# IL-25 (IL-17E): Complete Research Profile — IL-17RA/IL-17RB Receptor Complex, Epithelial Alarmin Signaling, ILC2 and Th2 Activation, Type 2 Immunity, and Allergic Inflammation Research Applications (2026)
For Research Use Only (RUO) — Not for human or veterinary use
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Introduction: IL-25 as the Upstream Initiator of Type 2 Immunity
Interleukin-25 (IL-25), also designated IL-17E, is a cytokine that occupies a unique strategic position in the immune signaling hierarchy: it is one of three epithelial "alarmins" — alongside TSLP (thymic stromal lymphopoietin) and IL-33 — that translate barrier tissue damage, pathogen sensing, or allergen exposure into the initiation of type 2 immunity. Unlike most cytokines in the IL-17 family, which promote pro-inflammatory Th17-associated responses, IL-25 paradoxically drives type 2 (Th2/ILC2) immunity, making it the most functionally divergent member of the IL-17 family.
IL-25 was independently identified by Fort et al. and Wang et al. in 2001 as a cytokine produced by Th2 cells that promoted eosinophilia, IgE production, and IL-4/IL-5/IL-13 secretion. Subsequent work revealed that while adaptive Th2 cells can produce IL-25, its dominant physiological sources are non-hematopoietic — particularly tuft cells in the gut and airway epithelium, along with mast cells, basophils, eosinophils, and type 2 innate lymphoid cells (ILC2s) in positive feedback contexts. This non-hematopoietic origin means IL-25 represents a hard-wired epithelial sentinel function that precedes and drives adaptive immunity.
The biological consequences of IL-25 signaling are broad and research-rich: ILC2 activation and proliferation (the most potent known ILC2 stimulus alongside IL-33), Th2 cell differentiation amplification, eosinophil recruitment, goblet cell hyperplasia, smooth muscle hyperresponsiveness in lung models, and intestinal tuft cell — ILC2 — innate lymphoid circuit activation in response to helminths and protozoa. This profile provides the mechanistic and practical research framework for investigators studying type 2 immunity, allergic disease models, ILC2 biology, and gut innate immunity.
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Molecular Structure and IL-17 Family Context
IL-25 Protein Architecture
Mature human IL-25 comprises approximately 145 amino acids (16 kDa) after signal peptide cleavage. Unlike most IL-17 family members that form disulfide-linked homodimers, IL-25 is predominantly secreted as a monomer under most conditions, though some reports describe disulfide-linked dimers at high concentrations. The protein contains a cystine-knot-like core with conserved IL-17 family cysteines but adopts a distinct tertiary structure that reflects its unique receptor specificity.
Sequence identity of IL-25 with other IL-17 family members is low (16–27%), consistent with its distinct biological role. The IL-25 N-terminus and loop regions that determine receptor selectivity diverge substantially from IL-17A and IL-17F, explaining why IL-25 signals through IL-17RB rather than the IL-17RC used by IL-17A/F heterodimers.
The IL-17 Cytokine Family: Distinguishing IL-25
The IL-17 family comprises six members (IL-17A through IL-17F) plus IL-25:
| Member | Receptor | Primary Producer | Main Function |
|---|---|---|---|
| IL-17A | IL-17RA/RC | Th17, γδ T, ILC3 | Neutrophil recruitment, tissue inflammation |
| IL-17F | IL-17RA/RC | Th17 | Similar to IL-17A, lower potency |
| IL-17C | IL-17RA/RE | Epithelial cells | Epithelial antimicrobial defense |
| IL-17D | IL-17RA/RD | CD8⁺ T, NK | Anti-tumor, anti-viral (emerging) |
| IL-25 (IL-17E) | IL-17RA/RB | Tuft cells, Th2, mast cells | Type 2 immunity, ILC2 activation |
The key distinguishing feature: all other IL-17 family members drive pro-inflammatory, Th17-type, or neutrophil-recruiting responses. IL-25 alone drives type 2 (Th2/ILC2) responses — an evolutionary and functional outlier within its structural family.
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Receptor Complex: IL-17RA and IL-17RB
IL-17RB: The IL-25-Specific Binding Chain
IL-17RB (also designated IL-17Rh1 or EVI27) is the cytokine-selective receptor chain that confers IL-25 specificity. IL-17RB binds IL-25 with high affinity (Kd ~1–10 nM) and is the defining component for IL-25 responsiveness.
