{"gene":"IL15","run_date":"2026-04-28T18:06:53","timeline":{"discoveries":[{"year":1994,"finding":"IL-15 was cloned as a novel T cell growth factor that interacts with the β chain of the IL-2 receptor (CD122); monoclonal antibodies to the IL-2R β chain inhibited IL-15 biological activity, and IL-15 competed for IL-2 binding, establishing that IL-15 uses components of the IL-2 receptor complex.","method":"cDNA cloning, receptor competition binding assay, neutralizing monoclonal antibody inhibition","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — original cloning paper with direct receptor binding competition and antibody neutralization; foundational, highly cited","pmids":["8178155"],"is_preprint":false},{"year":1994,"finding":"IL-15 utilizes both the β chain (CD122) and γc chain (CD132) of the IL-2 receptor for high-affinity binding and signaling; the IL-2Rα subunit is not involved in IL-15 binding, implying the existence of a distinct IL-15-specific receptor component.","method":"Transfection of IL-2R subunits into cells, direct binding assays, signaling assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — reconstitution in transfected cells with defined receptor subunits, replicated independently of cloning paper","pmids":["8026467"],"is_preprint":false},{"year":1995,"finding":"A high-affinity IL-15-specific receptor α chain (IL-15Rα) was identified and cloned; IL-15Rα alone binds IL-15 with affinity equivalent to the full heterotrimeric IL-2R for IL-2, and together with IL-2Rβ and γc forms a functional trimeric IL-15 receptor complex. IL-15Rα is structurally related to IL-2Rα, defining a new cytokine receptor subfamily.","method":"Molecular cloning, direct binding assays, reconstitution of receptor complex in myeloid cell line","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — receptor cloning with reconstitution and direct binding quantification; foundational paper","pmids":["7641685"],"is_preprint":false},{"year":1995,"finding":"IL-15 rapidly induces tyrosine phosphorylation and activation of JAK1 and JAK3, and activates STAT3 and STAT5 transcription factors in human T cells, similar to IL-2; IL-4 activates STAT3 but not STAT5, distinguishing the downstream signaling of these cytokines.","method":"Immunoprecipitation, Western blot for phosphotyrosine, EMSA (DNA-binding assays for STAT complexes)","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 — biochemical signaling assays (IP + Western + EMSA) identifying specific kinase-STAT pathway; highly cited foundational paper","pmids":["7568001"],"is_preprint":false},{"year":1996,"finding":"The IL-15 mRNA contains 10 upstream AUGs in its 5′ UTR that function as negative regulators of translation. An HTLV-I R-region/IL-15 chimeric mRNA that lacks most upstream AUGs is translated much more efficiently, demonstrating that IL-15 protein expression is regulated post-transcriptionally at the level of mRNA translation.","method":"RT-PCR characterization of mRNA isoforms, translational analysis comparing upstream AUG content, analysis of HTLV-I fusion transcript","journal":"Journal of leukocyte biology","confidence":"High","confidence_rationale":"Tier 2 — molecular characterization of 5′ UTR regulatory elements with functional comparison; replicated concept in later structural studies","pmids":["8613692"],"is_preprint":false},{"year":2000,"finding":"CD8+ memory-phenotype T cells undergo slow homeostatic division in vivo that requires IL-15; this division is markedly increased by inhibition of IL-2, showing that IL-15 and IL-2 exert opposing control over CD8+ memory T cell homeostasis.","method":"In vivo proliferation assays in IL-15-deficient mice and IL-2 inhibition experiments; adoptive transfer system","journal":"Science","confidence":"High","confidence_rationale":"Tier 2 — genetic KO combined with IL-2 inhibition establishing opposing cytokine balance; highly cited","pmids":["10784451"],"is_preprint":false},{"year":2003,"finding":"IL-15Rα is not required for IL-15-induced proliferation or pro-survival effects on CD8+ T cells, but greatly enhances sensitivity to low concentrations of IL-15; the β and γ chains of IL-15R are absolutely required for both proliferative and pro-survival effects. IL-15 promotes survival of both naive and memory CD8+ T cells via upregulation of Bcl-2.","method":"In vitro survival and proliferation assays with IL-15Rα-deficient and β/γ-chain-deficient cells; Bcl-2 and Bcl-xL expression analysis","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — defined receptor subunit requirements using KO cells with specific survival/proliferation readouts and molecular markers","pmids":["12734346"],"is_preprint":false},{"year":2003,"finding":"IL-15 is the dominant survival signal for peripheral NK cells, maintaining them via upregulation of the anti-apoptotic factor Bcl-2. MHC class I molecules do not regulate NK cell survival or homeostatic expansion.","method":"Adoptive transfer of NK cells into IL-15-deficient hosts; Bcl-2 expression analysis; NK cell survival assays","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — adoptive transfer with genetic KO host, specific molecular mechanism (Bcl-2) identified","pmids":["12586624"],"is_preprint":false},{"year":2003,"finding":"SOCS1 is an essential negative regulator of IL-15 receptor signaling in CD8+ thymocytes. In SOCS1-deficient CD8+ thymocytes, IL-15 selectively induces sustained STAT5 phosphorylation, massive proliferation, and strong upregulation of Bcl-xL and CD44, demonstrating that SOCS1 attenuates IL-15 signaling in a cell-type-specific manner.","method":"SOCS1−/− and SOCS1−/−IFNγ−/− mouse models; fetal thymic organ culture; intrathymic transfer; STAT5 phosphorylation assays; proliferation assays","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with biochemical STAT5 readout and multiple complementary approaches","pmids":["12907450"],"is_preprint":false},{"year":2003,"finding":"Murine mast cells express three novel IL-15Rα isoforms generated by alternative splicing (lacking exon 4; exons 3 and 4; or exons 3, 4, and 5). These isoforms localize to the Golgi, ER, perinuclear space, and cell membrane, bind IL-15 with high affinity, and mediate signaling through phosphorylation of STAT3, STAT5, STAT6, JAK2, and Syk kinase.","method":"RT-PCR, sequencing, transient transfection in COS-7 cells, glycosylation analysis, IL-15 binding assay in BA/F3 transfectants, STAT/JAK phosphorylation analysis","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 — molecular cloning plus binding and signaling in transfected cells; single lab","pmids":["12734349"],"is_preprint":false},{"year":2005,"finding":"The sushi domain of soluble IL-15Rα acts as a potent agonist of IL-15 action through the IL-15Rβ/γ heterodimer by enhancing IL-15 binding and biological effects, whereas the full extracellular domain acts as an antagonist. Fusion proteins (RLI) linking IL-15 to the sushi domain are hyperagonists that bind IL-15Rβ/γ, are internalized, and induce potent lymphocyte proliferation and survival.","method":"Recombinant protein production, binding assays, cell proliferation assays, apoptosis assays, receptor internalization studies","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — reconstitution with defined receptor fragments, functional and binding assays; mechanistically detailed","pmids":["16284400"],"is_preprint":false},{"year":2006,"finding":"Binding of soluble IL-15Rα to IL-15 markedly enhances biological activity, rapidly inducing strong expansion of memory-phenotype CD8+ T cells and NK cells in vivo. This suggests that IL-15Rα binding induces a conformational change that potentiates IL-15 recognition by the βγc receptor. In contrast, IL-2 function is inhibited by binding to soluble IL-2Rα.","method":"In vivo injection of IL-15/IL-15Rα complexes in mice; flow cytometry of lymphocyte populations","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — in vivo functional assay with recombinant protein complex; mechanistic inference supported by contrast with IL-2 data","pmids":["16757567"],"is_preprint":false},{"year":2006,"finding":"IL-15 plays a critical role in protecting effector CD8+ T cells from apoptosis during the contraction phase following microbial infection, via induction of Bcl-2 expression. Enforced Bcl-2 expression rescues effector T cells from death in IL-15-KO mice, placing Bcl-2 downstream of IL-15 signaling.","method":"Adoptive transfer into IL-15 KO and IL-15 transgenic mice, in vivo rIL-15 administration, Bcl-2 transgenic rescue experiment","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis (Bcl-2 transgene rescue of KO phenotype) establishing pathway hierarchy","pmids":["16365444"],"is_preprint":false},{"year":2006,"finding":"IL-15 mediates mechanical hypernociception through a sequential pathway: IL-15 → IFN-γ → endothelin-1 (ET-1) via ETA receptor → prostaglandin E2 (PGE2). IL-15 failed to induce hypernociception in IFN-γ−/− mice, and IL-15 induced ET-1 production in an IFN-γ-dependent manner.","method":"Mouse peritoneal injection models; IFN-γ−/− mice; pharmacological inhibitors (ETA/ETB antagonists, COX inhibitors); cytokine measurement","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO plus pharmacological inhibition defining sequential pathway; single lab","pmids":["16766656"],"is_preprint":false},{"year":2006,"finding":"IL-15-deficient mice lack the CD44hiCD122hi memory-phenotype CD8+ T cell subset, while ITK-deficient mice lack the CD44loCD122lo conventional CD8+ T cell subset; double-KO mice have severe depletion of all CD8+ T cells. These findings establish that IL-15 specifically supports a CD8+ T cell subset with both adaptive and innate immune functions.","method":"IL-15−/−, ITK−/−, and IL-15−/−ITK−/− double-KO mouse analysis; flow cytometry; functional assays (TCR and NK receptor stimulation)","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — double-KO genetic epistasis defining non-overlapping subsets; rigorous controls","pmids":["16880398"],"is_preprint":false},{"year":2007,"finding":"Intracellular IL-15 stored in mast cells acts as a specific negative transcriptional regulator of the mast cell chymase MCP-2 gene. Deletion of IL-15 markedly increases chymase activity and neutrophil-recruiting chemokine processing, leading to increased bactericidal responses and survival in murine septic peritonitis.","method":"Il15 KO mouse model; cecal ligation and puncture (CLP) sepsis model; chymase activity assays; chemokine processing assays; transcriptional analysis","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 2 — in vivo KO model with mechanistic characterization of transcriptional regulation by intracellular cytokine; multiple readouts","pmids":["17643110"],"is_preprint":false},{"year":2007,"finding":"IL-15 mediates antigen-induced neutrophil migration by triggering a sequential cytokine cascade: IL-15 induces IL-18 production, which then drives MIP-2, MIP-1α, TNF-α, and leukotriene B4 release to promote neutrophil migration. IL-18−/−, MIP-1α−/−, TNFR1−/−, and 5-LOX−/− mice are resistant to IL-15-induced neutrophil migration.","method":"Mouse peritoneal model; IL-18−/−, MIP-1α−/−, TNFR1−/−, 5-LOX−/− KO mice; neutralizing antibodies; cytokine measurement","journal":"European journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic KO models defining pathway cascade; confirmed with OVA antigen model","pmids":["17979156"],"is_preprint":false},{"year":2008,"finding":"Dendritic cells (DCs) transpresent IL-15 to memory CD8+ T cells, driving their homeostatic proliferation. A transgenic model restricting IL-15 transpresentation to DCs shows that DC-mediated transpresentation is largely sufficient for normal homeostatic proliferation of established memory CD8+ T cells, preferentially supporting a KLRG-1+CD27− subset.","method":"IL-15Rα transgenic mouse model limiting transpresentation to DCs; adoptive transfer; flow cytometry; viral infection model","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — cell-type-specific transgenic rescue model identifying the cellular source of trans-presentation; multiple T cell subset readouts","pmids":["18812469"],"is_preprint":false},{"year":2011,"finding":"IL-15 regulates NKT cell survival through Bcl-xL (but not other Bcl-2 family members), and controls thymic stage 2 to stage 3 lineage progression and terminal NKT cell differentiation by regulating T-bet (Tbx21) expression, which in turn controls IFN-γ, granzyme A/C, and NK receptor expression.","method":"IL-15 KO mouse analysis; in vitro IL-15 stimulation; global gene expression profiling; validation by RT-PCR and flow cytometry; Bcl-xL-specific dependency assessment","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — KO model with gene expression profiling and mechanistic validation linking IL-15 to T-bet→effector molecule axis","pmids":["22084435"],"is_preprint":false},{"year":2011,"finding":"Different developmental events of NK cells (homeostasis, mature differentiation, Ly49 acquisition, and effector function) require quantitatively different levels of IL-15 trans-presentation. The level of IL-15Rα on accessory cells (both bone marrow-derived DCs and radiation-resistant stromal cells) directly determines the level of STAT5 phosphorylation in NK cells and the degree of each developmental outcome; the IL-15Rα on NK cells themselves is not required.","method":"IL-15Rα knockin/transgenic mice with graded IL-15Rα expression; STAT5 phosphorylation assays in NK cells cocultured with DCs; in vivo NK cell development analysis","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — quantitative dose-response with biochemical STAT5 readout; multiple developmental stages assessed","pmids":["21715685"],"is_preprint":false},{"year":2012,"finding":"Crystal structures of the IL-15–IL-15Rα–IL-2Rβ–γc quaternary complex show that IL-15 binds IL-2Rβ and γc in a geometry nearly indistinguishable from IL-2 in the IL-2–IL-2Rα–IL-2Rβ–γc complex. IL-15Rα substantially increases the affinity of IL-15 for IL-2Rβ (allosteric effect required for IL-15 trans-signaling). The functional differences between IL-2 and IL-15 in lymphocytes result from disparate receptor affinities rather than distinct signaling geometries.","method":"X-ray crystallography of quaternary receptor complex; surface plasmon resonance for affinity measurements; functional signaling assays in lymphocytes","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 1 — crystal structure plus biophysical affinity measurements plus functional validation; mechanistically definitive","pmids":["23104097"],"is_preprint":false},{"year":2013,"finding":"IL-15 promoter activity is restricted to myeloid lineages during hematopoiesis; lymphoid cells extinguish IL-15 expression in a stepwise, Notch-dependent manner during development. Hematopoietic stem cells (LSK) express high IL-15. IL-15 expression is regulated at the pre-DC branch point, generating IL-15+CD8+ and IL-15−/lowCD8− DC subsets.","method":"IL-15 reporter transgenic mouse; flow cytometry of defined hematopoietic populations; Notch inhibition experiments","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 — reporter mouse with Notch inhibition establishing Notch-dependent transcriptional regulation; single