The role of cell-mediated immunity in candidiasis

Ssa1-targeted antibody prevents host invasion by Candida albicans

INTRODUCTION

Candida albicans is a commensal fungus that colonizes most healthy individuals' skin and mucosal surfaces but can also cause life-threatening invasive infections, particularly in immunocompromised patients. Despite antifungal treatment availability, drug resistance is increasing, and mortality rates remain unacceptably high. Heat shock protein Ssa1, a conserved member of the Hsp70 family in yeast, is a novel invasin that binds to host cell cadherins, induces host cell endocytosis, and enables C. albicans to cause maximal damage to host cells and induces disseminated and oropharyngeal disease.

RESULT

Here we discovered a mouse monoclonal antibody (mAb 13F4) that targeting C. albicans Ssa1 with high affinity (EC50 = 39.78 ng/mL). mAb 13F4 prevented C. albicans from adhering to and invading human epithelial cells, displayed antifungal activity, and synergized with fluconazole in proof of concept in vivo studies. mAb 13F4 significantly prolonged the survival rate of the hematogenous disseminated candidiasis mice to 75%. We constructed a mAb 13F4 three-dimensional structure using homology modeling methods and found that the antigen-binding fragment (Fab) interacts with the Ssa1 N-terminus.

DISCUSSION

These results suggest that blocking Ssa1 cell surface function may effectively control invasive C. albicans infections and provide a potential new treatment strategy for invasive fungal infections.

An exaggerated monocyte-derived cytokine response to Candida hyphae in patients with recurrent vulvovaginal candidiasis

Background

Recurrent vulvovaginal candidiasis (RVVC) affects up to 8% of women. The immunopathogenesis is poorly understood but it has been suggested that RVVC might be due to dysregulated innate immune response. The aim of this study was to compare cytokine profiles in stimulated primary mononuclear cells (PBMCs) from RVVC and healthy individuals.

Methods

PBMCs isolated from RVVC patients (n = 24) and healthy volunteers (n = 30) were stimulated with unspecific and pathogen-specific antigens. Cytokine production was assessed after 24 hours, 48 hours, and 7 days using ELISA.

Results

No significant differences in cytokine production were found in T helper 1 (Th1), Th2, and Th17 immunity in response to both unspecific and pathogen-specific stimulations. Tumor necrosis factor-α (TNF-α) production in response to C. albicans hyphae was significantly higher in patients than controls and within the patient group, a significant positive correlation was found between interleukin-1β (IL-1β) and both TNF-α and IL-6. Both IL-1β/IL-1Ra and TNF-α/IL-10 ratios in Candida hyphae-stimulated PBMCs were significantly higher in patients than controls.

Conclusions

Women affected by RVVC showed increased monocytes-derived cytokine production, which might contribute to an exaggerated vaginal immune response to Candida hyphae. RVVC patients show no defective Th-dependent adaptive immune response upon Candida stimulation.

Baofukang suppository promotes the repair of vaginal epithelial cells in response to Candida albicans

Vulvovaginal candidiasis (VVC) is an opportunistic fungal infection predominantly caused by Candida albicans affecting a significant number of women of reproductive age. The Chinese medicine, the Baofukang suppository is widely used in the clinic for its antimicrobial activity and is therefore of great interest as a potential antifungal drug for the prevention of VVC. We evaluated the cytotoxic activity of the Baofukang suppository using the VK2/E6E7 vaginal epithelial cell (VEC) line. When treated with the Baofukang suppository, all of the immunocompetent cytokines and chemokines (e.g., IL-2, IL-4, IL-6, IL-8, and IL-17) by infected VK2/E6E7 cells was statistically up-regulated (P < 0.05), except IL-4 (11.70 ± 1.82 vs. 14.88 ± 4.72, P = 0.343) compared to the infected control cells. The secretion of non-B IgG also exhibited the same trend. Our scanning electron microscopy results revealed that C. albicans can invade VECs by both induced endocytosis and active penetration. The Baofukang suppository could effectively inhibit the adhesion, hyphal formation, and proliferation, as well as notably restore the vaginal epithelial cell morphology, viability, and enhance the local immune function of the VECs. These preliminary results suggest promising antimicrobial properties of the Baofukang suppository, which may be efficacious as an antifungal therapy candidate via up-regulating Th1 cellular immunity, the Th17-axis of the innate immune response, and the secretion of vaginal epithelial-derived IgG. These combined effects collectively restore the immune function of the infected VECs against C. albicans in vitro.

Cytokines in the host response to Candida vaginitis: Identifying a role for non-classical immune mediators, S100 alarmins

Vulvovaginal candidiasis (VVC), caused by Candida albicans, affects a significant number of women during their reproductive years. More than two decades of research have been focused on the mechanisms associated with susceptibility or resistance to symptomatic infection. Adaptive immunity by Th1-type CD4(+) T cells and downstream cytokine responses are considered the predominant host defense mechanisms against mucosal Candida infections. However, numerous clinical and animal studies have indicated no or limited protective role of cells and cytokines of the Th1 or Th2 lineage against vaginal infection. The role for Th17 is only now begun to be investigated in-depth for VVC with results already showing significant controversy. On the other hand, a clinical live-challenge study and an established animal model have shown that a symptomatic condition is intimately associated with the vaginal infiltration of polymorphonuclear leukocytes (PMNs) but with no effect on vaginal fungal burden. Subsequent studies identified S100A8 and S100A9 alarmins as key chemotactic mediators of the acute PMN response. These chemotactic danger signals appear to be secreted by vaginal epithelial cells upon interaction and early adherence of Candida. Thus, instead of a putative immunodeficiency against Candida involving classical immune cells and cytokines of the adaptive response, the pathological inflammation in VVC is now considered a consequence of a non-productive innate response initiated by non-classical immune mediators.

