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

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

Transcriptional network of multiple capsule and melanin genes governed by the Cryptococcus neoformans cyclic AMP cascade

Cryptococcus neoformans is an opportunistic human fungal pathogen that elaborates several virulence attributes, including a polysaccharide capsule and melanin pigments. A conserved Galpha protein/cyclic AMP (cAMP) pathway controls melanin and capsule production. To identify targets of this pathway, we used an expression profiling approach to define genes that are transcriptionally regulated by the Galpha protein Gpa1. This approach revealed that Gpa1 transcriptionally regulates multiple genes involved in capsule assembly and identified two additional genes with a marked dependence on Gpa1 for transcription. The first is the LAC1 gene, encoding the laccase enzyme that catalyzes a rate-limiting step in diphenol oxidation and melanin production. The second gene identified (LAC2) is adjacent to the LAC1 gene and encodes a second laccase that shares 75% nucleotide identity with LAC1. Similar to the LAC1 gene, LAC2 is induced in response to glucose deprivation. However, LAC2 basal transcript levels are much lower than those for LAC1. Accordingly, a lac2 mutation results in only a modest delay in melanin formation. LAC2 overexpression suppresses the melanin defects of gpa1 and lac1 mutants and partially restores virulence of these strains. These studies provide mechanistic insights into the regulation of capsule and melanin production by the C. neoformans cAMP pathway and demonstrate that multiple laccases contribute to C. neoformans melanin production and pathogenesis.

Development of an enzyme-linked immunosorbent assay for the serodiagnosis of several clinical forms of sporotrichosis

We performed a serological study with sera from 92 patients with confirmed sporotrichosis registered between 1999 and 2004 in two hospitals in Rio de Janeiro State, Brazil. The clinical presentation of sporotrichosis was distributed as follows: lymphocutaneous, 67%; fixed cutaneous, 23%; disseminated cutaneous, 8%; and extracutaneous, 2%. Sera were assayed by ELISA against a cell wall antigen of Sporothrix schenckii, SsCBF, that we have previously described. The cross-reactivity was determined with 77 heterologous sera. The serological test showed a sensitivity of 90% and a global efficiency of 86%. A group of 55 patients with several clinical presentations of sporotrichosis was clinically and serologically followed-up for at least 6 months. We observed by ELISA data a decrease in the antibody serum titers which correlated with the progress in healing. An HIV-positive patient with meningeal sporotrichosis was serologically followed-up for over 2 years. Serum and cerebrospinal fluid specimens were examined and significant antibodies levels against the antigen SsCBF were detected. Our results strongly suggest that this serological test is valuable for the differential diagnosis and follow-up of all clinical forms of sporotrichosis.

Low virulent strains ofCandida albicans: Unravelling the antigens for a future vaccine

Several low virulent Candida albicans mutant strains: CM1613 (deleted in the Mitogen Activated Protein (MAP) Kinase MKC1), CNC13 (deleted in the MAP-kinase HOG1) and the morphological mutant 92' were used as vaccines employing a murine model of systemic candidiasis. In this vaccination trial, only the CNC13 strain was able to induce protection against a subsequent infection with a lethal dose of the wild-type strain. The protection induced by CNC13 vaccinated animals resulted in 60-70% percent of survival. These results demonstrate that collaboration between cellular and humoral responses, induced by the CNC13 mutant, elicited a long lasting and effective protection. Using a proteomic approach (two-dimensional gel electrophoresis followed by Western blotting), twenty-five C. albicans immunogenic proteins were detected and identified by matrix-assisted laser desorption/ionization and/or tandem mass spectrometry. We were able to define an antibody pattern in the sera from the nonvaccinating strains (92' and CM1613), which was different from the profile detected in the sera from surviving animals (vaccinated with the CNC13 mutant). The utility of this proteomic approach has allowed us to identify antigens that induce protective IgG2a antibody isotype in the sera from vaccinated animals: enolase (Eno1p), pyruvate kinase (Cdc19p), pyruvate decarboxylase (Pdc11p), a component from the 40S ribosomal subunit (Bel1p), triosephosphate isomerase (Tpi1p), DL-glycerol phosphatase (Rhr2p), fructose-bisphosphate aldolase (Fba1p) and two new protective antigens: IMP dehydrogenase (Imh3p), and acetyl-CoA synthetase (Acs2p). The antigenic proteins that promote protective antibodies described in this work are excellent candidates for a future fungal vaccine; their heterologous expression and vaccine design is currently underway.

