Impact of IL-1β on lung pathology caused by Mycobacterium abscessus infection and its association with IL-17 production

Mycobacterium abscessus (MAB), a non-tuberculous mycobacterium (NTM), causes chronic pulmonary inflammation in humans. The NLRP3 inflammasome is a multi-protein complex that triggers IL-1β maturation and pyroptosis through the cleavage of caspase-1. In this study, we investigated the roles of NLRP3 and IL-1β in the host's defense against MAB. The IL-1β production by MAB was completely abolished in NLRP3, but not NLRC4, deficient macrophages. The NLRP3 inflammasome components, which are ASC and caspase-1 were also found to be essential for IL-1β production in response to MAB. NLRP3 and IL-1β deficiency did not affect the intracellular growth of MAB in macrophages, and the bacterial burden in lungs of NLRP3- and IL-1β-deficient mice was also comparable to the burden observed in WT mice. In contrast, IL-1β deficiency ameliorated lung pathology in MAB-infected mice. Notably, the lung homogenates of IL-1β-deficient mice had reduced levels of IL-17, but not IFN-γ and IL-4 when compared with WT counterparts. Furthermore, in vitro co-culture analysis showed that IL-1β signaling was essential for IL-17 production in response to MAB. Finally, we observed that the anti-IL-17 antibody administration moderately mitigated MAB-induced lung pathology. These findings indicated that IL-1β production contribute to MAB-induced lung pathology via the elevation of IL-17 production.

Cutting Edge: Cytosolic Receptor AIM2 Is Induced by Peroxisome Proliferator-activated Receptor γ following Mycobacterium tuberculosis Infection of Human Macrophages but Does Not Contribute to IL-1β Release

AIM2 (absent in melanoma 2), an inflammasome component, mediates IL-1β release in murine macrophages and cell lines. AIM2 and IL-1β contribute to murine control of Mycobacterium tuberculosis (M.tb) infection, but AIM2's impact in human macrophages, the primary niche for M.tb, remains unclear. We show that M.tb, Mycobacterium bovis bacillus Calmette-Guérin (BCG), and M. smegmatis induce AIM2 expression in primary human macrophages. M.tb-induced AIM2 expression is peroxisome proliferator-activated receptor γ (PPARγ)-dependent and M.tb ESX-1-independent, whereas BCG- and M. smegmatis-induced AIM2 expression is PPARγ-independent. PPARγ and NLRP3, but not AIM2, are important for IL-1β release in response to M.tb, and NLRP3 colocalizes with M.tb. This is in contrast to the role for AIM2 in inflammasome activation in mice and peritoneal macrophages. Altogether, we show that mycobacteria induce AIM2 expression in primary human macrophages, but AIM2 does not contribute to IL-1β release during M.tb infection, providing further evidence that AIM2 expression and function are regulated in a cell- and/or species-specific manner.

Host and microbial regulation of mitochondrial reactive oxygen species during mycobacterial infections

Mycobacteria, including Mycobacterium tuberculosis (Mtb) and non-tuberculous mycobacteria (NTM), pose challenges in treatment due to their increased resistance to antibiotics. Following infection, mycobacteria and their components trigger robust innate and inflammatory immune responses intricately associated with the modulation of mitochondrial functions, including oxidative phosphorylation (OXPHOS) and metabolism. Certainly, mitochondrial reactive oxygen species (mtROS) are an inevitable by-product of OXPHOS and function as a bactericidal weapon; however, an excessive accumulation of mtROS are linked to pathological inflammation and necroptotic cell death during mycobacterial infection. Despite previous studies outlining various host pathways involved in regulating mtROS levels during antimicrobial responses in mycobacterial infection, our understanding of the precise mechanisms orchestrating the fine regulation of this response remains limited. Emerging evidence suggests that mycobacterial proteins play a role in targeting the mitochondria of the host, indicating the potential influence of microbial factors on mitochondrial functions within host cells. In this review, we provide an overview of how both host and Mtb factors influence mtROS generation during infection. A comprehensive study of host and microbial factors that target mtROS will shed light on innovative approaches for effectively managing drug-resistant mycobacterial infections.

New insights into nucleic acid sensor AIM2: The potential benefit in targeted therapy for cancer

The AIM2 inflammasome represents a multifaceted oligomeric protein complex within the innate immune system, with the capacity to perceive double-stranded DNA (dsDNA) and engage in diverse physiological reactions and disease contexts, including cancer. While originally conceived as a discerning DNA sensor, AIM2 has demonstrated its capability to discern various nucleic acid variations, encompassing RNA and DNA-RNA hybrids. Through its interaction with nucleic acids, AIM2 orchestrates the assembly of a complex involving multiple proteins, aptly named the AIM2 inflammasome, which facilitates the enzymatic cleavage of proinflammatory cytokines, namely pro-IL-1β and pro-IL-18. This process, in turn, underpins its pivotal biological role. In this review, we provide a systematic summary and discussion of the latest advancements in AIM2 sensing various types of nucleic acids. Additionally, we discuss the modulation of AIM2 activation, which can cause cell death, including pyroptosis, apoptosis, and autophagic cell death. Finally, we fully illustrate the evidence for the dual role of AIM2 in different cancer types, including both anti-tumorigenic and pro-tumorigenic functions. Considering the above information, we uncover the therapeutic promise of modulating the AIM2 inflammasome in cancer treatment.

Reactive oxygen species trigger inflammasome activation after intracellular microbial interaction

The intracellular production of reactive oxygen species (ROS), composed of oxygen-reduced molecules, is important not only because of their lethal effects on microorganisms but also due to their potential inflammatory and metabolic regulation properties. The ROS pro-inflammatory properties are associated with the second signal to inflammasome activation, leading to cleaving pro-IL-1β and pro-IL18 before their secretion, as well as gasdermin-D, leading to pyroptosis. Some microorganisms can modulate NLRP3 and AIM-2 inflammasomes through ROS production: whilst Mycobacterium bovis, Mycobacterium kansasii, Francisella novicida, Brucella abortus, Listeria monocytogenes, Influenza virus, Syncytial respiratory virus, Porcine reproductive and respiratory syndrome virus, SARS-CoV, Mayaro virus, Leishmania amazonensis and Plasmodium sp. enhance inflammasome assembly, Hepatitis B virus, Mycobacterium marinum, Mycobacterium tuberculosis, Francisella tularensis and Leishmania sp. disrupt it. This process represents a recent cornerstone in our knowledge of the immunology of intracellular pathogens, which is reviewed in this mini-review.

