23 interface.","evidence":"Monoclonal antibody epitope mapping with overlapping peptides and CD23 competition binding","pmids":["2459242"],"confidence":"Medium","gaps":["Peptide-level mapping only; no structural data on the CD23 contact residues","Does not address the contribution of the CD23 stalk to IgE binding"]},{"year":1991,"claim":"Two foundational discoveries established CD23 as a signaling receptor and a transcriptional target: cross-linking CD23 activates the Src-family kinase Fyn and induces IL-2R expression, while EBNA-2 transactivates the CD23a promoter through a 186-bp cis-element, linking EBV infection to CD23 upregulation.","evidence":"Co-IP of Fyn with CD23 in transfected YT cells plus cross-linking assay; CD23 promoter-reporter deletional analysis in EBV-negative B-lymphoma cells","pmids":["1717997","1649318"],"confidence":"Medium","gaps":["Fyn association shown by single co-IP without reciprocal validation","Signaling downstream of Fyn not mapped","EBNA-2 mechanism of action on CD23 promoter (direct DNA binding vs. adaptor) not resolved"]},{"year":1992,"claim":"Identification of CD21 as a direct ligand of CD23 that enhances IL-4-induced IgE production established the CD23–CD21 axis as a key regulatory circuit for IgE synthesis on B cells.","evidence":"Fluorescent liposome binding with recombinant CD23, CD21-transfected cells, anti-CD21/anti-CD23 blocking antibodies, functional IgE assay","pmids":["1386409"],"confidence":"High","gaps":["Stoichiometry of CD23–CD21 complex unknown","Whether CD23–CD21 interaction occurs in cis or in trans on FDCs not resolved"]},{"year":1997,"claim":"Demonstrating that Egr-1 overexpression represses CD23 transcription in B cells identified the first negative transcriptional regulator and linked BCR activation to CD23 downregulation.","evidence":"Egr-1 cDNA transfection into murine K46 and human Ramos B cells, flow cytometry","pmids":["9300687"],"confidence":"Medium","gaps":["Direct binding of Egr-1 to the CD23 promoter not demonstrated","Single gain-of-function approach without loss-of-function confirmation"]},{"year":1998,"claim":"Two parallel advances defined the shedding mechanism and an in vivo feedback loop: biochemical characterization showed CD23 is cleaved by a ~63-kDa membrane metalloprotease, while IgE-deficient mice revealed that IgE itself positively regulates surface CD23 levels, establishing a ligand-receptor positive feedback circuit.","evidence":"Membrane fractionation and inhibitor profiling of CD23 sheddase activity; IgE−/− mouse with in vivo IgE infusion rescue","pmids":["9677315","9786437"],"confidence":"High","gaps":["The ~63-kDa protease was not molecularly identified at this stage","Mechanism of IgE-mediated CD23 stabilization (transcriptional vs. post-translational) not distinguished"]},{"year":1999,"claim":"CD23 cross-linking activates the IKKβ–NF-κB pathway via upstream tyrosine kinase activity, and soluble CD23 binds αv integrins/CD47 to trigger proinflammatory cytokine release, revealing two distinct CD23 signaling modalities — membrane-proximal NF-κB activation and soluble CD23-mediated integrin signaling.","evidence":"Dominant-negative IKKβ/IκBα, kinase assays, EMSA in U937 cells; sCD23 binding to αv/β3/CD47 transfectants with blocking antibodies and cytokine ELISA","pmids":["10490984","10037797"],"confidence":"High","gaps":["The upstream tyrosine kinase connecting CD23 to IKKβ is unidentified","Physiological relevance of integrin-mediated sCD23 signaling in vivo not confirmed"]},{"year":2000,"claim":"Demonstrating that epithelial CD23 mediates IgE-dependent transcytosis of luminal antigen across intestinal enterocytes in sensitized rats established CD23 as a transepithelial antigen shuttle driving allergic inflammation.","evidence":"Sensitized rat model, immunogold EM co-localization, anti-CD23 blocking in Ussing chambers","pmids":["11018076"],"confidence":"High","gaps":["Directionality and kinetics of transcytosis not fully characterized","Isoform specificity (CD23a vs. CD23b) not addressed in this system"]},{"year":2001,"claim":"CD23 on follicular dendritic cells suppresses IgE responses via a non-lymphoid radioresistant cell compartment, and CD23 forms a surface complex with HLA-DR that recycles through antigen-loading compartments, linking CD23 to MHC class II antigen presentation.","evidence":"Reciprocal adoptive transfers in CD23-Tg mice with FDC co-culture; co-IP of CD23 with HLA-DR and confocal trafficking in B cells","pmids":["11290762","11454061"],"confidence":"High","gaps":["Whether CD23–HLA-DR association is direct or adaptor-mediated is unclear","FDC-mediated suppression mechanism (competitive trapping vs. signaling) not resolved"]},{"year":2002,"claim":"Identification of Notch2/CBF1 as a transcriptional activator complex at the CD23a promoter connected CD23 regulation to the Notch signaling pathway and explained EBNA-2-driven CD23 upregulation through shared CBF1 binding sites.","evidence":"EMSA/supershift with Notch2 antibody, activated Notch2 transfection inducing endogenous CD23a in pre-B cells","pmids":["11986231"],"confidence":"High","gaps":["Whether Notch1 or other Notch paralogs also regulate CD23 not tested","Chromatin-level confirmation (ChIP) absent"]},{"year":2003,"claim":"ADAM8, ADAM15, and ADAM28 were identified as CD23 sheddases, and mouse enterocytes were shown to express a CD23b splice variant (Δ5) with distinct internalization properties, resolving both the protease identity and isoform-specific trafficking in epithelial transcytosis.","evidence":"Synthetic peptide screening, co-IP of ADAM8 with CD23, active-site mutant; RT-PCR of enterocyte RNA, CD23−/− mouse transport assay","pmids":["12777399","12637252"],"confidence":"High","gaps":["Relative contributions of ADAM8/15/28 vs. ADAM10 in physiological shedding unresolved","Human enterocyte isoform repertoire not fully mapped at this point"]},{"year":2005,"claim":"NMR structure of the CD23 lectin domain revealed calcium-independent self-trimerization and simultaneous but spatially distinct binding sites for IgE and CD21, while mutagenesis of CD23a/b intracytoplasmic exons defined the sorting signals governing isoform-specific endocytosis, basolateral targeting, and plasma membrane retention.","evidence":"NMR chemical shift perturbation mapping; exon-swap mutagenesis in polarized MDCK cells, endocytosis/recycling assays; adoptive transfer of CD23+ B cells into CD23−/− mice demonstrating IgE-mediated antigen presentation","pmids":["16172256","15843555","16034084"],"confidence":"High","gaps":["Full atomic structure of the CD23 trimer in complex with IgE not available at this stage","Whether simultaneous CD21+IgE binding occurs on the intact trimer vs. monomer unclear"]},{"year":2006,"claim":"Showing that only the CD23a isoform (not CD23b) mediates bidirectional IgE transcytosis in primary human intestinal epithelial cells, diverting allergen–IgE complexes from degradation to trigger subepithelial mast cell degranulation, provided the definitive isoform-specific mechanism for epithelial allergic inflammation.","evidence":"Retroviral transduction of CD23a or CD23b into polarized T84 cells, transcytosis assay, RBL degranulation assay","pmids":["16831589"],"confidence":"High","gaps":["Mechanism by which CD23a avoids lysosomal routing not molecularly defined","Whether lipid raft association contributes to isoform-specific sorting unknown"]},{"year":2007,"claim":"ADAM10 was established as the primary physiological CD23 sheddase cleaving at two stalk sites, and the oligomerization state of the resulting soluble fragments was shown to be the key determinant of IgE regulation: monomeric sCD23 inhibits while trimeric sCD23 stimulates IgE synthesis; additionally, epithelial CD23 