Immunochemical study on the mannans of Candida albicans NIH A-207, NIH B-792, and J-1012 strains prepared by fractional precipitation with cetyltrimethylammonium bromide

Relative abundance of oligosaccharides in Candida species as determined by fluorophore-assisted carbohydrate electrophoresis

Fluorophore-assisted carbohydrate electrophoresis (FACE) is a straightforward, sensitive method for determining the presence and relative abundance of individual oligomannosyl residues in Candida mannoprotein, the major antigenic determinant located on the outer surface of the yeast cell wall. The single terminal aldehydes of oligomannosyl residues released by hydrolysis were tagged with the charged fluorophore 8-aminonaphthalene-1,3,6-trisulfonate (ANTS) and separated with high resolution on the basis of size by polyacrylamide gel electrophoresis. ANTS fluorescence labeling was not biased by oligomannoside length; therefore, band fluorescence intensity was directly related to the relative abundance of individual oligomannoside moieties in heterogeneous samples. FACE analysis revealed the major oligomannosides released by acid hydrolysis and beta-elimination of Fehling-precipitated mannan from Candida albicans, which were the same as those previously reported in studies based on mass and nuclear magnetic spectroscopic analysis. FACE was also amenable to the analysis of samples obtained by direct hydrolysis of whole yeast cells. Whole-cell acid hydrolysis and whole-cell beta-elimination of two isolates each of C. albicans, C. glabrata, C. krusei, C. lusitaniae, C. parapsilosis, C. rugosa, C. stellatoidea, and C. tropicalis resulted in oligomannoside gel banding patterns that were species and strain specific for the 16 isolates surveyed. Whereas some bands were specific for an individual isolate or species, other bands were shared by two or three species in various groupings. Differences in the mannoprotein composition of C. albicans A9 and four spontaneous cell surface mutants were also detected. Mannan "fingerprints," or banding pattern profiles, derived from the electrophoretic mobilities of individual bands relative to the migration of acid-hydrolyzed dextran (relative migration index) yielded profiles characteristic of individual isolates not revealed by standard assimilation and biochemical profiles. FACE represents an accessible, sensitive, and quantitative analytical tool enabling the characterization of yeast mannan complexity.

beta-1,2-linked oligomannosides from Candida albicans bind to a 32-kilodalton macrophage membrane protein homologous to the mammalian lectin galectin-3

beta-1,2-linked oligomannoside residues are present, associated with mannan and a glycolipid, the phospholipomannan, at the Candida albicans cell wall surface. beta-1,2-linked oligomannoside residues act as adhesins for macrophages and stimulate these cells to undergo cytokine production. To characterize the macrophage receptor involved in the recognition of C. albicans beta-1,2-oligomannoside we used the J774 mouse cell line, which is devoid of the receptor specific for alpha-linked mannose residues. A series of experiments based on affinity binding on either C. albicans yeast cells or beta-1,2-oligomannoside-conjugated bovine serum albumin (BSA) and subsequent disclosure with biotinylated conjugated BSA repeatedly led to the detection of a 32-kDa macrophage protein. An antiserum specific for this 32-kDa protein inhibited C. albicans binding to macrophages and was used to immunoprecipitate the molecule. Two high-pressure liquid chromatography-purified peptides from the 32-kDa tryptic digest showed complete homology to galectin-3 (previously designated Mac-2 antigen), an endogenous lectin with pleiotropic functions which is expressed in a wide variety of cell types with which C. albicans interacts as a saprophyte or a parasite.

The Candida albicans phospholipomannan is a family of glycolipids presenting phosphoinositolmannosides with long linear chains of beta-1,2-linked mannose residues

In a series of studies, we have shown that Candida albicans synthesizes a glycolipid, phospholipomannan (PLM), which reacted with antibodies specific for beta-1,2-oligomannosides and was biosynthetically labeled by [(3)H]mannose, [(3)H]palmitic acid, and [(32)P]phosphorus. PLM has also been shown to be released from the C. albicans cell wall and to bind to and stimulate macrophage cells. In this study, we show by thin layer chromatography scanning of metabolically radiolabeled extracts that the C. albicans PLM corresponds to a family of mannose and inositol co-labeled glycolipids. We describe the purification process of the molecule and the release of its glycan fraction through alkaline hydrolysis. Analysis of this glycan fraction by radiolabeling and methylation-methanolysis confirmed the presence of inositol and of 1, 2-linked mannose units. NMR studies evidenced linear chains of beta-1,2-oligomannose as the major PLM components. Mass spectrometry analysis revealed that these chains were present in phosphoinositolmannosides with degrees of polymerization varying from 8 to 18 sugar residues. The PLM appears as a new type of eukaryotic inositol-tagged glycolipid in relationship to both the absence of glucosamine and the organization of its glycan chains. This first structural evidence for the presence of beta-1, 2-oligomannosides in a glycoconjugate other than the C. albicans phosphopeptidomannan may have some pathophysiological relevance to the adhesive, protective epitope, and signaling properties thus far established for these residues.

Overview of N- and O-linked oligosaccharide structures found in various yeast species

Yeast and most higher eukaryotes utilize an evolutionarily conserved N-linked oligosaccharide biosynthetic pathway that involves the formation of a Glc3Man9GlcNAc2-PP-dolichol lipid-linked precursor, the glycan portion of which is co-translationally transferred in the endoplasmic reticulum (ER) to suitable Asn residues on nascent polypeptides. Subsequently, ER processing glycohydrolases remove the three glucoses and, with the exception of Schizosaccharomyces pombe, a single, specific mannose residue. Processing sugar transferases in the Golgi lead to the formation of core-sized structures (Hex<15GlcNac2) as well as cores with an extended poly-alpha1,6-Man 'backbone' that is derivatized with various carbohydrate side chains in a species-specific manner (Hex50-200GlnNAc2). In some cases these are short alpha1,2-linked Man chains with (Saccharomyces cerevisiae) or without (Pichia pastoris) alpha1,3-Man caps, while in other yeast (S. pombe), the side chains are alpha1,2-linked Gal, some of which are capped with beta-1,3-linked pyruvylated Gal residues. Charged groups are also found in S. cerevisiae and P. pastoris N-glycans in the form of mannose phosphate diesters. Some pathogenic yeast (Candida albicans) add poly-beta1,2-Man extension through a phosphate diester to their N-glycans, which appears involved in virulence. O-Linked glycan synthesis in yeast, unlike in animal cells where it is initiated in the Golgi using nucleotide sugars, begins in the ER by addition of a single mannose from Man-P-dolichol to selected Ser/Thr residues in newly made proteins. Once transported to the Golgi, sugar transferases add one (C. albicans) or more (P. pastoris) alpha1,2-linked mannose that may be capped with one or two alpha1,3-linked mannoses (S. cerevisiae). S. pombe is somewhat unique in that it synthesizes a family of mixed O-glycans with additional alpha1,2-linked Man and alpha1,2- and 1, 3-linked Gal residues.

