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

Fungal Ribotoxins: A Review of Potential Biotechnological Applications

Fungi establish a complex network of biological interactions with other organisms in nature. In many cases, these involve the production of toxins for survival or colonization purposes. Among these toxins, ribotoxins stand out as promising candidates for their use in biotechnological applications. They constitute a group of highly specific extracellular ribonucleases that target a universally conserved sequence of RNA in the ribosome, the sarcin-ricin loop. The detailed molecular study of this family of toxic proteins over the past decades has highlighted their potential in applied research. Remarkable examples would be the recent studies in the field of cancer research with promising results involving ribotoxin-based immunotoxins. On the other hand, some ribotoxin-producer fungi have already been studied in the control of insect pests. The recent role of ribotoxins as insecticides could allow their employment in formulas and even as baculovirus-based biopesticides. Moreover, considering the important role of their target in the ribosome, they can be used as tools to study how ribosome biogenesis is regulated and, eventually, may contribute to a better understanding of some ribosomopathies.

Epitope Mapping of Rhi o 1 and Generation of a Hypoallergenic Variant: A CANDIDATE MOLECULE FOR FUNGAL ALLERGY VACCINES

Efficacy of allergen-specific immunotherapy is often severely impaired by detrimental IgE-mediated side effects of native allergen during vaccination. Here, we present the molecular determinants for IgE recognition of Rhi o 1 and eventually converting the allergen into a hypoallergenic immunogen to restrain health hazards during desensitization. Rhi o 1 is a respiratory fungal allergen. Despite having cross-reactivity with cockroach allergen, we observed that non-cross-reactive epitope predominantly determined IgE binding to Rhi o 1. Denaturation and refolding behavior of the allergen confirmed that its IgE reactivity was not essentially conformation-dependent. A combinatorial approach consisting of computational prediction and a peptide-based immunoassay identified two peptides ((44)TGEYLTQKYFNSQRNN and (311)GAEKNWAGQYVVDCNK) of Rhi o 1 that frequently reacted with IgE antibodies of sensitized patients. Interestingly, these peptides did not represent purely linear IgE epitopes but were presented in a conformational manner by forming a spatially clustered surface-exposed epitope conferring optimal IgE-binding capacity to the folded allergen. Site-directed alanine substitution identified four residues of the IgE epitope that were crucial for antibody binding. A multiple mutant (T49A/Y52A/K314A/W316A) showing 100-fold lower IgE binding and reduced allergenic activity was generated. The TYKW mutant retained T-cell epitopes, as evident from its lymphoproliferative capacity but down-regulated pro-allergic IL-5 secretion. The TYKW mutant induced enhanced focusing of blocking IgG antibodies specifically toward the IgE epitope of the allergen. Anti-TYKW mutant polyclonal IgG antibodies competitively inhibited binding of IgE antibodies to Rhi o 1 up to 70% and suppressed allergen-mediated histamine release by 10-fold. In conclusion, this is a simple yet rational strategy based on epitope mapping data to develop a genetically modified hypoallergenic variant showing protective antibody response for immunotherapeutic applications.

Molecular biology and immunology of fungal allergens

Fungi are non-chlorophyllus microorganisms, which constitutes the main source of outdoor and indoor allergens. The antigens present in the spores and fragments of hyphae induce allergic responses in sensitized patients. The frequently recognized fungi associated with asthma include Alternaria, Cladosporium, Aspergillus, and Penicillium. With the advent of molecular biology techniques a number of fungal genes encoding relevant allergens have been cloned and the expressed allergens purified and characterized. In this review, we have presented the recent developments, where recombinant allergens have been used in the precise diagnosis of fungal allergy. We have also discussed the role played by these allergens and the T- and B-cell epitopes in the immune mechanism in fungal allergy.

[Fungal infections in cystic fibrosis]

Fungal colonization in cystic fibrosis patient is frequent and dominated by Aspergillus fumigatus (A. fumigatus). Mycological analysis on specific media showed other filamentous species Scedosporium, Geosmithia argillacea. Prospective studies are necessary to appreciate prevalence and pathogenicity in this pathology. A. fumigatus causes the most frequently allergic bronchopulmonary aspergillosis (ABPA). Invasive infection is exceptional in this context. An early diagnosis is important to avoid bronchial deterioration but is very difficult despite international consensus. New more specific biological markers are evaluated. Oral corticotherapy is the cornerstone of therapy but adverse effects are more frequent in cystic fibrosis. Antifungal therapy has a corticosteroid-sparing effect. New therapeutic strategies have to be evaluated.

