Tyrosine phosphatase SHP-2 mediates C-type lectin receptor-induced activation of the kinase Syk and anti-fungal TH17 responses.

Fungal infection stimulates the canonical C-type lectin receptor (CLR) signaling pathway via activation of the tyrosine kinase Syk. Here we identify a crucial role for the tyrosine phosphatase SHP-2 in mediating CLR-induced activation of Syk. Ablation of the gene encoding SHP-2 (Ptpn11; called 'Shp-2' here) in dendritic cells (DCs) and macrophages impaired Syk-mediated signaling and abrogated the expression of genes encoding pro-inflammatory molecules following fungal stimulation. Mechanistically, SHP-2 operated as a scaffold, facilitating the recruitment of Syk to the CLR dectin-1 or the adaptor FcRγ, through its N-SH2 domain and a previously unrecognized carboxy-terminal immunoreceptor tyrosine-based activation motif (ITAM). We found that DC-derived SHP-2 was crucial for the induction of interleukin 1ß (IL-1ß), IL-6 and IL-23 and anti-fungal responses of the TH17 subset of helper T cells in controlling infection with Candida albicans. Together our data reveal a mechanism by which SHP-2 mediates the activation of Syk in response to fungal infection.

Inflammasome Activation Triggers Caspase-1-Mediated Cleavage of cGAS to Regulate Responses to DNA Virus Infection.

Viral infection triggers host innate immune responses that result in the production of various cytokines including type I interferons (IFN), activation of inflammasomes, and programmed cell death of the infected cells. Tight control of inflammatory cytokine production is crucial for the triggering of an effective immune response that can resolve the infection without causing host pathology. In examining the inflammatory response of Asc-/- and Casp1-/- macrophages, we found that deficiency in these molecules resulted in increased IFN production upon DNA virus infection, but not RNA virus challenge. Investigation of the underlying mechanism revealed that upon canonical and non-canonical inflammasome activation, caspase-1 interacted with cyclic GMP-AMP (cGAMP) synthase (cGAS), cleaving it and dampening cGAS-STING-mediated IFN production. Deficiency in inflammasome signaling enhanced host resistance to DNA virus in vitro and in vivo, and this regulatory role extended to other inflammatory caspases. Thus, inflammasome activation dampens cGAS-dependent signaling, suggesting cross-regulation between intracellular DNA-sensing pathways.

Antibody-mediated spike activation promotes cell-cell transmission of SARS-CoV-2.

The COVID pandemic fueled by emerging SARS-CoV-2 new variants of concern remains a major global health concern, and the constantly emerging mutations present challenges to current therapeutics. The spike glycoprotein is not only essential for the initial viral entry, but is also responsible for the transmission of SARS-CoV-2 components via syncytia formation. Spike-mediated cell-cell transmission is strongly resistant to extracellular therapeutic and convalescent antibodies via an unknown mechanism. Here, we describe the antibody-mediated spike activation and syncytia formation on cells displaying the viral spike. We found that soluble antibodies against receptor binding motif (RBM) are capable of inducing the proteolytic processing of spike at both the S1/S2 and S2' cleavage sites, hence triggering ACE2-independent cell-cell fusion. Mechanistically, antibody-induced cell-cell fusion requires the shedding of S1 and exposure of the fusion peptide at the cell surface. By inhibiting S1/S2 proteolysis, we demonstrated that cell-cell fusion mediated by spike can be re-sensitized towards antibody neutralization in vitro. Lastly, we showed that cytopathic effect mediated by authentic SARS-CoV-2 infection remain unaffected by the addition of extracellular neutralization antibodies. Hence, these results unveil a novel mode of antibody evasion and provide insights for antibody selection and drug design strategies targeting the SARS-CoV-2 infected cells.

SARS-CoV-2 spike engagement of ACE2 primes S2' site cleavage and fusion initiation.

The COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has resulted in tremendous loss worldwide. Although viral spike (S) protein binding of angiotensin-converting enzyme 2 (ACE2) has been established, the functional consequences of the initial receptor binding and the stepwise fusion process are not clear. By utilizing a cell-cell fusion system, in complement with a pseudoviral infection model, we found that the spike engagement of ACE2 primed the generation of S2' fragments in target cells, a key proteolytic event coupled with spike-mediated membrane fusion. Mutagenesis of an S2' cleavage site at the arginine (R) 815, but not an S2 cleavage site at arginine 685, was sufficient to prevent subsequent syncytia formation and infection in a variety of cell lines and primary cells isolated from human ACE2 knock-in mice. The requirement for S2' cleavage at the R815 site was also broadly shared by other SARS-CoV-2 spike variants, such as the Alpha, Beta, and Delta variants of concern. Thus, our study highlights an essential role for host receptor engagement and the key residue of spike for proteolytic activation, and uncovers a targetable mechanism for host cell infection by SARS-CoV-2.

Homeostatic regulation of T follicular helper and antibody response to particle antigens by IL-1Ra of medullary sinus macrophage origin.

Hepatitis B virus (HBV) vaccines are composed of surface antigen HBsAg that spontaneously assembles into subviral particles. Factors that impede its humoral immunity in 5% to 10% of vaccinees remain elusive. Here, we showed that the low-level interleukin-1 receptor antagonist (IL-1Ra) can predict antibody protection both in mice and humans. Mechanistically, murine IL-1Ra-inhibited T follicular helper (Tfh) cell expansion and subsequent germinal center (GC)-dependent humoral immunity, resulting in significantly weakened protection against the HBV challenge. Compared to soluble antigens, HBsAg particle antigen displayed a unique capture/uptake and innate immune activation, including IL-1Ra expression, preferably of medullary sinus macrophages. In humans, a unique polymorphism in the RelA/p65 binding site of IL-1Ra enhancer associated IL-1Ra levels with ethnicity-dependent vaccination outcome. Therefore, the differential IL-1Ra response to particle antigens probably creates a suppressive milieu for Tfh/GC development, and neutralization of IL-1Ra would resurrect antibody response in HBV vaccine nonresponders.

TRAF6-TAK1-IKKß pathway mediates TLR2 agonists activating "one-step" NLRP3 inflammasome in human monocytes.

Gram-positive bacterial infection causes high morbidity and mortality worldwide, while the underlying mechanism for host sensing bacterial components and initiating immune responses remains elusive. The NLRP3 inflammasome is a cytosolic multi-protein complex sensing a broad spectrum of endogenous danger signals and environmental irritants. In contrast to canonical NLRP3 inflammasome activation that needs both priming and activation signals, Lipopolysaccharide (LPS) from gram-negative bacteria activates the "one-step" NLRP3 inflammasome in human monocytes, which relies on the TLR4-TRIF-Caspase-8 signaling. Here, we show that in human monocytes, TLR2 agonists such as heat-killed gram-positive bacteria, peptidoglycan (PGN) or synthetic bacterial lipoprotein analog Pam3CysSerLys4 (Pam3CSK4) are able to induce the "one-step" NLRP3 inflammasome activation. Using genetic targeting and pharmacological inhibition approaches, it was found that TLR2 propagates signal through TRAF6, TAK1 and IKKß, ultimately activated NLRP3 independent of RelA. In addition, IKKß interacts with NLRP3 directly and affects NLRP3 inflammasome activation. These results reveal the signaling cascade downstream of TLR2 upon sensing gram-positive bacterial infection and activating the "one-step" NLRP3 inflammasome in human monocytes, which provides clue for controlling gram-positive bacterial infection-related inflammation.

Alterations in the microbiota drive interleukin-17C production from intestinal epithelial cells to promote tumorigenesis.