cross-linking by IgE–allergen complexes activates ERK/JNK–AP-1 to induce CCL20/IL-8 and dendritic cell recruitment.","evidence":"siRNA, dominant-negative ADAM10, specific inhibitors, peptide cleavage assays; recombinant monomeric vs. oligomeric sCD23 in B cell IgE assays; CD23 shRNA knockdown in Caco-2 cells with phospho-signaling","pmids":["17389606","17576766","18054562"],"confidence":"High","gaps":["How ADAM10 access to CD23 stalk is regulated in vivo not known","Whether CCL20 release occurs in vivo in human airway epithelium not confirmed"]},{"year":2009,"claim":"TLR4 stimulation by LPS induces CD23 upregulation and MMP9-dependent sCD23 release specifically from transitional B cells, revealing an innate-immune trigger for CD23 shedding distinct from ADAM10.","evidence":"MMP9 knockout mice, qRT-PCR, flow cytometry, ELISA, in vivo and in vitro LPS treatment","pmids":["19635918"],"confidence":"High","gaps":["Whether MMP9 cleaves CD23 at the same stalk sites as ADAM10 is unknown","Relative physiological importance of MMP9 vs. ADAM10 shedding in innate responses not quantified"]},{"year":2012,"claim":"Trimeric sCD23 stimulates IgE by co-capping mIgE and CD21 on B cell membranes, whereas monomeric sCD23 inhibits IgE, mechanistically explaining the oligomerization-dependent switch; separately, CD23 was identified as a receptor for the cytokine AIMP1/p43, triggering ERK1/2-dependent TNF-α release.","evidence":"Recombinant defined sCD23 oligomers with ADAM10 inhibitor uncoupling, capping assay; receptor screen of 499 targets, siRNA knockdown, ELISA","pmids":["22393152","22767513"],"confidence":"High","gaps":["Structural basis of mIgE/CD21 co-capping by trimeric sCD23 unknown","AIMP1–CD23 interaction awaits independent replication and in vivo validation"]},{"year":2013,"claim":"β2-adrenergic signaling on primed B cells upregulates CD23 and ADAM10 co-localization on exosomes via PKA/p38 MAPK; transfer of these exosomes to recipient B cells enhances IgE production, revealing an intercellular amplification loop.","evidence":"β2AR agonist treatment, exosome isolation/EM, PKA/p38 inhibitors, β2AR-KO B cells, ELISPOT","pmids":["24140643"],"confidence":"Medium","gaps":["Whether exosomal CD23/ADAM10 transfer occurs in vivo not demonstrated","Mechanism by which exosome-delivered CD23 enhances IgE in recipient cells not defined"]},{"year":2014,"claim":"P2X7 receptor activation by extracellular ATP was identified as a rapid trigger of ADAM10-mediated CD23 shedding from B cells, linking danger-signal sensing to acute regulation of surface CD23 levels.","evidence":"P2X7 KO mice, P2X7 antagonist, ADAM10-specific inhibitor, flow cytometry, ELISA","pmids":["25155463"],"confidence":"High","gaps":["Downstream signaling between P2X7 and ADAM10 activation not mapped","In vivo relevance during infection or tissue damage not shown"]},{"year":2015,"claim":"Bone marrow chimera experiments demonstrated that CD23 on radioresistant airway epithelial cells is required for transepithelial allergen–IgE transport and the full allergic airway inflammatory response in vivo, including eosinophilia, collagen deposition, and airway hyperreactivity.","evidence":"CD23 KO mice, bone marrow chimeras, OVA challenge, airway function, histology, anti-CD23 antibody inhalation","pmids":["25783969"],"confidence":"High","gaps":["Whether CD23 transcytosis in airway epithelium is apical-to-basal, basal-to-apical, or bidirectional in vivo not fully resolved"]},{"year":2016,"claim":"CD23 negatively regulates BCR signaling by limiting actin-dependent BCR clustering, Btk and WASp phosphorylation, and cell spreading upon encounter with membrane-associated antigen; separately, the CD23 stalk was identified as a second IgE-binding site, and non-glycosylated monomeric CD23 was shown to bind IgE more effectively than glycosylated forms.","evidence":"CD23 KO mouse B cells on antigen-presenting surfaces, confocal/flow/phospho-Western; recombinant CD23 structural variants with glycosylation-site mutations, EM, binding assays","pmids":["27181049","27343203"],"confidence":"High","gaps":["Molecular mechanism by which CD23 restrains actin polymerization and BCR clustering unknown","Structural basis of stalk–IgE interaction not resolved at atomic level"]},{"year":2017,"claim":"Crystal structure of CD23–IgE-Fc revealed asymmetric binding with two lectin heads engaging IgE-Fc at markedly different affinities due to IgE conformational asymmetry; JNK1 was shown to suppress CD23 expression by inhibiting NFATc1 at the CD23 promoter, with JNK1 deficiency enhancing CD23-dependent antifungal immunity via nitric oxide production.","evidence":"X-ray crystallography and ITC; JNK1 KO mice with C. albicans infection, promoter reporter assays, CD23 blockade epistasis, human cell pharmacological validation","pmids":["28361904","28112734"],"confidence":"High","gaps":["Full trimeric CD23–intact IgE complex structure unavailable","Whether JNK1–NFATc1–CD23 axis operates in human B cells in vivo not confirmed"]},{"year":null,"claim":"Key unresolved questions include: the structural basis of trimeric CD23 simultaneously engaging IgE and CD21 in the context of IgE regulation; the molecular mechanism by which membrane CD23 restrains BCR clustering/actin dynamics; the intracellular trafficking pathway by which CD23a avoids lysosomal degradation during transcytosis; and the relative in vivo contributions of ADAM10, ADAM8, and MMP9 to CD23 shedding across different immune contexts.","evidence":"","pmids":[],"confidence":"Low","gaps":["No full-length trimeric CD23–IgE–CD21 ternary complex structure","Mechanism linking CD23 to actin/BCR clustering restraint uncharacterized","CD23a lysosomal avoidance pathway not molecularly defined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0038024","term_label":"cargo receptor activity","supporting_discovery_ids":[0,1,2,10,11,19,32]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[8,9,22,23]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[6,7,18]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,4,5,8,14,18,19]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[3,4,6,7,15,16,17]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[10,13,14]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[24]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,6,7,18,28,30,31]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[8,9,15,22,25]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[10,11,12,13,20,21]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[25,26,27,31]}],"complexes":["CD23–CD21 complex","CD23–HLA-DR complex"],"partners":["CR2","ADAM10","ADAM8","FYN","MMP9","ITGAV","CD47","AIMP1"],"other_free_text":[]},"mechanistic_narrative":"CD23 (FcεRII/FCER2) is a type II transmembrane C-type lectin that serves as the low-affinity IgE receptor, functioning as a central regulator of IgE homeostasis, IgE-dependent antigen transport across epithelial barriers, and B-cell activation. Its C-type lectin head domain binds IgE in a calcium-independent manner at sites spanning both the head and stalk regions, while simultaneously engaging CD21 at a distinct site to co-regulate IgE synthesis; the oligomerization state of soluble CD23 fragments released by ADAM10 (and context-dependently by ADAM8 or MMP9) determines whether IgE production is stimulated (trimeric sCD23 via CD21/mIgE co-capping) or inhibited (monomeric sCD23) [PMID:16172256, PMID:27343203, PMID:17389606, PMID:22393152]. On epithelial cells, the CD23a isoform mediates bidirectional transcytosis of IgE and IgE–allergen immune complexes — diverting them from lysosomal degradation — to initiate subepithelial mast cell degranulation and allergic inflammation in both gut and airway, a process dependent on isoform-specific intracytoplasmic sorting signals that direct clathrin-dependent endocytosis and basolateral targeting [PMID:16831589, PMID:15843555, PMID:25783969]. On B cells, membrane CD23 negatively regulates BCR signaling by restraining actin-dependent BCR clustering and downstream Btk/WASp phosphorylation, signals through Fyn kinase and the IKKβ–NF-κB pathway upon cross-linking, and facilitates CD23-dependent antigen capture for MHC class II presentation to T cells; its transcription is positively driven by EBNA-2/Notch2–CBF1, IL-4, IgE itself, and NFATc1 (the latter tonically suppressed by JNK1), and negatively regulated by Egr-1 [PMID:27181049, PMID:10490984, PMID:16034084, PMID:11986231, PMID:28112734]."