IL-17RB expression:
- •ILC2s: Highest expression; IL-17RB is a canonical surface marker for ILC2 identification (alongside ST2/IL-33R and CRTH2)
- •Mast cells: Constitutive; important for IL-25's amplification of mast cell effector functions
- •Basophils: Express IL-17RB; IL-25 activates basophil IL-4/IL-13 production
- •Eosinophils: Express IL-17RB; IL-25 promotes eosinophil survival and activation
- •Tuft cells: Auto/paracrine — tuft cells produce IL-25 and express IL-17RB, creating a positive feedback loop
- •Some epithelial cells: Low-level expression in certain intestinal and airway epithelial contexts
IL-17RA: The Shared Signal-Transducing Chain
IL-17RA is the common receptor chain shared across most IL-17 family receptor complexes. For IL-25 signaling:
- •IL-25 binds IL-17RB first (high-affinity docking)
- •IL-17RA is recruited to form the functional IL-17RB:IL-17RA heterodimeric signaling complex
- •IL-17RA provides the primary intracellular signal-transducing capacity through its SEF/IL-17R (SEFIR) domain
The SEFIR domain of IL-17RA recruits the adaptor protein Act1 (also known as CIKS/TRAF3IP2), which is the critical intracellular adaptor for IL-17 family signaling. Act1 contains its own SEFIR domain enabling homotypic SEFIR:SEFIR interaction with IL-17RA, and also recruits TRAF6 to propagate NF-κB and MAPK activation. This Act1 dependence is the mechanistic basis for why IL-17RA/Act1/TRAF6 pathway inhibition blocks both IL-17A and IL-25 signaling simultaneously.
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Downstream Signaling
NF-κB Pathway
IL-25:IL-17RB:IL-17RA engagement → Act1 recruitment → TRAF6 activation → IKK complex → IκBα phosphorylation/degradation → NF-κB (p50/p65) nuclear translocation. NF-κB drives IL-25 target gene expression in ILC2s (GATA3, IL-5, IL-13), mast cells (IL-4, TNF-α), and epithelial cells where IL-25 signals directly (TSLP, eotaxin).
MAPK Cascades
IL-25 activates ERK1/2, p38 MAPK, and JNK via Act1-dependent TRAF6 → TAK1 → MAP kinase kinase cascades:
- •ERK1/2: Drives proliferation and survival signals in ILC2s; contributes to IL-5 and IL-13 mRNA induction
- •p38: Contributes to mRNA stability of IL-25 target cytokines (ARE-mediated post-transcriptional regulation — similar to the p38/MK2/TTP axis described for IL-8)
- •JNK: AP-1 activation (c-Jun/c-Fos) contributing to transcriptional synergy with NF-κB at cytokine gene promoters
PI3K/Akt in ILC2s
In ILC2s, IL-25 activates PI3K-δ → Akt → mTORC1, which coordinates:
- •ILC2 proliferation (mTORC1-driven S6K1 and 4EBP1 for cap-dependent translation)
- •Metabolic reprogramming: IL-25 promotes glycolysis and oxidative phosphorylation in ILC2s via mTORC1-HIF-1α
- •Bcl-2 upregulation for ILC2 survival
The PI3K-δ specificity (not PI3K-γ as in neutrophils) makes PI3K-δ inhibitors (idelalisib/CAL-101, GS-1101) useful tools for selectively blocking IL-25-driven ILC2 responses without affecting neutrophil PI3K-γ-dependent pathways.
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IL-25 Biology in Innate Type 2 Immunity
ILC2 Activation: The Central IL-25 Response
Type 2 innate lymphoid cells (ILC2s) are the primary and most potent target of IL-25. ILC2s lack antigen-specific receptors but respond to epithelial alarmins to rapidly produce large quantities of Th2 cytokines without requiring adaptive immune activation. IL-25 effects on ILC2s:
Rapid cytokine production (hours):
- •IL-4, IL-5, IL-13 — the canonical type 2 effector cytokines
- •Amphiregulin — promotes tissue repair and epithelial proliferation
- •IL-9 — mast cell growth factor; amplifies the type 2 cascade
Proliferation (days):
IL-25 is a potent ILC2 mitogen; ILC2 numbers expand 5–20-fold in vitro within 5–7 days of IL-25 exposure (50–100 ng/mL) in the presence of stromal cell support or IL-2/IL-7 survival factors.