Although the microbiota has been shown to drive production of interleukin-17A (IL-17A) from T helper 17 cells to promote cell proliferation and tumor growth in colorectal cancer, the molecular mechanisms for microbiota-mediated regulation of tumorigenesis are largely unknown. Here, we found that the innate-like cytokine IL-17C was upregulated in human colorectal cancers and in mouse intestinal tumor models. Alterations in the microbiota drove IL-17C upregulation specifically in intestinal epithelial cells (IECs) through Toll-like receptor (TLR)-MyD88-dependent signaling during intestinal tumorigenesis. Microbiota-driven IL-17C induced Bcl-2 and Bcl-xL expression in IECs in an autocrine manner to promote cell survival and tumorigenesis in both chemically induced and spontaneous intestinal tumor models. Thus, IL-17C promotes cancer development by increasing IEC survival, and the microbiota can mediate cancer pathogenesis through regulation of IL-17C.

Immune Cell-Related Genes in Juvenile Idiopathic Arthritis Identified Using Transcriptomic and Single-Cell Sequencing Data.

Juvenile idiopathic arthritis (JIA) is the most common chronic rheumatic disease in children. The heterogeneity of the disease can be investigated via single-cell RNA sequencing (scRNA-seq) for its gap in the literature. Firstly, five types of immune cells (plasma cells, naive CD4 T cells, memory-activated CD4 T cells, eosinophils, and neutrophils) were significantly different between normal control (NC) and JIA samples. WGCNA was performed to identify genes that exhibited the highest correlation to differential immune cells. Then, 168 differentially expressed immune cell-related genes (DE-ICRGs) were identified by overlapping 13,706 genes identified by WGCNA and 286 differentially expressed genes (DEGs) between JIA and NC specimens. Next, four key genes, namely SOCS3, JUN, CLEC4C, and NFKBIA, were identified by a protein-protein interaction (PPI) network and three machine learning algorithms. The results of functional enrichment revealed that SOCS3, JUN, and NFKBIA were all associated with hallmark TNF-α signaling via NF-κB. In addition, cells in JIA samples were clustered into four groups (B cell, monocyte, NK cell, and T cell groups) by single-cell data analysis. CLEC4C and JUN exhibited the highest level of expression in B cells; NFKBIA and SOCS3 exhibited the highest level of expression in monocytes. Finally, real-time quantitative PCR (RT-qPCR) revealed that the expression of three key genes was consistent with that determined by differential analysis. Our study revealed four key genes with prognostic value for JIA. Our findings could have potential implications for JIA treatment and investigation.

Engineered Pigs Carrying a Gain-of-Function NLRP3 Homozygous Mutation Can Survive to Adulthood and Accurately Recapitulate Human Systemic Spontaneous Inflammatory Responses.

The NLRP3 inflammasome is associated with a variety of human diseases, including cryopyrin-associated periodic syndrome (CAPS). CAPS is a dominantly inherited disease with NLRP3 missense mutations. Currently, most studies on the NLRP3-inflammasome have been performed with mice, but the activation patterns and the signaling pathways of the mouse NLRP3 inflammasome are not always identical with those in humans. The NLRP3 inflammasome activation in pigs is similar to that in humans. Therefore, pigs with precise NLRP3-point mutations may model human CAPS more accurately. In this study, an NLRP3 gain-of-function pig model carrying a homozygous R259W mutation was generated by combining CRISPR/Cpf1-mediated somatic cell genome editing with nuclear transfer. The newborn NLRP3 R259W homozygous piglets showed early mortality, poor growth, and spontaneous systemic inflammation symptoms, including skin lesion, joint inflammation, severe contracture, and inflammation-mediated multiorgan failure. Severe myocardial fibrosis was also observed. The tissues of inflamed skins and several organs showed significantly increased expressions of NLRP3, Caspase-1, and inflammation-associated cytokines and factors (i.e., IL-1ß, TNF-α, IL-6, and IL-17). Notably, approximately half of the homozygous piglets grew up to adulthood and even gave birth to offspring. Although the F1 heterozygous piglets showed improved survival rate and normal weight gain, 39.1% (nine out of 23) of the piglets died early and exhibited spontaneous systemic inflammation symptoms. In addition, similar to homozygotes, adult heterozygotes showed increased delayed hypersensitivity response. Thus, the NLRP3 R259W pigs are similar to human CAPS and can serve as an ideal animal model to bridge the gap between rodents and humans.

