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

Can Physicochemical Properties Alter the Potency of Aeroallergens? Part 2 - Impact of Physicochemical Properties

PURPOSE OF REVIEW

A holistic perspective on how physicochemical properties modulate the allergenicity of proteins has recently been performed for food allergens, launching the challenge of a similar analysis for aeroallergens. After a first review on aeroallergen classification into protein families (Part 1), this second part (Part 2) will exploit the impact of physicochemical properties (abundance/biological function, protein structure/presence of post-translational modifications, ligand/cofactor/lipid-binding) on inhalant protein allergenicity.

RECENT FINDINGS

The abundance linked to biological function is correlated with increased allergenic risk for most protein families, while the loss of structural integrity with consequent destruction of conformational epitopes is well linked with decreased allergenicity. Ligand-binding effect totally depends on the ligand type being highly variable among aeroallergens. Knowledge about the physicochemical properties of aeroallergens is still scarce, which highlights the need for research using integrated approaches (in silico and experimental) to generate and analyze new data on known/new aeroallergens.

Airborne indoor allergen serine proteases and their contribution to sensitisation and activation of innate immunity in allergic airway disease

Common airborne allergens (pollen, animal dander and those from fungi and insects) are the main triggers of type I allergic disorder in the respiratory system and are associated with allergic rhinitis, allergic asthma, as well as immunoglobulin E (IgE)-mediated allergic bronchopulmonary aspergillosis. These allergens promote IgE crosslinking, vasodilation, infiltration of inflammatory cells, mucosal barrier dysfunction, extracellular matrix deposition and smooth muscle spasm, which collectively cause remodelling of the airways. Fungus and insect (house dust mite and cockroaches) indoor allergens are particularly rich in proteases. Indeed, more than 40 different types of aeroallergen proteases, which have both IgE-neutralising and tissue-destructive activities, have been documented in the Allergen Nomenclature database. Of all the inhaled protease allergens, 85% are classed as serine protease activities and include trypsin-like, chymotrypsin-like and collagenolytic serine proteases. In this article, we review and compare the allergenicity and proteolytic effect of allergen serine proteases as listed in the Allergen Nomenclature and MEROPS databases and highlight their contribution to allergic sensitisation, disruption of the epithelial barrier and activation of innate immunity in allergic airways disease. The utility of small-molecule inhibitors of allergen serine proteases as a potential treatment strategy for allergic airways disease will also be discussed.

Outdoor airborne allergens: Characterization, behavior and monitoring in Europe

Aeroallergens or inhalant allergens, are proteins dispersed through the air and have the potential to induce allergic conditions such as rhinitis, conjunctivitis, and asthma. Outdoor aeroallergens are found predominantly in pollen grains and fungal spores, which are allergen carriers. Aeroallergens from pollen and fungi have seasonal emission patterns that correlate with plant pollination and fungal sporulation and are strongly associated with atmospheric weather conditions. They are released when allergen carriers come in contact with the respiratory system, e.g. the nasal mucosa. In addition, due to the rupture of allergen carriers, airborne allergen molecules may be released directly into the air in the form of micronic and submicronic particles (cytoplasmic debris, cell wall fragments, droplets etc.) or adhered onto other airborne particulate matter. Therefore, aeroallergen detection strategies must consider, in addition to the allergen carriers, the allergen molecules themselves. This review article aims to present the current knowledge on inhalant allergens in the outdoor environment, their structure, localization, and factors affecting their production, transformation, release or degradation. In addition, methods for collecting and quantifying aeroallergens are listed and thoroughly discussed. Finally, the knowledge gaps, challenges and implications associated with aeroallergen analysis are described.

Respiratory Epithelial Cells: More Than Just a Physical Barrier to Fungal Infections

The respiratory epithelium is highly complex, and its composition varies along the conducting airways and alveoli. In addition to their primary function in maintaining the respiratory barrier and lung homeostasis for gas exchange, epithelial cells interact with inhaled pathogens, which can manipulate cell signaling pathways, promoting adhesion to these cells or hosting tissue invasion. Moreover, pathogens (or their products) can induce the secretion of chemokines and cytokines by epithelial cells, and in this way, these host cells communicate with the immune system, modulating host defenses and inflammatory outcomes. This review will focus on the response of respiratory epithelial cells to two human fungal pathogens that cause systemic mycoses: Aspergillus and Paracoccidioides. Some of the host epithelial cell receptors and signaling pathways, in addition to fungal adhesins or other molecules that are responsible for fungal adhesion, invasion, or induction of cytokine secretion will be addressed in this review.

