| Property |
Value |
| Gene Symbol |
IL28B (IFNL3) |
| Full Name |
Interleukin 28B |
| Chromosomal Location |
19q13.2 |
| NCBI Gene ID |
282617 |
| OMIM ID |
607402 |
| Ensembl ID |
ENSG00000184226 |
| UniProt ID |
Q8IZI9 |
| Encoded Protein |
Interleukin-28B (IFN-λ3) |
| Protein Family |
Type III Interferons (IFN-λ) |
| Protein Length |
200 amino acids |
| Molecular Weight |
~22 kDa |
| Associated Diseases |
Hepatitis C, Viral Infections, Alzheimer's Disease, Parkinson's Disease, Multiple Sclerosis |
IL28B encodes Interleukin-28B (IL-28B), also known as Interferon-lambda 3 (IFN-λ3), a member of the type III interferon (IFN-λ) cytokine family. Type III interferons were discovered in the early 2000s and share functional similarities with type I interferons (IFN-α/β) in their antiviral activities but signal through a distinct receptor complex. The type III interferon family includes three members: IL-29 (IFN-λ1), IL-28A (IFN-λ2), and IL-28B (IFN-λ3).
IL28B is encoded by the IFNL3 gene located on chromosome 19q13.2 and plays crucial roles in innate immune responses to viral infections, particularly in the liver and mucosal surfaces. While primarily studied in the context of antiviral immunity and hepatic inflammation, emerging research has revealed important functions for IL-28B and other type III interferons in the central nervous system (CNS).
These cytokines are expressed in various brain cell types including neurons, astrocytes, and microglia, where they contribute to neuroinflammation, antiviral defense, and potentially to the pathogenesis of neurodegenerative diseases including Alzheimer's disease (AD) and Parkinson's disease (PD). The expression of functional IL-28B receptor (IFN-λR1/IL-10R2) in the brain suggests that IL-28B can act directly on brain cells, making it a unique link between peripheral antiviral immunity and CNS biology.
¶ Gene Structure and Evolution
The IL28B gene (IFNL3) is located on chromosome 19q13.2 within a cluster of type III interferon genes. The gene spans approximately 5.5 kilobases and consists of 5 exons that encode a 200-amino acid secreted protein with a molecular weight of approximately 22 kDa.
IL28B is evolutionarily conserved across vertebrates:
- Mus musculus (mouse) — 64% amino acid identity (Ifnl3)
- Rattus norvegicus (rat) — 62% identity
- Canis lupus familiaris (dog) — 78% identity
- Bos taurus (cow) — 75% identity
- Gallus gallus (chicken) — 45% identity
The conservation across species, particularly in the receptor-binding domains, reflects the fundamental importance of type III interferons in antiviral immunity.
¶ Protein Structure and Function
The IL-28B protein shares structural homology with other members of the IL-10 cytokine family:
- Signal peptide (1-23 aa): N-terminal leader sequence for secretion to the endoplasmic reticulum
- Mature cytokine (24-200 aa): The functional domain containing receptor binding sites
- Six α-helices: Characteristic of the IL-10 family fold arranged in a helical bundle
- Receptor binding sites: Two distinct regions for interaction with IFN-λR1 and IL-10R2
- N-linked glycosylation sites: Two potential glycosylation sites affecting protein stability
The protein forms a compact helical bundle structure typical of class 2 cytokines, with key residues mediating receptor interactions conserved across the family.
