Null mutants of Candida albicans for cell-wall-related genes form fragile biofilms that display an almost identical extracellular matrix proteome.

By two-dimensional gel electrophoresis (2-DE) and mass spectrometry, we have characterized the polypeptide species present in extracts obtained by 60% ethanol treatment of whole mature (48 h) biofilms formed by a reference strain (CAI4-URA3) and four Candida albicans null mutants for cell-wall-related genes (ALG5, CSA1, MNN9 and PGA10) Null mutants form fragile biofilms that appeared partially split and weakly attached to the substratum contrary to those produced by the reference strain. An almost identical, electrophoretic profile consisting of about 276 spots was visualized in all extracts examined. Proteomic analysis led to the identification of 131 polypeptides, corresponding to 86 different protein species, being the rest isoforms-83 displayed negative hydropathic indexes and 82 lack signal peptide. The majority of proteins appeared at pI between 4 and 6, and molecular mass between 10 and 94 kDa. The proteins identified belonged to the following Gene Ontology categories: 21.9% unknown molecular function, 16.2% oxidoreductase activity, 13.3% hydrolase activity and 41.8% distributed between other different GO categories. Strong defects in biofilm formation appreciated in the cell-wall mutant strains could be attributed to defects in aggregation due to abnormal cell wall formation rather than to differences in the biofilm extracellular matrix composition.

Retinal layer location of increased retinal thickness in eyes with subclinical and clinical macular edema in diabetes type 2.

PURPOSE: To identify the retinal layer predominantly affected in eyes with subclinical and clinical macular edema in diabetes type 2. METHODS: A cohort of 194 type 2 diabetic eyes/patients with mild nonproliferative diabetic retinopathy (ETDRS levels 20/35) were examined with Cirrus spectral-domain optical coherence tomography (OCT) at the baseline visit (ClinicalTrials.gov identifier: NCT01145599). Automated segmentation of the retinal layers of the eyes with subclinical and clinical macular edema was compared with a sample of 31 eyes from diabetic patients with normal OCT and an age-matched control group of 58 healthy eyes. RESULTS: From the 194 eyes in the study, 62 had subclinical macular edema and 12 had clinical macular edema. The highest increases in retinal thickness (RT) were found in the inner nuclear layer (INL; 33.6% in subclinical macular edema and 81.8% in clinical macular edema). Increases were also found in the neighboring layers. Thinning of the retina was registered in the retinal nerve fiber, ganglion cells and inner plexiform layers in the diabetic eyes without macular edema. CONCLUSIONS: The increase in RT occurring in diabetic eyes with macular edema is predominantly located in the INL but extends to neighboring retinal layers indicating that it may be due to extracellular fluid accumulation.

One-year progression of diabetic subclinical macular edema in eyes with mild nonproliferative diabetic retinopathy: location of the increase in retinal thickness.

PURPOSE: To characterize the 1-year progression of retinal thickness (RT) increase occurring in eyes with subclinical macular edema in type 2 diabetes. METHODS: Forty-eight type 2 diabetic eyes/patients with mild nonproliferative diabetic retinopathy (NPDR; levels 20 and 35 in the Early Treatment Diabetic Retinopathy Study) classified as presenting subclinical macular edema at baseline completed the 1-year follow-up period, from a sample of 194 followed in a 12-month observational and prospective study (ClinicalTrials.gov identifier: NCT01145599). Automated segmentation of the retinal layers in these eyes was performed, followed by verification and correction by a human grader. RESULTS: The highest increase in RT over the 1-year follow-up period for the 48 eyes/patients with subclinical macular edema was found in the inner nuclear layer (INL). Progression to clinical macular edema was also associated with increased thickening of other retinal layers aside from the INL. The microvascular disease activity shown by microaneurysm (MA) turnover ≥6 was associated with progression from subclinical to clinical macular edema. CONCLUSIONS: Increases in RT occurring over a period of 1 year in diabetic eyes with mild NPDR and subclinical macular edema occur mainly in the INL. The development of clinical macular edema appears to be associated with increased thickening of other retinal layers and microvascular disease activity.

