Glycosylation of Candida albicans Cell Wall Proteins Is Critical for Induction of Innate Immune Responses and Apoptosis of Epithelial Cells

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.     

Transcriptional Analysis of the Candida albicans Cell Cycle

We have examined the periodic expression of genes through the cell cycle in cultures of the human pathogenic fungus Candida albicans synchronized by mating pheromone treatment. Close to 500 genes show increased expression during the G1, S, G2, or M transitions of the C. albicans cell cycle. Comparisons of these C. albicans periodic genes with those already found in the budding and fission yeasts and in human cells reveal that of 2200 groups of homologous genes, close to 600 show periodicity in at least one organism, but only 11 are periodic in all four species. Overall, the C. albicans regulatory circuit most closely resembles that of Saccharomyces cerevisiae but contains a simplified structure. Although the majority of the C. albicans periodically regulated genes have homologues in the budding yeast, 20% (100 genes), most of which peak during the G1/S or M/G1 transitions, are unique to the pathogenic yeast.     

Candida albicans Increases Tumor Cell Adhesion to Endothelial Cells In Vitro: Intraspecific Differences and Importance of the Mannose Receptor

The dimorphic fungus Candida albicans is able to trigger a cytokine-mediated pro-inflammatory response that increases tumor cell adhesion to hepatic endothelium and metastasis. To check the intraspecific differences in this effect, we used an in vitro murine model of hepatic response against C. albicans, which made clear that tumor cells adhered more to endothelium incubated with blastoconidia, both live and killed, than germ tubes. This finding was related to the higher carbohydrate/protein ratio found in blastoconidia. In fact, destruction of mannose ligand residues on the cell surface by metaperiodate treatment significantly reduced tumor cell adhesion induced. Moreover, we also noticed that the effect of clinical strains was greater than that of the reference one. This finding could not be explained by the carbohydrate/protein data, but to explain these differences between strains, we analyzed the expression level of ten genes (ADH1, APE3, IDH2, ENO1, FBA1, ILV5, PDI1, PGK1, QCR2 and TUF1) that code for the proteins identified previously in a mannoprotein-enriched pro-metastatic fraction of C. albicans. The results corroborated that their expression was higher in clinical strains than the reference one. To confirm the importance of the mannoprotein fraction, we also demonstrate that blocking the mannose receptor decreases the effect of C. albicans and its mannoproteins, inhibiting IL-18 synthesis and tumor cell adhesion increase by around 60%. These findings could be the first step towards a new treatment for solid organ cancers based on the role of the mannose receptor in C. albicans-induced tumor progression and metastasis.     

Innate Immune Responses of Pulmonary Epithelial Cells to Burkholderia pseudomallei Infection

Background

Burkholderia pseudomallei, a facultative intracellular pathogen, causes systemic infection in humans with high mortality especially when infection occurs through an infectious aerosol. Previous studies indicated that the epithelial cells in the lung are an active participant in host immunity. In this study, we aimed to investigate the innate immune responses of lung epithelial cells against B. pseudomallei.

Methodology and Principal Findings

Using a murine lung epithelial cell line, primary lung epithelial cells and an inhalational murine infection model, we characterized the types of innate immunity proteins and peptides produced upon B. pseudomallei infection. Among a wide panel of immune components studied, increased levels of major pro-inflammatory cytokines IL-6 and TNFα, chemokine MCP-1, and up-regulation of secretory leukocyte protease inhibitor (SLPI) and chemokine (C-C motif) ligand 20 (CCL20) were observed. Inhibition assays using specific inhibitors suggested that NF-κB and p38 MAPK pathways were responsible for these B. pseudomallei-induced antimicrobial peptides.

Conclusions

Our findings indicate that the respiratory epithelial cells, which form the majority of the cells lining the epithelial tract and the lung, have important roles in the innate immune response against B. pseudomallei infection.     

Commensal Candida albicans Positively Calibrates Systemic Th17 Immunological Responses

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白色念珠菌胃癌株对细胞粘附作用的研究

研究白色念珠菌 (candidaalbicans)正常人口腔株与胃癌株对口腔粘膜细胞及肺上皮细胞的粘附性能。将白色念珠菌与正常人口腔颊粘膜细胞或培养的人肺上皮细胞于 37℃温育一定时间后 ,计算每个细胞粘附白色念珠菌数。白色念珠菌胃癌株对两类细胞粘附能力均较正常人口腔株强 ,其差异有显著性 (p <0 .0 1)。粘附性是致病菌侵袭力的重要机制 ,粘附性增强是白色念珠菌由正常微生物群成员转变为条件致病菌的重要条件。     

In-vitro susceptibility of Candida albicans and Candida stellatoidea to sulfamethoxazole

The susceptibility of organisms of the speciesCandida to sulfamethoxazole were tested in-vitro using the disc sensitivity method.Under specified conditions a zone of growth inhibition surrounding sulfamethoxazole tablet sensi disc was consistently produced in cultures ofCandida albicans, Candida stellatoidea andSaccharomyces cervisiae.Diameters of growth inhibition zone were measured and found to be greatest in cultures ofCandida stellatoidea andSaccharomyces, but growth inhibition inCandida albicans cultures was observed to a lesser degree.The correlation between in vivo pathogenicity of organisms of the speciesCandida, and degree of growth inhibition by sulfamethoxazole sensi disc presents an interesting relationship.     

Delayed hypersensitivity to Candida albicans

Conditions and factors influencing the formation of delayed hypersensitivity (DH) to yeast-like fungi of the species C. albicans under experimental conditions have been studied. The intensity of this reaction has been found to depend on the dose and method used for infecting mice, the time of the test and the qualitative state of fungal cells. As the result of this study, the infectious model of DH to C. albicans has been proposed. This model may be used for the study of the influence of different exogenous and endogenous factors of cell-mediated immune response to candidiasis.