Fungal-mediated lung allergic airway disease: The critical role of macrophages and dendritic cells

Aspergillus fumigatus escape mechanisms from its harsh survival environments

Aspergillus fumigatus is a ubiquitous pathogenic mold and causes several diseases, including mycotoxicosis, allergic reactions, and systemic diseases (invasive aspergillosis), with high mortality rates. In its ecological niche, the fungus has evolved and mastered many reply strategies to resist and survive against negative threats, including harsh environmental stress and deficiency of essential nutrients from natural environments, immunity responses and drug treatments in host, and competition from symbiotic microorganisms. Hence, treating A. fumigatus infection is a growing challenge. In this review, we summarized A. fumigatus reply strategies and escape mechanisms and clarified the main competitive or symbiotic relationships between A. fumigatus, viruses, bacteria, or fungi in host microecology. Additionally, we discussed the contemporary drug repertoire used to treat A. fumigatus and the latest evidence of potential resistance mechanisms. This review provides valuable knowledge which will stimulate further investigations and clinical applications for treating and preventing A. fumigatus infections. KEY POINTS: • Harsh living environment was a great challenge for A. fumigatus survival. • A. fumigatus has evolved multiple strategies to escape host immune responses. • A. fumigatus withstands antifungal drugs via intrinsic escape mechanisms.

Long-chain acyl-CoA synthetase 4-mediated mitochondrial fatty acid metabolism and dendritic cell antigen presentation

OBJECTIVE

This study aims to investigate the role of Acyl-CoA synthetase 4 (ACSL4) in mediating mitochondrial fatty acid metabolism and dendritic cell (DC) antigen presentation in the immune response associated with asthma.

METHODS

RNA sequencing was employed to identify key genes associated with mitochondrial function and fatty acid metabolism in DCs. ELISA was employed to assess the levels of fatty acid metabolism in DCs. Mitochondrial morphology was evaluated using laser confocal microscopy, structured illumination microscopy, and transmission electron microscopy. Flow cytometry and immunofluorescence were utilized to detect changes in mitochondrial superoxide generation in DCs, followed by immunofluorescence co-localization analysis of ACSL4 and the mitochondrial marker protein COXIV. Subsequently, pathological changes and immune responses in mouse lung tissue were observed. ELISA was conducted to measure the levels of fatty acid metabolism in lung tissue DCs. qRT-PCR and western blotting were employed to respectively assess the expression levels of mitochondrial-associated genes (ATP5F1A, VDAC1, COXIV, TFAM, iNOS) and proteins (ATP5F1A, VDAC1, COXIV, TOMM20, iNOS) in lung tissue DCs. Flow cytometry was utilized to analyze changes in the expression of surface antigens presented by DCs in lung tissue, specifically the MHCII molecule and the co-stimulatory molecules CD80/86.

RESULTS

The sequencing results reveal that ACSL4 is a crucial gene regulating mitochondrial function and fatty acid metabolism in DCs. Inhibiting ACSL4 reduces the levels of fatty acid oxidases in DCs, increases arachidonic acid levels, and decreases A-CoA synthesis. Simultaneously, ACSL4 inhibition leads to an increase in mitochondrial superoxide production (MitoSOX) in DCs, causing mitochondrial rupture, vacuolization, and sparse mitochondrial cristae. In mice, ACSL4 inhibition exacerbates pulmonary pathological changes and immune responses, reducing the fatty acid metabolism levels within lung tissue DCs and the expression of mitochondria-associated genes and proteins. This inhibition induces an increase in the expression of MHCII antigen presentation molecules and co-stimulatory molecules CD80/86 in DCs.

CONCLUSIONS

The research findings indicate that ACSL4-mediated mitochondrial fatty acid metabolism and dendritic cell antigen presentation play a crucial regulatory role in the immune response of asthma. This discovery holds promise for enhancing our understanding of the mechanisms underlying asthma pathogenesis and potentially identifying novel targets for its prevention and treatment.

Tolerogenic dendritic cells in radiation-induced lung injury

Radiation-induced lung injury is a common complication associated with radiotherapy. It is characterized by early-stage radiation pneumonia and subsequent radiation pulmonary fibrosis. However, there is currently a lack of effective therapeutic strategies for radiation-induced lung injury. Recent studies have shown that tolerogenic dendritic cells interact with regulatory T cells and/or regulatory B cells to stimulate the production of immunosuppressive molecules, control inflammation, and prevent overimmunity. This highlights a potential new therapeutic activity of tolerogenic dendritic cells in managing radiation-induced lung injury. In this review, we aim to provide a comprehensive overview of tolerogenic dendritic cells in the context of radiation-induced lung injury, which will be valuable for researchers in this field.

