| IL13 |
|---|
| Full Name | Interleukin 13 |
| Chromosome | 5q31.1 |
| NCBI Gene ID | [3605](https://www.ncbi.nlm.nih.gov/gene/3605) |
| Ensembl ID | ENSG00000169194 |
| OMIM ID | 147683 |
| UniProt ID | [P08960](https://www.uniprot.org/uniprot/P08960) |
| Protein Class | Th2 cytokine |
| Associated Diseases | Neuroinflammation, Alzheimer's Disease, Parkinson's Disease, Multiple Sclerosis, Asthma, Atopic Dermatitis |
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 1. In the brain, IL-13 primarily acts on microglia and astrocytes, influencing their activation states and the inflammatory milieu of the central nervous system.
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. 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.
This page covers IL-13's molecular biology, receptor signaling, functions in the nervous system, and implications for neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, and multiple sclerosis.
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
The promoter region contains binding sites for transcription factors including GATA3, STAT6, and NF-κB, linking IL-13 expression to Th2 cell differentiation and inflammatory signals.
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.
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
These variants may have distinct functional properties, though their biological significance remains under investigation.
IL-13 signals through two receptor complexes 1:
Type I receptor (signaling competent):
- IL13Rα1 (low affinity)
- IL4Rα (shared chain, signal transduction)
- Expression: Wide, including brain cells
- Signaling: STAT6, PI3K/Akt, MAPK
Type II receptor (decoy):
- IL13Rα2 (high affinity)
- Expression: Limited, inducible
- Function: Decoy receptor, inhibits signaling
STAT6 pathway (primary):
- Receptor binding activates JAK kinases
- STAT6 phosphorylation and dimerization
- Nuclear translocation
- Gene transcription (M2 markers, anti-inflammatory genes)
PI3K/Akt pathway:
- Cell survival signals
- Metabolic regulation
- Anti-apoptotic effects
MAPK pathway:
- Cell proliferation
- Differentiation
- Stress responses
The balance between these pathways determines the cellular outcome of IL-13 signaling.
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
IL-13 promotes Th2 differentiation in an autocrine manner and suppresses Th1/Th17 responses.
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
IL-13 is a key driver of M2 (alternative) microglial activation 3:
M2 microglia characteristics:
- Enhanced phagocytosis
- Anti-inflammatory cytokine production (IL-10, TGF-β)
- Tissue repair functions
- Reduced oxidative stress
- Neuroprotective in some contexts
The M1/M2 polarization model is now recognized as oversimplified, but IL-13 consistently shifts microglia toward a more anti-inflammatory, tissue-repair phenotype.
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
IL-13 modulates neuroinflammation through:
- Suppression of M1 microglia: Reduced pro-inflammatory cytokines
- Promotion of M2 microglia: Enhanced clearance, repair
- Treg recruitment: Regulatory T cell attraction
- BBB modulation: Effects on blood-brain barrier permeability
IL-13 affects multiple aspects of AD pathogenesis 4:
Aβ metabolism:
- Modulates microglial Aβ phagocytosis
- M2 microglia show enhanced Aβ clearance
- May reduce Aβ accumulation
- Alternative activation promotes plaque removal
Tau pathology:
- Effects on tau phosphorylation unclear
- May modulate kinase/phosphatase balance
- Neuroinflammationtau interactions
Pro-inflammatory effects (M1 context):
- When microglias are in M1 state, IL-13 can have complex effects
- May enhance some pro-inflammatory responses
Anti-inflammatory effects (M2 context):
- Dominant effect is anti-inflammatory
- Reduces IL-1β, TNF-α, IL-6 production
- Promotes neuroprotective phenotype
- May improve cognitive outcomes
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
IL-13 affects dopaminergic neuron survival through 5:
Neuroprotection mechanisms:
- M2 microglial support neuron survival
- Reduced oxidative stress
- Enhanced neurotrophic factor production
- Anti-apoptotic signaling
In vivo evidence:
- IL-13 reduces MPTP-induced dopaminergic loss
- Alters microglial morphology in SNc
- Improves behavioral outcomes in models
Connections to α-synuclein:
- M2 microglia may clear α-synuclein aggregates
- IL-13 modulates autophagy in microglia
- Effects on protein aggregation unclear
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
¶ Demyelination and Remyelination
IL-13 has complex, context-dependent roles in MS:
Demyelination phase:
- May promote some inflammatory responses
- Role in lesion formation unclear
Remyelination phase:
- Promotes oligodendrocyte differentiation
- Supports myelin repair
- Enhances astrocyte-mediated repair
EAE models:
- IL-13 administration reduces severity
- Some studies show protective effects
- May promote repair after demyelination
- 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
¶ Stroke and Brain Injury
- IL-13 increases after ischemic stroke
- Promotes M2 microglial activation
- May enhance tissue repair
- Neuroprotective in some models
- Altered IL-13 expression in ALS models
- May modulate neuroinflammation
- Unclear whether protective or harmful
- IL-13 implicated in depression
- Altered in schizophrenia
- Links to neuroinflammation hypothesis
| 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 |
- Cortex: Moderate expression
- Hippocampus: Detectable
- Basal ganglia: Variable
- White matter: Limited data
- Spinal cord: Under investigation
IL-13 expression is regulated by:
- Th2 differentiation signals (IL-4, GATA3)
- Antigen receptor engagement
- Cytokines (IL-2, IL-33)
- Epigenetic modifications
Approved anti-IL-13 biologics (non-CNS):
- Lebrikizumab: Asthma, atopic dermatitis
- Tralokinumab: Atopic dermatitis
- Dupilumab: Also targets IL-4Rα (shared)
Clinical trials:
- Asthma: FDA approved for lebrikizumab, tralokinumab
- Atopic dermatitis: Positive results
- CNS applications: Not yet in trials
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
- Systemic delivery: For BBB-disrupted states
- Intrathecal delivery: Direct CNS administration
- Gene therapy: AAV-mediated expression
- Cell-penetrant peptides: Modified IL-13 variants
- Small molecules: Downstream pathway targeting
- CSF IL-13 levels in neurological diseases
- Correlation with disease progression
- Therapeutic monitoring potential
- Primary microglial cultures
- iPSC-derived microglia and neurons
- Animal models (EAE, MPTP, APP/PS1)
- Human postmortem brain studies
- Limited CNS trials to date
- Asthma biologics being repurposed
- Combination approaches under development
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.