Cell mediated immunity to fungi: a reassessment

Protective immunity against fungal pathogens is achieved by the integration of two distinct arms of the immune system, the innate and adaptive responses. Innate and adaptive immune responses are intimately linked and controlled by sets of molecules and receptors that act to generate the most effective form of immunity for protection against fungal pathogens. The decision of how to respond will still be primarily determined by interactions between pathogens and cells of the innate immune system, but the actions of T cells will feed back into this dynamic equilibrium to regulate the balance between tolerogenic and inflammatory responses. In the last two decades, the immunopathogenesis of fungal infections and fungal diseases was explained primarily in terms of Th1/Th2 balance. Although Th1 responses driven by the IL-12/IFN-gamma axis are central to protection against fungi, other cytokines and T cell-dependent pathways have come of age. The newly described Th17 developmental pathway may play an inflammatory role previously attributed to uncontrolled Th1 responses and serves to accommodate the seemingly paradoxical association of chronic inflammatory responses with fungal persistence in the face of an ongoing inflammation. Regulatory T cells in their capacity to inhibit aspects of innate and adaptive antifungal immunity have become an integral component of immune resistance to fungi, and provide the host with immune defense mechanisms adequate for protection, without necessarily eliminating fungal pathogens which would impair immune memory--or causing an unacceptable level of tissue damage. The enzyme indoleamine 2,3-dioxygenase and tryptophan metabolites contribute to immune homeostasis by inducing Tregs and taming overzealous or heightened inflammatory responses.

Fonsecaea pedrosoi infection induces differential modulation of costimulatory molecules and cytokines in monocytes from patients with severe and mild forms of chromoblastomycosis

The host defense mechanism in chromoblastomycosis has not been thoroughly investigated. It has been suggested that cell-mediated immunity in patients with long-standing chromoblastomycosis is somehow impaired. As a result, these individuals became unable to develop an efficient immune reaction. Many studies have shown that monocyte-derived macrophages exhibit critical activities in immunity to microorganisms. Moreover, the ability of cells from the monocytic lineage to process and present antigens, to produce cytokines, and to provide costimulatory signals confirms their pivotal role in the initiation of specific immune responses. In the present study, it was observed that monocytes from patients with a severe form of disease had a higher production of IL-10 and a lower expression of HLA-DR and costimulatory molecules when stimulated with specific antigen or LPS. Immune modulation with recombinant IL-12 or anti-IL-10 can restore the antigen-specific Th1-type immune response in chromoblastomycosis patients by up-regulating HLA-DR and costimulatory molecules in monocytes. Therefore, our data show that monocytes from patients with different clinical forms of chromoblastomycosis present distinct phenotypic and functional profiles. This observation suggests possible mechanisms that control the T cell response and influence their role in the development of pathology.

Glycoconjugates and polysaccharides of fungal cell wall and activation of immune system

Glycoproteins, glycosphingolipids and polysaccharides exposed at the most external layers of the wall are involved in several types of interactions of fungal cells with the exocellular environment. These molecules are fundamental building blocks of organisms, contributing to the structure, integrity, cell growth, differentiation and signaling. Several of them are immunologically active compounds with potential as regulators of pathogenesis and the immune response of the host. Some of these structures can be specifically recognized by antibodies from patients’ sera, suggesting that they can be also useful in the diagnosis of fungal infections.

Cell and antibody mediated immunity induced by vaccination with novel Candida dubliniensis mannan immunogenic conjugate

Antigen-specific humoral response, as well as the induction of cellular immunity generated by Candida dubliniensis mannan-human serum albumin (HSA) conjugate, a novel proposed immunogenic structure for subcellular vaccine, were evaluated in rabbits. Mannan-HSA conjugate-induced specific IgG and IgA increased significantly after boosters (IgG: P<0.001 and IgA: P<0.01). Mannan-HSA conjugate up-regulation of cell-surface expression of B-lymphocyte and granulocyte activation antigens CD25 and CD11b indicated the effective activation. Immunogenic effect of conjugate on T lymphocytes was demonstrated via inductive increase of CD4+ T lymphocyte subset and CD4+/CD8+ ratio and via induction of T(H)1 cytokines. Immunogenic effectiveness of mannan-HSA conjugate at a dose of 0.25 mg of mannan antigenic moiety overcame that of the mannan alone and of yeast whole cells, thus promising further application in Candida vaccine development.

beta-Glucan of Candida albicans cell wall causes the subversion of human monocyte differentiation into dendritic cells

The functional consequences of treating human monocytes with purified and chemically characterized Candida albicans beta-glucan -- a major microbial pathogen associated molecular pattern -- on their differentiation into dendritic cells (DC) were investigated. We show here that beta-glucan-treated monocytes differentiated into mature DC (Glu-MoDC) with altered phenotype and functional behavior, similarly to DC derived from C. albicans germ-tubes-infected monocytes (Gt-MoDC). They failed to express CD1a and to up-regulate CD80 and DR molecules. Moreover, they produced IL-10 but not IL-12 and primed naive T cells without inducing their functional polarization into effector cells. Since C. albicans beta-glucan is a mixture of both beta-(1,3) and beta-(1,6) glucan, we investigated their relative contribution by the use of non-Candida beta-glucan structural analogs. We found that high molecular weight (MW) glucans beta-(1,6) pustulan and beta-(1,3) curdlan totally mimicked the effect of C. albicans beta-glucan, while the low MW beta-(1,3) glucan laminarin did not have any effect. Because beta-glucan is a common constituent of all fungi and is abundantly released in vivo during systemic fungal infection, this novel effect of beta-glucan has potential implications for host-parasite relationship in candidiasis and other mycoses. In particular, our data suggest that beta-glucan could bias noninfected, bystander monocytes, thus aggravating the general immunodeficiency, predisposing to systemic fungal infection.

History and update on host defense against vaginal candidiasis

Vulvovaginal candidiasis (VVC), caused by Candida albicans, remains a significant problem in women of childbearing age. While cell-mediated immunity is considered the predominant host defense mechanism against mucosal candidal infections, two decades of research from animal models and clinical studies have revealed a lack of a protective role for adaptive immunity against VVC caused by putative immunoregulatory mechanisms. Moreover, natural protective mechanisms and factors associated with susceptibility to infection have remained elusive. That is until recently, when through a live challenge model in humans, it was revealed that protection against vaginitis coincides with a non-inflammatory innate presence, whereas symptomatic infection correlates with a neutrophil infiltrate in the vaginal lumen and elevated fungal burden. Thus, instead of VVC being caused by a putative deficient adaptive immune response, it is now being considered that symptomatic vaginitis is caused by an aggressive innate response.

