IL-18 is induced and IL-18 receptor alpha plays a critical role in the pathogenesis of cigarette smoke-induced pulmonary emphysema and inflammation

The activation of the AIM2 inflammasome after cigarette smoke exposure leads to an immunosuppressive lung microenvironment

Cigarette smoke is widely known as contributing to chronic inflammation underlying several airway diseases, such as chronic obstructive pulmonary disease (COPD) and lung cancer. In our previous studies we found that the lung of both COPD and cancer patients were characterized by the presence and activation of the AIM2 inflammasome. Here, we wanted to investigate the upstream step during the establishment of chronic lung inflammation after cigarette smoke exposure. We took advantage of a mouse model of smoking exposure and public scRNAseq data. We found that AIM2 mRNA was expressed in both alveolar type II, B cells, T regulatory (Treg) and macrophages detected in the lung of non-smokers (n = 4) and smokers (n = 3). The activation of AIM2 in smoking mice by using PolydA:dT did not alter cigarette-smoke-induced alveoli enlargement and mucus production, rather it induced higher recruitment of immunosuppressive cells, such as non-active dendritic cells (DCs), Arginase I+ macrophages, myeloid-derived suppressor cells (MDSC) and Tregs. In addition, the inflammatory environment after AIM2 activation in smoking mice was characterized by higher levels of IL-1α, IL-1β, IL-33, TNFα, LDH, IL-10 and TGFβ. This scenario was not altered after the pharmacological inhibition of both caspase-1 and STING pathway. In conclusion, these data suggest that chronic inflammation after cigarette smoke exposure is associated with AIM2 activation, which could lead towards cigarette smoke-associated lung diseases.

Animal models and mechanisms of tobacco smoke-induced chronic obstructive pulmonary disease (COPD)

Chronic obstructive pulmonary disease (COPD) is the third leading cause of death worldwide, and its global health burden is increasing. COPD is characterized by emphysema, mucus hypersecretion, and persistent lung inflammation, and clinically by chronic airflow obstruction and symptoms of dyspnea, cough, and fatigue in patients. A cluster of pathologies including chronic bronchitis, emphysema, asthma, and cardiovascular disease in the form of hypertension and atherosclerosis variably coexist in COPD patients. Underlying causes for COPD include primarily tobacco use but may also be driven by exposure to air pollutants, biomass burning, and workplace related fumes and chemicals. While no single animal model might mimic all features of human COPD, a wide variety of published models have collectively helped to improve our understanding of disease processes involved in the genesis and persistence of COPD. In this review, the pathogenesis and associated risk factors of COPD are examined in different mammalian models of the disease. Each animal model included in this review is exclusively created by tobacco smoke (TS) exposure. As animal models continue to aid in defining the pathobiological mechanisms of and possible novel therapeutic interventions for COPD, the advantages and disadvantages of each animal model are discussed.

[Alteration of pulmonary epithelial permeability by cathepsin S in chronic obstructive pulmonary disease]

Smoking is accountable for most of the chronic obstructive pulmonary disease (COPD) cases. COPD, which is characterized by the development of chronic bronchitis, could be associated with emphysema. In active smokers, there is an overexpression of cathepsin S, a cysteine protease, which participates in the development of emphysema via its elastinolytic activity. Likewise, we demonstrated that cathepsin S could degrade one or more protein constituents of cell junctions. This deleterious proteolytic activity leads to an alteration of the integrity of the lung epithelial barrier, which in turn could aggravate chronic inflammation and promote the exacerbation phases associated with infections.

Initial and ongoing tobacco smoking elicits vascular damage and distinct inflammatory response linked to neurodegeneration

Tobacco smoking is strongly linked to vascular damage contributing to the development of hypertension, atherosclerosis, as well as increasing the risk for neurodegeneration. Still, the involvement of the innate immune system in the development of vascular damage upon chronic tobacco use before the onset of clinical symptoms is not fully characterized. Our data provide evidence that a single acute exposure to tobacco elicits the secretion of extracellular vesicles expressing CD105 and CD49e from endothelial cells, granting further recognition of early preclinical biomarkers of vascular damage. Furthermore, we investigated the effects of smoking on the immune system of healthy asymptomatic chronic smokers compared to never-smokers, focusing on the innate immune system. Our data reveal a distinct immune landscape representative for early stages of vascular damage in clinically asymptomatic chronic smokers, before tobacco smoking related diseases develop. These results indicate a dysregulated immuno-vascular axis in chronic tobacco smokers that are otherwise considered as healthy individuals. The distinct alterations are characterized by increased CD36 expression by the blood monocyte subsets, neutrophilia and increased plasma IL-18 and reduced levels of IL-33, IL-10 and IL-8. Additionally, reduced levels of circulating BDNF and elevated sTREM2, which are associated with neurodegeneration, suggest a considerable impact of tobacco smoking on CNS function in clinically healthy individuals. These findings provide profound insight into the initial and ongoing effects of tobacco smoking and the potential vascular damage contributing to neurodegenerative disorders, specifically cerebrovascular dysfunction and dementia.

Chronic Obstructive Pulmonary Disease and Cigarette Smoke Lead to Dysregulated Mucosal-associated Invariant T-Cell Activation

Chronic obstructive pulmonary disease (COPD) is associated with airway inflammation, increased infiltration by CD8+ T lymphocytes, and infection-driven exacerbations. Although cigarette smoke is the leading risk factor for COPD, the mechanisms driving the development of COPD in only a subset of smokers are incompletely understood. Lung-resident mucosal-associated invariant T (MAIT) cells play a role in microbial infections and inflammatory diseases. The role of MAIT cells in COPD pathology is unknown. Here, we examined MAIT cell activation in response to cigarette smoke-exposed primary human bronchial epithelial cells (BECs) from healthy, COPD, or smoker donors. We observed significantly higher baseline MAIT cell responses to COPD BECs than healthy BECs. However, infected COPD BECs stimulated a smaller fold increase in MAIT cell response despite increased microbial infection. For all donor groups, cigarette smoke-exposed BECs elicited reduced MAIT cell responses; conversely, cigarette smoke exposure increased ligand-mediated MR1 surface translocation in healthy and COPD BECs. Our data demonstrate that MAIT cell activation is dysregulated in the context of cigarette smoke and COPD. MAIT cells could contribute to cigarette smoke- and COPD-associated inflammation through inappropriate activation and reduced early recognition of bacterial infection, contributing to microbial persistence and COPD exacerbations.

Cross-talk between IL-6 trans-signaling and AIM2 inflammasome/IL-1β axes bridge innate immunity and epithelial apoptosis to promote emphysema

Pulmonary emphysema is associated with dysregulated innate immune responses that promote chronic pulmonary inflammation and alveolar apoptosis, culminating in lung destruction. However, the molecular regulators of innate immunity that promote emphysema are ill-defined. Here, we investigated whether innate immune inflammasome complexes, comprising the adaptor ASC, Caspase-1 and specific pattern recognition receptors (PRRs), promote the pathogenesis of emphysema. In the lungs of emphysematous patients, as well as spontaneous gp130^F/F and cigarette smoke (CS)-induced mouse models of emphysema, the expression (messenger RNA and protein) and activation of ASC, Caspase-1, and the inflammasome-associated PRR and DNA sensor AIM2 were up-regulated. AIM2 up-regulation in emphysema coincided with the biased production of the mature downstream inflammasome effector cytokine IL-1β but not IL-18. These observations were supported by the genetic blockade of ASC, AIM2, and the IL-1 receptor and therapy with AIM2 antagonistic suppressor oligonucleotides, which ameliorated emphysema in gp130^F/F mice by preventing elevated alveolar cell apoptosis. The functional requirement for AIM2 in driving apoptosis in the lung epithelium was independent of its expression in hematopoietic-derived immune cells and the recruitment of infiltrating immune cells in the lung. Genetic and inhibitor-based blockade of AIM2 also protected CS-exposed mice from pulmonary alveolar cell apoptosis. Intriguingly, IL-6 trans-signaling via the soluble IL-6 receptor, facilitated by elevated levels of IL-6, acted upstream of the AIM2 inflammasome to augment AIM2 expression in emphysema. Collectively, we reveal cross-talk between the AIM2 inflammasome/IL-1β and IL-6 trans-signaling axes for potential exploitation as a therapeutic strategy for emphysema.

