Neutrophils restrain allergic airway inflammation by limiting ILC2 function and monocyte-dendritic cell antigen presentation

Airway extracellular LTA4H concentrations are governed by release from liver hepatocytes and changes in lung vascular permeability

Leukotriene A4 hydrolase (LTA4H) is a bifunctional enzyme, with dual activities critical in defining the scale of tissue inflammation and pathology. LTA4H classically operates intracellularly, primarily within myeloid cells, to generate pro-inflammatory leukotriene B4. However, LTA4H also operates extracellularly to degrade the bioactive collagen fragment proline-glycine-proline to limit neutrophilic inflammation and pathological tissue remodeling. While the dichotomous functions of LTA4H are dictated by location, the cellular source of extracellular enzyme remains unknown. We demonstrate that airway extracellular LTA4H concentrations are governed by the level of pulmonary vascular permeability and influx of an abundant repository of blood-borne enzyme. In turn, blood LTA4H originates from liver hepatocytes, being released constitutively but further upregulated during an acute phase response. These findings have implications for our understanding of how inflammation and repair are regulated and how perturbations to the LTA4H axis may manifest in pathologies of chronic diseases.

Saharan dust induces the lung disease-related cytokines granulocyte-macrophage colony-stimulating factor and granulocyte colony-stimulating factor

Desert dust exposure is associated with adverse respiratory health effects. Desert dust is a complex pollutant mixtures that includes respirable crystalline and amorphous particles, metals, and microbial constituents. Given the health effects of desert dust and its heterogeneity, as yet unidentified harmful biological pathways may be triggered. Therefore, we exposed human in vitro air-liquid interface co-cultures of alveolar epithelial A549 cells and THP-1 macrophages to Saharan dust (SD). For comparison, we used the known pulmonary toxicant DQ12 quartz dust. Via RNA sequencing, we identified that SD but not DQ12 increased the gene expression of granulocyte-macrophage colony-stimulating factor (GMCSF) and granulocyte colony-stimulating factor (GCSF). These findings were confirmed by quantitative reverse transcriptase PCR. SD dose-dependently upregulated GMCSF and GCSF expression with significant 7 and 9-fold changes, respectively, at the highest tested concentration of 31 µg/cm2. Furthermore, we observed that SD significantly enhanced the secretion of GM-CSF and G-CSF by 2-fold. Both cytokines have previously been associated with lung diseases such as asthma and fibrosis. Hence, we present two molecular messengers that may contribute to the adverse health effects of desert dust and might serve as drug targets for this globally relevant non-anthropogenic air pollutant.

Single-cell analysis reveals alterations in cellular composition and cell-cell communication associated with airway inflammation and remodeling in asthma

BACKGROUND

Asthma is a heterogeneous disease characterized by airway inflammation and remodeling, whose pathogenetic complexity was associated with abnormal responses of various cell types in the lung. The specific interactions between immune and stromal cells, crucial for asthma pathogenesis, remain unclear. This study aims to determine the key cell types and their pathological mechanisms in asthma through single-cell RNA sequencing (scRNA-seq).

METHODS

A 16-week mouse model of house dust mite (HDM) induced asthma (n = 3) and controls (n = 3) were profiled with scRNA-seq. The cellular composition and gene expression profiles were assessed by bioinformatic analyses, including cell enrichment analysis, trajectory analysis, and Gene Set Enrichment Analysis. Cell-cell communication analysis was employed to investigate the ligand-receptor interactions.

RESULTS

The asthma model results in airway inflammation coupled with airway remodeling and hyperresponsiveness. Single-cell analysis revealed notable changes in cell compositions and heterogeneities associated with airway inflammation and remodeling. GdT17 cells were identified to be a primary cellular source of IL-17, related to inflammatory exacerbation, while a subpopulation of alveolar macrophages exhibited numerous significantly up-regulated genes involved in multiple pathways related to neutrophil activities in asthma. A distinct fibroblast subpopulation, marked by elevated expression levels of numerous contractile genes and their regulators, was observed in increased airway smooth muscle layer by immunofluorescence analysis. Asthmatic stromal-immune cell communication significantly strengthened, particularly involving GdT17 cells, and macrophages interacting with fibroblasts. CXCL12/CXCR4 signaling was remarkedly up-regulated in asthma, predominantly bridging the interaction between fibroblasts and immune cell populations. Fibroblasts and macrophages could jointly interact with various immune cell subpopulations via the CCL8/CCR2 signaling. In particular, fibroblast-macrophage cell circuits played a crucial role in the development of airway inflammation and remodeling through IL1B paracrine signaling.

CONCLUSIONS

Our study established a mouse model of asthma that recapitulated key pathological features of asthma. ScRNA-seq analysis revealed the cellular landscape, highlighting key pathological cell populations associated with asthma pathogenesis. Cell-cell communication analysis identified the crucial ligand-receptor interactions contributing to airway inflammation and remodeling. Our findings emphasized the significance of cell-cell communication in bridging the possible causality between airway inflammation and remodeling, providing valuable hints for therapeutic strategies for asthma.

Obesity dysregulates the pulmonary antiviral immune response

Obesity is a well-recognized risk factor for severe influenza infections but the mechanisms underlying susceptibility are poorly understood. Here, we identify that obese individuals have deficient pulmonary antiviral immune responses in bronchoalveolar lavage cells but not in bronchial epithelial cells or peripheral blood dendritic cells. We show that the obese human airway metabolome is perturbed with associated increases in the airway concentrations of the adipokine leptin which correlated negatively with the magnitude of ex vivo antiviral responses. Exogenous pulmonary leptin administration in mice directly impaired antiviral type I interferon responses in vivo and ex vivo in cultured airway macrophages. Obese individuals hospitalised with influenza showed dysregulated upper airway immune responses. These studies provide insight into mechanisms driving propensity to severe influenza infections in obesity and raise the potential for development of leptin manipulation or interferon administration as novel strategies for conferring protection from severe infections in obese higher risk individuals.

TLR7 activation at epithelial barriers promotes emergency myelopoiesis and lung antiviral immunity

Monocytes are heterogeneous innate effector leukocytes generated in the bone marrow and released into circulation in a CCR2-dependent manner. During infection or inflammation, myelopoiesis is modulated to rapidly meet the demand for more effector cells. Danger signals from peripheral tissues can influence this process. Herein we demonstrate that repetitive TLR7 stimulation via the epithelial barriers drove a potent emergency bone marrow monocyte response in mice. This process was unique to TLR7 activation and occurred independently of the canonical CCR2 and CX3CR1 axes or prototypical cytokines. The monocytes egressing the bone marrow had an immature Ly6C-high profile and differentiated into vascular Ly6C-low monocytes and tissue macrophages in multiple organs. They displayed a blunted cytokine response to further TLR7 stimulation and reduced lung viral load after RSV and influenza virus infection. These data provide insights into the emergency myelopoiesis likely to occur in response to the encounter of single-stranded RNA viruses at barrier sites.