Necrotic Cell Death and Inflammasome NLRP3 Activity in Mycobacterium bovis-Infected Bovine Macrophages

Mycobacterium bovis is a facultative intracellular bacterium that produces cellular necrosis in granulomatous lesions in bovines. Although M. bovis-induced inflammation actively participates in granuloma development, its role in necrotic cell death and in bovine macrophages has not been fully explored. In this study, we evaluate the effect of M. bovis AN5 and its culture filtrate protein extract (CFPE) on inflammasome activation in bovine macrophages and its consequences on cell death. Our results show that both stimuli induce necrotic cell death starting 4 h after incubation. CFPE treatment and M. bovis infection also induce the maturation of IL-1β (>3000 pg/mL), oligomerization of ASC (apoptosis-associated speck-like protein containing CARD), and activation of caspase-1, following the canonical activation pathway of the NLRP3 inflammasome. Inhibiting the oligomerization of NLRP3 and caspase-1 decreases necrosis among the infected or CFPE-stimulated macrophages. Furthermore, histological lymph node sections of bovines naturally infected with M. bovis contained cleaved gasdermin D, mainly in macrophages and giant cells within the granulomas. Finally, the induction of cell death (apoptosis and pyroptosis) decreased the intracellular bacteria count in the infected bovine macrophages, suggesting that cell death helps to control the intracellular growth of the mycobacteria. Our results indicate that M. bovis induces pyroptosis-like cell death that is partially related to the NLRP3 inflammasome activation and that the cell death process could control bacterial growth.

Mechanisms of lung damage in tuberculosis: implications for chronic obstructive pulmonary disease

Pulmonary tuberculosis is increasingly recognized as a risk factor for COPD. Severe lung function impairment has been reported in post-TB patients. Despite increasing evidence to support the association between TB and COPD, only a few studies describe the immunological basis of COPD among TB patients following successful treatment completion. In this review, we draw on well-elaborated Mycobacterium tuberculosis-induced immune mechanisms in the lungs to highlight shared mechanisms for COPD pathogenesis in the setting of tuberculosis disease. We further examine how such mechanisms could be exploited to guide COPD therapeutics.

Interaction of Mycobacteria With Host Cell Inflammasomes

The inflammasome complex is important for host defense against intracellular bacterial infections. Mycobacterium tuberculosis (Mtb) is a facultative intracellular bacterium which is able to survive in infected macrophages. Here we discuss how the host cell inflammasomes sense Mtb and other related mycobacterial species. Furthermore, we describe the molecular mechanisms of NLRP3 inflammasome sensing of Mtb which involve the type VII secretion system ESX-1, cell surface lipids (TDM/TDB), secreted effector proteins (LpqH, PPE13, EST12, EsxA) and double-stranded RNA acting on the priming and/or activation steps of inflammasome activation. In contrast, Mtb also mediates inhibition of the NLRP3 inflammasome by limiting exposure of cell surface ligands via its hydrolase, Hip1, by inhibiting the host cell cathepsin G protease via the secreted Mtb effector Rv3364c and finally, by limiting intracellular triggers (K+ and Cl- efflux and cytosolic reactive oxygen species production) via its serine/threonine kinase PknF. In addition, Mtb inhibits the AIM2 inflammasome activation via an unknown mechanism. Overall, there is good evidence for a tug-of-war between Mtb trying to limit inflammasome activation and the host cell trying to sense Mtb and activate the inflammasome. The detailed molecular mechanisms and the importance of inflammasome activation for virulence of Mtb or host susceptibility have not been fully investigated.

From pyroptosis, apoptosis and necroptosis to PANoptosis: A mechanistic compendium of programmed cell death pathways

Pyroptosis, apoptosis and necroptosis are the most genetically well-defined programmed cell death (PCD) pathways, and they are intricately involved in both homeostasis and disease. Although the identification of key initiators, effectors and executioners in each of these three PCD pathways has historically delineated them as distinct, growing evidence has highlighted extensive crosstalk among them. These observations have led to the establishment of the concept of PANoptosis, defined as an inflammatory PCD pathway regulated by the PANoptosome complex with key features of pyroptosis, apoptosis and/or necroptosis that cannot be accounted for by any of these PCD pathways alone. In this review, we provide a brief overview of the research history of pyroptosis, apoptosis and necroptosis. We then examine the intricate crosstalk among these PCD pathways to discuss the current evidence for PANoptosis. We also detail the molecular evidence for the assembly of the PANoptosome complex, a molecular scaffold for contemporaneous engagement of key molecules from pyroptosis, apoptosis, and/or necroptosis. PANoptosis is now known to be critically involved in many diseases, including infection, sterile inflammation and cancer, and future discovery of novel PANoptotic components will continue to broaden our understanding of the fundamental processes of cell death and inform the development of new therapeutics.

The complex role of AIM2 in autoimmune diseases and cancers

Absent in melanoma 2 (AIM2) is a novel member of interferon (IFN)-inducible PYHIN proteins. In innate immune cells, AIM2 servers as a cytoplasmic double-stranded DNA sensor, playing a crucial role in the initiation of the innate immune response as a component of the inflammasome. AIM2 expression is increased in patients with systemic lupus erythematosus (SLE), psoriasis, and primary Sjogren's syndrome, indicating that AIM2 might be involved in the pathogenesis of autoimmune diseases. Meanwhile, AIM2 also plays an antitumorigenesis role in an inflammasome independent-manner. In melanoma, AIM2 is initially identified as a tumor suppressor factor. However, AIM2 is also found to contribute to lung tumorigenesis via the inflammasome-dependent release of interleukin 1β and regulation of mitochondrial dynamics. Additionally, AIM2 reciprocally dampening the cGAS-STING pathway causes immunosuppression of macrophages and evasion of antitumor immunity during antibody treatment. To summarize the complicated effect and role of AIM2 in autoimmune diseases and cancers, herein, we provide an overview of the emerging research progress on the function and regulatory pathway of AIM2 in innate and adaptive immune cells, as well as tumor cells, and discuss its pathogenic role in autoimmune diseases, such as SLE, psoriasis, primary Sjogren's syndrome, and cancers, such as melanomas, non-small-cell lung cancer, colon cancer, hepatocellular carcinoma, renal carcinoma, and so on, hopefully providing potential therapeutic and diagnostic strategies for clinical use.

