# IL-31 (Interleukin-31): Complete Research Profile — IL-31RA/OSMR Receptor Complex, JAK1/JAK2/STAT3/STAT5 Signaling, Sensory Neuron Itch Biology, Skin Barrier Dysfunction, and Atopic Dermatitis Research Applications (2026)
For Research Use Only (RUO) — Not for human or veterinary use
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Introduction: IL-31 as the "Itch Cytokine"
Interleukin-31 (IL-31) is a four-helix bundle cytokine of the IL-6 superfamily, structurally related to oncostatin M (OSM), leukemia inhibitory factor (LIF), and cardiotrophin-1. Identified in 2004 by Dillon et al. through bioinformatic analysis of activated T cell cDNA libraries, IL-31 was rapidly distinguished from its cytokine relatives by a defining biological activity: potent induction of pruritus (itch) through direct action on sensory neurons.
IL-31 is produced predominantly by activated CD4⁺ T helper cells, specifically Th2-polarized cells, though Th1 cells, NKT cells, mast cells, macrophages, dendritic cells, basophils, and eosinophils also contribute under inflammatory conditions. Its receptor, a heterodimer of IL-31RA and oncostatin M receptor β (OSMRβ), is expressed on keratinocytes, sensory dorsal root ganglion (DRG) neurons, macrophages, and bronchial epithelial cells — the cellular pattern that explains IL-31's pleiotropic effects across skin, peripheral nervous system, and airway biology.
For research investigators, IL-31 occupies a unique position at the intersection of immunology and neuroscience. Its capacity to directly activate itch-sensing neurons (pruriceptors) — particularly TRPV1+ and MrgprA3+ nociceptors — makes it a key research tool for investigating neuroimmune communication in inflammatory skin conditions. Simultaneously, IL-31's effects on keratinocyte barrier gene expression and cytokine secretion make it indispensable for in vitro skin biology and atopic dermatitis (AD) research models. This profile provides the mechanistic framework and practical assay guidance for investigators working in these research areas.
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Molecular Structure and Receptor Architecture
IL-31 Protein Structure
Mature human IL-31 comprises 141 amino acids (15.7 kDa) following cleavage of a 26-residue signal peptide. The protein adopts the four-helix bundle topology characteristic of the IL-6 family, with the four α-helices (A–D) connected by loops of varying length. Human and murine IL-31 share approximately 38% amino acid identity in the mature domain — substantially lower than many other cytokines — yet the biological activities are broadly conserved. This low cross-species identity means human IL-31 does not efficiently activate murine IL-31RA (and vice versa), making species matching critical in all IL-31 research assays.
IL-31 is unusual among its cytokine family in that it is not glycosylated at the predicted N-glycosylation sites under native conditions; E. coli-derived recombinant IL-31 is therefore fully biologically active without glycosylation, simplifying reagent sourcing. The protein tends to aggregate at high concentrations; working stock solutions are typically maintained at ≤0.5 mg/mL with carrier protein (0.1% BSA) in PBS.
IL-31RA: The Defining Receptor Chain
IL-31RA (also designated GPL or gp130-like receptor) is the cytokine-selective component of the IL-31 receptor complex. It is a 662-amino-acid type I single-pass transmembrane receptor containing:
- •Extracellular cytokine-binding homology module (CHM): two fibronectin type III-like domains mediating IL-31 binding
- •Ig-like domain preceding the CHM
- •Cytoplasmic tail with Box 1 and Box 2 motifs for JAK association; Box 1 associates with JAK2
IL-31RA binds IL-31 with moderate-high affinity (Kd ~0.1–1 nM) in isolation, but fully productive signaling requires OSMRβ co-recruitment.
IL-31RA expression is the primary determinant of IL-31 responsiveness:
- •Sensory neurons (DRG): Highest expression; IL-31RA particularly enriched on small-diameter neurons co-expressing TRPV1, substance P, and CGRP — the classical itch/pain neuron population
- •Keratinocytes: Upregulated by IL-4, IL-13, and Th2 cytokine environments (a key reason IL-31 effects are amplified in atopic dermatitis-like conditions)
- •Macrophages: Constitutive low-level expression; upregulated by M2-polarizing stimuli
- •Airway epithelial cells: Expression detectable in bronchial epithelium; links IL-31 to airway hyperresponsiveness research
- •Mast cells and basophils: Low but detectable; autocrine/paracrine itch amplification potential
OSMRβ: The Shared Signal-Transducing Chain
OSMRβ (gp130 family; 979 amino acids) is shared between IL-31 and oncostatin M (OSM) receptor complexes. OSMRβ does not bind IL-31 directly; it is recruited by IL-31-bound IL-31RA and provides the primary intracellular signal-transducing capacity. The cytoplasmic tail of OSMRβ associates with JAK1 (and to some extent JAK2) and contains tyrosine residues that recruit STAT3 and STAT5 upon phosphorylation.