Cellular immune response of patients with chromoblastomycosis undergoing antifungal therapy

One of the most characteristic features of the chromoblastomycosis is its unresponsiveness to treatment. In order to analyzed whether during therapy could be observed a change of cellular immune response pattern, we evaluated the production of IL-10, TNF-alpha and IFN-gamma, as well as proliferation of peripheral blood mononuclear cell (PBMC) from patients in different periods of chemotherapy treatment. Our results showed that after 6 months of treatment cells from patients proliferated to fungal antigens and produced a significant level of IFN-gamma. However, after 1 year of treatment a low proliferation of T cells and production of IFN-gamma accompanied by an increase of IL-10 were observed when compared with 6 months of treatment.

Candida-induced oral epithelial cell responses

OBJECTIVE

Oropharyngeal candidiasis (OPC), caused by Candida albicans, is the most common oral infection in HIV(+) persons. Oral epithelial cells are considered important for innate host defense against OPC with production of cytokines in response to C. albicans and the ability to inhibit Candida growth in vitro. The purpose of this study was to determine if Candida similarly induces cytokines by oral epithelial cells from HIV(+) persons, including those with OPC, as well as to determine if cytokines can influence the oral epithelial cell anti-Candida activity.

METHODS

Supernatants from oral epithelial cells from HIV(+) persons with and without OPC cultured with Candida were evaluated for cytokines by ELISA, or cytokines were added to the standard growth inhibition assay using epithelial cells from HIV(-) persons.

RESULTS

Results showed low Candida-induced epithelial cell cytokine production from HIV(+) persons, but with some elevated proinflammatory cytokines (TNF-alpha, IL-6) in those with OPC compared to those without OPC. The addition of specific proinflammatory or Th cytokines had no effect on oral epithelial cell anti-Candida activity in healthy HIV(-) persons.

CONCLUSION

These results suggest that oral epithelial cells from HIV(+) persons can contribute at some level to the oral cytokine milieu in response to Candida during OPC, but that cytokines do not appear to influence oral epithelial cell anti-Candida activity.

Distinct roles for interleukin-12p40 and tumour necrosis factor in resistance to oral candidiasis defined by gene-targeting

Cell-mediated immunity is important for anti-Candida host defence in mucosal tissues. In this study we used cytokine-specific gene knockout mice to investigate the requirement for T helper type 1 (Th1) and Th2 cytokines in recovery from oral candidiasis. Knockout mice used in this study included interleukin-4 (IL-4), IL-10, IL-12p40, interferon-gamma (IFN-gamma), and tumour necrosis factor (TNF). The mice were challenged either orally or systemically with Candida albicans yeasts, and levels of colonization were determined. IL-12p40 knockout mice developed chronic oropharyngeal candidiasis, but were not more susceptible to systemic challenge. On the other hand, TNF knockout mice displayed increased susceptibility to both oral and systemic challenge, but only in the acute stages of infection. TNF apparently has a protective effect in the acute stages of both oral and systemic candidiasis, whereas IL-12p40 is essential for recovery from oral but not systemic candidiasis. The role of IL-12p40, and its relation to T-cell-mediated responses remain to be determined.

Assessment of the Association Between HIV Viral Load and CD4 Cell Count on the Occurrence of Oropharyngeal Candidiasis in HIV-Infected Patients

BACKGROUND

Oropharyngeal candidiasis (OPC) is the most frequently observed oral infection in HIV-infected individuals. Historically, lower CD4 counts have been associated with an increased prevalence of OPC in HIV-infected patients, but HIV viral load has also recently been recognized as a possible predictive factor.

OBJECTIVE

We examined the impact of viral load and blood CD4 cell count on the occurrence of OPC using modern exploratory statistical analyses.

METHODS

The exploratory and inferential methods of classification and regression trees (CARTs) and logistic regression were used to compare the impact of viral load and CD4 cell counts on OPC status in 161 HIV-infected individuals from an outpatient clinic population in New Orleans.

RESULTS

The use of stepwise logistic regression and CART to classify individual OPC status both identified viral load as the most important covariate, followed by CD4 cells counts. Age, sex, and highly active antiretroviral therapy use were also found to be associated with OPC status.

CONCLUSIONS

These data strongly suggest that low viral load distinguishes those not at risk for OPC with high viral load, which also includes a heterogeneous set of predictors for OPC status, has the highest impact on OPC classification.

Candida albicans mannoprotein influences the biological function of dendritic cells

Cell wall components of fungi involved in induction of host immune response are predominantly proteins and glycoproteins, the latter being mainly mannoproteins (MP). In this study we analyse the interaction of the MP from Candida albicans (MP65) with dendritic cells (DC) and demonstrate that MP65 stimulates DC and induces the release of TNF-alpha, IL-6 and the activation of IL-12 gene, with maximal value 6 h post treatment. MP65 induces DC maturation by increasing costimulatory molecules and decreasing CD14 and FcgammaR molecule expression. The latter effect is partly mediated by toll-like receptor 2 (TLR2) and TLR4, and the MyD88-dependent pathway is involved in the process. MP65 enables DC to activate T cell response, its protein core is essential for induction of T cell activation, while its glycosylated portion primarily promotes cytokine production. The mechanisms involved in induction of protective response against C. albicans could be mediated by the MP65 antigen, suggesting that MP65 may be a suitable candidate vaccine.