In Vivo and In Vitro Studies of Cigarette Smoke Effects on Innate Responses to Influenza Virus: A Matter of Models?

Cigarette smoke (CS) is a significant public health problem and a leading risk factor for the development of chronic obstructive pulmonary disease (COPD) in the developed world. Respiratory viral infections, such as the influenza A virus (IAV), are associated with acute exacerbations of COPD and are more severe in cigarette smokers. To fight against viral infection, the host has developed an innate immune system, which has complicated mechanisms regulating the expression and activation of cytokines and chemokines to maximize the innate and adaptive antiviral response, as well as limiting the immunopathology that leads to exaggerated lung damage. In the case of IAV, responders include airway and alveolar epithelia, lung macrophages and dendritic cells. To achieve a successful infection, IAV must overcome these defenses. In this review, we summarize the detrimental role of CS in influenza infections. This includes both immunosuppressive and proinflammatory effects on innate immune responses during IAV infection. Some of the results, with respect to CS effects in mouse models, appear to have discordant results, which could be at least partially addressed by standardization of animal viral infection models to evaluate the effect of CS exposure in this context.

No smoke without fire: the impact of cigarette smoking on the immune control of tuberculosis

Cigarette smoke (CS) exposure is a key risk factor for both active and latent tuberculosis (TB). It is associated with delayed diagnosis, more severe disease progression, unfavourable treatment outcomes and relapse after treatment. Critically, CS exposure is common in heavily populated areas with a high burden of TB, such as China, India and the Russian Federation. It is therefore prudent to evaluate interventions for TB while taking into account the immunological impacts of CS exposure. This review is a mechanistic examination of how CS exposure impairs innate barrier defences, as well as alveolar macrophage, neutrophil, dendritic cell and T-cell functions, in the context of TB infection and disease.

Aim2 suppresses cigarette smoke-induced neutrophil recruitment, neutrophil caspase-1 activation and anti-Ly6G-mediated neutrophil depletion

Increased inflammasome responses are strongly implicated in inflammatory diseases; however, their specific roles are incompletely understood. Therefore, we sought to examine the roles of nucleotide‐binding oligomerization domain–like receptor (NLR) family, pyrin domain–containing 3 (NLRP3) and absent in melanoma‐2 (AIM2) inflammasomes in cigarette smoke–induced inflammation in a model of experimental chronic obstructive pulmonary disease (COPD). We targeted NLRP3 with the inhibitor MCC950 given prophylactically or therapeutically and examined Aim2^−/− mice in cigarette smoke–induced experimental COPD. MCC950 treatment had minimal effects on disease development and/or progression. Aim2^−/− mice had increased airway neutrophils with decreased caspase‐1 levels, independent of changes in lung neutrophil chemokines. Suppressing neutrophils with anti‐Ly6G in experimental COPD in wild‐type mice reduced neutrophils in bone marrow, blood and lung. By contrast, anti‐Ly6G treatment in Aim2^−/− mice with experimental COPD had no effect on neutrophils in bone marrow, partially reduced neutrophils in the blood and had no effect on neutrophils or neutrophil caspase‐1 levels in the lungs. These findings identify that following cigarette smoke exposure, Aim2 is important for anti‐Ly6G–mediated depletion of neutrophils, suppression of neutrophil recruitment and mediates activation of caspase‐1 in neutrophils.

Evaluation of exposure to secondhand smoke and serum level of interleukin 18 in non-smokers

Objective

Smoking is one significant global health care problems, that not only affects the users but also endangers the health of people inhaling the smoke (passive smoking/secondhand smoke). The serum level of IL-18, an important regulator of inherent and acquired immune response, is affected by cigarette smoking. The aim of this study was to evaluate the effect of secondhand smoke (SHS) exposure on IL-18 serum level in non-smoker adults.

Methods

In a case-control study, using easy sampling method, 76 non-smokers who were exposed to cigarette smoke for at least 1 h daily during the past year were considered as exposure group, while 76 of their companions without exposure to cigarette smoke (after matching age) were considered as non-exposure group. Serum IL-18 levels were measured for all participants and finally compared between the two groups using Chi-square test. P value < 0.05 was considered to be statistically significant.

Results

The exposure and non-exposure groups included 58 (76.3%) and 25 (32.9%) males, respectively (P < 0.001). The mean ± SD of age for the exposure and non-exposure groups was 35.42 ± 10.37 and 38.47 ± 12.49 years, respectively (P = 0.102). There was no significant difference between the mean serum levels of IL-18 in the exposure (54.81 ± 57.03 ng/ml) and non-exposure (41.49 ± 42.14 ng/ml) groups (P = 0.104).

Conclusion

The exposure to secondhand smoke has no significant effect on serum level of IL-18 in exposed adult individuals. However, more studies with larger sample sizes on different populations are required to confirm these results.

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Smoking is one significant global health care problems.

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That not only affects the users but also endangers the health of people inhaling the smoke.

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The serum level of IL-18, an important regulator of inherent and acquired immune response.

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The exposure to secondhand smoke has no significant effect on serum level of IL-18.

Nicotine promotes chronic obstructive pulmonary disease via inducing pyroptosis activation in bronchial epithelial cells

Nicotine is one of the primary components in cigarettes, which is responsible for addiction. Numerous studies have investigated the effects of nicotine on pulmonary disease. The health of epithelial cells is important in the development of chronic obstructive pulmonary disease (COPD). Accumulating evidence has suggested that epithelial cell death may initiate or contribute to the progression of a number of lung diseases via airway remodeling. Pyroptosis is a unique form of inflammatory cell death mediated by the activation of caspase‑1 and the NOD‑like receptor protein‑3 (NLRP3) inflammasome. The present study aimed to evaluate whether pyroptosis of epithelial cells was involved in the progression of COPD. The normal human bronchial epithelial cell line 16HBE was treated with 0.1 or 1 µM nicotine. Then the proliferation ability of 16HBE cells was detected by CCK‑8. Cell death was detected by flow cytometry analysis and TUNEL assay. Subsequently, the levels of pro‑caspase 1, caspase 1, IL‑1β, IL‑18, NLRP3, ASC and cleaved GSDMD were examined by western blotting. It was revealed that nicotine treatment significantly induced cell death and suppressed proliferation of 16HBE cells. Furthermore, nicotine exposure increased the expression levels of caspase‑1, IL‑1β, IL‑18, NLRP3, apoptosis‑associated speck‑like protein and gasdermin D in 16HBE cells. Therefore, the present study concluded that nicotine treatment induced pyroptosis in 16HBE cells, which may be associated with the progression of COPD.

The Role of Interleukin 18/Interleukin 18-Binding Protein in Adult-Onset Still's Disease and Systemic Juvenile Idiopathic Arthritis

Interleukin 18 (IL-18) is a pro-inflammatory cytokine of the IL-1 family, whose activity is tightly controlled at the level of production, as well as signalization. Notably, it is buffered by its natural inhibitor, IL-18 binding protein (IL-18BP), which is massively present in circulation in normal and in most pathological conditions, thus preventing harmful pro-inflammatory systemic effects of IL-18. IL-18 has long been considered to be involved in the pathophysiology of various inflammatory diseases. However, a first clinical trial using recombinant IL-18BP for the treatment of rheumatoid arthritis and psoriasis gave disappointing results. Direct measurements of unbound, bioactive, free form of circulating IL-18 demonstrated that IL-18 was more specifically involved in adult-onset Still’s disease (AOSD) and systemic juvenile idiopathic arthritis (sJIA) but also in their most severe complication, macrophage activation syndrome (MAS). More importantly, administration of recombinant IL-18BP to patients with AOSD, and sJIA with MAS, showed promising results. This review summarizes available data regarding IL-18 and IL-18BP in AOSD and sJIA in mouse models and humans and shows the importance of IL-18/IL-18BP imbalance in these conditions, leading to the conclusion that IL-18, particularly free IL-18, may be a useful biomarker in these diseases and an interesting therapeutic target.

