Cytoplasmic nucleic acid sensors in antiviral immunity

The innate immune system uses pattern recognition receptors (PRRs) to sense invading microbes and initiate a rapid protective response. PRRs bind and are activated by structural motifs, such as nucleic acids or bacterial and fungal cell wall components, collectively known as pathogen-associated molecular patterns. PRRs that recognize pathogen-derived nucleic acids are present in vesicular compartments and in the cytosol of most cell types. Here, we review recent studies of these cytosolic sensors, focusing on the nature of the ligands for DNA-dependent activator of interferon (DAI)-regulatory factors, absent in melanoma 2 (AIM2), and the retinoic acid-inducible gene I-like helicase (RLH) family of receptors, the basis of ligand recognition and the signaling pathways triggered by the activation of these receptors. An increased understanding of these molecular aspects of innate immunity will guide the development of novel antiviral therapeutics.