Oral epithelial cell antifungal activity: approaches to evaluate a broad range of clinical conditions

Anti-Candida activity by oral epithelial cells is considered one of several innate mucosal defense mechanisms against oropharyngeal candidiasis (OPC). OPC is the most common fungal infection in HIV disease. Previously we reported that oral epithelial cell anti-Candida activity is reduced in those with OPC, potentially representing a contributing factor to OPC. However, testing clinical epithelial cells possessing high levels of Candida has been limiting due to high background in the assay controls. HIV+ smokers often develop OPC sooner than non-smokers during progression to AIDS, suggesting additional immune aberrations. The purpose of this study was to design a means to reduce Candida associated with epithelial cells collected from saliva without affecting their in vitro growth inhibitory activity, and to employ that approach to evaluate antifungal activity in HIV+ smokers. To do so, oral epithelial cells with and without known levels of Candida were subjected to various treatments including azole, polyene, or echinocandin antifungal drugs or fixation followed by the standard growth inhibition (GI) assay. The results indicated that antifungal drugs, while effectively reducing cell-associated Candida, also affected epithelial cell function. In contrast, fixation with paraformaldehyde eliminated cell-associated Candida and had minimal effects on epithelial cell anti-Candida activity. Employing the fixation design that allowed a broad range of patients to be evaluated showed no difference in oral epithelial anti-Candida activity between HIV+ smokers and non-smokers. Therefore, oral epithelial cell antifungal activity does not appear compromised in those who smoke, reducing it as a contributing factor in susceptibility to premature OPC.

Cytokines and lymphocyte proliferation in patients with different clinical forms of chromoblastomycosis

Chromoblastomycosis is a chronic, often debilitating, suppurative, granulomatus mycosis of the skin and subcutaneous tissues beginning after inoculation trauma. It occurs world-wide, but is more frequently observed in tropical countries such as Brazil. The disease is usually insidious, and the lesions increase slowly but progressively, not responding to the usual treatments and quite often reappearing. The host defense mechanism in chromoblastomycosis has not been extensively investigated. Some studies have focused on fungus-host interaction, showing a predominantly cellular immune response, with the activation of macrophages involved in fungus phagocytosis. Although phagocytosis did occur, death of fungal cells was rarely observed. The ability of Fonsecaea pedrosoi to produce secreted or cell wall-associated melanin-like components, protects against destruction by host immune cells in vitro. Until now, the T cell immune response in chromoblastomycosis is undefined. In the present work, it was shown that, in patients with the severe form of the disease, predominant production of IL-10 cytokine, low levels of IFN-gamma and inefficient T cell proliferation were induced. In contrast, in patients with a mild form of the disease, predominant production of IFN-gamma cytokine, low levels of IL-10 and efficient T cell proliferation were observed.

Involvement of peptidorhamnomannan in the interaction of Pseudallescheria boydii and HEp2 cells

Pseudallescheria boydii is an emerging fungal pathogen that has a worldwide distribution. Virulence mechanisms of P. boydii are largely unknown. We studied the interaction between P. boydii and HEp2 cells and demonstrated that conidia of P. boydii attached to, and were ingested by, HEp2 cells in a time-dependent process. After 2 h of interaction, the conidia produced a germ-tube like projection, which was able to penetrate the epithelial cell membrane. Recently, our group characterized a peptidorhamnomannan (PRM) antigen on the cell surface of P. boydii. In order to better understand the role played by this surface glycoconjugate during cell adhesion and endocytosis, inhibition assays were performed using intact PRM and anti-PRM polyclonal antibody. When HEp2 cells were pre-treated with whole PRM molecule, the adhesion and endocytic indices were, respectively, 50% and 60% lower than in non-treated epithelial cells. Moreover, when the conidial cells were pre-incubated with anti-PRM antibodies, the adherence and endocytosis processes were inhibited in a dose-dependent manner. As PRM influenced the conidia P. boydii-HEp2 cell interaction, we also performed inhibition assays in order to observe which PRM moieties could be involved in this process. Treatment of PRM with proteinase K promoted a slight inhibition of adhesion. However, the de-O-glycosylated PRM molecule as well as the monosaccharide mannose was able to efficiently inhibit the adhesion and endocytic processes. In addition, our results indicate for the first time that P. boydii PRM binds to a polypeptide of 25 kDa on the HEp2 cell surface.

Prevalence and exoenzyme secretion by Candida albicans isolates from oral and vaginal mucosas of HIV-infected women

A cross-sectional study was performed to evaluate the prevalence and the aetiology of forms of mucosal fungal infections of HIV-negative and HIV-positive women. Candida albicans was the predominate specie isolated from both groups of patients, with remarkable proportion of isolation from symptomatic women. All 239 C. albicans isolates, regardless of their source, showed activity of proteinase and phospholipase. It was verified that isolates with particularly higher levels of exoenzymes production were significantly more common in HIV-positive patients. However, isolates obtained from the HIV-positive patients in use of HAART, with protease inhibitor, presented lower levels of these exoenzymes, similar to the levels observed in the isolates from HIV-negative patients.

Immunity to fungal infections

The topic of immunity to fungal infections is of interest to a wide range of disciplines, from microbiology to immunology. It is of particular interest in terms of therapy of HIV-infected individuals, and patients with cancer or individuals who have received transplants. Understanding the nature and function of the immune response to fungi is an exciting challenge that might set the stage for new approaches to the treatment of fungal diseases, from immunotherapy to vaccines. The past decade has witnessed the development of a wide range of new approaches to elucidate events that occur at the host-fungus interface.