Identifying novel allergens from a common indoor mould Aspergillus ochraceus

The increasing burden of respiratory disease is a rising concern in India. Although chronic colonisation is primarily caused by pathogenic fungi, the common environmental fungi also play an important role in developing sensitisation. This study aims to examine the allergenic potency of mycelial proteins of a common indoor fungus Aspergillus ochraceus to a selected atopic patient cohort as well as to identify the novel IgE-binding proteins through an immunoproteomic approach. 1-D and 2-D IgE specific western blot detected the IgE reactive proteins which were identified through MALDI-TOF/TOF and manual de novo peptide sequencing. The results revealed the detection of 10 cross-reactive IgE-binding proteins. Cluster analysis of 1-D immunoblot with individual patient sera identified NADP(+)-dependent glycerol dehydrogenase (GldB) homologous protein as a major allergen, which was further purified and the allergenicity was assessed. Other IgE-binding proteins showed homology with allergens like short-chain dehydrogenase, NAD-dependent mannitol dehydrogenase, and subtilisin-like serine protease. GldB purified under native conditions showed IgE reactivity amongst the selected patient cohort, which is reported for the first time in this study. The identified IgE-binding proteins can act as candidate molecules for developing hypoallergenic vaccines for designing specific immunotherapeutic techniques to fungal allergy. THE SIGNIFICANCE OF THE STUDY: Exposure to environmental fungal allergens is directly associated with promoting allergic response as well as complicating existing respiratory disease, leading to poor respiratory health. Amongst others, Aspergillus spp. contributes to the majority of the fungal derived atopic diseases. Aspergillus ochraceus is a common indoor mould in India, however, its allergenic potency was not explored till date. In this study, we establish A. ochraceus responsible to cause an allergic response to susceptible individuals and identified 10 IgE-binding proteins using an immunoproteomics approach for the first time. A. ochraceus being unsequenced, a homology-driven proteomics approach was used to identify the IgE-binding proteins which can be extended to identify proteins from other unsequenced species. The information on the IgE-binding proteins could be used as a step towards characterising them by molecular and structural methods to investigate the molecular basis of allergenicity. This will also help to enrich the existing database of allergenic proteins and pave a way towards developing therapeutic avenues.

Allergenicity assessment of fungal species using immunoclinical and proteomic techniques: a study on Fusarium lateritium

Airborne fungal spores are extensively reported as the elicitors of respiratory allergies in human. Fusarium lateritium is one such fungal species reported for eliciting significant skin prick results from India. The present study aims to analyze the allergenic potential of F. lateritium followed by the identification of allergens. The total protein of F. lateritium was subjected to 1dimensional (1D) and 2D gel electrophoresis followed by corresponding IgE-specific immunoblots. We found 8 immunoreactive bands/zones in (1D) immunoblot using 11 F. lateritium-sensitised patient sera. In 1D immunoblot, a 34 kDa band was detected in >80% of the patients and hence considered as a potential allergen of F. lateritium. Corresponding 34 kDa spot in 2D-immunoblot was analyzed by mass spectrometric analysis and identified as Glyceraldehyde 3-phosphate dehydrogenase. The identified F. lateritium allergen holds the potential to instigate vaccine development for immunotherapy of F. lateritium sensitized patients.

Pseudogymnoascus destructans transcriptome changes during white-nose syndrome infections

White nose syndrome (WNS) is caused by the psychrophilic fungus Pseudogymnoascus destructans that can grow in the environment saprotrophically or parasitically by infecting hibernating bats. Infections are pathological in many species of North American bats, disrupting hibernation and causing mortality. To determine what fungal pathways are involved in infection of living tissue, we examined fungal gene expression using RNA-Seq. We compared P. destructans gene expression when grown in culture to that during infection of a North American bat species, Myotis lucifugus, that shows high WNS mortality. Cultured P. destructans was grown at 10 to 14 C and P. destructans growing in vivo was presumably exposed to temperatures ranging from 4 to 8 C during torpor and up to 37 C during periodic arousals. We found that when P. destructans is causing WNS, the most significant differentially expressed genes were involved in heat shock responses, cell wall remodeling, and micronutrient acquisition. These results indicate that this fungal pathogen responds to host-pathogen interactions by regulating gene expression in ways that may contribute to evasion of host responses. Alterations in fungal cell wall structures could allow P. destructans to avoid detection by host pattern recognition receptors and antibody responses. This study has also identified several fungal pathways upregulated during WNS infection that may be candidates for mitigating infection pathology. By identifying host-specific pathogen responses, these observations have important implications for host-pathogen evolutionary relationships in WNS and other fungal diseases.

Vacuolar Serine Protease Is a Major Allergen of Fusarium proliferatum and an IgE-Cross Reactive Pan-Fungal Allergen

Purpose

Fusarium species are among prevalent airborne fungi and causative agents of human respiratory atopic disorders. We previously identified a 36.5-kDa F. proliferatum component recognized by IgE antibodies in 9 (53%) of the 17 F. proliferatum-sensitized atopic serum samples. The purpose of this study is to characterize the 36.5-kDa allergen of F. proliferatum.

Methods

Characterization of allergens and determination of IgE cross-reactivity were performed by cDNA cloning/expression and immunoblot inhibition studies.

Results

Based on the finding that the 36.5-kDa IgE-binding component reacted with the mouse monoclonal antibody FUM20 against fungal vacuolar serine protease allergens, the cDNA of F. proliferatum vacuolar serine protease (Fus p 9.0101) was subsequently cloned. Nine serum samples from respiratory atopic patients with IgE binding to the vacuolar serine protease allergen of Penicillium chrysogenum (Pen ch 18) also showed IgE-immunoblot reactivity to rFus p 9.0101. The purified rFus p 9.0101 can inhibit IgE and FUM20 binding to the 36.5-kDa component of F. proliferatum. Thus, a novel and important Fus p 9.0101 was identified. The rPen ch 18 can inhibit IgE binding to Fus p 9.0101. It indicates that IgE cross-reactivity between Fus p 9.0101 and Pen ch 18 also exists. Furthermore, neither rFus p 9.0101 K88A nor rPen ch 18 K89A mutants inhibited IgE binding to rFus p 9.0101. Lys88 was considered a critical core amino acid in IgE binding to r Fus p 9.0101 and a residue responsible for IgE cross-reactivity between Fus p 9.0101 and Pen ch 18 allergens.

