Neutrophils Induce a Novel Chemokine Receptors Repertoire During Influenza Pneumonia

Blockade of the CCR3 receptor reduces neutrophil recruitment to the lung during acute inflammation

Neutrophils represent one of the host's first lines of defense against invading pathogens. However, an aberrant activation can cause damage to the host. In the case of respiratory infections with viral or bacterial pathogens, one of the most common complications is the development of acute respiratory distress syndrome, in which neutrophil infiltration into the lung is a hallmark. Neutrophils gain expression of chemokine receptors under inflammatory conditions, and their activation can amplify the neutrophil responses. Earlier studies showed that neutrophils recruited to the lung mucosa during bacterial infection upregulate expression of CCR3 and ex vivo stimulation of CCR3 results in an increased neutrophil activation. Therefore, the modulation of effector functions or migration of neutrophils to target sites through chemokine receptors constitutes an opportunity for pharmacological intervention. We aimed to determine whether the blockade of the CCR3 using the specific antagonist SB-328437 reduces neutrophil recruitment and inflammation in the lung in the lipopolysaccharide (LPS)-induced lung injury model and influenza infection in mice. We found that neutrophils acquire CCR3 expression in the lung alveolar space. The intraperitoneal administration of SB-328437 reduced neutrophil recruitment to the lung alveolar space and reduced tissue damage in both the LPS-induced lung injury model and influenza infection. Moreover, treatment with SB-328437 reduced the percentage of neutrophils producing TNFα and neutrophil activation in the alveolar space. Together, these data suggest that CCR3 blockade might be a pharmacological strategy to prevent the aberrant neutrophil activation that results detrimental for the host but preserves sufficient effector response to control the pathogen.

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.

Characterization of Neutrophil Functional Responses to SARS-CoV-2 Infection in a Translational Feline Model for COVID-19

There is a complex interplay between viral infection and host innate immune response regarding disease severity and outcomes. Neutrophil hyperactivation, including excessive release of neutrophil extracellular traps (NETs), is linked to exacerbated disease in acute COVID-19, notably in hospitalized patients. Delineating protective versus detrimental neutrophil responses is essential to developing targeted COVID-19 therapies and relies on high-quality translational animal models. In this study, we utilize a previously established feline model for COVID-19 to investigate neutrophil dysfunction in which experimentally infected cats develop clinical disease that mimics acute COVID-19. Specific pathogen-free cats were inoculated with SARS-CoV-2 (B.1.617.2; Delta variant) (n = 24) or vehicle (n = 6). Plasma, bronchoalveolar lavage fluid, and lung tissues were collected at various time points over 12 days post-inoculation. Systematic and temporal evaluation of the kinetics of neutrophil activation was conducted by measuring markers of activation including myeloperoxidase (MPO), neutrophil elastase (NE), and citrullinated histone H3 (citH3) in SARS-CoV-2-infected cats at 4 and 12 days post-inoculation (dpi) and compared to vehicle-inoculated controls. Cytokine profiling supported elevated innate inflammatory responses with specific upregulation of neutrophil activation and NET formation-related markers, namely IL-8, IL-18, CXCL1, and SDF-1, in infected cats. An increase in MPO-DNA complexes and cell-free dsDNA in infected cats compared to vehicle-inoculated was noted and supported by histopathologic severity in respiratory tissues. Immunofluorescence analyses further supported correlation of NET markers with tissue damage, especially 4 dpi. Differential gene expression analyses indicated an upregulation of genes associated with innate immune and neutrophil activation pathways. Transcripts involved in activation and NETosis pathways were upregulated by 4 dpi and downregulated by 12 dpi, suggesting peak activation of neutrophils and NET-associated markers in the early acute stages of infection. Correlation analyses conducted between NET-specific markers and clinical scores as well as histopathologic scores support association between neutrophil activation and disease severity during SARS-CoV-2 infection in this model. Overall, this study emphasizes the effect of neutrophil activation and NET release in SARS-CoV-2 infection in a feline model, prompting further investigation into therapeutic strategies aimed at mitigating excessive innate inflammatory responses in COVID-19.

CCL28 modulates neutrophil responses during infection with mucosal pathogens

The chemokine CCL28 is highly expressed in mucosal tissues, but its role during infection is not well understood. Here, we show that CCL28 promotes neutrophil accumulation in the gut of mice infected with Salmonella and in the lung of mice infected with Acinetobacter. Neutrophils isolated from the infected mucosa expressed the CCL28 receptors CCR3 and, to a lesser extent, CCR10, on their surface. The functional consequences of CCL28 deficiency varied between the two infections: Ccl28-/- mice were highly susceptible to Salmonella gut infection but highly resistant to otherwise lethal Acinetobacter lung infection. In vitro, unstimulated neutrophils harbored pre-formed intracellular CCR3 that was rapidly mobilized to the cell surface following phagocytosis or inflammatory stimuli. Moreover, CCL28 stimulation enhanced neutrophil antimicrobial activity, production of reactive oxygen species, and formation of extracellular traps, all processes largely dependent on CCR3. Consistent with the different outcomes in the two infection models, neutrophil stimulation with CCL28 boosted the killing of Salmonella but not Acinetobacter. CCL28 thus plays a critical role in the immune response to mucosal pathogens by increasing neutrophil accumulation and activation, which can enhance pathogen clearance but also exacerbate disease depending on the mucosal site and the infectious agent.

Exploring the immune-inflammatory mechanism of Maxing Shigan Decoction in treating influenza virus A-induced pneumonia based on an integrated strategy of single-cell transcriptomics and systems biology

BACKGROUND

Influenza is an acute respiratory infection caused by influenza virus. Maxing Shigan Decoction (MXSGD) is a commonly used traditional Chinese medicine prescription for the prevention and treatment of influenza. However, its mechanism remains unclear.

METHOD

The mice model of influenza A virus pneumonia was established by nasal inoculation. After 3 days of intervention, the lung index was calculated, and the pathological changes of lung tissue were detected by HE staining. Firstly, transcriptomics technology was used to analyze the differential genes and important pathways in mouse lung tissue regulated by MXSGD. Then, real-time fluorescent quantitative PCR (RT-PCR) was used to verify the changes in mRNA expression in lung tissues. Finally, intestinal microbiome and intestinal metabolomics were performed to explore the effect of MXSGD on gut microbiota.

RESULTS

The lung inflammatory cell infiltration in the MXSGD group was significantly reduced (p < 0.05). The results of bioinformatics analysis for transcriptomics results show that these genes are mainly involved in inflammatory factors and inflammation-related signal pathways mediated inflammation biological modules, etc. Intestinal microbiome showed that the intestinal flora Actinobacteriota level and Desulfobacterota level increased in MXSGD group, while Planctomycetota in MXSGD group decreased. Metabolites were mainly involved in primary bile acid biosynthesis, thiamine metabolism, etc. This suggests that MXSGD has a microbial-gut-lung axis regulation effect on mice with influenza A virus pneumonia.

CONCLUSION

MXSGD may play an anti-inflammatory and immunoregulatory role by regulating intestinal microbiome and intestinal metabolic small molecules, and ultimately play a role in the treatment of influenza A virus pneumonia.

A Narrative Review: The Role of NETs in Acute Respiratory Distress Syndrome/Acute Lung Injury

Nowadays, acute respiratory distress syndrome (ARDS) still has a high mortality rate, and the alleviation and treatment of ARDS remains a major research focus. There are various causes of ARDS, among which pneumonia and non-pulmonary sepsis are the most common. Trauma and blood transfusion can also cause ARDS. In ARDS, the aggregation and infiltration of neutrophils in the lungs have a great influence on the development of the disease. Neutrophils regulate inflammatory responses through various pathways, and the release of neutrophils through neutrophil extracellular traps (NETs) is considered to be one of the most important mechanisms. NETs are mainly composed of DNA, histones, and granuloproteins, all of which can mediate downstream signaling pathways that can activate inflammatory responses, generate immune clots, and cause damage to surrounding tissues. At the same time, the components of NETs can also promote the formation and release of NETs, thus forming a vicious cycle that continuously aggravates the progression of the disease. NETs are also associated with cytokine storms and immune balance. Since DNA is the main component of NETs, DNase I is considered a viable drug for removing NETs. Other therapeutic methods to inhibit the formation of NETs are also worthy of further exploration. This review discusses the formation and mechanism of NETs in ARDS. Understanding the association between NETs and ARDS may help to develop new perspectives on the treatment of ARDS.

Machine-learning-algorithms-based diagnostic model for influenza A in children

BACKGROUND

At present, nucleic acid testing is the gold standard for diagnosing influenza A, however, this method is expensive, time-consuming, and unsuitable for promotion and use in grassroots hospitals. This study aimed to establish a diagnostic model that could accurately, quickly, and simply distinguish between influenza A and influenza like diseases.

METHODS

Patients with influenza-like symptoms were recruited between December 2019 and August 2023 at the Children's Hospital Affiliated to Shandong University and basic information, nasopharyngeal swab and blood routine test data were included. Computer algorithms including random forest, GBDT, XGBoost and logistic regression (LR) were used to create the diagnostic model, and their performance was evaluated using the validation data sets.

RESULTS

A total of 4188 children with influenza-like symptoms were enrolled, of which 1992 were nucleic acid test positive and 2196 were matched negative. The diagnostic models based on the random forest, GBDT, XGBoost and logistic regression algorithms had AUC values of 0.835,0.872,0.867 and 0.784, respectively. The top 5 important features were lymphocyte (LYM) count, age, serum amyloid A (SAA), white blood cells (WBC) count and platelet-to-lymphocyte ratio (PLR). GBDT model had the best performance, the sensitivity and specificity were 77.23% and 80.29%, respectively.

CONCLUSIONS

A computer algorithm diagnosis model of influenza A in children based on blood routine test data was established, which could identify children with influenza A more accurately in the early stage, and was easy to popularize.

Phillyrin ameliorates influenza a virus-induced pulmonary inflammation by antagonizing CXCR2 and inhibiting NLRP3 inflammasome activation

Influenza is an acute viral respiratory illness with high morbidity rates worldwide. Excessive pulmonary inflammation is the main characteristic of lethal influenza A virus (IAV) infections. Therapeutic options for managing influenza are limited to vaccines and some antiviral medications. Phillyrin is one of the major bioactive components of the Chinese herbal medicine Forsythia suspensa, which has the functions of sterilization, heat clearing and detoxification. In this work, the effect and mechanism of phillyrin on H1N1 influenza (PR8)-induced pneumonia were investigated. We reported that phillyrin (15 mg/kg) treatment after viral challenge significantly improved the weight loss, ameliorated pulmonary inflammation and inhibited the accumulation of multiple cytokines and chemokines in bronchoalveolar lavage fluid on 7 days post infection (dpi). In vitro, phillyrin suppressed influenza viral replication (Matrixprotein and nucleoprotein messenger RNA level) and reduced influenza virus-induced cytopathic effect (CPE). Furthermore,chemokine receptor CXCR2 was confirmed to be markedly inhibited by phillyrin. Surface plasmon resonance results reveal that phillyrin exhibits binding affinity to CXCR2, having a binding affinity constant (KD) value of 1.858e-5 M, suggesting that CXCR2 is a potential therapeutic target for phillyrin. Moreover, phillyrin inhibited the mRNA and protein expression levels of Caspase1, ASC and NLRP3 in the lungs of mice with H1N1-induced pneumonia.This study reveals that phillyrin ameliorates IAV-induced pulmonary inflammation by antagonizing CXCR2 and inhibiting NLRP3 inflammasome activation partly.

Prevention of severe lung immunopathology associated with influenza infection through adeno-associated virus vector administration

BACKGROUND

Influenza A viruses (IAVs) have long posed a threat to humans, occasionally causing significant morbidity and mortality. The initial immune response is triggered by infected epithelial cells, alveolar macrophages and dendritic cells. However, an exaggerated innate immune response can result in severe lung injury and even host mortality. One notable pathology observed in hosts succumbing to severe influenza is the excessive influx of neutrophils and monocytes into the lung. In this study, we investigated a strategy for controlling lung immunopathology following severe influenza infection.

RESULTS

To evaluate the impact of innate immunity on influenza-associated lung injury, we employed CB17.SCID and NOD.SCID mice. NOD.SCID mice exhibited slower weight loss and longer survival than CB17.SCID mice following influenza infection. Lung inflammation was reduced in NOD.SCID mice compared to CB17.SCID mice. Bulk RNA sequencing analysis of lung tissue showed significant downregulation of 827 genes, and differentially expressed gene analysis indicated that the cytokine-cytokine receptor interaction pathway was predominantly downregulated in NOD.SCID mice. Interestingly, the expression of the Cxcl14 gene was higher in the lungs of influenza-infected NOD.SCID mice than in CB17.SCID mice. Therefore, we induced overexpression of the Cxcl14 gene in the lung using the adeno-associated virus 9 (AAV9)-vector system for target gene delivery. However, when we administered the AAV9 vector carrying the Cxcl14 gene or a control AAV9 vector to BALB/c mice from both groups, the morbidity and mortality rates remained similar. Both groups exhibited lower morbidity and mortality than the naive group that did not receive the AAV9 vector prior to IAV infection, suggesting that the pre-administration of the AAV9 vector conferred protection against lethal influenza infection, irrespective of Cxcl14 overexpression. Furthermore, we found that pre-inoculation of BALB/c mice with AAV9 attenuated the infiltration of trans-macrophages, neutrophils and monocytes in the lungs following IAV infection. Although there was no difference in lung viral titers between the naive group and the AAV9 pre-inoculated group, pre-inoculation with AAV9 conferred lung injury protection against lethal influenza infection in mice.

CONCLUSIONS

Our study demonstrated that pre-inoculation with AAV9 prior to IAV infection protected mouse lungs from immunopathology by reducing the recruitment of inflammatory cells.

A spatial sequencing atlas of age-induced changes in the lung during influenza infection

Influenza virus infection causes increased morbidity and mortality in the elderly. Aging impairs the immune response to influenza, both intrinsically and because of altered interactions with endothelial and pulmonary epithelial cells. To characterize these changes, we performed single-cell RNA sequencing (scRNA-seq), spatial transcriptomics, and bulk RNA sequencing (bulk RNA-seq) on lung tissue from young and aged female mice at days 0, 3, and 9 post-influenza infection. Our analyses identified dozens of key genes differentially expressed in kinetic, age-dependent, and cell type-specific manners. Aged immune cells exhibited altered inflammatory, memory, and chemotactic profiles. Aged endothelial cells demonstrated characteristics of reduced vascular wound healing and a prothrombotic state. Spatial transcriptomics identified novel profibrotic and antifibrotic markers expressed by epithelial and non-epithelial cells, highlighting the complex networks that promote fibrosis in aged lungs. Bulk RNA-seq generated a timeline of global transcriptional activity, showing increased expression of genes involved in inflammation and coagulation in aged lungs. Our work provides an atlas of high-throughput sequencing methodologies that can be used to investigate age-related changes in the response to influenza virus, identify novel cell-cell interactions for further study, and ultimately uncover potential therapeutic targets to improve health outcomes in the elderly following influenza infection.

Association between CCR2 and CCL2 expression and NET stimulation in adult-onset Still's disease

Adult-onset Still's disease (AOSD) is a systemic inflammatory disease characterized by the activation of monocyte-derived cells and the release of neutrophil extracellular traps (NET). C-C motif ligand (CCL) 2 is a chemoattractant that interacts with the C-C motif chemokine receptor (CCR) 2, resulting in monocyte recruitment and activation. CCL2 and CCR2 were measured with enzyme-linked immunosorbent assay (ELISA) at the serum level, and using immunohistochemical staining at the skin and lymph node tissues levels. THP-1 cell lysates were analyzed using western blot and ELISA after NET stimulation in patients with AOSD. Serum CCL2 level was higher in patients with AOSD than in patients with rheumatoid arthritis and healthy controls (HCs). In patients with AOSD, the percentage of CCL2-positive inflammatory cells in the skin tissues and CCR2-positive inflammatory cells in the lymph nodes increased, compared to that in HCs and in patients with reactive lymphadenopathy, respectively. NET induced in patients with AOSD enhanced the secretion of CCR2, higher CCR2 expression in monocytes, and the levels of interleukin (IL)-1β, IL-6, and IL-18 from THP-1 cells. Our findings suggest that upregulation of the CCL2-CCR2 axis may contribute to the clinical and inflammatory characteristics of AOSD.

Characterization of Chemotaxis-Associated Gene Dysregulation in Myeloid Cell Populations in the Lungs during Lipopolysaccharide-Mediated Acute Lung Injury

During endotoxin-induced acute lung injury (ALI), immune cell recruitment resulting from chemotaxis is mediated by CXC and CC chemokines and their receptors. In this study, we investigated the role of chemokines and their receptors in the regulation of myeloid cell populations in the circulation and the lungs of C57BL/6J mice exhibiting LPS-mediated ALI using single-cell RNA sequencing. During ALI, there was an increase in the myeloid cells, M1 macrophages, monocytes, neutrophils, and other granulocytes, whereas there was a decrease in the residential alveolar macrophages and M2 macrophages. Interestingly, LPS triggered the upregulation of CCL3, CCL4, CXCL2/3, and CXCL10 genes associated with cellular migration of various subsets of macrophages, neutrophils, and granulocytes. Furthermore, there was an increase in the frequency of myeloid cells expressing CCR1, CCR3, CCR5, and CXCR2 receptors during ALI. MicroRNA sequencing studies of vehicle versus LPS groups identified several dysregulated microRNAs targeting the upregulated chemokine genes. This study suggests that chemokine ligand-receptors interactions are responsible for myeloid cell heterogenicity and cellular recruitment to the lungs during ALI. The single-cell transcriptomics allowed for an in-depth assessment and characterization of myeloid cells involved in immune cell trafficking during ALI.

Integrative profiling of gene expression and chromatin accessibility elucidates specific transcriptional networks in porcine neutrophils

Neutrophils are vital components of the immune system for limiting the invasion and proliferation of pathogens in the body. Surprisingly, the functional annotation of porcine neutrophils is still limited. The transcriptomic and epigenetic assessment of porcine neutrophils from healthy pigs was performed by bulk RNA sequencing and transposase accessible chromatin sequencing (ATAC-seq). First, we sequenced and compared the transcriptome of porcine neutrophils with eight other immune cell transcriptomes to identify a neutrophil-enriched gene list within a detected neutrophil co-expression module. Second, we used ATAC-seq analysis to report for the first time the genome-wide chromatin accessible regions of porcine neutrophils. A combined analysis using both transcriptomic and chromatin accessibility data further defined the neutrophil co-expression network controlled by transcription factors likely important for neutrophil lineage commitment and function. We identified chromatin accessible regions around promoters of neutrophil-specific genes that were predicted to be bound by neutrophil-specific transcription factors. Additionally, published DNA methylation data from porcine immune cells including neutrophils were used to link low DNA methylation patterns to accessible chromatin regions and genes with highly enriched expression in porcine neutrophils. In summary, our data provides the first integrative analysis of the accessible chromatin regions and transcriptional status of porcine neutrophils, contributing to the Functional Annotation of Animal Genomes (FAANG) project, and demonstrates the utility of chromatin accessible regions to identify and enrich our understanding of transcriptional networks in a cell type such as neutrophils.

Constraint-induced movement therapy alleviates motor impairment by inhibiting the accumulation of neutrophil extracellular traps in ischemic cortex

Stroke is a major cause of mortality and morbidity and most acute strokes are ischemic. Evidence-based medicine has demonstrated the effectiveness of constraint-induced movement therapy (CIMT) in the recovery of motor function in patients after ischemic stroke, but the specific treatment mechanism remains unclear. Herein, our integrated transcriptomics and multiple enrichment analysis studies, including Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and gene set enrichment analysis (GSEA) studies show that CIMT conduction broadly curtails immune response, neutrophil chemotaxis, and chemokine-mediated signaling pathway, CCR chemokine receptor binding. Those suggest the potential effect of CIMT on neutrophils in ischemic mice brain parenchyma. Recent studies have found that accumulating granulocytes release extracellular web-like structures composed of DNA and proteins called neutrophil extracellular traps (NETs), which destruct neurological function primarily by disrupting the blood-brain barrier and promoting thrombosis. However, the temporal and spatial distribution of neutrophils and their released NETs in parenchyma and their damaging effects on nerve cells remain unclear. Thus, utilizing immunofluorescence and flow cytometry, our analyses uncovered that NETs erode multiple regions such as primary motor cortex (M1), striatum (Str), nucleus of the vertical limb of the diagonal band (VDB), nucleus of the horizontal limb of the diagonal band (HDB) and medial septal nucleus (MS), and persist in the brain parenchyma for at least 14 days, while CIMT can reduce the content of NETs and chemokines CCL2 and CCL5 in M1. Intriguingly, CIMT failed to further reduce neurological deficits after inhibiting the NET formation by pharmacologic inhibition of peptidylarginine deiminase 4 (PAD4). Collectively, these results demonstrate that CIMT could alleviate cerebral ischemic injury induced locomotor deficits by modulating the activation of neutrophils. These data are expected to provide direct evidence for the expression of NETs in ischemic brain parenchyma and novel insights into the mechanisms of CIMT protecting against ischemic brain injury.

Sweetener System Intervention Shifted Neutrophils from Homeostasis to Priming

BACKGROUND

Non-nutritive sweeteners (NNS) are part of personalized nutrition strategies supporting healthy glycemic control. In contrast, the consumption of non-nutritive sweeteners has been related to person-specific and microbiome-dependent glycemic impairments. Reports on the effects of NNS on our highly individual cellular immune system are sparse. The recent identification of taste receptor expression in a variety of immune cells, however, suggested their immune-modulatory relevance.

METHODS

We studied the influence of a beverage-typical NNS system on the transcriptional profiling of sweetener-cognate taste receptors, selected cytokines and their receptors, and on Ca²⁺ signaling in isolated blood neutrophils. We determined plasma concentrations of saccharin, acesulfame-K, and cyclamate by HPLC-MS/MS, upon ingestion of a soft drink-typical sweetener surrogate. In an open-labeled, randomized intervention study, we determined pre- versus post-intervention transcript levels by RT-qPCR of sweetener-cognate taste receptors and immune factors.

RESULTS

Here we show that the consumption of a food-typical sweetener system modulated the gene expression of cognate taste receptors and induced the transcriptional regulation signatures of early homeostasis- and late receptor/signaling- and inflammation-related genes in blood neutrophils, shifting their transcriptional profile from homeostasis to priming. Notably, sweeteners at postprandial plasma concentrations facilitated fMLF (N-formyl-Met-Leu-Phe)-induced Ca²⁺ signaling.

CONCLUSIONS

Our results support the notion of sweeteners priming neutrophils to higher alertness towards their adequate stimuli.

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.

Innate immune responses in pneumonia

The lungs are an immunologically unique environment; they are exposed to innumerable pathogens and particulate matter daily. Appropriate clearance of pathogens and response to pollutants is required to prevent overwhelming infection, while preventing tissue damage and maintaining efficient gas exchange. Broadly, the innate immune system is the collection of immediate, intrinsic immune responses to pathogen or tissue injury. In this review, we will examine the innate immune responses of the lung, with a particular focus on their role in pneumonia. We will discuss the anatomic barriers and antimicrobial proteins of the lung, pathogen and injury recognition, and the role of leukocytes (macrophages, neutrophils, and innate lymphocytes) and lung stromal cells in innate immunity. Throughout the review, we will focus on new findings in innate immunity as well as features that are unique to the lung.

Mice inflammatory responses to inhaled aerosolized LPS: effects of various forms of human alpha1-antitrypsin

Rodent models of lipopolysaccharide (LPS)-induced pulmonary inflammation are used for anti-inflammatory drug testing. We aimed to characterize mice responses to aerosolized LPS alone or with intraperitoneal (i.p.) delivery of alpha1-antitrypsin (AAT). Balb/c mice were exposed to clean air or aerosolized LPS (0.21 mg/mL) for 10 min per day, for 3 d. One hour after each challenge, animals were treated i.p. with saline or with (4 mg/kg body weight) one of the AAT preparations: native (AAT), oxidized (oxAAT), recombinant (recAAT), or peptide of AAT (C-36). Experiments were terminated 6 h after the last dose of AATs. Transcriptome data of mice lungs exposed to clean air versus LPS revealed 656 differentially expressed genes and 155 significant gene ontology terms, including neutrophil migration and toll-like receptor signaling pathways. Concordantly, mice inhaling LPS showed higher bronchoalveolar lavage fluid neutrophil counts and levels of myeloperoxidase, inducible nitric oxide synthase, IL-1β, TNFα, KC, IL-6, and granulocyte-macrophage colony-stimulating factor (GM-CSF). Plasma inflammatory markers did not increase. After i.p. application of AATs, about 1% to 2% of proteins reached the lungs but, except for GM-CSF, none of the proteins significantly influenced inflammatory markers. All AATs and C-36 significantly inhibited LPS-induced GM-CSF release. Surprisingly, only oxAAT decreased the expression of several LPS-induced inflammatory genes, such as Cxcl3, Cd14, Il1b, Nfkb1, and Nfkb2, in lung tissues. According to lung transcriptome data, oxAAT mostly affected genes related to transcriptional regulation while native AAT or recAAT affected genes of inflammatory pathways. Hence, we present a feasible mice model of local lung inflammation induced via aerosolized LPS that can be useful for systemic drug testing.

Biomarkers of cell damage, neutrophil and macrophage activation associated with in-hospital mortality in geriatric COVID-19 patients

BACKGROUND

The risk for symptomatic COVID-19 requiring hospitalization is higher in the older population. The course of the disease in hospitalised older patients may show significant variation, from mild to severe illness, ultimately leading to death in the most critical cases. The analysis of circulating biomolecules involved in mechanisms of inflammation, cell damage and innate immunity could lead to identify new biomarkers of COVID-19 severity, aimed to improve the clinical management of subjects at higher risk of severe outcomes. In a cohort of COVID-19 geriatric patients (n= 156) who required hospitalization we analysed, on-admission, a series of circulating biomarkers related to neutrophil activation (neutrophil elastase, LL-37), macrophage activation (sCD163) and cell damage (nuclear cfDNA, mithocondrial cfDNA and nuclear cfDNA integrity). The above reported biomarkers were tested for their association with in-hospital mortality and with clinical, inflammatory and routine hematological parameters. Aim of the study was to unravel prognostic parameters for risk stratification of COVID-19 patients.

RESULTS

Lower n-cfDNA integrity, higher neutrophil elastase and higher sCD163 levels were significantly associated with an increased risk of in-hospital decease. Median (IQR) values observed in discharged vs. deceased patients were: 0.50 (0.30-0.72) vs. 0.33 (0.22-0.62) for n-cfDNA integrity; 94.0 (47.7-154.0) ng/ml vs. 115.7 (84.2-212.7) ng/ml for neutrophil elastase; 614.0 (370.0-821.0) ng/ml vs. 787.0 (560.0-1304.0) ng/ml for sCD163. The analysis of survival curves in patients stratified for tertiles of each biomarker showed that patients with n-cfDNA integrity < 0.32 or sCD163 in the range 492-811 ng/ml had higher risk of in-hospital decease than, respectively, patients with higher n-cfDNA integrity or lower sCD163. These associations were further confirmed in multivariate models adjusted for age, sex and outcome-related clinical variables. In these models also high levels of neutrophil elastase (>150 ng/ml) appeared to be independent predictor of in-hospital death. An additional analysis of neutrophil elastase in patients stratified for n-cfDNA integrity levels was conducted to better describe the association of the studied parameters with the outcome.

CONCLUSIONS

On the whole, biomarkers of cell-free DNA integrity, neutrophil and macrophage activation might provide a valuable contribution to identify geriatric patients with high risk of COVID-19 in-hospital mortality.

Reactive oxygen species associated immunoregulation post influenza virus infection

An appropriate level of reactive oxygen species (ROS) is necessary for cell proliferation, signaling transduction, and apoptosis due to their highly reactive character. ROS are generated through multiple metabolic pathways under a fine-tuned control between oxidant and antioxidant signaling. A growing number of evidence has proved their highly relevant role in modulating inflammation during influenza virus infection. As a network of biological process for protecting organism from invasion of pathogens, immune system can react and fight back through either innate immune system or adaptive immune system, or both. Herein, we provide a review about the mechanisms of ROS generation when encounter influenza virus infection, and how the imbalanced level of ROS influences the replication of virus. We also summarize the pathways used by both the innate and adaptive immune system to sense and attack the invaded virus and abnormal levels of ROS. We further review the limitation of current strategies and discuss the direction of future work.

Eicosanoid-Activated PPARα Inhibits NFκB-Dependent Bacterial Clearance During Post-Influenza Superinfection

Secondary bacterial infection (superinfection) post influenza is a serious clinical complication often leading to pneumonia and death. Eicosanoids are bioactive lipid mediators that play critical roles in the induction and resolution of inflammation. CYP450 lipid metabolites are anti-inflammatory lipid mediators that are produced at an excessive level during superinfection potentiating the vulnerability to secondary bacterial infection. Using Nanostring nCounter technology, we have defined the targeted transcriptional response where CYP450 metabolites dampen the Toll-like receptor signaling in macrophages. CYP450 metabolites are endogenous ligands for the nuclear receptor and transcription factor, PPARα. Activation of PPARα hinders NFκB p65 activities by altering its phosphorylation and nuclear translocation during TLR stimulation. Additionally, activation of PPARα inhibited anti-bacterial activities and enhanced macrophage polarization to an anti-inflammatory subtype (M2b). Lastly, Ppara^–/– mice, which are partially protected in superinfection compared to C57BL/6 mice, have increased lipidomic responses and decreased M2-like macrophages during superinfection.

Role of the chemokine system in liver fibrosis: a narrative review

BACKGROUND AND OBJECTIVE

Liver fibrosis is a disease with characteristics of an aberrant wound healing response. Fibrosis is commonly the end-stage for chronic liver diseases like alcohol-associated liver disease (ALD), metabolic-associated liver disease, viral hepatitis, and hepatic autoimmune disease. Innate immunity contributes to the progression of many diseases through multiple mechanisms including production of pro-inflammatory mediators, leukocyte infiltration and tissue injury. Chemokines and their receptors orchestrate accumulation and activation of immune cells in tissues and are associated with multiple liver diseases; however, much less is known about their potential roles in liver fibrosis. This is a narrative review of current knowledge of the relationship of chemokine biology to liver fibrosis with insights into potential future therapeutic opportunities that can be explored in the future.

METHODS

A comprehensive literature review was performed searching PubMed for relevant English studies and texts regarding chemokine biology, chronic liver disease and liver fibrosis published between 1993 and 2021. The review was written and constructed to detail the intriguing chemokine biology, the relation of chemokines to tissue injury and resolution, and identify areas of discovery for fibrosis treatment.

KEY CONTENT AND FINDINGS

Chemokines are implicated in many chronic liver diseases, regardless of etiology. Most of these diseases will progress to fibrosis without appropriate treatment. The contributions of chemokines to liver disease and fibrosis are diverse and include canonical roles of modulating hepatic inflammation as well as directly contributing to fibrosis via activation of hepatic stellate cells (HSCs). Limited clinical evidence suggests that targeting chemokines in certain liver diseases might provide a therapeutic benefit to patients with hepatic fibrosis.

CONCLUSIONS

The chemokine system of ligands and receptors is a complex network of inflammatory signals in nearly all diseases. The specific sources of chemokines and cellular targets lend unique pathophysiological consequences to chronic liver diseases and established fibrosis. Although most chemokines are pro-inflammatory and contribute to tissue injury, others likely aid in the resolution of established fibrosis. To date, very few targeted therapies exist for the chemokine system and liver disease and/or fibrosis, and further study could identify viable treatment options to improve outcomes in patients with end-stage liver disease.

Telmisartan ameliorates LPS-induced pneumonia in rats through regulation of the PPARγ/NF-κB pathway

Pneumonia is a common disorder of the respiratory system associated with inflammation. Telmisartan (TEL) has been reported to treat inflammatory-related diseases. The current study is aimed to make investigations for the possible role and action mechanism of TEL on lipopolysaccharide (LPS)-induced pneumonia rats. Forty male Sprague Dawley (SD) rats aged 8 weeks were assigned into four groups ad libitum: a control group received saline only, an experimental group received LPS, a group received TEL (5 mg/kg), followed by LPS treatment, and a group received TEL (10 mg/kg), followed by LPS treatment. LPS (2 mg/kg) and equal saline were administered intratracheally. TEL was orally administrated 5 days before LPS. After LPS treatment for 24 h, bronchoalveolar lavage fluid (BALF) and serum were collected for the analysis of cell counts and/or cytokines. Lung tissues were used to perform histological examination, assess oxidative stress levels, and determine the levels of PPARγ/NF-κB pathway-related proteins. Rats received LPS treatment exhibited high levels of lung wet/dry ratio, ALP, LDH, BALF polymorphonuclear leukocytes count, inflammatory cytokines, and oxidative stress. Meanwhile, LPS also resulted in severe interstitial edema and inflammatory cells infiltration. Interestingly, TEL by oral administration remarkably ameliorated the adverse effects on pneumonia rats caused by LPS. In addition, western blotting further revealed that TEL could activate PPARγ and repress NF-κB (p65). TEL is protective against pneumonia through inhibition of the inflammation and oxidative stress via the PPARγ/NF-κB pathway. This article is protected by copyright. All rights reserved.

lincRNA-Cox2 Functions to Regulate Inflammation in Alveolar Macrophages during Acute Lung Injury

Our respiratory system is vital to protect us from the surrounding nonsterile environment; therefore, it is critical for a state of homeostasis to be maintained through a balance of inflammatory cues. Recent studies have shown that actively transcribed noncoding regions of the genome are emerging as key regulators of biological processes, including inflammation. lincRNA-Cox2 is one such example of an inflammatory inducible long intergenic noncoding RNA functioning to fine-tune immune gene expression. Using bulk and single-cell RNA sequencing, in addition to FACS, we find that lincRNA-Cox2 is most highly expressed in the lung and is most upregulated after LPS-induced lung injury (acute lung injury [ALI]) within alveolar macrophages, where it functions to regulate inflammation. We previously reported that lincRNA-Cox2 functions to regulate its neighboring protein Ptgs2 in cis, and in this study, we use genetic mouse models to confirm its role in regulating gene expression more broadly in trans during ALI. Il6, Ccl3, and Ccl5 are dysregulated in the lincRNA-Cox2-deficient mice and can be rescued to wild type levels by crossing the deficient mice with our newly generated lincRNA-Cox2 transgenic mice, confirming that this gene functions in trans. Many genes are specifically regulated by lincRNA-Cox2 within alveolar macrophages originating from the bone marrow because the phenotype can be reversed by transplantation of wild type bone marrow into the lincRNA-Cox2-deficient mice. In conclusion, we show that lincRNA-Cox2 is a trans-acting long noncoding RNA that functions to regulate immune responses and maintain homeostasis within the lung at baseline and on LPS-induced ALI.

Neutrophil Functional Heterogeneity and Implications for Viral Infections and Treatments

Evidence suggests that neutrophils exert specialized effector functions during infection and inflammation, and that these cells can affect the duration, severity, and outcome of the infection. These functions are related to variations in phenotypes that have implications in immunoregulation during viral infections. Although the complexity of the heterogeneity of neutrophils is still in the process of being uncovered, evidence indicates that they display phenotypes and functions that can assist in viral clearance or augment and amplify the immunopathology of viruses. Therefore, deciphering and understanding neutrophil subsets and their polarization in viral infections is of importance. In this review, the different phenotypes of neutrophils and the roles they play in viral infections are discussed. We also examine the possible ways to target neutrophil subsets during viral infections as potential anti-viral treatments.

Effects of systemic inflammation due to hepatic ischemia-reperfusion injury upon lean or obese visceral adipose tissue

Purpose:

To evaluate how the induction of liver damage by ischemia and reperfusion affects the adipose tissue of lean and obese mice.

Methods:

Lean and diet-induced obese mice were subjected to liver ischemia (30 min) followed by 6 h of reperfusion. The vascular stromal fraction of visceral adipose tissue was analyzed by cytometry, and gene expression was evaluated by an Array assay and by RT-qPCR. Intestinal permeability was assessed by oral administration of fluorescein isothiocyanate (FITC)-dextran and endotoxemia by serum endotoxin measurements using a limulus amebocyte lysate assay.

Results:

It was found that, after liver ischemia and reperfusion, there is an infiltration of neutrophils, monocytes, and lymphocytes, as well as an increase in the gene expression that encode cytokines, chemokines and their receptors in the visceral adipose tissue of lean mice. This inflammatory response was associated with the presence of endotoxemia in lean mice. However, these changes were not observed in the visceral adipose tissue of obese mice.

Conclusions:

Liver ischemia and reperfusion induce an acute inflammatory response in adipose tissue of lean mice characterized by an intense chemokine induction and leukocyte infiltration; however, inflammatory alterations are already present at baseline in the obese adipose tissue and liver ischemia and reperfusion do not injure further.

Chemokines as Regulators of Neutrophils: Focus on Tumors, Therapeutic Targeting, and Immunotherapy

Simple Summary

Neutrophils are the main leukocyte subset present in human blood and play a fundamental role in the defense against infections. Neutrophils are also an important component of the tumor stroma because they are recruited by selected chemokines produced by both cancer cells and other cells of the stroma. Even if their presence has been mostly associated with a bad prognosis, tumor-associated neutrophils are present in different maturation and activation states and can exert both protumor and antitumor activities. In addition, it is now emerging that chemokines not only induce neutrophil directional migration but also have an important role in their activation and maturation. For these reasons, chemokines and chemokine receptors are now considered targets to improve the antitumoral function of neutrophils in cancer immunotherapy.

Abstract

Neutrophils are an important component of the tumor microenvironment, and their infiltration has been associated with a poor prognosis for most human tumors. However, neutrophils have been shown to be endowed with both protumor and antitumor activities, reflecting their heterogeneity and plasticity in cancer. A growing body of studies has demonstrated that chemokines and chemokine receptors, which are fundamental regulators of neutrophils trafficking, can affect neutrophil maturation and effector functions. Here, we review human and mouse data suggesting that targeting chemokines or chemokine receptors can modulate neutrophil activity and improve their antitumor properties and the efficiency of immunotherapy.

The Dual Role of CCR5 in the Course of Influenza Infection: Exploring Treatment Opportunities

Influenza is one of the most relevant respiratory viruses to human health causing annual epidemics, and recurrent pandemics. Influenza disease is principally associated with inappropriate activation of the immune response. Chemokine receptor 5 (CCR5) and its cognate chemokines CCL3, CCL4 and CCL5 are rapidly induced upon influenza infection, contributing to leukocyte recruitment into the airways and a consequent effective antiviral response. Here we discuss the existing evidence for CCR5 role in the host immune responses to influenza virus. Complete absence of CCR5 in mice revealed the receptor’s role in coping with influenza via the recruitment of early memory CD8+ T cells, B cell activation and later recruitment of activated CD4+ T cells. Moreover, CCR5 contributes to inflammatory resolution by enhancing alveolar macrophages survival and reprogramming macrophages to pro-resolving phenotypes. In contrast, CCR5 activation is associated with excessive recruitment of neutrophils, inflammatory monocytes, and NK cells in models of severe influenza pneumonia. The available data suggests that, while CCL5 can play a protective role in influenza infection, CCL3 may contribute to an overwhelming inflammatory process that can harm the lung tissue. In humans, the gene encoding CCR5 might contain a 32-base pair deletion, resulting in a truncated protein. While discordant data in literature regarding this CCR5 mutation and influenza severity, the association of CCR5delta32 and HIV resistance fostered the development of different CCR5 inhibitors, now being tested in lung inflammation therapy. The potential use of CCR5 inhibitors to modulate the inflammatory response in severe human influenza infections is to be addressed.

The State of Art of Extracellular Traps in Protozoan Infections (Review)

Protozoan parasite infection causes severe diseases in humans and animals, leading to tremendous economic and medical pressure. Natural immunity is the first line of defence against parasitic infection. Currently, the role of natural host immunity in combatting parasitic infection is unclear, so further research on natural host immunity against parasites will provide a theoretical basis for the prevention and treatment of related parasitic diseases. Extracellular traps (ETs) are an important natural mechanism of immunity involving resistance to pathogens. When immune cells such as neutrophils and macrophages are stimulated by external pathogens, they release a fibrous network structure, consisting mainly of DNA and protein, that can capture and kill a variety of extracellular pathogenic microorganisms. In this review, we discuss the relevant recently reported data on ET formation induced by protozoan parasite infection, including the molecular mechanisms involved, and discuss the role of ETs in the occurrence and development of parasitic diseases.

Dietary Polyphenol and Methylsulfonylmethane Supplementation Improves Immune, DAMP Signaling, and Inflammatory Responses During Recovery From All-Out Running Efforts

Nutritional ingredients with defined mechanisms of action can be useful in the recovery of the body from the physical demands of a habitual training plan. The purpose of this study was to determine the effect of dietary supplementation with optimized curcumin, pomegranate ellagitannins, and MSM (R + MSM) on immune-associated mRNA during early recovery (i.e., up to 8 h post-exercise) following all-out running efforts (5-km, 10-km, and 21.1-km). Subjects (N = 14) were randomized to either a supplement (R + MSM) or a control group using an open label design. The study was completed over a period of 31-day prior to a scheduled half-marathon race. Venous blood samples were collected into PAXgene tubes at baseline, subsequent samples were collected at 2, 4, and 8 h after each running effort. A 574-plex mRNA Immunology Array (NanoString) was measured for each sample and ROSALIND^® Advanced Analysis Software was used to examined changes in 31 annotated immune response pathways and specific mRNA changes. The greatest change in immune pathways occurred at 2 h (GSS > 3) followed by 4 h (GSS 2–3) and 8 h (GSS 1–2). R + MSM was associated with an increase in innate immunity (CAMP, LTF, TIRAP, CR1, IL1R1, CXCR1, PDCDILG2, and GNLY) and a blunted/smaller increase in damage-associated molecular pattern (DAMP) signaling/inflammation (TLR4, TLR5, S100A8, S100A9, and IFP35). We also found changes in immune-associated mRNA that have not been previously linked to exercise recovery (SOCS1, SOCS2, MME, CECAM6, MX1, IL-1R2, KLRD1, KLRK1, and LAMP3). Collectively these results demonstrate that supplementation with a combination of optimized curcumin, pomegranate ellagitannins, and methylsulfonylmethane resulted in changes that may improve biological recovery from all-out running efforts.

The effect of an isoquinoline alkaloid on treatment of periodontitis by regulating the neutrophils chemotaxis

Neutrophil plays a critical role in the progression of periodontitis. In general, its chemotaxis and activation are benefit for the host defense of bacterial infection and inflammation. However, previous studies have reported that the hyperactive and reactive neutrophils appear to be one of the reasons for tissue destruction in periodontitis tissues. In this study, we investigated an isoquinoline alkaloid Litcubanine A (LA), which from the Traditional Chinese medicinal plant, Litsea cubeba. We found LA showed significant activity in inhibiting neutrophils chemotaxis in the zebrafish yolk sac microinjection model in vivo and in mouse neutrophils in vitro. Further investigation proved that LA could inhibit the expression levels of neutrophil respiratory burst-related and inflammation-related genes CYBB and NCF2, as well as inhibit the activation of MAPK signaling pathway. Moreover, using LA, we successfully achieved the effect of reducing periodontitis bone loss by regulating neutrophil chemotaxis and related functions in a mouse ligature-induced periodontitis model.

A Fragile Balance: Does Neutrophil Extracellular Trap Formation Drive Pulmonary Disease Progression?

Neutrophils act as the first line of defense during infection and inflammation. Once activated, they are able to fulfil numerous tasks to fight inflammatory insults while keeping a balanced immune response. Besides well-known functions, such as phagocytosis and degranulation, neutrophils are also able to release "neutrophil extracellular traps" (NETs). In response to most stimuli, the neutrophils release decondensed chromatin in a NADPH oxidase-dependent manner decorated with histones and granule proteins, such as neutrophil elastase, myeloperoxidase, and cathelicidins. Although primarily supposed to prevent microbial dissemination and fight infections, there is increasing evidence that an overwhelming NET response correlates with poor outcome in many diseases. Lung-related diseases especially, such as bacterial pneumonia, cystic fibrosis, chronic obstructive pulmonary disease, aspergillosis, influenza, and COVID-19, are often affected by massive NET formation. Highly vascularized areas as in the lung are susceptible to immunothrombotic events promoted by chromatin fibers. Keeping this fragile equilibrium seems to be the key for an appropriate immune response. Therapies targeting dysregulated NET formation might positively influence many disease progressions. This review highlights recent findings on the pathophysiological influence of NET formation in different bacterial, viral, and non-infectious lung diseases and summarizes medical treatment strategies.

CCR5 Antagonist Maraviroc Inhibits Acute Exacerbation of Lung Inflammation Triggered by Influenza Virus in Cigarette Smoke-Exposed Mice

Influenza A virus (IAV) infection is a common cause of acute exacerbations of chronic obstructive pulmonary disease (AECOPD). Since macrophage inflammatory protein 1 α, a chemokine that acts through CC-chemokine receptor (CCR)-5, appears elevated in COPD patients’ airways, we evaluated whether CCR5 antagonist Maraviroc could inhibit the exacerbated lung inflammatory response noted after IAV H1N1 infection in mice exposed to cigarette smoke (Cs). C57BL/6 mice, subjected or not to Cs inhalation for 11 days, were infected with H1N1 at day 7. Maraviroc (10 mg/kg) or dexamethasone (1 mg/kg) were given in a therapeutic schedule, followed by the analyses of lung function, survival rate, and inflammatory changes. As compared to mice subjected to Cs or H1N1 alone, the insult combination significantly worsened airway obstruction, neutrophil infiltration in the airways, and the survival rate. All changes were sensitive to Maraviroc but not dexamethasone. Maraviroc also reduced the accumulation of neutrophils and macrophages as well as CXCL1 production in the lung tissue, and serum levels of IL-6, whereas comparable viral titers in the lungs were noted in all infected groups. Collectively, these findings suggest that Maraviroc oral treatment could be an effective therapy for controlling acute exacerbations of respiratory diseases such as COPD.

The role of circTMOD3 in regulating LPS-induced acute inflammation and injury in human lung fibroblast WI-38 cells

BACKGROUND

Circular RNAs (circRNAs) have been implicated in the molecular etiology of pediatric pneumonia. Here, we investigated the precise action of circRNA tropomodulin 3 (circTMOD3, hsa_circ_0035292) in cell injury and inflammation induced by lipopolysaccharide (LPS). Methods: Cell viability was gauged by Cell Counting Kit-8 (CCK-8) assay. Cell apoptosis and cycle distribution were assessed by flow cytometry. Enzyme-linked immunosorbent assay (ELISA) was used to measure interleukin-6 (IL-6), IL-1β and tumor necrosis factor alpha (TNF-α) production. The levels of circTMOD3, microRNA (miR)-146b-3p, and C-X-C motif chemokine receptor 1 (CXCR1) were detected by quantitative real-time polymerase chain reaction (qRT-PCR) or western blot. Ribonuclease (RNase) R, Actinomycin D and subcellular localization assays were done to characterize circTMOD3. The direct relationship between miR-146b-3p and circTMOD3 or CXCR1 was confirmed by dual-luciferase reporter assays. Results: Our data showed that LPS induced the expression of circTMOD3 in WI-38 cells. CircTMOD3 was resistant to RNase R and was mainly present in the cytoplasm. Silencing endogenous circTMOD3 alleviated WI-38 cell injury and inflammation triggered by LPS. Mechanistically, circTMOD3 directly targeted miR-146b-3p, and CXCR1 was a direct and functional target of miR-146b-3p. CircTMOD3 regulated LPS-induced cell inflammation and injury by targeting miR-146b-3p, and miR-146b-3p-mediated suppression of CXCR1 impacted LPS-evoked cytotoxicity and inflammation. Furthermore, circTMOD3 functioned as a competing endogenous RNA (ceRNA) for miR-146b-3p to induce CXCR1 expression. Conclusion: Our findings demonstrated the regulation of circTMOD3 in LPS-induced cell injury and inflammation at least partially via miR-146b-3p-independent modulation of CXCR1.

MiR-144-induced KLF2 inhibition and NF-kappaB/CXCR1 activation promote neutrophil extracellular trap-induced transfusion-related acute lung injury

Transfusion‐related acute lung injury (TRALI) is a clinical syndrome which is associated with the formation of neutrophil extracellular trap (NET). Recent studies have demonstrated the roles of microRNAs (miRNAs) in the pathophysiological process of TRALI. Here, the study focused on the role of miR‐144 and the molecular mechanisms in NET‐induced TRALI. Up‐regulated miR‐144 and under‐expressed KLF2 were determined in patients with TRALI. In the mouse model of a two‐event TRALI induced by intraperitoneal injections with lipopolysaccharide and anti‐H‐2Kd mAb, we determined expression patterns of miR‐144, Krüppel‐like factor 2 (KLF2), chemokine (C‐X‐C motif) receptor 1 (CXCR1) and nuclear factor kappa‐B (NF‐kappaB) p65. The results confirmed that miR‐144 was highly expressed, while KLF2 was poorly expressed in mice with TRALI. Dual‐luciferase reporter gene assay identified that miR‐144 could target KLF2. Using gain‐ and loss‐of‐function approaches, we analysed the effects of miR‐144 and its interaction with KLF2 on TRALI. Enforced expression of miR‐144 was found to aggravate NET‐induced TRALI by down‐regulating KLF2 and activating the NF‐kappaB/CXCR1 signalling pathway in TRALI mice. Collectively, miR‐144‐targeted inhibition of KLF2 and activation of NF‐kappaB/CXCR1 are possible mechanisms responsible for NET‐caused TRALI. These findings aid in the development of therapeutic modalities for the treatment of TRALI.

Invasive pulmonary aspergillosis associated with viral pneumonitis

The occurrence of invasive pulmonary aspergillosis (IPA) in critically ill patients with viral pneumonitis has increasingly been reported in recent years. Influenza-associated pulmonary aspergillosis (IAPA) and COVID-19-associated pulmonary aspergillosis (CAPA) are the two most common forms of this fungal infection. These diseases cause high mortality in patients, most of whom were previously immunocompetent. The pathogenesis of IAPA and CAPA is still not fully understood, but involves viral, fungal and host factors. In this article, we discuss several aspects regarding IAPA and CAPA, including their possible pathogenesis, the use of immunotherapy, and future challenges.

The twilight zone: plasticity and mixed ontogeny of neutrophil and eosinophil granulocyte subsets

It is now becoming clear that neutrophils and eosinophils are heterogeneous cells with potentially multiple subsets in health and disease. With greater marker coverage by multi-color flow cytometry and single-cell level sequencing of granulocyte populations, novel phenotypes of these cells began to emerge. Intriguingly, many newly described subsets blend distinctions between classical myeloid lineage phenotypes, which are especially true for tissue resident or recruited cells in contexts of inflammation and disease. This includes reports of neutrophils with features of eosinophils, monocytes and dendritic cells, and eosinophil subsets expressing neutrophil markers. Moreover, novel studies show the ability of immature neutrophils to transdifferentiate into mature cells belonging to other myeloid lineages (eosinophils, monocytes/macrophages). In this review, we summarize novel findings in this exciting research frontier and shed light on potential processes driving the plasticity and heterogeneity of granulocyte subsets. Specifically, we discuss the hematopoietic flexibility of granulocyte precursors in bone marrow and the adaptation of myeloid cells to local tissue microenvironments. The understanding of such intermediate and developmental phenotypes is very important, as it can teach us about origins of functionally distinct myeloid cells during inflammation, and explain reasons for successes and failures of biologics targeting terminally differentiated granulocytes.

Classes of drugs that target the cellular components of inflammation under clinical development for COPD

INTRODUCTION

The persistent inflammation that characterizes COPD and affects its natural course also impacting on symptoms has prompted research to find molecules that can regulate the inflammatory process but still available anti-inflammatory therapies provide little or no benefit in COPD patients. Consequently, numerous anti-inflammatory molecules that are effective in animal models of COPD have been or are being evaluated in humans.

AREAS COVERED

In this article we describe several classes of drugs that target the cellular components of inflammation under clinical development for COPD.

EXPERT OPINION

Although the results of many clinical trials with new molecules have often been disappointing, several studies are underway to investigate whether some of these molecules may be effective in treating specific subgroups of COPD patients. Indeed, the current perspective is to apply a more personalized treatment to the patient. This means being able to better define the patient's inflammatory state and treat it in a targeted manner. Unfortunately, the difficulty in translating encouraging experimental data into human clinical trials, the redundancy in the effects induced by signal-transmitting substances and the nonspecific effects of many classes that are undergoing clinical trials, do not yet allow specific inflammatory cell types to be targeted.

A specific low-density neutrophil population correlates with hypercoagulation and disease severity in hospitalized COVID-19 patients

SARS coronavirus 2 (SARS-CoV-2) is a novel viral pathogen that causes a clinical disease called coronavirus disease 2019 (COVID-19). Although most COVID-19 cases are asymptomatic or involve mild upper respiratory tract symptoms, a significant number of patients develop severe or critical disease. Patients with severe COVID-19 commonly present with viral pneumonia that may progress to life-threatening acute respiratory distress syndrome (ARDS). Patients with COVID-19 are also predisposed to venous and arterial thromboses that are associated with a poorer prognosis. The present study identified the emergence of a low-density inflammatory neutrophil (LDN) population expressing intermediate levels of CD16 (CD16Int) in patients with COVID-19. These cells demonstrated proinflammatory gene signatures, activated platelets, spontaneously formed neutrophil extracellular traps, and enhanced phagocytic capacity and cytokine production. Strikingly, CD16Int neutrophils were also the major immune cells within the bronchoalveolar lavage fluid, exhibiting increased CXCR3 but loss of CD44 and CD38 expression. The percentage of circulating CD16Int LDNs was associated with D-dimer, ferritin, and systemic IL-6 and TNF-α levels and changed over time with altered disease status. Our data suggest that the CD16Int LDN subset contributes to COVID-19-associated coagulopathy, systemic inflammation, and ARDS. The frequency of that LDN subset in the circulation could serve as an adjunct clinical marker to monitor disease status and progression.

Administration of a CXC Chemokine Receptor 2 (CXCR2) Antagonist, SCH527123, Together with Oseltamivir Suppresses NETosis and Protects Mice from Lethal Influenza and Piglets from Swine-Influenza Infection

Excessive neutrophil influx, their released neutrophil extracellular traps (NETs), and extracellular histones are associated with disease severity in influenza-infected patients. Neutrophil chemokine receptor CXC chemokine receptor 2 (CXCR2) is a critical target for suppressing neutrophilic inflammation. Herein, temporal dynamics of neutrophil activity and NETosis were investigated to determine the optimal timing of treatment with the CXCR2 antagonist, SCH527123 (2-hydroxy-N,N-dimethyl-3-[2-([(R)-1-(5-methyl-furan-2-yl)-propyl]amino)-3,4-dioxo-cyclobut-1-enylamino]-benzamide), and its efficacy together with antiviral agent, oseltamivir, was tested in murine and piglet influenza-pneumonia models. SCH527123 plus oseltamivir markedly improved survival of mice infected with lethal influenza, and diminished lung pathology in swine-influenza-infected piglets. Mechanistically, addition of SCH527123 in the combination treatment attenuated neutrophil influx, NETosis, in both mice and piglets. Furthermore, neutrophils isolated from influenza-infected mice showed greater susceptibility to NETotic death when stimulated with a CXCR2 ligand, IL-8. In addition, CXCR2 stimulation induced nuclear translocation of neutrophil elastase, and enhanced citrullination of histones that triggers chromatin decondensation during NET formation. Studies on temporal dynamics of neutrophils and NETs during influenza thus provide important insights into the optimal timing of CXCR2 antagonist treatment for attenuating neutrophil-mediated lung pathology. These findings reveal that pharmacologic treatment with CXCR2 antagonist together with an antiviral agent could significantly ameliorate morbidity and mortality in virulent and sublethal influenza infections.

Beneficial effect of Indigo Naturalis on acute lung injury induced by influenza A virus

Background

Infections induced by influenza viruses, as well as coronavirus disease 19 (COVID-19) pandemic induced by severe acute respiratory coronavirus 2 (SARS-CoV-2) led to acute lung injury (ALI) and multi organ failure, during which traditional Chinese medicine (TCM) played an important role in treatment of the pandemic. The study aimed to investigate the effect of Indigo Naturalis on ALI induced by influenza A virus (IAV) in mice.

Method

The anti-influenza and anti-inflammatory properties of aqueous extract of Indigo Naturalis (INAE) were evaluated in vitro. BALB/c mice inoculated intranasally with IAV (H1N1) were treated intragastrically with INAE (40, 80 and 160 mg/kg/day) 2 h later for 4 or 7 days. Animal lifespan and mortality were recorded. Expression of high mobility group box-1 protein (HMGB-1) and toll-like receptor 4 (TLR4) were evaluated through immunohistological staining. Inflammatory cytokines were also monitored by ELISA.

Result

INAE inhibited virus replication on Madin-Darby canine kidney (MDCK) cells and decreased nitric oxide (NO) production from lipopolysaccharide (LPS)-stimulated peritoneal macrophages in vitro. The results showed that oral administration of 160 mg/kg of INAE significantly improved the lifespan (P < 0.01) and survival rate of IAV infected mice, improved lung injury and lowered viral replication in lung tissue (P < 0.01). Treatment with INAE (40, 80 and 160 mg/kg) significantly increased liver weight and liver index (P < 0.05), as well as weight and organ index of thymus and spleen at 160 mg/kg (P < 0.05). Serum alanine transaminase (ALT) and aspartate aminotransferase (AST) levels were reduced by INAE administration (P < 0.05). The expression of HMGB-1 and TLR4 in lung tissue were also suppressed. The increased production of myeloperoxidase (MPO) and methylene dioxyamphetamine (MDA) in lung tissue were inhibited by INAE treatment (P < 0.05). Treatment with INAE reduced the high levels of interferon α (IFN-α), interferon β (IFN-β), monocyte chemoattractant protein-1 (MCP-1), regulated upon activation normal T cell expressed and secreted factor (RANTES), interferon induced protein-10 (IP-10), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) (P < 0.05), with increased production of interferon γ (IFN-γ) and interleukin-10 (IL-10) (P < 0.05).

Conclusion

The results showed that INAE alleviated IAV induced ALI in mice. The mechanisms of INAE were associated with its anti-influenza, anti-inflammatory and anti-oxidation properties. Indigo Naturalis might have clinical potential to treat ALI induced by IAV.

NLRP3 Regulated CXCL12 Expression in Acute Neutrophilic Lung Injury

Background and Purpose

Both NLRP3 inflammasome and chemokines are involved in the initiation and development of acute lung inflammation, but the underlying mechanism is still elusive. The present study investigated the role of chemokines and NLRP3 in recruiting neutrophils in the early phase of acute lung injury.

Methods

In an endotoxin (lipopolysaccharide [LPS])-induced acute lung injury model, we measured the lung injury severity, myeloperoxidase (MPO) activity and chemokine profiles in wild-type (WT) and NLRP3 knockout (NLRP3^–/–) mice, and then identified the key chemokines by specific antibody blockage.

Results

The results showed that NLRP3 deficiency was associated with alleviating lung damage, by reducing alveolar epithelial cell apoptosis and decreasing neutrophil accumulation. Furthermore, compared with WT mice, IL-1β, CCL2, CXCL1, CXCL5 and CXCL12 levels from the serum of NLRP3^–/– mice were much lower after exposure to LPS. However, in lung tissue, only lower CXCL12 levels were observed from the NLRP3^–/– ALI mice, and higher levels of CXCR4 were expressed in NLRP3^–/– neutrophils. Blockage of CXCL12 dramatically relieved the severity of ALI and reduced neutrophil accumulation in the lung.

Conclusion

NLRP3 alters CXCL12 expression in acute lung injury. CXCL12 is crucial for neutrophil recruitment in NLRP3-mediated neutrophilic lung injury.

Multiple Roles for Chemokines in Neutrophil Biology

Chemokines are recognized as the most critical mediators for selective neutrophil recruitment during inflammatory conditions. Furthermore, they are considered fundamental regulators of neutrophil mobilization from the bone marrow (BM) to the bloodstream and for their homing back at the end of their life for apoptosis and clearance. However, chemokines are also important mediators of neutrophil effector functions including oxidative burst, degranulation, neutrophil extracellular trap (NET)osis, and production of inflammatory mediators. Neutrophils have been historically considered as a homogeneous population. In recent years, several maturation stages and subsets with different phenotypic profiles and effector functions were described both in physiological and pathological conditions such as infections, autoimmunity, and cancer. The aim of this review is to give an overview of the current evidence regarding the role of chemokines and chemokine receptors in neutrophil biology, including their possible role in neutrophil maturation, differentiation, and in defining emerging neutrophil subsets.

Neutrophil extracellular traps in COVID-19

In severe cases of coronavirus disease 2019 (COVID-19), viral pneumonia progresses to respiratory failure. Neutrophil extracellular traps (NETs) are extracellular webs of chromatin, microbicidal proteins, and oxidant enzymes that are released by neutrophils to contain infections. However, when not properly regulated, NETs have the potential to propagate inflammation and microvascular thrombosis - including in the lungs of patients with acute respiratory distress syndrome. We now report that sera from patients with COVID-19 have elevated levels of cell-free DNA, myeloperoxidase-DNA (MPO-DNA), and citrullinated histone H3 (Cit-H3); the latter 2 are specific markers of NETs. Highlighting the potential clinical relevance of these findings, cell-free DNA strongly correlated with acute-phase reactants, including C-reactive protein, D-dimer, and lactate dehydrogenase, as well as absolute neutrophil count. MPO-DNA associated with both cell-free DNA and absolute neutrophil count, while Cit-H3 correlated with platelet levels. Importantly, both cell-free DNA and MPO-DNA were higher in hospitalized patients receiving mechanical ventilation as compared with hospitalized patients breathing room air. Finally, sera from individuals with COVID-19 triggered NET release from control neutrophils in vitro. Future studies should investigate the predictive power of circulating NETs in longitudinal cohorts and determine the extent to which NETs may be novel therapeutic targets in severe COVID-19.

Beyond HIV infection: Neglected and varied impacts of CCR5 and CCR5Δ32 on viral diseases

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CCR5 regulates multiple cell types (e.g., T regulatory and Natural Killer cells) and immune responses.

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The effects of CCR5, CCR5Δ32 (variant associated with reduced CCR5 expression) and CCR5 antagonists vary between infections.

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CCR5 affects the pathogenesis of flaviviruses, especially in the brain.

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The genetic variant CCR5Δ32 increases the risk of symptomatic West Nile virus infection.

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The triad “CCR5, extracellular vesicles and infections” is an emerging topic.

The interactions between chemokine receptors and their ligands may affect susceptibility to infectious diseases as well as their clinical manifestations. These interactions mediate both the traffic of inflammatory cells and virus-associated immune responses. In the context of viral infections, the human C-C chemokine receptor type 5 (CCR5) receives great attention from the scientific community due to its role as an HIV-1 co-receptor. The genetic variant CCR5Δ32 (32 base-pair deletion in CCR5 gene) impairs CCR5 expression on the cell surface and is associated with protection against HIV infection in homozygous individuals. Also, the genetic variant CCR5Δ32 modifies the CCR5-mediated inflammatory responses in various conditions, such as inflammatory and infectious diseases. CCR5 antagonists mimic, at least in part, the natural effects of the CCR5Δ32 in humans, which explains the growing interest in the potential benefits of using CCR5 modulators for the treatment of different diseases. Nevertheless, beyond HIV infection, understanding the effects of the CCR5Δ32 variant in multiple viral infections is essential to shed light on the potential effects of the CCR5 modulators from a broader perspective. In this context, this review discusses the involvement of CCR5 and the effects of the CCR5Δ32 in human infections caused by the following pathogens: West Nile virus, Influenza virus, Human papillomavirus, Hepatitis B virus, Hepatitis C virus, Poliovirus, Dengue virus, Human cytomegalovirus, Crimean-Congo hemorrhagic fever virus, Enterovirus, Japanese encephalitis virus, and Hantavirus. Subsequently, this review addresses the impacts of CCR5 gene editing and CCR5 modulation on health and viral diseases. Also, this article connects recent findings regarding extracellular vesicles (e.g., exosomes), viruses, and CCR5. Neglected and emerging topics in “CCR5 research” are briefly described, with focus on Rocio virus, Zika virus, Epstein-Barr virus, and Rhinovirus. Finally, the potential influence of CCR5 on the immune responses to coronaviruses is discussed.

Neutrophil extracellular traps (NETs) as markers of disease severity in COVID-19

In severe cases of coronavirus disease 2019 (COVID-19), viral pneumonia progresses to respiratory failure. Neutrophil extracellular traps (NETs) are extracellular webs of chromatin, microbicidal proteins, and oxidant enzymes that are released by neutrophils to contain infections. However, when not properly regulated, NETs have potential to propagate inflammation and microvascular thrombosis, including in the lungs of patients with acute respiratory distress syndrome. While elevated levels of blood neutrophils predict worse outcomes in COVID-19, the role of NETs has not been investigated. We now report that sera from patients with COVID-19 (n=50 patients, n=84 samples) have elevated levels of cell-free DNA, myeloperoxidase(MPO)-DNA, and citrullinated histone H3 (Cit-H3); the latter two are highly specific markers of NETs. Highlighting the potential clinical relevance of these findings, cell-free DNA strongly correlated with acute phase reactants including C-reactive protein, D-dimer, and lactate dehydrogenase, as well as absolute neutrophil count. MPO-DNA associated with both cell-free DNA and absolute neutrophil count, while Cit-H3 correlated with platelet levels. Importantly, both cell-free DNA and MPO-DNA were higher in hospitalized patients receiving mechanical ventilation as compared with hospitalized patients breathing room air. Finally, sera from individuals with COVID-19 triggered NET release from control neutrophils in vitro. In summary, these data reveal high levels of NETs in many patients with COVID-19, where they may contribute to cytokine release and respiratory failure. Future studies should investigate the predictive power of circulating NETs in longitudinal cohorts, and determine the extent to which NETs may be novel therapeutic targets in severe COVID-19.

Neutrophil chemoattractant receptors in health and disease: double-edged swords

Neutrophils are frontline cells of the innate immune system. These effector leukocytes are equipped with intriguing antimicrobial machinery and consequently display high cytotoxic potential. Accurate neutrophil recruitment is essential to combat microbes and to restore homeostasis, for inflammation modulation and resolution, wound healing and tissue repair. After fulfilling the appropriate effector functions, however, dampening neutrophil activation and infiltration is crucial to prevent damage to the host. In humans, chemoattractant molecules can be categorized into four biochemical families, i.e., chemotactic lipids, formyl peptides, complement anaphylatoxins and chemokines. They are critically involved in the tight regulation of neutrophil bone marrow storage and egress and in spatial and temporal neutrophil trafficking between organs. Chemoattractants function by activating dedicated heptahelical G protein-coupled receptors (GPCRs). In addition, emerging evidence suggests an important role for atypical chemoattractant receptors (ACKRs) that do not couple to G proteins in fine-tuning neutrophil migratory and functional responses. The expression levels of chemoattractant receptors are dependent on the level of neutrophil maturation and state of activation, with a pivotal modulatory role for the (inflammatory) environment. Here, we provide an overview of chemoattractant receptors expressed by neutrophils in health and disease. Depending on the (patho)physiological context, specific chemoattractant receptors may be up- or downregulated on distinct neutrophil subsets with beneficial or detrimental consequences, thus opening new windows for the identification of disease biomarkers and potential drug targets.

Antiviral activity of iridoid glycosides extracted from Fructus Gardeniae against influenza A virus by PACT-dependent suppression of viral RNA replication

Epidemic and pandemic influenza A virus (IAV) poses a significant threat to human populations worldwide. Iridoid glycosides are principal bioactive components from the Gardenia jasminoides J. Ellis fruit that exhibit antiviral activity against several strains of IAV. In the present study, we evaluated the protective effect of Fructus Gardeniae iridoid glycoside extracts (IGEs) against IAV by cytopathogenic effect(CPE), MTT and a plaque formation assay in vitro and examined the reduction in the pulmonary index (PI), restoration of body weight, reduction in mortality and increases in survival time in vivo. As a host factor, PACT provides protection against the pathogenic influenza A virus by interacting with IAV polymerase and activating the IFN-I response. To verify the whether IGEs suppress IAV replication in a PACT-dependent manner, IAV RNA replication, expression of PACT and the phosphorylation of eIF2α in A549 cells were detected; the levels of IFNβ, PACT and PKR in mouse lung tissues were determined; and the activity of IAV polymerase was evaluated in PACT-compromised cells. The results indicated that IGEs sufficiently alleviated cell damage and suppressed IAV replication in vitro, protecting mice from IAV-induced injury and lethal IAV infection. These anti-IAV effects might be related to disrupted interplay between IVA polymerase and PACT and/or prevention of a PACT-dependent overactivated IFN-I antiviral response. Taken together, our findings reveal a new facet of the mechanisms by which IGEs fight the influenza A virus in a PACT-dependent manner.

Changes in macrophage inflammatory protein-1 (MIP-1) family members expression induced by traumatic brain injury in mice

A deep knowledge of the profound immunological response induced by traumatic brain injury (TBI) raises the possibility of novel therapeutic interventions. Existing studies have highlighted the important roles of C-C motif ligands in the development of neuroinflammation after brain injury; however, the participation of macrophage inflammatory protein-1 (MIP-1) family members in this phenomenon is still undefined. Therefore, the goal of our study was to evaluate changes in macrophage inflammatory protein-1 (MIP-1) family members (CCL3, CCL4, and CCL9) and their receptors (CCR1 and CCR5) in a mouse model of TBI (induced by controlled cortical impact (CCI)). We also investigated the pattern of activation of immunological cells (such as neutrophils, microglia and astroglia), which on one hand express CCR1/CCR5, and on the other hand might be a source of the tested chemokines in the injured brain. We investigated changes in mRNA (RT-qPCR) and/or protein (ELISA and Western blot) expression in brain structures (the cortex, hippocampus, thalamus, and striatum) at different time points (24 h, 4 days, 7 days, 2 weeks, and/or 5 weeks) after trauma. Our time-course studies revealed the upregulation of the mRNA expression of all members of the MIP-1 family (CCL3, CCL4, and CCL9) in all tested brain structures, mainly in the early stages after injury. A similar pattern of activation was observed at the protein level in the cortex and thalamus, where the strongest activation was observed 1 day after CCI; however, we did not observe any change in CCL3 in the thalamus. Analyses of CCR1 and CCR5 demonstrated the upregulation of the mRNA expression of both receptors in all tested cerebral structures, mainly in the early phases post injury (24 h, 4 days and 7 days). Protein analysis showed the upregulation of CCR1 and CCR5 in the thalamus 24 h after TBI, but we did not detect any change in the cortex. We also observed the upregulation of neutrophil marker (MPO) at the early time points (24 h and 7 days) in the cortex, while the profound activation of microglia (IBA-1) and astroglia (GFAP) was observed mainly on day 7. Our findings highlight for the first time that CCL3, CCL4, CCL9 and their receptors offer promising targets for influencing secondary neuronal injury and improving TBI therapy. The results suggest that the MIP-1 family is an important target for pharmacological intervention for brain injury.