The cytokine interleukin-1β (IL-1β) is a key mediator of the inflammatory response. Essential for the host-response and resistance to pathogens, it also exacerbates damage during chronic disease and acute tissue injury. It is not surprising therefore that there is a huge level of interest in how this protein is produced and exported from cells. However, the mechanism of IL-1β release has proven to be elusive. It does not follow the conventional ER-Golgi route of secretion. A literature full of disparate observations arising from numerous experimental systems, has contributed to a complicated mix of diverse proposals. Here we summarise these observations and propose that secretion of IL-1β occurs on a continuum, dependent upon stimulus strength and the extracellular IL-1β requirement.

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Assembly of the NLRP3 inflammasome activates caspase-1 and mediates the processing and release of the leaderless cytokine IL-1β and thereby serves a central role in the inflammatory response and in diverse human diseases. Here we found that upon activation of caspase-1, oligomeric NLRP3 inflammasome particles were released from macrophages. Recombinant oligomeric protein particles composed of the adaptor ASC or the p.D303N mutant form of NLRP3 associated with cryopyrin-associated periodic syndromes (CAPS) stimulated further activation of caspase-1 extracellularly, as well as intracellularly after phagocytosis by surrounding macrophages. We found oligomeric ASC particles in the serum of patients with active CAPS but not in that of patients with other inherited autoinflammatory diseases. Our findings support a model whereby the NLRP3 inflammasome, acting as an extracellular oligomeric complex, amplifies the inflammatory response.

The immunogenicity of malignant cells has recently been acknowledged as a critical determinant of efficacy in cancer therapy. Thus, besides developing direct immunostimulatory regimens, including dendritic cell-based vaccines, checkpoint-blocking therapies, and adoptive T-cell transfer, researchers have started to focus on the overall immunobiology of neoplastic cells. It is now clear that cancer cells can succumb to some anticancer therapies by undergoing a peculiar form of cell death that is characterized by an increased immunogenic potential, owing to the emission of the so-called “damage-associated molecular patterns” (DAMPs). The emission of DAMPs and other immunostimulatory factors by cells succumbing to immunogenic cell death (ICD) favors the establishment of a productive interface with the immune system. This results in the elicitation of tumor-targeting immune responses associated with the elimination of residual, treatment-resistant cancer cells, as well as with the establishment of immunological memory. Although ICD has been characterized with increased precision since its discovery, several questions remain to be addressed. Here, we summarize and tabulate the main molecular, immunological, preclinical, and clinical aspects of ICD, in an attempt to capture the essence of this phenomenon, and identify future challenges for this rapidly expanding field of investigation.

Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit cyclooxygenase-1 (COX-1) and COX-2 enzymes. The NLRP3 inflammasome is a multi-protein complex responsible for the processing of the proinflammatory cytokine interleukin-1β and is implicated in many inflammatory diseases. Here we show that several clinically approved and widely used NSAIDs of the fenamate class are effective and selective inhibitors of the NLRP3 inflammasome via inhibition of the volume-regulated anion channel in macrophages, independently of COX enzymes. Flufenamic acid and mefenamic acid are efficacious in NLRP3-dependent rodent models of inflammation in air pouch and peritoneum. We also show therapeutic effects of fenamates using a model of amyloid beta induced memory loss and a transgenic mouse model of Alzheimer's disease. These data suggest that fenamate NSAIDs could be repurposed as NLRP3 inflammasome inhibitors and Alzheimer's disease therapeutics.

Inflammation that contributes to acute cerebrovascular disease is driven by the proinflammatory cytokine interleukin-1 and is known to exacerbate resulting injury. The activity of interleukin-1 is regulated by multimolecular protein complexes called inflammasomes. There are multiple potential inflammasomes activated in diverse diseases, yet the nature of the inflammasomes involved in brain injury is currently unknown. Here, using a rodent model of stroke, we show that the NLRC4 (NLR family, CARD domain containing 4) and AIM2 (absent in melanoma 2) inflammasomes contribute to brain injury. We also show that acute ischemic brain injury is regulated by mechanisms that require ASC (apoptosis-associated specklike protein containing a CARD), a common adaptor protein for several inflammasomes, and that the NLRP3 (NLR family, pyrin domain containing 3) inflammasome is not involved in this process. These discoveries identify the NLRC4 and AIM2 inflammasomes as potential therapeutic targets for stroke and provide new insights into how the inflammatory response is regulated after an acute injury to the brain.inflammation | inflammasome | cerebral ischemia | brain injury | cell death

HighlightsIschaemic brain injury drives profound changes in the gut microbiota.The effects of brain injury on the gut microbiota include changes in goblet cells and noradrenaline.Traumatic brain injury (TBI) also changes the gut microbiota.

The pro-inflammatory cytokine interleukin-1β is a key mediator of inflammation and is implicated in the pathogenesis of diverse disease states. Despite its biological importance, the mechanisms of its processing to an active form and its trafficking to the extracellular compartment remain poorly understood. Interleukin-1β secretion is proposed to occur via several distinct mechanisms including microvesicle shedding and the regulated secretion of lysosomes. In this study, we report for the first time that caspase-1-dependent processing of pro-interleukin-1β can occur in the cytosol following activation of P2X7-receptor. We also provide evidence that the pathway of secretion in this model is independent of the lysosomal trafficking regulator, a protein involved in lysosome secretion. Although release of interleukin-1β occurred before the appearance of significant levels of lactate dehydrogenase in the supernatant, the cells ultimately died. It is clear that structural changes preceding cell death, occurring after caspase-1 activation, promote the cellular release of interleukin-1β. We investigated the involvement of lipid rafts in this process and discovered that depleting the plasma membrane of cholesterol did not adversely affect interleukin-1β secretion in response to ATP. We propose that, in macrophages, ATP-induced interleukin-1β processing occurs in the cytosol by a mechanism that resembles pyroptosis.