Serologic response to cell wall mannoproteins and proteins of Candida albicans

The cell wall of Candida albicans not only is the structure in which many biological functions essential for the fungal cells reside but also is 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 the carbohydrate and protein moieties are able to trigger immune responses. Although cell-mediated immunity is often considered to be the most important line of defense against candidiasis, cell wall protein and glycoprotein components also elicit a potent humoral response from the host that may include some protective antibodies. 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 influence profoundly the host-parasite interaction by affecting antibody-mediated functions such as opsonin-enhanced phagocytosis and blocking the binding activity of fungal adhesins for host ligands. In this review, the various members of the protein and glycoprotein fraction of the C. albicans cell wall that elicit an antibody response in vivo are examined. Although a number of proteins have been shown to stimulate an antibody response, for some of these species the response is not universal. On the other hand, 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 candidasis, particularly the disseminated form. In addition, recent studies have focused on the potential for antibodies to cell wall protein determinants to protect the host against infection. Hence, a better understanding of the humoral response to 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 for the management of this type of infection.

Definitive chemical evidence for the constitutive ability of Candida albicans serotype A strains to synthesize beta-1,2 linked oligomannosides containing up to 14 mannose residues

We have previously reported the presence of phosphate bound beta-1,2 linked oligomannosides with unusually high degrees of polymerization (DP > 7) in the mannan of Candida albicans strain VW32. To confirm this observation, we have prepared these oligomannosides from the mannan of C. albicans strain NIH A 207. Gel filtration chromatography and TLC analysis revealed DP up to 14. For both strains, NMR analysis confirmed the exclusive presence of beta-1,2 linkages in the pools of oligomannosides with a DP higher than 6 which presented an average DP of 10.6 (VW32) and 10.4 (NIH A 207). These results are important to consider in relation with the ability of these C. albicans derived oligomannosides to trigger TNFalpha synthesis according to their DP.

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.

Characterization of beta-1,2-mannosyltransferase in Candida guilliermondii and its utilization in the synthesis of novel oligosaccharides

A particulate insoluble enzyme fraction containing mannosyltransferases from Candida guilliermondii IFO 10279 strain cells was obtained as the residue after extracting a 105,000 x g pellet of cell homogenate with 1% Triton X-100. Incubation of this fraction with a mannopentaose, Manalpha1-->3(Manalpha1-->6)Manalpha1-->2Manalpha1+ ++-->2Man, in the presence of GDP-mannose and Mn2+ ion at pH 6.0 gave a third type of beta-1,2 linkage-containing mannohexaose, Manbeta1-->2Manalpha1-->3(Manalpha1-->6)Manalpha1++ +-->2Manalpha1-->2Man , the structure of which was identified by means of a sequential NMR assignment. The results of a substrate specificity study indicated that the beta-1,2-mannosyltransferase requires a mannobiosyl unit, Manalpha1--> 3Manalpha1-->, at the nonreducing terminal site. We synthesized novel oligosaccharides using substrates possessing a nonreducing terminal alpha-1,3-linked mannose unit prepared from various yeast mannans. Further incubation of the enzymatically synthesized oligosaccharide with the enzyme fraction gave the following structure, Manbeta1-->2Manbeta1-->2Manalpha1-->3(Manalpha1- ->6)Manalpha1--> 2Manalpha1-->2Man, which has been found to correspond to antigenic factor 9. Incubation of Candida albicans serotype B mannan with the enzyme fraction gave significantly transformed mannan, which contains the third type of beta-1,2-linked mannose units.

Demonstration of the presence of alpha-1,6-branched side chains in the mannan of Candida stellatoidea

A mild acetolysis of the mannans of Candida stellatoidea was performed after acetylation to yielded an alpha-1,6-branched mannohexaose, the presence of which had been predicted from the appearance of a specific H1-H2-correlated cross-peak in two-dimensional homonuclear Hartmann-Hahn spectroscopy. In this study, we found that the de-O-acetylation of a 4-O-acetyl group at the branching point, the 3,6-di-O-substituted mannose unit, of an acetylated oligosaccharide by sodium methoxide is significantly slower than that of other acetyl groups. We could separate the 4-O-acetylated branching oligosaccharide from linear isomer using high-performance liquid chromatography. Before and after the de-O-acetylation of the purified branching oligosaccharide, their 1H-NMR signals were sequentially assigned by means of the nuclear Overhauser effect. In the sequential NMR assignment study, we showed that the alpha-1,6-linked mannose unit is attached to the 3-O-substituted unit based on the presence of NOE cross-peak between H1 of the branching mannose unit and H6 of the 3-O-substituted mannose unit. An enzyme-linked immunosorbent inhibition assay of the reactivity of factor 4 serum to C. stellatoidea mannan by several oligosaccharides indicated that the alpha-1,6-branched oligosaccharide and the beta-1,2 linkage-containing oligosaccharides showed inhibitory activity. This result indicates that factor 4 serum, as well as factor 5 and 6 sera, contains antibodies against beta-1,2-linked mannose units which have been reported to participate in pathogenicity via cytokine production and/or adherence. From the assignment results of H1-H2-correlated cross-peaks of oligosaccharides and mannans, the molar ratio of the mannan side chains was proposed. In this study, we demonstrated that the epitope structure of the C. stellatoidea type I strains was the same as that of the C. albicans NIH B-792 (serotype B) strain.

Characterization of alpha-1,6-mannosyltransferase responsible for the synthesis of branched side chains in Candida albicans mannan

A particulate insoluble fraction from Candida albicans NIH B-792 (serotype B) strain cells was obtained as the residue after extracting a 105000 x g pellet of cell homogenate with 1% Triton X-100. Incubation of this fraction with a mannopentaose, Man alpha 1-->3Man alpha 1-->2Man alpha 1-->Man alpha 1-->2Man, in the presence of GDP-mannose and Mn2+ at pH 6.0 gave a branched mannohexaose, [sequence: see text] 6 the structure of which was identified by means of sequential off assignment. However, the enzyme fraction obtained from Candida parapsilosis gave Man alpha 1-->2Man alpha 1-->3Man alpha 1-->2Man alpha 1-->2 Man alpha 1-->2Man under the same conditions. These results demonstrate the finding that the structural difference in the mannans of these two species is due to the presence of alpha-1.6-linked branching mannose units in the C. albicans mannan [Shibata, N., Ikuta, K., Imai, T., Satoh, Y., Satoh, R., Suzuki, A., Kojima, C., Kobayashi, H., Hisamichi, K. & Suzuki, S. (1995) J. Biol. Chem. 270, 1113-1122]. The substrate-specificity study of the enzyme indicated that the structural requirement of the alpha-1,6-mannosyltransferase is Man alpha 1-->3Man alpha 1-->. The alpha-1,6-mannosyltransferase also transferred the alpha-1,6-linked branching mannose unit to the mannan of Saccharomyces cerevisiae. The transformation of the mannan was detected by the appearance of antigenic factor 4 using an enzyme-linked immunosorbent assay and two-dimensional homonuclear Hartmann-Hahn spectroscopy.

The morphology of Candida albicans in two different Earle base media in the presence of tunicamycin

The effect of tunicamycin on the morphology of Candida albicans yeast cells and germ tubes grown in two different Earle's minimal essential media was investigated. Tunicamycin inhibited germ tube and mycelia formation. Inhibition increased the size and caused aberrant morphology of yeast cells, including bud formation. These cells are hydrophobic and could be used for the production of two monoclonal antibodies suitable for the study of adhesion phenomena as well as ectomural properties.

