Variability in expression of a cell surface determinant on Candida albicans as evidenced by an agglutinating monoclonal antibody

Candida identification: a journey from conventional to molecular methods in medical mycology

The incidence of Candida infections have increased substantially in recent years due to aggressive use of immunosuppressants among patients. Use of broad-spectrum antibiotics and intravascular catheters in the intensive care unit have also attributed with high risks of candidiasis among immunocompromised patients. Among Candida species, C. albicans accounts for the majority of superficial and systemic infections, usually associated with high morbidity and mortality often caused due to increase in antimicrobial resistance and restricted number of antifungal drugs. Therefore, early detection of candidemia and correct identification of Candida species are indispensable pre-requisites for appropriate therapeutic intervention. Since blood culture based methods lack sensitivity, and species-specific identification by conventional method is time-consuming and often leads to misdiagnosis within closely related species, hence, molecular methods may provide alternative for accurate and rapid identification of Candida species. Although, several molecular approaches have been developed for accurate identification of Candida species but the internal transcribed spacer 1 and 2 (ITS1 and ITS2) regions of the rRNA gene are being used extensively in a variety of formats. Of note, ITS sequencing and PCR-RFLP analysis of ITS region seems to be promising as a rapid, easy, and cost-effective method for identification of Candida species. Here, we review a number of existing techniques ranging from conventional to molecular approaches currently in use for the identification of Candida species. Further, advantages and limitations of these methods are also discussed with respect to their discriminatory power, reproducibility, and ease of performance.

Antifungals: need to search for a new molecular target

In the 1990s, drug resistance has become an important problem in a variety of infectious diseases including human immunodeficiency virus infection, tuberculosis, and other bacterial infections which have profound effects on human health. At the same time, there have been dramatic increase in the incidence of fungal infections, which are probably the result of alterations in immune status associated with the acquired immuno deficiency syndrome epidemic, cancer chemotherapy, and organ and bone marrow transplantation. The rise in the incidence of fungal infections has exacerbated the need for the next generation of antifungal agents, since many of the currently available drugs have undesirable side effects, are ineffective against new or reemerging fungi, or lead to the rapid development of the resistance. This review will focus on the pathogenic yeast Candida albicans, since a large body of work on the factors and mechanism associated with antifungal drug resistance in this organism is reported sufficiently. It will certainly elaborate the probable molecular targets for drug design, discovered to date.

Preparation and Characterization of a Monoclonal Antibody Against Mannoprotein ofCandida albicans

BALB/c mice were immunized via injection with whole cell of Candida albicans serotype A. The spleens were fused with myeloma cells of SP2/0 origin. A mannoprotein-reactive monoclonal antibody (MAb) was selected and characterized by ELISA technique. This MAb reacted with strains of Candida such as C. albicans, C. tropicalis, and C. albicans of the Persian Type Culture Collection (PTCC). However, our antibody did not react with other Candida species such as C. parapsilosis, C. glabrata, C. stellatoidae, C. lusitania, C. krusei, and S. cervisiae. These antibodies also did not recognize extracts of other fungal species such as Aspergillus fumigatus and Aspergillus flavus, and bacterial strains such as Staphylococcus aureus and Pseudomonas aeruginosa. Polyclonal antibody produced in this study could not differentiate the above species and was reactive towards all fungal species mentioned above except bacterial strains of S. aureus and P. aeruginosa. Western blot analysis of ligand affinity-purified mannoproteins of C. albicans wall protein using this MAb showed reactivity toward a single protein band in the region of 55-65 kDa molecular weight. The same antibody, when examined with unpurified C. albicans extract, reacted with a broad band in the region of 55-105 kDa, which we concluded was due to a possible different glycosylation pattern of mannoprotein in crude extract in which the higher molecular weight protein was eliminated by ligand-binding affinity purification.

Candida albicans Als1p: an adhesin that is a downstream effector of the EFG1 filamentation pathway

Filamentation and adherence to host cells are critical virulence factors of Candida albicans. Multiple filamentation regulatory pathways have been discovered in C. albicans using Saccharomyces cerevisiae as a model. In S. cerevisiae, these pathways converge on Flo11p, which functions as a downstream effector of filamentation and also mediates cell-cell adherence (flocculation). In C. albicans, such effector(s) have not yet been identified. Here, we demonstrate that the cell surface protein Als1p is an effector of filamentation in C. albicans. We show that Als1p expression is controlled by the transcription factor Efg1p, which is known to be a key regulator of filamentation in C. albicans. Further, disruption of ALS1 inhibited filamentation, and autonomous expression of Als1p restored filamentation in an efg1 homozygous null mutant. Thus, Als1p functions as a downstream effector of the EFG1 filamentation pathway. In addition, we found that Als1p mediates both flocculation and adherence of C. albicans to endothelial cells in vitro. As a cell surface glycoprotein that mediates filamentation and adherence, Als1p has both structural and functional similarity to S. cerevisiae Flo11p. Consistent with our in vitro results, Als1p was required for both normal filamentation and virulence in the mouse model of haematogenously disseminated candidiasis.

Antifungal effects of lysozyme and lactoferrin against genetically similar, sequential Candida albicans isolates from a human immunodeficiency virus-infected southern Chinese cohort

A variety of innate defense factors in saliva such as lysozyme and lactoferrin contribute to mucosal protection and modulate Candida populations in the oral cavity. It is also known that in human immunodeficiency virus (HIV)-infected individuals significant variations in the concentrations of lysozyme and lactoferrin in saliva occur during disease progression. Therefore, the aim of this study was to determine the in vitro susceptibility to human lactoferrin and hen egg white lysozyme of genotypically similar oral Candida albicans isolates obtained from six HIV-infected ethnic Chinese during sequential visits over a 12-month period. The similarity of the genotypes (50 in total) was evaluated using a randomly amplified polymorphic DNA assay. A blastospore viability assay was performed to evaluate the sensitivity of the organisms to lysozyme and lactoferrin. Exposure to physiological concentrations of either lysozyme (30 microg/ml) or lactoferrin (20 microg/ml) caused a rapid loss of viability among all isolates to a varying extent. None of the sequential C. albicans isolates demonstrated significant differences in sensitivity to either protein from one visit to the next; similar results were noted when the different genotypes from the same individual were compared. On Spearman correlation analysis of two genotypes that were sequentially isolated from a single patient, a significant negative correlation between lysozyme (r = -0.88; P < 0.02) (but not lactoferrin) resistance and the duration of HIV disease was seen. These results imply that a minority of C. albicans isolates that persist intraorally in individuals with HIV disease develop progressive resistance to innate salivary antifungal defenses such as lysozyme, possibly as an adaptive response. However, the vast majority of the Candida isolates appear to succumb to these nonspecific host immune mediators abundantly present in the oral environment.

