Nature of Candida albicans-derived carbohydrate antigen recognized by a monoclonal antibody in patient sera and distribution over Candida species

Antigenic Relatedness between Mannans from Coccidioides immitis and Coccidioides posadasii Spherules and Mycelia

Immunoassays for cell wall mannans that are excreted into serum and urine have been used as an aid in the diagnosis of many disseminated fungal infections, including coccidioidomycosis. Antigen-detection immunoassays are critically dependent on the detection of an analyte, such as mannan, by antibodies that are specific to the analyte. The goal of this study was to evaluate the extent of cross-reactivity of polyclonal antibodies raised against Coccidioides spp. Analysis of antigenic relatedness between mannans from C. posadasii and C. immitis spherules and mycelia showed complete relatedness when evaluated by the method of Archetti and Horsfall, which was originally used to study the antigenic relationships between Influenzae virus isolates. In a further effort to validate the suitability of the antigenic relatedness calculation methodology for polysaccharide antigens, we also applied the method of Archetti and Horsfall to published results that had previously identified the major capsular serotypes of Cryptococcus species. The results of this analysis showed that Archetti and Horsfall's antigenic relatedness calculation correctly identified the major cryptococcal serotypes. Together, these results suggest that the method is applicable to polysaccharide antigens, and that immunoassays that detect Coccidioides mannans are likely to have good reactivity across Coccidioides species (inclusivity) due to the species' high level of antigenic relatedness.

ASCA-related antibodies in the blood sera of healthy donors and patients with colorectal cancer: characterization with oligosaccharides related to Saccharomyces cerevisiae mannan

Mannans are polysaccharide antigens expressed on the cell wall of different fungal species including Saccharomyces cerevisiae and Candida spp. These fungi are components of the normal intestinal microflora, and the presence of antibodies to fungal antigens is known to reflect the features of the patient's immune system. Thus, titers of IgG and IgA antibodies against Saccharomyces cerevisiae mannan (ASCA) are markers for clinical diagnostics of inflammatory bowel diseases. The complex organization and heterogeneity of cell-wall mannans may reduce the quality and reproducibility of ELISA results due to interference by different antigenic epitopes. In this research, we analyzed the levels of IgG antibodies in the sera of healthy donors and patients with colorectal cancer using an array of synthetic oligosaccharides related to distinct fragments of fungal mannan. This study aimed to establish the influence of oligosaccharide structure on their antigenicity. Variations in the structure of the previously established ASCA epitope (changing type of linkage, chain length, and the presence of branches) significantly modified the ability of ligands to bind to circulating antibodies in blood sera. The study showed that surface presentation density of the ligand critically affects the results of enzyme immunoassay. The transition from natural coating antigens to their corresponding synthetic mimetics with a defined structure opens new opportunities for improving existing ELISA test systems, as well as developing diagnostic kits with new properties.

Detailed β-(1→3)-D-glucan and mannan antigen kinetics in patients with candidemia

Fungal antigens such as β-(1→3)-D-glucan (BDG) or mannan (Mn) are useful for detection of candidemia. However, detailed data on serum levels before diagnosis and during treatment are scarce. We conducted a prospective study at two German tertiary care centers for 36 months. Sera from adult patients with candidemia were tested for BDG (Fungitell assay) and Mn (Platelia Candida Ag-Plus assay). For each patient, the clinical course and biomarker kinetics were closely followed and compared. 1,243 sera from 131 candidemia episodes and 15 relapses were tested. In 35% of episodes, empirical therapy included an antifungal drug. Before blood culture sampling, BDG and Mn levels were elevated in 62.4% and 30.8% of patients, respectively. Sensitivity at blood culture sampling was 78.6% (BDG) and 35.1% (Mn). BDG levels of non-survivors were significantly higher than those of survivors. During follow-up, a therapeutic response was associated with decreasing BDG and Mn levels in 84.3% or 70.5% of episodes, respectively. A median increase of 513 pg BDG/mL and 390 pg Mn/mL indicated a relapse of candidemia with a sensitivity of 80% or 46.7%, respectively. In 72.9% and 46.8% of patients, increasing BDG or Mn levels were associated with a fatal outcome. Prior to discharge, BDG and Mn levels had dropped or normalized in 65.7% or 82.1% of patients, respectively. Summarising, in patients with candidemia, biomarker positivity usually precedes culture positivity. Relapses are mostly accompanied by secondary biomarker increases. Rising concentrations of BDG and Mn predict lethality, whereas decreasing levels suggest a favorable outcome in the majority of patients.

Rapid oxidative release of fungal mannan for detection by immunoassay

Detection of fungal cells in infected tissue by procedures such as KOH microscopy and histopathology are well-established methods in medical mycology. However, microscopy requires skilled personnel, specialized equipment, and may take considerable time to a result. An alternative approach is immunoassay for detection of fungal mannans in tissue as a biomarker for the presence of fungal cells. However, mannan is a component of the fungal cell wall, and detection of mannan would require a facile means for mannan extraction prior to detection by immunoassay. In this study we evaluated a broad spectrum of extraction reagents using Trichophyton rubrum mycelia and Saccharomyces cerevisiae Mnn2 blastoconidia as model fungi. Oxidative release by treatment with dilute bleach proved to be a novel and highly effective procedure. Complete extraction occurred in as little as 2-4 min. Detergents, chaotropes and acid were ineffective. Strong base released mannan but was less efficient than oxidative release and required the use of highly corrosive reagents. Oxidative release of cell wall mannans from fungal mycelia and blastoconidia may be an effective first step in immunodetection of fungi in tissues from infected humans, animals or plants that could be done at or near the diagnostic point of need.