Individual and joint association of phenols, parabens, and phthalates with childhood lung function: Exploring the mediating role of peripheral immune responses

The functioning of the respiratory system can be interfered with by exposure to mixtures of environmental chemicals, however, the evidence is still ambiguous. We evaluated the association of exposure to mixtures of 14 chemicals, including 2 phenols, 2 parabens, and 10 phthalates, with four major lung function metrics. Based on data from the National Health and Nutrition Examination Survey 2007-2012, this analysis was conducted among 1462 children aged 6-19 years. Linear regression, Bayesian kernel machine regression, quantile-based g-computation regression, and a generalized additive model were performed to estimate the associations. Mediation analyses were performed to investigate plausible biological pathways mediated by immune cells. Our results indicated that the phenols, parabens, and phthalates mixture was negatively related to lung function parameters. And BPA and PP were identified as important contributors to negative associations with FEV₁, FVC, and PEF, with non-linear relationships observed between BPA and those outcomes. The most influential factor for a probable FEF_{25-75 %} decline was MCNP. BPA, and MCNP had an interaction effect on FEF_{25-75 %}. The association of PP with FVC and FEV₁ has been postulated to be mediated by neutrophils and monocytes. The findings offer insights into the associations of chemical mixtures with respiratory health and the possible driving mechanism, which would be of significance in adding novel evidence of the role of peripheral immune responses, as well as calling for remediation actions to be prioritized during childhood.

Increased expression of CSF1 in patients with eosinophilic asthma

BACKGROUND

The link between colony-stimulating factor 1 (CSF1) and asthma was reported recently. However, the role and mechanism of CSF1 in asthma remain poorly understood. In this study, we aimed to explore the expression and its potential mechanism of CSF1 in asthma.

METHODS

CSF1 expression in the airway samples from asthmatics and healthy controls were examined, then the correlations between CSF1 and eosinophilic indicators were analyzed. Subsequently, bronchial epithelial cells (BEAS-2B) with CSF1 overexpression and knockdown were constructed to investigate the potential molecular mechanism of CSF1. Finally, the effect of CSF1R inhibitor on STAT1 was investigated.

RESULTS

The expression of CSF1 was significantly increased in patients with asthma compared to healthy controls, especially in patients with severe and eosinophilic asthma. Upregulated CSF1 positively correlated with airway-increased eosinophil inflammation. In vitro, cytokines interleukin 13 (IL-13) and IL-33 can stimulate the upregulation of CSF1 expression. CSF1 overexpression enhanced p-CSF1R/CSF1R and p-STAT1/STAT1 expression, while knockdown CSF1 using anti-CSF1 siRNAs decreased p-CSF1R/CSF1R and p-STAT1/STAT1 expression. Furthermore, the inhibitor of CSF1R significantly decreased p-STAT1/STAT1 expression.

CONCLUSIONS

Sputum CSF1 may be involved in asthmatic airway eosinophil inflammation by interacting with CSF1R and further activating the STAT1 signaling. Interfering this potential pathway could serve as an anti-inflammatory therapy for asthma.

Helper innate lymphoid cells as cell therapy for cancer

Although the first cancer immunotherapy was given in the clinic more than a century ago, this line of treatment has remained more of a distant goal than a practical therapy due to limited understanding of the tumour microenvironment and the mechanisms at play within it, which led to failures of numerous clinical trials. However, in the last two decades, the immune checkpoint inhibitors (ICIs) and chimeric antigen receptor-T cell therapies have revolutionized the treatment of cancer and provided proof-of-concept that immunotherapies are a viable option. So far, immunotherapies have majoritarily focused on utilizing T cells; however, T cells are not autonomous but rather function as part of, and therefore are influenced by, a vast cast of other immune cells, including innate lymphoid cells (ILCs). Here, we summarize the role of ILCs, especially helper ILCs, in tumour development, progression and metastasis, as well as their potential to be used as immunotherapy for cancer. By reviewing the studies that used helper ILCs as adoptive cell therapy (ACT), we highlight the rationale behind considering these cells as novel ACT for cancer as well as identify open questions and areas for future research.

Neutrophils in host defense, healing, and hypersensitivity: Dynamic cells within a dynamic host

Neutrophils are cells of the innate immune system that are extremely abundant in vivo and respond quickly to infection, injury, and inflammation. Their constant circulation throughout the body makes them some of the first responders to infection, and indeed they play a critical role in host defense against bacterial and fungal pathogens. It is now appreciated that neutrophils also play an important role in tissue healing after injury. Their short life cycle, rapid response kinetics, and vast numbers make neutrophils a highly dynamic and potentially extremely influential cell population. It has become clear that they are highly integrated with other cells of the immune system and can thus exert critical effects on the course of an inflammatory response; they can further impact tissue homeostasis and recovery after challenge. In this review, we discuss the fundamentals of neutrophils in host defense and healing; we explore the relationship between neutrophils and the dynamic host environment, including circadian cycles and the microbiome; we survey the field of neutrophils in asthma and allergy; and we consider the question of neutrophil heterogeneity-namely, whether there could be specific subsets of neutrophils that perform different functions in vivo.

OMIP-086: Full spectrum flow cytometry for high-dimensional immunophenotyping of mouse innate lymphoid cells

This 25-parameter, 22-color full spectrum flow cytometry panel was designed and optimized for the comprehensive enumeration and functional characterization of innate lymphoid cell (ILC) subsets in mouse tissues. The panel presented here allows the discrimination of ILC progenitors (ILCP), ILC1, ILC2, NCR+ ILC3, NCR- ILC3, CCR6+ lymphoid tissue-inducer (LTi)-like ILC3 and mature natural killer (NK) cell populations. Further characterization of ILC and NK cell functional profiles in response to stimulation is provided by the inclusion of subset-specific cytokine markers, and proliferation markers. Development and optimization of this panel was performed on freshly isolated cells from adult BALB/c lungs and small intestine lamina propria, and ex vivo stimulation with phorbol 12-myrisate 13-acetate, ionomycin, and pro-ILC activating cytokines.

Diagnostic and Prognostic Risk Assessment of Heat Shock Protein HSPA1B rs2763979 Gene Variant in Asthma

Given the significant role the heat shock protein Hsp70 plays in modulating cellular homeostasis in several chronic inflammatory disorders, the genetic variation of the inducible HSP70 (HSPA1B) gene may impact protein expression and disease phenotype. The HSPA1B rs2763979 variant has been associated with multiple inflammatory scenarios, but no previous studies have explored its association with asthma. In this sense, this cross-sectional study enrolled 90 children with asthma and 218 age-/sex-matched healthy volunteers for rs2763979 variant genotyping by TaqMan allelic discrimination analysis. The results were investigated under several genetic models and associated with disease susceptibility and clinicolaboratory data. Overall analysis, including the 308 participants, revealed a higher C allele frequency among patients relative to controls (43.0% vs. 33%, p = 0.006). Furthermore, patients with the C variant initially had a higher risk of asthma under heterozygous (OR = 2.75, 95%CI = 1.46-5.18, p = 0.003), homozygous (OR = 3.35, 95%CI = 1.19-9.39, p = 0.008), dominant (OR = 2.83, 95%CI = 1.52-5.25, p < 0.001), and overdominant (OR = 2.12, 95%CI = 1.20-3.74, p = 0.008) models. However, after employing a 1:1 nearest propensity matching analysis, the studied variant showed only borderline significance with asthma under the dominant model in 71 matched cohorts. Interestingly, patients who carry the rs2763979 CC genotype showed favorable spirometric parameters in terms of better (mean ± SD) forced vital capacity (86.3 ± 7.4 vs. 77.7 ± 6.1 and 75.7 ± 7.2 for CT and TT, respectively, p = 0.021), forced expiratory volume in one second before bronchodilation (60.7 ± 12.9 vs. 54.9 ± 7.6 and 56.1 ± 7.5 for CT and TT, respectively, p = 0.021), and an improvement in peak expiratory flow rate after inhaled salbutamol bronchodilator (p = 0.044) relative to the counterpart genotypes. In conclusion, the HSPA1B rs2763979 variant might have prognostic utility as a genetic marker for asthma in our population. Further larger studies on different ethnicities are recommended to validate the results.

