Molecular mimicry in Candida albicans. Role of an integrin analogue in adhesion of the yeast to human endothelium

A new perspective in sepsis treatment: could RGD-dependent integrins be novel targets?

Sepsis is a life-threatening condition caused by the response of the body to an infection, and has recently been regarded as a global health priority because of the lack of effective treatments available. Vascular endothelial cells have a crucial role in sepsis and are believed to be a major target of pathogens during the early stages of infection. Accumulating evidence suggests that common sepsis pathogens, including bacteria, fungi, and viruses, all contain a critical integrin recognition motif, Arg-Gly-Asp (RGD), in their major cell wall-exposed proteins that might act as ligands to crosslink to vascular endothelial cells, triggering systemic dysregulation resulting in sepsis. In this review, we discuss the potential of anti-integrin therapy in the treatment of sepsis and septic shock.

Mechanisms of Pathogenic Candida Species to Evade the Host Complement Attack

Candida species are common colonizers of the human skin, vagina, and the gut. As human commensals, Candida species do not cause any notable damage in healthy individuals; however, in certain conditions they can initiate a wide range of diseases such as chronic disseminated candidiasis, endocarditis, vaginitis, meningitis, and endophthalmitis. The incidence of Candida caused infections has increased worldwide, with mortality rates exceeding 70% in certain patient populations. C. albicans, C. glabrata, C. tropicalis, C. parapsilosis, and C. krusei are responsible for more than 90% of Candida-related infections. Interestingly, the host immune response against these closely related fungi varies. As part of the innate immune system, complement proteins play a crucial role in host defense, protecting the host by lysing pathogens or by increasing their phagocytosis by phagocytes through opsonization. This review summarizes interactions of host complement proteins with pathogenic Candida species, including C. albicans and non-albicans Candida species such as C. parapsilosis. We will also highlight the various ways of complement activation, describe the antifungal effects of complement cascades and explore the mechanisms adopted by members of pathogenic Candida species for evading complement attack.

Utilization of complement receptors in immune cell-microbe interaction

The complement system is a major humoral component of immunity and is essential for the fast elimination of pathogens invading the body. In addition to its indispensable role in innate immunity, the complement system is also involved in pathogen clearance during the effector phase of adaptive immunity. The fastest way of killing the invader is lysis by the membrane attack complex, which is formed by the terminal components of the complement cascade. Not all pathogens are lysed however and, if opsonized by a variety of molecules, they undergo phagocytosis and disposal inside immune cells. The most important complement-derived opsonins are C1q, the first component of the classical pathway, MBL, the initiator of the lectin pathway and C3-derived activation fragments, including C3b, iC3b and C3d, which all serve as ligands for their corresponding receptors. In this review, we discuss how complement receptors are utilized by various immune cells to tackle invading microbes, or by pathogens to evade host response.

Body site-dependent variations of microbiota in pancreatic cancer pathophysiology

Lack of specific symptoms and reliable biomarkers, along with aggressive nature and resistance to therapies makes pancreatic cancer (PC) one of the leading causes of death from cancer worldwide. The search for new diagnostic, prognostic, predictive, and therapeutic tools that could improve clinical outcomes of patients has led, in recent years, to the investigation of potential roles for the microbiota in the pathogenesis of this disease. The human microbiota encompasses trillions of microorganisms residing within several body tissues and organs, where they provide beneficial functions for host homeostasis and health. Derangements of the microbial ecology in different anatomic districts have been described in PC, as in many other diseases, both in patients and in animal models. In detail, infection from the gastric pathogen Helicobacter pylori and changes in composition and diversity of oral, intestinal, and pancreatic microbiota have been found to associate with PC. Future research should assess how to potentially exploit such differences in microbiota composition as diagnostic, prognostic, or predictive biomarkers, and as targets for therapeutic interventions, in the hope of improving the dismal prognosis of this insidious cancer.

High glucose-mediated overexpression of ICAM-1 in human vaginal epithelial cells increases adhesion of Candida albicans

To investigate the involvement of ICAM-1 in the adhesion of Candida to the genitourinary epithelial cells in high glucose, we examined the adhesion of Candida albicans or Candida glabrata to human vaginal epithelial cells (VK2/E6E7) or human vulvovaginal epidermal cells (A431). These cells were cultured in 100, 500 or 3000 mg/dL glucose for three days and inoculated with Candida for 60 minutes. Followed by, adhering of Candida to the cells, which were counted. While the adhesion of Candida albicans to VK2/E6E7 significantly increased in the high glucose, A431 did not. We next examined the expression of ICAM-1 as a ligand on the epithelial cells. ICAM-1 expression was increased in VK2/E6E7 cultured in the high glucose; however, the expression level in A431 was not high compared with VK2/E6E7. This data suggested that ICAM-1 functions as one of ligands in the adhesion of Candida albicans to the vaginal epithelial cells in a high glucose environment. Impact statement What is already known on the subject: Candida's complement receptor is involved in the adhesion to epithelial cells. The expression of this receptor has been reported to increase as glucose concentration increases. This is considered as a contributing factor to the high risk for vulvovaginal candidiasis (VVC) in diabetes. On the host side, diabetic patients have a factor that facilitates adhesion of Candida to epithelial cells. This factor has been unknown until recently. What the results of this study add: In this study, we used a vaginal epithelial cell line and showed that the adhesion of C. albicans to cells increased at higher glucose concentrations. At the same time, ICAM-1 expression of cells also increased. Thereby, it is suggested that the expression of ICAM-1 in vaginal epithelial cells is increased by glucose such as urinary sugar in diabetic patients and is a condition for facilitating adhesion of Candida. What the implications are of these findings for clinical practice and/or further research: We expect not only host immune dysfunction but also alteration in epithelial cells will be focussed on as a cause of VVC in diabetic patients.

Cancer risk in patients with candidiasis: a nationwide population-based cohort study

BACKGROUND

Candidiasis and certain types of cancer are related to immunocompromised status. This study aimed to evaluate whether Candida infection (CI) is associated with subsequent cancer risk in Taiwan.

METHODS

Data from the National Health Insurance system of Taiwan were used to evaluate the association between CI and cancer risk. The CI cohort comprised 34,829 patients. Each patient was randomly frequency matched with one person from the general population without CI on the basis of age, sex, year of index date of CI diagnosis, and other characteristics to generate the control group. We used Cox's proportional hazard regression analysis to estimate the effects of CI on subsequent cancer risk.

RESULTS

Compared with the control group, patients with CI had a significantly higher risk of overall cancer (adjusted hazard ratio = 1.19, 95% confidence interval = 1.09-1.30). For subsite analysis, the risks of hematologic malignancy and head and neck, pancreatic, skin, and thyroid cancers were significantly higher in the CI group. Stratified analyses by sex, age, and follow-up time revealed different patterns.

CONCLUSION

Our study suggested that CI can significantly increase overall and some individual cancer risks, which is partially compatible with previous findings.

Candida albicans and cancer: Can this yeast induce cancer development or progression?

