A 360° view of the inflammasome: Mechanisms of activation, cell death, and diseases.

Inflammasomes are critical sentinels of the innate immune system that respond to threats to the host through recognition of distinct molecules, known as pathogen- or damage-associated molecular patterns (PAMPs/DAMPs), or disruptions of cellular homeostasis, referred to as homeostasis-altering molecular processes (HAMPs) or effector-triggered immunity (ETI). Several distinct proteins nucleate inflammasomes, including NLRP1, CARD8, NLRP3, NLRP6, NLRC4/NAIP, AIM2, pyrin, and caspases-4/-5/-11. This diverse array of sensors strengthens the inflammasome response through redundancy and plasticity. Here, we present an overview of these pathways, outlining the mechanisms of inflammasome formation, subcellular regulation, and pyroptosis, and discuss the wide-reaching effects of inflammasomes in human disease.

Structural transitions enable interleukin-18 maturation and signaling.

Several interleukin-1 (IL-1) family members, including IL-1ß and IL-18, require processing by inflammasome-associated caspases to unleash their activities. Here, we unveil, by cryoelectron microscopy (cryo-EM), two major conformations of the complex between caspase-1 and pro-IL-18. One conformation is similar to the complex of caspase-4 and pro-IL-18, with interactions at both the active site and an exosite (closed conformation), and the other only contains interactions at the active site (open conformation). Thus, pro-IL-18 recruitment and processing by caspase-1 is less dependent on the exosite than the active site, unlike caspase-4. Structure determination by nuclear magnetic resonance uncovers a compact fold of apo pro-IL-18, which is similar to caspase-1-bound pro-IL-18 but distinct from cleaved IL-18. Binding sites for IL-18 receptor and IL-18 binding protein are only formed upon conformational changes after pro-IL-18 cleavage. These studies show how pro-IL-18 is selected as a caspase-1 substrate, and why cleavage is necessary for its inflammatory activity.

A metabolic switch orchestrated by IL-18 and the cyclic dinucleotide cGAMP programs intestinal tolerance.

Tissues are exposed to diverse inflammatory challenges that shape future inflammatory responses. While cellular metabolism regulates immune function, how metabolism programs and stabilizes immune states within tissues and tunes susceptibility to inflammation is poorly understood. Here, we describe an innate immune metabolic switch that programs long-term intestinal tolerance. Intestinal interleukin-18 (IL-18) stimulation elicited tolerogenic macrophages by preventing their proinflammatory glycolytic polarization via metabolic reprogramming to fatty acid oxidation (FAO). FAO reprogramming was triggered by IL-18 activation of SLC12A3 (NCC), leading to sodium influx, release of mitochondrial DNA, and activation of stimulator of interferon genes (STING). FAO was maintained in macrophages by a bistable switch that encoded memory of IL-18 stimulation and by intercellular positive feedback that sustained the production of macrophage-derived 2'3'-cyclic GMP-AMP (cGAMP) and epithelial-derived IL-18. Thus, a tissue-reinforced metabolic switch encodes durable immune tolerance in the gut and may enable reconstructing compromised immune tolerance in chronic inflammation.

The NLR family of innate immune and cell death sensors.

Nucleotide-binding oligomerization domain (NOD)-like receptors, also known as nucleotide-binding leucine-rich repeat receptors (NLRs), are a family of cytosolic pattern recognition receptors that detect a wide variety of pathogenic and sterile triggers. Activation of specific NLRs initiates pro- or anti-inflammatory signaling cascades and the formation of inflammasomes-multi-protein complexes that induce caspase-1 activation to drive inflammatory cytokine maturation and lytic cell death, pyroptosis. Certain NLRs and inflammasomes act as integral components of larger cell death complexes-PANoptosomes-driving another form of lytic cell death, PANoptosis. Here, we review the current understanding of the evolution, structure, and function of NLRs in health and disease. We discuss the concept of NLR networks and their roles in driving cell death and immunity. An improved mechanistic understanding of NLRs may provide therapeutic strategies applicable across infectious and inflammatory diseases and in cancer.