Citrobacter freundii Activation of NLRP3 Inflammasome via the Type VI Secretion System.

Citrobacter freundii is a significant cause of human infections, responsible for food poisoning, diarrhea, and urinary tract infections. We previously identified a highly cytotoxic and adhesive C. freundii strain CF74 expressing a type VI secretion system (T6SS). In this study, we showed that in mice-derived macrophages, C. freundii CF74 activated the Nucleotide Oligomerization Domain -Like Receptor Family, Pyrin Domain Containing 3(NLRP3) inflammasomes in a T6SS-dependent manner. The C. freundii T6SS activated the inflammasomes mainly through caspase 1 and mediated pyroptosis of macrophages by releasing the cleaved gasdermin-N domain. The CF74 T6SS was required for flagellin-induced interleukin 1ß release by macrophages. We further show that the T6SS tail component and effector, hemolysin co-regulation protein-2 (Hcp-2), was necessary and sufficient to trigger NLRP3 inflammasome activation. In vivo, the T6SS played a key role in mediating interleukin 1ß secretion and the survival of mice during C. freundii infection in mice. These findings provide novel insights into the role of T6SS in the pathogenesis of C. freundii.

Critical role for mast cells in interleukin-1ß-driven skin inflammation associated with an activating mutation in the nlrp3 protein.

Cryopyrin-associated periodic syndromes (CAPS) are caused by aberrant interleukin-1ß (IL-1ß) production induced by mutations in the NLRP3 protein in humans, but the mechanisms involved remain poorly understood. Using a mouse model, we show a role for the indigenous microbiota and mast cells (MCs) in skin disease associated with mutant Nlrp3 protein. Unlike normal cells, MCs expressing mutant Nlrp3 produced IL-1ß in response to lipopolysaccharide or tumor necrosis factor-α (TNF-α). In neonatal mice, the microbiota induced TNF-α and IL-1ß and promoted skin disease. MC deficiency greatly reduced disease in Nlrp3 mutant mice, and reconstitution of MC-deficient mice with mutant MCs restored skin disease, which required the expression of IL-1ß in MCs. Surprisingly, neutralization of TNF-α abrogated IL-1ß production and skin disease in neonatal Nlrp3 mutant mice, but not in affected adult mice. Thus, the microbiota and MCs initiate cellular events leading to dysregulated IL-1ß production and skin inflammation in neonatal mice with the CAPS-associated Nlrp3 mutation.

Gasdermin D Drives the Nonexosomal Secretion of Galectin-3, an Insulin Signal Antagonist.

The inflammasomes play critical roles in numerous pathological conditions largely through IL-1ß and/or IL-18. However, additional effectors have been implied from multiple studies. In this study, through two independent mass spectrometry-based secretome screening approaches, we identified galectin-3 as an effector protein of the NLRP3 inflammasome. Although the activation of AIM2 or NLRC4 inflammasome also led to galectin-3 secretion, only the NLRP3 inflammasome controlled the serum galectin-3 level under physiological condition. Mechanistically, active gasdermin D drove the nonexosomal secretion of galectin-3 through the plasma membrane pores. In vivo, high-fat diet-fed Nlrp3-/- mice exhibited decreased circulating galectin-3 compared with wild-type animals. Of note, the improved insulin sensitivity in such Nlrp3-/- mice was aggravated by infusion of recombinant galectin-3. Moreover, galectin-3 was essential for insulin resistance induction in mice harboring the hyperactive Nlrp3A350V allele. Thus, the inflammasome-galectin-3 axis has been demonstrated as a promising target to intervene inflammasome and/or galectin-3 related diseases.

