Noëlline Guillou

IL-33, a new member of the IL-1 family cytokine, is involved in Th2-type responses in a wide range of diseases and signals through the ST2 receptor expressed on many immune cells. Since the effects of IL-33 on DCs remain controversial, we investigated the ability of IL-33 to modulate DC functions in vitro and in vivo. Here, we report that IL-33 activates myeloid DCs to produce IL-6, IL-1b, TNF, CCL17 and to express high levels of CD40, CD80 OX40L and CCR7. Importantly, IL-33-activated DCs prime naive lymphocytes to produce the Th2 cytokines IL-5 and IL-13, but not IL-4. In vivo, IL-33 exposure induces DC recruitment and activation in the lung. Using an OVA-induced allergic lung inflammation model, we demonstrate that the reduced airway inflammation in ST2-deficient mice correlates with the failure in DC activation and migration to the draining LN. Finally, we show that adoptive transfer of IL-33-activated DCs exacerbates lung inflammation in a DC-driven model of allergic airway inflammation. These data demonstrate for the first time that IL-33 activates DCs during antigen presentation and thereby drives a Th2-type response in allergic lung inflammation.

Deposition of uric acid crystals in joints causes the acute and chronic inflammatory disease known as gout and prolonged airway exposure to silica crystals leads to the development of silicosis, an irreversible fibrotic pulmonary disease. Aluminum salt (Alum) crystals are frequently used as vaccine adjuvant. The mechanisms by which crystals activate innate immunity through the Nlrp3 inflammasome are not well understood. Here, we show that uric acid, silica and Alum crystals trigger the extracellular delivery of endogenous ATP, which just precedes the secretion of mature interleukin-1β (IL-1β) by macrophages, both events depending on purinergic receptors and connexin/pannexin channels. Interestingly, not only ATP but also ADP and UTP are involved in IL-1β production upon these Nlrp3 inflammasome activators through multiple purinergic receptor signaling. These findings support a pivotal role for nucleotides as danger signals and provide a new molecular mechanism to explain how chemically and structurally diverse stimuli can activate the Nlrp3 inflammasome.

The NLR pyrin domain containing 3 (NLRP3) inflammasome is a major component of the innate immune system, but its mechanism of activation by a wide range of molecules remains largely unknown. Widely used nano-sized inorganic metal oxides such as silica dioxide (nano-SiO2) and titanium dioxide (nano-TiO2) activate the NLRP3 inflammasome in macrophages similarly to silica or asbestos micro-sized particles. By investigating towards the molecular mechanisms of inflammasome activation in response to nanoparticles, we show here that active adenosine triphosphate (ATP) release and subsequent ATP, adenosine diphosphate (ADP) and adenosine receptor signalling are required for inflammasome activation. Nano-SiO2 or nano-TiO2 caused a significant increase in P2Y1, P2Y2, A2A and/or A2B receptor expression, whereas the P2X7 receptor was downregulated. Interestingly, IL-1β secretion in response to nanoparticles is increased by enhanced ATP and ADP hydrolysis, whereas it is decreased by adenosine degradation or selective A2A or A2B receptor inhibition. Downstream of these receptors, our results show that nanoparticles activate the NLRP3 inflammasome via activation of PLC-InsP3 and/or inhibition of adenylate cyclase (ADCY)-cAMP pathways. Finally, a high dose of adenosine triggers inflammasome activation and IL-1β secretion through adenosine cellular uptake by nucleotide transporters and by its subsequent transformation in ATP by adenosine kinase. In summary, we show for the first time that extracellular adenosine activates the NLRP3 inflammasome by two ways: by interacting with adenosine receptors at nanomolar/micromolar concentrations and through cellular uptake by equilibrative nucleoside transporters at millimolar concentrations. These findings provide new molecular insights on the mechanisms of NLRP3 inflammasome activation and new therapeutic strategies to control inflammation.

BACKGROUND: Inflammasome activation with the production of IL-1β received substantial attention recently in inflammatory diseases. However, the role of inflammasome in the pathogenesis of asthma is not clear. Using an adjuvant-free model of allergic lung inflammation induced by ovalbumin (OVA), we investigated the role of NLRP3 inflammasome and related it to IL-1R1 signaling pathway. METHODS: Allergic lung inflammation induced by OVA was evaluated in vivo in mice deficient in NLRP3 inflammasome, IL-1R1, IL-1β or IL-1α. Eosinophil recruitment, Th2 cytokine, and chemokine levels were determined in bronchoalveolar lavage fluid, lung homogenates, and mediastinal lymph node cells ex vivo. RESULTS: Allergic airway inflammation depends on NLRP3 inflammasome activation. Dendritic cell recruitment into lymph nodes, Th2 lymphocyte activation in the lung and secretion of Th2 cytokines and chemokines are reduced in the absence of NLRP3. Absence of NLRP3 and IL-1β is associated with reduced expression of other proinflammatory cytokines such as IL-5, IL-13, IL-33, and thymic stromal lymphopoietin. Furthermore, the critical role of IL-1R1 signaling in allergic inflammation is confirmed in IL-1R1-, IL-1β-, and IL-1α-deficient mice. CONCLUSION: NLRP3 inflammasome activation leading to IL-1 production is critical for the induction of a Th2 inflammatory allergic response.

The cysteine protease caspase-1 (Casp-1) contributes to innate immunity through the assembly of NLRP3, NLRC4, AIM2, and NLRP6 inflammasomes. Here we ask whether caspase-1 activation plays a regulatory role in house dust mite (HDM)-induced experimental allergic airway inflammation. We report enhanced airway inflammation in caspase-1-deficient mice exposed to HDM with a marked eosinophil recruitment, increased expression of IL-4, IL-5, IL-13, as well as full-length and bioactive IL-33. Furthermore, mice deficient for NLRP3 failed to control eosinophil influx in the airways and displayed augmented Th2 cytokine and chemokine levels, suggesting that the NLPR3 inflammasome complex controls HDM-induced inflammation. IL-33 neutralization by administration of soluble ST2 receptor inhibited the enhanced allergic inflammation, while administration of recombinant IL-33 during challenge phase enhanced allergic inflammation in caspase-1-deficient mice. Therefore, we show that caspase-1, NLRP3, and ASC, but not NLRC4, contribute to the upregulation of allergic lung inflammation. Moreover, we cannot exclude an effect of caspase-11, because caspase-1-deficient mice are deficient for both caspases. Mechanistically, absence of caspase-1 is associated with increased expression of IL-33, uric acid, and spleen tyrosine kinase (Syk) production. This study highlights a critical role of caspase-1 activation and NLPR3/ASC inflammasome complex in the down-modulation of IL-33 in vivo and in vitro, thereby regulating Th2 response in HDM-induced allergic lung inflammation.