Prophylactic and Therapeutic Potential of Asp f1 Epitopes in Naïve and Sensitized BALB/c Mice

BACKGROUND

The present study examines a hypothesis that short allergen-derived peptides may shift an Aspergillus fumigatus (Afu-) specific TH2 response towards a protective TH1. Five overlapping peptides (P1-P5) derived from Asp f1, a major allergen/antigen of Afu, were evaluated for prophylactic or therapeutic efficacy in BALB/c mice.

METHODS

To evaluate the prophylactic efficacy, peptides were intranasally administered to naïve mice and challenged with Afu-allergens/antigens. For evaluation of therapeutic efficacy, the mice were sensitized with Afu-allergens/antigens followed by intranasal administration of peptides. The groups were compared for the levels of Afu-specific antibodies in sera and splenic cytokines evaluated by ELISA. Eosinophil peroxidase activity was examined in the lung cell suspensions and lung inflammation was assessed by histopathogy.

RESULTS

Peptides P1-, P2- and P3 decreased Afu-specific IgE (84.5~98.9%) and IgG antibodies (45.7~71.6%) in comparison with Afu-sensitized mice prophylactically. P1- and P2-treated ABPA mice showed decline in Afu-specific IgE (76.4~88%) and IgG antibodies (15~54%). Increased IgG2a/IgG1 and IFN-gamma/IL-4 ratios were observed. P1-P3 prophylactically and P1 therapeutically decreased IL-5 levels and eosinophil peroxidase activity. P1 decreased inflammatory cells' infiltration in lung tissue comparable to non-challenged control.

CONCLUSION

Asp f1-derived peptide P1, prophylactically and therapeutically administered to Balb/c mice, is effective in regulating allergic response to allergens/antigens of Afu, and may be explored for immunotherapy of allergic aspergillosis in humans.

T-cell epitopes of aeroallergens

OBJECTIVE

To describe the current knowledge of the T-cell epitopes of common aeroallergens, how they were discovered, and implications for future therapy.

DATA SOURCES

PubMed search of English-language articles without date limits pertaining to T-cell epitopes of aeroallergens included on a standard skin test panel.

STUDY SELECTION

A total of 127 articles were screened based on the results of the PubMed search and cross-indexed as needed. The highest quality and most clinically relevant articles were included for discussion.

RESULTS

Of the 47 allergen extracts included on the standard skin test panel at our instittition, T-cell epitopes have been described for 13. Immunodominant epitopes have been used for peptide immunotherapy trials.

CONCLUSIONS

T-cell epitopes have been characterized for a minority of common aeroallergens. However, knowledge is rapidly expanding and can lay the groundwork for therapies that specifically target T cells.

A DNA aptamer recognizes the Asp f 1 allergen of Aspergillus fumigatus

Allergies are caused by the binding of IgE antibodies onto specific sites on allergens. However, in the assessment of exposure to airborne allergens, current techniques such as whole spore counts fail to account for the presence of these allergenic epitopes that trigger allergic reactions. The objective of the research is to develop a DNA aptamer for the Asp f 1 allergen of the pathogenic fungus Aspergillus fumigatus, using an IgE-binding epitope of the allergen as the target for aptamer selection. Through in vitro SELEX, an aptamer has been produced that binds with nanomolar affinity to the Asp f 1 IgE-epitope. The aptamer is also able to recognize the native Asp f 1 allergen, and does not bind to allergenic proteins from non-target mold species such as Alternaria alternata. Production of this aptamer provides proof-of-principle that allergen measurement methods can be developed to indicate the potent fraction, or allergenicity, of allergens.

The spectrum of fungal allergy

Fungi can be found throughout the world. They may live as saprophytes, parasites or symbionts of animals and plants in indoor as well as outdoor environment. For decades, fungi belonging to the ascomycota as well as to the basidiomycota have been known to cause a broad panel of human disorders. In contrast to pollen, fungal spores and/or mycelial cells may not only cause type I allergy, the most prevalent disease caused by molds, but also a large number of other illnesses, including allergic bronchopulmonary mycoses, allergic sinusitis, hypersensitivity pneumonitis and atopic dermatitis; and, again in contrast to pollen-derived allergies, fungal allergies are frequently linked with allergic asthma. Sensitization to molds has been reported in up to 80% of asthmatic patients. Although research on fungal allergies dates back to the 19th century, major improvements in the diagnosis and therapy of mold allergy have been hampered by the fact that fungal extracts are highly variable in their protein composition due to strain variabilities, batch-to-batch variations, and by the fact that extracts may be prepared from spores and/or mycelial cells. Nonetheless, about 150 individual fungal allergens from approximately 80 mold genera have been identified in the last 20 years. First clinical studies with recombinant mold allergens have demonstrated their potency in clinical diagnosis. This review aims to give an overview of the biology of molds and diseases caused by molds in humans, as well as a detailed summary of the latest results on recombinant fungal allergens.

