IL1R2 Protein

IL1R2 Protein

Overview

Interleukin-1 receptor type 2 (IL1R2, CD121b) is a high-affinity decoy receptor in the interleukin-1 axis. Unlike [IL1R1](/proteins/il1r1), IL1R2 binds IL-1 ligands but does not propagate canonical pro-inflammatory signaling, so it functions as an endogenous brake on excessive cytokine activity.

IL1R2 is relevant to neurodegeneration because [interleukin-1 beta (IL-1β)](/biomarkers/interleukin-1-beta-il1b) is consistently implicated in [Alzheimer's disease](/diseases/alzheimers-disease), [Parkinson's disease](/diseases/parkinsons-disease), and related neuroinflammatory states.[@garlanda2018][@shaftel2008] Current evidence supports IL1R2 primarily as a modulator of inflammatory tone rather than a standalone disease-causal protein in CNS degeneration.[@garlanda2018][@ji2024]

IL1R2 Protein

Overview

Interleukin-1 receptor type 2 (IL1R2, CD121b) is a high-affinity decoy receptor in the interleukin-1 axis. Unlike [IL1R1](/proteins/il1r1), IL1R2 binds IL-1 ligands but does not propagate canonical pro-inflammatory signaling, so it functions as an endogenous brake on excessive cytokine activity.

IL1R2 is relevant to neurodegeneration because [interleukin-1 beta (IL-1β)](/biomarkers/interleukin-1-beta-il1b) is consistently implicated in [Alzheimer's disease](/diseases/alzheimers-disease), [Parkinson's disease](/diseases/parkinsons-disease), and related neuroinflammatory states.[@garlanda2018][@shaftel2008] Current evidence supports IL1R2 primarily as a modulator of inflammatory tone rather than a standalone disease-causal protein in CNS degeneration.[@garlanda2018][@ji2024]

<div class="infobox infobox-protein">
<div class="infobox-header">IL1R2 Protein</div>
<table>
<tr><td class="infobox-label">Protein Name</td><td>Interleukin-1 Receptor Type 2</td></tr>
<tr><td class="infobox-label">Aliases</td><td>IL-1R2, IL-1RT2, CD121b</td></tr>
<tr><td class="infobox-label">Gene</td><td><a href="/genes/il1r2">IL1R2</a></td></tr>
<tr><td class="infobox-label">UniProt ID</td><td><a href="https://www.uniprot.org/uniprotkb/P27930">P27930</a></td></tr>
<tr><td class="infobox-label">Protein Class</td><td>Type I cytokine receptor, decoy receptor</td></tr>
<tr><td class="infobox-label">Localization</td><td>Cell membrane and soluble extracellular form</td></tr>
<tr><td class="infobox-label">Primary Function</td><td>Negative regulation of IL-1 signaling</td></tr>
<tr><td class="infobox-label">Major Context</td><td>Innate immunity, neuroinflammation buffering</td></tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>
</div>

Molecular Architecture

IL1R2 is structurally related to signaling IL-1 receptors but differs in its intracellular region:

• The extracellular immunoglobulin-like domains retain strong IL-1 ligand-binding capacity.[@colotta1993]
• The intracellular tail is truncated and lacks the signaling-competent architecture needed for downstream [NF-κB](/entities/nf-kb)/MAPK activation seen with IL1R1.[@colotta1993][@mantovani1995]
• IL1R2 therefore captures ligand without initiating a full inflammatory program, creating a receptor-level sink for IL-1 family cytokines.[@mantovani1995][@garlanda2018]

Membrane and Soluble IL1R2 Forms

IL1R2 biology operates through two complementary forms:

Membrane IL1R2

• Expressed on myeloid-lineage immune cells, including monocytes and neutrophils, and inducible in inflammatory states.[@mantovani1995][@garlanda2018]
• Competes with IL1R1 for IL-1α and IL-1β binding, reducing signaling receptor occupancy.[@mantovani1995]

Soluble IL1R2 (sIL1R2)

• Generated by proteolytic shedding and/or alternative transcript processing.[@garlanda2018][@cui2003]
• Acts in extracellular space (including blood and tissue compartments) as a cytokine trap that limits IL-1 bioavailability.[@garlanda2018][@cui2003]

