Inflammasome activation: from inflammatory disease to infection

The recognition of pathogen-derived molecules by the innate immune system is mediated by a number of receptors, including members of the TLR (Toll-like receptor), RLH [RIG (retinoic acid-inducible gene)-like helicase] and the NLR (NOD-like receptor) families. NLRs in particular are also involved in the recognition of host-derived 'danger'-associated molecules which are produced under conditions of cellular stress or injury. Activation of these receptors leads to the assembly of high-molecular-mass complexes called inflammasomes which in turn leads to the generation of active caspase 1 and to the production of mature IL-1 beta (interleukin 1 beta). The discovery that NLRP3 (NLR-related protein 3) can recognize host-derived particulate matter such as uric acid and cholesterol crystals has led to this inflammasome being implicated in a number of inflammatory diseases, including gout, atherosclerosis and Type 2 diabetes. In addition, aberrant NLRP3 activation has also been observed in a number of heritable disorders now referred to as cryopyrinopathies. On the other hand, a number of studies have reported that recognition of both viral and bacterial products by NLRs is required for effective pathogen clearance. The present review discusses both aspects of NLR activation and will highlight the role of additional inflammasome complexes in sensing infection.