New Insights into the Role of NLRP3 Inflammasome in Pathogenesis and Treatment of Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is an inflammatory lung disease characterized by chronic airway obstruction and emphysema. Accumulating studies have shown that the onset and development of COPD are related to an aberrant immune response induced by the dysregulation of a number of genetic and environmental factors, while the exact pathogenesis of this disease is not well defined. Emerging studies based on tests on samples from COPD patients, animal models, pharmacological and genetic data suggest that the NLR family pyrin domain containing 3 (NLRP3) inflammasome activation is required in the lung inflammatory responses in the development of COPD. Although the available clinical studies targeting the inflammasome effector cytokine, IL-1β, or IL-1 signaling do not show positive outcomes for COPD treatment, many alternative strategies have been proposed by recent emerging studies. Here, we highlight the recent progress in our understanding of the role of the NLRP3 inflammasome in COPD and propose possible future studies that may further elucidate the roles of the inflammasome in the pathogenesis or the intervention of this inflammatory lung disease.

Innate Immune Responses and Pulmonary Diseases

Innate immunity is the first defense line of the host against various infectious pathogens, environmental insults, and other stimuli causing cell damages. Upon stimulation, pattern recognition receptors (PRRs) act as sensors to activate innate immune responses, containing NF-κB signaling, IFN response, and inflammasome activation. Toll-like receptors (TLRs), retinoic acid-inducible gene I-like receptors (RLRs), NOD-like receptors (NLRs), and other nucleic acid sensors are involved in innate immune responses. The activation of innate immune responses can facilitate the host to eliminate pathogens and maintain tissue homeostasis. However, the activity of innate immune responses needs to be tightly controlled to ensure the optimal intensity and duration of activation under various contexts. Uncontrolled innate immune responses can lead to various disorders associated with aberrant inflammatory response, including pulmonary diseases such as COPD, asthma, and COVID-19. In this chapter, we will have a broad overview of how innate immune responses function and the regulation and activation of innate immune response at molecular levels as well as their contribution to various pulmonary diseases. A better understanding of such association between innate immune responses and pulmonary diseases may provide potential therapeutic strategies.

A novel anti-human IL-1R7 antibody reduces IL-18-mediated inflammatory signaling

Unchecked inflammation can result in severe diseases with high mortality, such as macrophage activation syndrome (MAS). MAS and associated cytokine storms have been observed in COVID-19 patients exhibiting systemic hyperinflammation. Interleukin-18 (IL-18), a proinflammatory cytokine belonging to the IL-1 family, is elevated in both MAS and COVID-19 patients, and its level is known to correlate with the severity of COVID-19 symptoms. IL-18 binds its specific receptor IL-1 receptor 5 (IL-1R5, also known as IL-18 receptor alpha chain), leading to the recruitment of the coreceptor, IL-1 receptor 7 (IL-1R7, also known as IL-18 receptor beta chain). This heterotrimeric complex then initiates downstream signaling, resulting in systemic and local inflammation. Here, we developed a novel humanized monoclonal anti-IL-1R7 antibody to specifically block the activity of IL-18 and its inflammatory signaling. We characterized the function of this antibody in human cell lines, in freshly obtained peripheral blood mononuclear cells (PBMCs) and in human whole blood cultures. We found that the anti-IL-1R7 antibody significantly suppressed IL-18-mediated NFκB activation, reduced IL-18-stimulated IFNγ and IL-6 production in human cell lines, and reduced IL-18-induced IFNγ, IL-6, and TNFα production in PBMCs. Moreover, the anti-IL-1R7 antibody significantly inhibited LPS- and Candida albicans–induced IFNγ production in PBMCs, as well as LPS-induced IFNγ production in whole blood cultures. Our data suggest that blocking IL-1R7 could represent a potential therapeutic strategy to specifically modulate IL-18 signaling and may warrant further investigation into its clinical potential for treating IL-18-mediated diseases, including MAS and COVID-19.

Therapeutic Inhibition of Cathepsin S Reduces Inflammation and Mucus Plugging in Adult βENaC-Tg Mice

BACKGROUND

Elevated levels of the cysteine protease cathepsin S (CatS) are associated with chronic mucoobstructive lung diseases such as cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD). We have previously demonstrated that prophylactic treatment with a CatS inhibitor from birth reduces inflammation, mucus plugging, and lung tissue damage in juvenile β-epithelial Na+ channel-overexpressing transgenic (βENaC-Tg) mice with chronic inflammatory mucoobstructive lung disease. In this study, we build upon this work to examine the effects of therapeutic intervention with a CatS inhibitor in adult βENaC-Tg mice with established disease.

METHODS

βENaC-Tg mice and wild-type (WT) littermates were treated with a CatS inhibitor from 4 to 6 weeks of age, and CatS-/- βENaC-Tg mice were analysed at 6 weeks of age. Bronchoalveolar lavage (BAL) fluid inflammatory cell counts were quantified, and lung tissue destruction and mucus obstruction were analysed histologically.

RESULTS

At 6 weeks of age, βENaC-Tg mice developed significant airway inflammation, lung tissue damage, and mucus plugging when compared to WT mice. CatS-/- βENaC-Tg mice and βENaC-Tg mice receiving inhibitor had significantly reduced airway mononuclear and polymorphonuclear (PMN) cell counts as well as mucus plugging. However, in contrast to CatS-/- βENaC-Tg mice, therapeutic inhibition of CatS in βENaC-Tg mice had no effect on established emphysema-like lung tissue damage.

CONCLUSIONS

These results suggest that while early CatS targeting may be required to prevent the onset and progression of lung tissue damage, therapeutic CatS targeting effectively inhibited airway inflammation and mucus obstruction. These results indicate the important role CatS may play in the pathogenesis and progression of mucoobstructive lung disease.

Development and validation of an open-source, disposable, 3D-printed in vitro environmental exposure system for Transwell culture inserts

Accessible in vitro models recapitulating the human airway that are amenable to study whole cannabis smoke exposure are needed for immunological and toxicological studies that inform public health policy and recreational cannabis use. In the present study, we developed and validated a novel three-dimensional (3D)-printed in vitro exposure system (IVES) that can be directly applied to study the effect of cannabis smoke exposure on primary human bronchial epithelial cells.

Using commercially available design software and a 3D printer, we designed a four-chamber Transwell insert holder for exposures to whole smoke. COMSOL Multiphysics software was used to model gas distribution, concentration gradients, velocity profile and shear stress within IVES. Following simulations, primary human bronchial epithelial cells cultured at the air–liquid interface on Transwell inserts were exposed to whole cannabis smoke using a modified version of the Foltin puff procedure. Following 24 h, outcome measurements included cell morphology, epithelial barrier function, lactate dehydrogenase (LDH) levels, cytokine expression and gene expression.

Whole smoke delivered through IVES possesses velocity profiles consistent with uniform gas distribution across the four chambers and complete mixing. Airflow velocity ranged between 1.0 and 1.5 µm·s⁻¹ and generated low shear stresses (<<1 Pa). Human airway epithelial cells exposed to cannabis smoke using IVES showed changes in cell morphology and disruption of barrier function without significant cytotoxicity. Cannabis smoke elevated interleukin-1 family cytokines and elevated CYP1A1 and CYP1B1 expression relative to control, validating IVES smoke exposure impacts in human airway epithelial cells at a molecular level.

The growing legalisation of cannabis on a global scale must be paired with research related to potential health impacts of lung exposures. IVES represents an accessible, open-source, exposure system that can be used to model varying types of cannabis smoke exposures with human airway epithelial cells grown under air–liquid interface culture conditions.