lab","pmids":["23966624"],"is_preprint":false},{"year":2015,"finding":"Type I IFN-driven IL-15 expression during viral infection drives memory CD8+ T cells into rapid cell-cycle progression via mTORC1 (independently of antigen re-exposure), providing a proliferative advantage. IL-15 prepares memory cells for faster division upon subsequent antigen encounter.","method":"Murine viral infection and peptide immunization models; IL-15 KO mice; mTORC1 inhibitor (rapamycin) treatment; BrdU incorporation cell-cycle analysis","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — genetic KO plus pharmacological mTORC1 inhibition establishing signaling pathway; multiple experimental systems","pmids":["26241055"],"is_preprint":false},{"year":2016,"finding":"IL-15 activates the JAK3/STAT3 signaling pathway in skeletal muscle cells to stimulate glucose uptake and GLUT4 translocation to the plasma membrane. IL-15 does not activate Akt, AMPK, JAK1, or STAT5 in this context. STAT3 inhibition abolishes IL-15-induced glucose uptake, and HIF1α expression is dependent on IL-15-induced STAT3 activation.","method":"C2C12 differentiated myotube treatment with IL-15; phosphorylation assays (Western blot); co-immunoprecipitation of JAK3/STAT3; STAT3 nuclear translocation imaging; GLUT4 translocation assay; STAT3 inhibitor rescue experiments","journal":"Frontiers in physiology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple biochemical assays plus inhibitor rescue; single lab, single cell line model","pmids":["28066259"],"is_preprint":false},{"year":2018,"finding":"Ligation of NKG2D by ULBP2 (but not MICA) induces enlargement of NKG2D nanoclusters at the NK cell surface and causes the cytokine receptor subunit IL-2/IL-15Rβ to coalesce into these nanoclusters, enabling cooperative signaling between NKG2D and the IL-15 receptor. This nanoscale receptor co-organization amplifies NK cell responses to ULBP2 + IL-15.","method":"Superresolution (dSTORM) microscopy on primary human NK cells; functional NK cell activation assays; IL-15Rα-coated surface trans-presentation experiments","journal":"Science signaling","confidence":"High","confidence_rationale":"Tier 1-2 — superresolution structural imaging combined with functional validation; ligand-specific mechanistic distinction","pmids":["29636390"],"is_preprint":false},{"year":2018,"finding":"Sorafenib reduces expression of the transcription factor ATF4 in FLT3-ITD+ AML cells, thereby relieving ATF4-mediated negative regulation of IRF7, which enhances IL-15 transcription. IRF7 knockdown or ATF4 overexpression abolishes sorafenib-induced IL-15 production, defining the ATF4–IRF7–IL-15 transcriptional axis.","method":"siRNA knockdown of IRF7; ATF4 overexpression; Western blot; chromatin state analysis; IL-15 ELISA; in vitro and in vivo mouse AML models","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 2 — genetic gain/loss-of-function experiments (siRNA + overexpression) establishing mechanistic transcriptional pathway; validated in human patient samples","pmids":["29431743"],"is_preprint":false},{"year":2019,"finding":"IL-15 expansion of CAR-T cells reduces mTORC1 activity, decreases glycolytic enzyme expression, and improves mitochondrial fitness, preserving a stem cell memory (Tscm; CD62L+CD45RA+CCR7+) phenotype. Culturing CAR-T cells in rapamycin (mTORC1 inhibitor) recapitulates the IL-15 effect, demonstrating that IL-15-mediated mTORC1 suppression is responsible for maintaining the Tscm phenotype.","method":"In vitro CAR-T expansion with IL-15 vs IL-2; rapamycin treatment; mTORC1 activity assays; metabolic profiling; phenotypic flow cytometry; in vivo xenograft tumor model","journal":"Cancer immunology research","confidence":"High","confidence_rationale":"Tier 2 — pharmacological epistasis (rapamycin phenocopy) plus metabolic profiling linking IL-15 to mTORC1–metabolism–phenotype axis","pmids":["30890531"],"is_preprint":false},{"year":2019,"finding":"De novo designed protein Neo-2/15 mimics IL-2 and IL-15 by binding to IL-2Rβγc but lacking binding sites for IL-2Rα or IL-15Rα. Crystal structures of Neo-2/15 alone and in complex with IL-2Rβγc confirm the designed model and show the protein elicits downstream cell signaling independently of the private α chains.","method":"Computational de novo protein design; X-ray crystallography of Neo-2/15 alone and in IL-2Rβγc complex; cell signaling assays; in vivo mouse tumor models","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — crystal structure validation of designed mimic in receptor complex; functional signaling confirmed","pmids":["30626941"],"is_preprint":false},{"year":2020,"finding":"In a mouse model of coeliac disease, overexpression of IL-15 is required simultaneously in both the gut epithelium and lamina propria to drive villous atrophy. CD4+ T cells and HLA-DQ8 license cytotoxic CD8+ T cells to mediate intestinal epithelial cell lysis; IFN-γ and TG2 contribute to tissue destruction downstream of IL-15.","method":"Transgenic mouse model with compartment-specific IL-15 overexpression (epithelium and/or lamina propria); HLA-DQ8 expression; gluten feeding; histopathology; T cell depletion studies; IFN-γ KO","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — compartment-specific genetic model with multiple cellular depletions defining location-dependent IL-15 mechanism","pmids":["32051586"],"is_preprint":false},{"year":2025,"finding":"CREM (cyclic AMP response element modulator) is induced in CAR-NK cells by both CAR activation and IL-15 signaling via the PKA–CREB pathway (downstream of ITAM signaling or IL-15). CREM deletion enhances CAR-NK cell effector function in vitro and in vivo and increases resistance to immunosuppression. CREM exerts its regulatory functions through epigenetic reprogramming of CAR-NK cells.","method":"Transcriptomic analysis; CREM deletion (genetic KO); PKA/CREB pathway inhibition; epigenetic profiling; in vivo tumor mouse model; CAR-NK rechallenge assays","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — genetic deletion plus pathway inhibition plus epigenomic profiling; mechanistic dissection of IL-15 downstream signaling in NK cells","pmids":["40468083"],"is_preprint":false}],"current_model":"IL-15 is a secreted/trans-presented four-helix cytokine that signals through a trimeric receptor (IL-15Rα/IL-2Rβ/γc): IL-15Rα on presenting cells binds IL-15 with picomolar affinity and allosterically potentiates its delivery in trans to IL-2Rβ/γc on responding cells, activating JAK1/JAK3 and STAT3/STAT5, as well as PI3K–mTORC1 and Ras–MEK–MAPK pathways, to promote survival (via Bcl-2/Bcl-xL), proliferation, and differentiation of NK cells, NKT cells, and CD8+ memory T cells; IL-15 expression itself is regulated post-transcriptionally by upstream AUGs in its 5′ UTR, transcriptionally through the ATF4–IRF7 axis and Notch signaling during hematopoiesis, and intracellularly in mast cells where it acts as a transcriptional repressor of chymase, while nanoscale co-clustering of IL-2/IL-15Rβ with NKG2D after ULBP2 ligation provides a mechanism for cooperative receptor activation."},"narrative":{"teleology":[{"year":1994,"claim":"The discovery that IL-15 is a T cell growth factor that shares IL-2Rβ (CD122) and γc (CD132) but not IL-2Rα established it as a second cytokine exploiting the IL-2 receptor system, raising the question of how specificity is achieved.","evidence":"cDNA cloning, receptor competition binding, and neutralizing antibody inhibition in two independent studies","pmids":["8178155","8026467"],"confidence":"High","gaps":["The IL-15-specific receptor component was not yet identified","Downstream signaling pathways were unknown"]},{"year":1995,"claim":"Cloning of IL-15Rα as a high-affinity private α chain structurally related to IL-2Rα resolved how IL-15 achieves receptor specificity and defined the complete trimeric receptor complex (IL-15Rα/IL-2Rβ/γc).","evidence":"Molecular cloning, reconstitution of trimeric complex, and direct binding quantification in myeloid cells","pmids":["7641685"],"confidence":"High","gaps":["Whether IL-15Rα functions in cis or trans was unknown","Three-dimensional receptor architecture was unresolved"]},{"year":1995,"claim":"Identification of JAK1/JAK3 activation and STAT3/STAT5 induction downstream of IL-15 established the proximal signaling cascade, paralleling IL-2 but foreshadowing cell-type-specific differences.","evidence":"Immunoprecipitation, phosphotyrosine blotting, and EMSA in human T cells","pmids":["7568001"],"confidence":"High","gaps":["Whether additional pathways (MAPK, PI3K) are engaged was not addressed","Cell-type-specific signaling differences were unexplored"]},{"year":1996,"claim":"Demonstration that 10 upstream AUGs in the IL-15 5′ UTR suppress translation revealed that IL-15 protein output is tightly controlled post-transcriptionally, explaining the discrepancy between widespread mRNA expression and limited protein detection.","evidence":"RT-PCR characterization and translational efficiency comparison of chimeric mRNAs with varying upstream AUG content","pmids":["8613692"],"confidence":"High","gaps":["Which trans-acting factors relieve translational repression was unknown","In vivo relevance of individual upstream AUGs was not tested"]},{"year":2000,"claim":"Showing that CD8⁺ memory T cell homeostatic proliferation requires IL-15 while being opposed by IL-2 established IL-15 as the non-redundant survival cytokine for immunological memory, distinct from IL-2.","evidence":"In vivo proliferation in IL-15-deficient mice combined with IL-2 blockade; adoptive transfer system","pmids":["10784451"],"confidence":"High","gaps":["The cellular source of IL-15 for memory T cell maintenance was unresolved","Downstream survival effectors were not identified"]},{"year":2003,"claim":"Concurrent studies defined IL-15 as the dominant NK cell survival signal via Bcl-2, showed that IL-15Rα enhances sensitivity but is dispensable on responding cells (β/γc are essential), identified SOCS1 as a negative regulator of IL-15–STAT5 signaling, and revealed alternative IL-15Rα splice variants in mast cells with distinct signaling profiles.","evidence":"Adoptive transfer into IL-15 KO hosts; receptor subunit KO cell assays; SOCS1 KO thymic organ culture; mast cell IL-15Rα isoform cloning with signaling reconstitution","pmids":["12586624","12734346","12907450","12734349"],"confidence":"High","gaps":["Whether IL-15Rα on accessory cells trans-presents IL-15 in vivo was not directly demonstrated","Quantitative relationship between IL-15 dose and specific developmental outcomes was unknown","Mast cell IL-15Rα isoform findings from a single lab awaited independent confirmation"]},{"year":2005,"claim":"Dissection of the IL-15Rα sushi domain as an agonist versus the full ectodomain as an antagonist explained how soluble IL-15Rα fragments allosterically modulate IL-15 potency, enabling rational design of IL-15 superagonists (RLI).","evidence":"Recombinant domain fragments tested in binding, proliferation, apoptosis, and receptor internalization assays","pmids":["16284400"],"confidence":"High","gaps":["Structural basis for the allosteric enhancement was not yet resolved at atomic level","In vivo pharmacokinetics of sushi-domain fusions were not characterized"]},{"year":2006,"claim":"A convergence of in vivo studies established that IL-15/IL-15Rα complexes potently expand memory CD8⁺ T cells and NK cells, that IL-15 protects effector CD8⁺ T cells from contraction-phase apoptosis via Bcl-2 (shown by Bcl-2 transgene rescue in IL-15 KO), and that IL-15 is required specifically for the CD44ʰⁱCD122ʰⁱ memory-phenotype CD8⁺ T cell subset.","evidence":"IL-15/sIL-15Rα complex injection; IL-15 KO and transgenic mice with Bcl-2 rescue; IL-15/ITK double-KO epistasis","pmids":["16757567","16365444","16880398"],"confidence":"High","gaps":["Which accessory cell types are the physiological source of trans-presented IL-15 was still unresolved","Whether IL-15 supports CD8⁺ memory via Bcl-2 versus proliferative mechanisms was debated"]},{"year":2007,"claim":"Two studies revealed unexpected non-canonical IL-15 functions: intracellular IL-15 in mast cells acts as a transcriptional repressor of chymase, and extracellular IL-15 orchestrates neutrophil migration through a sequential IL-18→MIP-2/TNF-α/LTB4 cytokine cascade.","evidence":"IL-15 KO mice in CLP sepsis model with chymase activity assays; peritoneal neutrophil migration in multiple cytokine/receptor KO mice","pmids":["17643110","17979156"],"confidence":"High","gaps":["Mechanism by which intracellular IL-15 represses chymase transcription was not defined","Whether the neutrophil-recruiting cascade operates in tissues beyond the peritoneum was unknown"]},{"year":2008,"claim":"Restricting IL-15Rα expression to dendritic cells proved sufficient for homeostatic memory CD8⁺ T cell proliferation, identifying DCs as a physiologically relevant trans-presenting cell type.","evidence":"IL-15Rα transgenic mouse model limiting expression to DCs; adoptive transfer with viral infection","pmids":["18812469"],"confidence":"High","gaps":["Contribution of non-DC populations (macrophages, stromal cells) was not excluded","Whether DC trans-presentation is sufficient for NK cell homeostasis was not tested"]},{"year":2011,"claim":"Quantitative studies showed that graded IL-15 trans-presentation levels on accessory cells determine distinct NK cell developmental thresholds via proportional STAT5 phosphorylation, and that IL-15 controls NKT cell terminal differentiation through a Bcl-xL survival and T-bet transcriptional program.","evidence":"IL-15Rα knockin mice with titrated expression; NK-DC coculture with STAT5 readout; IL-15 KO NKT cell gene expression profiling","pmids":["21715685","22084435"],"confidence":"High","gaps":["How specific STAT5 phosphorylation thresholds activate distinct gene programs was not mechanistically resolved","Whether T-bet is directly or indirectly regulated by STAT5 downstream of IL-15 was unclear"]},{"year":2012,"claim":"Crystal structures of the quaternary IL-15–IL-15Rα–IL-2Rβ–γc complex revealed near-identical receptor engagement geometry to the IL-2 quaternary complex, demonstrating that IL-15Rα allosterically increases IL-15 affinity for IL-2Rβ and that functional differences between IL-2 and IL-15 arise from differential receptor affinities rather than distinct signaling geometries.","evidence":"X-ray crystallography of the quaternary complex; surface plasmon resonance; functional signaling assays","pmids":["23104097"],"confidence":"High","gaps":["How identical β/γc engagement produces differential STAT activation kinetics between IL-2 and IL-15 remained unexplained","Structural basis for IL-15Rα's allosteric effect on IL-2Rβ binding was not fully delineated"]},{"year":2015,"claim":"Type I IFN-driven IL-15 was shown to push memory CD8⁺ T cells into rapid mTORC1-dependent cell-cycle entry independently of antigen, establishing mTORC1 as a key downstream effector of IL-15 in bystander activation of memory T cells.","evidence":"IL-15 KO mice during viral infection; rapamycin treatment; BrdU incorporation","pmids":["26241055"],"confidence":"High","gaps":["How IL-15 activates mTORC1 (via PI3K–Akt or alternative route) in memory T cells was not resolved","Whether mTORC1-independent IL-15 effects