Molecular cloning and expression of a recombinant Aspergillus fumigatus protein Asp f II with significant immunoglobulin E reactivity in allergic bronchopulmonary aspergillosis

Utility of recombinant Aspergillus fumigatus antigens in the diagnosis of allergic bronchopulmonary aspergillosis: A systematic review and diagnostic test accuracy meta-analysis

BACKGROUND

The role of recombinant A. fumigatus (rAsp) antigens in the diagnosis of allergic bronchopulmonary aspergillosis (ABPA) has not been systematically evaluated. Herein, we evaluate the utility of recombinant A. fumigatus (rAsp) antigens in diagnosing ABPA.

METHODS

We systematically reviewed the PubMed, EmBase and Scopus databases for studies evaluating rAsp antigens in ABPA. The QUADAS-2 tool and the GRADE approach were used to assess the risk of bias and the quality of evidence, respectively. The diagnostic performance of IgE or skin test against rAsp f1, f2, f3, f4, f6 and their combination was evaluated separately for ABPA complicating asthma or cystic fibrosis (CF), using an HSROC model. The reference standard for diagnosing ABPA was the composite (clinical, radiological, immunological) criteria.

RESULTS

Our search yielded 26 studies (n = 1694) and 17 studies (n = 1131) for inclusion in the systematic review and meta-analysis, respectively. In asthmatics, the pooled sensitivity for diagnosing ABPA was best for IgE against a combination of rAsp f1 or f3 (96.7%; 95% confidence interval [CI], 87.6-99.2). The pooled specificity for diagnosing ABPA was highest (99.2%; 95% CI, 88.2-99.9) for IgE against a combination of f4 or f6. In CF patients, the pooled sensitivity of rAsp f1 or f3 was 93.3% (95% CI, 55.2-99.9) while the pooled specificity of rAsp f4 or f6 was 93.9% (95% CI, 68.8-99.9). The quality of evidence was low as per the GRADE approach.

CONCLUSIONS

A combination of IgE against rAsp antigens (f1, f2, f3, f4 and f6) is likely to be helpful in the diagnosis of ABPA.

Characterization of VdASP F2 Secretory Factor from Verticillium dahliae by a Fast and Easy Gene Knockout System

The vascular wilt fungus Verticillium dahliae produces persistent resting structures known as microsclerotia, which enable long-term survival of this plant pathogen in soil. The completed genome sequence of V. dahliae has facilitated large-scale investigations of individual gene functions using gene-disruption strategies based on Agrobacterium tumefaciens-mediated transformation. However, the construction of gene-deletion vectors and screening of deletion mutants have remained challenging in V. dahliae. In this study, we developed a fast and easy gene knockout system for V. dahliae using ligation-independent cloning and fluorescent screening. We identified secretory factor VdASP F2 in a T-DNA insertion library of V. dahliae and deleted the VdASP F2 gene using the developed knockout system. Phenotypic analysis suggests that VdASP F2 is not necessary for V. dahliae growth on potato dextrose agar under various stress conditions. However, on semisynthetic medium or under limited nutrient conditions at lower temperatures, the VdASP F2 deletion mutant exhibited vigorous mycelium growth, less branching, and a significant delay in melanized microsclerotial formation. Further assessment revealed that VdASP F2 was required for the expression of VDH1 and VMK1, two genes involved in microsclerotial formation. Cotton inoculated with the VdASP F2 deletion mutant wilted, demonstrating that VdASP F2 is not associated with pathogenicity under normal conditions. However, after inducing microsclerotial formation and incubation at low temperatures, cotton infected with the VdASP F2 deletion mutant did not exhibit wilt symptoms. In conclusion, our results show that VdASP F2 plays an important role in the response of V. dahliae to adverse environmental conditions and is involved in a transition to a dormant form for prolonged survival.

Host-induced gene silencing in barley powdery mildew reveals a class of ribonuclease-like effectors

Obligate biotrophic pathogens of plants must circumvent or counteract defenses to guarantee accommodation inside the host. To do so, they secrete a variety of effectors that regulate host immunity and facilitate the establishment of pathogen feeding structures called haustoria. The barley powdery mildew fungus Blumeria graminis f. sp. hordei produces a large number of proteins predicted to be secreted from haustoria. Fifty of these Blumeria effector candidates (BEC) were screened by host-induced gene silencing (HIGS), and eight were identified that contribute to infection. One shows similarity to β-1,3 glucosyltransferases, one to metallo-proteases, and two to microbial secreted ribonucleases; the remainder have no similarity to proteins of known function. Transcript abundance of all eight BEC increases dramatically in the early stages of infection and establishment of haustoria, consistent with a role in that process. Complementation analysis using silencing-insensitive synthetic cDNAs demonstrated that the ribonuclease-like BEC 1011 and 1054 are bona fide effectors that function within the plant cell. BEC1011 specifically interferes with pathogen-induced host cell death. Both are part of a gene superfamily unique to the powdery mildew fungi. Structural modeling was consistent, with BEC1054 adopting a ribonuclease-like fold, a scaffold not previously associated with effector function.

Mechanisms of immune evasion in fungal pathogens

The incidence of life-threatening fungal infections has continued to increase in recent years, predominantly in patients debilitated by iatrogenic interventions or immunological dysfunctions. While the picture of the immunology of fungal infections grows increasingly complex, it is clear that the phagocyte-pathogen interaction is a critical determinant of establishing an infection. About 10 years ago, genome-scale approaches began to elucidate the intricate and extensive fungal response to phagocytosis and in the last few years it has become clear that some of this response actively modulates immune cell function. Fungal pathogens avoid detection by masking pathogen-associated molecular patterns, such as cell wall carbohydrates, and by downregulating the complement cascade. Once detected, various species interfere with phagocytosis and intracellular trafficking, and can repress production of antimicrobials like nitric oxide (NO). For the most part, the molecular mechanisms behind these behaviors are not yet known. This review discusses recent discoveries and insights into how fungi manipulate the host-pathogen interaction.

Immune escape of the human facultative pathogenic yeast Candida albicans: the many faces of the Candida Pra1 protein

Infectious diseases caused by human pathogenic fungi represent a major and global health problem. Based on the limited efficacy of existing drugs and the increasing resistance to antifungal compounds, new strategies are urgently needed to fight such fungal infections. The medically important pathogen Candida albicans can exist as an opportunistic yeast, but can also cause severe diseases, septicaemia, and death. In order to establish new strategies to fight Candida infections and to interfere with survival of the pathogen, it is highly relevant to understand the molecular and immunology interactions between the pathogen C. albicans and the human host. This immune cross talk has moved into the focus of infectious disease research. In this review, we summarize the diverse and multiple levels of the immune cross talk between the fungal pathogen C. albicans and the human host. In particular, we define how one single fungal protein Pra1 (pH-regulated antigen 1) interferes and controls host immune attack at multiple levels and thus contributes to fungal immune escape. Candida Pra1 represents a promising candidate for immune interference.

