Comparison of glucan detection and galactomannan enzyme immunoassay in gastrointestinal and systemic murine candidiasis

Mouse models of systemic and gastrointestinal infection with the yeast Candida albicans were used to investigate the ability of a commercial mannan antigen enzyme immunoassay and a commercial (1-->3) beta-D-glucan limulus assay to detect systemic infection and to differentiate between colonization and infection. Both assays were positive in all i.v. infected mice and negative in all uninfected control mice. In gastrointestinal infection both tests were positive whenever organ cultures were positive. In colonized mice with no detectable dissemination, there were mostly negative results with the glucan assay whereas the mannan assay was positive or intermediate in all colonized mice. Therefore, in the mouse model used, glucan detection appeared to be superior for differentiation between colonization and dissemination.

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.

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.

Serial monitoring of Aspergillus antigen in the early diagnosis of invasive aspergillosis. Preliminary investigations with two examples

A recently developed sandwich ELISA, which detects Aspergillus galactomannan, was tested retrospectively in serial serum samples from an allogeneic bone marrow transplant recipient with proven invasive aspergillosis (patient 1) and another with suspected disease (patient 2). Galactomannan was detected in the serum 4 and 28 days, respectively, before pulmonary infiltrates suggestive of fungal infection first became apparent on the chest X-ray. Aspergillus was detected by ELISA and PCR in BAL fluid samples from both patients, and in CSF from patient 1. The diagnosis was confirmed at autopsy for patient 1 by histopathology and the recovery of Aspergillus fumigatus from the lung and brain. Furthermore, in both patients the course of the antigen titer in the serum during antifungal treatment corresponded with the clinical outcome. These results confirm that the sandwich ELISA appears to be useful for the early diagnosis of invasive aspergillosis. The value of the test for monitoring the response to antifungal treatment remains to be established in prospective trials.

Differential susceptibility of yeast and hyphal forms of Candida albicans to proteolytic activity of macrophages

The dimorphic transition of Candida albicans from the yeast (Y-Candida) to the hyphal (H-Candida) form is a complex event whose relevance in fungal pathogenicity is still poorly understood. Using a cloned macrophage (M phi) cell line (ANA-1), we have previously shown that a M phi can discriminate between the two fungal forms, eliciting different secretory responses. In the present study, we investigated the susceptibility of Y-Candida and H-Candida to M phi proteolytic activity. In particular, sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot (immunoblot) techniques were employed to analyze the patterns of lyticase proteinaceous extracts from cell walls of Y-Candida and H-Candida which had been unexposed or exposed to ANA-1 M phis for 3 h. Silver staining allowed detection of a complex protein pattern in both forms of C. albicans, qualitatively and quantitatively differing from each other, mainly at molecular masses below 106 kDa. Western blot staining with anti-C. albicans mannan antibodies and convalescent-phase sera of mice previously infected systemically or intracerebrally with C. albicans showed that, after contact with M phis, Y-Candida but not H-Candida proteinaceous cell wall components are profoundly modified, with substantial reduction and/or disappearance of many bands. Our experimental approach provides initial insights into the differential susceptibility of Y-Candida and H-Candida to the proteolytic activity of M phis.

A new sensitive sandwich enzyme-linked immunosorbent assay to detect galactofuran in patients with invasive aspergillosis

A double-direct sandwich enzyme-linked immunosorbent assay that uses a rat anti-galactomannan monoclonal antibody as the acceptor and detector antibody was designed. This immunoassay, which detects less than 1 ng of galactomannan per ml, was assessed in a retrospective study with samples from patients with invasive aspergillosis. Serum is more appropriate than urine for use in the search for circulating galactomannan. Antigenemia does not have a transient character. Galactomannan can be detected at least 39 days before the death of the patients.

