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. IntroductionAllergic asthma is a chronic disorder characterized by eosinophilic airway inflammation, mucus hypersecretion, antigenspecific-IgE antibodies, airway remodeling and increased airway hyperreactivity [1,2]. The process of airway inflammation involves various cells types, such as eosinophils, mast cells, epithelial cells, lymphocytes and DCs. Th2 cells have been shown to play a predominant role in allergic asthma and Th2 cytokines, such as IL-4, IL-5 and IL-13, exacerbate disease severity [3,4]. IL-33, the recently discovered Th2 cytokine, is found at high levels in the plasma of asthmatic patients [5,6] and in the lungs of mice during experimental allergic asthma [7,8].IL-33 is a member of IL-1 family [9][10][11]. Like IL-1b or IL-18, IL-33 is synthesized as a precursor and can be cleaved by caspase-1 and 3 but the cleavage products are biologically less active than the precursor [12,13]. In contrast to the other IL-1 family members, IL-33 is mainly expressed in non-hematopoietic cells such as fibroblasts, epithelial cells and endothelial cells [10,14,15]. Because of its nuclear localization sequence, IL-33 is usually present in the nucleus, where it acts as a potential transcriptional repressor [16]. Recently, IL-33 has been shown to be released from necrotic cells and may act as an alarmin in a similar manner to IL-1a [17] or high mobility group box1 protein HMGB1 [18,19]. [14]. In accordance with its Th2 functions, administration of IL-33 into naive mice induces severe inflammation in the lung and digestive tract with elevated levels of IL-4, IL-5 and IL-13, splenomegaly and increased serum Ig [10]. In vitro, IL-33 has also been reported to polarize naive CD4 1 T cells to produce IL-5 and IL-13, but not . Polarization of this atypical Th2 population is independent of IL-4, STAT6 and GATA3. On macrophages, IL-33 amplifies IL-13-mediated polarization...
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.
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