Identification of fungal trehalose for the diagnosis of invasive candidiasis by mass spectrometry

The rapidity of the diagnosis of invasive candidiasis (IC) is crucial to allow the early introduction of antifungal therapy that dramatically increases the survival rate of patients. Early diagnosis is unfortunately often delayed because Candida blood culture, the gold standard diagnostic test, is positive in only 50% of cases of IC and takes several days to obtain this result. Complementary non-culture-based methods relying on the detection of Candida cell wall polysaccharides in the serum, β-glucans and mannans, by enzymatic and immunological reagents have been successfully developed to allow a more efficient patients care. We have previously demonstrated that detection of circulating glycans by mass spectrometry could provide a reliable and cost-effective early diagnosis method called MS-DS for Mass Spectrometry of Di-Saccharide. Here, by comparing patient's sera and Candida albicans strains deficient in carbohydrates synthesis, we demonstrate that trehalose derived from fungal metabolism can be specifically targeted by MS-DS to allow early diagnosis. In particular, the use of C. albicans strains deficient in the synthesis of trehalose synthesizing enzymes Tps1 and Tps2 show that MS-DS results were correlated to the metabolism of trehalose. Finally, we demonstrate that the performance of the IC diagnosis can be significantly improved by using high resolution mass spectrometry, which opens new perspectives in the management of the disease.

Reinvestigation of Carbohydrate Specificity of EBCA-1 Monoclonal Antibody Used for the Detection of Candida Mannan

Monoclonal antibody EBCA-1 is used in the sandwich immune assay for the detection of circulating Candida mannan in blood sera samples for the diagnosis of invasive candidiasis. To reinvestigate carbohydrate specificity of EBCA-1, a panel of biotinylated oligosaccharides structurally related to distinct fragments of Candida mannan were loaded onto a streptavidin-coated plate to form a glycoarray. Its use demonstrated that EBCA-1 recognizes the trisaccharide β-Man-(1→2)-α-Man-(1→2)-α-Man and not homo-α-(1→2)-linked pentamannoside, as was reported previously.

Dissection of the anti-Candida albicans mannan immune response using synthetic oligomannosides reveals unique properties of β-1,2 mannotriose protective epitopes

Candida albicans mannan consists of a large repertoire of oligomannosides with different types of mannose linkages and chain lengths, which act as individual epitopes with more or less overlapping antibody specificities. Although anti-C. albicans mannan antibody levels are monitored for diagnostic purposes nothing is known about the qualitative distribution of these antibodies in terms of epitope specificity. We addressed this question using a bank of previously synthesized biotin sulfone tagged oligomannosides (BSTOs) of α and β anomery complemented with a synthetic β-mannotriose described as a protective epitope. The reactivity of these BSTOs was analyzed with IgM isotype monoclonal antibodies (MAbs) of known specificity, polyclonal sera from patients colonized or infected with C. albicans, and mannose binding lectin (MBL). Surface plasmon resonance (SPR) and multiple analyte profiling (MAP) were used. Both methods confirmed the usual reactivity of MAbs against either α or β linkages, excepted for MAb B6.1 (protective epitope) reacting with β-Man whereas the corresponding BSTO reacted with anti-α-Man. These results were confirmed in western blots with native C. albicans antigens. Using patients' sera in MAP, a significant correlation was observed between the detection of anti-mannan antibodies recognizing β- and α-Man epitopes and detection of antibodies against β-linked mannotriose suggesting that this epitope also reacts with human polyclonal antibodies of both specificities. By contrast, the reactivity of human sera with other α- and β-linked BSTOs clearly differed according to their colonized or infected status. In these cases, the establishment of an α/β ratio was extremely discriminant. Finally SPR with MBL, an important lectin of innate immunity to C. albicans, classically known to interact with α-mannose, also interacted in an unexpected way with the protective epitope. These cumulative data suggest that structure/activity investigations of the finely tuned C. albicans anti-mannose immune response are worthwhile to increase our basic knowledge and for translation in medicine.

N-Oxy lipid-based click chemistry for orthogonal coupling of mannan onto nanoliposomes prepared by microfluidic mixing: Synthesis of lipids, characterisation of mannan-coated nanoliposomes and in vitro stimulation of dendritic cells

New synthetic aminooxy lipid was designed and synthesized as a building block for the formulation of functionalised nanoliposomes (presenting onto the outer surface of aminooxy groups) by microfluidic mixing. Orthogonal binding of cellular mannan (Candida glabrata (CCY 26-20-1) onto the outer surface of functionalised nanoliposomes was modified by orthogonal binding of reducing termini of mannans to oxime lipids via a click chemistry reaction based on aminooxy coupling (oxime ligation). The aminooxy lipid was proved as a suitable active component for preparation of functionalised nanoliposomes by the microfluidic mixing method performed with the instrument NanoAssemblr™. This "on-chip technology" can be easily scaled-up. The structure of mannan-liposomes was visualized by transmission and scanning electron microscopy, including immunogold staining of recombinant mannan receptor bound onto mannosylated-liposomes. The observed structures are in a good correlation with data obtained by DLS, NTA, and TPRS methods. In vitro experiments on human and mouse dendritic cells demonstrate selective internalisation of fluorochrome-labelled mannan-liposomes and their ability to stimulate DC comparable to lipopolysaccharide. We describe a potentially new drug delivery platform for mannan receptor-targeted antimicrobial drugs as well as for immunotherapeutics. Furthermore, the platform based on mannans bound orthogonally onto the surface of nanoliposomes represents a self-adjuvanted carrier for construction of liposome-based recombinant vaccines for both systemic and mucosal routes of administration.