Fungal ribotoxins: molecular dissection of a family of natural killers

RNase T1 is the best known representative of a large family of ribonucleolytic proteins secreted by fungi, mostly Aspergillus and Penicillium species. Ribotoxins stand out among them by their cytotoxic character. They exert their toxic action by first entering the cells and then cleaving a single phosphodiester bond located within a universally conserved sequence of the large rRNA gene, known as the sarcin-ricin loop. This cleavage leads to inhibition of protein biosynthesis, followed by cellular death by apoptosis. Although no protein receptor has been found for ribotoxins, they preferentially kill cells showing altered membrane permeability, such as those that are infected with virus or transformed. Many steps of the cytotoxic process have been elucidated at the molecular level by means of a variety of methodological approaches and the construction and purification of different mutant versions of these ribotoxins. Ribotoxins have been used for the construction of immunotoxins, because of their cytotoxicity. Besides this activity, Aspf1, a ribotoxin produced by Aspergillus fumigatus, has been shown to be one of the major allergens involved in allergic aspergillosis-related pathologies. Protein engineering and peptide synthesis have been used in order to understand the basis of these pathogenic mechanisms as well as to produce hypoallergenic proteins with potential diagnostic and immunotherapeutic applications.

Comparative genomics of fungal allergens and epitopes shows widespread distribution of closely related allergen and epitope orthologues

BACKGROUND

Allergy is a common debilitating and occasionally life threatening condition. The fungal kingdom contains a number of species that produce a wide range of well defined protein allergens although the vast majority of fungal species have unknown allergenic potential. The recent genome sequencing of a variety of fungi provides the opportunity to assess the occurrence of allergen orthologues across the fungal kingdom. Here we use comparative genomics to survey the occurrence of allergen orthologues in fungi.

RESULTS

A database of 82 allergen sequences was compiled and used to search 22 fungal genomes. Additionally we were able to model allergen structure for representative members of several highly homologous allergen orthologue classes. We found that some allergen orthologue classes that had predicted structural congruence to allergens and allergen epitopes were ubiquitous in all fungi. Other allergen orthologues classes were less well conserved and may not possess conserved allergen epitope orthologues in all fungi. A final group of allergen orthologues, including the major allergens Asp f 1 and Alt a 1, appear to be present in only a limited number of species.

CONCLUSION

These results imply that most fungi may possess proteins that have potential to be allergens or to cross react with allergens. This, together with the observation that important allergens such as Asp f 1 are limited to genera or species, has significant implications for understating fungal sensitization, and interpreting diagnosis and management of fungal allergy.

Production and characterization of a noncytotoxic deletion variant of the Aspergillus fumigatus allergen Aspf1 displaying reduced IgE binding

Aspergillus fumigatus is responsible for many allergic respiratory diseases, the most notable of which - due to its severity - is allergic bronchopulmonary aspergillosis. Aspf1 is a major allergen of this fungus: this 149-amino acid protein belongs to the ribotoxin family, whose best characterized member is alpha-sarcin (EC 3.1.27.10). The proteins of this group are cytotoxic ribonucleases that degrade a unique bond in ribosomal RNA impairing protein biosynthesis. Aspf1 and its deletion mutant Aspf1Delta(7-22) have been produced as recombinant proteins; the deleted region corresponds to an exposed beta-hairpin. The conformation of these two proteins has been studied by CD and fluorescence spectroscopy. Their enzymatic activity and cytotoxicity against human rhabdomyosarcoma cells was also measured and their allergenic properties have been studied by using 58 individual sera of patients sensitized to Aspergillus. Aspf1Delta(7-22) lacks cytotoxicity and shows a remarkably reduced IgE reactivity. From these studies it can be concluded that the deleted beta-hairpin is involved in ribosome recognition and is a significant allergenic region.