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- Colton CA, et al. IL-13 in Alzheimer's disease models. J Neuroinflammation. 2014
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- Brenner D, et al. M2 microglia in neurodegeneration. Nat Rev Neurosci. 2018
- Butovsky O, et al. Microglial plasticity in neurodegeneration. Nat Rev Neurol. 2019
- Cherry JD, et al. Neuroinflammation in AD. Lab Invest. 2020
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- Liddelow SA, et al. Neurotoxic reactive astrocytes. Nature. 2017
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- Vainchtein ID, et al. Astrocyte-oligodendrocyte interaction. Nat Neurosci. 2018
- Kierdorf K, et al. Microglia development. Nat Rev Neurosci. 2019
- Bachstetter AD, et al. Microglial IL-13 in aging brain. Aging Cell. 2017
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- Hammond TR, et al. Single-cell astrocyte analysis. Cell. 2019
- Zhao X, et al. Microglial dynamics in AD model. Nat Neurosci. 2017
- Suh HS, et al. Astrocyte IL-13 responses. Glia. 2020
- Zuroff L, et al. IL-13 in autoimmune disease. Front Immunol. 2019
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- Bennett FC, et al. Microglia in brain development. Neuron. 2020
- Masgrau R, et al. Cytokines in psychiatric disorders. Dialogues Clin Neurosci. 2017
- Cai W, et al. IL-13 and stroke recovery. J Cereb Blood Flow Metab. 2018
¶ Receptor Structure and Binding Kinetics
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)
Intracellular domain:
- Box 1 motif for STAT binding
- No intrinsic kinase activity
- Associates with JAKs for signaling
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)
JAK activation:
- JAK1 and JAK3 associated with IL4Rα
- Proximity-induced transphosphorylation
- Activation of kinase domains
STAT6 phosphorylation:
- STAT6 (not STAT3/5) is primary effector
- Y641 phosphorylation by JAKs
- Dimer formation via SH2 domains
- Nuclear translocation
Gene transcription:
- STAT6 binds GAS and ISRE elements
- M2-associated genes: Arg1, Ym1, Fizz1, CD206
- Anti-inflammatory mediators: IL-10, TGF-β
- Tissue repair factors
Activation:
- IRS-1/2 recruitment to IL4Rα
- PI3K recruitment and activation
- PIP3 generation
Effects:
- Cell survival signals
- Metabolic regulation
- mTOR activation
- Anti-apoptotic effects
Signaling cascades:
- Ras/Raf/MEK/ERK activation
- P38 MAPK activation
- JNK activation (cell-type dependent)
Cellular outcomes:
- Proliferation signals
- Differentiation programs
- Stress responses
¶ 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
M2 microglia undergo metabolic changes:
- Increased glycolysis
- Glutamine metabolism
- Arginine metabolism via arginase
- Fatty acid oxidation
- Metabolic support for repair functions
Monoclonal antibodies:
- Limited BBB penetration
- F(ab')2 fragments may be better
- Engineered variants under development
Recombinant IL-13:
- Short half-life in CNS
- Need for sustained delivery
- Gene therapy approaches
JAK inhibitors:
- Target downstream signaling
- Broader effects (multiple cytokines)
- Under investigation for CNS
STAT6 inhibitors:
- More selective
- Fewer side effects
- Preclinical development
Intranasal delivery:
- Direct nose-to-brain pathway
- Bypasses BBB
- Shows promise in preclinical models
Intrathecal delivery:
- Direct CNS administration
- Invasive but effective
- For severe cases
CSF IL-13 as biomarker:
- Detectable in healthy individuals
- Altered in various diseases
- Correlation with disease progression
- Therapeutic monitoring potential
Peripheral measurements:
- More accessible than CSF
- Less clear CNS relevance
- Systemic inflammation marker
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