Candida glabrata: review of epidemiology, pathogenesis, and clinical disease with comparison to C. albicans

Until recently, Candida glabrata was considered a relatively nonpathogenic commensal fungal organism of human mucosal tissues. However, with the increased use of immunosuppressive agents, mucosal and systemic infections caused by C. glabrata have increased significantly, especially in the human immunodeficiency virus-infected population. A major obstacle in C. glabrata infections is their innate resistance to azole antimycotic therapy, which is very effective in treating infections caused by other Candida species. Candida glabrata, formerly known as Torulopsis glabrata, contrasts with other Candida species in its nondimorphic blastoconidial morphology and haploid genome. C. glabrata currently ranks second or third as the causative agent of superficial (oral, esophageal, vaginal, or urinary) or systemic candidal infections, which are often nosocomial. Currently, however, there are few recognized virulence factors of C. glabrata and little is known about the host defense mechanisms that protect against infection. Two established animal models (systemic and vaginal) have been established to study treatment, pathogenesis, and immunity. Treatment of C. glabrata infections can include azoles but often requires amphotericin B or flucytosine. This review summarizes all known clinical and experimental information about C. glabrata infections with comparisons to C. albicans as a means of contrasting the two species commonly observed and emphasizing the many recognized differences.

Identification of Candida albicans ALS2 and ALS4 and localization of als proteins to the fungal cell surface

Additional genes in the growing ALS family of Candida albicans were isolated by PCR screening of a genomic fosmid library with primers designed from the consensus tandem-repeat sequence of ALS1. This procedure yielded fosmids encoding ALS2 and ALS4. ALS2 and ALS4 conformed to the three-domain structure of ALS genes, which consists of a central domain of tandemly repeated copies of a 108-bp motif, an upstream domain of highly conserved sequences, and a domain of divergent sequences 3' of the tandem repeats. Alignment of five predicted Als protein sequences indicated conservation of N- and C-terminal hydrophobic regions which have the hallmarks of secretory signal sequences and glycosylphosphatidylinositol addition sites, respectively. Heterologous expression of an N-terminal fragment of Als1p in Saccharomyces cerevisiae demonstrated function of the putative signal sequence with cleavage following Ala17. This signal sequence cleavage site was conserved in the four other Als proteins analyzed, suggesting identical processing of each protein. Primary-structure features of the five Als proteins suggested a cell-surface localization, which was confirmed by indirect immunofluorescence with an anti-Als antiserum. Staining was observed on mother yeasts and germ tubes, although the intensity of staining on the mother yeast decreased with elongation of the germ tube. Similar to other ALS genes, ALS2 and ALS4 were differentially regulated. ALS4 expression was correlated with the growth phase of the culture; ALS2 expression was not observed under many different in vitro growth conditions. The data presented here demonstrate that ALS genes encode cell-surface proteins and support the conclusion that the size and number of Als proteins on the C. albicans cell surface vary with strain and growth conditions.

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.

Biochemical characterization of Candida albicans epitopes that can elicit protective and nonprotective antibodies

We previously reported that the immunoglobulin M (IgM) monoclonal antibody (MAb) B6.1 protects mice against disseminated candidiasis, whereas the IgM MAb B6 does not. Both MAbs are specific for an adhesin fraction isolated from the cell surface of Candida albicans, but their epitope specificities differ. In the present study, we examined the surface locations of both epitopes and obtained structural information regarding the B6.1 epitope. Immunofluorescence confocal microscopic analysis of C. albicans yeast forms showed that epitope B6.1 is displayed rather homogeneously over the entire cell surface, whereas epitope B6 appears to have a patchy distribution. Both antibodies were essentially nonreactive with the surfaces of mycelial forms of the fungus, indicating that neither epitope is expressed on the surfaces of these forms. For isolation of the B6.1 epitope, the adhesin fraction consisting of cell surface phosphomannan was subjected to mildly acidic (10 mM HCl) hydrolysis and was fractionated into acid-labile and acid-stable portions by size exclusion chromatography. Antibody blocking experiments showed that the B6.1 epitope is an acid-labile moiety of the phosphomannan and that the B6 epitope is located in the acid-stable fraction. The B6 epitope appeared to be mannan because it was stable to heat (boiling) and protease treatments but was destroyed by alpha-mannosidase digestion. The B6.1 epitope eluted from the size exclusion column in two fractions. Mass spectroscopic analyses showed that one fraction contained material with the size of a mannotriose and that the other was a mixture of mannotriose- and mannotetraose-size substances. Dose response inhibition tests of the fractions indicated that the B6.1 epitope is associated with the mannotriose. Nuclear magnetic resonance (NMR) spectroscopic analysis of the epitope yielded data consistent with a beta-(1-->2)-linked mannotriose. The fine structure of the B6 epitope is under investigation. Information derived from these investigations will be useful both in understanding protective versus nonprotective antibody responses to C. albicans and in improving anti-Candida vaccine formulations.

Evaluation of latex reagents for rapid identification of Candida albicans and C. krusei colonies

A total of 322 yeast strains and yeastlike organisms belonging to the genera Candida, Cryptococcus, Geotrichum, Saccharomyces, and Trichosporon were tested with the new monoclonal antibody-based Bichro-latex albicans and Krusei color latex tests. Comparison of results with those obtained by conventional identification methods showed 100% sensitivity for both latex tests and 100% and 95% specificity for the Bichro-latex albicans and Krusei color tests, respectively. Because the test is easy to read and quick to perform, the Bichro-latex albicans test may be useful for rapid identification of Candida albicans colonies in the clinical laboratory.

Paracoccidioides brasiliensis antigen batches from the same isolate show immunological and biochemical differences

We investigated the occurrence of antigenic and biochemical variability among Paracoccidioides brasiliensis antigen batches prepared according to the same protocol. Initially (experiment #1), we analyzed two antigen lots of two human isolates (Bt1 & Bt2), cultured in two media (PYG: bactopeptone, yeast extract, glucose; MMM: McVeigh & Morton medium) in SDS-PAGE and in two immunological tests (immunodiffusion-ID and footpad swelling test-FPT). Afterwards (experiment #2), we compared the antigenic profile of three antigen batches from three human isolates (Bt1, Bt2 & Bt3) by two-dimensional immunoelectrophoresis (2 D-IEP) against a reference system for P. brasiliensis antigens. In experiment #1, there were important intra- and inter-strain antigenic differences between batches of the fungal isolates cultured on both media. The block titration of the antigen batches for the immunological tests revealed correlation between protein concentration and biological activity in ID and no correlation in FPT. In experiment #2, the reference system for P. brasiliensis showed 26 antigen peaks. There were important differences between batches prepared from the same isolate and between batches from different isolates. Our data suggested the occurrence of instability in the synthesis of antigenic components by a same P. brasiliensis isolate, under controlled incubation conditions.