There is currently increasing concern about the relation between microbial infections and cancer. More and more studies support the view that there is an association, above all, when the causal agents are bacteria or viruses. This review adds to this, summarizing evidence that the opportunistic fungus Candida albicans increases the risk of carcinogenesis and metastasis. Until recent years, Candida spp. had fundamentally been linked to cancerous processes as it is an opportunist pathogen that takes advantage of the immunosuppressed state of patients particularly due to chemotherapy. In contrast, the most recent findings demonstrate that C. albicans is capable of promoting cancer by several mechanisms, as described in the review: production of carcinogenic byproducts, triggering of inflammation, induction of Th17 response and molecular mimicry. We underline the need not only to control this type of infection during cancer treatment, especially given the major role of this yeast species in nosocomial infections, but also to find new therapeutic approaches to avoid the pro-tumor effect of this fungal species.

Structure and function of a fungal adhesin that binds heparin and mimics thrombospondin-1 by blocking T cell activation and effector function

Blastomyces adhesin-1 (BAD-1) is a 120-kD surface protein on B. dermatitidis yeast. We show here that BAD-1 contains 41 tandem repeats and that deleting even half of them impairs fungal pathogenicity. According to NMR, the repeats form tightly folded 17-amino acid loops constrained by a disulfide bond linking conserved cysteines. Each loop contains a highly conserved WxxWxxW motif found in thrombospondin-1 (TSP-1) type 1 heparin-binding repeats. BAD-1 binds heparin specifically and saturably, and is competitively inhibited by soluble heparin, but not related glycosaminoglycans. According to SPR analysis, the affinity of BAD-1 for heparin is 33 nM±14 nM. Putative heparin-binding motifs are found both at the N-terminus and within each tandem repeat loop. Like TSP-1, BAD-1 blocks activation of T cells in a manner requiring the heparan sulfate-modified surface molecule CD47, and impairs effector functions. The tandem repeats of BAD-1 thus confer pathogenicity, harbor motifs that bind heparin, and suppress T-cell activation via a CD47-dependent mechanism, mimicking mammalian TSP-1.

Membrane microdomain components of Histoplasma capsulatum yeast forms, and their role in alveolar macrophage infectivity

Analysis of membrane lipids of Histoplasma capsulatum showed that ~40% of fungal ergosterol is present in membrane microdomain fractions resistant to treatment with non-ionic detergent at 4°C. Specific proteins were also enriched in these fractions, particularly Pma1p a yeast microdomain protein marker (a plasma membrane proton ATPase), a 30kDa laminin-binding protein, and a 50kDa protein recognized by anti-α5-integrin antibody. To better understand the role of ergosterol-dependent microdomains in fungal biology and pathogenicity, H. capsulatum yeast forms were treated with a sterol chelator, methyl-beta-cyclodextrin (mβCD). Removal of ergosterol by mβCD incubation led to disorganization of ergosterol-enriched microdomains containing Pma1p and the 30kDa protein, resulting in displacement of these proteins from detergent-insoluble to -soluble fractions in sucrose density gradient ultracentrifugation. mβCD treatment did not displace/remove the 50kDa α5-integrin-like protein nor had effect on the organization of glycosphingolipids present in the detergent-resistant fractions. Ergosterol-enriched membrane microdomains were also shown to be important for infectivity of alveolar macrophages; after treatment of yeasts with mβCD, macrophage infectivity was reduced by 45%. These findings suggest the existence of two populations of detergent-resistant membrane microdomains in H. capsulatum yeast forms: (i) ergosterol-independent microdomains rich in integrin-like proteins and glycosphingolipids, possibly involved in signal transduction; (ii) ergosterol-enriched microdomains containing Pma1p and the 30kDa laminin-binding protein; ergosterol and/or the 30kDa protein may be involved in macrophage infectivity.

Serum IgG against Candida predict survival in patients with metastatic renal cell carcinoma

BACKGROUND AND AIM

In contrast to hematologic malignancies, little is known about the role of fungi in the development and progression of solid tumors. This prompted us to analyze and correlate serum levels of different fungal IgG with survival of patients with metastatic renal cell carcinoma.

PATIENTS AND METHODS

Serum IgG to Candida sp., Saccharomyces cerevisiae and Aspergillus fumigatus were measured in a cross-sectional study in 64 patients with advanced disease. Univariate and multivariate analyses were chosen to study serum IgG as prognostic indicators.

RESULTS

Median follow-up was 29.0 months (range 0.3-122). Median overall survival of patients, which tested negative for Candida IgG, was significantly increased (median not reached, >29 months) compared with Candida IgG positive patients (17.8 months, P = 0.002). Median survival of Saccharomyces IgG negative patients was 33.1 months as opposed to 19.4 months in Saccharomyces IgG positive patients, although this difference was not significant (P = 0.281). No difference in overall survival was found between Aspergillus IgG positive patients (28.0 months) and Aspergillus IgG negative patients (29.1 months) (P = 0.181). Cox backward-stepwise regression confirmed Candida IgG as the strongest predictor of survival in metastatic renal cell carcinoma patients (risk ratio 3.27, P = 0.001, [95% CI 1.86-5.73]).

CONCLUSION

Our findings suggest that IgG antibodies directed against yeast fungi and particularly against Candida but not against mold fungi have prognostic relevance.

Hgc1 mediates dynamic Candida albicans-endothelium adhesion events during circulation

Common iatrogenic procedures can result in translocation of the human pathogenic fungus Candida albicans from mucosal surfaces to the bloodstream. Subsequent disseminated candidiasis and infection of deep-seated organs may occur if the fungus is not eliminated by blood cells. In these cases, fungal cells adhere to the endothelial cells of blood vessels, penetrate through endothelial layers, and invade deeper tissue. In this scenario, endothelial adhesion events must occur during circulation under conditions of physiological blood pressure. To investigate the fungal and host factors which contribute to this essential step of disseminated candidiasis, we have developed an in vitro circulatory C. albicans-endothelium interaction model. We demonstrate that both C. albicans yeast and hyphae can adhere under flow at a pressure similar to capillary blood pressure. Serum factors significantly enhanced the adhesion potential of viable but not killed C. albicans cells to endothelial cells. During circulation, C. albicans cells produced hyphae and the adhesion potential first increased, then decreased with time. We provide evidence that a specific temporal event in the yeast-to-hyphal transition, regulated by the G(1) cyclin Hgc1, is critical for C. albicans-endothelium adhesion during circulation.