Relevance of Retinal Thickness Changes in the OCT Inner and Outer Rings to Predict Progression to Clinical Macular Edema: An Attempt of Composite Grading of Macular Edema.

PURPOSE: To characterize the relevance of macular thickness changes in the inner and outer rings in the progression of macular edema in eyes/patients with diabetes type 2. METHODS: A total of 374 type 2 diabetic patients with mild nonproliferative diabetic retinopathy (ETDRS levels 20-35) were included in a 12-month prospective observational study to identify retinopathy progression. Retinal thickness analyses were performed in 194 eyes/patients using Cirrus SD- OCT and 166 eyes/patients using Spectralis SD-OCT. The DRCR.net classification of subclinical and clinical macular edema was used. A composite grading of macular edema is proposed in this study. RESULTS: A total of 317 eyes/patients completed the study. SD-OCT identified clinical macular edema in 24 eyes/patients (6.7%) and subclinical macular edema in 104 eyes/patients (28.9%) at baseline. Increased thickness of the central subfield is the best predictor for the development of clinical macular edema, with 85.7% sensitivity and 71.9% specificity (OR: 2.57, 95% CI: 0.82-7.99). However, the involvement of the inner and outer rings is a cumulative predictor of progression to clinical macular edema (OR: 8.69, 95% CI: 2.85-26.52). CONCLUSIONS: A composite OCT grading of macular edema taking into account the retinal thickness changes in the inner and outer macular rings offers a simple way to characterize macular edema, with added clinical value.

Cell aggregations in yeasts and their applications.

Yeasts can display four types of cellular aggregation: sexual, flocculation, biofilm formation, and filamentous growth. These cell aggregations arise, in some yeast strains, as a response to environmental or physiological changes. Sexual aggregation is part of the yeast mating process, representing the first step of meiotic recombination. The flocculation phenomenon is a calcium-dependent asexual reversible cellular aggregation that allows the yeast to withstand adverse conditions. Biofilm formation consists of multicellular aggregates that adhere to solid surfaces and are embedded in a protein matrix; this gives the yeast strain either the ability to colonize new environments or to survive harsh environmental conditions. Finally, the filamentous growth is the ability of some yeast strains to grow in filament forms. Filamentous growth can be attained by two different means, with the formation of either hyphae or pseudohyphae. Both hyphae and pseudohyphae arise when the yeast strain is under nutrient starvation conditions and they represent a means for the microbial strain to spread over a wide area to survey for food sources, without increasing its biomass. Additionally, this filamentous growth is also responsible for the invasive growth of some yeast.

Some biological features of Candida albicans mutants for genes coding fungal proteins containing the CFEM domain.

Several biological features of Candida albicans genes (PGA10, RBT5 and CSA1) coding for putative polypeptide species belonging to a subset of fungal proteins containing an eight-cysteine domain referred as common in several fungal extracellular membrane (CFEM) are described. The deletion of these genes resulted in a cascade of pleiotropic effects. Thus, mutant strains exhibited higher cell surface hydrophobicity levels and an increased ability to bind to inert or biological substrates. Confocal scanning laser microscopy using concanavalin A-Alexafluor 488 (which binds to mannose and glucose residues) and FUN-1 (a cytoplasmic fluorescent probe for cell viability) dyes showed that mutant strains formed thinner and more fragile biofilms. These apparently contained lower quantities of extracellular matrix material and less metabolically active cells than their parental strain counterpart, although the relative percentage of mycelial forms was similar in all cases. The cell surface of C. albicans strains harbouring deletions for genes coding CFEM-domain proteins appeared to be severely altered according to atomic force microscopy observations. Assessment of the relative gene expression within individual C. albicans cells revealed that CFEM-coding genes were upregulated in mycelium, although these genes were shown not to affect virulence in animal models. Overall, this study has demonstrated that CFEM domain protein-encoding genes are pleiotropic, influencing cell surface characteristics and biofilm formation.

Pga26 mediates filamentation and biofilm formation and is required for virulence in Candida albicans.