The pathogenetic significance of intestinal Candida colonization--a systematic review from an interdisciplinary and environmental medical point of view

The etiological significance of intestinal Candida colonization continues to be controversial. This is a systematic review to determine the pathogenetic significance of intestinal Candida colonization. The search was essentially performed from 1990 to 12/7/2000 in Medline and the Cochrane-Library. The data source was restricted to articles in English and German. Selection criteria covered the topics "Epidemiology", "Infectious Diseases", "Candida-Syndrome" and "Therapy" and were essentially confined to in-vivo examination of immunocompetent adults. Two reviewers extracted independently data using predefined criteria. In total, 96 citations that proved suitable for use in the systematic review were found. Depending on the localization in the gastrointestinal tract, the recovery technique employed, and transport times, Candida colonization is frequently detected in healthy, immunocompetent adults (prevalence: 4-88%). None of the studies available so far furnish any evidence that nutritional factors, food additives, pollutants, anti-ovulants, other types of medication or diabetes mellitus might be predisposing factors for intestinal Candida colonization. However, therapeutic studies point to the possibility of Candida playing a role in antibiotic-associated diarrhea. On the other hand, antibiotics seem to favor bacterial dysbiosis, and this, like the direct side effects of drugs, offers a more plausible explanation for diarrhea or gastrointestinal symptoms. The role of intestinal colonization by Candida in Candida-associated vulvovaginitis and IgE-mediated disorders remains contradictory. Nevertheless, neither epidemiological nor therapeutic studies provide evidence for the existence of the so-called "Candida-syndrome" or "Candida-hypersensitivity-syndrome". At present, there are no proven treatment indications for antifungal "bowel decontamination".

Lymphocyte adhesion to Candida albicans

Adherence of lymphocytes to the fungus is the first step in the direct lymphocyte-mediated antifungal effect against Candida albicans. In this study we identified macrophage-1 antigen (Mac-1) (CD11b/CD18, alpha(M)/beta(2)) as the lymphocyte surface structure responsible for the adhesion of activated lymphocytes to the hyphal form of the fungus. Antibodies specific for epitopes of the alpha-subunit (CD11b) and the beta(2)-subunit (CD18) of Mac-1 were shown to completely eliminate lymphocyte adhesion to C. albicans hyphae. Lymphocyte adhesion to C. albicans was also inhibited significantly by known ligands of Mac-1, including the extracellular matrix proteins laminin and fibrinogen, as well as engineered peptides containing arginine-glycine-aspartic acid sequences and the disintegrin echistatin. N-Acetyl-D-glucosamine and beta-glucan, which inhibit Mac-1-mediated adhesion to the yeast, blocked lymphocyte adhesion to hyphae. NIH 3T3 fibroblast transfectants expressing human CD11b/CD18 bound to C. albicans, and their binding was inhibited by antibodies specific for CD11b/CD18. Finally, antibodies specific for CD11b/CD18 effectively inhibited the capacity of activated lymphocytes to have an antifungal effect against hyphae. Our results clearly identify Mac-1 (CD11b/CD18) as the lymphocyte surface structure that mediates activated lymphocyte adhesion to C. albicans and the resultant antifungal effect of the lymphocytes.

Th1/Th2 cytokine profiles in saliva of HIV-positive smokers with oropharyngeal candidiasis

Oropharyngeal candidiasis (OPC) is a common opportunistic infection among HIV-positive individuals and often correlates with a CD4 cell number < 200 cells/microl. This study further examined the association of smoking and OPC in HIV-positive persons. A strong association between smoking and OPC was seen in HIV-positive individuals with > or =200 CD4 cells/microl. In HIV-positive persons with > or =200 CD4 cells/microl, OPC+ smokers had lower gamma-interferon (IFN-gamma) concentrations and a trend toward higher interleukin (IL)-4 concentrations in whole saliva compared to OPC- persons with > or =200 CD4 cells/microl, a cytokine profile consistent with that observed in HIV+OPC+ persons with < 200 CD4 cells/microl. These results suggest that premature OPC in HIV-positive smokers is associated with altered oral host defence mechanisms that cannot be overcome by levels of systemic CD4 cells that are otherwise sufficient to protect against OPC.

Ras links cellular morphogenesis to virulence by regulation of the MAP kinase and cAMP signalling pathways in the pathogenic fungus Candida albicans

The pathogenic fungus Candida albicans is capable of responding to a wide variety of environmental cues with a morphological transition from a budding yeast to a polarized filamentous form. We demonstrate that the Ras homologue of C. albicans, CaRas1p, is required for this morphological transition and thereby contributes to the development of pathogenicity. However, CaRas1p is not required for cellular viability. Deletion of both alleles of the CaRAS1 gene caused in vitro defects in morphological transition that were reversed by either supplementing the growth media with cAMP or overexpressing components of the filament-inducing mitogen-activated protein (MAP) kinase cascade. The induction of filament-specific secreted aspartyl proteinases encoded by the SAP4-6 genes was blocked in the mutant cells. The defects in filament formation were also observed in situ after phagocytosis of C. albicans cells in a macrophage cell culture assay and, in vivo, after infection of kidneys in a mouse model for systemic candidiasis. In the macrophage assay, the mutant cells were less resistant to phagocytosis. Moreover, the defects in filament formation were associated with reduced virulence in the mouse model. These results indicate that, in response to environmental cues, CaRas1p is required for the regulation of both a MAP kinase signalling pathway and a cAMP signalling pathway. CaRas1p-dependent activation of these pathways contributes to the pathogenicity of C. albicans cells through the induction of polarized morphogenesis. These findings elucidate a new medically relevant role for Ras in cellular morphogenesis and virulence in an important human infectious disease.

Antigenic properties and processing requirements of 65-kilodalton mannoprotein, a major antigen target of anti-Candida human T-cell response, as disclosed by specific human T-cell clones

T-cell-mediated immunity is known to play a central role in the host response to Candida albicans. T-cell clones are useful tools for the exact identification of fungal T-cell epitopes and the processing requirements of C. albicans antigens. We isolated human T-cell clones from an HLA-DRB1*1101 healthy donor by using an antigenic extract (MP-F2) of the fungus. Specific clones were T-cell receptor alpha/beta and CD4(+)/CD8(-) and showed a T-helper type 1 cytokine profile (production of gamma interferon and not interleukin-4). The large majority of these clones recognized both the natural (highly glycosylated) and the recombinant (nonglycosylated) 65-kDa mannoprotein (MP65), an MP-F2 minor constituent that was confirmed to be an immunodominant antigen of the human T-cell response. Surprisingly, most of the clones recognized two synthetic peptides of different MP65 regions. However, the peptides shared the amino acid motif IXSXIXXL, which may be envisaged as a motif sequence representing the minimal epitope recognized by these clones. Three clones recognized natural and pronase-treated MP65 but did not detect nonglycosylated, recombinant MP65 or the peptides, suggesting a possible role for polysaccharides in T-cell recognition of C. albicans. Finally, lymphoblastoid B-cell lines were efficient antigen-presenting cells (APC) for recombinant MP65 and peptides but failed to present natural, glycosylated antigens, suggesting that nonprofessional APC might be defective in processing highly glycosylated yeast proteins. In conclusion, this study provides the first characterization of C. albicans-specific human T-cell clones and provides new clues for the definition of the cellular immune response against C. albicans.