Candida albicans stress mannoproteins expression in superficial and systemic candidiasis. Stress mannoproteins in Candida albicans

The presence of heat shock mannoproteins (HSMPs) reactive with sIgA was demonstrated in several C. albicans strains. The subculture of the C. albicans isolated from mucosal surfaces on Sabouraud's dextrose agar at 25 degrees C switched off the HSMP expression. A re-expression of the HSMPs was obtained in the same medium by shifting the temperature of incubation to 37 degrees C. However, expression of HSMPs in two strains isolated from deep infections was maintained during several subcultures on Sabouraud's dextrose agar at 25 degrees C. A glycoprotein of 200 kDa seemed to be the main HSMP reacting with vaginal sIgA. The data presented in this study suggest that factors other than temperature can influence the expression of C. albicans HSMPs and therefore these antigens should be referred as stress mannoproteins.

Antibody response that protects against disseminated candidiasis

We previously showed that surface mannans of Candida albicans function as adhesins during yeast cell attachment to mouse splenic marginal zone macrophages. The mannan adhesin fraction was encapsulated into liposomes and used to vaccinate mice over a 5- to 6-week period. Circulating agglutinins specific for the fraction correlated with increased resistance to disseminated candidiasis. Antiserum from vaccinated animals protected naive BALB/cByJ mice against C. albicans serotype A and B strains and Candida tropicalis. Antiserum also protected SCID mice against disseminated disease. The serum protective ability was stable at 56 degrees C, but this ability was adsorbed by C. albicans cells. The antiserum was divided into three fractions after separation by high-performance liquid chromatography. One fraction contained all of the agglutinin activity and transferred resistance to naive mice. A second fraction also transferred resistance. Two monoclonal antibodies (MAbs) specific for candidal surface determinants were obtained. MAb B6.1 is specific for a mannan epitope in the adhesin fraction, and MAb B6 is specific for a different epitope in the fraction. Both MAbs are immunoglobulin M, and both strongly agglutinate candidal cells, but only MAb B6.1 protected both normal and SCID mice against disseminated candidiasis. In one experiment, 10 normal mice were given MAb B6.1 and challenged with yeast cells. Six mice survived the 67-day observation period; 4 of the survivors were cured as evidenced by the lack of CFU in the kidney and spleen. Our studies show that antibodies against certain cell surface antigens of C. albicans help the host resist disseminated candidiasis.

A comparative study on cell wall antigens and cell surface hydrophobicity in clinical isolates of Candida albicans

Characterization of common cell surface-bound antigens in Candida albicans strains, particularly those expressed in the walls of mycelial cells might be useful in the diagnosis of systemic candidiasis. Hence, antigenic similarities among wall proteins and mannoproteins from C. albicans clinical serotype A and B isolates, were studied using polyclonal (mPAbs) and monoclonal (MAb 4C12) antibodies raised against wall antigens from the mycelial form of a common C. albicans serotype A laboratory strain (ATCC 26555). Zymolyase digestion of walls isolated from cells of the different strains studied grown at 37 degrees C (germination conditions), released, in all cases, numerous protein and mannoprotein components larger than 100 kDa, along with a 33-34 kDa species. The pattern of major antigens exhibiting reactivity towards the mPAbs preparation was basically similar for all the serotype A and B isolates, though minor strain-specific bands were also observed. The immunodeterminant recognized by MAb 4C12 was found to be absent or present in very low amounts in C. albicans isolates other than the ATCC 26555 strain, yet high molecular weight species similar in size (e.g., 260 kDa) to the wall antigen against which MAb 4C12 was raised, were observed, particularly in wall digests from serotype A strains. Cell surface hydrophobicity, an apparently important virulence factor in C. albicans, of the cell population of each serotype B strain was lower than that of the corresponding serotype A counterparts, which is possibly due to the fact that the former strains exhibited a reduced ability to form mycelial filaments under the experimental conditions used.

Characterization of a major cell wall antigen and potential adhesin in three strains of Candida albicans

Selected strains of Candida albicans were examined to reveal the surface antigenicity and biochemical nature of major cell wall proteins that also were shown to serve as cellular adhesins on human buccal epithelial cells. Confirmation of the adhesive properties of these cells was made by scanning electron microscopy and immunofluorescence microscopy. Particular attention was directed at the clinical isolate KM-302. By means of indirect immunofluorescence staining, the KM-302 blastoconidia absorbed rabbit anti-C. albicans ATCC-32354 serum, revealing specific localization of surface antigens on germ tubes and pseudohyphae. Extracellular polymeric material and the cell wall extract of C. albicans KM-302 blastoconidia were found to contain a major surface antigen of 49 kDa that exhibited 42% adhesion inhibition in vitro. Of considerable significance is that immunogold localization by electron microscopy showed the antigen to be almost exclusively cell wall bound. This major antigen, identified in affinity and gel filtration chromatography fractions, was composed of 4% carbohydrate and 95.7% protein and had an isoelectric point of 6.1. The major antigen also showed a high level of similarity with that of C. albicans strain SC-5314 inasmuch as the major antigen of that strain had carbohydrate and protein compositions of 4 and 95.5%, respectively. Both of these strains also possessed the same percent of adhesion inhibition on human buccal epithelial cells.

Identification and immunochemical characterization of a germ tube specific antigen of Candida albicans

Germ tube specific fractions of the dimorphic pathogenic fungus Candida albicans were fractionated according to their ability to link to fibrinogen. These fibrinogen binding factors were used as immunogens to prepare monoclonal antibodies (mAbs) with BALB/c mice. Among the resulting mAbs, one (mAb 3D9.3) was shown by indirect immunofluorescence to be specific to the surface of the mycelial phase of the C. albicans species. No labelling of the cell wall of any other Candida species was observed. This morphological shape specificity was confirmed by immunoblotting where a polydispersed high molecular mass component was identified. The molecular mass varied with the extraction procedure used; over 210 kDa with EDTA-2ME treatment, and ranging from 110 to 220 kDa after Zymolyase digestion. This phase-specific epitope was sensitive to proteolysis with pronase E, proteinase K and trypsin, but not to periodate treatment. Further purification of this material would allow further development of new serodiagnostic assays that might be more specific for invasive disease than currently available tests.

Characterization of mutant strains of Candida albicans deficient in expression of a surface determinant

Monoclonal antibody (MAb) 17E4 reacts with a surface carbohydrate determinant and agglutinates cells of Candida albicans. Using this MAb, we have isolated N-methyl-N'-nitro-N-nitrosoguanidine-induced nonagglutinating mutants. Eleven of these were characterized for the presence and expression of the surface antigen recognized by MAb 17E4 by immunoblot analysis of whole cells and by fluorescence flow cytometry. Soluble cell wall extracts from five mutant strains were negative by immunoblot analysis. The reactivities of the strains with several other MAbs and commercial antisera (Candida Check; Iatron Laboratories, Tokyo, Japan) which also recognize carbohydrate determinants were examined by immunoblot analysis of whole cells. Mutant strains showed no or reduced expression of the MAb 17E4 antigen and could be placed into at least two distinct phenotypic classes. Recognition by the other MAbs tested showed a similar pattern, while recognition by the commercial antisera was unchanged in the mutant strains. 1H and 13C nuclear magnetic resonance spectral analysis of mannan prepared from the wild type and nonexpressing mutant-strain 4A showed that the spectra from the mutant strain were simpler than those of the wild type. Most of the beta-1,2 linkages and all of the C-1 phosphate linkages were absent in the 4A mannan spectra, which suggested that the mutant mannan lacked the phosphate-bound beta-1,2-linked mannooligosaccharides. The effect of the surface defect on the ability of mutant strain 4A to adhere and to invade host tissue was examined in two murine models. In ex vivo binding assays, strain 4A showed reduced binding to the marginal zone and increased binding to the white pulp of splenic tissue, decreased binding to kidney tissue, and no change in binding to liver tissue compared with the wild type. In vivo, no difference was observed in translocation of the wild type or strain 4A to liver following immuno-compromising treatment of infant mice which had been challenged with either strain by the oral-intragastric route.