AFMP2 encodes a novel immunogenic protein of the antigenic mannoprotein superfamily in Aspergillus fumigatus

We cloned the Aspergillus fumigatus mannoprotein 2 (AFMP2) gene, which encodes a novel immunogenic protein (Afmp2p) of the antigenic mannoprotein superfamily, in A. fumigatus. Sequence analysis revealed that Afmp2p has 510 amino acid residues, with a predicted molecular mass of 51.5 kDa. Afmp2p has a putative N-terminal signal peptide, a putative C-terminal glycosylphosphatidylinositol membrane attachment signal sequence, and an upstream GAA cleavage site commonly used for cytoplasmic membrane attachment and implicated in fungal cell wall assembly. Upstream of the GAA cleavage site, Afmp2p contains a 302-amino-acid serine- and threonine-rich region as a site for potential O-glycosylation. Within this serine- and threonine-rich region, 13 repeats of ETSTPCE(T)(n) were observed. Western blot analysis of Afmp2p in A. fumigatus fungal cell lysate and culture supernatant and immunogold staining and electron microscopy showed that Afmp2p is predominantly secreted into the culture supernatant, whereas only minimal amounts can be detected in the cell lysate and cell wall. Finally, it was observed that patients with aspergilloma and invasive aspergillosis due to A. fumigatus develop a specific antibody response against recombinant Afmp2p. The abundance of Afmp2p in secreted form, its minimal cross-reactivity with Afmp1p, and the presence of an antibody response against Afmp2p in patients with A. fumigatus infections suggest that Afmp2p is a good candidate for complementing Afmp1p in serodiagnosis of A. fumigatus infections.

Antigen characterization of major cork moulds in Suberosis (cork worker's pneumonitis) by immunoblotting

BACKGROUND

We characterized by immunoblotting the antigenicity of the most frequent fungi colonizing cork during its industrial processing, Penicillium glabrum and Chrysonilia sitophila. Penicillium glabrum is the main causative agent of Suberosis, a hypersensitivity pneumonitis of cork workers. Chrysonilia sitophila induces both IgE sensitization and occupational asthma in the wood processing industry.

METHODS

Serum-specific IgG, IgG4 and IgE to P. glabrum and C. sitophila from nine cork workers with hypersensitivity pneumonitis (HP) and seven with asthma (four with occupational asthma) were analysed by immunoblotting.

RESULTS

Both HP and asthmatic patients' sera showed immunoreactivity to several proteins resolved in the specific immunoblot strips. The frequency of specific IgG recognition to 12-13.5 and 33 kDa proteins of P. glabrum was significantly higher in HP patients. The sera of HP patients had significantly higher specific IgG recognition to 16 and 51-55 kDa proteins of C. sitophila. There was no specific IgE recognition in the sera of HP or asthmatic patients to both fungi.

CONCLUSIONS

Different patterns of antibody reactivity to P. glabrum and C. sitophila are seen in cork workers with hypersensitivity pneumonitis or asthma. The 12-13.5 and 33 kDa proteins of P. glabrum and the 16 and 51-55 kDa proteins of C. sitophila may be major antigens in Suberosis.

Distribution of antigenic oligomannosyl side chains in the cell wall mannans of several strains of Candida tropicalis

In order to clarify the distribution of antigenic oligomannosyl side chains in the cell wall mannans of the pathogenic yeast Candida tropicalis, the chemical structure of mannans isolated from four C. tropicalis strains was investigated using nuclear magnetic resonance, two-dimensional homonuclear Hartmann-Hahn (2D-HOHAHA) spectroscopy. Two-dimensional maps of the 2D-HOHAHA clearly showed the distribution of oligomannosyl side chains in the mannans. The linear side chain Manalpha1-3Manalpha1-(2Manalpha1-)(n)2Man [n> or =2] is present in the mannans from C. tropicalis IFO 0589 and IFO 1400, but not in the mannans from IFO 0199 and IFO 1647. The mannan of IFO 0589 is the only mannan with the branched side chains, Manalpha1-3[Manalpha1-6]Manalpha1-(2Manalpha1-)(n)2Man and Manalpha1-2Manalpha1-3[Manalpha1-6]Manalpha1-(2Manalpha1-)(n)2Man [n> or =2]. However, this mannan lacked the phosphate group and the beta-1,2-linked oligomannosyl side chain which are features of this group. The mannans of the C. tropicalis strains IFO 0589 and IFO 1400 possessed the side chains containing an alpha-1,3-linked mannose residue previously observed in Candida albicans.