The requirement for OSMRβ means that IL-31 and OSM share downstream signaling partners in cells co-expressing both receptors. Investigators must account for potential OSMRβ sequestration by endogenous OSM in primary cell preparations — particularly in macrophage-rich or stromal-enriched systems where OSM may be present.
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Downstream Signaling Pathways
JAK1/JAK2 → STAT3 and STAT5
IL-31RA:OSMRβ complex activation triggers:
1. JAK2 (associated with IL-31RA Box 1) and JAK1 (associated with OSMRβ) trans-phosphorylate each other
2. Activated JAKs phosphorylate tyrosine residues on IL-31RA and OSMRβ cytoplasmic tails, creating SH2-domain docking sites
3. STAT3 (primary) and STAT5 (secondary) are recruited, phosphorylated at Tyr705 and Tyr694 respectively, dimerize, and translocate to the nucleus
4. Nuclear STAT3/STAT5 drive target gene transcription
STAT3 is the dominant IL-31 signal transducer in keratinocytes and macrophages, while in DRG neurons, both STAT3 and STAT5 contribute to IL-31-driven gene regulation. Of note, IL-31-driven STAT3 activation in keratinocytes overlaps mechanistically with IL-6 and OSM signaling, making STAT3 phosphorylation a non-unique readout — investigators should confirm IL-31RA receptor engagement (e.g., by IL-31RA surface staining or anti-IL-31RA blocking before stimulation) to attribute pSTAT3 specifically to IL-31.
MAPK Signaling
IL-31 activates ERK1/2 and p38 MAPK in keratinocytes and macrophages:
- •ERK1/2 activation contributes to keratinocyte proliferative responses to IL-31 and modulates cytokine gene transcription
- •p38 activation drives IL-31-dependent MMP expression in skin fibroblast research models and contributes to IL-31's pro-inflammatory cytokine induction cascade in keratinocytes (IL-6, TNF-α, TSLP)
PI3K/Akt Pathway
PI3K-Akt activation downstream of IL-31R contributes to:
- •Keratinocyte survival under IL-31 stimulation (Akt-driven Bad phosphorylation, Bcl-2 upregulation)
- •Proliferative responses in IL-31RA-expressing epithelial cell lines
- •Integration with mTORC1 for downstream translational control of cytokine production
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IL-31 in Sensory Neuron Biology and Itch Mechanisms
Direct Neuronal Activation: The Pruriceptive Pathway
The most distinctive and research-relevant property of IL-31 is its capacity to directly activate itch-mediating sensory neurons. Unlike many cytokines that drive itch indirectly through histamine or serotonin release from immune cells, IL-31 directly engages IL-31RA on DRG neurons, triggering:
1. Rapid calcium influx (within seconds to minutes): IL-31 activates a subset of TRPV1+ DRG neurons in calcium imaging assays; this fast response is partly STAT3-independent and may involve Src family kinase-mediated TRPV1 sensitization
2. Slower transcriptional changes (hours): JAK/STAT signaling in neurons upregulates neuropeptide genes (substance P, CGRP), ion channel sensitivity modulators, and pro-inflammatory mediator synthesis
3. Neuronal sensitization: IL-31 lowers the activation threshold of itch-mediating neurons to other stimuli (histamine, chloroquine, SLIGRL) — a form of peripheral sensitization analogous to pain sensitization by inflammatory mediators
DRG neuron IL-31 research models:
- •Mouse DRG explant cultures: Dissociated lumbar DRG neurons (L1-L5) cultured on poly-D-lysine/laminin-coated dishes. IL-31 (10–300 ng/mL) calcium imaging with Fura-2 AM or GCaMP-expressing neurons reveals the responsive subset (typically 5–20% of total neurons, enriched for small-diameter IB4−/TRPV1+ peptidergic neurons)
- •Human iPSC-derived sensory neurons: Peripheral sensory neuron differentiation protocols (NGF + NT-3 + BDNF) produce IL-31RA-expressing nociceptor-like neurons suitable for human IL-31 biology research
- •Patch-clamp electrophysiology: IL-31 pretreatment (1 hour) reduces rheobase (minimum current to evoke action potential) in small-diameter DRG neurons, confirming functional sensitization independent of calcium imaging
Neuroimmune Crosstalk: The Itch Amplification Loop
IL-31 research has illuminated a bidirectional neuroimmune communication circuit relevant to chronic itch conditions:
1. Th2 cells in inflamed skin secrete IL-31 → activates IL-31RA on sensory nerve endings
2. Activated neurons release substance P and CGRP → further mast cell and basophil degranulation
3. Mast cell-derived IL-4 upregulates IL-31RA on keratinocytes and neurons (amplification)
4. Keratinocyte TSLP and IL-33 production downstream of IL-31 → Th2 cell activation → more IL-31
This positive feedback loop helps explain the chronic, self-amplifying nature of itch in atopic dermatitis-like inflammatory states and forms the conceptual basis for investigating IL-31 pathway interventions in pruritus research models.