Recognition between Candida albicans and host cells

The cell surface of Candida albicans is a complex mosaic of polysaccharide and protein, of which mannoproteins constitute the major antigens and host cell recognition molecules. One group of mannoproteins is known as 'adhesins' and has properties similar to lectins and integrins. The adhesins recognize either host cell fucosyl glycosides or peptides containing the amino acid sequence arginine-glycine-aspartic acid (RGD peptides).

Mapping of Candida albicans oligomannosidic epitopes by using monoclonal antibodies

Six monoclonal antibodies (MAbs) from various laboratory sources (EB-CA1, EB-CA2, H5, AF1, C6, and 5B2), reacting with the polysaccharidic moieties of Candida albicans mannoproteins, were used for epitope mapping by an enzyme-linked immunosorbent assay (ELISA) with neoglycolipids and by Western blotting (immunoblotting) of a C. albicans germ tube extract. The ELISA involved neoglycolipids constructed from three families of oligomannosides released by sequential depolymerization of C. albicans phosphopeptidomannan by acid hydrolysis (NGLH), beta-elimination (NGLO), and acetolysis (NGLA). All of the MAbs exhibited low reactivities against NGLO. MAbs EB-CA1, EB-CA2, and H5 reacted mainly against NGLA, and MAbs C6 and AF1 recognized mainly NGLH, whereas MAb 5B2 reacted with both families of neoantigens. When this method was compared with Western blotting, strong reactivity to NGLA was associated with the presence of epitopes shared by high-molecular-weight mannoproteins, whereas strong reactivity to NGLH was associated with a reactivity to a family of 14- to 18-kDa antigens. The reactivity of MAb 5B2 was associated with both high-molecular-weight mannoproteins and the 14- to 18-kDa antigens. In relation to the present knowledge about the structure of the C. albicans phosphopeptidomannan oligomannosidic repertoire, these results provide preliminary data concerning the molecular basis of the recognition of mannopyranosyl sequences by MAbs and their distribution among C. albicans mannoproteins.

Cytological immunodetection of yeast glycoprotein secretion

Expression of antigenic epitopes shared by secreted yeast glycoproteins was studied using specific immunological probes. Application of cytological and ultrastructural methods of immunodetection, employing monoclonal antibodies, permitted us to localize these glycoproteins in the cytoplasm, through the cell wall and at the yeast cell surface. Importance of glycosylation-secretion relationships were evaluated in the secretion process of these molecules. The cell wall crossing and the cell surface distribution of antigenic glycoproteins was described in immunoelectron microscopy and immunofluorescence. Some preferential secretion "ways" were suspected through the yeast cell wall leading to an heterogenous distribution of cell surface glycoproteins destined to be excreted into the medium. Antigenic variability of cell wall glycoproteins expression was discussed in relation with the glycoprotein secretion.

Serotype prevalence of Candida albicans from blood culture isolates

Blood culture isolates of Candida albicans were collected from 102 patients in Seattle, Wash., hospitals (n = 77) and Hong Kong (n = 25). The patients were classified by immune status into two groups. Group I patients were severely immunosppression, and group II patients had underlying risk factors for candidemia but no underlying immunosuppression. Serotyping by Hasenclever tube agglutination was done. In the Seattle area, the odds of fungemia with type B C. albicans were 3.62 times greater than the odds of type B fungemia in group II patients. Although the odds ratio could not be computed for Hong Kong patients, the direction of the relationship in this population was consistent with the data on Seattle patients. Despite the magnitude of the odds ratios, the relative prevalence of type B over type A in group I compared with group II was not significant when analyzed separately by region, probably because of relatively low numbers of isolates in group II. Accepting that the effect of immune status on serotype is equivalent across regions but presupposing that a regional effect on type B prevalence exists, the pooled odds for fungemia with serotype B in group I patients are increased 5.4-fold over those of group II patients. Logistic regression analysis controlling for region gave similar results.

Evidence for expression of the C3d receptor of Candida albicans in vitro and in vivo obtained by immunofluorescence and immunoelectron microscopy

The complement conversion product C3d binds to a receptor on the cell surface of Candida albicans. While the function of this receptor is still uncertain, we investigated whether it is expressed during a murine infection. Rabbit antiserum raised against purified receptor was used in conjunction with immunofluorescence microscopy and immunocolloidal gold electron microscopy to examine kidney tissue and peritoneal lavages from infected mice for receptor expression by C. albicans in vivo. Specificity of the antiserum was indicated by reactivity with purified receptor (55 to 60 kDa) and with a protein of similar molecular mass from whole hyphal extracts in Western blots (immunoblots). In vitro analysis by immunofluorescence microscopy showed that the antiserum reacted with both yeast and pseudohyphal forms of the organism, but reactivity was strongest with pseudohyphae. Immunocolloidal gold electron microscopy of fungal cells from peritoneal lavages revealed intense staining of mother cells of germinative forms, germ tubes, and pseudohyphae. Staining of the mother cells was heaviest at the innermost layers of the cell wall but only scant on the cell surface. In contrast, staining was observed throughout the cell walls of germ tubes and pseudohyphae. In kidney, expression of the C3d receptor was found primarily on the cell walls of hyphae and pseudohyphae, although some staining was observed in the cytoplasm. These data support that the C3d receptor of C. albicans is expressed in vivo.

Comparison between methods for serotyping of Candida albicans produces discrepancies in results

Serotyping of 101 clinical isolates of Candida albicans was done with two sets of Hasenclever original anti-Candida typing sera (HSN 1 and 2) and Iatron Candida Check factor 6 typing serum (IF6). The results of these two methods were compared with slide agglutination reactions of yeast with monoclonal antibody H9. Agglutination reactions with this antibody have been previously shown to correlate with serotype. Results indicate the following correlations: between HSN 1 and HSN 2 serotyping, 93% (kappa = 0.85; 95% confidence interval [CI], 0.70 to 0.99); between IF6 and HSN 1, 60% (kappa = 0.39, 95% CI, 0.19 to 0.58); and between IF6 and HSN 2, 74% (kappa = 0.77; 95% CI, 0.64 to 0.90). Results with HSN 1 and 2 antisera correlated with H9 reactivity at 85 and 89% (kappa = 0.88; 95% CI, 0.75 to 1.00; and kappa = 0.85; CI, 0.70 to 0.99, respectively), while agreement between IF6 and H9 reactivities was less than or equal to 64% (kappa less than or equal to 0.43; 95% CI, 0.14 to 0.60). Autoagglutination of yeast during IF6 serotyping occurred with 21 of the 101 (20.8%) yeast strains. In every case, these yeast strains were serotyped by the HSN methods without autoagglutination and were uniformly type B. This study implies that it may not be possible to make valid comparisons between studies which compare serotype prevalence unless the same methods are used to serotype the yeast. The practicality and utility of serotyping in epidemiological studies are discussed, as are some of the problems associated with the available methods.

