Subsequent IL-1β Release Research Articles

Saturated Fatty Acids Undergo Intracellular Crystallization and Activate the NLRP3 Inflammasome in Macrophages

Inflammation provoked by the imbalance of fatty acid composition, such as excess saturated fatty acids (SFAs), is implicated in the development of metabolic diseases. Recent investigations suggest the possible role of the NLRP3 (nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domain containing 3) inflammasome, which regulates IL-1β (interleukin 1β) release and leads to inflammation, in this process. Therefore, we investigated the underlying mechanism by which SFAs trigger NLRP3 inflammasome activation. The treatment with SFAs, such as palmitic acid and stearic acid, promoted IL-1β release in murine primary macrophages while treatment with oleic acid inhibited SFA-induced IL-1β release in a dose-dependent manner. Analyses using polarized light microscopy revealed that intracellular crystallization was provoked in SFA-treated macrophages. As well as IL-1β release, the intracellular crystallization and lysosomal dysfunction were inhibited in the presence of oleic acid. These results suggest that SFAs activate NLRP3 inflammasome through intracellular crystallization. Indeed, SFA-derived crystals activated NLRP3 inflammasome and subsequent IL-1β release via lysosomal dysfunction. Excess SFAs also induced crystallization and IL-1β release in vivo. Furthermore, SFA-derived crystals provoked acute inflammation, which was impaired in IL-1β-deficient mice. These findings demonstrate that excess SFAs cause intracellular crystallization and subsequent lysosomal dysfunction, leading to the activation of the NLRP3 inflammasome, and provide novel insights into the pathogenesis of metabolic diseases.

Cancer cells induce interleukin-22 production from memory CD4+ T cells via interleukin-1 to promote tumor growth

IL-22 has been identified as a cancer-promoting cytokine that is secreted by infiltrating immune cells in several cancer models. We hypothesized that IL-22 regulation would occur at the interface between cancer cells and immune cells. Breast and lung cancer cells of murine and human origin induced IL-22 production from memory CD4+ T cells. In the present study, we found that IL-22 production in humans is dependent on activation of the NLRP3 inflammasome with the subsequent release of IL-1β from both myeloid and T cells. IL-1 receptor signaling via the transcription factors AhR and RORγt in T cells was necessary and sufficient for IL-22 production. In these settings, IL-1 induced IL-22 production from a mixed T helper cell population comprised of Th1, Th17, and Th22 cells, which was abrogated by the addition of anakinra. We confirmed these findings in vitro and in vivo in two murine tumor models, in primary human breast and lung cancer cells, and in deposited expression data. Relevant to ongoing clinical trials in breast cancer, we demonstrate here that the IL-1 receptor antagonist anakinra abrogates IL-22 production and reduces tumor growth in a murine breast cancer model. Thus, we describe here a previously unrecognized mechanism by which cancer cells induce IL-22 production from memory CD4+ T cells via activation of the NLRP3 inflammasome and the release of IL-1β to promote tumor growth. These findings may provide the basis for therapeutic interventions that affect IL-22 production by targeting IL-1 activity.

The cardiac glycoside ouabain activates NLRP3 inflammasomes and promotes cardiac inflammation and dysfunction.

Cardiac glycosides such as digoxin are Na+/K+-ATPase inhibitors that are widely used for the treatment of chronic heart failure and cardiac arrhythmias; however, recent epidemiological studies have suggested a relationship between digoxin treatment and increased mortality. We previously showed that nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasomes, which regulate caspase-1-dependent interleukin (IL)-1β release, mediate the sterile cardiovascular inflammation. Because the Na+/K+–ATPase is involved in inflammatory responses, we investigated the role of NLRP3 inflammasomes in the pathophysiology of cardiac glycoside-induced cardiac inflammation and dysfunction. The cardiac glycoside ouabain induced cardiac dysfunction and injury in wild-type mice primed with a low dose of lipopolysaccharide (LPS), although no cardiac dysfunction was observed in mice treated with either ouabain or LPS alone. Ouabain also induced cardiac inflammatory responses, such as macrophage infiltration and IL-1β release, when mice were primed with LPS. These cardiac manifestations were all significantly attenuated in mice deficient in IL-1β. Furthermore, deficiency of NLRP3 inflammasome components, NLRP3 and caspase-1, also attenuated ouabain-induced cardiac dysfunction and inflammation. In vitro experiments revealed that ouabain induced NLRP3 inflammasome activation as well as subsequent IL-1β release from macrophages, and this activation was mediated by K+ efflux. Our findings demonstrate that cardiac glycosides promote cardiac inflammation and dysfunction through NLRP3 inflammasomes and provide new insights into the mechanisms underlying the adverse effects of cardiac glycosides.