Development of an open-source, disposable, 3D-printed in vitro environmental exposure system for Transwell culture inserts that can be used for environmental exposures important for lung health, and validation with cannabis smoke exposurehttps://bit.ly/2JjgDrm

Emerging Role of the Inflammasome and Pyroptosis in Hypertension

Inflammasomes are components of the innate immune response that have recently emerged as crucial controllers of tissue homeostasis. In particular, the nucleotide-binding domain, leucine-rich-containing (NLR) family pyrin domain containing 3 (NLRP3) inflammasome is a complex platform involved in the activation of caspase-1 and the maturation of interleukin (IL)-1β and IL-18, which are mainly released via pyroptosis. Pyroptosis is a caspase-1-dependent type of cell death that is mediated by the cleavage of gasdermin D and the subsequent formation of structurally stable pores in the cell membrane. Through these pores formed by gasdermin proteins cytosolic contents are released into the extracellular space and act as damage-associated molecular patterns, which are pro-inflammatory signals. Inflammation is a main contributor to the development of hypertension and it also is known to stimulate fibrosis and end-organ damage. Patients with essential hypertension and animal models of hypertension exhibit elevated levels of circulating IL-1β. Downregulation of the expression of key components of the NLRP3 inflammasome delays the development of hypertension and pharmacological inhibition of this inflammasome leads to reduced blood pressure in animal models and humans. Although the relationship between pyroptosis and hypertension is not well established yet, pyroptosis has been associated with renal and cardiovascular diseases, instances where high blood pressure is a critical risk factor. In this review, we summarize the recent literature addressing the role of pyroptosis and the inflammasome in the development of hypertension and discuss the potential use of approaches targeting this pathway as future anti-hypertensive strategies.

Intestinal IL-17R Signaling Constrains IL-18-Driven Liver Inflammation by the Regulation of Microbiome-Derived Products

Interleukin (IL)-17 signaling to the intestinal epithelium regulates the intestinal microbiome. Given the reported links between intestinal dysbiosis, bacterial translocation, and liver disease, we hypothesize that intestinal IL-17R signaling plays a critical role in mitigating hepatic inflammation. To test this, we study intestinal epithelium-specific IL-17RA-deficient mice in an immune-driven hepatitis model. At the naive state, these mice exhibit microbiome dysbiosis and increased translocation of bacterial products (CpG DNA), which drives liver IL-18 production. Upon disease induction, absence of enteric IL-17RA signaling exacerbates hepatitis and hepatocyte cell death. IL-18 is necessary for disease exacerbation and is associated with increased activated hepatic lymphocytes based on Ifng and Fasl expression. Thus, intestinal IL-17R regulates translocation of TLR9 ligands and constrains susceptibility to hepatitis. These data connect enteric Th17 signaling and the microbiome in hepatitis, with broader implications on the effects of impaired intestinal immunity and subsequent release of microbial products observed in other extra-intestinal pathologies.

Castillo-dela Cruz et al. describe a unique protective role of intestinal IL-17RA in hepatitis. Disruption of intestinal IL-17RA signaling results in microbiome dysbiosis and translocation of bacterial products, specifically unmethylated CpG DNA, to the liver. This promotes IL-18 production and subsequent lymphocyte activation and cell death to exacerbate liver inflammation.

Relationship of Serum Levels of IL-17, IL-18, TNF-α, and Lung Function Parameters in Patients with COPD, Asthma-COPD Overlap, and Bronchial Asthma

Determination of markers of systemic inflammation is one of the important directions in the study of pathogenesis and improvement of diagnosis of chronic obstructive pulmonary disease (COPD), asthma-COPD overlap (ACO), and bronchial asthma (BA). The aim of our work was a comparative study of the features of changes in serum levels of IL-17, IL-18, and TNF-α in patients with COPD, ACO, and BA with various severity of the disease, as well as evaluation of the relationship between the level of these cytokines and lung ventilation function. A total of 147 patients with COPD (n = 58), ACO (n = 57), and BA (n = 32) during a stable period have been examined in this study. The control group included 21 healthy nonsmokers with similar sex-age indicators. Serum levels of IL-17, IL-18, and TNF-α were determined by ELISA. The concentrations of these cytokines in the circulation in the studied patients with COPD, ACO, and BA were higher than those in healthy nonsmokers (p ≤ 0.001). IL-17 and IL-18 levels in the blood serum were comparable in all examined patients. The mean TNF-α concentrations in the circulation in COPD and ACO were significantly higher than those in BA (p < 0.001). In patients with COPD, the levels of IL-17 and TNF-α increased progressively against the background of a decrease in numerous spirometric indicators, which allows us to consider these cytokines as systemic biomarkers of disease severity. In BA, the inverse correlations between the level of IL-17 and FEV1/FVC (%) and FEV1 have been found. In patients with ACO, the increase in IL-18 levels was associated with a decrease in FEV1 and TNF-α with FEV1/FVC (%). These findings indicate that IL-17, IL-18, and TNF-α can participate in the mechanisms of systemic inflammation and the genesis of disorders of airway obstruction in COPD, AСO, and BA. An increase in the levels of IL-17 and TNF-α may be associated with impaired bronchial patency in COPD and BA. The established associations of the IL-18 concentration in the blood serum and FEV1 only in patients with ACO allow using the level of IL-18 as a potential marker of the degree of impaired airway obstruction in this disease.

Chitinases and Chitinase-Like Proteins in Obstructive Lung Diseases - Current Concepts and Potential Applications

Chitinases, enzymes that cleave chitin’s chain to low molecular weight chitooligomers, are widely distributed in nature. Mammalian chitinases belong to the 18-glycosyl-hydrolase family and can be divided into two groups: true chitinases with enzymatic activity (AMCase and chitotriosidase) and chitinase-like proteins (CLPs) molecules which can bind to chitin or chitooligosaccharides but lack enzymatic activity (eg, YKL-40). Chitinases are thought to be part of an innate immunity against chitin-containing parasites and fungal infections. Both groups of these hydrolases are lately evaluated also as chemical mediators or biomarkers involved in airway inflammation and fibrosis. The aim of this article is to present the current knowledge on the potential role of human chitinases and CLPs in the pathogenesis, diagnosis, and course of obstructive lung diseases. We also assessed the potential role of chitinase and CLPs inhibitors as therapeutic targets in chronic obstructive pulmonary disease and asthma.

Oxidation of cathepsin S by major chemicals of cigarette smoke

Lung cysteine cathepsin S (CatS) that is a potent elastase plays a deleterious role in alveolar remodeling during smoke-induced emphysema. Despite the presence of a reactive nucleophilic cysteine (Cys25) within its active site, most of its elastinolytic activity is preserved after exposure to cigarette smoke extract (CSE), a major source of sulfhydryl oxidants. This result led us to decipher CatS resistance to major and representative CSE oxidants: hydrogen peroxide, formaldehyde, acrolein and peroxynitrite. CatS was inactivated by hydrogen peroxide, peroxynitrite and acrolein in a time- and dose-dependent manner, while formaldehyde was a weaker oxidant. Hydrogen peroxide, but not CSE, formaldehyde, and peroxynitrite impaired the autocatalytic maturation of pro-CatS, whereas acrolein prevented the formation of mature CatS without hindering the initial step of the two-step autocatalytic process. Far-UV CD spectra analysis supported that oxidation by CSE and hydrogen peroxide did not led to a structural alteration of CatS, despite a notable increase of protein carbonylation, a major hallmark of oxidative damage. Evaluation of the oxidation status of Cys25 by specific biotinylated redox sensing probes suggested the formation of sulfenic acid followed by a slower conversion to sulfinic acid after incubation with hydrogen peroxide. Addition of reducing reagents (dithiothreitol, glutathione and N-acetyl cysteine) led to a partial recovery of CatS activity following incubation with CSE, hydrogen peroxide and peroxynitrite. Current results provide some mechanistic evidence of CatS stability and activity in the presence of CSE, supporting its harmful contribution to the pathophysiology of emphysema.

Regulation of the Proteolytic Activity of Cysteine Cathepsins by Oxidants

Besides their primary involvement in the recycling and degradation of proteins in endo-lysosomal compartments and also in specialized biological functions, cysteine cathepsins are pivotal proteolytic contributors of various deleterious diseases. While the molecular mechanisms of regulation via their natural inhibitors have been exhaustively studied, less is currently known about how their enzymatic activity is modulated during the redox imbalance associated with oxidative stress and their exposure resistance to oxidants. More specifically, there is only patchy information on the regulation of lung cysteine cathepsins, while the respiratory system is directly exposed to countless exogenous oxidants contained in dust, tobacco, combustion fumes, and industrial or domestic particles. Papain-like enzymes (clan CA, family C1, subfamily C1A) encompass a conserved catalytic thiolate-imidazolium pair (Cys25-His159) in their active site. Although the sulfhydryl group (with a low acidic pKa) is a potent nucleophile highly susceptible to chemical modifications, some cysteine cathepsins reveal an unanticipated resistance to oxidative stress. Besides an introductory chapter and peculiar attention to lung cysteine cathepsins, the purpose of this review is to afford a concise update of the current knowledge on molecular mechanisms associated with the regulation of cysteine cathepsins by redox balance and by oxidants (e.g., Michael acceptors, reactive oxygen, and nitrogen species).

