Oropharyngeal candidiasis (OPC), caused by Candida albicans, is the most frequent opportunistic fungal infection in human immunodeficiency virus (HIV)-positive persons. Although Th1-type CD4+ T cells are considered important for host defense against mucosal C. albicans infections, there is a paucity of information regarding the presence and/or role of T cells in OPC lesions. In pursuit of this, initial chromophore immunohistochemical studies showed a majority of CD8+ rather than CD4+ cells equally distributed throughout the buccal mucosa of OPC− persons (HIV− or HIV+), irrespective of blood CD4+ cell numbers. In contrast, CD8+ cells in lesions from HIV+ OPC+ persons were in significantly higher numbers and concentrated at the lamina propria-epithelium interface, a considerable distance from the Candida at the outer epithelium. Dual fluorescence and confocal microscopy confirmed that the majority of CD8+, but not CD4+, cells were T cells by the presence or absence, respectively, of CD3 on each cell type. These results suggest that CD8+ T cells may be important for oral host defense against OPC, especially when CD4 cell numbers are reduced, with a potential CD8 cell-specific dysfunction associated with susceptibility to OPC.
Oropharyngeal candidiasis (OPC) remains the most common oral infection in human immunodeficiency virus (HIV) disease. In a high percentage of HIV+ persons with reduced CD4+ T cells, oral lesions with Candida present at the outer epithelium have an accumulation of CD8+ T cells at the epithelium-lamina propria interface associated with reduced expression of the mucosal cell-trafficking adhesion molecule E-cadherin. The purpose of the present study was to characterize the immune status of these CD8+ T cells. Immunohistochemical staining for phenotypic and activation and costimulation markers was performed on frozen biopsy tissue sections from HIV+ OPC+ persons with accumulated CD8+ T cells. CD8+ T cells consisted primarily of central memory cells by virtue of positive CD45RO (memory) and CD27 (central memory) expression. However, concomitant negative expression of CD62L and CCR7 (effector memory) was suggestive of a transitioning memory phenotype within the tissue. Despite this, the cells are considered to be activated on the basis of positive expression of CD69. The CD8+ T cells are not considered to be NK T cells or anti-HIV CD8+ T cells because of negative or low expression of CD161 and vascular cell adhesion molecule, respectively. These results suggest that the accumulated mucosal migratory-challenged CD8+ T cells are otherwise normal memory T cells in an activated state.
Oropharyngeal candidiasis (OPC), the most common oral infection in human immunodeficiency virus-positive persons, correlates with reduced blood CD4+ T cells. In those with OPC, CD8+ T cells accumulate at the lamina propria-epithelium interface at a distance from the organism at the outer epithelium. The present study aimed to characterize the tissue-associated CD8+ T cells and tissue microenvironment in both OPC+ and OPC− persons. The results show that the majority of CD8+ T cells possess the αβ T-cell receptor, the thymus-derived αβ CD8 antigen heterodimer, and similar levels of the α4β7, α4β1, and αeβ7 homing receptors. Studies to evaluate the tissue microenvironment showed that in OPC+ persons, the adhesion molecule for T cells to enter mucosa, mucosal addressin cell adhesion molecule, is significantly increased, whereas E-cadherin, which allows T cells to migrate through mucosa, is significantly decreased compared to OPC− persons. These results continue to support a role for CD8+ T cells against OPC under conditions of reduced numbers of CD4+T cells, with susceptibility to infection potentially associated with a dysfunction in mucosal CD8+ T-cell migration by reduced tissue-associated E-cadherin.
Oropharyngeal candidiasis (OPC) is the most common oral infection in HIV+ persons. Previous studies suggest a role for CD8+ T-cells against OPC when CD4+ T-cells are lost, but enhanced susceptibility to infection occurs when CD8+ T-cell migration is inhibited by reduced tissue E-cadherin.
Conduct a longitudinal study of tissue CD8+ T-cells and E-cadherin expression before, during, and after episodes of OPC.
Oral fungal burden was monitored and tissue was evaluated for CD8+ T-cells and E-cadherin over a one-year period in HIV+ persons with a history of, or an acute episode of OPC.