IL-27 enhances LPS-induced IL-1β in human monocytes and murine macrophages.

IL-27 bridges innate and adaptive immunity by modulating cytokine production from myeloid cells and regulating Th cell differentiation. During bacterial infection, TLR4 triggering by LPS induces IL-27 production by monocytes and macrophages. We have previously shown that IL-27 can prime monocytes for LPS responsiveness by enhancing TLR4 expression and intracellular signaling. If unregulated, this could result in damaging inflammation, whereas on the other hand, this may also provide greater responses by inflammatory processes induced in response to bacterial pathogens. A key process in fine-tuning inflammatory responses is activation of the inflammasome, which ultimately results in IL-1β production. Herein, we investigated the molecular mechanisms by which IL-27 modulates LPS-induced IL-1β secretion in monocytes and macrophages. We found that when delivered simultaneously with LPS, IL-27 augments activation of caspase-1 and subsequent release of IL-1β. Furthermore, we determined that IL-27 primes cells for enhanced IL-1β production by up-regulating surface expression of TLR4 and P2X purinoceptor 7 (P2X7) for enhanced LPS and ATP signaling, respectively. These findings provide new evidence that IL-27 plays an important role in the proinflammatory capacity of monocytes and macrophages via enhancing IL-1β secretion levels triggered by dual LPS-ATP stimulation.

Urinary excretion of IL-1β, IL-6 and IL-8 cytokines during relapse and remission of idiopathic nephrotic syndrome.

Background/aimThe role of pro-inflammatory cytokines in the immunopathogenesis of idiopathic nephrotic syndrome had been widely postulated. Reports on the release of cytokines, during idiopathic nephrotic syndrome (INS) activation, were conflicting in defining a specific interleukin pattern during relapse and remission of the disease. The aim of this study was to explore the role of IL-1β, IL-6 and IL-8 in the pathophysiology of INS during relapse and remission.Patients and methodsA total of 37 INS patients were included. Their demographic and biochemical data were reviewed. Levels of IL-1β, IL-6 and IL-8 were measured in the urine of patients during relapse and remission of the disease. Urine samples from 30 age- and sex-matched controls were checked for the same 3 cytokines.ResultsMean age of patients at study was 6.4 ± 3.2 years (range: 14 months–12 years). Male:female ratio was 24:13. Mean serum creatinine was 47 ± 13 μmol/L, and mean serum albumin was 21 ± 7 g/L. Mean urinary IL-1β, IL6 and IL8 levels, corrected to urinary creatinine, in patients during relapse were 132.94 ± 654.97, 217.82 ± 1124.31 and 150.227 ± 523.97 pg/μmol compared to 9.11 ± 40.75, 0.146 ± 0.652, and 6.455 ± 24.53 pg/μmol in controls, respectively (P = 0.02, 0.03 and 0.014, respectively). No significant difference was reported in the mean level of the 3 cytokines compared to controls during remission (P = 0.94, 0.092 and 0.076).ConclusionOur results support the role of T-cell activation and the subsequent release of IL-1β, IL6 and IL8 in the pathogenesis of relapses in INS. The use of steroid-sparing cytokine blockers in managing relapses of INS remains a tempting challenge.

