The Cag pathogenicity island and interaction between TLR2/NOD2 and NLRP3 regulate IL‐1β production in Helicobacter pylori infected dendritic cells

Helicobacter pylori colonization of the stomach affects about half of the world population and is associated with the development of gastritis, ulcers, and cancer. Polymorphisms in the IL1B gene are linked to an increased risk of H. pylori associated cancer, but the bacterial and host factors that regulate interleukin (IL)‐1β production in response to H. pylori infection remain unknown. Using murine BM‐derived DCs, we show that the bacterial virulence factors cytotoxin‐associated genes pathogenicity island and CagL, but not vacuolating cytotoxin A or CagA, regulate the induction of pro‐IL‐1β and the production of mature IL‐1β in response to H. pylori infection. We further show that the host receptors, Toll‐like receptor 2 (TLR2) and nucleotide‐binding oligomerization domain 2 (NOD2), but not NOD1, are required for induction of pro‐IL‐1β and NOD‐like receptor pyrin domain containing 3 (NLRP3) in H. pylori infected DCs. In contrast, NLRP3 and the adaptor ASC were essential for the activation of caspase‐1, processing of pro‐IL‐1β into IL‐1β, and IL‐1β secretion. Finally, we show that mice deficient in caspase‐1, IL‐1β, and IL‐1 receptor, but not NLRP3, are impaired in the clearance of CagA‐positive H. pylori from the stomach when compared with WT mice. These studies identify bacterial cag pathogenicity island and the cooperative interaction among host innate receptors TLR2, NOD2, and NLRP3 as important regulators of IL‐1β production in H. pylori infected DCs.     

Toll‐like receptor‐induced granulocyte‐macrophage colony‐stimulating factor secretion is impaired in Crohn's disease by nucleotide oligomerization domain 2‐dependent and ‐independent pathways

Pattern recognition receptors (PRRs) are an integral part of the innate immune system and govern the early control of foreign microorganisms. Single nucleotide polymorphisms (SNPs) in the intracellular pattern recognition receptor nucleotide‐binding oligomerization domain‐containing protein (NOD2, nucleotide oligomerization domain 2) are associated with Crohn's disease (CD). We investigated the impact of NOD2 polymorphisms on cytokine secretion and proliferation of peripheral blood mononuclear cells (PBMCs) in response to Toll‐like receptor (TLR) and NOD2 ligands. Based on NOD2 SNP analyses, 41 CD patients and 12 healthy controls were studied. PBMCs were stimulated with NOD2 and TLR ligands. After 18 h culture supernatants were measured using multiplex assays for the presence of human cytokines granulocyte–macrophage colony‐stimulating factor (GM‐CSF), interleukin (IL)‐1β and tumour necrosis factor (TNF)‐α. In CD patients, TLR‐induced GM‐CSF secretion was impaired by both NOD2‐dependent and ‐independent mechanisms. Moreover, TNF‐α production was induced by a TLR‐2 ligand, but a down‐regulatory function by the NOD2 ligand, muramyl dipeptide, was impaired significantly in CD patients. Intracellular TLR ligands had minimal effect on GM‐CSF, TNF‐α and IL‐1β secretion. CD patients with NOD2 mutations were able to secrete TNF‐α, but not GM‐CSF, upon stimulation with NOD2 and TLR‐7 ligands. CD patients have impaired GM‐CSF secretion via NOD2‐dependent and ‐independent pathways and display an impaired NOD2‐dependent down‐regulation of TNF‐α secretion. The defect in GM‐CSF secretion suggests a hitherto unknown role of NOD2 in the pathogenesis of CD and is consistent with the hypothesis that impaired GM‐CSF secretion in part constitutes a NOD2‐dependent disease risk factor.     

