Cellular interactions of Candida albicans with human oral epithelial cells and enterocytes

The human pathogenic fungus Candida albicans can cause systemic infections by invading epithelial barriers to gain access to the bloodstream. One of the main reservoirs of C. albicans is the gastrointestinal tract and systemic infections predominantly originate from this niche. In this study, we used scanning electron and fluorescence microscopy, adhesion, invasion and damage assays, fungal mutants and a set of fungal and host cell inhibitors to investigate the interactions of C. albicans with oral epithelial cells and enterocytes. Our data demonstrate that adhesion, invasion and damage by C. albicans depend not only on fungal morphology and activity, but also on the epithelial cell type and the differentiation stage of the epithelial cells, indicating that epithelial cells differ in their susceptibility to the fungus. C. albicans can invade epithelial cells by induced endocytosis and/or active penetration. However, depending on the host cell faced by the fungus, these routes are exploited to a different extent. While invasion into oral cells occurs via both routes, invasion into intestinal cells occurs only via active penetration.     

Candida morphogenesis and host-pathogen interactions

The human fungal pathogen Candida albicans has many morphological forms. Recent advances in genomics and cell biology are providing an improved understanding of the molecular regulation of cell shape, and providing insights into the relationships between morphogenesis and virulence. This understanding may improve our ability to develop strategies to combat Candida infections.     

Proteomics on its way to study host-pathogen interaction in Candida albicans

Candida albicans is a common fungal pathogen of humans, but also exists as a commensal in the population. Proteomics of C. albicans has been used since the early 1980s, however, only the recent publication of the genome sequence of C. albicans and improvements in mass spectrometry technologies have made it possible to apply proteomics to C. albicans on a larger scale. This includes analysing the cell wall, investigating drug response or changes in mutants with defects in virulence. In addition, serological responses to systemic candidiasis have been monitored and screens for virulence factors using patient sera, have been described. These promising approaches are just emerging, anticipating further contributions in C. albicans proteomics that will advance our understanding of host-pathogen interaction in the near future.     

Adherence of Candida albicans to buccal and vaginal epithelial cells: ultrastructural observations

The adherence of Candida albicans to human buccal and vaginal epithelial cells was studied by transmission electron microscopy. Adherence to epithelial cells was confirmed by both a radiometric assay as well as direct microscopic examination of stained cell preparations. Ultramicroscopic preparations revealed that yeast cells were closely appressed to epithelial cell surfaces and were often partially enclosed within phagocyticlike invaginations of the epithelial cells. A murine model of vaginitis caused by C. albicans was also used to study adherence to epithelial cells and to follow the course of colonization. Ultramicroscopic preparations of murine vaginal tissue revealed that within 2 h postinfection, yeast cells could be seen adhering to epithelial cells. At 6 h postinfection, hyphae and yeast cells were not only found on the epithelial cell surface but also within the submucosal tissue. When observed on the epithelial cell surface, Candida cells were either attached to host cells, or when infected tissue was stained with ruthenium red, Candida cells were observed on the epithelial surface embedded within an electron-dense matrix. Fungal elements were abundant in the submucosa at 24 h postinfection and were still observed on the epithelial cell surface; all of this was accompanied by an inflammatory response.     

Candida albicans interactions with epithelial cells and mucosal immunity

Candida albicans interactions with epithelial cells are critical for commensal growth, fungal pathogenicity and host defence. This review will outline our current understanding of C. albicans-epithelial interactions and will discuss how this may lead to the induction of a protective mucosal immune response.     

Glycosylphosphatidylinositol-anchored proteases of Candida albicans target proteins necessary for both cellular processes and host-pathogen interactions

Intracellular and secreted proteases fulfill multiple functions in microorganisms. In pathogenic microorganisms extracellular proteases may be adapted to interactions with host cells. Here we describe two cell surface-associated aspartic proteases, Sap9 and Sap10, which have structural similarities to yapsins of Saccharomyces cerevisiae and are produced by the human pathogenic yeast Candida albicans. Sap9 and Sap10 are glycosylphosphatidylinositol-anchored and located in the cell membrane or the cell wall. Both proteases are glycosylated, cleave at dibasic or basic processing sites similar to yapsins and Kex2-like proteases, and have functions in cell surface integrity and cell separation during budding. Overexpression of SAP9 in mutants lacking KEX2 or SAP10, or of SAP10 in mutants lacking KEX2 or SAP9, only partially restored these phenotypes, suggesting distinct target proteins of fungal origin for each of the three proteases. In addition, deletion of SAP9 and SAP10 modified the adhesion properties of C. albicans to epithelial cells and caused attenuated epithelial cell damage during experimental oral infection suggesting a unique role for these proteases in both cellular processes and host-pathogen interactions.     

