Biology subjects

Fontaine, T.

Publications and source records attributed to Fontaine, T..

8 recordsLinked to original sources

bioRxiv2026

Hijacking of inflammasome responses by the complement system during Pseudomonas aeruginosa-Aspergillus fumigatus sur-infection

Patients with cystic fibrosis (pwCF) are highly susceptible to chronic pulmonary infections due to mutations in the CFTR gene. From early childhood, pwCF experience repeated lung infections and often develop chronic bacterial and/or fungal colonization. Among the most clinically relevant pathogens, Pseudomonas aeruginosa and Aspergillus fumigatus frequently co-infect and are associated with worse outcomes, including excessive IL-1{beta}-driven inflammation and accelerated lung function decline. Here we investigated the mechanisms underlying inflammasome overactivation during super-infection. We found that inflammasome hyperactivation occurred across macrophage populations, was independent of exogenous priming, and required live co-infection with both pathogens. P. aeruginosa and A. fumigatus cooperatively activated the NLRP3 inflammasome, and this response required both caspase-1 and caspase-8. Unexpectedly, gasdermin D was dispensable for IL-1{beta} release. Bacterial flagellin, type IV pili and the type III secretion system, as well as the fungal polysaccharide galactosaminogalactan (GAG), were each required for overactivation. Mechanistically, P. aeruginosa activated the MyD88-TLR pathway, enhancing macrophage responses and promoting ITGAM (CD11b) expression. Under fungal super-infection, macrophages secreted complement component C3, which may bound fungal surface and engaged the complement receptor C3R (CD11b/CD18). Downstream SYK and ERK signaling amplified inflammasome activation and IL-1{beta} release. Single-cell transcriptomic analysis of pwCF broncho-alveolar lavage and lung samples supported coordinated upregulation of complement and inflammasome pathways during bacterial-fungal infection. Together, these findings identify a complement-inflammasome signaling axis that drives pathological inflammation during bacterial-fungal co-infection in airways of pwCF and may represent a therapeutic target.

immunology↗

bioRxiv2024

Beta-1,6-glucan plays a central role in the structure and remodeling of the bilaminate fungal cell wall

The cell wall of human fungal pathogens plays critical roles as an architectural scaffold and as a target and modulator of the host immune response. Although the cell wall of the pathogenic yeast Candida albicans is intensively studied, one of the major fibrillar components in its cell wall, {beta}-1,6- glucan, has been largely neglected. Here, we show that {beta}-1,6-glucan is essential for bilayered cell wall organization, cell wall integrity and filamentous growth. For the first time, we show that {beta}-1,6- glucan production compensates the defect in mannan elongation in the outer layer of the cell wall. In addition, {beta}-1,6-glucan dynamics are also coordinated by host environmental stimuli and stresses with wall remodeling, where the regulation of {beta}-1,6-glucan structure and chain length is a crucial process. As we point out that {beta}-1,6-glucan is exposed at the yeast surface and modulate immune response, {beta}-1,6-glucan must be considered a key factor in host-pathogen interactions.

microbiology↗

bioRxiv2023

The unique Legionella longbeachae capsule favors intracellular replication and immune evasion

Legionella longbeachae and Legionella pneumophila cause Legionnaires disease despite species-specific differences in environmental niches, disease epidemiology, and genomic content. Here, we characterized a new L. longbeachae virulence factor, a capsule that is expressed in post-exponential growth phase as shown by electron microscopy. Analysis of the capsule composition via HLPC revealed the presence of a highly anionic polysaccharide absent in a capsule mutant. The capsule is crucial for replication and virulence in vivo in a mouse model of infection and in the natural host Acanthamoeba castellanii. It has anti-phagocytic function when encountering innate immune cells, it is involved in a low cytokine responses in mice and in human monocyte derived macrophages and helps to dampen the innate immune response. The L. longbeachae capsule is a novel virulence factor, unique among known Legionella species, that aids L. longbeachae to survive in specific niches and partly confers L. longbeachae its unique infection characteristics.

microbiology↗

bioRxiv2023

CD56-mediated activation of human natural killer cells is triggered by Aspergillus fumigatus galactosaminogalactan