Pannexin‐1‐dependent caspase‐1 activation and secretion of IL‐1β is regulated by zinc

Inflammatory processes induced by IL‐1β are critical for host defence responses, but are also implicated in disease. Zinc deficiency is a common consequence of, or contributor to, human inflammatory disease. However, the molecular mechanisms through which zinc contributes to inflammatory disease remain largely unknown. We report here that zinc metabolism regulates caspase‐1 activation and IL‐1β secretion. One of the endogenous mediators of IL‐1β secretion is adenosine triphosphate, acting via the P2X7‐receptor and caspase‐1 activation in cells primed with an inflammatory stimulus such as LPS. We show that this process is selectively abolished by a brief pre‐treatment with the zinc chelator N,N,N′,N′‐tetrakis‐(2‐pyridylmethyl) ethylene diamine (TPEN). These effects on IL‐1β secretion were independent of rapid changes in free zinc within the cell, not a direct effect on caspase‐1 activity, and upstream of caspase‐1 activation. TPEN did however inhibit the activity of pannexin‐1, a hemi‐channel critical for adenosine triphosphate and nigericin‐induced IL‐1β release. These data provide new insights into the mechanisms of caspase‐1 activation and how zinc metabolism contributes to inflammatory mechanisms.     

A role for IL‐18 in protective immunity against Mycobacterium tuberculosis

Tuberculosis remains the most hazardous bacterial infection worldwide. The causative agent, Mycobacterium tuberculosis, is a facultative intracellular pathogen of resting MΦ. IFN‐γ secreted by natural killer, CD4 Th 1 and CD8 T cells upon instruction by IL‐12 and ‐18 activates MΦ to restrict mycobacterial growth. Production of both cytokines is induced by TLR signalling in DC and MΦ. Mice deficient for the TLR adaptor, MyD88, are highly susceptible to M. tuberculosis infection. Shared usage of MyD88 by signalling cascades for TLR and receptors for IL‐1 and IL‐18 prompted us to revisit the role of IL‐18 during experimental infection with M. tuberculosis. We show that mice deficient for IL‐18 and MyD88 but not for IL‐18 receptor promptly succumbed to M. tuberculosis infection in contrast to WT or TLR‐2/‐4 double KO mice indicating that lack of IL‐18 contributes to the high susceptibility of MyD88 KO mice to M. tuberculosis. Without IL‐18, the protective Th1 response was decreased and hence, mycobacterial propagation was favoured. Neutrophil‐driven lung immunopathology concomitant with unrestrained growth of tubercle bacilli are most likely responsible for the premature death of IL‐18 KO mice. Thus, IL‐18 plays a decisive role in protective immunity against tuberculosis.     

RIP2/RICK‐Dependent Cytokine Production Upon Yersinia enterocolitica Infection in Macrophages with TLR4 Deficiency

Receptor‐interacting protein 2 (RIP2) is a caspase recruitment domain (CARD)‐containing serine/threonine kinase that is activated by NOD1 or NOD2 recognition of their ligands and essential for the activation of NF‐κB and mitogen‐activated protein kinase (MAPK). RIP2 has been known to play an important role in innate immune responses against certain bacterial infection. However, the role and interplay of RIP2 with TLR signalling on cytokine production in macrophages against Yersinia enterocolitica infection remains poorly understood. In the present study, we examined whether RIP2 is essential for Yersinia‐induced production of cytokines in macrophages. Our results showed that naïve RIP2‐deficient macrophages produced similar level of IL‐6, TNF‐α and IL‐10 upon Y. enterocolitica infection compared with wild‐type macrophages. However, the production of IL‐6, TNF‐α and IL‐10 by Y. enterocolitica was impaired in RIP2‐deficient macrophages after lipopolysaccharide (LPS) pretreatment, a TLR4‐tolerant condition. In addition, RIP2 inhibitors, SB203580, PP2, and gefitinib, reduced IL‐6 production in TLR4‐deficient macrophages in response to Y. enterocolitica, whereas they did not affect the cytokines production in WT cells. These results demonstrate that RIP2 may play an important role in proinflammatory cytokine production in macrophages at the absence of TLR signalling.     

