Structural and Signaling Events Driving Aspergillus fumigatus-Induced Human Eosinophil Extracellular Trap Release

Abstract

Eosinophils are granulocytes classically involved in allergic diseases and in the host immune responses to helminths, fungi, bacteria and viruses. The release of extracellular DNA traps by leukocytes is an important mechanism of the innate immune response to pathogens in various infectious conditions, including fungal infections. Aspergillus fumigatus is an opportunistic fungus responsible for allergic bronchopulmonary aspergillosis (ABPA), a pulmonary disease marked by prominent eosinophilic inflammation. Previously, we demonstrated that isolated human eosinophils release extracellular DNA traps (eosinophil extracellular traps; EETs) when stimulated by A. fumigatus in vitro. This release occurs through a lytic non-oxidative mechanism that involves CD11b and Syk tyrosine kinase. In this work, we unraveled different intracellular mechanisms that drive the release of extracellular DNA traps by A. fumigatus-stimulated eosinophils. Ultrastructurally, we originally observed that A. fumigatus-stimulated eosinophils present typical signs of extracellular DNA trap cell death (ETosis) with the nuclei losing both their shape (delobulation) and the euchromatin/heterochromatin distinction, followed by rupture of the nuclear envelope and EETs release. We also found that by targeting class I PI3K, and more specifically PI3Kδ, the release of extracellular DNA traps induced by A. fumigatus is inhibited. We also demonstrated that A. fumigatus-induced EETs release depends on the Src family, Akt, calcium and p38 MAPK signaling pathways in a process in which fungal viability is dispensable. Interestingly, we showed that A. fumigatus-induced EETs release occurs in a mechanism independent of PAD4 histone citrullination. These findings may contribute to a better understanding of the mechanisms that underlie EETs release in response to A. fumigatus, which may lead to better knowledge of ABPA pathophysiology and treatment.

The Immune System Throws Its Traps: Cells and Their Extracellular Traps in Disease and Protection

“…In a recent study on the characterization of the mechanisms involved in EETs formation in ABPA, the dependence on the signaling pathways p38 MAPK, Akt, Src, calcium, and PI3 was demonstrated, regardless of the viability of the fungus. Remarkably, the release of EETs was independent of histone citrullination by PAD-4 [197]. In concert, the results suggest that EETs may be produced by several pathways in response to antigenic stimuli.…”

“…Table 4 shows a summary of EETs and their possible roles in eosinophilic, autoimmune, and cardiovascular diseases discussed in this document. [183] Eosinophil In vitro (Human PBMC) Vital (mtDNA) ROS-dependent [183] NADPH oxidase-dependent [184,188] Suicidal (Nuclear DNA) dependent of histone citrullination, CD11b, and the Syk tyrosine kinase pathway [185,187,189] Suicidal-independent of PAD4 histone citrullination and depends on the Src family, Akt, Ca, and p38 MAPK signaling pathways [197] LPS, C5a, cotaxin/CCL11 [183] Opsonized E. coli [183] A. fumigatus [189,197] Thymic stromal lymphopoietin [184] Immobilized immunoglobulins (IgG, IgA), cytokines with PAF, Ca ionophore, or PMA [185,187] IL-5 and LPS [188] Bactericidal activity [183] Entrapment of fungi [197] Airway inflammation and obstruction in Asthma [188] Eosinophils in Eosinophilic Diseases Suicidal (Nuclear DNA) [187,194] Not described [186,190,195,202] Ex vivo Secretions and tissue slides ECRS patients [187,190,195] Secretions from EOM patients Tissue slides [187,194] Biopsies from EOE patients [186] Skin biopsy tissues of 25 different eosinophilic skin diseases [202] Firewall against the invasion of pathogens [186,195] Increase in secretion viscosity [187,194] Inflammation …”

Value of CT Radiomics Combined with Clinical Features in the Diagnosis of Allergic Bronchopulmonary Aspergillosis

“…ABPA is common in patients with asthma or cystic fibrosis, and it is also related to the gene-phenotype of the host [ 16 ]. When Aspergillus is inhaled by genetically susceptible individuals, it releases antigens, proteolytic enzymes, and other toxic substances activate T lymphocytes, releases interleukin- (IL-) 4, IL-5, and IL-13, and secretes IgE and IgG antibodies, which act on mast cells, alveolar macrophages, and eosinophils, causing an inflammatory reaction in the airway wall and surrounding lung tissues, leading to increased secretion of mucus glands accompanied by bronchospasm [ 17 , 18 ]. With the development of the disease, bronchial mucus impaction and eosinophil pneumonia can be seen, followed by bronchiolitis obliterans and pulmonary interstitial fibrosis [ 19 ].…”

Unveiling Leukocyte Extracellular Traps in Inflammatory Responses of the Central Nervous System

“…The extrusion of histone-positive ETs associated with cell death by eosinophils occurs also in response to fungi such as A. fumigatus, however, these chromatin fibers do not exert antimicrobial or fungistatic activities (64). Interestingly, eosinophilic ETs induced in response to A. fumigatus originate independently of PAD4 but involve the Src family, Akt, calcium and p38 MAPK signaling pathways (65). More recently, the engagement of Dectin-1 receptor on eosinophils was found to trigger the extrusion of ETs composed of both nuclear and mitochondrial DNA fibers, ECP, acetylated histones, and citrullinated histones (66).…”