Glycemic control in the medical intensive care unit

Hyperglycemia in the critically ill is a well-known phenomenon, even in those without known diabetes. The stress response is due to a complex interplay between counter-regulatory hormones, cytokines, and changes in insulin sensitivity. Illness/infection, overfeeding, medications (e.g., corticosteroids), insufficient insulin, and/or volume depletion can be additional contributors. Acute hyperglycemia can adversely affect fluid balance (through glycosuria and dehydration), immune and endothelial function, inflammation, and outcome. While there are several insulin infusion protocols that are able to safely and effectively treat hyperglycemia, the bulk of accumulated evidence does not support a causal relationship between acute hyperglycemia and adverse outcomes in the medical intensive care unit. Meta-analysis of randomized controlled trials suggests there is no benefit to tightening glucose control to normal levels compared to a reasonable and achievable goal of 140 to 180 mg/dl. There is a significantly increased risk of hypoglycemia. Although there is some evidence that patients without known diabetes have worse outcomes than those with known diabetes, more recent evidence is conflicting. Glycemic control in critically ill patients should not be neglected, as studies have not tested tight versus no/poor control, but tight versus good control. A moderate approach to managing critical illness hyperglycemia seems most prudent at this juncture. Future research should ascertain whether there are certain subgroups of patients that would benefit from tighter glycemic goals. It also remains to be seen if tight glucose control is beneficial once hypoglycemia is minimized with technological advances such as continuous glucose monitoring systems.

The iC3b receptor of Candida albicans and its roles in pathogenesis

On the basis of biochemical and immunologic studies, a receptor for iC3b with some activities reminiscent of the integrins CD11b and CD11c was defined on the cell wall of clinical and laboratory isolates of Candida albicans. The INT1 gene encodes a protein of 1659 amino acids; the Int1 protein participates in adhesion to epithelial cells in vitro and in vivo. Int1 is essential for hyphal morphogenesis and virulence in a murine model. Recent evidence points to the amino terminus of Int1 as the source of a peptide, Pep263, with superantigen-like activities.

Antibody response to the 45 kDa Candida albicans antigen in an animal model and potential role of the antigen in adherence

The Candida antigen CR3-RP (complement receptor 3-related protein) is supposed to be a 'mimicry' protein because of its ability to bind antibody directed against the alpha subunit of the mammalian CR3 (CD11b/CD18). This study aimed to (i) investigate the specific humoral isotypic response to immunization with CR3-RP in vivo in a rabbit animal model, and (ii) determine the role of CR3-RP in the adherence of Candida albicans in vitro using the model systems of buccal epithelial cells (BECs) and biofilm formation. The synthetic C. albicans peptide DINGGGATLPQ corresponding to 11 amino-acids of the CR3-RP sequence DINGGGATLPQALXQITGVIT, determined by N-terminal sequencing, was used for immunization of rabbits to obtain polyclonal anti-CR3-PR serum and for subsequent characterization of the humoral isotypic response of rabbits. A significant increase of IgG, IgA and IgM anti-CR3-RP specific antibodies was observed after the third (P<0.01) and the fourth (P<0.001) immunization doses. The elevation of IgA levels suggested peptide immunomodulation of the IgA1 subclass, presumably in coincidence with Candida epithelial adherence. Blocking CR3-RP with polyclonal anti-CR3-RP serum reduced the ability of Candida to adhere to BECs, in comparison with the control, by up to 35 % (P<0.001), and reduced biofilm formation by 28 % (P<0.001), including changes in biofilm thickness and integrity detected by confocal laser scanning microscopy. These properties of CR3-RP suggest that it has potential for future vaccine development.

Complement and fungal pathogens: an update

Fungal infections are a serious complication in immunocompromised patients such as human immunodeficiency virus-infected individuals, patients with organ transplantations or with haematological neoplasia. The lethality of opportunistic fungal infection is high despite a growing arsenal of antimycotic drugs, implying the urgent need for supportive immunological therapies to strengthen the current inefficient antimicrobial defences of the immunocompromised host. Therefore, increasing effort has been directed to investigating the interplay between fungi and the host immunity and thus to find starting points for additional therapeutic approaches. In this article, we review the actual state of the art concerning the role of complement in the pathogenesis of fungal infections. Important aspects include the activation of the complement system by the fungal pathogen, the efficiency of the complement-associated antimicrobial functions and the arsenal of immune evasion strategies applied by the fungi. The twin functions of complement as an interactive player of the innate immunity and at the same time as a modulator of the adaptive immunity make this defence weapon a particularly interesting therapeutic candidate to mobilise a more effective immune response and to strengthen in one fell swoop a broad spectrum of different immune reactions. However, we also mention the 'Yin-Yang' nature of the complement system in fungal infections, as growing evidence assigns to complement a contributory part in the pathogenesis of fungus-induced allergic manifestations.

Glycemic control and nutrition in the intensive care unit

PURPOSE OF REVIEW

Hospital clinicians frequently encounter hyperglycemia due to diabetes or the stress of critical illness in patients who are receiving nutrition support.

RECENT FINDINGS

A growing body of evidence suggests that hyperglycemia in the hospital is associated with adverse outcomes (e.g. disability after acute cardiovascular events, infection and death) and that improvement in outcomes can be achieved with improved glycemic control or insulin. Therefore, familiarity with the implications of hyperglycemia and with its treatment are essential for clinicians practicing in hospital settings.

SUMMARY

Questions persist regarding the optimal glucose goal range in differing patient groups. In addition, while the technology to deliver glycemic control in intensive care unit settings is widely available, data are limited about effective and safe insulin infusions. Research should focus on the risks and benefits of providing nutrition support in this group of patients, optimal glucose goal ranges, and on methods of achieving desired glucose goal ranges.

Antimycotic Drug Discovery in the Age of Genomics

Genomic-based methodologies are increasingly used at all stages of drug development. The most extensive applications have occurred in early drug discovery stages due to advances in technologies that allow for automated synthesis and characterization of organic compounds, and for high-throughput screening of these molecules against known drug targets. The adaptation of genomic-based methodologies in later stages of drug development presents a more difficult task. In this review we describe how genomics can be used to identify previously uncharacterized pharmacologic actions that provide a basis for the development of new classes of antimycotic agents or for adverse event aversion. Clinically, novel antimycotics are gravely needed. This review provides a perspective on new technologies that will bridge the gap between drug discovery and development that may enable more rapid access to new antimycotic agents.

Clinical microbiology of bacterial and fungal sepsis in very-low-birth-weight infants

Twenty percent of very-low-birth-weight (<1500 g) preterm infants experience a serious systemic infection, and despite advances in neonatal intensive care and antimicrobials, mortality is as much as threefold higher for these infants who develop sepsis than their counterparts without sepsis during their hospitalization. Outcomes may be improved by preventative strategies, earlier and accurate diagnosis, and adjunct therapies to combat infection and protect the vulnerable preterm infant during an infection. Earlier diagnosis on the basis of factors such as abnormal heart rate characteristics may offer the ability to initiate treatment prior to the onset of clinical symptoms. Molecular and adjunctive diagnostics may also aid in diagnosing invasive infection when clinical symptoms indicate infection but no organisms are isolated in culture. Due to the high morbidity and mortality, preventative and adjunctive therapies are needed. Prophylaxis has been effective in preventing early-onset group B streptococcal sepsis and late-onset Candida sepsis. Future research in prophylaxis using active and passive immunization strategies offers prevention without the risk of resistance to antimicrobials. Identification of the differences in neonatal intensive care units with low and high infection rates and implementation of infection control measures remain paramount in each neonatal intensive care unit caring for preterm infants.