Invasive aspergillosis causes significant morbidity and mortality in immunocompromised patients. Natural killer (NK) cells are pivotal for antifungal defense. Thus far, CD56 is the only known pathogen recognition receptor on NK cells triggering potent antifungal activity against Aspergillus fumigatus. However, the underlying cellular mechanisms and the fungal ligand of CD56 have remained unknown. Using purified cell wall components, biochemical treatments, and A. fumigatus mutants with altered cell wall composition, we herein found that CD56 interacts with the A. fumigatus cell wall carbohydrate galactosaminogalactan (GAG). This interaction induced NK cell activation, degranulation, and secretion of immune-enhancing chemokines and cytotoxic effectors. Supernatants from GAG-stimulated NK cells elicited antifungal activity and enhanced antifungal effector responses of polymorphonuclear cells. In conclusion, we identified A. fumigatus GAG as a ligand of CD56 on human primary NK cells, stimulating potent antifungal effector responses and activating other immune cells.

microbiology↗

bioRxiv2023

Structural Remodeling of Fungal Cell Wall Promotes Resistance to Echinocandins

The insufficient efficacy of existing antifungal drugs and the rise in resistance necessitate the development of new therapeutic agents with novel functional mechanisms1,2. Echinocandins are an important class of antifungals that inhibit {beta}-1,3-glucan biosynthesis to interfere with cell wall structure and function3,4. However, their efficacy is limited by the fungistatic activity against Aspergillus species and the trailing effect during clinical application. Here, we describe how echinocandins remodel the supramolecular assembly of carbohydrate polymers in the fungal cell wall in an unexpected manner, possibly resulting in a subsequent inhibition of the activity of these drugs. Solid-state nuclear magnetic resonance (ssNMR) analysis of intact cells from the human pathogenic fungus Aspergillus fumigatus showed that the loss of {beta}-1,3-glucan and the increase of chitin content led to a decrease in cell wall mobility and water-permeability, thus enhancing resistance to environmental stresses. Chitosan and -1,3-glucan were found to be important buffering molecules whose physical association with chitin maintained the wall integrity. These new findings revealed the difficult-to-understand structural principles governing fungal pathogens response to echinocandins and opened new avenues for designing novel antifungal agents with improved efficacy.

biophysics↗

bioRxiv2022

Aspergillus fumigatus can exhibit persistence to the fungicidal drug voriconazole

Aspergillus fumigatus is a filamentous fungus that can infect the lungs of patients with immunosuppression and/or underlying lung-diseases. The mortality associated with chronic and invasive aspergillosis infections remain very high, despite availability of antifungal treatments. In the last decade, there has been a worrisome emergence and spread of resistance to the first line antifungals, the azoles. The mortality caused by resistant isolates is even higher, and patient management is complicated as the therapeutic options are reduced. Nevertheless, treatment failure is also common in patients infected with azole-susceptible isolates, which can be due to several non- mutually exclusive reasons, such as poor drug absorption. In addition, the phenomena of tolerance or persistence, where susceptible pathogens can survive the action of an antimicrobial for extended periods, have been associated with treatment failure in bacterial infections, and their occurrence in fungal infections already proposed. Here, we demonstrate that some isolates of A. fumigatus display persistence to voriconazole. A sub-population of the persister isolates can survive for extended periods and even grow at slow rates in the presence of supra-MIC (Minimum Inhibitory Concentration) of voriconazole and seemingly other azoles. Persistence cannot be eradicated with adjuvant drugs or antifungal combinations and seems to reduce the efficacy of treatment for certain individuals in a Galleria mellonella model of infection. Furthermore, persistence implies a distinct transcriptional profile, demonstrating that it is an active response. We propose that azole persistence might be a relevant and underestimated factor that could influence the outcome of infection in human aspergillosis. IMPORTANCEThe phenomena of antibacterial tolerance and persistence, where pathogenic microbes can survive for extended periods in the presence of cidal drug concentrations, have received significant attention in the last decade. Several mechanisms of action have been elucidated, and their relevance for treatment failure in bacterial infections demonstrated. In contrast, our knowledge about antifungal tolerance and, particularly, persistence are still very scarce. In this study, we have characterised the response of the prominent fungal pathogen Aspergillus fumigatus to the first line therapy antifungal voriconazole. We comprehensively show that some isolates display persistence to this fungicidal antifungal and identify various potential mechanisms of action. In addition, using an alternative model of infection, we provide initial evidence to suggest that persistence may cause treatment failure in some individuals. Therefore, we propose that azole persistence is an important factor to consider and further investigate in A. fumigatus.

