Ultrastructural viewpoints on the interaction events of Scedosporium apiospermum conidia with lung and macrophage cells

Abstract

BACKGROUND Scedosporium apiospermum is a ubiquitous, emerging and multidrug-resistant fungal pathogen with still rather unknown virulence mechanisms.OBJECTIVES/METHODS The cellular basis of the in vitro interaction between fungi and host cells/tissues is the determinant factor for the development of a successful in vivo infection. Herein, we evaluated the interaction of S. apiospermum conidia with lung epithelial (A549), lung fibroblast (MRC-5) and RAW 264.7 macrophages by light and scanning/transmission electron microscopy.FINDINGS After 4 h of fungi-host cell contact, the percentage of infected mammalian cells and the number of fungi per infected cell was measured by light microscopy, and the following association indexes were calculated for A549, MRC-5 and macrophage cells: 73.2 ± 25.9, 69.7 ± 22.5 and 59.7 ± 11.1, respectively. Both conidia and germinated conidia were regularly observed interacting with the evaluated cells, with a higher prevalence of non-germinated conidia. Interestingly, nests of germinated conidia were evidenced at the surface of lung cells by scanning electron microscopy. Some germination projections and hyphae were seen penetrating/evading the mammalian cells. Furthermore, internalised conidia were seen within vacuoles as visualised by transmission electron microscopy.MAIN CONCLUSIONS The present study contributes to a better understanding of S. apiospermum pathogenesis by demonstrating the first steps of the infection process of this opportunistic fungus.

Insights into the interaction of Scedosporium apiospermum, Scedosporium aurantiacum, Scedosporium minutisporum, and Lomentospora prolificans with lung epithelial cells

“…2). Our result is in accordance with previous works reported for S. boydii, S. apiospermum, and S. aurantiacum, in which after 4 h of interaction with different mammalian cells, nongerminated conidia were the predominantly adhered fungal morphotypes [7,11,14,19]. Conidia of A. fumigatus also started to germinate after approximately 4 h of in vivo infection using a murine experimental model [21]; whereas in in vitro contact with endothelial cell lines, resting conidia of A. fumigatus only start to germinate after 8 h [22].…”

“…This highlights the increase in levels of transcripts from genes associated with wound healing, cell repair, and protective response, like genes that encode the chemokines IL-6, IL-8, IL-11, TNF-α, and MUC5, a gene involved in mucin production that indicates the initiation of mucociliary clearance [19,20,26]. In addition, a fibrous-like network secreted by A549 cells surrounding S. apiospermum conidia was previously observed through scanning electron microscopy [7]. The type II Subsequently, the interaction systems were incubated with Calcofluor white (CW), to localize the mycelial cells, and propidium iodide (PI), to evidence the A549 plasma membrane injury.…”

“…The PRMs also mediate the in vitro adhesion between L. prolificans conidia and mouse peritoneal macrophages [16]. The conidial adhesion followed by its germination was also observed during the in vitro interaction events of S. apiospermum, S. boydii, and S. aurantiacum with lung epithelial cells (A549), lung fibroblasts (MRC-5), and mouse macrophages (RAW 264.7 line) [7,14,19,20]. Interesting studies were also conducted with peritoneal macrophages and polymorphonuclear cells in an effort to investigate the immune responses against Scedosporium/Lomentospora species [10,12,15].…”

“…The initial interaction between fungal propagules and host is a crucial step for the success of colonization as well as dissemination [6][7][8]. For filamentous fungi, some features are well known for the establishment of a successfully infectious process, such as cell wall composition, conidial germination, and secretion of metabolites and hydrolytic enzymes [8,9].…”

“…For filamentous fungi, some features are well known for the establishment of a successfully infectious process, such as cell wall composition, conidial germination, and secretion of metabolites and hydrolytic enzymes [8,9]. Some of those fungal structures have been studied on Scedosporium/Lomentospora species, such as (i) surface molecules (e.g., peptidorhamnomannans, glucosylceramides, and α-glucan) capable of interacting with host receptors as well as modulating the host immunity responses, (ii) proteases able to cleave key host proteins, including antimicrobial peptides, extracellular matrix proteins, and humoral immune components, (iii) high capacity of conidia to germinate under diverse environmental conditions, and (iv) biofilm formation on a variety of abiotic surfaces and also over mammalian cells [7,8,[10][11][12][13][14][15][16][17][18].…”