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1.  The Tick Salivary Protein Sialostatin L2 Inhibits Caspase-1-Mediated Inflammation during Anaplasma phagocytophilum Infection 
Infection and Immunity  2014;82(6):2553-2564.
Saliva from arthropod vectors facilitates blood feeding by altering host inflammation. Whether arthropod saliva counters inflammasome signaling, a protein scaffold that regulates the activity of caspase-1 and cleavage of interleukin-1β (IL-1β) and IL-18 into mature molecules, remains elusive. In this study, we provide evidence that a tick salivary protein, sialostatin L2, inhibits inflammasome formation during pathogen infection. We show that sialostatin L2 targets caspase-1 activity during host stimulation with the rickettsial agent Anaplasma phagocytophilum. A. phagocytophilum causes macrophage activation and hemophagocytic syndrome features. The effect of sialostatin L2 in macrophages was not due to direct caspase-1 enzymatic inhibition, and it did not rely on nuclear factor κB or cathepsin L signaling. Reactive oxygen species from NADPH oxidase and the Loop2 domain of sialostatin L2 were important for the regulatory process. Altogether, our data expand the knowledge of immunoregulatory pathways of tick salivary proteins and unveil an important finding in inflammasome biology.
doi:10.1128/IAI.01679-14
PMCID: PMC4019176  PMID: 24686067
2.  Mycobacterium tuberculosis but not non-virulent mycobacteria inhibit IFN-β and AIM2-inflammasome dependent IL-1β production via their ESX-1 secretion system 
Mycobacterium tuberculosis (Mtb) extracellular DNA (eDNA) gains access to the host cell cytosol via the ESX-1 secretion system. It is puzzling that this eDNA of Mtb does not induce activation of the AIM2-inflammasome since AIM2 recognizes cytosolic DNA. Here we show that non-virulent mycobacteria such as M. smegmatis induce AIM2-inflammasome activation, which is dependent upon their strong induction of IFN-β production. In contrast, Mtb, but not an ESX-1 deficient mutant, inhibits the AIM2-inflammasome activation induced by either M. smegmatis or transfected dsDNA. The inhibition does not involve changes in host cell AIM2 mRNA or protein levels but led to decreased activation of caspase-1. We furthermore demonstrate that Mtb inhibits IFN-β production and signaling, which was partially responsible for the inhibition of AIM2 activation. In conclusion, we report a novel immune evasion mechanism of Mtb that involves the ESX-1-dependent, direct or indirect, suppression of the host cell AIM2-inflammasome activation during infection.
doi:10.4049/jimmunol.1301331
PMCID: PMC3799997  PMID: 23997220
4.  Mitochondrial cardiolipin is required for Nlrp3 inflammasome activation 
Immunity  2013;39(2):311-323.
Summary
Nlrp3 inflammasome activation occurs in response to numerous agonists but the specific mechanism by which this takes place remains unclear. All previously evaluated activators of the Nlrp3 inflammasome induce the generation of mitochondrial reactive oxygen species (ROS), suggesting a model in which ROS is a required upstream mediator of Nlrp3 inflammasome activation. Here we have identified the oxazolidinone antibiotic, linezolid, as a Nlrp3 agonist that activates the Nlrp3 inflammasome independently of ROS. The pathways for ROS-dependent and ROS-independent Nlrp3 activation converged upon mitochondrial dysfunction and specifically the mitochondrial lipid cardiolipin. Cardiolipin bound to Nlrp3 directly and interference with cardiolipin synthesis specifically inhibited Nlrp3 inflammasome activation. Together these data suggest that mitochondria play a critical role in the activation of the Nlrp3 inflammasome through the direct binding of Nlrp3 to cardiolipin.
doi:10.1016/j.immuni.2013.08.001
PMCID: PMC3779285  PMID: 23954133
5.  Candida albicans Triggers NLRP3-Mediated Pyroptosis in Macrophages 
Eukaryotic Cell  2014;13(2):329-340.