Impaired NLRP3 inflammasome activity during fetal development regulates IL‐1β production in human monocytes

Interleukin‐1β (IL‐1β) production is impaired in cord blood monocytes. However, the mechanism underlying this developmental attenuation remains unclear. Here, we analyzed the extent of variability within the Toll‐like receptor (TLR)/NLRP3 inflammasome pathways in human neonates. We show that immature low CD14 expressing/CD16^pos monocytes predominate before 33 weeks of gestation, and that these cells lack production of the pro‐IL‐1β precursor protein upon LPS stimulation. In contrast, high levels of pro‐IL‐1β are produced within high CD14 expressing monocytes, although these cells are unable to secrete mature IL‐1β. The lack of secreted IL‐1β in these monocytes parallels a reduction of NLRP3 induction following TLR stimulation resulting in a lack of caspase‐1 activity before 29 weeks of gestation, whereas expression of the apoptosis‐associated speck‐like protein containing a CARD and function of the P2×7 receptor are preserved. Our analyses also reveal a strong inhibitory effect of placental infection on LPS/ATP‐induced caspase‐1 activity in cord blood monocytes. Lastly, secretion of IL‐1β in preterm neonates is restored to adult levels during the neonatal period, indicating rapid maturation of these responses after birth. Collectively, our data highlight important developmental mechanisms regulating IL‐1β responses early in gestation, in part due to a downregulation of TLR‐mediated NLRP3 expression. Such mechanisms may serve to limit potentially damaging inflammatory responses in a developing fetus.     

NLRP3 inflammasome activation downstream of cytoplasmic LPS recognition by both caspase‐4 and caspase‐5

Humans encode two inflammatory caspases that detect cytoplasmic LPS, caspase‐4 and caspase‐5. When activated, these trigger pyroptotic cell death and caspase‐1‐dependent IL‐1β production; however the mechanism underlying this process is not yet confirmed. We now show that a specific NLRP3 inhibitor, MCC950, prevents caspase‐4/5‐dependent IL‐1β production elicited by transfected LPS. Given that both caspase‐4 and caspase‐5 can detect cytoplasmic LPS, it is possible that these proteins exhibit some degree of redundancy. Therefore, we generated human monocytic cell lines in which caspase‐4 and caspase‐5 were genetically deleted either individually or together. We found that the deletion of caspase‐4 suppressed cell death and IL‐1β production following transfection of LPS into the cytoplasm, or in response to infection with Salmonella typhimurium. Although deletion of caspase‐5 did not confer protection against transfected LPS, cell death and IL‐1β production were reduced after infection with Salmonella. Furthermore, double deletion of caspase‐4 and caspase‐5 had a synergistic effect in the context of Salmonella infection. Our results identify the NLRP3 inflammasome as the specific platform for IL‐1β maturation, downstream of cytoplasmic LPS detection by caspase‐4/5. We also show that both caspase‐4 and caspase‐5 are functionally important for appropriate responses to intracellular Gram‐negative bacteria.     

Brucella abortus nitric oxide metabolite regulates inflammasome activation and IL‐1β secretion in murine macrophages

NLRP3 inflammasome is a protein complex crucial to caspase‐1 activation and IL‐1β and IL‐18 maturation. This receptor participates in innate immune responses to different pathogens, including the bacteria of genus Brucella. Our group recently demonstrated that Brucella abortus‐induced IL‐1β secretion involves NLRP3 inflammasome and it is partially dependent on mitochondrial ROS production. However, other factors could be involved, such as P2X7‐dependent potassium efflux, membrane destabilization, and cathepsin release. Moreover, there is increasing evidence that nitric oxide acts as a modulator of NLRP3 inflammasome. The aim of this study was to unravel the mechanism of NLRP3 inflammasome activation induced by B. abortus, as well as the involvement of bacterial nitric oxide (NO) as a modulator of this inflammasome pathway. We demonstrated that NO produced by B. abortus can be used by the bacteria to modulate IL‐1β secretion in infected murine macrophages. Additionally, our results suggest that B. abortus‐induced IL‐1β secretion depends on a P2X7‐independent potassium efflux, lysosomal acidification, cathepsin release, mechanisms clearly associated to NLRP3 inflammasome. In summary, our results help to elucidate the molecular mechanisms of NLRP3 activation and regulation during an intracellular bacterial infection.     