Identification of novel allergens of Aspergillus fumigatus using immunoproteomics approach

BACKGROUND

Approximately 20% of the world's asthmatics are suffering from Aspergillus fumigatus (Afu)-induced allergies. The characterization of specific IgE-inducing allergens in allergic aspergillosis patients is fundamental for clinical diagnosis and for immunotherapy.

METHODS

Immunoproteomics combined with mass spectrometric analysis was used to identify proteins of third-week culture filtrate (3wcf) potentially responsible for Afu-specific IgE immunoreactivity, using pooled sera from Afu-sensitized asthmatics. Their allergenic potential was also tested against patients with allergic bronchopulmonary aspergillosis (ABPA), by two-dimensional (2-D) gel electrophoresis immunoblotting of 3wcf proteins with individual sera from such patients. This helped us to establish a set of candidate allergens, which could be explored further for diagnostic application in allergic aspergillosis asthmatics including ABPA.

RESULTS

Peptide mass fingerprint using matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) and/or de novo sequencing by MS/MS analysis of the protein spots from 2-D gels led to the identification of a total of 16 allergens of Afu. Eleven of them are being reported as allergens for the first time and five had been reported earlier. Putative isoforms of the proteins Asp f 13 and chitosanase have been observed for the first time. When studied for reactivity of these proteins among patients with ABPA using their individual sera, these patients exhibited sensitization although the pattern was varying. Taken together, these proteins could thus be considered as potential allergens even among patients with ABPA. Three of these proteins viz. the hypothetical protein (# spot no. 5), extracellular arabinase (# spot no. 6) and chitosanase (# spot no. 11) could be major allergens with specific IgE immunoreactivity with six out of eight patients' sera.

CONCLUSIONS

The immunoproteomic approach applied to the analysis of culture filtrate proteins resulted in the identification of several candidate allergens, many of them novel, contributing to the catalogue of Afu allergenic proteins, which would facilitate improved serodiagnosis for allergic aspergillosis. In addition, the immunoreactivity of these proteins observed among the patients with ABPA may be potentially useful for its serodiagnosis and opens up further opportunities for the development of personalized immunotherapeutics for patients with ABPA.

Cryptic B-cell epitope identification through informational analysis of protein sequenses

A comparison of the location of B-cell epitopes and information structure (IS) of protein sequences was attempted. Analysis of 62 known B-cell epitopes located in five different proteins showed that they concentrated in IS sites with increased degree of information coordination. Based on the analysis of IS six peptides from two proteins were selected and produced in a recombinant form as yeast virus-like particles (VLPs). Immunization of mice with recombinant VLP-peptides has induced the production of IgG capable of recognizing full-length antigens. This result suggests that the analysis of IS of proteins can be useful in the selection of peptides possessing cryptic B-cell epitope activity.

Selection of cryptic B-cell epitopes using informational analysis of protein sequences

Sub-unit vaccines are synthetic or recombinant peptides representing T- or B-cell epitopes of major protein antigens from a particular pathogen. Epitope selection requires the synthesis of peptides that overlap the protein sequences and screening for the most effective ones. In this study a new method of immunogenic peptide selection based on the analysis of information structure of protein sequences is suggested. The analysis of known B-cell epitope location in the information structure of Aspergillus fumigatus proteins Asp f 2 and Asp f 3 has shown that epitopes are scattered along the sequences of proteins for the exception of sites with Increased Degree Information Coordination (IDIC). Based on these results peptides from different allergens such as Asp f 2, Der p 1, and Fel d 1 were selected and produced in a recombinant form in the context of yeast virus-like particles (VLPs). Immunization of mice with VLPs containing peptides form allergens has induced the production of IgG able to recognize full-length antigens. This result suggests that the analysis of information structure of proteins can be used for the selection of peptides possessing cryptic B-cell epitope activity.

Serodiagnosis of mycoses using recombinant antigens

The early diagnosis of mycoses is important for the institution of an effective antifungal therapy. Detection of antibodies against crude antigenic extracts is one of the standard techniques for the diagnosis of most mycoses. However, while these crude antigenic extracts are relatively easy to obtain, they usually show low reproducibility and are not very specific, since antibodies from patients with different mycoses may show cross-reactivity. The application of molecular biology techniques to the study of fungal antigens has allowed the production of recombinant antigens that may help to solve these problems. The purpose of this review is to discuss the use of recombinant fungal antigens in the diagnosis of mycoses.

Aspergillus antigens: which are important?

Aspergillus fumigatus is a ubiquitous fungus that causes a variety of diseases in man and animals. A number of protein, carbohydrate, and glycoprotein antigens have been identified from A. fumigatus. The diseases are diverse, and therefore are the antigens and their roles in causing or modulating the diseases. The induction and binding of antibodies and the interaction of antigen and various immune cells are of immense significance in the diagnosis and prognosis of the disease. In recent years, over 20 genes encoding A. fumigatus antigens have been cloned and the proteins expressed. Among these allergens, Asp f 1, f 2, f 3, f 4, and f 6 showed strong but diverse IgE binding with sera from different groups of patients. Results currently available suggest that Asp f 2, f 3, and f 6 together reacted with IgE from more patients with asthma and allergic bronchopulmonary aspergillosis (ABPA), although they are only marginally effective in demonstrating specific IgE in patients with cystic fibrosis and ABPA. The molecular structure of allergens also plays a major role in the immunological response in the allergic patients. Antigens can be engineered with less or more binding with IgE, and such antigens may have significant roles as specific reagents or as immunomodulators.

Role of C-terminal cysteine residues of Aspergillus fumigatus allergen Asp f 4 in immunoglobulin E binding

Among the several allergens cloned and expressed from Aspergillus fumigatus, Asp f 4 is a major one associated with allergic bronchopulmonary aspergillosis (ABPA). The structure-function relationship of allergens is important in understanding the immunopathogenesis, diagnosis, and treatment of allergic diseases. These include the epitopes, conformational or linear, deletion of the N or C terminus or both N and C termini, and glycosylation or nonglycosylation, all of which affect immune responses. Similarly, the role of cysteine residues present in allergens may yield useful information regarding the conformational structure of allergens and the immunoglobulin E (IgE) epitope interaction. Such information may help in developing new strategies towards immunotherapy. In order to define the role of cysteine in the interaction of the antibody with Asp f 4, we have constructed mutants by selectively deleting cysteine residues from the C-terminal region of the Asp f 4. Immunological evaluation of these engineered recombinant constructs was conducted by using sera from patients with ABPA, Aspergillus skin test-positive asthmatics, and healthy controls. The results demonstrate strong IgE binding with Asp f 4 and two truncated mutants, Asp f 4(1-234) (amino acids [aa] 1 to 234) and Asp f 4(1-241) (aa 1 to 241), while another mutant, Asp f 4(1-196) (aa 1 to 196), showed reactivity with fewer patients. The result suggests that deletion of cysteines and the alteration of IgE epitopes at the C-terminal end resulted in conformational changes, which may have a potential role in the immunomodulation of the disease.