Contribution of myeloperoxidase to coronary artery vasculitis associated with MPO-ANCA production

The role of myeloperoxidase (MPO) in the pathogenesis of vasculitis associated with MPO-specific anti-neutrophil cytoplasmic autoantibody (MPO-ANCA) was examined in a murine animal model. Coronary artery vasculitis was induced in C57BL/6 mice with and without endogenous MPO by intraperitoneal injection of Candida albicans-derived substances (CADS). The corresponding levels of MPO-ANCA in sera of mice with and without vasculitis were measured and compared in both wild-type and MPO-deficient animals. The MPO-ANCA titers in sera were significantly higher in mice with vasculitis than in vasculitis-negative mice, indicating that MPO-ANCA correlated with vasculitis formation. However, the increase of MPO-ANCA titers observed in sera of wild C57BL/6 mice were strongly suppressed in MPO-deficient C57BL/6 mice, accompanied with prevention of vasculitis formation. These results show that MPO acted as an antigen for MPO-ANCA production by CADS and was followed by the vasculitis formation. Vasculitis did develop in a few MPO-deficient mice, though the incidence of vasculitis was much lower in MPO-deficient mice than in C57BL/6 mice.

Antibodies to alpha5beta1 and alpha(v)beta3 integrins react with Candida albicans alcohol dehydrogenase

It has been hypothesized that Candida albicans possesses integrin-like receptors on its cell surface. This is because C. albicans binds numerous fluid-phase extracellular matrix (ECM) proteins on its cell surface and adheres to the same ECM proteins when immobilized. In addition, numerous antibodies to human integrins (receptors for ECM proteins) bind to the fungal cell surface and in so doing inhibit the binding of the respective proteins. To demonstrate the presence of such a cell surface integrin, a cDNA library of C. albicans yeast cells was screened with polyclonal antiserum to the human fibronectin receptor (alpha5beta1 integrin). Clones isolated by this screening technique also reacted specifically to antiserum against the human vitronectin receptor (alpha(v)beta3 integrin). DNA sequence analysis of the cloned insert predicted a 350 aa protein (37 kDa). This predicted protein showed 75% homology at the nucleotide sequence level to alcohol dehydrogenase (ADH) of Saccharomyces cerevisiae. In vitro transcription/translation of the cloned inserts yielded a 37 kDa protein that was immunoprecipitated with antibodies to the alpha5beta1 and alpha(v)beta3 integrins and an antibody to a C. albicans fibronectin receptor. These antibodies and an mAb to the human vitronectin receptor demonstrated an antigen of -37 kDa present in the cell-wall preparations of C. albicans and in spent growth medium. All four antibodies reacted with authentic ADH. The possible significance of these results in relation to C. albicans adherence is discussed.

Involvement of alpha(v)beta3 integrin-like receptor and glycosaminoglycans in Candida albicans germ tube adhesion to vitronectin and to a human endothelial cell line

The present study was undertaken to investigate the expression of alpha(v)beta3 and alpha(v)beta5 integrin-like vitronectin receptors (VNRs) on Candida albicans germ tube and their involvement in its adhesion to vitronectin (VN) and human endothelial cells. By immunofluorescence and FACS analysis, several monoclonal antibodies directed against human alpha(v) or beta3 integrin subunit or alpha(v)beta3 and alpha(v)beta5 heterodimers, positively stained C. albicans germ tubes. C. albicans germ tubes specifically adhered (45-50%) to VN and this adhesion was markedly inhibited by RGD-, but not RGE-containing peptides. Adhesion of C. albicans germ tubes to VN was strongly inhibited by anti-alphav, anti-beta3 or anti-alpha(v)beta3, but not by alpha(v)beta5 monoclonal antibody. C. albicans germ tube adhesion to VN was also inhibited by glycosaminoglycans (GAGs) such as heparin or chondroitin sulphate. Finally, we show that C. albicans germ tubes adhere to the human EA.hy 926 endothelial cell line. This adhesion is markedly blocked by anti-beta3 monoclonal antibody, GRGDSP peptide or heparin, and is completely abolished by their combination. Overall these results indicate that C. albicans germ tube adherence to VN and to a human endothelial cell line is mediated by alpha(v)beta3, but not by alpha(v)beta5-like integrin, and depends on GAGs which may act by regulating alpha(v)beta3 integrin-like/VN adhesive interaction.

Inhibition of hydrophobic protein-mediated Candida albicans attachment to endothelial cells during physiologic shear flow

Adhesion interactions during hematogenous dissemination of Candida albicans likely involve a complex array of host and fungal factors. Possible C. albicans factors include changes in cell surface hydrophobicity and exposed antigens that have been shown in static adhesion assays to influence attachment events. We used a novel in vitro shear analysis system to investigate host-pathogen interactions and the role of fungal cell surface hydrophobicity in adhesion events with human endothelial cells under simulated physiologic shear. Endothelial monolayers were grown in capillary tubes and tested with and without interleukin-1 beta activation in buffered medium containing human serum. Hydrophobic and hydrophilic stationary-phase C. albicans yeast cells were infused into the system under shear flow and found to adhere with widely varying efficiencies. The average number of adherent foci was determined from multiple fields, sampled via video microscopy, between 8 and 12 min after infusion. Hydrophobic C. albicans cells demonstrated significantly more heterotypic binding events (Candida-endothelial cell) and greater homotypic binding events (Candida-Candida) than hydrophilic yeast cells. Cytokine activation of the endothelium significantly increased binding by hydrophobic C. albicans compared to unactivated host cells. Preincubation of hydrophobic yeast cells with a monoclonal antibody against hydrophobic cell wall proteins significantly blocked adhesion interactions with the endothelial monolayers. Because the antibody also blocks C. albicans binding to laminin and fibronectin, results suggest that vascular adhesion events with endothelial cells and exposed extracellular matrix may be blocked during C. albicans dissemination. Future studies will address the protective efficacy of blocking or redirecting blood-borne fungal cells to favor host defense mechanisms.

Surface attachment and pre-penetration stage development by plant pathogenic fungi

Fungal pathogens cause many of the most serious crop diseases. One of the principal reasons for the success of this group is their ability to locate and perceive appropriate host surfaces and then to elaborate specialized infection structures. Here we review the processes implicated in surface attachment, germ tube elongation, and development of appressoria. The involvement of surface-acting proteins such as fungal hydrophobins and integrins in these processes is evaluated, along with a description of studies that have revealed the existence of conserved signaling pathways that regulate appressorium formation. Finally, we anticipate the prospect of genome-level analysis of fungal pathogens and the key research questions that will need to be addressed.