Adherence of Candida albicans and Candida dubliniensis to buccal and vaginal cells

Twenty-seven Candida albicans strains and 26 Candida dubliniensis strains, isolated from HIV patients, were tested for their adherence to buccal and vaginal epithelial cells. Both species showed important levels of adhesion to buccal and vaginal epithelial cells, although C. albicans showed the highest levels of adhesion. These results suggest that both Candida species are well adapted, in terms of adhesion capability, to the oral and vaginal environment.     

Role of nuclear factor-kappaB in providing interactions of human neutrophils and epithelial cells from oral cavity with Candida albicans

Contribution of intracellular signal pathways associated with nuclear factor kappaB (NF-kappaB) in realization of interactions of human neutrophils and epithelial cells from oral cavity with Candida albicans was studied. Supression of NF-kappaB in epitheliocytes resulted in decreased adsorption of C. albicans to buccal cells (buccal mucosa). Inhibition of NF-kappaB led to decrease in receptor-dependent oxidative activity of neutrophils in systems with native and IgG-opsonized C. albicans as well as to increase of phagocytic activity during contact with C3b-/iC3b-opsonized C. albicans. It has been concluded that NF-kappaB participates in regulation of specific interactions of neurophils and epitheliocytes with C. albicans.     

Correlative relationship between adherence of Candida albicans to human vaginal epithelial cells in vitro and candidal vaginitis

This study investigated whether a correlation exists between predisposition to candidal vaginitis and adherence of Candida albicans to vaginal epithelial cells in vitro. Vaginal epithelial cells from 120 fecund women who were pregnant and/or diabetic had a greater propensity to bind C. albicans than did 71 oral contraceptive users and 75 non-pregnant, non-diabetic controls. The highest level of adherence occurred in pregnant diabetic women. Among 48 non-diabetic postmenopausal females, C. albicans adherence was lower than for fecund controls, but it was higher for cells from 33 postmenopausal diabetic women. The hormonal status of the fecund and postmenopausal women was assayed cytologically by the Karyopyknotic and Maturation Indices, which determine the ratios of superficial, intermediate and parabasal vaginal epithelial cells. Our findings point to increased C. albicans adherence in situations where there is an increase in the number of intermediate epithelial cells: pregnancy, the first or fourth weeks of the menstrual cycle, or diabetes. The adherence of 41 C. albicans isolates from patients with vaginitis was significantly higher than that of 36 isolates from asymptomatic carriers.     

Animal models in the analysis of Candida host-pathogen interactions

An increasingly diverse array of clinically relevant animal models of candidiasis have been established that mimic both the immune perturbations of the host and tissue-specific features of candidiasis in humans. Cause-and-effect analysis of Candida host-pathogen interactions using these animal models has made a quantum leap forward in the genomic era, with the concurrent construction of C. albicans mutants with targeted mutations of putative virulence factors, the application of microarrays and other emerging technologies to comprehensively assess C. albicans gene expression in vivo, and construction of transgenic and knockout mice to simulate specific host immunodeficiencies. The opportunity to combine these powerful tools will yield an unprecedented wealth of new information on the molecular and cellular pathogenesis of candidiasis.     

