Interference of Aspergillus fumigatus with the immune response

Aspergillus fumigatus conidial surface-associated proteome reveals factors for fungal evasion and host immunity modulation

Aspergillus fumigatus causes aspergillosis and relies on asexual spores (conidia) for initiating host infection. There is scarce information about A. fumigatus proteins involved in fungal evasion and host immunity modulation. Here we analysed the conidial surface proteome of A. fumigatus, two closely related non-pathogenic species, Aspergillus fischeri and Aspergillus oerlinghausenensis, as well as pathogenic Aspergillus lentulus, to identify such proteins. After identifying 62 proteins exclusively detected on the A. fumigatus conidial surface, we assessed null mutants for 42 genes encoding these proteins. Deletion of 33 of these genes altered susceptibility to macrophage, epithelial cells and cytokine production. Notably, a gene that encodes a putative glycosylasparaginase, modulating levels of the host proinflammatory cytokine IL-1β, is important for infection in an immunocompetent murine model of fungal disease. These results suggest that A. fumigatus conidial surface proteins are important for evasion and modulation of the immune response at the onset of fungal infection.

Manipulation of host phagocytosis by fungal pathogens and therapeutic opportunities

An important host defence mechanism against pathogens is intracellular killing, which is achieved through phagocytosis, a cellular process for engulfing and neutralizing extracellular particles. Phagocytosis results in the formation of matured phagolysosomes, which are specialized compartments that provide a hostile environment and are considered the end point of the degradative pathway. However, all fungal pathogens studied to date have developed strategies to manipulate phagosomal function directly and also indirectly by redirecting phagosomes from the degradative pathway to a non-degradative pathway with the expulsion and even transfer of pathogens between cells. Here, using the major human fungal pathogens Aspergillus fumigatus, Candida albicans, Cryptococcus neoformans and Histoplasma capsulatum as examples, we discuss the processes involved in host phagosome-fungal pathogen interactions, with a focus on fungal evasion strategies. We also discuss recent approaches to targeting intraphagosomal pathogens, including the redirection of phagosomes towards degradative pathways for fungal pathogen eradication.

Therapeutic effect of oxidized bletilla striata polysaccharide-natamycin eye drops on fungal keratitis

OBJECTIVE

Fungal keratitis (FK) usually develops to a poor clinical prognosis due to the fungal invasion and excessive inflammatory reaction. In order to enhance the therapeutic effect of natamycin (NAT), we used the anti-inflammatory biological polysaccharide bletilla striata polysaccharide (BSP) combined with NAT to prepare a new eye drop -- oxidized bletilla striata polysaccharide-natamycin (OBN).

METHODS

UV-vis, FT-IR, and fluorescence spectroscopy were used to identify the synthesis of OBN. Biocompatibility of OBN was determined by CCK-8, scratch assay, and corneal toxicity test. RAW264.7 cells and C57BL/6 mice were stimulated with A. fumigatus and treated with PBS, OBN, or NAT. The anti-inflammatory activity of OBN was detected by RT-PCR and ELISA. In mice with FK, the clinical scores were used to evaluate the effect of OBN; HE staining was performed to assess the corneal pathological changes; MPO assay and immunofluorescence staining were used to investigate neutrophil infiltration.

RESULTS

OBN was synthesized by combining oxidized bletilla striata polysaccharide (OBSP) with NAT through Schiff base reaction. OBN did not affect cell viability at a concentration of 160 μg/mL in HCECs, RAW264.7 cells, and mouse corneas. OBN versus NAT significantly improved the prognosis of A. fumigatus keratitis by reducing disease severity, neutrophil infiltration, and expression of inflammatory factors in vivo. Additionally, OBN treatment down-regulated the mRNA and protein expression levels of inflammatory factors IL-1β, TNF-α, and IL-6 in RAW264.7 and mouse models.

CONCLUSION

OBN is a compound prepared by covalently linking OBSP to the imino group of NAT through Schiff base reaction. OBN treatment down-regulated inflammation and improved the prognosis of mice with A. fumigatus keratitis.

Gut-Derived Short-Chain Fatty Acids and Macrophage Modulation: Exploring Therapeutic Potentials in Pulmonary Fungal Infections

Short-chain fatty acids (SCFAs), such as acetate, propionate, and butyrate, modulate immune cell functions, particularly macrophages. This review explores the potential therapeutic applications of SCFAs in pulmonary fungal infections, a critical concern due to their high mortality rates and antifungal resistance. SCFAs enhance macrophage functions by promoting phagosome-lysosome fusion, increasing reactive oxygen species production, and balancing cytokine responses. Pulmonary fungal infections, caused by pathogens like Aspergillus fumigatus, are prevalent in immunocompromised patients, including those with diabetes, chronic obstructive pulmonary disease, and those on high-dose corticosteroids. SCFAs have shown promise in improving macrophage function in these contexts. However, the application of SCFAs must be balanced against potential side effects, including gut microbiota disruption and metabolic disorders. Further research is needed to optimize SCFA therapy for managing pulmonary fungal infections.

The Inflammatory Response Induced by Aspergillus fumigatus Conidia Is Dependent on Complement Activation: Insight from a Whole Blood Model

INTRODUCTION

We aimed to elucidate the inflammatory response of Aspergillus fumigatus conidia in a whole-blood model of innate immune activation and to compare it with the well-characterized inflammatory reaction to Escherichia coli.

METHODS

Employing a human lepirudin whole-blood model, we analyzed complement and leukocyte activation by measuring the sC5b-9 complex and assessing CD11b expression. A 27-multiplex system was used for quantification of cytokines. Selective cell removal from whole blood and inhibition of C3, C5, and CD14 were also applied.

RESULTS

Our findings demonstrated a marked elevation in sC5b-9 and CD11b post-A. fumigatus incubation. Thirteen cytokines (TNF, IL-1β, IL-1ra, IL-4, IL-6, IL-8, IL-17, IFNγ, MCP-1, MIP-1α, MIP-1β, FGF-basic, and G-CSF) showed increased levels. A generally lower level of cytokine release and CD11b expression was observed with A. fumigatus conidia than with E. coli. Notably, monocytes were instrumental in releasing all cytokines except MCP-1. IL-1ra was found to be both monocyte and granulocyte-dependent. Pre-inhibiting with C3 and CD14 inhibitors resulted in decreased release patterns for six cytokines (TNF, IL-1β, IL-6, IL-8, MIP-1α, and MIP-1β), with minimal effects by C5-inhibition.

CONCLUSION

A. fumigatus conidia induced complement activation comparable to E. coli, whereas CD11b expression and cytokine release were lower, underscoring distinct inflammatory responses between these pathogens. Complement C3 inhibition attenuated cytokine release indicating a C3-level role of complement in A. fumigatus immunity.

A comprehensive review on the role of T cell subsets and CAR-T cell therapy in Aspergillus fumigatus infection

Understanding the immune response to Aspergillus fumigatus, a common cause of invasive fungal infections (IFIs) in immunocompromised individuals, is critical for developing effective treatments. Tcells play a critical role in the immune response to A. fumigatus, with different subsets having distinct functions. Th1 cells are important for controlling fungal growth, while Th2 cells can exacerbate infection. Th17 cells promote the clearance of fungi indirectly by stimulating the production of various antimicrobial peptides from epithelial cells and directly by recruiting and activating neutrophils. Regulatory T cells have varied functions in A.fumigatus infection. They expand after exposure to A. fumigatus conidia and prevent organ injury and fungal sepsis by downregulating inflammation and inhibiting neutrophils or suppressing Th17 cells. Regulatory T cells also block Th2 cells to stop aspergillosis allergies. Immunotherapy with CAR T cells is a promising treatment for fungal infections, including A. fumigatus infections, especially in immunocompromised individuals. However, further research is needed to fully understand the mechanisms underlying the immune response to A. fumigatus and to develop effective immunotherapies with CAR-T cells for this infection. This literature review explores the role of Tcell subsets in A.fumigatus infection, and the effects of CAR-T cell therapy on this fungal infection.

