Is there a role for antibody testing in the diagnosis of invasive candidiasis?

During the last decades, the use of antibody tests for the diagnosis of invasive mycoses has declined as a consequence of the general belief that they are insensitive and non-specific. However, there is a clear evidence that antibodies can be detected in highly immunodeficient patients (such as bone marrow transplant recipients), and that those antibodies are useful for the diagnosis. Antibody tests are currently in use as diagnostic tools for some primary mycoses, such as the endemic mycoses, aspergilloma, allergic bronchopulmonary aspergilosis and sporothrichosis. For invasive candidiasis, diagnostic methods must differentiate Candida colonization of mucous membranes or superficial infection from tissue invasion by this microorganism. Substantial progress has been made in diagnosis of invasive candidiasis with the development of a variety of methods for the detection of antibodies and antigens. However, no single test has found widespread clinical use and there is a consensus that diagnosis based on a single specimen lacks sensitivity. It is necessary to test sequential samples taken while the patient is at greatest risk for developing invasive candidiasis to optimize the diagnosis. Results obtained from a panel of diagnostic tests in association with clinical aspects will likely be the most useful strategy for early diagnosis and therapy.     

Characterization of Candida albicans antigenic determinants by two-dimensional polyacrylamide gel electrophoresis and enhanced chemiluminescence

The use of a two-dimensional polyacrylamide gel electrophoresis joined with Western blotting allowed us to investigate the reactivities of antibodies present in sera from mice and humans to antigens of Candida albicans blastoconidia. The analysis of the antibody response in the two models studied and the comparison between the antibody response in infected and noninfected individuals showed that the infection by C. albicans produces changes in the antibody response which may be of relevance in the serodiagnosis of invasive candidiasis. These changes include the induction of antibodies against new antigens, the disappearance of antibodies against a group of antigens and variations in the reactivity of antibodies directed to a different group of antigens. The technique used resolved the isoforms of several antigens including enolase. It is concluded that the antibody response in humans and mice with candidiasis is not homogeneously directed to all the isoforms of an antigen.     

Antibodies to Candida albicans germ tubes in two intensive care patients with invasive candidiasis

Two cases of invasive candidiasis in intensive care patients are presented to illustrate the usefulness of detection of antibodies to Candida albicans germ tubes in the diagnosis of invasive candidiasis and in monitoring the efficacy of the antifungal treatment.     

Antibodies to Candida albicans germ tubes in two intensive care patients with invasive candidiasis

Two cases of invasive candidiasis in intensive care patients are presented to illustrate the usefulness of detection of antibodies to Candida albicans germ tubes in the diagnosis of invasive candidiasis and in monitoring the efficacy of the antifungal treatment.     

Kinetics of Anti-Mannan Antibodies Useful in Confirming Invasive Candidiasis in Immunocompromised Patients

In studying the anti-mannan antibodies longitudinally in serial serum samples of three immunocompromised patients, it was observed that anti-mannan antibodies started to increase shortly after the moment that cultures of deep-tissue sites became positive with Candida albicans. The mean anti-mannan antibody titers determined in a group of 36 immunocompromised patients with invasive candidiasis increased within two weeks after the probable onset of invasive candidiasis. In contrast, anti-mannan antibody levels in serial serum samples of 14 immunocompromised patients who were only colonized with C. albicans remained stable or decreased over time. The HA test measuring the anti-mannan antibodies was 64% sensitive and 89% specific in determining invasive candidiasis. In contrast, antibodies specific for candidal cytoplasmic antigens or enolase alone were of little value in confirming invasive candidiasis in these immunocompromised patients.     

Advances and limitations in the early diagnosis of invasive yeast infections

In the last years, the main advances in the serological diagnosis of mycoses caused by yeasts have occurred in the area of antibody and (1-3)-beta-D-glucan detection. Commercialization of the Candida albicans IFA IgG test and detection of antibodies against recombinant antigens Hwp1 and enolase are the most important contributions to the first area. Detection of (1-3)-beta-D-glucan confirms its usefulness as a good marker for the diagnosis of invasive candidiasis. The most recent studies suggest that combination of two tests to detect antígen, antibodies, (1-3)-beta-D-glucan and DNA will be needed to optimize the diagnosis of systemic yeast infections.     