contribute to bystander activation was not tested"]},{"year":2018,"claim":"Two mechanistic advances emerged: NKG2D ligation by ULBP2 induces nanoscale co-clustering of NKG2D with IL-2/IL-15Rβ to enable cooperative signaling in NK cells, and the ATF4–IRF7 transcriptional axis was identified as a regulator of IL-15 expression in AML cells.","evidence":"Super-resolution dSTORM imaging on primary NK cells with functional validation; siRNA/overexpression of IRF7/ATF4 in AML cells with chromatin analysis","pmids":["29636390","29431743"],"confidence":"High","gaps":["Whether NKG2D–IL-15Rβ co-clustering occurs with other NKG2D ligands beyond ULBP2 was unknown","Generalizability of ATF4–IRF7–IL-15 axis beyond FLT3-ITD+ AML was not tested"]},{"year":2019,"claim":"IL-15 was shown to preserve stem cell memory (Tscm) phenotype in CAR-T cells through mTORC1 suppression and metabolic reprogramming toward mitochondrial fitness, and a de novo designed protein (Neo-2/15) that binds IL-2Rβγc without engaging α chains confirmed that β/γc engagement alone is sufficient for downstream signaling.","evidence":"CAR-T expansion with IL-15 versus IL-2 plus rapamycin phenocopy; metabolic profiling; crystal structure of Neo-2/15 in complex with IL-2Rβγc","pmids":["30890531","30626941"],"confidence":"High","gaps":["Whether IL-15-mediated mTORC1 suppression in CAR-T cells is dose-dependent or context-dependent was not determined","Neo-2/15 structure did not address IL-15Rα allosteric mechanism"]},{"year":2020,"claim":"A compartment-specific transgenic model demonstrated that IL-15 overexpression must occur simultaneously in both gut epithelium and lamina propria to drive coeliac-like villous atrophy, placing IL-15 as a central pathogenic mediator linking innate and adaptive intestinal immunity.","evidence":"Transgenic mice with compartment-restricted IL-15 overexpression; HLA-DQ8; gluten feeding; T cell depletion; IFN-γ KO","pmids":["32051586"],"confidence":"High","gaps":["Whether epithelial versus lamina propria IL-15 engages distinct receptor configurations or cell types was not resolved","Applicability to human coeliac disease pathogenesis requires clinical confirmation"]},{"year":2025,"claim":"Identification of CREM as an IL-15-induced negative regulator of CAR-NK cell function via PKA–CREB signaling and epigenetic reprogramming revealed a previously unknown feedback restraint downstream of IL-15 in engineered NK cells.","evidence":"CREM deletion in CAR-NK cells; PKA/CREB pathway inhibition; epigenomic profiling; in vivo tumor models","pmids":["40468083"],"confidence":"High","gaps":["Whether CREM-mediated restraint operates in endogenous NK cells or is specific to CAR-NK expansion conditions is unknown","The specific epigenetic targets of CREM in NK cells were not fully catalogued"]},{"year":null,"claim":"Key unresolved questions include how identical IL-2Rβ/γc engagement geometry by IL-2 and IL-15 produces distinct signaling kinetics and biological outcomes, the structural mechanism of IL-15Rα's allosteric enhancement of IL-15 affinity for IL-2Rβ, how intracellular IL-15 represses chymase transcription in mast cells, and whether quantitative STAT5 thresholds downstream of trans-presented IL-15 specify gene programs through distinct transcription factor assemblies.","evidence":"","pmids":[],"confidence":"High","gaps":["No structural model for IL-15Rα allosteric transmission to the IL-2Rβ binding interface","Mechanism of intracellular IL-15 transcriptional repression in mast cells is undefined","How STAT5 dose-response translates into binary developmental decisions in NK/NKT cells remains unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[0,1,2,10,11,20]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[15]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[15]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,10,11,20]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,1,2,3,5,6,7,8,12,14,17,18,19,24,28]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,8,19,22,23,24,25,26,29]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[18,19,21]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[6,7,12]}],"complexes":[],"partners":["IL15RA","IL2RB","IL2RG","JAK1","JAK3","STAT5A","STAT3"],"other_free_text":[]},"mechanistic_narrative":"IL-15 is a pleiotropic four-helix-bundle cytokine that signals through a trimeric receptor comprising a private high-affinity IL-15Rα chain and the shared IL-2Rβ/γc heterodimer, activating JAK1/JAK3–STAT3/STAT5 and PI3K–mTORC1 pathways to govern survival, proliferation, and differentiation of NK cells, NKT cells, and CD8⁺ memory T cells [PMID:8178155, PMID:7641685, PMID:7568001]. IL-15Rα on dendritic cells and stromal cells trans-presents IL-15 to responding lymphocytes, with the sushi domain allosterically enhancing IL-15 affinity for IL-2Rβ; graded levels of trans-presented IL-15 specify distinct NK-cell developmental outcomes and CD8⁺ T cell homeostatic proliferation through quantitative differences in STAT5 phosphorylation [PMID:23104097, PMID:18812469, PMID:21715685, PMID:16284400]. IL-15 promotes lymphocyte survival via Bcl-2 and Bcl-xL induction and drives antigen-independent memory CD8⁺ T cell cycling through mTORC1, while its expression is regulated post-transcriptionally by inhibitory upstream AUGs in the 5′ UTR and transcriptionally through the ATF4–IRF7 axis and Notch-dependent silencing during hematopoietic lineage commitment [PMID:16365444, PMID:22084435, PMID:26241055, PMID:8613692, PMID:29431743, PMID:23966624]. Beyond canonical immune roles, intracellular IL-15 functions as a transcriptional repressor of mast cell chymase, and compartment-specific IL-15 overexpression in both gut epithelium and lamina propria drives villous atrophy in a coeliac disease model [PMID:17643110, PMID:32051586]."},"prefetch_data":{"uniprot":{"accession":"P40933","full_name":"Interleukin-15","aliases":[],"length_aa":162,"mass_kda":18.1,"function":"Cytokine that plays a major role in the development of inflammatory and protective immune responses to microbial invaders and parasites by modulating immune cells of both the innate and adaptive immune systems (PubMed:15123770). Stimulates the proliferation of natural killer cells, T-cells and B-cells and promotes the secretion of several cytokines (PubMed:8178155, PubMed:9326248). In monocytes, induces the production of IL8 and monocyte chemotactic protein 1/CCL2, two chemokines that attract neutrophils and monocytes respectively to sites of infection (PubMed:9326248). Unlike most cytokines, which are secreted in soluble form, IL15 is expressed in association with its high affinity IL15RA on the surface of IL15-producing cells and delivers signals to target cells that express IL2RB and IL2RG receptor subunits (PubMed:10233906, PubMed:23104097, PubMed:8026467). Binding to its receptor triggers the phosphorylation of JAK1 and JAK3 and the recruitment and subsequent phosphorylation of signal transducer and activator of transcription-3/STAT3 and STAT5 (PubMed:7568001). In mast cells, induces the rapid tyrosine phosphorylation of STAT6 and thereby controls mast cell survival and release of cytokines such as IL4 (By similarity)","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/P40933/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/IL15","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/IL15","total_profiled":1310},"omim":[{"mim_id":"618495","title":"IMMUNODEFICIENCY 63 WITH LYMPHOPROLIFERATION AND AUTOIMMUNITY; IMD63","url":"https://www.omim.org/entry/618495"},{"mim_id":"617827","title":"IMMUNODEFICIENCY 55; IMD55","url":"https://www.omim.org/entry/617827"},{"mim_id":"613562","title":"Fc RECEPTOR-LIKE PROTEIN 6; FCRL6","url":"https://www.omim.org/entry/613562"},{"mim_id":"612169","title":"Fc FRAGMENT OF IgG RECEPTOR IIc; FCGR2C","url":"https://www.omim.org/entry/612169"},{"mim_id":"612006","title":"CELIAC DISEASE, SUSCEPTIBILITY TO, 8; CELIAC8","url":"https://www.omim.org/entry/612006"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Nuclear speckles","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/IL15"},"hgnc":{"alias_symbol":["IL-15","MGC9721"],"prev_symbol":[]},"alphafold":{"accession":"P40933","domains":[{"cath_id":"-","chopping":"5-41","consensus_level":"high","plddt":67.6243,"start":5,"end":41},{"cath_id":"1.20.1250.70","chopping":"49-160","consensus_level":"high","plddt":92.9795,"start":49,"end":160}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P40933","model_url":"https://alphafold.ebi.ac.uk/files/AF-P40933-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P40933-F1-predicted_aligned_error_v6.png","plddt_mean":84.69},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=IL15","jax_strain_url":"https://www.jax.org/strain/search?query=IL15"},"sequence":{"accession":"P40933","fasta_url":"https://rest.uniprot.org/uniprotkb/P40933.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P40933/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P40933"}},"corpus_meta":[{"pmid":"23160470","id":"PMC_23160470","title":"IL-7 and IL-15 instruct the generation of human memory stem T cells from naive precursors.","date":"2012","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/23160470","citation_count":526,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"30626941","id":"PMC_30626941","title":"De novo design of potent and selective mimics of IL-2 and IL-15.","date":"2019","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/30626941","citation_count":412,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"16757567","id":"PMC_16757567","title":"Converting IL-15 to a superagonist by binding to soluble IL-15R{alpha}.","date":"2006","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/16757567","citation_count":341,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"12734346","id":"PMC_12734346","title":"IL-15 promotes the survival of naive and memory phenotype CD8+ T cells.","date":"2003","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/12734346","citation_count":276,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"12586624","id":"PMC_12586624","title":"IL-15 is an essential mediator of peripheral NK-cell homeostasis.","date":"2003","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/12586624","citation_count":271,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"26567920","id":"PMC_26567920","title":"IL-15 functions as a danger signal to regulate tissue-resident T cells and tissue destruction.","date":"2015","source":"Nature reviews. 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Hyperagonist IL-15 x IL-15R alpha fusion proteins.","date":"2005","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16284400","citation_count":259,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"29431743","id":"PMC_29431743","title":"Sorafenib promotes graft-versus-leukemia activity in mice and humans through IL-15 production in FLT3-ITD-mutant leukemia cells.","date":"2018","source":"Nature medicine","url":"https://pubmed.ncbi.nlm.nih.gov/29431743","citation_count":243,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"17703412","id":"PMC_17703412","title":"Genetic susceptibility to respiratory syncytial virus bronchiolitis is predominantly associated with innate immune genes.","date":"2007","source":"The Journal of infectious diseases","url":"https://pubmed.ncbi.nlm.nih.gov/17703412","citation_count":223,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"21988832","id":"PMC_21988832","title":"Toward an understanding of the protein interaction network of the human liver.","date":"2011","source":"Molecular systems biology","url":"https://pubmed.ncbi.nlm.nih.gov/21988832","citation_count":207,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"11581322","id":"PMC_11581322","title":"Interleukin 15 skews monocyte differentiation into dendritic cells with features of Langerhans cells.","date":"2001","source":"The Journal of experimental medicine","url":"https://pubmed.ncbi.nlm.nih.gov/11581322","citation_count":200,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"12244150","id":"PMC_12244150","title":"IL-21 up-regulates the expression of genes associated with innate immunity and Th1 response.","date":"2002","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/12244150","citation_count":199,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"25736261","id":"PMC_25736261","title":"The shared and contrasting roles of IL2 and IL15 in the life and death of normal and neoplastic lymphocytes: implications for cancer therapy.","date":"2015","source":"Cancer immunology research","url":"https://pubmed.ncbi.nlm.nih.gov/25736261","citation_count":197,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"23104097","id":"PMC_23104097","title":"Mechanistic and structural insight into the functional dichotomy between IL-2 and IL-15.","date":"2012","source":"Nature immunology","url":"https://pubmed.ncbi.nlm.nih.gov/23104097","citation_count":194,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"20190192","id":"PMC_20190192","title":"IL-7 and IL-21 are superior to IL-2 and IL-15 in promoting human T cell-mediated rejection of systemic lymphoma in immunodeficient mice.","date":"2010","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/20190192","citation_count":187,"is_preprint":false,"source_track":"gene2pubmed"}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":46859,"output_tokens":7985,"usd":0.130176},"stage2":{"model":"claude-opus-4-6","input_tokens":12043,"output_tokens":4584,"usd":0.262223},"total_usd":0.809668,"stage1_batch_id":"msgbatch_01DzrsgVgYngY1hvM3DU1yF2","stage2_batch_id":"msgbatch_01KA9b7iRzKFdhoBUT7vCvSe","note":"batch pricing = 50% of standard","round2_stage1":{"model":"claude-sonnet-4-6","input_tokens":61095,"output_tokens":7654,"usd":0.149047},"round2_rules_fired":"R3","round2_stage2":{"model":"claude-opus-4-6","input_tokens":12018,"output_tokens":4749,"usd":0.268222}},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2006,\n      \"finding\": \"Soluble IL-15 biological activity is markedly enhanced when bound to recombinant soluble IL-15Rα; the IL-15/IL-15Rα complex functions as a superagonist that selectively drives expansion of memory-phenotype CD8+ T cells and NK cells, suggesting IL-15Rα binding creates a conformational change that potentiates recognition by the βγc receptor on T cells.\",\n      \"method\": \"In vivo injection of soluble IL-15/IL-15Rα complexes in mice; comparison with IL-2/IL-2Rα complexes; flow cytometry of lymphocyte subsets\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal functional comparison with multiple cytokine/receptor pairs, replicated in vivo with clear mechanistic interpretation\",\n      \"pmids\": [\"16757567\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"IL-15 is primarily delivered to responding cells via trans-presentation: IL-15 bound to cell-surface IL-15Rα on one cell stimulates opposing cells through the IL-2/IL-15Rβ and common γ-chain receptor complex, rather than being secreted as a free soluble cytokine.