Interferons in host defense.

The Type I interferons are a group of related glycoproteins that play a key role in host defenses against viral infections. The interferons bind to a cell surface receptor and initiate the transcription of a wide range of proteins that have potent antiviral properties. The mechanism by which interferon binding to the cell surface initiates gene transcription has recently been elucidated and involves activation of protein kinases (JAK 1 and Tyk 2) followed by phosphorylation and activation of transcriptional regulators (the STAT proteins). These signal transduction molecules are not unique to the interferon signaling pathway, and other cytokines as diverse as erythropoietin and IL-2 use the same, or related proteins. To overcome the antiviral effects of the type I interferons, some viruses that cause chronic infections have developed interferon inhibitors that reduce the effectiveness of endogenous and exogenous interferon.