Antigenicity of cell wall mannans of Candida albicans NIH B-792 (serotype B) strain cells cultured at high temperature in yeast extract-containing sabouraud liquid medium

Cultivation of Candida albicans NIH B-792 (serotype B) at high temperature (37 degrees C) for 48 h in yeast extract-containing Sabouraud liquid medium (YSLM) provided the following findings in comparison with the findings obtained after incubation at 27 degrees C. Growth of the blastoconidia of this strain was decreased, with a dry weight of 9%, and the cells were deficient in cytokinesis. The cells did not undergo agglutination with serum factor 5 from a commercially available serum factor kit (Candida Check). Mannan (B-37-M) obtained from the cells cultured at 37 degrees C had partially lost its reactivity against serum factor 4 and lost most of its reactivity against serum factor 5 in an enzyme-linked immunosorbent assay (ELISA) in contrast to that (B-27-M) at 27 degrees C. Both cells and mannan prepared by cultivation first at 37 degrees C and then at 27 degrees C entirely recovered their reactivities with serum factors 4 and 5. 1H-nuclear magnetic resonance analysis also revealed that B-37-M had lost a beta-1,2-linked mannopyranose unit and retained a phosphate group. Similar changes were observed in the three other serotype B strains used in the study. The beta-1,2-linked mannooligosaccharides longer than mannotetraose were not included among the products released from B-37-M by mild acid treatment. The results of the inhibition ELISA with a series of beta-1,2-linked mannooligosaccharides from biose to octaose (M2 to M8, respectively) showed that the reactivity against serum factor 4 was inhibited most strongly by the oligosaccharides M4 to M8 and that the reactivity against serum factor 5 was inhibited completely by relatively longer oligosaccharides, M5 to M8, indicating their participation as the antigenic factor 5 epitopes.

Existence of novel branched side chains containing beta-1,2 and alpha-1,6 linkages corresponding to antigenic factor 9 in the mannan of Candida guilliermondii

Isolation of beta-linkage-containing side chain oligosaccharides from the mannan of Candida guilliermondii IFO 10279 strain has been conducted by acetolysis under mild conditions. A structural study of these oligosaccharides by one- and two-dimensional NMR and methylation analyses indicated the presence of extended oligosaccharide side chains with two consecutive beta-1,2-linked mannose units at the nonreducing terminal of alpha-linked oligosaccharides. The linkage sequence present in this mannan, Man beta 1-->2Man alpha 1-->3Man alpha-->, has also been found in the mannan of Saccharomyces kluyveri but not in the mannan of Candida species. Furthermore, these oligosaccharides are branched at position 6 of the 3-O-substituted mannose units as follows. (Carbohydrate sequence in text) Structure 1 and (Carbohydrate sequence in text) Structure 2 The H-1 signals of the mannose units substituted by a 3,6-di-O-substituted unit showed a significant upfield shift (delta delta = 0.04-0.08 ppm) due to a steric effect. The inhibition of an enzyme-linked immunosorbent assay between the mannan of C. guilliermondii and factor 9 serum with oligosaccharides obtained from several mannans indicated that only the oligosaccharides with the above structure were active, suggesting that these correspond to the epitope of antigenic factor 9.

Specific antibody response to oligomannosidic epitopes in Crohn's disease

Elevated antibody levels against the yeast Saccharomyces cerevisiae have been reported in sera from patients with Crohn's disease and not with ulcerative colitis. The aim of the study was to identify the nature of the epitopes supporting this antibody response. Whole cells from different S. cerevisiae strains were selected in immunofluorescence assay for their ability to differentiate the antibody responses of patients with Crohn's disease and ulcerative colitis. Their cell wall phosphopeptidomannans were then tested as antigen in enzyme-linked immunosorbent assay (ELISA) against sera from 42 patients with Crohn's disease, 20 patients with ulcerative colitis, and 34 healthy controls. Graded chemical degradations were performed on the most reactive strain phosphopeptidomannan. The discriminating epitope was determined through gas-liquid chromatography-mass spectrometry. The greatest discrimination among patients with Crohn's disease, ulcerative colitis, and controls was obtained with Su1, a S. cerevisiae strain used in brewing of beer. ELISA directed against phosphopeptidomannan of this strain was 64% sensitive and 77% specific for discriminating Crohn's disease versus ulcerative colitis and 71% sensitive and 89% specific for Crohn's disease versus controls. Periodate oxidation and selective degradation demonstrated that the most important polysaccharide epitope was shared by both the acid-stable and the alkali-labile domains of the phosphopeptidomannan. The determination of oligomannose sequences of S. cerevisiae Su1 phosphopeptidomannans suggested that a mannotetraose, Man (1 --> 3)Man(1 --> 2)Man(1 --> 2)Man, supported the serological response seen in Crohn's disease. Further identification of the immunogen eliciting this antibody response as a marker of the disease may help to understand its etiology.

Detection of beta-1,2-mannosyltransferase in Candida albicans cells

A particulate insoluble fraction from Candida albicans J-1012 (serotype A) strain cells was obtained as the residue after extracting a 105,000 x g pellet of cell homogenate with 1% Triton X-100. Incubation of this fraction with a mannopentaose, Man beta 1-->2Man alpha 1-->(2Man alpha 1-->)(2)2Man (alpha beta Man5), in the presence of GDP-mannose followed by high performance liquid chromatography showed the formation of a mannohexaose. Analysis of the product by 1H NMR indicates that alpha beta Man5 was changed to Man beta 1-->2Man beta 1-->2Man alpha 1-->(2Man alpha 1-->)2 2Man (alpha beta Man6). This beta-1,2-mannosyltransferase (ManTase) II activity was completely inhibited by Zn2+ and was not restored by the addition of EDTA. The corresponding enzyme fraction from C. albicans NIH B-792 (serotype B) strain cells, the mannan of which does not possess both the alpha beta Man5 and alpha beta Man6 side chains, also exhibited the same beta-1,2-ManTase II activity.

Existence of branched side chains in the cell wall mannan of pathogenic yeast, Candida albicans. Structure-antigenicity relationship between the cell wall mannans of Candida albicans and Candida parapsilosis

Isolation of side chain oligosaccharides from mannans of Candida albicans NIH B-792 (serotype B) and Candida parapsilosis IFO 1396 strains has been conducted by acetolysis under mild conditions. Structural study of these oligosaccharides by 1H and 13C NMR and methylation analyses indicated the presence of novel branched side chains with the following structures in C. albicans mannan. [sequence: see text] It was observed that the H-1 proton chemical shifts of the second and the third mannose units from the reducing terminus in each oligosaccharide are shifted upfield by substitution with an alpha-linked mannose unit at position 6 of the 3-O-substituted mannose unit. An agglutination inhibition assay between factor 4 serum and cells of Candida stellatoidea IFO 1397 lacking the beta-1,2-linked mannose unit, with oligosaccharides obtained from these mannans, indicated that only the branched oligosaccharides were active. This finding suggests that the branched oligosaccharides correspond to the epitope of antigenic factor 4. The presence of the branched structure in other mannans was detected by the characteristic H-1-H-2-correlated cross-peak of the alpha-1,2-linked mannose unit connected with the 3,6-di-O-substituted one by two-dimensional homonuclear Hartmann-Hahn spectroscopy.