The Cek1‑mediated MAP kinase pathway regulates exposure of α‑1,2 and β‑1,2‑mannosides in the cell wall of Candida albicans modulating immune recognition

The Cek1 MAP kinase (MAPK) mediates vegetative growth and cell wall biogenesis in the fungal pathogen Candida albicans. Alterations in the fungal cell wall caused by a defective Cek1‑mediated signaling pathway leads to increased β‑1,3‑glucan exposure influencing dectin‑1 fungal recognition by immune cells. We show here that cek1 cells also display an increased exposure of α‑1,2 and β‑1,2‑mannosides (α‑M and β‑M), a phenotype shared by strains defective in the activating MAPKK Hst7, suggesting a general defect in cell wall assembly. cek1 cells display walls with loosely bound material as revealed by transmission electron microscopy and are sensitive to tunicamycin, an inhibitor of N‑glycosylation. Transcriptomal analysis of tunicamycin treated cells revealed a differential pattern between cek1 and wild type cells which involved mainly cell wall and stress related genes. Mapping α‑M and β‑M epitopes in the mannoproteins of different cell wall fractions (CWMP) revealed an important shift in the molecular weight of the mannan derived from mutants defective in this MAPK pathway. We have also assessed the role of galectin‑3, a member of a β‑galactoside‑binding protein family shown to bind to and kill C. albicans through β‑M recognition, in the infection caused by cek1 mutants. Increased binding of cek1 to murine macrophages was shown to be partially blocked by lactose. Galectin-3(-/-) mice showed increased resistance to fungal infection, although galectin-3 did not account for the reduced virulence of cek1 mutants in a mouse model of systemic infection. All these data support a role for the Cek1‑mediated pathway in fungal cell wall maintenance, virulence and antifungal discovery.

Mannosylation in Candida albicans: role in cell wall function and immune recognition

The fungal cell wall is a dynamic organelle required for cell shape, protection against the environment and, in pathogenic species, recognition by the innate immune system. The outer layer of the cell wall is comprised of glycosylated mannoproteins with the majority of these post‐translational modifications being the addition of O‐ and N‐linked mannosides. These polysaccharides are exposed on the outer surface of the fungal cell wall and are, therefore, the first point of contact between the fungus and the host immune system. This review focuses on O‐ and N‐linked mannan biosynthesis in the fungal pathogen Candida albicans and highlights new insights gained from the characterization of mannosylation mutants into the role of these cell wall components in host–fungus interactions. In addition, we discuss the use of fungal mannan as a diagnostic marker of fungal disease.

Comparison of (1->3)-β-D-glucan, mannan/anti-mannan antibodies, and Cand-Tec Candida antigen as serum biomarkers for candidemia

We conducted a case-control study using the Fungitell assay, the novel Platelia Candida Antigen (Ag) Plus and Candida Antibody (Ab) Plus assays, and the Cand-Tec latex agglutination test to evaluate the usefulness of (1→3)-β-D-glucan (BDG), mannan antigen with/without anti-mannan antibody, and Cand-Tec Candida antigen measurement for the diagnosis of candidemia. A total of 56 patients fulfilled the inclusion criteria and were enrolled. One hundred patients with bacteremia and 100 patients with sterile blood cultures served as negative controls. In the candidemia group, median (1→3)-β-D-glucan, mannan antigen, and anti-mannan antibody levels were 427 pg/ml, 190 pg/ml, and 18.6 antibody units (AU)/ml, respectively. All three parameters were significantly elevated in patients with candidemia. The sensitivity and specificity were, respectively, 87.5% and 85.5% for (1→3)-β-D-glucan, 58.9% and 97.5% for mannan antigen, 62.5% and 65.0% for anti-mannan antibody, 89.3% and 63.0% for mannan antigen plus anti-mannan antibody, 89.3% and 85.0% for BDG plus mannan antigen, and 13.0% and 93.9% for Cand-Tec Candida antigen. The low mannan antigen sensitivity was in part caused by Candida parapsilosis and Candida guilliermondii fungemias, which were not detected by the Platelia Candida Ag Plus assay. When the cutoff was lowered from 125 pg/ml to 50 pg/ml, mannan antigen sensitivity increased to 69.6% without severely affecting the specificity (93.5%). Contrary to recently published data, superficial candidiasis was not associated with elevated mannan antigen levels, not even after the cutoff was lowered. Combining procalcitonin (PCT) with (1→3)-β-D-glucan to increase specificity provided a limited advantage because the benefit of the combination did not outweigh the loss of sensitivity. Our results demonstrate that the Cand-Tec Candida antigen and the mannan antigen plus anti-mannan antibody measurements have unacceptably low sensitivity or specificity. Of the four tests compared, (1→3)-β-D-glucan and mannan antigen are the superior biomarkers, depending on whether a sensitivity-driven or specificity-driven approach is used.

The use of mannan antigen and anti-mannan antibodies in the diagnosis of invasive candidiasis: recommendations from the Third European Conference on Infections in Leukemia

Introduction

Timely diagnosis of invasive candidiasis (IC) remains difficult as the clinical presentation is not specific and blood cultures lack sensitivity and need a long incubation time. Thus, non-culture-based methods for diagnosing IC have been developed. Mannan antigen (Mn) and anti-mannan antibodies (A-Mn) are present in patients with IC. On behalf of the Third European Conference on Infections in Leukemia, the performance of these tests was analysed and reviewed.

Methods

The literature was searched for studies using the commercially available sandwich enzyme-linked immunosorbent assays (Platelia™, Bio-Rad Laboratories, Marnes-la-Coquette, France) for detecting Mn and A-Mn in serum. The target condition of this review was IC defined according to 2008 European Organization for Research and Treatment of Cancer/Mycoses Study Group criteria. Sensitivity, specificity and diagnostic odds ratios (DOR) were calculated for Mn, A-Mn and combined Mn/A-Mn testing.

