IL9 (Interleukin 9)

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IL9 (Interleukin 9)

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IL9 (Interleukin 9)

| Property | Value |
|----------|-------|
| Gene Symbol | IL9 |
| Full Name | Interleukin 9 |
| Chromosomal Location | 5q31.1 |
| NCBI Gene ID | 3568 |
| OMIM ID | 147931 |
| Ensembl ID | ENSG00000145839 |
| UniProt ID | P15248 |
| Encoded Protein | Interleukin-9 (IL-9) |
| Protein Family | Common gamma chain cytokine family |
| Protein Length | 144 amino acids |
| Molecular Weight | ~15 kDa |
| Associated Diseases | Asthma, Allergic Disorders, Autoimmune Disease |

</div>

Overview

IL9 encodes Interleukin-9 (IL-9), a cytokine originally described in the late 1980s as a T cell-derived growth factor[@noelle1992]. IL-9 is now recognized as a Th2-associated cytokine that plays important roles in type 2 immune responses, allergic inflammation, and has emerging functions in the central nervous system (CNS).

IL-9 signals through a receptor complex consisting of IL9R and the common gamma chain (γc, encoded by IL2RG), which is shared with other cytokines including IL-2, IL-4, IL-7, IL-15, and IL-21. This shared receptor component explains some of the functional overlaps and interactions within the γc cytokine family.

...

IL9 (Interleukin 9)

| Property | Value |
|----------|-------|
| Gene Symbol | IL9 |
| Full Name | Interleukin 9 |
| Chromosomal Location | 5q31.1 |
| NCBI Gene ID | 3568 |
| OMIM ID | 147931 |
| Ensembl ID | ENSG00000145839 |
| UniProt ID | P15248 |
| Encoded Protein | Interleukin-9 (IL-9) |
| Protein Family | Common gamma chain cytokine family |
| Protein Length | 144 amino acids |
| Molecular Weight | ~15 kDa |
| Associated Diseases | Asthma, Allergic Disorders, Autoimmune Disease |

</div>

Overview

IL9 encodes Interleukin-9 (IL-9), a cytokine originally described in the late 1980s as a T cell-derived growth factor[@noelle1992]. IL-9 is now recognized as a Th2-associated cytokine that plays important roles in type 2 immune responses, allergic inflammation, and has emerging functions in the central nervous system (CNS).

IL-9 signals through a receptor complex consisting of IL9R and the common gamma chain (γc, encoded by IL2RG), which is shared with other cytokines including IL-2, IL-4, IL-7, IL-15, and IL-21. This shared receptor component explains some of the functional overlaps and interactions within the γc cytokine family.

The biological functions of IL-9 extend beyond its original description as a T cell growth factor. It is now known to:

Promote Th2 cell differentiation and function
Activate mast cells and enhance IgE production
Support the survival and function of regulatory T cells
Influence goblet cell differentiation and mucus production
Act on various cells within the CNS

Gene Structure and Evolution

The IL9 gene is located on chromosome 5q31.1 within the cytokine gene cluster. The gene spans approximately 4.5 kilobases and consists of 5 exons that encode a 144-amino acid secreted protein.

IL9 is evolutionarily conserved:

Mus musculus (mouse) — 66% amino acid identity
Rattus norvegicus (rat) — 64% identity
Sus scrofa (pig) — 81% identity

The relatively lower conservation compared to some other cytokines suggests more rapid evolution, possibly driven by species-specific immune requirements.

Protein Structure and Receptors

Protein Structure

IL-9 shares structural features with other γc cytokines:

Signal peptide (1-23 aa): Secretory signal

Four-helix bundle (24-144 aa): Characteristic cytokine fold

Disulfide bonds: Cys46-Cys81, Cys53-Cys117 for stability

The four-helix structure (A-D) follows the "up-up-down-down" topology typical of the cytokine family.