Pathogenicity and virulence of Aspergillus fumigatus

Pulmonary infections caused by the mould pathogen Aspergillus fumigatus are a major cause of morbidity and mortality globally. Compromised lung defences arising from immunosuppression, chronic respiratory conditions or more recently, concomitant viral or bacterial pulmonary infections are recognised risks factors for the development of pulmonary aspergillosis. In this review, we will summarise our current knowledge of the mechanistic basis of pulmonary aspergillosis with a focus on emerging at-risk populations.

A scoping review: What are the cellular mechanisms that drive the allergic inflammatory response to fungal allergens in the lung epithelium?

Allergic airway disease (AAD) is a collective term for respiratory disorders that can be exacerbated upon exposure to airborne allergens. The contribution of fungal allergens to AAD has become well established over recent years. We conducted a comprehensive review of the literature using Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines to better understand the mechanisms involved in the allergic response to fungi in airway epithelia, identify knowledge gaps and make recommendations for future research. The search resulted in 61 studies for final analysis. Despite heterogeneity in the models and methods used, we identified major pathways involved in fungal allergy. These included the activation of protease-activated receptor 2, the EGFR pathway, adenosine triphosphate and purinergic receptor-dependent release of IL33, and oxidative stress, which drove mucin expression and goblet cell metaplasia, Th2 cytokine production, reduced barrier integrity, eosinophil recruitment, and airway hyperresponsiveness. However, there were several knowledge gaps and therefore we recommend future research should focus on the use of more physiologically relevant methods to directly compare key allergenic fungal species, clarify specific mechanisms of fungal allergy, and assess the fungal allergy in disease models. This will inform disease management and future interventions, ultimately reducing the burden of disease.

Immunity to fungi in the lung

The respiratory tree maintains sterilizing immunity against human fungal pathogens. Humans inhale ubiquitous filamentous molds and geographically restricted dimorphic fungal pathogens that form small airborne conidia. In addition, pathogenic yeasts, exemplified by encapsulated Cryptococcus species, and Pneumocystis pose significant fungal threats to the lung. Classically, fungal pneumonia occurs in immune compromised individuals, specifically in patients with HIV/AIDS, in patients with hematologic malignancies, in organ transplant recipients, and in patients treated with corticosteroids and targeted biologics that impair fungal immune surveillance in the lung. The emergence of fungal co-infections during severe influenza and COVID-19 underscores the impairment of fungus-specific host defense pathways in the lung by respiratory viruses and by medical therapies to treat viral infections. Beyond life-threatening invasive syndromes, fungal antigen exposure can exacerbate allergenic disease in the lung. In this review, we discuss emerging principles of lung-specific antifungal immunity, integrate the contributions and cooperation of lung epithelial, innate immune, and adaptive immune cells to mucosal barrier immunity, and highlight the pathogenesis of fungal-associated allergenic disease. Improved understanding of fungus-specific immunity in the respiratory tree has paved the way to develop improved diagnostic, pre-emptive, therapeutic, and vaccine approaches for fungal diseases of the lung.

More than Just Protein Degradation: The Regulatory Roles and Moonlighting Functions of Extracellular Proteases Produced by Fungi Pathogenic for Humans

Extracellular proteases belong to the main virulence factors of pathogenic fungi. Their proteolytic activities plays a crucial role in the acquisition of nutrients from the external environment, destroying host barriers and defenses, and disrupting homeostasis in the human body, e.g., by affecting the functions of plasma proteolytic cascades, and playing sophisticated regulatory roles in various processes. Interestingly, some proteases belong to the group of moonlighting proteins, i.e., they have additional functions that contribute to successful host colonization and infection development, but they are not directly related to proteolysis. In this review, we describe examples of such multitasking of extracellular proteases that have been reported for medically important pathogenic fungi of the Candida, Aspergillus, Penicillium, Cryptococcus, Rhizopus, and Pneumocystis genera, as well as dermatophytes and selected endemic species. Additional functions of proteinases include supporting binding to host proteins, and adhesion to host cells. They also mediate self-aggregation and biofilm formation. In addition, fungal proteases affect the host immune cells and allergenicity, understood as the ability to stimulate a non-standard immune response. Finally, they play a role in the proper maintenance of cellular homeostasis. Knowledge about the multifunctionality of proteases, in addition to their canonical roles, greatly contributes to an understanding of the mechanisms of fungal pathogenicity.