Interactions among the transcription factors Runx1, RORgammat and Foxp3 regulate the differentiation of interleukin 17-producing T cells.

The molecular mechanisms underlying the differentiation of interleukin 17-producing T helper cells (T(H)-17 cells) are still poorly understood. Here we show that optimal transcription of the gene encoding interleukin 17 (Il17) required a 2-kilobase promoter and at least one conserved noncoding (enhancer) sequence, CNS-5. Both cis-regulatory elements contained regions that bound the transcription factors RORgammat and Runx1. Runx1 influenced T(H)-17 differentiation by inducing RORgammat expression and by binding to and acting together with RORgammat during Il17 transcription. However, Runx1 also interacts with the transcription factor Foxp3, and this interaction was necessary for the negative effect of Foxp3 on T(H)-17 differentiation. Thus, our data support a model in which the differential association of Runx1 with Foxp3 and with RORgammat regulates T(H)-17 differentiation.

Deficiency of the AIM2-ASC Signal Uncovers the STING-Driven Overreactive Response of Type I IFN and Reciprocal Depression of Protective IFN-γ Immunity in Mycobacterial Infection.

The nucleic acids of Mycobacterium tuberculosis can be detected by intracellular DNA sensors, such as cyclic GMP-AMP synthase and absent in melanoma 2 (AIM2), which results in the release of type I IFN and the proinflammatory cytokine IL-1ß. However, whether cross-talk occurs between AIM2-IL-1ß and cyclic GMP-AMP synthase-type I IFN signaling upon M. tuberculosis infection in vivo is unclear. In this article, we demonstrate that mycobacterial infection of AIM2-/- mice reciprocally induces overreactive IFN-ß and depressive IFN-γ responses, leading to higher infection burdens and more severe pathology. We also describe the underlying mechanism whereby activated apoptosis-associated speck-like protein interacts with a key adaptor, known as stimulator of IFN genes (STING), and inhibits the interaction between STING and downstream TANK-binding kinase 1 in bone marrow-derived macrophages and bone marrow-derived dendritic cells, consequently reducing the induction of type I IFN. Of note, apoptosis-associated speck-like protein expression is inversely correlated with IFN-ß levels in PBMCs from tuberculosis patients. These data demonstrate that the AIM2-IL-1ß signaling pathway negatively regulates the STING-type I IFN signaling pathway by impeding the association between STING and TANK-binding kinase 1, which protects the host from M. tuberculosis infection. This finding has potential clinical significance.

Intestinal Epithelial Cell-Derived LKB1 Suppresses Colitogenic Microbiota.

Dysregulation of the immune barrier function of the intestinal epithelium can often result in dysbiosis. In this study we report a novel role of intestinal epithelial cell (IEC)-derived liver kinase B1 (LKB1) in suppressing colitogenic microbiota. IEC-specific deletion of LKB1 (LKB1ΔIEC) resulted in an increased susceptibility to dextran sodium sulfate (DSS)-induced colitis and a definitive shift in the composition of the microbial population in the mouse intestine. Importantly, transfer of the microbiota from LKB1ΔIEC mice was sufficient to confer increased susceptibility to DSS-induced colitis in wild-type recipient mice. Collectively, the data indicate that LKB1 deficiency in intestinal epithelial cells nurtures the outgrowth of colitogenic bacteria in the commensal community. In addition, LKB1 deficiency in the intestinal epithelium reduced the production of IL-18 and antimicrobial peptides in the colon. Administration of exogenous IL-18 restored the expression of antimicrobial peptides, corrected the outgrowth of several bacterial genera, and rescued the LKB1ΔIEC mice from increased sensitivity to DSS challenge. Taken together, our study reveals an important function of LKB1 in IECs for suppressing colitogenic microbiota by IL-18 expression.

