Bioactive interleukin-1alpha is cytolytically released from Candida albicans-infected oral epithelial cells

Assessment of Oxidative Stress-Induced Oral Epithelial Toxicity

Reactive oxygen species (ROS) are highly reactive molecules generated in living organisms and an excessive production of ROS culminates in oxidative stress and cellular damage. Notably, oxidative stress plays a critical role in the pathogenesis of a number of oral mucosal diseases, including oral mucositis, which remains one of cancer treatments' most common side effects. We have shown previously that oral keratinocytes are remarkably sensitive to oxidative stress, and this may hinder the development and reproducibility of epithelial cell-based models of oral disease. Here, we examined the oxidative stress signatures that parallel oral toxicity by reproducing the initial events taking place during cancer treatment-induced oral mucositis. We used three oral epithelial cell lines (an immortalized normal human oral keratinocyte cell line, OKF6, and malignant oral keratinocytes, H357 and H400), as well as a mouse model of mucositis. The cells were subjected to increasing oxidative stress by incubation with hydrogen peroxide (H2O2) at concentrations of 100 μM up to 1200 μM, for up to 24 h, and ROS production and real-time kinetics of oxidative stress were investigated using fluorescent dye-based probes. Cell viability was assessed using a trypan blue exclusion assay, a fluorescence-based live-dead assay, and a fluorometric cytotoxicity assay (FCA), while morphological changes were analyzed by means of a phase-contrast inverted microscope. Static and dynamic real-time detection of the redox changes in keratinocytes showed a time-dependent increase of ROS production during oxidative stress-induced epithelial injury. The survival rates of oral epithelial cells were significantly affected after exposure to oxidative stress in a dose- and cell line-dependent manner. Values of TC50 of 800 μM, 800 μM, and 400 μM were reported for H400 cells (54.21 ± 9.04, p < 0.01), H357 cells (53.48 ± 4.01, p < 0.01), and OKF6 cells (48.64 ± 3.09, p < 0.01), respectively. Oxidative stress markers (MPO and MDA) were also significantly increased in oral tissues in our dual mouse model of chemotherapy-induced mucositis. In summary, we characterized and validated an oxidative stress model in human oral keratinocytes and identified optimal experimental conditions for the study of oxidative stress-induced oral epithelial toxicity.

Oral Fungal Infections: Past, Present, and Future

Oral fungal infections have afflicted humans for millennia. Hippocrates (ca. 460-370 BCE) described two cases of oral aphthae associated with severe underlying diseases that could well have been oral candidiasis. While oral infections caused by other fungi such as cryptococcosis, aspergillosis, mucormycosis, histoplasmosis, blastomycosis, and coccidioidomycosis occur infrequently, oral candidiasis came to the fore during the AIDS epidemic as a sentinel opportunistic infection signaling the transition from HIV infection to AIDS. The incidence of candidiasis in immunocompromised AIDS patients highlighted the importance of host defenses in preventing oral fungal infections. A greater understanding of the nuances of human immune systems has revealed that mucosal immunity in the mouth delivers a unique response to fungal pathogens. Oral fungal infection does not depend solely on the fungus and the host, however, and attention has now focussed on interactions with other members of the oral microbiome. It is evident that there is inter-kingdom signaling that affects microbial pathogenicity. The last decade has seen significant advances in the rapid qualitative and quantitative analysis of oral microbiomes and in the simultaneous quantification of immune cells and cytokines. The time is ripe for the application of machine learning and artificial intelligence to integrate more refined analyses of oral microbiome composition (including fungi, bacteria, archaea, protozoa and viruses—including SARS-CoV-2 that causes COVID-19). This analysis should incorporate the quantification of immune cells, cytokines, and microbial cell signaling molecules with signs of oral fungal infections in order to better diagnose and predict susceptibility to oral fungal disease.

The impact of the Fungus-Host-Microbiota interplay upon Candida albicans infections: current knowledge and new perspectives

Candida albicans is a major fungal pathogen of humans. It exists as a commensal in the oral cavity, gut or genital tract of most individuals, constrained by the local microbiota, epithelial barriers and immune defences. Their perturbation can lead to fungal outgrowth and the development of mucosal infections such as oropharyngeal or vulvovaginal candidiasis, and patients with compromised immunity are susceptible to life-threatening systemic infections. The importance of the interplay between fungus, host and microbiota in driving the transition from C. albicans commensalism to pathogenicity is widely appreciated. However, the complexity of these interactions, and the significant impact of fungal, host and microbiota variability upon disease severity and outcome, are less well understood. Therefore, we summarise the features of the fungus that promote infection, and how genetic variation between clinical isolates influences pathogenicity. We discuss antifungal immunity, how this differs between mucosae, and how individual variation influences a person's susceptibility to infection. Also, we describe factors that influence the composition of gut, oral and vaginal microbiotas, and how these affect fungal colonisation and antifungal immunity. We argue that a detailed understanding of these variables, which underlie fungal-host-microbiota interactions, will present opportunities for directed antifungal therapies that benefit vulnerable patients.

