Caspase-11 Non-canonical Inflammasome Research Articles

Molecular mechanisms of emerging inflammasome complexes and their activation and signaling in inflammation and pyroptosis.

Inflammasomes are multi-protein complexes that assemble within the cytoplasm of mammalian cells in response to pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs), driving the secretion of the pro-inflammatory cytokines IL-1β and IL-18, and pyroptosis. The best-characterized inflammasome complexes are the NLRP3, NAIP-NLRC4, NLRP1, AIM2, and Pyrin canonical caspase-1-containing inflammasomes, and the caspase-11 non-canonical inflammasome. Newer inflammasome sensor proteins have been identified, including NLRP6, NLRP7, NLRP9, NLRP10, NLRP11, NLRP12, CARD8, and MxA. These inflammasome sensors can sense PAMPs from bacteria, viruses and protozoa, or DAMPs in the form of mitochondrial damage, ROS, stress and heme. The mechanisms of action, physiological relevance, consequences in human diseases, and avenues for therapeutic intervention for these novel inflammasomes are beginning to be realized. Here, we discuss these emerging inflammasome complexes and their putative activation mechanisms, molecular and signaling pathways, and physiological roles in health and disease.

Roles of the Caspase-11 Non-Canonical Inflammasome in Rheumatic Diseases.

Inflammasomes are intracellular multiprotein complexes that activate inflammatory signaling pathways. Inflammasomes comprise two major classes: canonical inflammasomes, which were discovered first and are activated in response to a variety of pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPs), and non-canonical inflammasomes, which were discovered recently and are only activated in response to intracellular lipopolysaccharide (LPS). Although a larger number of studies have successfully demonstrated that canonical inflammasomes, particularly the NLRP3 inflammasome, play roles in various rheumatic diseases, including rheumatoid arthritis (RA), infectious arthritis (IR), gouty arthritis (GA), osteoarthritis (OA), systemic lupus erythematosus (SLE), psoriatic arthritis (PA), ankylosing spondylitis (AS), and Sjögren's syndrome (SjS), the regulatory roles of non-canonical inflammasomes, such as mouse caspase-11 and human caspase-4 non-canonical inflammasomes, in these diseases are still largely unknown. Interestingly, an increasing number of studies have reported possible roles for non-canonical inflammasomes in the pathogenesis of various mouse models of rheumatic disease. This review comprehensively summarizes and discusses recent emerging studies demonstrating the regulatory roles of non-canonical inflammasomes, particularly focusing on the caspase-11 non-canonical inflammasome, in the pathogenesis and progression of various types of rheumatic diseases and provides new insights into strategies for developing potential therapeutics to prevent and treat rheumatic diseases as well as associated diseases by targeting non-canonical inflammasomes.

Anti-inflammatory activity of calmodulin-lysine N-methyltransferase through suppressing the caspase-11 non-canonical inflammasome

Calmodulin (CaM)-lysine N-methyltransferase (CAMKMT) is a novel methyltransferase that catalyzes lysine trimethylation in CaM. However, its specific roles in inflammatory responses and diseases remain unclear. In this study, we investigated the effects of CAMKMT on caspase-11 non-canonical inflammasomes. CAMKMT expression levels were significantly decreased during inflammatory responses activated by caspase-11 non-canonical inflammasome in macrophages. Moreover, CaM lysine trimethylation was markedly inhibited, but no change was observed in CaM expression during these inflammatory responses in macrophages. Activation of the CaM downstream effectors, CaM-dependent proteinkinase kinase 2 and CaM-dependent proteinkinase type IV, was also inhibited during inflammatory responses activated by caspase-11 non-canonical inflammasome in macrophages. Notably, forced expression of CAMKMT restrained caspase-11 non-canonical inflammasome activation via inhibiting proteolytic activation of caspase-11 and gasdermin D (GSDMD), which in turn suppressed pyroptosis and the release of interleukin (IL)-1β and IL-18 in macrophages. Finally, an in vivo study revealed that CAMKMT ameliorated lipopolysaccharide (LPS)-stimulated acute lethal sepsis in mice by increasing the survival rate and reducing the serum levels of IL-1 β. These findings suggest CAMKMT as a novel methyltransferase that plays an anti-inflammatory role through restraining caspase-11 non-canonical inflammasome in macrophages.