HIF‑1 and macrophage activation signalling pathways are potential biomarkers of invasive aspergillosis

Invasive aspergillosis (IA) is a severe disease, the pathogenesis of which remains unclear. The present study aimed to determine the molecular mechanism of IA and to identify potential biomarkers using bioinformatics analysis. The GSE78000 dataset, which includes data from patients with IA and healthy individuals, was downloaded from Gene Expression Omnibus. Differentially expressed genes (DEGs) between the IA and control groups were identified with the 'affy' package in R software. The Gene Ontology (GO) and Kyoto Encyclopaedia of Genes and Genomes (KEGG) databases were then used to analyse the function and pathway enrichment of DEGs. The protein-protein interaction network was analysed with the Search Tool for the Retrieval of Interacting Genes (STRING) website. In addition, DEGs were confirmed using reverse transcription-quantitative PCR and western blotting in samples with IA (n=6) and control samples (n=6) collected from the Department of Respiratory and Critical Care Medicine of the First Affiliated Hospital of Henan University of Science and Technology (Luoyang, China). The present study identified 735 DEGs, including 312 upregulated and 423 downregulated genes. Through GO and KEGG analyses of the DEGs, macrophage activation and hypoxia-inducible factor 1 (HIF-1) signalling pathways were revealed to be significantly upregulated and downregulated, respectively, in patients with IA compared with that of the healthy individuals. Subsequently, correlation analysis of macrophage activation and HIF-1 signalling pathways was revealed using correlation as a distance metric for hierarchical clustering correlation analysis. However, there was no protein-protein interaction between the macrophage activity regulation and HIF-1 signalling pathways based on STRING analysis. In summary, the present study identified candidate genes and associated molecules that may be associated to IA and revealed potential biomarkers and therapeutic targets for IA.

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.

Mechanisms of Alternaria pathogenesis in animals and plants

Alternaria species are cosmopolitan fungi darkly pigmented by melanin that infect numerous plant species causing economically important agricultural spoilage of various food crops. Alternaria spp. also infect animals, being described as entomopathogenic fungi but also infecting warm-blooded animals, including humans. Their clinical importance in human health, as infection agents, lay in the growing number of immunocompromised patients. Moreover, Alternaria spp. are considered some of the most abundant and potent sources of airborne sensitizer allergens causing allergic respiratory diseases, as severe asthma. Among the numerous strategies deployed by Alternaria spp. to attack their hosts, the production of toxins, carrying critical concerns to public health as food contaminant, and the production of hydrolytic enzymes such as proteases, can be highlighted. Alternaria proteases also trigger allergic symptoms in individuals with fungal sensitization, acting as allergens and facilitating antigen access to the host subepithelium. Here, we review the current knowledge about the mechanisms of Alternaria pathogenesis in plants and animals, the strategies used by Alternaria to cope with the host defenses, and the involvement Alternaria allergens and mechanisms of sensitization.

A phylogenetic approach to explore the Aspergillus fumigatus conidial surface-associated proteome and its role in pathogenesis

Aspergillus fumigatus, an important pulmonary fungal pathogen causing several diseases collectively called aspergillosis, relies on asexual spores (conidia) for initiating host infection. Here, we used a phylogenomic approach to compare proteins in the conidial surface of A. fumigatus, two closely related non-pathogenic species, Aspergillus fischeri and Aspergillus oerlinghausenensis, and the cryptic pathogen Aspergillus lentulus. After identifying 62 proteins uniquely expressed on the A. fumigatus conidial surface, we assessed null mutants for 42 genes encoding conidial proteins. Deletion of 33 of these genes altered susceptibility to macrophage killing, penetration and damage to epithelial cells, and cytokine production. Notably, a gene that encodes glycosylasparaginase, which modulates levels of the host pro-inflammatory cytokine IL-1β, is important for infection in an immunocompetent murine model of fungal disease. These results suggest that A. fumigatus conidial surface proteins and effectors are important for evasion and modulation of the immune response at the onset of fungal infection.

A phylogenetic approach to explore the Aspergillus fumigatus conidial surface-associated proteome and its role in pathogenesis

Aspergillus fumigatus , an important pulmonary fungal pathogen causing several diseases collectively called aspergillosis, relies on asexual spores or conidia for initiating host infection. Here, we used a phylogenomic approach to compare proteins in the conidial surface of A. fumigatus , two closely related non-pathogenic species, Aspergillus fischeri and Aspergillus oerlinghausenensis , and the cryptic pathogen Aspergillus lentulus . After identifying 62 proteins uniquely expressed on the A. fumigatus conidial surface, we deleted 42 genes encoding conidial proteins. We found deletion of 33 of these genes altered susceptibility to macrophage killing, penetration and damage to epithelial cells, and cytokine production. Notably, a gene that encodes glycosylasparaginase, which modulates levels of the host pro-inflammatory cytokine IL-1β, is important for infection in an immunocompetent murine model of fungal disease. These results suggest that A. fumigatus conidial surface proteins and effectors are important for evasion and modulation of the immune response at the onset of fungal infection.

The Lipid Raft-Associated Protein Stomatin Is Required for Accumulation of Dectin-1 in the Phagosomal Membrane and for Full Activity of Macrophages against Aspergillus fumigatus

Alveolar macrophages belong to the first line of defense against inhaled conidia of the human-pathogenic fungus Aspergillus fumigatus. In lung alveoli, they contribute to phagocytosis and elimination of conidia. As a counterdefense, conidia have a gray-green pigment that enables them to survive in phagosomes of macrophages for some time. Previously, we showed that this conidial pigment interferes with the formation of flotillin-dependent lipid raft microdomains in the phagosomal membrane, thereby preventing the formation of functional phagolysosomes. Besides flotillins, stomatin is a major component of lipid rafts and can be targeted to the membrane. However, only limited information on stomatin is available, in particular on its role in defense against pathogens. To determine the function of this integral membrane protein, a stomatin-deficient macrophage line was generated by CRISPR/Cas9 gene editing. Immunofluorescence microscopy and flow cytometry revealed that stomatin contributes to the phagocytosis of conidia and is important for recruitment of the β-glucan receptor dectin-1 to both the cytoplasmic membrane and phagosomal membrane. In stomatin knockout cells, fusion of phagosomes and lysosomes, recruitment of the vATPase to phagosomes, and tumor necrosis factor alpha (TNF-α) levels were reduced when cells were infected with pigmentless conidia. Thus, our data suggest that stomatin is involved in maturation of phagosomes via fostering fusion of phagosomes with lysosomes. IMPORTANCE Stomatin is an integral membrane protein that contributes to the uptake of microbes, e.g., spores of the human-pathogenic fungus Aspergillus fumigatus. By generation of a stomatin-deficient macrophage line by advanced genetic engineering, we found that stomatin is involved in the recruitment of the β-glucan receptor dectin-1 to the phagosomal membrane of macrophages. Furthermore, stomatin is involved in maturation of phagosomes via fostering fusion of phagosomes with lysosomes. The data provide new insights on the important role of stomatin in the immune response against human-pathogenic fungi.

Targeting of phagolysosomes containing conidia of the fungus Aspergillus fumigatus with polymeric particles

Conidia of the airborne human-pathogenic fungus Aspergillus fumigatus are inhaled by humans. In the lung, they are phagocytosed by alveolar macrophages and intracellularly processed. In macrophages, however, conidia can interfere with the maturation of phagolysosomes to avoid their elimination. To investigate whether polymeric particles (PPs) can reach this intracellular pathogen in macrophages, we formulated dye-labeled PPs with a size allowing for their phagocytosis. PPs were efficiently taken up by RAW 264.7 macrophages and were found in phagolysosomes. When macrophages were infected with conidia prior to the addition of PPs, we found that they co-localized in the same phagolysosomes. Mechanistically, the fusion of phagolysosomes containing PPs with phagolysosomes containing conidia was observed. Increasing concentrations of PPs increased fusion events, resulting in 14% of phagolysosomes containing both conidia and PPs. We demonstrate that PPs can reach conidia-containing phagolysosomes, making these particles a promising carrier system for antimicrobial drugs to target intracellular pathogens. KEY POINTS: • Polymer particles of a size larger than 500 nm are internalized by macrophages and localized in phagolysosomes. • These particles can be delivered to Aspergillus fumigatus conidia-containing phagolysosomes of macrophages. • Enhanced phagolysosome fusion by the use of vacuolin1 can increase particle delivery.