While longitudinal analyses precluded formal interpretations, point prevalence analyses of the dataset revealed that when patients experiencing OPC were successfully treated, tissue E-cadherin expression was similar to patients who had not experienced OPC, and higher numbers of CD8+ T-cells were distributed throughout OPC− tissue under normal expression of E-cadherin.
These results suggest that 1) reduction in tissue E-cadherin expression in OPC+ patients is not permanent, and 2) high numbers of CD8+ T-cells can be distributed throughout OPC− tissue under normal E-cadherin expression. Together these results extend our previous studies and continue to support a role for CD8+ T-cells in host defense against OPC.
oropharyngeal candidiasis; HIV; CD8+ T-cells; E-cadherin
The commensal fungus Candida albicans causes oropharyngeal candidiasis (OPC; thrush) in settings of immunodeficiency. Although disseminated, vaginal, and oral candidiasis are all caused by C. albicans species, host defense against C. albicans varies by anatomical location. T helper 1 (Th1) cells have long been implicated in defense against candidiasis, whereas the role of Th17 cells remains controversial. IL-17 mediates inflammatory pathology in a gastric model of mucosal candidiasis, but is host protective in disseminated disease. Here, we directly compared Th1 and Th17 function in a model of OPC. Th17-deficient (IL-23p19−/−) and IL-17R–deficient (IL-17RA−/−) mice experienced severe OPC, whereas Th1-deficient (IL-12p35−/−) mice showed low fungal burdens and no overt disease. Neutrophil recruitment was impaired in IL-23p19−/− and IL-17RA−/−, but not IL-12−/−, mice, and TCR-αβ cells were more important than TCR-γδ cells. Surprisingly, mice deficient in the Th17 cytokine IL-22 were only mildly susceptible to OPC, indicating that IL-17 rather than IL-22 is vital in defense against oral candidiasis. Gene profiling of oral mucosal tissue showed strong induction of Th17 signature genes, including CXC chemokines and β defensin-3. Saliva from Th17-deficient, but not Th1-deficient, mice exhibited reduced candidacidal activity. Thus, the Th17 lineage, acting largely through IL-17, confers the dominant response to oral candidiasis through neutrophils and antimicrobial factors.
The impact of antiretroviral therapy (ART) on opportunistic conditions in HIV patients continues to evolve. We specifically studied the changing epidemiology of oropharyngeal candidiasis (OPC) in 215 HIV/AIDS patients. Status of yeast colonization was assessed from oral rinse samples, and preliminary yeast identification was made using CHROMagar Candida and confirmed with standard microbiological techniques and/or molecular sequencing. Susceptibility to fluconazole was determined by CHROMagar Candida agar dilution screening and CLSI broth microdilution. 176 (82%) patients were colonized and 59 (27%) patients had symptomatic OPC. Candida albicans was the most prevalent species, though C. glabrata and C. dubliniensis were detected in 29% of isolates. Decreased fluconazole susceptibility occurred in 10% of isolates. Previous ART reduced the risk of OPC, while smoking increased the risk of colonization. Oral yeast colonization and symptomatic infection remain common even with advances in HIV therapy. C. albicans is the most common species, but other yeasts are prevalent and may have decreased susceptibility to fluconazole.