},"prefetch_data":{"uniprot":{"accession":"P06734","full_name":"Low affinity immunoglobulin epsilon Fc receptor","aliases":["BLAST-2","C-type lectin domain family 4 member J","Fc-epsilon-RII","Immunoglobulin E-binding factor","Lymphocyte IgE receptor"],"length_aa":321,"mass_kda":36.5,"function":"Low-affinity receptor for immunoglobulin E (IgE) and CR2/CD21. Has essential roles in the regulation of IgE production and in the differentiation of B cells. On B cells, initiates IgE-dependent antigen uptake and presentation to T cells (PubMed:2167225). On macrophages, upon IgE binding and antigen cross-linking induces intracellular killing of parasites through activation of L-Arginine-nitric oxide pathway (PubMed:7544003)","subcellular_location":"Cell membrane; Cell membrane; Secreted","url":"https://www.uniprot.org/uniprotkb/P06734/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/FCER2","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/FCER2","total_profiled":1310},"omim":[{"mim_id":"620105","title":"C-TYPE LECTIN DOMAIN FAMILY 4, MEMBER F; CLEC4F","url":"https://www.omim.org/entry/620105"},{"mim_id":"616256","title":"C-TYPE LECTIN DOMAIN FAMILY 4, MEMBER G; CLEC4G","url":"https://www.omim.org/entry/616256"},{"mim_id":"604590","title":"Fc FRAGMENT OF IgG RECEPTOR IIb; FCGR2B","url":"https://www.omim.org/entry/604590"},{"mim_id":"604002","title":"RHO-ASSOCIATED COILED-COIL-CONTAINING PROTEIN KINASE 2; ROCK2","url":"https://www.omim.org/entry/604002"},{"mim_id":"602192","title":"A DISINTEGRIN AND METALLOPROTEINASE DOMAIN 10; ADAM10","url":"https://www.omim.org/entry/602192"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"lymphoid tissue","ntpm":39.5}],"url":"https://www.proteinatlas.org/search/FCER2"},"hgnc":{"alias_symbol":["CLEC4J","CD23","FCErII","FcepsilonRII"],"prev_symbol":["CD23A","FCE2"]},"alphafold":{"accession":"P06734","domains":[{"cath_id":"3.10.100.10","chopping":"162-290","consensus_level":"high","plddt":92.6336,"start":162,"end":290}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P06734","model_url":"https://alphafold.ebi.ac.uk/files/AF-P06734-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P06734-F1-predicted_aligned_error_v6.png","plddt_mean":86.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=FCER2","jax_strain_url":"https://www.jax.org/strain/search?query=FCER2"},"sequence":{"accession":"P06734","fasta_url":"https://rest.uniprot.org/uniprotkb/P06734.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P06734/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P06734"}},"corpus_meta":[{"pmid":"1386409","id":"PMC_1386409","title":"CD21 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anti-CD21/anti-CD23 monoclonal antibodies, Western blot, and functional IgE production assay\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstitution with recombinant protein, transfected cell lines, multiple orthogonal methods, replicated functionally\",\n      \"pmids\": [\"1386409\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The NMR solution structure of the CD23 C-type lectin domain reveals that CD23 self-associates into a trimer, binds IgE and CD21 at distinct sites on the lectin head, and can bind both ligands simultaneously; none of these interactions require calcium despite the C-type lectin fold. IgE and CD23 can also form high-molecular-mass multimeric complexes.\",\n      \"method\": \"NMR spectroscopy, concentration-dependent chemical shift perturbation mapping, ligand-induced chemical shift analysis\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR structure with functional ligand-binding site mapping, multiple orthogonal NMR experiments\",\n      \"pmids\": [\"16172256\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Crystal structure of a CD23/IgE-Fc complex shows that two lectin-like head domains of CD23 bind IgE-Fc with affinities differing by more than an order of magnitude, with only one head domain bound to one of the two identical IgE heavy chains in the asymmetrically bent IgE-Fc, revealing asymmetric binding.\",\n      \"method\": \"X-ray crystallography, isothermal titration calorimetry\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus ITC binding quantification\",\n      \"pmids\": [\"28361904\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"ADAM8, ADAM15, and ADAM28 (MDC-L) catalyze ectodomain shedding of CD23; ADAM8-dependent sCD23 release requires proteolytically active ADAM8, which physically associates with membrane-bound CD23, and this release is inhibited by hydroxamic acid metalloprotease inhibitors.\",\n      \"method\": \"Synthetic peptide substrate library screening, in vitro ectodomain shedding assay, co-immunoprecipitation of ADAM8 with CD23, metalloprotease inhibitor treatment\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro enzymatic assay, physical association demonstrated, active-site mutant used, inhibitor confirmation\",\n      \"pmids\": [\"12777399\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"ADAM10 is the primary metalloprotease responsible for cleaving CD23 at two distinct stalk sites to release soluble CD23 (sCD23); tissue inhibitors of metalloproteinases, a prodomain-based ADAM10 inhibitor, dominant-negative ADAM10, and siRNA knockdown of ADAM10 all partially inhibit sCD23 release and cause accumulation of membrane CD23.\",\n      \"method\": \"Peptide cleavage assays, ADAM10 dominant-negative construct expression, siRNA knockdown, ADAM10-specific inhibitor treatment, ELISA for sCD23\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple complementary loss-of-function approaches (dominant-negative, siRNA, inhibitor) with direct substrate cleavage assays\",\n      \"pmids\": [\"17389606\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"CD23 is cleaved from the cell surface by an integral membrane metalloprotease of ~63 kDa; this activity is inhibited by metalloprotease inhibitors (1,10-phenanthroline, imidazole, batimastat) but not by serine, cysteine, or acid protease inhibitors, and the same or similar activity is present in fibroblasts and monocytic cell lines not expressing CD23.\",\n      \"method\": \"Plasma membrane fractionation, gel-filtration chromatography, neo-epitope antibody cleavage assay, pharmacological inhibitor panel\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — biochemical characterization with purified CD23 substrate and comprehensive inhibitor profiling\",\n      \"pmids\": [\"9677315\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Soluble CD23 monomers (derCD23 and exCD23) inhibit IgE synthesis in human B cells, whereas trimeric/oligomeric soluble CD23 (lzCD23) stimulates IgE synthesis; trimeric sCD23 binds cells co-expressing mIgE and mCD21 and caps these proteins on the B cell membrane, indicating that oligomerization state determines the functional outcome of sCD23 on IgE regulation.