a natural glycoprotein cytokine released by cells invaded by viruses. Interferon is not itself an antiviral agent but rather acts as a stimulant to noninfected cells, causing them to synthesize another protein with antiviral characteristics, probably by initiating DNA-directed RNA synthesis and, thus, protein synthesis.
The natural production of interferon is not restricted to viral infections; it can be released in response to a wide variety of inducers, including certain nonviral and infectious agents such as rickettsiae, bacteria and synthetic double-strand RNA polymers.
Interferon acts as a regulator of cell growth and has a variety of effects on the immune system by either activating or suppressing selected components of the immune system. For example, interferon can activate macrophages and thereby increase phagocytosis, enhance some primary antibody responses and inhibit others, enhance the expression of major histocompatibility antigens, and affect the specific cytotoxicity of lymphocytes. In regard to cell growth, interferon has the ability to inhibit the proliferation of certain cells.
There are three major classes of interferon depending on the cell of origin: INF-α, which is produced by fibroblasts; INF-β, which is produced by nonlymphocyte leukocytes; and INF-γ, which is a lymphokine, produced by T lymphocytes and also called immune interferon.