Mechanisms regulating neutrophil responses in immunity, allergy, and autoimmunity

Neutrophil granulocytes, or neutrophils, are the most abundant circulating leukocytes in humans and indispensable for antimicrobial immunity, as exemplified in patients with inborn and acquired defects of neutrophils. Neutrophils were long regarded as the foot soldiers of the immune system, solely destined to execute a set of effector functions against invading pathogens before undergoing apoptosis, the latter of which was ascribed to their short life span. This simplistic understanding of neutrophils has now been revised on the basis of insights gained from the use of mouse models and single-cell high-throughput techniques, revealing tissue- and context-specific roles of neutrophils in guiding immune responses. These studies also demonstrated that neutrophil responses were controlled by sophisticated feedback mechanisms, including directed chemotaxis of neutrophils to tissue-draining lymph nodes resulting in modulation of antimicrobial immunity and inflammation. Moreover, findings in mice and humans showed that neutrophil responses adapted to different deterministic cytokine signals, which controlled their migration and effector function as well as, notably, their biologic clock by affecting the kinetics of their aging. These mechanistic insights have important implications for health and disease in humans, particularly, in allergic diseases, such as atopic dermatitis and allergic asthma bronchiale, as well as in autoinflammatory and autoimmune diseases. Hence, our improved understanding of neutrophils sheds light on novel therapeutic avenues, focusing on molecularly defined biologic agents.

Screening and identification of tissue-infiltrating immune cells and genes for patients with emphysema phenotype of COPD

Objective

To study the tissue-infiltrating immune cells of the emphysema phenotype of chronic obstructive pulmonary disease (COPD) and find the molecular mechanism related to the development of emphysema to offer potential targets for more precise treatment of patients with COPD.

Methods

Combined analyses of COPD emphysema phenotype lung tissue-related datasets, GSE47460 and GSE1122, were performed. CIBERSORT was used to assess the distribution of tissue-infiltrating immune cells. Weighted gene co-expression network analysis (WGCNA) was used to select immune key genes closely related to clinical features. Rt-qPCR experiments were used for the validation of key genes. Emphysema risk prediction models were constructed by logistic regression analysis and a nomogram was developed.

Results

In this study, three immune cells significantly associated with clinical features of emphysema (FEV1 post-bronchodilator % predicted, GOLD Stage, and DLCO) were found. The proportion of neutrophils (p=0.025) infiltrating in the emphysema phenotype was significantly increased compared with the non-emphysema phenotype, while the proportions of M2 macrophages (p=0.004) and resting mast cells (p=0.01) were significantly decreased. Five immune-related differentially expressed genes (DEGs) were found. WGCNA and clinical lung tissue validation of patients with emphysema phenotype were performed to further screen immune-related genes closely related to clinical features. A key gene (SERPINA3) was selected and included in the emphysema risk prediction model. Compared with the traditional clinical prediction model (AUC=0.923), the combined prediction model, including SERPINA3 and resting mast cells (AUC=0.941), had better discrimination power and higher net benefit.

Conclusion

This study comprehensively analyzed the tissue-infiltrating immune cells significantly associated with emphysema phenotype, including M2 macrophages, neutrophils, and resting mast cells, and identified SERPINA3 as a key immune-related gene.

Airway immune response in the mouse models of obesity-related asthma

The prevalence rates of obesity and its complications have increased dramatically worldwide. Obesity can lead to low-grade chronic systemic inflammation, which predisposes individuals to an increased risk of morbidity and mortality. Although obesity has received considerable interest in recent years, the essential role of obesity in asthma development has not been explored. Asthma is a common chronic inflammatory airway disease caused by various environmental allergens. Obesity is a critical risk factor for asthma exacerbation due to systemic inflammation, and obesity-related asthma is listed as an asthma phenotype. A suitable model can contribute to the understanding of the in-depth mechanisms of obese asthma. However, stable models for simulating clinical phenotypes and the impact of modeling on immune response vary across studies. Given that inflammation is one of the central mechanisms in asthma pathogenesis, this review will discuss immune responses in the airways of obese asthmatic mice on the basis of diverse modeling protocols.

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.

Neutrophils and Asthma

Although eosinophilic inflammation is characteristic of asthma pathogenesis, neutrophilic inflammation is also marked, and eosinophils and neutrophils can coexist in some cases. Based on the proportion of sputum cell differentiation, asthma is classified into eosinophilic asthma, neutrophilic asthma, neutrophilic and eosinophilic asthma, and paucigranulocytic asthma. Classification by bronchoalveolar lavage is also performed. Eosinophilic asthma accounts for most severe asthma cases, but neutrophilic asthma or a mixture of the two types can also present a severe phenotype. Biomarkers for the diagnosis of neutrophilic asthma include sputum neutrophils, blood neutrophils, chitinase-3-like protein, and hydrogen sulfide in sputum and serum. Thymic stromal lymphoprotein (TSLP)/T-helper 17 pathways, bacterial colonization/microbiome, neutrophil extracellular traps, and activation of nucleotide-binding oligomerization domain-like receptor family, pyrin domain-containing 3 pathways are involved in the pathophysiology of neutrophilic asthma and coexistence of obesity, gastroesophageal reflux disease, and habitual cigarette smoking have been associated with its pathogenesis. Thus, targeting neutrophilic asthma is important. Smoking cessation, neutrophil-targeting treatments, and biologics have been tested as treatments for severe asthma, but most clinical studies have not focused on neutrophilic asthma. Phosphodiesterase inhibitors, anti-TSLP antibodies, azithromycin, and anti-cholinergic agents are promising drugs for neutrophilic asthma. However, clinical research targeting neutrophilic inflammation is required to elucidate the optimal treatment.

Cannabinoid receptor 2 engagement promotes group 2 innate lymphoid cell expansion and enhances airway hyperreactivity

BACKGROUND

Cannabinoids modulate the activation of immune cells and physiologic processes in the lungs. Group 2 innate lymphoid cells (ILC2s) are central players in type 2 asthma, but how cannabinoids modulate ILC2 activation remains to be elucidated.

OBJECTIVE

Our goal was to investigate the effects of cannabinoids on ILC2s and their role in asthma.

METHODS

A combination of cannabinoid receptor (CB)2 knockout (KO) mice, CB2 antagonist and agonist were used in the mouse models of IL-33, IL-25, and Alternaria alternata ILC2-dependent airway inflammation. RNA sequencing was performed to assess transcriptomic changes in ILC2s, and humanized mice were used to assess the role of CB2 signaling in human ILC2s.

RESULTS

We provide evidence that CB2 signaling in ILC2s is important for the development of ILC2-driven airway inflammation in both mice and human. We showed that both naive and activated murine pulmonary ILC2s express CB2. CB2 signaling did not affect ILC2 homeostasis at steady state, but strikingly it stimulated ILC2 proliferation and function upon activation. As a result, ILC2s lacking CB2 induced lower lung inflammation, as we made similar observations using a CB2 antagonist. Conversely, CB2 agonism remarkably exacerbated ILC2-driven airway hyperreactivity and lung inflammation. Mechanistically, transcriptomic and protein analysis revealed that CB2 signaling induced cyclic adenosine monophosphate-response element binding protein (CREB) phosphorylation in ILC2s. Human ILC2s expressed CB2, as CB2 antagonism and agonism showed opposing effects on ILC2 effector function and development of airway hyperreactivity in humanized mice.

CONCLUSION

Collectively, our results define CB2 signaling in ILC2s as an important modulator of airway inflammation.

Steroid-induced fibroblast growth factors drive an epithelial-mesenchymal inflammatory axis in severe asthma

Asthma and inflammatory airway diseases restrict airflow in the lung, compromising gas exchange and lung function. Inhaled corticosteroids (ICSs) can reduce inflammation, control symptoms, and improve lung function; however, a growing number of patients with severe asthma do not benefit from ICS. Using bronchial airway epithelial brushings from patients with severe asthma or primary human cells, we delineated a corticosteroid-driven fibroblast growth factor (FGF)-dependent inflammatory axis, with FGF-responsive fibroblasts promoting downstream granulocyte colony-stimulating factor (G-CSF) production, hyaluronan secretion, and neutrophilic inflammation. Allergen challenge studies in mice demonstrate that the ICS, fluticasone propionate, inhibited type 2-driven eosinophilia but induced a concomitant increase in FGFs, G-CSF, hyaluronan, and neutrophil infiltration. We developed a model of steroid-induced neutrophilic inflammation mediated, in part, by induction of an FGF-dependent epithelial-mesenchymal axis, which may explain why some individuals do not benefit from ICS. In further proof-of-concept experiments, we found that combination therapy with pan-FGF receptor inhibitors and corticosteroids prevented both eosinophilic and steroid-induced neutrophilic inflammation. Together, these results establish FGFs as therapeutic targets for severe asthma patients who do not benefit from ICS.

Nonresolving inflammation redux

Nonresolving inflammation contributes to many diseases, including COVID-19 in its fatal and long forms. Our understanding of inflammation is rapidly evolving. Like the immune system of which it is a part, inflammation can now be seen as an interactive component of a homeostatic network with the endocrine and nervous systems. This review samples emerging insights regarding inflammatory memory, inflammatory aging, inflammatory cell death, inflammatory DNA, inflammation-regulating cells and metabolites, approaches to resolving or modulating inflammation, and inflammatory inequity.

A neutrophil/TGF-β axis limits the pathogenicity of allergen-specific CD4+ T cells

The intensity and longevity of inflammatory responses to inhaled allergens is determined largely by the balance between effector and regulatory immune responses, but the mechanisms that determine the relative magnitudes of these opposing forces remain poorly understood. We have found that the type of adjuvant used during allergic sensitization has a profound effect on both the nature and longevity of the pulmonary inflammation triggered by subsequent reexposure to that same provoking allergen. TLR ligand adjuvants and house dust extracts primed immune responses characterized by a mixed neutrophilic and eosinophilic inflammation that was suppressed by multiple daily allergen challenges. During TLR ligand–mediated allergic sensitization, mice displayed transient airway neutrophilia, which triggered the release of TGF-β into the airway. This neutrophil-dependent production of TGF-β during sensitization had a delayed, suppressive effect on eosinophilic responses to subsequent allergen challenge. Neutrophil depletion during sensitization did not affect numbers of Foxp3⁺ Tregs but increased proportions of Gata3⁺CD4⁺ T cells, which, upon their transfer to recipient mice, triggered stronger eosinophilic inflammation. Thus, a neutrophil/TGF-β axis acts during TLR-mediated allergic sensitization to fine-tune the phenotype of developing allergen-specific CD4⁺ T cells and limit their pathogenicity, suggesting a novel immunotherapeutic approach to control eosinophilia in asthma.

Pulmonary Eosinophils at the Center of the Allergic Space-Time Continuum

Eosinophils are typically a minority population of circulating granulocytes being released from the bone-marrow as terminally differentiated cells. Besides their function in the defense against parasites and in promoting allergic airway inflammation, regulatory functions have now been attributed to eosinophils in various organs. Although eosinophils are involved in the inflammatory response to allergens, it remains unclear whether they are drivers of the asthma pathology or merely recruited effector cells. Recent findings highlight the homeostatic and pro-resolving capacity of eosinophils and raise the question at what point in time their function is regulated. Similarly, eosinophils from different physical locations display phenotypic and functional diversity. However, it remains unclear whether eosinophil plasticity remains as they develop and travel from the bone marrow to the tissue, in homeostasis or during inflammation. In the tissue, eosinophils of different ages and origin along the inflammatory trajectory may exhibit functional diversity as circumstances change. Herein, we outline the inflammatory time line of allergic airway inflammation from acute, late, adaptive to chronic processes. We summarize the function of the eosinophils in regards to their resident localization and time of recruitment to the lung, in all stages of the inflammatory response. In all, we argue that immunological differences in eosinophils are a function of time and space as the allergic inflammatory response is initiated and resolved.

Our evolving view of neutrophils in defining the pathology of chronic lung disease

Neutrophils are critical components of the body's immune response to infection, being loaded with a potent arsenal of toxic mediators and displaying immense destructive capacity. Given the potential of neutrophils to impart extensive tissue damage, it is perhaps not surprising that when augmented these cells are also implicated in the pathology of inflammatory diseases. Prominent neutrophilic inflammation is a hallmark feature of patients with chronic lung diseases such as chronic obstructive pulmonary disease, severe asthma, bronchiectasis and cystic fibrosis, with their numbers frequently associating with worse prognosis. Accordingly, it is anticipated that neutrophils are central to the pathology of these diseases and represent an attractive therapeutic target. However, in many instances, evidence directly linking neutrophils to the pathology of disease has remained somewhat circumstantial and strategies that have looked to reduce neutrophilic inflammation in the clinic have proved largely disappointing. We have classically viewed neutrophils as somewhat crude, terminally differentiated, insular and homogeneous protagonists of pathology. However, it is now clear that this does not do the neutrophil justice, and we now recognize that these cells exhibit heterogeneity, a pronounced awareness of the localized environment and a remarkable capacity to interact with and modulate the behaviour of a multitude of cells, even exhibiting anti-inflammatory, pro-resolving and pro-repair functions. In this review, we discuss evidence for the role of neutrophils in chronic lung disease and how our evolving view of these cells may impact upon our perceived assessment of their contribution to disease pathology and efforts to target them therapeutically.

Ruxolitinib Ameliorates Airway Hyperresponsiveness and Lung Inflammation in a Corticosteroid-Resistant Murine Model of Severe Asthma

Asthma prevalence has increased considerably over the decades and it is now considered as one of the most common chronic disorders in the world. While the current anti-asthmatic therapies are effective for most asthma patients, there are 5-10% subjects whose disease is not controlled by such agents and they account for about 50% of the asthma-associated healthcare costs. Such patients develop severe asthma (SA), a condition characterized by a dominant Th1/Th17 cytokine response that is accompanied by Type 2 (T2)-low endotype. As JAK (Janus Kinase) signaling is very important for the activation of several cytokine pathways, we examined whether inhibition of JAKs might lessen the clinical and laboratory manifestations of SA. To that end, we employed a recently described murine model that recapitulates the complex immune response identified in the airways of human SA patients. To induce SA, mice were sensitized with house dust mite extract (HDME) and cyclic (c)-di-GMP and then subsequently challenged with HDME and a lower dose of c-di-GMP. In this model, treatment with the JAK inhibitor, Ruxolitinib, significantly ameliorated all the features of SA, including airway hyperresponsiveness and lung inflammation as well as total IgE antibody titers. Thus, these studies highlight JAKs as critical targets for mitigating the hyper-inflammation that occurs in SA and provide the framework for their incorporation into future clinical trials for patients that have severe or difficult-to manage asthma.

Characteristics of tissue-resident ILCs and their potential as therapeutic targets in mucosal and skin inflammatory diseases

Discovery of innate lymphoid cells (ILCs), which are non-T and non-B lymphocytes that have no antigen-specific receptors, changed the classical concept of the mechanism of allergy, which had been explained mainly as antigen-specific acquired immunity based on IgE and Th2 cells. The discovery led to dramatic improvement in our understanding of the mechanism of non-IgE-mediated allergic inflammation. Numerous studies conducted in the past decade have elucidated the characteristics of each ILC subset in various organs and tissues and their ontogeny. We now know that each ILC subset exhibits heterogeneity. Moreover, the functions and activating/suppressing factors of each ILC subset were found to differ among both organs and types of tissue. Therefore, in this review, we summarize our current knowledge of ILCs by focusing on the organ/tissue-specific features of each subset to understand their roles in various organs. We also discuss ILCs' involvement in human inflammatory diseases in various organs and potential therapeutic/preventive strategies that target ILCs.

The Role of Innate Lymphoid Cells in Chronic Respiratory Diseases

The lung is a vital mucosal organ that is constantly exposed to the external environment, and as such, its defenses are continuously under threat. The pulmonary immune system has evolved to sense and respond to these danger signals while remaining silent to innocuous aeroantigens. The origin of the defense system is the respiratory epithelium, which responds rapidly to insults by the production of an array of mediators that initiate protection by directly killing microbes, activating tissue-resident immune cells and recruiting leukocytes from the blood. At the steady-state, the lung comprises a large collection of leukocytes, amongst which are specialized cells of lymphoid origin known as innate lymphoid cells (ILCs). ILCs are divided into three major helper-like subsets, ILC1, ILC2 and ILC3, which are considered the innate counterparts of type 1, 2 and 17 T helper cells, respectively, in addition to natural killer cells and lymphoid tissue inducer cells. Although ILCs represent a small fraction of the pulmonary immune system, they play an important role in early responses to pathogens and facilitate the acquisition of adaptive immunity. However, it is now also emerging that these cells are active participants in the development of chronic lung diseases. In this mini-review, we provide an update on our current understanding of the role of ILCs and their regulation in the lung. We summarise how these cells and their mediators initiate, sustain and potentially control pulmonary inflammation, and their contribution to the respiratory diseases chronic obstructive pulmonary disease (COPD) and asthma.

Neonatal LPS Administered Before Sensitization Reduced the Number of Inflammatory Monocytes and Abrogated the Development of OVA-Induced Th2 Allergic Airway Inflammation

It is becoming increasingly clear that environment factors during early life play a pivotal role in the development of allergic asthma. Among these, a traditional farm is one of the strongest protective environments, and the protective effects have been, at least in part, attributed to the high-level exposure to lipopolysaccharide (LPS) on farms. However, the underlying mechanisms remain elusive, especially in ovalbumin (OVA)-induced neonatal allergic asthma model. Here, we used the OVA-induced asthma model in two age groups, neonatal and adult, when mice were first sensitized with peritoneal OVA/alum as neonates and adults, respectively. LPS was injected in the peritoneal cavity before OVA/alum sensitization. The effects of LPS treatment on allergic airway inflammation in the lung and the immune milieu in the peritoneal cavity were determined and compared between these two age groups. We found that LPS treatment abrogated the development of Th2 allergic airway responses in the neonatal group. In the adult group, the ameliorated Th2 allergic responses were accompanied with Th17 responses and neutrophil infiltration upon LPS treatment. We further investigated the immune milieu in the peritoneal cavity to elucidate the underlying mechanisms of this age-dependent difference. Our data show that in neonatal mice, LPS treatment significantly reduced the number of inflammatory monocytes in the peritoneal cavity. In the adult group, LPS treatment shifted the function of these cells which associated with Th1 and Th17 polarization. Our results provide more evidence that immunity in early life is distinct from that in adults, especially in the peritoneal cavity, and emphasize the importance of timing for the intervention of allergic asthma. Our results suggest that LPS treatment during early life is protective for the development of Th2 allergic responses. On the other hand, it might lead to a more severe phenotype of asthma when dampening the Th2 responses in adult mice.

Neutrophils Affect IL-33 Processing in Response to the Respiratory Allergen Alternaria alternata

Future precision medicine requires further clarifying the mechanisms of inflammation in the severe endotypes of chronic airway diseases such as asthma and chronic rhinosinusitis (CRS). The presence of neutrophils in the airways is often associated with severe airway inflammation, while their precise contribution to the severe inflammation is largely unknown. We aimed to study the role of neutrophils in BALB/c and C57BL/6 mice exposed to Alternaria alternata (Alt). The mice were exposed to Alt extract for twelve hours or ten days to induce allergic airway inflammation. C57BL/6 mice exposed to Alt responded with eosinophilic infiltration and the characteristic IL-5 upregulation. In contrast, the inflammatory response to Alt extract in BALB/c mice was characterized by a neutrophilic response, high levels of G-CSF, and elastase in the lungs. The lack of neutrophils affected the processing of IL-33 in BALB/c mice, as was demonstrated by depletion of neutrophils through intraperitoneal injections of anti-Ly6G antibody. Our data identifies the key role of neutrophils in airway inflammation through IL-33 cleavage in the Alt-induced airway inflammation in mice, which could potentially underline the different endotypes in human disease.

G-CSFR antagonism reduces mucosal injury and airways fibrosis in a virus-dependent model of severe asthma

BACKGROUND AND PURPOSE

Asthma is a chronic disease that displays heterogeneous clinical and molecular features. A phenotypic subset of late-onset severe asthmatics has debilitating fixed airflow obstruction, increased neutrophilic inflammation and a history of pneumonia. Influenza A virus (IAV) is an important viral cause of pneumonia and asthmatics are frequently hospitalised during IAV epidemics. This study aims to determine whether antagonising granulocyte colony stimulating factor receptor (G-CSFR) prevents pneumonia-associated severe asthma.

EXPERIMENTAL APPROACH

Mice were sensitised to house dust mite (HDM) to establish allergic airway inflammation and subsequently infected with IAV (HKx31/H3N2 subtype). A neutralising monoclonal antibody against G-CSFR was therapeutically administered.

KEY RESULTS

In IAV-infected mice with prior HDM sensitisation, a significant increase in airway fibrotic remodelling and airways hyper-reactivity was observed. A mixed granulocytic inflammatory profile consisting of neutrophils, macrophages and eosinophils was prominent and at a molecular level, G-CSF expression was significantly increased in HDMIAV-treated mice. Blockage of G-CSFR reduced neutrophilic inflammation in the bronchoalveolar and lungs by over 80% in HDMIAV-treated mice without altering viral clearance. Markers of NETosis (dsDNA and myeloperoxidase in bronchoalveolar), tissue injury (LDH activity in bronchoalveolar) and oedema (total bronchoalveolar-fluid protein) were also significantly reduced with anti-G-CSFR treatment. In addition, anti-G-CSFR antagonism significantly reduced bronchoalveolar gelatinase activity, active TFGβ lung levels, collagen lung expression, airways fibrosis and airways hyper-reactivity in HDMIAV-treated mice.

CONCLUSIONS AND IMPLICATIONS

We have shown that antagonising G-CSFR-dependent neutrophilic inflammation reduced pathological disruption of the mucosal barrier and airways fibrosis in an IAV-induced severe asthma model.

Protection against neonatal respiratory viral infection via maternal treatment during pregnancy with the benign immune training agent OM-85

Objectives

Incomplete maturation of immune regulatory functions at birth is antecedent to the heightened risk for severe respiratory infections during infancy. Our forerunner animal model studies demonstrated that maternal treatment with the microbial‐derived immune training agent OM‐85 during pregnancy promotes accelerated postnatal maturation of mechanisms that regulate inflammatory processes in the offspring airways. Here, we aimed to provide proof of concept for a novel solution to reduce the burden and potential long‐term sequelae of severe early‐life respiratory viral infection through maternal oral treatment during pregnancy with OM‐85, already in widespread human clinical use.

Methods

In this study, we performed flow cytometry and targeted gene expression (RT‐qPCR) analysis on lungs from neonatal offspring whose mothers received oral OM‐85 treatment during pregnancy. We next determined whether neonatal offspring from OM‐85 treated mothers demonstrate enhanced protection against lethal lower respiratory infection with mouse‐adapted rhinovirus (vMC₀), and associated lung immune changes.

Results

Offspring from mothers treated with OM‐85 during pregnancy display accelerated postnatal seeding of lung myeloid populations demonstrating upregulation of function‐associated markers. Offspring from OM‐85 mothers additionally exhibit enhanced expression of TLR4/7 and the IL‐1β/NLRP3 inflammasome complex within the lung. These treatment effects were associated with enhanced capacity to clear an otherwise lethal respiratory viral infection during the neonatal period, with concomitant regulation of viral‐induced IFN response intensity.

Conclusion

These results demonstrate that maternal OM‐85 treatment protects offspring against lethal neonatal respiratory viral infection by accelerating development of innate immune mechanisms crucial for maintenance of local immune homeostasis in the face of pathogen challenge.

IL-33/ST2 axis deficiency exacerbates neutrophil-dominant allergic airway inflammation

Objective

The IL‐33/ST2 axis has been extensively investigated in type 2 eosinophilic inflammation. Here, we aimed to investigate the role of the IL‐33/ST2 axis in neutrophil‐dominant allergic airway inflammation.

Methods

House‐dust mite (HDM) extract and lipopolysaccharide (LPS) were administered to establish a murine model of neutrophil‐dominant allergic airway inflammation. The formation of neutrophilic extracellular traps (NETs) in the lung tissues was demonstrated by immunofluorescence imaging. Mature IL‐33 in bronchoalveolar lavage fluid (BALF) was detected by Western blotting. The neutrophilic chemokine KC produced by bone marrow‐derived macrophages (BMDMs) or primary alveolar epithelial cells was measured with a commercial ELISA kit.

Results

In the present study, we observed neutrophilic inflammation and tight junction damage in the lungs of mice sensitised with HDM and LPS. Furthermore, sensitisation with HDM and LPS resulted in the formation of NETs, accompanied by increased levels of mature IL‐33 in the BALF. Moreover, LPS damaged the epithelial tight junction protein occludin directly or indirectly by inducing NET formation. Surprisingly, IL‐33 deficiency augmented neutrophilia and epithelial barrier injury in the lungs of mice after sensitisation with HDM and LPS. Similarly, the absence of ST2 exacerbated the neutrophilic inflammatory response, decreased the expression of occludin and exacerbated the severity of neutrophil‐dominant allergic airway inflammation in an HDM/LPS‐induced mouse model. Mechanistically, BMDMs and alveolar epithelial cells from IL‐33‐ or ST2‐deficient mice tended to produce higher levels of the neutrophilic chemokine KC.

Conclusions

These results demonstrated that the IL‐33/ST2 axis may play a protective role in neutrophil‐dominant allergic airway inflammation.

Roles of innate lymphoid cells (ILCs) in allergic diseases: The 10-year anniversary for ILC2s

In the 12 years since the discovery of innate lymphoid cells (ILCs), our knowledge of their immunobiology has expanded rapidly. Group 2 ILCs (ILC2s) respond rapidly to allergen exposure and environmental insults in mucosal organs, producing type 2 cytokines. Early studies showed that epithelium-derived cytokines activate ILC2s, resulting in eosinophilia, mucus hypersecretion, and remodeling of mucosal tissues. We now know that ILC2s are regulated by other cytokines, eicosanoids, and neuropeptides as well, and interact with both immune and stromal cells. Furthermore, ILC2s exhibit plasticity by adjusting their functions depending on their tissue environment and may consist of several heterogeneous subpopulations. Clinical studies show that ILC2s are involved in asthma, allergic rhinitis, chronic rhinosinusitis, food allergy, and eosinophilic esophagitis. However, much remains unknown about the immunologic mechanisms involved. Beneficial functions of ILCs in maintenance or restoration of tissue well-being and human health also need to be clarified. As our understanding of the crucial functions ILCs play in both homeostasis and disease pathology expands, we are poised to make tremendous strides in diagnostic and therapeutic options for patients with allergic diseases. This review summarizes discoveries in immunobiology of ILCs and their roles in allergic diseases in the past 5 years, discusses controversies and gaps in our knowledge, and suggests future research directions.

Group 2 Innate Lymphoid Cells: Team Players in Regulating Asthma

Type 2 immunity helps protect the host from infection, but it also plays key roles in tissue homeostasis, metabolism, and repair. Unfortunately, inappropriate type 2 immune reactions may lead to allergy and asthma. Group 2 innate lymphoid cells (ILC2s) in the lungs respond rapidly to local environmental cues, such as the release of epithelium-derived type 2 initiator cytokines/alarmins, producing type 2 effector cytokines such as IL-4, IL-5, and IL-13 in response to tissue damage and infection. ILC2s are associated with the severity of allergic asthma, and experimental models of lung inflammation have shown how they act as playmakers, receiving signals variously from stromal and immune cells as well as the nervous system and then distributing cytokine cues to elicit type 2 immune effector functions and potentiate CD4⁺ T helper cell activation, both of which characterize the pathology of allergic asthma. Recent breakthroughs identifying stromal- and neuronal-derived microenvironmental cues that regulate ILC2s, along with studies recognizing the potential plasticity of ILC2s, have improved our understanding of the immunoregulation of asthma and opened new avenues for drug discovery.

Single-cell characterization of a model of poly I:C-stimulated peripheral blood mononuclear cells in severe asthma

Background

Asthma has been associated with impaired interferon response. Multiple cell types have been implicated in such response impairment and may be responsible for asthma immunopathology. However, existing models to study the immune response in asthma are limited by bulk profiling of cells. Our objective was to Characterize a model of peripheral blood mononuclear cells (PBMCs) of patients with severe asthma (SA) and its response to the TLR3 agonist Poly I:C using two single-cell methods.

Methods

Two complementary single-cell methods, DropSeq for single-cell RNA sequencing (scRNA-Seq) and mass cytometry (CyTOF), were used to profile PBMCs of SA patients and healthy controls (HC). Poly I:C-stimulated and unstimulated cells were analyzed in this study.

Results

PBMCs (n = 9414) from five SA (n = 6099) and three HC (n = 3315) were profiled using scRNA-Seq. Six main cell subsets, namely CD4 + T cells, CD8 + T cells, natural killer (NK) cells, B cells, dendritic cells (DCs), and monocytes, were identified. CD4 + T cells were the main cell type in SA and demonstrated a pro-inflammatory profile characterized by increased JAK1 expression. Following Poly I:C stimulation, PBMCs from SA had a robust induction of interferon pathways compared with HC. CyTOF profiling of Poly I:C stimulated and unstimulated PBMCs (n = 160,000) from the same individuals (SA = 5; HC = 3) demonstrated higher CD8 + and CD8 + effector T cells in SA at baseline, followed by a decrease of CD8 + effector T cells after poly I:C stimulation.