Conclusions

Results obtained from this study indicate that vacuolar serine protease may be a major allergen of F. proliferatum and an important IgE cross-reactive pan-fungal allergen, and provide important bases for clinical diagnosis of fungal allergy.

EAACI Molecular Allergology User's Guide

The availability of allergen molecules ('components') from several protein families has advanced our understanding of immunoglobulin E (IgE)-mediated responses and enabled 'component-resolved diagnosis' (CRD). The European Academy of Allergy and Clinical Immunology (EAACI) Molecular Allergology User's Guide (MAUG) provides comprehensive information on important allergens and describes the diagnostic options using CRD. Part A of the EAACI MAUG introduces allergen molecules, families, composition of extracts, databases, and diagnostic IgE, skin, and basophil tests. Singleplex and multiplex IgE assays with components improve both sensitivity for low-abundance allergens and analytical specificity; IgE to individual allergens can yield information on clinical risks and distinguish cross-reactivity from true primary sensitization. Part B discusses the clinical and molecular aspects of IgE-mediated allergies to foods (including nuts, seeds, legumes, fruits, vegetables, cereal grains, milk, egg, meat, fish, and shellfish), inhalants (pollen, mold spores, mites, and animal dander), and Hymenoptera venom. Diagnostic algorithms and short case histories provide useful information for the clinical workup of allergic individuals targeted for CRD. Part C covers protein families containing ubiquitous, highly cross-reactive panallergens from plant (lipid transfer proteins, polcalcins, PR-10, profilins) and animal sources (lipocalins, parvalbumins, serum albumins, tropomyosins) and explains their diagnostic and clinical utility. Part D lists 100 important allergen molecules. In conclusion, IgE-mediated reactions and allergic diseases, including allergic rhinoconjunctivitis, asthma, food reactions, and insect sting reactions, are discussed from a novel molecular perspective. The EAACI MAUG documents the rapid progression of molecular allergology from basic research to its integration into clinical practice, a quantum leap in the management of allergic patients.

Sensibilisation of asthmatic patients to extracted antigens from strains of Aspergillus fumigatus, Aspergillus flavus and Aspergillus niger

OBJECTIVE

The main purpose of this study sought to evaluate the frequency of sensitivity of Iranian asthmatic patients to three regional Aspergillus species of fumigatus, flavus and niger, by detection of antigen-specific IgE in the patients' sera.

PATIENTS AND METHODS

Crude extracts were prepared following the disruption of fungi cell walls by the application of glass beads and their protein fractions were isolated by SDS-PAGE. After electrotransfer of protein bands into the nitrocellulose membrane, IgE-immunoblotting was performed against the sera from 32 asthmatic patients in addition to 20 healthy controls.

RESULTS

Our results interestingly showed that all of the studied Iranian asthmatic patients were sensitive to A. fumigatus and A. flavus antigens. This frequency was 65.6% in the case of A. niger, however, all control samples were negative. Age/sex analysis generally indicated higher sensitivities of young patients (<30 years old) to Aspergillus species with a statistical significance in the case of A. niger (P=0.02) and additionally more sensitivity of females. Using Immunoblotting assay, 23 IgE-reactive allergenic components from A. fumigatus, 15 from A. flavus and 13 from A. niger in a broad molecular weight spectrum were identified, among which several fragments were not previously reported.

CONCLUSION

Overall, this study found a high frequency of sensitivity of Iranian asthmatic patients to regional isolates of A. fumigatus, A. flavus and A. niger, which suggested the importance of these species in development of asthma. Moreover, we reported allergenic profiles of Iranian isolates in different patterns not previously observed.

Occupational exposure to Aspergillus by swine and poultry farm workers in Portugal

Aspergillus is among a growing list of allergens that aggravate asthmatic responses. Significant pulmonary pathology is associated with Aspergillus-induced allergic and asthmatic lung disease. Environments with high levels of exposure to fungi are found in animal production facilities such as for swine and poultry, and farmers working with these are at increased risk for occupational respiratory diseases. Seven Portuguese poultry and seven swine farms were analyzed in order to estimate the prevalence, amount, and distribution of Aspergillus species, as well as to determine the presence of clinical symptoms associated with asthma and other allergy diseases in these highly contaminated settings. From the collected fungal isolates (699), an average incidence of 22% Aspergillus was detected in poultry farms, while the prevalence at swine farms was 14%. The most frequently isolated Aspergillus species were A. versicolor, A. flavus, and A. fumigatus. In poultry farms, A. flavus presented the highest level of airborne spores (>2000 CFU/m³), whereas in swine farms the highest was A. versicolor, with an incidence fourfold greater higher than the other mentioned species. Eighty workers in these settings were analyzed, ranging in age from 17 to 93 yr. The potentially hazardous exposure of poultry workers to mold allergens using sensitization markers was evaluated. Although no significant positive association was found between fungal contamination and sensitization to fungal antigens, a high incidence of respiratory symptoms in professionals without asthma was observed, namely, wheezing associated with dyspnea (23.8%) and dyspnea after strenuous activities (12.3%), suggesting underdiagnosed respiratory disturbances. Further, 32.5% of all exposed workers noted an improvement of respiratory ability during resting and holidays. From all the analyzed workers, seven were previously diagnosed with asthma and four reported the first attack after the age of 40 yr, which may be associated with their occupational exposure. Some of the fungi, namely, the Aspergillus species detected in this study, are known to induce hypersensitivity reactions in humans. This study confirmed the presence and distribution of Aspergillus in Portuguese poultry and swine farms, suggesting a possible occupational health problem and raising the need for preventive and protective measures to apply to avoid exposure in both occupational settings.