IgE antibody to Aspergillus fumigatus recombinant allergens in cystic fibrosis patients with allergic bronchopulmonary aspergillosis

BACKGROUND

Allergic bronchopulmonary aspergillosis (ABPA) in cystic fibrosis (CF) is characterized by a heightened Th2 CD4+ T-cell response to Aspergillus fumigatus (Af) allergens and a hyper-immunoglobulin E (IgE) state compared with cystic fibrosis patients without ABPA. The IgE serologic differentiation of ABPA from atopic CF patients can be difficult. We propose as the reactivity with purified antigens varies qualitatively and quantitatively and that the antibody response is more specific than with crude Af antigen extract, the IgE responses to purified recombinant Af allergens may differentiate ABPA from atopic CF patients.

METHODS

Serum IgE reactivity to seven recombinant purified allergens and to a crude extract of Af was measured in 15 ABPA, in 23 Af skin test positive (ST+), and in 19 Af skin test negative (ST-) CF patients. Four of the ABPA CF patients were studied before and after developing ABPA. Nine ABPA patients were studied during flares and remissions of ABPA.

RESULTS

Allergic bronchopulmonary aspergillosis patients had significantly increased IgE reactivity to Asp f2, f3, f4, f6, and f16 compared with the Af ST+ and ST- non-ABPA CF patients. In the ABPA patients studied before and after developing ABPA, IgE reactivity also increased to Asp f2, f3, f4, and f6, and to the crude extract. In ABPA CF patients, IgE reactivity to Asp f1, f2, f3, and f6 significantly increased during periods of ABPA flares compared with periods of remission. Analysis of the receiver operating curve demonstrated that IgE reactivity to Asp f3 and f4 gave the best sensitivity and specificity and were better than IgE reactivity to a crude extract of Aspergillus. Furthermore, in ABPA patients studied during periods of remission the IgE reactivity to Asp f3 and f4 remained significantly elevated compared with Af ST+ non-ABPA patients. The IgE responses when considered either to be positive or negative to Asp f3 and f4 significantly differentiated ABPA from Af ST+ and ST- non-ABPA CF patients. In contrast, IgE reactivity was considered positive to the crude extract in 89% of ABPA, 61% of Af ST+, and 0% of Af ST- non-ABPA CF patients.

CONCLUSIONS

Immunoglobulin E reactivity to a panel of purified Af allergens, especially to Asp f3 and f4, differentiates ABPA from atopic Af ST+ non-ABPA CF patients. Serial determinations of IgE reactivity to individual purified Aspergillus antigens, especially Asp f3, demonstrates that increases in IgE reactivity may provide improved distinction between stages of flares and remission compared with changes in IgE reactivity to a crude Aspergillus extract.

Increased sensitivity to IL-4 in cystic fibrosis patients with allergic bronchopulmonary aspergillosis

BACKGROUND

Allergic bronchopulmonary aspergillosis (ABPA) is characterized by a heightened Th2 CD4+ T-cell response to Aspergillus fumigatus allergens and a hyper-immunoglobulin (Ig)E state compared with cystic fibrosis patients without ABPA. We hypothesize that one reason for this response is increased sensitivity to interleukin (IL)-4 in ABPA resulting in increased expression of CD23 and CD86 and leading to a positive amplification mechanism that increases Th2 CD4+ T cell responses.

METHODS

Peripheral blood mononuclear cells (PBMC) were isolated from seven ABPA CF and 19 non-ABPA CF patients and 16 nonatopic controls and stimulated with rIL-4 (range 0.1-10 ng/ml) and rIL-13 (range 1-10 ng/ml) for 48 h. The number of CD23 molecules and percentages of CD23+ B cells were quantified by flow cytometry. Both phorbol 12-myristate 13-acetate (PMA)/ionomycin (IO) and antigen stimulated, toxoid and Asp f2/f3/f4, PBMC were examined for cytoplasmic cytokine synthesis enumerated by cytokine staining using flow cytometry to measure Th2 and Th1 CD3+ T cells.

RESULTS

The numbers of CD23 molecules on B-cells were significantly elevated at time 0 in ABPA CF patients compared with both non-ABPA CF patients and nonatopic controls. Following IL-4 stimulation in vitro, the numbers and percentages of CD23 expression on B cells were significantly up-regulated in ABPA CF patients compared with non-ABPA CF patients and controls. The IL-13 stimulation up-regulated CD23 expression; however, there was no significant difference in ABPA CF patients compared with non-ABPA CF patients and controls. The percentages of interferon (IFN)-gamma+ CD3+T cells following PMA/IO stimulation were significantly decreased in both ABPA and non-ABPA CF patients compared with controls. There were no significant differences of IL-4+ and IL-13+ CD3+ T cells between ABPA and non-ABPA CF patients. When tetanus toxoid stimulated T cells were examined, both ABPA and non-ABPA CF patients had significantly decreased IFN-gamma+ CD3+ T cells compared with controls. In Asp f2/f3/f4 stimulated T cells, ABPA CF patients had significantly increased IL-4+ CD3+ T cells compared with non-ABPA CF patients and controls.

CONCLUSIONS

ABPA CF patients have increased sensitivity to IL-4 but not to IL-13 up-regulation of CD23 molecules compared with non-ABPA CF patients. There were decreased percentages of IFN-gamma+ and IL-2+ Th1 T cells in CF patients compared with nonatopic controls but similar percentages of IL-4+ Th2 T cells in all three groups. However, ABPA CF patients had increased frequency of Aspergillus-stimulated Th2 T cells. This indicated that there is skewing of Th2 T cells in ABPA CF patients. Thus, in CF ABPA patients there is increased Th2 T cells and increased sensitivity to IL-4.

cDNA cloning, expression and characterization of an allergenic L3 ribosomal protein of Aspergillus fumigatus