Cathelicidin peptide LL-37 induces UVB-triggered inflammasome activation and angiogenesis: Possible implications for rosacea

In patients with rosacea, skin lesions are characterized by inflammation and vascular hyperactivity. UVB radiation is well defined as one of exacerbation factors, but, the mechanism by which UVB induce inflammation and angiogenesis are still incompletely understood. In addition, previous studies have shown that overexpression of LL-37 plays an important role in rosacea lesion. Recently we reported that UVB irradiation triggered the inflammasome-mediated processing and release of IL-1β in keratinocytes. LL-37 augmented this UVB-induced IL-1β secretion by acting on the P2X7 purinergic receptor (P2X7R) on keratinocytes. P2X7R activation by UVB and LL-37 resulted in an increase in intracellular calcium concentrations, which enhances inflammasome activation and subsequent IL-1β release. We also demonstrated that IL-1β and LL-37 led to increase the angiogenic potential in human umbilical vein endothelial cells (HUVEC). Recent investigations have revealed significant increased dermal expression of VEGF in rosacea lesion. Therefore, we studied how LL-37 led to angiogenesis via VEGF increase in HUVEC. We revealed that LL-37 upregulated VEGF secretion rather than expression from HUVEC and led to angiogenesis in vitro. Both ERK and NF-κB inhibitors clearly abrogated the increase in VEGF levels induced by LL-37 in HUVEC, and angiogenic potential of endothelial cells. In conclusion, our study indicates that LL-37 additionally modulates the inflammasome activation effects of UVB radiation in keratinocytes and proangiogenic effects depending on VEGF release via ERK and NF-κB signaling cascades in HUVEC. These molecular mechanisms might be involved in the exacerbation of rosacea by UVB.

Chronic Nonbacterial Osteomyelitis: Pathophysiological Concepts and Current Treatment Strategies.

Chronic nonbacterial osteomyelitis (CNO) is an autoinflammatory bone disorder, covering a clinical spectrum with asymptomatic inflammation of single bones at the one end, and chronic recurrent multifocal osteomyelitis (CRMO) at the other end. The exact molecular pathophysiology of CNO remains largely unknown. Provided familial clusters and the association with inflammatory disorders of the skin and intestine suggest a genetic predisposition. Recently, profound dysregulation of cytokine responses was demonstrated in CRMO. Failure to produce antiinflammatory cytokines interleukin (IL)-10 and IL-19 contributes to activation of inflammasomes and subsequent IL-1β release. In IL-10-deficient and in CNO-prone chronic multifocal osteomyelitis mice, IL-1β was linked to bone inflammation. Further, alterations to the gut microbiome were suggested in contributing to IL-1β release from innate immune cells in mice, offering an interesting target in the search for molecular mechanisms in CNO. Here, we summarize clinical presentation and treatment options in CNO/CRMO, current pathophysiological concepts, available mouse models, and promising future scientific directions.

TLR4-Upregulated IL-1β and IL-1RI Promote Alveolar Macrophage Pyroptosis and Lung Inflammation through an Autocrine Mechanism.

Acute lung injury (ALI) is a major component of multiple organ dysfunction syndrome (MODS) following pulmonary infection. Alveolar macrophages (AM) are at the center of the pathogenesis of the development of ALI. Interleukin-1β (IL-1β) is one of the key pro-inflammatory mediators, and its maturation is tightly controlled by the formation and activation of the inflammasome. The biological effects of IL-1β are mediated through IL-1 receptor (IL-1R). In this study, we investigated the influence of LPS-induced IL-1β release and IL-1RI upregulation on the development of lung inflammation. We demonstrated that in AM, LPS-TLR4 signaling not only activates Nlrp3 inflammasome activation and subsequent release of IL-1β, but also up-regulates IL-1RI expression on AM surface through MyD88 and NF-κB dependent signaling. The upregulated IL-1RI, therefore, sensitizes AM to IL-1β and results in pyroptosome formation, which in turn leads to AM pyroptosis, a type of caspase-1-dependent inflammatory cell death. We further showed that AM pyroptosis exaggerates lung inflammation. The present study demonstrates a novel mechanism underlying LPS-induced innate immunity; that is, a secondary upregulation of IL-1β-IL-1RI signaling is responsible for AM pyroptosis and augmented lung injury in response to LPS.

NLRP3 tyrosine phosphorylation is controlled by protein tyrosine phosphatase PTPN22.