Induction of mucin and MUC5AC expression by the protease activity of Aspergillus fumigatus in airway epithelial cells

Allergic bronchopulmonary mycosis, characterized by excessive mucus secretion, airflow limitation, bronchiectasis, and peripheral blood eosinophilia, is predominantly caused by a fungal pathogen, Aspergillus fumigatus. Using DNA microarray analysis of NCI-H292 cells, a human bronchial epithelial cell line, stimulated with fungal extracts from A. fumigatus, Alternaria alternata, or Penicillium notatum, we identified a mucin-related MUC5AC as one of the genes, the expression of which was selectively induced by A. fumigatus. Quantitative RT-PCR, ELISA, and histochemical analyses confirmed an induction of mucin and MUC5AC expression by A. fumigatus extracts or the culture supernatant of live microorganisms in NCI-H292 cells and primary cultures of airway epithelial cells. The expression of MUC5AC induced by A. fumigatus extracts diminished in the presence of neutralizing Abs or of inhibitors of the epidermal growth factor receptor or its ligand, TGF-α. We also found that A. fumigatus extracts activated the TNF-α-converting enzyme (TACE), critical for the cleavage of membrane-bound pro-TGF-α, and its inhibition with low-molecular weight inhibitors or small interfering RNA suppressed the expression of MUC5AC. The protease activity of A. fumigatus extracts was greater than that of other fungal extracts, and treatment with a serine protease inhibitor, but not with a cysteine protease inhibitor, eliminated its ability to activate TACE or induce the expression of MUC5AC mRNA in NCI-H292. In conclusion, the prominent serine protease activity of A. fumigatus, which caused the overproduction of mucus by the bronchial epithelium via the activation of the TACE/TGF-α/epidermal growth factor receptor pathway, may be a pathogenetic mechanism of allergic bronchopulmonary mycosis.

Fungal proteases and their pathophysiological effects

Proteolytic enzymes play an important role in fungal physiology and development. External digestion of protein substrates by secreted proteases is required for survival and growth of both saprophytic and pathogenic species. Extracellular serine, aspartic, and metalloproteases are considered virulence factors of many pathogenic species. New findings focus on novel membrane-associated proteases such as yapsins and ADAMs and their role in pathology. Proteases from fungi induce inflammatory responses by altering the permeability of epithelial barrier and by induction of proinflammatory cytokines through protease-activated receptors. Many fungal allergens possess proteolytic activity that appears to be essential in eliciting Th2 responses. Allergenic fungal proteases can act as adjuvants, potentiating responses to other allergens. Proteolytic enzymes from fungi contribute to inflammation through interactions with the kinin system as well as the coagulation and fibrinolytic cascades. Their effect on the host protease-antiprotease balance results from activation of endogenous proteases and degradation of protease inhibitors. Recent studies of the role of fungi in human health point to the growing importance of proteases not only as pathogenic agents in fungal infections but also in asthma, allergy, and damp building related illnesses. Proteolytic enzymes from fungi are widely used in biotechnology, mainly in food, leather, and detergent industries, in ecological bioremediation processes and to produce therapeutic peptides. The involvement of fungal proteases in diverse pathological mechanisms makes them potential targets of therapeutic intervention and candidates for biomarkers of disease and exposure.

What makes Aspergillus fumigatus a successful pathogen? Genes and molecules involved in invasive aspergillosis