IL-1α released from oral epithelial cells upon candidalysin exposure initiates an early innate epithelial response

Candida albicans is a commensal fungus that predominantly resides on mucosal surfaces and can cause lethal systemic infection when the host defense is compromised. Candidalysin is a cytolytic peptide toxin produced by C. albicans hyphae that is essential for mucosal tissue damage and is believed to contribute to the establishment of systemic infection and mortality. Candidalysin is also required for the epithelial innate response in which proinflammatory cytokines and chemokines are produced and neutrophil recruitment is initiated. It was recently reported that epidermal growth factor receptor (EGFR) was essential for the candidalysin-triggered epithelial response. The present study identified IL-1α as another component of candidalysin-mediated initial epithelial activation. We found that human oral epithelial cells released IL-1α rapidly after candidalysin exposure. Blockade of IL-1α/IL-1 receptor (IL-1R) signaling in candidalysin-exposed cells resulted in decreased phosphorylation of IκBα, decreased induction of IκBζ and decreased production of granulocyte-macrophage colony-stimulating factor and IL-8. Expression of c-Fos, which is induced downstream of EGFR signaling in candidalysin-treated cells, is less affected by IL-1R blockade. Inversely, blockade of EGFR signaling does not affect candidalysin-mediated phosphorylation of IκBα and induction of IκBζ, suggesting that independent signaling pathways contribute to the induction of NF-κB and c-Fos downstream of the candidalysin pore formation site. Consistently, antibody inhibition of both EGFR and IL-1R enhanced the suppressive effect of cytokine production in candidalysin-treated cells. Thus, we identified the immediate release of IL-1α and its synergistic role with EGFR ligands on the initial activation of oral epithelial cells in response to candidalysin.

Glucose effect on Candida albicans biofilm during tissue invasion

OBJECTIVE

To evaluate, in vitro, the effect of two glucose concentrations (0.1 mM and 1.0 mM, simulating glucose concentration in saliva of healthy and diabetic individuals) on Candida albicans biofilm grown on epithelial monolayer.

MATERIAL AND METHODS

C. albicans was inoculated on epithelial monolayers supplemented with 0.1 mM, 1.0 mM or no glucose. Control groups without C. albicans were also evaluated. Tissue response was assessed through the production of Interleukin-1α, Interleukin-8, Interleukin-6, Interleukin-10 and tumor necrosis factor-α. The complex of monolayer and biofilms were evaluated by quantitative reverse transcription polymerase chain reaction for expression of E-cadherin (CDH1), Caspase-3 (CASP3), β-defensin-1 (DEFB-1) and β-defensin-3 (DEFB-3). The biofilm architecture was visualized by confocal laser scanning microscopy.

RESULTS

The production of Interleukin-1α and Interleukin-8 were increased in the presence of C. albicans (p < 0.05). Glucose did not interfere in the release of any cytokine evaluated. C. albicans downregulated transcripts for CDH1 (p < 0.05). Glucose did not induce a significant change in CDH1, CASP3, DEFB-1 and DEFB-3 messenger RNA expression. The biofilms were more structured in the presence of glucose, but no difference in the diffusion of hyphae through the epithelial cells were observed.

CONCLUSIONS

The data suggest that glucose concentration does not affect the behavior of C. albicans during tissue invasion and other mechanisms must be related to the greater susceptibility of diabetic individuals to candidiasis.