\",\n      \"method\": \"Recombinant protein production, human B cell IL-4/anti-CD40 IgE synthesis assay, ADAM10 inhibitor (GI254023X) to uncouple cleavage from sCD23 effects, siRNA knockdown, cell-surface capping assay\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstituted recombinant fragments with defined oligomeric states, multiple orthogonal approaches including siRNA and pharmacological inhibition\",\n      \"pmids\": [\"22393152\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Soluble CD23 monomers inhibit and oligomers stimulate IgE synthesis in human B cells after heavy-chain class switching; three defined fragments (monomeric derCD23, monomeric exCD23, oligomeric lzCD23) were characterized biochemically to establish this structure–activity relationship.\",\n      \"method\": \"Recombinant fragment preparation, B cell IgE synthesis assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted defined recombinant fragments tested in functional assay\",\n      \"pmids\": [\"17576766\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"CD23/FcεRII is physically associated with the Src-family tyrosine kinase p59Fyn (but not p56Lck); cross-linking of CD23 in CD23-transfected YT cells activates IL-2 receptor (p55/Tac) expression, indicating that CD23 delivers activation signals via Fyn kinase.\",\n      \"method\": \"cDNA transfection of YT cells, anti-FcεRII crosslinking, co-immunoprecipitation with anti-Fyn antibody, IL-2 receptor induction assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP of endogenous kinase with receptor, functional crosslinking assay, single lab\",\n      \"pmids\": [\"1717997\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Cross-linking of CD23 in monocytic U937 cells activates IKKβ, which phosphorylates IκBα at Ser32/Ser36, leading to IκBα degradation and NF-κB activation; this pathway requires upstream tyrosine kinase activity. A dominant-negative IκBα(S32A/S36A) or dominant-negative IKKβ completely blocks CD23-induced NF-κB activation and gene transcription.\",\n      \"method\": \"Dominant-negative IκBα and IKKβ overexpression, co-transfection assays, IKK activity assays, NF-κB EMSA, phosphospecific IκBα immunoblotting\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — dominant-negative constructs, biochemical kinase assays, multiple orthogonal readouts in single study\",\n      \"pmids\": [\"10490984\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"CD23 expressed on intestinal epithelial cells mediates IgE-dependent transcytosis of antigen (HRP) across enterocytes in sensitized rats; anti-CD23 antibody applied luminally inhibits both antigen transport and the hypersensitivity reaction, and sensitization induces CD23 expression on enterocytes.\",\n      \"method\": \"Active sensitization rat model, immunohistochemistry for CD23, immunogold EM co-localization of CD23 and antigen in endosomes, serum transfer, anti-CD23 blocking antibody in Ussing chamber\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal in vivo and ex vivo methods, including serum transfer, EM co-localization, and receptor blocking\",\n      \"pmids\": [\"11018076\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"CD23a isoform (but not CD23b) is constitutively expressed by primary human intestinal epithelial cells and acts as a bidirectional transporter of IgE; CD23a diverts allergen-IgE complexes away from lysosomal degradation and delivers them transcellularly, enabling degranulation of mast cells below the epithelial barrier.\",\n      \"method\": \"RT-PCR of primary IECs, retroviral transfection of polarized T84 cells with CD23a or CD23b, transcytosis assay, RBL degranulation assay\",\n      \"journal\": \"Gastroenterology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — isoform-specific gain-of-function in polarized epithelial cells with multiple functional readouts\",\n      \"pmids\": [\"16831589\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Mouse intestinal enterocytes express only the CD23b isoform; a novel alternative splice variant CD23b-Δ5 (lacking exon 5) mediates constitutive internalization and uptake of free IgE or anti-CD23, whereas classic CD23b is less efficiently internalized but transports IgE/allergen complexes; CD23-deficient mice lack enhanced transepithelial antigen transport.\",\n      \"method\": \"RT-PCR and sequencing of enterocyte RNA, CD23-/- mouse intestinal transport assay, exon-specific functional comparison\",\n      \"journal\": \"American journal of physiology. Gastrointestinal and liver physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — knockout mouse functional assay plus isoform-specific molecular characterization\",\n      \"pmids\": [\"12637252\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"CD23a undergoes constitutive clathrin-dependent endocytosis directed by an internalization signal in its CD23a-specific intracytoplasmic exon, which also serves as a basolateral targeting signal in polarized epithelial cells; CD23b is stable at the plasma membrane due to a negative regulatory signal in its CD23b-specific intracellular exon.\",\n      \"method\": \"Mutagenesis of intracellular exons, transfection into MDCK polarized cells, endocytosis/recycling assays in multiple cell lines\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — exon-swap mutagenesis, polarized cell trafficking assays, multiple CD23 splice forms compared\",\n      \"pmids\": [\"15843555\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"CD23 forms a non-covalent complex with HLA-DR (MHC class II) on the surface of human B cells; following endocytosis triggered by an IgE-antigen complex or anti-HLA-DR antibody, the HLA-DR–CD23 complex recycles to the cell surface via compartments resembling peptide-loading compartments, on a time scale consistent with antigen presentation.\",\n      \"method\": \"Surface labeling and intracellular trafficking of RPMI 8866 B cells, co-immunoprecipitation of CD23 with HLA-DR, confocal microscopy of endosomal routing\",\n      \"journal\": \"Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — co-IP plus live-cell trafficking assay, single lab\",\n      \"pmids\": [\"11454061\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Soluble CD23 binds directly to the αv integrin subunit and the vitronectin receptor (αvβ3); co-expression of CD47 augments sCD23 binding; the vitronectin receptor/CD47 complex mediates sCD23-induced proinflammatory TNF-α, IL-12, and IFN-γ release from monocytes.\",\n      \"method\": \"Binding assays on αv+β3+ cell lines with/without CD47, purified αv protein binding, CHO single-chain transfectant binding, cytokine release inhibition by anti-CD47, anti-β3, and anti-αv monoclonal antibodies\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple transfected cell lines, purified protein binding, functional cytokine assays, single lab\",\n      \"pmids\": [\"10037797\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"TLR4 ligation by LPS induces transcriptional upregulation of CD23 and generation of soluble CD23 from B cells; this shedding requires matrix metalloprotease 9 (MMP9), as MMP9-deficient B cells fail to release sCD23 in response to LPS. Type 1 transitional B cells uniquely produce MMP9 upon LPS stimulation.\",\n      \"method\": \"MMP9 knockout mice, quantitative RT-PCR, flow cytometry, ELISA for sCD23, in vitro and in vivo LPS treatment of murine and human B cells\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — MMP9 KO mice with in vitro and in vivo confirmation, human B cell validation\",\n      \"pmids\": [\"19635918\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"P2X7 receptor activation by extracellular ATP induces rapid shedding of CD23 from primary human and murine B cells via ADAM10; this process is blocked by the P2X7 antagonist AZ10606120, is absent in P2X7 knockout mouse B cells, and is inhibited by the ADAM10 antagonist GI254023X and the broad metalloprotease inhibitor BB-94.