Innate Lymphoid Cells in the Airways: Their Functions and Regulators

Since the airways are constantly exposed to various pathogens and foreign antigens, various kinds of cells in the airways—including structural cells and immune cells—interact to form a precise defense system against pathogens and antigens that involve both innate immunity and acquired immunity. Accumulating evidence suggests that innate lymphoid cells (ILCs) play critical roles in the maintenance of tissue homeostasis, defense against pathogens and the pathogenesis of inflammatory diseases, especially at body surface mucosal sites such as the airways. ILCs are activated mainly by cytokines, lipid mediators and neuropeptides that are produced by surrounding cells, and they produce large amounts of cytokines that result in inflammation. In addition, ILCs can change their phenotype in response to stimuli from surrounding cells, which enables them to respond promptly to microenvironmental changes. ILCs exhibit substantial heterogeneity, with different phenotypes and functions depending on the organ and type of inflammation, presumably because of differences in microenvironments. Thus, ILCs may be a sensitive detector of microenvironmental changes, and analysis of their phenotype and function at local sites may enable us to better understand the microenvironment in airway diseases. In this review, we aimed to identify molecules that either positively or negatively influence the function and/or plasticity of ILCs and the sources of the molecules in the airways in order to examine the pathophysiology of airway inflammatory diseases and facilitate the issues to be solved.

A comprehensive pathway map of IL-18-mediated signalling

Interleukin-18 (IL-18) is a member of the IL-1 family of cytokines and was initially described as an IFN-γ-inducing factor derived from anti-CD3-stimulated T-helper (Th)1 cells. IL-18 plays a significant role in the activation of hematopoietic cell types mediating both Th1 and Th2 responses and is the primary inducer of interferon-γ in these cells. The biological activity of IL-18 is mediated through its binding to the IL-18 receptor complex and activation of nuclear factor-κB (NF-κB), culminating in the production and release of several cytokines, chemokines, and cellular adhesion molecules. In certain cell types, IL-18 also activates mitogen-activated protein kinases (MAPKs) and phosphoinositide 3-kinase/ AKT serine/threonine kinase (PI3K/AKT) signaling modules leading to the production and release of proinflammatory cytokines. IL-18-mediated signaling acts as one of the vital components of the immunomodulatory cytokine networks involved in host defense, inflammation, and tissue regeneration. Albeit its biomedical importance, a comprehensive resource of IL-18 mediated signaling pathway is currently lacking. In this study, we report on the development of an integrated pathway map of IL-18/IL-18R signaling. The pathway map was developed through literature mining from published literature based on manual curation guidelines adapted from NetPath and includes information on 16 protein-protein interaction events, 38 enzyme-catalysis events, 12 protein translocation events, 26 activations/inhibition events, transcriptional regulators, 230 gene regulation events and 84 induced protein expression events. The IL-18 signaling pathway can be freely accessed through the WikiPathways database (https://www.wikipathways.org/index.php/Pathway:WP4754).

Cigarette smoke induces overexpression of active human cathepsin S in lungs from current smokers with or without COPD

Cigarette smoking has marked effects on lung tissue, including induction of oxidative stress, inflammatory cell recruitment, and a protease/antiprotease imbalance. These effects contribute to tissue remodeling and destruction resulting in loss of lung function in chronic obstructive pulmonary disease (COPD) patients. Cathepsin S (CatS) is a cysteine protease that is involved in the remodeling/degradation of connective tissue and basement membrane. Aberrant expression or activity of CatS has been implicated in a variety of diseases, including arthritis, cancer, cardiovascular, and lung diseases. However, little is known about the effect of cigarette smoking on both CatS expression and activity, as well as its role in smoking-related lung diseases. Here, we evaluated the expression and activity of human CatS in lung tissues from never-smokers and smokers with or without COPD. Despite the presence of an oxidizing environment, CatS expression and activity were significantly higher in current smokers (both non-COPD and COPD) compared with never-smokers, and correlated positively with smoking history. Moreover, we found that the exposure of primary human bronchial epithelial cells to cigarette smoke extract triggered the activation of P2X7 receptors, which in turns drives CatS upregulation. The present data suggest that excessive CatS expression and activity contribute, beside other proteases, to the deleterious effects of cigarette smoke on pulmonary homeostasis.

Potential CD34 signaling through phosphorylated-BAD in chemotherapy-resistant acute myeloid leukemia

Acute myeloid leukemia (AML) constitutively express growth factors and cytokines for survival. Chemotherapy alters these signals to induce cell death. However, drug resistance in AML remains a major hindrance to successful treatment and early warning is unavailable. Modulation of signaling pathways during chemotherapy may provide a window to detect response and predict treatment outcome. Blood samples collected from AML patients before and at day-3 of induction therapy were compared for changes in expression of CD117, CD34, pro-inflammatory cytokines and mediators of Akt and MAPK pathways, using multi-color flow cytometry. Nine patients were diagnosed as drug-resistant and seven sensitive to chemotherapy. Twelve were paired. Average percentages of CD34 (66.8 ± 11.7% vs. 26.2 ± 5.8%, p = 0.033) and pBAD (66.9 ± 8.2% vs. 28.9 ± 8.2%, p = 0.016) were significantly increased in chemo-resistant (N = 9) compared to chemo-sensitive (N = 5) samples. Percentages of CD34 were strongly correlated with pBAD (R = 0.785; p = 0.001; N = 14) and pFKHR (R = 0.755; p = 0.002; N = 14) at day-3 induction. Chemo-sensitive cases expressed significantly higher percentages of IL-18Rα (71.9 ± 9.6% vs. 29.8 ± 5.8%, p = 0.016). Though not significantly different in the outcome, IL-1β was strongly associated with activated Akt-S473, IL-6 with phosphorylated JNK and FKHR while TNF-α appeared to trigger Bim, in treated samples. These preliminary results suggested AML cells resistant to chemotherapy increased expression of CD34 and may signal through pBAD while cells sensitive to chemotherapy-induced IL18Rα expression. These were observed early during induction therapy. Identifying CD34 is interesting as it is a convenient marker to monitor drug-resistance in AML patients. Inhibition of CD34 and pBAD signaling may be important in treating drug-resistant AML.

Impact of Cigarette Smoke Exposure on the Lung Fibroblastic Response after Influenza Pneumonia

Influenza viruses can result in significant lung injury with significant morbidity and mortality. In this study, we evaluated the impact of cigarette smoke (CS) exposure on the pulmonary fibroblastic response after influenza infection. We used a murine model in which animals were exposed to CS or room air and subsequently infected with H1N1 influenza virus. Inflammatory and fibrotic responses were measured at different time points after influenza infection. Primary fibroblasts were isolated from the lungs of mice and their characteristics were evaluated. Exposure to CS significantly increased the amount of collagen in the lungs of mice infected with influenza virus compared with the nonsmoking group at 30 days after infection. Furthermore, the presence of fibroblast-specific protein-positive cells increased in the lungs of influenza-infected mice that were exposed to CS compared with the infection-alone group. The smoking group also showed delays in weight recovery and higher cell counts in BAL fluid after infection. Active transforming growth factor β1 levels in BAL fluid increased in both groups; however, CS-exposed mice had a later surge in active transforming growth factor β1 (Day 24). Ex vivo cultures of lung-derived fibroblasts from CS-exposed mice with influenza infection showed rapid proliferation, increased expression of α-smooth muscle actin-stained stress fibers, and higher expression of growth factors compared with fibroblasts from room air-exposed lungs after infection. These results suggest that CS exposure changes the fibroblastic potential, leading to increased fibrosis after influenza infection.