Evaluation of the role of Candida albicans agglutinin-like sequence (Als) proteins in human oral epithelial cell interactions

The fungus C. albicans uses adhesins to interact with human epithelial surfaces in the processes of colonization and pathogenesis. The C. albicans ALS (agglutinin-like sequence) gene family encodes eight large cell-surface glycoproteins (Als1-Als7 and Als9) that have adhesive function. This study utilized C. albicans Δals mutant strains to investigate the role of the Als family in oral epithelial cell adhesion and damage, cytokine induction and activation of a MAPK-based (MKP1/c-Fos) signaling pathway that discriminates between yeast and hyphae. Of the eight Δals mutants tested, only the Δals3 strain showed significant reductions in oral epithelial cell adhesion and damage, and cytokine production. High fungal:epithelial cell multiplicities of infection were able to rescue the cell damage and cytokine production phenotypes, demonstrating the importance of fungal burden in mucosal infections. Despite its adhesion, damage and cytokine induction phenotypes, the Δals3 strain induced MKP1 phosphorylation and c-Fos production to a similar extent as control cells. Our data demonstrate that Als3 is involved directly in epithelial adhesion but indirectly in cell damage and cytokine induction, and is not the factor targeted by oral epithelial cells to discriminate between the yeast and hyphal form of C. albicans.     

Cross-kingdom interactions: Candida albicans and bacteria

Bacteria and fungi are found together in a myriad of environments and particularly in a biofilm, where adherent species interact through diverse signaling mechanisms. Yet, despite billions of years of coexistence, the area of research exploring fungal–bacterial interactions, particularly within the context of polymicrobial infections, is still in its infancy. However, reports describing a multitude of wide-ranging interactions between the fungal pathogen Candida albicans and various bacterial pathogens are on the rise. An example of a mutually beneficial interaction is coaggregation, a phenomenon that takes place in oral biofilms where the adhesion of C. albicans to oral bacteria is considered crucial for its colonization of the oral cavity. In contrast, the interaction between C. albicans and Pseudomonas aeruginosa is described as being competitive and antagonistic in nature. Another intriguing interaction is that occurring between Staphylococcus aureus and C. albicans , which although not yet fully characterized, appears to be initially synergistic. These complex interactions between such diverse and important pathogens would have significant clinical implications if they occurred in an immunocompromised host. Therefore, understanding the mechanisms of adhesion and signaling involved in fungal–bacterial interactions may lead to the development of novel therapeutic strategies for impeding microbial colonization and development of polymicrobial disease.     

乳杆菌优良菌株的筛选及对小鼠阴道白假丝酵母菌过度增殖干预

目的探讨乳杆菌优良菌株的筛选及其对小鼠阴道白假丝酵母菌过度增殖干预作用。方法对德氏乳杆菌DM8909菌株进行诱变筛选,得到耐抗生素突变株208,以ICR小鼠为实验对象,用甲硝唑进行小鼠阴道菌群脱污染,将白假丝酵母菌接种到小鼠阴道内,构建小鼠阴道白假丝酵母菌过度增殖模型。采用阴道接种德氏乳杆菌DM8909突变株208菌液（2×108CFU/mL）处理,取其阴道冲洗液进行阴道菌群分析,并进行阴道上皮细胞的电镜检查。结果乳杆菌干预后显著清除阴道内的假丝酵母菌,肠杆菌恢复正常水平,与模型组比较,差异有统计学意义（P〈0.05）。结论德氏乳杆菌DM8909抗性菌株208能调整白假丝酵母菌在小鼠阴道内定植,对小鼠阴道上皮细胞有恢复作用。     

Interactions of Candida albicans with epithelial cells

The fungus, Candida albicans, interacts with epithelial cells in the human host both as a normal commensal and as an invasive pathogen. It has evolved multiple complementary mechanisms to adhere to epithelial cells. Adherent C. albicans cells can invade epithelial surfaces both by penetrating into individual epithelial cells, and by degrading interepithelial cell junctions and passing between epithelial cells. Invasion into epithelial cells is mediated by both induced endocytosis and active penetration, whereas degradation of epithelial cell junction proteins, such as E‐cadherin, occurs mainly via proteolysis by secreted aspartyl proteinases. C. albicans invasion of epithelial cells results in significant epithelial cell damage, which is probably induced by lytic enzymes, such as proteases and phospholipase secreted by the organism. Future challenges include identifying the epithelial cell targets of adhesins and invasins, and determining the mechanisms by which C. albicans actively penetrates epithelial cells and induces epithelial cell damage.