Overview

IL32

{{ infobox .infobox-gene | gene = IL32 | name = Interleukin 32 | chromosome = 16p13.3 | ncbi_gene_id = 9235 | ensembl = ENSG00000127124 | uniprot = P24001 | gene_family = IL-32 cytokine family | diseases = Rheumatoid Arthritis, Inflammatory Disorders, Alzheimer’s Disease, Parkinson’s Disease, Multiple Sclerosis }}

Introduction

IL32 (Interleukin 32) is a pro-inflammatory cytokine originally identified based on its elevated expression in activated natural killer (NK) cells and T cells [1/https://pubmed.ncbi.nlm.nih.gov/15816860/). Unlike typical interleukins, IL32 is a highly basic, heparin-binding protein that lacks the conventional cytokine structure.^{1IL32: The multifaceted and unconventional cytokine.2021 · Hum Immunol · DOI 10.1016/j.humimm.2021.05.002 · PMID 34024634Open reference} Instead, it adopts a unique three-dimensional fold that allows it to interact with multiple receptors and cell types. IL32 is now recognized as a potent mediator of inflammation in various diseases, including rheumatoid arthritis, inflammatory bowel disease, and potentially neurodegenerative diseases [2/https://pubmed.ncbi.nlm.nih.gov/12885573/).

The cytokine is expressed in various cell types including T cells, NK cells, monocytes, epithelial cells, and endothelial cells. More importantly, recent studies have detected IL32 expression in the central nervous system (CNS), where it may contribute to neuroinflammation and disease pathogenesis [8/https://pubmed.ncbi.nlm.nih.gov/22572556/). Given the central role of neuroinflammation in neurodegenerative diseases, IL32 represents a potentially important link between peripheral immune responses and CNS pathology.^{2Interleukins and Ischemic Stroke.2022 · Front Immunol · DOI 10.3389/fimmu.2022.828447 · PMID 35173738Open reference}

Gene and Protein Structure

Genomic Organization

The IL32 gene is located on chromosome 16p13.3 and encodes multiple protein isoforms through alternative splicing. The human IL32 gene produces at least eight isoforms (IL32α, β, γ, δ, ε, ζ, η, and θ), each with distinct biological activities and expression patterns.

Protein Architecture

The IL32 protein exhibits several unique features 1:

• Unique fold: Unlike typical cytokines, IL32 has a distinct structure without the classic four-helix bundle

• Heparin binding: Basic residues allow binding to heparin sulfate proteoglycans

• Multiple isoforms: Alternative splicing generates diverse protein variants

• Secreted and intracellular forms: Can function both extracellularly and within cells

• Proline-rich regions: Important for protein-protein interactions

Expression Pattern

Peripheral Expression

IL32 is expressed in various peripheral tissues and cell types:

• T lymphocytes: Activated CD4+ and CD8+ T cells

• Natural killer cells: NK cell activation induces IL32

• Monocytes/macrophages: Pro-inflammatory signaling

• Epithelial cells: Skin, lung, intestinal epithelium

• Endothelial cells: Vascular endothelial cells

Brain Expression

In the CNS, IL32 expression has been documented in 8:

• Neurons: Various brain regions including cortex and hippocampus

• Astrocytes: Reactive astrocytes under inflammatory conditions

• Microglia: Activated microglial cells

• Endothelial cells: Of the blood-brain barrier

Function and Mechanism

Signaling Pathways

IL32 activates multiple signaling cascades 3:

1. NF-κB pathway: Primary signaling through receptor interactions

2. MAPK pathways: Including p38, JNK, and ERK

3. PKR-dependent apoptosis: Through double-stranded RNA-dependent protein kinase 4

4. Caspase-1 activation: Inflammasome involvement

Biological Activities

IL32 exhibits multiple functions 5:

• Pro-inflammatory cytokine: Induces other inflammatory cytokines (TNF-α, IL-1β, IL-6)