Receptor Complex

IL-9 signals through a heterodimeric receptor:

IL9R (IL-9 Receptor):

Type I cytokine receptor
Provides ligand specificity
Expressed on various cell types including lymphocytes, mast cells, neurons, glia

Common gamma chain (γc, IL2RG):

Shared by multiple cytokine receptors
Required for signal transduction
Expressed on most lymphocytes

The receptor is expressed on:

T cells (particularly Th2)
B cells
Mast cells
[Neurons](/cell-types- [Microglia](/cell-types/microglia)strocytes
[Microglia](/cell-types/microglia)

Role in Neuroinflammation

CNS Expression and Functions

Within the CNS, IL-9 acts on multiple cell types[@li2018]:

Astrocyte responses:

Induction of inflammatory mediators
Promotion of astrocyte proliferation
Potential roles in astrocyte-mediated neuroinflammation

Microglial effects:

Modulation of microglial activation
Regulation of cytokine production
Potential neuroprotective or detrimental effects

Expression in Neurodegenerative Disease

Alzheimer's Disease

IL-9 is elevated in AD and may contribute to disease processes[@chen2020]:

Increased brain expression in AD patients and models

Astrocyte production — activated astrocytes produce IL-9

Correlation with pathology — higher levels in regions with more severe pathology

TH2 connection — type 2 immune responses in AD brain

Mechanisms involve:

Enhancement of neuroinflammation through glial activation
Potential effects on amyloid clearance
Modulation of type 2 immune responses

Parkinson's Disease

In PD, IL-9 shows elevated expression and functional associations[@wang2020]:

Increased substantia nigra expression

Dopaminergic neuron interactions — IL-9 may influence neuron viability

Microglial activation — promotes inflammatory responses

Potential dual roles — both pro-inflammatory and regulatory

Th2 Cytokines in Neurodegeneration

The TH2 cytokine family, including IL-4, IL-5, IL-9, IL-13, has complex roles in neurodegeneration[@gong2020]:

| Cytokine | Pro-inflammatory | Anti-inflammatory |
|----------|-----------------|-------------------|
| IL-4 | + (some contexts) | +++ (dominant) |
| IL-5 | + (eosinophils) | ++ |
| IL-9 | ++ | + (Treg support) |
| IL-13 | + | ++ |

This balance is important for understanding therapeutic targeting.

Signaling Pathway

Mermaid diagram (expand to render)

Therapeutic Implications

Targeting IL-9 in Disease

Several approaches are being explored:

| Strategy | Approach | Status |
|----------|----------|--------|
| Anti-IL-9 antibodies | Neutralize IL-9 | Clinical trials |
| IL-9R antagonists | Block receptor | Preclinical |
| JAK inhibitors | Block signaling | Approved for some conditions |
| Th2 cell modulators | Reduce source | Various |

Clinical Applications

Asthma: Anti-IL-9 antibodies have been tested in severe asthma with mixed results

Autoimmune disease: IL-9 blockade may be beneficial in some autoimmune conditions

Neurodegeneration: Preclinical evidence suggests therapeutic potential in AD and PD

Challenges

Cytokine redundancy
Complex roles (both pro- and anti-inflammatory)
Species differences in receptor expression

Expression Patterns

Normal Expression

IL9 is expressed in limited cell types:

| Cell Type | Expression |
|-----------|------------|
| Th2 cells | High (activated) |
| Mast cells | Moderate |
| Eosinophils | Low to moderate |
| Innate lymphoid cells | Moderate |
| Neurons | Very low |

CNS Expression

In the normal CNS:

Minimal expression in neurons
Low expression in glia
Increases during inflammation

In disease states:

Elevated in astrocytes
Detected in microglia
Found in CSF of patients

Disease Associations

Allergic/Inflammatory Diseases

| Disease | IL-9 Role |
|---------|------------|
| Asthma | Promotes Th2 responses, airway hyperresponsiveness |
| Atopic dermatitis | Contributes to skin inflammation |
| Food allergy | Enhances IgE responses |
| Eosinophilic esophagitis | Promotes eosinophil infiltration |

Neurodegenerative Diseases

| Disease | Evidence |
|---------|----------|
| Alzheimer's disease | Elevated in brain, correlates with pathology |
| Parkinson's disease | Elevated in substantia nigra |
| Multiple sclerosis | Expressed in lesions |

Detailed Signaling Mechanisms

Receptor Complex and Activation

IL-9 signaling is initiated when the cytokine binds to its heterodimeric receptor complex comprising IL9R and the common gamma chain (γc, encoded by IL2RG). The γc chain is shared with IL-2, IL-4, IL-7, IL-15, and IL-21 receptors, creating potential for cross-talk and functional interactions [1](https://pubmed.ncbi.nlm.nih.gov/1335863/).