Caspase-1 inhibits IFN-β production via cleavage of cGAS during M. bovis infection

Mycobacterium bovis (M. bovis) infection triggers cytokine production via pattern recognition receptors. These cytokines include type I interferons (IFNs) and interleukin-1β (IL-1β). Excessive type I IFN levels impair host resistance to M. bovis infection. Therefore, strict control of type I IFN production is helpful to reduce pathological damage and bacterial burden. Here, we found that a deficiency in caspase-1, which is the critical component of the inflammasome responsible for IL-1β production, resulted in increased IFN-β production upon M. bovis infection. Subsequent experiments demonstrated that caspase-1 activation reduced cyclic GMP-AMP synthase (cGAS) expression, thereby inhibiting downstream TANK-binding kinase 1 (TBK1)- interferon regulatory factor 3 (IRF3) signaling and ultimately reducing IFN production. A deficiency in caspase-1 activation enhanced the bacterial burden during M. bovis infection in vitro and in vivo and aggravated pathological lesion formation. Thus, caspase-1 activation reduced IFN-β production upon M. bovis infection by dampening cGAS-TBK1-IRF3 signaling, suggesting that the inflammasome protects hosts by negatively regulating harmful cytokines.

Mycobacterium tuberculosis stimulates IL-1β production by macrophages in an ESAT-6 dependent manner with the involvement of serum amyloid A3

Despite its critical roles in immune responses against tuberculosis infection and immune pathology, the molecular details of interleukin (IL)-1β production in tuberculosis infection remain elusive. To explore IL-1β production in tuberculosis infection, we infected mouse bone marrow-derived macrophages (BMDM) with Mycobacterium tuberculosis (Mtb) H37Rv, its early secreted antigenic target protein of 6 kDa (ESAT-6) gene deletion (H37Rv:Δ3875) or complemented strain (H37Rv:Δ3875C) and evaluated IL-1β production. H37Rv induced significantly increased IL-1β production by BMDMs compared to non-infected BMDMs. In contrast, H37Rv:Δ3875 induced significantly less mature IL-1β production despite eliciting comparable levels of pro-IL-1β and IL-8 from BMDMs compared to H37Rv and H37Rv:Δ3875C. Blocking either NLRP3 or K⁺ efflux diminished H37Rv-induced IL-1β production by BMDMs. Infection of mice intranasally with H37Rv:Δ3875 induced less IL-1β production in the lungs compared with H37Rv. Intranasal delivery of ESAT-6 but not CFP10 induced production of IL-1β in mouse lungs and RNA-Seq analysis identified serum amyloid A (SAA) 3 as one of the highly expressed genes in mouse lungs. Infection of mice with H37Rv but not H37Rv:Δ3875 induced expression of lung SAA3 mRNA and protein, consistent with the effect of intranasal delivery of ESAT-6. Silencing SAA3 reduced Mtb-induced IL-1β production by BMDMs. We conclude that SAA3 plays critical role in ESAT-6 dependent IL-1β production by macrophages in tuberculosis infection.

Single-Nucleotide Variants in the AIM2 - Absent in Melanoma 2 Gene (rs1103577) Associated With Protection for Tuberculosis

Tuberculosis (TB) remains a serious public health burden worldwide. TB is an infectious disease caused by the Mycobacterium tuberculosis Complex. Innate immune response is critical for controlling mycobacterial infection. NOD-like receptor pyrin domain containing 3/ absent in melanoma 2 (NLRP3/AIM2) inflammasomes are suggested to play an important role in TB. NLRP3/AIM2 mediate the release of pro-inflammatory cytokines IL-1β and IL-18 to control M. tuberculosis infection. Variants of genes involved in inflammasomes may contribute to elucidation of host immune responses to TB infection. The present study evaluated single-nucleotide variants (SNVs) in inflammasome genes AIM2 (rs1103577), CARD8 (rs2009373), and CTSB (rs1692816) in 401 patients with pulmonary TB (PTB), 133 patients with extrapulmonary TB (EPTB), and 366 healthy control (HC) subjects with no history of TB residing in the Amazonas state. Quantitative Real Time PCR was performed for allelic discrimination. The SNV of AIM2 (rs1103577) is associated with protection for PTB (padj: 0.033, ORadj: 0.69, 95% CI: 0.49-0.97). CTSB (rs1692816) is associated with reduced risk for EPTB when compared with PTB (padj: 0.034, ORadj: 0.50, 95% CI: 0.27-0.94). Serum IL-1β concentrations were higher in patients with PTB than those in HCs (p = 0,0003). The SNV rs1103577 of AIM2 appeared to influence IL-1β release. In a dominant model, individuals with the CC genotype (mean 3.78 ± SD 0.81) appeared to have a higher level of IL-1β compared to carriers of the T allele (mean 3.45 ± SD 0.84) among the patients with PTB (p = 0,0040). We found that SNVs of AIM2 and CTSB were associated with TB, and the mechanisms involved in this process require further study.

The Roles of Inflammasomes in Host Defense against Mycobacterium tuberculosis

Mycobacterium tuberculosis (MTB) infection is characterized by granulomatous lung lesions and systemic inflammatory responses during active disease. Inflammasome activation is involved in regulation of inflammation. Inflammasomes are multiprotein complexes serving a platform for activation of caspase-1, which cleaves the proinflammatory cytokines such as interleukin-1β (IL-1β) and IL-18 into their active forms. These cytokines play an essential role in MTB control. MTB infection triggers activation of the nucleotide-binding domain, leucine-rich-repeat containing family, pyrin domain-containing 3 (NLRP3) and absent in melanoma 2 (AIM2) inflammasomes in vitro, but only AIM2 and apoptosis-associated speck-like protein containing a caspase-activation recruitment domain (ASC), rather than NLRP3 or caspase-1, favor host survival and restriction of mycobacterial replication in vivo. Interferons (IFNs) inhibits MTB-induced inflammasome activation and IL-1 signaling. In this review, we focus on activation and regulation of the NLRP3 and AIM2 inflammasomes after exposure to MTB, as well as the effect of inflammasome activation on host defense against the infection.