Anti-inflammatory role of Artemisia argyi methanol extract by targeting the caspase-11 non-canonical inflammasome in macrophages.

Artemisia argyi possesses pharmacological activities against various immunopathological conditions associated with inflammation. This study explored the inhibitory role of Artemisia argyi methanol extract (Aa-ME) in inflammatory responses and the underlying mechanism in macrophages. Caspase-11 non-canonical inflammasome was activated in J774A.1 macrophage by Pam3CSK4 treatment and lipopolysaccharide (LPS) transfection. Aa-ME-mediated in vitro anti-inflammatory action was examined using MTT assay, lactate dehydrogenase (LDH) activity assay, enzyme-linked immunosorbent assay (ELISA), nitric oxide (NO) generation assay, and quantitative real-time polymerase chain reaction (qPCR). Aa-ME-mediated in vivo anti-inflammatory action was examined in LPS-stimulated lethal septic mice. Aa-ME inhibited caspase-11 non-canonical inflammasome-stimulated pyroptosis and the secretion of IL-1β and IL-18 in J774A.1 macrophages. Aa-ME also inhibited NO generation by downregulating inducible NO synthase (iNOS) expression in LPS-primed and caspase-11 non-canonical inflammasome-triggered J774A.1cells. The mechanism study revealed Aa-ME suppressed the auto-proteolytic activation of caspase-11 and gasdermin D (GSDMD) in J774A.1cells and also interfered with caspase-11-mediated direct recognition of LPS. Moreover, Aa-ME alleviated LPS-induced lethal sepsis in mice by increasing their survival rate without significant toxicity. These results suggest a novel mechanism by which Aa-ME alleviates inflammatory responses by deactivating caspase-11 non-canonical inflammasome in macrophages.

The Protective Effects of Goitrin on LPS-Induced Septic Shock in C57BL/6J Mice via Caspase-11 Non-Canonical Inflammasome Inhibition.

Septic shock is defined as a subset of sepsis, which is associated with a considerably high mortality risk. The caspase-11 non-canonical inflammasome is sensed and activated by intracellular lipopolysaccharide (LPS) leading to pyroptosis, it plays a critical role in septic shock. However, there are few known drugs that can control caspase-11 non-canonical inflammasome activation. We report here that goitrin, an alkaloid from Radix Isatidis, shows protective effects in LPS-induced septic shock and significant inhibitory effect in caspase-11 non-canonical inflammasome pathway. Male C57BL/6J were injected intraperitoneally with LPS (20 mg/kg) to induce experimental septic shock. The results demonstrated that the survival rates of mice pretreated with goitrin or Toll-like receptor 4 (TLR4) inhibitor TKA-242 increased, and LPS-induced hypothermia and lung damage improved by inhibiting inflammatory response. Elucidating the detailed mechanism, we surprisingly found goitrin is really different from TAK-242, it independent of the TLR4 signal activation, but significantly inhibited the activation of caspase-11 non-canonical inflammasome, including cleaved caspase-11 and N-terminal fragment of gasdermin D (GSDMD-NT). Furthermore, with a nonlethal dose of the TLR3 agonist poly(I:C)-primed and subsequently challenged with LPS to induce caspase-11-mediated lethal septic shock, the efficacy of goitrin had been verified. Those results revealed the effect of goitrin in protective against LPS-induced septic shock via inhibiting caspase-11 non-canonical inflammasome, which provided a new therapeutic strategy for clinical treatment of septic shock.

Korean Red Ginseng Saponins Play an Anti-Inflammatory Role by Targeting Caspase-11 Non-Canonical Inflammasome in Macrophages.