Aspergillus fumigatus (Afu) is an important fungal pathogen causing allergic and invasive respiratory disorders. A plethora of multi-functional allergens/antigens secreted by Afu have been implicated in pathogenesis. The present study was undertaken to identify and characterize novel Afu allergen/antigen by cDNA library approach. cDNA library of Afu was immunoscreened with pooled sera of allergic bronchopulmonary aspergillosis (ABPA) patients. The cDNA clone, TS1, reacting significantly with specific IgG antibodies, was selected. cDNA was subcloned and expressed in Escherichia coli. Sequencing of the cDNA revealed an open reading frame (ORF) of 1179 bases coding for a protein with an approximate molecular weight of 44 kDa. Immunoreactivity of the recombinant TS1 protein (rTS1) was evaluated by ELISA and Western blot analysis using pooled sera of ABPA patients. The rTS1 exhibited binding to specific IgG and IgE antibodies present in sera of ABPA patients. The deduced amino acid sequence showed homology to 60S ribosomal protein L3 (RpL3) of Aspergillus nidulans, Saccharomyces cerevisiae and Homo sapiens. The RpL3 of S. cerevesiae, tcm1, to which TS1 sequence shows significant homology (72% identity), is known to be responsible for conferring resistance against trichodermin (antibiotic, inhibiting protein synthesis). The present study has led to identification, cloning and expression of a 44-kDa novel allergen/antigen of Afu with sequence homology to L3 ribosomal protein with a probable role in resistance of Afu to antifungal drugs. Sixty-four per cent sequence identity of Afu RpL3 with human RpL3 and common regions in their predicted epitopes suggest a possibility of involvement of Afu RpL3 in autoimmune reactions due to molecular mimicry.

Fungal allergens

Many fungi are capable of causing IgE-mediated hypersensitivity in humans. However, the most predominant fungi implicated in allergy belong to the genera Aspergillus, Alternaria, Cladosporium, and Penicillium. Pure and relevant allergens are essential for diagnosis as well as for understanding the immunopathogenesis of the disease. Until recently, pure and standardizable antigens from fungi were not available. In recent years, many recombinant allergens have been produced by molecular cloning. Using these allergens, novel methods are being developed to improve diagnosis of mold-induced allergy. By understanding the immunopathogenesis of allergens, new avenues might open up leading to improved patient care, including immunotherapy and vaccination. This review covers the current status of fungal allergens, their role in reliable immunodiagnosis, and their probable use in immunotherapy and vaccination.

Animal models of allergic bronchopulmonary aspergillosis

Among the allergic fungi, Aspergillus fumigatus, a saprophytic mold, distributed widely in the environment is a frequently recognized etiologic agent in a number of allergic conditions. Among the different allergic diseases caused by this fungus, allergic bronchopulmonary aspergillosis (ABPA) is by far the most significant one. The immunopathogenesis of this disease is not fully understood. Although several immunomodulatory treatments are available for allergic disease, none of them are applicable or relevant or useful in fungal induced allergy. It is essential to understand the pathogenesis of the disease including the antigen induced immunoregulation and the resulting factors, such as cytokine, chemokines, pathways activating factors, inflammatory and airway remodeling factors need to be understood for intervening with appropriate treatment. Animal models are essential in understanding these features of the disease. Several models of allergic aspergillosis have been developed in recent years in various animals. However, murine models have been studied more carefully and extensively. The exposure to antigen in mice leads to allergy very similar to ABPA with high IgE, elevated peripheral blood and lung eosinophils, pulmonary inflammation, and airway hyperreactivity. The role of various cytokines and chemokines and their receptors were also studied. In addition, immunotherapy and vaccination have been attempted in recent years using the murine model of ABPA. This review covers the murine model of Aspergillus induced allergy and asthma and presented critically our current understanding of the subject and the potential application of such a model in future for developing treatment modalities.

C-terminal cysteine residues determine the IgE binding of Aspergillus fumigatus allergen Asp f 2

The knowledge of the structure function relationship of the allergen is essential to design allergenic variants with reduced IgE binding capacity but intact T cell reactivity. Asp f 2 is a major allergen from the fungus Aspergillus fumigatus and >90% of A. fumigatus-sensitized individuals displayed IgE binding to Asp f 2. In the present study, we evaluated the involvement of C-terminal cysteine residues in IgE binding conformation of Asp f 2. The deletion mutants were constructed by adding three C-terminal cysteines of the native Asp f 2 one at a time to the non-IgE binding Asp f 2 (68-203). The point mutants of Asp f 2 (68-268) with C204A and C257A substitutions were constructed to study the role of C-terminal cysteines in IgE binding. Immunological evaluation of reduced and alkylated Asp f 2 and its mutants were conducted to determine the contribution of free sulfhydryl groups as well as the disulfide bonds in allergen Ab interaction. Four-fold increase in IgE Ab binding of Asp f 2 (68-267) compared with Asp f 2 (68-266) and complete loss in IgE binding of C204A mutant of Asp f 2 (68-268) indicate the involvement of C(204) and C(267) in IgE binding conformation of Asp f 2. A significant reduction in IgE binding of wild and mutated Asp f 2 after reduction and alkylation emphasizes the importance of cysteine disulfide bonds in epitope Ab interaction. The hypoallergenic variants may be explored further to develop safe immunotherapeutic strategy for allergic disorders.

IgE binding conformational epitopes of Asp f 3, a major allergen of Aspergillus fumigatus

sp f 3 has been identified as one of the major allergens of Aspergillus fumigatus associated with the sensitization and immune responses in allergic bronchopulmonary aspergillosis (ABPA). In order to understand the structure/function relationship of Asp f 3, we studied synthetic peptides and constructed mutants deleted of specific IgE binding regions. The mutated allergens were obtained by expressing the genes and studied by ELISA for their reactivity with IgE from patients with ABPA. Seven linear IgE binding regions spanning the whole Asp f 3 molecule were demonstrated. The results demonstrated strong binding of IgE from ABPA patients with Asp f 3 and one mutant, Asp f 3(1-150), but not with other mutant constructs. The results identified 12 amino acids at the N-terminal end and 8 amino acids (143-150) at the C-terminal end as significant in the conformational constraints for IgE binding. The Fourier transfer spectra showed comparable beta-sheet structure of Asp f 3(1-150) and Asp f 3, indicating the role of secondary structure in IgE binding. The primary and secondary structures may help understanding of the functional role the allergens play in the disease and may have implications in immunodiagnosis and probably immunotherapy.

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.

Characterization of Aspergillus fumigatus protein disulfide isomerase family gene

Aspergillus fumigatus is an opportunistic fungus which causes pulmonary complications in humans and animals. The clinical spectrum observed with A. fumigatus is attributed to the multifunctional nature of its antigens. Lack of understanding on the molecular processes and complexity of the fungus have spurred interest in the identification and characterization of its antigens/allergens with biological activities and virulence functions. For identification of some of these antigens/allergens, a cDNA library of A. fumigatus was screened with antibodies of allergic bronchopulmonary aspergillosis (ABPA) patients. One of the reactive clones was sequenced and observed to have an open reading frame of 1095 nucleotides corresponding to a polypeptide of 364 amino acids. The nucleotide and deduced amino acid sequence showed significant homology with the protein disulfide isomerase (PDI) superfamily. The expressed recombinant fusion protein exhibited specific IgG and IgE binding with antibodies present in ABPA patients' sera. The recombinant protein in vitro catalyzed folding of scrambled RNase. The probable epitopic regions of the deduced amino acid sequence were mapped by algorithmic analysis. This is the first report of isolation of a gene encoding a member of the PDI family from A. fumigatus. The PDI superfamily of proteins may play an important role in the protein folding mechanisms of A. fumigatus antigens/allergens for their interaction with the host.