Production of the bullous pemphigoid antigen 230 (BP230) by Saccharomyces cerevisiae and Pichia pastoris

BP230 is a cytoskeletal linker protein of 2649 amino acids originally identified as the target autoantigen in bullous pemphigoid, a potentially devastating autoimmune skin blistering disorder. To better define its function, we sought to generate recombinant forms of BP230 in both Saccharomyces cerevisiae and Pichia pastoris after cloning its entire cDNA. By immunoblot analysis, full-length BP230 was not found in extracts of P. pastoris, whereas minor amounts of degraded BP230 were detected in extracts of S. cerevisiae. In contrast, both S. cerevisiae and P. pastoris were able to produce the 770-amino acid COOH-terminal domain of BP230. Furthermore, the production level of the recombinant BP230 tail in S. cerevisiae was significantly higher than that observed in P. pastoris and that of endogenous BP230 in cultured human keratinocytes. Finally, 12 of 17 (71%) BP sera recognized the recombinant BP230 protein in yeast extracts. Our results indicate that S. cerevisiae occasionally constitutes a better tool for recombinant protein production than P. pastoris. Although both its large size and poor solubility limit production of BP230, the developed yeast system provides cellular fractions enriched in BP230 recombinant proteins that constitute useful tools for the diagnosis of bullous pemphigoid.

Existence of novel beta-1,2 linkage-containing side chain in the mannan of Candida lusitaniae, antigenically related to Candida albicans serotype A

The antigenicity of Candida lusitaniae cells was found to be the same as that of Candida albicans serotype A cells, i.e. both cell wall mannans react with factors 1, 4, 5, and 6 sera of Candida Check. However, the structure of the mannan of C. lusitaniae was significantly different from that of C. albicans serotype A, and we found novel beta-1,2 linkages among the side-chain oligosaccharides, Manbeta1-->2Manbeta1--> 2Manalpha1-->2Manalpha1-->2Man (LM5), and Manbeta1-->2Man-beta1-->2Manbeta1-->2Manalpha1-->2Manalpha1-->2Man (LM6). The assignment of these oligosaccharides suggests that the mannoheptaose containing three beta-1,2 linkages obtained from the mannan of C. albicans in a preceding study consisted of isomers. The molar ratio of the side chains of C. lusitaniae mannan was determined from the complete assignment of its H-1 and H-2 signals and these signal dimensions. More than 80% of the oligomannosyl side chains contained beta-1,2-linked mannose units; no alpha-1,3 linkages or alpha-1,6-linked branching points were found in the side chains. An enzyme-linked immunosorbent inhibition assay using oligosaccharides indicated that LM5 behaves as factor 6, which is the serotype A-specific epitope of C. albicans. Unexpectedly, however, LM6 did not act as factor 6.

Molecular cloning and immunological characterisation of potential allergens from the mould Fusarium culmorum

BACKGROUND

High quality and stability are essential requirements of commercial allergen preparations. Recently we have demonstrated the very low stability of protein allergens in an extract of the ubiquitous mould Fusarium culmorum.

OBJECTIVE

The present study was performed to identify, isolate and characterise allergens of F. culmorum as a basis for a stable allergenic reference material. In addition, the significance of IgE binding to carbohydrate structures in the natural allergen source was investigated.

METHODS

Sera of 52 subjects with suspected mould allergy were used to determine the IgE binding capacity of a commercial F. culmorum extract and an in-house extract by immunoblotting and enzyme allergo sorbent test (EAST). Binding of IgE-antibodies to putative carbohydrate structures located on glycoproteins was verified by periodate treatment of blot strips prior to immunodetection. A complementary (c)DNA expression library of F. culmorum was prepared and screened for IgE-binding clones using sera from F. culmorum-sensitive individuals. Positive clones were isolated, and the open reading frames were subcloned into expression vectors to produce recombinant proteins in E. coli. The recombinant proteins were tested for their IgE reactivity by immunoblotting and EAST.

