IL1R2 Human

What is the molecular structure of IL1R2 and how does it differ from other IL-1 receptors?

IL1R2 differs fundamentally from other IL-1 receptors due to its lack of the intracellular Toll/IL-1R (TIR) domain required for signal transduction. This structural characteristic enables IL1R2 to act as a decoy receptor that binds IL-1 without initiating downstream signaling cascades .

Key structural characteristics include:

• Extracellular domain that binds IL-1α and IL-1β with high affinity

• Transmembrane domain for cell surface expression

• Absence of the cytoplasmic TIR domain essential for signaling

• Ability to form complexes with IL-1RAcP (IL-1R3)

The absence of the TIR domain is particularly significant as it enables IL1R2 to function as a molecular trap for both the ligands (IL-1α/β) and the signaling accessory protein (IL-1RAcP), effectively inhibiting IL-1 signaling through multiple mechanisms simultaneously .

What are the primary mechanisms through which IL1R2 regulates IL-1 signaling?

IL1R2 regulates IL-1 signaling through several distinct mechanisms:

• As a membrane-bound receptor:

  • Acts as a dominant negative molecule by sequestering IL-1R3 (IL-1RAcP), preventing formation of the signaling-competent IL-1R1/IL-1R3 complex

  • Competes with IL-1R1/IL-1R3 for binding to IL-1α and IL-1β

• As a soluble receptor (sIL-1R2):

  • Generated through enzymatic cleavage by ADAM17 or alternative splicing

  • Binds IL-1α and IL-1β in the bloodstream

  • Prevents pro-IL-1β processing by binding to it and preventing caspase-1 cleavage

  • Forms complexes with soluble IL-1R3, which increases binding affinity for the ligands

• As an intracellular molecule:

  • Interacts with pro-IL-1α in the cytosol

  • Prevents enzymatic cleavage of pro-IL-1α by calpain and other inflammatory proteases

  • This complex can be disrupted by caspase-1, allowing for IL-1α release during inflammation

This multi-level regulation makes IL1R2 a powerful and versatile inhibitor of IL-1 signaling across different cellular compartments.

How is IL1R2 expression regulated in different cell types?

IL1R2 expression is tightly controlled and varies significantly depending on cell type, activation state, and environmental cues:

• Cell type-specific expression:

  • High expression in neutrophils, monocytes, macrophages, dendritic cells, and B cells

  • Expression in epithelial cells, particularly in the differentiated compartment of colonic crypts

  • Expression in regulatory T cells (Tregs) in specific contexts

• Regulation by polarization signals:

  • Anti-inflammatory stimuli (IL-4, IL-13, IL-10, IL-27, glucocorticoids) upregulate IL1R2

  • Pro-inflammatory stimuli (LPS, IFNγ, TNFα) downregulate IL1R2

  • Chemoattractants and reactive oxygen intermediates decrease expression

• Developmental regulation:

  • In colonic epithelium, IL1R2 expression follows a gradient along the crypt

  • Higher expression in the upper half (differentiated epithelial cells)

  • Lower expression in the lower crypt (stem cell compartment)

  • Expression increases as epithelial stem cells differentiate

• Pathway-specific regulation:

  • Negatively regulated by Wnt/β-catenin signaling in colonic crypts

  • Induced by IL-33 in Group 2 Innate lymphoid cells (ILC2s) as a negative feedback mechanism

This complex regulation enables precise control of IL-1 signaling in different physiological and pathological contexts.

What methods are commonly used to detect and quantify IL1R2 expression?

Researchers employ several complementary techniques to detect and quantify IL1R2 expression:

• Transcriptional analysis:

  • Quantitative PCR (qPCR) for measuring IL1R2 mRNA levels

  • Microarray analysis for comparative expression studies

  • RNA sequencing (RNA-seq) for comprehensive transcriptional profiling

  • Single-cell RNA sequencing (scRNA-seq) for cell-specific expression patterns

• Protein detection methods:

  • Immunofluorescence for cellular and tissue localization

  • Flow cytometry for quantifying cell surface expression

  • Western blotting for total protein levels

  • ELISA for measuring soluble IL1R2 in serum, plasma, or culture supernatants

• Functional assays:

  • Isolation of epithelial crypts for ex vivo culture and analysis

  • T-cell cultures stimulated with biopsy supernatants

  • Cytokine production assays (e.g., IL-1β-dependent cytokine responses)

• Combined approaches:

  • Single-cell RNA-seq with TCR sequencing for clonality studies

  • Multi-parameter flow cytometry for identifying IL1R2+ cell subsets

For comprehensive assessment, researchers typically combine multiple techniques to analyze both transcriptional and protein expression across different experimental conditions.