Do T helpers 1 and 2 recognize different class II MHC molecules? Humoral and cellular immune responses to soluble allergen from Aspergillus fumigatus Asp f2

Cellular signals leading to T helper (Th)1/Th2 shift are not well known. Here we demonstrate that Th1 possibly recognizes peptides presented by the IE molecule of MHC class II while Th2 is activated by the recognition of peptides presented by the IA molecule. BALB/c mice immunized with Asp f2 developed stable IA-restricted Th2 immune response to the 12th day after immunization, as analyzed by IL-2 production. On the contrary, early Th0 cells did not secrete IL-2 upon Asp f2 stimulation but did produce a high level of IL-2 if stimulated in the presence of anti-IA Abs. This effect of anti-IA Abs on early Th0 cells was both MHC IE and CD4(+) cell restricted. In vivo blocking of Asp f2 peptide presentation by the IA molecule led to the formation of antigen-specific cytotoxicity as demonstrated using immune splenocytes as effector cells and Asp f2 loaded P815 cells as targets.

Assessment and control of fungal allergens

Fungal sensitivity is a significant cause of allergic disease. Understanding the role fungi play in allergic disease, and how to best control exposure among those with allergy, can have important clinical ramifications.

T cell proliferation and cytokine secretion to T cell epitopes of Asp f 2 in ABPA patients

The pathogenesis of allergic bronchopulmonary aspergillosis (ABPA) involves specific cytokines secreted by lymphocytes in response to Aspergillus fumigatus (Af) allergens. To gain information about the lymphoproliferative response and cytokine production against a major Af allergen, Asp f 2, we studied Asp-f-2-specific T cell clones (TCCs) from ABPA patients. TCCs were stimulated with rAsp f 2, its deletion mutants, and synthetic peptides to identify the T cell epitope(s) and to understand cytokine production. PBMCs from four of five ABPA patients showed proliferation in response to Asp f 2. Three TCCs from one patient showed higher IL-5 secretion compared to IL-4 and IFN-gamma. Two TCCs from the second patient showed a mixed Th1/Th2 response, as evidenced by production of IL-4, IL-5, and IFN-gamma. An epitope from the N-terminal region of Asp f 2 induced only IL-5 secretion. High IL-5 secretion might explain the marked eosinophilia observed in ABPA patients.

Cloning and expression of Aspergillus fumigatus allergen Asp f 16 mediating both humoral and cell-mediated immunity in allergic bronchopulmonary aspergillosis (ABPA)

BACKGROUND

Aspergillus fumigatus, a ubiquitous fungus, is responsible for a number of lung disorders in atopic and non-atopic individuals. Standardized, pure, and relevant allergens are desirable for reliable immunodiagnosis of the disease and to understand the structural and functional properties of these allergens and the role they play in causing ABPA.

OBJECTIVE

Molecular cloning and characterization of a relevant allergen from A. fumigatus cDNA library.

MATERIALS AND METHODS

A cDNA library was constructed from 96 h old mycelium of A. fumigatus using lambda ZAP expression vector. A novel gene encoding an A. fumigatus allergen was identified by screening the library with sera from ABPA patients. The gene was cloned and the allergen over-expressed in Escherichia coli. This recombinant allergen, Asp f 16, was evaluated in ELISA and Western blots using sera from patients and normal subjects and peripheral blood mononuclear cells (PBMC) for antigen-induced stimulation.

RESULTS

Seventy percent of the patients with ABPA demonstrated high levels of serum IgE antibodies to Asp f 16, a 43-kDa protein, whereas patients with allergic asthma, Aspergillus skin test-positive asthmatics without clinical evidence of ABPA, and normal controls failed to show Asp f 16-specific IgE binding by ELISA. The deduced amino acid sequences of Asp f 16 showed extensive sequence homology to 30.6-kDa Asp f 9 at the N-terminal region of the protein. PBMC from the majority of patients with ABPA exhibited significant proliferation with the recombinant Asp f 16 allergen.

CONCLUSION

Specific humoral and cell-mediated immune responses of Af-sensitized patients against Asp f 16 suggest its usefulness in the immunodiagnosis of hypersensitivity diseases due to Af and understanding the pathophysiology of ABPA.

Identification of continuous B-cell epitopes on the protein moiety of the 58-kiloDalton cell wall mannoprotein of Candida albicans belonging to a family of immunodominant fungal antigens

The 58-kiloDalton mannoprotein (mp58) on the surface of Candida albicans is highly immunogenic, is expressed by all C. albicans isolates tested, and elicits strong antibody responses during candidiasis. It belongs to a family of immunodominant fungal antigens with representatives also in different species of Aspergillus. The amino acid sequence of the protein portion of mp58 as deduced from the DNA sequence of its encoding gene (FBP1/PRA1) was used to synthesize a complete set of overlapping dodecapeptides (overlap, 7; offset, 5) covalently attached to the surface of derivatized polyethylene pins. The pin-coupled peptides were used in a modified enzyme-linked immunosorbent assay (ELISA) to identify continuous epitopes recognized by a number of antiserum preparations containing anti-mp58 antibodies. This comprehensive epitope-scanning study revealed the presence of multiple immunoreactive continuous B-cell epitopes within the protein sequence. Regions of increased reactivity included both the amino and carboxy termini of the mature protein (encompassing amino acid residues 16 to 50 and 286 to 299, respectively) and four internal regions spanning amino acids at positions 66 to 92, 121 to 142, 148 to 192, and 211 to 232. Further delineation of epitopic regions and identification of the boundaries of the antigenic sites was performed upon ELISA testing with a second Pepset consisting of completely overlapping 8-mer peptides spanning these reactive regions in the protein moiety of mp58. The highly reactive epitopic region at the C terminus of the protein was further evaluated using both window net and replacement net analyses. A synthetic peptide corresponding to the last 10 amino acid residues at the C terminus of the protein was immunogenic when injected into mice after being coupled to a carrier protein. Moreover, antibodies in the resulting sera specifically recognized the homologous mp58 in ELISAs and immunoblot assays. Delineation of the antibody responses to mp58 could provide the basis for the development of novel immunity-based prophylactic, therapeutic, and diagnostic techniques for the management of candidiasis.