The continuous changes in the aetiology and epidemiology of invasive candidiasis: from familiar <Emphasis Type="Italic">Candida albicans</Emphasis> to multiresistant <Emphasis Type="Italic">Candida auris</Emphasis>

Recent changes in the aetiology and epidemiology of invasive candidiasis have serious implications for current and future diagnosis, treatment and prognosis. The aim of the current review was to discuss the epidemiology of invasive candidiasis, the distribution of Candida species in different regions of the world, the medical concerns of the changing aetiology and the emergence of antifungal resistance. Overall burden of invasive candidiasis remains high, especially in vulnerable persons, such as the elderly, immunosuppressed or debilitated patients. Moreover, there is a progressive shift in the aetiology of invasive candidiasis from Candida albicans to other species of Candida, probably related to the increased use of azole drugs with a clear trend towards increased antifungal resistance. Finally, the emergence and rise of multiresistant species, such as Candida auris or Candida glabrata, is a major threat making necessary invasive candidiasis worldwide surveillances. These changes have serious implications for the diagnosis, treatment and prognosis of invasive candidiasis. Updated knowledge of the current local epidemiology of invasive candidiasis is critical for the clinical management.     

Identification of protein and mannoprotein antigens of Candida albicans of relevance for the serodiagnosis of invasive candidiasis.

Antigens from Candida albicans blastoconidia and germ tubes were identified by two-dimensional electrophoresis and Western blotting and characterized by microsequencing, reactivity with concanavalin A, and a panel of human sera. Antigens identified included a polydispersed area in the acidic high-molecular-mass regions of blastoconidium and germ-tube extracts, and 16 antigens varying in molecular masses and isoelectric points (pIs). The majority of the detected antigens, especially those in the polydispersed region, showed mannosyl groups, as determined by concanavalin A reactivity. Antibodies present in sera from patients with invasive candidiasis showed high reactivity with a number of antigens not detected with sera from blood donors. Eight of the 16 antigens could be identified by reactivity with monoclonal antibodies or by microsequencing. Five antigens showed homology with five enzymes previously described as antigens in C. albicans: enolase, phosphoglycerate kinase, malate dehydrogenase, and two isoforms of the fructose biphosphate aldolase. However, to our knowledge, this is the first report of the immunogenic activity of a kexin precursor, a mitochondrial complex I chaperone, and a diacylglycerol kinase catalytic domain from C. albicans. Antigens described in this study may be of potential interest for the serodiagnosis of invasive candidiasis.     

Defining criteria for anti-mannan antibodies to protect against candidiasis

Prevention of hematogenously disseminated candidiasis and mucocutaneous disease, including Candida vaginitis, through immunological approaches is appealing for the following reason. A long-acting and safe vaccine that protects against both serotypes of Candida albicans and other important species, such as C. tropicalis and C. glabrata, should significantly reduce the incidence of various forms of candidiasis by these etiologic agents. Through extensive experimentation on protective responses in experimental animals against Candida mannan components, others and we have evidence that antibodies specific for short-chain beta-linked oligomannosides are protective against candidiasis. Although the mechanism of protection against vaginal infection requires further investigation, experimentally the ability of antibody to rapidly deposit high amounts of complement factor C3 onto the yeast cell wall is requisite for enhancing resistance against disseminated candidiasis.     

Proteomics-based identification of novel Candida albicans antigens for diagnosis of systemic candidiasis in patients with underlying hematological malignancies

Systemic candidiasis remains a major cause of disease and death, particularly among patients suffering from hematological malignancies. In an attempt to contribute to the discovery of useful biomarkers for its diagnosis and therapeutic monitoring, we embarked on a mapping of Candida albicans immunogenic proteins specifically recognized by antibodies produced during the natural course of systemic Candida infection in this high-risk population. About 85 immunoreactive protein species were detected with systemic candidiasis patients' serum specimens by using immunoproteomics (i.e., two-dimensional electrophoresis followed by Western blotting), and identified through a combination of peptide mass fingerprinting by matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS), de novo peptide sequencing using nano-electrospray ionization-ion trap (ESI-IT) MS, and genomic database searches. This proteomic approach has led to the characterization of 42 different housekeeping enzymes as C. albicans antigens. Their biological significance is also discussed. Furthermore, this study is the first to report that 26 of them exhibit antigenic properties in C. albicans, and 35 of them become targets of the human antibody response to systemic candidiasis. Our findings suggest that the production of antibodies to C. albicans phosphoglycerate kinase and alcohol dehydrogenase during systemic candidiasis could be associated with a differentiation of the human immune response. We also highlight the relationship between changes in maintenance of circulating levels of specific anti-Candida antibodies and patients' outcome. Some of these variations, especially the rise of high anti-enolase antibody concentrations, appear to be related to recovery from systemic candidiasis in these patients, which might serve as markers for predicting their outcome. This approach could therefore provide new challenges for diagnosis and clinical follow-up of these fungal infections, and even for antifungal drug or vaccine design.     

