Pseudomonas aeruginosa isolates from cystic fibrosis patients induce neutrophil extracellular traps with different morphologies that could correlate with their disease severity

Neutrophil Extracellular Traps and Respiratory Disease

Extracellular traps made by neutrophils (NETs) and other leukocytes such as macrophages and eosinophils have a key role in the initial immune response to infection but are highly inflammatory and may contribute to tissue damage. They are particularly relevant to lung disease, with the pulmonary anatomy facilitating their ability to fully extend into the airways/alveolar space. There has been a rapid expansion in the number of published studies demonstrating their role in a variety of important respiratory diseases including chronic obstructive pulmonary disease, cystic fibrosis, bronchiectasis, asthma, pneumonia, COVID-19, rhinosinusitis, interstitial lung disease and lung cancer. The expression of NETs and other traps is a specific process, and diagnostic tests need to differentiate them from other inflammatory pathways/causes of cell death that are also characterised by the presence of extracellular DNA. The specific targeting of this pathway by relevant therapeutics may have significant clinical benefit; however, current clinical trials/evidence are at a very early stage. This review will provide a broad overview of the role of NETs and their possible treatment in respiratory disease.

Role of innate immunity and systemic inflammation in cystic fibrosis disease progression

Pathophysiological manifestations of cystic fibrosis (CF) result from a functional defect in the cystic fibrosis transmembrane conductance regulator (CFTR) paving way for mucus obstruction and pathogen colonization. The role of CFTR in modulating immune cell function and vascular integrity, irrespective of mucus thickening, in determining the host cell response to pathogens/allergens and causing systemic inflammation is least appreciated. Since CFTR plays a key role in the conductance of anions like Cl-, loss of CFTR function could affect various basic cellular processes, such as cellular homeostasis, lysosome acidification, and redox balance. CFTR aids in endotoxin tolerance by regulating Toll-like receptor-mediated signaling resulting in uncontrolled activation of innate immune cells. Although leukocytes of CF patients are hyperactivated, they exhibit compromised phagosome activity thus favouring the orchestration of sepsis from defective pathogen clearance. This review will emphasize the importance of innate immunity and systemic inflammatory response in the development of CF and other CFTR-associated pathologies.

Immune escape strategies of Pseudomonas aeruginosa to establish chronic infection

The infection caused by P. aeruginosa still is dangerous throughout the world. This is partly due to its immune escape mechanisms considerably increasing the bacterial survival in the host. By escape from recognition by TLRs, interference with complement system activation, phagocytosis inhibition, production of ROS, inhibition of NET production, interference with the generation of cytokines, inflammasome inhibition, reduced antigen presentation, interference with cellular and humoral immunity, and induction of apoptotic cell death and MDSc, P. aeruginosa breaks down the barriers of the immune system and causes lethal infections in the host. Recognition of other immune escape mechanisms of P. aeruginosa may provide a basis for the future treatment of the infection. This manuscript may provide new insights and information for the development of new strategies to combat P. aeruginosa infection. In the present manuscript, the escape mechanisms of P. aeruginosa against immune response would be reviewed.

Neutrophil extracellular traps: Modulation mechanisms by pathogens

Neutrophils, as innate effector cells, play an essential role in the containment and elimination of pathogens. Among the main neutrophil mechanisms use for these processes is the release of neutrophil extracellular traps (NETs), which consist of decondensed DNA decorated with various cytoplasmic proteins. NETs' principal role is the trapping and elimination of infectious agents; therefore, the formation of NETs is regulated by bacteria, fungi, parasites, and viruses through different mechanisms: the presence of virulence factors (adhered or secreted), microbial load, size of the microorganism, and even due to other immune cells activation (mainly platelets). This review summarizes the significant aspects that contribute to NETs modulation by pathogens and their components, and the effect NETs have on these pathogens as a cellular defense mechanism.

Trichinella spiralis excretory-secretory antigens selectively inhibit the release of extracellular traps from neutrophils without affecting their additional antimicrobial functions

Neutrophil extracellular traps (NETs) are fiber structures composed of chromatin and granular proteins that capture and eliminate microorganisms. The NETs formation is induced in response to pathogens and physiological stimuli; however, some pathogens have developed strategies to evade NETs activity. Trichinella spiralis excretory-secretory (ES) antigens are proteins that allow the establishment of the parasite in the host, facilitating penetration, migration, nutrition, and survival. In this paper we described that ES antigens inhibit NETs release, since neutrophils incubated with these antigens maintains a delobulated nucleus, without the release fibers structures indicative of NETs. We also found that other antimicrobial functions of neutrophils, such as phagocytic activity, degranulation, and ROS production, remain unchanged after incubation with ES antigens. This is relevant since it could constitute a novel strategy for the treatment of autoimmune pathologies in which the formation of NETs performs an important role.