Inflammasomes form as the result of the intracellular presence of danger-associated molecular patterns and mediate the release of active IL-1β, which influences a variety of inflammatory responses. Excessive inflammasome activation results in severe inflammatory conditions, but physiological IL-1β secretion is necessary for intestinal homeostasis. Here, we have described a mechanism of NLRP3 inflammasome regulation by tyrosine phosphorylation of NLRP3 at Tyr861. We demonstrated that protein tyrosine phosphatase non-receptor 22 (PTPN22), variants in which are associated with chronic inflammatory disorders, dephosphorylates NLRP3 upon inflammasome induction, allowing efficient NLRP3 activation and subsequent IL-1β release. In murine models, PTPN22 deficiency resulted in pronounced colitis, increased NLRP3 phosphorylation, but reduced levels of mature IL-1β. Conversely, patients with inflammatory bowel disease (IBD) that carried an autoimmunity-associated PTPN22 variant had increased IL-1β levels. Together, our results identify tyrosine phosphorylation as an important regulatory mechanism for NLRP3 that prevents aberrant inflammasome activation.

NLRP3 tyrosine phosphorylation is controlled by protein tyrosine phosphatase PTPN22.

Inflammasomes form as the result of the intracellular presence of danger-associated molecular patterns and mediate the release of active IL-1β, which influences a variety of inflammatory responses. Excessive inflammasome activation results in severe inflammatory conditions, but physiological IL-1β secretion is necessary for intestinal homeostasis. Here, we have described a mechanism of NLRP3 inflammasome regulation by tyrosine phosphorylation of NLRP3 at Tyr861. We demonstrated that protein tyrosine phosphatase non-receptor 22 (PTPN22), variants in which are associated with chronic inflammatory disorders, dephosphorylates NLRP3 upon inflammasome induction, allowing efficient NLRP3 activation and subsequent IL-1β release. In murine models, PTPN22 deficiency resulted in pronounced colitis, increased NLRP3 phosphorylation, but reduced levels of mature IL-1β. Conversely, patients with inflammatory bowel disease (IBD) that carried an autoimmunity-associated PTPN22 variant had increased IL-1β levels. Together, our results identify tyrosine phosphorylation as an important regulatory mechanism for NLRP3 that prevents aberrant inflammasome activation.

Oligomerized CARD16 promotes caspase-1 assembly and IL-1β processing

Increasing evidence indicates that caspase recruitment domain (CARD)-mediated caspase-1 (CASP1) assembly is an essential process for its activation and subsequent interleukin (IL)-1β release, leading to the initiation of inflammation. Both CARD16 and CARD17 were previously reported as inhibitory homologs of CASP1; however, their molecular function remains unclear. Here, we identified that oligomerization activity allows CARD16 to function as a CASP1 activator. We investigated the molecular characteristics of CARD16 and CARD17 in transiently transfected HeLa cells. Although both CARD16 and CARD17 interacted with CASP1CARD, only CARD16 formed a homo-oligomer. Oligomerized CARD16 formed a filament-like structure with CASP1CARD and a speck with apoptosis-associated speck-like protein containing a CARD. A filament-like structure formed by CARD16 promoted CASP1 filament assembly and IL-1β release. In contrast, CARD17 did not form a homo-oligomer or filaments and inhibited CASP1-dependent IL-1β release. Mutated CARD16D27G, mimicking the CARD17 amino acid sequence, formed a homo-oligomer but failed to form a filament-like structure. Consequently, CARD16D27G weakly promoted CASP1 filament assembly and subsequent IL-1β release. These results suggest that oligomerized CARD16 promotes CARD-mediated molecular assembly and CASP1 activation.

ADP-Ribosylation of NLRP3 by Mycoplasma pneumoniae CARDS Toxin Regulates Inflammasome Activity

ABSTRACTThe inflammasome is a major regulator of inflammation through its activation of procaspase-1, which cleaves prointerleukin-1β (pro-IL-1β) into its mature form. IL-1β is a critical proinflammatory cytokine that dictates the severity of inflammation associated with a wide spectrum of inflammatory diseases. NLRP3 is a key component of the inflammasome complex, and multiple signals and stimuli trigger formation of the NLRP3 inflammasome complex. In the current study, we uncovered a yet unknown mechanism of NLRP3 inflammasome activation by a pathogen-derived factor. We show that the unique bacterial ADP-ribosylating and vacuolating toxin produced by Mycoplasma pneumoniae and designated community-acquired respiratory distress syndrome (CARDS) toxin activates the NLRP3 inflammasome by colocalizing with the NLRP3 inflammasome and catalyzing the ADP-ribosylation of NLRP3. Mutant full-length CARDS toxin lacking ADP-ribosyltransferase (ADPRT) activity and truncated CARDS toxins unable to bind to macrophages and be internalized failed to activate the NLRP3 inflammasome. These studies demonstrate that CARDS toxin-mediated ADP-ribosylation constitutes an important posttranslational modification of NLRP3, that ADPRT activity of CARDS toxin is essential for NLRP3 inflammasome activation, and that posttranslational ADPRT-mediated modification of the inflammasome is a newly discovered mechanism for inflammasome activation with subsequent release of IL-1β and associated pathologies.

