IL-33/ST2 Signaling: From Tissue Damage to Immune Activation
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From tissue injury to immune activation
IL-33 is stored inside tissue cells and can act as an extracellular alarmin after injury. Learn how its ST2 receptor pathway works—and why detecting IL-33 does not, by itself, prove immune activation.
IL-33: an alarm already stored at tissue barriers
IL-33 has a prominent nuclear pool in epithelial, endothelial and stromal cells. Tissue injury or selected stress responses can increase extracellular availability, but intracellular abundance, extracellular concentration and receptor activation are different biological endpoints.
A local IL-33 reservoir
IL-33 can be present in intact tissue-cell nuclei without continuously activating nearby immune cells.
Injury changes availability
Release kinetics, proteolytic processing and oxidation shape the IL-33 forms available after tissue disruption.
Receptor expression matters
Membrane ST2 and IL-1RAcP permit responses in susceptible immune populations, depending on context.
How IL-33 triggers ST2-dependent responses
After ligand binding, membrane ST2 (IL1RL1) associates with IL-1 receptor accessory protein (IL-1RAcP). MyD88/IRAK-associated signaling can then engage NF-κB and MAPK pathways. Resulting cytokine and cell responses depend on the model and receptor-expressing cell type.
Tissue-cell IL-33
Nuclear reservoir in barrier-associated cells.
Extracellular IL-33
Injury, processing and oxidation affect availability.
ST2 + IL-1RAcP
Receptor engagement initiates signal transduction.
Immune-cell effects
Context-specific activity, including some ILC2 responses.
Measuring IL-33 by sandwich ELISA
An IL-33 immunoassay quantifies the antigenic forms recognized by its antibodies in supported matrices. Biological interpretation requires suitable controls and, when appropriate, complementary receptor and functional measurements.
Assay selection checklist
- Species: match human, mouse or rat samples to the appropriate assay.
- Matrix: confirm the validated sample type and collection conditions.
- Quantification: plan standards, blanks, dilutions and replicates.
- Interference: consider binding proteins and detectable IL-33 forms.
- Readouts: add functional controls when assessing ST2 pathway activity.
What ELISA can show: assay-dependent amounts of recognized IL-33 antigen in a validated sample matrix.
What ELISA cannot show alone: receptor engagement, ligand bioactivity, downstream signaling or causation.
Where the IL-33/ST2 axis is studied
Experimental questions span barrier injury, type 2 immunity and tissue remodeling. Interpret IL-33 results in the context of the particular tissue, cell populations and time course.
Airway and allergy
Examine epithelial stress and downstream immune-cell responses.
ILC2 and type 2 immunity
Study ST2-expressing cells alongside IL-5 and IL-13 endpoints.
Skin and mucosal tissues
Investigate local barrier-derived inflammatory signals.
Tissue repair
Explore context-dependent inflammatory or remodeling responses.
IL-33 ELISA kits by species
Torvigen lists separate research assays for human, mouse and rat IL-33. Review the current product documentation for sample compatibility, analytical range and protocol requirements before ordering.
Human IL-33 ELISA Kit
Catalogue reference TRV-046793-01. For immunoreactive human IL-33 research.
Explore human kit →Mouse IL-33 ELISA Kit
Catalogue reference TRV-047566-01. Match the assay to the mouse sample matrix.
Explore mouse kit →Rat IL-33 ELISA Kit
Catalogue reference TRV-049449-01. Confirm current instructions and model suitability.
Explore rat kit →IL-33 research: quick answers
Does higher IL-33 confirm ST2 activity?
No. Antigen abundance is not equivalent to receptor engagement or functional signaling.
How does soluble ST2 differ?
Membrane ST2 participates in signaling with IL-1RAcP; soluble ST2 can act as an extracellular decoy.
Can one assay cover several species?
Only where cross-species recognition is specifically validated. Use the appropriate assay reference.
What other endpoints are useful?
Depending on the model: ST2 expression, downstream cytokines, signaling markers and injury controls.
Selected research literature
- Cayrol C, Girard JP. Interleukin-33 (IL-33): A critical review of its biology and the mechanisms involved in its release as a potent extracellular cytokine. PubMed ↗
- Epithelial cell–derived cytokines: more than just signaling the alarm. JCI Review ↗
- Zylstra J et al. Quantitation of reduced IL-33 levels in human serum: mitigating interference from endogenous binding partners. PubMed ↗
Choose the assay that fits your model.
Compare species-specific IL-33 assays and confirm matrix suitability before planning measurements.
Research-use scientific content only. Illustrations are conceptual and are not experimental data. The cited literature does not validate the performance of specific Torvigen products.