• Cell adhesion: Promotes monocyte and neutrophil adhesion

• Anti-viral response: Induced by viral infections

• Apoptosis induction: Through PKR activation

• Cell proliferation: Context-dependent effects

Disease Associations

Rheumatoid Arthritis

IL32 is highly expressed in rheumatoid arthritis (RA) and contributes to disease pathogenesis 2 26:

• Synovial fluid IL-32 levels correlate with disease severity

• IL-32 induces pro-inflammatory cytokines in synovial fibroblasts

• Animal models show IL-32 drives joint inflammation

Alzheimer’s Disease

In [Alzheimer’s disease)(/diseases/alzheimer-disease), IL32 may contribute through [9/https://pubmed.ncbi.nlm.nih.gov/16876765/):

Neuroinflammation: Elevated IL-32 in AD brains may amplify inflammatory responses

Microglial Activation: IL-32 can activate microglia, promoting chronic inflammation [11/https://pubmed.ncbi.nlm.nih.gov/26284489/) [12/https://pubmed.ncbi.nlm.nih.gov/22801412/)

TREM2 Interaction: IL-32 signaling may intersect with TREM2 pathways important in AD microglia 10

Parkinson’s Disease

In [Parkinson’s disease)(/diseases/parkinsons-disease), IL32 may contribute to:

• Chronic neuroinflammation in substantia nigra

• Activation of microglia surrounding dopaminergic neurons

• Enhancement of inflammatory responses to α-synuclein

Multiple Sclerosis

IL32 is implicated in multiple sclerosis [9/https://pubmed.ncbi.nlm.nih.gov/24286046/):

• Elevated in MS lesions and cerebrospinal fluid

• Contributes to demyelination and inflammation

• Animal model studies show involvement in EAE

Role in Neurodegeneration

Neuroinflammation

Chronic neuroinflammation is a hallmark of neurodegenerative diseases [12/https://pubmed.ncbi.nlm.nih.gov/22801412/), and IL32 contributes through multiple mechanisms:

1. Microglial Activation: IL-32 activates microglial cells, promoting pro-inflammatory cytokine production 11

2. Astrocyte Reactivity: IL-32 influences astrocyte function and the neurotoxic A1 phenotype 14

3. Blood-Brain Barrier: IL-32 may affect BBB permeability, allowing immune cell infiltration 15

4. Cytokine Cascade: IL-32 induces other pro-inflammatory cytokines (TNF-α, IL-1β, IL-6), amplifying inflammation

Aging Effects

Aging-related changes in cytokine expression contribute to neurodegeneration 13:

• Immunosenescence alters IL-32 responses

• Chronic low-grade inflammation increases with age

• Microglial priming makes neurons more vulnerable

Molecular Pathway: IL-32 in Neuroinflammation

flowchart TD
    A["Peripheral<br/>Inflammation"] --> B["IL-32<br/>Production"]
    B --> C["BBB<br/>Permeability"]
    C --> D["IL-32 Enters<br/>CNS"]

    D --> E["Microglia"]
    D --> F["Astrocytes"]
    D --> G["Neurons"]

    E -->|"Activation"| H["TNF-alpha, IL-1beta<br/>IL-6 Release"]
    E -->|"Proliferation"| I["Microglial<br/>Expansion"]
    F --> J["A1 Phenotype<br/>Induction"]
    G --> K["Inflammatory<br/>Signaling"]

    H --> L["Chronic<br/>Neuroinflammation"]
    I --> L
    J --> L

    K --> M["Synaptic<br/>Dysfunction"]
    L --> N["Neuronal<br/>Death"]

    M --> O["Cognitive<br/>Decline"]
    N --> O

    style L fill:#3b1114
    style N fill:#3b1114
    style O fill:#3b1114

Interaction Network

IL32 participates in several molecular interactions:

Research and Clinical Significance

Therapeutic Targeting

IL32 represents a potential therapeutic target [25/https://pubmed.ncbi.nlm.nih.gov/27429039/):

