IL13 — Interleukin 13

IL13 — Interleukin-13

<div class="infobox infobox-gene">
<table>
<tr><th colspan="2" style="background:#f0f0f0;">IL13</th></tr>
<tr><td><b>Full Name</b></td><td>Interleukin 13</td></tr>
<tr><td><b>Chromosome</b></td><td>5q31.1</td></tr>
<tr><td><b>NCBI Gene ID</b></td><td>[3605](https://www.ncbi.nlm.nih.gov/gene/3605)</td></tr>
<tr><td><b>Ensembl ID</b></td><td>ENSG00000169194</td></tr>
<tr><td><b>OMIM ID</b></td><td>147683</td></tr>
<tr><td><b>UniProt ID</b></td><td>[P08960](https://www.uniprot.org/uniprot/P08960)</td></tr>
<tr><td><b>Protein Class</b></td><td>Th2 cytokine</td></tr>
<tr><td><b>Associated Diseases</b></td><td>Neuroinflammation, Alzheimer's Disease, Parkinson's Disease, Multiple Sclerosis, Asthma, Atopic Dermatitis</td></tr>
</table>
</div>

Pathway / Interaction Diagram

Overview

IL13 — Interleukin-13

<div class="infobox infobox-gene">
<table>
<tr><th colspan="2" style="background:#f0f0f0;">IL13</th></tr>
<tr><td><b>Full Name</b></td><td>Interleukin 13</td></tr>
<tr><td><b>Chromosome</b></td><td>5q31.1</td></tr>
<tr><td><b>NCBI Gene ID</b></td><td>[3605](https://www.ncbi.nlm.nih.gov/gene/3605)</td></tr>
<tr><td><b>Ensembl ID</b></td><td>ENSG00000169194</td></tr>
<tr><td><b>OMIM ID</b></td><td>147683</td></tr>
<tr><td><b>UniProt ID</b></td><td>[P08960](https://www.uniprot.org/uniprot/P08960)</td></tr>
<tr><td><b>Protein Class</b></td><td>Th2 cytokine</td></tr>
<tr><td><b>Associated Diseases</b></td><td>Neuroinflammation, Alzheimer's Disease, Parkinson's Disease, Multiple Sclerosis, Asthma, Atopic Dermatitis</td></tr>
</table>
</div>

Pathway / Interaction Diagram

Overview

IL13 (Interleukin-13) is a Th2-associated cytokine encoded by the IL13 gene on chromosome 5q31.1. Originally characterized for its role in allergic inflammation and tissue remodeling, IL-13 has emerged as a critical modulator of neuroinflammation and CNS immune responses[@[th2-cytokines]] [1](https://pubmed.ncbi.nlm.nih.gov/14525402/). In the brain, IL-13 primarily acts on [microglia](/cell-types/microglia-neuroinflammation) and [astrocytes](/entities/astrocytes), influencing their activation states and the inflammatory milieu of the central nervous system[@[microglia]].

IL-13 signals through a complex receptor system involving IL13Rα1, IL13Rα2, and the shared IL-4Rα chain, activating downstream pathways including STAT6, PI3K/Akt, and MAPK[@[il13-signaling]]. The balance between pro-inflammatory and anti-inflammatory effects of IL-13 varies by disease context and cell type, making it a nuanced therapeutic target [2](https://pubmed.ncbi.nlm.nih.gov/18362965/).

This page covers IL-13's molecular biology, receptor signaling, functions in the nervous system, and implications for neurodegenerative diseases including [Alzheimer's disease](/diseases/alzheimers-disease), [Parkinson's disease](/diseases/parkinsons-disease), and [multiple sclerosis](/diseases/multiple-sclerosis).

Molecular Biology

Gene Structure

The IL13 gene spans approximately 4kb on chromosome 5q31.1, within the Th2 cytokine gene cluster that also includes IL4, IL5, and IL13. The gene consists of 5 exons encoding a 146-amino acid protein (132 amino acids after signal peptide cleavage).

Gene organization:

• Exon 1: 5' UTR and signal peptide
• Exons 2-4: Coding sequence
• Exon 5: 3' UTR with regulatory elements

Protein Structure

IL-13 is a 146-amino acid secreted cytokine with a characteristic four-helix bundle fold:

| Domain | Position | Function |
|--------|----------|----------|
| Signal peptide | 1-20 | Secretory signal |
| Helix A | 21-45 | Receptor binding |
| Helix B | 46-70 | Dimer interface |
| Helix C | 71-95 | Receptor binding |
| Helix D | 96-130 | Stability |
| C-terminal tail | 131-146 | Processing |

The mature protein (amino acids 21-146) forms a disulfide-bonded homodimer. The crystal structure reveals a compact globular protein with significant similarity to IL-4, explaining their overlapping receptor usage.

