Nucleotide-binding oligomerization domain (NOD)-containing protein-like receptors (NLRs) are a recently discovered class of innate immune receptors that play a crucial role in initiating the inflammatory response following pathogen recognition. Some NLRs form the framework for cytosolic platforms called inflammasomes, which orchestrate the early inflammatory process via IL-1b activation. Mutations and polymorphisms in NLR-coding genes or in genetic loci encoding inflammasome-related proteins correlate with a variety of autoinflammatory diseases. Moreover, the activity of certain inflammasomes is associated with susceptibility to infections as well as autoimmunity and tumorigenesis. In this review, we will discuss how identifying the genetic characteristics of inflammasomes is assisting our understanding of both autoinflammatory diseases as well as other immune system-driven disorders.

Uric acid is released from damaged cells and serves as a danger signal that alerts the immune system to potential threats, even in the absence of microbial infection. Uric acid modulation of innate immune responses has been extensively studied, but the impact of this damage-associated molecular pattern on adaptive responses remains largely unknown. In this study, we report that, in the presence of NF-κB signaling, uric acid crystals were capable of stimulating dendritic cells to promote the release of cytokines associated with Th17 polarization. Accordingly, naive CD4+ T cells cocultured with uric acid-treated dendritic cells differentiated toward the Th17 lineage. Th17 differentiation required the inflammasome-dependent cytokines IL-1α/β and IL-18 in both in vitro and in vivo models, and the inflammasome adaptor protein ASC and caspase-1 were essential for Th17 responses. Collectively, our findings indicate a novel role for the danger signal uric acid, in cooperation with NF-κB activation, in driving proinflammatory Th17 differentiation. Our data indicate that sterile inflammation shapes adaptive immunity, in addition to influencing early innate responses.

The NOD-like receptor (NLR) family pyrin domain-containing 3 (NLRP3) inflammasome is a cytoplasmic protein complex that mediates inflammatory responses to a broad array of danger signals. The inflammasome drives caspase-1 activation and promotes secretion of the pro-inflammatory cytokines IL-1β and IL-18, and might also participate in other cellular processes. Here, we tried to identify new pathways regulated by the NLRP3 inflammasome in murine dendritic cells (DCs) in response to monosodium urate (MSU) crystals. Using a transcriptomic approach, we found that DCs fromAdditional supporting information may be found in the online version of this article at the publisher's web-site IntroductionMulticellular organisms are constantly exposed to environmental assaults and have evolved several mechanisms that either promote cellular repair or induce cell death in order to maintain Correspondence: Dr. Alessandra Mortellaro e-mail: alessandra_mortellaro@immunol.a-star.edu.sg tissue integrity. In particular, the immune system has evolved specialized innate cells that mediate recognition of invading microbes and host perturbations to initiate a potent set of defense mechanisms. To this end, innate cells are equipped with a * These authors contributed equally to this work.C 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu Eur. J. Immunol. 2013. 43: 2126-2137 Innate immunity 2127 range of surface and intracellular receptors that recognize both microbial-associated molecular patterns and danger-associated molecular patterns (DAMPs). When damage is not repairable, the damaged cells die and release a multitude of poorly defined DAMPs, which in turn elicit an inflammatory response. Inflammation can be both good and bad, depending on the situation. The NOD-like receptor (NLR) family pyrin domaincontaining 3 (NLRP3) inflammasome is a multiprotein complex, which can drive inflammatory responses by promoting the release of IL-1β and IL-18 from innate cells [1]. Through the adaptor protein ASC (apoptosis-associated specklike protein containing a CARD domain), NLRP3 recruits and activates caspase-1, leading to cleavage and activation of IL-1β and IL-18 precursors. Recent studies have identified a variety of NLRP3 inflammasome activators including whole live bacteria, fungal and viral pathogens, as well as various microbial-associated molecular patterns and DAMPs [2]. In addition, cellular stress triggered by factors ranging from oxidative stress to lysosomal damage appears sufficient to activate NLRP3 [3].The mechanisms by which these molecules of diverse origins and structures can each trigger the NLRP3 inflammasome remain unclear. However, the generation of ROS seems to be a unifying factor, consistently mediating NLRP3 activation across several stimuli [4]. Recently, Zhou and colleagues demonstrated that mitochondrial (mt) ROS are critical for NLRP3 inflammasome activation [5]. Accumulation of ROS-producing mitochondria either by repressing mitochondrial autophagy or by pharmacological inhibition of the mitochondri...