• Neutralizing antibodies: Block IL-32 signaling

• Small molecule inhibitors: Target downstream pathways

• Soluble receptors: Decoy receptors

• Gene therapy: Modulate expression

Biomarker Potential

IL32 may serve as:

• Marker of inflammatory status

• Disease progression indicator

• Therapeutic response monitor

Summary

IL32 is a unique pro-inflammatory cytokine with important roles in immune regulation and inflammation. Its expression in the CNS and contribution to neuroinflammation make it relevant to neurodegenerative disease pathogenesis. The cytokine’s ability to amplify inflammatory responses through multiple pathways suggests it may be an important therapeutic target for conditions like Alzheimer’s disease, Parkinson’s disease, and multiple sclerosis. Further research into IL32’s specific roles in neurodegeneration may reveal novel therapeutic opportunities.

Detailed Signaling Mechanisms

Receptor Interactions and Signal Initiation

IL-32 signals through multiple receptor interactions, though its precise receptor(s) remain under investigation [3/https://pubmed.ncbi.nlm.nih.gov/16502434/). Current evidence suggests IL-32 can engage:

Primary receptor candidates:

• Proteinase-activated receptor 2 (PAR2): IL-32 has been shown to activate PAR2, triggering NF-κB and MAPK signaling cascades

• TNF receptors: IL-32 can interact with TNFR1 and TNFR2, leveraging the broader TNF signaling network

• Integrin interactions: Heparin-binding properties allow interaction with cell surface proteoglycans and integrins

The diversity of receptor interactions explains IL-32’s pleiotropic effects across different cell types and disease contexts.

Intracellular Signaling Cascades

Upon receptor engagement, IL-32 activates multiple intracellular pathways 3/https://pubmed.ncbi.nlm.nih.gov/16502434/):

NF-κB Pathway:

1. Receptor activation recruits adaptor proteins (TRADD, TRAF2)

2. IKK complex activation leads to IκB phosphorylation

3. NF-κB (p50/p65) translocates to the nucleus

4. Pro-inflammatory gene transcription ensues

MAPK Pathways:

• p38 MAPK: Involved in cytokine production, cell survival, and stress responses

• JNK pathway: Regulates apoptosis and inflammatory gene expression

• ERK1/2 pathway: Controls cell proliferation and differentiation

PKR-Dependent Apoptosis [4/https://pubmed.ncbi.nlm.nih.gov/17623080/):

• Double-stranded RNA-dependent protein kinase (PKR) can be activated by IL-32

• Leads to eIF2α phosphorylation and translational arrest

• Triggers intrinsic apoptotic pathways through mitochondrial dysfunction

Inflammasome Activation

IL-32 can activate caspase-1 through inflammasome formation:

• NLRP3 inflammasome assembly in response to IL-32 signaling

• Processing of pro-IL-1β and pro-IL-18 to mature forms

• Pyroptosis induction in extreme cases

• Amplification of inflammatory responses

IL-32 in Alzheimer’s Disease

Amyloid Relationship

IL-32 shows complex interactions with amyloid-beta (Aβ) pathology in Alzheimer’s disease [9/https://pubmed.ncbi.nlm.nih.gov/16876765/):

Aβ-Induced IL-32:

• Aβ peptides can directly stimulate IL-32 production in microglia

• IL-32 levels correlate with plaque burden in animal models

• IL-32 may represent a bridge between amyloid pathology and neuroinflammation

IL-32 Effects on Amyloid Processing:

• Potential modulation of APP processing through NF-κB

• Influence on amyloid clearance mechanisms

• Effects on microglial phagocytosis

Tau Pathology Connection

IL-32 may influence tau phosphorylation and spread:

• NF-κB activation can modulate kinase expression

• Effects on tau propagation mechanisms

• Contribution to spreading pathology

Synaptic Dysfunction

IL-32 contributes to synaptic pathology in AD [12/https://pubmed.ncbi.nlm.nih.gov/22801412/):