Pyroptosis is an inflammasome-mediated programmed cell death pathway triggered in macrophages by a variety of stimuli, including intracellular bacterial pathogens. Activation of pyroptosis leads to the secretion of interleukin-1β (IL-1β) and pore-mediated cell lysis. Although not considered an intracellular pathogen, Candida albicans is able to kill and, thereby, escape from macrophages. Here, we show that C. albicans-infected bone marrow-derived macrophages (BMDM) and murine J774 macrophages undergo pyroptotic cell death that is suppressed by glycine and pharmacologic inhibition of caspase-1. Infection of BMDM harvested from mice lacking components of the inflammasome revealed that pyroptosis was dependent on caspase-1, ASC, and NLRP3 and independent of NLRC4. In contrast to its role during intracellular bacterial infection, pyroptosis does not restrict C. albicans replication. Nonfilamentous Candida spp. did not trigger pyroptosis, while Candida krusei, which forms pseudohyphae in macrophages, triggered much lower levels than did C. albicans. Interestingly, a Saccharomyces cerevisiae strain from the filamentous background Σ1278 also triggered low, but significant, levels of pyroptosis. We have found that deletion of the transcription factor UPC2 decreases pyroptosis but has little effect on filamentation in the macrophage. In addition, a gain-of-function mutant of UPC2 induces higher levels of pyroptosis than does a matched control strain. Taken together, these data are most consistent with a model in which filamentation is necessary but not sufficient to trigger NLRP3 inflammasome-mediated pyroptosis. This is the first example of a fungal pathogen triggering pyroptosis and indicates that C. albicans-mediated macrophage damage is not solely due to hypha-induced physical disruption of cellular integrity.
doi:10.1128/EC.00336-13
PMCID: PMC3910967  PMID: 24376002
6.  Damage control: management of cellular stress by the NLRP3 inflammasome 
European journal of immunology  2013;43(8):10.1002/eji.201343848.
The NLRP3 inflammasome plays a critical role in regulating inflammatory and cell death pathways in response to a diverse array of stimuli. Activation of the NLRP3 inflammasome results in activation of the cysteine protease caspase-1 and the subsequent processing and secretion of the pro-inflammatory cytokines IL-1β and IL-18. In this issue of the European Journal of Immunology, Licandro and colleagues [Eur. J. Immunol. 2013. 43: DOI 10.1002/eji.201242918] show that the NLRP3 inflammasome contributes to oxidative DNA damage. In addition, activation of the NLRP3 inflammasome modulates a number of pathways involved in DNA damage repair, cell cycle, and apoptosis; suggesting a novel role for the NLRP3 inflammasome in DNA damage responses following cellular stress.
doi:10.1002/eji.201343848
PMCID: PMC3807240  PMID: 23928964
NLRP3 inflammasome; dendritic cell; caspase-1; genotoxic stress
7.  Catching Fire: Candida albicans, Macrophages, and Pyroptosis 
PLoS Pathogens  2014;10(6):e1004139.
doi:10.1371/journal.ppat.1004139
PMCID: PMC4072798  PMID: 24967821
8.  Inflammasomes in cancer: a double-edged sword 
Protein & Cell  2014;5(1):12-20.
Chronic inflammatory responses have long been observed to be associated with various types of cancer and play decisive roles at different stages of cancer development. Inflammasomes, which are potent inducers of interleukin (IL)-1β and IL-18 during inflammation, are large protein complexes typically consisting of a Nod-like receptor (NLR), the adapter protein ASC, and Caspase-1. During malignant transformation or cancer therapy, the inflammasomes are postulated to become activated in response to danger signals arising from the tumors or from therapy-induced damage to the tumor or healthy tissue. The activation of inflammasomes plays diverse and sometimes contrasting roles in cancer promotion and therapy depending on the specific context. Here we summarize the role of different inflammasome complexes in cancer progression and therapy. Inflammasome components and pathways may provide novel targets to treat certain types of cancer; however, using such agents should be cautiously evaluated due to the complex roles that inflammasomes and pro-inflammatory cytokines play in immunity.
doi:10.1007/s13238-013-0001-4
PMCID: PMC3938856  PMID: 24474192
inflammasome; cancer; inflammation
9.  Inflammasomes in cancer: a double-edged sword 
Protein & Cell  2014;5(1):12-20.