\",\n      \"method\": \"P2X7 knockout mice, P2X7-specific antagonist, ADAM10-specific inhibitor, broad metalloprotease inhibitor, flow cytometry, ELISA\",\n      \"journal\": \"Immunology and cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO plus pharmacological validation with pathway-specific inhibitors, orthogonal assays\",\n      \"pmids\": [\"25155463\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CD23 negatively regulates B-cell receptor (BCR) signaling: CD23 knockout B cells show increased cell spreading area, BCR clustering, phosphotyrosine levels, Btk phosphorylation, F-actin accumulation, and phospho-WASp in the contact zone upon stimulation with membrane-associated antigen.\",\n      \"method\": \"CD23 knockout mice, membrane antigen presentation assay, flow cytometry, confocal microscopy, phospho-Western blotting\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse with multiple defined molecular readouts (Btk, WASp, actin), mechanistically linked to actin-mediated BCR clustering\",\n      \"pmids\": [\"27181049\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"The stalk region of CD23 contains a previously unrecognized IgE-binding site; non-N-glycosylated monomeric CD23 shows superior IgE binding compared with glycosylated CD23; the therapeutic anti-IgE antibody omalizumab blocks IgE binding to both FcεRI and CD23.\",\n      \"method\": \"Expression of four CD23 variants (full extracellular, N-glycosylation site mutant, complete head, truncated head), gel filtration, circular dichroism, binding and inhibition assays, negative-stain electron microscopy\",\n      \"journal\": \"The Journal of allergy and clinical immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple defined structural variants with glycosylation mutagenesis, EM, and inhibition assays\",\n      \"pmids\": [\"27343203\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Epithelial CD23 on airway epithelial cells transcytoses IgE and OVA-IgE immune complexes across the airway epithelial barrier in vivo; CD23 knockout mice or chimeric mice lacking CD23 on radioresistant airway structural/epithelial cells have significantly reduced allergic airway inflammation, eosinophilia, collagen deposition, and airway hyperreactivity after OVA challenge.\",\n      \"method\": \"CD23 knockout mice, bone-marrow chimera experiments, in vivo OVA sensitization/challenge, airway hyperreactivity measurement, histology, CD23-blocking antibody inhalation\",\n      \"journal\": \"Mucosal immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO, bone marrow chimeras delineating cell compartment, in vivo functional readouts, antibody blocking validation\",\n      \"pmids\": [\"25783969\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"CD23-dependent transcytosis of IgE and IgE-immune complexes occurs across polarized human airway epithelial (Calu-3) cells and primary human airway epithelial monolayers; IL-4 upregulates CD23 expression and enhances transcytosis; anti-CD23 antibody or soluble CD23 competitively reduces transcytosis efficiency; transcytosed IgE-antigen complexes retain biological activity to induce mast cell degranulation.\",\n      \"method\": \"Transcytosis assay in polarized Calu-3 monolayers, primary human airway epithelial cells, IL-4 stimulation, CD23-blocking antibody/soluble CD23, human mast cell degranulation assay\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple cell models, receptor-specific blocking, functional downstream readout, primary human cells\",\n      \"pmids\": [\"21307287\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"CD23 cross-linking on human intestinal epithelial Caco-2 cells by IgE-allergen complexes activates ERK and JNK MAP kinases and AP-1, triggering upregulation and release of CCL20 and IL-8; silencing CD23 expression with shRNA abrogates this response; secreted CCL20 induces dendritic cell migration.\",\n      \"method\": \"IgE-antigen complex stimulation of Caco-2, RT-PCR and ELISA for CCL20/IL-8, phospho-Western blotting (ERK, JNK, p38, NF-κB), stable CD23 shRNA knockdown, dendritic cell migration assay\",\n      \"journal\": \"Gastroenterology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — shRNA knockdown with multiple signaling readouts and functional downstream assay\",\n      \"pmids\": [\"18054562\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CD23 is identified as a functional receptor for the proinflammatory cytokine AIMP1/p43; AIMP1 binds CD23 with high affinity (identified in a screen of 499 soluble receptors), CD23 knockdown attenuates AIMP1-induced TNF-α secretion from THP-1 and PBMCs, and AIMP1-induced TNF-α release via CD23 involves ERK1/2 activation.\",\n      \"method\": \"Screen of 499 soluble receptors, AIMP1 binding to CD23 confirmed by pull-down, CD23 siRNA knockdown, ERK1/2 phosphorylation assay, cytokine ELISA\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — receptor screen validated by knockdown and signaling assay, single lab\",\n      \"pmids\": [\"22767513\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"β2-adrenergic receptor engagement on IL-4/CD40L-primed murine B cells increases CD23 and ADAM10 protein expression and promotes their co-localization on exosomes in a PKA- and p38 MAPK-dependent manner; transfer of these exosomes to recipient primed B cells increases IgE production per cell.\",\n      \"method\": \"β2AR agonist treatment, ADAM10/CD23 Western blot, flow cytometry of exosomes, electron microscopy, PKA and p38 MAPK inhibitors, ELISPOT for IgE, β2AR-deficient B cells as controls\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — multiple biochemical methods, genetic (β2AR-KO) and pharmacological controls, exosome transfer functional assay, single lab\",\n      \"pmids\": [\"24140643\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Notch2 intracellular domain (NotchIC) is a component of a transcription factor complex (C1) that binds CBF1-recognition sites in the CD23a core promoter; EBV infection and activated Notch2 drive CD23a transcription; transfection of activated Notch2 into REH pre-B cells induces endogenous CD23a expression, identifying CD23a as a Notch2/CBF1 target gene.\",\n      \"method\": \"EMSA with CBF1-site probes, supershift assays with Notch2 antibody, transient transfection of activated Notch2, RT-PCR for endogenous CD23a, EBV-infected B cells as model\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — EMSA, supershift, and gain-of-function transfection with endogenous gene induction, multiple complementary approaches\",\n      \"pmids\": [\"11986231\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"EBNA-2 transactivates CD23a transcription through a 186-bp cis-acting element located at positions -275/-89 relative to the type a CD23 mRNA start site; this element confers EBNA-2 responsiveness to a heterologous promoter in either orientation and at variable distances, and type 1 EBNA-2 is more potent than type 2 EBNA-2 at activating this element.\",\n      \"method\": \"Transfection of CD23 promoter-reporter constructs with deletional analysis into EBV-negative B-lymphoma cells, heterologous promoter (HSV-TK) assays, Northern blot for mRNA\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — systematic deletion mapping of cis-element, orientation-independence test, heterologous promoter assay, mRNA quantification\",\n      \"pmids\": [\"1649318\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Egr-1 transcription factor overexpression in murine B cells (K46 line) and human Ramos B cells down-regulates CD23 and CD95 (Fas) expression, establishing CD23 as a transcriptional target repressed by Egr-1 following BCR activation.