Interferon

Interferons are antiviral agents and they modulate functions of the immune system. Administration of Type I IFN has been shown experimentally to inhibit tumor growth in animals. A virus-infected cell releases viral particles that can infect nearby cells. However, the infected cell can protect neighboring cells against a potential infection of the virus by releasing interferons. In response to interferon, cells produce large amounts of an enzyme known as protein kinase R (PKR). This enzyme phosphorylates a protein known as eIF-2 in response to new viral infections; the phosphorylated eIF-2 forms an inactive complex with another protein, called eIF2B, to reduce protein synthesis within the cell. Another cellular enzyme, RNAse L—also induced by interferon action—destroys RNA within the cells to further reduce protein synthesis of both viral and host genes. Inhibited protein synthesis impairs both virus replication and infected host cells. In addition, interferons induce production of hundreds of other proteins—known collectively as interferon-stimulated genes (ISGs)—that have roles in combating viruses and other actions produced by interferon. They also limit viral spread by increasing p53 activity, which kills virus-infected cells by promoting apoptosis. 

Another function of interferons is to up-regulate major histocompatibility complex molecules, MHC I and MHC II, and increase immunoproteasome activity.

All interferons significantly enhance the presentation of MHC I dependent antigens. 

Interferons can also suppress angiogenesis by down regulation of angiogenic stimuli deriving from tumor cells. They also suppress the proliferation of endothelial cells. Such suppression causes a decrease in tumor angiogenesis, a decrease in its vascularization and subsequent growth inhibition.