Purified recombinant A. fumigatus allergens induce different responses in mice

Aspergillus fumigatus an opportunistic fungus is associated with a number of diseases in humans. Allergy resulting from exposure to the A. fumigatus allergens has been recognized frequently. The damage caused by the disease is very striking in patients with atopy and those with cystic fibrosis. Avoidance to exposure is not feasible because A. fumigatus spores are ubiquitously distributed in the environment. Hence, immunotherapeutic regimens in severe forms of A. fumigatus allergy may have a high potential. However, before such forms of therapy can be envisaged, it is essential to understand the immunopathogenesis. In the present study, we investigated the role of purified A. fumigatus allergens in the development of allergic asthma in mice. We have used four major recombinant A. fumigatus allergens in the murine model. Mice exposed to Asp f 1, f 3, and f 4 showed inflammatory changes in the lungs and airway hyperreactivity. The immune responses, including elevated serum IgE, enhanced eosinophils, recruitment in the peripheral blood and lungs, and expression of regulatory cytokines, are characteristic of a Th2 response. Asp f 6 demonstrated only a reduced response in these animals. The results suggest that the pathology induced by crude A. fumigatus extract results from the cumulative effects of the allergens and the individual responses varied considerably with different purified antigens.

Identification of vacuolar serine proteinase as a major allergen of Aspergillus fumigatus by immunoblotting and N-terminal amino acid sequence analysis

Aspergillus species are common airborne fungi that have been identified as causative agents of extrinsic bronchial asthma. More than 10 allergens from A. fumigatus have been recently characterized by cDNA cloning. The objective of this study is to identify A. fumigatus allergens through immunoblot analysis using sera from asthmatic patients. IgE-binding components of A. fumigatus and IgE cross-reactivity among allergens of different prevalent airborne fungal species were analysed by immunoblot and immunoblot inhibition, respectively, using sera from asthmatic patients. The N-terminal amino acid sequences of major allergens identified were determined by Edman degradation. Among two batches (70 and 41 sera) of asthmatic sera tested, 19 (27%) and 14 (34%), respectively, have IgE immunoblot reactivity towards components of A. fumigatus. A 34-kDa protein that reacts with IgE antibodies in 15 (79%) and 11 (79%) of the 19 and 14 positive samples, respectively, may be considered a major allergen of A. fumigatus. The N-terminal amino acid sequences of the 34 kDa major allergen and the 30.5 and 30 kDa IgE-binding components of A. fumigatus showed sequence identity to that of the vacuolar serine proteinase from A. fumigatus. The results from immunoblot inhibition show IgE cross-reactivity among major allergens of A. fumigatus, P. notatum and P. oxalicum. Results obtained suggest that the 34 kDa major allergen of A. fumigatus may be a vacuolar serine proteinase. There is IgE cross-reactivity among serine proteinase allergens of A. fumigatus, P. notatum and P. oxalicum.

Selected recombinant Aspergillus fumigatus allergens bind specifically to IgE in ABPA

BACKGROUND

Allergic bronchopulmonary aspergillosis (ABPA) is a hypersensitivity lung disease resulting from exposure to Aspergillus fumigatus allergens. Patients with ABPA show elevated Aspergillus-specific serum IgE, a major criterion used in the diagnosis of the disease. Crude culture filtrate and mycelial antigens have been used widely to demonstrate IgE antibody to Aspergillus in the sera of patients. While these antigens have been useful in the diagnosis of ABPA, occasionally they present inconsistency in their reactivity and lack of specificity. Although in recent years, a number of purified A. fumigatus allergens have been produced by molecular cloning, no attempt was made to evaluate them systematically.

OBJECTIVE

To evaluate the recombinant proteins from A. fumigatus for their IgE antibody binding, we studied sera from ABPA patients and controls by antigen specific enzyme linked immunosorbent assay (ELISA).

METHODS

Recombinant Aspergillus allergens Asp f 1, f 2, f 3, f 4, and f 6 were studied for their specific binding to IgE in the sera of ABPA patients, A. fumigatus skin prick test positive asthmatics, and normal controls from the USA and Switzerland. The sera were blinded and studied by ELISA in two different laboratories.

RESULTS

All the recombinant allergens showed IgE antibody binding with sera from patients with ABPA, whereas only fewer asthmatics and normal sera showed significant binding. The three selected recombinant allergens together reacted with all the ABPA patients studied.

CONCLUSIONS

The results demonstrate that Asp f 2, f 4, and f 6 can be used in the serodiagnosis of ABPA, while IgE antibody binding to Asp f 1 and f 3 was not specific.

Antibody binding of deletion mutants of Asp f 2, the major Aspergillus fumigatus allergen

Asp f 2, a 268 amino acid major allergen from Aspergillus fumigatus (Af) demonstrated nine linear IgE binding regions. It is not known whether any of these linear epitopes are also conformatory epitopes. Hence, we constructed deletion mutants of Asp f 2 devoid of one or more epitopes, and the IgE binding of these proteins with sera from patients with ABPA was compared with the full-length Asp f 2 expressed in E. coli and Pichia. The Pichia expressed protein reacted weakly with IgE, but strongly with IgG of ABPA sera compared to E. coli expressed Asp f 2. Weak IgE binding only was seen when the C-terminal or N-terminal was deleted, while depletion of both ends negated all reactivity. The monoclonal antibody IL-B8 and IgE and IgG of ABPA sera bound significantly to the Asp f 2 E-4 fragment indicating that the major B-cell epitope is located at the N-terminal end of Asp f 2.

Expression of an epitopic region of AspfI, an allergen/antigen/cytotoxin of Aspergillus fumigatus

The gene for an 18 kD allergen/cytotoxin of Aspergillus fumigatus was cloned in pUC-19 vector and expressed in Escherichia coli JM109. Digestion of this gene with AluI resulted in four fragments of 216bp, 120bp, 39bp and 21bp. These fragments were cloned in the Sma-I site of pUC-19. The recombinants thus, generated after transformation in E. coli JM109, were screened using monoclonal antibodies raised against the AspfI. The fusion protein containing 120 bp AluI fragment was recognised by the MoAb indicating presence of epitope(s) in the 120 bp region. The study indicates a viable strategy for identification and expression of an immunologically active domain of a major allergen/antigen of A. fumigatus for the first time.

