IL-10 Protein

IL-10 Protein — Interleukin-10

<div class="infobox infobox-protein">
<table>
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">Interleukin-10 (IL-10)</th></tr>
<tr><td><strong>Protein Name</strong></td><td>Interleukin-10</td></tr>
<tr><td><strong>Gene Symbol</strong></td><td>[IL10](/genes/il10)</td></tr>
<tr><td><strong>UniProt ID</strong></td><td><a href="https://www.uniprot.org/uniprot/P08917" target="_blank">P08917</a></td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>~18 kDa (monomer), ~36 kDa (homodimer)</td></tr>
<tr><td><strong>Subcellular Localization</strong></td><td>Secreted (extracellular)</td></tr>
<tr><td><strong>Protein Family</strong></td><td>IL-10 cytokine family (class 2 cytokines)</td></tr>
<tr><td><strong>Brain Expression</strong></td><td>[Microglia](/cell-types/microglia-neuroinflammation), astrocytes, neurons, Tregs</td></tr>
<tr><td><strong>Receptor</strong></td><td>IL-10R1 (CDW210a) + IL-10R2 (CRFB4)</td></tr>
<tr><td><strong>Signaling Pathway</strong></td><td>JAK-STAT3 (primary), PI3K-AKT, MAPK</td></tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/atherosclerosis" style="color:#ef9a9a">Atherosclerosis</a>, <a href="/wiki/cancer" style="color:#ef9a9a">Cancer</a>, <a href="/wiki/carcinoma" style="color:#ef9a9a">Carcinoma</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7"

IL-10 Protein — Interleukin-10

<div class="infobox infobox-protein">
<table>
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">Interleukin-10 (IL-10)</th></tr>
<tr><td><strong>Protein Name</strong></td><td>Interleukin-10</td></tr>
<tr><td><strong>Gene Symbol</strong></td><td>[IL10](/genes/il10)</td></tr>
<tr><td><strong>UniProt ID</strong></td><td><a href="https://www.uniprot.org/uniprot/P08917" target="_blank">P08917</a></td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>~18 kDa (monomer), ~36 kDa (homodimer)</td></tr>
<tr><td><strong>Subcellular Localization</strong></td><td>Secreted (extracellular)</td></tr>
<tr><td><strong>Protein Family</strong></td><td>IL-10 cytokine family (class 2 cytokines)</td></tr>
<tr><td><strong>Brain Expression</strong></td><td>[Microglia](/cell-types/microglia-neuroinflammation), astrocytes, neurons, Tregs</td></tr>
<tr><td><strong>Receptor</strong></td><td>IL-10R1 (CDW210a) + IL-10R2 (CRFB4)</td></tr>
<tr><td><strong>Signaling Pathway</strong></td><td>JAK-STAT3 (primary), PI3K-AKT, MAPK</td></tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/atherosclerosis" style="color:#ef9a9a">Atherosclerosis</a>, <a href="/wiki/cancer" style="color:#ef9a9a">Cancer</a>, <a href="/wiki/carcinoma" style="color:#ef9a9a">Carcinoma</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">264 edges</a></td>
</tr>
</table>
</div>

Overview

Interleukin-10 (IL-10) is a potent anti-inflammatory and immunomodulatory cytokine produced by a wide range of immune and non-immune cells, including [microglia](/cell-types/microglia-neuroinflammation), [astrocytes](/entities/astrocytes), neurons, regulatory T cells (Tregs), B cells, and macrophages[@saraiva2020]. As a cornerstone of the immune system's negative feedback mechanisms, IL-10 suppresses pro-inflammatory cytokine production, inhibits antigen presentation by myeloid cells, and promotes the development of regulatory immune populations. In the context of neurodegenerative diseases, IL-10 has emerged as a critical counterbalance to the chronic neuroinflammation that drives [Alzheimer's disease](/diseases/alzheimers-disease) (AD) and [Parkinson's disease](/diseases/parkinsons-disease) (PD) progression[@zhou2022].

Unlike classical pro-inflammatory cytokines, IL-10 generally does not induce cell proliferation or direct cytotoxicity. Instead, it functions primarily to de-escalate immune responses once they have been initiated, preventing collateral damage to host tissues. However, the pleiotropic nature of IL-10 — its effects vary by cell type, concentration, and disease context — makes it a complex therapeutic target[@thompson2023]. In neurodegeneration, the key questions are whether insufficient IL-10 signaling contributes to disease onset, and whether augmenting IL-10 could slow progression without causing harmful immunosuppression.

