A unique population of neutrophils generated by air pollutant-induced lung damage exacerbates airway inflammation

Nociceptor neurons suppress alveolar macrophage-induced Siglec-F+ neutrophil-mediated inflammation to protect against pulmonary fibrosis

Pulmonary fibrosis results from persistent and pathological tissue repair, which is therapeutically challenging to attenuate and often fatal. The immune processes involved in fibrosis remain ill defined. Using a bleomycin-induced lung fibrosis murine model, we discovered that vagal TRPV1+ nociceptors are protective. Pharmacological ablation or genetic deletion of nociceptors resulted in worsened fibrosis and outcomes. Without nociceptors, alveolar macrophages aberrantly produced vasoactive intestinal peptide (VIP), leading to cytokine TGF-β1-mediated alternative proinflammatory Siglec-F+ neutrophil recruitment to the lung with a high propensity for neutrophil extracellular trap (NET) formation. VIP inhibition or Vip deletion in hematopoietic cells improved outcomes and attenuated Siglec-F+ neutrophil recruitment to the lungs in nociceptor-deficient mice, while VIP administration had the opposite effect. Thus, nociceptors are essential regulators of inflammation during pulmonary fibrosis. These findings provide mechanistic insights into how the nervous system impacts the progression of fibrotic lung diseases.

The cGAS-STING pathway promotes acute ischemia-induced neutropoiesis and neutrophil priming in the bone marrow

Our previous work demonstrated that the DNA-sensing receptor cyclic GMP-AMP synthase (cGAS) negatively affects post-infarct repair by promoting pro-inflammatory macrophages. However, whether cGAS and its downstream partner STING (Stimulator of Interferon Genes) regulate neutrophil production and function in the context of acute myocardial ischemia remains unclear. This study investigated the role of the cGAS-STING pathway in neutropoiesis (neutrophil production and differentiation) and examined whether ischemia primes neutrophils in the bone marrow via this pathway, enhancing their functionality and contributing to cardiac inflammatory injury. Using myocardial infarction (MI) models in wild-type (WT), Cgas-/-, and Sting-/- mice, we analyzed neutrophils from the bone marrow, peripheral blood, and infarcted tissue. Additionally, we generated neutrophil-specific conditional knockouts of Cgas and performed adoptive transfer experiments with Cgas-deficient neutrophils. RNA sequencing revealed that ischemia increased neutrophil production in the bone marrow and activated pathways involved in cytokine signaling, phagocytosis, chemotaxis, and degranulation. Inhibiting the cGAS-STING pathway reduced neutrophil production by decreasing lineage committed neutrophil precursors including early neutrophil precursors (eNP) and preNeu and downregulated ischemia-induced pathways. Neutrophil conditional Cgas deletion or adoptive transfer of Cgas-deficient neutrophils improved survival but did not significantly impact ischemia-induced remodeling. In conclusion, we demonstrate for the first time that ischemia enhanced neutrophil functionality before recruitment to infarcted tissue, and the cGAS-STING pathway played an important role in neutrophil production and priming. Furthermore, our findings demonstrate a neutrophil-specific role of cGAS in promoting cardiac rupture and mortality in MI. This study provides a more comprehensive understanding of the cGAS-STING pathway in acute ischemia and may support the translation of cGAS-STING modulators, an emerging therapeutic field.

Non-T2 asthma

PURPOSE OF REVIEW

This review provides a comprehensive overview of the non-T asthma phenotypes. Asthma is an umbrella term that defines a complex group of heterogenous airway disorders, which are broadly categorized into predominantly T2 or non-T2 phenotypes depending on the presence and levels of airway and systemic biomarkers associated with a T2 inflammatory response. Individuals with predominant T2 asthma have greater numbers of peripheral blood eosinophils, exhaled nitric oxide and IgE. These patients have more atopy and earlier onset asthma. In contrast, the absence or low levels of these biomarkers define non-T2 asthma. This is a heterogenous group with a later onset of asthma that is also more commonly associated with obesity and with females.

RECENT FINDINGS

This article summarizes new information regarding the plasticity that exists between T2 and non-T2 mechanisms, including their role in exacerbation-prone and nonexacerbating asthma, and many of the risk factors associated with the non-T2 phenotype, such as viral infections, ambient air pollution exposure, smoking, genetic and metabolic factors. It also provides new information on the immunological and metabolic mechanisms associated with non-T2 asthma. We also discuss how to manage this asthma phenotype and how treatment responses differ for these patients.

SUMMARY

Non-T2 asthma defines a heterogenous group of asthma phenotypes. However, acknowledging that the absence of T2 biomarkers is influenced by several factors is important and can longitudinally change in relation to exacerbations, particularly in children.