Chronic inflammatory responses have long been observed to be associated with various types of cancer and play decisive roles at different stages of cancer development. Inflammasomes, which are potent inducers of interleukin (IL)-1β and IL-18 during inflammation, are large protein complexes typically consisting of a Nod-like receptor (NLR), the adapter protein ASC, and Caspase-1. During malignant transformation or cancer therapy, the inflammasomes are postulated to become activated in response to danger signals arising from the tumors or from therapy-induced damage to the tumor or healthy tissue. The activation of inflammasomes plays diverse and sometimes contrasting roles in cancer promotion and therapy depending on the specific context. Here we summarize the role of different inflammasome complexes in cancer progression and therapy. Inflammasome components and pathways may provide novel targets to treat certain types of cancer; however, using such agents should be cautiously evaluated due to the complex roles that inflammasomes and pro-inflammatory cytokines play in immunity.
doi:10.1007/s13238-013-0001-4
PMCID: PMC3938856  PMID: 24474192
inflammasome; cancer; inflammation
10.  Nlrp3 Prevents Early Renal Interstitial Edema and Vascular Permeability in Unilateral Ureteral Obstruction 
PLoS ONE  2014;9(1):e85775.
Progressive renal disease is characterized by tubulo-interstitial injury with ongoing inflammation and fibrosis. The Nlrp3 inflammasome contributes to these pathophysiological processes through its canonical effects in cytokine maturation. Nlrp3 may additionally exert inflammasome-independent effects following tissue injury. Hence, in this study we investigated potential non-canonical effects of Nlrp3 following progressive renal injury by subjecting WT and Nlrp3-deficient (−/−) mice to unilateral ureter obstruction (UUO).
Our results revealed a progressive increase of renal Nlrp3 mRNA in WT mice following UUO. The absence of Nlrp3 resulted in enhanced tubular injury and dilatation and an elevated expression of injury biomarker NGAL after UUO. Moreover, interstitial edema was significantly elevated in Nlrp3−/− mice. This could be explained by increased intratubular pressure and an enhanced tubular and vascular permeability. In accordance, renal vascular leakage was elevated in Nlrp3−/− mice that associated with reduced mRNA expression of intercellular junction components. The decreased epithelial barrier function in Nlrp3−/− mice was not associated with increased apoptosis and/or proliferation of renal epithelial cells. Nlrp3 deficiency did not affect renal fibrosis or inflammation.
Together, our data reveal a novel non-canonical effect of Nlrp3 in preserving renal integrity and protection against early tubular injury and interstitial edema following progressive renal injury.
doi:10.1371/journal.pone.0085775
PMCID: PMC3893260  PMID: 24454932
11.  Control of innate and adaptive immunity by the inflammasome 
The importance of innate immunity lies not only in directly confronting pathogenic and non-pathogenic insults but also in instructing the development of an efficient adaptive immune response. The Nlrp3 inflammasome provides a platform for the activation of caspase-1 with the subsequent processing and secretion of IL-1 family members. Given the importance of IL-1 in a variety of inflammatory diseases, understanding the role of Nlrp3 inflammasome in the initiation of innate and adaptive immune responses cannot be overstated. This review examines recent advances in inflammasome biology with an emphasis on its roles in sterile inflammation and triggering of adaptive immune responses.
doi:10.1016/j.micinf.2012.07.007
PMCID: PMC3511629  PMID: 22841804
inflammasome; innate immunity; adaptive immunity
12.  TRPM2 links oxidative stress to the NLRP3 inflammasome activation 
Nature communications  2013;4:1611.
Exposure to particulate crystals can induce oxidative stress in phagocytes, which triggers NLRP3 inflammasome-mediated interleukin 1β (IL-1β) secretion to initiate undesirable inflammatory responses that are associated with both autoinflammatory and metabolic diseases. Although mitochondrial reactive oxygen species (ROS) play a central role in NLRP3 inflammasome activation, how ROS signal assembly of the NLRP3 inflammasome remains elusive. Here, we identify liposomes as novel activators of NLRP3 inflammasome and further demonstrate that liposome-induced inflammasome activation also requires mitochondrial ROS. Moreover, we found that stimulation with liposomes/crystals induced ROS-dependent calcium influx via the TRPM2 channel and that macrophages deficient in TRPM2 displayed drastically impaired NLRP3 inflammasome activation and IL-1β secretion. Consistently, Trpm2−/− mice were resistant to crystal-/liposome-induced IL-1β-mediated peritonitis in vivo. Together, these results identify TRPM2 as a key player that links oxidative stress to the NLRP3 inflammasome activation. Therefore, targeting TRPM2 may be effective for the treatment of NLRP3 inflamamsome-associated inflammatory disorders.