Emerging roles of absent in melanoma 2 in cardiovascular diseases

Absent in melanoma 2 (AIM2) is a member of the PYHIN (pyrin and HIN domain-containing protein) family with important roles in sensing double-stranded DNA (dsDNA) and assembling the AIM2 inflammasome, which has wide-ranging, pro-inflammatory and pro-pyroptotic properties. The AIM2 inflammasome can become activated in atherosclerotic plaque, abdominal aortic aneurysm wall and injured myocardium, and its activation is tightly regulated by a variety of atherogenic factors. Activation of the AIM2 inflammasome has close links to the progression of several cardiovascular diseases. This review will summarize the current knowledge of AIM2 biology, providing the latest insights into the mechanisms and contributions of atherogenic factors to AIM2 inflammasome activation. In addition, we will also explore crosstalk between AIM2 and the pathologies of atherosclerosis, abdominal aortic aneurysm, myocardial infarction and heart failure. A better understanding of the pathological roles of AIM2 in these disorders will be helpful in developing novel therapeutic approaches.

Mycobacterial PPE13 activates inflammasome by interacting with the NATCH and LRR domains of NLRP3

Pathogenic mycobacteria, such as Mycobacterium tuberculosis, Mycobacterium bovis, and Mycobacterium marinum, can trigger NLRP3 inflammasome activation leading to maturation and secretion of interleukin 1β (IL-1β). However, the mycobacterial factors involved in the activation of NLRP3 inflammasome are not fully understood. Here, we identified that the PPE family protein PPE13 was responsible for the induction of IL-1β secretion in a NLRP3 inflammasome-dependent manner. We found that the recombinant Mycobacterium smegmatis expressing PPE13 activates NLRP3 inflammasome, thereby inducing caspase-1 cleavage and IL-1β secretion in J774A.1, BMDMs, and THP-1 macrophages. To examine whether this inflammasome activation was triggered by PPE13 rather than components of M. smegmatis, PPE13 was introduced into the aforementioned macrophages by lentivirus as a delivery vector. Similarly, this led to the activation of NLRP3 inflammasome, indicating that PPE13 is a direct activator of NLRP3 cascade. We further demonstrated that the NLRP3 complex activated the inflammasome cascade, and the assembly of this complex was facilitated by PPE13 through interacting with the LRR and NATCH domains of NLRP3. Finally, we found that all PPE13 proteins isolated from M. tuberculosis, M. bovis, and M. marinum can activate NLRP3 inflammasome through binding to NLRP3, which requires C-terminal repetitive MPTR domain of PPE13. Thus, we, for the first time, revealed that PPE13 triggers the inflammasome-response by interacting with the MPTR domain of PPE13 and the LRR and NATCH domains of NLRP3. These findings provide a novel perspective on the function of PPE proteins in the immune system during mycobacteria invasion.

New insights into the evasion of host innate immunity by Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) is an extremely successful intracellular pathogen that causes tuberculosis (TB), which remains the leading infectious cause of human death. The early interactions between Mtb and the host innate immune system largely determine the establishment of TB infection and disease development. Upon infection, host cells detect Mtb through a set of innate immune receptors and launch a range of cellular innate immune events. However, these innate defense mechanisms are extensively modulated by Mtb to avoid host immune clearance. In this review, we describe the emerging role of cytosolic nucleic acid-sensing pathways at the host-Mtb interface and summarize recently revealed mechanisms by which Mtb circumvents host cellular innate immune strategies such as membrane trafficking and integrity, cell death and autophagy. In addition, we discuss the newly elucidated strategies by which Mtb manipulates the host molecular regulatory machinery of innate immunity, including the intranuclear regulatory machinery, the ubiquitin system, and cellular intrinsic immune components. A better understanding of innate immune evasion mechanisms adopted by Mtb will provide new insights into TB pathogenesis and contribute to the development of more effective TB vaccines and therapies.

AIM2 in health and disease: Inflammasome and beyond

Nucleic acid sensing is a critical mechanism by which the immune system monitors for pathogen invasion. A set of germline-encoded innate immune receptors detect microbial DNA in various compartments of the cell, such as endosomes, the cytosol, and the nucleus. Sensing of microbial DNA through these receptors stimulates, in most cases, interferon regulatory factor-dependent type I IFN synthesis followed by JAK/STAT-dependent interferon-stimulated gene expression. In contrast, the detection of DNA in the cytosol by AIM2 assembles a macromolecular complex called the inflammasome, which unleashes the proteolytic activity of a cysteine protease caspase-1. Caspase-1 cleaves and activates the pro-inflammatory cytokines such as IL-1β and IL-18 and a pore-forming protein, gasdermin D, which triggers pyroptosis, an inflammatory form of cell death. Research over the past decade has revealed that AIM2 plays essential roles not only in host defense against pathogens but also in inflammatory diseases, autoimmunity, and cancer in inflammasome-dependent and inflammasome-independent manners. This review discusses the latest advancements in our understanding of AIM2 biology and its functions in health and disease.

Human Alveolar and Splenic Macrophage Populations Display a Distinct Transcriptomic Response to Infection With Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) infects alveolar macrophages (AMs), causing pulmonary tuberculosis (PTB), the most common form of the disease. Less frequently, Mtb is disseminated to many other organs and tissues, resulting in different extrapulmonary forms of TB. Nevertheless, very few studies have addressed the global mRNA response of human AMs, particularly from humans with the active form of the disease. Strikingly, almost no studies have addressed the response of human extrapulmonary macrophages to Mtb infection. In this pilot study, using microarray technology, we examined the transcriptomic ex vivo response of AMs from PTB patients (AMTBs) and AMs from control subjects (AMCTs) infected with two clinical isolates of Mtb. Furthermore, we also studied the infection response of human splenic macrophages (SMs) to Mtb isolates, as a model for extrapulmonary infection, and compared the transcriptomic response between AMs and SMs. Our results showed a striking difference in global mRNA profiles in response to infection between AMs and SMs, implicating a tissue-specific macrophage response to Mtb.