Requirement of a putative mitochondrial GTPase, GemA, for azole susceptibility, virulence, and cell wall integrity in Aspergillus fumigatus

Drug resistance in fungal pathogens is a new challenge in clinical aspergillosis treatment. Mitochondria as dynamic organelles are involved in numerous biological processes in fungi, including drug resistance. However, little is known about the mechanism underlying mitochondrial regulation of the response of fungal pathogens to antifungal drugs. Here, we showed that a putative mitochondrial GTPase, GemA, a yeast Gem1 homolog, is crucial for the azole response and cell wall integrity in the opportunistic pathogen Aspergillus fumigatus. The fluorescence observation showed that GFP-labeled GemA is located in mitochondria, and loss of gemA results in aberrant giant mitochondrial morphology and abnormal mitochondrial membrane potential. Moreover, a ΔgemA mutant attenuates fungal virulence in the Galleria mellonella model of aspergillosis. Furthermore, gemA loss increases resistance to azoles and terbinafine but not to amphotericin B. Of note, RNA-seq combined with RT-qPCR showed that a series of drug efflux pumps were upregulated in the gemA deletion mutant. Deleting mdr1 or inhibiting the expression of drug efflux pumps can partially decrease the resistance to azoles resulting from the gemA mutant, implying that GemA influences azole response by affecting the expression of drug efflux pumps. Importantly, the ΔgemA mutant is susceptible to the cell wall-perturbing reagent CR, but not to CFW, and this defect can be partly rescued by hyperosmotic stress. TEM revealed that the cell wall of ΔgemA was thicker than that of the WT strain, demonstrating that GemA plays a role in cell wall composition and integrity. Collectively, we identified a putative mitochondrial GTPase, GemA, which is critical for hyphal growth, virulence, azole susceptibility, and cell wall integrity and acts by affecting mitochondrial function.

Therapeutic Potential of Green Synthesized Gold Nanoparticles Using Extract of Leptadenia hastata against Invasive Pulmonary Aspergillosis

Gold nanoparticles are widely used in the biomedical field for the treatment of several diseases, including cancer, inflammatory diseases, and immune system disorders, due to their distinctive physicochemical characteristics. In this study, we investigated the therapeutic potential of green synthesized gold nanoparticles using ethanolic leaf extract of Leptadenia hastata (LH-AuNPs) against invasive pulmonary aspergillosis (IPA) in mice. UV/visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and zeta potential were used to characterize the biofabricated LH-AuNPs. Antifungal activity of LH-AuNPs was determined by MTT assay, (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide), time-kill assay, and radial growth inhibition. TEM and SEM were used to examine the mode of the antifungal action of LH-AuNPs. The in vivo activity of LH-AuNPs against IPA was studied using a well-established IPA mouse model. LH-AuNPs excreted antifungal activity against Aspergillus fumigatus with MIC 64 µg/mL and inhibited the radial growth of A. fumigatus by 30% compared to the control. LH-AuNPs caused distortion and collapse of fungal hyphae and deterioration of cell walls. Interestingly, LH-AuNPs did not display any cytotoxicity on cultured primary bone marrow stem cells (BMSCs) or A549 human lung cell line in vitro at MIC concentration. IPA mice treated with LH-AuNPs displayed significant lung tissue repair without any in vivo cytotoxicity. LH-AuNPs administration showed significant suppression of fungal burden and gliotoxin production in the lung. In addition, LH-AuNPs inhibited IPA-induced pro-inflammatory cytokines production, including interleukin-1 (IL-1), interleukin-17 (IL-17), and tumor necrosis factor-alpha (TNF-α), and reduced oxidative stress in lung. In conclusion, our data provide LH-AuNPs as a novel nanoparticle therapy for IPA.

PLB-985 Neutrophil-Like Cells as a Model To Study Aspergillus fumigatus Pathogenesis

Fungal infections remain a major global concern. Emerging fungal pathogens and increasing rates of resistance mean that additional research efforts and resources must be allocated to advancing our understanding of fungal pathogenesis and developing new therapeutic interventions. Neutrophilic granulocytes are a major cell type involved in protection against the important fungal pathogen Aspergillus fumigatus, where they employ numerous defense mechanisms, including production of antimicrobial extracellular vesicles. A major drawback to work with neutrophils is the lack of a suitable cell line system for the study of fungal pathogenesis. To address this problem, we assessed the feasibility of using differentiated PLB-985 neutrophil-like cells as an in vitro model to study A. fumigatus infection. We find that dimethylformamide-differentiated PLB-985 cells provide a useful recapitulation of many aspects of A. fumigatus interactions with primary human polymorphonuclear leukocytes. We show that differentiated PLB-985 cells phagocytose fungal conidia and acidify conidia-containing phagolysosomes similar to primary neutrophils, release neutrophil extracellular traps, and also produce antifungal extracellular vesicles in response to infection. In addition, we provide an improved method for the isolation of extracellular vesicles produced during infection by employing a size exclusion chromatography-based approach. Advanced liquid chromatography-tandem mass spectrometry (LC-MS/MS) proteomics revealed an enrichment of extracellular vesicle marker proteins and a decrease of cytoplasmic proteins in extracellular vesicles isolated using this improved method. Ultimately, we find that differentiated PLB-985 cells can serve as a genetically tractable model to study many aspects of A. fumigatus pathogenesis. IMPORTANCE Polymorphonuclear leukocytes are an important defense against human fungal pathogens, yet our model systems to study this group of cells remain very limited in scope. In this study, we established that differentiated PLB-985 cells can serve as a model to recapitulate several important aspects of human polymorphonuclear leukocyte interactions with the important human fungal pathogen Aspergillus fumigatus. The proposed addition of a cultured neutrophil-like cell line to the experimental toolbox to study fungal pathogenesis will allow for a more mechanistic description of neutrophil antifungal biology. In addition, the easier handling of the cell line compared to primary human neutrophils allowed us to use PLB-985 cells to provide an improved method for isolation of neutrophil-derived extracellular vesicles using size exclusion chromatography. Together, these results provide significant tools and a baseline knowledge for the future study of neutrophil-derived extracellular vesicles in the laboratory.

Chromatin profiling reveals heterogeneity in clinical isolates of the human pathogen Aspergillus fumigatus

Invasive Pulmonary Aspergillosis, which is caused by the filamentous fungus Aspergillus fumigatus, is a life-threatening infection for immunosuppressed patients. Chromatin structure regulation is important for genome stability maintenance and has the potential to drive genome rearrangements and affect virulence and pathogenesis of pathogens. Here, we performed the first A. fumigatus global chromatin profiling of two histone modifications, H3K4me3 and H3K9me3, focusing on the two most investigated A. fumigatus clinical isolates, Af293 and CEA17. In eukaryotes, H3K4me3 is associated with active transcription, while H3K9me3 often marks silent genes, DNA repeats, and transposons. We found that H3K4me3 deposition is similar between the two isolates, while H3K9me3 is more variable and does not always represent transcriptional silencing. Our work uncovered striking differences in the number, locations, and expression of transposable elements between Af293 and CEA17, and the differences are correlated with H3K9me3 modifications and higher genomic variations among strains of Af293 background. Moreover, we further showed that the Af293 strains from different laboratories actually differ in their genome contents and found a frequently lost region in chromosome VIII. For one such Af293 variant, we identified the chromosomal changes and demonstrated their impacts on its secondary metabolites production, growth and virulence. Overall, our findings not only emphasize the influence of genome heterogeneity on A. fumigatus fitness, but also caution about unnoticed chromosomal variations among common laboratory strains.

Effective Inhibition of Invasive Pulmonary Aspergillosis by Silver Nanoparticles Biosynthesized with Artemisia sieberi Leaf Extract

Aspergillus fumigatus is one of the most common fungal pathogens that can cause a diversity of diseases ranging from invasive pulmonary aspergillosis (IPA) and aspergilloma to allergic syndromes. In this study, we investigated the antifungal effect of silver nanoparticles biosynthesized with Artemisia sieberi leaf extract (AS-AgNPs) against A. fumigatus in vitro and in vivo. The biosynthesized AS-AgNPs were characterized by imaging (transmission electron microscopy (TEM)), UV-VIS spectroscopy, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The microdilution method showed the antifungal activity of AS-AgNPs against A. fumigatus, with an MIC of 128 µg/mL. AS-AgNPs significantly inhibited the growth of hyphae in all directions, as imaged by SEM. Additionally, TEM on biofilm revealed invaginations of the cell membrane, a change in the vacuolar system, and the presence of multilamellar bodies within vacuoles. Interestingly, AS-AgNPs displayed low cytotoxicity on the A549 human lung cell line in vitro. Treatment of an invasive pulmonary aspergillosis (IPA) mouse model with AS-AgNPs demonstrated the potency of AS-AgNPs to significantly reduce lung tissue damage and to suppress the elevated levels of pro-inflammatory cytokines, tumor necrosis factor-alpha (TNF-α), interleukin-1 (IL-1), and interleukin-17 (IL-17). The therapeutic potential of AS-AgNPs was found to be due to their direct action to suppress the fungal burden and gliotoxin production in the lungs. In addition, AS-AgNPs reduced the oxidative stress in the lungs by increasing the enzymatic activities of catalase (CAT) and superoxide dismutase (SOD). Thus, our data indicate the biosynthesized AS-AgNPs as a novel antifungal alternative treatment against aspergillosis.