\",\n      \"method\": \"Egr-1 cDNA transfection into B cell lines, flow cytometry for CD23 and CD95, functional apoptosis assay with anti-CD95\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — gain-of-function transfection with functional readout, replicated in two cell lines, single lab\",\n      \"pmids\": [\"9300687\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"In vivo, IgE directly regulates CD23 expression on murine B cells: IgE-deficient mice have ~3-fold less surface CD23 despite normal B cell numbers; intravenous infusion of IgE into IgE-/- mice restores CD23 expression to wild-type levels, demonstrating a positive feedback loop whereby IgE ligand stabilizes/upregulates its own low-affinity receptor.\",\n      \"method\": \"IgE-deficient mouse model, flow cytometry for CD23, in vivo IgE infusion rescue experiment, in vitro IL-4/CD40L stimulation controls\",\n      \"journal\": \"International immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO mouse with in vivo rescue by IgE infusion, mechanistically defined positive feedback\",\n      \"pmids\": [\"9786437\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Suppression of IgE responses in CD23-transgenic mice is mediated by radioresistant non-lymphoid cells, not by transgenic B or T cells: adoptive transfer of normal lymphocytes into transgenic mice still shows IgE suppression, whereas transgenic lymphocytes in normal hosts give normal IgE responses; follicular dendritic cells (FDC) expressing high CD23 are identified as candidate suppressors, as CD23-Tg FDCs inhibit IgE production by normal B cells in vitro.\",\n      \"method\": \"Adoptive transfer experiments (normal ↔ CD23-Tg bone marrow), B cell proliferation and IgE synthesis assays in vitro, germinal center histology, co-culture of Tg FDCs with normal B cells\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal bone marrow transfers plus in vitro co-culture, mechanistically distinguishes cell compartments\",\n      \"pmids\": [\"11290762\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"IgE-mediated enhancement of antibody and T-cell responses in vivo requires CD23+ B cells: transfer of CD23+ B cells into CD23-deficient mice rescues the ability to respond to IgE-antigen; B cells can take up antigen via CD23 and present it to activate naïve T cells in vivo, leading to T-cell expansion and enhanced antibody responses.\",\n      \"method\": \"Adoptive transfer of CD23+ B cells into CD23-deficient mice, TCR-transgenic CD4+ T cell transfer, in vivo immunization with IgE-antigen, flow cytometry, splenic immunohistochemistry\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic rescue by cell transfer, in vivo antigen presentation assay, multiple readouts\",\n      \"pmids\": [\"16034084\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"JNK1 suppresses CD23 expression through negative regulation of NFATc1-mediated transcription at the CD23 gene promoter; JNK1-deficient mice upregulate CD23 and show enhanced antifungal immunity dependent on CD23-mediated nitric oxide production; pharmacological JNK inhibition recapitulates this antifungal effect in mouse and human cells.\",\n      \"method\": \"JNK1-deficient mice, C. albicans infection model, CD23 promoter reporter assays, NFATc1 transcription factor analysis, CD23 blockade experiment, NO production assay, JNK inhibitor treatment of mouse and human cells\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO, promoter mechanistic studies, pathway epistasis via CD23 blockade, human cell validation\",\n      \"pmids\": [\"28112734\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1988,\n      \"finding\": \"A monoclonal antibody recognizing amino acids 367–376 (CH3 domain) of IgE inhibits IgE binding to CD23 (FcεRII), mapping the CD23-binding site on IgE to a 10-amino acid stretch near N-glycosylation site Asn-371 in the Cε3 domain; the antibody does not recognize a carbohydrate epitope as it binds E. coli-derived IgE peptides.\",\n      \"method\": \"Anti-IgE monoclonal antibody binding to recombinant overlapping peptides, heat-denatured IgE, competition binding assay with CD23\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — epitope mapping by peptide binding plus functional inhibition of CD23 interaction\",\n      \"pmids\": [\"2459242\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CD23 (FcεRII) is a type II transmembrane C-type lectin that functions as the low-affinity IgE receptor on B cells and epithelial cells, binding IgE at a site spanning the lectin head and stalk region (without requiring calcium), associating with CD21 and HLA-DR as co-receptors, transducing signals through Fyn kinase and the IKKβ–NF-κB pathway, being shed as soluble fragments by ADAM10 (and ADAM8/MMP9 in specific contexts), with soluble monomers inhibiting and trimeric sCD23 stimulating IgE synthesis; epithelial CD23a mediates transcytosis of IgE and IgE-allergen complexes to initiate allergic inflammation, while membrane CD23 negatively regulates BCR signaling by limiting actin-mediated BCR clustering, and its transcription is positively controlled by EBNA-2/CBF1, Notch2, IL-4, and IgE itself, and negatively by Egr-1.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CD23 (FcεRII/FCER2) is a type II transmembrane C-type lectin that serves as the low-affinity IgE receptor, functioning as a central regulator of IgE homeostasis, IgE-dependent antigen transport across epithelial barriers, and B-cell activation. Its C-type lectin head domain binds IgE in a calcium-independent manner at sites spanning both the head and stalk regions, while simultaneously engaging CD21 at a distinct site to co-regulate IgE synthesis; the oligomerization state of soluble CD23 fragments released by ADAM10 (and context-dependently by ADAM8 or MMP9) determines whether IgE production is stimulated (trimeric sCD23 via CD21/mIgE co-capping) or inhibited (monomeric sCD23) [PMID:16172256, PMID:27343203, PMID:17389606, PMID:22393152]. On epithelial cells, the CD23a isoform mediates bidirectional transcytosis of IgE and IgE–allergen immune complexes — diverting them from lysosomal degradation — to initiate subepithelial mast cell degranulation and allergic inflammation in both gut and airway, a process dependent on isoform-specific intracytoplasmic sorting signals that direct clathrin-dependent endocytosis and basolateral targeting [PMID:16831589, PMID:15843555, PMID:25783969]. On B cells, membrane CD23 negatively regulates BCR signaling by restraining actin-dependent BCR clustering and downstream Btk/WASp phosphorylation, signals through Fyn kinase and the IKKβ–NF-κB pathway upon cross-linking, and facilitates CD23-dependent antigen capture for MHC class II presentation to T cells; its transcription is positively driven by EBNA-2/Notch2–CBF1, IL-4, IgE itself, and NFATc1 (the latter tonically suppressed by JNK1), and negatively regulated by Egr-1 [PMID:27181049, PMID:10490984, PMID:16034084, PMID:11986231, PMID:28112734].\",\n  \"teleology\": [\n    {\n      \"year\": 1988,\n      \"claim\": \"Mapping the CD23-binding epitope on IgE to a 10-amino-acid stretch in the Cε3 domain (CH3, residues 367–376) provided the first molecular definition of the IgE–CD23 interface.\",\n      \"evidence\": \"Monoclonal antibody epitope mapping with overlapping peptides and CD23 competition binding\",\n      \"pmids\": [\"2459242\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Peptide-level mapping only; no structural data on the CD23 contact residues\", \"Does not address the contribution of the CD23 stalk to IgE binding\"]\n    },\n    {\n      \"year\": 1991,\n      \"claim\": \"Two foundational discoveries established CD23 as a signaling receptor and a transcriptional target: cross-linking CD23 activates the Src-family kinase Fyn and induces IL-2R expression, while EBNA-2 transactivates the CD23a promoter through a 186-bp cis-element, linking EBV infection to CD23 upregulation.