An inflammatory response initiated by the NLRP3 inflammasome is triggered by a variety of situations of host 'danger', including infection and metabolic dysregulation. Previous studies suggested that NLRP3 inflammasome activity is negatively regulated by autophagy and positively regulated by reactive oxygen species (ROS) derived from an uncharacterized organelle. Here we show that mitophagy/autophagy blockade leads to the accumulation of damaged, ROS-generating mitochondria, and this in turn activates the NLRP3 inflammasome. Resting NLRP3 localizes to endoplasmic reticulum structures, whereas on inflammasome activation both NLRP3 and its adaptor ASC redistribute to the perinuclear space where they co-localize with endoplasmic reticulum and mitochondria organelle clusters. Notably, both ROS generation and inflammasome activation are suppressed when mitochondrial activity is dysregulated by inhibition of the voltage-dependent anion channel. This indicates that NLRP3 inflammasome senses mitochondrial dysfunction and may explain the frequent association of mitochondrial damage with inflammatory diseases.

Nanoparticles are increasingly used in various fields, including biomedicine and electronics. One application utilizes the opacifying effect of nano-TiO 2 , which is frequently used as pigment in cosmetics. Although TiO 2 is believed to be biologically inert, an emerging literature reports increased incidence of respiratory diseases in people exposed to TiO 2 . Here, we show that nano-TiO 2 and nano-SiO 2 , but not nano-ZnO, activate the NLR pyrin domain containing 3 (Nlrp3) inflammasome, leading to IL-1β release and in addition, induce the regulated release of IL-1α. Unlike other particulate Nlrp3 agonists, nano-TiO 2 -dependent-Nlrp3 activity does not require cytoskeleton-dependent phagocytosis and induces IL-1α/β secretion in nonphagocytic keratinocytes. Inhalation of nano-TiO 2 provokes lung inflammation which is strongly suppressed in IL-1R-and IL-1α-deficient mice. Thus, the inflammation caused by nano-TiO 2 in vivo is largely caused by the biological effect of IL-1α. The current use of nano-TiO 2 may present a health hazard due to its capacity to induce IL-1R signaling, a situation reminiscent of inflammation provoked by asbestos exposure.

Through their capacity to sense danger signals and to generate active interleukin-1β (IL-1β), inflammasomes occupy a central role in the inflammatory response. In contrast to IL-1β, little is known about how IL-1α is regulated. We found that all inflammasome activators also induced the secretion of IL-1α, leading to the cosecretion of both IL-1 cytokines. Depending on the type of inflammasome activator, release of IL-1α was inflammasome dependent or independent. Calcium influx induced by the opening of cation channels was sufficient for the inflammasome-independent IL-1α secretion. In both cases, IL-1α was released primarily in a processed form, resulting from intracellular cleavage by calpain-like proteases. Inflammasome-caspase-1-dependent release of IL-1α and IL-1β was independent of caspase-1 catalytic activity, defining a mode of action for caspase-1. Because inflammasomes contribute to the pathology of numerous chronic inflammatory diseases such as gout and diabetes, IL-1α antagonists may be beneficial in the treatment of these disorders.

No therapeutic cancer vaccine has yet shown sufficient efficacy to be approved in the U.S., in part because of the complex immune response to vaccination. A study in Cancer Cell helps refine the tactics for developing pancreatic cancer vaccines, showing that local activity by tumor-seeking helper T cells can retard-or promote-tumor development. 1 The study, conducted by a team led by Martin Röcken, professor of dermatology at Eberhard Karls University, could help cancer vaccine makers design therapies that direct T cells to the right place and elicit the right kind of immune response. The group used an established mouse model in which overexpression of a viral oncoprotein called T antigen (TAG) promotes islet cell adeno-mas and, eventually, carcinomas in the pancreas. 2 Such tumors develop extensive vascular structures that facilitate tumor growth. The researchers raised helper T cells that recognized a TAG fragment in cell culture. The T cells were labeled with a fluorescent dye and injected into mice. Within days, the TAG-seeking T cells migrated to pancreatic lymph nodes in TAG-expressing mice but not in wild-type controls. Once on the scene, the T cells prevented both the appearance of new tumors and the expansion of existing ones beyond the adenoma stage. Compared with mock-treated controls, mice that received TAG-specific T cell transfusions had fewer and smaller pancreatic tumors with less extensive vascularization. T cell-treated mice, including those treated after tumors started to form, lived longer than mock-treated controls. "We show that T cells can induce tumor dormancy, " Röcken told SciBX. Playing TAG with tumors According to conventional wisdom, helper T cells act indirectly in cancer vaccines by secreting cytokines that prompt cytotoxic T cells to attack tumors. This principle is the basis of several therapeutic cancer vaccines. 3 However, Röcken's team found that mice lacking most of their cytotoxic T cells still could benefit from TAG-specific helper T cells. Although the pancreatic tumors of these T cell-treated mice showed no signs of apoptosis, which would be indicative of cytotoxic T cell attack, the researchers did see a decrease in the pancreatic incorporation of bro-modeoxyuridine (BrdU) compared with that seen in wild-type controls. BrdU labels newly replicated DNA in proliferating tumors.

