Nuclear transport factor 2 represents a novel cross-reactive fungal allergen

Allergy to fungi: Advances in the understanding of fungal allergens

Allergic diseases are a major health problem due to their increasing incidence and high prevalence worldwide. Asthma has several aetiologies, and allergy plays an important role in its development in approximately 60% of adults and 80% of children and adolescents. Although the link between aeroallergen sensitization and asthma exacerbations has been long recognized, the investigations of the triggering allergens may be superficial in many asthma cases. The main allergenic sources related to asthma, and other allergic diseases, are pollens, mites, fungi, and animal epithelia. Fungi are considered the third most frequent cause of respiratory pathologies. Asthma caused by several fungi species may have a bad prognosis in some cases due to its severity and difficulty in avoidance methods. Despite the recognised relevance of fungi in respiratory allergies, the knowledge about fungal allergens seems to be scarce, with few descriptions of new allergens, compared to other allergenic sources. The study of major, minor, and cross-reactive fungal allergens, and their relevance in the allergic disease, might be crucial, not only to accurately diagnose these allergies, but also to predict exacerbations and responses to therapies, as well as for the development of personalized treatment plans in a fast-changing climate scenario.

Going over Fungal Allergy: Alternaria alternata and Its Allergens

Fungal allergy is the third most frequent cause of respiratory pathologies and the most related to a poor prognosis of asthma. The genera Alternaria and Cladosporium are the most frequently associated with allergic respiratory diseases, with Alternaria being the one with the highest prevalence of sensitization. Alternaria alternata is an outdoor fungus whose spores disseminate in warm and dry air, reaching peak levels in temperate summers. Alternaria can also be found in damp and insufficiently ventilated houses, causing what is known as sick building syndrome. Thus, exposure to fungal allergens can occur outdoors and indoors. However, not only spores but also fungal fragments contain detectable amounts of allergens and may function as aeroallergenic sources. Allergenic extracts of Alternaria hyphae and spores are still in use for the diagnosis and treatment of allergic diseases but are variable and insufficiently standardised, as they are often a random mixture of allergenic ingredients and casual impurities. Thus, diagnosis of fungal allergy has been difficult, and knowledge about new fungal allergens is stuck. The number of allergens described in Fungi remains almost constant while new allergens are being found in the Plantae and Animalia kingdoms. Given Alt a 1 is not the unique Alternaria allergen eliciting allergy symptoms, component-resolved diagnosis strategies should be applied to diagnose fungal allergy. To date, twelve A. alternata allergens are accepted in the WHO/IUIS Allergen Nomenclature Subcommittee, many of them are enzymes: Alt a 4 (disulfide isomerase), Alt a 6 (enolase), Alt a 8 (mannitol de-hydrogenase), Alt a 10 (aldehyde dehydrogenase), Alt a 13 (glutathione-S-transferase) and Alt a MnSOD (Mn superoxide dismutase), and others have structural and regulatory functions such as Alt a 5 and Alt a 12, Alt a 3, Alt a 7. The function of Alt a 1 and Alt a 9 remains unknown. Other four allergens are included in other medical databases (e.g., Allergome): Alt a NTF2, Alt a TCTP, and Alt a 70 kDa. Despite Alt a 1 being the A. alternata major allergen, other allergens, such as enolase, Alt a 6 or MnSOD, Alt a 14 have been suggested to be included in the diagnosis panel of fungal allergy.

Alternaria as an Inducer of Allergic Sensitization

Alternaria alternata is a saprophytic mold whose spores are disseminated in warm dry air, the typical weather of the Mediterranean climate region (from 30° to 45°), with a peak during the late summer and early autumn. Alternaria spores are known to be biological contaminants and a potent source of aeroallergens. One consequence of human exposure to Alternaria is an increased risk of developing asthma, with Alt a 1 as its main elicitor and a marker of primary sensitization. Although the action mechanism needs further investigation, a key role of the epithelium in cytokine production, TLR-activated alveolar macrophages and innate lymphoid cells in the adaptive response was demonstrated. Furthermore, sensitization to A. alternata seems to be a trigger for the development of co-sensitization to other allergen sources and may act as an exacerbator of symptoms and an elicitor of food allergies. The prevalence of A. alternata allergy is increasing and has led to expanding research on the role of this fungal species in the induction of IgE-mediated respiratory diseases. Indeed, recent research has allowed new perspectives to be considered in the assessment of exposure and diagnosis of fungi-induced allergies, although more studies are needed for the standardization of immunotherapy formulations.