The Candida albicans gene PGA26 encodes a small cell wall protein and is upregulated during de novo wall synthesis in protoplasts. Disruption of PGA26 caused hypersensitivity to cell wall-perturbing compounds (Calcofluor white and Congo red) and to zymolyase, which degrades the cell wall ß-1,3-glucan network. However, susceptibility to caspofungin, an inhibitor of ß-1,3-glucan synthesis, was decreased. In addition, pga26Δ mutants show increased susceptibility to antifungals (fluconazol, posaconazol or amphotericin B) that target the plasma membrane and have altered sensitivities to environmental (heat, osmotic and oxidative) stresses. Except for a threefold increase in ß-1,6-glucan and a slightly widened outer mannoprotein layer, the cell wall composition and structure was largely unaltered. Therefore, Pga26 is important for proper cell wall integrity, but does not seem to be directly involved in the synthesis of cell wall components. Deletion of PGA26 further leads to hyperfilamentation, increased biofilm formation and reduced virulence in a mouse model of disseminated candidiasis. We propose that deletion of PGA26 may cause an imbalance in the morphological switching ability of Candida, leading to attenuated dissemination and infection.

Candida albicans ABG1 gene is involved in endocytosis.

The human fungal pathogen Candida albicans undergoes reversible morphogenetic transitions between yeast, hyphal and pseudohyphal forms. The fungal vacuole actively participates in differentiation processes and plays a key role supporting hyphal growth. The ABG1 gene of C. albicans encodes an essential protein located in the vacuolar membranes of both yeast and hyphae. Using fluorescence microscopy of a green fluorescent protein-tagged version of Abg1p, a fraction of the protein was detected in hyphal tips, not associated with vacuolar membranes. Live cell imaging of emerging germ tubes showed that Abg1p migrated to the polarized growth site and colocalized with endocytic vesicles. Phenotypic analysis of a methionine-regulated conditional mutant confirmed that Abg1p is involved in endocytosis.

An Automated System for the Detection and Classification of Retinal Changes Due to Red Lesions in Longitudinal Fundus Images.

People with diabetes mellitus need annual screening to check for the development of diabetic retinopathy (DR). Tracking small retinal changes due to early diabetic retinopathy lesions in longitudinal fundus image sets is challenging due to intra- and intervisit variability in illumination and image quality, the required high registration accuracy, and the subtle appearance of retinal lesions compared to other retinal features. This paper presents a robust and flexible approach for automated detection of longitudinal retinal changes due to small red lesions by exploiting normalized fundus images that significantly reduce illumination variations and improve the contrast of small retinal features. To detect spatio-temporal retinal changes, the absolute difference between the extremes of the multiscale blobness responses of fundus images from two time points is proposed as a simple and effective blobness measure. DR related changes are then identified based on several intensity and shape features by a support vector machine classifier. The proposed approach was evaluated in the context of a regular diabetic retinopathy screening program involving subjects ranging from healthy (no retinal lesion) to moderate (with clinically relevant retinal lesions) DR levels. Evaluation shows that the system is able to detect retinal changes due to small red lesions with a sensitivity of at an average false positive rate of 1 and 2.5 lesions per eye on small and large fields-of-view of the retina, respectively.

Accuracy assessment of intra- and intervisit fundus image registration for diabetic retinopathy screening.