Increased serum and salivary immunoglobulins against Candida albicans in HIV-infected patients with oral candidiasis

The aim of this study was to explore anti-Candida albicans systemic and mucosal humoral responses against Candida virulence antigens such as somatic antigen and secreted aspartic proteases (Saps) in HIV-infected patients with oral candidiasis. Twenty-eight subjects were included in the study: 11 HIV-positive patients without oral candidiasis (group A), 6 HIV-positive patients with oral candidiasis (group B) and 11 HIV-negative healthy controls (group C). Total IgA, IgG and IgM concentrations and antibodies to C. albicans (somatic antigen, Sap1, Sap6) were measured in serum and saliva. We developed a time-resolved immunofluorometric assay with biotin and europium-labeled streptavidin for this purpose. Salivary total IgA, IgG and IgM concentrations were higher in group B. IgA, IgG and IgM anti-C. albicans antibodies (against somatic antigen, Sap1, Sap6) were higher in saliva and serum from patients from group B compared with patients from group A and controls. Our results suggest that, in oral candidiasis, HIV-infected patients have a high mucosal response, specifically directed against C. albicans virulence antigens, such as somatic antigen, Sap1 and Sap6.

Complement activation in SCID and nude mice is related to severity of tissue inflammation in the Candida mastitis model

A small animal model of localised candidiasis is needed for the evaluation of new antifungal compounds. Mammary glands of immunocompetent (BALB/cJ) and immunodeficient (SCID and athymic nude) mice were infected with a wild-type of Candida albicans. Some of the animals were treated with amphotericin B (AmB) while others were treated with saline and acted as controls. The histologic changes of infected mammary gland tissues and a number of other organs were evaluated. Complement (C) activation was analysed by immunoelectrophoretic quantification of molecules with C3c epitopes (C3, C3b, iC3b, and C3c) in serum. In all animals the organisms were confined to the mammary glands. Serum C3c levels were significantly higher (P<0.05) in infected untreated BALB/cJ and SCID mice, which also had severe mammary gland tissue inflammation, compared with control mice treated with AmB (4 mg kg(-1) i.p. once daily for 4 days). Both treated and control nude mice showed less tissue inflammation compared to BALB/cJ and SCID mice, and revealed insignificant activation of the complement system. It is concluded that innate immune response is important in the control of candidiasis and that the murine mastitis model is useful for immunopathological studies as well as evaluation of potential antifungal compounds.

Interleukin 18 restores defective Th1 immunity to Candida albicans in caspase 1-deficient mice

Caspase 1, formerly designated interleukin 1beta (IL-1beta)-converting enzyme, processes pro-IL-1beta and pro-IL-18 to yield active cytokines that play a pivotal role in inflammation and cell activation. We show here the effect of caspase 1 deficiency on the inflammatory and adaptive immune responses to the fungus Candida albicans. Caspase 1 deficiency did not affect susceptibility to primary systemic infection with the fungus, as revealed by survival and fungal growth. However, Th1-mediated resistance to reinfection was greatly impaired in caspase 1-deficient mice, and this correlated with low-level production of IL-12 and gamma interferon. Early in infection, production of these cytokines and that of tumor necrosis factor alpha, IL-6, and, interestingly, IL-1beta occurred normally in caspase 1-deficient mice, while that of IL-18 was severely impaired. Exogenous administration of IL-18, more than IL-12, restored the Th1-mediated resistance to the infection. We conclude that, while caspase 1 is not indispensable for release of mature IL-1beta in candidiasis, the caspase 1-dependent production of IL-18 may represent an important and novel pathway for the expression of sustained Th1 reactivity to the fungus.

Normal thymic architecture and negative selection are associated with Aire expression, the gene defective in the autoimmune-polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED)

T cell development is tightly controlled by thymic stromal cells. Alterations in stromal architecture affect T cell maturation and the development of self-tolerance. The monogenic autoimmune syndrome APECED (autoimmune-polyendocrinopathy-candidiasis-ectodermal dystrophy) is characterized by the loss of self-tolerance to multiple organs. Although mutations in the autoimmune regulator (AIRE) gene are responsible for this disease, the function of AIRE is not known. Here we report on the spatial and temporal pattern of murine Aire expression during thymic ontogeny and T cell selection. Early during development, thymic Aire transcription is critically dependent on RelB and occurs in epithelial cells in response to lymphocyte-mediated signals. In adult tissue, Aire expression is confined to the medulla and the corticomedullary junction, where it is modulated by thymocytes undergoing negative selection. Aire may determine thymic stromal organization and with it the induction of self-tolerance.

Esophageal candidiasis in pediatric acquired immunodeficiency syndrome: clinical manifestations and risk factors

BACKGROUND

Little is known about the epidemiology and clinical features of esophageal candidiasis (EC) in pediatric AIDS. We therefore investigated the clinical presentation and risk factors of EC in a large prospectively monitored population of HIV-infected children at the National Cancer Institute.

PATIENTS AND METHODS

We reviewed the records of all HIV-infected children (N = 448) followed between 1987 and 1995 for a history of esophageal candidiasis to characterize the epidemiology, clinical features, therapeutic interventions and outcome of esophageal candidiasis. To understand further the risk factors for EC in pediatric AIDS, we then performed a matched case-control analysis of 25 patients for whom control cases were available.