Results

Overall, 14 studies that comprised 453 patients and 767 controls were reviewed. The patient populations included in the studies were mainly haematological and cancer cases in seven studies and mainly intensive care unit and surgery cases in the other seven studies. All studies but one were retrospective in design. Mn sensitivity was 58% (95% confidence interval [CI], 53-62); specificity, 93% (95% CI, 91-94) and DOR, 18 (95% CI 12-28). A-Mn sensitivity was 59% (95% CI, 54-65); specificity, 83% (95% CI, 79-97) and DOR, 12 (95% CI 7-21). Combined Mn/A-Mn sensitivity was 83% (95% CI, 79-87); specificity, 86% (95% CI, 82-90) and DOR, 58 (95% CI 27-122). Significant heterogeneity of the studies was detected. The sensitivity of both Mn and A-Mn varied for different Candida species, and it was the highest for C. albicans, followed by C. glabrata and C. tropicalis. In 73% of 45 patients with candidemia, at least one of the serological tests was positive before the culture results, with mean time advantage being 6 days for Mn and 7 days for A-Mn. In 21 patients with hepatosplenic IC, 18 (86%) had Mn or A-Mn positive test results at a median of 16 days before radiological detection of liver or spleen lesions.

Conclusions

Mn and A-Mn are useful for diagnosis of IC. The performance of combined Mn/A-Mn testing is superior to either Mn or A-Mn testing.

Early mannan detection in bronchoalveolar lavage fluid with preemptive treatment reduces the incidence of invasive Candida infections in preterm infants

BACKGROUND

Candida colonization is an important predictor for development of invasive fungal infection (IFI). We investigated whether early detection of Candida mannan (Mn) in bronchoalveolar lavage fluid (BALF) reduces IFI among preterm infants.

METHODS

We conducted an observational study of infants with gestational age of < or =28 weeks, where a group undergoing Candida surveillance cultures (pre-Mn detection group) was compared with a group defined after the initiation of routine use of Candida Mn detection in BALF (Mn detection group). Antifungal treatment was started based on positive microbiologic (surveillance culture or Mn-antigen assay) results.

RESULTS

No significant differences were detected when the groups were compared for several predictors of IFI. IFI was observed for 12 (23%) of 51 infants in the pre-Mn detection group, and for 0 (0%) of 29 infants in the Mn detection group (P = 0.003). Surveillance cultures in the pre-Mn detection group became positive at 15.0 +/- 7.2 days after birth, whereas the mean age at time of positive Mn antigen results in the Mn detection group was 4.3 +/- 3.1 days (P < 0.0001). Among 16 infants positive for surveillance cultures, 12 (75%) developed IFI (P < 0.0001).

CONCLUSIONS

This study suggests that Candida Mn detection in BALF may be useful for earlier identification and preemptive therapy targeting preterm infants at high risk of IFI.

Prospective evaluation of mannan and anti-mannan antibodies for diagnosis of invasive Candida infections in patients with neutropenic fever

The diagnostic performance and usefulness of the Platelia antigen and antibody test (Bio-Rad) was investigated in a prospective study of haematological patients at risk for invasive Candida infections. Among 100 patients, 86 were eligible, of whom invasive candidiasis (IC) occurred in 12 (14%), according to the criteria of the European Organization for Research and Treatment of Cancer/Mycoses Study Group. These included candidaemia due to Candida albicans (one patient) or Candida tropicalis (four patients), and hepatosplenic candidiasis (seven patients). The comparator group of 74 patients included 50 with febrile neutropenia alone and 24 with mould infections. A strategy was developed to determine diagnostic cut-offs from receiver operating characteristic curves with maximal sensitivity and, given this sensitivity, maximal specificity, both being greater than 0. In this patient population, these values were 0.25 ng ml(-1) for mannan (M) and 2.6 arbitrary units ml(-1) for anti-mannan (AM), which are lower than those recommended by the manufacturer. All patients developed at least one positive diagnostic M or AM result during the 10 days of persistent febrile neutropenia (PFN). The optimal overall performance was found when two consecutive positive tests for both M and AM were used [sensitivity, specificity, positive predictive value and negative predictive value (NPV) (95 % confidence intervals) of 0.73 (0.39-0.94), 0.80 (0.69-0.89), 0.36 (0.17-0.59) and 0.95 (0.86-0.99), respectively]. There was a positive correlation of M with beta-D-glucan (r=0.28, P=0.01). The first positive M test was found up to a mean+/-sd of 8.8+/-8.5 (range 2-23) days prior to a clinical/mycological diagnosis of IC. Day-to-day variation in quantitative M levels was high. High-level AM responses were delayed until leucopenia resolved. The low specificities of the test performance may have been due to some of the comparator patients having subclinical Candida infections as evidenced by the high incidence of colonization among them (60% had a colonization index of >or=0.5). The high NPVs suggest that the tests may be particularly useful in excluding IC. It is feasible to explore the use of serial measurements of M and AM as part of a broader diagnostic strategy for selecting PFN patients to receive antifungal drug therapy.