Production and secretion of collagen-binding proteins from Aeromonas veronii

Collagen-binding protein (CNBP) synthesized by Aeromonas veronii is located conserved within the subcellular fraction. The results of this study show that 98% of the total CNBP produced by Aer. veronii is present in the extracellular medium, and that the remaining CNBP is distributed either on the cell surface, within the periplasm or anchored on the outer membrane. CNBP is specifically secreted from Aer. veronii into the culture medium, because all the beta-lactamase activity was located in the cells and could be released by polymixin B extraction of periplasmic proteins. CNBP was produced at growth temperatures from 12 degrees C to 42 degrees C, but not at 4 degrees C. The findings indicate that the level of CNBP in the medium increases during the exponential growth phase and reaches a maximum during the early stationary phase. There was less CNBP production in poor nutrient MMB medium than in the rich LB nutrient medium. CNBP secretion, in contrast to aerolysin secretion, was unaffected by the exeA mutation of Aer. hydrophila. It is concluded that CNBP secretion from Aer. veronii must be achieved by a mechanism different from that reported for aerolysin secretion.

Systemic candidiasis in extremely low birth weight infants receiving topical petrolatum ointment for skin care: a case-control study

BACKGROUND AND OBJECTIVE

An increase in the incidence of systemic candidiasis (SC) followed a change in skin care for extremely low birth weight (ELBW) infants in our neonatal intensive care unit (NICU). We sought to determine whether the use of topical petrolatum ointment (TPO) for skin care of ELBW infants was associated with risk for SC.

STUDY DESIGN

Case-control study.

SETTING

A 48-bed NICU in a private hospital in Houston, Texas.

PATIENTS

Ten ELBW infants with and 30 without SC admitted to the NICU from December 1, 1997 through July 31, 1998.

METHODS

ELBW infants with SC were identified using hospital microbiology and infectious disease consultation databases. A case was defined as an infant weighing </=1000 g at birth with Candida spp isolated from a normally sterile body site. Three infants without SC were matched to each case by birth weight, admission date, and survival to the age of SC onset for the case. Data were collected by retrospective medical record review. Molecular analysis of Candida isolates was performed by karyotyping and restriction fragment length polymorphism using pulsed-field gel electrophoresis.

RESULTS

Case infants had a mean (+/- standard deviation) age of onset of 21.5 +/- 24 days. Infants with SC and controls did not differ in birth weight, gestational age, or duration of therapy with steroids, antibiotics, insulin, or total parenteral nutrition. Although cases were more likely to be born vaginally and had a longer duration endotracheal intubation than controls, these differences were not significant. The odds ratio for skin care with TPO in case infants versus control infants was 11 (95% confidence interval: 1.9-63). Skin care with TPO was discontinued and the incidence of SC decreased to baseline. Several Candida spp and genetic profiles were identified, suggesting that there was not a common source outbreak.

CONCLUSIONS

We conclude that the use of TPO promoted an increase in the incidence of SC in ELBW infants. Additional investigation of potential infectious risks for ELBW infants receiving TPO skin care is warranted.

Oral colonization by Candida albicans

Candida albicans is a commensal yeast normally present in small numbers in the oral flora of a large proportion of humans. Colonization of the oral cavity by C. albicans involves the acquisition and maintenance of a stable yeast population. Micro-organisms are continually being removed from the oral cavity by host clearance mechanisms, and so, in order to survive and inhabit this eco-system, C. albicans cells have to adhere and replicate. The oral cavity presents many niches for C. albicans colonization, and the yeast is able to adhere to a plethora of ligands. These include epithelial and bacterial cell-surface molecules, extracellular matrix proteins, and dental acrylic. In addition, saliva molecules, including basic proline-rich proteins, adsorbed to many oral surfaces promote C. albicans adherence. Several adhesins present in the C. albicans cell wall have now been partially characterized. Adherence involves lectin, protein-protein, and hydrophobic interactions. As C. albicans cells evade host defenses and colonize new environments by penetrating tissues, they are exposed to new adherence receptors and respond by expressing alternative adhesins. The relatively small number of commensal Candida cells in the oral flora raises the possibility that strategies can be devised to prevent oral colonization and infection. However, the variety of oral niches and the complex adherence mechanisms of the yeast mean that such a goal will remain elusive until more is known about the contribution of each mechanism to colonization.

Mechanisms of hyphal tip growth: tube dwelling amebae revisited

Over 100 years ago, Reinhardt suggested that hyphal tip growth is comparable to ameboid movement inside a tube; the apical cytoplasm being protruded like a pseudopodium with the wall assembled on its surface. There are increasing data from hyphae which are explicable by this model. Fungi produce pseudopodia-like structures and their cytoplasm contains all of the major components implicated in pseudopodium production in animal cells. Most of these components are concentrated in hyphal tips and tip growth involves actin, a major component of pseudopodia. Together these data indicate that the essence of the ameboid model is still tenable. However, detailed mechanisms of tip growth remain too poorly known to provide definitive proof of the model and the behavior of the trailing cytoplasm indicates differences which are probably a response to the walled lifestyle.

Interactions between Candida albicans and the human extracellular matrix component tenascin-C

Tenascins are large multimeric proteins that contain repeated structural motifs that include epidermal growth factor (EGF)-like repeats, fibronectin type III repeats and a globular fibrinogen-like domain, and are involved in tissue and organ morphogenesis, as well as in adhesion and migration of cells. C. albicans germ-tubes, but not blastospores, were able to bind to soluble human tenascin-C as revealed by an indirect immunofluorescence assay. However, materials present in cell wall extracts from both morphologies attached to tenascin-C immobilized in wells of a microtiter plate. The binding specificity was demonstrated by the inhibitory effect of antibodies against C. albicans cell wall components and an anti-tenascin antibody, but not anti-laminin antibody. Fibronectin, but not fibrinogen, inhibited binding, thus indicating a role of the fibronectin type III repeats in the interaction between the fungus and tenascin-C. Binding of C. albicans cell wall materials to tenascin was RGD- and divalent cation-independent.

Candida dubliniensis: phylogeny and putative virulence factors

Candida dubliniensis is a recently identified species which is implicated in oral candidosis in HIV-infected and AIDS patients. The species shares many phenotypic characteristics with, and is phylogenetically closely related to, Candida albicans. In this study the phylogenetic relationship between these two species was investigated and a comparison of putative virulence factors was performed. Four isolates of C. dubliniensis from different clinical sources were chosen for comparison with two reference C. albicans strains. First, the distinct phylogenetic position of C. dubliniensis was further established by the comparison of the sequence of its small rRNA subunit with representative Candida species. The C. dubliniensis isolates formed true unconstricted hyphae under most induction conditions tested but failed to produce true hyphae when induced using N-acetylglucosamine. Oral C. dubliniensis isolates were more adherent to human buccal epithelial cells than the reference C. albicans isolates when grown in glucose and equally adherent when grown in galactose. The C. dubliniensis isolates were sensitive to fluconazole, itraconazole, ketoconazole and amphotericin B. Homologues of seven tested C. albicans secretory aspartyl proteinase (SAP) genes were detected in C. dubliniensis by Southern analysis. In vivo virulence assays using a systemic mouse model suggest that C. dubliniensis is marginally less virulent than C. albicans. These data further confirm the distinct phenotypic and genotypic nature of C. dubliniensis and suggest that this species may be particularly adapted to colonization of the oral cavity.