Characterization of a novel allergen, a major IgE-binding protein from Aspergillus flavus, as an alkaline serine protease

Aspergillus species of fungi have been known to be one of the most prevalent aeroallergens. One important A. flavus allergen (Asp fl 1) was identified by means of immunoblotting with a serum pool of allergic patients on a two-dimensional electrophoretic gel. The cDNA coding for Asp fl 1 was cloned and sequenced. The clone encodes a full-length protein of 403 amino acid precursors of 42 kDa. After cleavage of a putative signal peptide of 21 amino acids and a prepeptide of 100 amino acids, a mature protein of 282 amino acids was obtained with a molecular mass of 33 kDa and a pI of 6.3. A degree of identity was found in a range of 27 to 84% among related allergens derived from bacteria allergen subtilisin, mold allergen Pen c 1, and virulence factor of A. fumigatus. Recombinant Asp fl 1 (rAsp fl 1) was cloned into vector pQE-30 and expressed in E. coli M15 as a histidine-tag fusion protein and purified to homogeneity. The IgE binding capacity of rAsp fl 1 was tested by immunoblotting using a serum pool of Aspergillus-allergic patients. Recombinant allergen cross-reacted strongly with IgE specific for natural Asp fl 1 and Pen c 1, indicating that common IgE epitopes may exist between allergens of A. flavus and P. citrinum.

Humoral and cell-mediated autoimmune reactions to human acidic ribosomal P2 protein in individuals sensitized to Aspergillus fumigatus P2 protein

A panel of cDNAs encoding allergenic proteins was isolated from an Aspergillus fumigatus cDNA library displayed on the surface of filamentous phage. Solid phase-immobilized serum immunoglobulin E (IgE) from A. fumigatus-allergic individuals was used to enrich phage displaying IgE-binding molecules. One of the cDNAs encoded a 11.1-kD protein that was identified as acidic ribosomal phosphoprotein type 2 (P2 protein). The allergen, formally termed rAsp f 8, shares >62% sequence identity and >84% sequence homology to corresponding eukaryotic P2 proteins, including human P2 protein. The sequences encoding human and fungal P2 protein were subcloned, expressed in Escherichia coli as His6-tagged fusion proteins, and purified by Ni2+-chelate affinity chromatography. Both recombinant P2 proteins were recognized by IgE antibodies from allergic individuals sensitized to the A. fumigatus P2 protein and elicited strong type 1-specific skin reactions in these individuals. Moreover, human and fungal P2 proteins induced proliferative responses in peripheral blood mononuclear cells of A. fumigatus- allergic subjects sensitized to the fungal P2 protein. These data provide strong evidence for in vitro and in vivo humoral and cell-mediated autoreactivity to human P2 protein in patients suffering from chronic A. fumigatus allergy.

Zinc-regulated biosynthesis of immunodominant antigens from Aspergillus spp

ASPND1 and ASPF2 are immunodominant antigens from Aspergillus nidulans and A. fumigatus, respectively, that are readily synthesized in infections in the human host, as demonstrated by their reactivity with more than 80% of sera from patients with aspergilloma or allergic bronchopulmonary aspergillosis. We demonstrate here that both antigens are exclusively produced under situations of low bioavailability of free Zn2+. Addition of micromolar concentrations of Zn2+ to the culture medium strongly stimulated Aspergillus growth but totally inhibited ASPND1 or ASPF2 production. This effect was specific, since other divalent metals had no effect. Removal of endogenous Zn2+ by a chelator also stimulated ASPND1 production, and the effect was specifically reversed by Zn2+. These results suggest a possible role of these antigens in the survival of the fungus in the lungs.

Conformational and linear B-cell epitopes of Asp f 2, a major allergen of Aspergillus fumigatus, bind differently to immunoglobulin E antibody in the sera of allergic bronchopulmonary aspergillosis patients

Asp f 2 is a major Aspergillus fumigatus allergen involved in allergic bronchopulmonary aspergillosis. Knowledge of the B-cell epitopes may contribute to the understanding of immunoregulation and immunodiagnosis. To elucidate the immunoglobulin E (IgE) binding epitopes in the linear sequence of Asp f 2, we synthesized decamer peptides spanning the whole molecule of Asp f 2 on derivatized cellulose membranes and evaluated IgE binding in ABPA patient and control sera. Peptides three to five amino acids long were synthesized based on amino acid sequences within the IgE binding regions and evaluated for the specificity of epitope antibody interactions. Nine IgE binding regions were recognized in this protein of 268 amino acid residues. Of the nine epitopes, seven (ATQRRQI, RKYFG, HWR, YTTRR, DHFAD, ALEAYA, and THEGGQ) are present in the hydrophilic regions of Asp f 2. Immunologic evaluation of the three recombinant fragments, Asp f 2A encompassing the N-terminal epitope region, Asp f 2B without N- and C-terminal regions of the protein, and Asp f 2C representing C-terminal epitopes, revealed that either the N- or C-terminal region of the protein is essential for the correct folding and conformation for IgE antibody binding.

Aspergillus fumigatus and aspergillosis

Aspergillus fumigatus is one of the most ubiquitous of the airborne saprophytic fungi. Humans and animals constantly inhale numerous conidia of this fungus. The conidia are normally eliminated in the immunocompetent host by innate immune mechanisms, and aspergilloma and allergic bronchopulmonary aspergillosis, uncommon clinical syndromes, are the only infections observed in such hosts. Thus, A. fumigatus was considered for years to be a weak pathogen. With increases in the number of immunosuppressed patients, however, there has been a dramatic increase in severe and usually fatal invasive aspergillosis, now the most common mold infection worldwide. In this review, the focus is on the biology of A. fumigatus and the diseases it causes. Included are discussions of (i) genomic and molecular characterization of the organism, (ii) clinical and laboratory methods available for the diagnosis of aspergillosis in immunocompetent and immunocompromised hosts, (iii) identification of host and fungal factors that play a role in the establishment of the fungus in vivo, and (iv) problems associated with antifungal therapy.

Immunological characterization of Asp f 2, a major allergen from Aspergillus fumigatus associated with allergic bronchopulmonary aspergillosis

The 37-kDa recombinant protein Asp f 2, encoding an allergen of Aspergillus fumigatus, was expressed in a prokaryotic expression system and immunologically evaluated for its functional and structural properties. The open reading frame for a 310-amino-acid-long protein was shown to encode a signal peptide of 31 amino acids. A native 37-kDa culture filtrate protein and a 55-kDa mycelial glycoprotein (gp55) exhibited complete N-terminal sequence homology to Asp f 2. A GenBank search for homologous proteins revealed 60 and 44% sequence homologies to the cytosolic protein ASPND1 from Aspergillus nidulans and fibrinogen binding protein from Candida albicans, respectively. The glycosylation sites and cysteine molecules are conserved in all the three proteins. The extracellular matrix protein laminin showed a dose-dependent interaction with Asp f 2. This protein, expressed as a major cell-associated protein within 24 h of in vitro fungal culture, comprises 20 to 40% of total fungal protein. Furthermore, both native and recombinant Asp f 2 exhibited specific immunoglobulin (IgE) binding with allergic bronchopulmonary aspergillosis (ABPA) and cystic fibrosis-ABPA patients, whereas A. fumigatus-sensitized allergic asthma and normal control subjects failed to show IgE binding with Asp f 2. These results indicate that Asp f 2 is a major allergen of A. fumigatus exhibiting IgE antibody binding with sera from patients with ABPA. The antigen should be explored further for its potential role in the differential diagnosis of A. fumigatus-associated allergic diseases.

