Evaluation of a new laboratory test measuring plasma (1-->3)-beta-D-glucan in the diagnosis of Candida deep mycosis: comparison with a serologic test

The Screening Performance of Serum 1,3-Beta-D-Glucan in Patients with Invasive Fungal Diseases: A Meta-Analysis of Prospective Cohort Studies

The serum 1,3-beta-D-glucan (BG) assay aids in the early diagnosis of invasive fungal diseases (IFDs) and has been approved for their diagnosis. However, reports on the screening performance of BG are scarce. We performed a meta-analysis of data extracted from only prospective cohort studies to evaluate the screening performance of the BG assay in the diagnosis of IFDs. We specifically searched 4 databases (the PubMed, Web of Science, Elsevier, and Cochrane Collaboration databases) according to EORTC-MSG criteria. A total of 1068 patients in 11 studies were analyzed. Deeks’ funnel plot asymmetry test suggested a low likelihood of publication bias for the included studies (p = 0.055). The pooled sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, diagnostic odds ratio, and area under the summary receiver operating characteristic curve, with 95% confidence intervals, were 0.75(0.63,0.84), 0.87(0.81,0.92), 5.85(3.96,8.63), 0.30(0.20,0.45), 19.53(11.16,34.18), and 0.89(0.86,0.91), respectively. The findings of this meta-analysis suggest that the BG assay is a useful screening tool with high sensitivity and specificity for discriminating between patients with and without IFDs. In clinical practice, BG assay results should be evaluated together with clinical and microbiological findings.

Soluble glucan is internalized and trafficked to the Golgi apparatus in macrophages via a clathrin-mediated, lipid raft-regulated mechanism

Glucans are natural product carbohydrates that stimulate immunity. Glucans are internalized by the pattern recognition receptor, Dectin-1. Glucans were thought to be trafficked to phagolysosomes, but this is unproven. We examined the internalization and trafficking of soluble glucans in macrophages. Incubation of macrophages with glucan resulted in internalization of Dectin-1 and glucan. Inhibition of clathrin blocked internalization of the Dectin-1/glucan complex. Lipid raft depletion resulted in decreased Dectin levels and glucan uptake. Once internalized, glucans colocalized with early endosomes at 0 to 15 min, with the Golgi apparatus at 15 min to 24 h, and with Dectin-1 immediately (0 h) and again later (15 min-24 h). Glucans did not colocalize with lysosomes at any time interval examined. We conclude that the internalization of Dectin-1/glucan complexes in macrophages is mediated by clathrin and negatively regulated by lipid rafts and/or caveolin-1. Upon internalization, soluble glucans are trafficked via endosomes to the Golgi apparatus, not lysosomes.

Leukocyte Dectin-1 expression is differentially regulated in fungal versus polymicrobial sepsis

OBJECTIVE

To examine peripheral leukocyte Dectin-1 regulation in clinically relevant models of fungal and polymicrobial sepsis.

DESIGN

Prospective animal study.

SETTING

University medical school research laboratory.

SUBJECTS

Age, weight, and sex matched ICR/HSD mice.

INTERVENTIONS

Mice were infected with Candida albicans (1 x 10, intravenously) or were subjected to cecal ligation and puncture to induce polymicrobial sepsis.

MEASUREMENTS

Blood, spleen, and peritoneal exudate were harvested and leukocytes were isolated. Leukocytes were evaluated for membrane-associated Dectin-1 expression and cell phenotype by flow cytometry.

MAIN RESULTS

In C. albicans infection, Dectin-1-positive blood and splenic leukocytes were increased from 23.5% to 58.9% over the course of infection. The increased percentage of Dectin-1-expressing cells was primarily attributable to neutrophilia. However, the amount of Dectin-1 expressed by blood and splenic neutrophils in C. albicans-infected mice was decreased by a range of 49.0% to 53.3%. C. albicans infection also resulted in an infiltration of Dectin-1-positive macrophages and neutrophils into the kidney. In contrast, polymicrobial sepsis decreased blood leukocyte Dectin-1-expressing cells by up to 51.4%. This reduction was due to a decrease in Dectin-1-positive neutrophils in the periphery. However, the percentage of Dectin-1-expressing cells in the peritoneal cavity increased by 774% with cecal ligation and puncture. Treatment of isolated neutrophils with three soluble glucans, mannan, lipopolysaccharide, or a variety of cytokines revealed that glucans, alone or in combination, were the only treatment that resulted in a decrease in Dectin-1-positive neutrophils.