Cell wall and secreted proteins of Candida albicans: identification, function, and expression

The cell wall is essential to nearly every aspect of the biology and pathogenicity of Candida albicans. Although it was initially considered an almost inert cellular structure that protected the protoplast against osmotic offense, more recent studies have demonstrated that it is a dynamic organelle. The major components of the cell wall are glucan and chitin, which are associated with structural rigidity, and mannoproteins. The protein component, including both mannoprotein and nonmannoproteins, comprises some 40 or more moieties. Wall proteins may differ in their expression, secretion, or topological location within the wall structure. Proteins may be modified by glycosylation (primarily addition of mannose residues), phosphorylation, and ubiquitination. Among the secreted enzymes are those that are postulated to have substrates within the cell wall and those that find substrates in the extracellular environment. Cell wall proteins have been implicated in adhesion to host tissues and ligands. Fibrinogen, complement fragments, and several extracellular matrix components are among the host proteins bound by cell wall proteins. Proteins related to the hsp70 and hsp90 families of conserved stress proteins and some glycolytic enzyme proteins are also found in the cell wall, apparently as bona fide components. In addition, the expression of some proteins is associated with the morphological growth form of the fungus and may play a role in morphogenesis. Finally, surface mannoproteins are strong immunogens that trigger and modulate the host immune response during candidiasis.

Linkage of adhesion, filamentous growth, and virulence in Candida albicans to a single gene, INT1

Adhesion and the ability to form filaments are thought to contribute to the pathogenicity of Candida albicans, the leading cause of fungal disease in immunocompromised patients. Int1p is a C. albicans surface protein with limited similarity to vertebrate integrins. INT1 expression in Saccharomyces cerevisiae was sufficient to direct the adhesion of this normally nonadherent yeast to human epithelial cells. Furthermore, disruption of INT1 in C. albicans suppressed hyphal growth, adhesion to epithelial cells, and virulence in mice. Thus, INT1 links adhesion, filamentous growth, and pathogenicity in C. albicans and Int1p may be an attractive target for the development of antifungal therapies.

Microbial immunology: a new mechanism for immune subversion

The number of mechanisms that have evolved in microbes to subvert the immune response seems limitless. Tubercle bacilli have found a novel way to coat themselves with the C3 complement protein and invade macrophages by interactions with complement receptors.

The effects of monoclonal antibodies against iC3b receptors in mice with experimentally induced disseminated candidiasis

CR3 (iC3b receptor), composed of CD11b/CD18, is a beta 2 integrin. A protein that shares antigenic and structural homology with the alpha-chain of CD11b/CD18 has been isolated from the surface of Candida albicans. This molecule is thought to be essential in the pathogenesis of disseminated candidiasis. To evaluate the effects of anti-iC3b receptor antibodies on adhesion between human dermal microvascular endothelial cells (HDMEC) and C. albicans, and in treatment of candidal infection, a binding assay of C. albicans to cultured HDMEC was performed in vitro. An anti-iC3b receptor-specific monoclonal antibody was administered to mice infected with C. albicans. The mice were monitored for mortality and renal involvement by culture and histopathological findings. Flow cytometric analysis demonstrated surface expression of iC3b receptor on C. albicans. The adherence of C. albicans to HDMEC was significantly decreased by treatment with anti-iC3b receptor antibodies. Anti-iC3b receptor antibodies significantly increased the survival time and rate while lowering the renal fungal burden. The iC3b receptors are involved in the adherence of C. albicans to vascular endothelial cells and are likely to be involved in the pathogenesis of disseminated candidiasis. The increased survival in mice infected with C. albicans after treatment with anti-iC3b receptor antibodies indicates that this modality may be beneficial for future development of a new therapy for candidiasis.

Molecular bases of adhesion of Candida albicans

The purpose of this review is to focus on the location and the adhesion activity of the protein (peptide) and the mannan moieties of the mannoprotein in the outer surface of the Candida albicans cell wall. A macromolecule of the mannoprotein located on the outermost surface is undoubtedly a strong adhesin comprising several adhesion molecules including protein and mannan. Mannoproteins can be divided into two classes, higher molecular weight peptidomannans (260 kDa) and lower molecular weight mannoproteins (50-66 kDa), both of which consist of similar mannans and disparate proteins or peptides which have distinct adhesion specificities. The protein moiety of mannoprotein can be divided functionally into two groups, lectin-like proteins and proteins recognizing arginine-glycine-aspartic acid (RGD) ligands. The latter proteins are further subdivided into two groups, CR2/CR3-like proteins and proteins binding extracellular matrix (ECM) proteins. Hydrophobicity of the cell surface of C. albicans influences adhesion of the organisms to epithelial cells. Degree of glycosylation of cell surface mannoproteins that affect yeast cell surface hydrophobicity affects adhesion of C. albicans to epithelial cells. The hydrophobic proteins may have low levels of glycosylation, and changes in glycosylation may determine exposure of hydrophobic protein regions at the cell surface. The serotype A-specific oligosaccharide of antigen 6 (pentaose or hexaose of mannan moiety) has been shown to exhibit marked adhesion ability for epithelial cells, and mannotetraose related to antigenic factor 5 which is present in both serotypes A and B showed adhesive activity for tissue macrophages. Proteinoceous adhesins of C. albicans are expressed preferably on the mycelial form. It is suggested that several of the adhesion molecules of C. albicans described above appear to complementarily utilize multiple adhesion mechanisms.

The highly immunogenic enolase and Hsp70p are adventitious Candida albicans cell wall proteins

Screening cDNA libraries with polyclonal antibody preparations against Candida albicans yeast or mycelial cell walls resulted in isolation of several positive clones. Some of them encoded enolase; others encoded a protein of the 70 kDa heat-shock protein family (Hsp70p), etc. The presence of these cytosolic proteins in the cell wall of actively growing C. albicans was discovered by analytical (SDS-PAGE and Western blot) and cytological (indirect immunofluorescence) experiments. Supplementation of cell cultures with papulacandin B, an antibiotic that inhibits formation of the beta-glucan skeleton, resulted in the release of enolase to the supernatant fluids; this release was prevented when 0.6 M KCl was present as an osmotic stabilizer. The cell wall of C. albicans incorporated exogenously added proteins (enolase and Escherichia coli and C., albicans cytosolic proteins). The presence in the C. albicans cell wall of enolase, Hsp70p, and probably other intracellular proteins that are highly immunogenic might help the fungal cells to evade the host defences, and consequently could represent a survival mechanism for C. albicans 'in vivo'.

The yeast to hyphal transition following hematogenous candidiasis induces shock and organ injury independent of circulating tumor necrosis factor-alpha

OBJECTIVES

Dimorphic Candida albicans spp. increasingly cause lethal septic shock and disseminated infection in the critically ill. Following candidemia, production of specific fungal exotoxins coincident with the yeast to hyphal phenotypic transition is believed to be important in the pathogenesis of Candida septic shock. However, overexpression of the pleiotropic cytokine tumor necrosis factor (TNF)-alpha by the host following hyphal germination is also thought to be a mechanism of Candida-related cardiopulmonary dysfunction, as well as of bacteremic shock. In this study, we hypothesized that increases in circulating TNF-alpha coinciding with the yeast to hyphal transition modulate the onset and progression of shock with multiple organ injury early after hematogenous candidiasis.