The role of inflammasomes in kidney disease

Inflammasomes are multiprotein innate immune complexes that regulate caspase-dependent inflammation and cell death. Pattern recognition receptors, such as nucleotide-binding oligomerization domain (NOD)-like receptors and absent in melanoma 2 (AIM2)-like receptors, sense danger signals or cellular events to activate canonical inflammasomes, resulting in caspase 1 activation, pyroptosis and the secretion of IL-1β and IL-18. Non-canonical inflammasomes can be activated by intracellular lipopolysaccharides, toxins and some cell signalling pathways. These inflammasomes regulate the activation of alternative caspases (caspase 4, caspase 5, caspase 11 and caspase 8) that lead to pyroptosis, apoptosis and the regulation of other cellular pathways. Many inflammasome-related genes and proteins have been implicated in animal models of kidney disease. In particular, the NLRP3 (NOD-, LRR- and pyrin domain-containing 3) inflammasome has been shown to contribute to a wide range of acute and chronic microbial and non-microbial kidney diseases via canonical and non-canonical mechanisms that regulate inflammation, pyroptosis, apoptosis and fibrosis. In patients with chronic kidney disease, immunomodulation therapies targeting IL-1β such as canakinumab have been shown to prevent cardiovascular events. Moreover, findings in experimental models of kidney disease suggest that small-molecule inhibitors targeting NLRP3 and other inflammasome components are promising therapeutic agents.

Role of AIM2 inflammasome in inflammatory diseases, cancer and infection

AIM2 is a cytosolic innate immune receptor which recognizes double-stranded DNA (dsDNA) released during cellular perturbation and pathogenic assault. AIM2 recognition of dsDNA leads to the assembly of a large multiprotein oligomeric complex termed the inflammasome. This inflammasome assembly leads to the secretion of bioactive interleukin-1β (IL-1β) and IL-18 and induction of an inflammatory form of cell death called pyroptosis. Sensing of dsDNA by AIM2 in the cytosol is crucial to mediate protection against the invading pathogens including bacteria, virus, fungi and parasites. AIM2 also responds to dsDNA released from damaged host cells, resulting in the secretion of the effector cytokines thereby driving the progression of sterile inflammatory diseases such as skin disease, neuronal disease, chronic kidney disease, cardiovascular disease and diabetes. Additionally, the protection mediated by AIM2 in the development of colorectal cancer depends on its ability to regulate epithelial cell proliferation and gut microbiota in maintaining intestinal homeostasis independently of the effector cytokines. In this review, we will highlight the recent progress on the role of the AIM2 inflammasome as a guardian of cellular integrity in modulating chronic inflammatory diseases, cancer and infection.

The absent in melanoma 2 (AIM2) inflammasome in microbial infection

Inflammasomes play a very important role in the host defense against multiple pathogenic microbes, including bacteria and viruses. Inflammasomes are multiprotein complex platforms that mediate the processing of the two most important inflammatory cytokines, pro-IL-1β and pro-IL-18, to their active forms. The inflammasome is formed by the apoptosis-associated speck-like protein containing a CARD (ASC), procaspase-1 and a sensor protein, either a NOD-like receptor (NLR) or an absent in melanoma 2 (AIM2)-like receptor. The sensor molecule determines inflammasome specificity by detecting specific and conserved microbial products or cell stress signals. Compared with the other inflammasomes, there is much more unknown about the activation or regulation mechanisms of the AIM2 inflammasome. In this review, we will discuss these mechanisms and the specific roles of the AIM2 inflammasome in response to diverse pathogens.

Endoplasmic Reticulum Stress Induces Macrophages to Produce IL-1β During Mycobacterium bovis Infection via a Positive Feedback Loop Between Mitochondrial Damage and Inflammasome Activation

Mycobacterium bovis, the causative agent of tuberculosis in cattle and humans, infects host macrophages and induces endoplasmic reticulum stress (ERS), mitochondrial damage, and interleukin (IL)-1β production. The relationship between these phenotypes is yet to be elucidated. In this study, we investigated the role of ERS in mitochondrial damage and IL-1β production in macrophages during infection with a virulent M. bovis strain. We found that ERS activates the inflammasome via NOD-like receptor family, pyrin domain-containing 3 (NLRP3)-caspase-8 and that IFN-inducible protein absent in melanoma 2 (AIM2) triggered mitochondrial damage. ERS increased reactive oxygen species (ROS), which promoted translocation of the inflammasome to the mitochondria. NLRP3, but not AIM2, was involved in the ERS-induced cleavage of caspase-8 and Bid, leading to mitochondrial damage, which was required for the production of mature IL-1β. Our data suggest that ERS induces macrophages to produce mature IL-1β during infection with virulent M. bovis through a positive feedback loop between mitochondrial damage and inflammasome activation. To the best of our knowledge, this is the first evidence of the involvement of ERS and mitochondrial damage in inflammasome activation during M. bovis infection.

Common Differences: The Ability of Inflammasomes to Distinguish Between Self and Pathogen Nucleic Acids During Infection

The innate immune system detects the presence of pathogens based on detection of non-self. In other words, most pathogens possess intrinsic differences that can distinguish them from host cells. For example, bacteria and fungi have cell walls comprised of peptidoglycan and carbohydrates (like mannans), respectively. Germline encoded pattern recognition receptors (PRRs) of the Toll-like receptor (TLR) and C-type lectin receptor (CLR) family have the ability to detect such unique pathogen associated features. However, some TLRs and members of the RIG-I-like receptor (RLR), NOD-like receptor (NLR), or AIM2-like receptor (ALR) family can sense pathogen invasion based on pathogen nucleic acids. Nucleic acids are not unique to pathogens, thus raising the question of how such PRRs evolved to detect pathogens but not self. In this chapter, we will examine the PRRs that sense pathogen nucleic acids and subsequently activate the inflammasome signaling pathway. We will examine the selective mechanisms by which these receptors distinguish pathogens from "self" and discuss the importance of such pathways in disease development in animal models and human patients.

Cytosolic Nucleic Acid Sensors in Inflammatory and Autoimmune Disorders

Innate immunity employs germline-encoded pattern recognition receptors (PRRs) to sense microbial pattern molecules. Recognition of pathogen-associated molecular patterns (PAMPs) by various PPRs located on the cell membrane or in the cytosol leads to the activation of cell signaling pathways and production of inflammatory mediators. Nucleic acids including DNA, RNA, and their derivatives are potent PAMPs which can be recognized by multiple PRRs to induce inflammatory responses. While nucleic acid sensors can also sense endogenous nucleic acids, they are capable of discriminating self from non-self. However, defects in nucleic acid sensing PRRs or dysregulation of nucleic acid sensing signaling pathways may cause excessive activation of the immune system resulting in the development of inflammatory and autoimmune diseases. This review will discuss the major pathways for sensing intracellular nucleic acids and how defects in these nucleic acid sensing are associated with different kinds of autoimmune and inflammatory disorders.