CLEC5A is critical in Pseudomonas aeruginosa-induced acute lung injury

Pseudomonas aeruginosa is one of the most common nosocomial infections worldwide, and it frequently causes ventilator-associated acute pneumonia in immunocompromised patients. Abundant neutrophil extracellular traps (NETs) contribute to acute lung injury, thereby aggravating ventilator-induced lung damage. While pattern recognition receptors (PRRs) TLR4 and TLR5 are required for host defense against P. aeruginosa invasion, the PRR responsible for P. aeruginosa–induced NET formation, proinflammatory cytokine release, and acute lung injury remains unclear. We found that myeloid C-type lectin domain family 5 member A (CLEC5A) interacts with LPS of P. aeruginosa and is responsible for P. aeruginosa–induced NET formation and lung inflammation. P. aeruginosa activates CLEC5A to induce caspase-1–dependent NET formation, but it neither causes gasdermin D (GSDMD) cleavage nor contributes to P. aeruginosa–induced neutrophil death. Blockade of CLEC5A attenuates P. aeruginosa–induced NETosis and lung injury, and simultaneous administration of anti-CLEC5A mAb with ciprofloxacin increases survival rate and decreases collagen deposition in the lungs of mice challenged with a lethal dose of P. aeruginosa. Thus, CLEC5A is a promising therapeutic target to reduce ventilator-associated lung injury and fibrosis in P. aeruginosa–induced pneumonia.

Investigating neutrophil cell death in TB pathogenesis

Background: Neutrophils are one of the major early role players in antimycobacterial immunity. Upon infection, neutrophils can undergo NETosis, a cell death characterized by release of neutrophil extracellular traps (NETs). The role of NETosis in TB progression remains poorly characterized. We aim to characterize mechanisms underlying NETosis during TB pathogenesis by identifying genes that drive the cell death, and to determine their potential as markers of disease progression in high-risk individuals. Finally, we intend to evaluate neutrophil associated genes as targets for host directed therapy to reduce pathological damage caused by NETosis. Methods: Quantitative PCR will be used to quantify expression of specific genes identified in the blood of individuals with active lung disease (n=30), compared to those from healthy (n=30) and latently infected individuals (LTBI) (n=30). In addition, temporal events associated with NETosis will be measured using live microscopy in a neutrophil in vitro model of Mycobacterium tuberculosis (Mtb) infection. Candidate genes found to be associated with NETosis will be targeted with pharmaceutical inhibitors. Conclusion: Genes associated with neutrophil mediated cell death may serve as potential biomarkers of pathological damage and disease progression, as well as targets for host-directed therapy.

Neutrophil extracellular traps in chronic lung disease: implications for pathogenesis and therapy

Neutrophilic inflammation has a key role in the pathophysiology of multiple chronic lung diseases. The formation of neutrophil extracellular traps (NETs) has emerged as a key mechanism of disease in neutrophilic lung diseases including asthma, COPD, cystic fibrosis and, most recently, bronchiectasis. NETs are large, web-like structures composed of DNA and anti-microbial proteins that are able to bind pathogens, prevent microbial dissemination and degrade bacterial virulence factors. The release of excess concentrations of proteases, antimicrobial proteins, DNA and histones, however, also leads to tissue damage, impaired mucociliary clearance, impaired bacterial killing and increased inflammation. A number of studies have linked airway NET formation with greater disease severity, increased exacerbations and overall worse disease outcomes across the spectrum of airway diseases. Treating neutrophilic inflammation has been challenging in chronic lung disease because of the delicate balance between reducing inflammation and increasing the risk of infections through immunosuppression. Novel approaches to suppressing NET formation or the associated inflammation are in development and represent an important therapeutic target. This review will discuss the relationship between NETs and the pathophysiology of cystic fibrosis, asthma, COPD and bronchiectasis, and explore the current and future development of NET-targeting therapies.