DESIGN

Prospective, controlled laboratory animal study.

SETTING

University hospital animal research facility.

SUBJECTS

Pathogen-free, male Sprague-Dawley rats (n = 26).

INTERVENTIONS

Conscious, antibiotic-treated animals with chronic indwelling carotid arterial and jugular venous catheters were intravenously infected with 10(9) viable blastoconidia of the C. albicans clinical pathogen, CA-MEN (n = 10), over 30 mins and ending at t = 0 hr, compared with an equivalent inoculum of its viable agerminative mutant, CA-MM2002 n = 11), or an intravenous infusion of 0.9% sodium chloride (n = 5).

MEASUREMENTS AND MAIN RESULTS

Mean arterial pressure (MAP), pulse rate, respiratory frequency, rectal temperature, acid-base status, quantitative blood cultures, circulating alanine aminotransferase (ALT), and bioactive TNF-alpha were serially measured in all three groups over 24 hrs or until death. Organ cultures, wet/dry weight ratios, and histopathologic changes in the lungs, heart, liver, and kidneys were determined in Candida-infected and 0.9% sodium chloride (normal saline)-infused subgroups at 6 and 24 hrs. Animals hematogenously infected with the C. albicans clinical isolate developed lethal nonendotoxemic shock in < or = 6 hrs (MAP 49 +/- 7 mm Hg [SEM]; p < .05 vs. t = 0 hr), and at death (7.0 +/- 0.3 hrs) were acidotic, hypocapnic, and hypothermic (rectal temperature 33.2 +/- 0.7 degrees C). Despite similar peak concentrations of circulating fungal colony-forming units (cfu) and kinetics of vascular clearance in both Candida-infected groups, survival and MAP in rats challenged with the agerminative C. albicans mutant were unchanged for > 8 hrs, as were pH, Pco2, and rectal temperature. No germination of the agerminative fungal strain occurred in vivo over 6 hrs. Serum TNF was nearly undetectable at t = 0 hr in all three groups. Although shock developed soon after fungemia with the C. albicans clinical isolate, TNF-alpha concentrations did not increase above normal saline values in either candidemic group at t = 1.5, 4.5, or 6 hrs (17 +/- 7 vs. 14 +/- 1 U/mL in the parent C. albicans organism vs. its agerminative mutant at t = 6 hrs). Greater numbers of agerminative C. albicans than its dimorphic parent strain were recovered from the lungs (5.41 +/- 1.0 vs. 2.02 +/- 0.38 x 10(7) cfu/g, respectively; p < .05) and kidneys (p < .01). By 24 hrs, modest germination of the mutant Candida strain was observed in the tissues. However, lung wet/dry ratios, intrapulmonary hyphal proliferation, and alveolar hemorrhage were all greater after infection with the parent fungal isolate. Likewise, myocardial necrosis and hepatic glycogen depletion with vacuolization were more severe after infection with the C. albicans clinical isolate vs. candidemia with its agerminative mutant, although serum ALT values did not differ between these groups.

CONCLUSIONS

Lethal C. albicans sepsis with lung injury and multiple organ damage are temporally associated with the in vivo yeast to hyphal transition in this model. However, this candidemic septic shock syndrome is modulated by circulating fungal virulence factors or host mediators other than TNF-alpha, a cytokine considered essen

Migration of the fungal pathogen Candida albicans across endothelial monolayers

Migration of the fungal pathogen Candida albicans across the endothelial cell layer is considered a prerequisite for the invasion of multiple organs occurring in systemic candidiasis. We developed an experimental system in which C. albicans migrates from a luminal compartment across a monolayer of bovine aortic endothelial cells on a porous filter support to an abluminal compartment. In this system, a C. albicans wild-type strain (ATCC 10261) traverses the endothelial monolayer in a time-, glucose-, and cell concentration-dependent manner. A mutant derivative unable to grow and form hyphae (SGY-243) migrates at a reduced rate. Concomitant to transendothelial migration, the permeability of the endothelial monolayer for dextran diffusion markers is significantly increased. This increase in transendothelial exchange occurs before fungal cells are detectable in the abluminal compartment and is time, glucose, and cell concentration dependent. A mutant strain (hOG301) unable to interact with endothelial cells does not alter endothelial permeability. Thus, transendothelial migration of C. albicans is able to damage the barrier function of an endothelial monolayer. Our experimental system, which reflects key stages of transendothelial migration of C. albicans including adherence and passage across endothelial cells and the extracellular matrix, may be a useful model for comparisons of transendothelial migration characteristics of Candida strains.

Immune evasion properties of herpes simplex virus type 1 glycoprotein gC

Herpes simplex virus type I (HSV-1) glycoprotein gC binds complement component C3b, and purified gC inhibits complement activation. Two HSV strains carrying mutations in the gC gene which rendered them unable to bind C3b were compared with wild-type and marker-rescued viruses to evaluate the role of gC on the virion in protecting HSV-1 from complement-mediated neutralization. The gC mutant viruses were markedly susceptible to neutralization by nonimmune human serum, showing up to a 5,000-fold decline in titer after 1 h of incubation with serum. In contrast, wild-type or marker-rescued viruses showed a twofold reduction in titer. Studies with hypogammaglobulinemic and immunoglobulin G-depleted serum supported the observation that neutralization occurred in the absence of antibody. Neutralization of gC mutant strains by nonimmune serum was rapid; their half-life was 2 to 2.5 min, compared with 1 h for wild-type virus. Ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA)-treated human serum or C4-deficient guinea pig serum failed to neutralize gC mutant strains, indicating a role for components of the classical complement pathway. gC had little additional effect on neutralization by the combination of antibody plus complement compared with complement alone. The results indicate that the magnitude of the protection offered by gC-1 is larger than previously recognized; that in the absence of gC-1, complement neutralization is rapid and is mediated by components of the classical complement pathway; and that gC mainly protects against antibody-independent complement neutralization, suggesting a probable role for gC early in infection, before antibodies develop.

Cloning and expression of a gene encoding an integrin-like protein in Candida albicans

The existence of integrin-like proteins in Candida albicans has been postulated because monoclonal antibodies to the leukocyte integrins alpha M and alpha X bind to blastospores and germ tubes, recognize a candidal surface protein of approximately 185 kDa, and inhibit candidal adhesion to human epithelium. The gene alpha INT1 was isolated from a library of C. albicans genomic DNA by screening with a cDNA probe from the transmembrane domain of human alpha M. The predicted polypeptide (alpha Int1p) of 188 kDa contains several motifs common to alpha M and alpha X: a putative I domain, two EF-hand divalent cation-binding sites, a transmembrane domain, and a cytoplasmic tail with a single tyrosine residue. An internal RGD tripeptide is also present. Binding of anti-peptide antibodies raised to potential extracellular domains of alpha Int1p confirms surface localization in C. albicans blastopores. By Southern blotting, alpha INT1 is unique to C. albicans. Expression of alpha INT1 under control of a galactose-inducible promoter led to the production of germ tubes in haploid Saccharomyces cerevisiae and in the corresponding ste12 mutant. Germ tubes were not observed in haploid yeast transformed with vector alone, in transformants expressing a galactose-inducible gene from Chlamydomonas, or in transformants grown in the presence of glucose or raffinose. Transformants producing alpha Int1p bound an anti-alpha M monoclonal antibody and exhibited enhanced aggregation. Studies of alpha Int1p reveal novel roles for primitive integrin-like proteins in adhesion and in STE12-independent morphogenesis.