Species diversity, novel interactions and absence of well-supported host-guided phylogenetic groupings of Neotropical Alternaria isolates causing foliar lesions in Solanaceae

AIM

To report the characterization of 120 Alternaria isolates inducing early blight-like foliar lesions in nine species of five Solanaceae genera collected across all macrogeographical Brazilian regions.

MATERIAL AND RESULTS

Phylogenetic relationships were assessed via analyses of the Alternaria alternata allergenic protein-coding, glyceraldehyde-3-phosphate dehydrogenase and the calmodulin gene sequences. Most of the tomato isolates were placed into the Alternaria linariae cluster, whereas most of the potato isolates were grouped with Alternaria grandis. Novel host-pathogen interactions were also reported. Seventeen isolates were selected for morphometrical characterization, and a subsample of 13 isolates was employed in pathogenicity assays on tomato, potato, eggplant, scarlet eggplant, Capsicum annuum, Datura stramonium, Physalis angulata and Nicotiana tabacum. Eleven isolates were able to induce foliar lesions in tomatoes but none in C. annuum. Potato was susceptible to a subgroup of isolates but displayed a subset of isolate-specific interactions. Morphological traits were in overall agreement with molecular and host range data.

CONCLUSION

Alternaria linariae and A. grandis were confirmed as the major causal agents of tomato and potato early blight, respectively. However other Alternaria species are also involved with early blight in solanaceous hosts in Brazil.

SIGNIFICANCE AND IMPACT OF THE STUDY

The diversity and host-specific patterns of the Alternaria isolates from Solanaceae may have practical implications in establishing effective early blight genetic resistance and cultural management strategies especially for tomato and potato crops.

Innate Immunity Induced by the Major Allergen Alt a 1 From the Fungus Alternaria Is Dependent Upon Toll-Like Receptors 2/4 in Human Lung Epithelial Cells

Allergens are molecules that elicit a hypersensitive inflammatory response in sensitized individuals and are derived from a variety of sources. Alt a 1 is the most clinically important secreted allergen of the ubiquitous fungus, Alternaria. It has been shown to be a major allergen causing IgE-mediated allergic response in the vast majority of Alternaria-sensitized individuals. However, no studies have been conducted in regards to the innate immune eliciting activities of this clinically relevant protein. In this study, recombinant Alt a 1 was produced, purified, labeled, and incubated with BEAS-2B, NHBE, and DHBE human lung epithelial cells. Alt a 1 elicited strong induction of IL-8, MCP-1, and Gro-a/b/g. Using gene-specific siRNAs, blocking antibodies, and chemical inhibitors such as LPS-RS, it was determined that Alt a 1-induced immune responses were dependent upon toll-like receptors (TLRs) 2 and 4, and the adaptor proteins MYD88 and TIRAP. Studies utilizing human embryonic kidney cells engineered to express single receptors on the cell surface such as TLRs, further confirmed that Alt a 1-induced innate immunity is dependent upon TLR4 and to a lesser extent TLR2.

Alternaria alternata allergens: Markers of exposure, phylogeny and risk of fungi-induced respiratory allergy

Alternaria alternata spores are considered a well-known biological contaminant and a very common potent aeroallergen source that is found in environmental samples. The most intense exposure to A. alternata allergens is likely to occur outdoors; however, Alternaria and other allergenic fungi can colonize in indoor environments and thereby increase the fungal aeroallergen exposure levels. A consequence of human exposure to fungal aeroallergens, sensitization to A. alternata, has been unequivocally associated with increased asthma severity. Among allergenic proteins described in this fungal specie, the major allergen, Alt a 1, has been reported as the main elicitor of airborne allergies in patients affected by a mold allergy and considered a marker of primary sensitization to A. alternata. Moreover, A. alternata sensitization seems to be a triggering factor in the development of poly-sensitization, most likely because of the capability of A. alternata to produce, in addition to Alt a 1, a broad and complex array of cross-reactive allergens that present homologs in several other allergenic sources. The study and understanding of A. alternata allergen information may be the key to explaining why sensitization to A. alternata is a risk factor for asthma and also why the severity of asthma is associated to this mold. Compared to other common environmental allergenic sources, such as pollens and dust mites, fungi are reported to be neglected and underestimated. The rise of the A. alternata allergy has enabled more research into the role of this fungal specie and its allergenic components in the induction of IgE-mediated respiratory diseases. Indeed, recent research on the identification and characterization of A. alternata allergens has allowed for the consideration of new perspectives in the categorization of allergenic molds, assessment of exposure and diagnosis of fungi-induced allergies.