Candida dubliniensis is an opportunistic yeast that has been increasingly implicated in oropharyngeal candidiasis (OPC) in human immunodeficiency virus (HIV)-infected patients but may be underreported due to its similarity with Candida albicans. Although most C. dubliniensis isolates are susceptible to fluconazole, the inducibility of azole resistance in vitro has been reported. Thus, the use of fluconazole prophylaxis in the treatment of these patients may have contributed to the increasing rates of isolation of C. dubliniensis. In this study, yeast strains were collected from the oral cavities of HIV-infected patients enrolled in a longitudinal study of OPC. Patients received fluconazole for the suppression or treatment of OPC, and isolates collected at both study entry and end of study were chosen for analysis. Samples were plated on CHROMagar Candida medium for initial isolation and further identified by Southern blot analysis with the species-specific probes Ca3 (for C. albicans) and Cd25 (for C. dubliniensis). Fluconazole MICs were determined by using NCCLS methods. At study entry, susceptible C. albicans isolates were recovered from oral samples in 42 patients who were followed longitudinally (1 to 36 months). C. albicans strains from 12 of these patients developed fluconazole resistance (fluconazole MIC, ≥64 μg/ml). C. dubliniensis was not detected at end of study in any of these patients. Of the remaining 30 patients, eight (27%) demonstrated a replacement of C. albicans by C. dubliniensis when a comparison of isolates obtained at baseline and those from the last culture was done. For the 22 of these 30 patients in whom no switch in species was detected, the fluconazole MICs for initial and end-of-study C. albicans isolates ranged from 0.125 to 2.0 μg/ml. For the eight patients in whom a switch to C. dubliniensis was detected, the fluconazole MICs for C. dubliniensis isolates at end of study ranged from 0.25 to 64 μg/ml: the fluconazole MICs for isolates from six patients were 0.25 to 2.0 μg/ml and those for the other two were 32 and 64 μg/ml, respectively. In conclusion, a considerable number of patients initially infected with C. albicans strains that failed to develop fluconazole resistance demonstrated a switch to C. dubliniensis. C. dubliniensis in this setting may be underestimated due to lack of identification and may occur due to the impact of fluconazole on the ecology of oral yeast species.
Oropharyngeal candidiasis (OPC, thrush) is an opportunistic infection caused by the commensal fungus Candida albicans. An understanding of immunity to Candida has recently begun to unfold with the identification of fungal pattern-recognition receptors such as C-type lectin receptors, which trigger protective T-helper (Th)17 responses in the mucosa. Hyper-IgE syndrome (HIES/Job’s syndrome) is a rare congenital immunodeficiency characterized by dominant-negative mutations in signal transducer and activator of transcription 3, which is downstream of the Th17-inductive cytokines interleukin (IL)-6 and IL-23, and hence patients with HIES exhibit dramatic Th17 deficits. HIES patients develop oral and mucocutaneous candidiasis, supporting a protective role for Th17 cells in immunity to OPC. However, the Th17-dependent mechanisms of antifungal immunity in OPC are still poorly defined. An often unappreciated aspect of oral immunity is saliva, which is rich in antimicrobial proteins (AMPs) and exerts direct antifungal activity. In this study, we show that HIES patients show significant impairment in salivary AMPs, including β-defensin 2 and Histatins. This tightly correlates with reduced candidacidal activity of saliva and concomitantly elevated colonization with Candida. Moreover, IL-17 induces histatins in cultured salivary gland cells. This is the first demonstration that HIES is associated with defective salivary activity, and provides a mechanism for the severe susceptibility of these patients to OPC.
A study of oropharyngeal candidiasis (OPC) in Indian human immunodeficiency virus (HIV)/AIDS patients was conducted over a period of 15 months. This study revealed that 75% of the HIV/AIDS patients had OPC. MIC testing revealed that 5% of the Candida isolates were fluconazole resistant. A correlation between CD4+-T-cell counts and development of OPC in HIV/AIDS patients was also observed. Molecular typing of C. albicans isolates showed that all were genetically unrelated.
Candida albicans causes oropharyngeal candidiasis (OPC) but rarely disseminates to deep organs in human immunodeficiency virus (HIV) infection. Here, we used a model of OPC in CD4C/HIVMut transgenic (Tg) mice to investigate the role of polymorphonuclear leukocytes (PMNs) and CD8+ T cells in limiting candidiasis to the mucosa. Numbers of circulating PMNs and their oxidative burst were both augmented in CD4C/HIVMutA Tg mice expressing rev, env, and nef of HIV type 1 (HIV-1), while phagocytosis and killing of C. albicans were largely unimpaired compared to those in non-Tg mice. Depletion of PMNs in these Tg mice did not alter oral or gastrointestinal burdens of C. albicans or cause systemic dissemination. However, oral burdens of C. albicans were increased in CD4C/HIVMutG Tg mice expressing only the nef gene of HIV-1 and bred on a CD8 gene-deficient background (CD8−/−), compared to control or heterozygous CD8+/− CD4C/HIVMutG Tg mice. Thus, CD8+ T cells contribute to the host defense against oral candidiasis in vivo, specifically in the context of nef expression in a subset of immune cells.