RESULTS

Using the in-house extract for EAST and immunoblot experiments 44% (23/52) of the sera were found to contain F. culmorum-specific IgE antibodies. Compared to the in-house extract, nearly all IgE-reactivties in the range of 15-30kD were lacking in the commercial preparation as examined by immunoblot analysis and only 10% (5/52) of the sera were found to contain F. culmorum-specific IgE by EAST. IgE binding to putative carbohydrate structures was observed in the high molecular weight range in approximately 50% (12/23) of the IgE-positive sera by both extracts. Three IgE binding clones were isolated from the cDNA-library. One clone (Fus c 1) is homologous to the highly conserved 60S acidic ribosomal protein P2 described as minor allergen in other moulds. The second (Fus c 2) shows high similarity (64%) to a respiratory allergen from the basidiomycete Coprinus comatus (Cop c 2). The third clone (Fus c 3) was not related to known proteins. With sera from 26 individuals sensitised to F. culmorum the IgE prevalence of recombinant proteins rFus c 1, rFus c 2 and rFus c 3 was found to be 35, 50, and 15%, respectively.

CONCLUSIONS

F. culmorum may represent an underestimated source of aeroallergens. In contrast to highly labile and poorly standardised F. culmorum extracts, the new recombinant allergens may serve as stable allergenic reference material. A combination of rFus c 1 and rFus c 2 is suitable to diagnose 81% of F. culmorum-sensitised subjects. IgE reactivity to putative carbohydrate structures is relatively frequent, and can not be detected by these allergens.

Purification and characterization of a cross-reactive 45-kD major allergen of Fusarium solani

BACKGROUND

Fusarium solani (FS) is an important source of fungal allergen. A 45-kD major allergen of FS showed reactivity with patients' sera sensitive to many fungi.

OBJECTIVES

To purify and characterize a 45-kD common allergenic protein from FS, which may be useful for the diagnosis of and therapy for fungal allergy.

METHODS

FS culture filtrate extract was seperated on SDS-PAGE; 45-kD protein was electroeluted and purified on C18 column using reverse-phase high-pressure liquid chromatography (rpHPLC). The purified protein was functionally and biochemically characterized by in vitro and in vivo methods.

RESULTS

The 45-kD protein showed a single peak on rpHPLC. The N-terminal amino acid sequence of this protein did not show homology to enolase or known fungal proteins. It showed cross-reactivity with Epicoccum nigrum, Curvularia lunata, Cladosporium herbarum and Alternaria alternata by ELISA and ELISA inhibition using rabbit antibodies raised against these fungi. IgE ELISA inhibition with patients' sera positive to different fungi demonstrated allergenic cross-reactivity of the 45-kD protein with other fungal extracts. This 45-kD protein released a significant amount of histamine in FS-allergenic patients.

CONCLUSION

A cross-reactive 45-kD allergenic/antigenic protein was purified to homogeneity and characterized. It has prospects for use in allergen therapy.

Choline head groups stabilize the matrix loop regions of the ATP/ADP carrier ScAAC2

ATP/ADP carriers (AACs) are essential to the cell as they exchange ATP produced in mitochondria for cytosolic ADP. Monoclonal antibodies against the isoform 2 of Saccharomyces cerevisiae AAC (ScAAC2) were used to probe the accessibility of the matrix loops 1 and 3 depending on the environment of the carrier. In mitochondrial membranes ScAAC2 was not recognized, whereas in dodecylmaltoside the antibodies bound to the carrier, suggesting that the epitopes are hidden in the native environment. Exposure of the epitopes by detergents was reversed by reconstitution of the carrier in phospholipids or by exchanging with detergents having a choline or a trimethylammonium head group. Circular dichroism spectroscopy on peptides representing the C-terminal regions of all three matrix loops showed that only phosphocholine detergents induced a structural reorganization. Since in addition phosphatidylcholine was found to be tightly associated with the purified carrier, the matrix loop regions are likely to be associated to the membrane by phosphatidylcholine.