CONCLUSIONS

We conclude that peripheral leukocyte Dectin-1 expression is differentially regulated in fungal vs. polymicrobial sepsis. These data demonstrate that leukocyte Dectin-1 levels are modulated in response to infections of fungal and nonfungal origin.

Serum glucan levels are not specific for presence of fungal infections in intensive care unit patients

Fungal infections in the critically ill patient are difficult to diagnose and are associated with a high mortality rate. A major obstacle to managing fungal infection is the lack of a reliable clinical assay that will rapidly identify patients with fungal sepsis. Glucans are polymers of glucose that are found in the cell wall of fungi and certain bacteria. Glucans are also released from the fungal cell wall into the extracellular milieu. Several studies have reported that detection of fungal glucan in serum or plasma is useful in the diagnosis of mycoses. However, recent studies have questioned the clinical utility of this assay. In this study, we examined serum glucan levels in intensive care unit (ICU) patients and attempt to correlate serum glucan levels with the presence of fungal infection. Following attainment of informed consent, serum was harvested from 46 ICU patients with confirmed fungal infections, confirmed bacterial infections, or no evidence of infection. Sera from eight healthy volunteers served as control. Serum glucan was assayed with a glucan-specific Limulus assay. Serum glucan levels were increased (69.6 +/- 17 pg/ml; P < 0.001) in ICU patients versus the normal (11.5 +/- 1.3 pg/ml) and noninfected ICU (27.4 +/- 17 pg/ml) controls. However, serum glucan levels were not different in patients with confirmed fungal infections versus those with confirmed bacterial infections. Thus, serum glucan levels did not show a correlation with the presence of fungal infections and do not appear to be specific for fungal infections. However, the assay may be useful as a negative predictor of infection.

Structural characterization of (1-->3)-beta-D-glucans isolated from blastospore and hyphal forms of Candida albicans

Glucans are (1-->3)-beta-linked linear and branched polymers containing anhydroglucose repeat units. They comprise a major portion of the cell wall of saprophytic and pathogenic fungi. Glucans activate a wide range of innate immune responses. They are also released from the fungal cell wall as exopolymers into the blood of patients with fungal infections. Extensive studies have been done on glucans isolated from saprophytic fungi, such as Saccharomyces cerevisiae; however, much less is known about the glucans produced by the polymorphic fungal pathogen Candida albicans. We have undertaken an extensive structural characterization and comparison of glucans isolated from C. albicans blastospores and hyphae using high-resolution, solution-state proton nuclear magnetic resonance spectroscopy (NMR). In addition, we developed a simple and straightforward method for the production of Candida hyphae that resulted in gram quantities of hyphal mass. Also, we compared and contrasted the Candida glucans isolated by two different protocols with those isolated from S. cerevisiae. Isolation protocols provide high purity glucans with source-based structural differences. Structural details provided by this NMR analysis included the degree of polymerization, molecular weight, degree and type of branching, and structural composition. We observed that Candida glucans, derived from blastospores or hyphae, are different compared to those isolated from S. cerevisiae with regard to side-chain branching along the backbone and at the reducing terminus. These structural details are an important prerequisite for biomedical studies on the interaction of isolated fungal cell wall glucans with the innate immune system.