Candida albicans is a causative agent of oropharyngeal candidiasis (OPC), a biofilm-like infection of the oral mucosa. Biofilm formation depends upon the C. albicans transcription factor Bcr1, and previous studies indicate that Bcr1 is required for OPC in a mouse model of infection. Here we have used a nanoString gene expression measurement platform to elucidate the role of Bcr1 in OPC-related gene expression. We chose for assays a panel of 134 genes that represent a range of morphogenetic and cell cycle functions as well as environmental and stress response pathways. We assayed gene expression in whole infected tongue samples. The results sketch a portrait of C. albicans gene expression in which numerous stress response pathways are activated during OPC. This one set of experiments identifies 64 new genes with significantly altered RNA levels during OPC, thus increasing substantially the number of known genes in this expression class. The bcr1Δ/Δ mutant had a much more limited gene expression defect during OPC infection than previously reported for in vitro growth conditions. Among major functional Bcr1 targets, we observed that ALS3 was Bcr1 dependent in vivo while HWP1 was not. We used null mutants and complemented strains to verify that Bcr1 and Hwp1 are required for OPC infection in this model. The role of Als3 is transient and mild, though significant. Our findings suggest that the versatility of C. albicans as a pathogen may reflect its ability to persist in the face of multiple stresses and underscore that transcriptional circuitry during infection may be distinct from that detailed during in vitro growth.
Mechanisms of resistance to azoles in Candida albicans, the main etiologic agent of oropharyngeal candidiasis (OPC), include alterations in the target enzyme (lanosterol demethylase) and increased efflux of drug. Previous studies on mechanisms of resistance have been limited by the fact that only a single isolate from each OPC episode was available for study. Multiple isolates from each OPC episode were evaluated with oral samples plated in CHROMagar Candida with and without fluconazole to maximize detection of resistant yeasts. A total of 101 isolates from each of three serial episodes of OPC from four different patients were evaluated. Decreasing geometric means of fluconazole MICs with serial episodes of infection were detected in the four patients. However, 8-fold or larger (up to 32-fold) differences in fluconazole MICs were detected within isolates recovered at the same time point in 7 of 12 episodes. Strain identity was analyzed by DNA typing techniques and indicated that isolates from each patient represented mainly isogenic strains, but differed among patients. A Northern blot technique was used to monitor expression of ERG11 (encoding lanosterol demethylase) and genes coding for efflux pumps. This analysis revealed that clinical isolates obtained from the same patient and episode were phenotypically heterogeneous in their patterns of expression of these genes involved in fluconazole resistance. These results demonstrate the complexity of the distribution of the molecular mechanisms of antifungal drug resistance and indicate that different subpopulations of yeasts may coexist at a given time in the same patient and may develop resistance through different mechanisms.
The occurrence of oropharyngeal candidiasis (OPC) in combination with HIV disease progression is a very common phenomenon. However, not all HIV-infected patients develop OPC, even when they progress to low CD4+ T cell counts. Because T-cell immunity is defective in AIDS, the innate defence mechanisms are likely to have a central role in antifungal immunity in these patients. We investigated whether genetic variations in the innate immune genes DECTIN-1, TLR2, TLR4, TIRAP and CASPASE-12 are associated with the presence of OPC in HIV-infected subjects from East-Africa.
A total of 225 HIV patients were genotyped for several single nucleotide polymorphisms (SNP) and this was correlated with the occurrence of OPC in these patients. In addition, primary immune cells obtained from individuals with different genotypes were stimulated with C.albicans and cytokine production was measured.
The analysis revealed that no significant differences in the polymorphism frequencies could be observed, although a tendency towards a protective effect on OPC of the DECTIN-1 I223S SNP was apparent. Furthermore, IFNγ production capacity was markedly lower in cells bearing the DECTIN-1 SNP I223S. It could also be demonstrated that the 223S mutated form of the DECTIN-1 gene exhibits a lower capacity to bind zymosan.
These data demonstrate that common polymorphisms of TLR2, TLR4, TIRAP and CASPASE-12 do not influence susceptibility to OPC in HIV-infected patients in East-Africa but suggest an immunomodulatory effect of the I223S SNP on dectin-1 function and possibly the susceptibility to OPC in HIV patients.