[Molecular aspects and diagnostic value of fungal allergens]

Cloning, sequencing and production of highly pure recombinant allergens allows to produce perfectly standardised allergen preparations. The development of a new cloning system based on filamentous phage allowed the fast isolation and characterisation of allergens from the fungus Aspergillus fumigatus. The produced recombinant allergens were tested in serological and clinical studies as well as for their performance for routine assessments in the ImmunoCAP-system. Thereby, a perfect correlation between skin test results and serology was found showing the potential of recombinant allergens for the diagnosis of allergic diseases. Moreover, the characterisation of fungal allergens substantially contributes to our understanding of the molecular nature of proteins involved in the elicitation of allergic reactions. Apart from allergenic proteins with unknown biological function, fungal allergens can be subdivided into two classes: 1. Species-specific, secreted proteins and 2. cytoplasmic, even in phylogenetically distant organisms, well conserved proteins. These fungal allergens show extended sequence similarity, a high level of IgE cross-reactivity and in some cases also cross-reactivity with homologous human proteins indicating autoimmune reactions involved in fungal allergy.

The recombinant antigen ASPND1r from Aspergillus nidulans is specifically recognized by sera from patients with aspergilloma

A 996 bp Aspergillus nidulans cDNA encoding the ASPND1 immunodominant antigen was cloned and expressed in Escherichia coli as a fusion protein with the enzyme glutathione S-transferase (GST) from Schistosoma japonicum. The GST-ASPND1 fusion protein was purified from isolated bacterial inclusion bodies by preparative SDS-PAGE. After cleavage with thrombin, the ASPND1 recombinant antigen (ASPND1r) and the GST protein were separated by SDS-PAGE and immunoblotted with a number of different human sera. The sera from 22 (88%) of 25 patients with an aspergilloma recognized the ASPND1r recombinant antigen on immunoblots. Forty-nine normal human sera and 14 sera from patients with other infections were unreactive. The ASPND1r expressed in E. coli could therefore be used, in combination with previously reported recombinant antigens, as a standardized antigen for serological and clinical diagnosis of Aspergillus-associated diseases.

Immunodominant peptide epitopes of allergen, Asp f 1 from the fungus Aspergillus fumigatus

Aspergillus fumigatus ribotoxin Asp f 1 is a major allergen with IgE binding activity to serum of a majority of patients with allergic bronchopulmonary aspergillosis (ABPA). The IgE binding epitopes or the T-cell stimulatory peptides of this molecule have not been studied. In the present investigation, we have synthesized linear decapeptides spanning the whole molecule of Asp f 1 and analyzed their IgE binding properties. We have also synthesized peptides based on their possible T-cell stimulatory properties and studied the stimulation of peripheral blood mononuclear cells from ABPA patients and normal controls. Several peptides demonstrated distinct IgE antibody binding response against sera from ABPA patients and proliferative response against peripheral blood mononuclear cells from the patients. From the results, it can be concluded that the carboxy-terminal region of Asp f 1 representing amino acid residues 115-149 involved in both humoral and cell mediated immunoresponses in ABPA.

Cloning and characterization of PRA1, a gene encoding a novel pH-regulated antigen of Candida albicans

Candida albicans is an opportunistic fungal pathogen of humans. The cell wall of the organism defines the interface between the pathogen and host tissues and is likely to play an essential and pivotal role in the host-pathogen interaction. The components of the cell wall critical to this interaction are undefined. Immunoscreening of a lambda expression library with sera raised against mycelial cell walls of C. albicans was used to identify genes encoding cell surface proteins. One of the positive clones represented a candidal gene that was differentially expressed in response to changes in the pH of the culture medium. Maximal expression occurred at neutral pH, with no expression detected below pH 6.0. On the basis of the expression pattern, the corresponding gene was designated PRA1, for pH-regulated antigen. The protein predicted from the nucleotide sequence was 299 amino acids long with motifs characteristic of secreted glycoproteins. The predicted surface localization and N glycosylation of the protein were directly demonstrated by cell fractionation and immunoblot analysis. Deletion of the gene imparted a temperature-dependent defect in hypha formation, indicating a role in morphogenesis. The PRA1 protein was homologous to surface antigens of Aspergillus spp. which react with serum from aspergillosis patients, suggesting that the PRA1 protein may have a role in the host-parasite interaction during candidal infection.

Cloning of a cDNA fragment encoding part of the protein moiety of the 58-kDa fibrinogen-binding mannoprotein of Candida albicans

Immunoscreening of a Candida albicans expression library with antibodies against the 58 kDa fibrinogen-binding mannoprotein (mp58) of the fungus resulted in the isolation of clones encoding the protein moiety of this molecule. Sequence of the 0.9 kb cDNA of one of the clones selected for further analysis, revealed an open reading frame coding for 292 amino acids, which displays sequence similarity to proteins belonging to a family of immunodominant antigens of Aspergillus spp. The gene corresponding to this cDNA was named FBP1 (fibrinogen-binding protein). These results represent the first report on the identification of C. albicans genes encoding surface receptors for host proteins.

Characterization of the Aspergillus nidulans aspnd1 gene demonstrates that the ASPND1 antigen, which it encodes, and several Aspergillus fumigatus immunodominant antigens belong to the same family

For the first time, an immunodominant Aspergillus nidulans antigen (ASPND1) consistently reactive with serum samples from aspergilloma patients has been purified and characterized, and its coding gene (aspnd1) has been cloned and sequenced. ASPND1 is a glycoprotein with four N-glycosidically-bound sugar chains (around 2.1 kDa each) which are not necessary for reactivity with immune human sera. The polypeptide part is synthesized as a 277-amino-acid precursor of 30.6 kDa that after cleavage of a putative signal peptide of 16 amino acids, affords a mature protein of 261 amino acids with a molecular mass of 29 kDa and a pI of 4.24 (as deduced from the sequence). The ASPND1 protein is 53.1% identical to the AspfII allergen from Aspergillus fumigatus and 48% identical to an unpublished Candida albicans antigen. All of the cysteine residues and most of the glycosylation sites are perfectly conserved in the three proteins, suggesting a similar but yet unknown function. Analysis of the primary structure of the ASPND1 coding gene (aspnd1) has allowed the establishment of a clear relationship between several previously reported A. fumigatus and A. nidulans immunodominant antigens.