Structure of cell wall mannan of Candida kefyr IFO 0586

We conducted a structural analysis of the antigenic cell wall mannoprotein (mannan) isolated from Candida kefyr (formerly Candida pseudotropicalis) IFO 0586. The result of two-dimensional homonuclear Hartmann-Hahn analysis of this mannan indicates that the molecule is constructed from alpha-1,2- and alpha-1,6-linked mannopyranose residues. Upon alkali treatment (beta-elimination reaction), this mannan released two alpha-1,2-linked mannooligosaccharides, biose and triose. The structure of the alkali-stable mannan (outer chain) moiety was investigated by acetolysis. The structures of the resultant oligosaccharides, biose and triose, from the outer chain moiety were found to be the same as those of the alkali-released ones. Further, the treatment of the parent mannan with an Arthrobacter GJM-1 exo-alpha-mannosidase gave a linear mannan consisting solely of alpha-1,6-linked mannopyranose residues. These results indicate that the mannan forms the long backbone of the alpha-1,6 linkage, with a large number of short alpha-1,2-linked oligomannosyl side chains forming a comblike structure. Moreover, we investigated the serological properties of this mannan by performing an inhibition assay of a slide agglutination reaction with mannooligosaccharides and polyclonal factor sera (Candida Check; Iatron). The result indicates that the factor 1 serum preferentially recognizes the alpha-1,2-linked oligomannosyl side chains in this mannan. On the other hand, the fact that the mannan does not contain an antigenic determinant(s) corresponding to factor 8 suggests that the epitope(s) of this factor resides in other molecules on the cell surface of this strain.

Temperature-dependent change of serological specificity of Candida albicans NIH A-207 cells cultured in yeast extract-added Sabouraud liquid medium: disappearance of surface antigenic factors 4, 5, and 6 at high temperature

The cells of Candida albicans NIH A-207 strain (A-strain) cultivated in YSLM at high temperatures (37 and 40 degrees C) did not undergo agglutination with the factor sera 4, 5, and 6 in a commercially available factor serum kit, 'Candida Check', and formed a grape-like shape. The mannans isolated from the cells had lost their reactivity against the factor sera in ELISA. It was also revealed by 1H NMR analysis that the mannans contained neither a phosphate group nor a beta-1,2-linked mannopyranose unit, although these mannans increased the non-reducing terminal alpha-1,3-linked mannopyranose unit. The cells and the mannans prepared by cultivation at such high temperatures followed by 27 degrees C in the same medium entirely recovered the reactivity with the factor sera.

Expression of alpha-1,3 linkage-containing oligomannosyl residues in a cell-wall mannan of Candida tropicalis grown in yeast extract-Sabouraud liquid medium under acidic conditions

We investigated the cell-wall mannan obtained from Candida tropicalis IFO 1647 strain cells grown in yeast extract-Sabouraud medium at pH 3.0 by two-dimensional homonuclear Hartmann-Hahn spectroscopy. The results indicate that the phosphate group and the side chains containing a beta-1,2-linked mannopyranose unit decreased compared to those of mannan from cells grown under conventional conditions (pH 5.9) with concomitant expression of alpha-1,3 linkage-containing oligomannosyl side chains. The results of acetolysis of these mannans indicated that the presence of alpha-1,3-linked mannopyranose unit existed in side chains corresponding to pentaose and hexaose, Manp alpha 1-3 Manp alpha 1-2Manp alpha 1-2 Manp alpha 1-2Man, and Manp alpha 1-2Manp alpha 1-3Manp alpha 1-2Manp alpha 1-2Manp alpha 1-2Man, in the mannan from cells grown at pH 3.0.

Cross-reactivity between the mannan of Candida species, Klebsiella K24 polysaccharide and Salmonella C1 and E O-antigens is mediated by a terminal non-reducing beta-mannosyl residue

Rat monoclonal antibody MASC1-MR9 (MR9) binds to a mannan of Candida species and the O-antigenic polysaccharides of Salmonella bacteria of serogroups C1 (CO) and E (EO). Mannan and glycoconjugates comprising BSA and O-antigen polysaccharides, decasaccharide-BSA (CO-BSA) or trisaccharide-BSA (EO-BSA), inhibited each other's reactivity with MR9. The saccharides beta-D-Manp-(1-->6)-alpha-D-Manp-1-OMe, beta-D-Manp(1-->3)-alpha-D-Manp-1-OMe, beta-D-Manp(1-->2)-alpha-D-Manp-1-OMe (corresponds to the terminal non-reducing end of Salmonella serogroup C1 O-antigen) and beta-D-Manp(1-->4)-alpha-L-Rhap(1-->3)-alpha-D-Galp-1-O-p-++ +trifluoroacetamido aniline (corresponds to the backbone of Salmonella serogroup E O-antigen) inhibited the binding of MR9 to these antigens whereas alpha-D-Manp(1-->3)-alpha-D-Manp-1-OMe and alpha-D-Manp(1-->4)-alpha-L- Rhap-1-O-p-nitrophenyl did not. Saccharides (3-10 residues) of mammalian origin with terminal and internal Manp alpha-1-->2, Manp alpha-1-->3 and Manp alpha-1-->6 residues also failed to inhibit at any concentration. None of the saccharides with internal beta-mannosyl residue was able to inhibit the MR9 antibody. Monosaccharides D-mannose, beta-D-Manp-1-OMe and 1,5 anhydro-D-mannitol inhibited the MR9 monoclonal antibody whereas alpha-D-Manp-1-OMe, beta-D-Glcp-1-OMe, and beta-D-Galp-1-OMe did not. In addition a Klebsiella K24 capsular polysaccharide containing a beta-D-Manp(1-->4)-alpha-D- GlcA (GlcA, glucuronic acid) as a structural element possessed an inhibitory activity. MR9 therefore recognizes an epitope within beta-mannose monosaccharide residues at the terminal non-reducing ends of carbohydrate chains in mannan, and polysaccharides in Salmonella serogroups CO and EO and Klebsiella K24.

Structural modification of cell wall mannans of Candida albicans serotype A strains grown in yeast extract-Sabouraud liquid medium under acidic conditions

The cell wall mannans of two Candida albicans serotype A strains, NIH A-207 and J-1012 (abbreviated as A and J strains, respectively), cultured in yeast extract-Sabouraud liquid medium at pH 2.0, contained neither a phosphate group nor a beta-1,2-linked mannopyranose unit (H. Kobayashi, P. Giummelly, S. Takahashi, M. Ishida, J. Sato, M. Takaku, Y. Nishidate, N. Shibata, Y. Okawa, and S. Suzuki, Biochem. Biophys. Res. Commun. 175:1003-1009, 1991). In this study, the mannans obtained from A and J strains grown in pH 2.0 medium (abbreviated as mannans A2 and J2, respectively) exhibited quite different reactivities against rabbit anti-C. albicans and anti-Saccharomyces cerevisiae sera compared with those of mannans from the corresponding strains cultured in conventional medium at pH 5.9 (abbreviated as mannans A and J, respectively). Namely, mannans A2 and J2 lost reactivity against the former serum but reacted with the latter serum to a higher extent than mannans A and J. In order to account for these difference in more detail, mannans A2 and J2 were subjected to acetolysis. Elution profiles of the acetolysates were completely different from those of acetolysates obtained from mannans A and J reported in our previous papers. The 1H nuclear magnetic resonance spectra of the oligosaccharides from mannans A2 and J2 obtained by this procedure indicate that the side chains are composed of alpha-linked mannopyranose units densely linked to the alpha-1,6-linked backbone. The long side chains containing one alpha-1,3-linked mannopyranose unit are markedly increased.