microbiology↗

bioRxiv2022

The C-type Lectin Receptor Dectin-2 is a receptor for Aspergillus fumigatus galactomannan

Aspergillus fumigatus is a ubiquitous environmental mold that causes significant mortality particularly amongst immunocompromised patients. The detection of the Aspergillus-derived carbohydrate galactomannan in patient sera and bronchoalveolar lavage fluid is the major biomarker used to detect A. fumigatus infection in clinical medicine. Despite the clinical relevance of this carbohydrate, we lack a fundamental understanding of how galactomannan is recognized by the immune system and its consequences. Galactomannan is composed of a linear mannan backbone with galactofuranose sidechains and is found both attached to the cell surface of Aspergillus and as a soluble carbohydrate in the extracellular milieu. In this study, we utilized fungal-like particles composed of highly purified Aspergillus galactomannan to identify a C-type lectin host receptor for this fungal carbohydrate. We identified a novel and specific interaction between Aspergillus galactomannan and the C-type lectin receptor Dectin-2. We demonstrate that galactomannan bound to Dectin-2 and induced Dectin-2 dependent signaling including activation of spleen tyrosine kinase and potent TNF production. Deficiency of Dectin-2 increased immune cell recruitment to the lungs but was dispensable for survival in a mouse model of pulmonary aspergillosis. Our results identify a novel interaction between galactomannan and Dectin-2 and demonstrate that Dectin-2 is a receptor for galactomannan which leads to a pro-inflammatory immune response in the lung. IMPORTANCEAspergillus fumigatus is a fungal pathogen that causes serious and often fatal disease in humans. The surface of Aspergillus is composed of complex sugar molecules. Recognition of these carbohydrates by immune cells by carbohydrate lectin receptos can lead to clearance of the infection or, in some cases, benefit the fungus by dampening the host response. Galactomannan is a carbohydrate that is part of the cell surface of Aspergillus but is also released during infection and is found in patient lungs as well as their bloodstreams. The significance of our research is that we have identified a mammalian immune cell receptor that recognizes, binds, and signals in response to galactomannan. These results enhance our understanding of how this carbohydrate interacts with the immune system at the site of infection and will lead to broader understanding of how release of galactomannan by Aspergillus effects the immune response in infected patients.

immunology↗

bioRxiv2018

Decoration of the enterococcal polysaccharide antigen EPA is essential for virulence, cell surface charge and sensitivity to effector molecules of innate immunity

Enterococcus faecalis is an opportunistic pathogen with an intrinsically high resistance to lysozyme, a key effector of the innate immune system. This high level of resistance requires several genes (oatA, pgdA, dltA and sigV) acting synergistically to inhibit both the enzymatic and cationic antimicrobial peptide activities of lysozyme. We sought to identify novel genes modulating E. faecalis resistance to lysozyme. Random transposon mutagenesis carried out in the quadruple oatA/pgdA/dltA/sigV mutant led to the identification of several independent insertions clustered on the chromosome. These mutations were located in a locus referred to as the enterococcal polysaccharide antigen (EPA) variable region located downstream of the highly conserved epaA-epaR genes proposed to encode a core synthetic machinery. The epa variable region was previously proposed to be responsible for EPA decorations, but the role of this locus remains largely unknown. Here, we show that EPA decoration contributes to resistance towards charged antimicrobials and underpins virulence in the zebrafish model of infection by conferring resistance to phagocytosis. Collectively, our results indicate that the production of the EPA rhamnopolysaccharide backbone is not sufficient to promote E. faecalis infections and reveal an essential role of the modification of this surface polymer for enterococcal pathogenesis.

microbiology↗