\",\n      \"method\": \"Review synthesizing genetic knockout studies, transgenic models, and cell-based assays establishing trans-presentation as the dominant in vivo delivery mechanism\",\n      \"journal\": \"Immunology letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — concept supported by multiple independent genetic and cellular experiments across labs, strongly replicated\",\n      \"pmids\": [\"19818367\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Dendritic cells (DCs) trans-present IL-15 to memory CD8+ T cells to drive their homeostatic proliferation; IL-15Rα+ DCs were largely sufficient to support normal homeostatic proliferation of established memory CD8+ T cells but only partially restored naive CD8+ T cell numbers.\",\n      \"method\": \"Transgenic mouse model limiting IL-15 trans-presentation to DCs; adoptive transfer; flow cytometry of CD8+ T cell subsets\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic model with defined cellular phenotype and specific lymphocyte readout\",\n      \"pmids\": [\"18812469\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"IL-15 promotes survival of both naive (CD44low) and memory-phenotype (CD44high) CD8+ T cells by upregulating Bcl-2 in both populations, and additionally upregulating Bcl-xL in CD44high but not CD44low cells; IL-15Rβ and γc chains are absolutely required for pro-survival and proliferative effects, while IL-15Rα greatly enhances sensitivity to low concentrations but is not essential.\",\n      \"method\": \"In vitro culture of CD8+ T cells from IL-15Rα-deficient, β-chain-deficient mice; apoptosis assays; Bcl-2/Bcl-xL protein measurement\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic dissection of receptor subunit requirements with multiple orthogonal readouts\",\n      \"pmids\": [\"12734346\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"IL-15 maintains peripheral NK cell homeostasis primarily through upregulation of the anti-apoptotic factor Bcl-2, as demonstrated in an adoptive transfer system where IL-15 availability determined NK cell survival.\",\n      \"method\": \"Adoptive transfer of NK cells into γc-cytokine-deficient hosts; Bcl-2 expression analysis; IL-15 and IL-7 knockout comparisons\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo adoptive transfer with defined molecular mechanism (Bcl-2 upregulation)\",\n      \"pmids\": [\"12586624\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"IL-15 regulates NKT cell survival via Bcl-xL expression, and controls stage 2-to-stage 3 thymic NKT cell developmental progression and terminal differentiation by regulating T-bet (Tbx21) expression, which in turn controls effector molecule expression (IFN-γ, granzymes A and C, NK receptors).\",\n      \"method\": \"IL-15 knockout mice; in vitro IL-15 stimulation; global gene expression analysis; flow cytometry of NKT developmental stages\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with multiple orthogonal methods and defined molecular pathway (IL-15→T-bet→effector molecules)\",\n      \"pmids\": [\"22084435\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"IL-15 protects effector CD8+ T cells from apoptosis during the contraction phase following microbial infection by inducing Bcl-2 expression; enforced Bcl-2 expression recapitulated the protective effect of IL-15 in IL-15 KO mice.\",\n      \"method\": \"Adoptive transfer of OT-I cells into IL-15 KO and IL-15 transgenic mice; Listeria monocytogenes infection; in vivo rIL-15 administration; Bcl-2 measurement; Bcl-2 transgene rescue experiment\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — epistasis via Bcl-2 transgene rescue in IL-15 KO background, replicated mechanistically\",\n      \"pmids\": [\"16365444\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"IL-15 mRNA translation is negatively regulated by 10 upstream AUG codons in its 5' UTR; deletion of these upstream AUGs (as occurs in HTLV-I-R fusion transcripts in ATL cells) relieves translational repression and allows efficient IL-15 protein production.\",\n      \"method\": \"Comparative RT-PCR of normal vs. HTLV-I-transformed cells; analysis of chimeric mRNA junction; upstream AUG functional analysis\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — molecular dissection of translational regulatory mechanism with functional validation\",\n      \"pmids\": [\"8613692\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"De novo designed protein Neo-2/15 mimics IL-2 and IL-15 by binding to IL-2Rβγc heterodimer but lacks binding sites for IL-2Rα or IL-15Rα; crystal structures of Neo-2/15 alone and in complex with IL-2Rβγc confirmed the designed binding mode, and the protein elicits downstream cell signaling independently of IL-2Rα and IL-15Rα.\",\n      \"method\": \"Computational de novo protein design; crystal structure determination of free and receptor-bound forms; cell signaling assays; in vivo mouse tumor models\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus functional validation plus mutagenesis-level design confirmation\",\n      \"pmids\": [\"30626941\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"IL-15 activates the Jak3/STAT3 signaling pathway in skeletal muscle cells to stimulate glucose uptake and GLUT4 translocation to the plasma membrane; IL-15 increased phospho-Jak3 and phospho-STAT3, induced STAT3 nuclear translocation, and upregulated HIF1α in a STAT3-dependent manner; STAT3 inhibition abolished IL-15-induced glucose uptake.\",\n      \"method\": \"C2C12 myotube treatment with IL-15; phospho-protein analysis; STAT3 inhibitor experiments; GLUT4 localization by fractionation/imaging; glucose uptake assays\",\n      \"journal\": \"Frontiers in physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods in a single lab study\",\n      \"pmids\": [\"28066259\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"SOCS1 acts as an essential negative regulator of IL-15 signaling in CD8+ thymocytes; SOCS1 deficiency leads to sustained STAT5 phosphorylation and massive proliferation specifically in response to IL-15, as well as strong upregulation of Bcl-xL and CD44, driving skewed CD8 lineage development independently of IFN-γ.\",\n      \"method\": \"SOCS1-/- IFNγ-/- double-knockout mice; fetal thymic organ cultures; intrathymic transfer; IL-15 stimulation assays; STAT5 phosphorylation measurement\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean double-KO genetic dissection with specific cytokine stimulation and signaling readouts\",\n      \"pmids\": [\"12907450\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Mast cells express novel alternatively spliced IL-15Rα isoforms (lacking exon 4; exons 3 and 4; or exons 3, 4, and 5); these isoforms associate with the Golgi, ER, perinuclear space, and cell membrane; IL-15 binds with high affinity to these isoforms and promotes cell survival, with signaling through STAT3, STAT5, STAT6, JAK2, and Syk kinase.\",\n      \"method\": \"RT-PCR cloning; transient transfection in COS-7 cells; stable transfection of BA/F3 cells; binding assays; Western blot for STAT/kinase phosphorylation\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — molecular identification of isoforms with functional binding and signaling validation\",\n      \"pmids\": [\"12734349\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"IL-15 stored intracellularly in mast cells acts as a specific negative transcriptional regulator of mouse mast cell chymase (mast cell protease-2); deletion of IL-15 markedly increases chymase activities, leading to greater bactericidal responses and higher survival after septic peritonitis.\",\n      \"method\": \"IL-15 knockout mice; cecal ligation and puncture model; chymase activity assays; transcriptional analysis of mast cell protease-2\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo KO model with defined intracellular transcriptional mechanism and survival readout\",\n      \"pmids\": [\"17643110\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"IL-15 mediates mechanical hypernociception through a sequential IFN-γ → endothelin-1 → prostaglandin E2 pathway; IL-15 induced IFN-γ production, which stimulated ET-1 production and preproET-1 mRNA expression, and subsequent PGE2 release; neutralization at each step blocked hypernociception.\",\n      \"method\": \"In vivo mouse injection; IFN-γ knockout mice; pharmacological blockade of endothelin receptors and cyclooxygenase; soluble IL-15Rα neutralization; OVA immunization model\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis (IFN-γ KO) combined with pharmacological pathway dissection\",\n      \"pmids\": [\"16766656\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"IL-15 mediates antigen-induced neutrophil migration by triggering a sequential cascade: IL-15 → IL-18 → MIP-1α (CCL3) → TNF-α → MIP-2 (CXCL2) → leukotriene B4 → neutrophil migration; this cascade was absent in IL-18−/−, MIP-1α−/−, TNFR1−/−, and 5-LOX−/− mice.\",\n      \"method\": \"Multiple gene-knockout mouse strains; peritoneal lavage cytokine measurements; anti-MIP-2 antibody neutralization; OVA immunization model; soluble IL-15Rα neutralization\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multi-gene epistasis with orthogonal pharmacological confirmation in vivo\",\n      \"pmids\": [\"17979156\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Different levels of IL-15 trans-presentation (quantified by IL-15Rα expression levels on accessory cells) are required for distinct NK cell developmental events: NK cell homeostasis, mature NK cell differentiation, Ly49 receptor acquisition, and effector function acquisition each require different thresholds of IL-15Rα-mediated STAT5 phosphorylation on NK cells; IL-15Rα on NK cells themselves is not required.\",\n      \"method\": \"IL-15Rα knockin and transgenic mice with graded IL-15Rα expression; STAT5 phosphorylation assays in NK cells; bone marrow chimeras; flow cytometric analysis of NK developmental stages\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — elegant quantitative genetic model with direct signaling readouts (pSTAT5) correlated to developmental outcomes\",\n      \"pmids\": [\"21715685\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Type I IFN-driven expression of IL-15 during viral infection transiently induces cell-cycle progression in memory CD8+ T cells through an mTORC1-dependent pathway, independently of antigen re-exposure, thereby priming them for rapid proliferation upon subsequent antigen encounter.\",\n      \"method\": \"Murine models of viral infection; IL-15 neutralization; mTORC1 inhibitor (rapamycin) treatment; BrdU incorporation; antigen-independent proliferation assays\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo genetic and pharmacological dissection identifying IFN→IL-15→mTORC1 pathway\",\n      \"pmids\": [\"26241055\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Continuous IL-15 signaling causes NK cell exhaustion associated with a specific metabolic defect: reduced mitochondrial spare respiratory capacity dependent on fatty acid oxidation (FAO); inhibition of mTOR rescued NK cell functionality in continuously IL-15-treated NK cells.\",\n      \"method\": \"In vitro continuous vs. intermittent IL-15 treatment of human NK cells; Seahorse metabolic assays; FAO inhibition; mTOR inhibitor rescue; in vivo tumor xenograft model\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (metabolic assays, mTOR inhibitor rescue, in vivo validation) in single lab\",\n      \"pmids\": [\"29415897\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IL-15 is required for resident memory T cell (TRM) maintenance in skin; keratinocytes upregulate CD215 (IL-15Rα) to display IL-15 on their surface and activate TRM expressing CD122 (IL-2/IL-15Rβ); anti-CD122 antibody treatment depletes skin TRM and reverses vitiligo in mice.\",\n      \"method\": \"IL-15-deficient mice; anti-CD122 antibody treatment; intravital imaging; flow cytometry of skin TRM; short- and long-term treatment in established vitiligo mouse model\",\n      \"journal\": \"Science translational medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic dissection of trans-presentation in skin with functional disease reversal, multiple readouts\",\n      \"pmids\": [\"30021889\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"ULBP2 ligation of NKG2D on NK cells induces reorganization of IL-2/IL-15Rβ nanoclusters to coalesce with NKG2D nanoclusters at the cell surface; this coalescence functionally augments NK cell responses when IL-15 is simultaneously trans-presented by IL-15Rα-coated surfaces, revealing ligand-specific crosstalk between NKG2D and the IL-15 receptor.\",\n      \"method\": \"Superresolution (dSTORM) microscopy of primary human NK cells; IL-15Rα-coated surfaces for trans-presentation; functional NK activation assays; comparison of MICA vs. ULBP2 ligands\",\n      \"journal\": \"Science signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — superresolution structural imaging combined with functional validation\",\n      \"pmids\": [\"29636390\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"In human NK cells, stimulation with γc-chain cytokines induces sequential expression of IL-15Rα then IL-2Rα at the cell surface (switching high-affinity receptor from IL-15R to IL-2R between 18 and 48 h), making NK cells progressively refractory to free soluble IL-15 but retaining responsiveness to trans-presented IL-15 (IL-15 complexed to soluble IL-15Rα).\",\n      \"method\": \"Kinetic cytokine receptor expression analysis; cytokine binding assays; STAT5 phosphorylation assays; functional NK assays (IFN-γ, CD107a) at different time points; IL-15/IL-15Rα complex stimulation\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods in single lab demonstrating temporal receptor switch with functional consequence\",\n      \"pmids\": [\"19414780\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"IL-15 promoter activity is differentially regulated during hematopoiesis: expression is largely limited to myeloid lineages; hematopoietic stem cells express high IL-15; IL-15 expression is extinguished during lymphoid development in a Notch-dependent, stepwise manner; at the DC level, IL-15 production is regulated at the pre-DC branch point, generating IL-15+CD8+ and IL-15-/low CD8- DC subsets.\",\n      \"method\": \"IL-15 reporter transgenic mice; flow cytometry of hematopoietic progenitors; Notch inhibition experiments; analysis of DC developmental stages\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reporter mouse with Notch inhibition identifies transcriptional regulatory mechanism\",\n      \"pmids\": [\"23966624\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"IL-15 positively regulates IL-21 production in celiac disease mucosa by activating Akt and STAT3 signaling in lamina propria lymphocytes; blockade of IL-15 in active celiac disease biopsies reduces IL-21 levels.\",\n      \"method\": \"Flow cytometry of IELs and LPLs; IL-15 stimulation of control LPLs; Akt and STAT3 phosphorylation assays; IL-15 blockade in mucosal biopsies\",\n      \"journal\": \"Mucosal immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct ex vivo blockade and signaling measurements, multiple methods, single lab\",\n      \"pmids\": [\"22785229\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"In a mouse model of celiac disease, overexpression of IL-15 in both the gut epithelium and lamina propria is required for the development of villous atrophy; compartment-specific IL-15 overexpression alone is insufficient, establishing location-dependent cooperativity of IL-15 in driving tissue destruction; CD4+ T cells and HLA-DQ8 license cytotoxic T cells, and IFN-γ and transglutaminase 2 contribute to tissue destruction.