Structure and Biophysics

Primary and Quaternary Structure

Human IL-10 is a non-covalent homodimer composed of two 160-amino acid monomers (approximately 18 kDa each), yielding a mature protein of approximately 36 kDa[@walter2021]. Each monomer adopts a characteristic four-helix bundle fold (经典的Class 2 cytokine fold) shared by other members of the IL-10 family (IL-19, IL-20, IL-22, IL-24, IL-26). The six helices (named A through F) are arranged in an anti-parallel bundle, with two disulphide bonds (Cys-12 to Cys-108, Cys-70 to Cys-112) providing structural stability. The dimer interface is formed primarily through interactions between the C-terminal helices D, E, and F of each monomer.

The homodimeric structure of IL-10 is essential for its biological activity. Each monomer contains one receptor-binding site, and the dimer simultaneously engages two IL-10R1 molecules (one per monomer), creating a 2:2 stoichiometric complex that is further stabilized by the accessory receptor IL-10R2. The structural basis for receptor recognition has been resolved by X-ray crystallography, revealing that IL-10 engages IL-10R1 primarily through its helices B, C, D, and F[@walter2021].

Receptor Architecture

IL-10 signals through a heterodimeric receptor complex consisting of:

• IL-10R1 (CDW210a): The ligand-binding chain, expressed on most hematopoietic cells and, importantly, on microglia, astrocytes, and some neurons. It belongs to the Class II cytokine receptor family
• IL-10R2 (CRFB4): The signal-transducing accessory chain, broadly expressed on nearly all cell types. It does not bind IL-10 directly but is required for signal propagation

Signal Transduction

JAK-STAT3 Pathway (Primary)

IL-10R1 is constitutively associated with the tyrosine kinases TYK2 (tyrosine kinase 2) and JAK1. Upon receptor engagement, these kinases phosphorylate tyrosine residues on the intracellular domain of IL-10R1, creating docking sites for STAT3 (Signal Transducer and Activator of Transcription 3)[@walter2021]. STAT3 binds via its SH2 domain, is then phosphorylated by JAK/TYK2, dimerizes, and translocates to the nucleus where it drives transcription of an extensive anti-inflammatory gene program:

STAT3 target genes include:

• Suppressors of cytokine signaling (SOCS3) — negative feedback inhibitor of JAK/STAT
• IL-1 receptor antagonist (IL-1RA) — blocks IL-1R1 signaling
• IL-10 itself (autocrine positive feedback)
• Arginase-1 (promotes tissue repair)
• Fizz1, Ym1 (alternatively activated macrophage markers)

Alternative Pathways

While JAK-STAT3 is the dominant pathway, IL-10 also activates:

• PI3K-AKT pathway: Promotes cell survival and anti-apoptotic gene expression
• MAPK/ERK pathway: Involved in some of the immunomodulatory effects
• NF-κB inhibition: STAT3 can directly or indirectly suppress NF-κB transcriptional activity, creating powerful anti-inflammatory effects

Biological Functions in the Healthy CNS

Physiological Roles

In the healthy central nervous system (CNS), IL-10 performs several important regulatory functions:

Immune homeostasis: IL-10 is the primary anti-inflammatory cytokine that prevents excessive immune responses to self-antigens, commensal microbiota, and environmental antigens that gain access to the CNS. Microglia and astrocytes produce low levels of IL-10 constitutively, maintaining a state of active immune tolerance[@kelley2022].

Neuroprotection: IL-10 promotes the survival of neurons, oligodendrocytes, and neural progenitor cells under conditions of stress. This is achieved through STAT3-mediated upregulation of anti-apoptotic proteins (Bcl-2, Bcl-xL), inhibition of excitotoxic pathways, and promotion of neurotrophic factor production.

Myelin maintenance: In the healthy CNS, IL-10 supports oligodendrocyte function and myelin integrity. Deficiency of IL-10 or IL-10R1 leads to increased susceptibility to demyelination in animal models[@chen2021].

Synaptic plasticity: Emerging evidence suggests that IL-10 participates in the regulation of synaptic plasticity, potentially through effects on microglial surveillance of synaptic function. Under normal conditions, IL-10 may support the synaptic pruning and remodeling that underlies learning and memory.