Eosinophils and pleural macrophages counter regulate IL-33-elicited airway inflammation via the 12/15-lipoxygenase pathway

Introduction

Fatty acid metabolism plays a crucial role in regulating airway inflammation through the synthesis of lipid mediators. We have previously demonstrated that a 12/15-lipoxygenase (12/15-LOX or Alox15)-derived mediator attenuates IL-33-induced eosinophilic airway inflammation in mice. However, the cellular sources of these mediators remain unclear.

Methods

To identify the cellular sources, we used several cell type-specific conditional 12/15-LOX-deficient mice.

Results

We found that eosinophils and pleural macrophages were the major 12/15-LOX-expressing cell types responsible for attenuating airway inflammation. Eosinophils were the major population of 12/15-LOX-expressing cells found in inflamed lung tissue. In addition, pleural macrophages were the major population of 12/15-LOX-expressing cells in the thoracic cavity and were found to translocate into inflamed lung tissue in response to airway inflammation.

Discussion

This study suggests that eosinophils and pleural macrophages cooperatively regulate eosinophilic airway inflammation via 12/15-LOX expression. Targeting 12/15-LOX metabolism in these cells may offer new therapeutic strategies for severe asthma.

Helminth infection favors reprogramming and proliferation of lung neutrophils

Neutrophils are a granulocytic population of myeloid cells that have critical effector functions during infectious disease but are generally thought to be short-lived and nonproliferative with markedly limited activation states. In these studies, we directly compared lung neutrophil activation following infection with different groups of pathogens including bacteria, fungi, and helminths. Our results demonstrate considerable heterogeneity depending on the type of infectious agent. In contrast to bacterial and fungal infection, after helminth infection neutrophils expressed markers associated with characteristic type 2 responses and unexpectedly upregulated genes associated with cell cycling and protein synthesis. Further studies showed reduced neutrophil cell death following helminth infection and increased proliferation, which was dependent on IL-4R signaling. This distinct subset of proliferating neutrophils expanded following helminth infection and was released from the endothelial niche to colocalize with invading parasites in the airways. These studies demonstrate a novel long-lived cycling phenotype for neutrophils following helminth infection.

NLRP3 deficiency abrogates silica-induced neutrophil infiltration, pulmonary damage and fibrosis

BACKGROUND

Silicosis is a progressive and often fatal occupational lung disease. The NLRP3 inflammasome is an innate immune sensor that is activated by silica. Accumulating evidence has implicated a role for NLRP3 in silicosis pathogenesis. In this study, we mechanistically elucidated the contribution of NLRP3 to silica-induced pulmonary disease.

METHODS

The in vivo role of NLRP3 was investigated following intranasal delivery of 2 mg of silica or diluent alone to wildtype, NLRP3 reporter, and NLRP3-deficient mice. Protein expression, inflammation, and histopathology were analyzed in the lung.

RESULTS

Intranasal administration of silica recapitulated the key pathological features of human silicosis, including nonresolving inflammation, the formation of silicotic nodules, and diffuse lung fibrosis. A reporter mouse placed under the native NLRP3 promoter revealed silica rapidly upregulated NLRP3 expression throughout the lung. NLRP3-deficient mice displayed marked early reductions in silica-induced IL-1β and IL-18 levels in the airways. Additionally, NLRP3 deficiency impaired the rapid infiltration of conventional Siglec-F- and fibrotic Siglec-F+ neutrophils, which correlated with reduced levels of neutrophil elastase. Deficiency in acute NLRP3-mediated inflammation correlated with significantly reduced pulmonary transforming growth factor beta and alpha smooth muscle actin expression, tissue damage, and fibrosis in the chronic phase of disease progression. Importantly, this included reduced silicotic nodule size and cellularity.

CONCLUSIONS

These findings highlight a major detrimental role for the NLRP3 inflammasome in driving silica-induced pulmonary neutrophil infiltration, TGFβ-mediated myofibroblast activation, tissue damage, and fibrosis.

Periodontitis-related myocardial fibrosis by expansion of collagen-producing SiglecF+ neutrophils

BACKGROUNDS AND AIMS

Patients with periodontitis (PD) are prone to developing myocardial infarction (MI), yet the prognosis and mechanisms remain unclear. Given the presumed close association of neutrophils with both conditions, this study aims to elucidate the roles of neutrophils in mediating the interaction between PD and MI.

METHODS

Three prospective cohorts and PD + MI mouse model were investigated to assess the effects of PD on MI prognosis. Single-cell-RNA sequencing and genome-wide association study were employed to identify the neutrophil subtype involved. To characterize the function of SiglecF+ neutrophils, bone marrow transplantation, Edu-pulse chasing, lineage tracing, and collagen contraction assay were utilized. Adoptive neutrophil transfer, conditional Siglecf knockout and lipid nanoparticles facilitating local SiglecF+ neutrophils depletion was harnessed to explore the roles of SiglecF+ neutrophils in MI repair.