What is the role of epithelial IL1R2 in intestinal homeostasis during ulcerative colitis remission?

Epithelial IL1R2 serves as a critical homeostatic regulator during remission of ulcerative colitis (UC), acting through several coordinated mechanisms:

• Expression pattern in UC phases:

  • Significantly upregulated (>5-fold) in UC patients in remission compared to active disease

  • Overexpressed (>2-fold) compared to non-IBD controls and uninvolved segments

  • This contrasts with IL1B, IL1A, IL1RAP, and IL1R1 genes, which are upregulated during active inflammation

• Cellular source in remitting mucosa:

  • Epithelial cells are the primary source of increased IL1R2 during remission

  • Expression follows a gradient along colonic crypts, with higher expression in differentiated cells

  • Negatively regulated by Wnt/β-catenin signaling in colonic crypts

• Functional significance:

  • Blocking IL1R2 in isolated colonic crypt cultures from UC patients in remission increases IL-1β-dependent production of inflammatory cytokines

  • Similar effects observed in T-cell cultures stimulated with biopsy supernatant from UC patients in remission

  • Acts as a counterbalance to low persistent or locally arising IL-1β production in chronic UC patients

• Protein secretion:

  • Soluble IL1R2 secretion is elevated specifically in the involved mucosa of UC patients in remission

  • This contrasts with IL-1β and IL-1Ra, which show highest secretion in active disease

These findings suggest that epithelial IL1R2 functions as an endogenous anti-inflammatory mechanism that helps maintain remission in UC by dampening residual IL-1 signaling. The gradient expression along colonic crypts and its regulation during epithelial differentiation point to a developmentally programmed mechanism for inflammatory control.

How does IL1R2 expression correlate with disease progression in different inflammatory conditions?

IL1R2 expression demonstrates distinct patterns across various inflammatory conditions, often serving as both a biomarker and functional regulator:

• Ulcerative colitis (UC):

  • Highest expression during remission phases

  • Lower expression during active inflammation

  • Negatively correlates with IL1R1 expression (rho=-0.43)

  • Positively correlates with IL1RN (rho=0.53)

  • Serum levels do not correlate with disease activity, unlike tissue expression

• Infectious diseases:

  • Marks a subset of CD14+, HLA-DR low exhausted monocytes in sepsis

  • Similar IL1R2+ monocytes expand in COVID-19 patients

  • These IL1R2+ cells show functional exhaustion with poor TNFα production upon LPS stimulation

  • Originate from bone marrow mononuclear cells exposed to pathogen-associated molecular patterns

• Arthritis and bone disorders:

  • Reduced expression in arthritis and osteoarthritis

  • Poor expression in large osteoclasts involved in exacerbation of bone loss

  • Transplantation of sIL1R2-secreting cells ameliorates collagen-induced arthritis

  • IL1R2-deficient mice show increased susceptibility to arthritis with enhanced production of inflammatory mediators (IL-6, CXCL2, NOS2, IL-1β)

• Neuroinflammation:

  • Upregulated in microglial cells and brain endothelial cells during CNS inflammation

  • Attenuates inflammation in experimental models of IL-1β-induced neurotoxicity

  • Functions in cerebral ischemia and kainic acid-induced inflammation

• Metabolic inflammation:

  • Downregulated in hyperlipidemic patients

  • Reduced expression in monocytes/macrophages exposed to modified lipoproteins

These expression patterns suggest IL1R2 serves as a compensatory anti-inflammatory mechanism that may be inadequate in certain conditions, pointing to potential therapeutic opportunities through IL1R2 augmentation.

What are the molecular mechanisms regulating IL1R2 shedding and soluble IL1R2 production?

The production of soluble IL1R2 (sIL1R2) involves distinct molecular processes that are precisely regulated under different conditions:

• Enzymatic cleavage mechanism:

  • Primary mechanism involves metalloproteinase ADAM17 (a disintegrin and metalloproteinase 17)

  • ADAM17 cleaves membrane-bound IL1R2 to release the soluble form

  • This enzymatic cleavage is activated by specific pro-inflammatory stimuli:

    • TNFα

    • LPS (lipopolysaccharide)

    • Leukotriene B4

    • fMLF (formyl-methionyl-leucyl-phenylalanine)

• Alternative splicing:

  • Alternative mRNA splicing represents a secondary mechanism for sIL1R2 generation

  • Results in direct production of the soluble form without requiring enzymatic cleavage

  • Regulation of this alternative splicing pathway is less well characterized

• Functional interactions of sIL1R2:

  • Circulates in bloodstream at significant levels

  • Binds IL-1α and IL-1β with high affinity

  • Interacts with pro-IL-1β, preventing its enzymatic cleavage by caspase-1

  • Forms complexes with soluble IL-1R3 (sIL-1R3), which circulates at high concentrations (~300ng/ml)

  • The sIL1R2/sIL-1R3 complex shows increased binding affinity for IL-1 ligands

• Cellular regulation patterns:

  • "M2" anti-inflammatory stimuli increase IL1R2 expression and potentially shedding

  • "M1" pro-inflammatory molecules generally decrease IL1R2 expression but can activate ADAM17

  • This creates a complex regulatory balance depending on the inflammatory milieu

Understanding these molecular mechanisms provides insights for therapeutic approaches targeting IL1R2 shedding to modulate IL-1 signaling in inflammatory diseases.