Alternaria alternata and its allergens: a comprehensive review

Alternaria alternata is mainly an outdoor fungus whose spores disseminate in warm, dry air, so in temperate climates, their count peaks in the summers. Alternaria may also be found in damp, insufficiently ventilated houses, where its allergenic properties cocreate the sick building syndrome. Mold-induced respiratory allergies and research on Alternaria both have a lengthy history: the first was described as early as 1698 and the second dates back to 1817. However, the two were only linked in 1930 when Alternaria spores were found to cause allergic asthma. The allergenic extracts from Alternaria hyphae and spores still remain in use but are variable and insufficiently standardized as they are often a random mixture of allergenic ingredients and coincidental impurities. In contrast, contemporary biochemistry and molecular biology make it possible to obtain pure allergen molecules. To date, 16 allergens of A. alternata have been isolated, many of which are enzymes: Alt a 4 (disulfide isomerase), Alt a 6 (enolase), Alt a 8 (mannitol dehydrogenase), Alt a 10 (alcohol dehydrogenase), Alt a 13 (glutathione-S-transferase), and Alt a MnSOD (Mn superoxide dismutase). Others have structural and regulatory functions: Alt a 5 and Alt a 12 comprise the structure of large ribosomal subunits and mediate translation, Alt a 3 is a molecular chaperone, Alt a 7 regulates transcription, Alt a NTF2 facilitates protein import into the nucleus, and Alt a TCTP acts like a cytokine. The function of four allergenic proteins, Alt a 1, Alt a 2, Alt a 9, and Alt a 70 kDa, remains unknown.

Fungi: the neglected allergenic sources

Allergic diseases are considered the epidemics of the twentieth century estimated to affect more than 30% of the population in industrialized countries with a still increasing incidence. During the past two decades, the application of molecular biology allowed cloning, production and characterization of hundreds of recombinant allergens. In turn, knowledge about molecular, chemical and biologically relevant allergens contributed to increase our understanding of the mechanisms underlying IgE-mediated type I hypersensitivity reactions. It has been largely demonstrated that fungi are potent sources of allergenic molecules covering a vast variety of molecular structures including enzymes, toxins, cell wall components and phylogenetically highly conserved cross-reactive proteins. Despite the large knowledge accumulated and the compelling evidence for an involvement of fungal allergens in the pathophysiology of allergic diseases, fungi as a prominent source of allergens are still largely neglected in basic research as well as in clinical practice. This review aims to highlight the impact of fungal allergens with focus on asthma and atopic dermatitis.

Alternaria alternata TCTP, a novel cross-reactive ascomycete allergen

Defining more comprehensively the allergen repertoire of the ascomycete Alternaria alternata is undoubtedly of immense medical significance since this mold represents one of the most important, worldwide occurring fungal species responsible for IgE-mediated hypersensitivity reactions ranging from rhinitis and ocular symptoms to severe involvement of the lower respiratory tract including asthma with its life-threatening complications. Performing a hybridization screening of an excised A. alternata cDNA library with a radioactively labeled Cladosporium herbarum TCTP probe, we were able to identify, clone and purify the respective A. alternata homologue of TCTP which again represents a multifunctional protein that has been evolutionarily conserved from unicellular eukaryotes like yeasts to humans and appears, summarizing current literature, to be involved in housekeeping processes such as cell growth as well as cell-cycle progression, the protection of cells against various stress conditions including for instance apoptosis, and in higher organisms even in the allergic response. In this context, our present study characterizes recombinant A. alternata TCTP as a novel minor allergen candidate that displays a prevalence of IgE reactivity of approximately 4% and interestingly shares common, cross-reactive IgE epitopes with its C. herbarum and human counterparts as determined via Western blotting and in vitro inhibition approaches.

