Pattern recognition of viral nucleic acids by RIG-I-like helicases

Recognition of pathogenic microbes by the innate immune system is based on the principle of pathogen-associated molecular patterns (PAMPs). These are conserved molecular structures that are present in the pathogen but not in the host. Cells of the innate immune system or, in some cases, virtually all cells of our body express receptors that are able to specifically recognize PAMPs and trigger the appropriate responses including the production of cytokines. In the case of viruses, an interesting complication exists: Viruses use the host's cellular metabolism and building blocks to replicate. As a consequence, protein modifications, lipid or carbohydrate configurations restricted to viruses do not exist. Instead, parts of the innate immune system have evolved to detect viral nucleic acids mainly by virtue of their (non-physiological) localization and structure. Understanding the molecules involved in anti-viral defence and the patterns they recognize will allow harnessing them for therapeutic strategies targeting viral and autoimmune diseases and tumours. This review presents important recent advances in understanding intracellular recognition of nucleic acid patterns by the innate immune system.