Cytosolic Recognition of Microbes and Pathogens: Inflammasomes in Action

Infection is a dynamic biological process underpinned by a complex interplay between the pathogen and the host. Microbes from all domains of life, including bacteria, viruses, fungi, and protozoan parasites, have the capacity to cause infection. Infection is sensed by the host, which often leads to activation of the inflammasome, a cytosolic macromolecular signaling platform that mediates the release of the proinflammatory cytokines interleukin-1β (IL-1β) and IL-18 and cleavage of the pore-forming protein gasdermin D, leading to pyroptosis. Host-mediated sensing of the infection occurs when pathogens inject or carry pathogen-associated molecular patterns (PAMPs) into the cytoplasm or induce damage that causes cytosolic liberation of danger-associated molecular patterns (DAMPs) in the host cell. Recognition of PAMPs and DAMPs by inflammasome sensors, including NLRP1, NLRP3, NLRC4, NAIP, AIM2, and Pyrin, initiates a cascade of events that culminate in inflammation and cell death. However, pathogens can deploy virulence factors capable of minimizing or evading host detection. This review presents a comprehensive overview of the mechanisms of microbe-induced activation of the inflammasome and the functional consequences of inflammasome activation in infectious diseases. We also explore the microbial strategies used in the evasion of inflammasome sensing at the host-microbe interaction interface.

H1/pAIM2 nanoparticles exert anti-tumour effects that is associated with the inflammasome activation in renal carcinoma

Renal cell carcinoma (RCC) is a high metastasis tumour with less effective treatment available currently. Absent in melanoma 2 (AIM2) as a tumour suppressor might be used as a potential therapeutic target for RCC treatment. Here, we found that AIM2 expression was significantly decreased in RCC patient specimens and renal carcinoma cell lines (786‐O and OSRC‐2). To establish a safe and effective AIM2 gene delivery system, we formed the nanoparticles consisting of a folate grafted PEI600‐CyD (H1) nanoparticle‐mediated AIM2 gene (H1/pAIM2) as an effective delivery agent. Delivery of H1/pAIM2 in renal carcinoma cells could remarkably increase the expression of AIM2, and subsequently decrease cell proliferation, migration, and invasion as well as enhance cell apoptosis. In order to evaluate the therapeutic efficacy of AIM2 in vivo, H1/pAIM2 nanoparticles were injected intratumorally into 786‐O‐xenograft mice. Administration of H1/pAIM2 nanoparticles could inhibit the tumour growth as evidenced by reduced tumour volume and weight. Furthermore, Blockade of inflammasome activation triggered by H1/pAIM2 nanoparticles using inflammasome inhibitor YVAD‐CMK abrogated the anti‐tumoral activities of H1/AIM2. These results indicated the therapeutic effect of H1/pAIM2 nanoparticles was mainly attributable to its capability to enhance the inflammasome activation. H1/AIM2 nanoparticles might act as an efficient therapeutic approach for RCC treatment.

Macrophage Uptake of Necrotic Cell DNA Activates the AIM2 Inflammasome to Regulate a Proinflammatory Phenotype in CKD

Nonmicrobial inflammation contributes to CKD progression and fibrosis. Absent in melanoma 2 (AIM2) is an inflammasome-forming receptor for double-stranded DNA. AIM2 is expressed in the kidney and activated mainly by macrophages. We investigated the potential pathogenic role of the AIM2 inflammasome in kidney disease. In kidneys from patients with diabetic or nondiabetic CKD, immunofluorescence showed AIM2 expression in glomeruli, tubules, and infiltrating leukocytes. In a mouse model of unilateral ureteral obstruction (UUO), Aim2 deficiency attenuated the renal injury, fibrosis, and inflammation observed in wild-type (WT) littermates. In bone marrow chimera studies, UUO induced substantially more tubular injury and IL-1β cleavage in Aim2^-/- or WT mice that received WT bone marrow than in WT mice that received Aim2^-/- bone marrow. Intravital microscopy of the kidney in LysM^(gfp/gfp) mice 5-6 days after UUO demonstrated the significant recruitment of GFP⁺ proinflammatory macrophages that crawled along injured tubules, engulfed DNA from necrotic cells, and expressed active caspase-1. DNA uptake occurred in large vacuolar structures within recruited macrophages but not resident CX₃CR1⁺ renal phagocytes. In vitro, macrophages that engulfed necrotic debris showed AIM2-dependent activation of caspase-1 and IL-1β, as well as the formation of AIM2⁺ ASC specks. ASC specks are a hallmark of inflammasome activation. Cotreatment with DNaseI attenuated the increase in IL-1β levels, confirming that DNA was the principal damage-associated molecular pattern in this process. Therefore, the activation of the AIM2 inflammasome by DNA from necrotic cells drives a proinflammatory phenotype that contributes to chronic injury in the kidney.

AIM2 inhibits autophagy and IFN-β production during M. bovis infection

Mycobacteria can trigger the AIM2 inflammasome, autophagy activation and type-I interferon release, which are both activated by cytosolic DNA. We have recently demonstrated that activation of the AIM2 inflammasome during M. bovis infection is the result of mycobacterial translocation into the cytosol. To elucidate the effects of inflammasome activation on autophagy, we investigated the role of the AIM2 inflammasome from macrophages infected with a virulent strain of M. bovis. The results showed that the M. bovis-induced AIM2 inflammasome activation decreases autophagy in immortalized and primary murine macrophages. This relied on the inflammasome sensor AIM2 which conjugates with cytosolic DNA to inhibit the STING-dependent pathway involved in selective autophagy and interferon-β release in Mycobacterium-infected macrophages. These results suggest that the AIM2 cytosolic DNA sensor may conjugate competitively with cytosolic M. bovis DNA to restrict M. bovis induced STING-TBK1-dependent autophagy activation and IFN-β secretion.

The Central Role of IFI204 in IFN-β Release and Autophagy Activation during Mycobacterium bovis Infection

Mycobacterium bovis (M. bovis) is the pathogen of animals and humans that can replicate in the phagosomes of myeloid cells. Cytosolic detection of bacterial products plays a crucial role in initiating the innate immune response, including autophagy activation and interferon-β (IFN-β) release. Although IFN-β release and autophagy activation have been reported during mycobacterium infection, the mechanisms underlying remains poorly defined. Here, we demonstrated that IFN-β release increases in macrophages exposed to M. bovis and this requires the activation of the DNA sensor of interferon-γ inducible protein 204 (IFI204). Knockdown of the IFI204 in immortalized and primary murine macrophages blocked IFN-β production and autophagy marker LC3 expression. Thus, our results indicate that the IFI204 is an important sensor for innate immune responses of M. bovis infection.