Structures of cell wall mannans of pathogenic Candida tropicalis IFO 0199 and IFO 1647 yeast strains

We conducted a structural analysis of the cell wall mannans isolated from two Candida tropicalis strains, IFO 0199 and IFO 1647, exhibiting strong agglutinabilities against anti-Candida factor sera 5 and 6. The products released from these mannans by acid treatment were identified as the oligosaccharides, from biose to pentaose, consisting solely of beta-1,2-linked mannopyranose units corresponding to common epitopes of Candida albicans serotypes A and B (factor 5). Mild acetolysis of acid- and alkali-treated mannans produced large amounts of hexaose and heptaose, Man rho beta 1-2Man rho beta 1-2Man rho alpha 1-2Man rho alpha 1-2Man rho alpha 1-2Man and Man rho beta 1-2Man rho beta 1-2Man rho beta 1-2Man rho alpha 1-2 Man rho alpha 1-2Man, corresponding to the C. albicans serotype A-specific epitopes (factor 6). However, the homologous pentaose, Man rho beta 1-2Man rho alpha 1-2 Man, was not generated by this procedure. The oligosaccharides (biose to hexaose) obtained from the mannans by conventional acetolysis were composed exclusively of alpha-1,2-linked mannopyranose units. Therefore, the mannans of C. tropicalis IFO 0199 and IFO 1647 do not have the alpha-1,3-linked mannopyranose units previously observed in the mannans of C. albicans and Candida stellatoidea. The results of this study and previous findings indicate that the similarity of the antigenicities of three Candida species, C. albicans serotype A, C. stellatoidea type II, and C. tropicalis, reside in the beta-1,2 and alpha-1,2 linkages containing oligomannosyl side chain (factor 6) in the cell wall mannan.

Fungal polysaccharides

Fungal polysaccharides are cell wall components which may act as antigens or as structural substrates. As antigens, the role of mannans in Saccharomyces cerevisiae and Candida albicans, and of glycoproteins in Aspergillus fumigatus are discussed. Analyses on beta-glucan synthetase in Paracoccidioides brasiliensis and the inhibitory effect of Hansenula mrakii killer toxin on beta-glucan biosynthesis are also considered.

Structural study of a cell-wall mannan of Saccharomyces kluyveri IFO 1685 strain. Presence of a branched side chain and beta-1,2-linkage

Acetolysis of the cell-wall mannan of Saccharomyces kluyveri under mild conditions, gave fragments with 1-6 mannose residues. The structures of mannopentaose and mannohexaose were determined to be [Formula; see text] respectively, by two-dimensional homonuclear Hartmann-Hahn spectroscopy and a sequential NMR assignment method that combines 1H-13C correlated spectroscopy, relayed coherence transfer spectroscopy, 1H-detected heteronuclear multiple-bond connectivity and methylation analysis. The H1 proton chemical shift of a neighboring alpha-1,2-linked mannose unit of the 3-O-substituted structure was shifted upfield by the addition of a mannose unit to the adjacent 3-O-substituted unit by an alpha-1,6 linkage. The characteristic H1--H2-correlated cross-peak of the alpha-1,3-linked mannose unit substituted by a beta-1,2 linkage, beta 1-->2Man alpha 1-->3, in the mannan of S. kluyveri, as also found by two-dimensional homonuclear Hartmann-Hahn spectroscopy in the mannan of Candida guilliermondii, a pathogenic yeast in man.

Complete 1H- and 13C-resonance assignments for D-mannooligosaccharides of the beta-D-(1-->2)-linked series released from the phosphopeptidomannan of Candida albicans VW.32 (serotype A)

D-Mannooligosaccharides (dp 1 to > 17) were released by mild acid hydrolysis from the phosphopeptidomannan of a Candida albicans strain of A serotype (VW.32). Among these, mannooligosaccharides ranging from bi- to hepta-ose, which were obtained in appreciable amounts, were structurally investigated and found to belong to the beta-D-(1-->2)-linked series. The occurrence of such compounds has already been reported in other Candida albicans strains. The complete 1H- and 13C-resonance assignments for manno-tri- to manno-hepta-ose are reported and general rules applicable for the 1NMR spectrum analysis of linear mannooligosaccharide of the general structure, beta-D-Man p-(1-->2)-[beta-D-Man p-(1-->2)]n-beta-D-Man p are proposed.

Structural identification of an epitope of antigenic factor 5 in mannans of Candida albicans NIH B-792 (serotype B) and J-1012 (serotype A) as beta-1,2-linked oligomannosyl residues

In previous articles, we reported the presence of phosphate-bound beta-1,2-linked oligomannosyl residues in the mannans of strains of Candida albicans serotypes A and B and Candida stellatoidea. To identify the antigenic factor corresponding to this type of oligomannosyl residue, a relationship between chemical structure and antigenic specificity in the mannans of C. albicans NIH B-792 (serotype B, B-strain) and C. albicans J-1012 (serotype A, J-strain) was investigated by using a combination of two-dimensional 1H nuclear magnetic resonance spectroscopy of H-1, H-2, and H-5 regions in the mannans and an enzyme-linked immunosorbent assay that employed concanavalin A-coated microtiter plates. It was shown in the present 1H nuclear magnetic resonance study that an examination of chemical shifts not only in the H-1 region but also in the H-5 region was useful for the quantitative determination of the phosphate-bound beta-1,2-linked oligomannosyl residues. In the enzyme-linked immunosorbent assay using concanavalin A-coated plates, it was revealed that, of factor sera 1, 4, and 5, only factor serum 5 showed a reactivity proportional to the densities of the beta-1,2-linked oligomannosyl residues of the mannan subfractions of different phosphate contents that had been prepared from the bulk B-strain mannan by DEAE-Sephadex chromatography. The above results indicate that the phosphate-bound beta-1,2-linked oligomannosyl residues, Manp beta 1----(2Manp beta 1----)n2Man (n = 0-5), correspond to antigenic factor 5.

