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.

Invariant NKT (iNKT) cells play an effector/adjuvant function during antimicrobial and antitumoral immunity and a regulatory role to induce immune tolerance and prevent autoimmunity. iNKT cells that differentially modulate adaptive immunity do not bear a unique phenotype and/or specific cytokine secretion profile, thus opening questions on how a single T cell subset can exert opposite immunological tasks. In this study, we show that iNKT cells perform their dual roles through a single mechanism of action relying on the cognate interaction with myeloid dendritic cells (DCs) and leading to opposite effects depending on the presence of other maturation stimuli simultaneously acting on DCs. The contact of murine purified iNKT cells with immature autologous DCs directly triggers the tolerogenic maturation of DCs, rendering them able to induce regulatory T cell differentiation and prevent autoimmune diabetes in vivo. Conversely, the interaction of the same purified iNKT cells with DCs, in the presence of simultaneous TLR4 stimulation, significantly enhances proinflammatory DC maturation and IL-12 secretion. The different iNKT cell effects are mediated through distinct mechanisms and activation of different molecular pathways within the DC: CD1d signaling and activation of the ERK1/2 pathway for the tolerogenic action, and CD40–CD40L interaction and NF-κB activation for the adjuvant effect. Our data suggest that the DC decision to undergo proinflammatory or tolerogenic maturation results from the integration of different signals received at the time of iNKT cell contact and could have important therapeutic implications for exploiting iNKT cell adjuvant/regulatory properties in autoimmune diseases, infections, and cancer.

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...

NLRs are cytoplasmic proteins that sense cellular stress and intracellular damage resulting from pathogen uptake. To date, the role of NLRs has been studied using combinations of NLR and TLR agonists, but the interplay between two different NLRs remains uncharacterized. In this study, we employed microarrays to investigate in DCs the regulation of gene transcription mediated by activation of NOD2 and NLRP3 pathways using MDP and MSU. MDP and MSU co-stimulation of murine BMDCs up-regulated the expression of genes encoding molecules for antigen presentation and co-stimulation (MHC class II, CD80, CD86), integrins (ITGB3, ITGAV), cytokines (IL-1α, IL-1β, IL-6, IL-2, IL-23p19, IL-12p40), and chemokines (CXCL1, CXCL2). Transcription of the cytokine genes induced by MDP and MSU partially depended on NOD2 but was independent of NLRP3. Finally, we showed that ERK1 and c-JUN activation increased upon MDP and MSU co-stimulation. As a whole, the results indicate that two different NLR activators synergize at the transcriptional level, leading to unique differential expression of genes involved in the innate immune response.

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Non-microbial molecules released from damaged cells act as natural adjuvants capable of promoting an efficient immune response mediated by innate cells, including macrophages and dendritic cells (DCs). Among these molecules, uric acid (UA) in its crystallized form has been found to trigger inflammation through the activation of NLRP3 inflammasome, which leads to secretion of the proinflammatory cytokines IL-1β and IL-18. UA modulation of innate immune responses has been extensively studied, but the impact of this damage-associated molecular pattern on adaptive responses remains largely undocumented. As one of the most ubiquitous sterile danger signals in mammals, and in view of the key role played by UA in alum adjuvanticity, we sought to determine how UA crystals shape adaptive immune responses. In the present study, we focused on adaptive CD4+ T cell polarization since adjuvants that are able to direct appropriately polarized responses will be key to the success of next-generation vaccination strategies. In the presence of NF-κB signaling delivered by muramyl dipeptide, UA crystals were capable of stimulating DCs to promote the release of cytokines associated with Th17 polarization. Accordingly, UA crystals potently induced Th17 responses both in vitro and in vivo. These effects were dependent on the inflammasome-related cytokines IL-1α/β and IL-18, as well as on ASC and caspase-1. Accordingly, NLRP3 deficiency significantly impaired Th17 polarization, at least in vitro.