Deviant Behavior: Tick-Borne Pathogens and Inflammasome Signaling

In the face of an assault, host cells mount an immediate response orchestrated by innate immunity. Two of the best described innate immune signaling networks are the Toll- and the Nod-like receptor pathways. Extensive work has been done characterizing both signaling cascades with several recent advances on the forefront of inflammasome biology. In this review, we will discuss how more commonly-studied pathogens differ from tick-transmitted microbes in the context of Nod-like receptor signaling and inflammasome formation. Because pathogens transmitted by ticks have unique characteristics, we offer the opinion that these microbes can be used to uncover novel principles of Nod-like receptor biology.

DNA-sensing inflammasomes: regulation of bacterial host defense and the gut microbiota

DNA sensors are formidable immune guardians of the host. At least 14 cytoplasmic DNA sensors have been identified in recent years, each with specialized roles in driving inflammation and/or cell death. Of these, AIM2 is a sensor of dsDNA, and forms an inflammasome complex to activate the cysteine protease caspase-1, mediates the release of the proinflammatory cytokines IL-1β and IL-18, and induces pyroptosis. The inflammasome sensor NLRP3 can also respond to DNA in the forms of oxidized mitochondrial DNA and the DNA derivative RNA:DNA hybrids produced by bacteria, whereas the putative inflammasome sensor IFI16 responds to viral DNA in the nucleus. Although inflammasomes provoke inflammation for anti-microbial host defense, they must also maintain homeostasis with commensal microbiota. Here, we outline recent advances highlighting the complex relationship between DNA-sensing inflammasomes, bacterial host defense and the gut microbiota.

Virulent Mycobacterium bovis Beijing Strain Activates the NLRP7 Inflammasome in THP-1 Macrophages

Mycobacterium bovis is the causative agent of tuberculosis in a wide range of mammals, including humans. Macrophages are the first line of host defense. They secrete proinflammatory cytokines, such as interleukin-1 beta (IL-1β), in response to mycobacterial infection, but the underlying mechanisms by which human macrophages are activated and release IL-1β following M. bovis infection are poorly understood. Here we show that the ‘nucleotide binding and oligomerization of domain-like receptor (NLR) family pyrin domain containing 7 protein’ (NLRP7) inflammasome is involved in IL-1β secretion and caspase-1 activation induced by M. bovis infection in THP-1 macrophages. NLRP7 inflammasome activation promotes the induction of pyroptosis as well as the expression of tumor necrosis factor alpha (TNF-α), Chemokine (C-C motif) ligand 3 (CCL3) and IL-1β mRNAs. Thus, the NLRP7 inflammasome contributes to IL-1β secretion and induction of pyroptosis in response to M. bovis infection in THP-1 macrophages.

Pyroptotic cell death defends against intracellular pathogens

Inflammatory caspases play a central role in innate immunity by responding to cytosolic signals and initiating a twofold response. First, caspase-1 induces the activation and secretion of the two prominent pro-inflammatory cytokines, interleukin-1β (IL-1β) and IL-18. Second, either caspase-1 or caspase-11 can trigger a form of lytic, programmed cell death called pyroptosis. Pyroptosis operates to remove the replication niche of intracellular pathogens, making them susceptible to phagocytosis and killing by a secondary phagocyte. However, aberrant, systemic activation of pyroptosis in vivo may contribute to sepsis. Emphasizing the efficiency of inflammasome detection of microbial infections, many pathogens have evolved to avoid or subvert pyroptosis. This review focuses on molecular and morphological characteristics of pyroptosis and the individual inflammasomes and their contribution to defense against infection in mice and humans.

AIM2 inflammasome in infection, cancer, and autoimmunity: Role in DNA sensing, inflammation, and innate immunity

Recognition of DNA by the cell is an important immunological signature that marks the initiation of an innate immune response. AIM2 is a cytoplasmic sensor that recognizes dsDNA of microbial or host origin. Upon binding to DNA, AIM2 assembles a multiprotein complex called the inflammasome, which drives pyroptosis and proteolytic cleavage of the proinflammatory cytokines pro-IL-1β and pro-IL-18. Release of microbial DNA into the cytoplasm during infection by Francisella, Listeria, Mycobacterium, mouse cytomegalovirus, vaccinia virus, Aspergillus, and Plasmodium species leads to activation of the AIM2 inflammasome. In contrast, inappropriate recognition of cytoplasmic self-DNA by AIM2 contributes to the development of psoriasis, dermatitis, arthritis, and other autoimmune and inflammatory diseases. Inflammasome-independent functions of AIM2 have also been described, including the regulation of the intestinal stem cell proliferation and the gut microbiota ecology in the control of colorectal cancer. In this review we provide an overview of the latest research on AIM2 inflammasome and its role in infection, cancer, and autoimmunity.

The inflammasome: Learning from bacterial evasion strategies

The innate immune system plays a critical role in defense against microbial infection and employs germline-encoded pattern recognition receptors to detect broadly conserved microbial structures or activities. Pattern recognition receptors of the nucleotide binding domain/leucine rich repeat (NLR) family respond to particular microbial products or disruption of cellular physiology, and mediate the activation of an arm of the innate immune response termed the inflammasome. Inflammasomes are multiprotein complexes that are inducibly assembled in response to the contamination of the host cell cytosol by microbial products. Individual NLRs sense the presence of their cognate stimuli, and initiate assembly of inflammasomes via the adaptor protein apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) and the effector pro-enzyme caspase-1. Inflammasome activation leads to rapid release of pro-inflammatory mediators of the IL-1 family as well as the release of intracellular alarmins due to a lytic form of programmed cell death termed pyroptosis. Over the past 15 years, a great deal has been learned about the mechanisms that drive inflammasome activation in response to infection by diverse pathogens. However, pathogens have also evolved mechanisms to evade or suppress host defenses, and the mechanisms by which pathogens evade inflammasome activation are not well-understood. Here, we will discuss emerging evidence on how diverse pathogens evade inflammasome activation, and what these studies have revealed about inflammasome biology. Deeper understanding of pathogen evasion of inflammasome activation has the potential to lead to development of novel classes of immunomodulatory factors that could be used in the context of human inflammatory diseases.