RESULTS

Persisting but not short-term PD upset MI prognosis (cardiac fibrosis and function) in human and mice. Bone marrow neutrophils of PD were intrinsically skewed toward longer-lived SiglecF+ neutrophil differentiation, a subtype that was converted by GMCSF or TGFβ in PPARγ-dependent manner. SiglecF+ neutrophils were expanded in infarcted PD heart where they deposit collagen and activate fibroblasts to instigate excessive fibrosis. SiglecF+ neutrophil depletion was efficacious for mitigating fibrosis.

CONCLUSIONS

This study demonstrated that long-lasting PD-aggravated MI prognosis by expanding scar-associated SiglecF+ neutrophils into the heart and highlighted the clinical relevance of oral health examination for treating MI in a holistic fashion.

Exposure to bacterial PAMPs before RSV infection exacerbates innate inflammation and disease via IL-1α and TNF-α

Respiratory syncytial virus (RSV) can cause severe lower respiratory tract infections. Understanding why some individuals get more serious disease may help with diagnosis and treatment. One possible risk factor underlying severe disease is bacterial exposure before RSV infection. Bacterial exposure has been associated with increased respiratory viral-induced disease severity but the mechanism remains unknown. Respiratory bacterial infections or exposure to their pathogen associated molecular patterns (PAMPs) trigger innate immune inflammation, characterised by neutrophil and inflammatory monocyte recruitment and the production of inflammatory cytokines. We hypothesise that these changes to the lung environment alter the immune response and disease severity during subsequent RSV infection. To test this, we intranasally exposed mice to LPS, LTA or Acinetobacter baumannii (an airway bacterial pathogen) before RSV infection and observed an early induction of disease, measured by weight loss, at days 1-3 after infection. Neutrophils or inflammatory monocytes were not responsible for driving this exacerbated weight loss. Instead, exacerbated disease was associated with increased IL-1α and TNF-α, which orchestrated the recruitment of innate immune cells into the lung. This study shows that exposure to bacterial PAMPs prior to RSV infection increases the expression of IL-1α and TNF-α, which dysregulate the immune response resulting in exacerbated disease.

γδ T Cells Mediate Protection against Neutrophil-associated Lung Inflammation in Pulmonary Melioidosis

Pulmonary melioidosis is a severe tropical infection caused by Burkholderia pseudomallei and is associated with high mortality, despite early antibiotic treatment. γδ T cells have been increasingly implicated as drivers of the host neutrophil response during bacterial pneumonia, but their role in pulmonary melioidosis is unknown. Here, we report that in patients with melioidosis, a lower peripheral blood γδ T-cell concentration is associated with higher mortality, even when adjusting for severity of illness. γδ T cells were also enriched in the lung and protected against mortality in a mouse model of pulmonary melioidosis. γδ T-cell deficiency in infected mice induced an early recruitment of neutrophils to the lung, independent of bacterial burden. Subsequently, γδ T-cell deficiency resulted in increased neutrophil-associated inflammation in the lung as well as impaired bacterial clearance. In addition, γδ T cells influenced neutrophil function and subset diversity in the lung after infection. Our results indicate that γδ T cells serve a novel protective role in the lung during severe bacterial pneumonia by regulating excessive neutrophil-associated inflammation.

A chronic Pseudomonas aeruginosa mouse lung infection modeling the pathophysiology and inflammation of human cystic fibrosis

Investigation of chronic cystic fibrosis (CF) lung infections has been limited by a lack of murine models that reproduce obstructive lung pathology, chronicity of bacterial infections, and complex inflammation in human CF lung pathology. Three different approaches have been used separately to address these limitations, including using transgenic Scnn1b-Tg mice overexpressing a lung epithelial sodium channel to mimic the mucus-rich and hyperinflammatory CF lung environment, using synthetic CF sputum medium (SCFM) in an acute infection to induce bacterial phenotypes consistent with human CF, or using agar beads to promote chronic infections. Here, we combine these three models to establish a chronic Pseudomonas aeruginosa lung infection model using SCFM agar beads and Scnn1b-Tg mice (SCFM-Tg-mice) to recapitulate nutrients, mucus, and inflammation characteristic of the human CF lung environment. Like people with CF, SCFM-Tg-mice failed to clear bacterial infections. Lung function measurements showed that infected SCFM-Tg-mice had decreased inspiratory capacity and compliance, elevated airway resistance, and significantly reduced FVC and FEV0.1. Using spectral flow cytometry and multiplex cytokine arrays we show that, like people with CF, SCFM-Tg-mice developed inflammation characterized by eosinophil infiltration and Th2 lymphocytic cytokine responses. Chronically infected SCFM-Tg-mice developed an exacerbated mix of innate and Th1, Th2, and Th17-mediated inflammation, causing higher lung cellular damage, and elevated numbers of unusual Siglec F+ neutrophils. Thus, SCFM-Tg-mice represents a powerful tool to investigate bacterial pathogenesis and potential treatments for chronic CF lung infections and reveal a potential role for Siglec F+ neutrophils in CF inflammation.