doi:10.1038/ncomms2608
PMCID: PMC3605705  PMID: 23511475
13.  Francisella tularensis Live Vaccine Strain Folate Metabolism and Pseudouridine Synthase Gene Mutants Modulate Macrophage Caspase-1 Activation 
Infection and Immunity  2013;81(1):201-208.
Francisella tularensis is a Gram-negative bacterium and the causative agent of the disease tularemia. Escape of F. tularensis from the phagosome into the cytosol of the macrophage triggers the activation of the AIM2 inflammasome through a mechanism that is not well understood. Activation of the AIM2 inflammasome results in autocatalytic cleavage of caspase-1, resulting in the processing and secretion of interleukin-1β (IL-1β) and IL-18, which play a crucial role in innate immune responses to F. tularensis. We have identified the 5-formyltetrahydrofolate cycloligase gene (FTL_0724) as being important for F. tularensis live vaccine strain (LVS) virulence. Infection of mice in vivo with a F. tularensis LVS FTL_0724 mutant resulted in diminished mortality compared to infection of mice with wild-type LVS. The FTL_0724 mutant also induced increased inflammasome-dependent IL-1β and IL-18 secretion and cytotoxicity in macrophages in vitro. In contrast, infection of macrophages with a F. tularensis LVS rluD pseudouridine synthase (FTL_0699) mutant resulted in diminished IL-1β and IL-18 secretion from macrophages in vitro compared to infection of macrophages with wild-type LVS. In addition, the FTL_0699 mutant was not attenuated in vivo. These findings further illustrate that F. tularensis LVS possesses numerous genes that influence its ability to activate the inflammasome, which is a key host strategy to control infection with this pathogen in vivo.
doi:10.1128/IAI.00991-12
PMCID: PMC3536133  PMID: 23115038
14.  Nlrp10 is essential for protective anti-fungal adaptive immunity against Candida albicans †† 
Nucleotide-binding domain leucine-rich repeat containing receptors (NLRs) are cytosolic receptors that initiate immune responses to sterile and infectious insults to the host. Studies have demonstrated that Nlrp3 is critical for the control of Candida albicans infections and in the generation of anti-fungal Th17 responses. Here we show that the NLR family member Nlrp10 also plays a unique role in the control of disseminated C. albicans infection in vivo. Nlrp10-deficient mice had increased susceptibility to disseminated candidiasis as indicated by decreased survival and increased fungal burdens. In contrast to Nlrp3, Nlrp10-deficiency did not affect innate proinflammatory cytokine production from macrophages and dendritic cells challenged with C. albicans. However, Nlrp10-deficient mice displayed a profound defect in Candida-specific Th1 and Th17 responses. These results demonstrate a novel role for Nlrp10 in the generation of adaptive immune responses to fungal infection.
doi:10.4049/jimmunol.1201715
PMCID: PMC3548226  PMID: 23071280
15.  Annexin A2 binds to endosomes following organelle destabilization by particulate wear debris 
Nature communications  2012;3:755.
Endosomal functions are contingent on the integrity of the organelle-limiting membrane, whose disruption induces inflammation and cell death. Here we show that phagocytosis of ultrahigh molecular weight polyethylene particles induces damage to the endosomal-limiting membrane and results in the leakage of cathepsins into the cytosol and NLRP3-inflammasome activation. Annexin A2 recruitment to damaged organelles is shown by two-dimensional DIGE protein profiling, endosomal fractionation, confocal analysis of endogenous and annexin A2–GFP transfected cells, and immunogold labelling. Binding experiments, using fluorescent liposomes, confirms annexin A2 recruitment to endosomes containing phagocytosed polyethylene particles. Finally, an increase in cytosolic cathepsins, NLRP3-inflammasome activation, and IL-1 production is seen in dendritic cells from annexin A2-null mice, following exposure to polyethylene particles. Together, the results indicate a functional role of annexin A2 binding to endosomal membranes following organelle destabilization.
doi:10.1038/ncomms1754
PMCID: PMC3606553  PMID: 22453828
16.  Sterile inflammatory responses mediated by the NLRP3 inflammasome 
European journal of immunology  2010;40(3):607-611.