HIV; oropharyngeal candidiasis; dectin-1; TLR2; TLR4; Mal/TIRAP; caspase-12
Candida albicans is both a commensal and a pathogen at the oral mucosa. Although an intricate network of host defense mechanisms are expected for protection against oropharyngeal candidiasis, anti-Candida host defense mechanisms at the oral mucosa are poorly understood. Our laboratory recently showed that primary epithelial cells from human oral mucosa, as well as an oral epithelial cell line, inhibit the growth of blastoconidia and/or hyphal phases of several Candida species in vitro with a requirement for cell contact and with no demonstrable role for soluble factors. In the present study, we show that oral epithelial cell-mediated anti-Candida activity is resistant to gamma-irradiation and is not mediated by phagocytosis, nitric oxide, hydrogen peroxide, and superoxide oxidative inhibitory pathways or by nonoxidative components such as soluble defensin and calprotectin peptides. In contrast, epithelial cell-mediated anti-Candida activity was sensitive to heat, paraformaldehyde fixation, and detergents, but these treatments were accompanied by a significant loss in epithelial cell viability. Treatments that removed existing membrane protein or lipid moieties in the presence or absence of protein synthesis inhibitors had no effect on epithelial cell inhibitory activity. In contrast, the epithelial cell-mediated anti-Candida activity was abrogated after treatment of the epithelial cells with periodic acid, suggesting a role for carbohydrates. Adherence of C. albicans to oral epithelial cells was unaffected, indicating that the carbohydrate moiety is exclusively associated with the growth inhibition activity. Subsequent studies that evaluated specific membrane carbohydrate moieties, however, showed no role for sulfated polysaccharides, sialic acid residues, or glucose- and mannose-containing carbohydrates. These results suggest that oral epithelial cell-mediated anti-Candida activity occurs exclusively with viable epithelial cells through contact with C. albicans by an as-yet-undefined carbohydrate moiety.
Oropharyngeal candidiasis (OPC) remains a common problem in the HIV-infected population despite the availability of antiretroviral therapy (ART). Although Candida albicans is the most frequently implicated pathogen, other Candida spp. may also cause infection. The emergence of antifungal resistance within these causative yeasts, especially in patients with recurrent oropharyngeal infection or with long-term use of antifungal therapies, requires a working knowledge of alternative antifungal agents. Identification of the infecting organism and antifungal susceptibility testing enhances the ability of clinicians to prescribe appropriate antifungal therapy. Characterization of the responsible mechanisms has improved our understanding of the development of antifungal resistance and could enhance the management of these infections. Immune reconstitution has been shown to reduce rates of oropharyngeal candidiasis but few studies have evaluated the current impact of ART on the epidemiology of oropharyngeal candidiasis and antifungal resistance in these patients. Preliminary results from an ongoing clinical study showed that in patients with advanced AIDS oral yeast colonization was extensive, occurring in 81.1% of the 122 patients studied and symptomatic infection occurred in a third. In addition, resistant yeasts were still common occurring in 25.3% of patients colonized with yeasts or with symptomatic infection. Thus, oropharyngeal candidasis remains a significant infection in advanced AIDS even with ART. Current knowledge of the epidemiology, pathogenesis, clinical presentation, treatment, and mechanisms of antifungal resistance observed in oropharyngeal candidiasis are important in managing patients with this infection and are the focus of this review.
thrush; OPC; oral candidiasis; Candida; resistance
The opportunistic fungal pathogen Candida albicans is the major causative agent of oropharyngeal candidiasis (OPC) in AIDS. The development of azoles, such as fluconazole, for the treatment of OPC has proven effective except in cases where C. albicans develops resistance to fluconazole during the course of treatment. In the present study, we used microarray technology to examine differences in gene expression from a fluconazole-susceptible and a fluconazole-resistant well-characterized, clinically obtained matched set of C. albicans isolates to identify genes which are differentially expressed in association with azole resistance. Among genes found to be differentially expressed were those involved in amino acid and carbohydrate metabolism; cell stress, cell wall maintenance; lipid, fatty acid, and sterol metabolism; and small molecule transport. In addition to CDR1, which has previously been demonstrated to be associated with azole resistance, the drug resistance gene RTA3, the ergosterol biosynthesis gene ERG2, and the cell stress genes CRD2, GPX1, and IFD5 were found to be upregulated. Several genes, such as the mitochondrial aldehyde dehydrogenase gene ALD5, the glycosylphosphatidylinositol synthesis gene GPI1, and the iron transport genes FET34 and FTR2 were found to be downregulated. Further study of these differentially regulated genes is warranted to evaluate how they may be involved in azole resistance. In addition to these novel findings, we demonstrate the utility of microarray analysis for studying the molecular mechanisms of drug resistance in pathogenic organisms.