Metabolically active neutrophils represent a permissive niche for Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb)-infected neutrophils are often found in the airways of patients with active tuberculosis (TB), and excessive recruitment of neutrophils to the lung is linked to increased bacterial burden and aggravated pathology in TB. The basis for the permissiveness of neutrophils for Mtb and the ability to be pathogenic in TB has been elusive. Here, we identified metabolic and functional features of neutrophils that contribute to their permissiveness in Mtb infection. Using single-cell metabolic and transcriptional analyses, we found that neutrophils in the Mtb-infected lung displayed elevated mitochondrial metabolism, which was largely attributed to the induction of activated neutrophils with enhanced metabolic activities. The activated neutrophil subpopulation was also identified in the lung granulomas from Mtb-infected non-human primates. Functionally, activated neutrophils harbored more viable bacteria and displayed enhanced lipid uptake and accumulation. Surprisingly, we found that interferon-γ promoted the activation of lung neutrophils during Mtb infection. Lastly, perturbation of lipid uptake pathways selectively compromised Mtb survival in activated neutrophils. These findings suggest that neutrophil heterogeneity and metabolic diversity are key to their permissiveness for Mtb and that metabolic pathways in neutrophils represent potential host-directed therapeutics in TB.

Increasing awareness regarding the relationship between environmental exposures and allergic disease

This review highlights studies from the past 3 years that add to the understanding of the impact of environmental exposures on allergic disease. These include aeroallergens, air quality, prenatal or early-life exposures, and occupational exposures. Recent studies have focused on the relationship between the environment, the microbiome, and allergic disease, and new therapeutic options have also been reviewed. Lastly, there has been significant recent research improving our knowledge of the link between health disparities and environmental exposures. These scientific advances have resulted in a better understanding that sets the foundation for current and future research dedicated to improving health outcomes by modifying environmental exposures.

The cGAS-STING Pathway Is Essential in Acute Ischemia-Induced Neutropoiesis and Neutrophil Priming in the Bone Marrow

Acute myocardial ischemia triggers a rapid mobilization of neutrophils from the bone marrow to peripheral blood, facilitating their infiltration into the infarcted myocardium. These cells are critical for inducing inflammation and contributing to myocardial repair. While neutrophils in infarcted tissue are better characterized, our understanding of whether and how ischemia regulates neutrophil production, differentiation, and functionality in the bone marrow remains limited. This study investigates these processes and the influence of the cGAS-STING pathway in the context of myocardial infarction. The cGAS-STING pathway detects aberrant DNA within cells, activates STING, and initiates downstream signaling cascades involving NFKB and IRF3. We analyzed neutrophils from bone marrow, peripheral blood, and infarct tissues using MI models generated from wild-type, Cgas -/- , and Sting -/- mice. These models are essential for studying neutropoiesis (neutrophil production and differentiation), as it involves multiple cell types. RNA sequencing analysis revealed that ischemia not only increased neutrophil production but also promoted cytokine signaling, phagocytosis, chemotaxis, and degranulation in the bone marrow before their release into the peripheral blood. Inhibition of the cGAS-STING pathway decreased neutrophil production after MI and down-regulated the same pathways activated by ischemia. Neutrophils lacking cGAS or STING were less mature, exhibited reduced activation, and decreased degranulation. Deletion of cGAS and STING decreased the expression of a large group of IFN-stimulated genes and IFIT1+ neutrophils from peripheral blood and the infarct tissue, suggesting that cGAS-STING plays an essential role in neutrophils with the IFN-stimulated gene signature. Importantly, transcriptomic analysis of Cgas -/- and Sting -/- neutrophils from bone marrow and MI tissues showed downregulation of similar pathways, indicating that the functionality developed in the bone marrow was maintained despite infarct-induced stimulation. These findings highlight the importance of neutropoiesis in dictating neutrophil function in target tissues, underscoring the critical role of the cGAS-STING pathway in neutrophil-mediated myocardial repair post-ischemia.

m6A-mediated HDAC9 upregulation promotes particulate matter-induced airway inflammation via epigenetic control of DUSP9-MAPK axis and acts as an inhaled nanotherapeutic target

Exposure to particulate matter (PM) can cause airway inflammation and worsen various airway diseases. However, the underlying molecular mechanism by which PM triggers airway inflammation has not been completely elucidated, and effective interventions are lacking. Our study revealed that PM exposure increased the expression of histone deacetylase 9 (HDAC9) in human bronchial epithelial cells and mouse airway epithelium through the METTL3/m6A methylation/IGF2BP3 pathway. Functional assays showed that HDAC9 upregulation promoted PM-induced airway inflammation and activation of MAPK signaling pathway in vitro and in vivo. Mechanistically, HDAC9 modulated the deacetylation of histone 4 acetylation at K12 (H4K12) in the promoter region of dual specificity phosphatase 9 (DUSP9) to repress the expression of DUSP9 and resulting in the activation of MAPK signaling pathway, thereby promoting PM-induced airway inflammation. Additionally, HDAC9 bound to MEF2A to weaken its anti-inflammatory effect on PM-induced airway inflammation. Then, we developed a novel inhaled lipid nanoparticle system for delivering HDAC9 siRNA to the airway, offering an effective treatment for PM-induced airway inflammation. Collectively, we elucidated the crucial regulatory mechanism of HDAC9 in PM-induced airway inflammation and introduced an inhaled therapeutic approach targeting HDAC9. These findings contribute to alleviating the burden of various airway diseases caused by PM exposure.