Splice Variants

Several IL-13 splice variants have been identified:

• IL-13v1: Full-length isoform (146 aa)
• IL-13v2: Truncated form with altered C-terminus
• IL-13ΔE4: Exon 4 deletion variant

Receptor System

Receptor Complexes

IL-13 signals through two receptor complexes [1](https://pubmed.ncbi.nlm.nih.gov/14525402/):

Type I receptor (signaling competent):

• IL13Rα1 (low affinity)
• IL4Rα (shared chain, signal transduction)
• Expression: Wide, including brain cells
• Signaling: STAT6, PI3K/Akt, MAPK

• IL13Rα2 (high affinity)
• Expression: Limited, inducible
• Function: Decoy receptor, inhibits signaling

Signaling Pathways

STAT6 pathway (primary):

PI3K/Akt pathway:

• Cell survival signals
• Metabolic regulation
• Anti-apoptotic effects

• Cell proliferation
• Differentiation
• Stress responses

Function in the Immune System

Th2 Cell Polarization

IL-13 is produced primarily by:

• CD4+ Th2 cells: Major source in adaptive immunity
• CD8+ Tc2 cells: Cytotoxic Th2 subset
• NKT cells: Innate-like T cells
• Basophils and eosinophils: Early sources
• Some neurons: CNS production reported

Effector Functions

Key effector functions include:

• B cell class switching: Promotes IgE production
• Eosinophil recruitment: Via eotaxin induction
• M2 macrophage polarization: Alternative activation
• Fibrosis: Stimulates collagen production
• Mucus production: Airway goblet cell hyperplasia

Functions in the Central Nervous System

Microglial Polarization

IL-13 is a key driver of M2 (alternative) microglial activation [3](https://pubmed.ncbi.nlm.nih.gov/21525280/):

M2 microglia characteristics:

• Enhanced phagocytosis
• Anti-inflammatory cytokine production (IL-10, TGF-β)
• Tissue repair functions
• Reduced oxidative stress
• Neuroprotective in some contexts

Astrocyte Modulation

IL-13 affects astrocytes in multiple ways:

• GLT-1 expression: Modulates glutamate uptake
• Cytokine production: Alters inflammatory milieu
• Proliferation: Can promote astrocyte growth
• Wound repair: Enhances scar formation

Neuroinflammation Regulation

IL-13 modulates neuroinflammation through:

Role in Alzheimer's Disease

Amyloid Pathology

IL-13 affects multiple aspects of AD pathogenesis [4](https://pubmed.ncbi.nlm.nih.gov/25452108/):

Aβ metabolism:

• Modulates microglial Aβ phagocytosis
• M2 microglia show enhanced Aβ clearance
• May reduce Aβ accumulation
• Alternative activation promotes plaque removal

• Effects on tau phosphorylation unclear
• May modulate kinase/phosphatase balance
• [Neuroinflammation](/mechanisms/neuroinflammation)tau interactions

Neuroinflammation

Pro-inflammatory effects (M1 context):

• When microglias are in M1 state, IL-13 can have complex effects
• May enhance some pro-inflammatory responses

• Dominant effect is anti-inflammatory
• Reduces IL-1β, TNF-α, IL-6 production
• Promotes neuroprotective phenotype
• May improve cognitive outcomes

Therapeutic Implications

IL-13 as a therapeutic target in AD:

• Enhancement strategies: Deliver IL-13 or enhance signaling
• Inhibition strategies: Block in specific contexts
• Challenge: Context-dependent effects
• Current status: Preclinical stages

Role in Parkinson's Disease

Dopaminergic Neuron Survival

IL-13 affects dopaminergic neuron survival through [5](https://pubmed.ncbi.nlm.nih.gov/26119118/):

Neuroprotection mechanisms:

• M2 microglial support neuron survival
• Reduced oxidative stress
• Enhanced neurotrophic factor production
• Anti-apoptotic signaling

• IL-13 reduces MPTP-induced dopaminergic loss
• Alters microglial morphology in SNc
• Improves behavioral outcomes in models

Alpha-Synuclein Pathology

Connections to α-synuclein:

• M2 microglia may clear α-synuclein aggregates
• IL-13 modulates autophagy in microglia
• Effects on protein aggregation unclear

Neuroinflammation

In PD, IL-13 generally exerts beneficial effects:

• Shifts microglia toward M2 phenotype
• Reduces pro-inflammatory cytokine production
• May protect dopaminergic neurons
• Therapeutic potential under investigation

Role in Multiple Sclerosis

Demyelination and Remyelination

IL-13 has complex, context-dependent roles in MS:

Demyelination phase:

• May promote some inflammatory responses
• Role in lesion formation unclear

• Promotes oligodendrocyte differentiation
• Supports myelin repair
• Enhances astrocyte-mediated repair

• IL-13 administration reduces severity
• Some studies show protective effects
• May promote repair after demyelination

Therapeutic Approaches

• IL-13 as therapeutic agent: Under investigation
• Anti-IL-13 antibodies: Used in asthma (lebolizumab, tralokinumab)
• CNS delivery challenges: Blood-brain barrier
• Combination approaches: With other immunomodulators

Role in Other Neurological Conditions

Stroke and Brain Injury

• IL-13 increases after ischemic stroke
• Promotes M2 microglial activation
• May enhance tissue repair
• Neuroprotective in some models

Amyotrophic Lateral Sclerosis

• Altered IL-13 expression in ALS models
• May modulate neuroinflammation
• Unclear whether protective or harmful

Psychiatric Disorders

• IL-13 implicated in depression
• Altered in schizophrenia
• Links to neuroinflammation hypothesis

Expression Patterns

Cellular Expression

| Cell Type | Expression Level | Function |
|-----------|------------------|----------|
| Th2 cells | High | Effector cytokine |
| Microglia | Moderate | M2 polarization |
| Astrocytes | Low-Moderate | Modulation |
| Neurons | Low | Possible production |
| Endothelial cells | Variable | BBB regulation |

Brain Region Expression

• Cortex: Moderate expression
• Hippocampus: Detectable
• Basal ganglia: Variable
• White matter: Limited data
• Spinal cord: Under investigation

Regulation

IL-13 expression is regulated by:

• Th2 differentiation signals (IL-4, GATA3)
• Antigen receptor engagement
• Cytokines (IL-2, IL-33)
• Epigenetic modifications

Therapeutic Targeting

Current Clinical Applications

Approved anti-IL-13 biologics (non-CNS):

• Lebrikizumab: Asthma, atopic dermatitis
• Tralokinumab: Atopic dermatitis
• Dupilumab: Also targets IL-4Rα (shared)

• Asthma: FDA approved for lebrikizumab, tralokinumab
• Atopic dermatitis: Positive results
• CNS applications: Not yet in trials

CNS Delivery Challenges

The major challenge for neurotherapeutics:

• Blood-brain barrier: Limits CNS delivery
• BBB disruption: May allow entry in some conditions
• Intrathecal delivery: Under investigation
• Engineered biologics: Enhanced BBB penetration

Potential Strategies

Research Directions

Biomarkers

• CSF IL-13 levels in neurological diseases
• Correlation with disease progression
• Therapeutic monitoring potential

Model Systems

• Primary microglial cultures
• iPSC-derived microglia and neurons
• Animal models (EAE, MPTP, APP/PS1)
• Human postmortem brain studies

Clinical Trials

• Limited CNS trials to date
• Asthma biologics being repurposed
• Combination approaches under development

Cross-Links to NeuroWiki Pages

Related Mechanisms

• [Neuroinflammation](/mechanisms/neuroinflammation)
• [Microglial Activation](/mechanisms/microglial-activation)
• [Cytokine Signaling in Neurodegeneration](/mechanisms/cytokine-signaling)
• [Blood-Brain Barrier Dysfunction](/mechanisms/blood-brain-barrier)

Related Cell Types

• [Microglia - Neuroinflammation](/cell-types/microglia-neuroinflammation)
• [Astrocytes](/entities/astrocytes)
• [Oligodendrocytes](/entities/oligodendrocytes)

Related Diseases

• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [Multiple Sclerosis](/diseases/multiple-sclerosis)
• [Amyotrophic Lateral Sclerosis](/diseases/als)

Summary

IL-13 is a Th2 cytokine with important functions in both peripheral immunity and CNS biology. In the brain, IL-13 primarily promotes M2 microglial activation, generally exerting anti-inflammatory and potentially neuroprotective effects. In Alzheimer's disease, the role is context-dependent but M2 microglia may enhance amyloid clearance. In Parkinson's disease, IL-13 shows promise in protecting dopaminergic neurons. The therapeutic modulation of IL-13 signaling faces challenges related to CNS delivery, but various strategies are under investigation.

