Inflammasomes and rheumatic diseases: evolving concepts

The realisation that the production of inflammatory cytokines in inflammatory rheumatic diseases may be induced by non-infectious endogenous signals has encouraged researchers to explore mechanisms of innate immunity and their contribution to the pathogenesis of these diseases. The nucleotide-binding and oligomerisation domain (NOD)-like receptors (NLRs) sense pathogens, products of damaged cells or endogenous metabolites and could potentially be involved in the initiation, amplification and progression of the inflammatory response in rheumatic diseases. NLRs are involved in the regulation of innate immune responses with some of them promoting the activation of inflammatory caspases within multiprotein complexes, called inflammasomes. A typical inflammasome consists of a sensor, an NLR protein, an adaptor protein such as ASC (for apoptosis-associated speck-like protein containing a caspase recruitment domain (CARD)) and an effector protein that is a caspase that activates pro-inflammatory cytokines such as interleukin (IL)1β and IL18. Recent data suggest a role of the inflammasome in the pathogenesis of autoinflammatory as well as inflammatory rheumatic diseases such as juvenile chronic arthritis, adult onset Still disease, rheumatoid arthritis and gout. Modulation of these pathways may be a potential therapeutic target for inflammatory rheumatic diseases.