Expression in bacteria of the gene encoding the gp43 antigen of paracoccidioides brasiliensis: immunological reactivity of the recombinant fusion proteins

gp43 is the major diagnostic antigen of Paracoccidioides brasiliensis, the agent of paracoccidioidomycosis (PCM) in humans. In the present study, cDNA of the gp43 gene (PbGP43) was obtained by reverse transcriptase PCR, inserted into a pGEX vector in frame with the glutathione S-transferase (GST) gene, and expressed in Escherichia coli as inclusion bodies. Immunoblotting showed that all sera from patients with chronic pulmonary and acute lymphatic forms of PCM reacted with the recombinant fusion protein of the mature gp43 (381 amino acids). Reactivity with fusion proteins containing subfragments of the N-terminal, internal, or C-terminal regions occurred eventually, and the C-terminal region was the most antigenic. Lack of reactivity with the subfragments may be due to the conformational nature of the gp43 epitopes. Sera from patients with aspergillosis, candidiasis, and histoplasmosis did not react with the gp43-GST fusion protein. Our results suggest that recombinant gp43 corresponding to the processed antigen can be a useful tool in the diagnosis of PCM.

Beta-1,2-mannosylation of Candida albicans mannoproteins and glycolipids differs with growth temperature and serotype

Increasing the growth temperature from 28 to 37 degrees C reduced the expression of beta-1,2-oligomannoside epitopes on mannoproteins of Candida albicans serotypes A and B. In contrast, beta-1,2-mannosylation of phospholipomannan (PLM) remained constant despite a slight decrease in the relative molecular weight (M(r)) of this compound. At all growth temperatures investigated, serotype A PLM displayed an M(r) and an antigenicity different from those of serotype B PLM when they were tested with a panel of monoclonal antibodies.

Optimal T cell responses to Cryptococcus neoformans mannoprotein are dependent on recognition of conjugated carbohydrates by mannose receptors

Cryptococcosis is a leading cause of death among individuals with compromised T cell function. Soluble Cryptococcus neoformans mannoproteins (MP) have emerged as promising vaccine candidates due to their capacity to elicit delayed-type hypersensitivity and Th type 1-like cytokines, both critical to the clearance of this pathogenic yeast. In this study, the mechanisms responsible for the potent immunostimulatory properties of MP were explored. Using Chinese hamster ovary cells expressing human macrophage mannose receptor (MMR), we determined that MP is a MMR ligand. Functionally, competitive blockade of multilectin mannose receptors (MR) on APCs diminished MP-dependent stimulation of primary T cells from immunized mice and the MP-reactive CD4(+) T cell hybridoma, P1D6, by 72 and 99%, respectively. Removal of O-linked saccharides from MP by beta-elimination inhibited MP-dependent stimulation of P1D6 and primary T cells by 89 and 90%, respectively. In addition, MP-dependent stimulation of P1D6 was abrogated after digestion with proteinase K, suggesting the protein core of MP contributed the antigenic moiety presented by APC. Stimulation of P1D6 by MP also was abolished using APC obtained from invariant chain-deficient mice, demonstrating Ag presentation was MHC class II restricted. Our data suggest that MP is a ligand for the MMR and that T cell stimulation is functionally inhibited either by competitive blockade of MR or by removal of carbohydrate residues critical for recognition. The demonstration that efficient T cell responses to MP require recognition of terminal mannose groups by MMR provides both a molecular basis for the immunogenicity of cryptococcal MP and support for vaccination strategies that target MR.

Comparison of the crystal structures of the human manganese superoxide dismutase and the homologous Aspergillus fumigatus allergen at 2-A resolution