NETs contribute to the pathophysiology of chronic lung disease. Immunomodulating therapies that may reduce inflammatory mediators and NET formation, without compromising bacterial clearance, offer a new treatment path for patients. https://bit.ly/3fyJC6I

Investigating neutrophil cell death in TB pathogenesis

Background: Neutrophils are one of the major early role players in antimycobacterial immunity. Upon infection, neutrophils can undergo NETosis, a cell death characterized by release of neutrophil extracellular traps (NETs). The role of NETosis in TB progression remains poorly characterized. We aim to characterize mechanisms underlying NETosis during TB pathogenesis by identifying genes that drive the cell death, and to determine their potential as markers of disease progression in high-risk individuals. Finally, we intend to evaluate neutrophil associated genes as targets for host directed therapy to reduce pathological damage caused by NETosis. Methods: Quantitative PCR will be used to quantify expression of specific genes identified in the blood of individuals with active lung disease (n=30), compared to those from healthy (n=30) and latently infected individuals (LTBI) (n=30). In addition, temporal events associated with NETosis will be measured using live microscopy in a neutrophil in vitro model of Mycobacterium tuberculosis (Mtb) infection. Candidate genes found to be associated with NETosis will be targeted with pharmaceutical inhibitors. Conclusion: Genes associated with neutrophil mediated cell death may serve as potential biomarkers of pathological damage and disease progression, as well as targets for host-directed therapy.

Pathophysiology of Bronchiectasis

Bronchiectasis is a complex, heterogeneous disorder defined by both a radiological abnormality of permanent bronchial dilatation and a clinical syndrome. There are multiple underlying causes including severe infections, mycobacterial disease, autoimmune conditions, hypersensitivity disorders, and genetic conditions. The pathophysiology of disease is understood in terms of interdependent concepts of chronic infection, inflammation, impaired mucociliary clearance, and structural lung damage. Neutrophilic inflammation is characteristic of the disease, with elevated levels of harmful proteases such as neutrophil elastase associated with worse outcomes. Recent data show that neutrophil extracellular trap formation may be the key mechanism leading to protease release and severe bronchiectasis. Despite the dominant of neutrophilic disease, eosinophilic subtypes are recognized and may require specific treatments. Neutrophilic inflammation is associated with elevated bacterial loads and chronic infection with organisms such as Pseudomonas aeruginosa. Loss of diversity of the normal lung microbiota and dominance of proteobacteria such as Pseudomonas and Haemophilus are features of severe bronchiectasis and link to poor outcomes. Ciliary dysfunction is also a key feature, exemplified by the rare genetic syndrome of primary ciliary dyskinesia. Mucus symptoms arise through goblet cell hyperplasia and metaplasia and reduced ciliary function through dyskinesia and loss of ciliated cells. The contribution of chronic inflammation, infection, and mucus obstruction leads to progressive structural lung damage. The heterogeneity of the disease is the most challenging aspect of management. An understanding of the pathophysiology of disease and their biomarkers can help to guide personalized medicine approaches utilizing the concept of "treatable traits."

It's Not Easy Being Green: A Narrative Review on the Microbiology, Virulence and Therapeutic Prospects of Multidrug-Resistant Pseudomonas aeruginosa

Pseudomonas aeruginosa is the most frequent cause of infection among non-fermenting Gram-negative bacteria, predominantly affecting immunocompromised patients, but its pathogenic role should not be disregarded in immunocompetent patients. These pathogens present a concerning therapeutic challenge to clinicians, both in community and in hospital settings, due to their increasing prevalence of resistance, and this may lead to prolonged therapy, sequelae, and excess mortality in the affected patient population. The resistance mechanisms of P. aeruginosa may be classified into intrinsic and acquired resistance mechanisms. These mechanisms lead to occurrence of resistant strains against important antibiotics-relevant in the treatment of P. aeruginosa infections-such as β-lactams, quinolones, aminoglycosides, and colistin. The occurrence of a specific resistotype of P. aeruginosa, namely the emergence of carbapenem-resistant but cephalosporin-susceptible (Car-R/Ceph-S) strains, has received substantial attention from clinical microbiologists and infection control specialists; nevertheless, the available literature on this topic is still scarce. The aim of this present review paper is to provide a concise summary on the adaptability, virulence, and antibiotic resistance of P. aeruginosa to a readership of basic scientists and clinicians.