Antibodies against glucan, chitin, and Saccharomyces cerevisiae mannan as new biomarkers of Candida albicans infection that complement tests based on C. albicans mannan

Antibodies against Saccharomyces cerevisiae mannan (ASCA) and antibodies against synthetic disaccharide fragments of glucans (ALCA) and chitin (ACCA) are biomarkers of Crohn's disease (CD). We previously showed that Candida albicans infection generates ASCA. Here, we explored ALCA and ACCA as possible biomarkers of invasive C. albicans infection (ICI). ASCA, ALCA, ACCA, and Candida mannan antigen and antibody detection tests were performed on 69 sera obtained sequentially from 18 patients with ICIs proven by blood culture, 59 sera from CD patients, 47 sera from hospitalized subjects colonized by Candida species (CZ), and 131 sera from healthy controls (HC). ASCA, ALCA, and ACCA levels in CD and ICI patients were significantly different from those in CZ and HC subjects (P<0.0001). In ICI patients, these levels increased as infection developed. Using ASCA, ALCA, ACCA, and Platelia Candida tests, 100% of ICIs were detected, with the kinetics of the antibody response depending on the patient during the time course of infection. A large number of sera presented with more than three positive tests. This is the first evidence that the detection of antibodies against chitin and glucans has diagnostic value in fungal infections and that these tests can complement more specific tests. Future trials are necessary to assess the value of these tests in multiparametric analysis, as well as their pathophysiological relevance.

In vivo and ex vivo comparative transcriptional profiling of invasive and non-invasive Candida albicans isolates identifies genes associated with tissue invasion

The human pathogenic fungus Candida albicans can cause a wide range of infections and invade multiple organs. To identify C. albicans genes that are expressed during invasion of the liver, we used genome-wide transcriptional profiling in vivo and ex vivo. By analysing the different phases of intraperitoneal infection from attachment to tissue penetration in a time-course experiment and by comparing the profiles of an invasive with those of a non-invasive strain, we identified genes and transcriptional pattern which are associated with the invasion process. This includes genes involved in metabolism, stress, and nutrient uptake, as well as transcriptional programmes regulating morphology and environmental sensing. One of the genes identified as associated with liver invasion was DFG16, a gene crucial for pH-dependent hyphal formation, correct pH sensing, invasion at physiological pH and systemic infection.

Specific recognition of Candida albicans by macrophages requires galectin-3 to discriminate Saccharomyces cerevisiae and needs association with TLR2 for signaling

Stimulation of cells of the macrophage lineage is a crucial step in the sensing of yeasts by the immune system. Glycans present in both Candida albicans and Saccharomyces cerevisiae cell walls have been shown to act as ligands for different receptors leading to different stimulating pathways, some of which need receptor co-involvement. However, among these ligand-receptor couples, none has been shown to discriminate the pathogenic yeast C. albicans. We explored the role of galectin-3, which binds C. albicans beta-1,2 mannosides. These glycans are specifically and prominently expressed at the surface of C. albicans but not on S. cerevisiae. Using a mouse cell line and galectin-3-deleted cells from knockout mice, we demonstrated a specific enhancement of the cellular response to C. albicans compared with S. cerevisiae, which depended on galectin-3 expression. However, galectin-3 was not required for recognition and endocytosis of yeasts. In contrast, using PMA-induced differentiated THP-1, we observed that the presence of TLR2 was required for efficient uptake and endocytosis of both C. albicans and S. cerevisiae. TLR2 and galectin-3, which are expressed at the level of phagosomes containing C. albicans, were shown to be associated in differentiated macrophages after incubation with this sole species. These data suggest that macrophages differently sense C. albicans and S. cerevisiae through a mechanism involving TLR2 and galectin-3, which probably associate for binding of ligands expressing beta-1,2 mannosides specific to the C. albicans cell wall surface.

Evaluation of a newly developed down-flow immunoassay for detection of serum mannan antigens in patients with candidaemia

A down-flow immunoassay has been developed to detect serum mannan antigens, and the test was recently marketed as the Unimedi Candida monotest. Using 251 serum samples from 105 patients with candidaemia, a comparison of the Unimedi Candida monotest with the Cand-Tec latex agglutination test and 2 microplate enzyme immunoassay tests (Platelia Candida Ag test and Unimedi Candida) was conducted. One hundred and seventy-five febrile patients without clinical and microbiological evidence of fungal infections and pneumocytosis were examined as controls. The Cand-Tec test had a sensitivity of 38% and a specificity of 82%. The sensitivity and specificity of the Platelia Candida Ag test, the Unimedi Candida and the Unimedi Candida monotest were 53 and 92%, 69 and 89% and 82 and 96%, respectively. The sensitivity of the Unimedi Candida monotest was significantly (P<0.01) higher than that of the Plateria Candida Ag test for diagnosing candidaemia caused by Candida parapsilosis. The beta-D-glucan assay had a high sensitivity of 95%, with a specificity of 84%. Of 74 patients with candidaemia whose sera were available before or on positive blood culture sampling, 29 (39%), 38 (51%) and 48 (65%) patients had antigenemia detected using the Platelia Candida Ag test, the Unimedi Candida and the Unimedi Candida monotest, respectively. The Unimedi Candida monotest seems to be a promising tool for the early diagnosis of invasive candidiasis, because the test was sensitive, simple, rapid (approx. 1 h) and cost-effective.

Effect of monosaccharide composition, glycosidic linkage position and anomericity on the electrophoretic mobility of labeled oligosaccharides

Fluorophore-assisted carbohydrate electrophoresis (FACE) is useful for separation and characterization of oligosaccharides from various sources and for comparing several samples at once. While characterizing fungal surface glycans by FACE we observed that samples and standards of the same mass did not comigrate as expected. Subsequent experiments showed that the samples did not contain contaminating sugars. Therefore, our observation suggested that glycan electrophoretic mobility is affected by factors in addition to molecular mass. This work assesses the contribution of monosaccharide composition, linkage position, and linkage anomericity to glycan mobility. Commercially available (and synthesized when available) bioses of known composition were derivatized with a charged fluorophore, and electrophoretic mobilities compared in a slab gel format. The results indicate that all three parameters mentioned above affect observed migration. Further, no migration patterns emerged to suggest a set of rules for assigning band identity based on mobility alone. These results emphasize the importance of including known, matched, standards to facilitate interpretation of FACE data.