PURPOSE: We evaluated the accuracy of a recently developed fundus image registration method (Weighted Vasculature Registration, or WeVaR) and compared it to two top-ranked state-of-the-art commercial fundus mosaicking programs (i2k Retina, DualAlign LLC, and Merge Eye Care PACS, formerly named OIS AutoMontage) in the context of diabetic retinopathy (DR) screening. METHODS: Fundus images of 70 diabetic patients who visited the Rotterdam Eye Hospital in 2012 and 2013 for a DR screening program were registered by all three programs. The registration results were used to produce mosaics from fundus photos that were normalized for luminance and contrast to improve the visibility of small details. These mosaics subsequently were evaluated and ranked by two expert graders to assess the registration accuracy. RESULTS: Merge Eye Care PACS had high registration failure rates compared to WeVaR and i2k Retina (P = 8 × 10(-6) and P = 0.002, respectively). WeVaR showed significantly higher registration accuracy than i2k Retina in intravisit (P ≤ 0.0036) and intervisit (P ≤ 0.0002) mosaics. Therefore, fundus mosaics processed by WeVaR were more likely to have a higher score (odds ratio [OR] = 2.5, P = 10(-5) for intravisit and OR = 2.2, P = 0.006 for intervisit mosaics). WeVaR was preferred more often by the graders than i2k Retina (OR = 6.1, P = 7 × 10(-6)). CONCLUSIONS: WeVaR produced intra- and intervisit fundus mosaics with higher registration accuracy than Merge Eye Care PACS and i2k Retina. Merge Eye Care PACS had higher registration failures than the other two programs. Highly accurate registration methods, such as WeVaR, may potentially be used for more efficient human grading and in computer-aided screening systems for detecting DR progression.

Characterization of Retinal Disease Progression in a 1-Year Longitudinal Study of Eyes With Mild Nonproliferative Retinopathy in Diabetes Type 2.

PURPOSE: To identify eyes of patients with diabetes type 2 that show progression of retinal disease within a 1-year period using noninvasive techniques. METHODS: Three hundred seventy-four type 2 diabetic patients with mild nonproliferative diabetic retinopathy (Early Treatment Diabetic Retinopathy Study [ETDRS] level 20 or 35) were included in a 12-month prospective observational study to identify retinopathy progression. Four visits were scheduled at 0, 3, 6, and 12 months. Microaneurysm (MA) activity using the RetmarkerDR and retinal thickness using spectral-domain optical coherence tomography (SD-OCT) were assessed by a central reading center at all visits and ETDRS severity level in the first and last visits. RESULTS: Three hundred thirty-one eyes/patients completed the study. Microaneurysm formation rate greater than or equal to 2 was present in 68.1% of the eyes and MA turnover greater than or equal to 6 in 54.0% at month 6. Higher MA turnover values were registered in eyes that showed progression in ETDRS severity level (P < 0.03). There were also significant correlations between increased microaneurysm activity and increases in retinal thickness. Spectral-domain OCT identified clinical macular edema in 24 eyes/patients (6.7%) and subclinical macular edema in 104 eyes/patients (28.9%) at baseline. Progression of retinal thickening was registered in eyes that had either subclinical or clinical macular edema at baseline. CONCLUSIONS: Changes in MA activity measured with RetmarkerDR and in central retinal thickness in eyes with mild nonproliferative diabetic retinopathy and diabetes type 2 are able to identify eyes at risk of progression. These eyes/patients should be selected for inclusion in future clinical trials of drugs targeted to prevent diabetic retinopathy progression to vision-threatening complications. (ClinicalTrials.gov number, NCT01145599.)

The C-terminal antibody binding domain of Candida albicans mp58 represents a protective epitope during candidiasis.

The 58-kDa surface mannoprotein of Candida albicans (mp58) elicits strong antibody responses during infection. Epitope mapping with sera from patients with candidiasis and control individuals indicated the presence of multiple IgG-reactive continuous epitopes on the protein, expanding both the amino- and carboxy-terminal domains and several internal regions. These immunoreactive regions were similar to the ones previously identified using sera from immunized animals. Two of the epitopic regions (including the C-terminal domain) showed increased reactivity with antibodies present in sera from patients with candidiasis as compared to control individuals. Patients who survived the infection displayed increased antibody reactivity towards the C-terminal epitope as compared to those succumbing to candidiasis. A monoclonal antibody directed towards this epitopic region conferred protection in serum therapy experiments in a murine model of hematogenously disseminated candidiasis. Together, these observations indicate the carboxy-terminal antibody binding domain of C. albicans mp58 represents a protective epitope during candidiasis.

Antibody response to Candida albicans cell wall antigens.