The NLRP6 Inflammasome Recognizes Lipoteichoic Acid and Regulates Gram-Positive Pathogen Infection.

The activator and composition of the NLRP6 inflammasome remain poorly understood. We find that lipoteichoic acid (LTA), a molecule produced by Gram-positive bacteria, binds and activates NLRP6. In response to cytosolic LTA or infection with Listeria monocytogenes, NLRP6 recruited caspase-11 and caspase-1 via the adaptor ASC. NLRP6 activation by LTA induced processing of caspase-11, which promoted caspase-1 activation and interleukin-1ß (IL-1ß)/IL-18 maturation in macrophages. Nlrp6-/- and Casp11-/- mice were less susceptible to L. monocytogenes infection, which was associated with reduced pathogen loads and impaired IL-18 production. Administration of IL-18 to Nlrp6-/- or Casp11-/- mice restored the susceptibility of mutant mice to L. monocytogenes infection. These results reveal a previously unrecognized innate immunity pathway triggered by cytosolic LTA that is sensed by NLRP6 and exacerbates systemic Gram-positive pathogen infection via the production of IL-18.

Host-Protozoan Interactions Protect from Mucosal Infections through Activation of the Inflammasome.

While conventional pathogenic protists have been extensively studied, there is an underappreciated constitutive protist microbiota that is an integral part of the vertebrate microbiome. The impact of these species on the host and their potential contributions to mucosal immune homeostasis remain poorly studied. Here, we show that the protozoan Tritrichomonas musculis activates the host epithelial inflammasome to induce IL-18 release. Epithelial-derived IL-18 promotes dendritic cell-driven Th1 and Th17 immunity and confers dramatic protection from mucosal bacterial infections. Along with its role as a "protistic" antibiotic, colonization with T. musculis exacerbates the development of T-cell-driven colitis and sporadic colorectal tumors. Our findings demonstrate a novel mutualistic host-protozoan interaction that increases mucosal host defenses at the cost of an increased risk of inflammatory disease.

Notch4 signaling limits regulatory T-cell-mediated tissue repair and promotes severe lung inflammation in viral infections.

A cardinal feature of COVID-19 is lung inflammation and respiratory failure. In a prospective multi-country cohort of COVID-19 patients, we found that increased Notch4 expression on circulating regulatory T (Treg) cells was associated with disease severity, predicted mortality, and declined upon recovery. Deletion of Notch4 in Treg cells or therapy with anti-Notch4 antibodies in conventional and humanized mice normalized the dysregulated innate immunity and rescued disease morbidity and mortality induced by a synthetic analog of viral RNA or by influenza H1N1 virus. Mechanistically, Notch4 suppressed the induction by interleukin-18 of amphiregulin, a cytokine necessary for tissue repair. Protection by Notch4 inhibition was recapitulated by therapy with Amphiregulin and, reciprocally, abrogated by its antagonism. Amphiregulin declined in COVID-19 subjects as a function of disease severity and Notch4 expression. Thus, Notch4 expression on Treg cells dynamically restrains amphiregulin-dependent tissue repair to promote severe lung inflammation, with therapeutic implications for COVID-19 and related infections.

Single-Cell RNA Sequencing of Tumor-Infiltrating NK Cells Reveals that Inhibition of Transcription Factor HIF-1α Unleashes NK Cell Activity.

Enhancing immune cell functions in tumors remains a major challenge in cancer immunotherapy. Hypoxia is a common feature of solid tumors, and cells adapt by upregulating the transcription factor HIF-1α. Here, we defined the transcriptional landscape of mouse tumor-infiltrating natural killer (NK) cells by using single-cell RNA sequencing. Conditional deletion of Hif1a in NK cells resulted in reduced tumor growth, elevated expression of activation markers, effector molecules, and an enriched NF-κB pathway in tumor-infiltrating NK cells. Interleukin-18 (IL-18) from myeloid cells was required for NF-κB activation and the enhanced anti-tumor activity of Hif1a-/- NK cells. Extended culture with an HIF-1α inhibitor increased human NK cell responses. Low HIF1A expression was associated with high expression of IFNG in human tumor-infiltrating NK cells, and an enriched NK-IL18-IFNG signature in solid tumors correlated with increased overall patient survival. Thus, inhibition of HIF-1α unleashes NK cell anti-tumor activity and could be exploited for cancer therapy.