Vacuolar serine protease is a major allergen of Cladosporium cladosporioides

BACKGROUND

Cladosporium is an important allergenic fungus worldwide. We report here a major allergen of C. cladosporioides.

METHODS

Major C. cladosporioides allergens were characterized by immunoblotting, N-terminal amino acid sequencing, protein purification and cDNA cloning.

RESULTS

Seventy-four sera (38%) from 197 bronchial asthmatic patients demonstrated IgE binding against C. cladosporioides extracts. Among these 74 sera, 41 (55%) and 38 (51%) showed IgE binding against a 36- and a 20-kDa protein of C. cladosporioides, respectively. Both IgE-reacting components reacted with FUM20, a monoclonal antibody against fungal serine proteases. N-terminal amino acid sequencing results suggest that they are vacuolar serine proteases, and the 20-kDa component is possibly a degraded product of the 36-kDa allergen. A corresponding 5'-truncated 1,425-bp cDNA fragment was isolated. The mature protein after N-terminal processing starts with an N-terminal serine that is the ninth residue encoded by the 5'-truncated cDNA. The protein sequence deduced shares 69-72% sequence identity with Penicillium vacuolar serine proteases and was designated as Cla c 9. The purified 36-kDa Cla c 9 allergen showed proteolytic activity with peptide Z-Ala-Ala-Leu-pNA as substrate. IgE cross-reactivity was detected between the purified Cla c 9 and serine protease allergens from Aspergillusfumigatus and Penicillium chrysogenum.

CONCLUSION

We identified a vacuolar serine protease as a major allergen of C. cladosporioides (Cla c 9) and a major pan-allergen of prevalent airborne fungi. IgE cross-reactivity among these highly conserved serine protease pan-fungal allergens was also detectable.

Molecular and immunological characterization of cytochrome c: a potential cross-reactive allergen in fungi and grasses

BACKGROUND

Recombinant allergens are required for component-resolved diagnosis/therapy of allergic disorders. The study was aimed to express and characterize an allergenic protein from Curvularia lunata and study its cross-reactivity.

METHODS

A clone encoding a 12-kDa protein screened from the cDNA library of C. lunata was sequenced and expressed in pET22b+ vector. The purified protein was characterized by biophysical and immunological methods.

RESULTS

The sequence of gene encoding a 12-kDa protein showed homology to cytochrome c. It was expressed in Escherichia coli yielding 0.5 mg protein/l culture and designated as Cur l 3. The absorption and circular dichroism spectrum of Cur l 3 were similar to horse cytochrome c and the protein reacted with cytochrome c antibody. ELISA with different fungal-positive patients' sera showed > or = 3 times specific IgE to Cur l 3 compared with healthy controls. Mice anti-Cur l 3 reacted with tropical and temperate grass extracts. Protein also reacted with grass-positive patients' sera. In vitro stimulation of peripheral blood mononuclear cells from C. lunata, fungi or grass-positive patients with it released significant levels of Th2 cytokines. In vivo testing of this protein in allergic patients showed marked positive skin reactivity in 60% fungal and 43% grass-positive cases. Cross inhibition assays (EC(50)) demonstrated allergenic cross-reactivity of Cur l 3 with fungi and grasses.

CONCLUSIONS

Cytochrome c, a major allergen from C. lunata was cloned, sequenced and expressed. It was identified as a cross-reactive allergen among fungi and grasses and has potential for clinical application.

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.

Alternaria alternata NADP-dependent mannitol dehydrogenase is an important fungal allergen

BACKGROUND

Alternaria alternata is one of the most important allergenic fungi worldwide. Mannitol dehydrogenase (MtDH) has previously been shown to be a major allergen of Cladosporium herbarum and cross-reactivity has been demonstrated for several fungal allergens.

OBJECTIVE

The present study's objective was to clone the MtDH from an A. alternata cDNA library, express and purify the recombinant non-fusion protein and test its IgE-binding properties. Methods A cDNA library prepared from A. alternata hyphae and spores was screened for mannitol dehydrogenase by DNA hybridization with the radioactively labelled C. herbarum homologue as a probe. The resulting clone was sequenced and heterologously expressed in Escherichia coli as a recombinant non-fusion protein, which was purified to homogeneity and analysed for its IgE-binding capacity.