Propionibacterium acnes activates caspase‐1 in human neutrophils

Propionibacterium acnes is a Gram‐positive, slow‐growing, anaerobic bacillus, predominantly found as a commensal on the skin and mucous membranes of adults. It is, however, also considered an opportunistic pathogen; mostly associated with acne vulgaris, but rarely also with severe infections such as infective endocarditis, prosthetic joint infections, and deep sternal wound infections following cardiothoracic surgery. In addition, P. acnes has recently been found in high frequency in prostate tissue from patients with prostatitis and prostate cancer. The NOD‐like receptors (NLR) act as intracellular sensors of microbial components, and a number of various bacteria have been found to induce assembling and activation of NLR‐inflammasomes; leading to a pro‐inflammatory response. The inflammasome‐mediated formation of the pro‐inflammatory cytokines interleukin‐1β (IL‐1β) and IL‐18 involves the auto‐proteolytic maturation of caspase‐1. This study investigated if P. acnes activates inflammasomes. Propionibacterium acnes isolates (n = 29) with diverse origin were used as stimuli for peripheral leukocytes obtained from blood donors (BDs). The activity of inflammasomes was determined by measuring caspase‐1 by flow cytometry and cytokine production by ELISA. A significant amount of caspase‐1 was found in neutrophils upon P. acnes stimulation, whereas only a modest activation was seen in monocytes. The activation was mainly produced by components of the bacterial cell and no exo‐products, because heat‐killed and live bacteria caused high activation of caspase‐1 as well as cytokine production, whereas the bacterial supernatant elicited minor effect. The response among different BDs varied significantly, almost fivefold. In addition, P. acnes of various origins showed considerable variation, however, the commensal isolates showed a stronger response compared with the invasive. In conclusion, although regarded as a harmless commensal of the skin, P. acnes strongly activates the inflammasome of human peripheral neutrophils.     

Virulence‐dependent induction of interleukin‐10‐producing‐tolerogenic dendritic cells by Mycobacterium tuberculosis impedes optimal T helper type 1 proliferation

Mycobacterium tuberculosis inhibits optimal T helper type 1 (Th1) responses during infection. However, the precise mechanisms by which virulent M. tuberculosis limits Th1 responses remain unclear. Here, we infected dendritic cells (DCs) with the virulent M. tuberculosis strain H37Rv or the attenuated strain H37Ra to investigate the phenotypic and functional alterations in DCs and resultant T‐cell responses. H37Rv‐infected DCs suppressed Th1 responses more strongly than H37Ra‐infected DCs. Interestingly, H37Rv, but not H37Ra, impaired DC surface molecule expression (CD80, CD86 and MHC class II) due to prominent interleukin‐10 (IL‐10) production while augmenting the expression of tolerogenic molecules including PD‐L1, CD103, Tim‐3 and indoleamine 2,3‐dioxygenase on DCs in a multiplicity‐of‐infection (MOI) ‐dependent manner. These results indicate that virulent M. tuberculosis drives immature DCs toward a tolerogenic phenotype. Notably, the tolerogenic phenotype of H37Rv‐infected DCs was blocked in DCs generated from IL‐10^−/− mice or DCs treated with an IL‐10‐neutralizing monoclonal antibody, leading to restoration of Th1 polarization. These findings suggest that IL‐10 induces a tolerogenic DC phenotype. Interestingly, p38 mitogen‐activated protein kinase (MAPK) activation predominantly mediates IL‐10 production; hence, H37Rv tends to induce a tolerogenic DC phenotype through expression of tolerogenic molecules in the p38 MAPK–IL‐10 axis. Therefore, suppressing the tolerogenic cascade in DCs is a novel strategy for stimulating optimal protective T‐cell responses against M. tuberculosis infection.     