Advances in non-type 2 severe asthma: from molecular insights to novel treatment strategies

Asthma is a prevalent pulmonary disease that affects more than 300 million people worldwide and imposes a substantial economic burden. While medication can effectively control symptoms in some patients, severe asthma attacks, driven by airway inflammation induced by environmental and infectious exposures, continue to be a major cause of asthma-related mortality. Heterogeneous phenotypes of asthma include type 2 (T2) and non-T2 asthma. Non-T2 asthma is often observed in patients with severe and/or steroid-resistant asthma. This review covers the molecular mechanisms, clinical phenotypes, causes and promising treatments of non-T2 severe asthma. Specifically, we discuss the signalling pathways for non-T2 asthma including the activation of inflammasomes, interferon responses and interleukin-17 pathways, and their contributions to the subtypes, progression and severity of non-T2 asthma. Understanding the molecular mechanisms and genetic determinants underlying non-T2 asthma could form the basis for precision medicine in severe asthma treatment.

The impact of outdoor pollution and extreme temperatures on asthma-related outcomes: A systematic review for the EAACI guidelines on environmental science for allergic diseases and asthma

Air pollution is one of the biggest environmental threats for asthma. Its impact is augmented by climate change. To inform the recommendations of the EAACI Guidelines on the environmental science for allergic diseases and asthma, a systematic review (SR) evaluated the impact on asthma-related outcomes of short-term exposure to outdoor air pollutants (PM2.5, PM10, NO2, SO2, O3, and CO), heavy traffic, outdoor pesticides, and extreme temperatures. Additionally, the SR evaluated the impact of the efficacy of interventions reducing outdoor pollutants. The risk of bias was assessed using ROBINS-E tools and the certainty of the evidence by using GRADE. Short-term exposure to PM2.5, PM10, and NO2 probably increases the risk of asthma-related hospital admissions (HA) and emergency department (ED) visits (moderate certainty evidence). Exposure to heavy traffic may increase HA and deteriorate asthma control (low certainty evidence). Interventions reducing outdoor pollutants may reduce asthma exacerbations (low to very low certainty evidence). Exposure to fumigants may increase the risk of new-onset asthma in agricultural workers, while exposure to 1,3-dichloropropene may increase the risk of asthma-related ED visits (low certainty evidence). Heatwaves and cold spells may increase the risk of asthma-related ED visits and HA and asthma mortality (low certainty evidence).

Mononuclear phagocyte sub-types in vitro display diverse transcriptional responses to dust mite exposure

Mononuclear phagocytes (MNP), including macrophages and dendritic cells form an essential component of primary responses to environmental hazards and toxic exposures. This is particularly important in disease conditions such as asthma and allergic airway disease, where many different cell types are present. In this study, we differentiated CD34+ haematopoietic stem cells towards different populations of MNP in an effort to understand how different cell subtypes present in inflammatory disease microenvironments respond to the common allergen house dust mite (HDM). Using single cell mRNA sequencing, we demonstrate that macrophage subtypes MCSPP1+ and MLCMARCO+ display different patterns of gene expression after HDM challenge, noted especially for the chemokines CXCL5, CXCL8, CCL5 and CCL15. MLCCD206Hi alternatively activated macrophages displayed the greatest changes in expression, while neutrophil and monocyte populations did not respond. Further work investigated how pollutant diesel exhaust particles could modify these transcriptional responses and revealed that CXC but not CC type chemokines were further upregulated. Through the use of diesel particles with adsorbed material removed, we suggest that soluble pollutants on these particles are the active constituents responsible for the modifying effects on HDM. This study highlights that environmental exposures may influence tissue responses dependent on which MNP cell type is present, and that these should be considerations when modelling such events in vitro. Understanding the nuanced responsiveness of different immune cell types to allergen and pollutant exposure also contributes to a better understanding of how these exposures influence the development and exacerbation of human disease.

Effect of diesel exhaust particles on RANK/RANKL expression in in vivo and in vitro models of middle ear inflammation

OBJECTIVE

Increasing evidence suggests a link between middle ear inflammation and the development of diesel exhaust particles (DEPs). Chronic middle ear inflammation can lead to bone damage and remodeling. This study aimed to explore the impact of DEPs on the expression of interleukin (IL)-6 and RANKL under conditions of middle ear inflammation.