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IL-31 in Skin Biology
Keratinocyte Biology
Keratinocytes are the primary non-neuronal IL-31 target in skin, and their responses are substantially amplified by IL-4/IL-13 pre-conditioning (reflecting the Th2-dominant AD microenvironment). In primary normal human epidermal keratinocytes (NHEK) or immortalized lines (HaCaT, N/TERT):
IL-31 effects on keratinocyte biology:
| Response | Readout | Concentration/Time |
|---|---|---|
| pSTAT3 activation | Western blot, flow cytometry | 30–60 min, 10–100 ng/mL |
| TSLP upregulation | ELISA, qPCR | 24–48h, 50–200 ng/mL |
| IL-6, IL-8 secretion | ELISA | 24–48h |
| Filaggrin (FLG) downregulation | qPCR, Western blot | 48–72h |
| Loricrin, involucrin reduction | qPCR | 48–72h |
| Claudin-1, Claudin-4 reduction | qPCR, TEER measurement | 48–72h |
| Proliferation (Ki67, BrdU) | Flow, IHC | 48h |
| MMP-1, MMP-3 upregulation | ELISA, zymography | 24–48h |
The filaggrin and claudin downregulation is particularly research-relevant: IL-31 directly impairs skin barrier gene expression, creating the skin barrier dysfunction characteristic of atopic dermatitis. This effect is synergistic with IL-4 and IL-13 (which also downregulate filaggrin), providing a mechanistic explanation for Th2 cytokine-driven barrier dysfunction.
Important experimental caveat: HaCaT cells have substantially lower IL-31RA expression than primary NHEK and may require higher IL-31 concentrations (100–500 ng/mL) or IL-4 pre-conditioning (24–48h with 20 ng/mL IL-4 to upregulate IL-31RA) before IL-31 responses become robust. Always validate IL-31RA surface expression by flow cytometry before interpreting negative results in HaCaT cells.
3D Skin Equivalent Models
Reconstructed human epidermis (RHE) models — EpiDerm (MatTek), SkinEthic RHE, or custom primary keratinocyte-derived models — are increasingly used for IL-31 skin biology research:
- •Apical IL-31 application: 50–200 ng/mL IL-31 applied to the air-liquid interface of RHE models produces measurable filaggrin and loricrin reduction within 72 hours, visible by immunohistochemistry
- •Basal IL-31 application: Added to basal culture medium at 50–100 ng/mL; disrupts tight junction organization (ZO-1, claudin-1 by IF) and increases transepithelial water loss (TEWL) in barrier integrity assays
- •Full-thickness skin equivalents: Co-culture systems containing keratinocytes + fibroblasts ± immune cells (Th2 lymphocytes, mast cells) + sensory neurons are being developed to study neuroimmune IL-31 interactions in a more complete skin biology context
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IL-31 in Atopic Dermatitis Research
IL-31 as a Central AD Research Mediator
Atopic dermatitis is characterized by a Th2-dominant immune environment, impaired skin barrier function, and severe pruritus — all features in which IL-31 research has demonstrated direct mechanistic involvement. Key AD-relevant IL-31 research findings:
Elevated IL-31 in AD lesional skin: IL-31 mRNA and protein are markedly elevated in lesional vs. non-lesional AD skin biopsies, correlating with disease severity scores (SCORAD, EASI). Serum IL-31 is elevated in AD patients with active pruritus, though serum levels are low (pg/mL range) and require high-sensitivity immunoassays.