Structure of the D-mannan of the pathogenic yeast, Candida stellatoidea ATCC 20408 (type II) strain, in comparison with that of C. stellatoidea ATCC 36232 (type I) strain

Acid treatment of the cell-wall D-mannas of Candida stellatoidea strains ATCC 36232 (Type I, A3 strain) and ATCC 20408 (Type II, A2 strain) gave (1----2)-linked beta-D-manno-oligosaccharides (dp 2-5), whereas treatment with alkali gave the (1----2)-linked alpha-D-mannobiose. Conventional acetolysis of the acid- and alkali-treated D-mannan of the A3 strain gave oligosaccharides consisting of (1----2)- and (1----3)-linked alpha-D-mannopyranose residues, similar to those of Candida albicans serotype B strain. Mild acetolysis of the acid- and alkali-treated D-mannan of the A2 strain gave higher oligosaccharides that were digested by the Arthrobacter GJM-1 strain exo-alpha-D-mannosidase. The results of 1H- and 13C-NMR analyses indicated this D-mannan to contain branches with the following structures: beta-D-Manp-(1----2)-alpha-D-Manp-(1----2)-alpha-D-Manp++ +-(1----2)-alpha-D-Manp- (1----2)-D-Man, beta-D-Manp-(1----2)-beta-D-Manp-(1----2)-alpha-D-Manp -(1----2)- alpha-D-Manp-(1----2)-D-Man, and beta-D-Manp-(1----2)-beta-D-Manp-(1----2)-beta- D-Manp-(1----2)-alpha-D-Manp-(1----2)-alpha-D-Manp-(1- ---2)-alpha-D-Manp- (1----2)-D-Man, in common with the D-mannans of C. albicans serotype A strains.

Sequential nuclear magnetic resonance assignment of beta-1,2-linked mannooligosaccharides isolated from the phosphomannan of the pathogenic yeast Candida albicans NIH B-792 strain

The H-1 and H-2 signals of beta-1,2-linked mannooligosaccharides isolated from the phosphomannan of Candida albicans NIH B-792 strain by mild acid hydrolysis were assigned by a sequential NMR assignment method that combines two-dimensional 1H-1H correlated spectroscopy (COSY) and two-dimensional nuclear Overhauser enhancement and exchange spectroscopy (NOESY). The results indicated that the H-1 and H-2 of each beta-1,2-linked mannopyranose unit show largely different signals compared with those of the alpha-linked ones and that the correlation between linkages and signals could not be explained by a conventional additivity rule. Furthermore, a regular proportional downfield shift of the H-1 signal was observed in the order of the mannose unit from the reducing terminal except those of the reducing and nonreducing terminal positions. Although the 1H NMR spectra of these oligosaccharides were complicated due to the presence of a large portion of the beta-anomer from the reducing terminal mannose unit, reduction of the oligosaccharides with NaBH4 to the corresponding alcohols gave simple and more readily interpretable 1H NMR spectra. Unexpectedly, however, a shift of H-1 signals by this reduction occurred not only on the second mannose unit but also on the third and fourth mannose units from the modified reducing terminal group of each oligosaccharide alcohol. This result indicates that the reducing terminal mannose unit is able to affect up to the fourth mannose unit from the reducing terminal. The presence of a long-distance interresidue NOE also suggests that the beta-1,2-linked mannooligosaccharides have a compactly folded conformation in solution.

Structural study of a cell wall mannan-protein complex of the pathogenic yeast Candida glabrata IFO 0622 strain

We conducted a structural analysis of the cell wall mannan-protein complex (mannan) isolated from a pathogenic yeast, Candida glabrata IFO 0622 strain. The chemical structure of mannobiose released from this mannan by treatment with 10 mM HCl at 100 degrees C for 1 h was identified as Manp beta 1-2Man. The treatment of this mannan with 100 mM NaOH at 25 degrees C for 18 h gave a mixture of alpha-1,2- and alpha-1,3-linked oligosaccharides, from tetraose to biose, and mannose. The acid- and alkali-stable mannan moiety was subjected to mild acetolysis with a 100:100:1 (v/v) mixture of (CH3CO)2O, CH3COOH, and H2SO4 at 40 degrees C for 36 h. The resultant three novel oligosaccharides, tetraose, hexaose, and heptaose, were identified as Manp beta 1-2Manp alpha 1-2Manp alpha 1-2Man, Manp alpha 1-2Manp alpha 1-2Manp alpha 1-6Manp alpha 1-2Manp alpha 1-2Man, and Manp alpha 1-3Manp alpha 1-2Manp alpha 1-2Manp alpha 1-6Manp alpha 1- 2Manp alpha 1-2Man, respectively, in addition to the three known oligosaccharides, Manp alpha 1-2Man, Manp alpha 1-2Manp alpha 1-2Man, and Manp alpha 1-3Manp alpha 1-2Manp alpha 1-2Man. A sequential analytical procedure involving partial acid hydrolysis with hot 0.3 M H2SO4, methylation, fast atom bombardment mass, and 1H NMR analyses was quite effective in the structural determination of the novel oligosaccharides. The results indicate that this mannan possesses a structure closely resembling that of Saccharomyces cerevisiae X2180-1A wild type strain, with the presence of small amounts of oligomannosyl residue, Manp beta 1-2Manp alpha 1-X, corresponding to one of the epitopes dominating serotype-A specificity of Candida spp., in addition to branches corresponding to hexaose and heptaose each containing one intermediary alpha-1,6 linkage.

Evaluation of an enzyme immunoassay using neoglycolipids constructed from Candida albicans oligomannosides to define the specificity of anti-mannan antibodies

In order to study the respective roles of oligomannoside sequences in the antigenicity of Candida albicans phosphopeptidomannan, a method was developed for constructing neoglycolipids from oligomannosides released by depolymerisation of this molecule. Oligomannosides released by acetolysis were converted to neoglycolipids by coupling them to 4-hexadecylaniline in an equimolar reaction checked by thin layer chromatography. When coated onto microEIA plates, the neoglycolipids exhibited strong reactions which were dose dependent and were saturable with concanavalin A. Reactivity of neoglycolipids with immunoglobulins were then tested with a panel of monoclonal and polyclonal antibodies reacting with epitopes present in the original phosphopeptidomannan. One of two IgM monoclonal antibodies and two of five monospecific rabbit polyclonal IgG reacted strongly with neoglycolipids therefore providing evidence of the presence of structures mimicking epitopes within the pool of neoglycolipids. When 38 sera from 18 hospital inpatients with various levels of antibodies to Candida albicans were tested, a correlation was observed between the EIA to detect neoglycolipids and the EIA to detect phosphopeptidomannan. Successive sera from all patients showing seroconversion in the immunofluorescence assay had increased EIA signals for neoglycolipids.

Presence of human antibodies reacting with Candida albicans O-linked oligomannosides revealed by using an enzyme-linked immunosorbent assay and neoglycolipids

In order to study the presence of antibodies directed against Candida albicans O-linked oligomannosides (oligomannosides O) in patient sera, we have developed an enzyme-linked immunosorbent assay (ELISA) involving neoglycolipids constructed with these residues (NGLO). Oligomannosides O released by mild alkaline degradation of the C. albicans cell wall phosphopeptidomannan (PPM) contained one to seven mannose residues, among which the quantitatively major components, mannobiose and mannotriose, were shown by 1H nuclear magnetic resonance to contain exclusively alpha (1-2) linkages. The pool of oligomannosides was converted to neoglycolipids by coupling them to 4-hexadecylaniline in an equimolar reaction checked by thin-layer chromatography. We have tested against these neoantigens, coated on ELISA plates, 15 pairs of sera corresponding to individual seroconversions observed in 15 patients during the course of a mycological and serological survey of candidiasis. For all patients, seroconversions resulted in an increased level of antibodies against NGLO. A significant correlation was observed between the results of ELISA-NGLO, ELISA involving the original PPM molecule, and routine antibody detection tests, indirect immunofluorescence assay, and cocounterimmunoelectrophoresis. These results therefore demonstrate the synthesis of human antibodies reactive with oligomannosides O constitutive of the C. albicans mannan molecule which have been previously described as exhibiting an inhibitory effect on human lymphocytic proliferation.