Signaling Logic in the IL-1 Axis

In simplified mechanistic terms:

This balance model is directly relevant to chronic neurodegenerative settings where low-grade inflammation persists for years.[@shaftel2008][@griffin1989]

Relevance to Neurodegeneration

Alzheimer's Disease Context

The IL-1 pathway is repeatedly linked to amyloid-associated neuroinflammation, glial activation, and synaptic dysfunction in AD literature.[@shaftel2008][@griffin1989] IL1R2 is not a dominant AD causal gene, but it is biologically plausible as a buffering node that can dampen IL-1 burden when induced.[@garlanda2018][@ji2024]

Clinical and translational studies of circulating IL-1 family proteins in AD support altered cytokine-receptor homeostasis, including decoy receptor behavior, although effect sizes and cohort reproducibility vary.[@licastro2000]

Parkinson's Disease Context

In PD, inflammatory activation of [microglia](/cell-types/microglia-neuroinflammation) and cytokine-network dysregulation are established contributors to neuronal stress.[@shaftel2008][@hirsch2012] IL1R2 is best interpreted as a candidate modulator in this environment rather than a validated monogenic PD driver. Mechanistically, higher effective IL1R2 activity could reduce IL-1-mediated amplification loops in vulnerable circuits (for example, nigrostriatal systems), but direct interventional proof remains limited.[@garlanda2018][@hirsch2012]

Broader Tauopathy/Proteinopathy Interpretation

Across tauopathies and synucleinopathies, the translational value of IL1R2 lies in pathway control:

• Reducing excessive IL-1 signal tone
• Potentially lowering secondary glial toxicity
• Improving immune-homeostasis set points

Biomarker and Therapeutic Considerations

Biomarker Role

sIL1R2 is measurable in plasma/serum and may reflect anti-inflammatory counter-regulation.[@cui2003][@licastro2000] In neurodegenerative cohorts, sIL1R2 should generally be interpreted alongside other inflammatory markers (for example IL-1β, IL-6, TNF family markers) rather than in isolation.[@shaftel2008][@licastro2000]

Therapeutic Strategy Space

Potential translational approaches include:

• Enhancing endogenous IL1R2-mediated buffering
• Delivering engineered decoy constructs (conceptually analogous to receptor-trap biologics)
• Combining IL-1 axis modulation with disease-specific therapies and glial-state interventions

Evidence Quality and Open Questions

Strengths

• Strong biochemical and immunology evidence for decoy receptor function.[@colotta1993][@mantovani1995][@garlanda2018]
• Robust pathway rationale linking IL-1 excess to neurodegenerative progression.[@shaftel2008][@griffin1989][@hirsch2012]

Limitations

• Limited IL1R2-specific causal evidence in human neurodegenerative disease cohorts.
• Heterogeneous study design and biomarker assays across clinical datasets.[@licastro2000]
• Unclear target-engagement thresholds for CNS-relevant IL1R2 modulation.

Priority Questions

• Which CNS and peripheral cell states most strongly regulate IL1R2 in AD/PD progression?
• Can IL1R2-guided biomarker panels stratify inflammatory endophenotypes for trials?
• What degree of IL-1 dampening preserves host defense while reducing chronic neurotoxicity?

See Also

• [IL1R2 Gene](/genes/il1r2)
• [Interleukin-1 Beta (IL-1β) - Biomarker](/biomarkers/interleukin-1-beta-il1b)
• [IL1R1 Gene](/genes/il1r1)
• [Interleukin-1 Receptor Type 1 Protein](/proteins/il1r1)
• [Neuroinflammation Pathway](/mechanisms/neuroinflammation-pathway)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [Alzheimer's Disease](/diseases/alzheimers-disease)

External Links

• [UniProt: IL1R2 (P27930)](https://www.uniprot.org/uniprotkb/P27930)
• [NCBI Gene: IL1R2](https://www.ncbi.nlm.nih.gov/gene/7850)
• [GeneCards: IL1R2](https://www.genecards.org/cgi-bin/carddisp.pl?gene=IL1R2)

References