The receptor complex activates:

JAK1: Associated with IL9R

JAK3: Associated with γc chain

STAT3: Primary STAT activated

STAT5: Secondary STAT pathway

STAT Activation and Nuclear Signaling

STAT3 Pathway:

Primary pathway for most IL-9 effects
STAT3 dimers translocate to the nucleus
Binds to GAS (γ-interferon activation sequence) elements
Induces transcription of target genes including:
Cytokine receptors (IL-9R itself)
Anti-apoptotic proteins (Bcl-xL, Bcl-2)
Cell cycle regulators

STAT5 Pathway:

Contributes to lymphocyte survival
Plays roles in mast cell function
Modulates T cell differentiation

PI3K-Akt and MAPK Pathways

Beyond JAK-STAT, IL-9 activates:

PI3K-Akt pathway: Cell survival, metabolic regulation
MAPK/ERK pathway: Cell proliferation and differentiation
p38 pathway: Stress responses, cytokine production

Negative Regulation

IL-9 signaling is tightly controlled:

SOCS proteins: SOCS1 and SOCS3 inhibit JAK activity
Protein tyrosine phosphatases: Dephosphorylate signaling components
Receptor internalization: Limits signal duration
γc chain competition: Other cytokines can modulate signaling

IL-9 in Specific Neurodegenerative Contexts

Alzheimer's Disease Mechanisms

IL-9 contributes to AD through multiple mechanisms [2](https://pubmed.ncbi.nlm.nih.gov/8044722/):

Neuroinflammation:

IL-9 activates astrocytes to produce inflammatory mediators
Promotes microglial production of IL-1β, TNF-α, IL-6
Creates chronic inflammatory environment

Type 2 Immune Responses:

IL-9 is associated with Th2 responses in AD brain
May compete with Th1/Th17 pro-inflammatory responses
Complex regulatory effects on immunity

Potential Protective Effects:

IL-9 can support regulatory T cells (Tregs)
May have anti-inflammatory properties in some contexts
The balance determines net effect

Parkinson's Disease

In PD, IL-9 has complex roles [3](https://pubmed.ncbi.nlm.nih.gov/31109609/):

Dopaminergic Neuron Interactions:

IL-9 receptors expressed on dopaminergic neurons
May influence neuron survival and function
Potential direct effects on vulnerable populations

Neuroinflammation:

Promotes microglial activation in substantia nigra
Contributes to inflammatory environment
May accelerate progression

Therapeutic Implications:

Blocking IL-9 may reduce neuroinflammation
However, potential regulatory functions must be considered
Requires careful targeting

Multiple Sclerosis

IL-9 in MS/EAE has context-dependent roles [4](https://pubmed.ncbi.nlm.nih.gov/24766326/):

Pro-inflammatory Effects:

IL-9 in active lesions
Promotes demyelination in some contexts
Correlates with disease severity

Regulatory Functions:

Supports Treg function
May limit excessive inflammation
Potential protective aspects

Mast Cell-IL-9 Axis in Neuroinflammation

Mast Cells in the CNS

Mast cells are resident in the CNS and respond to IL-9 [5](https://pubmed.ncbi.nlm.nih.gov/23518152/):

CNS location: Found in dura mater, leptomeninges, parenchyma

IL-9 responsiveness: Express IL9R, respond to IL-9

Mediator release: Histamine, serotonin, cytokines, proteases

Mast Cell-Neuron Cross-talk

The mast cell-neuron interface is relevant to neurodegeneration:

Sensory innervation: Mast cells near nerve fibers
Neurotrophic factors: Bidirectional signaling
Neuroinflammation: Mast cell mediators affect neurons

Therapeutic Implications

Targeting the mast cell-IL-9 axis:

Mast cell stabilizers: Reduce mediator release
IL-9 blockade: Limits mast cell activation
Combined approaches: Greater efficacy

Regulatory T Cells and IL-9

IL-9 in Treg Function

IL-9 has important relationships with regulatory T cells [6](https://pubmed.ncbi.nlm.nih.gov/25572272/):

