Antiviral action of interferon: Interferon (IFN) synthesis and release are often induced by a virus infection when cellular sensors recognize their pathogen-associated molecular patterns such as double-stranded RNA or cytoplasmic DNA. This releases transcription factors that stimulate the synthesis of mRNA, and the translated IFN protein is secreted onto a neighboring cell. IFN binds to receptor on the plasma membrane of a second cell, and that binding stimulates the activation of genes encoding antiviral proteins. Two important antiviral proteins are the enzymes 2–5 oligo (A) synthetase and protein kinase R (PKR). When an IFN-stimulated cell is infected, viral protein synthesis is inhibited by a 2–5 A-activated endoribonuclease that degrades viral mRNA and by the PKR, which phosphorylates and inactivates the initiation factor eIF-2 required for viral protein synthesis (Reproduced with permission from Wiley J, Sherwood L, Woolverton C, Eds. Prescott’s Principles of Microbiology, New York: McGraw-Hill; 2008)