Phenotypic changes:
- •Upregulates CRTH2 (prostaglandin D2 receptor), ST2 (IL-33R), KLRG1 — surface markers of ILC2 activation
- •Upregulates GATA3 (the ILC2 master transcription factor) and IRF4
- •Promotes "inflammatory ILC2" (iILC2) differentiation — a more potent, IL-25-responsive subset vs. natural ILC2s (nILC2s) which are more ST2-responsive
IL-25 vs. IL-33 in ILC2 activation:
Both IL-25 and IL-33 activate ILC2s, but they are not redundant:
- •IL-33 activates primarily pre-existing tissue-resident nILC2s; responses are rapid (2–4h peak)
- •IL-25 preferentially activates iILC2s and promotes de novo ILC2 differentiation from bone marrow precursors; responses are slower but more durable
- •Combined IL-25 + IL-33 produces strongly synergistic ILC2 activation (10–100 fold greater IL-5/IL-13 vs. either alone) — important for assay design in allergic model research
The Tuft Cell — ILC2 Circuit
A seminal discovery in intestinal innate immunity is the tuft cell — ILC2 circuit, characterized between 2016–2018 by the Bhatt, Locksley, and Artis groups. The circuit:
1. Luminal trigger: Helminth parasites, protozoa (Tritrichomonas species), and succinate (microbial metabolite) activate tuft cells (chemosensory epithelial cells expressing DCLK1, POU2F3, and taste receptor components)
2. Tuft cell IL-25 release: Activated tuft cells secrete IL-25 basally into the lamina propria
3. ILC2 activation: IL-25 activates lamina propria ILC2s → IL-13 production
4. IL-13 → tuft cell and goblet cell expansion: IL-13 drives tuft cell hyperplasia (self-amplifying) and goblet cell differentiation, increasing mucus production and gut motility for parasite expulsion
5. Positive feedback: Expanded tuft cell population produces more IL-25 → sustained ILC2 activation
This circuit is a model for studying how innate epithelial chemosensation translates to type 2 immunity and provides a mechanistic basis for intestinal IL-25 biology research.
In vitro tuft cell research models:
- •Intestinal organoids (enteroids): Mouse or human small intestinal organoids exposed to succinate (10 mM) or IL-4/IL-13 (10 ng/mL, 5 days) generate tuft cell–enriched organoids (DCLK1+ cells expand); IL-25 secretion quantifiable by ELISA from organoid supernatants
- •Tuft cell–ILC2 co-culture: Organoid-conditioned medium from succinate-stimulated enteroids activates human or mouse ILC2s; anti-IL-25 neutralization in the conditioned medium suppresses ILC2 activation, confirming IL-25 as the active mediator
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IL-25 in Lung and Airway Biology
Airway Epithelial IL-25 Production
Airway epithelial cells (AECs) produce IL-25 in response to:
- •Protease allergens (house dust mite Der p 1, Alternaria cysteine protease): Directly cleaves junctional proteins, activating TRPA1 ion channels and protease-activated receptors (PARs) on epithelial cells → IL-25 secretion
- •Double-stranded RNA / poly(I:C): TLR3-mediated innate antiviral sensing → IL-25 production (mechanistically links respiratory viral infections to exacerbation of type 2 airway inflammation)
- •IL-4/IL-13: Autocrine amplification — Th2 cytokines upregulate IL-25 production by AECs
Research models for AEC IL-25 production:
- •Primary bronchial epithelial cells (NHBE) at ALI: Air-liquid interface cultures exposed to HDM extract (10 µg/mL protein) or poly(I:C) (10 µg/mL) at the apical surface produce IL-25 detectable at 24–48h by ELISA (typically 10–500 pg/mL in basolateral medium)
- •A549/BEAS-2B immortalized lines: Lower baseline IL-25 production; require optimization with stronger stimuli; useful for mechanism studies but less representative than primary ALI cultures
- •16HBE14o- cells: More physiological barrier; good IL-25 signal with poly(I:C) + IL-4 co-stimulation
IL-25 in Airway ILC2 Activation and Type 2 Asthma Models
Airway ILC2 activation by IL-25 in type 2 airway inflammation research:
- •Intratracheal or intranasal delivery of IL-25 in mice robustly induces airway eosinophilia, goblet cell hyperplasia, airway hyperresponsiveness, and ILC2 expansion in the lung — making IL-25 instillation a standard method for generating innate type 2 airway inflammation in research models independent of adaptive immunity
- •In vitro, IL-25 (50–100 ng/mL) drives lung ILC2 (LinSca-1+ ST2+ CD127+) IL-5 and IL-13 production within 48–72h; this is used as the basis for ILC2 functional readout in drug discovery research platforms
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IL-25 in Intestinal Immunity and Helminth Research
Th2-Mediated Anti-Helminth Biology
IL-25 is essential for mounting effective type 2 immune responses against extracellular parasites. Key IL-25 functions in intestinal helminth immunity research:
- •IL-25 produced by tuft cells and mast cells initiates the ILC2 → IL-13 → goblet cell → mucus/motility expulsion program
- •IL-25 from mast cells amplifies the adaptive Th2 response by activating ILC2s before antigen-specific T cell help arrives
- •IL-25 drives alternative macrophage (M2) polarization (via ILC2-derived IL-4/IL-13), which contributes to worm encapsulation and expulsion
Helminth research model note: The widely studied model organism Nippostrongylus brasiliensis (Nb) in mice relies heavily on IL-25 for the type 2 expulsion response. IL-25−/− mice show profoundly impaired Nb expulsion. Recombinant IL-25 at 0.5–2 µg in PBS delivered intraperitoneally can restore type 2 immunity in IL-25-deficient contexts in mouse research systems.
