<Tr> <Th> PDB </Th> <Td> RCSB PDB; PDBe; PDBj </Td> </Tr> <Tr> <Th> PDBsum </Th> <Td> structure summary </Td> </Tr> <P> 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 . </P> <P> 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 . </P>

How do interferons protect the body against viruses
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