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Immunology & Cytokines
Interferons
Signaling proteins that play a critical role in the innate immune response against viral infections, bacteria, and tumors.
1. Biological Overview
Interferons are a group of signaling proteins produced by cells in response to viral infections, certain bacteria, parasites, cancer, and other immune triggers. They play a critical role in the immune response against pathogens and tumors. Interferons are part of the innate immune system and serve as one of the first lines of defense against infections.
2. Types of Interferons
There are three main types of interferons: Type I, Type II, and Type III
Type I Interferons
Includes IFN-α, IFN-β, IFN-ε, IFN-κ, and IFN-ω. Primarily produced by virus-infected cells and dendritic cells to induce antiviral responses, inhibit viral replication, and enhance natural killer cells and macrophages.
Type II Interferons
Consists mainly of IFN-γ. Produced by activated T cells and natural killer cells in response to antigens. Critical for activating macrophages and promoting immune responses against intracellular pathogens.
Type III Interferons
Includes IFN-λ. Features antiviral activity similar to Type I but acts through a different receptor complex. Produced by epithelial cells to defend against viral infections at mucosal surfaces.
3. Interferons and their Receptors
Signaling pathways of Type I, II, and III Interferons and their respective receptor complexes.
Type I Interferons (IFN-α and IFN-β)
Type I interferons bind to a heterodimeric receptor complex known as the interferon-alpha receptor (IFNAR). IFNAR consists of two subunits: IFNAR1 and IFNAR2. Both subunits are necessary for functional receptor signaling.
The binding of type I interferons to IFNAR activates Janus kinases (JAKs), specifically JAK1 and Tyk2, leading to phosphorylation and activation of signal transducer and activator of transcription (STAT) proteins, primarily STAT1 and STAT2. The activated STAT proteins form complexes with interferon regulatory factor 9 (IRF9), resulting in the formation of the interferon-stimulated gene factor 3 (ISGF3) complex.
ISGF3 translocates to the nucleus, where it binds to interferon-stimulated response elements (ISREs) in the promoter regions of interferon-stimulated genes (ISGs), leading to the transcriptional activation of a wide range of antiviral and immunomodulatory genes.
Type II Interferons (IFN-γ)
IFN-γ binds to a homodimeric receptor complex known as the interferon-gamma receptor (IFNGR). IFNGR consists of two subunits: IFNGR1 and IFNGR2. Both subunits are required for functional receptor signaling.
The binding of IFN-γ to IFNGR activates JAK1 and JAK2 kinases, which in turn phosphorylate STAT1. Phosphorylated STAT1 forms homodimers and translocates to the nucleus, where it binds to gamma interferon-activated sequence (GAS) elements in the promoter regions of target genes, leading to the transcriptional activation of various immune-related genes, including those involved in antigen presentation, immune cell activation, and antimicrobial responses.
Type III Interferons (IFN-λ)
Type III interferons bind to a receptor complex composed of IFNLR1 (also known as IL-28Rα) and IL-10Rβ (also known as IL-10R2).
The binding of type III interferons to IFNLR1/IL-10Rβ activates JAK1 and Tyk2 kinases, leading to phosphorylation and activation of STAT1 and STAT2.
Similar to type I interferons, the activated STAT proteins form complexes with IRF9, resulting in the activation of ISGs and induction of antiviral responses.