RESULTS

There were 51 episodes of EC documented in 36 patients with 23 male and 13 female patients (0.2 to 17 years; median CD4, count 11/microl), representing a frequency of EC of 8.0%. Concurrent oropharyngeal candidiasis (OPC) was the most common clinical presentation of EC (94%); other signs and symptoms included odynophagia (80%), retrosternal pain (57%), fever (29%), nausea/vomiting (24%), drooling (12%), dehydration (12%), hoarseness (6%) and upper gastrointestinal bleeding (6%). The causative organism documented in 36 episodes (18 from OPC, 17 from endoscopic biopsy and 1 from autopsy) was Candida albicans in all cases. Patients received treatment for EC with amphotericin B (63%), fluconazole (29%), ketoconazole (4%) or itraconazole (1%). A clinical response was documented in all 45 evaluable episodes. In 6 other cases, EC was a final event without contributing to the cause of death. By a conditional logistic regression model for matched data, the best predictor of EC was the presence of prior OPC (P<0.0001), followed by CD4 count and CD4 percentage (P = 0.0002) and use of antibacterial antibiotics (P = 0.0013). The risks associated with low CD4 count were independent of that of prior OPC.

CONCLUSION

EC in pediatric AIDS is a debilitating infection, which develops in the setting of prior OPC, low CD4 counts and previous antibiotics.

Measurement of T-cell-derived antigen binding molecules and immunoglobulin G specific to Candida albicans mannan in sera of patients with recurrent vulvovaginal candidiasis

Immunoglobulin G (IgG) and T-cell-derived antigen binding molecules (TABM) specific to whole Candida extract and to Candida-derived mannans prepared by both the cetryltrimethylammonium bromide (CTAB) and alkaline degradation (PEAT) methods were measured in the sera of women with vulvovaginal candidiasis and controls. In the patients there were significantly higher levels of IgG to both CTAB and PEAT mannans and of TABM to CTAB mannan. TABM specific to CTAB mannan was purified from the serum of a patient with a high titer of this TABM. The purified TABM bound specifically to CTAB mannan and to other yeast and mold extracts. This TABM preparation was associated with transforming growth factor beta2 (TGF-beta2), and on specific binding to mannan there was a marked increase in the level of detectable TGF-beta2. This increase in TGF-beta2 level was critically dependent on the relative concentrations of the purified TABM and mannan, being smallest when either was in excess. The TABM specific to CTAB mannan was also shown to inhibit Candida-stimulated gamma interferon production. The results suggest that CTAB mannan-specific TABM may increase susceptibility to vulvovaginal candidiasis in association with a shift in the immune response to the Th2 type.

Dendritic cells discriminate between yeasts and hyphae of the fungus Candida albicans. Implications for initiation of T helper cell immunity in vitro and in vivo

The fungus Candida albicans behaves as a commensal as well as a true pathogen of areas highly enriched in dendritic cells, such as skin and mucosal surfaces. The ability of the fungus to reversibly switch between unicellular yeast to filamentous forms is thought to be important for virulence. However, whether it is the yeast or the hyphal form that is responsible for pathogenicity is still a matter of debate. Here we show the interaction, and consequences, of different forms of C. albicans with dendritic cells. Immature myeloid dendritic cells rapidly and efficiently phagocytosed both yeasts and hyphae of the fungus. Phagocytosis occurred through different phagocytic morphologies and receptors, resulting in phagosome formation. However, hyphae escaped the phagosome and were found lying free in the cytoplasm of the cells. In vitro, ingestion of yeasts activated dendritic cells for interleukin (IL)-12 production and priming of T helper type 1 (Th1) cells, whereas ingestion of hyphae inhibited IL-12 and Th1 priming, and induced IL-4 production. In vivo, generation of antifungal protective immunity was induced upon injection of dendritic cells ex vivo pulsed with Candida yeasts but not hyphae. The immunization capacity of yeast-pulsed dendritic cells was lost in the absence of IL-12, whereas that of hypha-pulsed dendritic cells was gained in the absence of IL-4. These results indicate that dendritic cells fulfill the requirement of a cell uniquely capable of sensing the two forms of C. albicans in terms of type of immune responses elicited. By the discriminative production of IL-12 and IL-4 in response to the nonvirulent and virulent forms of the fungus, dendritic cells appear to meet the challenge of Th priming and education in C. albicans saprophytism and infections.

Molecular cloning of the CRM1 gene from Candida albicans

In a screen for Candida albicans genes capable of supressing a ste20Delta mutation in Saccharomyces cerevisiae, a homologue of the exportin-encoding gene CRM1 was isolated. The CaCRM1 gene codes for a protein of 1079 amino acids with a predicted molecular weight of 124 029 and isoelectric point of 5.04. Crm1p from C. albicans displays significant amino acid sequence homology with Crm1p from Saccharomyces cerevisiae (65% identity, 74% similarity), Schizosaccharomyces pombe (55% identity, 66% similarity), Caenorhabditis elegans (45% identity, 57% similarity), and Homo sapiens (48% identity, 59% similarity). Interestingly, CaCRM1 encodes a threonine rather than a cysteine at position 533 in the conserved central region, suggesting that CaCrm1p is leptomycin B-insensitive, like S. cerevisiae Crm1p. CaCRM1 on a high copy vector can complement a thermosensitive allele of CRM1 (xpo1-1) in S. cerevisiae, showing that CaCrm1p and S. cerevisiae Crm1p are functionally conserved. Southern blot analysis suggests that CaCRM1 is present at a single locus within the C. albicans genome. The nucleotide sequence of the CaCRM1 gene has been deposited at GenBank under Accession No. AF178855.