The intraspecies diversity of C. albicans triggers qualitatively and temporally distinct host responses that determine the balance between commensalism and pathogenicity

The host immune status is critical for preventing opportunistic infections with Candida albicans. Whether the natural fungal diversity that exists between C. albicans isolates also influences disease development remains unclear. Here, we used an experimental model of oral infection to probe the host response to diverse C. albicans isolates in vivo and found dramatic differences in their ability to persist in the oral mucosa, which inversely correlated with the degree and kinetics of immune activation in the host. Strikingly, the requirement of interleukin (IL)-17 signaling for fungal control was conserved between isolates, including isolates with delayed induction of IL-17. This underscores the relevance of IL-17 immunity in mucosal defense against C. albicans. In contrast, the accumulation of neutrophils and induction of inflammation in the infected tissue was strictly strain dependent. The dichotomy of the inflammatory neutrophil response was linked to the capacity of fungal strains to cause cellular damage and release of alarmins from the epithelium. The epithelium thus translates differences in the fungus into qualitatively distinct host responses. Altogether, this study provides a comprehensive understanding of the antifungal response in the oral mucosa and demonstrates the relevance of evaluating intraspecies differences for the outcome of fungal-host interactions in vivo.

The Host Cytokine Responses and Protective Immunity in Oropharyngeal Candidiasis

Over the last three decades, the prevalence of oropharyngeal fungal infections has increased enormously, mainly due to an increasing population of immunocompromised patients, including individuals with HIV infection, transplant recipients, and patients receiving cancer therapy. The vast majority of these infections are caused by Candida species. The presence of cytokines in infected tissues ultimately dictates the host defense processes that are specific to each pathogenic organism. During oral infection with Candida, a large number of pro-inflammatory and immunoregulatory cytokines are generated in the oral mucosa. The main sources of these cytokines are oral epithelial cells, which maintain a central role in the protection against fungal organisms. These cytokines may drive the chemotaxis and effector functions of innate and/or adaptive effector cells, such as infiltrating neutrophils and T-cells in immunocompetent hosts, and CD8+ T-cells in HIV+ hosts. Epithelial cells also have direct anti- Candida activity. Several studies have provided a potential link between lower levels of certain pro-inflammatory cytokines and susceptibility to oral C. albicans infection, suggesting that such cytokines may be involved in immune protection. The exact role of these cytokines in immune protection against oropharyngeal candidiasis is still incompletely understood and requires further investigation. Identification of such cytokines with the ability to enhance anti-fungal activities of immune effector cells may have therapeutic implications in the treatment of this oral infection in the severely immunocompromised host.

IL-1 Coordinates the Neutrophil Response to C. albicans in the Oral Mucosa

Mucosal infections with Candida albicans belong to the most frequent forms of fungal diseases. Host protection is conferred by cellular immunity; however, the induction of antifungal immunity is not well understood. Using a mouse model of oropharyngeal candidiasis (OPC) we show that interleukin-1 receptor (IL-1R) signaling is critical for fungal control at the onset of infection through its impact on neutrophils at two levels. We demonstrate that both the recruitment of circulating neutrophils to the site of infection and the mobilization of newly generated neutrophils from the bone marrow depended on IL-1R. Consistently, IL-1R-deficient mice displayed impaired chemokine production at the site of infection and defective secretion of granulocyte colony-stimulating factor (G-CSF) in the circulation in response to C. albicans. Strikingly, endothelial cells were identified as the primary cellular source of G-CSF during OPC, which responded to IL-1α that was released from keratinocytes in the infected tissue. The IL-1-dependent crosstalk between two different cellular subsets of the nonhematopoietic compartment was confirmed in vitro using a novel murine tongue-derived keratinocyte cell line and an established endothelial cell line. These data establish a new link between IL-1 and granulopoiesis in the context of fungal infection. Together, we identified two complementary mechanisms coordinating the neutrophil response in the oral mucosa, which is critical for preventing fungal growth and dissemination, and thus protects the host from disease.

The opportunistic pathogen Candida albicans is a major risk factor for immunosuppressed individuals, and oropharyngeal candidiasis (OPC) is a frequent complication in patients with weakened cellular immunity. The cytokine interleukin-17 (IL-17) plays a critical role for antifungal host defense and was proposed to act by regulating neutrophil recruitment to the oral mucosa. However, although IL-17 can promote neutrophil trafficking in some situations, we recently showed in a mouse model that this is not the case during OPC. Thus, the mechanism governing the neutrophil response to C. albicans remained to be determined. Here, we demonstrate an essential role of IL-1 receptor (IL-1R) signaling in the recruitment of neutrophils from the circulation to the infected tissue via enhanced secretion of chemokines and increased output of neutrophils from the bone marrow. We found that IL-1α is released from keratinocytes upon invasion of C. albicans and acts on endothelial cells to induce the production of granulocyte colony-stimulating factor (G-CSF), a key trigger of emergency granulopoiesis. Thereby, IL-1R signaling translates the local response to the fungus in the oral mucosa into a systemic response that critically contributes to protection from infection.