Human Vascular Endothelial Cells Express Pattern Recognition Receptors for Fungal Glucans Which Stimulates Nuclear Factor κB Activation and Interleukin 8 Production

Fungal cell wall glucans nonspecifically stimulate various aspects of innate immunity via interaction with membrane receptors on macrophages, neutrophils, and natural killer cells. We investigated the binding of water-soluble glucans in primary cultures of normal human coronary or dermal vascular endothelial cells (VECs). Membranes from VECs exhibited saturable binding. Competition studies demonstrated the presence of at least two glucan binding sites on VECs. Glucan phosphate competed for all binding sites with a KD of 3.7 μm for coronary VECs and 11 μm for dermal VECs, respectively. Laminarin, a low molecular weight glucan, competed for 47 to 51 per cent of binding ( KD = 2.8–2.9 μm), indicating the presence of at least two binding sites. Glucan (1 μg/mL) stimulated VEC nuclear factor κB nuclear binding activity and Interleukin 8 expression—but not that of vascular endothelial growth factor—in a time-dependent manner. This is the first report of pattern recognition receptors for glucan on human VECs. It also provides the first evidence that glucans can directly modulate the functional activity of VECs by stimulating cytokine gene. These results provide new insights into the mechanisms by which the host recognizes and responds to fungal cell wall products and suggests that the response to glucans may not be confined to leukocytes.

Normal human fibroblasts express pattern recognition receptors for fungal (1-->3)-beta-D-glucans

Fungal cell wall glucans nonspecifically stimulate various aspects of innate immunity. Glucans are thought to mediate their effects via interaction with membrane receptors on macrophages, neutrophils, and NK cells. There have been no reports of glucan receptors on nonimmune cells. We investigated the binding of a water-soluble glucan in primary cultures of normal human dermal fibroblasts (NHDF). Membranes from NHDF exhibited saturable binding with an apparent dissociation constant (K(D)) of 8.9 +/- 1.9 microg of protein per ml and a maximum binding of 100 +/- 8 resonance units. Competition studies demonstrated the presence of at least two glucan binding sites on NHDF. Glucan phosphate competed for all binding sites, with a K(D) of 5.6 microM (95% confidence interval [CI], 3.0 to 11 microM), while laminarin competed for 69% +/- 6% of binding sites, with a K(D) of 3.7 microM (95% CI, 1.9 to 7.3 microM). Glucan (1 microg/ml) stimulated fibroblast NF-kappaB nuclear binding activity and interleukin 6 (IL-6) gene expression in a time-dependent manner. NF-kappaB was activated at 4, 8, and 12 h, while IL-6 mRNA levels were increased by 48% at 8 h. This is the first report of pattern recognition receptors for glucan on human fibroblasts and the first demonstration of glucan binding sites on cells other than leukocytes. It also provides the first evidence that glucans can directly modulate the functional activity of NHDF. These results provide new insights into the mechanisms by which the host recognizes and responds to fungal (1-->3)-beta-D-glucans and suggests that the response to glucans may not be confined to cells of the immune system.

Rapid, sensitive and simple detection of candida deep mycosis by amplification of 18S ribosomal RNA gene; comparison with assay of serum beta-D-glucan level in clinical samples

We evaluated the clinical usefulness of a polymerase chain reaction (PCR) assay amplifying the 18S ribosomal RNA gene of fungi for the diagnosis of deep candidiasis, compared with that of the beta-glucan test or Cand-Tec test. Thirty critically ill patients who had received prolonged care with intravenous hyperalimentation and endotracheal intubation in the intensive care unit and were suspected of having deep fungal infections were examined. Twenty-one were fungi positive in the PCR assay (70%). Among 24 samples in which the PCR assay, beta-glucan test and Cand-Tec test were performed simultaneously, 75% of the samples (18/24) were fungi positive in the PCR assay, whereas only 54% (13/24) had positive reactions in the beta-glucan test and 21% (5/24) in the Cand-Tec test. The results of the Cand-Tec test showed no relationship with those of the PCR or beta-glucan test. The lower limit of detection in the PCR assay was 4-5 CFU/ml of C. albicans in blood. No fungal organism was amplified from the serum of 20 healthy individuals. The results of the PCR assay and beta-glucan test showed a significant correlation in this study, but the PCR assay proved to be more sensitive than the beta-glucan test (p < 0.05), and to be more useful for the clinical diagnosis and monitoring of deep Candidiasis.