PKC,ERK/p38 MAP kinases and NF‐κB targeted signalling play a role in the expression and release of IL‐1β and CXCL8 in Porphyromonas gingivalis‐infected THP1 cells

Porphyromonas gingivalis is a keystone pathogen in periodontitis and is gaining importance in cardiovascular pathogenesis. Protease‐activated receptors (PARs), toll‐like receptors (TLRs) and nucleotide‐binding oligomerization domain (NOD) on monocytes recognize the structural components on P. gingivalis, inducing inflammatory intermediates. Here, we elucidate the modulation of PARs, TLRs, NODs, and the role of MAPK and NF‐κB in IL‐1β and CXCL8 release. THP1 cells were stimulated with P. gingivalis wild‐type W50 and its isogenic gingipain mutants: Rgp mutant E8 and Kgp mutant K1A. We observed modulation of PARs, TLRs, NOD, IL‐1β and CXCL8 expression by P. gingivalis. Gingipains hydrolyse IL‐1β and CXCL8, which is more evident for IL‐1β accumulation at 24 h. Inhibition of PKC (protein kinase C), p38 and ERK (extracellular signal‐regulated kinases) partially reduced P. gingivalis‐induced IL‐1β at 6 h, whereas PKC and ERK reduced CXCL8 at both 6 and 24 h. Following NF‐κB inhibition, P. gingivalis‐induced IL‐1β and CXCL8 were completely suppressed to basal levels. Overall, TLRs, PARs and NOD possibly act in synergy with PKC, MAPK ERK/p38 and NF‐κB in P. gingivalis‐induced IL‐1β and CXCL8 release from THP1 cells. These pro‐inflammatory cytokines could affect leucocytes in circulation and exacerbate other vascular inflammatory conditions such as atherosclerosis.     

Caspase‐11 non‐canonical inflammasome: a critical sensor of intracellular lipopolysaccharide in macrophage‐mediated inflammatory responses

Inflammatory responses mediated by macrophages are part of the innate immune system, whose role is to protect against invading pathogens. Lipopolysaccharide (LPS) found in the outer membrane of Gram‐negative bacteria stimulates an inflammatory response by macrophages. During the inflammatory response, extracellular LPS is recognized by Toll‐like receptor 4, one of the pattern recognition receptors that activates inflammatory signalling pathways and leads to the production of inflammatory mediators. The innate immune response is also triggered by intracellular inflammasomes, and inflammasome activation induces pyroptosis and the secretion of pro‐inflammatory cytokines such as interleukin‐1β (IL‐1β) and IL‐18 by macrophages. Cysteine‐aspartic protease (caspase)‐11 and the human orthologues caspase‐4/caspase‐5 were recently identified as components of the ‘non‐canonical inflammasome’ that senses intracellular LPS derived from Gram‐negative bacteria during macrophage‐mediated inflammatory responses. Direct recognition of intracellular LPS facilitates the rapid oligomerization of caspase‐11/4/5, which results in pyroptosis and the secretion of IL‐1β and IL‐18. LPS is released into the cytoplasm from Gram‐negative bacterium‐containing vacuoles by small interferon‐inducible guanylate‐binding proteins encoded on chromosome 3 (GBP^chr3)‐mediated lysis of the vacuoles. In vivo studies have clearly shown that caspase‐11^−/− mice are more resistant to endotoxic septic shock by excessive LPS challenge. Given the evidence, activation of caspase‐11 non‐canonical inflammasomes by intracellular LPS is distinct from canonical inflammasome activation and provides a new paradigm in macrophage‐mediated inflammatory responses.     

IL‐1β activation in response to Staphylococcus aureus lung infection requires inflammasome‐dependent and independent mechanisms

Maintaining balanced levels of IL‐1β is extremely important to avoid host tissue damage during infection. Our goal was to understand the mechanisms behind the reduced pathology and decreased bacterial burdens in Ifnlr1^?/? mice during lung infection with Staphylococcus aureus. Intranasal infection of Ifnlr1^?/? mice with S. aureus led to significantly improved bacterial clearance, survival and decrease of proinflammatory cytokines in the airway including IL‐1β. Ifnlr1^?/? mice treated with recombinant IL‐1β displayed increased bacterial burdens in the airway and lung. IL‐1β levels in neutrophils from Ifnlr1^?/? infected mice lungs were decreased when compared to neutrophils from WT mice. Mice lacking NLRP3 and caspase‐1 had reduced IL‐1β levels 4 h after infection, due to reductions or absence of active caspase‐1 respectively, but levels at 24 h were comparable to WT infected mice. Ifnlr1^?/? infected mice had decreases in both active caspase‐1 and neutrophil elastase indicating an important role for the neutrophil serine protease in IL‐1β processing. By inhibiting neutrophil elastase, we were able to decrease IL‐1β levels by 39% in Nlrp3^?/? infected mice when compared to WT mice. These results highlight the crucial role of both proteases in IL‐1β processing, via inflammasome‐dependent and ‐independent mechanisms.     