Existence of branched side chains in the cell wall mannan of pathogenic yeast, Candida albicans. Structure-antigenicity relationship between the cell wall mannans of Candida albicans and Candida parapsilosis

Isolation of side chain oligosaccharides from mannans of Candida albicans NIH B-792 (serotype B) and Candida parapsilosis IFO 1396 strains has been conducted by acetolysis under mild conditions. Structural study of these oligosaccharides by 1H and 13C NMR and methylation analyses indicated the presence of novel branched side chains with the following structures in C. albicans mannan. [sequence: see text] It was observed that the H-1 proton chemical shifts of the second and the third mannose units from the reducing terminus in each oligosaccharide are shifted upfield by substitution with an alpha-linked mannose unit at position 6 of the 3-O-substituted mannose unit. An agglutination inhibition assay between factor 4 serum and cells of Candida stellatoidea IFO 1397 lacking the beta-1,2-linked mannose unit, with oligosaccharides obtained from these mannans, indicated that only the branched oligosaccharides were active. This finding suggests that the branched oligosaccharides correspond to the epitope of antigenic factor 4. The presence of the branched structure in other mannans was detected by the characteristic H-1-H-2-correlated cross-peak of the alpha-1,2-linked mannose unit connected with the 3,6-di-O-substituted one by two-dimensional homonuclear Hartmann-Hahn spectroscopy.

Diagnosis of invasive candidiasis by detection of mannan antigen by using the avidin-biotin enzyme immunoassay

The diagnosis of invasive candidiasis was attempted by detection of circulating mannan antigen by using an avidin-biotin-amplified enzyme-linked immunosorbent assay (AB-ELISA), and this method was compared with the conventional culture method. Mannan antigen was detected by AB-ELISA in the sera of 16 (84.2%) of the 19 patients with invasive candidiasis. On the other hand, for 34 immunocompromised candidiasis-free patients, including 8 with aspergillosis or cryptococcosis, mannan antigen was positive during only 1 of the 67 febrile episodes and in the serum of none of the 50 outpatients without infections. The results were also negative for all patients with deep-seated mycoses other than candidiasis. However, the mannan level was low (less than 2.0 ng/ml) in the serum of 63.2% of the patients with invasive candidiasis. The positivity rate of blood cultures was 31.6%, and that of blood cultures and/or cultures of samples from sterile sites combined was 47.4%. The advantages of the diagnosis based on antigen detection by AB-ELISA are considered to be a higher sensitivity and elimination of nonspecific reactions by the introduction of the avidin-biotin system and pretreatment of sera by heating. In addition, it is considered essential for high sensitivity that transient mannan antigenemia be determined frequently so that it is not overlooked. In light of its sensitivity and specificity, this method is considered to be clinically useful in the diagnosis of invasive candidiasis.

Mannan estimation as a measure of the growth of Candida albicans

Determination of Candida albicans mannan levels by an enzyme-linked immunosorbent assay was compared with dry weight measurement and viable counting as a means to estimate growth of the fungus in broth cultures. Levels of extracted mannan showed good correlation with fungal biomass (dry weight) (r = 0.984) and, although biomass and mannan levels correlated with viable counts, the correlation was not as strong (r = 0.954-0.959). The technique offered an accurate alternative to viable counts in the brain and kidney when mannan estimation was used to follow the distribution of C. albicans in an experimental model of systemic candidosis in mice. Mannan levels were less useful in following the course of the infection in the liver and spleen where accumulation of free and serum-bound mannan was a problem. Mannan estimation would therefore seem to offer an accurate alternative to viable counts for determining the quantity of Candida both in vitro and in certain infected organs of experimental animals, where measurement of fungal biomass is not feasible and viable counts can be grossly inaccurate.

Serological techniques for diagnosis of fungal infection

This review summarizes recent developments in the serodiagnosis of candidiasis, aspergillosis, cryptococcosis, histoplasmosis, blastomycosis, coccidioidomycosis, mucormycosis and sporotrichosis. A number of studies have substantiated the presence of circulating antigens in invasive candidiasis, invasive aspergillosis, disseminated histoplasmosis and coccidioidomycosis, and immunoassays for antigen detection provide moderate sensitivity but high specificity for disease. Improved detection may result mainly from repeated serum or concentrated urine samplings rather than from the development of more sensitive immunoassays. Immunoblot analysis of the serological response is a useful tool for the identification of immunogenic fungal components that elicit a specific antibody response in invasive disease. This method, and others, have been successfully applied to the study of the immune response to several fungi, including Candida, Aspergillus and Rhizopus.