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.     

Modulation of neutrophil function in host defense against disseminated Candida albicans infection in mice

Neutrophils (PMNs) constitute the main mechanism of host defense against acute invasive and disseminated candidiasis. Recent studies have demonstrated that tumor necrosis factor-alpha (TNFalpha), interleukin-6 (IL-6) and granulocyte colony-stimulating factor (G-CSF) play an important role in the recruitment of PMNs at the site of invasive Candida infection. In the absence of either TNFalpha or IL-6, the course of experimental disseminated candidiasis is more severe, due to defective PMN recruitment. Treatment of mice with recombinant G-CSF (rG-CSF) leads to a significantly reduced mortality during disseminated candidiasis. The outgrowth of Candida albicans from the organs of rG-CSF-treated mice is significantly decreased. Treatment with the combination of rG-CSF and fluconazole has an additive effect on the reduction of fungal load in the organs. In subacute or chronic disseminated Candida infection, rG-CSF is less effective, indicating that neutrophil recruitment and activation are crucial in acute, life-threatening candidiasis, whereas other host defense mechanisms control the outcome of less overwhelming invasive Candida infection.     

Probiotic bacteria for prophylaxis and therapy of candidiasis

A good deal of data support a role for probiotic intestinal bacteria in the prophylaxis and therapy of candidiasis. Candida spp. are highly infectious eukaryotes that can colonize and infect humans and other warm-blooded mammals, worldwide. Although most humans manifest antibody- and cell-mediated immune responses to Candida antigens a large percentage of the human population is colonized with Candida spp. in their alimentary and vaginal tracts. The bacterial flora plays a very important probiotic role in the prophylaxis of candidiasis by suppressing the growth of Candida spp. on mucosal and cutaneous surfaces; however, the specific bacteria and the mechanisms they use to inhibit Candida spp. and candidiasis are still poorly understood. The increased incidence of Candida infections, their increasing resistance to antifungal antibiotics and the fact that vaccines to protect against candidiasis are not yet available (and may not work in immunodeficient, Candida-susceptible, patients) provides a strong impetus for new research efforts to explore the use of probiotic, anti- Candida intestinal bacteria for the prophylaxis and therapy of candidiasis.     

Use of 65-kDa mannoprotein gene primers for real-time identification of Candida albicans

Invasive candidiasis is associated with high morbidity and mortality, especially in immunocompromised patients. Early diagnosis is often difficult because most clinical signs and symptoms are nonspecific and blood cultures are often negative or become positive too late. Consequently, effective treatment is often delayed. Therefore, there has been an increased interest in the development of molecular-based technology in the diagnosis of invasive candidiasis. In this review, we compare molecular diagnostic tests currently adopted and those under evaluation. We highlight the advantages and the limitations of these methods for the diagnosis of invasive candidiasis. We also describe recent methods based on real time with primers of a gene coding for a 65-kDa mannoprotein of Candida albicans.     

Nature of the restructuring of the T- and B-immunity systems in patients with cutaneous and visceral candidiasis

The examination of 90 patients with superficial and visceral candidiasis, as well as Candida carriers, has revealed that the heavy contamination of the body with fungi of the genus Candida is accompanied by the specific transformation of the immune system, manifested by differences in the character of sensitization to Candida antigens: in the patients with superficial and visceral candidiasis the B-system of immunity is sensitized to a greater degree, while in the Candida carriers the sensitization of the T-system is more pronounced. Despite the fact that the immune system of patients with the disseminated form of visceral candidiasis is capable of developing the delayed hypersensitivity (DH) reaction to bacterial allergens, such patients have been shown to develop DH to Candida antigens only in rare cases. This is probably due to disturbances in their immunocompetent systems, caused, seemingly, by the secondary immune insufficiency.     