Adherence and receptor relationships of Candida albicans

The cell surface of Candida albicans is composed of a variety of polysaccharides such as glucan, chitin, and mannan. The first two components primarily provide structure, while the mannan, often covalently linked to protein, constitutes the major antigen of the organism. Mannoproteins also have enzymatic activity (acid protease) and ligand-receptor functions. The complement receptors of C. albicans appear to be mannoproteins that are required for the adherence of the organism to endothelial cells. This is certainly true of the CR3-like protein of C. albicans. Proof that the CR3 is the Candida receptor for endothelial cells is derived from two observations. First, mutants lacking CR3 activity are less adherent in vitro and, in fact, less virulent. Second, the ligand recognized by the CR3 receptor (C3bi) as well as anti-CR3 antibodies blocks adherence of the organism to endothelial cells. The CR2 of C. albicans appears to promote the adherence of the organism to plastic substrates. Unlike the CR2 of mammalian cells, the Candida CR2 recognizes ligands containing the RGD sequence of amino acids in addition to the C3d ligand, which does not contain the RGD sequence. There is uncertainty as to whether the Candida CR2 and CR3 are, in fact, different proteins. A mannoprotein has also been described as the adhesin for epithelial cells. In this case, the receptor has a lectinlike activity and recognizes fucose- or glucosamine-containing glycoproteins of epithelial cells, depending on the strain of C. albicans. The oligosaccharide component of the receptor is probably not involved in ligand recognition and may serve to stabilize the receptor. However, the oligosaccharide factor 6 epitope of mannan may also provide adhesin activity in the recognition of epithelial cells. Mannoproteins can be extracted from cells by a number of reagents. Zymolyase, for instance, tends to remove structural mannoproteins, which contain relatively little protein and are linked to glucan. Reagents such as dithiothreitol, on the other hand, tend to extract mannoproteins containing higher amounts of protein that appear to have receptor function. The mannoproteins of C. albicans are dynamically expressed and may be growth phase and growth form specific.

Differential adherence of hydrophobic and hydrophilic Candida albicans yeast cells to mouse tissues

Using an ex vivo binding assay, we previously demonstrated that yeast cells grown at 37 degrees C display binding specificity in mouse spleen, lymph node, and kidney tissues. In spleen and lymph node tissues, binding was predominantly in regions rich in macrophages. Here, we tested the possibility that hydrophobic and hydrophilic cells bind differentially to host tissues. Hydrophobic and hydrophilic yeast cells of four Candida albicans strains were incubated for 15 min at 4 degrees C with cryostat sections of organs that had been rapidly frozen after removal from BALB/cByJ mice. Unattached cells were removed by washing, and the sections were examined. Hydrophobic cells bound diffusely and abundantly to all tissues, while hydrophilic cell attachment was restricted to specific sites. For example, hydrophobic cells bound to the white and red pulp and the marginal zones in spleens, whereas hydrophilic cells attached primarily to the marginal zones. Hydrophobic yeast cells attached throughout lymph node tissue including paracortical areas, but hydrophilic cell attachment occurred primarily at the subcapsular and trabecular sinuses, EDTA inhibited the adherence of hydrophilic cells but not hydrophobic cells to mouse tissues. Hydrophobic C. albicans strains displaying similar levels of hydrophobicity differed quantitatively in their levels of attachment to kidney and spleen tissues, confirming our earlier observation that surface hydrophobicity is not the sole determinant in adherence to host cells. Other studies have shown that hydrophobic and hydrophilic cells display different virulence characteristics related to their surface properties and that hydrophobic cells are more virulent than hydrophilic cells. Taken together, the present results suggest that the enhanced virulence of hydrophobic cells over hydrophilic cells may be due, in part, to the potential of hydrophobic cells to bind throughout various organs following clearance from the bloodstream.

Candida mannan: chemistry, suppression of cell-mediated immunity, and possible mechanisms of action

The ability of Candida albicans to establish an infection involves multiple components of this fungal pathogen, but its ability to persist in host tissue may involve primarily the immunosuppressive property of a major cell wall glycoprotein, mannan. Mannan and oligosaccharide fragments of mannan are potent inhibitors of cell-mediated immunity and appear to reproduce the immune deficit of patients with the mucocutaneous form of candidiasis. However, neither the exact structures of these inhibitory species nor their mechanisms of action have yet been clearly defined. Different investigators have proposed that mannan or mannan catabolites act upon monocytes or suppressor T lymphocytes, but research from unrelated areas has provided still other possibilities for consideration. These include interference with cytokine activities, lymphocyte-monocyte interactions, and leukocyte homing. To stimulate further research of the immunosuppressive property of C. albicans mannan, we have reviewed (i) the relationship of mannan to other antigens and virulence factors of the fungus; (ii) the chemistry of mannan, together with methods for preparation of mannan and mannan fragments; and (iii) the historical evidence for immunosuppression by Candida mannan and the mechanisms currently proposed for this property; and (iv) we have speculated upon still other mechanisms by which mannan might influence host defense functions. It is possible that understanding the immunosuppressive effects of mannan will provide clues to novel therapies for candidiasis that will enhance the efficacy of both available and future anti-Candida agents.

Evaluation of a gold-silver staining method for detection and identification of Candida species by light microscopy

A gold-silver staining procedure was evaluated for detection of Candida species of medical importance. Probes were prepared by coupling lectins or antibodies (polyclonal and monoclonal) directly or indirectly to colloidal gold particles. Structures reacting to these probes were specifically revealed by light microscopy in cells present in infected kidney tissue sections or in isolated yeast cells on glass slides. Definition, contrast and sensitivity were of a high order. Preliminary data showed that it was possible, using discriminating dilutions, to identify cells from different species of the genus Candida, grown in vitro, according to their ability to stain with polyclonal monospecific antisera. The advantages of gold-silver staining compared with other staining procedures currently used in routine mycological laboratories are its sensitivity, good definition, ease and rapidity, and long conservation of reaction. It is suggested that the procedure has applications for research and identification of yeasts in clinical samples.