Cell Death in the Lung: The Apoptosis-Necroptosis Axis

Regulated cell death is a major mechanism to eliminate damaged, infected, or superfluous cells. Previously, apoptosis was thought to be the only regulated cell death mechanism; however, new modalities of caspase-independent regulated cell death have been identified, including necroptosis, pyroptosis, and autophagic cell death. As an understanding of the cellular mechanisms that mediate regulated cell death continues to grow, there is increasing evidence that these pathways are implicated in the pathogenesis of many pulmonary disorders. This review summarizes our understanding of regulated cell death as it pertains to the pathogenesis of chronic obstructive pulmonary disease, asthma, idiopathic pulmonary fibrosis, acute respiratory distress syndrome, and pulmonary arterial hypertension.

NLRP3 Inflammasome Involves in the Acute Exacerbation of Patients with Chronic Obstructive Pulmonary Disease

The NLR pyrin domain-containing protein 3 (NLRP3) inflammasome, a multi-protein complex, produces the pro-inflammatory cytokines interleukin (IL)-1β and IL-18, which may contribute to the development of airway inflammation in chronic obstructive pulmonary disease (COPD). The aim of this study was to explore the correlation between circulating and local airway NLRP3 inflammasome activation with acute exacerbation of COPD (AECOPD). mRNA levels of NLRP3, Caspase (Casp)-1, apoptosis-associated speck-like protein containing CARD (ASC), IL-18, and IL-1β in peripheral blood mononuclear cells (PBMCs) and bronchial tissues were determined by real-time PCR in 32 smokers, 65 patients with AECOPD, 50 COPD patients in recovery stage, and 30 COPD patients in stable stage. The levels of IL-1β and IL-18 in serum and bronchoalveolar lavage fluid (BALF) supernatants were measured by ELISA. The load of six common pathogens in BALF samples were determined by real-time PCR. The potential correlation between the mRNA levels of NLRP3, Casp-1, ASC, IL-18 or IL-1β and the load of pathogens was evaluated individually. Significantly higher mRNA levels of NLRP3, Casp-1, ASC, IL-18, IL-1β and higher levels of IL-18 and IL-1β were found in patients with AECOPD than in smokers. These NLRP3 inflammasome mediators were significantly decreased when COPD patients in the same group became clinical stable. The increased mRNA levels of NLRP3 inflammasomes in bronchial tissues were positively correlated with the load of the six common pathogens in the lower respiratory tract. We conclude that systemic and local airway NLRP3 inflammasome activation is associated with the acute exacerbation, which might be predictive factors of the acute exacerbation and clinical outcomes in COPD patients.

NLRP3/Caspase-1 inflammasome activation is decreased in alveolar macrophages in patients with lung cancer

Lung cancer (LC) remains the leading cause of cancer-related mortality. The interaction of cancer cells with their microenvironment, results in tumor escape or elimination. Alveolar macrophages (AMs) play a significant role in lung immunoregulation, however their role in LC has been outshined by the study of tumor associated macrophages. Inflammasomes are key components of innate immune responses and can exert either tumor-suppressive or oncogenic functions, while their role in lung cancer is largely unknown. We thus investigated the NLRP3 pathway in Bronchoalveolar Lavage derived alveolar macrophages and peripheral blood leukocytes from patients with primary lung cancer and healthy individuals. IL-1β and IL-18 secretion was significantly higher in unstimulated peripheral blood leukocytes from LC patients, while IL-1β secretion could be further increased upon NLRP3 stimulation. In contrast, in LC AMs, we observed a different profile of IL-1β secretion, characterized mainly by the impairment of IL-1β production in NLRP3 stimulated cells. AMs also exhibited an impaired TLR4/LPS pathway as shown by the reduced induction of IL-6 and TNF-α. Our results support the hypothesis of tumour induced immunosuppression in the lung microenvironment and may provide novel targets for cancer immunotherapy.

Interleukin-18 is associated with the presence of interstitial lung disease in rheumatoid arthritis: a cross-sectional study

OBJECTIVE

Serum interleukin-18 (IL-18) levels are increased in patients with interstitial lung disease (ILD). In addition, IL-18 levels are increased in patients with rheumatoid arthritis (RA) and are associated with arthritis activity. We determined whether increased IL-18 levels are associated with ILD in RA.

METHOD

RA patients were enrolled using an RA cohort database. Plasma IL-18 levels were measured by enzyme-linked immunosorbent assay. ILD was determined by a pulmonologist and a radiologist based on chest radiography and computed tomography findings. IL-18 levels for RA with ILD and RA without ILD were compared. Associations between ILD and various markers including IL-18 and confounding factors (e.g. smoking history) were investigated by logistic regression analysis. Diagnostic values of IL-18 for the presence of ILD were investigated using receiver operating characteristics curve analysis.

RESULTS

ILD was complicated in 8.2% (n = 26) of the study population (N = 312). Plasma IL-18 levels were higher for RA patients with ILD than for RA patients without ILD (721.0 ± 481.4 vs 436.8 ± 438.9 pg/mL, p < 0.001). IL-18, Krebs von den Lungen-6, and anti-cyclic citrullinated peptide antibody titre and glucocorticoid doses were independently associated with the presence of ILD during multivariate logistic regression analysis. Sensitivity and specificity of IL-18 levels for the detection of ILD in RA patients were 65.3% and 76.3%, respectively (area under the curve = 0.73).

CONCLUSION

Plasma IL-18 levels were higher for RA patients with ILD than for those without ILD. Increased IL-18 levels were associated with the presence of ILD.

Proteases and Their Inhibitors in Chronic Obstructive Pulmonary Disease

In the context of respiratory disease, chronic obstructive pulmonary disease (COPD) is the leading cause of mortality worldwide. Despite much development in the area of drug development, currently there are no effective medicines available for the treatment of this disease. An imbalance in the protease: Antiprotease ratio in the COPD lung remains an important aspect of COPD pathophysiology and several studies have shown the efficacy of antiprotease therapy in both in vitro and in vivo COPD models. However more in-depth studies will be required to validate the efficacy of lead drug molecules targeting these proteases. This review discusses the current status of protease-directed drugs used for treating COPD and explores the future prospects of utilizing the potential of antiprotease-based therapeutics as a treatment for this disease.

Interleukin-18: Biological properties and role in disease pathogenesis

Initially described as an interferon (IFN)γ‐inducing factor, interleukin (IL)‐18 is indeed involved in Th1 and NK cell activation, but also in Th2, IL‐17‐producing γδ T cells and macrophage activation. IL‐18, a member of the IL‐1 family, is similar to IL‐1β for being processed by caspase 1 to an 18 kDa‐biologically active mature form. IL‐18 binds to its specific receptor (IL‐18Rα, also known as IL‐1R7) forming a low affinity ligand chain. This is followed by recruitment of the IL‐18Rβ chain. IL‐18 then uses the same signaling pathway as IL‐1 to activate NF‐kB and induce inflammatory mediators such as adhesion molecules, chemokines and Fas ligand. IL‐18 also binds to the circulating high affinity IL‐18 binding protein (BP), such as only unbound free IL‐18 is active. IL‐18Rα may also bind IL‐37, another member of the IL‐1 family, but in association with the negative signaling chain termed IL‐1R8, which transduces an anti‐inflammatory signal. IL‐18BP also binds IL‐37 and this acts as a sink for the anti‐inflammatory properties of IL‐37. There is now ample evidence for a role of IL‐18 in various infectious, metabolic or inflammatory diseases such as influenza virus infection, atheroma, myocardial infarction, chronic obstructive pulmonary disease, or Crohn's disease. However, IL‐18 plays a very specific role in the pathogenesis of hemophagocytic syndromes (HS) also termed Macrophage Activation Syndrome. In children affected by NLRC4 gain‐of‐function mutations, IL‐18 circulates in the range of tens of nanograms/mL. HS is treated with the IL‐1 Receptor antagonist (anakinra) but also specifically with IL‐18BP. Systemic juvenile idiopathic arthritis or adult‐onset Still's disease are also characterized by high serum IL‐18 concentrations and are treated by IL‐18BP.