\",\n      \"method\": \"Mouse model with compartment-specific IL-15 overexpression (epithelial and/or lamina propria); HLA-DQ8 transgenic; gluten feeding; histological analysis of villous atrophy; T cell depletion experiments\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — compartment-specific genetic model with direct tissue pathology readout and T cell epistasis experiments\",\n      \"pmids\": [\"32051586\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"IL-15 and its receptor (α, β, γ chains) are constitutively expressed in tubular epithelial cells (TECs), and IL-15 functions as an autocrine survival factor for TECs; TEC apoptosis is substantially greater in IL-15-/- mice; IL-15 also decreases induction of the nephritogenic chemokine MCP-1 during nephritis.\",\n      \"method\": \"IL-15 knockout mice; nephrotoxic serum nephritis model; TUNEL apoptosis assays; anti-Fas/actinomycin D apoptosis induction in isolated TECs; MCP-1 measurement\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo KO plus ex vivo TEC experiments with multiple mechanistic readouts\",\n      \"pmids\": [\"11927622\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"IL-15 acts as a chemoattractant for NK cells and enhances their adhesion to vascular endothelium primarily by stimulating LFA-1-dependent adhesion; IL-15-activated NK cells bound to resting and TNF-activated endothelial cells via LFA-1/ICAM-1 and VLA-4/VCAM-1 pathways, with preferential enhancement of LFA-1.\",\n      \"method\": \"Chemotaxis assays with checkerboard analysis; NK cell adhesion assays to cultured endothelial cells; ICAM-1-transfected NIH-3T3 binding assays; blocking antibodies for adhesion molecules\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple functional assays with receptor-blocking experiments identifying LFA-1 as primary pathway\",\n      \"pmids\": [\"9201264\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IL-15 maintains CMV-specific inflationary CD8+ T cells in peripheral tissues in an antigen-independent manner by promoting Bcl-2 expression; IL-15 is produced mainly by non-hematopoietic cells in lung tissue and acts via trans-presentation; no other common γ-chain cytokines (IL-2, IL-7, IL-21) substituted for this function.\",\n      \"method\": \"Murine CMV infection model; cytokine knockout and blocking experiments; BrdU half-life measurements; Bcl-2 protein expression; trans-presentation assays; IL-15Rα knockout mice\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple cytokine knockouts with defined molecular mechanism (Bcl-2) and trans-presentation mechanism\",\n      \"pmids\": [\"29652930\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"IL-15 promotes osteoclastogenesis in rheumatoid arthritis via upregulation of phospholipase D1 (PLD1), which generates phosphatidic acid (PA); PA then upregulates RANKL expression in synovial fibroblasts through MAPK and NF-κB signaling pathways; siRNA knockdown of PLD1 inhibited IL-15-stimulated RANKL expression.\",\n      \"method\": \"Rheumatoid synovial fibroblast cultures; siRNA knockdown of PLD1; pharmacological inhibition of PA production (1-butanol); RANKL qPCR; osteoclast formation assays; immunohistochemistry\",\n      \"journal\": \"Immunology letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA knockdown and pharmacological inhibition with multiple readouts in single lab\",\n      \"pmids\": [\"21620893\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"IL-15 supports two distinct CD8+ T cell subsets: IL-15-dependent CD44hiCD122hi cells (which express NK receptors and respond to both TCR and NK receptor engagement) and ITK-dependent CD44loCD122lo conventional CD8+ T cells; double-deficiency of IL-15 and ITK severely reduces all CD8+ T cells; IL-15-dependent CD44hi cells are generated as a distinct thymic lineage.\",\n      \"method\": \"IL-15-/- mice; ITK-/- mice; IL-15-/-ITK-/- double-knockout mice; flow cytometry of thymic and peripheral CD8+ T cell subsets; NK receptor expression analysis; functional stimulation assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — double-KO genetic epistasis clearly distinguishing two CD8+ T cell subsets with mechanistic pathway placement\",\n      \"pmids\": [\"16880398\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CAR activation and IL-15 signaling both rapidly induce upregulation of the transcription factor CREM in NK cells via the PKA-CREB signaling pathway (activated downstream of ITAM signaling or IL-15); CREM exerts regulatory functions through epigenetic reprogramming of CAR-NK cells, and CREM deletion enhances CAR-NK effector function and resistance to tumor-induced immunosuppression.\",\n      \"method\": \"Transcriptomic analysis of CAR-NK cells post-adoptive transfer; CREM deletion (CRISPR); PKA-CREB pathway inhibition; in vitro and in vivo functional assays; epigenetic profiling\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic pathway identified (PKA-CREB→CREM) with genetic deletion and in vivo functional validation\",\n      \"pmids\": [\"40468083\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IL-15 epithelial expression is essential for γδ IEL migration into the intestinal epithelial compartment and regulates their basal motility; compartmentalized overexpression of IL-15 in the lamina propria shifts γδ T cells out of the epithelium, which is rescued by epithelial IL-15; inhibition of IL-2Rβ signaling reduces γδ IEL motility and increases pathogen invasion.\",\n      \"method\": \"Transgenic mice with compartment-specific IL-15 overexpression; intravital microscopy; anti-IL-2Rβ antibody blocking; in vitro migration assays; bacterial translocation assays\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — compartment-specific genetic model with live imaging and functional pathogen challenge readout\",\n      \"pmids\": [\"29884699\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"HHV-6 infection of PBMCs upregulates NK cell cytotoxicity via induction of IL-15; anti-IL-15 antibodies (but not antibodies to IFN-α, IFN-γ, TNF-α, TNF-β, IL-2, or IL-12) abrogated HHV-6-induced NK activation; anti-CD122 also blocked activation; RT-PCR confirmed IL-15 mRNA upregulation in monocytes and NK cells post-infection.\",\n      \"method\": \"Antibody neutralization panel; RT-PCR for IL-15 mRNA; IL-15 protein measurement; NK cytotoxicity assays; HHV-6 neutralizing antibody controls\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — neutralization experiments with multiple antibody specificity controls, single lab\",\n      \"pmids\": [\"8617868\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"IL-15 functions primarily through trans-presentation, whereby IL-15 bound to cell-surface IL-15Rα on dendritic cells, stromal cells, or epithelial cells is delivered in trans to opposing lymphocytes bearing IL-2/IL-15Rβ and the common γ-chain, activating JAK-STAT5, PI3K-AKT-mTOR, and Ras-MEK-MAPK pathways to drive development, homeostasis, and effector function of NK cells, NKT cells, memory CD8+ T cells, and intraepithelial lymphocytes; its biological potency is dramatically enhanced when IL-15 is complexed with soluble IL-15Rα, forming a superagonist; translational output of IL-15 is constitutively suppressed by multiple upstream AUGs in the 5' UTR; and intracellular IL-15 can additionally act as a transcriptional regulator within mast cells to suppress chymase expression, revealing a non-canonical intracrine function.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1994,\n      \"finding\": \"IL-15 was cloned as a novel T cell growth factor that interacts with the β chain of the IL-2 receptor (CD122); monoclonal antibodies to the IL-2R β chain inhibited IL-15 biological activity, and IL-15 competed for IL-2 binding, establishing that IL-15 uses components of the IL-2 receptor complex.\",\n      \"method\": \"cDNA cloning, receptor competition binding assay, neutralizing monoclonal antibody inhibition\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — original cloning paper with direct receptor binding competition and antibody neutralization; foundational, highly cited\",\n      \"pmids\": [\"8178155\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"IL-15 utilizes both the β chain (CD122) and γc chain (CD132) of the IL-2 receptor for high-affinity binding and signaling; the IL-2Rα subunit is not involved in IL-15 binding, implying the existence of a distinct IL-15-specific receptor component.\",\n      \"method\": \"Transfection of IL-2R subunits into cells, direct binding assays, signaling assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution in transfected cells with defined receptor subunits, replicated independently of cloning paper\",\n      \"pmids\": [\"8026467\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"A high-affinity IL-15-specific receptor α chain (IL-15Rα) was identified and cloned; IL-15Rα alone binds IL-15 with affinity equivalent to the full heterotrimeric IL-2R for IL-2, and together with IL-2Rβ and γc forms a functional trimeric IL-15 receptor complex. IL-15Rα is structurally related to IL-2Rα, defining a new cytokine receptor subfamily.\",\n      \"method\": \"Molecular cloning, direct binding assays, reconstitution of receptor complex in myeloid cell line\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — receptor cloning with reconstitution and direct binding quantification; foundational paper\",\n      \"pmids\": [\"7641685\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"IL-15 rapidly induces tyrosine phosphorylation and activation of JAK1 and JAK3, and activates STAT3 and STAT5 transcription factors in human T cells, similar to IL-2; IL-4 activates STAT3 but not STAT5, distinguishing the downstream signaling of these cytokines.\",\n      \"method\": \"Immunoprecipitation, Western blot for phosphotyrosine, EMSA (DNA-binding assays for STAT complexes)\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — biochemical signaling assays (IP + Western + EMSA) identifying specific kinase-STAT pathway; highly cited foundational paper\",\n      \"pmids\": [\"7568001\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"The IL-15 mRNA contains 10 upstream AUGs in its 5′ UTR that function as negative regulators of translation. An HTLV-I R-region/IL-15 chimeric mRNA that lacks most upstream AUGs is translated much more efficiently, demonstrating that IL-15 protein expression is regulated post-transcriptionally at the level of mRNA translation.\",\n      \"method\": \"RT-PCR characterization of mRNA isoforms, translational analysis comparing upstream AUG content, analysis of HTLV-I fusion transcript\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — molecular characterization of 5′ UTR regulatory elements with functional comparison; replicated concept in later structural studies\",\n      \"pmids\": [\"8613692\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"CD8+ memory-phenotype T cells undergo slow homeostatic division in vivo that requires IL-15; this division is markedly increased by inhibition of IL-2, showing that IL-15 and IL-2 exert opposing control over CD8+ memory T cell homeostasis.\",\n      \"method\": \"In vivo proliferation assays in IL-15-deficient mice and IL-2 inhibition experiments; adoptive transfer system\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO combined with IL-2 inhibition establishing opposing cytokine balance; highly cited\",\n      \"pmids\": [\"10784451\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"IL-15Rα is not required for IL-15-induced proliferation or pro-survival effects on CD8+ T cells, but greatly enhances sensitivity to low concentrations of IL-15; the β and γ chains of IL-15R are absolutely required for both proliferative and pro-survival effects. IL-15 promotes survival of both naive and memory CD8+ T cells via upregulation of Bcl-2.\",\n      \"method\": \"In vitro survival and proliferation assays with IL-15Rα-deficient and β/γ-chain-deficient cells; Bcl-2 and Bcl-xL expression analysis\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — defined receptor subunit requirements using KO cells with specific survival/proliferation readouts and molecular markers\",\n      \"pmids\": [\"12734346\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"IL-15 is the dominant survival signal for peripheral NK cells, maintaining them via upregulation of the anti-apoptotic factor Bcl-2. MHC class I molecules do not regulate NK cell survival or homeostatic expansion.\",\n      \"method\": \"Adoptive transfer of NK cells into IL-15-deficient hosts; Bcl-2 expression analysis; NK cell survival assays\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — adoptive transfer with genetic KO host, specific molecular mechanism (Bcl-2) identified\",\n      \"pmids\": [\"12586624\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"SOCS1 is an essential negative regulator of IL-15 receptor signaling in CD8+ thymocytes. In SOCS1-deficient CD8+ thymocytes, IL-15 selectively induces sustained STAT5 phosphorylation, massive proliferation, and strong upregulation of Bcl-xL and CD44, demonstrating that SOCS1 attenuates IL-15 signaling in a cell-type-specific manner.\",\n      \"method\": \"SOCS1−/− and SOCS1−/−IFNγ−/− mouse models; fetal thymic organ culture; intrathymic transfer; STAT5 phosphorylation assays; proliferation assays\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with biochemical STAT5 readout and multiple complementary approaches\",\n      \"pmids\": [\"12907450\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Murine mast cells express three novel IL-15Rα isoforms generated by alternative splicing (lacking exon 4; exons 3 and 4; or exons 3, 4, and 5). These isoforms localize to the Golgi, ER, perinuclear space, and cell membrane, bind IL-15 with high affinity, and mediate signaling through phosphorylation of STAT3, STAT5, STAT6, JAK2, and Syk kinase.\",\n      \"method\": \"RT-PCR, sequencing, transient transfection in COS-7 cells, glycosylation analysis, IL-15 binding assay in BA/F3 transfectants, STAT/JAK phosphorylation analysis\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — molecular cloning plus binding and signaling in transfected cells; single lab\",\n      \"pmids\": [\"12734349\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The sushi domain of soluble IL-15Rα acts as a potent agonist of IL-15 action through the IL-15Rβ/γ heterodimer by enhancing IL-15 binding and biological effects, whereas the full extracellular domain acts as an antagonist. Fusion proteins (RLI) linking IL-15 to the sushi domain are hyperagonists that bind IL-15Rβ/γ, are internalized, and induce potent lymphocyte proliferation and survival.