Candida cell wall mannan: a polysaccharide with diverse immunologic properties

It is clear that mannan has the potential to influence multiple biologic functions in vivo and in vitro, including both mannan-specific and mannan-nonspecific activities. Based on in vitro studies, various mechanisms have been proposed for the regulatory activities observed, ranging from interference with normal PMNL and monocyte function to the induction of T suppressor cells. It may well be, in fact, that different mechanisms function at different levels depending upon the specific phenomenon being influenced. Approaches to determining the mechanisms involved in these regulatory phenomena, however, have been complicated by the fact that many studies were performed with mannan extracted in the laboratory by traditional methods and used as such without further purification. Most laboratory-acquired mannans appear to be heterogeneous mixtures containing polymers of differing size and charge. When such mixtures have been separated on the basis of size or charge, it has been shown that biologic function can be correlated with individual fractions, and that a single bulk preparation of mannan can contain components with opposing biologic activities. Resolution of the specific mechanisms involved in the regulatory phenomena described, therefore, will not be complete until homogeneous preparations of mannan are employed to investigate the mechanisms.

Studies on detection of Candida antigen in the sera of mice inoculated orally with Candida albicans

The authors succeeded in establishing a murine model of systemic candidiasis being disseminated from the primary gastrointestinal lesions caused by oral inoculation of Candida albicans. Using this model, an attempt was made for detecting the Candida antigen by enzyme-linked immunosorbent assay using avidin-biotin (AB-ELISA) from the serum of infected mice. Gastrointestinal candidiasis was formed in all of the 20 mice treated with the drugs (antibiotics, antineoplastic agents, hydrocortisone, etc.) and inoculated orally with C. albicans. Fourteen of these mice suffered from submucosal candidiasis, and C. albicans was cultured from the visceral organs in 12 of them. The assay by AB-ELISA was able to detect 1.0 ng/ml Candida mannan in the mouse serum. The Candida antigen was detected in the sera of 11 of the 14 mice with submucosal candidiasis. However, the antigen could not be detected in the sera of the 6 mice with intramucosal candidiasis. The assay by AB-ELISA is more sensitive and specific for the diagnosis of systemic candidiasis than other serological assays.

Detection of galactomannan antigenemia by enzyme immunoassay in experimental invasive aspergillosis

A sensitive enzyme immunoassay (EIA) for galactomannan antigenemia that avoids the use of radioisotopes was devised. Three carbohydrate-rich antigenic fractions were purified from Aspergillus fumigatus 2085: a cold alkali extract (CA) from mycelium, an acetone-precipitated pyridine extract (APSK-66) from mycelium, and a methanol precipitate from culture filtrate. CA and APSK-66 were further purified by gel filtration and ion-exchange chromatography, respectively. An acid hydrolysate of CA contained only mannose and galactose, as determined by gas-liquid chromatography. Rabbit antisera were raised against conidia, mycelia, and cell walls of A. fumigatus. By indirect EIA, the best immunoglobulin G response (1/8,000) was obtained against CA in rabbits immunized intravenously with cell walls. Antigenemia was detected by indirect EIA inhibition in heat-dissociated sera of four immunosuppressed rabbits that were infected intravenously but was absent in two uninfected controls. The circulating antigen was resistant to pronase, was adsorbed onto concanavalin A, and had a molecular size of 50 to 100 kilodaltons.

New developments in the diagnosis of opportunistic fungal infection

This review considers recent developments in the diagnosis of aspergillosis, candidosis and cryptococcosis and discusses the prospects for routine application of a number of novel methods. The introduction of lysis-centrifugation and radiometric methods for blood culture has improved the diagnosis of deep candidosis, but the value of these methods for the diagnosis of aspergillosis has not yet been determined. Recent developments in serological diagnosis have included the evaluation of newly discovered antigens of Candida albicans in an attempt to distinguish colonization from significant infection. Antigen detection, an established method for the diagnosis of cryptococcosis, has also been evaluated and appears promising for the diagnosis of aspergillosis and candidosis. Another promising approach has been the use of gas-liquid chromatography to detect fungal metabolites in serum and other host fluids.

