The extensive use of immunosuppressive therapies in recent years has increased the number of patients prone to or actually suffering from localised candidosis. As Candida species gain increasing resistance towards common antifungal drugs, new strategies are needed to prevent and treat infections caused by these pathogens. Probiotic bacteria have been in vogue in the past two decades. More and more dairy products containing such organisms offer promising potential beneficial effects on human health and well-being. Because of the ability of probiotic bacteria to inhibit the growth of pathogens and to modulate human immune responses, these bacteria could provide new possibilities in antifungal therapy. We summarise the recent findings concerning the usefulness of probiotic treatment in localised candidosis, as well as discussing possible risks of probiotic treatment and highlighting the molecular mechanisms that are believed to contribute to probiotic effects.
C. albicans is one of the most common fungal pathogen of humans, causing local and superficial mucosal infections in immunocompromised individuals. Given that the key structure mediating host-C. albicans interactions is the fungal cell wall, we aimed to identify features of the cell wall inducing epithelial responses and be associated with fungal pathogenesis. We demonstrate here the importance of cell wall protein glycosylation in epithelial immune activation with a predominant role for the highly branched N-glycosylation residues. Moreover, these glycan moieties induce growth arrest and apoptosis of epithelial cells. Using an in vitro model of oral candidosis we demonstrate, that apoptosis induction by C. albicans wild-type occurs in early stage of infection and strongly depends on intact cell wall protein glycosylation. These novel findings demonstrate that glycosylation of the C. albicans cell wall proteins appears essential for modulation of epithelial immunity and apoptosis induction, both of which may promote fungal pathogenesis in vivo.
The expansive use of immunosuppressive medications in fields such as transplantational medicine and oncology, the higher frequency of invasive procedures in an ageing population and the HIV/AIDS pandemic have increased the frequency of systemic fungal infections. At the same time, increased resistance of pathogenic fungi to classical antifungal agents has led to sustained research efforts targeting alternative antifungal strategies. In this review, we focus on two promising approaches: cationic peptides and the targeting of fungal virulence factors. Cationic peptides are small, predominantly positively charged protein fragments that exert direct and indirect antifungal activities, one mechanism of action being the permeabilization of the fungal membrane. They include lysozyme, defensins and cathelicidins as well as novel synthetic peptides. Among fungal virulence factors, the targeting of candidal secreted aspartic proteinases seems to be a particularly promising approach.
Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has an important role not only in glycolysis but also in nonmetabolic processes, including transcription activation and apoptosis. We report the isolation of a human GAPDH (hGAPDH) (2-32) fragment peptide from human placental tissue exhibiting antimicrobial activity. The peptide was internalized by cells of the pathogenic yeast Candida albicans and initiated a rapid apoptotic mechanism, leading to killing of the fungus. Killing was dose-dependent, with 10??g?ml (3.1??M) and 100??g?ml hGAPDH (2-32) depolarizing 45% and 90% of the fungal cells in a population, respectively. Experimental C. albicans infection induced epithelial hGAPDH (2-32) expression. Addition of the peptide significantly reduced the tissue damage as compared with untreated experimental infection. Secreted aspartic proteinase (Sap) activity of C. albicans was inhibited by the fragment at higher concentrations, with a median effective dose of 160?mg?l(-1) (50??M) for Sap1p and 200?mg?l(-1) (63??M) for Sap2p, whereas Sap3 was not inhibited at all. Interestingly, hGAPDH (2-32) induced significant epithelial IL-8 and GM-CSF secretion and stimulated Toll-like receptor 4 expression at low concentrations independently of the presence of C. albicans, without any toxic mucosal effects. In the future, the combination of different antifungal strategies, e.g., a conventional fungicidal with immunomodulatory effects and the inhibition of fungal virulence factors, might be a promising treatment option.
In this protocol, we describe the application of commercially available three-dimensional organotypic tissues of human oral mucosa to study the interaction between Candida albicans and epithelial cells. Infection experiments show high reproducibility and can be used to analyse directly pathogen/epithelial cell interactions. However, the system is also very flexible. Using histological, biochemical, immunological, and molecular methods, it is possible to analyse several stages of infection by C. albicans wild type or mutant strains and demonstrate the consequence of disrupting genes encoding putative virulence factors required for host cell invasion and immune defence induction. This model provides information about host and pathogen protein and gene expression during direct interactions with each other. It can additionally be supplemented with other host factors, such as immune cells, saliva, and probiotic bacteria, which are relevant for host immune defence in the oral cavity.
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