Cellular Sources in the CNS

Multiple cell types contribute to the IL-10 pool in the brain:

• Microglia: The primary source during steady-state and following inflammation; M2a/alternatively activated microglia produce high levels of IL-10
• Astrocytes: Respond to IL-10 and also produce it under certain conditions
• Regulatory T cells (Tregs): Traffic into the CNS during neuroinflammation and are potent IL-10 producers
• Neurons: Limited evidence suggests neurons can produce IL-10 under stress conditions
• B cells (particularly B10 cells): Contributed to the IL-10 pool in neuroinflammatory conditions

Role in Alzheimer's Disease

Evidence from Human Studies

The role of IL-10 in AD is complex, with both protective and potentially detrimental effects documented[@zhou2022]:

• Genetic studies: IL10 polymorphisms have been associated with AD risk in multiple cohorts. The −1082 A/G polymorphism (rs1800896) has been most frequently studied, though results are inconsistent across populations, suggesting gene-environment interactions and population-specific effects[@zhang2020]
• CSF and brain tissue studies: AD patients show variable IL-10 levels — some studies report elevated IL-10 (reflecting a compensatory anti-inflammatory response), others report decreased IL-10 (reflecting immune exhaustion)
• Functional studies: IL-10 production capacity by peripheral blood mononuclear cells (PBMCs) is reduced in AD patients compared to age-matched controls, suggesting a systemic anti-inflammatory deficit

Mechanisms of Action in AD

Modulation of Amyloid-Induced Microglial Activation

Microglia are the primary immune cells that encounter and attempt to clear amyloid deposits. In the presence of [amyloid-beta](/proteins/amyloid-beta) plaques, microglia adopt a disease-associated microglia (DAM) or neurodegenerative microglia (MGnD) phenotype characterized by the production of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6), reactive oxygen/nitrogen species, and reduced phagocytic activity[@yang2021].

IL-10 counteracts this phenotype by:

• Promoting the M2a/regulatory microglial phenotype through STAT3 activation
• Restoring amyloid phagocytosis and degradation
• Suppressing production of neurotoxic pro-inflammatory mediators
• Inducing microglial expression of neurotrophic factors (BDNF, GDNF)

Impact on Amyloid Clearance

The relationship between IL-10 and amyloid clearance is nuanced. While IL-10 promotes an anti-inflammatory milieu that may support microglial phagocytosis, excessive IL-10 signaling can impair amyloid clearance by suppressing the inflammatory signals needed for microglial activation and recruitment to plaques[@zhou2022]. This creates a therapeutic window challenge: too little IL-10 allows neuroinflammation, too much may prevent beneficial inflammatory clearance of amyloid.

Neuroprotective Effects

IL-10 protects neurons from amyloid-beta-induced toxicity through multiple mechanisms:

• STAT3-mediated upregulation of anti-apoptotic proteins
• Suppression of ER stress pathways
• Inhibition of NMDA receptor-mediated excitotoxicity
• Promotion of neurotrophic factor secretion from glia

Tau Pathology

Less is known about the relationship between IL-10 and tau pathology specifically. However, by reducing neuroinflammation (which drives tau kinase activation and phosphorylation), IL-10 may indirectly reduce [tau](/proteins/tau) pathology progression. STAT3 activation in neurons may also have direct protective effects on tau metabolism.

Therapeutic Implications in AD

Delivery of IL-10 to the CNS is challenging because:

• IL-10 is a large protein (36 kDa dimer) that does not readily cross the BBB
• Systemic IL-10 administration produces only modest CNS penetration
• Pleiotropic effects on peripheral immunity must be considered

• Gene therapy: AAV-delivered IL-10 expression in the CNS, showing efficacy in mouse models
• Cell-based therapy: Modified regulatory T cells (Tregs) engineered to produce IL-10 in the brain
• Small molecules: Compounds that enhance endogenous IL-10 production or amplify IL-10R1 signaling
• BBB-penetrant IL-10 variants: Engineered IL-10 derivatives with improved CNS bioavailability

Role in Parkinson's Disease

Evidence from Human Studies

IL-10 has shown consistent neuroprotective effects in PD models, with translational relevance to human disease[@johnston2021]:

• Post-mortem studies: IL-10 expression is detectable in the substantia nigra of both PD patients and age-matched controls, but the balance between IL-10 and pro-inflammatory cytokines is shifted toward inflammation in PD
• Genetic studies: IL10 polymorphisms (particularly the −1082 variant) show associations with PD susceptibility in some populations
• Therapeutic trials: Early-phase clinical trials of IL-10 in PD are being planned based on compelling pre-clinical data

Mechanisms of Action in PD

Protection of Dopaminergic Neurons

IL-10 directly protects [dopaminergic neurons](/entities/dopaminergic-neurons) in the [substantia nigra pars compacta](/brain-regions/substantia-nigra) from toxic insults[@johnston2021]:

• In MPTP and 6-OHDA mouse models of PD, IL-10 administration (via viral vectors, recombinant protein, or cell therapy) reduces dopaminergic neuron loss, preserves striatal dopamine levels, and improves motor function
• IL-10 neuroprotection is partially dependent on STAT3 signaling in neurons and partially on microglial modulation
• IL-10 reduces oxidative stress in dopaminergic neurons by promoting Nrf2-mediated antioxidant gene expression

Suppression of Neurotoxic Microglial Activation

Microglial activation in the substantia nigra is a major driver of dopaminergic neuron death in PD. IL-10 suppresses microglial production of:

• TNF-α and IL-1β (direct neurotoxins)
• Nitric oxide (NO) and superoxide (O2−) (reactive nitrogen/oxygen species)
• Prostaglandin E2 (PGE2)
• Quinolinic acid (an NMDA receptor agonist neurotoxin)

Effects on Alpha-Synuclein Pathology

The relationship between IL-10 and [alpha-synuclein](/proteins/alpha-synuclein) pathology in PD is being actively investigated. IL-10 may:

• Reduce microglial activation driven by α-synuclein aggregates and fibrils
• Promote clearance of α-synuclein through enhanced autophagy
• Modulate the spread of pathology by reducing the inflammatory environment that facilitates templated aggregation

Therapeutic Approaches in PD

The neuroprotective potential of IL-10 in PD has been demonstrated across multiple animal models and delivery platforms[@thompson2023]:

• AAV-mediated IL-10 gene therapy: Unilaterally delivered to the striatum or substantia nigra in MPTP-treated mice and 6-OHDA-lesioned rats, AAV-IL-10 reduces dopaminergic degeneration and behavioral deficits. Long-term expression (6+ months) shows sustained benefit[@lin2023]
• Recombinant IL-10 protein: Systemic or intracerebroventricular delivery has shown efficacy in acute models but is limited by protein stability and BBB penetration
• IL-10-secreting Tregs: Adoptive transfer of engineered Tregs provides sustained IL-10 delivery to the CNS and additional immunomodulatory benefits
• Combination therapy: IL-10 combined with other neuroprotective approaches (e.g., GLP-1 receptor agonists) shows additive or synergistic benefits

Role in Other Neurodegenerative Conditions

Multiple Sclerosis and Demyelinating Disease

IL-10 is a critical negative regulator of CNS autoimmunity. In multiple sclerosis and EAE (the animal model of MS), IL-10 deficiency accelerates disease onset and severity, while IL-10 overexpression or administration is protective[@chen2021]:

• IL-10-producing Tregs (Tr1 cells) are essential for maintaining peripheral tolerance to myelin antigens
• IL-10 suppresses Th1 and Th17 differentiation and function
• IL-10 inhibits microglial activation and demyelination
• Some MS patients show reduced IL-10 production capacity, correlating with more aggressive disease

Amyotrophic Lateral Sclerosis (ALS)

In SOD1 transgenic mice (an ALS model), IL-10 is expressed at higher levels in microglia as disease progresses, likely as a compensatory anti-inflammatory response. Overexpression of IL-10 in astrocytes delays disease onset and extends survival, while IL-10 deficiency accelerates disease[@saraiva2020]. This suggests that the IL-10 response in ALS, while present, is insufficient to counteract the intense neuroinflammation driving motor neuron death.

Huntington's Disease (HD)

Evidence for IL-10 in Huntington's disease is more limited, but studies in HD mouse models (R6/2, HdhQ150) suggest that boosting anti-inflammatory cytokines including IL-10 could modulate the microglial activation and neuroinflammation observed in HD.