Aspergillus fumigatus is an opportunistic pathogen that causes 90% of invasive aspergillosis (IA) due to Aspergillus genus, with a 50-95% mortality rate. It has been postulated that certain virulence factors are characteristic of A. fumigatus, but the "non-classical" virulence factors seem to be highly variable. Overall, published studies have demonstrated that the virulence of this fungus is multifactorial, associated with its structure, its capacity for growth and adaptation to stress conditions, its mechanisms for evading the immune system and its ability to cause damage to the host. In this review we intend to give a general overview of the genes and molecules involved in the development of IA. The thermotolerance section focuses on five genes related with the capacity of the fungus to grow at temperatures above 30°C (thtA, cgrA, afpmt1, kre2/afmnt1, and hsp1/asp f 12). The following sections discuss molecules and genes related to interaction with the host and with the immune responses. These sections include β-glucan, α-glucan, chitin, galactomannan, galactomannoproteins (afmp1/asp f 17 and afmp2), hydrophobins (rodA/hyp1 and rodB), DHN-melanin, their respective synthases (fks1, rho1-4, ags1-3, chsA-G, och1-4, mnn9, van1, anp1, glfA, pksP/alb1, arp1, arp2, abr1, abr2, and ayg1), and modifying enzymes (gel1-7, bgt1, eng1, ecm33, afpigA, afpmt1-2, afpmt4, kre2/afmnt1, afmnt2-3, afcwh41 and pmi); several enzymes related to oxidative stress protection such as catalases (catA, cat1/catB, cat2/katG, catC, and catE), superoxide dismutases (sod1, sod2, sod3/asp f 6, and sod4), fatty acid oxygenases (ppoA-C), glutathione tranferases (gstA-E), and others (afyap1, skn7, and pes1); and efflux transporters (mdr1-4, atrF, abcA-E, and msfA-E). In addition, this review considers toxins and related genes, such as a diffusible toxic substance from conidia, gliotoxin (gliP and gliZ), mitogillin (res/mitF/asp f 1), hemolysin (aspHS), festuclavine and fumigaclavine A-C, fumitremorgin A-C, verruculogen, fumagillin, helvolic acid, aflatoxin B1 and G1, and laeA. Two sections cover genes and molecules related with nutrient uptake, signaling and metabolic regulations involved in virulence, including enzymes, such as serine proteases (alp/asp f 13, alp2, and asp f 18), metalloproteases (mep/asp f 5, mepB, and mep20), aspartic proteases (pep/asp f 10, pep2, and ctsD), dipeptidylpeptidases (dppIV and dppV), and phospholipases (plb1-3 and phospholipase C); siderophores and iron acquisition (sidA-G, sreA, ftrA, fetC, mirB-C, and amcA); zinc acquisition (zrfA-H, zafA, and pacC); amino acid biosynthesis, nitrogen uptake, and cross-pathways control (areA, rhbA, mcsA, lysF, cpcA/gcn4p, and cpcC/gcn2p); general biosynthetic pathway (pyrG, hcsA, and pabaA), trehalose biosynthesis (tpsA and tpsB), and other regulation pathways such as those of the MAP kinases (sakA/hogA, mpkA-C, ste7, pbs2, mkk2, steC/ste11, bck1, ssk2, and sho1), G-proteins (gpaA, sfaD, and cpgA), cAMP-PKA signaling (acyA, gpaB, pkaC1, and pkaR), His kinases (fos1 and tcsB), Ca(2+) signaling (calA/cnaA, crzA, gprC and gprD), and Ras family (rasA, rasB, and rhbA), and others (ace2, medA, and srbA). Finally, we also comment on the effect of A. fumigatus allergens (Asp f 1-Asp f 34) on IA. The data gathered generate a complex puzzle, the pieces representing virulence factors or the different activities of the fungus, and these need to be arranged to obtain a comprehensive vision of the virulence of A. fumigatus. The most recent gene expression studies using DNA-microarrays may be help us to understand this complex virulence, and to detect targets to develop rapid diagnostic methods and new antifungal agents.

Expressed sequence tags of Aspergillus fumigatus: Extension of catalogue and their evaluation as putative drug targets and/or diagnostic markers

Aspergillus fumigatus a fungal pathogen is implicated in a spectrum of allergic and invasive disorders in humans. Validation of transcriptome of pathogen is essential for understanding its virulence mechanism and to identify new therapeutic targets/diagnostic markers. In order to rapidly identify genes of Aspergillus fumigatus we adopted sequencing of cDNA clones. Our earlier effort has lead to identification of 68 expressed sequence tags of Aspergillus fumigatus. Present study describes 52 more expressed sequence tags generated by sequencing 200 phage clones of a non-normalized cDNA library. One of the cDNA clones comprised of the complete coding region for tetratricopeptide repeat domain protein gene. Various homology search algorithms were employed to assign functions to expressed sequence tags coding for hypothetical proteins, and relevance of these expressed sequence tags or their protein products as drug targets/diagnostic markers was examined by searching for homologues in fungi and human.

Proteome analysis for pathogenicity and new diagnostic markers for Aspergillus fumigatus

With the completion of the Aspergillus fumigatus genome it is now possible to study protein regulation on a global scale. One of the most suitable protein separation techniques is based on 2D-gel electrophoresis, which allows the separation of proteins based on their charge and size in a gel matrix. In addition, gel-free proteomics techniques based on liquid-chromatography coupled with mass spectrometry have gained importance. With the application of proteomic tools a comprehensive overview about the proteins of A. fumigatus present or induced during environmental changes and stress conditions can be obtained. For A. fumigatus, several proteomic studies have already been published including the response of the fungus to oxidative stress that induced the up-regulation of many proteins including catalases and thioredoxin peroxidase. Since many of the identified proteins/genes were apparently regulated by a putative Saccharomyces cerevisiae Yap1 homolog, the corresponding gene of A. fumigatus was identified, designated Afyap1 and further characterized. In addition, some of the gene products expressed under stress conditions are also known fungal antigens, such as the thioredoxin peroxidase AspF3. Thus, besides pathogenicity studies, proteomics also delivers the tools to screen for new antigens which could improve the diagnosis of diseases caused by A. fumigatus.

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.

Aspergillus and Penicillium allergens: focus on proteases

Penicillium and Aspergillus species are prevalent airborne fungi. It is imperative to identify and characterize their major allergens. Alkaline and/or vacuolar serine proteases are major allergens of several prevalent Penicillium and Aspergillus species. They are also major immunoglobulin (Ig) E-reacting components of the most prevalent airborne yeast, Rhodotorula mucilaginosa, and the most prevalent Cladosporium species, C. cladosporioides. IgE cross-reactivity has been detected among these major pan-fungal serine protease allergens. In addition, the alkaline serine protease of P. chrysogenum (Pen ch 13) induces histamine release from basophils of asthmatic patients, degrades the tight junction protein occludin, and stimulates release of proinflammatory mediators from human bronchial epithelial cells. In addition to induction of IgE and inflammatory airway responses, the alkaline serine protease allergen of A. fumigatus (Asp f 13) has synergistic effects on Asp f 2-induced immune response in mice. Studies of these serine protease major allergens elucidate the diverse allergic disease mechanisms and facilitate the development of better therapeutic strategies.