Oropharyngeal and vaginal candidiases are the most common forms of mucosal fungal infections and are primarily caused by Candida albicans, a dimorphic fungal commensal organism of the gastrointestinal and lower female reproductive tracts. Clinical and experimental observations suggest that local immunity is important in host defense against candidiasis. Accordingly, cytokines and chemokines are present at the oral and vaginal mucosa during C. albicans infections. Since mucosal epithelial cells produce a variety of cytokines and chemokines in response to microorganisms and since C. albicans is closely associated with mucosal epithelial cells as a commensal, we sought to identify cytokines and/or chemokines produced by primary oral and vaginal epithelial cells and cell lines in response to C. albicans. The results showed that proinflammatory cytokines were produced by oral and/or vaginal epithelial cells at various levels constitutively with considerable interleukin-1α (IL-1α) and tumor necrosis factor alpha, but not IL-6, produced in response to C. albicans. In contrast, Th1-type (IL-12 and gamma interferon) and Th2-type-immunoregulatory (IL-10 and transforming growth factor β) cytokines and the chemokines monocyte chemoattractant protein 1 and IL-8 were produced in low to undetectable concentrations with little additional production in response to C. albicans. Taken together, these results indicate that cytokines and chemokines are variably produced by oral and vaginal epithelial cells constitutively, as well as in response to C. albicans, and are predominated by proinflammatory cytokines.
pH-responsive transcription factors of the Rim101/PacC family govern virulence in many fungal pathogens. These family members control expression of target genes with diverse functions in growth, morphology, and environmental adaptation, so the mechanistic relationship between Rim101/PacC and infection is unclear. We have focused on Rim101 from Candida albicans, which we find to be required for virulence in an oropharyngeal candidiasis (OPC) model. Rim101 affects the yeast-hyphal morphological transition, a major virulence requirement in disseminated infection models. However, virulence in the OPC model is independent of the yeast-hyphal transition because it is unaffected by an nrg1 mutation, which prevents formation of yeast cells. Here we have identified Rim101 target genes in an nrg1Δ/Δ mutant background and surveyed function using an overexpression-rescue approach. Increased expression of Rim101 target genes ALS3, CHT2, PGA7/RBT6, SKN1, or ZRT1 can partially restore pathogenic interaction of a rim101Δ/Δ mutant with oral epithelial cells. Four of these five genes govern cell wall structure. Our results indicate that Rim101-dependent cell wall alteration contributes to C. albicans pathogenic interactions with oral epithelial cells, independently of cell morphology.
Mucocutaneous candidiasis is frequently one of the first signs of human immunodeficiency virus (HIV) infection. Over 90% of patients with AIDS will develop oropharyngeal candidiasis (OPC) at some time during their illness. Although numerous antifungal agents are available, azoles, both topical (clotrimazole) and systemic (fluconazole, itraconazole, voriconazole, posaconazole) have replaced older topical antifungals (gentian violet and nystatin) in the management of oropharyngeal candidiasis in these patients. The systemic azoles, are generally safe and effective agents in HIV-infected patients with oropharyngeal candidiasis. A constant concern in these patients is relapse, which is dependent on the degree of immunosuppression commonly seen after topical therapy, rather than with systemic azole therapy. Candida esophagitis (CE) is also an important concern since it occurs in more than 10% of patients with AIDS and can lead to a decrease in oral intake and associated weight loss. Fluconazole has become the most widely used antifungal in the management of mucosal candidiasis. However, itraconazole and posaconazole have similar clinical response rates as fluconazole and are also effective alternative agents. In patients with fluconazole-refractory mucosal candidiasis, treatment options now include itraconazole solution, voriconazole, posaconazole, and the newer echinocandins (caspofungin, micafungin, and anidulafungin).