Manganese superoxide dismutase (MnSOD) of Aspergillus fumigatus, a fungus involved in many pulmonary complications, has been identified as IgE-binding protein. It has been shown also that MnSODs from other organisms, including human, are recognized by IgE Abs from individuals sensitized to A. fumigatus MnSOD. Comparison of the fungal and the human crystal structure should allow the identification of structural similarities responsible for IgE-mediated cross-reactivity. The three-dimensional structure of A. fumigatus MnSOD has been determined at 2-A resolution by x-ray diffraction analysis. Crystals belonged to space group P2(1)2(1)2(1) with unit cell dimensions of a = 65.88 A, b = 98.7 A, and c = 139.28 A. The structure was solved by molecular replacement using the structure of the human MnSOD as a search model. The final refined model included four chains of 199-200 amino acids, four manganese ions, and 745 water molecules, with a crystallographic R-factor of 19.4% and a free R-factor of 23.3%. Like MnSODs of other eukaryotic organisms, A. fumigatus MnSOD forms a homotetramer with the manganese ions coordinated by three histidines, one aspartic acid, and one water molecule. The fungal and the human MnSOD share high similarity on the level of both primary and tertiary structure. We identified conserved amino acids that are solvent exposed in the fungal and the human crystal structure and are therefore potentially involved in IgE-mediated cross-reactivity.

The unique solution structure and immunochemistry of the Candida albicans beta -1,2-mannopyranan cell wall antigens

Synthetic oligomers of the antigenic Candida albicans (1-->2)-beta-mannopyranans adopt a compact solution conformation that leads to numerous inter-residue nuclear Overhauser effects, including unprecedented nuclear Overhauser effects between n and n + 3 residues. In excellent agreement with experimentally determined distances, unrestrained molecular dynamics point to a single family of conformations that approximate a compact helical motif with a three-residue repeat for this unique homopolymer. When the synthetic di- to hexasaccharides were employed as inhibitors of monoclonal antibodies, which protect mice against a lethal dose of the yeast pathogen, a novel pattern of inhibitor activity was observed. Instead of the paradigm first reported by Kabat (Kabat, E. A. (1962) Fed. Proc. 21, 694-701; Kabat, E. A. (1966) J. Immunol. 97, 1-11), wherein homo-oligosaccharides exhibit increasing inhibitory activity with increasing size, here the maximum activity is reached for di- and trisaccharides and diminishes significantly for tetra-, penta-, and hexasaccharides. These immunochemical data correlate with the ordered conformation of the beta-1,2-linked mannopyranan and imply that a uniquely small antigenic determinant has potential as a component of synthetic conjugate vaccines against Candida albicans.

Paracoccidioides brasiliensis 87-kilodalton antigen, a heat shock protein useful in diagnosis: characterization, purification, and detection in biopsy material via immunohistochemistry

The 87-kDa antigen derived from the fungal pathogen Paracoccidioides brasiliensis can be detected in the sera of infected patients, and its levels have been shown to correlate well with response to treatment and with clinical cure. Despite its potential importance, the antigen has been poorly characterized. The 87-kDa antigen was purified to homogeneity via preparative gel electrophoresis; N-terminal amino acid sequencing revealed substantial homology with heat shock proteins (hsps) from a variety of organisms. A monoclonal antibody (MAb) raised against a Histoplasma capsulatum 80-kDa hsp showed cross-reactivity to the purified 87-kDa antigen via Western blotting, and the 87-kDa-specific MAb P1B demonstrated that the antigen was expressed at higher levels in yeast than in mycelia by the same technique. Enzyme-linked immunosorbent assay and immunofluorescence reactivity using P1B confirmed increased expression of the 87-kDa antigen during the temperature-induced transformation of mycelia to yeast. Yeast-to-mycelium transformation was accompanied by a fall in expression, although the 87-kDa antigen was clearly constitutively expressed in both phases. Immunochemical staining of tissues from patients with MAb P1B who were infected with P. brasiliensis confirmed in vivo expression of the 87-kDa antigen by yeasts, and identification of this antigen via this method appears to be a useful adjunct to other methods used to diagnose paracoccidioidomycosis.