Immunochemical comparison of the allergenic potency of spores and mycelium of Cladosporium cladosporioides extracts by a nitrocellulose electroblotting technique

BACKGROUND

The lack of well standardized or characterized extracts that contain the relevant allergens of the appropriate fungus is resulting in a high heterogeneity of the commercial preparation.

MATERIAL AND METHODS

Immunochemical detection of the allergens composition of spore and mycelium of C. cladosporioides was studied by electroblotting using sera from Cladosporium allergic patients and 125 I- anti- human IgE. A MW range of allergens between 16 to 88 KDa was identified. The most important with a MW of 16, 20,30, 39, 43, 50, 60 and 88 KDa.

RESULTS

The allergenic composition of spore and mycelium looked very similar. However, partial or total inhibition of the serum with a conidial or mycelial extract demonstrated that the total concentration of allergens (particulary 20 and 60 KDa molecules) was higher in the conidium than in the mycelium.

CONCLUSIONS

These results indicated that conidium and mycelium contained the same allergenic determinants but at different concentration in the two propagule. Results with 50 % inhibited sera demonstrated also that the total concentration of allergens was higher in the conidium than in the mycelium.

A Vacuolar Serine Protease (Rho m 2) Is a Major Allergen of Rhodotorula mucilaginosa and Belongs to a Class of Highly Conserved Pan-Fungal Allergens

BACKGROUND

Rhodotorula mucilaginosa is one of the most frequently encountered species of yeasts in our environment. We reported here a major allergen of R. mucilaginosa.

METHODS

A major R. mucilaginosa allergen (Rho m 2) was characterized by two-dimensional (2D) immunoblotting, protein sequencing, cDNA cloning and IgE cross-reactivity with fungal serine proteases.

RESULTS

Fourty-four sera (28%) from 157 bronchial asthmatic patients showed IgE-immunoblot reactivity against R. mucilaginosa extract. Among these 44 sera, 25 (57%) demonstrated IgE binding against a 31-kDa protein of R. mucilaginosa. Protein sequencing results suggest that it is a vacuolar serine protease. The corresponding cDNA clone encoding a mature protein of 312 residues was isolated. It shares 67-68% sequence identity with vacuolar serine protease allergens from three different Penicillium species (Pen ch 18, Pen o 18 and Pen c 18) and designated as Rho m 2 by the Allergen Nomenclature Committee. The native and recombinant Rho m 2 react with IgE antibodies and monoclonal antibody (MoAb) FUM20 against fungal serine proteases. IgE cross-reactivity between nRho m 2 and nPen ch 18 was observed. It was also detectable between rRho m 2 and rPen o 18.

CONCLUSION

Our results suggest that R. mucilaginosa may also be a significant causative agent of human respiratory allergic disorders. We identified a vacuolar serine protease as a major allergen of R. mucilaginosa (Rho m 2) and a pan allergen of prevalent airborne fungal species. We detected IgE cross-reactivity among these highly conserved serine protease pan-fungal allergens.

Genes and molecules involved in Aspergillus fumigatus virulence

Aspergillus fumigatus causes a wide range of diseases that include mycotoxicosis, allergic reactions and systemic diseases (invasive aspergillosis) with high mortality rates. Pathogenicity depends on immune status of patients and fungal strain. There is no unique essential virulence factor for development of this fungus in the patient and its virulence appears to be under polygenetic control. The group of molecules and genes associated with the virulence of this fungus includes many cell wall components, such as beta-(1-3)-glucan, galactomannan, galactomannanproteins (Afmp1 and Afmp2), and the chitin synthetases (Chs; chsE and chsG), as well as others. Some genes and molecules have been implicated in evasion from the immune response, such as the rodlets layer (rodA/hyp1 gene) and the conidial melanin-DHN (pksP/alb1 gene). The detoxifying systems for Reactive Oxygen Species (ROS) by catalases (Cat1p and Cat2p) and superoxide dismutases (MnSOD and Cu, ZnSOD), had also been pointed out as essential for virulence. In addition, this fungus produces toxins (14 kDa diffusible substance from conidia, fumigaclavin C, aurasperon C, gliotoxin, helvolic acid, fumagilin, Asp-hemolysin, and ribotoxin Asp fI/mitogilin F/restrictocin), allergens (Asp f1 to Asp f23), and enzymatic proteins as alkaline serin proteases (Alp and Alp2), metalloproteases (Mep), aspartic proteases (Pep and Pep2), dipeptidyl-peptidases (DppIV and DppV), phospholipase C and phospholipase B (Plb1 and Plb2). These toxic substances and enzymes seems to be additive and/or synergistic, decreasing the survival rates of the infected animals due to their direct action on cells or supporting microbial invasion during infection. Adaptation ability to different trophic situations is an essential attribute of most pathogens. To maintain its virulence attributes A. fumigatus requires iron obtaining by hydroxamate type siderophores (ornitin monooxigenase/SidA), phosphorous obtaining (fos1, fos2, and fos3), signal transductional falls that regulate morphogenesis and/or usage of nutrients as nitrogen (rasA, rasB, rhbA), mitogen activated kinases (sakA codified MAP-kinase), AMPc-Pka signal transductional route, as well as others. In addition, they seem to be essential in this field the amino acid biosynthesis (cpcA and homoaconitase/lysF), the activation and expression of some genes at 37 degrees C (Hsp1/Asp f12, cgrA), some molecules and genes that maintain cellular viability (smcA, Prp8, anexins), etc. Conversely, knowledge about relationship between pathogen and immune response of the host has been improved, opening new research possibilities. The involvement of non-professional cells (endothelial, and tracheal and alveolar epithelial cells) and professional cells (natural killer or NK, and dendritic cells) in infection has been also observed. Pathogen Associated Molecular Patterns (PAMP) and Patterns Recognizing Receptors (PRR; as Toll like receptors TLR-2 and TLR-4) could influence inflammatory response and dominant cytokine profile, and consequently Th response to infec tion. Superficial components of fungus and host cell surface receptors driving these phenomena are still unknown, although some molecules already associated with its virulence could also be involved. Sequencing of A. fumigatus genome and study of gene expression during their infective process by using DNA microarray and biochips, promises to improve the knowledge of virulence of this fungus.