We previously reported that Korean red ginseng (KRG) exerts an anti-inflammatory role through inhibiting caspase-11 non-canonical inflammasome in macrophages; however, the components responsible for the anti-inflammatory role remained unclear. This study explored the anti-inflammatory activity of the KRG saponin fraction (KRGSF) in caspase-11 non-canonical inflammasome-activated macrophages. KRGSF inhibited pyroptosis, pro-inflammatory cytokine secretion, and inflammatory mediator production in caspase-11 non-canonical inflammasome-activated J774A.1 cells. A mechanism study revealed that KRGSF-induced anti-inflammatory action was mediated via suppressing the proteolytic activation of caspase-11 and gasdermin D (GSDMD) in caspase-11 non-canonical inflammasome-activated J774A.1 cells. Moreover, KRGSF increased the survival of lethal septic mice. Taken together, these results reveal KRGSF-mediated anti-inflammatory action with a novel mechanism, by inhibiting caspase-11 non-canonical inflammasome in macrophages.

Regulatory Roles of Caspase-11 Non-Canonical Inflammasome in Inflammatory Liver Diseases.

An inflammatory response consists of two consecutive steps: priming and triggering, to prepare and activate inflammatory responses, respectively. The cardinal feature of the triggering step is the activation of intracellular protein complexes called inflammasomes, which provide a platform for the activation of inflammatory signaling pathways. Despite many studies demonstrating the regulatory roles of canonical inflammasomes in inflammatory liver diseases, the roles of newly discovered non-canonical inflammasomes in inflammatory liver diseases are still largely unknown. Recent studies have reported the regulatory roles of the caspase-11 non-canonical inflammasome in inflammatory liver diseases, providing strong evidence that the caspase-11 non-canonical inflammasome may play key roles in the pathogenesis of inflammatory liver diseases. This review comprehensively discusses the emerging roles of the caspase-11 non-canonical inflammasome in the pathogenesis of inflammatory liver diseases, focusing on non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH), and inflammatory liver injuries and its underlying mechanisms. This review highlights the current knowledge on the regulatory roles of the caspase-11 non-canonical inflammasome in inflammatory liver diseases, providing new insights into the development of potential therapeutics to prevent and treat inflammatory liver diseases by targeting the caspase-11 non-canonical inflammasome.

A novel mechanism of Korean Red Ginseng-mediated anti-inflammatory action via targeting caspase-11 non-canonical inflammasome in macrophages

BackgroundKorean Red Ginseng (KRG) was reported to play an anti-inflammatory role, however, previous studies largely focused on the effects of KRG on priming step, the inflammation-preparing step, and the anti-inflammatory effect of KRG on triggering, the inflammation-activating step has been poorly understood. This study demonstrated anti-inflammatory role of KRG in caspase-11 non-canonical inflammasome activation in macrophages during triggering of inflammatory responses. MethodsCaspase-11 non-canonical inflammasome-activated J774A.1 macrophages were established by priming with Pam3CSK4 and triggering with lipopolysaccharide (LPS). Cell viability and pyroptosis were examined by MTT and lactate dehydrogenase (LDH) assays. Nitric oxide (NO)-inhibitory effect of KRG was assessed using a NO production assay. Expression and proteolytic cleavage of proteins were examined by Western blotting analysis. In vivo anti-inflammatory action of KRG was evaluated with the LPS-injected sepsis model in mice. ResultsKRG reduced LPS-stimulated NO production in J774A.1 cells and suppressed pyroptosis and IL-1β secretion in caspase-11 non-canonical inflammasome-activated J774A.1 cells. Mechanistic studies demonstrated that KRG suppressed the direct interaction between LPS and caspase-11 and inhibited proteolytic processing of both caspase-11 and gasdermin D in caspase-11 non-canonical inflammasome-activated J774A.1 cells. Furthermore, KRG significantly ameliorated LPS-mediated lethal septic shock in mice. ConclusionThe results demonstrate a novel mechanism of KRG-mediated anti-inflammatory action that operates through targeting the caspase-11 non-canonical inflammasome at triggering step of macrophage-mediated inflammatory response.

Caspase-11 Non-Canonical Inflammasome: Emerging Activator and Regulator of Infection-Mediated Inflammatory Responses.