Dynamic optimization reveals alveolar epithelial cells as key mediators of host defense in invasive aspergillosis

Aspergillus fumigatus is an important human fungal pathogen and its conidia are constantly inhaled by humans. In immunocompromised individuals, conidia can grow out as hyphae that damage lung epithelium. The resulting invasive aspergillosis is associated with devastating mortality rates. Since infection is a race between the innate immune system and the outgrowth of A. fumigatus conidia, we use dynamic optimization to obtain insight into the recruitment and depletion of alveolar macrophages and neutrophils. Using this model, we obtain key insights into major determinants of infection outcome on host and pathogen side. On the pathogen side, we predict in silico and confirm in vitro that germination speed is an important virulence trait of fungal pathogens due to the vulnerability of conidia against host defense. On the host side, we found that epithelial cells, which have been underappreciated, play a role in fungal clearance and are potent mediators of cytokine release. Both predictions were confirmed by in vitro experiments on established cell lines as well as primary lung cells. Further, our model affirms the importance of neutrophils in invasive aspergillosis and underlines that the role of macrophages remains elusive. We expect that our model will contribute to improvement of treatment protocols by focusing on the critical components of immune response to fungi but also fungal virulence traits.

Characterisation of Aspergillus fumigatus Endocytic Trafficking within Airway Epithelial Cells Using High-Resolution Automated Quantitative Confocal Microscopy

The precise characterization of the mechanisms modulating Aspergillus fumigatus survival within airway epithelial cells has been impaired by the lack of live-cell imaging technologies and user-friendly quantification approaches. Here we described the use of an automated image analysis pipeline to estimate the proportion of A. fumigatus spores taken up by airway epithelial cells, those contained within phagolysosomes or acidified phagosomes, along with the fungal factors contributing to these processes. Coupling the use of fluorescent A. fumigatus strains and fluorescent epithelial probes targeting lysosomes, acidified compartments and cell membrane, we found that both the efficacy of lysosome recruitment to phagosomes and phagosome acidification determines the capacity of airway epithelial cells to contain A. fumigatus growth. Overall, the capability of the airway epithelium to prevent A. fumigatus survival was higher in bronchial epithelial than alveolar epithelial cells. Certain A. fumigatus cell wall mutants influenced phagosome maturation in airway epithelial cells. Taken together, this live-cell 4D imaging approach allows observation and measurement of the very early processes of A. fumigatus interaction within live airway epithelial monolayers.

Thymic stromal lymphopoietin participates in the TLR2-and TLR4-dependent immune response triggered by Aspergillus fumigatus in human corneal cells

Fungal keratitis constitutes a serious vision-threatening disease. Toll-like receptors (TLRs) comprise key mediators of innate immunity triggered by Aspergillus fumigatus (AF) in the cornea, but the messenger between innate and adaptive immunity remained unknown. Thymic stromal lymphopoietin (TSLP) represents a critical factor of adaptive immunity. Here we investigated the expression of TSLP in corneal epithelial and stromal cells challenged by AF and its relationship with TLRs. We stimulated corneal cells with TLR ligands zymosan or lipopolysaccharide (LPS), human recombinant TSLP, or AF hyphae for various periods, with or without prior TLR2, TLR4, or TSLP inhibition. TLR2, TLR4, TSLP, IL-8, and TNF-α release and expression were measured via enzyme-linked immunosorbent analysis, quantitative polymerase chain reaction, or western blot. Corneal cell stimulation with zymosan or LPS induced up-regulated TSLP expression. Enhanced TSLP expression was associated with AF treatment in human corneal cells; TLR2 or TLR4 inhibition impaired the AF-induced TSLP levels. Human recombinant TSLP augmented TLR2 and TLR4 expression; RNA interference of TSLP attenuated TLR, IL-8, and TNF-α expression stimulated by AF hyphae. These findings indicated that TSLP participates in the immune response of corneal cells triggered by AF, which is closely related to TLR function, and the innate immunity mediated by TLRs could be enhanced by TSLP. Innate immunity may therefore transmit inflammatory signals to adaptive immunity through activation of TSLP; in turn, adaptive immunity likely exerts certain regulatory effects on innate immunity via TSLP. That is, TSLP could interact with innate immunity mediated by TLR2 and TLR4 in human corneal cells challenged by AF and thus may serve as a messenger between the innate and adaptive immune responses in AF keratitis.

Lipoxin A4 activates ALX/FPR2 to attenuate inflammation in Aspergillus fumigatus keratitis

PURPOSE

To explore the anti-inflammatory effect of lipoxin A4 (LXA4) in Aspergillus fumigatus (A. fumigatus) keratitis and the underlying mechanisms.

METHODS

In A. fumigatus keratitis mouse models, enzyme-linked immunosorbent assay (ELISA) was used to detect the level of LXA4. Clinical scores were utilized to evaluate fungal keratitis (FK) severity. Fungal load was assessed by plate count. Immunofluorescence staining, HE staining and myeloperoxidase (MPO) assays were carried out to evaluate the neutrophil infiltration and activity. In A. fumigatus infected mouse corneas and inactivated A. fumigatus-stimulated RAW264.7 cells, quantitative real time polymerase chain reaction (qRT-PCR) and ELISA were applied to assess the expression of pro-inflammatory mediators and anti-inflammatory factors.Reactive oxygen species (ROS) was determined by 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) staining in RAW264.7 cells.

RESULTS

LXA4 level was significantly increased in mice with A. fumigatus keratitis. In an A. fumigatus keratitis mouse model, LXA4 treatment alleviated FK severity, reduced fungal load and repressed neutrophil infiltration and activity. Additionally, LXA4 inhibited the expression of pro-inflammatory mediators including IL-1β, TNF-α, IL-6, cyclooxygenase-2 (COX-2), TLR-2, TLR-4, Dectin-1 and iNOS, and promoted the expression of anti-inflammatory factors IL-10 and Arg-1. In RAW264.7 cells, LXA4 receptor/formyl peptide receptor 2 (ALX/FPR2) blockade reversed the anti-inflammatory effect of LXA4. LXA4 suppressed inactivated A. fumigatus induced elevated ROS production in RAW264.7 cells, which was abrogated by ALX/FPR2 antagonist Boc-2.

CONCLUSION

LXA4 ameliorated inflammatory response by suppressing neutrophil infiltration, downregulating the expression of pro-inflammatory mediators and ROS production through ALX/FPR2 receptor in A. fumigatus keratitis.

Galectin-3 plays an important pro-inflammatory role in A. fumigatus keratitis by recruiting neutrophils and activating p38 in neutrophils

PURPOSE

To determine the role of galectin-3 (Gal-3) in cornea infected by Aspergillus fumigatus (A. fumigatus).

METHODS

Gal-3 was tested in normal and infected corneas of C57BL/6 mice. Mice corneas were pretreated with or without rmGal-3 or Gal-3 siRNA and infected with A. fumigatus. Recombinant mouse (rm) Gal-3 stimulated polymorphonuclear neutrophilic leukocytes (PMNs). PMNs were stimulated with 75% ethanol-killed A. fumigatus with or without pretreatment of Gal-3 siRNA. Disease severity was documented by clinical score and photographs with a slit lamp. PCR, Western blot, and ELISA tested expression of Gal-3, interleukin (IL)-1β, IL-6, macrophage inflammatory protein 2 (MIP-2) and p-p38. PMNs infiltration was assessed by flow cytometry and myeloperoxidase (MPO) assay.

RESULTS

Gal-3 expression was significantly elevated by A. fumigatus in mice corneas. rmGal-3 treatment increased clinical scores, PMNs infiltration, and cytokines expression, which were decreased by Gal-3 siRNA treatment. In PMNs, Gal-3 expression was also significantly increased by A. fumigatus. The rmGal-3 treatment upregulated proinflammatory cytokines secretion and p-p38 expression, which was significantly inhibited by Gal-3 siRNA.

CONCLUSION

These data proved that A. fumigatus increased Gal-3 expression and elevated disease clinical scores, PMNs infiltration and cytokines expression through Gal-3. In PMNs, A. fumigatus upregulated IL-1β and IL-6 secretion through the Gal-3 / p38 pathway.

Mechanisms of fungal dissemination

Fungal infections are an increasing threat to global public health. There are more than six million fungal species worldwide, but less than 1% are known to infect humans. Most of these fungal infections are superficial, affecting the hair, skin and nails, but some species are capable of causing life-threatening diseases. The most common of these include Cryptococcus neoformans, Aspergillus fumigatus and Candida albicans. These fungi are typically innocuous and even constitute a part of the human microbiome, but if these pathogens disseminate throughout the body, they can cause fatal infections which account for more than one million deaths worldwide each year. Thus, systemic dissemination of fungi is a critical step in the development of these deadly infections. In this review, we discuss our current understanding of how fungi disseminate from the initial infection sites to the bloodstream, how immune cells eliminate fungi from circulation and how fungi leave the blood and enter distant organs, highlighting some recent advances and offering some perspectives on future directions.