Frontotemporal Dementia (FTD)

IL-10 levels in CSF and brain tissue of FTD patients show variable changes depending on the underlying pathology (TDP-43 vs. tau). The relationship is less well-characterized than in AD and PD.

IL-10 and the Microglial Life Cycle

Microglia adopt different functional phenotypes in response to environmental cues. The classical M1 (pro-inflammatory) vs. M2 (regulatory) paradigm has been refined by single-cell RNA sequencing studies that reveal much greater heterogeneity:

Disease-Associated Microglia (DAM): These cells show altered homeostatic gene expression (downregulation of P2ry12, Tmem119) and upregulated inflammatory genes. IL-10 can shift the DAM toward a more regulatory phenotype, promoting tissue repair functions.

Neurodegenerative Microglia (MGnD): Characterized by high expression of Trem2-dependent genes and a strong pro-inflammatory, phagocytic state. IL-10 suppresses key MGnD genes while promoting expression of neuroprotective factors[@park2024].

TREM2-dependent effects: [TREM2](/genes/trem2) is a critical microglial receptor for amyloid clearance and microglial survival. IL-10 signaling can enhance TREM2 expression and function, creating a positive interaction between two key neuroprotective pathways.

Therapeutic Strategies

Approaches to Enhancing IL-10 Signaling

Given its demonstrated neuroprotective potential, IL-10 is an attractive therapeutic target. However, the pleiotropic nature of this cytokine demands careful therapeutic design[@thompson2023]:

| Approach | Agent/Strategy | Status | Notes |
|----------|---------------|--------|-------|
| Recombinant IL-10 | rIL-10 (Tenovil) | Clinical trials (cancer, autoimmunity) | Limited BBB penetration; short half-life |
| AAV-IL-10 gene therapy | AAV-IL-10 | Preclinical | Sustained CNS expression; one-time treatment |
| IL-10-secreting Tregs | Adoptive cell therapy | Preclinical | Targeted delivery; additional immunomodulation |
| IL-10R agonists | Engineered variants | Preclinical | Enhanced potency, selectivity |
| IL-10 boosters | Small molecules, dietary interventions | Preclinical | Enhance endogenous IL-10 production |
| IL-10 fusion proteins | IL-10-Fc, BBB-penetrant variants | Preclinical | Improved half-life and CNS delivery |
| Combinatorial therapy | IL-10 + neurotrophic factors | Preclinical | Additive/synergistic effects |

Challenges and Risks

• Immunosuppression: Systemically elevated IL-10 could increase infection risk and impair tumor surveillance
• Dose-dependency: Different concentrations may produce different outcomes in different diseases
• BBB delivery: Requires novel delivery strategies for meaningful CNS effects
• Cell-type specificity: Effects vary dramatically between microglia, astrocytes, and neurons
• Timing: IL-10 may be beneficial in early-to-mid disease but less effective once neurodegeneration is advanced

Biomarkers and Diagnostics

CSF IL-10 levels are being evaluated as biomarkers of anti-inflammatory status in neurodegeneration:

• Higher CSF IL-10 may reflect a more robust anti-inflammatory response
• The ratio of IL-10 to pro-inflammatory cytokines (IL-1β, TNF-α, IL-6) may be more informative than absolute values
• IL-10 production capacity by stimulated PBMCs may serve as a functional biomarker of immune regulation

Cross-Links

• [IL10 Gene](/genes/il10)
• [IL-1β Protein](/proteins/il1b-protein) — the counterbalancing pro-inflammatory cytokine
• [IL-1α Protein](/proteins/il1a-protein) — the related pro-inflammatory alarmin
• [NLRP3 Inflammasome](/entities/nlrp3-inflammasome) — suppressed by IL-10 in microglia
• [TREM2 Signaling](/entities/trem2) — microglia receptor that cooperates with IL-10 signaling
• [NF-κB Signaling](/entities/nf-kb) — suppressed by IL-10 through STAT3 crosstalk
• [Microglia in Neurodegeneration](/cell-types/microglia-neuroinflammation) — primary cellular target of IL-10 in the CNS
• [Neuroinflammation Pathway](/mechanisms/neuroinflammation-pathway) — broader context
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [JAK-STAT Signaling Pathway](/mechanisms/jak-stat-pathway) — canonical IL-10 signaling