1H-NMR spectroscopy of manno-oligosaccharides of the beta-1,2-linked series released from the phosphopeptidomannan of Candida albicans VW-32 (serotype A)

Manno-oligosaccharides (DP 2 to greater than 15) were released by mild acid hydrolysis from the phosphopeptidomannan of a Candida albicans strain of A serotype (VW-32). Manno-oligosaccharides ranging from biose to heptaose were obtained in appreciable amount. Structural investigation of these oligosaccharides showed them to be of the beta-1,2-linked series. The occurrence of such compounds has already been reported in other strains of Candida albicans. We here report the assignment of the structural reporter groups of each of them, and general rules applicable for the 1H-NMR spectrum analysis of linear manno-oligosaccharide of general structure: Man(beta 1-2) [Man(beta 1-2)]nMan

Structural study on a phosphorylated mannotetraose obtained from the phosphomannan of Candida albicans NIH B-792 strain by acetolysis

A mixture of phosphorylated manno-oligosaccharides was isolated from the acid-stable domain of phosphomannan of Candida albicans NIH B-792 strain (serotype B) by acetolysis and was fractionated on a column of Bio-Gel P-2 equilibrated with 50 mM pyridine-CH3COOH buffer, pH 5.0. A monophosphorylated mannotetraose was isolated as the major constituent. Structural analyses of this phosphate-containing tetraose and its reduction product with NaBH4 by 1H, 13C, and two-dimensional homonuclear Hartmann-Hahn NMR spectroscopies, subsequently, gave results consistent with the structure described below (where Manp represents the mannopyranose unit): [formula: see text] It was unexpected that the major phosphorylated branch in the acid-stable domain of the parent phosphomannan of this C. albicans strain is a relatively short mannotetraosyl residue containing solely alpha-1,2-linked mannopyranose units, and a phosphate group as a 6-O-ester on the intermediary unit adjacent to the nonreducing terminal group. These findings indicate that the size of the major phosphorylated branch of this phosphomannan is the same as that of Saccharomyces cerevisiae.

Structural determination of D-mannans of pathogenic yeasts Candida stellatoidea type I strains: TIMM 0310 and ATCC 11006 compared to IFO 1397

The structures of the cell-wall D-mannans of pathogenic yeasts of Candida stellatoidea Type I strains, IFO 1397, TIMM 0310, and ATCC 11006, were investigated by mild acid and, alkaline hydrolysis, by digestion with the Arthrobacter GJM-1 strain exo-alpha-D-mannosidase, and by acetolysis. The modified D-mannans and their degradation products were studied by 1H- and 13C-n.m.r. analyses. D-Manno-oligosaccharides released by acid treatment from the parent D-mannans were identified as the homologous beta-(1----2)-linked D-manno-oligosaccharides from biose to hexaose, whereas those obtained by alkaline degradation were the homologous alpha-(1----2)-linked D-mannobiose and D-mannotriose. The acid- and alkali-modified D-mannans lacking 1H-n.m.r. signals above 4.900 p.p.m. [corresponding to beta-(1----2)-linked D-mannopyranose units] were acetolyzed with 10:10:1 (v/v) Ac2O-AcOH-H2SO4, and the resultant D-manno-oligosaccharides were also analyzed. It was found that the longest branches of these D-mannans, corresponding to hexaosyl residues, had the following structures: alpha-D-Manp-(1----3)-alpha-D-Manp-(1----2)-alpha-D-Manp+ ++-(1----2)-alpha-D-Manp- (1----2)-alpha-D-Manp-(1----2)-D-Man and alpha-D-Manp-(1----2)-alpha-D-Manp-(1----3)-alpha-D-Manp+ ++-(1----2)-alpha-D-Manp- (1----2)-alpha-D-Manp-(1----2)-D-Man. These results indicate that the D-mannans of C. stellatoidea Type I strains possess structures in common with the D-mannans of Candida albicans serotype B strain (see ref. 4) containing phosphate-bound beta-(1----2)-linked oligo-D-mannosyl residues.

In vitro production of tumor necrosis factor by murine splenic macrophages stimulated with mannoprotein constituents of Candida albicans cell wall

Mannoprotein components from Candida albicans were investigated for their ability to induce production of tumor necrosis factor (TNF) by cultured splenocytes from naive or Candida-infected mice. Two chromatographically separated mannoproteins preparations, designated F1 and F2, were as able as the heat-inactivated Candida cells to induce the production of TNF from splenocytes of naive animals. In addition, they caused a significant augmentation of basic TNF secretion by splenocytes of Candida-infected animals. Experiments using plastic and/or nylon wool adherence, as well as treatments with antibodies depleting T or NK cells, consistently indicated that most if not all TNF was produced by splenic macrophages. In cultures of splenocytes from Candida-infected mice, mannoprotein addition also stimulated interferon-gamma (IFN-gamma) production by Thy 1.2 positive cells. Depletion of these cells or addition of anti-IFN-gamma antibodies abolished IFN production and reduced TNF secretion by adherent cells to the levels found in the cultures of mannoprotein-stimulated spleen cells from naive mice. These data add further evidence to the immunomodulatory properties possessed by some cell wall constituents of the human commensal microorganism C. albicans and suggest that IFN-gamma is endowed with a regulatory role in TNF production by mouse macrophages in vitro.

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.

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.

Mannan composition of the hyphal form of two relatively avirulent mutants of Candida albicans

We have previously reported the characteristics of mannans isolated from the yeast forms of two relatively avirulent Candida albicans strains, designated 4918-2 and 4918-10. Investigations have been expanded to include an analysis of mannans from the hyphal form of these strains as well as from the hyphal form of the parental strain, 4918. After extraction, mannans were further purified by high-pressure liquid chromatography on a Bio-gel TSK DEAE-5-PW column. Subsequent to either mild acid hydrolysis, alkali hydrolysis, or acetylation followed by acetolysis, the resulting products were fractionated by high-pressure liquid chromatography on an Aminex HPX-42A column. The results of acid hydrolysis showed only minor quantitative differences in the products released from each strain, with mannose constituting the vast majority of product liberated. The profiles of mannooligosaccharides obtained from either alkali hydrolysis or acetolysis for strain 4918-2 showed distinct quantitative differences compared with profiles of the other two strains. Finally, a general characteristic noted is a decrease in the average chain length of mannooligosaccharides in hyphal mannans compared with the yeast counterpart.