IL-36α Exerts Proinflammatory Effects in Aspergillus fumigatus Keratitis of Mice Through the Pathway of IL-36α/IL-36R/NF-κB

Purpose

To explore the role of IL-36α in corneas infected by Aspergillus fumigatus.

Methods

The experimental group was comprised of 15 corneas with fungal keratitis, and 15 healthy donor corneas were included in the control group. IL-36α was detected in normal and infected corneas of humans and C57BL/6 mice. Mice corneas were infected with A. fumigatus with or without pretreatment of recombinant mouse (rm) IL-36α and IL-36α neutralizing antibody (Ab). Primary macrophages were stimulated with 75% ethanol-killed A. fumigatus with or without pretreatment of rmIL-36α. The severity of the disease was documented by clinical score and photographs with a slit lamp. PCR, western blot, and immunostaining were used to determine the expression of IL-36α, IL-1β, IL-6, and TNF-α. Polymorphonuclear neutrophilic leukocyte infiltration was assessed by myeloperoxidase (MPO) assay and flow cytometry. Macrophage infiltration was tested by immunofluorescent staining and flow cytometry.

Results

IL-36α mRNA and protein were significantly elevated in human and mice corneas after infection. The rmIL-36α treatment of C57BL/6 mice increased clinical score, MPO levels, macrophage infiltration, and expression of the proinflammatory cytokines IL-1β, IL-6, and TNF-α compared with the infected controls, which showed a decrease due to IL-36α Ab treatment. In primary macrophages, IL-36α expression was also significantly increased by A. fumigatus. The rmIL-36α treatment upregulated IL-1β, IL-6, and phosphorylated nuclear factor (NF)-κB expression, which was significantly inhibited by rmIL-36Ra.

Conclusions

IL-36α act as a proinflammatory cytokine in A. fumigatus keratitis by promoting the infiltration of neutrophils and macrophages and increasing the secretion of IL-1β, IL-6, and TNF-α, in addition to regulating expression of phosphorylated NF-κB.

Crossing Kingdoms: How the Mycobiota and Fungal-Bacterial Interactions Impact Host Health and Disease

The term “microbiota” invokes images of mucosal surfaces densely populated with bacteria. These surfaces and the luminal compartments they form indeed predominantly harbor bacteria.

The term “microbiota” invokes images of mucosal surfaces densely populated with bacteria. These surfaces and the luminal compartments they form indeed predominantly harbor bacteria. However, research from this past decade has started to complete the picture by focusing on important but largely neglected constituents of the microbiota: fungi, viruses, and archaea. The community of commensal fungi, also called the mycobiota, interacts with commensal bacteria and the host. It is thus not surprising that changes in the mycobiota have significant impact on host health and are associated with pathological conditions such as inflammatory bowel disease (IBD). In this review we will give an overview of why the mycobiota is an important research area and different mycobiota research tools. We will specifically focus on distinguishing transient and actively colonizing fungi of the oral and gut mycobiota and their roles in health and disease. In addition to correlative and observational studies, we will discuss mechanistic studies on specific cross-kingdom interactions of fungi, bacteria, and the host.

The impact of episporic modification of Lichtheimia corymbifera on virulence and interaction with phagocytes

Fungal infections caused by the ancient lineage Mucorales are emerging and increasingly reported in humans. Comprehensive surveys on promising attributes from a multitude of possible virulence factors are limited and so far, focused on Mucor and Rhizopus. This study addresses a systematic approach to monitor phagocytosis after physical and enzymatic modification of the outer spore wall of Lichtheimia corymbifera, one of the major causative agents of mucormycosis. Episporic modifications were performed and their consequences on phagocytosis, intracellular survival and virulence by murine alveolar macrophages and in an invertebrate infection model were elucidated. While depletion of lipids did not affect the phagocytosis of both strains, delipidation led to attenuation of LCA strain but appears to be dispensable for infection with LCV strain in the settings used in this study. Combined glucano-proteolytic treatment was necessary to achieve a significant decrease of virulence of the LCV strain in Galleria mellonella during maintenance of the full potential for spore germination as shown by a novel automated germination assay. Proteolytic and glucanolytic treatments largely increased phagocytosis compared to alive resting and swollen spores. Whilst resting spores barely (1–2%) fuse to lysosomes after invagination in to phagosomes, spore trypsinization led to a 10-fold increase of phagolysosomal fusion as measured by intracellular acidification. This is the first report of a polyphasic measurement of the consequences of episporic modification of a mucormycotic pathogen in spore germination, spore surface ultrastructure, phagocytosis, stimulation of Toll-like receptors (TLRs), phagolysosomal fusion and intracellular acidification, apoptosis, generation of reactive oxygen species (ROS) and virulence.

Recognition of Fungal Components by the Host Immune System

By being the first point of contact of the fungus with the host, the cell wall plays an important role in the pathogenesis, having many molecules that participate as antigens that are recognized by immune cells, and also that help the fungus to establish infection. The main molecules reported to trigger an immune response are chitin, glucans, oligosaccharides, proteins, melanin, phospholipids, and others, being present in the principal pathogenic fungi with clinical importance worldwide, such as Histoplasma capsulatum, Paracoccidioides brasiliensis, Aspergillus fumigatus, Candida albicans, Cryptococcus neoformans, Blastomyces dermatitidis, and Sporothrix schenckii. Knowledge and understanding of how the immune system recognizes and responds to fungal antigens are relevant for the future research and development of new diagnostic tools and treatments for the control of mycosis caused by these fungi.

Fungal iron homeostasis with a focus on Aspergillus fumigatus

To maintain iron homeostasis, fungi have to balance iron acquisition, storage, and utilization to ensure sufficient supply and to avoid toxic excess of this essential trace element. As pathogens usually encounter iron limitation in the host niche, this metal plays a particular role during virulence. Siderophores are iron-chelators synthesized by most, but not all fungal species to sequester iron extra- and intracellularly. In recent years, the facultative human pathogen Aspergillus fumigatus has become a model for fungal iron homeostasis of siderophore-producing fungal species. This article summarizes the knowledge on fungal iron homeostasis and its links to virulence with a focus on A. fumigatus. It covers mechanisms for iron acquisition, storage, and detoxification, as well as the modes of transcriptional iron regulation and iron sensing in A. fumigatus in comparison to other fungal species. Moreover, potential translational applications of the peculiarities of fungal iron metabolism for treatment and diagnosis of fungal infections is addressed.

Phagolysosomal Survival Enables Non-lytic Hyphal Escape and Ramification Through Lung Epithelium During Aspergillus fumigatus Infection

Aspergillus fumigatus is the most important mould pathogen in immunosuppressed patients. Suboptimal clearance of inhaled spores results in the colonisation of the lung airways by invasive hyphae. The first point of contact between A. fumigatus and the host is the lung epithelium. In vitro and ex vivo studies have characterised critical aspects of the interaction of invasive hyphae on the surface of epithelial cells. However, the cellular interplay between internalised A. fumigatus and the lung epithelium remains largely unexplored. Here, we use high-resolution live-cell confocal microscopy, 3D rendered imaging and transmission electron microscopy to define the development of A. fumigatus after lung epithelium internalisation in vitro. Germination, morphology and growth of A. fumigatus were significantly impaired upon internalisation by alveolar (A549) and bronchial (16HBE) lung epithelial cells compared to those growing on the host surface. Internalised spores and germlings were surrounded by the host phagolysosome membrane. Sixty per cent of the phagosomes containing germlings were not acidified at 24 h post infection allowing hyphal development. During escape, the phagolysosomal membrane was not ruptured but likely fused to host plasma membrane allowing hyphal exit from the intact host cell in an non-lytic Manner. Subsequently, escaping hyphae elongated between or through adjacent epithelial lung cells without penetration of the host cytoplasm. Hyphal tips penetrating new epithelial cells were surrounded by the recipient cell plasma membrane. Altogether, our results suggest cells of lung epithelium survive fungal penetration because the phagolysosomal and plasma membranes are never breached and that conversely, fungal spores survive due to phagosome maturation failure. Consequently, fungal hyphae can grow through the epithelial cell layer without directly damaging the host. These processes likely prevent the activation of downstream immune responses alongside limiting the access of professional phagocytes to the invading fungal hypha. Further research is needed to investigate if these events also occur during penetration of fungi in endothelial cells, fibroblasts and other cell types.