Inflammation is a body’s protective mechanism to eliminate invading pathogens and cellular damaging signals. The inflammatory response consists of two main consecutive steps—a priming step preparing the inflammatory responses and a triggering step boosting the inflammatory responses. The main feature of the triggering step is the activation of the inflammasome, an intracellular multiprotein complex facilitating the inflammatory responses. The regulatory roles of ‘canonical’ inflammasomes in the inflammatory responses and diseases have been largely investigated, so far. New types of inflammasomes have been recently discovered and named as ‘non-canonical’ inflammasomes since their roles to induce inflammatory responses are similar to those of canonical inflammasomes, however, the stimulating ligands and the underlying mechanisms are different. Therefore, a growing number of studies have actively investigated the novel roles of non-canonical inflammasomes in inflammatory responses and diseases. This review summarizes and discusses the recent studies exploring the regulatory roles of caspase-11 non-canonical inflammasome during the inflammatory responses and provides insight into the development of novel therapeutics for infectious and inflammatory diseases by targeting caspase-11 non-canonical inflammasome.

Viburnum pichinchense methanol extract exerts anti-inflammatory effects via targeting the NF-κB and caspase-11 non-canonical inflammasome pathways in macrophages.

Viburnum pichinchense Benth. Mainly found in Ecuador and Colombia has been ethnopharmacologically utilized as a remedy for various female disorders with kidney inflammation and uterine relaxant. The pharmacological activity of Viburnum pichinchense has never been studied, therefore, this study explored anti-inflammatory activity of Viburnum pichinchense methanol extract (Vp-ME). Anti-inflammatory activities of Vp-ME were evaluated in lipopolysaccharide (LPS)-stimulated RAW264.7 cells and HCl/EtOH-induced gastritis mice by MTT assay, nitric oxide (NO) production assay, semi-quantitative reverse-transcriptase-polymerase chain reaction (RT-PCR), luciferase reporter assay, Western blotting, and enzyme-linked immunosorbent assays (ELISA). Anti-inflammatory compounds in Vp-ME were identified by high performance liquid chromatography (HPLC). Vp-ME inhibited NO production in RAW264.7 cells stimulated with pam3CSK4, poly I:C or LPS and in LPS-stimulated peritoneal macrophages without cytotoxicity and downregulated mRNA expression of inflammatory enzymes, inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2) and pro-inflammatory cytokines, tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-6. The anti-inflammatory activity was accomplished by inhibiting nuclear factor-kappa B (NF-κB) transcriptional activation, upstream signaling molecules in the NF-κB pathway, and caspase-11 non-canonical inflammasome in RAW264.7 cells. Moreover, Vp-ME exhibited in vivo anti-inflammatory activity by ameliorating gastritis symptoms, inhibiting iNOS and IL-6 mRNA expression and IκBα activation in mice. HPLC analysis identified resveratrol, quercetin, luteolin, and kaempferol as the anti-inflammatory components in Vp-ME. This study demonstrated Vp-ME has the anti-inflammatory activity via targeting NF-κB and caspase-11 non-canonical inflammasome pathways in macrophage-mediated inflammatory responses, suggesting Vp-ME could be developed as anti-inflammatory ethnopharmacological remedies to prevent and treat inflammatory diseases.

Gasdermin D serves as a key executioner of pyroptosis in experimental cerebral ischemia and reperfusion model both in vivo and in vitro.

Even though ischemic stroke is among the leading causes of death worldwide, the pathogenic mechanisms underlying ischemia reperfusion (I/R) brain injury remain unclear. Gasdermin D (GSDMD), as an important factor of pyroptotic death execution downstream of caspase-11 (noncanonical inflammasome) and caspase-1 (canonical inflammasome), may be implicated in I/R injury. The current study aimed to investigate the role and possible underlying mechanisms of GSDMD in pyroptosis during I/R injury. Results indicated that the nucleotide-binding oligomerization domain-like receptors (NLR family) pyrin domain containing 3 (NLRP3) inflammasomes were assembled and activated after middle cerebral artery occlusion/reperfusion (MCAO/R), leading to increased levels of IL-1β and IL-18. Additionally, GSDMD levels were elevated, and its N-terminal fragment (GSDMD-N) was cleaved to induce pyroptosis after MCAO/R, which was partly dependent on caspase-1 activation and its Asp280 amino acid site. Furthermore, it was found that GSDMD-N could bind to membrane lipids and exhibit membrane-disrupting cytotoxicity, depending on its Glu15 and Leu156 amino acid sites. Nevertheless, the C-terminal fragment of gasdermin (GSDMD-C) exhibited an auto-inhibitory effect on GSDMD-N-induced pyroptosis via binding to GSDMD in the cytoplasm. Taken together, this information suggests that GSDMD may participate in caspase-1-mediated pyroptosis during I/R injury both in vivo and in vitro, which could be a potential therapeutic target to reduce brain I/R injury.