Structure of the D-mannan of Candida stellatoidea IFO 1397 strain. Comparison with that of the phospho-D-mannan of Candida albicans NIH B-792 strain

The structure of the D-mannan of Candida stellatoidea IFO 1397 strain, which has properties identical to those of the phospho-D-mannan of C. albicans serotype B strain, does not contain phosphate groups, and its 1H- and 13C-n.m.r. spectra are quite similar to those of the phospho-D-mannan of C. albicans NIH B-792 strain. However, the 1H-n.m.r. and 1H-13C-correlation n.m.r. spectra of the products obtained by digestion with alpha-D-mannosidase of C. stellatoidea D-mannan considerably differed from those of the corresponding digestion products of the C. albicans phospho-D-mannan. Additionally, the enzyme-linked immunosorbent assay, by means of a monoclonal antibody corresponding to (1----2)-linked beta-D-oligomannosyl residues, of the phospho-D-mannan of the same C. albicans strain indicated that the C. stellatoidea D-mannan does not contain any (1----2)-linked beta-D-oligomannosyl residues. The absence of these residues may be used as one of the criteria of chemotaxonomical identification of C. stellatoidea spp.

Structural study of cell wall phosphomannan of Candida albicans NIH B-792 (serotype B) strain, with special reference to 1H and 13C NMR analyses of acid-labile oligomannosyl residues

Chemical structures of manno-oligosaccharides, from biose to heptaose, released from the phosphomannan of Candida albicans NIH B-792 strain (serotype B) by mild acid hydrolysis were investigated. The results of 1H NMR, 13C NMR, and fast atom bombardment mass spectrometry analyses confirmed that these manno-oligosaccharides belong to a homologous beta-1,2-linked series. Although chemical shifts of 1H NMR patterns of these oligosaccharides were considerably too complicated to be assigned, their 13C NMR patterns were sufficiently simple to be interpreted, exhibiting a regular increase of downfield shift of ppm values of the C-1 atom from each mannopyranose residue in proportion to their molecular weights. In order to determine the whole chemical structure of the parent phosphomannan, the acid-stable domain was subjected to acetolysis and then enzymolysis with the Arthrobacter GJM-1 alpha-mannosidase and the resultant manno-oligosaccharides were investigated for their chemical structures by 1H NMR spectroscopy. The results of a precipitin-inhibition test using the beta-1,2-linked manno-oligosaccharides, from biose to hexaose, in comparison with the corresponding isomers containing alpha-1,2 linkage with small amounts of alpha-1,3 linkage, indicated that the haptens possessing the former linkage exhibited much higher inhibitory effects than the corresponding isomers containing the latter linkages did. Based on the present findings, a chemical structure of the phosphomannan of this C. albicans strain was proposed.

Structural study of phosphomannan of yeast-form cells of Candida albicans J-1012 strain with special reference to application of mild acetolysis

Structural analysis of the phosphomannan isolated from yeast-form cells of a pathogenic yeast, Candida albicans J-1012 strain, was conducted. Treatment of this phosphomannan (Fr. J) with 10 mM HCl at 100 degrees C for 60 min gave a mixture of beta-1,2-linked manno-oligosaccharides, from tetraose to biose plus mannose, and an acid-stable mannan moiety (Fr. J-a), which was then acetolyzed by means of an acetolysis medium, 100:100:1 (v/v) mixture of (CH3CO)2O, CH3COOH, and H2SO4, at 40 degrees C for 36 h in order to avoid cleavage of the beta-1,2 linkage. The resultant manno-oligosaccharide mixture was fractionated on a column of Bio-Gel P-2 to yield insufficiently resolved manno-oligosaccharide fractions higher than pentaose and lower manno-oligosaccharides ranging from tetraose to biose plus mannose. The higher manno-oligosaccharide fraction was then digested with the Arthrobacter GJM-1 alpha-mannosidase in order to cleave the enzyme-susceptible alpha-1,2 and alpha-1,3 linkages, leaving manno-oligosaccharides containing the beta-1,2 linkage at their nonreducing terminal sites, Manp beta 1----2Manp alpha 1----2Manp alpha 1----2Manp alpha 1----2Man, Manp beta 1----2Manp beta 1----2Manp alpha 1----2Manp alpha 1---- 2Manp alpha 1----2Man, and Manp beta 1----2Manp beta 1----2Manp beta 1----2Manp alpha 1---- 2Manp alpha 1----2Manp alpha 1----2Man. However, the result of acetolysis of Fr. J-a by means of a 10:10:1 (v/v) mixture of (CH3CO)2O, CH3COOH, and H2SO4 at 40 degrees C for 13 h was significantly different from that obtained by the mild acetolysis method; i.e., the amount of mannose was apparently larger than that formed by the mild acetolysis method. In summary, a chemical structure for Fr. J as a highly branched mannan containing 14 different branching moieties was proposed.

Structural analysis of phospho-D-mannan-protein complexes isolated from yeast and mold form cells of Candida albicans NIH A-207 serotype A strain

The immunochemical properties between phospho-D-mannan-protein complexes of yeast (Y) and mycelial (M) forms of Candida albicans NIH A-207 (serotype A) strain were compared. Hydrolysis of the Y-form complex gave a mixture of beta-(1----2)-linked D-mannooligosaccharides consisting mainly of tri- and tetra-ose, whereas the M-form complex gave preponderantly D-mannose. The antiserum against Y-form cells exhibited a lower reactivity with the M-form than with the Y-form complex, whereas the antiserum to M-form cells could not distinguish significantly between both complexes. Moreover, these acid-modified complexes showed lower antibody-precipitating effect than each corresponding intact complex against antisera of Y- and M-form cells. Digestion of the acid-modified Y- and M-form complexes with the Arthrobacter GJM-1 strain alpha-D-mannosidase yielded 35- and 40-% degradation products, respectively. Acetolysis of each modified complex under mild conditions gave the same D-mannohexaose, beta-D-Manp-(1----2)-beta-D-Manp-(1----2)-alpha-D-Manp -(1----2)-alpha-D-Manp- (1----2)-alpha-D-Manp-(1----2)-D-Man. Because the complexes of Y- and M-form cells of C. albicans NIH B-792 (serotype B) strain did not give any hexaose fraction containing beta-(1----2) linkages, the presence of this hexaose can be regarded as one of the dominant characteristics of the serotype-A specificity of C. albicans spp.

Analysis of mannans of two relatively avirulent mutant strains of Candida albicans

We previously reported the isolation of two cerulenin-resistant mutant strains of Candida albicans 4918 that differ in adherence properties and are less virulent than the parental strain. In addition, biochemical characterization demonstrated significant differences in both protein and polysaccharide composition of cell wall material between the mutant and wild-type strains. These observations prompted studies concerning the chemical structure of mannans in these strains. After extraction and subsequent purification by ion-exchange chromatography, mannan fractions were subjected to either mild acid hydrolysis, alkali hydrolysis, or acetylation followed by acetolysis. Acid- and alkali-modified mannans were studied by proton magnetic resonance spectroscopy, and released products were analyzed by high-performance liquid chromatography on an Aminex HPX-42A column. The results demonstrated quantitative and qualitative differences between mannooligosaccharides of the wild-type and mutant strains in the identity of released oligosaccharides as well as in linkage of the oligosaccharides to the protein backbone.