Natural Killer-like B Cells Prime Innate Lymphocytes against Microbial Infection.

Natural killer (NK) cells and non-cytotoxic interferon-γ (IFN-γ)-producing group I innate lymphoid cells (ILC1s) produce large amounts of IFN-γ and cause activation of innate and adaptive immunity. However, how NKs and ILC1s are primed during infection remains elusive. Here we have shown that a lymphocyte subpopulation natural killer-like B (NKB) cells existed in spleen and mesenteric lymph nodes (MLNs). NKBs had unique features that differed from T and B cells, and produced interleukin-18 (IL-18) and IL-12 at an early phase of infection. NKB cells played a critical role in eradication of microbial infection via secretion of IL-18 and IL-12. Moreover, IL-18 deficiency abrogated the antibacterial effect of NKBs. Upon bacterial challenge, NKB precursors (NKBPs) rapidly differentiated to NKBs that activated NKs and ILC1s against microbial infection. Our findings suggest that NKBs might be exploited to develop effective therapies for treatment of infectious diseases.

Granzyme B-activated IL18 potentiates αß and γδ CAR T cell immunotherapy in a tumor-dependent manner.

Interleukin (IL)18 is a potent pro-inflammatory cytokine that is activated upon caspase 1 cleavage of the latent precursor, pro-IL18. Therapeutic T cell armoring with IL18 promotes autocrine stimulation and positive modulation of the tumor microenvironment (TME). However, existing strategies are imperfect since they involve constitutive/poorly regulated activity or fail to modify the TME. Here, we have substituted the caspase 1 cleavage site within pro-IL18 with that preferred by granzyme B, yielding GzB-IL18. We demonstrate that GzB-IL18 is constitutively released but remains functionally latent unless chimeric antigen receptor (CAR) T cells are activated, owing to concomitant granzyme B release. Armoring with GzB-IL18 enhances cytolytic activity, proliferation, interferon (IFN)-γ release, and anti-tumor efficacy by a similar magnitude to constitutively active IL18. We also demonstrate that GzB-IL18 provides a highly effective armoring strategy for γδ CAR T cells, leading to enhanced metabolic fitness and significant potentiation of therapeutic activity. Finally, we show that constitutively active IL18 can unmask CAR T cell-mediated cytokine release syndrome in immunocompetent mice. By contrast, GzB-IL18 promotes anti-tumor activity and myeloid cell re-programming without inducing such toxicity. Using this stringent system, we have tightly coupled the biological activity of IL18 to the activation state of the host CAR T cell, favoring safer clinical implementation of this technology.

A "Prime and Expand" strategy using the multifunctional fusion proteins to generate memory-like NK cells for cell therapy.

Adoptive cellular therapy (ACT) using memory-like (ML) natural killer (NK) cells, generated through overnight ex vivo activation with IL-12, IL-15, and IL-18, has shown promise for treating hematologic malignancies. We recently reported that a multifunctional fusion molecule, HCW9201, comprising IL-12, IL-15, and IL-18 domains could replace individual cytokines for priming human ML NK cell programming ("Prime" step). However, this approach does not include ex vivo expansion, thereby limiting the ability to test different doses and schedules. Here, we report the design and generation of a multifunctional fusion molecule, HCW9206, consisting of human IL-7, IL-15, and IL-21 cytokines. We observed > 300-fold expansion for HCW9201-primed human NK cells cultured for 14 days with HCW9206 and HCW9101, an IgG1 antibody, recognizing the scaffold domain of HCW9206 ("Expand" step). This expansion was dependent on both HCW9206 cytokines and interactions of the IgG1 mAb with CD16 receptors on NK cells. The resulting "Prime and Expand" ML NK cells exhibited elevated metabolic capacity, stable epigenetic IFNG promoter demethylation, enhanced antitumor activity in vitro and in vivo, and superior persistence in NSG mice. Thus, the "Prime and Expand" strategy represents a simple feeder cell-free approach to streamline manufacturing of clinical-grade ML NK cells to support multidose and off-the-shelf ACT.