Systemic antibiotics and the risk of superinfection in peri-implantitis

Peri-implantitis has emerged in the last few years as a complication difficult to resolve. The etiopathogenesis consensus is mainly attributed to bacteria. Following the preferred reporting items for systematic reviews and meta-analysis (PRISMA) guidelines, a PubMed/Medline literature search was performed using the US National Library of Medicine database up to 2015 to analyze available scientific data on the rationale and risk of superinfection associated to systemic antimicrobials in human peri-implant disease. A hand search was also conducted on relevant medical and microbiology journals. The methodological index for non-randomized studies (MINORS) was independently assessed for quality on the selected papers. Proposed combined therapies use broad-spectrum antibiotics to halt the disease progression. A major associated risk, particularly when prescribed empirically without microbiological follow-up, is the undetected development of superinfections and overgrowth of opportunistic pathogens difficult to eradicate. Peri-implant superinfections with opportunistic bacteria, yeast and viruses, are plausible risks associated to the use of systemic antibiotics in immunocompetent individuals. Lack of microbiological follow-up and antibiotic susceptibility testing may lead to ongoing microbial challenges that exacerbate the disease progression. The increased proliferation of antimicrobial resistance, modern implant surface topography and indiscriminative empiric antibiotic regimens may promote the escalation of peri-implant disease in years to come. A personalized 3-month supportive therapy may help prevent risks by sustaining a normal ecological balance, decreasing specific pathogen proportions and maintaining ideal plaque control.

Computational approaches for discovery of common immunomodulators in fungal infections: towards broad-spectrum immunotherapeutic interventions

Background

Fungi are the second most abundant type of human pathogens. Invasive fungal pathogens are leading causes of life-threatening infections in clinical settings. Toxicity to the host and drug-resistance are two major deleterious issues associated with existing antifungal agents. Increasing a host’s tolerance and/or immunity to fungal pathogens has potential to alleviate these problems. A host’s tolerance may be improved by modulating the immune system such that it responds more rapidly and robustly in all facets, ranging from the recognition of pathogens to their clearance from the host. An understanding of biological processes and genes that are perturbed during attempted fungal exposure, colonization, and/or invasion will help guide the identification of endogenous immunomodulators and/or small molecules that activate host-immune responses such as specialized adjuvants.

Results

In this study, we present computational techniques and approaches using publicly available transcriptional data sets, to predict immunomodulators that may act against multiple fungal pathogens. Our study analyzed data sets derived from host cells exposed to five fungal pathogens, namely, Alternaria alternata, Aspergillus fumigatus, Candida albicans, Pneumocystis jirovecii, and Stachybotrys chartarum. We observed statistically significant associations between host responses to A. fumigatus and C. albicans. Our analysis identified biological processes that were consistently perturbed by these two pathogens. These processes contained both immune response-inducing genes such as MALT1, SERPINE1, ICAM1, and IL8, and immune response-repressing genes such as DUSP8, DUSP6, and SPRED2. We hypothesize that these genes belong to a pool of common immunomodulators that can potentially be activated or suppressed (agonized or antagonized) in order to render the host more tolerant to infections caused by A. fumigatus and C. albicans.

Conclusions

Our computational approaches and methodologies described here can now be applied to newly generated or expanded data sets for further elucidation of additional drug targets. Moreover, identified immunomodulators may be used to generate experimentally testable hypotheses that could help in the discovery of broad-spectrum immunotherapeutic interventions. All of our results are available at the following supplementary website: http://bioinformatics.cs.vt.edu/~murali/supplements/2013-kidane-bmc

Mucosal candidiasis elicits NF-κB activation, proinflammatory gene expression and localized neutrophilia in zebrafish

The epithelium performs a balancing act at the interface between an animal and its environment to enable both pathogen killing and tolerance of commensal microorganisms. Candida albicans is a clinically important human commensal that colonizes all human mucosal surfaces, yet is largely prevented from causing mucosal infections in immunocompetent individuals. Despite the importance of understanding host-pathogen interactions at the epithelium, no immunocompetent vertebrate model has been used to visualize these dynamics non-invasively. Here we demonstrate important similarities between swimbladder candidiasis in the transparent zebrafish and mucosal infection at the mammalian epithelium. Specifically, in the zebrafish swimmbladder infection model, we show dimorphic fungal growth, both localized and tissue-wide epithelial NF-κB activation, induction of NF-κB -dependent proinflammatory genes, and strong neutrophilia. Consistent with density-dependence models of host response based primarily on tissue culture experiments, we show that only high-level infection provokes widespread activation of NF-κB in epithelial cells and induction of proinflammatory genes. Similar to what has been found using in vitro mammalian models, we find that epithelial NF-κB activation can occur at a distance from the immediate site of contact with epithelial cells. Taking advantage of the ability to non-invasively image infection and host signaling at high resolution, we also report that epithelial NF-κB activation is diminished when phagocytes control the infection. This is the first system to model host response to mucosal infection in the juvenile zebrafish, and offers unique opportunities to investigate the tripartite interactions of C. albicans, epithelium and immune cells in an intact host.