METHODS

DEPs were collected by burning fuel in a diesel engine at the Gwangju Institute of Science and Technology. Human middle ear epithelial cells were cultured to 70-80% confluence in culture plates and then treated with DEPs at concentrations of 0, 5, 10, 20, 40, and 80 μg/mL for 24 h. Cell viability was assessed manually. B6.SJL mice, aged 9 weeks, were exposed to DEPs at a concentration of 200 μg/m3 for 1 h daily over a period of 28 days. The expression levels of IL-6, tumor necrosis factor α, RANKL, and RANK were evaluated using hematoxylin and eosin staining and western blot analysis of the harvested middle ear samples.

RESULTS

The viability of human middle ear epithelial cells was found to decrease in a dose-dependent manner after 24 h. The mRNA expression level of IL-6 exhibited the most significant increase at the 48-h mark. In contrast, the mRNA expression levels of RANKL and RANK showed a marked increase as early as 6 h post-exposure, with both genes subsequently displaying a time-dependent decrease. Histological analysis revealed that the middle ear mucosa was thicker in the group exposed to DEPs compared to the control group. Additionally, the protein expression levels of IL-6 and RANKL were elevated in the DEP-exposed group relative to the normal control group.

CONCLUSIONS

We confirmed the expression of osteoclast-related proteins in the mouse middle ear. These results imply that air pollutants might affect RANKL/RANK signaling, which is associated with bone remodeling.

Associations between air pollutants and acute exacerbation of drug-resistant tuberculosis: evidence from a prospective cohort study

BACKGROUND

Short-term exposure to air pollution may trigger symptoms of drug-resistant tuberculosis (DR-TB) through stimulating lung tissue, damaging tracheobronchial mucosa, the key anti-mycobacterium T cell immune function, and production and release of inflammatory cytokines.

OBJECTIVE

To investigate the association between acute exacerbations of DR-TB and short-term residential exposure to air pollutants (PM10, PM2.5, SO2, NO2, CO and O3) based on a large prospective cohort in Anhui Province, China.

METHOD

Patients were derived from a prospective cohort study of DR-TB in Anhui Province. All DR-TB patients underwent drug-susceptibility testing and prefecture-level reference laboratories confirmed their microbiologies. The case-crossover design was performed to evaluate the association between the risk of acute exacerbations of DR-TB and short-term residential exposure to air pollution.

RESULTS

Short-term NO2 exposure was significantly related to an elevated risk of first-time outpatient visit due to acute exacerbations of DR-TB(relative risk:1.159, 95% confidence interval:1.011 ~ 1.329). Stratification analyses revealed that the relationship between the risk of acute exacerbations and NO2 exposure was stronger in the elderly (age ≥ 65) DR-TB patients, and in individuals with a history of TB treatment.

CONCLUSIONS

NO2 Exposure was significantly associated with an elevated risk of acute exacerbation of DR-TB in Anhui Province, China.

Neutrophil extracellular traps and their implications in airway inflammatory diseases

Neutrophil extracellular traps (NETs) are essential for immune defense and have been increasingly recognized for their role in infection and inflammation. In the context of airway inflammatory diseases, there is growing evidence suggesting the involvement and significance of NETs. This review aims to provide an overview of the formation mechanisms and components of NETs and their impact on various airway inflammatory diseases, including acute lung injury/ARDS, asthma, chronic obstructive pulmonary disease (COPD) and cystic fibrosis. By understanding the role of NETs in airway inflammation, we can gain valuable insights into the underlying pathogenesis of these diseases and identify potential targets for future therapeutic strategies that either target NETs formation or modulate their harmful effects. Further research is warranted to elucidate the complex interactions between NETs and airway inflammation and to develop targeted therapies that can effectively mitigate their detrimental effects while preserving their beneficial functions in host defense.

Nepalese indoor cookstove smoke extracts alter human airway epithelial gene expression, DNA methylation and hydroxymethylation

Household air pollution caused by inefficient cooking practices causes 4 million deaths a year worldwide. In Nepal, 86% of the rural population use solid fuels for cooking. Over 25% of premature deaths associated with air pollution are respiratory in nature. Here we aimed to identify molecular signatures of different cookstove and fuel type exposures in human airway epithelial cells, to understand the mechanisms mediating cook stove smoke induced lung disease. Primary human airway epithelial cells in submerged culture were exposed to traditional cook stove (TCS), improved cook stove (ICS) and liquefied petroleum gas (LPG) stove smoke extracts. Changes to gene expression, DNA methylation and hydroxymethylation were measured by bulk RNA sequencing and HumanMethylationEPIC BeadChip following oxidative bisulphite conversion, respectively. TCS smoke extract alone reproducibly caused changes in the expression of 52 genes enriched for oxidative stress pathways. TCS, ICS and LPG smoke extract exposures were associated with distinct changes to DNA methylation and hydroxymethylation. A subset of TCS induced genes were associated with differentially methylated and/or hydroxymethylated CpGs sites, and enriched for the ferroptosis pathway and the upstream regulator NFE2L2. DNA methylation and hydroxymethylation changes not associated with a concurrent change in gene expression, were linked to biological processes and molecular pathways important to airway health, including neutrophil function, transforming growth factor beta signalling, GTPase activity, and cell junction organisation. Our data identified differential impacts of TCS, ICS and LPG cook stove smoke on the human airway epithelium transcriptome, DNA methylome and hydroxymethylome and provide further insight into the association between indoor air pollution exposure and chronic lung disease mechanisms.

