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;
- they increase the ability of uninfected host cells to resist new infection by virus. Certain symptoms, such as aching muscles and fever, are related to the production of IFNs during infection.
About ten distinct IFNs have been identified in mammals; seven of these have been described for humans. All IFNs are very important for fighting viral infections.