Anticandidal activity and biocompatibility of a rechargeable antifungal denture material

OBJECTIVES

Candida-associated denture stomatitis is a recurrent and debilitating oral mucosal disease. Development of anticandidal denture materials represents a promising strategy to manage this condition. We have previously shown that miconazole incorporated in methacrylic acid (MAA) copolymerized diurethane dimethacrylate (UDMA) denture materials has long-term anticandidal activity. In this study, we examined the ability of culture medium conditioned with drug-free- or miconazole-MAA-UDMA discs to prevent Candida infection in an in vitro oral epithelial cell/Candida albicans coculture system.

MATERIALS AND METHODS

Candida albicans (C. albicans)-induced OKF6/TERT-2 cell damage was quantified by the release of lactate dehydrogenase from epithelial cells, cytokine production was quantified using protein cytokine arrays, and the expression of C. albicans genes was measured by RT-qPCR.

RESULTS

Candida albicans had limited growth with altered expression levels of secreted aspartyl proteinase-2 and -5 in culture medium conditioned by miconazole-MAA-UDMA discs. Significantly, the ability of C. albicans to induce oral epithelial cell damage and trigger epithelial proinflammatory cytokine production was also inhibited by miconazole disc conditioned media.

CONCLUSION

Miconazole released from MAA-UDMA denture materials effectively prevents the development of candidal infection in an in vitro oral epithelial system. Further characterization of this drug-rechargeable denture material is warranted.

IL-1 receptor regulates S100A8/A9-dependent keratinocyte resistance to bacterial invasion

Previously, we reported that epithelial cells respond to exogenous interleukin (IL)-1α by increasing expression of several genes involved in the host response to microbes, including the antimicrobial protein complex calprotectin (S100A8/A9). Given that S100A8/A9 protects epithelial cells against invading bacteria, we studied whether IL-1α augments S100A8/A9-dependent resistance to bacterial invasion of oral keratinocytes. When inoculated with Listeria monocytogenes, human buccal epithelial (TR146) cells expressed and released IL-1α. Subsequently, IL-1α-containing media from Listeria-infected cells increased S100A8/A9 gene expression in naïve TR146 cells an IL-1 receptor (IL-1R)-dependent manner. Incubation with exogenous IL-1α decreased Listeria invasion into TR146 cells, whereas invasion increased with IL-1R antagonist. Conversely, when S100A8/A9 genes were knocked down using short hairpin RNA (shRNA), TR146 cells responded to exogenous IL-1α with increased intracellular bacteria. These data strongly suggest that infected epithelial cells release IL-1α to signal neighboring keratinocytes in a paracrine manner, promoting S100A8/A9-dependent resistance to invasive L. monocytogenes.

Candida albicans yeast and hyphae are discriminated by MAPK signaling in vaginal epithelial cells

We previously reported that a bi-phasic innate immune MAPK response, constituting activation of the mitogen-activated protein kinase (MAPK) phosphatase MKP1 and c-Fos transcription factor, discriminates between the yeast and hyphal forms of Candida albicans in oral epithelial cells (ECs). Since the vast majority of mucosal Candida infections are vaginal, we sought to determine whether a similar bi-phasic MAPK-based immune response was activated by C. albicans in vaginal ECs. Here, we demonstrate that vaginal ECs orchestrate an innate response to C. albicans via NF-κB and MAPK signaling pathways. However, unlike in oral ECs, the first MAPK response, defined by c-Jun transcription factor activation, is delayed until 2 h in vaginal ECs but is still independent of hypha formation. The 'second' or 'late' MAPK response, constituting MKP1 and c-Fos transcription factor activation, is identical to oral ECs and is dependent upon both hypha formation and fungal burdens. NF-κB activation is immediate but independent of morphology. Furthermore, the proinflammatory response in vaginal ECs is different to oral ECs, with an absence of G-CSF and CCL20 and low level IL-6 production. Therefore, differences exist in how C. albicans activates signaling mechanisms in oral and vaginal ECs; however, the activation of MAPK-based pathways that discriminate between yeast and hyphal forms is retained between these mucosal sites. We conclude that this MAPK-based signaling pathway is a common mechanism enabling different human epithelial tissues to orchestrate innate immune responses specifically against C. albicans hyphae.