Barriers built on claudins

The fundamental functions of epithelia and endothelia in multicellular organisms are to separate compositionally distinct compartments and regulate the exchange of small solutes and other substances between them. Tight junctions (TJs) between adjacent cells constitute the barrier to the passage of ions and molecules through the paracellular pathway and function as a 'fence' within the plasma membrane to create and maintain apical and basolateral membrane domains. How TJs achieve this is only beginning to be understood. Recently identified components of TJs include the claudins, a family of four-transmembrane-span proteins that are prime candidates for molecules that function in TJ permeability. Their identification and characterization have provided new insight into the diversity of different TJs and heterogeneity of barrier functions in different epithelia and endothelia.

Molecular and structural analysis of immunoglobulin E-binding epitopes of Pen ch 13, an alkaline serine protease major allergen from Penicillium chrysogenum

BACKGROUND

Through proteomic and genomic approaches we have previously identified and characterized an alkaline serine protease that is a major allergen (88% frequency of IgE binding) of Penicillium chrysogenum (Pen ch 13).

OBJECTIVE

The aim of the present study is to identify the linear IgE-binding epitopes of Pen ch 13.

METHODS

IgE-binding regions were identified by dot-blot immunoassay using 11 phage-displayed peptide fragments spanning the whole molecule of Pen ch 13. The minimal epitope requirements for IgE binding were further defined with overlapping peptides synthesized on derivatized cellulose membranes using SPOTs technology. The critical residues on the immunodominant epitopes were mapped through site-directed mutagenesis. The locations of the IgE epitopes identified were correlated with a three-dimensional structure of Pen ch 13.

RESULTS

IgE antibodies in 35 serum samples reacted with at least one of the 11 peptide fragments of Pen ch 13. Peptide f-2n (residues 31-61) showed a high-intensity and the highest frequency (77%) of IgE binding. The frequencies of IgE binding to peptide f-4 (residues 93-133), f-1 (residues 1-37) and f-7 (residues 168-206) were 51%, 34% and 31%, respectively. SPOTs assay narrowed down the region of IgE binding of f-2n to residues 48-55 (GHADFGGR). Three, two and one epitope(s) that are four to nine amino acids in length, within f-4, f-1 and f-7, respectively, were found. Site-directed mutagenesis of Pen ch 13 revealed that substitution of His49 and/or Phe52 on Pen ch 13 with methionine resulted in proteins with drastic loss of IgE binding in seven sera tested. Proteins with amino acid replacements at residues 15-18 (RISS), or at residues 112 (I) and 116 (D) have lower IgE-binding reactivity in one of the two patient's sera tested. Substituting residues 117 (W), 119 (V) and 120 (K) also block most of the IgE binding in one of the two patient's sera tested. In addition, replacing residues 203 (V) and 204 (D) along with a deletion at residue 206 (Y) diminished the IgE binding in two serum samples tested. A model was constructed based on the structure of P. cyclopium subtilisin protease that has >90% (256 out of 283 amino acids) sequence identity with Pen ch 13. The major epitope (GHADFGGR) on Pen ch 13 formed a loop-like structure and was located at the surface of the allergen.

CONCLUSIONS

Several linear IgE-reactive epitopes and their critical core amino acid residues were identified for the Pen ch 13 allergen. The major linear IgE-binding epitope, 48GHADFGGR55, formed a loop-like structure at the surface of the allergen. Substitution of His49 and/or Phe52 with methionine significantly reduced IgE-binding to Pen ch 13. Mapping of these results on a 3D model of the allergen provides valuable information about the molecular basis of allergenicity for Pen ch 13 and for designing specific immunotherapeutics.

Identification of serine protease as a major allergen of Curvularia lunata

BACKGROUND

Several proteins from Curvularia lunata have been identified as important fungal allergens. It will be worthwhile to study the functional aspects of these allergens. The present study aimed at purifying a major allergen and determining its biological function.

METHODS

Concanavalin A and Superdex 75 were used to purify Cur l 1 major allergen from C. lunata. Cur l 1 activity was determined qualitatively and quantitatively. Serine protease inhibitors and specific substrate was used to determine the biological function of the protein.

RESULTS

Concanavalin A-bound fraction showed five allergenic proteins, which on Superdex G-75 purification gave a homogenous Cur l 1 protein. Cur l 1 showed IgE reactivity with 80% of the C. lunata hypersensitive patient's sera indicating it to be a major allergen. It showed protease activity on different substrates. Cur l 1's amino terminal sequence, GLTQKSAPWGLGADTIVAVELDSY, showed homology with the alkaline serine protease precursor. Phenylmethylsulfonylfluoride, pefabloc, aprotinin and leupeptin inhibited 70-80% enzymatic activity of Cur l 1 and no inhibition was observed with ethylenediaminetetraacetic acid (EDTA). A dose-dependent hydrolysis of Nalpha-benzoyl-l-arginine ethyl ester-hydrochloride, a specific serine protease substrate was obtained with Cur l 1.