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IL-25 in Intestinal Inflammation — Dual Roles
IL-25 and Inflammatory Bowel Disease Research
IL-25's role in IBD research is complex and context-dependent:
Protective roles (intestinal barrier integrity):
- •IL-25 promotes goblet cell differentiation and mucus production (via ILC2-IL-13 axis), which contributes to barrier maintenance
- •In colitis research models (DSS colitis), IL-25 can suppress Th17-mediated inflammation by driving ILC2 activation and counter-regulatory IL-13 production
Pathological roles (eosinophilic inflammation):
- •Elevated IL-25 in eosinophilic esophagitis (EoE) research — IL-25 from esophageal epithelium drives eosinophil recruitment via ILC2-IL-5 axis
- •IL-25 can contribute to intestinal fibrosis through IL-13-driven TGF-β activation in stromal cells
This dual nature means IL-25 research in IBD models requires careful attention to timing, disease phase, and tissue compartment — early IL-25 may be protective while chronic IL-25 signaling may drive fibrostenotic remodeling via IL-13.
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Detection and Quantification
ELISA Considerations for IL-25
IL-25 presents several analytical challenges:
- •Low circulating concentrations: Serum IL-25 is typically below detection limits of standard ELISA in homeostatic conditions; requires ultra-sensitive assays (electrochemiluminescence platforms, e.g., Meso Scale Discovery) or single-molecule detection
- •Tissue sources dominant: IL-25 acts locally at epithelial surfaces; tissue homogenate or organ-conditioned medium measurements are more informative than serum
- •Species specificity: Human and murine IL-25 ELISAs are not cross-reactive due to low sequence identity; species-matched detection antibodies are required
- •Glycosylation: Native IL-25 may be partially N-glycosylated; E. coli recombinant IL-25 lacks glycosylation but retains bioactivity; glycosylation status can affect antibody recognition in some commercial ELISA kits — verify with kit documentation
ELISA platform recommendations:
- •R&D Systems DuoSet human IL-25 (DY1258): LOD ~4 pg/mL; suitable for conditioned medium, bronchial lavage
- •Luminex multiplex including IL-25 + IL-33 + TSLP: efficient profiling of all three epithelial alarmins simultaneously from a single sample
Flow Cytometry for IL-17RB/IL-25 Axis
For characterizing IL-25-responsive ILC2 populations:
- •IL-17RB (IL-25R) surface staining: Anti-human IL-17RB (BioLegend #314110, clone MHLR2); used alongside ST2 (IL-33R) and CRTH2 for full ILC2 surface panel
- •ILC2 gating strategy: LiveDump (Lin: CD3/CD14/CD19/CD56/CD11b) → CD45+ → CD127+ → CRTH2+ ST2+ → IL-17RB+ (identifies IL-25-responsive ILC2 subset)
- •Intracellular cytokine staining post IL-25 stimulation: Brefeldin A (5 µg/mL) added 4h after IL-25 (50 ng/mL) stimulation; stain for intracellular IL-5 and IL-13 to confirm functional IL-25 response in ILC2s
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In Vitro Research Protocols
ILC2 Expansion and Activation by IL-25
1. Isolate human peripheral blood ILC2s by negative selection (Miltenyi ILC2 isolation kit) or FACS sort (LinCRTH2+ ST2+ CD127+); typical yield from 50 mL blood: 5,000–50,000 ILC2s
2. Culture in IMDM + 10% FBS + IL-2 (10 ng/mL) + IL-7 (10 ng/mL) for baseline survival
3. Add IL-25 (10, 50, 100 ng/mL) ± IL-33 (10 ng/mL) for synergy experiments
4. Collect supernatants at 24h (cytokine induction) and 5–7 days (proliferation phase)
5. Readouts:
- IL-5, IL-13, IL-4 ELISA on 24h supernatants
- CFSE dilution or Ki-67 staining at day 5 for proliferation
- IL-17RB, ST2, CRTH2, KLRG1 surface staining to track activation phenotype
- Intracellular GATA3, IRF4 at day 5 for transcription factor upregulation
Expected: IL-25 (50 ng/mL) produces 5–20 ng/mL IL-13 and 1–5 ng/mL IL-5 in ILC2 supernatants within 24–48h; combined IL-25 + IL-33 (10 ng/mL each) typically produces 2–10-fold greater output than either alone.