Identification of the YMN-1 antigen protein and biochemical analyses of protein components in the mitochondrial nucleoid fraction of the yeast Saccharomyces cerevisiae

We analyzed the protein components contained in the mitochondrial nucleoid (mt-nucleoid) fraction of the yeast Saccharomyces cerevisiae. Immunoblotting with anti-Abf2p antibody demonstrated the association of Abf2p, a major mitochondrial DNA-binding protein, with the mt-nucleoids. In contrast, porin and cytochrome c oxidase subunit III (CoxIIIp) were not detected by immunoblotting in the mt-nucleoid fraction. The YMN-1 monoclonal antibody recognized a 48 kDa protein of the mt-nucleoid fraction. The N-terminal amino acid sequence of the protein and immunological evidence showed that the YMN-1 monoclonal antibody recognizes dihydrolipoyl transsuccinylase (KE2), which is one of the constituents of the alpha-ketoglutarate dehydrogenase complex (KGDC). alpha-Ketoglutarate dehydrogenase (KE1) and dihydrolipoyl dehydrogenase (E3), which are other subunits of KGDC, were also detected in the mt-nucleoid fraction. An enzyme assay of the mt-nucleoid fraction showed that cytochrome c oxidase and fumarase activity were barely detected in the fraction, but the specific activity of KGDC in the mt-nucleoid fraction was relatively high and was approximately 60% of the specific activity in the mitochondrial fraction. Three components of KGDC were detected in the DNA-binding protein fractions after DNA-cellulose column chromatography of mt-nucleoid proteins. These results suggested that a part of KGDC in the mitochondrial matrix is associated with mt-nucleoids in vivo.

Immune response modulation by recombinant peptides expressed in virus-like particles

Aspergillus fumigatus, a ubiquitous fungus, is implicated in the pathogenesis of a number of clinically different allergic diseases in man, including allergic bronchopulmonary aspergillosis. Peptide-based immunotherapy may offer an alternative treatment strategy for the management of allergic disease. The objective of this study was to alter the allergen-specific immune response using dominant T cell epitopes of a major A. fumigatus allergen, Asp f2, expressed in yeast as virus-like particles (VLP). The T cell epitopes of Asp f2, recognized in mice with an H-2d background, were determined by producing T-cell hybridomas. Two dominant T cell epitopes, aa60--71 and aa235--249, were identified and expressed in a yeast VLP system. To induce tolerance VLP-peptides were injected subcutaneously into mice previously immunized with recombinant Asp f2. The T cell immune response was abrogated totally in 3 weeks following a single injection of VLP but was restored 2 months later following intranasal antigen exposure. T-cell depletion resulted in the reduction of 20-30% of all antigen-specific immunoglobulin classes. Thus, recombinant peptides expressed in the VLP system can be used successfully in the modulation of Asp f2-induced immune response in mice, although a single administration is not sufficient to maintain a state of tolerance for a long period of time.

cDNA cloning, biological and immunological characterization of the alkaline serine protease major allergen from Penicillium chrysogenum

BACKGROUND

Penicillium chrysogenum (Penicillium notatum) is a prevalent airborne Penicillium species. A 34-kD major IgE-reacting component from P. chrysogenum has been identified as an alkaline serine protease (Pen ch 13, also known as Pen n 13 before) by immunoblot and N-terminal amino acid sequence analysis.

METHODS

In the present study, Pen ch 13 was further characterized in terms of cDNA cloning, protein purification, enzymatic activity, histamine release and IgE cross-reactivity with alkaline serine protease allergens from two other prevalent fungal species--P. citrinum (Pen c 13) and Aspergillus flavus (Asp fl 13).

RESULTS

A 1,478-bp cDNA (Pen ch 13) that encodes a 398-amino-acid alkaline serine protease from P. chrysogenum was isolated. This fungal protease has pre- and pro-enzyme sequences. The previously determined N-terminal amino acid sequence of the P. chrysogenum 34-kD major allergen is identical to that of residues 116-125 of the cDNA. Starting from Ala116, the deduced amino acid sequence (283 residues) of the mature alkaline serine protease has a calculated molecular mass of 28.105 kD with two cysteines and two putative N-glycosylation sites. It has 83 and 49% sequence identity with the alkaline serine proteases from P. citrinum and A. fumigatus, respectively. The recombinant Pen ch 13 was recovered from inclusion bodies and isolated under denaturing condition. This recombinant protein reacted with IgE antibodies in serum from an asthmatic patient and with monoclonal antibodies (PCM8, PCM10, PCM39) that reacted with the 34-kD component from P. chrysogenum. The N-terminal amino acid sequence of the purified native Pen ch 13 is identical to that determined previously for the 34-kD major allergen in crude P. chrysogenum extracts. The purified native Pen ch 13 has proteolytic activity with casein as the substrate at pH 8.0. This enzymatic activity was inhibited by phenylmethylsulfonyl fluoride or diethylpyrocarbonate. Pen ch 13 was also able to degrade gelatin and collagen but not elastin. Basophils from 5 asthmatic patients released histamine (12-73%) when exposed to the purified Pen ch 13. In ELISA (enzyme-linked immunosorbent assay) experiments, IgE for Pen ch 13 was able to compete with purified Pen ch 13, Pen c 13 or Asp fl 13 in a dose-related manner.