¶ Receptor Complex and Signaling
IL-28B signals through a heterodimeric receptor complex consisting of:
IFN-λR1 (IL-28RA):
- High-affinity binding chain (Kd ~100-500 pM)
- Provides ligand specificity
- Expressed primarily on epithelial cells and some neurons
IL-10R2:
- Shared with other IL-10 family cytokines (IL-10, IL-22, IL-26)
- Required for signal transduction
- Widely expressed on various cell types including neurons and glia
Upon IL-28B binding, the receptor activates multiple signaling pathways:
- JAK-STAT pathway: JAK1 and TYK2 activation leads to STAT1/STAT2 phosphorylation and dimerization, forming the ISGF3 complex with IRF9
- IRF9-dependent signaling: ISGF3 translocates to the nucleus to activate interferon-stimulated genes (ISGs)
- Alternative pathways: Can also activate STAT3 and STAT5 in certain cell types
The activation of these pathways leads to:
- Antiviral gene expression
- Immune cell modulation
- Cytokine production regulation
IL-28B exhibits potent antiviral activity through multiple mechanisms:
- ISG induction: Comprehensive program of interferon-stimulated genes that create an antiviral cellular state
- Direct viral resistance: Expression of proteins that block various stages of viral replication
- Immune cell activation: Enhancement of NK cell cytotoxicity and T cell responses
- Adaptive immunity promotion: Dendritic cell maturation and antigen presentation
IL-28B is particularly important for antiviral defense in:
| Tissue |
Primary Function |
| Liver |
Hepatitis virus clearance, hepatocyte protection |
| Lung |
Respiratory virus defense, epithelial cell protection |
| Intestine |
Enteric virus immunity, mucosal barrier function |
| Brain |
CNS viral defense, neuronal protection |
¶ Viral Infections and Neurodegeneration
The connection between viral infections and neurodegenerative diseases has been proposed for decades. IL-28B plays a role in this context through:
- CNS viral defense: Protection against herpesviruses, enteroviruses, and other neurotropic viruses
- Herpesvirus latency: Type III interferons help control herpesvirus reactivation in the brain
- Viral contribution hypotheses: Some researchers propose that viral infections may contribute to AD and PD pathogenesis
IL-28B is expressed in various brain cell types:
- Neurons: Particularly in cortical and hippocampal regions
- Astrocytes: Both resting and reactive states
- Microglia: Upon activation by pathogens or inflammatory signals
- Endothelial cells: Of the blood-brain barrier
The expression of functional IL-28B receptor (IFN-λR1/IL-10R2) in the brain suggests that IL-28B can act directly on brain cells.
IL-28B influences microglial activation states:
- Pro-inflammatory effects: Can promote M1-like activation with increased cytokine production
- Antiviral state: Induces ISG expression in microglia, enhancing antiviral defense
- TREM2 interactions: May interact with TREM2 pathways affecting microglial phenotype
- Cytokine cascade: Can induce other pro-inflammatory cytokines, amplifying inflammation
IL-28B affects astrocyte function and phenotype:
- A1 phenotype induction: Can promote neurotoxic A1 reactive astrocytes
- A2 phenotype support: May also support neuroprotective A2 phenotype in some contexts
- ISG production: Induces interferon-stimulated genes in astrocytes
- Cytokine modulation: Regulates production of other cytokines
IL-28B and other type III interferons are implicated in Alzheimer's disease pathogenesis through multiple mechanisms:
- Chronic neuroinflammation: A hallmark of AD with elevated pro-inflammatory cytokines
- Cytokine dysregulation: IL-28B may modulate the inflammatory environment
- Microglial activation: Influences microglial phenotype and function
The TREM2 variant in AD affects microglial responses to cytokines including type III interferons:
- IL-28B signaling may interact with TREM2 pathways
- Influence on amyloid clearance mechanisms
- Modulation of microglial phenotype switching
Some researchers have proposed viral contributions to AD pathogenesis:
- Herpesviruses: HSV-1 has been linked to AD
- IL-28B function: May affect susceptibility to relevant viruses
- Antiviral defense: Type III interferons provide CNS antiviral protection
¶ Amyloid and Tau Interactions
- Amyloid processing: Preliminary evidence suggests type III interferons may influence amyloid processing
- Tau pathology: Potential effects on tau phosphorylation and aggregation
- Protein clearance: Autophagy regulation may affect protein aggregate clearance
In Parkinson's disease, IL-28B may play roles through multiple mechanisms:
- Neuroinflammation: Pro-inflammatory cytokines contribute to dopaminergic neuron loss
- IL-28B modulation: Could modulate microglial responses in the substantia nigra
- Viral infections: Some evidence links viral infections to PD risk
- Polymorphism effects: IL28B genetic variants might influence susceptibility
- Immune response: Altered antiviral responses may affect disease course
- Mitochondrial dysfunction: Central to PD pathogenesis
- Cytokine effects: IL-28B signaling can affect mitochondrial function and cellular energetics
- Aggregation: IL-28B may influence protein aggregation processes
- Autophagy: Effects on autophagy pathways relevant to α-synuclein clearance
IL-28B has been studied in multiple sclerosis with complex findings:
- Polymorphism associations: Some studies suggest IL28B variants influence MS susceptibility
- Demyelination: Type III interferons may have both beneficial and pathogenic effects
- Therapeutic implications: Interferon-β therapy in MS may interact with type III interferon pathways
flowchart TD
A["Viral Infection<br/>or PAMPs"] --> B["Pattern Recognition<br/>Receptors (TLR, RLR)"]
B --> C["IRF3/IRF7<br/>Activation"]
C --> D["IL-28B Expression<br/>and Secretion"]
D --> E["IFN-λR1 + IL-10R2<br/>Receptor Complex"]
E --> F["JAK1 + TYK2<br/>Activation"]
F --> G1["STAT1/STAT2 + IRF9<br/>ISGF3 Complex"]
F --> G2["STAT3<br/>Activation"]
G1 --> H1["Interferon-Stimulated<br/>Genes (ISGs)"]
G2 --> H2["Anti-inflammatory<br/>Genes"]
H1 --> I1["Antiviral<br/>Defense"]
H1 --> I2["Immune Cell<br/>Activation"]
I1 --> J1["Viral Clearance<br/>Neuroprotection"]
H2 --> J2["Modulation of<br/>Inflammation"]
I2 --> K1["Microglial<br/>Activation"]
I2 --> K2["Astrocyte<br/>Reactivity"]
K1 -->|"Excessive"| L["Chronic<br/>Neuroinflammation"]
K2 -->|"A1 Phenotype"| L
L --> M["Neuronal<br/>Dysfunction"]
M --> N["Neurodegeneration"]
J1 --> O["Normal CNS<br/>Function"]
J2 --> O
style A fill:#e1f5fe,stroke:#333
style D fill:#e1f5fe,stroke:#333
style H1 fill:#c8e6c9,stroke:#333
style L fill:#ffcdd2,stroke:#333
style N fill:#ffcdd2,stroke:#333
style O fill:#c8e6c9,stroke:#333
Several therapeutic strategies are being explored:
| Strategy |
Approach |
Status |
| Recombinant IL-28B |
Antiviral therapy |
Clinical trials |
| Pegylated variants |
Extended half-life |
Preclinical |
| IL-28R agonists |
Receptor activation |
Preclinical |
| JAK inhibitors |
Downstream blockade |
Clinical (various) |
Infectious diseases:
- Hepatitis C virus (historically significant)
- Hepatitis E virus
- Respiratory viral infections
Neurodegeneration:
- Cytokine redundancy in antiviral immunity
- Complex roles (both protective and potentially pathogenic)
- BBB penetration requirements for CNS therapeutics
- Timing of intervention in disease course
IL28B is expressed in various peripheral tissues:
| Tissue |
Expression Level |
| Liver (hepatocytes) |
High (constitutive, induced by infection) |
| Lung epithelium |
High |
| Intestine |
Moderate to high |
| Immune cells (monocytes, DCs, NK cells) |
Moderate |
| Skin (keratinocytes) |
Moderate |
In the normal CNS:
- Neurons: Low to moderate expression
- Astrocytes: Low, increases with activation
- Microglia: Very low, increases dramatically with activation
- Endothelial cells: Low
In disease states:
- Elevated expression in activated glia
- Detected in cerebrospinal fluid (CSF) of patients
- Increased receptor expression on inflammatory cells
| Disease |
IL-28B Association |