Activation of the complement system by pathogenic fungi

Fungi have been studied as prototype activators of the complement cascade since the early 1900s. More recently, attention has focused on the role of the complement system in the pathogenesis of fungal infections. The interactions of Cryptococcus neoformans and Candida albicans with the complement system are the most widely characterized; however, all pathogenic fungi examined to date have the ability to initiate the complement cascade. The molecular mechanisms for initiation and regulation of the complement cascade differ from one fungus to another, most likely reflecting differences in the structure of the outer layers of the cell wall. The molecular bases for such differences remain to be identified. Studies of mycoses in experimental animals with induced or congenital deficiencies in the complement system demonstrate that complement is an important innate system for control of fungal infection. Contributions to host resistance include opsonization and generation of inflammatory mediators. Inflammation induced by chemotactic products of the complement system may contribute to the pathogenesis of some fungal infections.

Recognition of endothelial cells byCandida albicans: role of complement-binding proteins

Candida albicans, a commensal of humans, can cause either mucosal or systemic infections. The virulence properties of the organism include cell-surface adhesins that recognize ligands of host cells. Hyphal forms of the organism possess a 60-kDa mannoprotein that recognizes a variety of host-cell ligands including the complement C3 conversion products, C3bi and C3d. In addition, a protein of similar molecular mass also binds to endothelial extracellular matrix proteins such as laminin and fibronectin. While the 60-kDa protein is associated with the cell surface of hyphal forms of the organism, a protein of 50 kDa with similar ligand-binding activities is associated with the plasma membrane of blastoconidia. This protein cross reacts with antibodies to the 60-kDa protein. Isolation of the gene(s) encoding these cell-surface proteins is underway using both a human B-lymphocyte CR2 gene fragment or oligonucleotides based upon peptide sequence to screen libraries of C. albicans. Mutants of the organism with reduced expression of either C3d or C3bi-binding activity have been isolated. These strains are less virulent and also less adherent in vitro. Studies are currently underway to define the contribution of these proteins to the virulence of the organism. Key words: adherence, complement receptor, mannoprotein, virulence, ligand recognition.

Production and function of cytokines in natural and acquired immunity to Candida albicans infection

Host resistance against infections caused by the yeast Candida albicans is mediated predominantly by polymorphonuclear leukocytes and macrophages. Antigens of Candida stimulate lymphocyte proliferation and cytokine synthesis, and in both humans and mice, these cytokines enhance the candidacidal functions of the phagocytic cells. In systemic candidiasis in mice, cytokine production has been found to be a function of the CD4+ T helper (Th) cells. The Th1 subset of these cells, characterized by the production of gamma interferon and interleukin-2, is associated with macrophage activation and enhanced resistance against reinfection, whereas the Th2 subset, which produces interleukins-4, -6, and -10, is linked to the development of chronic disease. However, other models have generated divergent data. Mucosal infection generally elicits Th1-type cytokine responses and protection from systemic challenge, and identification of cytokine mRNA present in infected tissues of mice that develop mild or severe lesions does not show pure Th1- or Th2-type responses. Furthermore, antigens of C. albicans, mannan in particular, can induce suppressor cells that modulate both specific and nonspecific cellular and humoral immune responses, and there is an emerging body of evidence that molecular mimicry may affect the efficiency of anti-Candida responses within defined genetic contexts.

Complex interaction between different proteinaceous components within the cell-wall structure of Candida albicans

We have previously described a monoclonal antibody, MAb DC3:H10, which recognized an epitope preferentially expressed on the surface of Candida albicans germ tubes. In the present study we examined the MAb-reactive material further. Immunoblot analysis of the material purified partially by Sephadex G-200 and DEAE-Sephacel chromatography reacted with antibodies to the C. albicans C3d receptor (CR2). In an ELISA, MAb DC3:H10 captured antigen that was recognized by both anti-CR2 and anti-mp58 fibrinogen binding mannoprotein polyclonal antibodies. The MAb DC3:H10 failed to compete with either of these antisera in an ELISA. Indirect immunofluorescence (IIF) analysis showed differences in surface distribution for the MAb DC3:H10, the CR2, and the mp 58 epitopes. Dual labeling IIF experiments showed MAb DC3:H10 binding to be unaffected by binding of fibrinogen or anti-mp58 antibody. However, the binding patterns of MAb DC3:H10 were modified in the presence of anti-CR2 antibody, suggesting a complex interaction between these cell wall components.

Increased expression of Candida albicans secretory proteinase, a putative virulence factor, in isolates from human immunodeficiency virus-positive patients

The increased prevalence and the severity of oropharyngeal candidiasis in human immunodeficiency virus (HIV)-positive patients are attributed exclusively to the virus-induced immune deficiency of the host. The present study was aimed at answering the question of whether Candida albicans secretory proteinase, a putative virulence factor of the opportunistic C. albicans yeast, has any potential influence on the clinical manifestation of oropharyngeal candidiasis in HIV-positive patients. We measured the secretory proteinase activities of clinical C. albicans isolates from the oropharynges of either HIV-positive individuals (n = 100) or a control group (n = 122). The mean secretory proteinase activity of C. albicans isolates from the HIV-positive group (4,255 +/- 2,372 U/liter) was significantly higher compared with that of isolates from the control group (2,324 +/- 1,487 U/liter) (P < 0.05). The higher level of secretory proteinase activity in the culture supernatants of individual C. albicans isolates correlated with the increased level of proteinase expression on the cell surface, as revealed by cytofluorometry, and with higher levels of secretion of the immunodetectable protein, as shown by Western blotting (immunoblotting). Proteinase activity within the population of C. albicans isolates from HIV-positive individuals was independent of the patient's clinical disease stage and the CD4+/CD8+ cell numbers. Furthermore, no correlation of the proteinase activities with the C. albicans serotype was found, although C. albicans serotype B was significantly more frequent in the HIV-positive group (40%) compared with that in the control group (12%). However, a positive correlation of proteinase activity to antifungal susceptibility was evident. The C. albicans isolates from the HIV-positive group that were characterized by higher levels of proteinase activity were also less susceptible to the widely used azole antifungal ketoconazole and fluconazole. Collectively, the present data are consistent with a concept of early preferential selection of a subpopulation of C. albicans in HIV-infected patients.