Viral sensors: diversity in pathogen recognition

Innate sensors of viral infection detect viral products and initiate the signal cascades that lead to the antiviral response. Several proteins have been identified to play a role in this process, mostly members of the Toll-like receptor and retinoic acid-inducible gene I-like receptor families. These receptors have been demonstrated to function in part by recognizing a diverse yet unique repertoire of nucleic acid substrates. Upon recognition of their ligands, these sensors activate distinct signaling pathways that lead to the secretion of type I interferon and inflammatory cytokines. It remains to be seen, however, if these sensors are redundant or whether each serves a unique function. In this work, we review the current knowledge of viral sensors, speculate on how they may function in vivo, and explore the potential reasons for their diversity.