\",\n      \"evidence\": \"Co-IP of Fyn with CD23 in transfected YT cells plus cross-linking assay; CD23 promoter-reporter deletional analysis in EBV-negative B-lymphoma cells\",\n      \"pmids\": [\"1717997\", \"1649318\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Fyn association shown by single co-IP without reciprocal validation\", \"Signaling downstream of Fyn not mapped\", \"EBNA-2 mechanism of action on CD23 promoter (direct DNA binding vs. adaptor) not resolved\"]\n    },\n    {\n      \"year\": 1992,\n      \"claim\": \"Identification of CD21 as a direct ligand of CD23 that enhances IL-4-induced IgE production established the CD23–CD21 axis as a key regulatory circuit for IgE synthesis on B cells.\",\n      \"evidence\": \"Fluorescent liposome binding with recombinant CD23, CD21-transfected cells, anti-CD21/anti-CD23 blocking antibodies, functional IgE assay\",\n      \"pmids\": [\"1386409\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry of CD23–CD21 complex unknown\", \"Whether CD23–CD21 interaction occurs in cis or in trans on FDCs not resolved\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Demonstrating that Egr-1 overexpression represses CD23 transcription in B cells identified the first negative transcriptional regulator and linked BCR activation to CD23 downregulation.\",\n      \"evidence\": \"Egr-1 cDNA transfection into murine K46 and human Ramos B cells, flow cytometry\",\n      \"pmids\": [\"9300687\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct binding of Egr-1 to the CD23 promoter not demonstrated\", \"Single gain-of-function approach without loss-of-function confirmation\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Two parallel advances defined the shedding mechanism and an in vivo feedback loop: biochemical characterization showed CD23 is cleaved by a ~63-kDa membrane metalloprotease, while IgE-deficient mice revealed that IgE itself positively regulates surface CD23 levels, establishing a ligand-receptor positive feedback circuit.\",\n      \"evidence\": \"Membrane fractionation and inhibitor profiling of CD23 sheddase activity; IgE−/− mouse with in vivo IgE infusion rescue\",\n      \"pmids\": [\"9677315\", \"9786437\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The ~63-kDa protease was not molecularly identified at this stage\", \"Mechanism of IgE-mediated CD23 stabilization (transcriptional vs. post-translational) not distinguished\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"CD23 cross-linking activates the IKKβ–NF-κB pathway via upstream tyrosine kinase activity, and soluble CD23 binds αv integrins/CD47 to trigger proinflammatory cytokine release, revealing two distinct CD23 signaling modalities — membrane-proximal NF-κB activation and soluble CD23-mediated integrin signaling.\",\n      \"evidence\": \"Dominant-negative IKKβ/IκBα, kinase assays, EMSA in U937 cells; sCD23 binding to αv/β3/CD47 transfectants with blocking antibodies and cytokine ELISA\",\n      \"pmids\": [\"10490984\", \"10037797\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The upstream tyrosine kinase connecting CD23 to IKKβ is unidentified\", \"Physiological relevance of integrin-mediated sCD23 signaling in vivo not confirmed\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Demonstrating that epithelial CD23 mediates IgE-dependent transcytosis of luminal antigen across intestinal enterocytes in sensitized rats established CD23 as a transepithelial antigen shuttle driving allergic inflammation.\",\n      \"evidence\": \"Sensitized rat model, immunogold EM co-localization, anti-CD23 blocking in Ussing chambers\",\n      \"pmids\": [\"11018076\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Directionality and kinetics of transcytosis not fully characterized\", \"Isoform specificity (CD23a vs. CD23b) not addressed in this system\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"CD23 on follicular dendritic cells suppresses IgE responses via a non-lymphoid radioresistant cell compartment, and CD23 forms a surface complex with HLA-DR that recycles through antigen-loading compartments, linking CD23 to MHC class II antigen presentation.\",\n      \"evidence\": \"Reciprocal adoptive transfers in CD23-Tg mice with FDC co-culture; co-IP of CD23 with HLA-DR and confocal trafficking in B cells\",\n      \"pmids\": [\"11290762\", \"11454061\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CD23–HLA-DR association is direct or adaptor-mediated is unclear\", \"FDC-mediated suppression mechanism (competitive trapping vs. signaling) not resolved\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Identification of Notch2/CBF1 as a transcriptional activator complex at the CD23a promoter connected CD23 regulation to the Notch signaling pathway and explained EBNA-2-driven CD23 upregulation through shared CBF1 binding sites.\",\n      \"evidence\": \"EMSA/supershift with Notch2 antibody, activated Notch2 transfection inducing endogenous CD23a in pre-B cells\",\n      \"pmids\": [\"11986231\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Notch1 or other Notch paralogs also regulate CD23 not tested\", \"Chromatin-level confirmation (ChIP) absent\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"ADAM8, ADAM15, and ADAM28 were identified as CD23 sheddases, and mouse enterocytes were shown to express a CD23b splice variant (Δ5) with distinct internalization properties, resolving both the protease identity and isoform-specific trafficking in epithelial transcytosis.\",\n      \"evidence\": \"Synthetic peptide screening, co-IP of ADAM8 with CD23, active-site mutant; RT-PCR of enterocyte RNA, CD23−/− mouse transport assay\",\n      \"pmids\": [\"12777399\", \"12637252\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contributions of ADAM8/15/28 vs. ADAM10 in physiological shedding unresolved\", \"Human enterocyte isoform repertoire not fully mapped at this point\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"NMR structure of the CD23 lectin domain revealed calcium-independent self-trimerization and simultaneous but spatially distinct binding sites for IgE and CD21, while mutagenesis of CD23a/b intracytoplasmic exons defined the sorting signals governing isoform-specific endocytosis, basolateral targeting, and plasma membrane retention.\",\n      \"evidence\": \"NMR chemical shift perturbation mapping; exon-swap mutagenesis in polarized MDCK cells, endocytosis/recycling assays; adoptive transfer of CD23+ B cells into CD23−/− mice demonstrating IgE-mediated antigen presentation\",\n      \"pmids\": [\"16172256\", \"15843555\", \"16034084\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full atomic structure of the CD23 trimer in complex with IgE not available at this stage\", \"Whether simultaneous CD21+IgE binding occurs on the intact trimer vs. monomer unclear\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Showing that only the CD23a isoform (not CD23b) mediates bidirectional IgE transcytosis in primary human intestinal epithelial cells, diverting allergen–IgE complexes from degradation to trigger subepithelial mast cell degranulation, provided the definitive isoform-specific mechanism for epithelial allergic inflammation.