Expression and characterization of Asp fI, an immunodominant allergen/antigen of A. fumigatus in insect cell

Asp fI is a major allergen/antigen/cytotoxin of Aspergillus fumigatus and exhibits ribonuclease activity. This allergen plays a role in allergic and invasive Aspergillosis and reported as a major cytotoxin with ribonuclease activity. To express the protein in large quantity and to characterize the multifunctional nature of Asp fI, we have generated recombinant baculovirus by introducing the gene in pFastBac HTa expression vector and expressed in insect cell. The baculovirus expression vector system has been used as a versatile system for the efficient expression of proteins with most eukaryotic posttranslational modification. Recombinant Asp fI was expressed as approximately 1% of the total cellular protein in infected Sf9 insect cells. The protein was purified using Ni2+ affinity column chromatography and the yield of purified protein was approximately 10 mg/l g of total cellular protein. Immunoreactivity of the protein was determined by immunoblot analysis using both poly His monoclonal antibody, IgG and IgE antibodies present in the sera of ABPA patients. The protein was glycosylated as revealed by the glycoprotein staining and was observed to retain both ribonuclease and cytotoxic activities. These results suggest that Asp fI expressed in insect cell was post translationally modified and biologically active that can be used as a diagnostic marker for biochemical studies.

Use of a synthetic peptide epitope of Asp f 1, a major allergen or antigen of Aspergillus fumigatus, for improved immunodiagnosis of allergic bronchopulmonary aspergillosis

Allergic bronchopulmonary aspergillosis (ABPA) is an immunologically complex allergic disorder caused by the fungal pathogen Aspergillus fumigatus. Elevated levels of total immunoglobulin E (IgE), specific IgE, and IgG antibodies in sera are important immunodiagnostic criteria for ABPA. International reference standards or standardized immunodiagnostic assays are not available due to a lack of well-defined diagnostic antigens. The present study was carried out to identify and evaluate the immunodiagnostic relevance of synthetic epitopic peptides of Asp f 1, a major allergen, antigen, or cytotoxin of A. fumigatus. Five overlapping peptides were synthesized from the N terminus of Asp f 1, one of the potential immunodominant regions predicted by algorithmic programs. The 11-amino-acid synthetic peptide (P1) significantly inhibited both IgG binding (89.10% +/- 4.45%) and IgE binding (77.32% +/- 3.38%) of the standardized diagnostic antigen (SDA) (a well-defined pool of diagnostically relevant allergens and antigens of A. fumigatus). With a panel of sera of ABPA patients, allergic patients with skin test negativity to A. fumigatus, and healthy individuals, P1 showed a higher diagnostic efficiency than SDA (specific IgG, 100%; specific IgE, 98.3%). The diagnostic efficiency of P1 could be attributed to the presence of homologous epitopes in various immunodominant allergens or antigens of A. fumigatus. The ability of P1 to induce histamine release from sensitized mast cells and a Th2 type of cytokine profile in peripheral blood mononuclear cells of ABPA patients suggests its potential for use in intradermal testing. P1 could be further explored for development of a standardized, specific, and sensitive immunodiagnostic test for aspergillosis.

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.

IgE binding synthetic peptides of Alt a 1, a major allergen of Alternaria alternata

Alternaria alternata protein, Alt a 1 is a major allergen associated with allergy in atopic patients. Although the molecule binds strongly to IgE antibody from patients, the epitopes involved have not been identified or defined. In the present study, we synthesized overlapping peptides spanning the whole sequence and evaluated their IgE binding with sera from patients with Alternaria-induced allergy. The results identified four IgE binding linear regions. Two of these regions K41-P50 and Y54-K63 showed consistent reactivity with all four patients studied. The specific epitopes involved in the immune response may be of value in the immunodiagnosis and probably also in specific immunotherapy.

Immunobiology of fungal allergens

In recent years, considerable attention has been paid in obtaining purified relevant allergens from fungi associated with allergy. Using molecular biology techniques, a number of mold allergens have been obtained by cloning the genes encoding the allergens. Currently, about 70 fungal allergens have been approved by the International Allergen Nomenclature Committee. In this review, we have presented major allergens from Aspergillus, Penicillium, Cladosporium, and Alternaria and discussed their immunochemical characteristics and their role in the diagnosis of allergy and possible usefulness in understanding the pathogenesis of the disease. The structure-function properties and the potential role of these recombinant allergens in the immunomodulatory therapy also are presented.

