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Interferons (IFNs) are a group of signaling proteins made and released by host cells in response to the presence of several pathogens, such as viruses, bacteria, parasites, and also tumor cells. In a typical scenario, a virus-infected cell will release interferons causing nearby cells to heighten their anti-viral defenses. IFNs belong to the large class of proteins known as cytokines, molecules used for communication between cells to trigger the protective defenses of the immune system that help eradicate pathogens. Interferons are named for their ability to "interfere" with viral replication〔 by protecting cells from virus infections. IFNs also have various other functions: they activate immune cells, such as natural killer cells and macrophages; they increase host defenses by up-regulating antigen presentation by virtue of increasing the expression of major histocompatibility complex (MHC) antigens. Certain symptoms of infections, such as fever, muscle pain and "flu-like symptoms", are also caused by the production of IFNs and other cytokines. More than twenty distinct IFN genes and proteins have been identified in animals, including humans. They are typically divided among three classes: Type I IFN, Type II IFN, and Type III IFN. IFNs belonging to all three classes are important for fighting viral infections and for the regulation of the immune system. ==Types of interferon== Based on the type of receptor through which they signal, human interferons have been classified into three major types. * Interferon type I: All type I IFNs bind to a specific cell surface receptor complex known as the IFN-α/β receptor (IFNAR) that consists of IFNAR1 and IFNAR2 chains. The type I interferons present in humans are IFN-α, IFN-β, IFN-ε, IFN-κ and IFN-ω. In general, type I interferons are produced when the body recognizes a virus has invaded it. They are produced by fibroblasts and monocytes. However, the production of type I IFN-α is prohibited by another cytokine known as Interleukin-10. Once released, type I interferons will activate molecules which prevent the virus from producing and replicating its RNA and DNA. Overall, IFN-α can be used to treat hepatitis B and C infections, while IFN-β can be used to treat multiple sclerosis.〔 * Interferon type II (IFN-γ in humans): This is also known as immune interferon and is activated by Interleukin-12.〔 Furthermore, type II interferons are released by T helper cells, type 1 specifically. However, they block the proliferation of T helper cells type two. The previous results in an inhibition of Th2 immune response and a further induction of Th1 immune response, which leads to the development of debilitating diseases such as multiple sclerosis. IFN type II binds to IFNGR, which consists of IFNGR1 and IFNGR2 chains and has a different receptor than type I IFN.〔 * Interferon type III: Signal through a receptor complex consisting of IL10R2 (also called CRF2-4) and IFNLR1 (also called CRF2-12). Although discovered more recently than type I and type II IFNs, recent information demonstrates the importance of Type III IFNs in some types of virus infections.〔Vilcek, Novel interferons, Nature Immunol. 4, 8-9. 2003〕〔Hermant, P, Michiels, T., Interferon-λ in the Context of Viral Infections: Production, Response and Therapeutic Implications.J Innate Immun (2014) Apr. 17〕 In general, type I and II interferons are responsible for regulating and activating the immune response.〔 Expression of type I and III IFNs can be induced in virtually all cell types upon recognition of viral components, especially nucleic acids, by cytoplasmic and endosomal receptors, whereas type II interferon is induced by cytokines such as IL-12, and its expression is restricted to immune cells such as T cells and NK cells. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Interferon」の詳細全文を読む スポンサード リンク
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