Interferons represent the body's most rapid defence against virus infection. Natural recovery from viral infections is correlated with interferon production; the inhibition of interferon enhances the severity of infection and interferon has been shown to protect animals from some viral infections. β-Interferon is produced by fibroblasts in response to viral infection. Leucocyte (α) interferon may be induced by foreign or infected cells or by viruses, and it is continuously released into the bloodstream during infection, declining with time. γ-Interferons are produced later in viral infection by virus-sensitized T lymphocytes. The antiviral action of interferon is induced by interaction with specific receptors on cell surfaces leading to translation of antiviral proteins. Interferons may also enhance immune responses by increasing expression of lymphocyte surface antigens and by increasing the cytotoxic activity of natural killer cells. In chronic hepatitis B and C, it seems likely that interferon's antiviral activity is responsible for the early fall of viral products, while its immunomodulatory activity is responsible for long-term effects, including the destruction of infected hepatocytes, with persistent loss of viral antigens and sereconversion.
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