Alkaline serine proteinase from Aspergillus fumigatus has synergistic effects on Asp-f-2-induced immune response in mice

BACKGROUND

Exposure to Aspergillus fumigatus allergens results in the sensitization and the development of allergic bronchopulmonary aspergillosis in susceptible individuals. Aspergillus antigen consists of a number of chemically diverse components and their cumulative or synergistic effect may result in disease. When mice were challenged with individual recombinant allergens, there was only reduced inflammation and immunological responses compared to the whole antigen. Various enzymes identified from A. fumigatus have been thought to cause airway damage. In the present study, we evaluated the effect of exposure to Asp f 13, an alkaline serine proteinase, and Asp f 2 in mice.

METHODS

BALB/c mice were challenged intranasally with Asp f 2 and Asp f 13 alone and in combination. The antibody response, pulmonary inflammation, and airway hyperreactivity were studied.

RESULTS

Results demonstrated no major difference in antibody response and airway responses among the different groups. The inflammatory responses in the lungs, however, showed marked differences in the various groups.

CONCLUSION

In spite of the similar immunological responses in the different groups of mice studied, the results demonstrate enhanced inflammation in the lungs of mice exposed to a combination of both allergens. Allergens with proteinase activity have been found to be involved in airway inflammation and remodeling, which may also apply for Aspergillus-induced allergy.

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.

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.

Fusarium solani major allergen peptide IV-1 binds IgE but does not release histamine

BACKGROUND

Fusarium solani (FS) is an important allergen source afflicting 4% of the nasobronchial allergy patients. Fus s I3596*, a 65 kDa major glycoprotein allergen of FS reacts with 95% fungus sensitive patients.

OBJECTIVES

To purify and characterize a potent peptide from Fus s I3596* which may be useful for therapeutic purposes.

METHODS

The 65 kDa protein was sequentially cleaved with trypsin and cyanogen bromide (CNBr). The cleaved products were purified on reverse phase high performance liquid chromatography (rpHPLC) column and functionally characterized by in vitro and in vivo methods for its IgE binding and histamine release.

RESULTS

The protein on cleavage showed 11 peaks (I to XI). Of these, peaks I, III, IV and V were highly allergenic as determined by IgE ELISA. These peaks were further purified and peptide IV-1 was most potent in comparison to other peptides by ELISA-inhibition. This peptide showed IgE binding but could not evoke intradermal response in Fusarium-sensitive patients. Heparinized blood challenged with peptide IV-1 does not release histamine. Preincubation of heparinized blood with peptide IV-1 and challenging with crude extract blocked histamine release in a dose dependent manner.

CONCLUSION

Peptide IV-1 binds to IgE but does not release histamine, demonstrating its potential use in therapy of Fusarium-allergic 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.

Fungal allergens and peptide epitopes

Fungal allergens represent a major cause of atopic disorders. Immunochemical and molecular characterization of fungal allergens has been hampered by the lack of pure proteins and to inherent variation among fungal proteins and in their poor yields. With the advent of molecular biology techniques, a number of allergens have been cloned, sequenced, and expressed from a variety of fungal species. The knowledge of the primary, secondary, and tertiary structures of these allergens, the immunodominant regions of these proteins, and their interaction with T and B-cell epitopes, results in better understanding of the molecular mechanisms of allergy and may provide avenues of immunologic intervention to treat patients. The present review deals with the current understanding of fungal allergen epitopes.

Intravenous injection of major and cryptic peptide epitopes of ribotoxin, Asp f 1 inhibits T cell response induced by crude Aspergillus fumigatus antigens in mice

Aspergillus fumigatus, a ubiquitous fungus, is implicated in the pathogenesis of a number of clinically different allergic diseases in man. Peptide-based immunotherapy may offer an alternative in patient care and management. The purpose of this study was to evaluate the role of T cell epitopes of A. fumigatus ribotoxin, Asp f 1 in inducing tolerance in mice exposed to A. fumigatus antigen. The epitope analysis in BALB/c mice using synthetic peptides of Asp f 1 demonstrated both cryptic and dominant epitopes detected from 42 through 54 and 155 through 167 aa, accordingly. Intravenous injection of these peptides markedly inhibited the response induced by the exposure to crude A. fumigatus extract in mice as evidenced by the in vitro interleukin-2 (IL-2) production and proliferation of T-lymphocytes. Cytokine transcription studies indicate that, when stimulated with the peptides in immunogenic conditions, the major peptide (aa 155-167) specific T cell clone produced only IFN-gamma, but not IL-4. The ability of both dominant and cryptic peptide epitopes of a single molecule to induce tolerance against the immune response to a multi-molecular allergen complex has significant implication for peptide-based immunotherapy.

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.