How does the interaction between IL1R2 and other components of the IL-1 system influence inflammatory responses?

The complex interplay between IL1R2 and other IL-1 system components creates a sophisticated regulatory network:

• Interactions with signaling receptors:

  • Sequesters IL-1R3 (IL-1RAcP), preventing formation of functional IL-1R1/IL-1R3 signaling complexes

  • Negatively correlates with IL-1R1 expression in ulcerative colitis mucosa (rho=-0.43)

  • This competitive mechanism reduces the signaling capacity of the system

• Interactions with IL-1 ligands:

  • Binds IL-1α and IL-1β with high affinity

  • Unique ability to interact with pro-IL-1β, preventing its processing

  • Interacts with cell-surface pro-IL-1α (csIL-1α) in macrophages

  • Together with glycosylphosphatidylinositol (GPI), anchors csIL-1α on plasma membrane

  • IL-1R2-deficient macrophages display low levels of csIL-1α

• Coordination with IL-1Ra:

  • IL-1Ra (IL-1 receptor antagonist) represents a complementary negative regulator

  • Acts as a competitive inhibitor preventing IL-1 interaction with IL-1R1

  • Positive correlation between IL1R2 and IL1RN expression in UC (rho=0.53)

  • Different expression kinetics suggest distinct biological roles:

    • IL-1Ra predominantly functions as a soluble inhibitor

    • IL1R2 acts at multiple levels (membrane, soluble, intracellular)

• Influence on inflammatory cell polarization:

  • Expression regulated by polarization signals

  • "M2" anti-inflammatory stimuli increase IL1R2

  • "M1" pro-inflammatory stimuli decrease IL1R2

  • This creates a feedback loop where polarization state influences IL-1 sensitivity

• Impact on downstream inflammatory mediators:

  • Blocking IL1R2 in UC remission tissue increases production of inflammation-related cytokines

  • IL1R2-deficient macrophages produce more IL-6, CXCL2, NOS2, and IL-1β

  • In osteoarthritis, sIL1R2 inhibits proteoglycan biosynthesis, nitric oxide (NO) and prostaglandin E2 (PGE2) production

This intricate web of interactions allows for fine-tuning of inflammatory responses across different tissues and disease states.

What experimental approaches can be used to study IL1R2 function in primary human cells and tissues?

Investigating IL1R2 function in primary human samples requires sophisticated experimental approaches:

• Ex vivo tissue culture systems:

  • Colonic crypt isolation and culture from patient biopsies

  • Comparison between different disease states (active UC, remission UC, control)

  • Blocking experiments using anti-IL1R2 antibodies

  • Measurement of cytokine production in response to IL-1β stimulation

• Primary epithelial organoid cultures:

  • Isolation and culture of colonic stem cells (CoSCs)

  • Differentiation protocols to study IL1R2 regulation

  • Manipulation of Wnt/β-catenin signaling to assess effects on IL1R2 expression

  • Genetic modification approaches (siRNA, CRISPR) to modulate IL1R2 levels

• T-cell stimulation assays:

  • Isolation of T cells from patient blood

  • Culture with biopsy supernatants from different patient groups

  • Addition of IL1R2 blocking antibodies or recombinant sIL1R2

  • Analysis of T-cell activation and cytokine production

• Single-cell analysis approaches:

  • scRNA-seq combined with TCR sequencing for regulatory T cells

  • Analysis of IL1R2+ cell clonality in different conditions

  • Identification of unique transcriptional signatures in IL1R2+ cells

• Immunofluorescence and imaging techniques:

  • Multi-color immunofluorescence to identify IL1R2+ cell populations

  • Co-staining with markers like Ep-CAM (epithelial), CD45 (immune cells)

  • Quantification of IL1R2+ cells across tissue compartments

  • Analysis of IL1R2 expression gradients along crypts

• Protein interaction studies:

  • Co-immunoprecipitation of IL1R2 with binding partners

  • Analysis of IL1R2/IL-1R3 complex formation

  • Investigation of interactions with IL-1 ligands

These methodologies enable comprehensive analysis of IL1R2 biology in primary human samples, providing insights into its role in health and disease.