Differential Interactions of Serum and Bronchoalveolar Lavage Fluid Complement Proteins with Conidia of Airborne Fungal Pathogen Aspergillus fumigatus

Even though both cellular and humoral immunities contribute to host defense, the role played by humoral immunity against the airborne opportunistic fungal pathogen Aspergillus fumigatus has been underexplored. In this study, we aimed at deciphering the role of the complement system, the major humoral immune component, against A. fumigatus Mass spectrometry analysis of the proteins extracted from A. fumigatus conidial (asexual spores and infective propagules) surfaces opsonized with human serum indicated that C3 is the major complement protein involved. Flow cytometry and immunolabeling assays further confirmed C3b (activated C3) deposition on the conidial surfaces. Assays using cell wall components of conidia indicated that the hydrophobin RodAp, β-(1,3)-glucan (BG) and galactomannan (GM) could efficiently activate C3. Using complement component-depleted sera, we showed that while RodAp activates C3 by the alternative pathway, BG and GM partially follow the classical and lectin pathways, respectively. Opsonization facilitated conidial aggregation and phagocytosis, and complement receptor (CR3 and CR4) blockage on phagocytes significantly inhibited phagocytosis, indicating that the complement system exerts a protective role against conidia by opsonizing them and facilitating their phagocytosis mainly through complement receptors. Conidial opsonization with human bronchoalveolar lavage fluid (BALF) confirmed C3 to be the major complement protein interacting with conidia. Nevertheless, complement C2 and mannose-binding lectin (MBL), the classical and lectin pathway components, respectively, were not identified, indicating that BALF activates the alternative pathway on the conidial surface. Moreover, the cytokine profiles were different upon stimulation of phagocytes with serum- and BALF-opsonized conidia, highlighting the importance of studying interaction of conidia with complement proteins in their biological niche.

Characterization and pro-inflammatory potential of indoor mold particles

A number of epidemiological studies find an association between indoor air dampness and respiratory health effects. This is often suggested to be linked to enhanced mold growth. However, the role of mold is obviously difficult to disentangle from other dampness-related exposure including microbes as well as non-biological particles and chemical pollutants. The association may partly be due to visible mycelial growth and a characteristic musty smell of mold. Thus, the potential role of mold exposure should be further explored by evaluating information from experimental studies elucidating possible mechanistic links. Such studies show that exposure to spores and hyphal fragments may act as allergens and pro-inflammatory mediators and that they may damage airways by the production of toxins, enzymes, and volatile organic compounds. In the present review, we hypothesize that continuous exposure to mold particles may result in chronic low-grade pro-inflammatory responses contributing to respiratory diseases. We summarize some of the main methods for detection and characterization of fungal aerosols and highlight in vitro research elucidating how molds may induce toxicity and pro-inflammatory reactions in human cell models relevant for airway exposure. Data suggest that the fraction of fungal hyphal fragments in indoor air is much higher than that of airborne spores, and the hyphal fragments often have a higher pro-inflammatory potential. Thus, hyphal fragments of prevalent mold species with strong pro-inflammatory potential may be particularly relevant candidates for respiratory diseases associated with damp/mold-contaminated indoor air. Future studies linking of indoor air dampness with health effects should assess the toxicity and pro-inflammatory potential of indoor air particulate matter and combined this information with a better characterization of biological components including hyphal fragments from both pathogenic and non-pathogenic mold species. Such studies may increase our understanding of the potential role of mold exposure.

Soluble mediators in anti-fungal immunity

Although soluble mediators of our innate immune system have a substantial impact on invading microbes, their role against fungal pathogens has been underexplored. Constituting the humoral immunity, soluble mediators comprise the complement system, collectins, acute-phase proteins, antibodies and antimicrobial peptides. These components can prevent fungal infection either by directly interacting with invading microbes, leading to their aggregation (microbistatic), destruction (microbicidal) or linking them to cellular immunity. The composition of soluble-mediator varies with human body-fluids, resulting in different antifungal mechanisms. Moreover, cellular immune system deploys both oxidative and non-oxidative mechanisms to destroy extracellular or internalized fungal pathogens; however, cellular immune activation is mainly influenced as well as regulated by soluble mediators. This review outlines the antifungal mechanism employed, directly or indirectly, by soluble mediators, and in response, the evading strategies of the fungal pathogens.

High-Throughput Gene Replacement in Aspergillus fumigatus

Aspergillus fumigatus is a human pathogen and the principal etiologic agent of invasive and chronic aspergillosis leading to several hundreds of thousands of deaths every year. Very few antifungals are available to treat infections caused by A. fumigatus, and resistance is developing to those we have. Our understanding of the molecular mechanisms that drive pathogenicity and drug resistance have been hampered by the lack of large mutant collections, which limits our ability to perform functional genomics analysis. Here we present a high‐throughput gene knockout method that combines a highly reproducible fusion PCR method to enable generation of gene replacement cassettes with a multiwell format transformation procedure. This process can be used to generate 96 null mutants within 5 days by a single person at a cost of less than £18 ($24) per mutant and is being employed in our laboratory to generate a barcoded genome‐wide knockout library in A. fumigatus. © 2019 The Authors.

The anti-inflammatory regulation of calcitonin gene-related peptide in mouse Aspergillus fumigatus keratitis

AIM

To analyze the impact of calcitonin gene-related peptide (CGRP) in mouse keratitis after Aspergillus fumigatus (A. fumigatus) infection.

METHODS

C57BL/6 mice were treated subconjunctivally with different concentrations of exogenous CGRP, and BALB/c mice were treated with CGRP8-37 (a CGRP antagonist) before corneas were infected with A. fumigatus. The cornea was assessed under the slit-lamp and the clinical score was recorded. The mRNA levels of IL-1β, TNF-α, IL-6, and MIP-2 were detected by quantitative real-time polymerase chain reaction (PCR), while the protein level of IL-1β was determined by Western blotting. In vitro, RAW264.7 cells were used to investigate NLRP3 and IL-1β expression induced by A. fumigatus after the pretreatment of exogenous CGRP or CGRP8-37. Cytokines expression in RAW264.7 cells was evaluated by real-time PCR and Western blotting.

RESULTS

Using exogenous CGRP resulted in down-regulated synthesis of IL-1β and MIP-2 stimulated by A. fumigatus in C57BL/6 mice keratitis, and the synthesis of IL-1β, MIP-2 and IL-6 was up-regulated in BALB/c mice corneas after the pretreatment with CGRP8-37. Pretreatment with exogenous CGRP and CGRP8-37 did not influence TNF-α mRNA levels either in BALB/c or C57BL/6 mice keratitis. The levels of NLRP3 and IL-1β were both reduced in A. fumigatus stimulated-macrophages after treatment with exogenous CGRP. And CGRP8-37 pretreatment would increase NLRP3 and IL-1β levels.

CONCLUSION

CGRP may alleviate the inflammatory reaction in mice keratitis after infection with A. fumigatus. The anti-inflammatory effect may be related to the inhibition of NLRP3 expression by CGRP.

Caspofungin Functionalized Polymethacrylates with Antifungal Properties

We describe the synthesis of hydrophilic poly(poly(ethylene glycol) methyl ether methacrylate) (PmPEGMA) and hydrophobic poly(methyl methacrylate) (PMMA) caspofungin conjugates by a post-polymerization modification of copolymers containing 10 mol % pentafluorophenyl methacrylate (PFPMA), which were obtained via reversible addition-fragmentation chain transfer copolymerization. The coupling of the clinically used antifungal caspofungin was confirmed and quantified in detail by a combination of ¹H-, ¹⁹F- and diffusion-ordered NMR spectroscopy, UV-vis spectroscopy, and size exclusion chromatography. The trifunctional amine-containing antifungal was attached via several amide bonds to the hydrophobic PMMA, but sterical hindrance induced by the mPEGMA side chains prohibited intramolecular double functionalization. Both polymer-drug conjugates revealed activity against important human-pathogenic fungi, that is, two strains of Aspergillus fumigatus and one strain of Candida albicans (2.5 mg L^-1 < MEC < 8 mg L^-1, MIC₅₀ = 4 mg L^-1), whereas RAW 264.7 macrophages as well as HeLa cells remained unaffected at these concentrations.

