RIG-I-like receptors and intracellular Toll-like receptors in antiviral immunity

Viral recognition by pattern recognition receptors is a crucial step in antiviral immunity. Toll-like receptors (TLRs) and RIG-I-like receptors (RLRs) represent two classes of nucleic acid-sensing pattern recognition receptors that play a major role in inducing an antiviral response. Whereas nucleic acid-recognizing TLRs are transmembrane receptors localized in endosomes, RLRs are distributed within the cytoplasm. Recognition of viral nucleic acid by either class of receptors results in activation of downstream signaling pathways. This eventually induces expression of type I IFN and inflammatory cytokines via activation of the transcription factors IRF3, NF-kappa B and AP-1. Many viruses, such as the extensively studied family of Paramyxoviridae, have evolved sophisticated mechanisms to evade these responses. This review focuses on the differences between viral recognition, signaling pathways and induction of adaptive immunity evoked by RLRs and intracellular TLRs