RESULTS

The coding sequence of the full-length cDNA clone comprises 798 bp encoding a protein with a molecular mass of 28.6 kDa and a predicted pI of 5.88. Protein sequence analysis revealed an identity of 75% and a homology of 86% between the MtDHs of A. alternata and C. herbarum. The functional mannitol dehydrogenase was expressed in the E. coli strain BL21(DE3) transformed with the vector pMW172 and purified to homogeneity. The enzyme catalyses the NADPH-dependent conversion of d-fructose to d-mannitol. In IgE-ELISA and immunoblots, MtDH is recognized by 41% of A. alternata-allergic patients. In vivo immunoreactivity of the recombinant MtDH was verified by skin prick testing. Finally, inhibition-ELISA experiments confirmed cross-reactivity between the MtDHs of A. alternata and C. herbarum.

CONCLUSION

Mannitol dehydrogenase (Alt a 8) represents an important new allergen of the ascomycete A. alternata that might be suitable for improving diagnostic and therapeutic procedures.

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.

Description of a novel panallergen of cross-reactivity between moulds and foods

The present investigation is undertaken to demonstrate a novel cross-reactivity between aeroallergens (moulds fungi imperfecti) and allergens from foods (spinach and mushroom Agaricus bisporus). We have performed a dual study in vivo and in vitro, in a population of atopic patients. Data from in vivo tests performed with spinach and mushroom have been statistically analysed. To the in vitro assays, mushroom and spinach extracts have been obtained, and sera from moulds allergic patients analysed by means of IgE-immunoblott assays. Inhibition experiments have been also performed to study a possible relation between proteins. Statistical analysis of data showed a relation between allergenicity to moulds (Alternaria alternata, Cladosporium herbarum and/or Aspergillus fumigatus), and positive skin prick tests with mushroom and/or spinach. The immunoblotts performed showed that seven moulds allergic patients had a strong recognition of a protein with a molecular weight of about 30 kD present both in spinach and mushroom extracts, and by means of inhibition assays we could determine that these two proteins were related. This study demonstrates the existence of a new allergen responsible for cross reactivity between moulds and two frequently consumed foods, mushroom and spinach. We conclude that a novel cross-reactive allergen between aeroallergens and foods has been identified.

Cladosporium herbarum and Pityrosporum ovale Allergen Extracts Share Cross-Reacting Glycoproteins

BACKGROUND

Patients sensitized to airborne fungi such as Alternaria alternata and Cladosporium herbarum often also show positive skin prick test results and specific serum IgE antibodies to a yeast, Pityrosporum ovale. We examined whether part of the IgE binding to these fungi is explained by cross-reacting mould and yeast allergens.

METHODS

Serum samples from 36 patients with positive skin prick test to A. alternata or C. herbarum were analyzed for IgE antibodies to fungal extracts by ELISA and immunoblot analysis. Cross-reactivity between mould and yeast extracts was studied by ELISA and immunoblot inhibition assays. In further analysis, the mannan-containing glycoproteins were removed from the yeast extract by concanavalin A-Sepharose chromatography, and the IgE binding properties of the extracts were compared.

RESULTS

Serum IgE reactivity to P. ovale was found in 40% of the mould-sensitized patients. The IgE antibody binding to A. alternata and C. herbarum moulds was partially inhibited by the yeast P. ovale in ELISA and immunoblot inhibition assays. When the glycoproteins were removed from the extract, cross-reactivity was markedly reduced.

CONCLUSION

Part of the IgE binding to mould and yeast allergen extracts is due to cross-reacting glycoproteins. False-positive IgE and skin prick test results should be taken into account in the diagnosis of mould allergy.