Key References

External Resources

• [NCBI Gene — IL13](https://www.ncbi.nlm.nih.gov/gene/3605)
• [UniProt — IL-13 (P08960)](https://www.uniprot.org/uniprot/P08960)
• [OMIM — IL13](https://www.omim.org/entry/147683)
• [Human Protein Atlas — IL13](https://www.proteinatlas.org/gene/IL13)
• [Cytokine database — IL13](https://www.cellsignal.com/)
• [Reactome — IL-13 signaling](https://reactome.org/REACTOME/ID)

Receptor Structure and Binding Kinetics

IL13Rα1 Structure

IL13Rα1 is a type I transmembrane protein with extracellular, transmembrane, and intracellular domains:

Extracellular domain:

• Four conserved cysteine residues forming disulfide bonds
• Fibronectin type III repeats for cytokine binding
• WSXWS motif characteristic of cytokine receptor family
• Low affinity for IL-13 alone (Kd ~ 10-50 nM)

• Box 1 motif for STAT binding
• No intrinsic kinase activity
• Associates with JAKs for signaling

IL13Rα2 Structure

IL13Rα2 has distinct properties from IL13Rα1:

• Shorter cytoplasmic tail (no signaling capacity)
• High affinity for IL-13 (Kd ~ 1 nM)
• Acts primarily as decoy receptor
• Inducible expression (NF-κB responsive)

Intracellular Signaling Cascade

JAK/STAT Pathway

JAK activation:

• JAK1 and JAK3 associated with IL4Rα
• Proximity-induced transphosphorylation
• Activation of kinase domains

• STAT6 (not STAT3/5) is primary effector
• Y641 phosphorylation by JAKs
• Dimer formation via SH2 domains
• Nuclear translocation

• STAT6 binds GAS and ISRE elements
• M2-associated genes: Arg1, Ym1, Fizz1, CD206
• Anti-inflammatory mediators: IL-10, TGF-β
• Tissue repair factors

PI3K/Akt Pathway

Activation:

• IRS-1/2 recruitment to IL4Rα
• PI3K recruitment and activation
• PIP3 generation

• Cell survival signals
• Metabolic regulation
• mTOR activation
• Anti-apoptotic effects

MAPK Pathway

Signaling cascades:

• Ras/Raf/MEK/ERK activation
• P38 MAPK activation
• JNK activation (cell-type dependent)

• Proliferation signals
• Differentiation programs
• Stress responses

M2 Microglia: Detailed Mechanisms

Markers and Functions

Classical M2 markers:

• CD206 (mannose receptor): Enhanced phagocytosis
• Arg1 (arginase-1): Polyamine synthesis, immunosuppression
• Ym1: Chitinase-like protein, tissue repair
• Fizz1 (Relm-α): Insulin resistance, wound healing
• CD163: Hemoglobin scavenger receptor

Metabolic Reprogramming

M2 microglia undergo metabolic changes:

• Increased glycolysis
• Glutamine metabolism
• Arginine metabolism via arginase
• Fatty acid oxidation
• Metabolic support for repair functions

Therapeutic Delivery Strategies

Biological Delivery

Monoclonal antibodies:

• Limited BBB penetration
• F(ab')2 fragments may be better
• Engineered variants under development

• Short half-life in CNS
• Need for sustained delivery
• Gene therapy approaches

Small Molecule Approaches

JAK inhibitors:

• Target downstream signaling
• Broader effects (multiple cytokines)
• Under investigation for CNS

• More selective
• Fewer side effects
• Preclinical development

Alternative Routes

Intranasal delivery:

• Direct nose-to-brain pathway
• Bypasses BBB
• Shows promise in preclinical models

• Direct CNS administration
• Invasive but effective
• For severe cases

Biomarker Potential

Cerebrospinal Fluid

CSF IL-13 as biomarker:

• Detectable in healthy individuals
• Altered in various diseases
• Correlation with disease progression
• Therapeutic monitoring potential

Blood

Peripheral measurements:

• More accessible than CSF
• Less clear CNS relevance
• Systemic inflammation marker

Key References (Continued)

Pathway Diagram

The following diagram shows the key molecular relationships involving IL13 — Interleukin 13 discovered through SciDEX knowledge graph analysis: