Neutrophil dysfunction in the pathogenesis of cystic fibrosis

Neutrophil diversity and function in health and disease

Neutrophils, the most abundant type of granulocyte, are widely recognized as one of the pivotal contributors to the acute inflammatory response. Initially, neutrophils were considered the mobile infantry of the innate immune system, tasked with the immediate response to invading pathogens. However, recent studies have demonstrated that neutrophils are versatile cells, capable of regulating various biological processes and impacting both human health and disease. Cytokines and other active mediators regulate the functional activity of neutrophils by activating multiple receptors on these cells, thereby initiating downstream signal transduction pathways. Dysfunctions in neutrophils and disruptions in neutrophil homeostasis have been implicated in the pathogenesis of numerous diseases, including cancer and inflammatory disorders, often due to aberrant intracellular signaling. This review provides a comprehensive synthesis of neutrophil biological functions, integrating recent advancements in this field. Moreover, it examines the biological roles of receptors on neutrophils and downstream signaling pathways involved in the regulation of neutrophil activity. The pathophysiology of neutrophils in numerous human diseases and emerging therapeutic approaches targeting them are also elaborated. This review also addresses the current limitations within the field of neutrophil research, highlighting critical gaps in knowledge that warrant further investigation. In summary, this review seeks to establish a comprehensive and multidimensional model of neutrophil regulation, providing new perspectives for potential clinical applications and further research.

Normalization of Cystic Fibrosis Immune System Reverses Intestinal Neutrophilic Inflammation and Significantly Improves the Survival of Cystic Fibrosis Mice

BACKGROUND & AIMS

Cystic fibrosis (CF) is an autosomal recessive genetic disorder, affecting multiple organ systems. CF intestinal disease develops early, manifesting as intestinal bacterial overgrowth/dysbiosis, neutrophilic inflammation, and obstruction. As unresolvable infection and inflammation reflect host immune deficiency, we sought to determine if the CF-affected immune system plays any significant role in CF intestinal disease pathogenesis.

METHODS

CF and sibling wild-type (WT) mice underwent reciprocal bone marrow transplantation. After immune reconstitution, their mortality, intestinal transit, fecal inflammatory markers, and mucosal immune cell composition were assessed. Moreover, reciprocal neutrophil transfusion was conducted to determine if neutrophil function affects intestinal movement. Furthermore, expression of induced nitric oxide synthase (iNOS) and production of nitric oxide (NO) in CF and WT neutrophils were compared. Lastly, specific iNOS inhibitor 1400W was tested to prevent CF intestinal obstruction.

RESULTS

Immune restoration in CF mice reversed the intestinal neutrophilic inflammation, improved the intestinal dysmotility, and rescued the mice from mortality. Transfusion of WT neutrophils into CF mice ameliorated the retarded bowel movement. CF neutrophils expressed significantly more iNOS and produced significantly more NO. Pharmaceutical blocking of iNOS significantly improved intestinal transit and survival of CF mice.

CONCLUSIONS

CF immune defect plays a critical role in CF intestinal disease development. Activation of iNOS in inflammatory cells produces excessive NO, slows the bowel movement, and facilitates intestinal paralysis and obstruction in CF. Thus, normalization of the CF immune system may offer a novel therapy to treat CF intestinal disease.

Chitosan-naphthalimide probes for dual channel recognition of HClO and H2S in cells and their application in photodynamic therapy

The combination of bio-imaging with photodynamic therapy (PDT) to accomplish theranostics is promising in cancer treatment. Three chitosan-naphthalimide probes were studied in this work. 4-(5-Bromothiophen-2-yl)-1,8-naphthalic anhydride was first synthesized, and then reacted with chitosan to obtain the macromolecules (CS-N-Br). The recognition group thiomorpholine or its derivatives were introduced into CS-N-Br to obtain nano-probes (CS-N-ML, CS-N-BSZ, CS-N-FSQ) eventually. The studies revealed that CS-N-ML and CS-N-FSQ exhibit high selectivity and can specifically recognize HClO and H2S. CS-N-ML and CS-N-FSQ can perform exogenous and endogenous confocal imaging of HClO and H2S in cells also. CS-N-ML's ability to target lysosomes positions indicated it could act as a lysosome-specific probe. It was discovered that the probes generate superoxide anions (O2•-) via a Type I mechanism. This discovery endows the probes with high photosensitizing activity even under hypoxic conditions. There is a positive correlation between the extent of the conjugated system and the photosensitivity of the probes, indicating that an enhanced conjugation leads to increased photosensitivity. Upon light irradiation, the probes generate ROS within HeLa cells. These results suggested that these probes can achieve theranostics for diseases associated with abnormal levels of HClO and H2S.

Chronic Coinfection with Pseudomonas aeruginosa and Normal Colony Staphylococcus aureus Causes Lung Structural Damage in the Cystic Fibrosis Rat

Cystic fibrosis (CF) respiratory outcomes are heavily influenced by complications of infection. Pseudomonas aeruginosa and Staphylococcus aureus are the most common colonizers of the cystic fibrosis lung, and frequently overlap to cause chronic and persistent coinfections associated with severe disease. However, the dynamics of P. aeruginosa and S. aureus coinfection and its impacts on the development of CF lung structural damage are poorly understood. Additionally, small colony variants (SCVs) of S. aureus have been associated with P. aeruginosa infections in people with CF, but their role in disease progression is largely unknown. In this work, the CF rat was used to model chronic lung coinfection with P. aeruginosa and S. aureus, using clinically and laboratory-derived normal colony and SCV strains of S. aureus to evaluate the impact of phenotype on clinical outcomes. Rats coinfected with clinically derived S. aureus of both phenotypes experienced increased inflammation in the lung, but only the combination of P. aeruginosa and clinically normal colony S. aureus led to lung structural decline, including mucus obstruction and bronchiectasis. In regression analyses, damage was associated with a higher burden of P. aeruginosa, indicating that chronic coinfection with normal colony S. aureus and P. aeruginosa may support the progression CF lung decline driven by P. aeruginosa, which might be avoided when coinfecting S. aureus exhibits the SCV phenotype.

Expression of neutrophil extracellular trap-related proteins and its correlation with IL-17 and TNF-α in patients with oral lichen planus

Background

Neutrophil extracellular traps (NETs) are produced by polymorphonuclear neutrophils (PMNs) stimulated by interleukin-17 (IL-17) and tumor necrosis factor α (TNF-α). However, the level and role of NETs in oral lichen planus (OLP) remain poorly understood.

Objective

This study aimed to investigate the expression of NETs in OLP and explore the correlation between NETs and the levels of IL-17 and TNF-α.

Methods

The expression and distribution of NET-related proteins in tissue samples from each group were assessed using hematoxylin-eosin (HE) staining and immunofluorescence (IF). Additionally, the expression of NET-related proteins in peripheral blood samples from each group was evaluated using cell IF technique and fluorescence spectrophotometry. The relative formation level of NETs in each group was determined by fluorescence spectrophotometry via plasma co-culture. Furthermore, the levels of inflammatory cytokines IL-17 and TNF-α in plasma and culture supernatant were measured using enzyme-linked immunosorbent assay (ELISA).

Results

NET-related proteins were located in the subepithelial and lamina propria layers of OLP lesions. OLP had significantly higher expression of NET-related proteins in lesion tissues and peripheral blood compared to the healthy control (HC) group (p < 0.05). The rate of NETs formation in the erosive-stage OLP (EOLP) group was significantly higher than that in the HC group (p < 0.05), in contrast, no significant increase was observed in the non-erosive OLP (NEOLP) group (p > 0.05). Furthermore, the levels of IL-17 and TNF-α in the EOLP group were significantly elevated compared to those in the NEOLP group and HC group (p < 0.05), while the levels in the NEOLP group did not significantly differ from those in the HC group (p > 0.05). The rate of NETs formation showed a positive correlation with the levels of IL-17 and TNF-α in plasma.

Conclusion

The expression of NET-related proteins was upregulated in OLP lesion tissues and peripheral blood. Elevated levels of IL-17 and TNF-α in peripheral blood plasma positively correlated with the rate of NETs formation, suggesting that IL-17 and TNF-α mediate the formation of NETs in OLP patients, and may thereby contribute to the development of OLP.

Flagellum-deficient Pseudomonas aeruginosa is more virulent than non-motile but flagellated mutants in a cystic fibrosis mouse model

Loss of the flagellum marks the pathoadaptation of Pseudomonas aeruginosa to the cystic fibrosis (CF) airway environment during lung disease. Losing the flagellum is advantageous to the bacterium as the flagellum can be recognized by immune cells. The primary purpose of the flagellum is, however, to provide motility to the bacterium. Our goal was to determine whether the loss of flagellar motility or the loss of flagellum expression contributes to P. aeruginosa lung infection in CF. To address this, wild-type and gut-corrected FABP-human cystic fibrosis transmembrane conductance regulator (hCFTR) mice deficient in the murine Cftr gene were infected intratracheally with lethal doses of wild-type or flagellum-deficient P. aeruginosa. While there was no significant difference in the survival of wild-type mice after infection with either of the bacterial strains, a significantly higher mortality was observed in FABP-hCFTR mice infected with flagellum-deficient P. aeruginosa, compared to mice infected with their flagellated counterparts. When FABP-hCFTR mice were infected with isogenic, motility-deficient flagellated mutants, animal survival and lung bacterial titers were similar to those observed in mice infected with the wild-type bacterium. Airway levels of neutrophils and the amount neutrophil elastase were similar in mice infected with either the wild-type bacteria or the flagellum-deficient P. aeruginosa. Our results show that FABP-hCFTR mice have a different response to flagellum loss in P. aeruginosa compared to wild-type animals. The loss of flagellum expression, rather than the loss of motility, is the main driver behind the increased virulence of flagellum-deficient P. aeruginosa in CF. These observations provide new insight into P. aeruginosa virulence in CF.IMPORTANCEPseudomonas aeruginosa, a major respiratory pathogen in cystic fibrosis, is known to lose its flagellum during the course of infection in the airways. Here, we show that the loss of flagellum leads to a more enhanced virulence in Cftr-deficient cystic fibrosis mice than in control animals. Loss of flagellum expression, rather than the loss of flagellar swimming motility, represents the main driver behind this increased virulence suggesting that this appendage plays a specific role in P. aeruginosa virulence in cystic fibrosis airways.

An integrated metaproteomics workflow for studying host-microbe dynamics in bronchoalveolar lavage samples applied to cystic fibrosis disease

Airway microbiota are known to contribute to lung diseases, such as cystic fibrosis (CF), but their contributions to pathogenesis are still unclear. To improve our understanding of host-microbe interactions, we have developed an integrated analytical and bioinformatic mass spectrometry (MS)-based metaproteomics workflow to analyze clinical bronchoalveolar lavage (BAL) samples from people with airway disease. Proteins from BAL cellular pellets were processed and pooled together in groups categorized by disease status (CF vs. non-CF) and bacterial diversity, based on previously performed small subunit rRNA sequencing data. Proteins from each pooled sample group were digested and subjected to liquid chromatography tandem mass spectrometry (MS/MS). MS/MS spectra were matched to human and bacterial peptide sequences leveraging a bioinformatic workflow using a metagenomics-guided protein sequence database and rigorous evaluation. Label-free quantification revealed differentially abundant human peptides from proteins with known roles in CF, like neutrophil elastase and collagenase, and proteins with lesser-known roles in CF, including apolipoproteins. Differentially abundant bacterial peptides were identified from known CF pathogens (e.g., Pseudomonas), as well as other taxa with potentially novel roles in CF. We used this host-microbe peptide panel for targeted parallel-reaction monitoring validation, demonstrating for the first time an MS-based assay effective for quantifying host-microbe protein dynamics within BAL cells from individual CF patients. Our integrated bioinformatic and analytical workflow combining discovery, verification, and validation should prove useful for diverse studies to characterize microbial contributors in airway diseases. Furthermore, we describe a promising preliminary panel of differentially abundant microbe and host peptide sequences for further study as potential markers of host-microbe relationships in CF disease pathogenesis.IMPORTANCEIdentifying microbial pathogenic contributors and dysregulated human responses in airway disease, such as CF, is critical to understanding disease progression and developing more effective treatments. To this end, characterizing the proteins expressed from bacterial microbes and human host cells during disease progression can provide valuable new insights. We describe here a new method to confidently detect and monitor abundance changes of both microbe and host proteins from challenging BAL samples commonly collected from CF patients. Our method uses both state-of-the art mass spectrometry-based instrumentation to detect proteins present in these samples and customized bioinformatic software tools to analyze the data and characterize detected proteins and their association with CF. We demonstrate the use of this method to characterize microbe and host proteins from individual BAL samples, paving the way for a new approach to understand molecular contributors to CF and other diseases of the airway.

Collagen concentration regulates neutrophil extravasation and migration in response to infection in an endothelium dependent manner

Introduction

As the body's first line of defense against disease and infection, neutrophils must efficiently navigate to sites of inflammation; however, neutrophil dysregulation contributes to the pathogenesis of numerous diseases that leave people susceptible to infections. Many of these diseases are also associated with changes to the protein composition of the extracellular matrix. While it is known that neutrophils and endothelial cells, which play a key role in neutrophil activation, are sensitive to the mechanical and structural properties of the extracellular matrix, our understanding of how protein composition in the matrix affects the neutrophil response to infection is incomplete.

Methods

To investigate the effects of extracellular matrix composition on the neutrophil response to infection, we used an infection-on-a-chip microfluidic device that replicates a portion of a blood vessel endothelium surrounded by a model extracellular matrix. Model blood vessels were fabricated by seeding human umbilical vein endothelial cells on 2, 4, or 6 mg/mL type I collagen hydrogels. Primary human neutrophils were loaded into the endothelial lumens and stimulated by adding the bacterial pathogen Pseudomonas aeruginosa to the surrounding matrix.

Results

Collagen concentration did not affect the cell density or barrier function of the endothelial lumens. Upon infectious challenge, we found greater neutrophil extravasation into the 4 mg/mL collagen gels compared to the 6 mg/mL collagen gels. We further found that extravasated neutrophils had the highest migration speed and distance in 2mg/mL gels and that these values decreased with increasing collagen concentration. However, these phenomena were not observed in the absence of an endothelial lumen. Lastly, no differences in the percent of extravasated neutrophils producing reactive oxygen species were observed across the various collagen concentrations.

Discussion

Our study suggests that neutrophil extravasation and migration in response to an infectious challenge are regulated by collagen concentration in an endothelial cell-dependent manner. The results demonstrate how the mechanical and structural aspects of the tissue microenvironment affect the neutrophil response to infection. Additionally, these findings underscore the importance of developing and using microphysiological systems for studying the regulatory factors that govern the neutrophil response.

Nanoparticle-neutrophils interactions for autoimmune regulation

Neutrophils play an essential role as 'first responders' in the immune response, necessitating many immune-modulating capabilities. Chronic, unresolved inflammation is heavily implicated in the progression and tissue-degrading effects of autoimmune disease. Neutrophils modulate disease pathogenesis by interacting with the inflammatory and autoreactive cells through effector functions, including signaling, degranulation, and neutrophil extracellular traps (NETs) release. Since the current gold standard systemic glucocorticoid administration has many drawbacks and side effects, targeting neutrophils in autoimmunity provides a new approach to developing therapeutics. Nanoparticles enable targeting of specific cell types and controlled release of a loaded drug cargo. Thus, leveraging nanoparticle properties and interactions with neutrophils provides an exciting new direction toward novel therapies for autoimmune diseases. Additionally, recent work has utilized neutrophil properties to design novel targeted particles for delivery into previously inaccessible areas. Here, we outline nanoparticle-based strategies to modulate neutrophil activity in autoimmunity, including various nanoparticle formulations and neutrophil-derived targeting.

CFTR dysfunction leads to defective bacterial eradication on cystic fibrosis airways

Dysfunction of the cystic fibrosis transmembrane conductance regulator (CFTR) anion channel by genetic mutations causes the inherited disease cystic fibrosis (CF). CF lung disease that involves multiple disorders of epithelial function likely results from loss of CFTR function as an anion channel conducting chloride and bicarbonate ions and its function as a cellular regulator modulating the activity of membrane and cytosol proteins. In the absence of CFTR activity, abundant mucus accumulation, bacterial infection and inflammation characterize CF airways, in which inflammation-associated tissue remodeling and damage gradually destroys the lung. Deciphering the link between CFTR dysfunction and bacterial infection in CF airways may reveal the pathogenesis of CF lung disease and guide the development of new treatments. Research efforts towards this goal, including high salt, low volume, airway surface liquid acidosis and abnormal mucus hypotheses are critically reviewed.

Lytic bacteriophages induce the secretion of antiviral and proinflammatory cytokines from human respiratory epithelial cells

Phage therapy is a therapeutic approach to treat multidrug-resistant (MDR) infections that employs lytic bacteriophages (phages) to eliminate bacteria. Despite the abundant evidence for its success as an antimicrobial in Eastern Europe, there is scarce data regarding its effects on the human host. Here, we aimed to understand how lytic phages interact with cells of the airway epithelium, the tissue site that is colonized by bacterial biofilms in numerous chronic respiratory disorders. Using a panel of Pseudomonas aeruginosa phages and human airway epithelial cells (AECs) derived from a person with cystic fibrosis (CF), we determined that interactions between phages and epithelial cells depend on specific phage properties as well as physiochemical features of the microenvironment. Although poor at internalizing phages, the airway epithelium responds to phage exposure by changing its transcriptional profile and secreting antiviral and proinflammatory cytokines that correlate with specific phage families. Overall, our findings indicate that mammalian responses to phages are heterogenous and could potentially alter the way that respiratory local defenses aid in bacterial clearance during phage therapy. Thus, besides phage receptor specificity in a particular bacterial isolate, the criteria to select lytic phages for therapy should be expanded to include mammalian cell responses.

Aberrant immune programming in neutrophils in cystic fibrosis

Cystic fibrosis is a life-shortening genetic disorder, caused by mutations in the gene that encodes cystic fibrosis transmembrane-conductance regulator, a cAMP-activated chloride and bicarbonate channel. Persistent neutrophilic inflammation is a major contributor to cystic fibrosis lung disease. However, how cystic fibrosis transmembrane-conductance regulator loss of function leads to excessive inflammation and its clinical sequela remains incompletely understood. In this study, neutrophils from F508del-CF and healthy control participants were compared for gene transcription. We found that cystic fibrosis circulating neutrophils have a prematurely primed basal state with significantly higher scores for activation, chemotaxis, immune signaling, and pattern recognition. Such an irregular basal state appeared not related to the blood environment and was also observed in neutrophils derived from the F508del-CF HL-60 cell line, indicating an innate characteristic of the phenotype. Lipopolysaccharides (LPS) stimulation drastically shifted the transcriptional landscape of healthy control neutrophils toward a robust immune response; however, cystic fibrosis neutrophils were immune-exhausted, reflected by abnormal cell aging and fate determination in gene programming. Moreover, cystic fibrosis sputum neutrophils differed significantly from cystic fibrosis circulating neutrophils in gene transcription with increased inflammatory response, aging, apoptosis, and necrosis, suggesting additional environmental influences on the neutrophils in cystic fibrosis lungs. Taken together, our data indicate that loss of cystic fibrosis transmembrane-conductance regulator function has intrinsic effects on neutrophil immune programming, leading to premature priming and dysregulated response to challenge.

Cystic fibrosis in the era of CFTR modulators: did the neutrophil slip through the cracks?

Neutrophil abnormalities are present in patients with cystic fibrosis treated with CFTR modulators.

Lytic bacteriophages interact with respiratory epithelial cells and induce the secretion of antiviral and proinflammatory cytokines

Phage therapy is a therapeutic approach to treat multidrug resistant infections that employs lytic bacteriophages (phages) to eliminate bacteria. Despite the abundant evidence for its success as an antimicrobial in Eastern Europe, there is scarce data regarding its effects on the human host. Here, we aimed to understand how lytic phages interact with cells of the airway epithelium, the tissue site that is colonized by bacterial biofilms in numerous chronic respiratory disorders. We determined that interactions between phages and epithelial cells depend on specific phage properties as well as physiochemical features of the microenvironment. Although poor at internalizing phages, the airway epithelium responds to phage exposure by changing its transcriptional profile and secreting antiviral and proinflammatory cytokines that correlate with specific phage families. Overall, our findings indicate that mammalian responses to phages are heterogenous and could potentially alter the way that respiratory local defenses aid in bacterial clearance during phage therapy. Thus, besides phage receptor specificity in a particular bacterial isolate, the criteria to select lytic phages for therapy should be expanded to include mammalian cell responses.

Cystic Fibrosis Carrier States Are Associated With More Severe Cases of Bronchiectasis

Background

People with cystic fibrosis (CF) are at increased risk for bronchiectasis, and several reports suggest that CF carriers may also be at higher risk for developing bronchiectasis. The purpose of this study was to determine if CF carriers are at risk for more severe courses or complications of bronchiectasis.

Methods

Using MarketScan data (2001-2021), we built a cohort consisting of 105 CF carriers with bronchiectasis and 300 083 controls with bronchiectasis but without a CF carrier diagnosis. We evaluated if CF carriers were more likely to be hospitalized for bronchiectasis. In addition, we examined if CF carriers were more likely to be infected with Pseudomonas aeruginosa or nontuberculous mycobacteria (NTM) or to have filled more antibiotic prescriptions. We considered regression models for incident and rate outcomes that controlled for age, sex, smoking status, and comorbidities.

Results

The odds of hospitalization were almost 2.4 times higher (95% CI, 1.116-5.255) for CF carriers with bronchiectasis when compared with non-CF carriers with bronchiectasis. The estimated odds of being diagnosed with a Pseudomonas infection for CF carriers vs noncarriers was about 4.2 times higher (95% CI, 2.417-7.551) and 5.4 times higher (95% CI, 3.398-8.804) for being diagnosed with NTM. The rate of distinct antibiotic fill dates was estimated to be 2 times higher for carriers as compared with controls (95% CI, 1.735-2.333), and the rate ratio for the total number of days of antibiotics supplied was estimated as 2.8 (95% CI, 2.290-3.442).

Conclusions

CF carriers with bronchiectasis required more hospitalizations and more frequent administration of antibiotics as compared with noncarriers. Given that CF carriers were also more likely to be diagnosed with Pseudomonas and NTM infections, CF carriers with bronchiectasis may have a phenotype more resembling CF-related bronchiectasis than non-CF bronchiectasis.

Association of low-density neutrophils with lung function and disease progression in adult cystic fibrosis

BACKGROUND

Cystic fibrosis (CF) neutrophils fail to eradicate infection despite their massive recruitment into the lung. While studies mostly focus on pathogen clearance by normal density neutrophils in CF, the contribution of low-density neutrophil (LDNs) subpopulations to disease pathogenesis remains unclear.

METHODS

LDNs were isolated from whole blood donations of clinically stable adult CF patients and from healthy donors. LDN proportion and immunophenotype was assessed by flow cytometry. Associations of LDNs with clinical parameters were determined.

RESULTS

LDN proportion was increased in CF patients' circulation compared with healthy donors. LDNs are a heterogeneous population of both mature and immature cells in CF and in healthy individuals. Moreover, a higher proportion of mature LDN correlates with a gradual decline in lung function and repeated pulmonary exacerbations in CF patients.

CONCLUSIONS

Collectively, our observations suggest that low-density neutrophils are linked to CF pathogenesis and underscore the potential clinical relevance of neutrophil subpopulations in CF.

Chronic daily respiratory care needs in people with cystic fibrosis treated with highly effective cystic fibrosis transmembrane conductance regulator modulators

PURPOSE OF REVIEW

Cystic fibrosis is a genetic disease that increases risk of death from respiratory failure because of impairment in mucociliary clearance. Complex daily care regimens including medications and airway clearance techniques (ACTs) aim to preserve lung function and alleviate symptoms for people with cystic fibrosis (pwCF). The success of highly effective modulator therapy (HEMT) permits evaluation of treatment simplification. In this review, we evaluate adjustments made in daily respiratory care among pwCF taking HEMT and the feasibility of treatment simplification.

RECENT FINDINGS

Treatment simplification has been identified as a top priority among pwCF, with recent studies showing pwCF are willing to sacrifice mild to moderate amounts of lung function and longevity to reduce treatment burden. Retrospective studies have shown that patients taking HEMT with better baseline lung function have lower adherence to and prescription of inhaled medications. A randomized, controlled trial found that short-term discontinuation of dornase alfa or hypertonic saline was clinically noninferior to continuation of these medications. Major knowledge gaps remain about withdrawing ACTs.

SUMMARY

This review highlights trials evaluating the feasibility of treatment simplification among pwCF taking HEMT. More data is needed to evaluate approaches to simplification in this phenotypically diverse patient population.

Neutrophil bactericidal activity and host defenses in cystic fibrosis: a narrative review

Background and Objective

Cystic fibrosis (CF) is a disorder that affects the cystic fibrosis transmembrane conductance regulator (CFTR). Without properly functioning CFTR channels, chloride does not exit respiratory epithelial cells, and consequently the mucus lining the surface of the cells becomes thick. This viscous mucus accumulates and causes abnormal function of the mucociliary apparatus, which can lead to bacterial colonization, infections with Staphylococcus aureus (S. aureus) and Pseudomonas aeruginosa (P. aeruginosa), and eventually lung damage. Recent studies have shown that the increased susceptibility to respiratory infections in CF patients may also be due to defects in neutrophil function, but the exact mechanism is uncertain.

Methods

The PubMed database was searched on February 10, 2023 and again on July 23, 2023 to compile a comprehensive list of clinical and experimental studies to evaluate neutrophil function in CF. The first search included a combination of MeSH terms: "cystic fibrosis" and "neutrophils/physiology". A separate second search included a combination of the MeSH terms: "neutrophils" and "cystic fibrosis transmembrane conductance regulator".

Key Content and Findings

Neutrophils from patients with CF have decreased transfer of chloride into phagolysosomes after bacterial ingestion and have dysregulated degranulation. This reduces the production of toxic oxidative radicals, especially hypochlorous acid (HOCl), and reduces bactericidal activity. CFTR potentiators correct the dysregulated degranulation in patients with CF and increased neutrophil killing activity. A reduced concentration of chloride in in vitro assays also reduces neutrophil killing activity; these observations are relevant to the reduced chloride concentrations in respiratory secretions in patients with CF.

Conclusions

This literature review summarizes studies that demonstrate that an important defect in CF neutrophils lies in the oxygen-dependent pathway in phagolysosomes and studies with ivacaftor demonstrate that this drug corrects CF neutrophil function. These studies demonstrate the potential utility of using easily available neutrophils to study drug effects in CF patients.

Molecular regulation of neutrophil swarming in health and disease: Lessons from the phagocyte oxidase

Neutrophil swarming is a complex coordinated process in which neutrophils sensing pathogen or damage signals are rapidly recruited to sites of infections or injuries. This process involves cooperation between neutrophils where autocrine and paracrine positive-feedback loops, mediated by receptor/ligand pairs including lipid chemoattractants and chemokines, amplify localized recruitment of neutrophils. This review will provide an overview of key pathways involved in neutrophil swarming and then discuss the cell intrinsic and systemic mechanisms by which NADPH oxidase 2 (NOX2) regulates swarming, including modulation of calcium signaling, inflammatory mediators, and the mobilization and production of neutrophils. We will also discuss mechanisms by which altered neutrophil swarming in disease may contribute to deficient control of infections and/or exuberant inflammation. Deeper understanding of underlying mechanisms controlling neutrophil swarming and how neutrophil cooperative behavior can be perturbed in the setting of disease may help to guide development of tools for diagnosis and precision medicine.

Sputum from People with Cystic Fibrosis Reduces the Killing of Methicillin-Resistant Staphylococcus aureus by Neutrophils and Diminishes Phagosomal Production of Reactive Oxygen Species

Cystic fibrosis (CF) airway disease is characterized by chronic polymicrobial infections and an infiltration of neutrophils (PMNs). Staphylococcus aureus has been the most prevalent respiratory pathogen in CF. In particular, methicillin-resistant S. aureus (MRSA) represents a huge clinical burden in CF due to its association with lung disease and increased resistance to antibiotics. In CF, PMNs are unable to kill and clear MRSA. The reason for this remains largely unknown. Our study found that CF PMNs are as equally capable of killing MRSA as healthy PMNs. We show that the CF sputum, however, significantly impairs the ability of human PMNs to kill CF MRSA isolates. In the absence of CF sputum, PMNs kill MRSA via intracellular mechanisms mediated by phagocytosis, rather than extracellular mechanisms via NET formation. CF sputum does not affect the phagocytosis of MRSA via healthy or CF PMNs. Our results demonstrate that CF sputum exposure impairs phagosomal levels of reactive oxygen species (ROS) in MRSA-phagocytosing PMNs. While phagosomal co-localizations of MRSA with primary granule markers, myeloperoxidase and cathepsin D, were significantly reduced upon CF sputum exposure, that of a third azurophilic granule marker, neutrophil elastase, remained unaffected. This suggests that CF sputum does not compromise the fusion of primary granules with phagosomes but diminishes phagosomal ROS levels via another, likely more specific, mechanism. Overall, we identified the airway environment as an important factor that restricts neutrophils' oxidative microbicidal activities in CF against MRSA. These results deliver new details of the complex host-pathogen interactions present in the CF lung.

Short chain fatty acids reduce the respiratory burst of human neutrophils in response to cystic fibrosis isolates of Staphylococcus aureus

Short chain fatty acids (SCFA) are produced by anaerobic bacteria. The most common SCFAs are acetate, propionate and butyrate. SCFAs have been implicated in several inflammatory diseases including cystic fibrosis (CF) where they are present in the airways at millimolar concentrations. Staphylococcus aureus is one of the main respiratory pathogens in CF. Polymorphonuclear neutrophil granulocytes (PMN) represent the most important immune defense the host uses against S. aureus. However, the reason why PMNs are unable to clear S. aureus in CF remains largely unclear. We hypothesized that SCFAs impair effector functions of PMNs in response to S. aureus. To test this, human PMNs were exposed to CF clinical isolates of S. aureus in vitro in the presence or absence of SCFAs and effector functions of PMNs were assessed. Our data show that SCFAs do not affect the viability of PMNs and do not stimulate the release of neutrophil extracellular traps (NET) from human PMNs. Production of reactive oxygen species (ROS), another important antimicrobial function of PMNs, on the other hand, was significantly inhibited by SCFAs in response to the bacterium. SCFAs did not compromise the ability of PMNs to kill CF isolates of S. aureus in vitro. Overall, our results provide new knowledge into the interactions between SCFAs and the immune system, and indicate that SCFAs produced by anaerobic bacteria in the CF lung could interfere with reactive oxidant production of PMNs in response to S. aureus, one of the prominent respiratory pathogens in this disease.

The formation and function of the neutrophil phagosome

Neutrophils are the most abundant circulating leukocyte and are crucial to the initial innate immune response to infection. One of their key pathogen-eliminating mechanisms is phagocytosis, the process of particle engulfment into a vacuole-like structure called the phagosome. The antimicrobial activity of the phagocytic process results from a collaboration of multiple systems and mechanisms within this organelle, where a complex interplay of ion fluxes, pH, reactive oxygen species, and antimicrobial proteins creates a dynamic antimicrobial environment. This complexity, combined with the difficulties of studying neutrophils ex vivo, has led to gaps in our knowledge of how the neutrophil phagosome optimizes pathogen killing. In particular, controversy has arisen regarding the relative contribution and integration of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-derived antimicrobial agents and granule-delivered antimicrobial proteins. Clinical syndromes arising from dysfunction in these systems in humans allow useful insight into these mechanisms, but their redundancy and synergy add to the complexity. In this article, we review the current knowledge regarding the formation and function of the neutrophil phagosome, examine new insights into the phagosomal environment that have been permitted by technological advances in recent years, and discuss aspects of the phagocytic process that are still under debate.

ABERRANT IMMUNE PROGRAMMING IN NEUTROPHILS IN CYSTIC FIBROSIS

Cystic fibrosis (CF) is a life-shortening genetic disorder, caused by mutations in the gene that encodes Cystic Fibrosis Transmembrane-conductance Regulator (CFTR), a cAMP-activated chloride and bicarbonate channel. Although multiple organ systems can be affected, CF lung disease claims the most morbidity and mortality due to chronic bacterial infection, persistent neutrophilic inflammation, and mucopurulent airway obstruction. Despite the clear predominance of neutrophils in these pathologies, how CFTR loss-of-function affects these cells per se remains incompletely understood. Here, we report the profiling and comparing of transcriptional signatures of peripheral blood neutrophils from CF participants and healthy human controls (HC) at the single-cell level. Circulating CF neutrophils had an aberrant basal state with significantly higher scores for activation, chemotaxis, immune signaling, and pattern recognition, suggesting that CF neutrophils in blood are prematurely primed. Such an abnormal basal state was also observed in neutrophils derived from an F508del-CF HL-60 cell line, indicating an innate characteristic of the phenotype. LPS stimulation drastically shifted the transcriptional landscape of HC circulating neutrophils towards a robust immune response, however, CF neutrophils were immune-exhausted. Moreover, CF blood neutrophils differed significantly from CF sputum neutrophils in gene programming with respect to neutrophil activation and aging, as well as inflammatory signaling, highlighting additional environmental influences on the neutrophils in CF lungs. Taken together, loss of CFTR function has intrinsic effects on neutrophil immune programming that leads to premature priming and dysregulated response to challenge.

Resolvins Lipid Mediators: Potential Therapeutic Targets in Alzheimer and Parkinson Disease

Inflammation and resolution are highly programmed processes involving a plethora of immune cells. Lipid mediators synthesized from arachidonic acid metabolism play a pivotal role in orchestrating the signaling cascades in the game of inflammation. The majority of the studies carried out so far on inflammation were aimed at inhibiting the generation of inflammatory molecules, whereas recent research has shifted more towards understanding the resolution of inflammation. Owing to chronic inflammation as evident in neuropathophysiology, the resolution of inflammation together with the class of lipid mediators actively involved in its regulation has attracted the attention of the scientific community as therapeutic targets. Both omega-three polyunsaturated fatty acids, eicosapentaenoic acid and docosahexaenoic acid, orchestrate a vital regulatory role in inflammation development. Resolvins derived from these fatty acids comprise the D-and E-series resolvins. A growing body of evidence using in vitro and in vivo models has revealed the pro-resolving and anti-inflammatory potential of resolvins. This systematic review sheds light on the synthesis, specialized receptors, and resolution of inflammation mediated by resolvins in Alzheimer's and Parkinson's disease.

Cftr deletion in mouse epithelial and immune cells differentially influence the intestinal microbiota

Cystic fibrosis (CF) is a life-threatening genetic disorder, caused by mutations in the CF transmembrane-conductance regulator gene (cftr) that encodes CFTR, a cAMP-activated chloride and bicarbonate channel. Clinically, CF lung disease dominates the adult patient population. However, its gastrointestinal illness claims the early morbidity and mortality, manifesting as intestinal dysbiosis, inflammation and obstruction. As CF is widely accepted as a disease of epithelial dysfunction, it is unknown whether CFTR loss-of-function in immune cells contributes to these clinical outcomes. Using cftr genetic knockout and bone marrow transplantation mouse models, we performed 16S rRNA gene sequencing of the intestinal microbes. Here we show that cftr deletion in both epithelial and immune cells collectively influence the intestinal microbiota. However, the immune defect is a major factor determining the dysbiosis in the small intestine, while the epithelial defect largely influences that in the large intestine. This finding revises the current concept by suggesting that CF epithelial defect and immune defect play differential roles in CF intestinal disease.

Impact of CFTR Modulators on the Impaired Function of Phagocytes in Cystic Fibrosis Lung Disease

Cystic fibrosis (CF), the most common genetically inherited disease in Caucasian populations, is a multi-systemic life-threatening autosomal recessive disorder caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. In 2012, the arrival of CFTR modulators (potentiators, correctors, amplifiers, stabilizers, and read-through agents) revolutionized the therapeutic approach to CF. In this review, we examined the physiopathological mechanism of chronic dysregulated innate immune response in the lungs of CF patients with pulmonary involvement with particular reference to phagocytes, critically analyzing the role of CFTR modulators in influencing and eventually restoring their function. Our literature review highlighted that the role of CFTR in the lungs is crucial not only for the epithelial function but also for host defense, with particular reference to phagocytes. In macrophages and neutrophils, the CFTR dysfunction compromises both the intricate process of phagocytosis and the mechanisms of initiation and control of inflammation which then reverberates on the epithelial environment already burdened by the chronic colonization of pathogens leading to irreversible tissue damage. In this context, investigating the impact of CFTR modulators on phagocytic functions is therefore crucial not only for explaining the underlying mechanisms of pleiotropic effects of these molecules but also to better understand the physiopathological basis of this disease, still partly unexplored, and to develop new complementary or alternative therapeutic approaches.

Approaches for neutrophil imaging: an important step in personalized medicine

Neutrophils are the most abundant circulating leukocytes and the first line of defense against invading pathogens. They are key components of the innate immune system. Neutrophils also cause tissue damage in various autoimmune and inflammatory diseases and play an important role in cancer progression. Due to the complex relationship between various diseases and neutrophils, these cells have become potentially important targets for therapeutic interventions. Monitoring neutrophils in the tumor microenvironment is critical for tumor treatment and prognostic analysis but remains challenging. Molecular imaging technology has made great progress as a valuable tool for noninvasively visualizing biological events and establishing effective cancer diagnoses and treatment methods. Molecular probes designed based on the characteristics of neutrophils, such as their flexible morphology, the abundance of surface receptors, and the absence of immunogenicity, have shown great potential. This has created an opportunity for novel ideas and research methods for the diagnosis and targeted therapy of inflammatory diseases and tumors, with the goal of integrated diagnosis and treatment. This review discusses the diverse tumor detection and diagnostic imaging strategies based on neutrophils. It is anticipated that neutrophil-based imaging will soon be gradually integrated into clinical applications.