Epithelial IL-25 Production Induction
For studying epithelial alarmin production:
1. Grow NHBE to full ALI differentiation (21 days) in PneumaCult-ALI
2. Apply stimuli apically: HDM extract (10 µg/mL protein), poly(I:C) (10 µg/mL), or IL-4 (20 ng/mL, basolateral)
3. Collect basolateral medium at 24h and 48h
4. ELISA: IL-25, TSLP, IL-33 simultaneously (multiplex or individual kits)
5. Compare IL-25 to TSLP and IL-33 outputs — in most HDM and poly(I:C) contexts, TSLP > IL-25 > IL-33 from AECs, but absolute outputs vary by donor and differentiation state
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Pharmacological Research Tools
| Tool | Target | Mechanism | Research Application |
|---|---|---|---|
| Recombinant IL-25 (human/murine — species-specific) | IL-17RB/IL-17RA | Full agonist | ILC2 activation; type 2 model induction |
| Anti-IL-25 neutralizing mAb (R&D MAB12211) | IL-25 | Neutralization | Block endogenous IL-25 in epithelial/ILC2 models |
| Anti-IL-17RB blocking mAb (R&D AF1207) | IL-17RB | Receptor block | Confirm IL-17RB-specific signaling |
| Idelalisib (GS-1101) | PI3K-δ | PI3K-δ inhibitor | Block IL-25-driven ILC2 proliferation |
| Tofacitinib | JAK1/JAK3 | Pan-JAK inhibitor | Indirect: block ILC2-derived cytokine signaling downstream |
| Act1 siRNA/CRISPR knockout | Act1 (TRAF3IP2) | Adaptor knockdown | Confirm Act1 dependence of IL-25 signaling |
| AMG-282 (anti-IL-33) | IL-33 | Neutralization | IL-33 negative control; isolate IL-25-specific effects |
| Anti-TSLP (Tezepelumab analog) | TSLP | Neutralization | TSLP negative control in alarmin combination studies |
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Key Research Citations
1. Fort MM, Cheung J, Yen D, et al. IL-25 induces IL-4, IL-5, and IL-13 and Th2-associated pathologies in vivo. Immunity. 2001;15(6):985–995. PMID: 11754819. https://pubmed.ncbi.nlm.nih.gov/11754819/
2. Wang YH, Angkasekwinai P, Lu N, et al. IL-25 augments type 2 immune responses by enhancing the expansion and functions of TSLP-DC-activated Th2 memory cells. J Exp Med. 2007;204(8):1837–1847. PMID: 17620363. https://pubmed.ncbi.nlm.nih.gov/17620363/
3. Moro K, Yamada T, Tanabe M, et al. Innate production of TH2 cytokines by adipose tissue-associated c-Kit+Sca-1+ lymphoid cells. Nature. 2010;463(7280):540–544. PMID: 20023630. https://pubmed.ncbi.nlm.nih.gov/20023630/
4. Howitt MR, Lavoie S, Michaudel M, et al. Tuft cells, taste-chemosensory cells, orchestrate parasite type 2 immunity in the gut. Science. 2016;351(6279):1329–1333. PMID: 26847546. https://pubmed.ncbi.nlm.nih.gov/26847546/
5. von Moltke J, Ji M, Liang HE, Locksley RM. Tuft-cell-derived IL-25 regulates an intestinal ILC2-epithelial response circuit. Nature. 2016;529(7585):221–225. PMID: 26675736. https://pubmed.ncbi.nlm.nih.gov/26675736/
6. Tait Wojno ED, Artis D, Pearce EJ. IL-25: a 'sentinel' cytokine for immune regulation of type 2 immunity. Cytokine. 2019;120:159–163. PMID: 31063911. https://pubmed.ncbi.nlm.nih.gov/31063911/
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All information is provided for research purposes only. IL-25 and related materials are research reagents for in vitro laboratory investigation. Not for use in humans or animals. Investigators should consult institutional biosafety guidelines when working with recombinant cytokines.