CGAS and viral infectious disease: In response to virus infection, which depends on the detection of pathogen-associated molecular patterns (PAMPs), innate immune cells such as macrophages and dendritic cells (DCs) are activated by germ line-encoded pattern recognition receptors (PRRs), including Toll-like receptor 3 (TLR3) (1), retinoic acid-inducible gene I (RIG-I) (2, –, 4), melanoma differentiation-associated protein 5 (MDA5) (5), and cyclic GMP-AMP synthase (cGAS) (6).