Enzyme-linked immunosorbent assay measurement of fluctuations in antibody titer and antigenemia in cancer patients with and without candidiasis

Antibody titers against purified sulfate-soluble fraction (PSSF) obtained from cytoplasmic extracts of Candida albicans were determined retrospectively over a 2-year period for 123 cancer patients by enzyme-linked immunosorbent assay. Antibody against cell wall mannan (CWM) was also measured by the hemagglutination test and the production of precipitins by a serum interacting with a yeast cell homogenate by immunodiffusion. Invasive candidiasis determined by histological evidence at autopsy was present in 10 patients. Fourfold or greater rises in anti-CWM and anti-PSSF antibodies were detected for eight of the patients with invasive candidiasis at 14 to 22 days after the onset of fever. The immunodiffusion test was positive for four patients with invasive candidiasis. For patients with no evidence of candidiasis, significant rises in anti-CWM and anti-PSSF antibodies were observed at a frequency of 20 and 10%, respectively. The concentrations of serum mannan were sequentially measured by the enzyme-linked immunosorbent assay. Antigenemia (greater than or equal to 3 ng/ml) was found in 9 of the 10 patients with invasive candidiasis and in 2 of the 4 patients with thrush, whereas the serum of 1 of the 36 patients with no evidence of candidiasis was positive for antigen. The first antigenemia antedated significant rises in antibody levels against Candida species by 6 to 23 days.

Enzymatic fluorometric method for the determination of D-arabinitol in serum by initial rate analysis

We describe a new, simple, fluorometric assay for D-arabinitol in serum. The method is based on oxidation of D-arabinitol by D-arabinitol dehydrogenase (EC 1.1.1.11), with the concomitant reduction of NAD. The initial rate of NAD reduction, which is proportional to the D-arabinitol content of serum, can be measured with a recording spectrofluorometer. Sensitivity, specificity, recovery and reproducibility experiments gave satisfactory results. The proposed method is suitable for clinical use, and may be helpful in the diagnosis of invasive candidiasis.

Antigenic variability of Candida albicans

The concepts of modern biology lead us to think that all structures are liable to continual changes. Ultrastructural and biochemical methods have been able to objectify such a dynamic in Candida albicans, an opportunistic yeast. A broad analysis of antigens is a reliable way to study the antigenic variations which concern this organism. Numerous information on somatic and metabolic antigens of C. albicans is available at the moment. Paradoxically, if one accepts studies dealing with dimorphism, very few works have shown antigenic variability of this species or investigated the mechanisms involved in such a variability. The few approaches done in this way tend to prove that it may be possible to link together the expression of particular antigens and the behavior of the yeast, particularly when it acts as a pathogen.

Identification and molecular weight characterization of antigens from Candida albicans that are recognized by human sera

Antigenic components in the cytoplasmic extract of Candida albicans were examined after fractionation by concanavalin A-Sepharose and DEAE-Sephacel ion-exchange chromatography. Fractions from the DEAE column were tested by fused rocket immunoelectrophoresis for their reactivity with antibodies in the sera of 20 patients with disseminated candidiasis. Three groups of fractions (regions A, B, and C) from the DEAE column were defined by their reactivity with these sera. Immunoblot analysis with 20 human sera identified 18 antigenic components in regions A, B, and C. Region A contained nine antigens, region B contained four antigens, and region C contained five antigens. Region A contained an antigen with an apparent molecular weight of 48,000 that was recognized by 7 of 10 sera from patients with disseminated candidiasis. Immunoprecipitation experiments with labeled proteins from region A and 51 human sera also demonstrated the presence of a major antigen whose apparent molecular weight is 48,000 to 52,000. The 48- to 52-kilodalton protein is an abundant protein in region A and is the most frequently recognized protein by antibodies in the sera of patients with disseminated candidiasis. Patients with disseminated candidiasis had significantly higher levels of antibody (immunoglobulin G) (P less than 0.001) directed against the 48- to 52-kilodalton protein than did patients with noninvasive forms of candidiasis, patients with other fungal infections, or normal, healthy persons.

Simultaneous determination of arabinitol and mannose by gas-liquid chromatography in experimental candidiasis

A method is described for the simultaneous quantitation of D-arabinitol and D-mannose in serum by gas-liquid chromatography as an aid for the diagnosis of disseminated candidiasis. Both variables were observed as per-O-acetylated aldononitrile derivatives in each chromatographic run of sera from immunosuppressed rabbits experimentally infected with Candida albicans 3181A.