Allergens induce upregulated IL-18 and IL-18Rα expression in blood Th2 and Th17 cells of patients with allergic asthma.

Allergic asthma (AA) is closely associated with the polarization of T helper (Th)2 and Th17 cells. Interleukin (IL)-18 acts as an inducer of Th2 and Th17 cell responses. However, expressions of IL-18 and IL-18 receptor alpha (IL-18Rα) in blood Th2 and Th17 cells of patients with AA remain unclear. We therefore investigated their expressions in Th2 and Th17 cells using flow cytometric analysis, quantitative real-time PCR (qPCR), and murine AA model. We observed increased proportions of Th2, Th17, IL-18+, IL-18+ Th2, and IL-18+ Th17 cells in blood CD4+ T cells of patients with AA. Additionally, house dust mite seemed to upregulate further IL-18 expression in Th2 and Th17, and upregulate IL-18Rα expression in CD4+ T, Th2, and Th17 cells of AA patients. It was also found that the plasma levels of IL-4, IL-17A, and IL-18 in AA patients were elevated, and they were correlated between each other. In ovalbumin (OVA)-induced asthma mouse (AM), we observed that the percentages of blood CD4+ T, Th2, and Th17 cells were increased. Moreover, OVA-induced AM expressed higher level of IL-18Rα in blood Th2 cells, which was downregulated by IL-18. Increased IL-18Rα expression was also observed in blood Th2 cells of OVA-induced FcεRIα-/- mice. Collectively, our findings suggest the involvement of Th2 cells in AA by expressing excessive IL-18 and IL-18Rα in response to allergen, and that IL-18 and IL-18Rα expressing Th2 cells are likely to be the potential targets for AA therapy.

Inflammatory biomarkers and long-term outcome in young patients three months after a first myocardial infarction.

BACKGROUND: Studies on predictive value of circulating inflammatory biomarkers after myocardial infarction (MI) have often been limited by blood sampling only in an acute setting and short follow-up time. We aimed to compare the long-term predictive value of nine inflammatory biomarkers, known to be involved in atherosclerosis, in young patients investigated three months after a first-time MI. METHODS: Nine biomarkers (high-sensitivity C-reactive protein, interleukin (IL)-6, IL-18, monocyte chemoattractant protein-1, matrix metalloproteinase (MMP)-1, MMP-3, MMP-9, serum amyloid A and tumor necrosis factor-alfa) were sampled in 382 young (<60 years) patients and in age and sex-matched controls, three months after a first-time MI between 1996 and 2000. Swedish national patient registers were used to determine cardiovascular (CV) outcomes during 20 years of follow-up. RESULTS: In cases, random forest models identified IL-6 as the most important predictor of the primary composite endpoint of death, heart failure (HF) or MI hospitalization, and the separate endpoints death and HF hospitalization. IL-18 was the most important predictor of MI hospitalization. In a Cox regression, the highest tertile of IL-6 was associated with the composite endpoint (HR (95% CI) 1.91 (1.31-2.79)), death (2.38 (1.42-3.98)) and HF hospitalization (2.70 (1.32-5.50)), when adjusting for age, sex and CV risk factors. The highest tertile of IL-18 was associated with MI hospitalization (2.31 (1.08-4.91)) when severity of coronary atherosclerosis was added to the same type of model. CONCLUSIONS: When nine inflammatory markers involved in atherosclerosis were analyzed three months after the acute event in young MI patients, IL-6 and IL-18 were the most important biomarkers to predict long-term CV outcomes during 20 years of follow-up.