Pro-inflammation and pro-atherosclerotic responses to short-term air pollution exposure associated with alterations in sphingolipid ceramides and neutrophil extracellular traps

Air pollution has been associated with the development of atherosclerosis; however, the pathophysiological mechanisms underlying pro-atherosclerotic effects of air pollution exposure remain unclear. We conducted a prospective panel study in Beijing and recruited 152 participants with four monthly visits from September 2019 to January 2020. Linear mixed-effect models were applied to estimate the associations linking short-term air pollution exposure to biomarkers relevant to ceramide metabolism, pro-inflammation (neutrophil extracellular traps formation and systemic inflammation) and pro-atherosclerotic responses (endothelial stimulation, plaque instability, coagulation activation, and elevated blood pressure). We further explored whether ceramides and inflammatory indicators could mediate the alterations in the profiles of pro-atherosclerotic responses. We found that significant increases in levels of circulating ceramides of 9.7% (95% CIs: 0.7, 19.5) to 96.9% (95% CIs: 23.1, 214.9) were associated with interquartile range increases in moving averages of ambient air pollutant metrics, including fine particulate matter (PM2.5), black carbon, particles in size fractions of 100-560 nm, nitrogen dioxide, carbon monoxide and sulfur dioxide at prior up to 7 days. Higher air pollution levels were also associated with activated neutrophils (increases in citrullinated histone H3, neutrophil elastase, double-stranded DNA, and myeloperoxidase) and exacerbation of pro-atherosclerotic responses (e.g., increases in vascular endothelial growth factor, lipoprotein-associated phospholipase A2, matrix metalloproteinase-8, P-selectin, and blood pressure). Mediation analyses further showed that dysregulated ceramide metabolism and potentiated inflammation could mediate PM2.5-associated pro-atherosclerotic responses. Our findings extend the understanding on potential mechanisms of air pollution-associated atherosclerosis, and suggest the significance of reducing air pollution as priority in urban environments.

Neutrophils are gatekeepers of mucosal immunity

Mucosal tissues are constantly exposed to the outside environment. They receive signals from the commensal microbiome and tissue-specific triggers including alimentary and airborne elements and are tasked to maintain balance in the absence of inflammation and infection. Here, we present neutrophils as sentinel cells in mucosal immunity. We discuss the roles of neutrophils in mucosal homeostasis and overview clinical susceptibilities in patients with neutrophil defects. Finally, we present concepts related to specification of neutrophil responses within specific mucosal tissue microenvironments.

RAGE contributes to allergen driven severe neutrophilic airway inflammation via NLRP3 inflammasome activation in mice

Background

Asthma is a major public healthcare burden, affecting over 300 million people worldwide. While there has been great progress in the treatment of asthma, subsets of patients who present with airway neutrophilia, often have more severe disease, and tend to be resistant to conventional corticosteroid treatments. The receptor for advanced glycation endproducts (RAGE) plays a central role in the pathogenesis of eosinophilic asthma, however, it's role in neutrophilic asthma remains largely uninvestigated.

Methods

A mouse model of severe steroid resistant neutrophilic airway disease (SSRNAD) using the common fungal allergen Alternaria alternata (AA) was employed to evaluate the effects of genetic ablation of RAGE and pharmacological inhibition of the NLRP3 inflammasome on neutrophilic airway inflammation.

Results

AA exposure induced robust neutrophil-dominant airway inflammation and increased BALF levels of Th1/Th17 cytokines in wild-type mice, which was significantly reduced in RAGE-/- mice. Serum levels of IgE and IgG1 were increased similarly in both wild-type and RAGE-/- mice. Pharmacological inhibition of NLRP3 blocked the effects of AA exposure and NLRP3 inflammasome activation was RAGE-dependent. Neutrophil extracellular traps were elevated in the BALF of wild-type but not RAGE-/- mice and an atypical population of SiglecF+ neutrophils were identified in the BALF. Lastly, time-course studies found that RAGE expression promoted sustained neutrophil accumulation in the BALF of mice in response to AA.

Asthma triggered by extreme temperatures: From epidemiological evidence to biological plausibility

BACKGROUND

There is rapidly growing evidence indicating that extreme temperature is a crucial trigger and potential activator of asthma; however, the effects of extreme temperature on asthma are inconsistently reported and the its potential mechanisms remain undefined.