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.

An essential role for the NLRP3 inflammasome in host defense against the human fungal pathogen Candida albicans

Candida albicans is an opportunistic fungal pathogen causing life-threatening mucosal and systemic infections in immunocompromised humans. Using a murine model of mucosal Candida infection, we investigated the role of the proinflammatory cytokine IL-1beta in host defense to Candida albicans. We find that the synthesis, processing, and release of IL-1beta in response to Candida are tightly controlled and first require transcriptional induction, followed by a second signal leading to caspase-1-mediated cleavage of the pro-IL-1beta cytokine. The known fungal pattern recognition receptors TLR2 and Dectin-1 regulate IL-1beta gene transcription, whereas the NLRP3-containing proinflammatory multiprotein complex, the NLRP3 inflammasome, controls caspase-1-mediated cleavage of pro-IL-1beta. Furthermore, we show that TLR2, Dectin-1, and NLRP3 are essential for defense against dissemination of mucosal infection and mortality in vivo. Therefore, in addition to sensing bacterial and viral pathogens, the NLRP3 inflammasome senses fungal pathogens and is critical in host defense against Candida.

[Characterization of the interaction between Candida albicans and host cells: In vitro model using reconstituted human skin and mucosa]

Basic research on the biology and immunology of microbial infection requires appropriate model systems. Currently most such studies involve animal studies which are a focus of ethical controversy. Possible alternatives, especially for localized infections, are provided by models using in vitro reconstituted human epithelium or epidermis (RHE). In recent years, these model systems have been successfully established to evaluate the effectiveness of topical anti-infectives, to characterize the role of fungal virulence factors, and to study the immune responses during localized Candida albicans infections. Most recently, these models have been supplemented with immune cells such as lymphocytes, polymorphonuclear leukocytes, mast cells or dendritic cells, to study their role during the course of infection and to characterize the interaction between the skin barrier and accessory immune cells. Although the most experience is with Candida albicans RHE infections, such model systems can also be used to study infections with other fungi or bacteria.

Development of a highly reproducible three-dimensional organotypic model of the oral mucosa

In this report we describe the development of a standardized three-dimensional (3D) system of the human oral mucosa based on an immortalized human oral keratinocyte cell line (OKF6/TERT-2). The procedure takes approximately 2-3 weeks to complete and includes three main stages: preparation of collagen-embedded fibroblasts, addition of the mucosal component and airlifting of cultures to ensure adequate differentiation/stratification. This procedure results in a multilayer epithelial structure in which layers are organized similarly to the cells in native oral mucosa. Specifically, this model system consists of a stratum basale, having one layer of columnar to round cells, a relatively flattened stratum spinosum and stratum granulosum, and a non-keratinizing stratum corneum. This 3D system resembles the commercially available system based on the cell line TR146 (SkinEthic), with the exception that our model system does not contain dyskeratotic changes and has a submucosal component, and thus better represents the normal human mucosa and submucosa.

IL-1alpha, IL-1ra and IL-8 are differentially induced by Candida in experimental oral candidiasis

OBJECTIVE

To investigate the expression of interleukin-1alpha (IL-1alpha), IL-1ra and IL-8 by the oral epithelium challenged by various Candida species.

MATERIALS AND METHODS

In vitro candidiasis was induced by C. albicans wild type SC5314, its EFG1, CPH1 and secretory aspartyl proteinase (SAP) mutants and, ATCC isolates of C. albicans, C. tropicalis and C. dubliniensis using a reconstituted human oral epithelium (RHOE) model. IL-1alpha, IL-1ra and IL-8 levels in culture media were quantified by an enzyme-linked immunosorbent assay at 12, 24 and 48 h. Fungal invasion and IL-1ra expression in RHOE were detected by periodic acid-Schiff staining and immunohistochemistry.

RESULTS

Overall, the invasive Candida induced relatively higher levels of IL-1alpha, IL-1ra and IL-8 in the culture media than the noninvasive isolates. IL-1alpha and IL-1ra levels induced by Candida with hyphal invasion were significantly higher (P < 0.05) than those induced by the isolates without hyphal invasion at 12, 24 and 48 h. Candida albicans SC5314 induced IL-1ra expression in RHOE at 12 and 24 h but not at 48 h consistent with its hyphal invasion; while the noninvasive mutants and non-albicans Candida induced IL-1ra expression at 48 h.