\",\n      \"method\": \"Recombinant protein production, binding assays, cell proliferation assays, apoptosis assays, receptor internalization studies\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstitution with defined receptor fragments, functional and binding assays; mechanistically detailed\",\n      \"pmids\": [\"16284400\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Binding of soluble IL-15Rα to IL-15 markedly enhances biological activity, rapidly inducing strong expansion of memory-phenotype CD8+ T cells and NK cells in vivo. This suggests that IL-15Rα binding induces a conformational change that potentiates IL-15 recognition by the βγc receptor. In contrast, IL-2 function is inhibited by binding to soluble IL-2Rα.\",\n      \"method\": \"In vivo injection of IL-15/IL-15Rα complexes in mice; flow cytometry of lymphocyte populations\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo functional assay with recombinant protein complex; mechanistic inference supported by contrast with IL-2 data\",\n      \"pmids\": [\"16757567\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"IL-15 plays a critical role in protecting effector CD8+ T cells from apoptosis during the contraction phase following microbial infection, via induction of Bcl-2 expression. Enforced Bcl-2 expression rescues effector T cells from death in IL-15-KO mice, placing Bcl-2 downstream of IL-15 signaling.\",\n      \"method\": \"Adoptive transfer into IL-15 KO and IL-15 transgenic mice, in vivo rIL-15 administration, Bcl-2 transgenic rescue experiment\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis (Bcl-2 transgene rescue of KO phenotype) establishing pathway hierarchy\",\n      \"pmids\": [\"16365444\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"IL-15 mediates mechanical hypernociception through a sequential pathway: IL-15 → IFN-γ → endothelin-1 (ET-1) via ETA receptor → prostaglandin E2 (PGE2). IL-15 failed to induce hypernociception in IFN-γ−/− mice, and IL-15 induced ET-1 production in an IFN-γ-dependent manner.\",\n      \"method\": \"Mouse peritoneal injection models; IFN-γ−/− mice; pharmacological inhibitors (ETA/ETB antagonists, COX inhibitors); cytokine measurement\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO plus pharmacological inhibition defining sequential pathway; single lab\",\n      \"pmids\": [\"16766656\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"IL-15-deficient mice lack the CD44hiCD122hi memory-phenotype CD8+ T cell subset, while ITK-deficient mice lack the CD44loCD122lo conventional CD8+ T cell subset; double-KO mice have severe depletion of all CD8+ T cells. These findings establish that IL-15 specifically supports a CD8+ T cell subset with both adaptive and innate immune functions.\",\n      \"method\": \"IL-15−/−, ITK−/−, and IL-15−/−ITK−/− double-KO mouse analysis; flow cytometry; functional assays (TCR and NK receptor stimulation)\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — double-KO genetic epistasis defining non-overlapping subsets; rigorous controls\",\n      \"pmids\": [\"16880398\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Intracellular IL-15 stored in mast cells acts as a specific negative transcriptional regulator of the mast cell chymase MCP-2 gene. Deletion of IL-15 markedly increases chymase activity and neutrophil-recruiting chemokine processing, leading to increased bactericidal responses and survival in murine septic peritonitis.\",\n      \"method\": \"Il15 KO mouse model; cecal ligation and puncture (CLP) sepsis model; chymase activity assays; chemokine processing assays; transcriptional analysis\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo KO model with mechanistic characterization of transcriptional regulation by intracellular cytokine; multiple readouts\",\n      \"pmids\": [\"17643110\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"IL-15 mediates antigen-induced neutrophil migration by triggering a sequential cytokine cascade: IL-15 induces IL-18 production, which then drives MIP-2, MIP-1α, TNF-α, and leukotriene B4 release to promote neutrophil migration. IL-18−/−, MIP-1α−/−, TNFR1−/−, and 5-LOX−/− mice are resistant to IL-15-induced neutrophil migration.\",\n      \"method\": \"Mouse peritoneal model; IL-18−/−, MIP-1α−/−, TNFR1−/−, 5-LOX−/− KO mice; neutralizing antibodies; cytokine measurement\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic KO models defining pathway cascade; confirmed with OVA antigen model\",\n      \"pmids\": [\"17979156\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Dendritic cells (DCs) transpresent IL-15 to memory CD8+ T cells, driving their homeostatic proliferation. A transgenic model restricting IL-15 transpresentation to DCs shows that DC-mediated transpresentation is largely sufficient for normal homeostatic proliferation of established memory CD8+ T cells, preferentially supporting a KLRG-1+CD27− subset.\",\n      \"method\": \"IL-15Rα transgenic mouse model limiting transpresentation to DCs; adoptive transfer; flow cytometry; viral infection model\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cell-type-specific transgenic rescue model identifying the cellular source of trans-presentation; multiple T cell subset readouts\",\n      \"pmids\": [\"18812469\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"IL-15 regulates NKT cell survival through Bcl-xL (but not other Bcl-2 family members), and controls thymic stage 2 to stage 3 lineage progression and terminal NKT cell differentiation by regulating T-bet (Tbx21) expression, which in turn controls IFN-γ, granzyme A/C, and NK receptor expression.\",\n      \"method\": \"IL-15 KO mouse analysis; in vitro IL-15 stimulation; global gene expression profiling; validation by RT-PCR and flow cytometry; Bcl-xL-specific dependency assessment\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KO model with gene expression profiling and mechanistic validation linking IL-15 to T-bet→effector molecule axis\",\n      \"pmids\": [\"22084435\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Different developmental events of NK cells (homeostasis, mature differentiation, Ly49 acquisition, and effector function) require quantitatively different levels of IL-15 trans-presentation. The level of IL-15Rα on accessory cells (both bone marrow-derived DCs and radiation-resistant stromal cells) directly determines the level of STAT5 phosphorylation in NK cells and the degree of each developmental outcome; the IL-15Rα on NK cells themselves is not required.\",\n      \"method\": \"IL-15Rα knockin/transgenic mice with graded IL-15Rα expression; STAT5 phosphorylation assays in NK cells cocultured with DCs; in vivo NK cell development analysis\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — quantitative dose-response with biochemical STAT5 readout; multiple developmental stages assessed\",\n      \"pmids\": [\"21715685\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Crystal structures of the IL-15–IL-15Rα–IL-2Rβ–γc quaternary complex show that IL-15 binds IL-2Rβ and γc in a geometry nearly indistinguishable from IL-2 in the IL-2–IL-2Rα–IL-2Rβ–γc complex. IL-15Rα substantially increases the affinity of IL-15 for IL-2Rβ (allosteric effect required for IL-15 trans-signaling). The functional differences between IL-2 and IL-15 in lymphocytes result from disparate receptor affinities rather than distinct signaling geometries.\",\n      \"method\": \"X-ray crystallography of quaternary receptor complex; surface plasmon resonance for affinity measurements; functional signaling assays in lymphocytes\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus biophysical affinity measurements plus functional validation; mechanistically definitive\",\n      \"pmids\": [\"23104097\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"IL-15 promoter activity is restricted to myeloid lineages during hematopoiesis; lymphoid cells extinguish IL-15 expression in a stepwise, Notch-dependent manner during development. Hematopoietic stem cells (LSK) express high IL-15. IL-15 expression is regulated at the pre-DC branch point, generating IL-15+CD8+ and IL-15−/lowCD8− DC subsets.\",\n      \"method\": \"IL-15 reporter transgenic mouse; flow cytometry of defined hematopoietic populations; Notch inhibition experiments\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reporter mouse with Notch inhibition establishing Notch-dependent transcriptional regulation; single lab\",\n      \"pmids\": [\"23966624\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Type I IFN-driven IL-15 expression during viral infection drives memory CD8+ T cells into rapid cell-cycle progression via mTORC1 (independently of antigen re-exposure), providing a proliferative advantage. IL-15 prepares memory cells for faster division upon subsequent antigen encounter.\",\n      \"method\": \"Murine viral infection and peptide immunization models; IL-15 KO mice; mTORC1 inhibitor (rapamycin) treatment; BrdU incorporation cell-cycle analysis\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO plus pharmacological mTORC1 inhibition establishing signaling pathway; multiple experimental systems\",\n      \"pmids\": [\"26241055\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"IL-15 activates the JAK3/STAT3 signaling pathway in skeletal muscle cells to stimulate glucose uptake and GLUT4 translocation to the plasma membrane. IL-15 does not activate Akt, AMPK, JAK1, or STAT5 in this context. STAT3 inhibition abolishes IL-15-induced glucose uptake, and HIF1α expression is dependent on IL-15-induced STAT3 activation.\",\n      \"method\": \"C2C12 differentiated myotube treatment with IL-15; phosphorylation assays (Western blot); co-immunoprecipitation of JAK3/STAT3; STAT3 nuclear translocation imaging; GLUT4 translocation assay; STAT3 inhibitor rescue experiments\",\n      \"journal\": \"Frontiers in physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple biochemical assays plus inhibitor rescue; single lab, single cell line model\",\n      \"pmids\": [\"28066259\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Ligation of NKG2D by ULBP2 (but not MICA) induces enlargement of NKG2D nanoclusters at the NK cell surface and causes the cytokine receptor subunit IL-2/IL-15Rβ to coalesce into these nanoclusters, enabling cooperative signaling between NKG2D and the IL-15 receptor. This nanoscale receptor co-organization amplifies NK cell responses to ULBP2 + IL-15.\",\n      \"method\": \"Superresolution (dSTORM) microscopy on primary human NK cells; functional NK cell activation assays; IL-15Rα-coated surface trans-presentation experiments\",\n      \"journal\": \"Science signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — superresolution structural imaging combined with functional validation; ligand-specific mechanistic distinction\",\n      \"pmids\": [\"29636390\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Sorafenib reduces expression of the transcription factor ATF4 in FLT3-ITD+ AML cells, thereby relieving ATF4-mediated negative regulation of IRF7, which enhances IL-15 transcription. IRF7 knockdown or ATF4 overexpression abolishes sorafenib-induced IL-15 production, defining the ATF4–IRF7–IL-15 transcriptional axis.\",\n      \"method\": \"siRNA knockdown of IRF7; ATF4 overexpression; Western blot; chromatin state analysis; IL-15 ELISA; in vitro and in vivo mouse AML models\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic gain/loss-of-function experiments (siRNA + overexpression) establishing mechanistic transcriptional pathway; validated in human patient samples\",\n      \"pmids\": [\"29431743\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"IL-15 expansion of CAR-T cells reduces mTORC1 activity, decreases glycolytic enzyme expression, and improves mitochondrial fitness, preserving a stem cell memory (Tscm; CD62L+CD45RA+CCR7+) phenotype. Culturing CAR-T cells in rapamycin (mTORC1 inhibitor) recapitulates the IL-15 effect, demonstrating that IL-15-mediated mTORC1 suppression is responsible for maintaining the Tscm phenotype.\",\n      \"method\": \"In vitro CAR-T expansion with IL-15 vs IL-2; rapamycin treatment; mTORC1 activity assays; metabolic profiling; phenotypic flow cytometry; in vivo xenograft tumor model\",\n      \"journal\": \"Cancer immunology research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological epistasis (rapamycin phenocopy) plus metabolic profiling linking IL-15 to mTORC1–metabolism–phenotype axis\",\n      \"pmids\": [\"30890531\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"De novo designed protein Neo-2/15 mimics IL-2 and IL-15 by binding to IL-2Rβγc but lacking binding sites for IL-2Rα or IL-15Rα. Crystal structures of Neo-2/15 alone and in complex with IL-2Rβγc confirm the designed model and show the protein elicits downstream cell signaling independently of the private α chains.\",\n      \"method\": \"Computational de novo protein design; X-ray crystallography of Neo-2/15 alone and in IL-2Rβγc complex; cell signaling assays; in vivo mouse tumor models\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure validation of designed mimic in receptor complex; functional signaling confirmed\",\n      \"pmids\": [\"30626941\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"In a mouse model of coeliac disease, overexpression of IL-15 is required simultaneously in both the gut epithelium and lamina propria to drive villous atrophy. CD4+ T cells and HLA-DQ8 license cytotoxic CD8+ T cells to mediate intestinal epithelial cell lysis; IFN-γ and TG2 contribute to tissue destruction downstream of IL-15.\",\n      \"method\": \"Transgenic mouse model with compartment-specific IL-15 overexpression (epithelium and/or lamina propria); HLA-DQ8 expression; gluten feeding; histopathology; T cell depletion studies; IFN-γ KO\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — compartment-specific genetic model with multiple cellular depletions defining location-dependent IL-15 mechanism\",\n      \"pmids\": [\"32051586\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CREM (cyclic AMP response element modulator) is induced in CAR-NK cells by both CAR activation and IL-15 signaling via the PKA–CREB pathway (downstream of ITAM signaling or IL-15). CREM deletion enhances CAR-NK cell effector function in vitro and in vivo and increases resistance to immunosuppression. CREM exerts its regulatory functions through epigenetic reprogramming of CAR-NK cells.\",\n      \"method\": \"Transcriptomic analysis; CREM deletion (genetic KO); PKA/CREB pathway inhibition; epigenetic profiling; in vivo tumor mouse model; CAR-NK rechallenge assays\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic deletion plus pathway inhibition plus epigenomic profiling; mechanistic dissection of IL-15 downstream signaling in NK cells\",\n      \"pmids\": [\"40468083\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"IL-15 is a secreted/trans-presented four-helix cytokine that signals through a trimeric receptor (IL-15Rα/IL-2Rβ/γc): IL-15Rα on presenting cells binds IL-15 with picomolar affinity and allosterically potentiates its delivery in trans to IL-2Rβ/γc on responding cells, activating JAK1/JAK3 and STAT3/STAT5, as well as PI3K–mTORC1 and Ras–MEK–MAPK pathways, to promote survival (via Bcl-2/Bcl-xL), proliferation, and differentiation of NK cells, NKT cells, and CD8+ memory T cells; IL-15 expression itself is regulated post-transcriptionally by upstream AUGs in its 5′ UTR, transcriptionally through the ATF4–IRF7 axis and Notch signaling during hematopoiesis, and intracellularly in mast cells where it acts as a transcriptional repressor of chymase, while nanoscale co-clustering of IL-2/IL-15Rβ with NKG2D after ULBP2 ligation provides a mechanism for cooperative receptor activation.