Although the importance of the NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome in health and disease is well appreciated, a precise characterization of NLRP3 expression is yet undetermined. To this purpose, we generated a knock-in mouse in which the Nlrp3 coding sequence was substituted for the GFP (enhanced GFP [egfp]) gene. In this way, the expression of eGFP is driven by the endogenous regulatory elements of the Nlrp3 gene. In this study, we show that eGFP expression indeed mirrors that of NLRP3. Interestingly, splenic neutrophils, macrophages, and, in particular, monocytes and conventional dendritic cells showed robust eGFP fluorescence, whereas lymphoid subsets, eosinophils, and plasmacytoid dendritic cells showed negligible eGFP levels. NLRP3 expression was highly inducible in macrophages, both by MyD88- and Trif-dependent pathways. In vivo, when mice were challenged with diverse inflammatory stimuli, differences in both the number of eGFP-expressing cells and fluorescence intensity were observed in the draining lymph node. Thus, NLRP3 levels at the site of adaptive response initiation are controlled by recruitment of NLRP3-expressing cells and by NLRP3 induction.

A single-point mutation in exon 15 of the BRAF gene has recently been reported in a high percentage in cultured melanoma cells and in 6 of 9 primary melanomas examined. To evaluate the impact of the T1796A BRAF mutation, we screened primary melanomas, various types of nevi and lesions where a melanoma developed in an underlying nevus. We could detect the mutation in 28 of 97 (29%) melanomas and in 39 of 187 (21%) nevi, including blue nevi (0/20) and Spitz nevi (0/69), which did not carry the mutation. In melanomas with an underlying nevus, either the mutation was present in both the laser-microdissected nevus cells and the laser-microdissected melanoma cells (3/14) or both lesions were negative for the BRAF mutation except one case. In conclusion, mutations in exon 15 of the BRAF gene are nonspecific for progression of a nevus to a melanoma. Other so far unknown cofactors seem to be of importance.

The gut microbiota regulate susceptibility to multiple human diseases. The Nlrp6-ASC inflammasome is widely regarded as a hallmark host innate immune axis that shapes the gut microbiota composition. This notion stems from studies reporting dysbiosis in mice lacking these inflammasome components when compared with non-littermate wild-type animals. Here, we describe microbial analyses in inflammasome-deficient mice while minimizing non-genetic confounders using littermate-controlled Nlrp6-deficient mice and ex-germ-free littermate-controlled ASC-deficient mice that were all allowed to shape their gut microbiota naturally after birth. Careful microbial phylogenetic analyses of these cohorts failed to reveal regulation of the gut microbiota composition by the Nlrp6- and ASC-dependent inflammasomes. Our results obtained in two geographically separated animal facilities dismiss a generalizable impact of Nlrp6- and ASC-dependent inflammasomes on the composition of the commensal gut microbiota and highlight the necessity for littermate-controlled experimental design in assessing the influence of host immunity on gut microbial ecology.

Background:The inflammasome generates IL-1 family proteins, but its role in neutrophils is poorly understood. Results: Neutrophils store key inflammasome components in distinct intracellular compartments and release IL-1␤ and IL-18, but not IL-1␣ or IL-33. Conclusion: Neutrophils store inflammasome components in intracellular compartments. Significance: Targeting the inflammasome in neutrophils represents a future anti-inflammatory strategy.