Cathelicidin peptide LL-37 increases UVB-triggered inflammasome activation: Possible implications for rosacea

BackgroundIn patients with rosacea, environmental stressors, especially UVB radiation, trigger disease flares that are characterized by inflammation and vascular hyperactivity. An altered innate immune detection and response system, modulated to a large extent by the aberrant production and processing of human cathelicidin LL-37, is thought to play a central role in disease pathogenesis. ObjectiveTo investigate whether the proinflammatory and proangiogenic effects of UV radiation are enhanced in the presence of cathelicidin LL-37. MethodsHuman skin ex vivo and epidermal keratinocytes in vitro were exposed to UVB irradiation. The proinflammatory effects of UVB exposure in the presence and absence of LL-37 were characterized using immunoblot, transfection, qPCR, and a cell-based second messenger assay. ELISA was used to assess cytokine release and the angiogenic potential of endothelial cells was evaluated using an in vitro angiogenesis assay. ResultsUVB irradiation triggered the inflammasome-mediated processing and release of IL-1β. LL-37 augmented this UV-induced IL-1β secretion by acting on the P2X7 receptor on keratinocytes. P2X7 receptor activation by UVB and LL-37 resulted in an increase in intracellular calcium concentrations, which enhances inflammasome activation and subsequent IL-1β release. Furthermore, IL-1β and LL-37 worked synergistically to increase the angiogenic potential of endothelial cells. ConclusionCathelicidin LL-37 modulates the proinflammatory and proangiogenic effects of UV radiation and thereby contributes to enhanced sensitivity to sun exposure in rosacea.

Mesenchymal Stem/Stromal Cells Inhibit the NLRP3 Inflammasome by Decreasing Mitochondrial Reactive Oxygen Species

Mesenchymal stem/stromal cells (MSCs) control excessive inflammatory responses by modulating a variety of immune cells including monocytes/macrophages. However, the mechanisms by which MSCs regulate monocytes/macrophages are unclear. Inflammasomes in macrophages are activated upon cellular "danger" signals and initiate inflammatory responses through the maturation and secretion of proinflammatory cytokines such as interleukin 1β (IL-1β). Here we demonstrate that human MSCs (hMSCs) negatively regulate NLRP3 inflammasome activation in human or mouse macrophages stimulated with LPS and ATP. Caspase-1 activation and subsequent IL-1β release were decreased in macrophages by direct or transwell coculture with hMSCs. Addition of hMSCs to macrophages either at a LPS priming or at a subsequent ATP step similarly inhibited the inflammasome activation. The hMSCs had no effect on NLRP3 and IL-1β expression at mRNA levels during LPS priming. However, MSCs markedly suppressed the generation of mitochondrial reactive oxygen species (ROS) in macrophages. Further analysis showed that NLRP3-activated macrophages stimulated hMSCs to increase the expression and secretion of stanniocalcin (STC)-1, an antiapoptotic protein. Addition of recombinant protein STC-1 reproduced the effects of hMSCs in inhibiting NLRP3 inflammasome activation and ROS production in macrophages. Conversely, the effects of hMSCs on macrophages were largely abrogated by an small interfering RNA (siRNA) knockdown of STC-1. Together, our results reveal that hMSCs inhibit NLRP3 inflammasome activation in macrophages primarily by secreting STC-1 in response to activated macrophages and thus by decreasing mitochondrial ROS.

Neutrophils, IL-1β, and gout: is there a link?