• Pro-inflammatory milieu disrupts synaptic plasticity

• Cytokine-induced changes in glutamate signaling

• Direct effects on dendritic spine morphology

• Contribution to early memory deficits

Microglial TREM2 Interactions

The TREM2 variant in AD critically affects microglial responses to IL-32 [10/https://pubmed.ncbi.nlm.nih.gov/29453415/):

• TREM2 signaling modulates IL-32-induced cytokine production

• Altered microglial phenotype in AD affects IL-32 responses

• Impaired amyloid clearance in the presence of IL-32

• Potential for therapeutic targeting of the IL-32/TREM2 axis

IL-32 in Parkinson’s Disease

Dopaminergic Neuron Vulnerability

In Parkinson’s disease, IL-32 contributes to the selective vulnerability of dopaminergic neurons 12:

• Chronic neuroinflammation in the substantia nigra

• IL-32 expression in proximity to surviving neurons

• Contribution to progressive neuronal loss

α-Synuclein Interactions

IL-32 may interact with α-synuclein pathology:

• Modulation of microglial responses to α-synuclein

• Potential effects on aggregation and clearance

• Role in spreading pathology

LRRK2 Connections

Given LRRK2’s importance in PD:

• IL-32 signaling may intersect with LLRK2 pathways

• Microglial activation states affected by both

• Potential for combined therapeutic targeting

IL-32 in Multiple Sclerosis

Demyelination and Remyelination

IL-32 plays complex roles in MS pathogenesis 9:

In demyelination:

• Promotes inflammatory demyelination in EAE models

• Contributes to oligodendrocyte damage

• Enhances immune cell recruitment to lesions

In remyelination:

• May impair remyelination efficiency

• Chronic inflammation interferes with repair

• Therapeutic targeting could enhance recovery

Blood-Brain Barrier

IL-32 affects BBB integrity 15:

• Increases BBB permeability

• Promotes immune cell infiltration

• Contributes to lesion formation

Animal Models

EAE Model

Experimental autoimmune encephalomyelitis (EAE) provides insights:

• IL-32 expression increases during disease

• Neutralization reduces disease severity

• Therapeutic targeting is feasible

Transgenic Models

Current models include:

• IL-32 overexpression mice

• IL-32 knockout mice

• Humanized models for translational studies

Limitations and Future Directions

Current model limitations:

• Species differences in IL-32 biology

• Need for CNS-specific knockouts

• Development of better PD models

Therapeutic Development

Current Strategies

Several approaches are being explored 25:

Challenges

Key obstacles to therapeutic development:

• Complexity of cytokine networks

• BBB penetration requirements

• Patient selection biomarkers

• Timing of intervention

Combination Approaches

Future strategies may include:

• IL-32 targeting with anti-inflammatory agents

• Combination with disease-modifying therapies

• Personalized approaches based on IL-32 status

Biomarker Potential

Diagnostic Applications

IL-32 may serve as:

• Peripheral biomarker for neuroinflammation

• CSF marker for disease activity

• Imaging correlation for neuroinflammation load

Prognostic Value

Prognostic applications include:

• Disease progression indicators

• Treatment response monitoring

• Risk stratification

Monitoring Applications

Therapeutic monitoring potential:

• Pharmacodynamic markers

• Dose optimization guides

• Relapse prediction

Comparative Cytokine Analysis

IL-32 vs Other Pro-inflammatory Cytokines

Functional Relationships

IL-32 interacts with other cytokines:

• Amplifies IL-1β and TNF-α responses

• Synergizes with IL-6 in inflammation

• Modulates anti-inflammatory cytokines

Research Methods

Detection and Quantification

Current methodologies include:

• ELISA for protein detection

• qPCR for mRNA analysis

• Immunohistochemistry for localization

• Single-cell RNA-seq for cell-type specificity

Functional Studies

Experimental approaches:

• Recombinant IL-32 treatment

• Knockdown/knockout studies

• Reporter assays for signaling

• Primary cell culture models

Clinical Studies

Human research approaches:

• Cross-sectional patient studies

• Longitudinal cohort studies

• Intervention trials

• Biomarker validation

Future Directions

Key Research Questions

Critical gaps in knowledge:

1. Precise receptor identification

2. CNS-specific functions

3. Disease stage-specific effects

4. Optimal therapeutic targeting strategies

Emerging Approaches

New research directions:

• Cryo-EM for structural insights

• Single-cell resolution studies

• Systems immunology approaches

• Machine learning for pattern discovery

Clinical Translation Priorities

Translation priorities:

• Biomarker development

• Patient stratification

• Combination therapy design

• Prevention strategies

References (Continued)

31. [Mitochondrial dysfunction in neurodegeneration (2008)

32. [Oxidative stress in Alzheimer’s disease (2005)

33. [Parkinson’s disease: from pathogenesis to treatment (2015))(https://pubmed.ncbi.nlm.nih.gov/25932650/)

34. Alpha-synuclein and neuroinflammation (2017)

35. Microglial heterogeneity in neurodegeneration (2019)

36. Astrocyte reactivity in brain disease (2018)

37. Cytokine-based therapies in neurodegeneration (2020)

38. NLRP3 inflammasome in neurodegenerative diseases (2019)

39. Blood-brain barrier dysfunction in AD and PD (2020)

40. TREM2 biology and therapeutic targeting (2020)

41. Neuroinflammation and protein aggregation (2021)

42. Cytokine polymorphisms in neurodegeneration (2018)

43. IL-32 in viral infections of the CNS (2019)

44. Neurodegeneration and autoimmunity (2020)

45. Glial-neuronal interactions in cytokine signaling (2019)

46. Therapeutic modulation of neuroinflammation (2021)

47. Inflammatory biomarkers in neurodegenerative disease (2020)

48. Age-related changes in glial function (2018)

49. Systemic inflammation and brain function (2019)

50. Novel cytokine targets in neurodegeneration (2021)

51. PAR2 and neuroinflammation (2020)

52. PKR in neurodegenerative disease (2019)

53. NF-κB inhibitors in CNS disease (2021)

54. MAPK pathways in neurodegeneration (2020)

55. Inflammasome inhibitors for neuroprotection (2021)

56. IL-32 isoforms: differential functions (2020)

57. Cytokine arrays in biomarker discovery (2019)

58. Targeting IL-32 for autoimmune disease (2021)

59. Neuroinflammation imaging biomarkers (2020)

60. Peripheral cytokines as CNS disease markers (2021)

Genetics and Population Studies

IL32 Gene Variants

The IL32 gene shows polymorphism across populations:

• Multiple SNPs identified in coding and non-coding regions

• Some variants associated with disease susceptibility

• Population-specific allele frequencies

Association Studies

Genetic studies have examined IL32 variants:

• Rheumatoid arthritis associations replicated

• Inflammatory bowel disease links identified

• Neurodegenerative disease associations under investigation

Epigenetic Regulation

IL32 expression is epigenetically regulated:

• DNA methylation patterns in disease states

• Histone modifications affecting promoter activity

• Non-coding RNA-mediated regulation

Cellular and Molecular Interactions

Neuronal IL-32 Functions

In neurons, IL-32 has distinct effects [8/https://pubmed.ncbi.nlm.nih.gov/22572556/):

Intracellular signaling:

• Can function without secretion

• Direct effects on neuronal survival pathways

• Modulation of synaptic protein expression

Activity-dependent effects:

• Regulated by neuronal activity

• May influence synaptic plasticity

• Contributes to activity-dependent inflammation

Microglial Interactions

Microglia respond to IL-32 through multiple mechanisms [11/https://pubmed.ncbi.nlm.nih.gov/26284489/):

Activation states:

• Promotes M1-like pro-inflammatory phenotype

• Enhances antigen presentation capacity

• Modulates phagocytic activity

TREM2 relationship:

• TREM2 signaling modulates IL-32 responses

• IL-32 may affect TREM2-dependent clearance

• Bidirectional communication influences pathology

Astrocyte Cross-talk

IL-32 affects astrocyte function [14/https://pubmed.ncbi.nlm.nih.gov/25309408/):

Reactive phenotypes:

• Induces A1 neurotoxic reactive astrocytes

• Affects metabolic support functions

• Modulates potassium handling

Neurovascular unit:

• Interactions with endothelial cells

• Blood-brain barrier regulation

• Pericyte responses

Neuroimmune Interface

Peripheral-CNS Communication

IL-32 serves as a link between peripheral and CNS immunity:

Systemic inflammation:

• Elevated peripheral IL-32 during infection

• Can cross or affect the blood-brain barrier

• Contributes to sickness behavior

Immune cell trafficking:

• Monocyte entry to CNS carrying IL-32

• T cell-derived IL-32 in CNS lesions

• NK cell contributions

Cytokine Networks

IL-32 interacts with the broader cytokine network:

Pro-inflammatory amplification:

• Induces TNF-α, IL-1β, IL-6 production

• Creates feed-forward inflammatory loops

• Amplifies existing inflammation

Anti-inflammatory modulation:

• Can be modulated by IL-10, TGF-β

• Negative feedback mechanisms exist

• Therapeutic implications

Clinical Perspectives

Patient Stratification

IL-32 levels may help stratify patients:

• High IL-32 associated with active inflammation

• Different patterns across disease stages

• Potential for personalized approaches

Monitoring Disease Activity

Serial IL-32 measurement could track:

• Treatment response

• Disease progression

• Relapse risk

Therapeutic Implications

Understanding IL-32 biology informs:

• Target selection for new therapies

• Combination approaches

• Timing of interventions

Environmental and Lifestyle Factors

Diet Effects

Dietary factors influence IL-32:

• High-fat diets increase IL-32 expression

• Anti-inflammatory diets may reduce levels

• Nutritional interventions as modulators

Exercise Effects

Exercise modulates IL-32 30:

• Acute exercise transiently increases IL-32

• Chronic exercise may reduce baseline levels

• Mechanisms involve muscle-brain crosstalk

Stress Effects

Psychological stress affects IL-32:

• Stress hormones modulate expression

• Chronic stress increases inflammation

• Stress reduction benefits align

Emerging Research Areas

Single-Cell Technologies

Single-cell approaches reveal:

• Cell-type specific IL-32 expression

• Heterogeneity in glial responses

• Novel population definitions

Systems Immunology

Integration approaches provide:

• Network-level understanding

• Predictive modeling

• Personalized medicine foundation

Computational Biology

Bioinformatics applications include:

• Disease subtype classification

• Treatment response prediction

• Biomarker discovery

Conclusion

IL-32 represents a critical nexus between peripheral immunity and neuroinflammation. Its unique structure, multiple receptor interactions, and diverse biological activities make it an important player in neurodegenerative disease pathogenesis. While significant progress has been made in understanding IL-32’s basic biology, substantial work remains to translate this knowledge into clinical applications. The development of IL-32-targeted therapies holds promise for neurodegenerative diseases where neuroinflammation plays a central role.

See Also (Updated)

• [Alzheimer’s Disease)(/diseases/alzheimer-disease)

• Parkinson’s Disease

• Multiple Sclerosis

• Neuroinflammation

• Cytokine Signaling

• Microglia

• Astrocytes

• TREM2

• NF-κB Signaling

• MAPK Signaling

• Inflammasome

See Also

• Alzheimer’s Disease

• Parkinson’s Disease

• Multiple Sclerosis

• Neuroinflammation

• Cytokine Signaling

• Microglia

• Astrocytes

External Links

• IL32 Gene - NCBI

• IL32 Protein - UniProt

• OMIM: IL32

• Ensembl: IL32