Correlation of the composition of biominerals with their ability of stimulating intracellular DNA sensors and inflammatory cytokines

Biominerals (or microcalcification) deposited in soft tissues are associated with a number of pathogeneses and cancer progressions. Biominerals have also shown promise for DNA delivery and tissue engineering. Biominerals themselves may stimulate NALP3 inflammasomes, and DNA delivered by biominerals can potentially engage with intracellular DNA sensors, resulting in unwanted inflammatory responses. In this study, a library of biominerals doped with or without DNA is formed through surface-induced biomineralization. It is demonstrated that empty biominerals stimulate NALP3 inflammasomes and induce the production of IL-1β. They are also able to activate mouse embryonic fibroblasts (MEFs) and induce inflammatory cytokines, i.e. IL-6. DNA delivered by biominerals escapes the detection of TLR9, but activates DAI and inflammasomes. Furthermore, it is shown that the level of both IL-1β and IL-6 is correlated with the composition of biominerals, in particular the ratio of Mg(Sr) to Ca, and the pH sensitivity of biominerals. These results provide insights into the design of safe and effective DNA delivery systems and biocompatible implants as well as the understanding of the pathogeneses of biominerals deposited in soft tissues.

Collaborative action of Toll-like and NOD-like receptors as modulators of the inflammatory response to pathogenic bacteria

Early sensing of pathogenic bacteria by the host immune system is important to develop effective mechanisms to kill the invader. Microbial recognition, activation of signaling pathways, and effector mechanisms are sequential events that must be highly controlled to successfully eliminate the pathogen. Host recognizes pathogens through pattern-recognition receptors (PRRs) that sense pathogen-associated molecular patterns (PAMPs). Some of these PRRs include Toll-like receptors (TLRs), nucleotide-binding oligomerization domain-like receptors (NLRs), retinoic acid-inducible gene-I- (RIG-I-) like receptors (RLRs), and C-type lectin receptors (CLRs). TLRs and NLRs are PRRs that play a key role in recognition of extracellular and intracellular bacteria and control the inflammatory response. The activation of TLRs and NLRs by their respective ligands activates downstream signaling pathways that converge on activation of transcription factors, such as nuclear factor-kappaB (NF-κB), activator protein-1 (AP-1) or interferon regulatory factors (IRFs), leading to expression of inflammatory cytokines and antimicrobial molecules. The goal of this review is to discuss how the TLRs and NRLs signaling pathways collaborate in a cooperative or synergistic manner to counteract the infectious agents. A deep knowledge of the biochemical events initiated by each of these receptors will undoubtedly have a high impact in the design of more effective strategies to control inflammation.

Innate immune sensing of nucleic acids from mycobacteria

Endosomal and cytosolic receptors engage recognition of mycobacterial-derived nucleic acids (MyNAs). In contrast, virulent mycobacteria may utilize nucleic acid recognition pathways to escape the host immune system. This short review will summarize the mechanisms by which MyNAs are sensed and how they influence host protective responses.

Critical role for the AIM2 inflammasome during acute CNS bacterial infection

Interleukin-1β (IL-1β) is essential for eliciting protective immunity during the acute phase of Staphylococcus aureus (S. aureus) infection in the central nervous system (CNS). We previously demonstrated that microglial IL-1β production in response to live S. aureus is mediated through the Nod-like receptor protein 3 (NLRP3) inflammasome, including the adapter protein ASC (apoptosis-associated speck-like protein containing a caspase-1 recruitment domain), and pro-caspase 1. Here, we utilized NLRP3, ASC, and caspase 1/11 knockout (KO) mice to demonstrate the functional significance of inflammasome activity during CNS S. aureus infection. ASC and caspase 1/11 KO animals were exquisitely sensitive, with approximately 50% of mice succumbing to infection within 24 h. Unexpectedly, the survival of NLRP3 KO mice was similar to wild-type animals, suggesting the involvement of an alternative upstream sensor, which was later identified as absent in melanoma 2 (AIM2) based on the similar disease patterns between AIM2 and ASC KO mice. Besides IL-1β, other key inflammatory mediators, including IL-6, CXCL1, CXCL10, and CCL2 were significantly reduced in the CNS of AIM2 and ASC KO mice, implicating autocrine/paracrine actions of IL-1β, as these mediators do not require inflammasome processing for secretion. These studies demonstrate a novel role for the AIM2 inflammasome as a critical molecular platform for regulating IL-1β release and survival during acute CNS S. aureus infection.

Detection of cytosolic bacteria by inflammatory caspases

The sanctity of the cytosolic compartment is rigorously maintained by a number of innate immune mechanisms. Inflammasomes detect signatures of microbial infection and trigger caspase-1 or caspase-11 activation, culminating in cytokine secretion and obliteration of the replicative niche via pyroptosis. Recent studies have examined inflammatory caspase responses to cytosolic bacteria, including Burkholderia, Shigella, Listeria, Francisella, and Mycobacterium species. For example, caspase-11 responds to LPS introduced into the cytosol after Gram-negative bacteria escape the vacuole. Not surprisingly, bacteria antagonize these responses; for example, Shigella delivers OspC3 to inhibit caspase-4, a potential human homolog of murine caspase-11. These findings underscore bacterial coevolution with the innate immune system, which has resulted in few, but highly specialized cytosolic pathogens.

Mycobacterium tuberculosis and the host cell inflammasome: a complex relationship

The production of IL-1β during the infection with Mycobacterium tuberculosis (Mtb) is important for successful host immune defense. In macrophages and dendritic cells the host cell inflammasome is crucial for generation of secreted IL-1β in response to Mtb infections. In these cell types Mtb infection only activates the NLRP3-inflammasome. New reports demonstrate that nitric oxide has an important function in the negative regulation of the NLRP3-inflammasome to reduce tissue damage during Mtb infections. The type I interferon, IFN-β, is induced after Mtb infections and can also suppress NLRP3-inflammasome activation. In contrast, IFN-β increases activity of the AIM2-inflammasome after infection with intracellular pathogens such as Francisella tularensis and Listeria monocytogenes. Recent results demonstrate that non-tuberculous mycobacteria but not virulent Mtb induce the AIM2-inflammasome in an IFN-β dependent matter. Indeed, Mtb inhibits AIM2-inflammasome activation via its ESX-1 secretion system. This novel immune evasion mechanism may help Mtb to allow the induction of low levels of IFN-β to suppress the NLRP3-inflammasome without activating the AIM2-inflammasome.