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"IL-15 is a pleiotropic cytokine that governs the development, homeostasis, and effector function of NK cells, NKT cells, memory CD8+ T cells, γδ intraepithelial lymphocytes, and tissue-resident memory T cells, primarily through trans-presentation of IL-15 bound to IL-15Rα on dendritic cells, stromal cells, or epithelial cells to responding lymphocytes bearing IL-2/IL-15Rβ–γc, which activates JAK–STAT5, PI3K–AKT–mTOR, and MAPK signaling to upregulate anti-apoptotic proteins Bcl-2 and Bcl-xL [PMID:19818367, PMID:12734346, PMID:12586624, PMID:21715685]. Soluble IL-15 complexed with IL-15Rα forms a superagonist that selectively expands memory CD8+ T cells and NK cells in vivo, while translational output of endogenous IL-15 is constitutively restrained by multiple upstream AUGs in the 5′ UTR [PMID:16757567, PMID:8613692]. Beyond lymphocyte biology, IL-15 functions as an autocrine survival factor in renal tubular epithelial cells, drives inflammatory cascades involving IFN-γ, endothelin-1, and prostaglandins that mediate hypernociception, and when overexpressed in both intestinal epithelium and lamina propria cooperates with CD4+ T cells to cause celiac-like villous atrophy [PMID:11927622, PMID:16766656, PMID:32051586]. Intracellular IL-15 also exerts a non-canonical intracrine function in mast cells by acting as a transcriptional repressor of chymase expression [PMID:17643110].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"The question of how IL-15 protein output is controlled was answered by demonstrating that 10 upstream AUGs in the 5′ UTR constitutively repress translation, a block relieved in HTLV-I fusion transcripts — establishing post-transcriptional regulation as the primary gatekeeper of IL-15 production.\",\n      \"evidence\": \"Comparative RT-PCR of normal vs. HTLV-I-transformed cells with functional analysis of upstream AUG codons\",\n      \"pmids\": [\"8613692\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which individual upstream ORFs repress the main ORF not fully dissected\", \"Whether additional post-transcriptional regulators (e.g., miRNAs) contribute in vivo\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Early evidence that IL-15 mediates innate antiviral NK activation came from showing that HHV-6-induced NK cytotoxicity is specifically abolished by anti-IL-15 but not by antibodies against other cytokines.\",\n      \"evidence\": \"Antibody neutralization panel with RT-PCR confirmation in HHV-6-infected PBMCs\",\n      \"pmids\": [\"8617868\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab study without genetic confirmation\", \"Source cell for IL-15 protein not definitively established beyond mRNA detection\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"IL-15 was shown to act as an NK cell chemoattractant and to enhance endothelial adhesion primarily through LFA-1, establishing a role in NK cell trafficking beyond proliferation and survival.\",\n      \"evidence\": \"Checkerboard chemotaxis assays and adhesion assays with blocking antibodies for LFA-1/ICAM-1 and VLA-4/VCAM-1\",\n      \"pmids\": [\"9201264\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo relevance of IL-15-driven chemotaxis not tested\", \"Receptor subunit requirement for chemotactic response not defined\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"IL-15 was revealed to function beyond the immune system as an autocrine survival factor for renal tubular epithelial cells, with IL-15-deficient mice showing increased TEC apoptosis and elevated MCP-1 during nephritis.\",\n      \"evidence\": \"IL-15 KO mice in nephrotoxic serum nephritis model; TUNEL assays and ex vivo TEC apoptosis assays\",\n      \"pmids\": [\"11927622\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether IL-15 signals via canonical βγc on TECs or through alternative receptor complexes\", \"Downstream signaling pathway in TECs not mapped\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Genetic dissection of receptor subunit requirements established that IL-15Rβ and γc are essential for IL-15's pro-survival signaling (Bcl-2 and Bcl-xL upregulation) in CD8+ T cells, while IL-15Rα amplifies sensitivity but is dispensable, and SOCS1 acts as a critical negative regulator constraining STAT5 phosphorylation downstream.\",\n      \"evidence\": \"IL-15Rα-deficient, β-chain-deficient, and SOCS1−/−IFNγ−/− mice; in vitro and in vivo stimulation with apoptosis, Bcl-2/Bcl-xL, and pSTAT5 readouts\",\n      \"pmids\": [\"12734346\", \"12907450\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SOCS1 regulation differs between NK and T cell lineages\", \"Quantitative threshold of IL-15Rα for physiological trans-presentation not yet defined\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"IL-15 was established as the dominant cytokine maintaining peripheral NK cell homeostasis through Bcl-2 upregulation, distinguishing it from IL-7 which had no such role.\",\n      \"evidence\": \"Adoptive transfer of NK cells into γc-cytokine-deficient hosts with Bcl-2 expression analysis\",\n      \"pmids\": [\"12586624\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether IL-15 also controls NK cell metabolic fitness at steady state\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Three advances consolidated the superagonist concept and IL-15's role in CD8+ T cell fate: soluble IL-15/IL-15Rα complexes selectively expanded memory CD8+ T cells and NK cells in vivo; IL-15 protected effector CD8+ T cells from contraction-phase apoptosis via Bcl-2 (rescued by Bcl-2 transgene in IL-15 KO); and IL-15 was shown to support a distinct thymic CD44hiCD122hi CD8+ lineage separate from conventional CD8+ T cells.\",\n      \"evidence\": \"In vivo IL-15/IL-15Rα complex injection; Bcl-2 transgene rescue in IL-15 KO mice during Listeria infection; IL-15−/−ITK−/− double-KO analysis\",\n      \"pmids\": [\"16757567\", \"16365444\", \"16880398\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for superagonist conformational change not resolved\", \"Whether IL-15-dependent CD44hi cells represent innate-like vs. conventional memory lineage\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"IL-15 was found to drive mechanical hypernociception through a sequential IFN-γ→endothelin-1→prostaglandin E2 inflammatory cascade, expanding its known biology beyond lymphocyte regulation.\",\n      \"evidence\": \"IFN-γ KO mice, pharmacological blockade of endothelin receptors and cyclooxygenase, soluble IL-15Rα neutralization in vivo\",\n      \"pmids\": [\"16766656\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cell type producing IL-15 in the pain context not identified\", \"Whether this cascade operates in human pain syndromes\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"A non-canonical intracrine function was discovered: intracellular IL-15 in mast cells acts as a transcriptional repressor of chymase (mast cell protease-2), with IL-15 deletion increasing bactericidal responses and survival during sepsis.\",\n      \"evidence\": \"IL-15 KO mice in cecal ligation and puncture model; chymase activity and transcriptional assays\",\n      \"pmids\": [\"17643110\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of intracellular IL-15 transcriptional repression unknown\", \"Whether intracrine IL-15 functions exist in other cell types\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Trans-presentation was proven as the physiological delivery mode: DCs expressing IL-15Rα were largely sufficient to drive homeostatic proliferation of memory CD8+ T cells in vivo, establishing the cell biology of IL-15 presentation.\",\n      \"evidence\": \"Transgenic mice limiting IL-15Rα to DCs; adoptive transfer of CD8+ T cell subsets\",\n      \"pmids\": [\"18812469\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Contribution of non-DC stromal cells to IL-15 trans-presentation in specific tissues\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Quantitative thresholds of IL-15 trans-presentation were mapped: graded IL-15Rα expression on accessory cells revealed that NK cell homeostasis, differentiation, Ly49 acquisition, and effector function each require distinct levels of STAT5 phosphorylation — while NKT cell development was shown to depend on IL-15 for T-bet-driven stage 2-to-3 progression.\",\n      \"evidence\": \"IL-15Rα knockin mice with graded expression; pSTAT5 quantification in NK cells; IL-15 KO with NKT developmental staging\",\n      \"pmids\": [\"21715685\", \"22084435\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether graded thresholds apply in human NK biology\", \"How T-bet induction is quantitatively coupled to IL-15 signal strength\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"During viral infection, type I IFN-induced IL-15 was shown to drive antigen-independent mTORC1-dependent cell-cycle entry in memory CD8+ T cells, revealing how bystander activation primes rapid recall responses.\",\n      \"evidence\": \"Murine viral infection models; IL-15 neutralization; rapamycin (mTORC1 inhibitor) treatment; BrdU incorporation\",\n      \"pmids\": [\"26241055\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether IFN→IL-15→mTORC1 axis operates similarly in human infections\", \"Downstream mTORC1 targets mediating cell-cycle entry not identified\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Multiple studies in 2018 resolved tissue-specific and metabolic dimensions: IL-15 trans-presented by keratinocytes maintains skin TRM (and anti-CD122 reverses vitiligo); continuous IL-15 drives NK exhaustion via reduced mitochondrial FAO capacity (rescued by mTOR inhibition); non-hematopoietic cells trans-present IL-15 to maintain CMV-specific inflationary CD8+ T cells via Bcl-2; and epithelial IL-15 is required for γδ IEL migration into the intestinal epithelium.\",\n      \"evidence\": \"IL-15-deficient mice and anti-CD122 in vitiligo model; Seahorse metabolic assays with mTOR inhibitor rescue in human NK cells; MCMV model with IL-15Rα KO; compartment-specific IL-15 transgenic mice with intravital microscopy\",\n      \"pmids\": [\"30021889\", \"29415897\", \"29652930\", \"29884699\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which continuous vs. intermittent IL-15 differentially affects FAO\", \"Whether keratinocyte trans-presentation is the sole pathway for skin TRM maintenance in humans\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Superresolution imaging revealed that NKG2D ligand engagement (specifically ULBP2) induces coalescence of IL-2/IL-15Rβ nanoclusters with NKG2D nanoclusters on NK cells, providing a nanoscale mechanism for costimulatory crosstalk during trans-presentation.\",\n      \"evidence\": \"dSTORM superresolution microscopy of primary human NK cells on IL-15Rα-coated surfaces; ULBP2 vs. MICA comparison\",\n      \"pmids\": [\"29636390\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether receptor nanocluster reorganization occurs in vivo at immune synapses\", \"Signaling consequences of nanocluster coalescence not fully characterized\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"De novo computational design of Neo-2/15, which binds IL-2Rβγc without IL-15Rα or IL-2Rα engagement, confirmed that the βγc heterodimer is the sufficient signaling unit and validated the structural model of IL-15–receptor interaction.\",\n      \"evidence\": \"Crystal structures of Neo-2/15 free and bound to IL-2Rβγc; cell signaling assays; in vivo tumor models\",\n      \"pmids\": [\"30626941\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Neo-2/15 does not address how IL-15Rα conformationally potentiates natural IL-15\", \"Long-term in vivo safety and pharmacokinetics not established\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Dual-compartment IL-15 overexpression (epithelium plus lamina propria) was shown to be necessary and sufficient for celiac-like villous atrophy in mice, resolving the long-standing question of why single-compartment IL-15 elevation is insufficient for tissue destruction.\",\n      \"evidence\": \"Compartment-specific IL-15 transgenic mice crossed with HLA-DQ8 transgenic; gluten feeding; histology; T cell depletion\",\n      \"pmids\": [\"32051586\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of cooperativity between epithelial and lamina propria IL-15 not molecularly defined\", \"Whether dual-compartment model applies to all celiac patients\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"IL-15 signaling was found to induce the transcriptional repressor CREM in NK cells via PKA-CREB, establishing a feedback circuit whereby IL-15 itself triggers epigenetic programs that limit NK effector function.\",\n      \"evidence\": \"CRISPR deletion of CREM in CAR-NK cells; PKA-CREB pathway inhibition; transcriptomic and epigenetic profiling; in vivo tumor models\",\n      \"pmids\": [\"40468083\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CREM-mediated exhaustion occurs with physiological IL-15 levels or only with therapeutic doses\", \"Specific epigenetic targets of CREM in NK cells not fully cataloged\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis for the IL-15Rα-induced superagonist conformational change, the molecular mechanism of intracrine IL-15 transcriptional repression in mast cells, whether graded IL-15 signaling thresholds observed in mouse NK/NKT biology are conserved in humans, and how continuous versus intermittent IL-15 differentially reprograms metabolic and epigenetic states in lymphocytes.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No crystal structure of natural IL-15/IL-15Rα superagonist complex explaining conformational potentiation\", \"Intracrine mechanism of IL-15 as transcriptional repressor uncharacterized at the molecular level\", \"Human in vivo validation of graded signaling thresholds for NK developmental checkpoints\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 1, 8]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [12]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [10, 29]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 1, 8]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [12]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [1, 2, 3, 4, 5, 6, 15, 18, 26, 28, 30]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 3, 9, 10, 11, 15, 29]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [3, 4, 6, 24, 26]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [5, 15, 21]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [22, 23]}\n    ],\n    \"complexes\": [\n      \"IL-15/IL-15Rα complex\"\n    ],\n    \"partners\": [\n      \"IL15RA\",\n      \"IL2RB\",\n      \"IL2RG\",\n      \"STAT5A\",\n      \"STAT3\",\n      \"JAK3\",\n      \"SOCS1\",\n      \"CREM\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"IL-15 is a pleiotropic four-helix-bundle cytokine that signals through a trimeric receptor comprising a private high-affinity IL-15Rα chain and the shared IL-2Rβ/γc heterodimer, activating JAK1/JAK3–STAT3/STAT5 and PI3K–mTORC1 pathways to govern survival, proliferation, and differentiation of NK cells, NKT cells, and CD8⁺ memory T cells [PMID:8178155, PMID:7641685, PMID:7568001]. IL-15Rα on dendritic cells and stromal cells trans-presents IL-15 to responding lymphocytes, with the sushi domain allosterically enhancing IL-15 affinity for IL-2Rβ; graded levels of trans-presented IL-15 specify distinct NK-cell developmental outcomes and CD8⁺ T cell homeostatic proliferation through quantitative differences in STAT5 phosphorylation [PMID:23104097, PMID:18812469, PMID:21715685, PMID:16284400]. IL-15 promotes lymphocyte survival via Bcl-2 and Bcl-xL induction and drives antigen-independent memory CD8⁺ T cell cycling through mTORC1, while its expression is regulated post-transcriptionally by inhibitory upstream AUGs in the 5′ UTR and transcriptionally through the ATF4–IRF7 axis and Notch-dependent silencing during hematopoietic lineage commitment [PMID:16365444, PMID:22084435, PMID:26241055, PMID:8613692, PMID:29431743, PMID:23966624]. Beyond canonical immune roles, intracellular IL-15 functions as a transcriptional repressor of mast cell chymase, and compartment-specific IL-15 overexpression in both gut epithelium and lamina propria drives villous atrophy in a coeliac disease model [PMID:17643110, PMID:32051586].