Pivotal Roles of cGAS-cGAMP Signaling in Antiviral Defense and Immune Adjuvant Effects

Alarm Bells The presence of DNA in the cytosol of mammalian cells is a danger signal, indicating, for example, that a DNA-containing virus has infected the cell. This signal triggers an innate immune response, which involves the expression of type I interferons, and is critical for antiviral immunity and responses to DNA vaccines. Cyclic GMP-AMP synthase (cGAS) was recently identified as a sensor of cytosolic DNA. Li et al. (p. 1390 , published online 29 August) now use knockout mice to provide genetic evidence that, in multiple cell types, cGAS is the primary DNA sensor required for the type I interferon response in vivo.