Immunoreactivity of neoglycolipids constructed from oligomannosidic residues of the Candida albicans cell wall

To establish a model to study the immunoreactivity of oligosaccharidic structures from the Candida albicans cell wall, we attempted to construct neoglycolipids with these residues by using oligomannosides released after mild acid hydrolysis of the phosphopeptidomannans isolated from yeast forms. From a mixture of manno-oligosaccharides ranging from mannobiose to mannononaose, the structure of a quantitatively major component (mannotriose) was determined to be Man (beta 1-2) Man (beta 1-2) Man alpha by 1H nuclear magnetic resonance analysis. After coupling of the pool of oligosaccharides to a lipid (4-hexadecylaniline), the synthesized molecules were injected into mice and rats. Antibody responses were detected on enzyme-linked immunosorbent assay plates coated with either phosphopeptidomannans or neoglycolipids. The hybrid molecules exhibited both immunogenicity and antigenicity. The kinetics of antibody responses as well as immunofluorescence patterns observed on whole C. albicans cells strongly mimicked results from the immunization of animals with natural antigens. Construction of neoglycolipids could therefore provide an interesting approach to the study of specific oligosaccharides of C. albicans and their recognition by the host immune system.

Candida albicans strain delineation

Candida albicans is a major opportunistic pathogen causing a wide spectrum of disease in human beings. Methods for strain delineation of this species to assess or predict virulence or to conduct epidemiologic or pathogenetic investigations have been developed. Although factors associated with virulence have been identified, there is no rapid system to quantitate them in a clinical laboratory. Therefore, many typing methods are based on variable phenotypic characteristics within this species including morphotyping, serotyping, antibiogram, resistogram typing, biotyping, biotyping based on commercial carbon assimilation patterns, enzyme profiles, sensitivity to yeast killer toxins, and typing based on protein variability. Phenotypically defined strains generally do not correlate with the pathogenic potential of a strain with the exception of morphotyping. However, these methods can be useful in epidemiologic investigations; for example, they have revealed that most individuals harbor one strain and that infections are frequently due to an endogenous strain. Problems with these methods usually relate to their discriminatory power. When this is maximized, reproducibility (especially between laboratories) suffers. Recently, methods based on differences in DNA structure (genotyping) for strain delineation have been developed, including electrophoretic karyotyping and restriction enzyme fragment length polymorphisms. The development of a computer-assisted data bank and analysis for these genotypic strain delineators will open investigations into the pathogenesis of this infection and permit epidemiologic studies previously not possible with this important human pathogen.

Production and characterization of monoclonal antibodies to cell wall antigens of Aspergillus fumigatus

Two murine monoclonal antibodies (MAbs) against Aspergillus fumigatus were produced and characterized. Splenocytes from cell wall-immunized BALB/c mice were fused with SP2/0 myeloma cells. The hybridomas were screened with a cold alkali (CA) extract of mycelium containing protein, mannose, and galactose, and two MAbs of the immunoglobulin M class were purified from ascites fluid. MAbs 1 and 40 were characterized by double immunodiffusion against CA antigen, indirect enzyme immunoassay with mannans of Candida albicans serotypes A or B or Candida tropicalis, indirect immunofluorescence with C. albicans- or A. fumigatus-infected tissues, indirect immunofluorescence with smears of other pathogenic fungi, Western blotting (immunoblotting) with the lectin concanavalin A or BS-1 from the seeds of Bandeirea simplicifolia, and immunoelectron microscopy. MAb 1 did not cross-react with Candida mannan and recognized a periodate-sensitive, pronase- and heat-resistant epitope in CA antigen and three mannose- and galactose-containing components (80, 62, and 49 kilodaltons) of a mycelial homogenate. Immunoelectron microscopy demonstrated binding of MAb 1 to the inner cell wall and intracellular membranes of hyphae and conidia of A. fumigatus. Circulating antigen was detected in experimental invasive aspergillosis by inhibition enzyme immunoassay with MAb 1 and CA antigen. MAb 40 was a nonprecipitating antibody cross-reactive with Candida species, and competition for an epitope located diffusely in the cell wall of A. fumigatus hyphae was demonstrated by incubating MAb 40 with mannan of C. albicans serotype A. These results suggest that MAb 1 recognizes immunodominant oligogalactoside side chains of A. fumigatus galactomannan, while MAb 40 binds to mannopyranosyl side chains common to A. fumigatus galactomannan and C. albicans mannan.

Characteristics of Candida albicans adherence to mouse tissues

An ex vivo binding assay originally described for determining lymphocyte homing receptors was adapted for studying Candida albicans-host cell interactions in unfixed tissue sections. BALB/cByJ mice were sacrificed, and various organs were removed, rapidly frozen on dry ice, and sectioned. C. albicans yeast cells were suspended to 1.5 x 10(8) cells per ml in Dulbecco modified Eagle medium supplemented with 5% newborn calf serum, and 100 microliters of the suspension was added to tissue sections for 15 min with rotation at 4 degrees C or at 22 to 24 degrees C. The sections were then fixed in glutaraldehyde, washed, and examined. Stationary-phase yeast cells adhered better than log-phase cells, and adherence characteristics were similar at 4 degrees C and 22 to 24 degrees C. Yeast cells from nine strains of C. albicans showed similar tissue specificity. Adherence to lymph node tissue was confined to subcapsular spaces and trabecular sinuses. In the spleen, yeast cells bound to the marginal zones. In both tissues, an association of yeast cells with tissue macrophages was suggested by results with macrophage-specific monoclonal antibodies and fluorescent or immunoperoxidase staining techniques. C. albicans adhered to convoluted tubules, glomeruli, and the tunica media of arterioles in the kidney. During experimentally induced fungemia in mice, C. albicans yeast cells associated with the same tissue sites as in the ex vivo assay, except that binding to renal arterioles was not seen in the in vivo test. A strain of Saccharomyces cerevisiae showed some adherence patterns in common with C. albicans, which indicates that tissue adherence is not sufficient for virulence. Mechanisms of attachment were not determined, but strains of C. albicans varied quantitatively in their ability to attach, and binding was inhibited by chelators of divalent cations.

Caveats in the investigation of form-specific molecules of Candida albicans

Numerous reports purporting the existence of form-specific antigens of Candida albicans have been published, but it is generally unclear whether antigenic variability is an acceptable alternative interpretation. In this study, we used indirect immunofluorescence and immunogold electron microscopy to determine the distribution and form specificities of two antigens during yeast and hyphal growth in several defined and complex media. The results confirmed that antigen expression varies with length of incubation, nutrition, and serotype and indicate that the form specificities of antigens may be misinterpreted when conclusions are based exclusively on indirect immunofluorescence and extraction procedures. We therefore suggest that investigations be designed to include serotype A and B isolates grown in both complex and chemically defined media and that agglutination, immunofluorescence, or enzyme-linked immunosorbent assays on whole cells or cell extracts be used as presumptive tests. Confirmation of form-specific antigens should be done by appropriate immunoelectron microscopic evaluation.