oropharyngeal candidiasis; esophageal candidiasis; HAART; antifungal agents; HIV; AIDS
Oropharyngeal and esophageal candidiases remain significant causes of morbidity in human immunodeficiency virus (HIV)-infected patients, despite the dramatic ability of antiretroviral therapy to reconstitute immunity. Notable advances have been achieved in understanding, at the molecular level, the relationships between the progression of HIV infection, the acquisition, maintenance, and clonality of oral candidal populations, and the emergence of antifungal resistance. However, the critical immunological defects which are responsible for the onset and maintenance of mucosal candidiasis in patients with HIV infection have not been elucidated. The devastating impact of HIV infection on mucosal Langerhans' cell and CD4+ cell populations is most probably central to the pathogenesis of mucosal candidiasis in HIV-infected patients. However, these defects may be partly compensated by preserved host defense mechanisms (calprotectin, keratinocytes, CD8+ T cells, and phagocytes) which, individually or together, may limit Candida albicans proliferation to the superficial mucosa. The availability of CD4C/HIV transgenic mice expressing HIV-1 in immune cells has provided the opportunity to devise a novel model of mucosal candidiasis that closely mimics the clinical and pathological features of candidal infection in human HIV infection. These transgenic mice allow, for the first time, a precise cause-and-effect analysis of the immunopathogenesis of mucosal candidiasis in HIV infection under controlled conditions in a small laboratory animal.
Candida glabrata colonization is common in patients receiving radiation treatment for head and neck cancer, but to our knowledge has never been described as the infecting organism with oropharyngeal candidiasis (OPC). This study presents the first three patients described with C. glabrata OPC in this patient population. Patient 1 developed C. glabrata OPC and required fluconazole, 800 mg/day, for clinical resolution. Antifungal susceptibility testing revealed a MIC of fluconazole of >64 μg/ml. Elapsed time from initial culturing to treatment decision was 7 days. Patients 2 and 3 developed C. glabrata OPC. They were patients in a study evaluating OPC infections, and cultures were taken immediately. CHROMagar Candida plates with 0, 8, and 16 μg of fluconazole/ml were employed for these cultures. Lavender colonies, consistent with C. glabrata, grew on the 0- and 8-μg plates but not on the 16-μg plate from patient 2 and grew on all three plates from patient 3. Based on these data, a fluconazole dose of 200 mg/day was chosen for patient 2 and a dose of 400 mg/day was chosen for patient 3, with clinical resolution in both. Elapsed time from initial culturing to treatment decision was 2 days. C. glabrata does cause OPC in head and neck radiation treatment patients, and the use of fluconazole-impregnated chromogenic agar may significantly reduce treatment decision time compared to that with conventional culturing and antifungal susceptibility testing.
Candida albicans Ssa1 and Ssa2 are members of the HSP70 family of heat shock proteins that are expressed on the cell surface and function as receptors for antimicrobial peptides such as histatins. We investigated the role of Ssa1 and Ssa2 in mediating pathogenic host cell interactions and virulence. A C. albicans ssa1Δ/Δ mutant had attenuated virulence in murine models of disseminated and oropharyngeal candidiasis, whereas an ssa2Δ/Δ mutant did not. In vitro studies revealed that the ssa1Δ/Δ mutant caused markedly less damage to endothelial cells and oral epithelial cell lines. Also, the ssa1Δ/Δ mutant had defective binding to endothelial cell N-cadherin and epithelial cell E-cadherin, receptors that mediate host cell endocytosis of C. albicans. As a result, this mutant had impaired capacity to induce its own endocytosis by endothelial cells and oral epithelial cells. Latex beads coated with recombinant Ssa1 were avidly endocytosed by both endothelial cells and oral epithelial cells, demonstrating that Ssa1 is sufficient to induce host cell endocytosis. These results indicate that Ssa1 is a novel invasin that binds to host cell cadherins, induces host cell endocytosis, and is critical for C. albicans to cause maximal damage to host cells and induce disseminated and oropharyngeal disease.