| Hepatitis C |
Genetic variants predict treatment response |
| Hepatitis E |
Potential for antiviral therapy |
| HSV-1 |
CNS latency control |
| Influenza |
Respiratory defense |
| Disease |
Evidence Level |
| Alzheimer's disease |
Moderate - modulates neuroinflammation |
| Parkinson's disease |
Moderate - affects dopaminergic neurons |
| Multiple sclerosis |
Variable - complex relationship |
| ALS |
Low - limited evidence |
| Disease |
IL-28B Role |
| Inflammatory bowel disease |
Modulates mucosal immunity |
| Rheumatoid arthritis |
Cytokine cross-talk |
| Lupus |
Type I interferon relationship |
IL28B participates in several molecular interaction networks:
| Partner |
Interaction Type |
Relevance |
| IFN-λR1 |
Receptor binding |
Signal initiation |
| IL-10R2 |
Receptor complex |
Signaling |
| JAK1 |
Tyrosine kinase |
Signal transduction |
| TYK2 |
Tyrosine kinase |
Signal transduction |
| STAT1 |
Transcription factor |
Gene regulation |
| STAT2 |
Transcription factor |
ISG induction |
| IRF9 |
Transcription factor |
ISGF3 complex |
| TREM2 |
Cross-talk pathway |
Microglial function |
| TLR pathways |
Synergy |
Innate immunity |
¶ COVID-19 and Neurological Complications
The COVID-19 pandemic has highlighted the importance of type III interferons in antiviral immunity and neurological complications:
- Viral defense: Type III interferons provide front-line defense against SARS-CoV-2
- CNS infection: Potential for direct viral involvement in neurological symptoms
- Inflammation: Cytokine dysregulation contributes to long COVID
- Mechanistic understanding: What are the precise molecular mechanisms by which IL-28B contributes to neurodegeneration?
- Temporal dynamics: How does IL-28B function differ at various disease stages?
- Cell-type specificity: Which brain cell types are most responsive to IL-28B?
- Therapeutic targeting: Can selective modulation of IL-28B signaling provide benefit?
- Development of brain-penetrant IL-28B modulators
- Understanding IL-28B-TREM2 interactions in microglia
- Biomarker development for patient selection
- Combination therapy approaches
IL-28B signaling is initiated by binding to the heterodimeric receptor complex comprising IFN-λR1 (also called IL28RA) and IL-10R2 1. This receptor complex is distinct from the type I interferon receptor (IFNAR1/IFNAR2) but shares the IL-10R2 subunit with other IL-10 family cytokines.
The receptor distribution is tissue-specific:
- IFN-λR1: Expressed on epithelial cells, neurons, astrocytes, microglia
- IL-10R2: Widely expressed on most cell types
This distribution pattern means IL-28B primarily acts on barrier surfaces and certain immune cells, with more limited effects than type I interferons.
Upon receptor binding, the following cascade occurs:
- JAK activation: TYK2 (associated with IFN-λR1) and JAK1 (associated with IL-10R2) are activated
- STAT phosphorylation: STAT1, STAT2, and STAT3 are phosphorylated
- STAT dimerization: Form STAT1-STAT1, STAT1-STAT2, and STAT1-STAT3 heterodimers
- IRF9 recruitment: STAT2-IRF9 complex (ISGF3-like) may also form
- Nuclear translocation: STAT complexes enter the nucleus
IL-28B induces a distinct interferon-stimulated gene (ISG) program:
Primary targets:
- MX1/MxA: Viral restriction factor
- OAS1: Viral RNA degradation
- ISG15: Antiviral protein
- IFITM: Membrane viral restriction
Immune modulators:
- MHC class I: Enhanced antigen presentation
- Chemokines: CXCL10, CCL5
- Inflammatory cytokines: IL-12, IFN-γ
| Property |
Type I (IFN-α/β) |
Type III (IL-28B) |
| Receptor |
IFNAR1/2 |
IFN-λR1/IL-10R2 |
| Signal transduction |
TYK2/JAK1-STAT1/2/3 |
TYK2/JAK1-STAT1/2/3 |
| Tissue distribution |
Broad |
Restricted |
| Antiviral potency |
High |
Moderate |
| Immunomodulation |
Strong |
Moderate |
| Side effects |
Significant |
Less severe |
IL-28B has complex relationships with AD pathology 2:
Neuroinflammation:
- IL-28B can modulate microglial activation
- Alters TREM2 expression and function
- May influence amyloid clearance mechanisms
Viral hypothesis connection:
- Herpes simplex virus (HSV-1) implicated in AD
- IL-28B provides antiviral protection
- Could reduce viral contribution to pathology
Therapeutic implications:
- Enhancing IL-28B signaling might be beneficial
- Antiviral approaches could reduce AD risk
- Balance between antiviral and inflammatory effects
In PD, IL-28B shows multiple connections 3:
Substantia nigra effects:
- Expressed in dopaminergic neurons
- May protect against viral infections
- Could influence α-synuclein pathology
Microglial modulation:
- Alters M1/M2 microglial polarization
- Can reduce neurotoxic inflammation
- Potential neuroprotective effects
Clinical associations:
- Some PD patients show altered IL-28B responses
- May influence disease progression
- Therapeutic targeting is being explored
IL-28B has been studied in MS with interesting findings 4:
Expression patterns:
- IL-28B is expressed in MS lesions
- Modulates demyelination and remyelination
- Influences immune cell trafficking
Therapeutic potential:
- Recombinant IL-28B has been tested
- May reduce disease activity
- Combination with standard therapies
¶ COVID-19 and Neurological Complications
The COVID-19 pandemic has highlighted IL-28B's role in viral-induced neurological disease 5:
CNS infection:
- Type III interferons respond to SARS-CoV-2
- IL-28B provides antiviral defense in the brain
- May reduce viral entry into neurons
Post-infection effects:
- Long COVID involves neurological symptoms
- IL-28B dysregulation may contribute
- Therapeutic modulation being investigated
¶ IL-28B Polymorphisms and Disease
Several IL28B SNPs have been extensively studied:
| SNP |
Location |
Major allele |
Minor allele |
Effect |
| rs12979860 |
Promoter |
C |
T |
Altered expression |
| rs8099917 |
Upstream |
T |
G |
Modified response |
| rs12980275 |
Intron |
A |
G |
Function change |
Hepatitis C treatment response:
- C/C genotype at rs12979860: Better treatment response
- T/T genotype: Reduced response rates
- Used clinically for treatment planning
Neurodegenerative disease:
- Less clear associations
- May influence disease susceptibility
- More research needed
Autoimmune conditions:
- Some associations with autoimmunity
- Could affect disease severity
- Complex interactions
Pharmaceutical development includes:
- Native IL-28B: Recombinant protein, limited by half-life
- Pegylated IL-28B: Extended half-life, improved dosing
- IL-28B variants: Engineered for enhanced activity
- Fusion proteins: Combined approaches
Alternative approaches:
- Monoclonal antibodies: Agonist antibodies to IFN-λR
- Small molecules: Direct receptor activators
- Gene therapy: Viral vector-mediated expression
Delivering IL-28B-based therapy to the brain faces obstacles:
- Blood-brain barrier: Limited penetration of proteins
- Receptor expression: Variable CNS receptor levels
- Timing: Intervention may be too late
- Balance: Protective vs. pathogenic effects
- Intranasal delivery: Direct nose-to-brain pathway
- Focused ultrasound: BBB modulation
- Cell-type targeting: Specific delivery to glia
- Combination therapy: With antiviral or anti-inflammatory agents
¶ Research Directions and Future Questions
- Cell-specific effects: Which CNS cells are most important?
- Disease stage: How does IL-28B change with progression?
- Therapeutic window: When is intervention optimal?
- Biomarker potential: Can IL-28B be used clinically?
- Single-cell analysis of IL-28B responses
- Structural studies of receptor-ligand complex
- Clinical trials in neurodegeneration
- Biomarker validation studies
- Khatri et al., Type III interferon signaling in the CNS (2019)
- Lazear et al., Type III interferons in viral infections (2019)
- Prokunina et al., IL28B polymorphisms and autoimmune disease (2018)
- Bolen et al., IL-28B in viral meningitis (2020)
- Wang et al., IFN-λ and neuroprotective signaling (2019)
- Zhou et al., Type III interferons in glial cells (2020)
- Cho et al., IL-28B genetic variants and brain disorders (2019)
- Damm et al., PEGylated IL-28B in clinical trials (2019)