Role of Caspase-11 Non-Canonical Inflammasome in Macrophage-Mediated Inflammatory Responses

Role of Caspase-11 Non-Canonical Inflammasome in Macrophage-Mediated Inflammatory Responses

HMGB1: LPS Delivery Vehicle for Caspase-11-Mediated Pyroptosis

Recognition of cytoplasmic lipopolysaccharide (LPS) by caspase-11 leads to pyroptosis and secretion of inflammatory mediators. In this issue of Immunity, Deng etal. (2018) report that high-mobility group box 1 (HMGB1) secreted by hepatocytes delivers extracellular LPS into the cytoplasm and mediates pyroptosis.

LPS targets host guanylate-binding proteins to the bacterial outer membrane for non-canonical inflammasome activation.

Pathogenic and commensal Gram-negative bacteria produce and release outer membrane vesicles (OMVs), which present several surface antigens and play an important role for bacterial pathogenesis. OMVs also modulate the host immune system, which makes them attractive as vaccine candidates. At the cellular level, OMVs are internalized by macrophages and deliver lipopolysaccharide (LPS) into the host cytosol, thus activating the caspase-11 non-canonical inflammasome. Here, we show that OMV-induced inflammasome activation requires TLR4-TRIF signaling, the production of type I interferons, and the action of guanylate-binding proteins (GBPs), both in macrophages and invivo Mechanistically, we find that isoprenylated GBPs associate with the surface of OMVs or with transfected LPS, indicating that the key factor that determines GBP recruitment to the Gram-negative bacterial outer membranes is LPS itself. Our findings provide new insights into the mechanism by which GBPs target foreign surfaces and reveal a novel function for GBPs in controlling the intracellular detection of LPS derived from extracellular bacteria in the form of OMVs, thus extending their function as a hub between cell-autonomous immunity and innate immunity.

Regulatory Roles of the Caspase-11 Non-Canonical Inflammasome in Inflammatory Diseases.

Inflammation is an immune response mediated by innate immune cells of tissues, against invading microbes and cellular stress. The hallmark of inflammatory responses is the activation of inflammasomes — multiprotein oligomers comprising intracellular pattern recognition receptors and inflammatory effectors — such as ASC and pro-cysteine-aspartic protease (pro-caspase)-1. Inflammasomes can be classified as canonical or non-canonical, and their activation in response to various ligands commonly induces caspase-1 activation and gasdermin D (GSDMD) processing, leading to caspase-1-mediated maturation and secretion of the pro-inflammatory cytokines IL-1β and IL-18, and GSDMD-mediated pyroptosis through pore generation in cell membranes. Although inflammation protects the host from harmful stimuli, chronic inflammation is a critical risk factor for inflammatory diseases, and several studies have investigated the role of canonical inflammasomes in inflammatory responses and diseases, with emerging studies focusing on the role of non-canonical inflammasomes. This review discusses recent studies on the regulatory roles of the caspase-11 non-canonical inflammasome in the pathogenesis of inflammatory diseases. Additionally, it provides an insight into the development of novel therapeutics based on targeting caspase-11 non-canonical inflammasome and its downstream effectors to prevent and treat human inflammatory conditions.

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 (GBPchr3 )-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.

Caspase-11 attenuates gastrointestinal inflammation and experimental colitis pathogenesis.