CONCLUSIONS

The cytokine expression profiles in experimental oral candidiasis may be associated with the invasive potential of Candida.

Oral epithelium?Candida glabrata interactions in vitro

BACKGROUND

Oropharyngeal candidiasis is a common opportunistic infection and Candida glabrata is the second or third most frequently isolated species from oropharyngeal candidiasis lesions, after Candida albicans. The aim of this study was to study the cytokine-inducing and cell-damaging potential of C. glabrata in oral epithelial cells and compare this to C. albicans.

METHODS

Oral epithelial cell lines and primary gingival epithelial cells were cocultured with C. glabrata strains GDH2269 and 94-11 or C. albicans strains SC5314 and ATCC28366. Supernatants were analysed for the presence of interleukin-1alpha (IL-1alpha), IL-8 and granulocyte-macrophage colony-stimulating factor (GM-CSF) by enzyme-linked immunosorbent assay. The cytotoxity of different strains was determined using the CytoTox-96 assay.

RESULTS

Compared to C. albicans, C. glabrata induced different proinflammatory cytokine responses in oral epithelial cells; a high level of GM-CSF induction was only detected in C. glabrata-infected cells and not in C. albicans-infected cells, regardless of the origin of these cells (cell lines or primary cells) or the strain used. Like C. albicans, C. glabrata induced an IL-1alpha response by oral epithelial cells, but this response was both strain-dependent and epithelial cell origin-dependent. Unlike C. albicans, C. glabrata failed to induce a strong IL-8 response in any of the cell systems studied. Finally, in these studies C. glabrata showed lower cytotoxicity than C. albicans.

CONCLUSIONS

C. glabrata is less cytotoxic than C. albicans and induces different proinflammatory cytokine responses in oral epithelial cells.

Cytotoxic and cytokine-inducing properties of Candida glabrata in single and mixed oral infection models

Oral candidiasis is a common opportunistic infection, with Candida albicans being the most prevalent etiologic agent and Candida glabrata emerging as an important pathogen. C. glabrata is frequently co-isolated with C. albicans from oral lesions. Although C. albicans has been shown to trigger significant cytokine responses and cell damage, C. glabrata has not been systematically studied yet. The purpose of this study was to characterize the ability of C. glabrata to induce proinflammatory cytokine responses and host damage as a single infecting organism and in combination with C. albicans, using in vitro models of the oral mucosa. In monolayer oral epithelial cell cultures, C. glabrata failed to induce a significant interleukin-1alpha and interleukin-8 cytokine response and showed lower cytotoxicity, compared to C. albicans. However, C. glabrata triggered a significantly higher granulocyte macrophage colony stimulating factor response than C. albicans. C. glabrata strains showed a strain-dependent tissue damaging ability and a superficial invasion of the mucosal compartment in a three-dimensional (3-D) in vitro model of the human oral mucosa and submucosa. In the 3-D system, co-infection failed to promote host damage beyond the levels of infection with C. albicans alone. These studies indicate that C. glabrata induces cytokines in human oral epithelium in a strain-specific manner, but its tissue/cell damaging ability, compared to C. albicans, is low. Synergy between C. glabrata and C. albicans in cytokine induction and host damage was not observed with the strains tested.

Development of a novel three-dimensional in vitro model of oral Candida infection

Oropharyngeal candidiasis is emerging as a serious health problem in the elderly as well as other chronically immunosuppressed patient populations. Several approaches have been used to study the interactions between Candida and the oral mucosa in vitro. Recently, three-dimensional organotypic systems of the oral mucosa have been developed, which provide an organizational complexity that is between the culture of single cell types and organ cultures in vivo. In this report we describe the development of a novel three-dimensional system of the human oral mucosa based on an immortalized oral keratinocyte cell line. Unlike the commercially available cell line systems, this system also contains a connective tissue cell component, which ensures the quality and resemblance of the tissue model to the human oral masticatory mucosa and submucosa. Using a panel of Candida albicans strains with variable virulence in vivo, we showed that the extent of tissue damage, fungal invasion and host inflammatory response in this system was proportional to the well-documented in vivo virulence potential of these strains. Therefore, this investigation has added another useful tool in the study of host pathogen interactions in oral candidiasis.