[Performance of the Candida mannan antigen detection in patients with fungemia]

For several years, the Platelia Candida mannan antigen enzyme immunoassay (Candida EIA) has been commercially available as a diagnostic test for invasive candidosis. We evaluated the Candida EIA with patients with proven fungemia caused by yeasts from which at least one serum sample was available. Fifty-nine patients with 121 serum samples were included in the study. Sixty-one different yeast strains were isolated from positive blood-cultures. The Candida EIA was positive (n = 35) or borderline positive (n = 8) in 43 of 59 patients with fungemia, resulting in an overall sensitivity of 73%. For the different yeast species, the following sensitivities were calculated: Candida albicans 30 of 39 (77%), Candida glabrata 7 of 11 (64%), Candida parapsilosis 1 of 3, Candida tropicalis 2 of 2, Candida kefyr 2 of 2, Candida lipolytica 0 of 1, Candida lusitaniae 1 of 1, Candida krusei 1 borderline positive of 1, Saccharomyces cerevisiae 1 of 1. In six patients the antigen levels over time were evaluable. In three cases the antigen was positive 3-4 days before the day the blood culture was drawn, in one case on the same day, and in two cases 2 and 5 days afterwards. In conclusion, the Candida EIA was suitable for the detection of fungemia due to the major facultatively pathogenic yeast species. The test was positive in about half of the patients before blood cultures became positive. In these cases, it contributed to an early diagnosis of invasive candidiasis.

Early diagnosis of invasive candidiasis with mannan antigenemia and antimannan antibodies

Late treatment of invasive candidiasis (IC) results in severe complications and high mortality. New tools are needed for early diagnosis. We conducted a retrospective study to assess the diagnostic utility of mannan antigenemia (Mn) and antimannan antibodies (anti-Mn) in neutropenic cancer patients at high risk for candidiasis. Twenty-eight patients with IC (based on European Organization for Research and Treatment of Cancer and Mycoses Study Group definitions) and 25 controls were studied. Mn and anti-Mn were positive (> or = 0.25 ng/mL and > or = 5 AU/mL, respectively) in 25/28 (89%) patients with candidiasis and in 4/25 (16%) controls: sensitivity, 89%; specificity, 84%; positive predictive value, 86%; negative predictive value, 88%. In patients with hepatosplenic lesions, assessing Mn/anti-Mn shortened the median time of diagnosis of candidiasis when compared with imaging (9 versus 25 days after fever onset as first sign of infection; P < 0.001). Candidiasis was diagnosed before neutrophil recovery in 78% and 11% of cases with Mn/anti-Mn and radiology, respectively (P < 0.001). Mn and anti-Mn may be useful for early noninvasive diagnosis of IC.

Erfahrungen mit dem PlateliaRCandida ELISA zur Diagnostik invasiver Candida-Infektionen bei neutropenischen Patienten. Experience with the PlateliaRCandida ELISA for the diagnostics of invasive candidosis in neutropenic patients

Invasive Candida infections (IC) belong to the most important opportunistic fungal infections in immunocompromised patients. IC is difficult to diagnose, because clinical symptoms are nonspecific and cultural methods lack sensitivity or specificity. We evaluated the Platelia Candida enzyme immunoassay (Candida EIA) for the diagnosis of IC in patients with haematological malignancies. A total of 62 neutropenic patients with 469 serum samples were included in the study. Candida colonization was monitored by weekly cultures of mouth washings, urine, and stool samples. Yeasts were grown from samples of 42 patients (68%), mainly Candida albicans (50%), followed by Candida glabrata (23%) and Candida krusei (20%). According to the criteria of the EORTC/NIH, the patients were categorized: (1) 3 patients with proven IC; (2) 6 patients with probable IC; (3) 34 patients colonized with Candida; (4) 19 patients without Candida colonization and without IC. In the patient categories (1) to (4), 3/3 (100%), 3/6 (50%), 20/34 (59%), and 7/19 (37%) patients were Candida EIA positive (>0.5 ng/ml) in at least one serum sample. The sensitivity of the assay for the detection of proven IC was 100%, for proven and probable IC 67%, the specificity was 49% for both groups. An increase of the cut-off value to 2.0 ng/ml raised the specificity to 61%, but lowered the sensitivity to 56%. In conclusion, the Platelia Candida EIA does not discriminate between Candida colonization and probable invasive infection in haematological patients.

Detection of the Candida antigen mannan in cerebrospinal fluid specimens from patients suspected of having Candida meningitis

Cerebrospinal fluid samples from five patients from which Candida cells were cultured were tested for the presence of mannan. Samples from four patients categorized as having proven candidosis reacted positively. Samples from the remaining patient and from patients with other central nervous system infections were negative. Detection of mannan may be valuable in the diagnosis of Candida meningitis.

Surface glycans of Candida albicans and other pathogenic fungi: physiological roles, clinical uses, and experimental challenges

Although fungi have always been with us as commensals and pathogens, fungal infections have been increasing in frequency over the past few decades. There is a growing body of literature describing the involvement of carbohydrate groups in various aspects of fungal disease. Carbohydrates comprising the cell wall or capsule, or as a component of glycoproteins, are the fungal cell surface entities most likely to be exposed to the surrounding environment. Thus, the fungus-host interaction is likely to involve carbohydrates before DNA, RNA, or even protein. The interaction between fungal and host cells is also complex, and early studies using whole cells or crude cell fractions often produced seemingly conflicting results. What was needed, and what has been developing, is the ability to identify specific glycan structures and determine how they interact with immune system components. Carbohydrate analysis is complicated by the complexity of glycan structures and by the challenges of separating and detecting carbohydrates experimentally. Advances in carbohydrate chemistry have enabled us to move from the foundation of composition analysis to more rapid characterization of specific structures. This, in turn, will lead to a greater understanding of how fungi coexist with their hosts as commensals or exist in conflict as pathogens.