CONCLUSION

A major glycoprotein allergen Cur l 1 was purified to homogeneity from C. lunata. Amino terminal sequence and biochemical assays identified it as a serine protease.

Molecular and immunological characterization of Pen ch 18, the vacuolar serine protease major allergen of Penicillium chrysogenum

BACKGROUND

We have suggested previously that the 32 and 34 kDa major allergens of Penicillium chrysogenum (also known as P. notatum) are the vacuolar (Pen ch 18) and the alkaline (Pen ch 13) serine proteases, respectively, of P. chrysogenum. The purpose of this study is to characterize the 32 kDa allergen of P. chrysogenum and its immunoglobulin E (IgE)cross-reactivity with Pen ch 13 allergen.

METHODS

The full-length cDNA of Pen ch 18 was isolated by reverse transcriptase-polymerase chain reaction and the 5'-rapid amplification cDNA end reaction. Recombinant Pen ch 18 was expressed as his-tagged proteins in Escherichia coli. Its reactivity with IgE and monoclonal antibodies against fungal serine protease allergens was analyzed by immunoblotting. The IgE cross-reactivity between Pen ch 18 and Pen ch 13 was analyzed by immunoblot inhibition. Overlapping recombinant fragments and synthetic peptides were used to map the B cell epitopes on Pen ch 18.

RESULTS

In this study, we isolated a 1857 bp cDNA fragment containing an open reading frame of 494 amino acids that encodes the preproenzyme of Pen ch 18. Similar to other vacuolar serine proteases, this precursor appears to undergo N- and possibly C-terminal cleavage upon maturation. The his-tagged recombinant Pen ch 18 containing the putative sequence of the mature protein reacted with IgE antibodies in serum samples from asthmatic patients. In addition, IgE-binding to the 32 kDa major allergen of P. chrysogenum was inhibited when a positive serum sample was absorbed with recombinant Pen ch 18 before immunoblotting. Both inhibition and almost no inhibition of IgE-binding to the 32 kDa major allergen of Pen ch 18 were detected when eight positive serum samples were preabsorbed individually with purified Pen ch 13 before immunoblotting. The major IgE binding region was located in a fragment (PN1) encompassing the N-terminal 102 amino acid residues of the recombinant Pen ch 18. A dominant linear IgE epitope was further mapped within residues 73-95 (peptide PN1-e) of the N-terminally processed allergen. Monoclonal antibody FUM20 that reacts with Pen ch 18 but not with Pen ch 13 binds a synthetic peptide with sequence encompassing the N-terminal 23 residues of the recombinant Pen ch 18. Monoclonal antibody PCM39 that reacts with both Pen ch 13 and Pen ch 18 recognizes a peptide containing residues 132-154 of the allergen.

CONCLUSIONS

Our results confirm that the Pen ch 18 allergen is a vacuolar serine protease of P. chrysogenum that matures through N- and possibly C-terminal processing. The finding that there are cross-reactive and allergen-specific IgE epitopes for Pen ch 18 and Pen ch 13 suggests that both major allergens should be included in clinically diagnostic P. chrysogenum extracts.

Allergen detection from 11 fungal species before and after germination

BACKGROUND

Allergens dispersed by airborne fungal spores play an important but poorly understood role in the underlying cause and exacerbation of asthma. Previous studies suggest that spores of Alternaria and Aspergillus release greater quantities of allergen after germination than before germination. It is unknown whether this is true of other allergenic fungi.

OBJECTIVE

Our purpose was to investigate the release of allergen from a range of individual fungal spores before and after germination.

METHODS

Allergen expression from spores of Alternaria alternata, Cladosporium herbarum, Aspergillus fumigatus, Botrytis cinerea, Epicoccum nigrum, Exserohilum rostratum, Penicillium chrysogenum, Stemphylium botryosum, Curvularia lunata, Trichoderma viride, and Bipolaris spicifera was examined by halogen immunoassays through the use of pooled serum IgE from patients allergic to fungus. Spores were deposited onto protein-binding membranes direct from culture. To germinate spores, samples were incubated in high humidity at room temperature for 48 hours. Ungerminated and germinated samples were then laminated with an adhesive film and immunostained by the halogen assay. The samples were examined by light microscopy, and positive counts (haloed particles) were expressed as percentages of total spores.

RESULTS

For 9 of 11 species, between 5.7% and 92% of spores released allergen before germination. Spores of Penicillium and Trichoderma did not release detectable allergen. After germination, all spores that germinated had allergen elution from their hyphae. Eight of 11 species showed a significant increase (P <.05) in the percentage of spores eluting detectable allergen. Localization of allergen along the hyphae varied with species, such that some eluted allergen mainly from hyphal tips and septal junctions whereas others eluted allergen along the entire length.

CONCLUSIONS

Increased elution of allergen after germination might be a common feature of many species of allergenic fungi. Although allergens from both spores and hyphae were recognized by human IgE, the extent to which human exposure occurs to allergens eluted from inhaled spores or from hyphae that germinate after deposition in the respiratory tract remains to be explored. The patterns of allergen expression might affect the clinical response to such exposure.