OBJECTIVES

This review aims to estimate the impacts of extreme heat, extreme cold, and temperature variations on asthma by systematically summarizing the existing studies from epidemiological evidence to biological plausibility.

METHODS

We conducted a systematic search in PubMed, Embase, and Web of Science from inception to June 30, 2022, and we retrieved articles of epidemiology and biological studies which assessed associations between extreme temperatures and asthma. This protocol was registered with PROSPERO (CRD42021273613).

RESULTS

From 12,435 identified records, 111 eligible studies were included in the qualitative synthesis, and 37 articles were included in the meta-analysis (20 for extreme heat, 16 for extreme cold, and 15 for temperature variations). For epidemiological evidence, we found that the synergistic effects of extreme temperatures, indoor/outdoor environments, and individual vulnerabilities are important triggers for asthma attacks, especially when there is extreme heat or cold. Meta-analysis further confirmed the associations, and the pooled relative risks for asthma attacks in extreme heat and extreme cold were 1.07 (95%CI: 1.03-1.12) and 1.20 (95%CI: 1.12-1.29), respectively. Additionally, this review discussed the potential inflammatory mechanisms behind the associations between extreme temperatures and asthma exacerbation, and highlighted the regulatory role of immunological pathways and transient receptor potential ion channels in asthma triggered by extreme temperatures.

CONCLUSIONS

We concluded that both extreme heat and cold could significantly increase the risk of asthma. Additionally, we proposed a potential mechanistic framework, which is important for understanding the disease pathogenesis that uncovers the complex mechanisms of asthma triggered by extreme temperatures and protects the sensitive individuals from impacts of extreme weather events and climate change.

Neutrophil Extracellular Traps in Asthma: Friends or Foes?

Asthma is a chronic inflammatory disease characterized by variable airflow limitation and airway hyperresponsiveness. A plethora of immune and structural cells are involved in asthma pathogenesis. The roles of neutrophils and their mediators in different asthma phenotypes are largely unknown. Neutrophil extracellular traps (NETs) are net-like structures composed of DNA scaffolds, histones and granular proteins released by activated neutrophils. NETs were originally described as a process to entrap and kill a variety of microorganisms. NET formation can be achieved through a cell-death process, termed NETosis, or in association with the release of DNA from viable neutrophils. NETs can also promote the resolution of inflammation by degrading cytokines and chemokines. NETs have been implicated in the pathogenesis of various non-infectious conditions, including autoimmunity, cancer and even allergic disorders. Putative surrogate NET biomarkers (e.g., double-strand DNA (dsDNA), myeloperoxidase-DNA (MPO-DNA), and citrullinated histone H3 (CitH3)) have been found in different sites/fluids of patients with asthma. Targeting NETs has been proposed as a therapeutic strategy in several diseases. However, different NETs and NET components may have alternate, even opposite, consequences on inflammation. Here we review recent findings emphasizing the pathogenic and therapeutic potential of NETs in asthma.

The Dynamic Contribution of Neutrophils in the Chronic Respiratory Diseases

Asthma, chronic obstructive pulmonary disease, and idiopathic pulmonary fibrosis are representative chronic respiratory diseases (CRDs). Although they differ in terms of disease presentation, they are all thought to arise from unresolved inflammation. Neutrophils are not only the first responders to acute inflammation, but they also help resolve the inflammation. Notably, emerging clinical studies show that CRDs are associated with systemic and local elevation of neutrophils. Moreover, murine studies suggest that airway-infiltrating neutrophils not only help initiate airway inflammation but also prolong the inflammation. Given this background, this review describes neutrophil-mediated immune responses in CRDs and summarizes the completed, ongoing, and potential clinical trials that test the therapeutic value of targeting neutrophils in CRDs. The review also clarifies the importance of understanding how neutrophils interact with other immune cells and how these interactions contribute to chronic inflammation in specific CRDs. This information may help identify future therapeutic strategies for CRDs.

Siglec-F-expressing neutrophils are essential for creating a pro-fibrotic microenvironment in the renal fibrosis

The roles of neutrophils in renal inflammation are currently unclear. On examining these cells in the unilateral ureteral obstruction murine model of chronic kidney disease, we found that the injured kidney bore a large and rapidly expanding population of neutrophils that expressed the eosinophil marker Siglec-F. We first confirmed that these cells were neutrophils. Siglec-F+ neutrophils were recently detected for the first time by several studies on other disease contexts. We then showed that (i) these cells were derived from conventional neutrophils in the renal vasculature by TGF-β1 and GM-CSF, (ii) they differed from their parent cells by more frequent hypersegmentation, higher expression of pro-fibrotic inflammatory cytokines, and, notably, expression of Collagen 1, and (iii) their depletion reduced collagen deposition and disease progression, but adoptive transfer increased renal fibrosis. These findings have thus unveiled a subtype of neutrophils that participate in renal fibrosis and maybe a new therapeutic target in chronic kidney disease.