The cell wall of Candida albicans is not only the structure where many essential biological functions reside but is also a significant source of candidal antigens. The major cell wall components that elicit a response from the host immune system are proteins and glycoproteins, the latter being predominantly mannoproteins. Both carbohydrate and protein moieties are able to trigger immune responses. Proteins and glycoproteins exposed at the most external layers of the wall structure are involved in several types of interactions of fungal cells with the exocellular environment. Thus, coating of fungal cells with host antibodies has the potential to profoundly influence the host-parasite interaction by affecting antibody-mediated functions such as opsonin-enhanced phagocytosis and blocking the binding activity of fungal adhesins to host ligands. In this review we examine various members of the protein and glycoprotein fraction of the C. albicans cell wall that elicit an antibody response in vivo. Some of the studies demonstrate that certain cell wall antigens and anti-cell wall antibodies may be the basis for developing specific and sensitive serologic tests for the diagnosis of candidiasis, particularly the disseminated form. In addition, recent studies have focused on the potential of antibodies against the cell wall protein determinants in protecting the host against infection. Hence, a better understanding of the humoral response triggered by the cell wall antigens of C. albicans may provide the basis for the development of (i) effective procedures for the serodiagnosis of disseminated candidiasis, and (ii) novel prophylactic (vaccination) and therapeutic strategies to control this type of infections.

A clinical exploratory study with itolizumab, an anti-CD6 monoclonal antibody, in patients with rheumatoid arthritis.

T cells are involved in the pathogenesis of rheumatoid arthritis (RA). CD6 is a co-stimulatory molecule, predominantly expressed on lymphocytes, that has been linked to autoreactive responses. The purpose of this study was to evaluate the safety, immunogenicity and preliminary efficacy of itolizumab, a humanized anti-CD6 monoclonal antibody, in patients with active rheumatoid arthritis. Fifteen patients were enrolled in a phase I, open-label, dose-finding study. Five cohorts of patients received a weekly antibody monotherapy with a dose-range from 0.1 to 0.8 mg/kg. Itolizumab showed a good safety profile, with no severe or serious adverse events reported so far. No signs or symptoms associated with immunosuppression were observed in the study. Objective clinical responses were achieved in more than 80% of patients after treatment completion, and these responses tend to be sustained afterwards. This clinical study constitutes the first evidence of the safety and positive clinical effect of a monotherapy using an anti-CD6 antibody in patients with rheumatoid arthritis.

Biofilm formation by Candida albicans mutants for genes coding fungal proteins exhibiting the eight-cysteine-containing CFEM domain.

Several features and functions of a Candida albicans gene, PGA10 (also designated as RBT51), coding for a putative polypeptide species belonging to a subset of fungal proteins containing an eight-cysteine domain referred as CFEM (Common in several Fungal Extracellular Membrane proteins), are described. The ORF of the gene (ORF19.5674) encoded a protein of 250 amino acids, with a predicted molecular mass of 25.17 kDa. The product of the PGA10 gene also exhibited some features reminiscent of a class II-type hydrophobin. Deletion of PGA10 resulted in a cascade of pleiotropic effects, mostly affecting cell-surface-related properties. Thus, the null pga10Delta mutant displayed an increased sensitivity to cell-wall-perturbing agents and formed fragile biofilms that appeared partially split and weakly attached to the substratum. The biofilm-forming ability of several C. albicans mutants with single, double and triple deletions of genes encoding other protein species also containing the CFEM domain (RBT5 and WAP1/CSA1) was determined. These mutants also exhibited an abnormal ability to form biofilms. Overall, the evidence presented here suggests that fungal proteins containing the CFEM domain (Pga10p/Rbt51p, Rbt5p and Wap1p/Csa1p) may play a key role in the formation, development and/or maintenance of the biofilm structure in C. albicans.

Rapid PCR-based test for identifying Candida albicans by using primers derived from the pH-regulated KER1 gene.