Protective effects of IL18-105G > A and IL18-137C > Ggenetic variants on severity of COVID-19.

OBJECTIVE AND DESIGN: A cross-sectional study evaluated the IL18-105G > A (rs360717) and IL18-137C > G (rs187238) variants on Coronavírus Disease 2019 (COVID-19) severity. SUBJECTS AND METHODS: 528 patients with COVID-19 classifed with mild (n = 157), moderate (n = 63) and critical (n = 308) disease were genotpyed for the IL18-105G > A and IL18-137C > G variants. RESULTS: We observed associations between severe + critical COVID-19 groups (reference group was mild COVID-19) and the IL18-105G > A (p = 0.008) and IL18-137C > G (p = 0.01) variants, which remained significant after adjusting for sex, ethnicity and age. Consequently, we have examined the associations between moderate + critical COVID-19 and the genotypes of both variants using different genetic models. The IL18-105G > A was associated with severe disease (moderate + critical), with effects of the GA genotype in the codominant [Odds ratio (OR), (95 % confidence interval) 0.55, 0.34-0.89, p = 0.015], overdominant (0.56, 0.35-0.89, p = 0.014) and dominant (0.60, 0.38-0.96, p = 0.031) models. IL18-105 GA coupled with age, chest computed tomograhy scan anormalities, body mass index, heart diseases, type 2 diabetes mellitus, hypertension, and inflammation may be used to predict the patients who develop severe disease with an accuracy of 84.3 % (sensitivity: 83.3 % and specificity: 86.5 %). Therefore, the presence of the IL18-105 A allele in homozygosis or heterozygosis conferred about 44.0 % of protection in the development of moderate and severe COVID-19. The IL18-137C > G variant was also associated with protective effects in the codominant (0.55, 0.34-0.89, p = 0.015), overdominant (0.57, 0.36-0.91, p = 0.018), and dominant models (0.59, 0.37-0.93, p = 0.025). Therefore, the IL18-137 G allele showed a protective effect against COVID-19 severity. CONCLUSION: The IL18-105G > A and IL18-137C > Gvariants may contribute with protective effects for COVID-19 severity and the effects of IL18-137C > G may be modulating IL-18 production and Th1-mediated immune responses.

Agree to disagree: The contradiction between IL-18 and IL-37 reveals shared targets in cancer.

IL-37 is a newly discovered member of the IL-1 cytokine family which plays an important role in regulating inflammation and maintaining physiological homeostasis. IL-37 showed a close relationship with IL-18, another key cytokine in inflammation regulation and cancer development. IL-37 affects the function of IL-18 either by binding to IL-18Rα, a key subunit of both IL-37 and IL-18 receptor, or by drastically neutralizing the IL-18 protein expression of IL-18 binding protein, an important natural inhibitory molecule of IL-18. Moreover, as another subunit receptor of IL-37, IL-1R8 can suppress IL-18Rα expression, functioning as a surveillance mechanism to prevent overactivation of both IL-18 and IL-37 signaling pathways. While IL-18 and IL-37 share the same receptor subunit, IL-18 would in turn interfere with IL-37 signal transduction by binding to IL-18Rα. It is also reported that IL-18 and IL-37 demonstrated opposing effects in a variety of cancers, such as glioblastoma, lung cancer, leukemia, and hepatocellular cancer. Although the mutual regulation of IL-18 and IL-37 and their diametrically opposed effects in cancers has been reported, IL-18 has not been taken into consideration when interpreting clinical findings and conducting mechanism investigations related to IL-37 in cancer. We aim to review the recent progress in IL-18 and IL-37 research in cancer and summarize the correlation between IL-18 and IL-37 in cancer based on their expression level and underlying mechanisms, which would provide new insights into elucidating the conflicting roles of IL-18 and IL-37 in cancer and bring new ideas for translational research related to IL-18 and IL-37.