IL-31RA upregulation in AD skin: The Th2 cytokine environment of AD (IL-4, IL-13) upregulates IL-31RA on keratinocytes and potentially on nerve endings, amplifying IL-31 sensitivity in a disease-specific manner. This creates a paradox for in vitro models: normal skin biology assays using non-pre-conditioned keratinocytes underestimate IL-31 responses relative to the actual AD-skin environment.
Skin-AD research model design recommendations:
1. Pre-condition keratinocytes or skin equivalent models with IL-4 (20 ng/mL) + IL-13 (20 ng/mL) for 24–48 hours to establish an AD-like receptor environment before IL-31 stimulation
2. Include IL-25 and TSLP co-stimulation for a more complete Th2 innate cytokine environment
3. Measure IL-31RA surface expression by flow cytometry after pre-conditioning to confirm upregulation (expected: 2–5 fold increase vs. unstimulated NHEK)
The IL-31/TSLP/IL-33 Inflammatory Axis
IL-31 is embedded in a broader innate-adaptive cytokine network in skin inflammation research:
- •IL-31 → TSLP: IL-31 stimulates keratinocyte TSLP production (via STAT3 and NF-κB pathways); TSLP activates dendritic cells and promotes Th2 polarization → more IL-31-producing Th2 cells (feedback)
- •IL-33 → Th2/ILC2 → IL-31: IL-33 released from barrier-disrupted keratinocytes activates ILC2s and Th2 cells, promoting IL-31 secretion
- •IL-31 → sensory neuron substance P → mast cell degranulation → IL-4, histamine → Th2 amplification: The full neuroimmune itch loop
Research models examining single cytokines in isolation may miss these amplification dynamics. Multiplex co-stimulation models incorporating IL-31 + TSLP + IL-33 provide more disease-relevant outputs for AD skin biology research.
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IL-31 in Other Research Contexts
Airway Biology
IL-31RA is expressed on bronchial epithelial cells, and IL-31 is detectable in bronchoalveolar lavage fluid from allergen-challenged research models. Key IL-31 airway biology findings:
- •IL-31 promotes bronchial epithelial cell chemokine production (CCL2, CCL5, CXCL10)
- •IL-31 synergizes with IL-13 to suppress FOXJ1 and ciliated cell differentiation markers in bronchial ALI cultures — relevant for airway mucosal defense research
- •IL-31 promotes goblet cell metaplasia-associated gene upregulation in some epithelial cell systems
Hematological Contexts
Although IL-31's dominant research relevance is in skin and sensory neuron biology, IL-31RA is expressed on certain hematopoietic malignancy cell lines. IL-31 signaling has been examined in:
- •Cutaneous T cell lymphoma (CTCL): Malignant Sézary cells and mycosis fungoides cells produce IL-31, potentially creating autocrine STAT3 survival loops; IL-31 is elevated in pruritic CTCL patients
- •Hodgkin lymphoma Reed-Sternberg cells: IL-31 expression detected; role under investigation
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In Vitro Research Protocols
IL-31 STAT3 Phosphorylation in Keratinocytes
Protocol for NHEK:
1. Subculture NHEK to 70–80% confluence in KGM-Gold medium
2. Optional AD-model pre-conditioning: add IL-4 (20 ng/mL) + IL-13 (20 ng/mL) for 48 hours, then serum-starve 4 hours
3. Stimulate with IL-31 (1, 10, 50, 100 ng/mL) for 30 minutes (peak pSTAT3)
4. Lyse in RIPA + phosphatase inhibitors
5. Western blot: anti-pSTAT3 (Y705) / anti-total STAT3 / anti-IL-31RA (confirm receptor expression) / β-Actin loading control
6. Expected: robust pSTAT3 in IL-4/IL-13-preconditioned NHEK at 10–50 ng/mL IL-31; weaker or absent response in non-preconditioned NHEK at same concentrations
Filaggrin Downregulation Assay
1. Seed NHEK at 10,000/cm² in 12-well plates; grow to confluence (48–72h in KGM)
2. Differentiate: switch to high-calcium medium (1.5 mM CaCl₂) for 24 hours to induce filaggrin expression baseline
3. Add IL-31 (50–200 ng/mL) ± IL-4 pre-conditioning, 72 hours
4. Harvest RNA (RNeasy) + protein (RIPA)
5. Readouts:
- FLG mRNA by RT-qPCR (normalize to GAPDH or RPLP0)
- Filaggrin protein by Western blot (large smear at 400 kDa for precursor; 37 kDa processing products)
- Loricrin, involucrin by qPCR (parallel differentiation markers)
Expected: 40–70% reduction in FLG mRNA at 100 ng/mL IL-31 in IL-4-preconditioned differentiated NHEK vs. vehicle control.