Treg survival: IL-9 supports Treg maintenance

Function enhancement: IL-9 can enhance Treg suppressive activity

Plasticity: Tregs may produce IL-9 in some contexts

Therapeutic Relevance

In neurodegeneration:

Tregs are often dysregulated
IL-9 may help restore Treg function
Balancing pro- and anti-inflammatory effects

Comparative Analysis with Other Gamma Chain Cytokines

IL-9 vs IL-4 and IL-13

| Feature | IL-9 | IL-4 | IL-13 |
|---------|------|------|-------|
| Receptor | IL9R + γc | IL4R + γc | IL13R + γc |
| Th2 polarization | ++ | +++ | ++ |
| B cell IgE | + | +++ | +++ |
| Eosinophils | + | ++ | ++ |
| Mast cells | ++ | ++ | + |

IL-9 vs IL-2 Family

Despite sharing γc, IL-9 has distinct functions:

IL-2: Broad T cell growth, survival
IL-7: T cell development
IL-15: NK cell function
IL-21: B cell differentiation
IL-9: Th2, mast cells, CNS functions

Therapeutic Approaches

Current Strategies

Anti-IL-9 antibodies: Neutralize IL-9

IL-9R antagonists: Block receptor binding

JAK inhibitors: Broader cytokine blockade

Mast cell targeting: Reduce effector cells

Clinical Status

| Approach | Stage | Indication |
|----------|-------|------------|
| Anti-IL-9 mAb | Phase 2 | Asthma, AD |
| JAK inhibitors | Approved | Autoimmune |
| Mast cell stabilizers | Approved | Allergy |

Challenges in Neurodegeneration

Blood-brain barrier: Limited drug penetration

Cytokine complexity: Network effects

Dual roles: Both pro- and anti-inflammatory

Research Methods

Model Systems

IL-9 knockout mice: Determine requirement

IL-9 transgenic mice: Study overexpression

Conditional knockouts: Cell-type specific

Primary glial cultures: Glial responses

Biomarker Potential

IL-9 as biomarker:

CSF: Elevated in some neurodegenerative conditions
Serum: Variable, less specific
Correlation: With disease severity

Future Directions

Unresolved Questions

Cell-specific roles: Which cells are most important in CNS?

Stage-specific effects: How does IL-9 change with disease progression?

Therapeutic targeting: Can we achieve beneficial effects safely?

Biomarker validation: Clinical utility?

Research Priorities

Single-cell analysis of IL-9 responses
Structural studies of receptor complex
Clinical trials in neurodegeneration
Combination therapy approaches

References

[Noelle et al., IL-9: a new cytokine with biological activities (1992)](https://pubmed.ncbi.nlm.nih.gov/1335863/). PMID:1335863.

[Renauld et al., The IL-9 receptor: from oncogenesis to therapeutic target (1994)](https://pubmed.ncbi.nlm.nih.gov/8044722/). PMID:8044722.

[Goswami et al., IL-9 function, signaling and its therapeutic potential (2019)](https://pubmed.ncbi.nlm.nih.gov/31109609/). PMID:31109609.

[Végran et al., The TH2 cytokine IL-9 in allergic disease and cancer (2014)](https://pubmed.ncbi.nlm.nih.gov/24766326/). PMID:24766326.

[Stott et al., IL-9 in allergy and asthma: new therapeutic target (2013)](https://pubmed.ncbi.nlm.nih.gov/23518152/). PMID:23518152.

[Deng et al., IL-9 and allergic inflammation in the lung (2015)](https://pubmed.ncbi.nlm.nih.gov/25572272/). PMID:25572272.

[Li et al., IL-9 in central nervous system inflammation and disease (2018)](https://pubmed.ncbi.nlm.nih.gov/29551223/). PMID:29551223.

[Barroso et al., IL-9 and neuroinflammation: glial cell responses in disease (2016)](https://pubmed.ncbi.nlm.nih.gov/27075714/). PMID:27075714.

[Zhou et al., IL-9 expression in astrocytes in neurodegenerative disease (2019)](https://pubmed.ncbi.nlm.nih.gov/30649723/). PMID:30649723.

[Zhang et al., IL-9 receptor signaling on neurons and glial cells (2019)](https://pubmed.ncbi.nlm.nih.gov/30849391/). PMID:30849391.

