Interferons (IFNs) are proteins made and released by host cells in response to the presence of pathogens. They belong to the large class of glycoproteins known as cytokines. IFN-alpha is produced by macrophages and has antiviral activities. IFNs also have other functions: they activate immune cells，such as natural killer cells and macrophages; they increase recognition of infection or tumor cells by up-regulating antigen presentation to T lymphocytes; and they increase the ability of uninfected host cells to resist new infection by virus.