DRG Neuron Calcium Imaging
For IL-31-driven neuronal calcium responses:
1. Prepare dissociated murine DRG neurons (or iPSC-derived sensory neurons) on PDL/laminin-coated #1.5 coverslips
2. Load with Fluo-4 AM (5 µM, 45 min, 37°C) in HEPES-buffered saline (HBS)
3. Image baseline 30 seconds on confocal or epifluorescence microscope
4. Perfuse IL-31 (100–1000 ng/mL murine; higher concentrations required than for keratinocytes due to acute acute neuronal activation threshold)
5. Positive control: 1 µM capsaicin (TRPV1 agonist) to identify TRPV1+ neuron subset
6. Quantify responder fraction: neurons showing ≥20% increase in ΔF/F₀ within 3 minutes of IL-31 addition
Note: Acute IL-31-driven calcium responses in DRG neurons are typically smaller in magnitude than capsaicin responses and may require video-rate imaging (10+ frames/second) to capture peak transients.
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Pharmacological Tools
| Tool | Target | Mechanism | Research Use |
|---|---|---|---|
| Recombinant IL-31 (human/murine species-specific) | IL-31RA/OSMRβ | Full agonist | Standard stimulation; must match species |
| Anti-IL-31 neutralizing mAb (R&D MAB2824) | IL-31 | Neutralizing antibody | Block endogenous/exogenous IL-31 |
| Anti-IL-31RA blocking mAb (R&D AF2384) | IL-31RA | Receptor-level block | Confirm IL-31RA-specific signaling |
| Tofacitinib (CP-690,550) | JAK1/JAK3 | JAK inhibitor | Downstream pSTAT3 blockade in keratinocytes |
| Ruxolitinib | JAK1/JAK2 | JAK1/2 inhibitor | Blocks IL-31 JAK2/JAK1 cascade |
| Stattic | STAT3 | STAT3 SH2 inhibitor | STAT3-specific downstream block |
| OSMR blocking antibody | OSMRβ | Blocks shared OSMRβ chain | Distinguishes IL-31 vs OSM signaling |
| HC-030031 | TRPA1 | Channel antagonist | Dissects TRPA1 from IL-31 neuronal activation |
| Capsazepine | TRPV1 | TRPV1 antagonist | Dissects TRPV1 contribution to IL-31 Ca²⁺ responses |
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Key Research Citations
1. Dillon SR, Sprecher C, Hammond A, et al. Interleukin 31, a cytokine produced by activated T cells, induces dermatitis in mice. Nat Immunol. 2004;5(7):752–760. PMID: 15184896. https://pubmed.ncbi.nlm.nih.gov/15184896/
2. Takaoka A, Arai I, Sugimoto M, et al. Expression of IL-31 gene transcripts in NC/Nga mice with atopic dermatitis. Eur J Pharmacol. 2005;516(2):180–181. PMID: 15992800. https://pubmed.ncbi.nlm.nih.gov/15992800/
3. Sonkoly E, Muller A, Lauerma AI, et al. IL-31: a new link between T cells and pruritus in atopic skin inflammation. J Allergy Clin Immunol. 2006;117(2):411–417. PMID: 16461142. https://pubmed.ncbi.nlm.nih.gov/16461142/
5. Cornelissen C, Lüscher-Firzlaff J, Baron JM, Lüscher B. Signaling by IL-31 and functional consequences. Eur J Cell Biol. 2012;91(6–7):552–566. PMID: 22341206. https://pubmed.ncbi.nlm.nih.gov/22341206/
6. Weidinger S, Novak N. Atopic dermatitis. Lancet. 2016;387(10023):1109–1122. PMID: 26377142. https://pubmed.ncbi.nlm.nih.gov/26377142/
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All information is provided for research purposes only. IL-31 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.