Involvement of CD4+ T cells and macrophages in acquired protection against infection with Sporothrix schenckii in mice

The cell-mediated immune response against infection with Sporothrix schenckii was investigated in vivo and in vitro. Following primary infection, mice were protected against a secondary subcutaneous inoculation with S. schenckii as determined by the local growth of fungi, and subcutaneously immunized mice were able to survive a lethal intravenous infection. Protection could be transferred to naive congenitally athymic nude mice using lymph node cells taken from immune mice. When immune lymph node cells had CD4+ cells depleted by antibody plus complement, the ability to transfer protection was significantly reduced. Treatment of mice with carrageenan, a macrophage blocker, before and after secondary inoculation abolished protection. An in vitro system, using either immune lymph node cells alone or macrophages alone, failed to kill the organism. However, inhibition of fungal growth was observed when both immune lymph node cells and macrophages were combined. Growth inhibition in vitro was reduced after depletion of CD4+ cells but not CD8+ cells. Addition of anti-interferon (IFN)-gamma monoclonal antibodies (MAb) also reduced growth inhibition. By using reverse transcription-polymerase chain reaction (RT-PCR) analysis, it was shown that immune lymph node cells expressed message for IFN-gamma, tumour necrosis factor (TNF)-alpha and interleukin (IL)-10 after stimulation with heat-killed S. schenckii. These results suggest that acquired immunity against S. schenckii is expressed mainly by macrophages activated by CD4+ T cells.

Limited effect of refined carbohydrate dietary supplementation on colonization of the gastrointestinal tract of healthy subjects by Candida albicans

BACKGROUND

Infections due to Candida albicans occur readily in situations in which ample glucose is available. In mice, dietary refined carbohydrate supplementation leads to higher rates of Candida growth in the gastrointestinal tract and favors mucosal invasion.

OBJECTIVE

The modulating properties of dietary carbohydrate supplementation on colonization of the human gastrointestinal tract by C. albicans were evaluated.

DESIGN

A 2-step study was conducted in 28 healthy volunteers. First, we determined the subjects' habitual uptake of refined carbohydrates and correlated these data with the C. albicans blastoconidia concentration in the mouth washes and feces of subjects with no intervention. Second, we compared C. albicans counts in the specimens before, during, and after a high-sugar diet.

RESULTS

No correlation between C. albicans counts in the specimens and the habitual uptake of refined carbohydrates was observed. A high-sugar diet did not increase the frequency of C. albicans-positive samples, the number of subjects positive for C. albicans in the mouth washes, or the concentration of candidal blastoconidia in the samples of the 28 subjects. However, in selected subjects with elevated counts of oral C. albicans, we observed an increase in fecal C. albicans counts in response to the diet.

CONCLUSIONS

The effect of adding a high amount of refined carbohydrates to the diet of healthy human subjects has a limited influence on Candida colonization. Follow-up studies should define whether selected patient groups might benefit from dietary restriction of refined carbohydrates.

Cloning of the APECED gene provides new insight into human autoimmunity

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is the only autoimmune disease characterized so far that is caused by a defect in a single gene. We have recently isolated the defective gene in this disease by positional cloning and have identified several different mutations in APECED patients. This novel gene, AIRE, contains two plant homeodomain (PHD)-type zinc finger motifs and a newly described putative DNA-binding domain SAND. We have further shown that the protein encoded by the AIRE gene is localized to the nuclear body-like structures of cell nuclei. Similar discrete speckles within the nucleus have been suggested to be involved in the regulation of transcription, oncogenesis and differentiation of cells. Together with the predicted structural features of the APECED protein the new data obtained both in vitro and ex vivo suggest that this protein participates in the regulation of gene expression in a restricted set of tissues and cells.

Pathology of human immunodeficiency virus infection: infectious conditions

Infection with the human immunodeficiency virus (HIV) and the subsequent derangement of host immunity place affected patients at risk for secondary infections. Some of the secondary pathogens occur with such frequency or are so rare in the non-immunosuppressed population that they have become part of the Centers for Disease Control and Prevention (CDC) classification for HIV/acquired immune deficiency syndrome (AIDS). Other infectious agents not yet included in the CDC definition are being reported in the HIV-infected population with increased frequency. General observations of the degree of immunosuppression associated with specific secondary infections have been useful in developing classification systems for HIV disease such as that of the CDC. However, the specific alterations in host immunity that promote infection with specific secondary pathogens are generally unknown. Geographic differences in the types and frequency of secondary infections also have been reported. Variation in strains of HIV, effect of malnutrition, lack of appropriate medical treatment, prevalence of virulent infectious diseases, and epidemiologic differences are possible contributing factors. Some infections that seemed likely to be closely associated with HIV infection have not occurred more frequently in HIV-infected patients. This review summarizes the histopathology of infectious conditions in the current CDC classification and highlights some conditions seen in HIV-infected individuals that are not currently HIV/AIDS-defining infections, yet may be seen by practicing pathologists.

Roles of the Candida albicans mitogen-activated protein kinase homolog, Cek1p, in hyphal development and systemic candidiasis

Extracellular signal-regulated protein kinase (ERK, or mitogen-activated protein kinase [MAPK]) regulatory cascades in fungi turn on transcription factors that control developmental processes, stress responses, and cell wall integrity. CEK1 encodes a Candida albicans MAPK homolog (Cek1p), isolated by its ability to interfere with the Saccharomyces cerevisiae MAPK mating pathway. C. albicans cells with a deletion of the CEK1 gene are defective in shifting from a unicellular budding colonial growth mode to an agar-invasive hyphal growth mode when nutrients become limiting on solid medium with mannitol as a carbon source or on glucose when nitrogen is severely limited. The same phenotype is seen in C. albicans mutants in which the homologs (CST20, HST7, and CPH1) of the S. cerevisiae STE20, STE7, and STE12 genes are disrupted. In S. cerevisiae, the products of these genes function as part of a MAPK cascade required for mating and invasiveness of haploid cells and for pseudohyphal development of diploid cells. Epistasis studies revealed that the C. albicans CST20, HST7, CEK1, and CPH1 gene products lie in an equivalent, canonical, MAPK cascade. While Cek1p acts as part of the MAPK cascade involved in starvation-specific hyphal development, it may also play independent roles in C. albicans. In contrast to disruptions of the HST7 and CPH1 genes, disruption of the CEK1 gene adversely affects the growth of serum-induced mycelial colonies and attenuates virulence in a mouse model for systemic candidiasis.