NADP-dependent mannitol dehydrogenase, a major allergen of Cladosporium herbarum

Cladosporium herbarum is an important allergenic fungal species that has been reported to cause allergic diseases in nearly all climatic zones. 5-30% of the allergic population displays IgE antibodies against molds. Sensitization to Cladosporium has often been associated with severe asthma and less frequently with chronic urticaria and atopic eczema. However, no dominant major allergen of this species has been found so far. We present cloning, production, and characterization of NADP-dependent mannitol dehydrogenase of C. herbarum (Cla h 8) and show that this protein is a major allergen that is recognized by IgE antibodies of approximately 57% of all Cladosporium allergic patients. This is the highest percentage of patients reacting with any Cladosporium allergen characterized so far. Cla h 8 was purified to homogeneity by standard chromatographic methods, and both N-terminal and internal amino acid sequences of protein fragments were determined. Enzymatic analysis of the purified natural protein revealed that this allergen represents a NADP-dependent mannitol dehydrogenase that interconverts mannitol and d-fructose. It is a soluble, non-glycosylated cytoplasmic protein. Two-dimensional protein analysis indicated that mannitol dehydrogenase is present as a single isoform. The cDNA encoding Cla h 8 was cloned from a lambda-ZAP library constructed from hyphae and spores. The recombinant non-fusion protein was expressed in Escherichia coli and purified to homogeneity. Its immunological and biochemical identity with the natural protein was shown by enzyme activity tests, CD spectroscopy, IgE immunoblots with sera of patients, and by skin prick testing of Cladosporium allergic patients. This protein therefore is a new major allergen of C. herbarum.

Wheat and maize thioredoxins: a novel cross-reactive cereal allergen family related to baker's asthma

BACKGROUND

Baker's asthma is a serious problem for a significant proportion of workers in bakeries, confectionaries, and the food industry. Although several wheat allergens related to baker's asthma have been described, standardized reagents for a reliable diagnosis are not yet available.

OBJECTIVE

To clone novel wheat allergens related to baker's asthma and investigate the cross-reactive potential of their maize and human homologues.

METHODS

A wheat cDNA phage display library was screened with sera from bakers with occupational asthma for IgE-binding structures. Homologous sequences from maize and human thioredoxins were amplified from corresponding cDNA libraries.

RESULTS

Within the enriched wheat cDNA repertoire we identified, among others, the sequence encoding wheat thioredoxin-hB (Triticum aestivum allergen 25 [Tri a 25]). The recombinant protein displayed enzymatic activity, and we observed a sensitization rate of 47% among bakers with occupational asthma and of 35% among patients with grass pollen allergy, but without a clinical history of cereal allergy. Furthermore, the previously characterized maize thioredoxin-h1 (Zea mays allergen 25 [Zea m 25]), sharing 74% identity with Tri a 25, exhibited distinct IgE cross-reactivity with its wheat homologue. Two bakers also showed sensitization to human thioredoxin, which shares 29% identity with Tri a 25. In a comparative study, we included recombinant alpha-amylase inhibitor 0.19, showing a sensitization rate of 65% in individuals with baker's asthma.

CONCLUSION

Thioredoxins represent a novel family of cross-reactive allergens that might contribute to the symptoms of baker's asthma and might in addition be related to grass pollen allergy, as indicated by the reactivity of grass pollen allergic patients to cereal thioredoxins.

CLINICAL IMPLICATIONS

The recombinant cereal thioredoxins will, together with the already reported wheat allergens, contribute to a more reliable diagnosis of baker's asthma and, perhaps, become a tool for the development of component-resolved immunotherapy.

Structural aspects and clinical relevance of Aspergillus fumigatus antigens/allergens

Robotics-based high throughput screening of Aspergillus fumigatus cDNA libraries displayed on phage surfaces revealed at last 81 different structures able to bind IgE from serum of patients sensitized to this fungus. Among these, species-specific as well as phylogenetically highly conserved structures and such with unknown function have been detected. A subset of cDNAs have been used to produce and characterize the corresponding recombinant allergens which have proven to be useful diagnostic reagents allowing specific detection of A. fumigatus sensitization and differential diagnosis of allergic bronchopulmonary aspergillosis. Phylogenetically highly conserved structures like manganese-dependent superoxide dismutase, P2 acidic ribosomal protein, cyclophilins and thioredoxins induce, beyond sensitization, IgE antibodies able to cross-react with the corresponding homologous self antigens. These reactions, likely to contribute to the exacerbation and perpetuation of allergic bronchopulmonary aspergillosis, can be traced back to shared conformational B-cell epitopes build up from conserved amino acid residues scattered over the surface of the molecules as shown by detailed analyses of the crystal structures.