Aspergillus fumigatus population dynamics and sensitivity to demethylation inhibitor fungicides in whole-crop corn, high moisture corn and wet grain corn silages

BACKGROUND

Aspergillus fumigatus, the causal agent of aspergillosis in humans, is commonly present as a saprophyte in various organic substrates, such as spoiled silages. Aspergillosis is generally combated with demethylation inhibitor (DMI) fungicides, but the recent appearance of resistant medical and environmental strains made current treatment strategies less reliable. The goal of this study was to determine the evolution of A. fumigatus populations during the ensiling process of whole-crop corn, high moisture corn and wet grain corn, and to monitor the sensitivity of isolates from treated and untreated fields to one medical and one agricultural DMI fungicide.

RESULTS

A. fumigatus was isolated from fresh forage at harvest at rather low concentrations (10²  cfu g^-1 ). The low frequency lingered during the silage process (at 60 and 160 days), whereas it significantly increased during air exposure (at 7 and 14 days of air exposure). Field treatment of corn with a mixture of prothioconazole and tebuconazole did not affect the sensitivity of A. fumigatus isolates. One of 29 isolates from the untreated plot was resistant to voriconazole. A unique amino acid substitution (E427K) was detected in the cyp51A gene of 10 of 12 sequenced isolates, but was not associated with DMI resistance.

CONCLUSION

A. fumigatus significantly increased during aerobic deterioration of ensilaged corn after silo opening, compared with the low presence in fresh corn and during ensiling. Field treatment of corn with DMI fungicides did not affect the sensitivity of A. fumigatus isolates collected from fresh and ensiled corn. © 2019 Society of Chemical Industry.

Characterization of the Proteomic Response of A549 Cells Following Sequential Exposure to Aspergillus fumigatus and Pseudomonas aeruginosa

Aspergillus fumigatus and Pseudomonas aeruginosa are the most prevalent fungal and bacterial pathogens associated with cystic-fibrosis-related infections, respectively. P. aeruginosa eventually predominates as the primary pathogen, though it is unknown why this is the case. Label-free quantitative proteomics was employed to investigate the cellular response of the alveolar epithelial cell line, A549, to coexposure of A. fumigatus and P. aeruginosa. These studies revealed a significant increase in the rate of P. aeruginosa proliferation where A. fumigatus was present. Shotgun proteomics performed on A549 cells exposed to either A. fumigatus or P. aeruginosa or to A. fumigatus and P. aeruginosa sequentially revealed distinct changes to the host cell proteome in response to either or both pathogens. While key signatures of infection were retained among all pathogen-exposed groups, including changes in mitochondrial activity and energy output, the relative abundance of proteins associated with endocytosis, phagosomes, and lysosomes was decreased in sequentially exposed cells compared to cells exposed to either pathogen. Our findings indicate that A. fumigatus renders A549 cells unable to internalize bacteria, thus providing an environment in which P. aeruginosa can proliferate. This research provides novel insights into the whole-cell proteomic response of A549 cells to A. fumigatus and P. aeruginosa and highlights distinct differences in the proteome following sequential exposure to both pathogens, which may explain why P. aeruginosa can predominate.

Enolase From Aspergillus fumigatus Is a Moonlighting Protein That Binds the Human Plasma Complement Proteins Factor H, FHL-1, C4BP, and Plasminogen

The opportunistic fungal pathogen Aspergillus fumigatus can cause severe infections, particularly in immunocompromised individuals. Upon infection, A. fumigatus faces the powerful and directly acting immune defense of the human host. The mechanisms on how A. fumigatus evades innate immune attack and complement are still poorly understood. Here, we identify A. fumigatus enolase, AfEno1, which was also characterized as fungal allergen, as a surface ligand for human plasma complement regulators. AfEno1 binds factor H, factor-H-like protein 1 (FHL-1), C4b binding protein (C4BP), and plasminogen. Factor H attaches to AfEno1 via two regions, via short conserved repeats (SCRs) 6-7 and 19-20, and FHL-1 contacts AfEno1 via SCRs 6-7. Both regulators when bound to AfEno1 retain cofactor activity and assist in C3b inactivation. Similarly, the classical pathway regulator C4BP binds to AfEno1 and bound to AfEno1; C4BP assists in C4b inactivation. Plasminogen which binds to AfEno1 via lysine residues is accessible for the tissue-type plasminogen activator (tPA), and active plasmin cleaves the chromogenic substrate S2251, degrades fibrinogen, and inactivates C3 and C3b. Plasmin attached to swollen A. fumigatus conidia damages human A549 lung epithelial cells, reduces the cellular metabolic activity, and induces cell retraction, which results in exposure of the extracellular matrix. Thus, A. fumigatus AfEno1 is a moonlighting protein and virulence factor which recruits several human regulators. The attached human regulators allow the fungal pathogen to control complement at the level of C3 and to damage endothelial cell layers and tissue components.

Increased Efficacy of Oral Fixed-Dose Combination of Amphotericin B and AHCC® Natural Adjuvant against Aspergillosis

Invasive pulmonary aspergillosis represents one of the most serious fungal infections among immunocompromised patients. In this study, we aimed to analyze the in vivo efficacy of prophylactic oral amphotericin B (AMB) encapsulated in modified chitosan-nanoparticles (Nanomerics’ Molecular Envelope Technology (MET)) supplemented with a standardized extract of cultured Lentinula edodes mycelia (AHCC^®) in a murine model of pulmonary aspergillosis. We determined fungal burden and survival of mice and additionally, we carried out a cytokine analysis in an attempt to understand the immunomodulation of the extract. Our results evidenced equivalent efficacy between orally administered AMB-MET and the intravenous liposomal AMB marketed formulation. Addition of the AHCC^® supplement significantly improved efficacy in terms of burden reduction and survival increase of both oral and intravenous AMB therapies compared to the untreated control group. Moreover, a protective effect of the extract was observed in terms of weight loss. Regarding the cytokine profiles, the Th1 immune response was stimulated in treated animals when compared to the control group. This response was marked by an enhancement in the MCP-1, GM-CSF, VEGF, RANTES and IL-17 levels and a decrease in the IL-6, a biomarker related to the severity of the infection.

Early Interaction of Alternaria infectoria Conidia with Macrophages

Fungi of the genus Alternaria are ubiquitous indoor and outdoor airborne agents, and individuals are daily exposed to their spores. Although its importance in human infections and, particularly in respiratory allergies, there are no studies of how Alternaria spp. spores interact with host cells. Our aim was to study the early interaction of Alternaria infectoria spores with macrophages, the first line of immune defense. RAW 264.7 macrophages were infected with A. infectoria conidia, and the internalization and viability of conidia once inside the macrophages were quantified during the first 6 h of interaction. Live cell imaging was used to study the dynamics of this interaction. TNF-α production was quantified by relative gene expression, and the concentration of other cytokines (IL-1α, IL-1β, IL-6, IL-4, IL-10, IL-17, GM-CSF and INF-γ) and a chemokine, MIP-1α, was quantified by ELISA. Conidia were rapidly internalized by macrophages, with approximately half internalized after 30 min of interaction. During the first 6 h of interaction, macrophages retained the ability to mitotically divide while containing internalized conidia. The classical macrophage-activated morphology was absent in macrophages infected with conidia, and TNF-α and other cytokines and chemokines failed to be produced. Thus, macrophages are able to efficiently phagocyte A. infectoria conidia, but, during the first 6 h, no effective antifungal response is triggered, therefore promoting the residence of these fungal conidia inside the macrophages.

Aspergillus fumigatus Challenged by Human Dendritic Cells: Metabolic and Regulatory Pathway Responses Testify a Tight Battle

Dendritic cells (DCs) are antigen presenting cells which serve as a passage between the innate and the acquired immunity. Aspergillosis is a major lethal condition in immunocompromised patients caused by the adaptable saprophytic fungus Aspergillus fumigatus. The healthy human immune system is capable to ward off A. fumigatus infections however immune-deficient patients are highly vulnerable to invasive aspergillosis. A. fumigatus can persist during infection due to its ability to survive the immune response of human DCs. Therefore, the study of the metabolism specific to the context of infection may allow us to gain insight into the adaptation strategies of both the pathogen and the immune cells. We established a metabolic model of A. fumigatus central metabolism during infection of DCs and calculated the metabolic pathway (elementary modes; EMs). Transcriptome data were used to identify pathways activated when A. fumigatus is challenged with DCs. In particular, amino acid metabolic pathways, alternative carbon metabolic pathways and stress regulating enzymes were found to be active. Metabolic flux modeling identified further active enzymes such as alcohol dehydrogenase, inositol oxygenase and GTP cyclohydrolase participating in different stress responses in A. fumigatus. These were further validated by qRT-PCR from RNA extracted under these different conditions. For DCs, we outlined the activation of metabolic pathways in response to the confrontation with A. fumigatus. We found the fatty acid metabolism plays a crucial role, along with other metabolic changes. The gene expression data and their analysis illuminate additional regulatory pathways activated in the DCs apart from interleukin regulation. In particular, Toll-like receptor signaling, NOD-like receptor signaling and RIG-I-like receptor signaling were active pathways. Moreover, we identified subnetworks and several novel key regulators such as UBC, EGFR, and CUL3 of DCs to be activated in response to A. fumigatus. In conclusion, we analyze the metabolic and regulatory responses of A. fumigatus and DCs when confronted with each other.