In vitro mechanisms of interleukin-8-mediated responses of human gingival epithelial cells to Candida albicans infection

Oral epithelial cells significantly influence host inflammatory responses against Candida albicans in oropharyngeal candidiasis. We sought to elucidate the pattern of interleukin-8 (IL-8) expression by oral epithelial cells, which may function as an early innate immune system mediator during C. albicans infection. Primary human gingival epithelial cells (HGECs) were co-cultured with either viable or heat-killed C. albicans or fungal-derived substances, such as fungal secretion, fungal extracted proteins, and alpha-mannan. In vitro cell injury due to viable C. albicans was detectable by an adenosine triphosphate-based assay after 12h of infection. Prior to the detection of cell injury, HGECs clearly increased production of interleukin-1 alpha (IL-1alpha) and IL-8 in response to C. albicans infection, as determined by enzyme-linked immunosorbent assay and real-time reverse transcription PCR. High concentrations of a suspension of heat-killed yeast and all fungal-derived substances examined also stimulated IL-8 production by HGECs. Incubation with neutralizing anti-IL-1alpha or anti-intercellular adhesion molecule-1 (ICAM-1) monoclonal antibodies (mAb) significantly inhibited C. albicans-induced IL-8 production. Use of mAbs against both IL-1alpha and ICAM-1 produced a more significant combined inhibitory effect on the IL-8 production than either mAb alone. These findings indicate that HGECs synthesize increased levels of IL-1alpha and IL-8 in response to viable C. albicans before cell injury is manifested. Fungal cell-wall components, alpha-mannan, and fungal protein extracts are all sufficient to increase IL-8 production. The molecular mechanisms governing the IL-8 response of HGECs to C. albicans infection likely involve multiple converging signal transduction pathways, including those mediated by IL-1alpha and ICAM-1 activation.

Candida albicans-infected oral epithelial cells augment the anti-fungal activity of human neutrophils in vitro

Oropharyngeal candidiasis (OPC) is the most common opportunistic infection in immunosuppressed patients. In OPC, Candida albicans persists intraepithelially triggering inflammatory events, without generally causing invasive infection. Since neutrophils play an important role in preventing invasive infection and since they establish contact with the microorganisms only within the epithelial cell layer, we examined the ability of Candida-infected oral epithelial cells to augment neutrophil-mediated hyphal damage in vitro. We found that challenge of neutrophils with hyphal organisms in the presence of C. albicans-infected oral epithelial cell supernatants resulted in a significantly greater suppression of hyphal cell metabolic activity compared to basal neutrophil anti-fungal function. Anti-hyphal activity in response to these supernatants was partly inhibited by neutralizing anti-IL-1alpha antibody and IL-1 receptor antagonist. Control supernatants from uninfected oral epithelial cells, as well as C. albicans conditioned-medium had a much less pronounced effect on neutrophil anti-fungal activity, which was not inhibited by these cytokine antagonists. We conclude that oral epithelial cells can act as activators of neutrophil anti-hyphal function, an effect that can be partly attributed to the generation of immunomodulatory cytokines during the interaction of oral mucosal cells with the pathogen.

Invasive phenotype of Candida albicans affects the host proinflammatory response to infection

Candida albicans is a major opportunistic pathogen in immunocompromised patients. Production of proinflammatory cytokines by host cells in response to C. albicans plays a critical role in the activation of immune cells and final clearance of the organism. Invasion of host cells and tissues is considered one of the virulence attributes of this organism. The purpose of this study was to investigate whether the ability of C. albicans to invade host cells and tissues affects the proinflammatory cytokine responses by epithelial and endothelial cells. In this study we used the invasion-deficient RIM101 gene knockout strain DAY25, the highly invasive strain SC5314, and highly invasive RIM101-complemented strain DAY44 to compare the proinflammatory cytokine responses by oral epithelial or endothelial cells. Using a high-throughput approach, we found both qualitative and quantitative differences in the overall inflammatory responses to C. albicans strains with different invasive potentials. Overall, the highly invasive strains triggered higher levels of proinflammatory cytokines in host cells than the invasion-deficient mutant triggered. Significant differences compared to the attenuated mutant were noted in interleukin-1alpha (IL-1alpha), IL-6, IL-8, and tumor necrosis factor alpha in epithelial cells and in IL-6, growth-related oncogene, IL-8, monocyte chemoattractant protein 1 (MCP-1), MCP-2, and granulocyte colony-stimulating factor in endothelial cells. Our results indicate that invasion of host cells and tissues by C. albicans enhances the host proinflammatory response to infection.