Mycoplasma pneumoniae lipids license TLR‐4 for activation of NLRP3 inflammasome and autophagy to evoke a proinflammatory response

Mycoplasma pneumoniae is an obligate pathogen that causes pneumonia, tracheobronchitis, pharyngitis and asthma in humans. It is well recognized that membrane lipoproteins are immunostimulants exerting as lipopolysaccharides (LPS) and play a crucial role in the pathogenesis of inflammatory responses upon M. pneumoniae infection. Here, we report that the M. pneumoniae‐derived lipids are another proinflammatory agents. Using an antibody‐neutralizing assay, RNA interference or specific inhibitors, we found that Toll‐like receptor 4 (TLR‐4) is essential for M. pneumoniae lipid‐induced tumour necrosis factor (TNF)‐α and interleukin (IL)‐1β production. We also demonstrate that NLR family pyrin domain containing 3 inflammasome (NLRP3) inflammasome, autophagy and nuclear factor kappa B (NF‐κB)‐dependent pathways are critical for the secretion of proinflammatory cytokines, while inhibition of TLR‐4 significantly abrogates these events. Further characterization revealed that autophagy‐mediated inflammatory responses involved the activation of NF‐κB. In addition, the activation of NF‐κB promoted lipid‐induced autophagosome formation, as revealed by assays using pharmacological inhibitors, 3‐methyladenine (3‐MA) and Bay 11‐7082, or silencing of atg5 and beclin‐1. These findings suggest that, unlike the response to lipoprotein stimulation, the inflammation in response to M. pneumoniae lipids is mediated by the TLR‐4 pathway, which subsequently initiates the activation of NLRP3 inflammasome and formation of a positive feedback loop between autophagy and NF‐κB signalling cascade, ultimately promoting TNF‐α and Il‐1β production in macrophages.     

Complement C5a potentiates uric acid crystal‐induced IL‐1β production

Anaphylatoxin C5a released upon complement activation is associated with both acute and chronic inflammations such as gout. The pathogenesis of gout was identified as uric acid crystal deposition in the joints that activates inflammasome, leading to IL‐1β release. However, little is known about the interaction between complement activation and monosodium urate/uric acid (MSU) crystal‐induced inflammasome activation or IL‐1β production. Here, we report that MSU crystal‐induced proinflammatory cytokines/chemokines in human whole blood is predominantly regulated by C5a through its interaction with C5a receptor. C5a induces pro‐IL‐1β and IL‐1β production in human primary monocytes, and potentiates MSU or cholesterol crystals in IL‐1β production. This potentiation is caspase‐1 dependent and requires intracellular Ca²⁺ mobilization, K⁺ efflux, and cathepsin B activity. Our results provide insight into the role of C5a as an endogenous priming signal that is required for the initiation of uric acid crystal‐induced IL‐1β production. C5a could potentially be a therapeutic target together with IL‐1β antagonists for the treatment of complement‐dependent and inflammasome‐associated diseases.     

The protein kinase PKR is critical for LPS‐induced iNOS production but dispensable for inflammasome activation in macrophages

Inflammasomes are multi‐protein platforms that drive the activation of caspase‐1 leading to the processing and secretion of biologically active IL‐1β and IL‐18. Different inflammasomes including NOD‐like receptor (NLR) family pyrin domain‐containing 3 (NLRP3), NLR caspase‐recruitment domain‐containing 4 (NLRC4) and absent in melanoma 2 (AIM2) are activated and assembled in response to distinct microbial or endogenous stimuli. However, the mechanisms by which upstream stimuli trigger inflammasome activation remain poorly understood. Double‐stranded RNA‐activated protein kinase (PKR), a protein kinase activated by viral infection, has been recently shown to be required for the activation of the inflammasomes. Using macrophages from two different mouse strains deficient in PKR, we found that PKR is important for the induction of the inducible nitric oxide synthase (iNOS). However, PKR was dispensable for caspase‐1 activation, processing of pro‐IL‐1β/IL‐18 and secretion of IL‐1β induced by stimuli that trigger the activation of NLRP3, NLRC4 and AIM2. These results indicate that PKR is not required for inflammasome activation in macrophages.     