Through pattern recognition receptors the innate immune system detects disruption of the normal function of the organism and initiates responses directed at correcting these derangements. Cellular damage from microbial or non-microbial insults causes the activation of nucleotide-binding domain leucine-rich repeat containing receptors (NLR) in multiprotein complexes called inflammasomes. Here we discuss the role of the NLRP3 inflammasome in the recognition of cellular damage and the initiation of sterile inflammatory responses.
doi:10.1002/eji.200940207
PMCID: PMC3601805  PMID: 20201012
caspase-1; necrosis; danger signals
17.  Anaplasma phagocytophilum Dihydrolipoamide Dehydrogenase 1 Affects Host-Derived Immunopathology during Microbial Colonization 
Infection and Immunity  2012;80(9):3194-3205.
Anaplasma phagocytophilum is a tick-borne rickettsial pathogen that provokes an acute inflammatory response during mammalian infection. The illness caused by A. phagocytophilum, human granulocytic anaplasmosis, occurs irrespective of pathogen load and results instead from host-derived immunopathology. Thus, characterizing A. phagocytophilum genes that affect the inflammatory process is critical for understanding disease etiology. By using an A. phagocytophilum Himar1 transposon mutant library, we showed that a single transposon insertion into the A. phagocytophilum dihydrolipoamide dehydrogenase 1 gene (lpda1 [APH_0065]) affects inflammation during infection. A. phagocytophilum lacking lpda1 revealed enlargement of the spleen, increased splenic extramedullary hematopoiesis, and altered clinicopathological abnormalities during mammalian colonization. Furthermore, LPDA1-derived immunopathology was independent of neutrophil infection and correlated with enhanced reactive oxygen species from NADPH oxidase and nuclear factor (NF)-κB signaling in macrophages. Taken together, these findings suggest the presence of different signaling pathways in neutrophils and macrophages during A. phagocytophilum invasion and highlight the importance of LPDA1 as an immunopathological molecule.
doi:10.1128/IAI.00532-12
PMCID: PMC3418742  PMID: 22753375
18.  Beneficial and Detrimental Roles of NLRs in Carcinogenesis 
Inflammation plays a critical role in tumorigenesis and can contribute to oncogenic mutations, tumor promotion, and angiogenesis. Tumor-promoting inflammation is driven by many factors including the presence of the pro-inflammatory cytokines interleukin (IL)-1β and IL-18. One major source of IL-1β and IL-18 secretion is through the activation of inflammasomes. Inflammasomes are multi-protein complexes that upon activation lead to the processing and secretion of IL-1β and IL-18 mediated by the cysteine protease caspase-1. Several inflammasomes, including NLRP3, NLRC4, and NLRP6, have been implicated in tumorigenesis. However, inflammasomes play divergent roles in different types of cancer reflecting the complexity of inflammation during tumorigenesis. Understanding the role of inflammasome activation during specific stages of tumorigenesis and also during cancer immunotherapy will help identify novel therapeutic targets that could improve treatment strategies for cancer patients. Here we will discuss recent advances in understanding the mechanism by which NLRs regulate carcinogenesis.
doi:10.3389/fimmu.2013.00370
PMCID: PMC3824244  PMID: 24273542
inflammasomes; NLR; cancer; interleukin-1; interleukin-18
19.  NLRP10 is a NOD-like receptor essential to initiate adaptive immunity by dendritic cells 
Nature  2012;484(7395):510-513.