Expression of an epitope by surface glycoproteins of Candida albicans. Variability among species, strains and yeast cells of the genus Candida

Expression of an antigenic epitope reactive with an IgM monoclonal antibody was studied in 253 Candida isolates by direct agglutination. Isolates of Candida albicans reacted significantly more often with the antibody than did isolates of other species. The agglutination scores for C. albicans isolates from sources associated with possible deep-seated Candida infection were significantly higher than for those from other sources. However, there was considerable overlap of scores between these two groups so that the functional significance of the association is uncertain. There were no associations between agglutination score and C. albicans biotype: multiple isolates from individual patients gave similar agglutination scores. Expression of the epitope within colonies of cloned strains was studied by autoradiography of colony blots on nitrocellulose and by immunoperoxidase staining of colonies in situ. It was found that the epitope was expressed variably by portions of colonies of both agglutination-positive and agglutination-negative strains. Indirect immunofluorescence revealed that expression of the epitope at the surface of C. albicans germ tubes and their associated buds was variable from cell to cell. It was not directly related to morphology or stage of growth of the cells.

Current trends in Candida albicans research

Candida albicans is an opportunistic pathogen of human beings and other mammals. Two other features, besides its pathogenicity, have made it a popular organism of study. It exists in different cellular forms and can change from one form to another, depending on growth conditions. Thus, it is being used as a model system to study cellular differentiation. It can also heritably and reversibly switch its cellular and colony morphologies. The yeast is diploid and lacks a sexual cycle. Thus, it has not been possible to apply the powerful methods of genetic analysis to understand morphogenesis or pathogenesis. Few clinical isolates are haploid, but they do not form hyphae and are not yet well characterized. Recombinant DNA techniques are increasingly being applied to C. albicans to solve many of the unanswered questions of morphogenesis and pathogenesis. Genetic transformation and gene-disruption techniques were recently developed for the yeast. Thus it is possible to study the role of any cloned gene through directed mutagenesis. However, the difficulty is to clone the putative genes involved in morphogenesis or pathogenesis. Candida albicans exists in four different cellular forms, namely blastospores, pseudohyphae, hyphae and chlamydospores. Blastospore-to-hypha conversion is well studied. A variety of conditions can induce this transition. It is not clear how cells sense such varied conditions and respond appropriately. In other systems where differentiation is well understood, regulatory genes which control differentiation have been uncovered. These genes cause differential expression of other genes, and ultimately differentiated phenotypes. Thus, it is likely that differential gene expression is involved in the bud-to-hypha transition in C. albicans. Certain proteins are expressed exclusively on the cell surface of hyphae. It should be possible to clone genes coding for these proteins. A study of the expression of these genes might allow us to identify the regulatory gene which determines differentiation. Another approach to understanding morphogenesis is to study how the difference in the shape of buds and hyphae is generated. This difference appears to be due to the differential activity of apical and general growth zones, which determine growth of the cell wall. Activity of these growth zones is apparently determined by actin localization. It remains a possibility that conditions which induce hyphae formation may directly affect actin localization or cell-wall growth zones and cause differences in cell shape. Candida albicans can also heritably switch its cellular phenotype. This has come to light from a study of colony-morphology switching. Some strains can switch their colony morphology, both heritably and reversibly.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of glutaraldehyde fixation on cell surface binding capacity of Candida albicans

The ability of viable and glutaraldehyde-fixed, stationary-phase yeast cells of Candida albicans to bind concanavalin A and monospecific antiserum for antigenic factor 1 was examined. Both fluorescence flow cytometric analysis and transmission electron microscopy indicated that glutaraldehyde-fixed cells bound less of the two reagents than did unfixed viable cells.

Oral Candida albicans isolates from nonhospitalized normal carriers, immunocompetent hospitalized patients, and immunocompromised patients with or without acquired immunodeficiency syndrome

A total of 128 human oral isolates of Candida albicans were collected from asymptomatic healthy carriers (64 isolates); asymptomatic, nonimmunosuppressed, hospitalized patients (25 isolates); immunosuppressed transplant patients (19 isolates); and human immunodeficiency virus-infected patients with symptoms of acquired immunodeficiency syndrome and oral candidiasis (20 isolates). Isolates were serotyped as A or B and tested for reactivity with an agglutinating immunoglobulin M monoclonal antibody (H9). Immunocompetent individuals colonized by oral C. albicans were almost equally likely to carry serotype A as serotype B cells, while immunocompromised individuals were at least twice as likely to be infected by serotype B than serotype A strains. The reactivity of isolates with H9 antibody followed a similar but more distinctive pattern. Approximately half of the strains from immunocompetent individuals reacted strongly with H9, and the remainder reacted weakly. However, up to 75% of the isolates from immunocompromised patients reacted weakly with H9, while the remainder reacted strongly. A correlation between H9 reactivity and the serotypes of these isolates existed (P = 0.16). The correlation between H9 reactivity and immune status was even stronger (P = 0.025). The monoclonal antibody activities described above were determined by agglutination tests during defined phases of C. albicans growth. Expression of antigen at various times during growth of several isolates was confirmed at the cellular level by analysis using fluorescence-activated cell sorting. Despite the correlation between serotype A and H9 reactivity, H9 antigen was not identical to the serotype A antigen because four serotype A strains reacted only weakly with H9 antibody, and one strain reacted strongly with H9 but was serotype B. These data indicate that oral strains of C. albicans from immunocompetent individuals differ as a group from C. albicans isolated from those who are immunosuppressed.

Identification of wall-specific antigens synthesized during germ tube formation by Candida albicans

Walls of the two cellular forms (blastoconidia and mycelia) of Candida albicans ATCC 26555 were obtained from cells metabolically labeled (6-h pulse) with 14C-protein hydrolysate and [3H]threonine. Walls were purified by thorough washings with buffered and sodium dodecyl sulfate solutions and digested with Zymolyase 20T. The enzymatic treatment released four major high-molecular-weight mannoproteins (HMWM), with apparent molecular masses of 650, 500, 340, and 200 kilodaltons (HMWM-650, HMWM-500, HMWM-340, and HMWM-200, respectively), from yeast cells, whereas two high-molecular-mass mannoproteins (HMWM-260 and HMWM-180) were solubilized from mycelial cells. Some additional minor low-molecular-weight species were also detected in the enzymatic digests of walls from both types of cell. Single and dual pulse-chase experiments indicated that the HMWM-260 and HMWM-180 species reflect de novo synthesis of new proteins specific for the mycelia and do not represent a topological rearrangement of blastoconidium wall components. Monoclonal antibodies were raised against the HMWM-260 species (quantitatively the predominant component in the mycelial walls), and polyclonal rabbit antibodies were obtained against yeast or mycelial cell walls. Anti-mycelial cell wall polyclonal antibodies were adsorbed to whole killed blastoconidia to remove antibodies against common blastoconidium and mycelial wall antigens. Titration by enzyme-linked immunosorbent assay revealed that the monoclonal antibodies could recognize an epitope of the protein moiety of the HMWM-260 mannoprotein. Immunoblotting and immunofluorescence techniques using these monoclonal and polyclonal antibodies confirmed that the HMWM-260 and HMWM-180 species are specific components of the envelope of the mycelial cell walls.