Pyroptosis Tuning in Intestinal Cryptosporidiosis via the Natural Histone Deacetylase Inhibitor Romidepsin.

Cryptosporidium is an opportunistic protozoan, with many species of cross-human infectivity. It causes life-threatening diarrhoea in children and CD4-defective patients. Despite its limited efficacy, nitazoxanide remains the primary anti-cryptosporidial drug. Cryptosporidium infects the intestinal brush border (intracellular-extracytoplasmic) and down-regulates pyroptosis to prevent expulsion. Romidepsin is a natural histone deacetylase inhibitor that triggers pyroptosis. Romidepsin's effect on cryptosporidiosis was assessed in immunocompromised mice via gasdermin-D (GSDM-D) immunohistochemical expression, IFN-γ, IL-1ß and IL-18 blood levels by ELISA, and via parasite scanning by modified Ziehl-Neelsen staining and scanning electron microscopy (SEM). Oocyst deformity and local cytokines were also assessed in ex vivo ileal explants. Following intraperitoneal injection of romidepsin, oocyst shedding significantly reduced at the 9th, 12th and 15th d.p.i. compared with infected-control and drug-control (nitazoxanide-treated) mice. H&E staining of intestinal sections from romidepsin-treated mice showed significantly low intestinal scoring with marked reduction in epithelial hyperplasia, villous blunting and cellular infiltrate. SEM revealed marked oocyst blebbing and paucity (in vivo and ex vivo) after romidepsin compared with nitazoxanide. Regarding pyroptosis, romidepsin triggered significantly higher intestinal GSDM-D expression in vivo, and higher serum/culture IFN-γ, IL-1ß and IL-18 levels in romidepsin-treated mice than in the control groups. Collectively, in cryptosporidiosis, romidepsin succeeded in enhancing pyroptosis in the oocysts and infected epithelium, reducing infection and shifting the brush border towards normalisation.

The discovery of novel and potent indazole NLRP3 inhibitors enabled by DNA-encoded library screening.

NLRP3 is an intracellular sensor protein that detects a broad range of danger signals and environmental insults. Its activation results in a protective pro-inflammatory response designed to impair pathogens and repair tissue damage via the formation of the NLRP3 inflammasome. Assembly of the NLRP3 inflammasome leads to caspase 1-dependent secretory release of the pro-inflammatory cytokines IL-1ß and IL-18 as well as to gasdermin d-mediated pyroptotic cell death. Herein, we describe the discovery of a novel indazole series of high affinity, reversible inhibitors of NLRP3 activation through screening of DNA-encoded libraries and the potent lead compound 3 (BAL-0028, IC50 = 25 nM) that was identified directly from the screen. SPR studies showed that compound 3 binds tightly (KD range 104-123 nM) to the NACHT domain of NLRP3. A CADD analysis of the interaction of compound 3 with the NLRP3 NACHT domain proposes a binding site that is distinct from those of ADP and MCC950 and includes specific site interactions. We anticipate that compound 3 (BAL-0028) and other members of this novel indazole class of neutral inhibitors will demonstrate significantly different physical, biochemical, and biological properties compared to NLRP3 inhibitors previously identified.

Human umbilical cord mesenchymal stem cells promoted tumor cell growth associated with increased interleukin-18 in hepatocellular carcinoma.