NLRs (nucleotide-binding domain leucine-rich repeat containing receptors; NOD-like receptors) are a class of pattern recognition receptor (PRR) that respond to host perturbation from either infectious agents or cellular stress1,2. The function of most NLR family members has not been characterized and their role in instructing adaptive immune responses remains unclear 2,3. NLRP10 (also known as PYNOD, NALP10, PAN5 and NOD8) is the only NLR lacking the putative ligand binding leucine rich repeat domain, and has been postulated to be a negative regulator of other NLR members including NLRP34–6. We did not find evidence that NLRP10 functions through an inflammasome to regulate caspase-1 activity nor that it regulates other inflammasomes. Instead, Nlrp10−/− mice had a profound defect in helper T cell-driven immune responses to a diverse array of adjuvants including lipopolysaccharide (LPS), aluminium hydroxide (alum) and complete Freund’s adjuvant (CFA). Adaptive immunity was impaired in the absence of NLRP10 due to a dendritic cell (DC) intrinsic defect in emigration from inflamed tissues while upregulation of DC costimulatory molecules and chemotaxis to CCR7-dependent and independent ligands remained intact. The loss of antigen transport to the draining LN by this migratory DC subset resulted in an almost absolute loss in naïve CD4+ T cell priming, highlighting the critical link between diverse innate immune stimulation, NLRP10 activity and the immune function of mature DCs.
doi:10.1038/nature11012
PMCID: PMC3340615  PMID: 22538615
Adjuvants; Alum; EAE; Multiple Sclerosis; Asthma; Complete Freund’s Adjuvant; NOD-like Receptors; Nalp; Caspase-1; Pattern Recognition Receptor
20.  Sensing damage by the NLRP3 inflammasome 
Immunological reviews  2011;243(1):152-162.
Summary
The NLRP3 inflammasome is activated in response to a variety of signals that are indicative of damage to the host including tissue damage, metabolic stress, and infection. Upon activation, the NLRP3 inflammasome serves as a platform for activation of the cysteine protease caspase-1, which leads to the processing and secretion of the proinflammatory cytokines interleukin-1β (IL-1β) and IL-18. Dysregulated NLRP3 inflammasome activation is associated with both heritable and acquired inflammatory diseases. Here we review new insights into the mechanism of NLRP3 inflammasome activation and its role in disease pathogenesis.
doi:10.1111/j.1600-065X.2011.01043.x
PMCID: PMC3170135  PMID: 21884174
NLRP3; inflammasome; caspase-1; sterile inflammation
21.  Cutting Edge: Caspase-1 Independent IL-1β Production Is Critical for Host Resistance to Mycobacterium tuberculosis and Does Not Require TLR Signaling In Vivo 
To investigate the respective contributions of TLR versus IL-1R mediated signals in MyD88 dependent control of Mycobacterium tuberculosis, we compared the outcome of M. tuberculosis infection in MyD88, TRIF/MyD88, IL-1R1, and IL-1β-deficient mice. All four strains displayed acute mortality with highly increased pulmonary bacterial burden suggesting a major role for IL-1β signaling in determining the MyD88 dependent phenotype. Unexpectedly, the infected MyD88 and TRIF/MyD88-deficient mice, rather than being defective in IL-1β expression, displayed increased cytokine levels relative to wild-type animals. Similarly, infected mice deficient in caspase-1 and ASC, which have critical functions in inflammasome-mediated IL-1β maturation, showed unimpaired IL-1β production and importantly, were considerably less susceptible to infection than IL-1β deficient mice. Together our findings reveal a major role for IL-1β in host resistance to M. tuberculosis and indicate that during this infection the cytokine can be generated by a mechanism that does not require TLR signaling or caspase-1. The Journal of Immunology, 2010, 184: 3326–3330.
doi:10.4049/jimmunol.0904189
PMCID: PMC3420351  PMID: 20200276
22.  Mycobacterium tuberculosis Infection of Dendritic Cells Leads to Partially Caspase-1/11-Independent IL-1β and IL-18 Secretion but Not to Pyroptosis 
PLoS ONE  2012;7(7):e40722.
Background
Interleukin-1β (IL-1β) is important for host resistance against Mycobacterium tuberculosis (Mtb) infections. The response of the dendritic cell inflammasome during Mtb infections has not been investigated in detail.