\",\n      \"evidence\": \"Retroviral transduction of CD23a or CD23b into polarized T84 cells, transcytosis assay, RBL degranulation assay\",\n      \"pmids\": [\"16831589\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which CD23a avoids lysosomal routing not molecularly defined\", \"Whether lipid raft association contributes to isoform-specific sorting unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"ADAM10 was established as the primary physiological CD23 sheddase cleaving at two stalk sites, and the oligomerization state of the resulting soluble fragments was shown to be the key determinant of IgE regulation: monomeric sCD23 inhibits while trimeric sCD23 stimulates IgE synthesis; additionally, epithelial CD23 cross-linking by IgE–allergen complexes activates ERK/JNK–AP-1 to induce CCL20/IL-8 and dendritic cell recruitment.\",\n      \"evidence\": \"siRNA, dominant-negative ADAM10, specific inhibitors, peptide cleavage assays; recombinant monomeric vs. oligomeric sCD23 in B cell IgE assays; CD23 shRNA knockdown in Caco-2 cells with phospho-signaling\",\n      \"pmids\": [\"17389606\", \"17576766\", \"18054562\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How ADAM10 access to CD23 stalk is regulated in vivo not known\", \"Whether CCL20 release occurs in vivo in human airway epithelium not confirmed\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"TLR4 stimulation by LPS induces CD23 upregulation and MMP9-dependent sCD23 release specifically from transitional B cells, revealing an innate-immune trigger for CD23 shedding distinct from ADAM10.\",\n      \"evidence\": \"MMP9 knockout mice, qRT-PCR, flow cytometry, ELISA, in vivo and in vitro LPS treatment\",\n      \"pmids\": [\"19635918\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether MMP9 cleaves CD23 at the same stalk sites as ADAM10 is unknown\", \"Relative physiological importance of MMP9 vs. ADAM10 shedding in innate responses not quantified\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Trimeric sCD23 stimulates IgE by co-capping mIgE and CD21 on B cell membranes, whereas monomeric sCD23 inhibits IgE, mechanistically explaining the oligomerization-dependent switch; separately, CD23 was identified as a receptor for the cytokine AIMP1/p43, triggering ERK1/2-dependent TNF-α release.\",\n      \"evidence\": \"Recombinant defined sCD23 oligomers with ADAM10 inhibitor uncoupling, capping assay; receptor screen of 499 targets, siRNA knockdown, ELISA\",\n      \"pmids\": [\"22393152\", \"22767513\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of mIgE/CD21 co-capping by trimeric sCD23 unknown\", \"AIMP1–CD23 interaction awaits independent replication and in vivo validation\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"β2-adrenergic signaling on primed B cells upregulates CD23 and ADAM10 co-localization on exosomes via PKA/p38 MAPK; transfer of these exosomes to recipient B cells enhances IgE production, revealing an intercellular amplification loop.\",\n      \"evidence\": \"β2AR agonist treatment, exosome isolation/EM, PKA/p38 inhibitors, β2AR-KO B cells, ELISPOT\",\n      \"pmids\": [\"24140643\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether exosomal CD23/ADAM10 transfer occurs in vivo not demonstrated\", \"Mechanism by which exosome-delivered CD23 enhances IgE in recipient cells not defined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"P2X7 receptor activation by extracellular ATP was identified as a rapid trigger of ADAM10-mediated CD23 shedding from B cells, linking danger-signal sensing to acute regulation of surface CD23 levels.\",\n      \"evidence\": \"P2X7 KO mice, P2X7 antagonist, ADAM10-specific inhibitor, flow cytometry, ELISA\",\n      \"pmids\": [\"25155463\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream signaling between P2X7 and ADAM10 activation not mapped\", \"In vivo relevance during infection or tissue damage not shown\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Bone marrow chimera experiments demonstrated that CD23 on radioresistant airway epithelial cells is required for transepithelial allergen–IgE transport and the full allergic airway inflammatory response in vivo, including eosinophilia, collagen deposition, and airway hyperreactivity.\",\n      \"evidence\": \"CD23 KO mice, bone marrow chimeras, OVA challenge, airway function, histology, anti-CD23 antibody inhalation\",\n      \"pmids\": [\"25783969\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CD23 transcytosis in airway epithelium is apical-to-basal, basal-to-apical, or bidirectional in vivo not fully resolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"CD23 negatively regulates BCR signaling by limiting actin-dependent BCR clustering, Btk and WASp phosphorylation, and cell spreading upon encounter with membrane-associated antigen; separately, the CD23 stalk was identified as a second IgE-binding site, and non-glycosylated monomeric CD23 was shown to bind IgE more effectively than glycosylated forms.\",\n      \"evidence\": \"CD23 KO mouse B cells on antigen-presenting surfaces, confocal/flow/phospho-Western; recombinant CD23 structural variants with glycosylation-site mutations, EM, binding assays\",\n      \"pmids\": [\"27181049\", \"27343203\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism by which CD23 restrains actin polymerization and BCR clustering unknown\", \"Structural basis of stalk–IgE interaction not resolved at atomic level\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Crystal structure of CD23–IgE-Fc revealed asymmetric binding with two lectin heads engaging IgE-Fc at markedly different affinities due to IgE conformational asymmetry; JNK1 was shown to suppress CD23 expression by inhibiting NFATc1 at the CD23 promoter, with JNK1 deficiency enhancing CD23-dependent antifungal immunity via nitric oxide production.\",\n      \"evidence\": \"X-ray crystallography and ITC; JNK1 KO mice with C. albicans infection, promoter reporter assays, CD23 blockade epistasis, human cell pharmacological validation\",\n      \"pmids\": [\"28361904\", \"28112734\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full trimeric CD23–intact IgE complex structure unavailable\", \"Whether JNK1–NFATc1–CD23 axis operates in human B cells in vivo not confirmed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: the structural basis of trimeric CD23 simultaneously engaging IgE and CD21 in the context of IgE regulation; the molecular mechanism by which membrane CD23 restrains BCR clustering/actin dynamics; the intracellular trafficking pathway by which CD23a avoids lysosomal degradation during transcytosis; and the relative in vivo contributions of ADAM10, ADAM8, and MMP9 to CD23 shedding across different immune contexts.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No full-length trimeric CD23–IgE–CD21 ternary complex structure\", \"Mechanism linking CD23 to actin/BCR clustering restraint uncharacterized\", \"CD23a lysosomal avoidance pathway not molecularly defined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0038024\", \"supporting_discovery_ids\": [0, 1, 2, 10, 11, 19, 32]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [8, 9, 22, 23]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [6, 7, 18]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 4, 5, 8, 14, 18, 19]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [3, 4, 6, 7, 15, 16, 17]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [10, 13, 14]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [24]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 6, 7, 18, 28, 30, 31]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [8, 9, 15, 22, 25]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [10, 11, 12, 13, 20, 21]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [25, 26, 27, 31]}\n    ],\n    \"complexes\": [\n      \"CD23–CD21 complex\",\n      \"CD23–HLA-DR complex\"\n    ],\n    \"partners\": [\n      \"CR2\",\n      \"ADAM10\",\n      \"ADAM8\",\n      \"FYN\",\n      \"MMP9\",\n      \"ITGAV\",\n      \"CD47\",\n      \"AIMP1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}