Detailed explanation of cytokines: interferon, the virus defender

1. What is interferon? 

Interferon (IFN) is the earliest discovered cytokine. It is a class of proteins produced by the body's cells when infected by viruses or other pathogens and has multiple biological functions such as antiviral, immune regulation and anti-tumor.

Interferon antiviral diagram

2. How should interferon be classified?

Interferon can be divided into several categories according to its molecular structure, source, mechanism of action and clinical application. The following is a detailed introduction to the classification of interferon .

1. Type I interferon family

Type I interferons mainly include IFN-α and IFN-β. IFN-α is produced by a variety of cell types, such as monocytes-macrophages, B cells and fibroblasts, and has more than 20 subtypes (such as IFN-α1, IFN-α2a, IFN-α2b, etc.). IFN-β is mainly produced by fibroblasts and has only one subtype. Type I interferons play an important role in anti-virus, anti-parasitic, inhibiting cell proliferation, participating in immune regulation and anti-tumor. They bind to the same receptors and are widely distributed on the surface of a variety of cells, such as monocytes-macrophages, polymorphonuclear leukocytes, B cells, T cells, etc., thereby inducing cells to produce antiviral proteins and inhibiting viral replication.

2. Type II interferon (IFN-γ)

Type II interferon only includes IFN-γ, and there is only one subtype. IFN-γ is mainly produced by activated T cells (including Th0, Th1 cells and CD8+ T cells) and natural killer cells (NK cells), and is an important lymphokine. The main biological activity of IFN-γ is immunomodulatory, including enhancing the activity of macrophages, NK cells and T lymphocytes, and promoting their ability to kill pathogens. In addition, IFN-γ also has certain antiviral and antiproliferative effects.

3. Type III interferon (IFN-λ)

Type III interferons include IFN-λ1 (IL-29), IFN-λ2 (IL-28a), IFN-λ3 (IL-28b), and the newly discovered IFN-λ4. They are similar to type I interferons and are involved in inhibiting viral infection, but have different receptors, binding to IFNLR1 and IL-10R2. Type III IFN is synthesized when the host recognizes pathogen-associated molecular patterns (PAMPs)and, similar to type I IFN, exerts its effects through the JAK-STAT pathway.

Interferon types and their receptors

3. Biological functions of interferon

The biological functions of interferon are mainly reflected in the following aspects:

1) Antiviral

Interferon cannot directly inactivate viruses, but exerts its antiviral effect by inducing cells to synthesize antiviral proteins (AVP). These antiviral proteins mainly include 2'-5'A synthetase and protein kinase, which degrade viral mRNA and inhibit the synthesis of viral polypeptide chains, blocking the transcription and translation process of the virus, thereby inhibiting the synthesis of viral proteins and terminating viral replication. Interferon has an inhibitory effect on a variety of viruses, including DNA viruses and RNA viruses. This broad spectrum makes interferon have important application value in antiviral treatment.

2 ) Immunomodulation

Interferon can activate immune cells such as macrophages and NK cells, and promote their ability to clear pathogens. At the same time, it can also promote the expression of cell MHC antigens and enhance the killing effect of lymphocytes on target cells. Interferon also plays an important role in regulating immune balance. For example, it can enhance the activity of TH1 cells and inhibit the proliferation of TH2 cells, thereby regulating the balance between humoral immunity and cellular immunity.

3 ) Anti-tumor

Interferon can inhibit the growth and division of tumor cells, and exert its anti-tumor effect by inducing tumor cell apoptosis and inhibiting tumor angiogenesis. This inhibitory effect is highly selective for tumor cells and has relatively little effect on normal cells. In some cases, interferon can also enhance the sensitivity of chemotherapy drugs to tumor cells and improve the effect of chemotherapy.

4 ) Other biological effects

Interferon also has an anti-proliferative effect and can inhibit the excessive proliferation of certain cells, such as inhibiting the proliferation of vascular smooth muscle cells. In addition, interferon can also induce the differentiation of certain cells, such as inducing the differentiation of bone marrow hematopoietic stem cells.

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