The fungus Candida albicans can proliferate in the mouth, causing oropharyngeal candidiasis. In other patients, it can enter the bloodstream and spread throughout the body, resulting in hematogenously disseminated candidiasis. Fungal invasion of host cells is a key feature of both types of infection. One mechanism by which C. albicans invades both the epithelial cell lining of the oropharynx and the endothelial cell lining of the blood vessels is by inducing its own uptake. This uptake is induced in part by the binding of the C. albicans invasin Als3 to host cell proteins, which include N- and E-cadherin. Here we show that C. albicans Ssa1, a member of the 70 kDa heat shock protein family, is expressed on the surface of C. albicans where it functions as an invasin. The key role of Ssa1 in host cell invasion is illustrated by the reduced capacity of an ssa1Δ/Δ null mutant to induce its own uptake by epithelial and endothelial cells in vitro, and by the significantly attenuated virulence of this mutant in mouse models of oropharyngeal candidiasis and disseminated candidiasis. Thus, Ssa1 is the second identified invasin of C. albicans.
Oral candidiasis is a collective name for a group of disorders caused by the dimorphic fungus Candida albicans. Host defenses against C. albicans essentially fall into two categories: specific immune mechanisms and local oral mucosal epithelial cell defenses. Since oral epithelial cells secrete a variety of cytokines and chemokines in response to oral microorganisms and since C. albicans is closely associated with oral epithelial cells as a commensal organism, we wanted to determine whether interleukin-18 (IL-18) and gamma interferon (IFN-γ) were produced by oral epithelial cells in response to C. albicans infection and lipopolysaccharide (LPS) stimulation. Our results showed that IL-18 mRNA and protein were constitutively expressed by oral epithelial cells and were down-regulated by Candida infections but increased following LPS stimulation. Both C. albicans and LPS significantly decreased pro-IL-18 (24 kDa) levels and increased active IL-18 (18 kDa) levels. This effect was IL-1β-converting-enzyme dependent. The increase in active IL-18 protein levels promoted the production of IFN-γ by infected cells. No effect was obtained with LPS. Although produced only at an early stage, secreted IFN-γ seemed to be a preferential response by oral epithelial cells to C. albicans growth. These results provide additional evidence for the contribution of oral epithelial cells to local (direct contact) and systemic (IL-18 and IFN-γ production) defense against exogenous stimulation such as C. albicans infection or LPS stimulation.
Candida albicans is the causative agent of acute and recurrent vulvovaginal candidiasis (VVC), a common mucosal infection affecting significant numbers of women in their reproductive years. While any murine host protective role for cell-mediated immunity (CMI), humoral immunity, and innate resistance by neutrophils against the vaginal infection appear negligible, significant in vitro growth inhibition of Candida species by vaginal and oral epithelial cell-enriched cells has been observed. Both oral and vaginal epithelial cell anti-Candida activity has a strict requirement for cell contact to C. albicans with no role for soluble factors, and oral epithelial cells inhibit C. albicans through a cell surface carbohydrate moiety. The present study further evaluated the inhibitory mechanisms by murine vaginal epithelial cells and the fate of C. albicans by oral and vaginal epithelial cells. Similar to human oral cells, anti-Candida activity produced by murine vaginal epithelial cells is unaffected by enzymatic cleavage of cell surface proteins and lipids but sensitive to periodic acid cleavage of surface carbohydrates. Analysis of specific membrane carbohydrate moieties, however, showed no role for sulfated polysaccharides, sialic acid residues, or glucose and mannose-containing carbohydrates, also similar to oral cells. Staining for live and dead Candida in the coculture with fluorescein diacetate (FDA) and propidium iodide (PI), respectively, showed a clear predominance of live organisms, suggesting a static rather than cidal action. Together, the results suggest that oral and vaginal epithelial cells retard or arrest the growth rather than kill C. albicans through an as-yet-unidentified carbohydrate moiety in a noninflammatory manner.
The disproportionate increase in oropharyngeal candidiasis (OPC) compared with systemic and vaginal candidiasis in female patients with AIDS has been a paradox for almost three decades. New data now show that severe OPC develops in Th17-deficient mice, but not Th1-deficient mice, implicating Th17-induced effector molecules in resistance to oral disease. These findings clarify and extend our current thinking about how CD4 T cell deficiency influences susceptibility to OPC.