CONCLUSIONS

These results demonstrated that the 34-kD major allergen of P. chrysogenum is an alkaline serine protease. These results also indicated that atopic patients primarily sensitized by either of these prevalent fungal species may develop allergic symptoms by exposure to other environmental fungi due to cross-reacting IgE antibodies against this protease.

Polysaccharides, mimotopes and vaccines for fungal and encapsulated pathogens

Vaccination is a rational alternative to treatment for Cryptococcus neoformans infections, as these infections are currently intractable in immunocompromised (including HIV-infected) individuals. Vaccines composed of the cryptococcal capsular polysaccharide glucuronoxylomannan (GXM), the key C. neoformans virulence factor, elicit protective antibodies in mice, although deleterious antibodies can also be induced. By contrast, polysaccharides are poor immunogens in HIV-infected humans and others with B-cell defects. Peptide mimotopes of GXM can induce protective immunity to C. neoformans in mice, however, our knowledge of the mechanisms of mimotope-induced protection is incomplete and further work is needed if polysaccharide- or mimotope-based vaccines are to be used to manage C. neoformans infection.

Molecular characterization of a mannoprotein with homology to chitin deacetylases that stimulates T cell responses to Cryptococcus neoformans

The fungus Cryptococcus neoformans is a major cause of morbidity and mortality in patients with impaired CD4(+) T cell function, particularly those with AIDS. To identify cryptococcal antigens that could serve as vaccine candidates by stimulating T cell responses, C. neoformans-reactive CD4(+) T cell hybridomas were generated by immunization of C57BL/6 mice and fusion of splenocytes with thymoma cells. The antigen that stimulated one of the hybridomas, designated P1D6, to produce IL-2 was purified to homogeneity by sequential anion exchange chromatography, hydrophobic interaction chromatography, and SDS/PAGE. Based on its apparent molecular mass of 98 kDa and mannosylation, the antigen of interest was named MP98. MP98 was N terminal-sequenced, and the gene encoding the protein was cloned and sequenced. Recombinant MP98, expressed in Saccharomyces cerevisiae, stimulated P1D6 to produce IL-2. Analysis of the derived 458-aa sequence of MP98 reveals an N-terminal cleavable signal sequence, a polysaccharide deacetylase domain found in fungal chitin deacetylases, and a serine/threonine-rich C-terminal region. Overall, there were 103 serine/threonine residues serving as potential O-linked glycosylation sites as well as 12 possible N-linked glycosylation sites. Thus, a C. neoformans mannoprotein has been characterized that stimulates T cell responses and has molecular properties of a chitin deacetylase.

Generation of anti-teliospores antibodies for immunolocalization and characterization of antigenic epitopes of teliospores of Karnal bunt (Tilletia indica) of wheat

Polyclonal antibodies raised against intact teliospores of T. indica in New Zealand albino rabbits were used for the development of indirect immunofluorescence tests. Specificity of anti-teliospore antibodies was evaluated by cross reactivity studies on other bunt, smut and related pathogens. The characteristic reactivity pattern indicated that the antibodies reacted with Tilletia species only. Chemical modifications, heat and enzyme treatments followed by indirect immunofluorescence tests were employed to delineate the molecular nature of the surface antigens. There was partial or no loss in immunoreactivity by methanol, periodate, heat or trypsin treatments. Extensive periodate treatment altered the fluorescence pattern due to changes in configuration of carbohydrate antigen present in episporium. Sequential treatment of periodate and trypsin showed diminished fluorescence due to access of proteolytic enzyme into inner site of episporium thereby cleaving peptide epitope(s) after reorientation of carbohydrate moietiesby periodate treatment. It indicated glycoprotein nature or peptide nature of epitopes on the teliospore surface.