Gout is a prototype crystal-induced inflammatory disorder, characterized by neutrophil infiltration into inflamed joints. The identification of the role of NLRP3 inflammasome in the recognition of monosodium urate crystals and the subsequent release of IL-1β was a milestone in the elucidation of the pathogenesis of this disorder. IL-1β signaling is considered nowadays as the initiatory event that induces gouty inflammation and promotes the recruitment of vast numbers of neutrophils at the sites of inflammation. Crystal-induced neutrophil activation results in apoptosis inhibition, degranulation, superoxide production, cytokine release and, as recently described, formation of neutrophil extracellular traps, further amplifying the inflammatory process. Finally, neutrophil apoptosis and uptake of apoptotic material by macrophages drive the resolution of acute inflammation. In this review, we discuss the recent experimental data regarding the crosstalk between IL-1β and neutrophils in the pathogenesis of acute gout.

TLR2/MyD88/NF-κB Pathway, Reactive Oxygen Species, Potassium Efflux Activates NLRP3/ASC Inflammasome during Respiratory Syncytial Virus Infection

Human respiratory syncytial virus (RSV) constitute highly pathogenic virus that cause severe respiratory diseases in newborn, children, elderly and immuno-compromised individuals. Airway inflammation is a critical regulator of disease outcome in RSV infected hosts. Although “controlled” inflammation is required for virus clearance, aberrant and exaggerated inflammation during RSV infection results in development of inflammatory diseases like pneumonia and bronchiolitis. Interleukin-1β (IL-1β) plays an important role in inflammation by orchestrating the pro-inflammatory response. IL-1β is synthesized as an immature pro-IL-1β form. It is cleaved by activated caspase-1 to yield mature IL-1β that is secreted extracellularly. Activation of caspase-1 is mediated by a multi-protein complex known as the inflammasome. Although RSV infection results in IL-1β release, the mechanism is unknown. Here in, we have characterized the mechanism of IL-1β secretion following RSV infection. Our study revealed that NLRP3/ASC inflammasome activation is crucial for IL-1β production during RSV infection. Further studies illustrated that prior to inflammasome formation; the “first signal” constitutes activation of toll-like receptor-2 (TLR2)/MyD88/NF-κB pathway. TLR2/MyD88/NF-κB signaling is required for pro-IL-1β and NLRP3 gene expression during RSV infection. Following expression of these genes, two “second signals” are essential for triggering inflammasome activation. Intracellular reactive oxygen species (ROS) and potassium (K+) efflux due to stimulation of ATP-sensitive ion channel promote inflammasome activation following RSV infection. Thus, our studies have underscored the requirement of TLR2/MyD88/NF-κB pathway (first signal) and ROS/potassium efflux (second signal) for NLRP3/ASC inflammasome formation, leading to caspase-1 activation and subsequent IL-1β release during RSV infection.

Amino-Functionalized Polystyrene Nanoparticles Activate the NLRP3 Inflammasome in Human Macrophages

Specifically designed and functionalized nanoparticles hold great promise for biomedical applications. Yet, the applicability of nanoparticles is critically predetermined by their surface functionalization. Here we demonstrate that amino-functionalized polystyrene nanoparticles (PS-NH(2)) of ∼100 nm in diameter, but not carboxyl- or nonfunctionalized particles, trigger NLRP3 inflammasome activation and subsequent release of proinflammatory interleukin 1β (IL-1β) by human macrophages. PS-NH(2) induced time-dependent proton accumulation in lysosomes associated with lysosomal destabilization, release of cathepsin B, and damage of the mitochondrial membrane. Accumulation of mitochondrial reactive oxygen species was accompanied by oxidation of thioredoxin, a protein playing a central role in maintaining the cellular redox balance. Upon oxidation, thioredoxin dissociated from the thioredoxin-interacting protein (TXNIP). Liberated TXNIP, in turn, interacted with the NLRP3 protein, resulting in a conformational change of the pyrin domain of the NLRP3 protein, as was predicted by molecular modeling. Consequently, this prompted assembly of the NLRP3 inflammasome complex with recruitment and activation of caspase-1, inducing IL-1β release by cleavage of pro-IL-1β. The central role of the NLRP3 inflammasome for cytokine production was confirmed by in vitro knockdown of NLRP3 and of the adaptor protein ASC, confirming that other inflammasomes were not activated by PS-NH(2). The PS-NH(2)-mediated proinflammatory macrophage activation could be antagonized by the radical scavenger N-acetyl-L-cysteine, which prevented mitochondrial damage, caspase-1 activation, and the subsequent release of IL-1β. Our study reveals the molecular mechanism of NLRP3 inflammasome activation by amino-functionalized nanoparticles and suggests a strategy as to how such adverse effects could be antagonized.

