Sensors of Viral Infection

The innate immune system constitutes the first line of defense against virus infections. This arm of the immune system uses germ line–encoded pattern recognition receptors to detect molecules which are either specific for microorganisms or present in aberrant locations during infection. Collectively, these immune-stimulating viral molecules are termed pathogen-associated molecular patterns. Virus-derived nucleic acids, including double-stranded RNA or DNA, are highly immunostimulatory, and are detected by Toll-like receptors, retinoic acid–inducible gene-I–like receptors, and cytosolic DNA sensors. Following recognition, signals are transduced to induce antiviral, inflammatory, and death programmes. Most notably, type I interferon (IFN) is a potent antiviral cytokine, and defects in production or responsiveness to IFN is associated with susceptibility to viral infections.