Asp f6, an Aspergillus allergen specifically recognized by IgE from patients with allergic bronchopulmonary aspergillosis, is differentially expressed during germination

BACKGROUND

Aspergillus fumigatus is a pathogenic mould causing allergic and invasive respiratory diseases. Allergic bronchopulmonary Aspergillosis (ABPA) is a severe pulmonary complication resulting from hypersensitivity to A. fumigatus proteins. Aspergillus allergen Asp f6 is recognized by IgE from ABPA patients, but not from sensitized individuals, a fact that can be used to differentiate between these two groups of allergic patients.

METHODS

Proteins from hyphae, resting and germinating conidia of A. fumigatus were compared by SDS-PAGE. Protein identification was performed using MALDI-TOF mass spectrometry. Recombinant A. fumigatus allergens were used to isolate specific monoclonal antibodies (mab) from a hybridoma bank generated against Aspergillus proteins.

RESULTS

A hyphae-specific 23 kDa A. fumigatus protein was identified as the allergen Asp f6/manganese-dependent superoxide dismutase (MnSOD). Differential expression of MnSOD was confirmed by immunoblot using a specific mab. In contrast, Asp f8 another intracellular, but not ABPA-specific allergen, was detected in hyphae and conidia.

CONCLUSIONS

Aspergillus fumigatus is able to colonize its environment by the formation of hyphae. Hyphae are found in the lung of ABPA patients, but not in patients suffering from atopic asthma. Our finding that Asp f6 is specifically expressed in hyphae might explain why an IgE response to Asp f6 is specific for ABPA patients.

Alt a 1 allergen homologs from Alternaria and related taxa: analysis of phylogenetic content and secondary structure

A gene for the Alternaria major allergen, Alt a 1, was amplified from 52 species of Alternaria and related genera, and sequence information was used for phylogenetic study. Alt a 1 gene sequences evolved 3.8 times faster and contained 3.5 times more parsimony-informative sites than glyceraldehyde-3-phosphate dehydrogenase (gpd) sequences. Analyses of Alt a 1 gene and gpd exon sequences strongly supported grouping of Alternaria spp. and related taxa into several species-groups described in previous studies, especially the infectoria, alternata, porri, brassicicola, and radicina species-groups and the Embellisia group. The sonchi species-group was newly suggested in this study. Monophyly of the Nimbya group was moderately supported, and monophyly of the Ulocladium group was weakly supported. Relationships among species-groups and among closely related species of the same species-group were not fully resolved. However, higher resolution could be obtained using Alt a 1 sequences or a combined dataset than using gpd sequences alone. Despite high levels of variation in amino acid sequences, results of in silico prediction of protein secondary structure for Alt a 1 demonstrated a high degree of structural similarity for most of the species suggesting a conservation of function.

Allergens of the entomopathogenic fungus Beauveria bassiana

Background

Beauveria bassiana is an important entomopathogenic fungus currently under development as a bio-control agent for a variety of insect pests. Although reported to be non-toxic to vertebrates, the potential allergenicity of Beauveria species has not been widely studied.

Methods

IgE-reactivity studies were performed using sera from patients displaying mould hypersensitivity by immunoblot and immunoblot inhibition. Skin reactivity to B. bassiana extracts was measured using intradermal skin testing.

Results

Immunoblots of fungal extracts with pooled as well as individual sera showed a distribution of IgE reactive proteins present in B. bassiana crude extracts. Proteinase K digestion of extracts resulted in loss of IgE reactive epitopes, whereas EndoH and PNGaseF (glycosidase) treatments resulted in minor changes in IgE reactive banding patterns as determined by Western blots. Immunoblot inhibitions experiments showed complete loss of IgE-binding using self protein, and partial inhibition using extracts from common allergenic fungi including; Alternaria alternata, Aspergillus fumigatus, Cladosporium herbarum, Candida albicans, Epicoccum purpurascens, and Penicillium notatum. Several proteins including a strongly reactive band with an approximate molecular mass of 35 kDa was uninhibited by any of the tested extracts, and may represent B. bassiana specific allergens. Intradermal skin testing confirmed the in vitro results, demonstrating allergenic reactions in a number of individuals, including those who have had occupational exposure to B. bassiana.

Conclusions

Beauveria bassiana possesses numerous IgE reactive proteins, some of which are cross-reactive among allergens from other fungi. A strongly reactive potential B. bassiana specific allergen (35 kDa) was identified. Intradermal skin testing confirmed the allergenic potential of B. bassiana.