A PCR-based method in combination with a simple, reliable and inexpensive DNA extraction procedure for rapid detection of Candida albicans clinical isolates is described here. The extraction protocol is based on a combination of chemical (NaOH and detergents) and physical (boiling) treatments, thus avoiding many of the problems inherent in the currently available DNA extraction protocols (basically the use of expensive and/or toxic chemical reagents), and may be useful for daily clinical routine. The PCR-based system described here uses a single pair of primers (SC1F and SC1R) deduced from the C. albicans-specific KER1 gene sequence. These primers amplify a 670-bp fragment of the KER1 gene. All the clinical C. albicans isolates generated the expected 670-bp amplicon. Other non-albicans Candida species, including the azole-resistant C. krusei and C. glabrata, and the very closely related C. dubliniensis, failed to amplify any DNA fragment. The PCR results reported here suggest that amplification with SC1F and SC1R primers is species specific and, consequently, may be useful for specifically identifying C. albicans strains.

ABG1, a novel and essential Candida albicans gene encoding a vacuolar protein involved in cytokinesis and hyphal branching.

Immunoscreening of a Candida albicans expression library resulted in the isolation of a novel gene encoding a 32.9-kDa polypeptide (288 amino acids), with 27.7% homology to the product of Saccharomyces cerevisiae YGR106c, a putative vacuolar protein. Heterozygous mutants in this gene displayed an altered budding growth pattern, characterized by the formation of chains of buds, decreasingly in size towards the apex, without separation of the daughter buds. Consequently, this gene was designated ABG1. A conditional mutant for ABG1 with the remaining allele under the control of the MET3 promoter did not grow in the presence of methionine and cysteine, demonstrating that ABG1 was essential for viability. Western analysis revealed the presence of a major 32.9-kDa band, mainly in a particulate fraction (P40) enriched in vacuoles, and tagging with green fluorescent protein confirmed that Abg1p localized to the vacuole. Vacuole inheritance has been linked to the regulation of branching frequency in C. albicans. Under repressing conditions, the conditional mutant had an increased frequency of branching under hyphal inducing conditions and an altered sensitivity to substances that interfered with cell wall assembly. Repression of ABG1 in the conditional mutant strain caused disturbance of normal size and number of vacuoles both in yeast and mycelial cells and also in the asymmetric vacuole inheritance associated with the characteristic pattern of germ tubes and branching in C. albicans. These observations indicate that ABG1 plays a key role in vacuole biogenesis, cytokinesis, and hyphal branching.

The Candida albicans pH-regulated KER1 gene encodes a lysine/glutamic-acid-rich plasma-membrane protein that is involved in cell aggregation.

Immunoscreening of a Candida albicans cDNA library with a polyclonal germ-tube-specific antibody (pAb anti-gt) resulted in the isolation of a gene encoding a lysine/glutamic-acid-rich protein, which was consequently designated KER1. The nucleotide and deduced amino acid sequences of this gene displayed no significant homology with any other known sequence. KER1 encodes a 134 kDa lysine (14.5%)/glutamic acid (16.7%) protein (Ker1p) that contains two potential transmembrane segments. KER1 was expressed in a pH-conditional manner, with maximal expression at alkaline pH and lower expression at pH 4.0, and was regulated by RIM101. A Deltaker1/Deltaker1 null mutant grew normally but was hyperflocculant under germ-tube-inducing conditions, yet this behaviour was also observed in stationary-phase cells grown under other incubation conditions. Western blotting analysis of different subcellular fractions, using as a probe a monospecific polyclonal antibody raised against a highly antigenic domain of Ker1p (pAb anti-Ker1p), revealed the presence of a 134 kDa band in the purified plasma-membrane fraction from the wild-type strain that was absent in the homologous preparation from Deltaker1/Deltaker1 mutant. The pattern of cell-wall protein and mannoprotein species released by digestion with beta-glucanases, reactive towards pAbs anti-gt and anti-Ker1p, as well as against concanavalin A, was also different in the Deltaker1/Deltaker1 mutant. Mutant strains also displayed an increased cell-surface hydrophobicity and sensitivity to Congo red and Calcofluor white. Overall, these findings indicate that the mutant strain was affected in cell-wall composition and/or structure. The fact that the ker1 mutant had attenuated virulence in systemic mouse infections suggests that this surface protein is also important in host-fungus interactions.