Methodology/Principal Findings
Here we show that Mtb infection of bone marrow-derived dendritic cells (BMDCs) induces IL-1β secretion and that this induction is dependent upon the presence of functional ASC and NLRP3 but not NLRC4 or NOD2. The analysis of cell death induction in BMDCs derived from these knock-out mice revealed the important induction of host cell apoptosis but not necrosis, pyroptosis or pyronecrosis. Furthermore, NLRP3 inflammasome activation and apoptosis induction were both reduced in BMDCs infected with the esxA deletion mutant of Mtb demonstrating the importance of a functional ESX-1 secretion system. Surprisingly, caspase-1/11-deficient BMDCs still secreted residual levels of IL-1βand IL-18 upon Mtb infection which was abolished in cells infected with the esxA Mtb mutant.
Conclusion
Altogether we demonstrate the partially caspase-1/11-independent, but NLRP3- and ASC- dependent IL-1β secretion in Mtb-infected BMDCs. These findings point towards a potential role of DCs in the host innate immune response to mycobacterial infections via their capacity to induce IL-1β and IL-18 secretion.
doi:10.1371/journal.pone.0040722
PMCID: PMC3404059  PMID: 22911706
23.  Cutting Edge: Mutation of Francisella tularensis mviN Leads to Increased Macrophage Absent in Melanoma 2 Inflammasome Activation and a Loss of Virulence 
The mechanisms by which the intracellular pathogen Francisella tularensis evades innate immunity are not well defined. We have identified a gene with homology to Escherichia coli mviN, a putative lipid II flippase, which F. tularensis uses to evade activation of innate immune pathways. Infection of mice with a F. tularensis mviN mutant resulted in improved survival and decreased bacterial burdens compared to infection with wild-type F. tularensis. The mviN mutant also induced increased AIM2 inflammasome-dependent IL-1β secretion and cytotoxicity in macrophages. The compromised in vivo virulence of the mviN mutant depended upon inflammasome activation, as caspase-1- and ASC-deficient mice did not exhibit preferential survival following infection. This study demonstrates that mviN limits F. tularensis-induced AIM2 inflammasome activation which is critical for its virulence in vivo.
doi:10.4049/jimmunol.1001610
PMCID: PMC2953561  PMID: 20679532
24.  A Yersinia secreted effector protein promotes virulence by preventing inflammasome recognition of the type III secretion system 
Cell host & microbe  2010;7(5):376-387.
Pattern recognition receptors (PRRs) detect conserved microbial structures generally absent from eukaryotes. Bacterial pathogens commonly utilize pore-forming toxins or specialized secretion systems to deliver virulence factors that promote bacterial replication by modulating host cell physiology. Detection of these secretion systems or toxins by nucleotide-binding oligomerization domain leucine-rich-repeat proteins (NLRs) triggers the assembly of multiprotein complexes, termed inflammasomes, necessary for caspase-1 activation. Here we demonstrate that caspase-1 activation in response to the Yersinia type III secretion system (T3SS) requires the adapter ASC, and involves both NLRP3 and NLRC4 inflammasomes. We further identify a Yersinia type III secreted effector protein, YopK, which prevents inflammasome activation by preventing cellular recognition of the T3SS. Inflammasome-mediated sensing of the T3SS promotes bacterial clearance from infected tissues in vivo. These data demonstrate that a class of bacterial proteins interferes with cellular recognition of bacterial secretion systems, which contributes to bacterial survival within host tissues.
doi:10.1016/j.chom.2010.04.009
PMCID: PMC2883865  PMID: 20478539
25.  Candida albicans hyphae formation triggers activation of the Nlrp3 inflammasome 
The proinflammatory cytokine IL-1β plays an important role in antifungal immunity; however the mechanisms by which fungal pathogens trigger IL-1β secretion are unclear. Here we show that infection with C. albicans is sensed by the Nlrp3 inflammasome resulting in the subsequent release of IL-1β. 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-1β secretion. Nlrp3-deficient mice also demonstrated increased susceptibility to infection with C. albicans consistent with a key role for Nlrp3 in innate immune responses to the pathogen C. albicans.
doi:10.4049/jimmunol.0901323
PMCID: PMC2739101  PMID: 19684085

Results 1-25 (36)