Caspase‐4 mediates non‐canonical activation of the NLRP3 inflammasome in human myeloid cells

Inflammasome activation culminates in activation of caspase‐1, which leads to the maturation and subsequent release of cytokines of the interleukin 1 (IL‐1) family and results in a particular form of cell death known as pyroptosis. In addition, in the murine system, a so‐called non‐canonical inflammasome involving caspase‐11 has been described that directly responds to cytosolic LPS. Here, we show that the human monocytic cell line THP1 activates the inflammasome in response to cytosolic LPS in a TLR4‐independent fashion. This response is mediated by caspase‐4 and accompanied by caspase‐1 activation, pyroptosis, and IL‐1β maturation. In addition to caspase‐4, efficient IL‐1β conversion upon intracellular LPS delivery relies on potassium efflux, NLRP3, ASC, and caspase‐1, indicating that although caspase‐4 activation alone is sufficient to induce pyroptosis, this process depends on the NLRP3 inflammasome activation to drive IL‐1β maturation. Altogether, this study provides evidence for the presence of a non‐canonical inflammasome in humans and its dependence on caspase‐4.     

Staphylococcus epidermidis from prosthetic joint infections induces lower IL‐1β release from human neutrophils than isolates from normal flora

The aim of this study was to test the hypothesis that Staphylococcus epidermidis isolated from prosthetic joint infections (PJIs) differs from S. epidermidis isolated from normal flora in terms of its capacity to induce activation of caspase‐1 and release of IL‐1β in human neutrophils. The amount of active caspase‐1 was determined over 6 h by detecting Ac‐YVAD‐AMC fluorescence in human neutrophils incubated with S. epidermidis isolates from PJIs (ST2) or normal flora. The amount of IL‐1β was detected by ELISA in neutrophil supernatants after 6 h of incubation. Mean IL‐1β release was lower after incubation with S. epidermidis from PJIs compared to isolates from normal flora, but no statistically significant difference was found in active caspase‐1. Substantial inter‐individual differences in both active caspase‐1 and IL‐1β were noted. These results suggest that evasion of innate immune response, measured as reduced capacity to induce release of IL‐1β from human neutrophils, might be involved in the predominance of ST2 in S. epidermidis PJIs, but that other microbe‐related factors are probably also important.     

Card9‐dependent IL‐1β regulates IL‐22 production from group 3 innate lymphoid cells and promotes colitis‐associated cancer

Inflammatory bowel diseases (IBD) are key risk factors for the development of colorectal cancer, but the mechanisms that link intestinal inflammation with carcinogenesis are insufficiently understood. Card9 is a myeloid cell‐specific signaling protein that regulates inflammatory responses downstream of various pattern recognition receptors and which cooperates with the inflammasomes for IL‐1β production. Because polymorphisms in Card9 were recurrently associated with human IBD, we investigated the function of Card9 in a colitis‐associated cancer (CAC) model. Card9^?/? mice develop smaller, less proliferative and less dysplastic tumors compared to their littermates and in the regenerating mucosa we detected dramatically impaired IL‐1β generation and defective IL‐1β controlled IL‐22 production from group 3 innate lymphoid cells. Consistent with the key role of immune‐derived IL‐22 in activating STAT3 signaling during normal and pathological intestinal epithelial cell (IEC) proliferation, Card9^?/? mice also exhibit impaired tumor cell intrinsic STAT3 activation. Our results imply a Card9‐controlled, ILC3‐mediated mechanism regulating healthy and malignant IEC proliferation and demonstrates a role of Card9‐mediated innate immunity in inflammation‐associated carcinogenesis.