Expression and role of calcitonin gene-related peptide in mouse Aspergillus fumigatus keratitis

AIM

To investigate the expression and role of calcitonin gene-related peptide (CGRP) in the mouse models induced by Aspergillus fumigatus (A. fumigatus).

METHODS

C57BL/6 mice were randomized into a control group and A. fumigatus keratitis group. The cornea photography was assessed under the slit lamp and the clinical score was recorded after infection. Western blot, real-time polymerase chain reaction (PCR) and immunohistofluorescence analysis were applied to detect CGRP expression in cornea of both groups. In vitro, tests were conducted with C57BL/6 mice macrophages to investigate CGRP expression after interaction with A. fumigatus. Cytokines expression induced by exogenous CGRP and the antagonist CGRP8-37 in A. fumigatus-exposed macrophages was evaluated by real-time PCR and ELISA.

RESULTS

The cornea expression of CGRP was significantly elevated in C57BL/6 mice corneas and macrophages after A. fumigatus infection. After treatment with exogenous CGRP, the levels of interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α) and IL-6 were reduced, and IL-10 level was increased in the A. fumigatus stimulated-macrophages. However, IL-1β, TNF-α and IL-6 levels were upregulated after pretreatment of CGRP8-37. But the mRNA levels of MIP-2, TGF-β and IL-10 were not changed.

CONCLUSION

This study provides evidence that A. fumigatus increased CGRP expression. CGRP may play a protective role against inflammation in A. fumigatus keratitis.

Copper Homeostasis in Aspergillus fumigatus: Opportunities for Therapeutic Development

Aspergillus fumigatus can cause severe invasive aspergillosis in immunocompromised individuals. Copper, an essential but potentially toxic trace element for A. fumigatus, plays a critical role at the host-pathogen axis during infection. Accumulating evidence demonstrates that the host utilizes copper compartmentalization within macrophages to combat A. fumigatus infection. To survive under host-imposed copper toxicity, A. fumigatus has evolved sophisticated machinery to regulate copper homeostasis. Thus, targeting molecular pathways critical for copper homeostasis regulation provides an opportunity to improve therapeutic options for aspergillosis caused by A. fumigatus. In this review, we describe the copper homeostatic mechanisms by which A. fumigatus acquires and controls copper levels and explores the responses of the pathogen to alter copper levels in the host. Finally, we discuss the regulatory mechanisms of copper homeostasis that could be targeted for antifungal drug development.

Copper Utilization, Regulation, and Acquisition by Aspergillus fumigatus

Copper is an essential micronutrient for the opportunistic human pathogen, Aspergillus fumigatus. Maintaining copper homeostasis is critical for survival and pathogenesis. Copper-responsive transcription factors, AceA and MacA, coordinate a complex network responsible for responding to copper in the environment and determining which response is necessary to maintain homeostasis. For example, A. fumigatus uses copper exporters to mitigate the toxic effects of copper while simultaneously encoding copper importers and small molecules to ensure proper supply of the metal for copper-dependent processes such a nitrogen acquisition and respiration. Small molecules called isocyanides recently found to be produced by A. fumigatus may bind copper and partake in copper homeostasis similarly to isocyanide copper chelators in bacteria. Considering that the host uses copper as a microbial toxin and copper availability fluctuates in various environmental niches, understanding how A. fumigatus maintains copper homeostasis will give insights into mechanisms that facilitate the development of invasive aspergillosis and its survival in nature.

The role of netrin-1 in the mouse cornea during Aspergillus fumigatus infection

PURPOSE

To explore the effects of netrin-1 on inflammation in Aspergillus fumigatus-infected mouse corneas and on proliferation and migration in human corneal epithelial cells (HCECs).

METHODS

Netrin-1 and the receptor A2BAR were detected in normal and infected corneas from C57BL/6 mice and RAW 264.7 cells. The mice were injected subconjunctivally with recombinant netrin-1. The severity of the disease was determined by clinical scores, photography with a slit lamp, RT-PCR, western blotting, myeloperoxidase (MPO) assays and immunofluorescence staining of polymorphonuclear neutrophilic leukocytes (PMNs). The effects of netrin-1 on RAW 264.7 cells in vitro were determined by RT-PCR. The role of A2BAR was demonstrated in vivo by detecting the expression of IL-1β, TNF-α, and IL-10 in corneas pretreated subconjunctivally with an A2BAR antagonist (PSB1115). RAW 264.7 cells were stimulated with Aspergillus fumigatus (A. fumigates) and netrin-1 with or without PSB1115 pretreatment. A cell counting kit-8 (CCK-8) assay was used to evaluate cell proliferation ability, and cell migration ability was determined by cell scratch experiments with HCECs.

RESULTS

Netrin-1 expression decreased slightly after A. fumigatus infection and then increased to its peak. A2BAR expression increased at 1 day post infection (p.i.), with a subsequent decline. Compared to the PBS control, exogenous netrin-1 attenuated the inflammatory response, PMN infiltration, and expression of the proinflammatory factors IL-1β and TNF-α, while IL-10 expression was up-regulated. In RAW 264.7 cells, recombinant netrin-1 obviously inhibited the mRNA expression of IL-1β and TNF-α and promoted the mRNA expression of the anti-inflammatory cytokine IL-10. Pretreatment with PSB1115 resulted in disease aggravation and higher levels of the proinflammatory factors IL-1β and TNF-α both in vivo and in vitro. And the effect of netrin-1 on inflammatory factors was abolished by PSB1115. Moreover, compared to the control treatment, exogenous netrin-1 significantly facilitated the proliferation and migration of HCECs.

CONCLUSIONS

Netrin-1 attenuates inflammation in C57BL/6 mice infected with A. fumigatus, and it may play this role via the receptor A2BAR. Additionally, netrin-1 can promote the proliferation and migration of HCECs.

Pro-Inflammatory Responses in Human Bronchial Epithelial Cells Induced by Spores and Hyphal Fragments of Common Damp Indoor Molds

Damp indoor environments contaminated with different mold species may contribute to the development and exacerbation of respiratory illnesses. Human bronchial epithelial BEAS-2B cells were exposed to X-ray treated spores and hyphal fragments from pure cultures of Aspergillus fumigatus, Penicillum chrysogenum, Aspergillus versicolor and Stachybotrys chartarum. Hyphal fragments of A. fumigatus and P. chrysogenum induced expression and release of the pro-inflammatory cytokine interleukin (IL)-6 and the chemokine IL-8, while none of the other hyphal preparations had effects. Hyphal fragments from A. fumigatus and P. chrysogenum also increased the expression of IL-1α, IL-1β and tumor necrosis factor (TNF)-α, but these cytokines were not released. X-ray treated spores had little or no inflammatory potential. Attenuating Toll-like receptor (TLR)-2 by blocking antibodies strongly reduced the A. fumigatus and P. chrysogenum hyphae-induced IL-6 and IL-8 release, whereas TLR4 antagonist treatment was without effects. Untreated A. fumigatus spores formed hyphae and triggered expression of pro-inflammatory genes with similarities to the effects of hyphal fragments. In conclusion, while X-ray treated spores induced no pro-inflammatory responses, hyphal fragments of A. fumigatus and P. chrysogenum enhanced a TLR2-dependent expression and release of IL-6 and IL-8.

Pathophysiological aspects of Aspergillus colonization in disease

Aspergillus colonization of the lower respiratory airways is common in normal people, and of little clinical significance. However, in some patients, colonization is associated with severe disease including poorly controlled asthma, allergic bronchopulmonary aspergillosis (ABPA) with sputum plugs, worse lung function in chronic obstructive pulmonary aspergillosis (COPD), invasive aspergillosis, and active infection in patients with chronic pulmonary aspergillosis (CPA). Therefore, understanding the pathophysiological mechanisms of fungal colonization in disease is essential to develop strategies to avert or minimise disease. Aspergillus cell components promoting fungal adherence to the host surface, extracellular matrix, or basal lamina are indispensable for pathogen persistence. However, our understanding of individual differences in clearance of A. fumigatus from the lung in susceptible patients is close to zero.