Conclusions

Single-cell profiling of an in vitro model using PBMCs in patients with SA identified activation of pro-inflammatory pathways at baseline and strong response to Poly I:C, as well as quantitative changes in CD8 + effector cells. Thus, transcriptomic and cell quantitative changes are associated with immune cell heterogeneity in this model to evaluate interferon responses in severe asthma.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-021-01709-9.

The Outcome of Neutrophil-T Cell Contact Differs Depending on Activation Status of Both Cell Types

Neutrophils and T cells exist in close proximity in lymph nodes and inflamed tissues during health and disease. They are able to form stable interactions, with profound effects on the phenotype and function of the T cells. However, the outcome of these effects are frequently contradictory; in some systems neutrophils suppress T cell proliferation, in others they are activatory or present antigen directly. Published protocols modelling these interactions in vitro do not reflect the full range of interactions found in vivo; they do not examine how activated and naïve T cells differentially respond to neutrophils, or whether de-granulating or resting neutrophils induce different outcomes. Here, we established a culture protocol to ask these questions with human T cells and autologous neutrophils. We find that resting neutrophils suppress T cell proliferation, activation and cytokine production but that de-granulating neutrophils do not, and neutrophil-released intracellular contents enhance proliferation. Strikingly, we also demonstrate that T cells early in the activation process are susceptible to suppression by neutrophils, while later-stage T cells are not, and naïve T cells do not respond at all. Our protocol therefore allows nuanced analysis of the outcome of interaction of these cells and may explain the contradictory results observed previously.

Neutrophils in asthma: the good, the bad and the bacteria

Airway inflammation plays a key role in asthma pathogenesis but is heterogeneous in nature. There has been significant scientific discovery with regard to type 2-driven, eosinophil-dominated asthma, with effective therapies ranging from inhaled corticosteroids to novel biologics. However, studies suggest that approximately 1 in 5 adults with asthma have an increased proportion of neutrophils in their airways. These patients tend to be older, have potentially pathogenic airway bacteria and do not respond well to classical therapies. Currently, there are no specific therapeutic options for these patients, such as neutrophil-targeting biologics.Neutrophils comprise 70% of the total circulatory white cells and play a critical defence role during inflammatory and infective challenges. This makes them a problematic target for therapeutics. Furthermore, neutrophil functions change with age, with reduced microbial killing, increased reactive oxygen species release and reduced production of extracellular traps with advancing age. Therefore, different therapeutic strategies may be required for different age groups of patients.The pathogenesis of neutrophil-dominated airway inflammation in adults with asthma may reflect a counterproductive response to the defective neutrophil microbial killing seen with age, resulting in bystander damage to host airway cells and subsequent mucus hypersecretion and airway remodelling. However, in children with asthma, neutrophils are less associated with adverse features of disease, and it is possible that in children, neutrophils are less pathogenic.In this review, we explore the mechanisms of neutrophil recruitment, changes in cellular function across the life course and the implications this may have for asthma management now and in the future. We also describe the prevalence of neutrophilic asthma globally, with a focus on First Nations people of Australia, New Zealand and North America.

The neutrophil antimicrobial peptide cathelicidin promotes Th17 differentiation

The host defence peptide cathelicidin (LL-37 in humans, mCRAMP in mice) is released from neutrophils by de-granulation, NETosis and necrotic death; it has potent anti-pathogen activity as well as being a broad immunomodulator. Here we report that cathelicidin is a powerful Th17 potentiator which enhances aryl hydrocarbon receptor (AHR) and RORγt expression, in a TGF-β1-dependent manner. In the presence of TGF-β1, cathelicidin enhanced SMAD2/3 and STAT3 phosphorylation, and profoundly suppressed IL-2 and T-bet, directing T cells away from Th1 and into a Th17 phenotype. Strikingly, Th17, but not Th1, cells were protected from apoptosis by cathelicidin. We show that cathelicidin is released by neutrophils in mouse lymph nodes and that cathelicidin-deficient mice display suppressed Th17 responses during inflammation, but not at steady state. We propose that the neutrophil cathelicidin is required for maximal Th17 differentiation, and that this is one method by which early neutrophilia directs subsequent adaptive immune responses.

C3 Drives Inflammatory Skin Carcinogenesis Independently of C5

Nonmelanoma skin cancer such as cutaneous squamous cell carcinoma (cSCC) is the most common form of cancer and can occur as a consequence of DNA damage to the epithelium by UVR or chemical carcinogens. There is growing evidence that the complement system is involved in cancer immune surveillance; however, its role in cSCC remains unclear. Here, we show that complement genes are expressed in tissue from patients with cSCC, and C3 activation fragments are present in cSCC biopsies, indicating complement activation. Using a range of complement-deficient mice in a two-stage mouse model of chemically-induced cSCC, where a subclinical dose of 7,12-dimethylbenz[a]anthracene causes oncogenic mutations in epithelial cells and 12-O-tetradecanoylphorbol-13-acetate promotes the outgrowth of these cells, we found that C3-deficient mice displayed a significantly reduced tumor burden, whereas an opposite phenotype was observed in mice lacking C5aR1, C5aR2, and C3a receptor. In addition, in mice unable to form the membrane attack complex, the tumor progression was unaltered. C3 deficiency did not affect the cancer response to 7,12-dimethylbenz[a]anthracene treatment alone but reduced the epidermal hyperplasia during 12-O-tetradecanoylphorbol-13-acetate-induced inflammation. Collectively, these data indicate that C3 drives tumorigenesis during chronic skin inflammation, independently of the downstream generation of C5a or membrane attack complex.

The Role of Heat Shock Protein 70 kDa in Asthma

Asthma is a complex chronic disorder of the airways, affecting immune and structural cells and inducing both protein and tissue remodeling. Heat shock proteins 70 kDa (HSP70s) are highly conserved members of the stress-induced family, possessing precisely described chaperone activity. There is growing evidence of a tight relationship between inflammatory diseases of different origins and the elevation of local HSP70 expression and secretion. Although extracellular HSP70 does not serve as a common marker of asthma, elevated HSP70 levels have been detected in the peripheral blood serum and sputum of patients with asthma, as well as in the bronchoalveolar lavage fluid of mice with induced allergic airway inflammation. Possessing diverse immunomodulating properties, extracellular HSP70 can manifest different activities in airway inflammatory processes and asthma, acting either as a pro-inflammatory trigger, or an anti-inflammatory agent. This review will discuss the effects and possible mechanisms concerning HSP70 implication in airway inflammation regulation in asthma. We examine ATPase and chaperone activities of HSP70 as potential modulators of immune responses in asthma. Given the crucial role of a chronic inflammatory response in asthma, understanding the effects of HSP70 on immune and structural cells may reveal new perspectives for the therapeutic control of inflammation.

Innate lymphoid cell composition associates with COVID-19 disease severity

OBJECTIVES

The role of innate lymphoid cells (ILCs) in coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is unknown. Understanding the immune response in COVID-19 could contribute to unravel the pathogenesis and identification of treatment targets. Here, we describe the phenotypic landscape of circulating ILCs in COVID-19 patients and identified ILC phenotypes correlated to serum biomarkers, clinical markers and laboratory parameters relevant in COVID-19.