Contribution of the Platelia Candida-specific antibody and antigen tests to early diagnosis of systemic Candida tropicalis infection in neutropenic adults

The Platelia Candida-specific antigen and antibody assays (Bio-Rad Laboratories) were used to test serial serum samples from seven neutropenic adult patients with hematological malignancies who had developed systemic Candida tropicalis infections. The diagnosis of candidiasis was based on a positive blood culture (all seven patients) and the isolation of C. tropicalis from a normally sterile site (six patients). All patients received early antifungal therapy with amphotericin B and/or an azole derivative and had successful outcomes. When the combined assays were applied to sera collected at different time points before and after the first positive blood culture, all patients tested positive. In six patients, at least one positive test was obtained with sera collected, on average, 5 days (range, 2 to 10 days) prior to the first positive blood culture, while blood cultures were constantly negative. High and persistent mannanemias were detected in all patients during the neutropenic period. In five patients, an increased antibody response was detected when the patients recovered from aplasia. Controls consisted of 48 serum samples from 12 febrile neutropenic patients with aspergillosis (n = 4), bacteremia (n = 4), or no evidence of infection (n = 4). A low level of mannanemia was detected in only one serum sample, and none showed significant Candida antibody titers. Our data thus confirm the value of the combined detection of mannanemia and antimannan antibodies in individuals at risk of candidemia and suggest that in neutropenic patients, an approach based on the regular monitoring of both markers could contribute to the earlier diagnosis of C. tropicalis systemic infection.

Beta-1,2- and alpha-1,2-linked oligomannosides mediate adherence of Candida albicans blastospores to human enterocytes in vitro

Candida albicans is a commensal dimorphic yeast of the digestive tract that causes hematogenously disseminated infections in immunocompromised individuals. Endogenous invasive candidiasis develops from C. albicans adhering to the intestinal epithelium. Adherence is mediated by the cell wall surface, a domain composed essentially of mannopyranosyl residues bound to proteins, the N-linked moiety of which comprises sequences of alpha-1,2- and beta-1,2-linked mannose residues. Beta-1,2-linked mannosides are also associated with a glycolipid, phospholipomannan, at the C. albicans surface. In order to determine the roles of beta-1,2 and alpha-1,2 oligomannosides in the C. albicans-enterocyte interaction, we developed a model of adhesion of C. albicans VW32 blastospores to the apical regions of differentiated Caco-2 cells. Preincubation of yeasts with monoclonal antibodies (MAbs) specific for alpha-1,2 and beta-1,2 mannan epitopes resulted in a dose-dependent decrease in adhesion (50% of the control with a 60- micro g/ml MAb concentration). In competitive assays beta-1,2 and alpha-1,2 tetramannosides were the most potent carbohydrate inhibitors, with 50% inhibitory concentrations of 2.58 and 6.99 mM, respectively. Immunolocalization on infected monolayers with MAbs specific for alpha-1,2 and beta-1,2 oligomannosides showed that these epitopes were shed from the yeast to the enterocyte surface. Taken together, our data indicate that alpha-1,2 and beta-1,2 oligomannosides are involved in the C. albicans-enterocyte interaction and participate in the adhesion of the yeasts to the mucosal surface.

Increased sensitivity of mannanemia detection tests by joint detection of alpha- and beta-linked oligomannosides during experimental and human systemic candidiasis

An enzyme immunoassay (EIA)-the commercially available Platelia Candida antigen test-developed for the diagnosis of systemic candidiasis is based on the detection of alpha-linked oligomannose residues (alpha-Man) released from Candida cells into the serum. This test has good specificity but has to be repeated frequently because of the rapid clearance of detectable mannanemia. We have developed a second EIA based on detection of beta-linked oligomannoses (beta-Man), since beta-Man are linked to different Candida molecules and interact differently with the host immune system and endogenous lectins and should therefore present different kinetics of serum clearance. In a guinea pig model of Candida albicans systemic infection, the relative amounts of detectable alpha- and beta-Man differed considerably according to the virulence of the strain, the infecting dose, and the time after challenge that serum samples were drawn. Detection of alpha-Man was more sensitive per serum sample than that of beta-Man, and the sensitivity for the combination reached 90%. The same tests were applied to 90 sera from 26 patients selected retrospectively for having been infected with the most-pathogenic Candida species: C. albicans (19), C. tropicalis (4), and C. glabrata (3). A total of 22 patients had positive antigenemia, 4 had alpha-mannanemia, 4 had beta-mannanemia, and 14 showed the presence of both. For the patients showing the presence of both forms of mannanemia, the use of both tests enhanced the duration of the detection of mannanemia. Mannanemia was correlated with early clinical symptoms and isolation of Candida in culture, which occurred in 55% of the patients at an average of 4.7 days after the first positive mannanemia test result. A combination of the two tests had a cumulated specificity of 95%, and positive and negative predictive values were 79 and 97%, respectively. These findings provide evidence for different kinetics of beta- and alpha-Man circulation during experimental and human candidiasis and suggest the joint detection of both types of epitopes as a rational approach contributing to increases in the sensitivity and earliness of diagnosis.