Lung Diseases

Inflammasomes are large innate cytoplasmic complexes that play a major role in promoting inflammation in the lung in response to a range of environmental and infectious stimuli. Inflammasomes are critical for driving acute innate immune responses that resolve infection and maintain tissue homeostasis. However, dysregulated or excessive inflammasome activation can be detrimental. Here, we discuss the plethora of recent data from clinical studies and small animal disease models that implicate excessive inflammasome responses in the pathogenesis of a number of acute and chronic respiratory inflammatory diseases. Understanding of the role of inflammasomes in lung disease is of great therapeutic interest.

Inflammasome in the Pathogenesis of Pulmonary Diseases

Lung diseases are common and significant causes of illness and death around the world. Inflammasomes have emerged as an important regulator of lung diseases. The important role of IL-1 beta and IL-18 in the inflammatory response of many lung diseases has been elucidated. The cleavage to turn IL-1 beta and IL-18 from their precursors into the active forms is tightly regulated by inflammasomes. In this chapter, we structurally review current evidence of inflammasome-related components in the pathogenesis of acute and chronic lung diseases, focusing on the "inflammasome-caspase-1-IL-1 beta/IL-18" axis.

Modeling the Causal Role of DNA Methylation in the Association Between Cigarette Smoking and Inflammation in African Americans: A 2-Step Epigenetic Mendelian Randomization Study

The association between cigarette smoking and inflammation is well known. However, the biological mechanisms behind the association are not fully understood, particularly the role of DNA methylation, which is known to be affected by smoking. Using 2-step epigenetic Mendelian randomization, we investigated the role of DNA methylation in the association between cigarette smoking and inflammation. In 822 African Americans from the Genetic Epidemiology Network of Arteriopathy, phase 2 (Jackson, Mississippi; 2000-2005), study population, we examined the association of cigarette smoking with DNA methylation using single nucleotide polymorphisms identified in previous genome-wide association studies of cigarette smoking. We then investigated the association of DNA methylation with levels of inflammatory markers using cis-methylation quantitative trait loci single nucleotide polymorphisms. We found that current smoking status was associated with the DNA methylation levels (M values) of cg03636183 in the coagulation factor II (thrombin) receptor-like 3 gene (F2RL3) (M = -0.64, 95% confidence interval (CI): -0.84, -0.45) and of cg19859270 in the G protein-coupled receptor 15 gene (GPR15) (M = -0.21, 95% CI: -0.27, -0.15). The DNA methylation levels of cg03636183 in F2RL3 were associated with interleukin-18 concentration (-0.11 pg/mL, 95% CI: -0.19, -0.04). These combined negative effects suggest that cigarette smoking increases interleukin-18 levels through the decrease in DNA methylation levels of cg03636183 in F2RL3.

Role of the inflammasome in chronic obstructive pulmonary disease (COPD)

Inflammation is central to the development of chronic obstructive pulmonary disease (COPD), a pulmonary disorder characterized by chronic bronchitis, chronic airway obstruction, emphysema, associated to progressive and irreversible decline of lung function. Emerging genetic and pharmacological evidence suggests that IL-1-like cytokines are highly detected in the sputum and broncho-alveolar lavage (BAL) of COPD patients, implying the involvement of the multiprotein complex inflammasome. So far, scientific evidence has focused on nucleotide-binding oligomerization domain-like receptors protein 3 (NLRP3) inflammasome, a specialized inflammatory signaling platform that governs the maturation and secretion of IL-1-like cytokines through the regulation of caspase-1-dependent proteolytic processing. Some studies revealed that it is involved during airway inflammation typical of COPD. Based on the influence of cigarette smoke in various respiratory diseases, including COPD, in this view we report its effects in inflammatory and immune responses in COPD mouse models and in human subjects affected by COPD. In sharp contrast to what reported on experimental and clinical studies, randomized clinical trials show that indirect inflammasome inhibitors did not have any beneficial effect in moderate to severe COPD patients.

Hydrogen Sulfide Prevents and Partially Reverses Ozone-Induced Features of Lung Inflammation and Emphysema in Mice

Hydrogen sulfide (H2S), a novel signaling gasotransmitter in the respiratory system, may have antiinflammatory properties in the lung. We examined the preventive and therapeutic effects of H2S on ozone-induced features of lung inflammation and emphysema. C57/BL6 mice were exposed to ozone or filtered air over 6 weeks. Sodium hydrogen sulfide (NaHS), an H2S donor, was administered to the mice either before ozone exposure (preventive effect) or after completion of 6 weeks of ozone exposure (therapeutic effect). The ozone-exposed mice developed emphysema, measured by micro-computed tomography and histology, airflow limitation, measured by the forced maneuver system, and increased lung inflammation with augmented IL-1β, IL-18, and matrix metalloproteinase-9 (MMP-9) gene expression. Ozone-induced changes were associated with increased Nod-like receptor pyrin domain containing 3 (NLRP3)-caspase-1 activation and p38 mitogen-activated protein kinase phosphorylation and decreased Akt phosphorylation. NaHS both prevented and reversed lung inflammation and emphysematous changes in alveolar space. In contrast, NaHS prevented, but did not reverse, ozone-induced airflow limitation and bronchial structural remodeling. In conclusion, NaHS administration prevented and partially reversed ozone-induced features of lung inflammation and emphysema via regulation of the NLRP3-caspase-1, p38 mitogen-activated protein kinase, and Akt pathways.

Cigarette smoke destabilizes NLRP3 protein by promoting its ubiquitination

BACKGROUND

Cigarette smoke suppresses innate immunity, making smokers more susceptible to infection. The NLRP3 inflammasome is a multi-protein complex that releases interleukin (IL) -1β and IL -18. These cytokines are critical for a timely host response to pathogens. Whether cigarette smoke affects NLRP3 protein levels, and its ability to form an inflammasome, is not known.

METHODS AND RESULTS

Using the human monocyte THP1 cell line and C57BL/6 mice, we show that cigarette smoke decreases NLRP3 levels in cells by increasing ubiquitin-mediated proteasomal processing. Half-life of NLRP3 is shortened with the exposure to cigarette smoke extract. Cigarette smoke extract reduces cellular NLRP3 protein abundance in the presence of lipopolysaccharide, a known inducer of NLRP3 protein, thereby decreasing the formation of NLRP3 inflammasomes. The release of IL-1β and IL-18 by inflammasome activation is also decreased with the exposure to cigarette smoke extract both in THP1 cells and primary human peripheral blood macrophages.

CONCLUSIONS

Cigarette smoke extract decreased NLRP3 protein abundance via increased ubiquitin-mediated proteasomal processing. The release of IL-1β and IL-18 is also decreased with cigarette smoke extract. Our findings may provide mechanistic insights on immunosuppression in smokers and unique opportunities to develop a strategy to modulate immune function.

A Mitochondrial Perspective of Chronic Obstructive Pulmonary Disease Pathogenesis

Chronic obstructive pulmonary disease (COPD) encompasses several clinical syndromes, most notably emphysema and chronic bronchitis. Most of the current treatments fail to attenuate severity and progression of the disease, thereby requiring better mechanistic understandings of pathogenesis to develop disease-modifying therapeutics. A number of theories on COPD pathogenesis have been promulgated wherein an increase in protease burden from chronic inflammation, exaggerated production of reactive oxygen species and the resulting oxidant injury, or superfluous cell death responses caused by enhanced cellular injury/damage were proposed as the culprit. These hypotheses are not mutually exclusive and together likely represent the multifaceted biological processes involved in COPD pathogenesis. Recent studies demonstrate that mitochondria are involved in innate immune signaling that plays important roles in cigarette smoke-induced inflammasome activation, pulmonary inflammation and tissue remodeling responses. These responses are reviewed herein and synthesized into a view of COPD pathogenesis whereby mitochondria play a central role.

The IL-1 cytokine family and its role in inflammation and fibrosis in the lung

The IL-1 cytokine family comprises 11 members (7 ligands with agonist activity, 3 receptor antagonists and 1 anti-inflammatory cytokine) and is recognised as a key mediator of inflammation and fibrosis in multiple tissues including the lung. IL-1 targeted therapies have been successfully employed to treat a range of inflammatory conditions such as rheumatoid arthritis and gouty arthritis. This review will introduce the members of the IL-1 cytokine family, briefly discuss the cellular origins and cellular targets and provide an overview of the role of these molecules in inflammation and fibrosis in the lung.