METHODS

Blood samples collected from moderately (n = 11) and severely ill (n = 12) COVID-19 patients, as well as healthy control donors (n = 16), were analysed with 18-parameter flow cytometry. Using supervised and unsupervised approaches, we examined the ILC activation status and homing profile. Clinical and laboratory parameters were obtained from all COVID-19 patients, and serum biomarkers were analysed with multiplex immunoassays.

RESULTS

Innate lymphoid cells were largely depleted from the circulation of COVID-19 patients compared with healthy controls. Remaining circulating ILCs revealed decreased frequencies of ILC2 in severe COVID-19, with a concomitant decrease of ILC precursors (ILCp) in all patients, compared with controls. ILC2 and ILCp showed an activated phenotype with increased CD69 expression, whereas expression levels of the chemokine receptors CXCR3 and CCR4 were significantly altered in ILC2 and ILCp, and ILC1, respectively. The activated ILC profile of COVID-19 patients was associated with soluble inflammatory markers, while frequencies of ILC subsets were correlated with laboratory parameters that reflect the disease severity.

CONCLUSION

This study provides insights into the potential role of ILCs in immune responses against SARS-CoV-2, particularly linked to the severity of COVID-19.

Novel Therapies for Pneumonia-Associated Severe Asthma Phenotypes

Distinct asthma phenotypes are emerging from well-defined cohort studies and appear to be associated with a history of pneumonia. Asthmatics are more susceptible to infections caused by Streptococcus pneumoniae; however, the mechanisms that underlie defective immunity to this pathogen are still being elucidated. Here, we discuss how alternatively activated macrophages (AAMs) in asthmatics are defective in bacterial phagocytosis and how respiratory viruses disrupt essential host immunity to cause bacterial dispersion deeper into the lungs. We also describe how respiratory pathogens instigate neutrophilic inflammation and amplify type-2 inflammation in asthmatics. Finally, we propose novel dual-acting strategies including granulocyte-colony-stimulating factor receptor (G-CSFR) antagonism and specialised pro-resolving mediators (SPMs) to suppress type-2 and neutrophilic inflammation without compromising pathogen clearance.

Role of myeloid cells in the regulation of group 2 innate lymphoid cell-mediated allergic inflammation

Group 2 innate lymphoid cells (ILC2s) are an important component of the innate immune system that execute important effector functions at barrier surfaces, such as lung and skin. Like T helper type 2 cells, ILC2s are able to release high amounts of type 2 cytokines that are essential in inducing allergic inflammation and eliminating helminth infections. The past few years have contributed to our better understanding of the interactions between ILC2s and other cells of the immune system via soluble factors or in a cell-cell contact manner. Myeloid cells, including mononuclear leukocytes and polymorphonuclear leukocytes, are excellent sensors of tissue damage and infection and can influence ILC2 responses in the process of allergic inflammation. In this review, we summarize recent insights on how myeloid cell subsets regulate ILC2 activation with focus on soluble factors in the context of allergic inflammation.

Effect of the CXCR4 antagonist plerixafor on endogenous neutrophil dynamics in the bone marrow, lung and spleen

Treatment with the CXCR4 antagonist, plerixafor (AMD3100), has been proposed for clinical use in patients with WHIM (warts, hypogammaglobulinemia, infections, and myelokathexis) syndrome and in pulmonary fibrosis. However, there is controversy with respect to the impact of plerixafor on neutrophil dynamics in the lung, which may affect its safety profile. In this study, we investigated the kinetics of endogenous neutrophils by direct imaging, using confocal intravital microscopy in mouse bone marrow, spleen, and lungs. Neutrophils are observed increasing their velocity and exiting the bone marrow following plerixafor administration, with a concomitant increase in neutrophil numbers in the blood and spleen, while the marginated pool of neutrophils in the lung microvasculature remained unchanged in terms of numbers and cell velocity. Use of autologous radiolabeled neutrophils and SPECT/CT imaging in healthy volunteers showed that plerixafor did not affect GM-CSF-primed neutrophil entrapment or release in the lungs. Taken together, these data suggest that plerixafor causes neutrophil mobilization from the bone marrow but does not impact on lung marginated neutrophil dynamics and thus is unlikely to compromise respiratory host defense both in humans and mice.

IL-23 in arthritic and inflammatory pain development in mice

Background

The cytokine, interleukin-23 (IL-23), can be critical for the progression of inflammatory diseases, including arthritis, and is often associated with T lymphocyte biology. We previously showed that certain lymphocyte-independent, inflammatory arthritis and pain models have a similar requirement for tumour necrosis factor (TNF), granulocyte macrophage-colony stimulating factor (GM-CSF), and C-C motif ligand 17 (CCL17). Given this correlation in cytokine requirements, we explored whether IL-23 might interact with this cytokine cluster in the control of arthritic and inflammatory pain.

Methods

The role of IL-23 in the development of pain-like behaviour was investigated using mouse arthritis models (zymosan-induced arthritis and GM-CSF-, TNF-, and CCL17-driven monoarticular arthritis) and inflammatory pain models (intraplantar zymosan, GM-CSF, TNF, and CCL17). Additionally, IL-23-induced inflammatory pain was measured in GM-CSF^−/−, Tnf^−/−, and Ccl17^E/E mice and in the presence of indomethacin. Pain-like behaviour and arthritis were assessed by relative weight distribution in hindlimbs and histology, respectively. Cytokine mRNA expression in knees and paw skin was analysed by quantitative PCR. Blood and synovial cell populations were analysed by flow cytometry.

Results

We report, using Il23p19^−/− mice, that innate immune (zymosan)-driven arthritic pain-like behaviour (herein referred to as pain) was completely dependent upon IL-23; optimal arthritic disease development required IL-23 (P < 0.05). Zymosan-induced inflammatory pain was also completely dependent on IL-23. In addition, we found that exogenous TNF-, GM-CSF-, and CCL17-driven arthritic pain, as well as inflammatory pain driven by each of these cytokines, were absent in Il23p19^−/− mice; optimal disease in these mBSA-primed models was dependent on IL-23 (P < 0.05). Supporting this cytokine connection, it was found conversely that IL-23 (200 ng) can induce inflammatory pain at 4 h (P < 0.0001) with a requirement for each of the other cytokines as well as cyclooxygenase activity.

Conclusions

These findings indicate a role for IL-23 in innate immune-mediated arthritic and inflammatory pain with potential links to TNF, GM-CSF, CCL17, and eicosanoid function.

Neutrophils do not impact viral load or the peak of disease severity during RSV infection

Lung and airway neutrophils are a hallmark of severe disease in infants with respiratory syncytial virus (RSV)-induced lower respiratory tract infections. Despite their abundance in the lungs during RSV infection of both mice and man, the role of neutrophils in viral control and in immune pathology is not clear. Here, antibody mediated neutrophil depletion was used to investigate the degree to which neutrophils impact the lung immune environment, the control of viral replication and the peak severity of disease after RSV infection of mice. Neutrophil depletion did not substantially affect the levels of inflammatory mediators such as type I interferons, IL-6, TNF-α or IL-1β in response to RSV. In addition, the lack of neutrophils did not change the viral load during RSV infection. Neither neutrophil depletion nor the enhancement of lung neutrophils by administration of the chemoattractant CXCL1 during RSV infection affected disease severity as measured by weight loss. Therefore, in this model of RSV infection, lung neutrophils do not offer obvious benefits to the host in terms of increasing anti-viral inflammatory responses or restricting viral replication and neutrophils do not contribute to disease severity.