Technical advance: Caspase-1 activation and IL-1β release correlate with the degree of lysosome damage, as illustrated by a novel imaging method to quantify phagolysosome damage.

In addition to the lysosome's important roles in digestion, antigen processing, and microbial destruction, lysosome damage in macrophages can trigger cell death and release of the inflammatory cytokine IL-1β. To examine the relationship among endocytosis, lysosome damage, and subsequent events, such as caspase-1 activation and IL-1β secretion, we developed a method for measuring lysosome disruption inside individual living cells, which quantifies release of Fdx from lysosomes. Unperturbed, cultured BMM exhibited low levels of lysosome damage, which were not increased by stimulation of macropinocytosis. Lysosome damage following phagocytosis differed with different types of ingested particles, with negligible damage after ingestion of sRBC ghosts, intermediate damage by polystyrene (PS) beads, and high levels of damage by ground silica. Pretreatment with LPS decreased the amount of lysosome damage following phagocytosis of PS beads, silica microspheres, or ground silica. Activation of caspase-1 and subsequent release of IL-1β were proportional to lysosome damage following phagocytosis. The low level of damage following PS bead phagocytosis was insufficient to activate caspase-1 in LPS-activated macrophages. These studies indicate that lysosome damage following phagocytosis is dependent on particle composition and dose and that caspase-1 activation and IL-1β secretion correlate with the extent of lysosome damage.

Cutting Edge: Candida albicans Hyphae Formation Triggers Activation of the Nlrp3 Inflammasome

The proinflammatory cytokine IL-1beta plays an important role in antifungal immunity; however, the mechanisms by which fungal pathogens trigger IL-1beta secretion are unclear. In this study we show that infection with Candida albicans is sensed by the Nlrp3 inflammasome, resulting in the subsequent release of IL-1beta. The ability of C. albicans to switch from a unicellular yeast form into a filamentous form is essential for activation of the Nlrp3 inflammasome, as C. albicans mutants incapable of forming hyphae were defective in their ability to induce macrophage IL- 1beta secretion. Nlrp3-deficient mice also demonstrated increased susceptibility to infection with C. albicans, which is consistent with a key role for Nlrp3 in innate immune responses to the pathogen C. albicans.

Role of cytokines in mediating mechanical hypernociception in a model of delayed-type hypersensitivity in mice

In the present study, we used the electronic version of the von Frey test to investigate the role of cytokines (TNF-α and IL-1β) and chemokines (KC/CXCL-1) in the genesis of mechanical hypernociception during antigen-induced inflammation in mice. The nociceptive test consisted of evoking a hindpaw flexion reflex with a hand-held force transducer (electronic anesthesiometer) adapted with a 0.5 mm 2 polypropylene tip. The intraplantar administration of methylated bovine serum albumin (mBSA) in previously immunized (IM), but not in sham-immunized (SI) mice, induced mechanical hypernociception in a dose-dependent manner. Hypernociception induced by antigen was reduced in animals pretreated with IL-1ra and reparixin (a non-competitive allosteric inhibitor of CXCR2), and in TNF receptor type 1 deficient (TNFR1−/−) mice. Consistently, antigen challenge induced a time-dependent release of TNF-α, IL-1β and KC/CXCL-1 in IM, but not in SI, mice. The increase in TNF-α levels preceded the increase in IL-1β and KC/CXCL1. Antigen-induced release of IL-1β and KC/CXCL1 was reduced in TNFR1−/− mice, and TNF-α-induced hypernociception was inhibited by IL-1ra and reparixin. Hypernociception induced by IL-1β in immunized mice was inhibited by indomethacin, whereas KC/CXCL1-induced hypernociception was inhibited by indomethacin and guanethidine. Antigen-induced hypernociception was reduced by indomethacin and guanethidine and abolished by the two drugs combined. Together, these results suggest that inflammation associated with an adaptive immune response induces hypernociception that is mediated by an initial release of TNF-α, which triggers the subsequent release of IL-1β and KC/CXCL1. The latter cytokines in turn stimulate the release of the direct-acting final mediators, prostanoids and sympathetic amines.