Inflammatory triggers associated with exacerbations of COPD orchestrate plasticity of group 2 innate lymphoid cells in the lungs

Innate lymphoid cells (ILCs) are critical mediators of mucosal immunity, and group 1 ILCs (ILC1 cells) and group 3 ILCs (ILC3 cells) have been shown to be functionally plastic. Here we found that group 2 ILCs (ILC2 cells) also exhibited phenotypic plasticity in response to infectious or noxious agents, characterized by substantially lower expression of the transcription factor GATA-3 and a concomitant switch to being ILC1 cells that produced interferon-γ (IFN-γ). Interleukin 12 (IL-12) and IL-18 regulated this conversion, and during viral infection, ILC2 cells clustered within inflamed areas and acquired an ILC1-like phenotype. Mechanistically, these ILC1 cells augmented virus-induced inflammation in a manner dependent on the transcription factor T-bet. Notably, IL-12 converted human ILC2 cells into ILC1 cells, and the frequency of ILC1 cells in patients with chronic obstructive pulmonary disease (COPD) correlated with disease severity and susceptibility to exacerbations. Thus, functional plasticity of ILC2 cells exacerbates anti-viral immunity, which may have adverse consequences in respiratory diseases such as COPD.

The association of IL-18 gene promoter polymorphisms and the levels of serum IL-18 on the risk of multiple sclerosis

OBJECTIVES

Multiple sclerosis is an inflammatory condition of the central nervous system whose etiology is influenced by immunologic, genetic, and environmental factors. Aim of the present study was to determine if any relation exists between IL-18 -137C/G and -607C/A gene promoter polymorphisms on the individual susceptibility of multiple sclerosis and also to investigate the possible effect of IL-18 activity regarding this kind of polymorphism and MS.

PATIENTS AND METHODS

113 patients with clinically definite MS and 135 ethnically-matched controls were participated in this study. IL-18 -137C/G and -607C/A gene promoter polymorphisms were analyzed by Sequence Specific Polymerase Chain Reaction (SS-PCR), while levels of serum IL-18 were measured by Enzyme Linked Immunoassay Assay (ELISA) in patients with MS and healthy controls.

RESULTS

Our results showed that the IL-18 -607AA genotype indicated 6 times higher risk in the development of MS (OR=6.883; 3.17-14.96; p<0.001). According to our findings, smoking seems to be an important confounding factor in MS patients with carrying IL-18 -607 AA and CA+AA genotypes. However, no meaningful association was found with IL-18 -137C/G gene promoter polymorphism.

CONCLUSION

In conclusion, we suggest that IL-18 -607C/A gene promoter polymorphism is a major genetic factor for determining individual susceptibility to MS, where smoking status also increases the risk of MS.

Role of Chitinase 3-Like-1 in Interleukin-18-Induced Pulmonary Type 1, Type 2, and Type 17 Inflammation; Alveolar Destruction; and Airway Fibrosis in the Murine Lung

Chitinase 3-like 1 (Chi3l1), which is also called YKL-40 in humans and BRP-39 in mice, is the prototypic chitinase-like protein. Recent studies have highlighted its impressive ability to regulate the nature of tissue inflammation and the magnitude of tissue injury and fibroproliferative repair. This can be appreciated in studies that highlight its induction after cigarette smoke exposure, during which it inhibits alveolar destruction and the genesis of pulmonary emphysema. IL-18 is also known to be induced and activated by cigarette smoke, and, in murine models, the IL-18 pathway has been shown to be necessary and sufficient to generate chronic obstructive pulmonary disease-like inflammation, fibrosis, and tissue destruction. However, the relationship between Chi3l1 and IL-18 has not been defined. To address this issue we characterized the expression of Chi3l1/BRP-39 in control and lung-targeted IL-18 transgenic mice. We also characterized the effects of transgenic IL-18 in mice with wild-type and null Chi3l1 loci. The former studies demonstrated that IL-18 is a potent stimulator of Chi3l1/BRP-39 and that this stimulation is mediated via IFN-γ-, IL-13-, and IL-17A-dependent mechanisms. The latter studies demonstrated that, in the absence of Chi3l1/BRP-39, IL-18 induced type 2 and type 17 inflammation and fibrotic airway remodeling were significantly ameliorated, whereas type 1 inflammation, emphysematous alveolar destruction, and the expression of cytotoxic T lymphocyte perforin, granzyme, and retinoic acid early transcript 1 expression were enhanced. These studies demonstrate that IL-18 is a potent stimulator of Chi3l1 and that Chi3l1 is an important mediator of IL-18-induced inflammatory, fibrotic, alveolar remodeling, and cytotoxic responses.

Damage to Olfactory Progenitor Cells Is Involved in Cigarette Smoke-Induced Olfactory Dysfunction in Mice

Exposure to cigarette smoke is a major cause of olfactory dysfunction. However, the underlying mechanisms by which cigarette smoke interferes with the highly regenerative olfactory nerve system remain unclear. To investigate whether cigarette smoke induces olfactory dysfunction by disrupting cell proliferation and cell survival in the olfactory epithelium (OE), we developed a mouse model of smoking that involved intranasal administration of a cigarette smoke solution (CSS). Immunohistological analyses and behavioral testing showed that CSS administration during a period of 24 days reduced the number of olfactory marker protein-positive mature olfactory receptor neurons (ORNs) in the OE and induced olfactory dysfunction. These changes coincided with a reduction in the number of SOX2(+) ORN progenitors and Ki-67(+) proliferating cells in the basal layer of the OE, an increase in the number of caspase-3(+) apoptotic cells, and an increase in the expression of mRNA for the inflammatory cytokines IL-1β and IL-6. Notably, the proliferating ORN progenitor population recovered after cessation of treatment with CSS, resulting in the subsequent restoration of mature ORN numbers and olfaction. These results suggest that SOX2(+) ORN progenitors are targets of CSS-induced impairment of the OE, and that by damaging the ORN progenitor population and increasing ORN death, CSS exposure eventually overwhelms the regenerative capacity of the epithelium, resulting in reduced numbers of mature ORNs and olfactory dysfunction.

Mitochondrial Regulation of Inflammasome Activation in Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is characterized by enhanced chronic airway and lung inflammatory responses to noxious particles or gases. It is a major unmet medical need worldwide, and in Western society is strongly associated with exposure to cigarette smoke (CS). CS-induced inflammation is believed to be a key immune driver in the pathogenesis of COPD. Since the concept of inflammasomes was first introduced nearly a decade ago, these have been increasingly recognized as a central player in innate immune and inflammatory responses. In addition, studies have emerged demonstrating that mitochondrial innate immune signaling plays an important role in CS-induced inflammasome activation, pulmonary inflammation and tissue remodeling responses. Here, recent discoveries about inflammasome activation and mitochondrial biology and their role in COPD pathogenesis are reviewed. In addition, the current limitations of our understanding of this theme and future research directions are discussed.

Antimicrobial proteins and peptides in human lung diseases: A friend and foe partnership with host proteases

Lung antimicrobial proteins and peptides (AMPs) are major sentinels of innate immunity by preventing microbial colonization and infection. Nevertheless bactericidal activity of AMPs against Gram-positive and Gram-negative bacteria is compromised in patients with chronic obstructive pulmonary disease (COPD), cystic fibrosis (CF) and asthma. Evidence is accumulating that expression of harmful human serine proteases, matrix metalloproteases and cysteine cathepsins is markedely increased in these chronic lung diseases. The local imbalance between proteases and protease inhibitors compromises lung tissue integrity and function, by not only degrading extracellular matrix components, but also non-matrix proteins. Despite the fact that AMPs are somewhat resistant to proteolytic degradation, some human proteases cleave them efficiently and impair their antimicrobial potency. By contrast, certain AMPs may be effective as antiproteases. Host proteases participate in concert with bacterial proteases in the degradation of key innate immunity peptides/proteins and thus may play immunomodulatory activities during chronic lung diseases. In this context, the present review highlights the current knowledge and recent discoveries on the ability of host enzymes to interact with AMPs, providing a better understanding of the role of human proteases in innate host defense.