Cross-reactivity of the PLATELIA CANDIDA antigen detection enzyme immunoassay with fungal antigen extracts

We studied the specificity of the PLATELIA CANDIDA Ag enzyme immunoassay by using 130 isolates of 63 clinically relevant fungal species. Antigen extracts of seven Candida spp. (Candida albicans, C. dubliniensis, C. famata, C. glabrata, C. guilliermondii, C. lusitaniae, and C. tropicalis) repeatedly yielded positive reactions (>0.5 ng/ml). Geotrichum candidum and Fusarium verticillioides were found to yield borderline-positive reactions (0.25 to 0.50 ng/ml). Antigen preparations from the other 54 fungal species, including yeasts, molds, dermatophytes, and dimorphic fungi, did not cross-react in the assay.

Synthetic analogues of beta-1,2 oligomannosides prevent intestinal colonization by the pathogenic yeast Candida albicans

The pathogenic yeast Candida albicans displays at its cell surface beta-1,2 oligomannosides (beta-1,2-Mans). In contrast to the ubiquitous alpha-Mans, beta-1,2-Mans bind to galectin-3, a major endogenous lectin expressed on epithelial cells. The specific role of beta-1,2-Mans in colonization of the gut by C. albicans was assessed in a mouse model. A selected virulent strain of C. albicans (expressing more beta-1,2-Man epitopes) induced more intense and sustained colonization than an avirulent strain (expressing less beta-1,2-Man epitopes). Synthetic (Sigma) beta-and alpha-linked tetramannosides with antigenicities that mimicked the antigenicities of C. albicans-derived oligomannosides were then constructed. Oral administration of Sigmabeta-1,2-Man (30 mg/kg of body weight) prior to inoculation with the virulent strain resulted in almost complete eradication of yeasts from stool samples, whereas administration of Sigmaalpha-Man at the same dose did not. As most cases of human systemic candidiasis are endogenous in origin, this first demonstration that a synthetic analogue of a yeast adhesin can prevent yeast colonization in the gut opens the possibility of new prophylactic strategies.

Contribution of phospholipomannan to the surface expression of beta-1,2-oligomannosides in Candida albicans and its presence in cell wall extracts

beta-1,2-Oligomannosides (beta-1,2-Man) derived from Candida albicans mannan have been shown to act as adhesins and to induce protective antibodies. We used monoclonal antibodies specific for beta-1,2-Man in electron, confocal, and fluorescence microscopy to study the surface expression of beta-1,2-Man epitopes. These monoclonal antibodies were also used for Western blotting of cell surface extracts to study the nature of the molecules expressing the beta-Man epitopes. Evidence was obtained for the contribution of a glycolipid, phospholipomannan (PLM), to the complex expression of beta-1,2-Man epitopes at the cell wall surfaces of yeasts grown on solid media. PLM was present in intercellular matrixes of colonies grown on agar and was detected as a contaminant in mannan batches prepared by conventional methods.

Current status of nonculture methods for diagnosis of invasive fungal infections

The incidence of invasive fungal infections has increased dramatically in recent decades, especially among immunocompromised patients. However, the diagnosis of these infections in a timely fashion is often very difficult. Conventional microbiologic and histopathologic approaches generally are neither sensitive nor specific, and they often do not detect invasive fungal infection until late in the course of disease. Since early diagnosis may guide appropriate treatment and prevent mortality, there has been considerable interest in developing nonculture approaches to diagnosing fungal infections. These approaches include detection of specific host immune responses to fungal antigens, detection of specific macromolecular antigens using immunologic reagents, amplification and detection of specific fungal nucleic acid sequences, and detection and quantitation of specific fungal metabolite products. This work reviews the current status and recent developments as well as problems in the design of nonculture diagnostic methods for invasive fungal infections.

Two-dimensional relayed-rotating-frame overhauser spectroscopy (1)H NMR experiments for the selective identification of 1,2-glycosidic linkages in polysaccharides

This communication describes the use of two-dimensional relayed (TOCSY)-ROESY experiments for the rapid and selective identification of alpha/beta1,2-glycosidic linkages in polysaccharides. The method assists in the identification of cross-peaks in crowded regions of ROESY spectra by moving them to less congested areas. In addition, the appearance of the spectra provides information relating the location of the glycosidic linkage within the sequence of the glycan under study. Selection of solely the 1,2- linkages is achieved by appropriately tuning the duration of the TOCSY mixing period. The method is demonstrated both theoretically and experimentally for a variety of test case polysaccharides.

New enzyme immunoassays for sensitive detection of circulating Candida albicans mannan and antimannan antibodies: useful combined test for diagnosis of systemic candidiasis

Two standardized enzyme immunoassays for the serological diagnosis of candidiasis were developed. The first one detects antimannan antibodies, while the second one detects mannan with a sensitivity of 0.1 ng/ml. These tests were applied to 162 serum samples retrospectively selected from 43 patients with mycologically and clinically proven candidiasis caused by Candida albicans. Forty-three serum samples were positive for mannan, and 63 had significant antibody levels. Strikingly, only five serum samples were simultaneously positive by both tests. When the results were analyzed per patient, 36 (84%) presented at least one serum positive by one test. For 30 of them, positivity by one test was always associated with negative results by the other test for any of the tested sera. For six patients whose sera were positive for either an antigen or an antibody response, a balance between positivity by each test was evidenced by kinetic analysis of sera drawn during the time course of the infection. Controls consisted of 98 serum samples from healthy individuals, 93 serum samples from patients hospitalized in intensive care units, and 39 serum samples from patients with deep mycoses. The sensitivities and specificities were 40 and 98% and 53 and 94% for mannanemia or antibody detection, respectively. These values reached 80 and 93%, respectively, when the results of both tests were combined. These observations, which clearly demonstrate a disparity between circulation of a given mannan catabolite and antimannan antibody response, suggest that use of both enzyme immunoassays may be useful for the routine diagnosis of candidiasis.