\",\n  \"teleology\": [\n    {\n      \"year\": 1994,\n      \"claim\": \"The discovery that IL-15 is a T cell growth factor that shares IL-2Rβ (CD122) and γc (CD132) but not IL-2Rα established it as a second cytokine exploiting the IL-2 receptor system, raising the question of how specificity is achieved.\",\n      \"evidence\": \"cDNA cloning, receptor competition binding, and neutralizing antibody inhibition in two independent studies\",\n      \"pmids\": [\"8178155\", \"8026467\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The IL-15-specific receptor component was not yet identified\", \"Downstream signaling pathways were unknown\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Cloning of IL-15Rα as a high-affinity private α chain structurally related to IL-2Rα resolved how IL-15 achieves receptor specificity and defined the complete trimeric receptor complex (IL-15Rα/IL-2Rβ/γc).\",\n      \"evidence\": \"Molecular cloning, reconstitution of trimeric complex, and direct binding quantification in myeloid cells\",\n      \"pmids\": [\"7641685\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether IL-15Rα functions in cis or trans was unknown\", \"Three-dimensional receptor architecture was unresolved\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Identification of JAK1/JAK3 activation and STAT3/STAT5 induction downstream of IL-15 established the proximal signaling cascade, paralleling IL-2 but foreshadowing cell-type-specific differences.\",\n      \"evidence\": \"Immunoprecipitation, phosphotyrosine blotting, and EMSA in human T cells\",\n      \"pmids\": [\"7568001\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether additional pathways (MAPK, PI3K) are engaged was not addressed\", \"Cell-type-specific signaling differences were unexplored\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Demonstration that 10 upstream AUGs in the IL-15 5′ UTR suppress translation revealed that IL-15 protein output is tightly controlled post-transcriptionally, explaining the discrepancy between widespread mRNA expression and limited protein detection.\",\n      \"evidence\": \"RT-PCR characterization and translational efficiency comparison of chimeric mRNAs with varying upstream AUG content\",\n      \"pmids\": [\"8613692\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which trans-acting factors relieve translational repression was unknown\", \"In vivo relevance of individual upstream AUGs was not tested\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Showing that CD8⁺ memory T cell homeostatic proliferation requires IL-15 while being opposed by IL-2 established IL-15 as the non-redundant survival cytokine for immunological memory, distinct from IL-2.\",\n      \"evidence\": \"In vivo proliferation in IL-15-deficient mice combined with IL-2 blockade; adoptive transfer system\",\n      \"pmids\": [\"10784451\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The cellular source of IL-15 for memory T cell maintenance was unresolved\", \"Downstream survival effectors were not identified\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Concurrent studies defined IL-15 as the dominant NK cell survival signal via Bcl-2, showed that IL-15Rα enhances sensitivity but is dispensable on responding cells (β/γc are essential), identified SOCS1 as a negative regulator of IL-15–STAT5 signaling, and revealed alternative IL-15Rα splice variants in mast cells with distinct signaling profiles.\",\n      \"evidence\": \"Adoptive transfer into IL-15 KO hosts; receptor subunit KO cell assays; SOCS1 KO thymic organ culture; mast cell IL-15Rα isoform cloning with signaling reconstitution\",\n      \"pmids\": [\"12586624\", \"12734346\", \"12907450\", \"12734349\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether IL-15Rα on accessory cells trans-presents IL-15 in vivo was not directly demonstrated\", \"Quantitative relationship between IL-15 dose and specific developmental outcomes was unknown\", \"Mast cell IL-15Rα isoform findings from a single lab awaited independent confirmation\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Dissection of the IL-15Rα sushi domain as an agonist versus the full ectodomain as an antagonist explained how soluble IL-15Rα fragments allosterically modulate IL-15 potency, enabling rational design of IL-15 superagonists (RLI).\",\n      \"evidence\": \"Recombinant domain fragments tested in binding, proliferation, apoptosis, and receptor internalization assays\",\n      \"pmids\": [\"16284400\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for the allosteric enhancement was not yet resolved at atomic level\", \"In vivo pharmacokinetics of sushi-domain fusions were not characterized\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"A convergence of in vivo studies established that IL-15/IL-15Rα complexes potently expand memory CD8⁺ T cells and NK cells, that IL-15 protects effector CD8⁺ T cells from contraction-phase apoptosis via Bcl-2 (shown by Bcl-2 transgene rescue in IL-15 KO), and that IL-15 is required specifically for the CD44ʰⁱCD122ʰⁱ memory-phenotype CD8⁺ T cell subset.\",\n      \"evidence\": \"IL-15/sIL-15Rα complex injection; IL-15 KO and transgenic mice with Bcl-2 rescue; IL-15/ITK double-KO epistasis\",\n      \"pmids\": [\"16757567\", \"16365444\", \"16880398\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which accessory cell types are the physiological source of trans-presented IL-15 was still unresolved\", \"Whether IL-15 supports CD8⁺ memory via Bcl-2 versus proliferative mechanisms was debated\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Two studies revealed unexpected non-canonical IL-15 functions: intracellular IL-15 in mast cells acts as a transcriptional repressor of chymase, and extracellular IL-15 orchestrates neutrophil migration through a sequential IL-18→MIP-2/TNF-α/LTB4 cytokine cascade.\",\n      \"evidence\": \"IL-15 KO mice in CLP sepsis model with chymase activity assays; peritoneal neutrophil migration in multiple cytokine/receptor KO mice\",\n      \"pmids\": [\"17643110\", \"17979156\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which intracellular IL-15 represses chymase transcription was not defined\", \"Whether the neutrophil-recruiting cascade operates in tissues beyond the peritoneum was unknown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Restricting IL-15Rα expression to dendritic cells proved sufficient for homeostatic memory CD8⁺ T cell proliferation, identifying DCs as a physiologically relevant trans-presenting cell type.\",\n      \"evidence\": \"IL-15Rα transgenic mouse model limiting expression to DCs; adoptive transfer with viral infection\",\n      \"pmids\": [\"18812469\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Contribution of non-DC populations (macrophages, stromal cells) was not excluded\", \"Whether DC trans-presentation is sufficient for NK cell homeostasis was not tested\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Quantitative studies showed that graded IL-15 trans-presentation levels on accessory cells determine distinct NK cell developmental thresholds via proportional STAT5 phosphorylation, and that IL-15 controls NKT cell terminal differentiation through a Bcl-xL survival and T-bet transcriptional program.\",\n      \"evidence\": \"IL-15Rα knockin mice with titrated expression; NK-DC coculture with STAT5 readout; IL-15 KO NKT cell gene expression profiling\",\n      \"pmids\": [\"21715685\", \"22084435\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How specific STAT5 phosphorylation thresholds activate distinct gene programs was not mechanistically resolved\", \"Whether T-bet is directly or indirectly regulated by STAT5 downstream of IL-15 was unclear\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Crystal structures of the quaternary IL-15–IL-15Rα–IL-2Rβ–γc complex revealed near-identical receptor engagement geometry to the IL-2 quaternary complex, demonstrating that IL-15Rα allosterically increases IL-15 affinity for IL-2Rβ and that functional differences between IL-2 and IL-15 arise from differential receptor affinities rather than distinct signaling geometries.\",\n      \"evidence\": \"X-ray crystallography of the quaternary complex; surface plasmon resonance; functional signaling assays\",\n      \"pmids\": [\"23104097\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How identical β/γc engagement produces differential STAT activation kinetics between IL-2 and IL-15 remained unexplained\", \"Structural basis for IL-15Rα's allosteric effect on IL-2Rβ binding was not fully delineated\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Type I IFN-driven IL-15 was shown to push memory CD8⁺ T cells into rapid mTORC1-dependent cell-cycle entry independently of antigen, establishing mTORC1 as a key downstream effector of IL-15 in bystander activation of memory T cells.\",\n      \"evidence\": \"IL-15 KO mice during viral infection; rapamycin treatment; BrdU incorporation\",\n      \"pmids\": [\"26241055\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How IL-15 activates mTORC1 (via PI3K–Akt or alternative route) in memory T cells was not resolved\", \"Whether mTORC1-independent IL-15 effects contribute to bystander activation was not tested\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Two mechanistic advances emerged: NKG2D ligation by ULBP2 induces nanoscale co-clustering of NKG2D with IL-2/IL-15Rβ to enable cooperative signaling in NK cells, and the ATF4–IRF7 transcriptional axis was identified as a regulator of IL-15 expression in AML cells.\",\n      \"evidence\": \"Super-resolution dSTORM imaging on primary NK cells with functional validation; siRNA/overexpression of IRF7/ATF4 in AML cells with chromatin analysis\",\n      \"pmids\": [\"29636390\", \"29431743\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether NKG2D–IL-15Rβ co-clustering occurs with other NKG2D ligands beyond ULBP2 was unknown\", \"Generalizability of ATF4–IRF7–IL-15 axis beyond FLT3-ITD+ AML was not tested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"IL-15 was shown to preserve stem cell memory (Tscm) phenotype in CAR-T cells through mTORC1 suppression and metabolic reprogramming toward mitochondrial fitness, and a de novo designed protein (Neo-2/15) that binds IL-2Rβγc without engaging α chains confirmed that β/γc engagement alone is sufficient for downstream signaling.\",\n      \"evidence\": \"CAR-T expansion with IL-15 versus IL-2 plus rapamycin phenocopy; metabolic profiling; crystal structure of Neo-2/15 in complex with IL-2Rβγc\",\n      \"pmids\": [\"30890531\", \"30626941\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether IL-15-mediated mTORC1 suppression in CAR-T cells is dose-dependent or context-dependent was not determined\", \"Neo-2/15 structure did not address IL-15Rα allosteric mechanism\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"A compartment-specific transgenic model demonstrated that IL-15 overexpression must occur simultaneously in both gut epithelium and lamina propria to drive coeliac-like villous atrophy, placing IL-15 as a central pathogenic mediator linking innate and adaptive intestinal immunity.\",\n      \"evidence\": \"Transgenic mice with compartment-restricted IL-15 overexpression; HLA-DQ8; gluten feeding; T cell depletion; IFN-γ KO\",\n      \"pmids\": [\"32051586\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether epithelial versus lamina propria IL-15 engages distinct receptor configurations or cell types was not resolved\", \"Applicability to human coeliac disease pathogenesis requires clinical confirmation\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identification of CREM as an IL-15-induced negative regulator of CAR-NK cell function via PKA–CREB signaling and epigenetic reprogramming revealed a previously unknown feedback restraint downstream of IL-15 in engineered NK cells.\",\n      \"evidence\": \"CREM deletion in CAR-NK cells; PKA/CREB pathway inhibition; epigenomic profiling; in vivo tumor models\",\n      \"pmids\": [\"40468083\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CREM-mediated restraint operates in endogenous NK cells or is specific to CAR-NK expansion conditions is unknown\", \"The specific epigenetic targets of CREM in NK cells were not fully catalogued\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include how identical IL-2Rβ/γc engagement geometry by IL-2 and IL-15 produces distinct signaling kinetics and biological outcomes, the structural mechanism of IL-15Rα's allosteric enhancement of IL-15 affinity for IL-2Rβ, how intracellular IL-15 represses chymase transcription in mast cells, and whether quantitative STAT5 thresholds downstream of trans-presented IL-15 specify gene programs through distinct transcription factor assemblies.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural model for IL-15Rα allosteric transmission to the IL-2Rβ binding interface\", \"Mechanism of intracellular IL-15 transcriptional repression in mast cells is undefined\", \"How STAT5 dose-response translates into binary developmental decisions in NK/NKT cells remains unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 1, 2, 10, 11, 20]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [15]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [15]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 10, 11, 20]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 1, 2, 3, 5, 6, 7, 8, 12, 14, 17, 18, 19, 24, 28]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 8, 19, 22, 23, 24, 25, 26, 29]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [18, 19, 21]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [6, 7, 12]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"IL15RA\",\n      \"IL2RB\",\n      \"IL2RG\",\n      \"JAK1\",\n      \"JAK3\",\n      \"STAT5A\",\n      \"STAT3\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}