Serum antibody response of gnotobiotic athymic and euthymic mice following alimentary tract colonization and infection with Candida albicans

Colonization and infection evoked specific immunoglobulin responses to Candida albicans antigens in gnotobiotic nu/+ mice which appeared to correlate with clearance of infected mucosal surfaces (tongue and stomach). Conversely, colonized and infected nu/nu mice formed some IgM but no detectable IgG or IgA antibodies against C. albicans antigens. Although chronic mucosal infections of tongue and stomach persisted in nu/nu mice, they were able to resist overwhelming mucosal and systemic infections with C. albicans. Thus, C. albicans specific antibodies may play a role in clearance of mucosal candidiasis (tongue and stomach), but these antibodies do not appear to be necessary for protecting athymic mice against systemic candidiasis of endogenous origin.     

Evaluation of three serological tests for detection of anti-candidal antibodies in diagnosis of invasive candidiasis

Immunoblot detection of antibody against 47 KD cytoplasmic antigen ofCandida albicans was evaluated in diagnosis of invasive candidiasis and compared to whole cell agglutination and gel diffusion tests for detection of anticandidal antibody in 64 patients. The patients included 17 with culture proved candidemia, 34 with significant candiduria (more than 10,000 colony forming units per ml of urine) and 13 with nonsignificant candiduria. Antibody against 47 KD antigen was found to be the best indicator for diagnosis of invasive candidiasis even in patients with malignancy. The sensitivity of this procedure was 82.4%, specificity 86.7%, positive predictive value 77.8%, negative predictive value 89.7% and efficacy 85.1%. The gel diffusion procedure lacked in sensitivity whereas whole cell agglutination lacked in specificity. Detection of antibody against 47 KD antigen proved to be a valuable adjunct in the diagnosis of invasive candidiasis.     

Unravelling fungal immunity through primary immune deficiencies

Fungal infections affect individuals with an impaired immune system and are on the increase, often with serious consequences. Recent studies in patients with primary immune deficiencies (PIDs) have led to important breakthroughs in our understanding of the different, mutually exclusive pathways underlying immunity to mucocutaneous as opposed to invasive fungal infections. Patients with defects affecting segments of innate (dectin-1, CARD9, IL12RB1) or adaptive immunity (interleukin (IL)17-F, IL-17 receptor, STAT1, STAT3, antibodies to Th-17 cytokines) that disrupt the Th-17 pathway, are unable to clear superficial Candida or Dermatophyte infections and suffer with chronic mucocutaneous candidiasis (CMC). Patients with defects affecting phagocyte function (oxidative killing, neutropenia) or a severely impaired immune system are at risk of developing invasive, often fatal fungal disease with Aspergillus, Candida, Cryptococcai and other fungi. PIDs are hugely beneficial in promoting our knowledge of fungal immunity and provide important contributions toward evidence-based diagnosis and improved patient care.     

Amphotericin B-metronidazole combination against Candida spp

Oropharyngeal candidiasis (OPC) remains a common opportunistic infection in HIV-infected patients. Candida albicans is the most frequent causative agent of OPC. However, non-albicans spp. are being increasingly isolated. Candidal cell wall proteins and mannoproteins play important roles in the biology and patogenesis of candidiasis. In the present study, we have analyzed the proteinaceous components associated with cell wall extracts from C. albicans, Candida tropicalis, Candida pseudotropicalis, Candida krusei, Candida glabrata, Candida parapsilosis, Candida guilliermondii and Candida rugosa obtained from HIV-infected patients with recurrent OPC. Cell wall proteinaceous components were extracted with beta-mercaptoethanol and analyzed using electrophoresis, immunoblotting (with antisera generated against C. albicans cell wall components, and with serum samples and oral saline rinses from patients with OPC), and lectin-blotting (concanavalin A) techniques. Numerous molecular species were solubilized from the various isolates. Major qualitative and quantitative differences in the polypeptidic and antigenic profiles associated with the cell wall extracts from the different Candida spp. were discernible. Some of the antibody preparations generated against C. albicans cell wall components were able to recognize homologous materials present in the extracts from non-albicans spp. Information on cell wall antigens of Candida species may be important in the therapy and prevention of HIV-related OPC.