Hyperactivation of the NLRP3 inflammasome protects mice against influenza A virus infection via IL-1ß mediated neutrophil recruitment.

Host innate immune system is critical for combating invading microbes including Influenza A virus (IAV). As an important arm of the innate immunity, the NLRP3 inflammasome has been found essential for protecting host against IAV challenge, while the mechanism remained elusive. Here we found that mice carrying a gain-of-function mutation in the Nlrp3 gene (Nlrp3R258W) are strongly resistant to IAV infection. Upon H1N1 IAV infection, the Nlrp3R258W mice exhibited decreased weight loss, increased survival rate and attenuated lung damage compared with WT littermate controls. Mechanistically, the resistance of Nlrp3R258W mice to IAV infection was dependent on IL-1ß-mediated neutrophil recruitment. Upon IAV infection, mice carrying the Nlrp3R258W mutation produced more IL-1ß than WT mice in the lung, which enhanced neutrophil recruitment locally. The recruited neutrophils facilitated IAV clearance, so that the viral load in Nlrp3R258W mice was lower than that in control mice. Conversely, neutrophil depletion in Nlrp3R258W mice compromised IAV clearance. Taken together, our results demonstrate a previously undescribed mechanism by which hyperactivation of the NLRP3 Inflammasome protects mice from IAV infection through IL-1ß mediated neutrophil recruitment, thus suggest that positively fine tuning the physiological function of NLRP3 inflammasome can be beneficial for a mammalian host against IAV challenge.

Cutting Edge: TRAF6 Mediates TLR/IL-1R Signaling-Induced Nontranscriptional Priming of the NLRP3 Inflammasome.

NLRP3 inflammasome activiation requires two sequential signals. The priming signal 1 from TLRs or cytokine receptors induces the transcription of NLRP3 and IL-1ß, and concomitantly promotes transcription-independent activation of caspase-1. The activating signal 2 can be provided by microbial products or danger signals. In this study we found that TRAF6 is necessary for the nontranscriptional priming of NLRP3 inflammasome by TLR/IL-1R derived signals. Deficiency of TRAF6 specifically inhibited TLR/IL-1R priming-initiated caspase-1 cleavage, pyroptosis, and secretion of presynthesized IL-18. Mechanistically, TRAF6 promoted NLRP3 oligomerization as well as the interaction between NLRP3 and apoptosis-associated speck-like protein containing a CARD. Of note, the nontranscriptional priming via TRAF6 did not involve mitochondrial reactive oxygen species or the phosphorylation of Jnk, Erk, and Syk, whereas the ubiquitin E3 ligase activity of TRAF6 was required. Our findings thus extended cognition on the mechanism of NLRP3 inflammasome activation, and provided a novel target for controlling NLRP3-related diseases.

Hyperactivation of the NLRP3 Inflammasome in Myeloid Cells Leads to Severe Organ Damage in Experimental Lupus.

Systemic lupus erythematosus (SLE) is an autoimmune syndrome associated with severe organ damage resulting from the activation of immune cells. Recently, a role for caspase-1 in murine lupus was described, indicating an involvement of inflammasomes in the development of SLE. Among multiple inflammasomes identified, the NLRP3 inflammasome was connected to diverse diseases, including autoimmune encephalomyelitis. However, the function of NLRP3 in SLE development remains elusive. In this study, we explored the role of NLRP3 in the development of SLE using the pristane-induced experimental lupus model. It was discovered that more severe lupus-like syndrome developed in Nlrp3-R258W mice carrying the gain-of-function mutation. Nlrp3-R258W mutant mice exhibited significantly higher mortality upon pristane challenge. Moreover, prominent hypercellularity and interstitial nephritis were evident in the glomeruli of Nlrp3-R258W mice. In addition, hyperactivation of the NLRP3 inflammasome in this mouse line resulted in proteinuria and mesangial destruction. Importantly, all of these phenotypes were largely attributed to the Nlrp3-R258W mutation expressed in myeloid cells, because Cre recombinase-mediated depletion of this mutant from such cells rescued mice from experimental lupus. Taken together, our study demonstrates a critical role for NLRP3 in the development of SLE and suggests that modulating the inflammasome signal may help to control the inflammatory damage in autoimmune diseases, including lupus.