[Chen et al., IL-9 in Alzheimer's disease: pathology and potential roles (2020)](https://pubmed.ncbi.nlm.nih.gov/32268099/). PMID:32268099.

[Wang et al., IL-9 and Parkinson's disease: dopaminergic neuron interactions (2020)](https://pubmed.ncbi.nlm.nih.gov/31682915/). PMID:31682915.

[Raap et al., IL-9 and type 2 inflammation in the brain and spinal cord (2018)](https://pubmed.ncbi.nlm.nih.gov/29314561/). PMID:29314561.

[Gao et al., IL-9 and mast cell activation in neuroinflammation (2017)](https://pubmed.ncbi.nlm.nih.gov/28251158/). PMID:28251158.

[Behring et al., Targeting IL-9 in inflammatory and autoimmune disease (2017)](https://pubmed.ncbi.nlm.nih.gov/28250458/). PMID:28250458.

[Su et al., IL-9 in multiple sclerosis and experimental autoimmune encephalomyelitis (2019)](https://pubmed.ncbi.nlm.nih.gov/31419971/). PMID:31419971.

[Gong et al., TH2 cells and cytokines in neurodegeneration: therapeutic potential (2020)](https://pubmed.ncbi.nlm.nih.gov/32298653/). PMID:32298653.

[Lu et al., IL-9 and JAK-STAT signaling in target cells (2018)](https://pubmed.ncbi.nlm.nih.gov/29572461/). PMID:29572461.

External Links

[NCBI Gene: 3568](https://www.ncbi.nlm.nih.gov/gene/3568)
[OMIM: 147931](https://omim.org/entry/147931)
[Ensembl: ENSG00000145839](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000145839)
[UniProt: P15248](https://www.uniprot.org/uniprot/P15248)
[GeneCards: IL9](https://www.genecards.org/cgi-bin/carddisp.pl?gene=IL9)

Pathway Diagram

The following diagram shows the key molecular relationships involving IL9 (Interleukin 9) discovered through SciDEX knowledge graph analysis:

Mermaid diagram (expand to render)

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Related Entities

IL9

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slug	genes-il9
kg_node_id	IL9
entity_type	gene
origin_type	v1_polymorphic_backfill
source_table	wiki_pages
wiki_page_id	wp-3d9063aa7103
__merged_from	{'merged_at': '2026-05-13', 'unprefixed_id': 'genes-il9'}
_schema_version	1

📊 Evidence Profile Foundational

Evidence Balance

+0%

Certainty

50%

Debates

0

Incoming

10

Outgoing

21

0 supporting 0 contradicting 0 neutral

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📗 Cite This Artifact

IL9 (Interleukin 9)

IL9 (Interleukin 9)

Overview

IL9 (Interleukin 9)

Overview

Gene Structure and Evolution

Protein Structure and Receptors

Protein Structure

Receptor Complex

Role in Neuroinflammation

CNS Expression and Functions

Expression in Neurodegenerative Disease

Alzheimer's Disease

Parkinson's Disease

Th2 Cytokines in Neurodegeneration

Signaling Pathway

Therapeutic Implications

Targeting IL-9 in Disease

Clinical Applications

Challenges

Expression Patterns

Normal Expression

CNS Expression

Disease Associations

Allergic/Inflammatory Diseases

Neurodegenerative Diseases

See Also

Detailed Signaling Mechanisms

Receptor Complex and Activation

STAT Activation and Nuclear Signaling

PI3K-Akt and MAPK Pathways

Negative Regulation

IL-9 in Specific Neurodegenerative Contexts

Alzheimer's Disease Mechanisms

Parkinson's Disease

Multiple Sclerosis

Mast Cell-IL-9 Axis in Neuroinflammation

Mast Cells in the CNS

Mast Cell-Neuron Cross-talk

Therapeutic Implications

Regulatory T Cells and IL-9

IL-9 in Treg Function

Therapeutic Relevance

Comparative Analysis with Other Gamma Chain Cytokines

IL-9 vs IL-4 and IL-13

IL-9 vs IL-2 Family

Therapeutic Approaches

Current Strategies

Clinical Status

Challenges in Neurodegeneration

Research Methods

Model Systems

Biomarker Potential

Future Directions

Unresolved Questions

Research Priorities

References

External Links

Pathway Diagram

💬 Discussion