Interactions of monospecific antisera with cell surface determinants of Candida albicans

Flow cytometric analysis of indirect immunofluorescence showed that surface determinants recognized by antisera (Candida Check; Iatron Laboratories, Tokyo, Japan) for factors 1, 4, 5, and 6 were expressed to the same extent by all cells of Candida albicans under each growth condition and for each morphology examined. Fluorescence intensity increased with increasing cell size.

Antigenic differences in the surface mannoproteins of Candida albicans as revealed by monoclonal antibodies

Monoclonal antibodies to Candida albicans were prepared with blastoconidia bearing germ tubes used as the immunogen. Four antibodies reacted by immunofluorescence with surfaces of C. albicans as well as Candida stellatoidea, Candida tropicalis, and several strains of C. albicans, but not with Torulopsis glabrata. One antibody reacted with Saccharomyces cerevisiae. In addition, the monoclonal antibodies precipitated material of approximately 200 kilodaltons when tested against metabolically labeled blastoconidia digests. The monoclonal antibodies exhibited heterogeneous staining of C. albicans surfaces, as shown by immunofluorescence. None of the monoclonal antibodies were specific to germ tubes. More importantly, however, two of the monoclonal antibodies reacted with the mannoprotein precipitin arc of C. albicans that was produced by reference rabbit polyclonal antisera by crossed immunoelectrophoresis, thus linking the heterogeneity seen by immunofluorescence to the heterogeneity in mannoproteins. Finally, three of the monoclonal antibodies reacted with a glycan fraction of cell digests, indicating their reactivity with the carbohydrate portion of the mannoprotein.

Production and characterization of monoclonal antibodies against secretory proteinase of Candida albicans CBS 2730

We describe the production and characterization of three murine monoclonal antibodies (M1-M3) which are directed against different epitopes of the secretory aspartic proteinase of Candida albicans CBS 2730. All antibodies belonged to the IgM class, and they recognized denatured enzyme. Only antibody M1 was capable to react with the active proteinase. Differential reactivity was also observed with a large fragment of the proteinase of C. albicans. All antibodies recognized the corresponding proteinase of C. tropicalis 293 both in the active, and in the denatured state. Denatured porcine pepsin was also recognized by all three antibodies. However, active pepsin was recognized only by antibodies M1 and M2. The antibodies did not inhibit enzymatic activity, and they were not suited for immunofluorescence detection of proteinase on fungal cells. However, employing Western blot analysis, proteinase antigen was detected by antibody M 1 in the serum of a patient suffering from candidal pneumonia. The circulating proteinase antigen was found to be bound to patient's IgM. Implications for the use of monoclonal antibodies in the serodiagnosis of candidosis, and first experiences with other monoclonal anti-proteinase antibodies are discussed.

[Cytologic analysis of the expression of an epitope carried by glycoproteins excreted by Candida albicans]

The present study concerns an epitope identified by a monoclonal IgM, named 5B2, generated against the parasitic phase of Candida albicans. The epitope was previously shown to be carried by excreted C. albicans glycoproteins and to be present in the sera of patients suffering from systemic candidiasis. The cytological analysis of the epitope expression was investigated in 3 different yeast strains: the C. albicans strain from which 5B2 was generated (VW.32); a C. albicans mutant, deficient in cell wall mannans (KD.102); and a Saccharomyces cerevisiae strain. Immunofluorescence assays using IgM-5B2 showed discontinuous labelling with the VW.32 strain and no labelling with the 2 other yeast strains; however, the superficial structures of the 3 strains reacted homogeneously with ConA. Ultrastructural immunodetection experiments performed with the VW.32 cells, using gold-conjugated monoclonal antibody, revealed the presence of the epitope in the vacuolo-vesicular system, the periphery of the cytoplasm, the periplasmic space and the cell wall. Under the same conditions, cells from the KD.102 strain only exhibited weak cytoplasmic labelling whereas the presence of the epitope in S. cerevisiae blastoconidia was restricted to the vesicles. Competition and double labelling experiments with IgM and ConA showed that the epitope, distributed on the great majority of VW.32 glycoproteins, is shared by a lesser proportion of the KD.102 glycoproteins and only by some vesicular glycoproteins of S. cerevisiae. Inhibition of the N-glycosylation process of the VW.32 strain by tunicamycin resulted in the absence of cytokinesis and germ tube formation. In such cells, epitope 5B2 was no longer expressed on the bud surface. These cytological results concerning the C. albicans epitope are discussed in relation to recent, more general biochemical data on the yeast glycosylation process.

Variable expression of a surface determinant during proliferation of Candida albicans

The surface expression of an antigenic determinant that is present in the cell wall of Candida albicans was investigated with monoclonal antibody 24 (MAb24), an immunoglobulin M MAb. The proportion of the cell population that expressed the epitope under different growing conditions was determined by indirect immunofluorescence microscopy. More than 90% of stationary-phase yeast cells of strain B311 grown at 28 degrees C expressed the antigen. Less than 50% of yeast cells grown exponentially at 28 degrees C or either growing or stationary-phase yeast cells cultivated at 37 degrees C expressed the epitope. Germ tubes, which were induced at 37 degrees C from stationary-phase yeast cells grown at 28 degrees C, expressed the determinant on the parent yeast but not the hyphal portion of the germ tube. The change in antigen expression by stationary-phase cells grown at 28 degrees C, when they resumed growth by bud formation, suggested that antigen expression was lost by cells in the inoculum prior to the first cell division. By using the same assay, strong positive reactions were observed in stationary-phase cultures of other isolates of C. albicans, C. guilliermondii, C. stellatoidea, and C. tropicalis, but not with isolates of C. krusei, C. parapsilosis, or Torulopsis glabrata. The identification of the antigenic determinant as a carbohydrate was based on three observations: (i) interaction with a mannan preparation from the same organism, (ii) sensitivity of the antigen to periodate but not proteases, and (iii) coincidence of the migration of antigen during electrophoresis with material which stained intensely with carbohydrate but not with protein reagents. These observations suggest that the expression of the antigenic determinant of MAb24 is dependent on the growth conditions, growth state, and morphology of the cell and that the topography of the cell surface is dynamic.

Temperature-modulated physiological characteristics of Candida albicans

Despite numerous investigations on candidiasis, definitive conclusions concerning virulence factors are few because of oftentimes confusing and contradictory results. By utilizing various physiologic tests, which include germ tube induction, inhibition of germination by a morphogenic autoregulatory substance, enzyme production, susceptibility to exogenous chemicals, and cell surface hydrophobicity, we demonstrated that such variability is due, in part, to the environmental conditions in which cells were grown in preparation for analysis. Room-temperature grown cells were generally less sensitive to environmental perturbation and germinated more uniformly than cells grown at 37 degrees C. The implication of these results in relation to pathogenic studies and the epidemiology of candidiasis is suggested.