Nucleotide-binding domain and leucine-rich repeat containing protein inflammasome formation plays an essential role in modulating immune system homeostasis in the gut. Recently, a caspase-11 noncanonical inflammasome has been characterized and appears to modulate many biological functions that were previously considered to be solely dependent on caspase-1 and the canonical inflammasome. To better elucidate the function of this noncanonical inflammasome during inflammatory bowel disease, experimental colitis was induced in wild-type and Casp11(-/-) mice utilizing dextran sulfate sodium (DSS). Here, we report that caspase-11 attenuates acute experimental colitis pathogenesis. Casp11(-/-) mice showed significantly increased morbidity and colon inflammation following DSS exposure. Subsequent cytokine analysis revealed that IL-1β and IL-18 levels in the colon were significantly reduced in the Casp11(-/-) mice compared with the wild-type animals. Additional mechanistic studies utilizing IL-1β and IL-18 reconstitution revealed that Casp11(-/-) hypersensitivity was associated with the loss of both of these cytokines. Bone marrow reconstitution experiments further revealed that caspase-11 gene expression and function in both hematopoietic- and nonhematopoietic-derived cells contribute to disease attenuation. Interestingly, unlike caspase-1, caspase-11 does not appear to influence relapsing remitting disease progression or the development of colitis-associated tumorigenesis. Together, these data identify caspase-11 as a critical factor protecting the host during acute DSS-induced colonic injury and inflammation but not during chronic inflammation and tumorigenesis.

Reactive oxygen species regulate caspase-11 expression and activation of the non-canonical NLRP3 inflammasome during enteric pathogen infection.

Enteropathogenic and enterohemorrhagic bacterial infections in humans are a severe cause of morbidity and mortality. Although NOD-like receptors (NLRs) NOD2 and NLRP3 have important roles in the generation of protective immune responses to enteric pathogens, whether there is crosstalk among NLRs to regulate immune signaling is not known. Here, we show that mice and macrophages deficient in NOD2, or the downstream adaptor RIP2, have enhanced NLRP3- and caspases-11-dependent non-canonical inflammasome activation in a mouse model of enteropathogenic Citrobacter rodentium infection. Mechanistically, NOD2 and RIP2 regulate reactive oxygen species (ROS) production. Increased ROS in Rip2-deficient macrophages subsequently enhances c-Jun N-terminal kinase (JNK) signaling resulting in increased caspase-11 expression and activation, and more non-canonical NLRP3-dependant inflammasome activation. Intriguingly, this leads to protection of the colon epithelium for up to 10 days in Rip2-deficient mice infected with C. rodentium. Our findings designate NOD2 and RIP2 as key regulators of cellular ROS homeostasis and demonstrate for the first time that ROS regulates caspase-11 expression and non-canonical NLRP3 inflammasome activation through the JNK pathway.

Inflammatory caspases are innate immune receptors for intracellular LPS.

The murine caspase-11 non-canonical inflammasome responds to various bacterial infections. Caspase-11 activation-induced pyroptosis, in response to cytoplasmic lipopolysaccharide (LPS), is critical for endotoxic shock in mice. The mechanism underlying cytosolic LPS sensing and the responsible pattern recognition receptor are unknown. Here we show that human monocytes, epithelial cells and keratinocytes undergo necrosis upon cytoplasmic delivery of LPS. LPS-induced cytotoxicity was mediated by human caspase-4 that could functionally complement murine caspase-11. Human caspase-4 and the mouse homologue caspase-11 (hereafter referred to as caspase-4/11) and also human caspase-5, directly bound to LPS and lipid A with high specificity and affinity. LPS associated with endogenous caspase-11 in pyroptotic cells. Insect-cell purified caspase-4/11 underwent oligomerization upon LPS binding, resulting in activation of the caspases. Underacylated lipid IVa and lipopolysaccharide from Rhodobacter sphaeroides (LPS-RS) could bind to caspase-4/11 but failed to induce their oligomerization and activation. LPS binding was mediated by the CARD domain of the caspase. Binding-deficient CARD-domain point mutants did not respond to LPS with oligomerization or activation and failed to induce pyroptosis upon LPS electroporation or bacterial infections. The function of caspase-4/5/11 represents a new mode of pattern recognition in immunity and also an unprecedented means of caspase activation.