NLRP3 Inflammasome Activation Contributes to Mechanical Stretch-Induced Endothelial-Mesenchymal Transition and Pulmonary Fibrosis.

OBJECTIVES: Mechanical ventilation can induce lung fibrosis. This study aimed to investigate whether ventilator-induced lung fibrosis was associated with endothelial-mesenchymal transition and to uncover the underlying mechanisms. DESIGN: Randomized, controlled animal study and cell culture study. SETTING: University research laboratory. SUBJECTS: Adult male Institute of Cancer Research, NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) knockout and wild-type mice. Primary cultured mouse lung vascular endothelial cells. INTERVENTIONS: Institute of Cancer Research, NLRP3 knockout and wild-type mice were subjected to mechanical ventilation (20 mL/kg) for 2 hours. Mouse lung vascular endothelial cells were subjected to cyclic stretch for 24 hours. MEASUREMENTS AND MAIN RESULTS: Mice subjected to mechanical ventilation exhibited increases in collagen deposition, hydroxyproline and type I collagen contents, and transforming growth factor-ß1 in lung tissues. Ventilation-induced lung fibrosis was associated with increased expression of mesenchymal markers (α smooth muscle actin and vimentin), as well as decreased expression of endothelial markers (vascular endothelial-cadherin and CD31). Double immunofluorescence staining showed the colocalization of CD31/α smooth muscle actin, CD31/vimentin, and CD31/fibroblast-specific protein-1 in lung tissues, indicating endothelial-mesenchymal transition formation. Mechanical ventilation also induced NLRP3 inflammasome activation in lung tissues. In vitro direct mechanical stretch of primary mouse lung vascular endothelial cells resulted in similar NLRP3 activation and endothelial-mesenchymal transition formation, which were prevented by NLRP3 knockdown. Furthermore, mechanical stretch-induced endothelial-mesenchymal transition and pulmonary fibrosis were ameliorated in NLRP3-deficient mice as compared to wild-type littermates. CONCLUSIONS: Mechanical stretch may promote endothelial-mesenchymal transition and pulmonary fibrosis through a NLRP3-dependent pathway. The inhibition of endothelial-mesenchymal transition by NLRP3 inactivation may be a viable therapeutic strategy against pulmonary fibrosis associated with mechanical ventilation.

A mutation in the Nlrp3 gene causing inflammasome hyperactivation potentiates Th17 cell-dominant immune responses.

Missense mutations of the gene encoding NLRP3 are associated with autoinflammatory disorders characterized with excessive production of interleukin-1beta (IL-1beta). Here we analyzed the immune responses of gene-targeted mice carrying a mutation in the Nlrp3 gene equivalent to the human mutation associated with Muckle-Wells Syndrome. We found that antigen-presenting cells (APCs) from such mice produced massive amounts of IL-1beta upon stimulation with microbial stimuli in the absence of ATP. This was likely due to a diminished inflammasome activation threshold that allowed a response to the small amount of agonist. Moreover, the Nlrp3 gene-targeted mice exhibited skin inflammation characterized by neutrophil infiltration and a Th17 cytokine-dominant response, which originated from hematopoietic cells. The inflammation of Nlrp3 gene-targeted mice resulted from excess IL-1beta production from APCs, which augmented Th17 cell differentiation. These results demonstrate that the NLRP3 mutation leads to inflammasome hyperactivation and consequently Th17 cell-dominant immunopathology in autoinflammation.