Pathogen recognition by innate receptors.

Microbial infection elicits host immune responses through germline-encoded pattern recognition receptors (PRRs). Toll-like receptors (TLRs) are evolutionarily conserved membrane-bound PRRs that recognize a broad spectrum of microbial components. Recent studies have clarified that two classes of cytosolic receptors, retinoic acid-inducible gene I (RIG-I)-like helicases (RLHs) and nucleotide binding oligomerization domain (NOD)-like receptors (NLRs), play important roles in the cytosolic recognition of invading pathogens. After microbial infection, the host utilizes these receptors differentially to mount robust immune responses. This review will describe pathogen recognition by these receptors, signaling pathways, and their in vivo roles in innate antiviral immunity.