BACKGROUND: Hepatocellular carcinoma (HCC) is experiencing a concerning rise in both incidence and mortality rates. Current therapeutic strategies are limited in their effectiveness, largely due to the complex causes of the disease and significant levels of drug resistance. Given the latest developments in human umbilical cord mesenchymal stem cells (hUC-MSCs) research, there is a debate over the continued use of stem cell transplantation for treating tumors. Consequently, this study seeks to explore the role of hUC-MSCs in the management of HCC. METHODS AND RESULTS: HUC-MSCs increased the number (10.75 ± 1.50) in the DEN/TCPOBOP-induced mice hepatoma model, compared with DMSO group (7.25 ± 1.71). Moreover, the liver index in hUC-MSCs group (0.21 ± 0.06) was greater than that in DMSO group (0.09 ± 0.01). Immunohistochemical (IHC) analysis revealed that while hUC-MSCs did not alter Foxp3 expression, they significantly stimulated Ki67 expression, indicative of increased tumor cellular proliferation. Additionally, immunofluorescence (IF) studies showed that hUC-MSCs increased CD8+ T cell counts without affecting macrophage numbers. Notably, granzyme B expression remained nearly undetectable. We observed that serum IL-18 levels were higher in the hUC-MSCs group (109.66 ± 0.38 pg/ml) compared to the DMSO group (91.14 ± 4.37 pg/ml). Conversely, IL-1ß levels decreased in the hUC-MSCs group (63.00 ± 0.53 pg/ml) relative to the DMSO group (97.38 ± 9.08 pg/ml). CONCLUSIONS: According to this study, hUC-MSCs promoted the growth of liver tumors. Therefore, we proposed that hUC-MSCs are not suitable for treating HCC, as they exhibit clinically prohibited abnormalities.

The role of NLRP6 in the development and progression of neurological diseases.

The nervous system possesses the remarkable ability to undergo changes in order to store information; however, it is also susceptible to damage caused by invading pathogens or neurodegenerative processes. As a member of nucleotide-binding oligomerization domain-like receptor (NLR) family, the NLRP6 inflammasome serves as a cytoplasmic innate immune sensor responsible for detecting microbe-associated molecular patterns. Upon activation, NLRP6 can recruit the adapter protein apoptosis-associated speck-like protein (ASC) and the inflammatory factors caspase-1 or caspase-11. Consequently, inflammasomes are formed, facilitating the maturation and secretion of pro-inflammatory cytokines such as inflammatory factors-18 (IL-18) and inflammatory factors-1ß (IL-1ß). Precise regulation of NLRP6 is crucial for maintaining tissue homeostasis, as dysregulated inflammasome activation can contribute to the development of various diseases. Furthermore, NLRP6 may also play a role in the regulation of extraintestinal diseases. In cells of the brain, such as astrocytes and neurons, NLRP6 inflammasome are also present. Here, the assembly and subsequent activation of caspase-1 mediated by NLRP6 contribute to disease progression. This review aims to discuss the structure and function of NLRP6, explain clearly the mechanisms that induce and activate NLRP6, and explore its role within the central and peripheral nervous system.

Keratinocytes stimulate MAIT cells to produce granzyme B via MR1 and cytokines in oral lichen planus.

OBJECTIVE: Oral lichen planus (OLP) is a chronic inflammatory disease characterized by a dense T-cell infiltration and the degeneration of basal keratinocytes. The potential functions of mucosal associated invariant T (MAIT) cells in OLP have been analyzed in our previous study. Keratinocytes under proinflammatory conditions have been demonstrated to activate T cells. This study was aimed to investigate how keratinocytes stimulate MAIT cells in OLP, and to explore the role of activated MAIT cells on keratinocytes. METHODS AND RESULTS: Increased MAIT cells and higher activation marker CD69 were detected in OLP lesions by flow cytometry. The enhanced expression of MHC class I-like molecule (MR1) required for MAIT cell activation in the epithelial layer of OLP lesions was determined by immunohistochemistry. Keratinocytes treated by 5-A-RU prodrug and lipopolysaccharide, respectively, exhibited higher expression of MR1 and secretion of IL-18. In direct coculture systems consisting of keratinocytes and peripheral blood mononuclear cells, both 5-A-RU prodrug-pretreated keratinocytes and lipopolysaccharide-pretreated keratinocytes activated MAIT cells to secrete granzyme B, contributing to elevated keratinocyte apoptosis. CONCLUSIONS: Keratinocytes were capable to activate MAIT cells via MR1 and cytokines in OLP, and granzyme B produced by activated MAIT cells intensified keratinocyte apoptosis, engaging in the pathogenesis of OLP.